technoHOLIC

How Lie Detectors Work

2008-10-10T14:01:00.002+07:00

For more than 15 years, Robert Hanssen led a double life. In one life he was a 25-year veteran with the Federal Bureau of Investigation (FBI) who had access to some of the nation's most-classified information. In his other life, he allegedly was spying for the Russian government. Hanssen's deception was finally discovered, and in February 2001 he was arrested and later pled guilty to 15 espionage-related charges. Spies are probably the world's best liars, because they have to be, but most of us practice deception on some level in our daily lives, even if it's just telling a friend that his horrible haircut "doesn't look that bad."

People tell lies and deceive others for many reasons. Most often, lying is a defense mechanism used to avoid trouble with the law, bosses or authority figures. Sometimes, you can tell when someone's lying, but other times it may not be so easy. Polygraphs, commonly called "lie detectors," are instruments that monitor a person's physiological reactions. These instruments do not, as their nickname suggests, detect lies. They can only detect whether deceptive behavior is being displayed.

Photo courtesy Lafayette Instrument
An analog polygraph instrument
Most analog polygraphs are being replaced by digital devices.

Do you think you can fool a polygraph machine and examiner? In this article, you'll learn how these instruments monitor your vital signs, how a polygraph exam works and about the legalities of polygraph testing.

A polygraph instrument is basically a combination of medical devices that are used to monitor changes occurring in the body. As a person is questioned about a certain event or incident, the examiner looks to see how the person's heart rate, blood pressure, respiratory rate and electro-dermal activity (sweatiness, in this case of the fingers) change in comparison to normal levels. Fluctuations may indicate that person is being deceptive, but exam results are open to interpretation by the examiner.

Source: Lafayette Instrument
Physiological responses recorded by a polygraph

Polygraph exams are most often associated with criminal investigations, but there are other instances in which they are used. You may one day be subject to a polygraph exam before being hired for a job: Many government entities, and some private-sector employers, will require or ask you to undergo a polygraph exam prior to employment.

Polygraph examinations are designed to look for significant involuntary responses going on in a person's body when that person is subjected to stress, such as the stress associated with deception. The exams are not able to specifically detect if a person is lying, according to polygrapher Dr. Bob Lee, former executive director of operations at Axciton Systems, a manufacturer of polygraph instruments. But there are certain physiological responses that most of us undergo when attempting to deceive another person. By asking questions about a particular issue under investigation and examining a subject's physiological reactions to those questions, a polygraph examiner can determine if deceptive behavior is being demonstrated.

Photo courtesy Lafayette Instrument
Today, most polygraph exams are administered with digital equipment like this.

The polygraph instrument has undergone a dramatic change in the last decade. For many years, polygraphs were those instruments that you see in the movies with little needles scribbling lines on a single strip of scrolling paper. These are called analog polygraphs. Today, most polygraph tests are administered with digital equipment. The scrolling paper has been replaced with sophisticated algorithms and computer monitors.

Photo courtesy Lafayette Instrument
Parts of a polygraph that monitor physiological responses

When you sit down in the chair for a polygraph exam, several tubes and wires are connected to your body in specific locations to monitor your physiological activities. Deceptive behavior is supposed to trigger certain physiological changes that can be detected by a polygraph and a trained examiner, who is sometimes called a forensic psychophysiologist (FP). This examiner is looking for the amount of fluctuation in certain physiological activities. Here's a list of physiological activities that are monitored by the polygraph and how they are monitored:

Respiratory rate - Two pneumographs, rubber tubes filled with air, are placed around the test subject's chest and abdomen. When the chest or abdominal muscles expand, the air inside the tubes is displaced. In an analog polygraph, the displaced air acts on a bellows, an accordion-like device that contracts when the tubes expand. This bellows is attached to a mechanical arm, which is connected to an ink-filled pen that makes marks on the scrolling paper when the subject takes a breath. A digital polygraph also uses the pneumographs, but employs transducers to convert the energy of the displaced air into electronic signals.
Blood pressure/heart rate - A blood-pressure cuff is placed around the subject's upper arm. Tubing runs from the cuff to the polygraph. As blood pumps through the arm it makes sound; the changes in pressure caused by the sound displace the air in the tubes, which are connected to a bellows, which moves the pen. Again, in digital polygraphs, these signals are converted into electrical signals by transducers.
Galvanic skin resistance (GSR) - This is also called electro-dermal activity, and is basically a measure of the sweat on your fingertips. The finger tips are one of the most porous areas on the body and so are a good place to look for sweat. The idea is that we sweat more when we are placed under stress. Fingerplates, called galvanometers, are attached to two of the subject's fingers. These plates measure the skin's ability to conduct electricity. When the skin is hydrated (as with sweat), it conducts electricity much more easily than when it is dry.

Some polygraphs also record arm and leg movements. As the examiner asks questions, signals from the sensors connected to your body are recorded on a single strip of moving paper. You will learn more about the examiner and the test itself later.

Detractors of the polygraph call lie detection a voodoo science, saying that polygraphs are no more accurate at detecting lies than the flip of a coin. "Despite claims of 'lie detector' examiners, there is no machine that can detect lies," reads a statement from the American Civil Liberties Union (ACLU). "The 'lie detector' does not measure truth-telling; it measures changes in blood pressure, breath rate and perspiration rate, but those physiological changes can be triggered by a wide range of emotions."

Take the Quiz
Think you're an expert on lie detectors? Test your knowledge with this quiz from Investigation Discovery:

Lie detector quiz

Lee, who has been performing polygraph exams for 18 years, agrees that polygraphs do not detect lies. "What has happened over the years is that the media has dubbed this lie detection, and that's what's clicked, but from a scientific perspective, absolutely not. There's no such thing as lie detection. I couldn't tell you what a lie looks like."

He does assert that polygraphs can detect deceptive behavior even through the stress brought on by the exam itself. "If the (forensic psychophysiologist) is properly trained and has the experience, he can penetrate that. Through the specific procedure that the FP will employ, anxiety will not penetrate into it."

Polygraph Examiners

There are only two people in the room during a polygraph exam -- the person conducting the exam and the subject being tested. Today, some polygraph examiners prefer to be called forensic psychophysiologists (FPs). Because polygraph examiners are alone in the room with a test subject, his or her behavior greatly influences the results of the exam.

"It's a very serious factor when someone is being accused of a crime," Lee said. "See, I don't care about the deceptive person. I'm looking for the innocent person. I'm their advocate. I'm totally unbiased and neutral when that person comes walking in. But as soon as I make that assessment that there's no deception indicated, I immediately become their advocate."

The forensic psychophysiologist has several tasks in performing a polygraph exam:

Setting up the polygraph and preparing the subject being tested
Asking questions
Profiling the test subject
Analyzing and evaluating test data

How the question is presented can greatly affect the results of a polygraph exam. There are several variables that an FP has to take into consideration, such as cultural and religious beliefs. Some topics may, by their mere mention, cause a specific reaction in the test subject that could be misconstrued as deceptive behavior. The design of the question affects the way the person processes the information and how he or she responds.

There are approximately 3,500 polygraph examiners in the United States, 2,000 of which belong to a professional organization, according to Dr. Frank Horvath, a Michigan State University professor of criminal justice and a member of the American Polygraph Association.

Who Uses Polygraphs? Polygraphs are limited in their use in the private sector, but they are frequently used by the U.S. government. Here are some entities and occasions that may call for the use of a polygraph:

National security (Central Intelligence Agency, Federal Bureau of Investigation, National Security Agency, etc.)

Criminal investigation

Pre-employment screening

Internal-affairs investigations of law enforcement

Banks

Horvath is concerned about the credentials and qualifications of many polygraph examiners in the United States who do not belong to some sort of professional organization. Laws regarding polygraph licensing vary from state to state, and there is no government or private entity that controls polygraph licensing. Horvath also feels that training of polygraph examiners is inadequate.

"I just do not think the field is at the state where we would say that any polygraph examiner is the equal of all other polygraph examiners. That's just not so," Horvath said. "We have a number of standardization problems in terms of examiner qualifications that concern me enormously. You could buy a polygraph [instrument] tomorrow and come to Michigan and you wouldn't be able to practice here because we have a rigorous licensing law, but you could move down to Ohio and open a business tomorrow."

Today, some polygraph examiners take classes and work an internship in order to become an accredited examiner with national associations. Some states also require examiners to be trained. There are many schools around the United States that have been set up to train people to conduct polygraph exams. One of these schools is the Axciton International Academy, which was started by Lee. The school is accredited by the American Polygraph Association and certified by the American Association of Police Polygraphists.

Here are the steps that students at the Axciton Academy must complete before becoming licensed forensic pyschophysiologists:

Prior to enrolling in the school, students must possess a baccalaureate degree or have five years of investigative experience and an associates degree.
Students must attend and pass a 10-week intensive course. Curriculum includes psychology, physiology, ethics, history, question construction, psychological analysis of speech, chart analysis and test-data analysis.
Students must enter an internship program and conduct a minimum of 25 exams for actual cases. These exams are faculty reviewed. This internship can take anywhere from eight months to one year.

Following the completion of these requirements, the student becomes a polygrapher and may obtain a license in his or her state if that state requires one. There is no standardized test that all polygraph examiners must pass in order to practice.

Going on the Box
Undergoing a lie detector test can be an intimidating experience that can challenge the nerves of even the most stoic person. You are sitting there with wires and tubes attached to and wrapped around your body. Even if you have nothing to hide, you could be afraid that the metal-box instrument sitting next to you will say otherwise. Fittingly, undergoing the uncomfortable experience of a polygraph test is often referred to as "going on the box."

Mouse-over the wire colors to see where they lead.

A polygraph exam is a long process that can be divided up into several stages. Here's how a typical exam might work:

Pretest - This consists of an interview between the examiner and examinee, where the two individuals get to learn about each other. This may last about one hour. At this point, the examiner gets the examinee's side of the story concerning the events under investigation. While the subject is sitting there answering questions, the examiner also profiles the examinee. The examiner wants to see how the subject responds to questions and processes information.
Design questions - The examiner designs questions that are specific to the issue under investigation and reviews these questions with the subject.
In-test - The actual exam is given. The examiner asks 10 or 11 questions, only three of four of which are relevant to the issue or crime being investigated. The other questions are control questions. A control question is a very general question, such as "Have you ever stolen anything in your life?" -- a type of question that is so broad that almost no one can honestly respond with a "no." If the person answers "no," the examiner can get an idea of the reaction that the examinee demonstrates when being deceptive.
Post-test - The examiner analyzes the data of physiological responses and makes a determination regarding whether the person has been deceptive. If there are significant fluctuations that show up in the results, this may signal that the subject has been deceptive, especially if the person displayed similar responses to a question that was asked repeatedly.

There are times when a polygraph examiner misinterprets a person's reaction to a particular question. The human factor of a polygraph exam and the subjective nature of the test are two reasons why polygraph exam results are seldom admissible in court. Here are the two ways that a response can be misinterpreted:

False positive - The response of a truthful person is determined to be deceptive.
False negative - The response of a deceptive person is determined to be truthful.

"If we look at laboratory-based studies, false-positive errors occur somewhat more often than false-negative errors," Horvath said.

Critics of polygraph exams say that even more false-positive errors occur in real-world scenarios, which biases the system against the truthful person. These errors are likely to occur if the examiner has not prepared the examinee properly or if the examiner misreads the data following an exam.

Countermeasures and Legalities

Often, people who are being given a polygraph exam will employ certain countermeasures in an attempt to beat the instrument. There are Web sites and books that instruct you on how to fool the polygraph. Here are just a few examples of how people try to trick the device:

Sedatives
Antiperspirant on fingertips
Tacks placed in the shoe
Biting tongue, lip or cheek

The idea of countermeasures is to cause (or curtail) a certain reaction that will skew the test's result. A subject may attempt to have the same reaction to every question so that the examiner cannot pick out the deceptive responses. For example, some people will place a tack in their shoe and press their foot down on the tack after each question is asked. The idea is that the physiological response to the tack may overpower the physiological response to the question, causing the response to each question to seem identical.

Whether you pass or fail a polygraph exam will often have very little legal ramification. Often, defense lawyers brag that their client has passed a polygraph. Of course, you will rarely hear of a defendant taking a polygraph if he or she failed it.

Polygraphs are rarely admissible in court. New Mexico is the only state in the United States that allows for open admissibility of polygraph exam results. Every other state requires some type of stipulation to be met prior to admitting polygraph exams into record. In most cases, both sides of a legal case have to agree prior to the trial that they will allow polygraphs to be admitted. On the federal level, the admissibility criteria are much more vague and admission typically depends on the approval of the judge.

The main argument over the admissibility of polygraph tests is based on their accuracy, or inaccuracy, depending on how you want to view it. The level of accuracy of a lie detector depends on who you talk to about it, Horvath said. Both sides of the argument have the same research to look at, but they come to very different conclusions.

"We have people in the scientific community who look at the same research that I look at and they reach a conclusion that is quite different," Horvath said. "From their point of view, they allege that polygraph testing is probably only around 70 percent accurate, and it has a great bias against truthful people. Then, what the proponents say, looking at the same research, they reach a quite different conclusion, and that is that polygraph testing is around 90 percent accurate."

Employee Polygraph Protection Act of 1988 Employees in the private sector are not subjected to polygraph exams like employees of the federal government. The U.S. federal government is the largest consumer of polygraph exams. Private sector employees are protected by the Employee Polygraph Protection Act of 1988 (EPPA). This law only affects commercial businesses. It does not apply to schools, prisons, other public agencies or some businesses under contract with the federal government.

EPPA provides that a business cannot require a pre-employment polygraph and cannot subject current employees to polygraph exams. A business is allowed to request an exam, but cannot force anyone to undergo a test. If an employee refuses a suggested exam, the business is not allowed discipline or discharge that employee based on his or her refusal.

At the federal level, there have been specific legal cases that have shaped the admissibility of polygraphs. The results of these cases are mixed: There have been some federal circuits that have admitted polygraph results, while others have flatly denied them. Here are just a few of the legal cases that have shaped how polygraphs are viewed by the U.S. courts:

Frye v. United States (1923) - U.S. Court of Appeals of District of Columbia - This is the original decision dealing with scientific evidence and its admissibility in court. Frye was accused of murdering a doctor. At the time, he took a unigraph, a precursor to the polygraph. The unigraph measured only the cardiovascular activities of the body. The examiner reported Frye to be truthful, and Frye moved to have that evidence admitted in court. The court ruled that before any scientific evidence could be admitted into the court of law it must first be accepted by the scientific community. At that time, there were no studies done on unigraphs or polygraphs, so the evidence was not admitted.
United States v. Piccinonna (1989) - U.S. Court of Appeals, 11th Circuit - This decision allowed for polygraph results to be admitted in court, but only if one of two requirements is met: Either the two parties in the case agree to allow it, or the judge decides to allow it based on criteria established by the 11th Circuit.
Daubert v. Merrell Dow Pharmaceuticals (1993) - U.S. Supreme Court - The court opened the door for scientific evidence, and gave judges broader discretion as to whether or not to admit polygraphs. This applies to all federal courts but does not apply in state courts, although particular states do accept this ruling.
United States v. Scheffer (1998) - U.S. Supreme Court - Moving beyond the broader topic of scientific evidence, this military case directly involved polygraphs. The court ruled that the U.S. president has the prerogative to deny polygraph results in military tribunals because polygraph testing is so controversial.

It seems clear that no final decision has been made on the federal level. At the state level, polygraph admissibility is generally handled on a case-by-case basis. The courts' ambiguity stems from the questionable validity of polygraph exams. Interestingly, the biggest opponent to polygraph admission in court is the U.S. federal government, which happens to be the largest consumer of polygraphs exams.

There are still many questions that must be answered before polygraphs are accepted by the courts and the public at large. Of course, we may never see this broad acceptance. No matter if you agree or disagree with the use of polygraphs, thousands of people undergo these tests every year, and many people's lives are changed forever by their results.

How Satellite Radio Works

2008-09-09T20:43:00.005+07:00

We all have our favorite radio stations that we preset into our car radios, flipping between them as we drive to and from work, on errands and around town. But when you travel too far away from the station, the signal breaks up and fades into static. Most radio signals can only travel about 30 or 40 miles from their source. On long trips, you might have to change radio stations every hour or so as the signals fade in and out. And it's not much fun scanning through static trying to find something -- anything -- to listen to.

Satellite Radio Image Gallery

Photo courtesy XM Satellite Radio
Satellite radio broadcasters promise crystal-clear music transmitted from thousands of miles into space.
See more pictures of satellite radio.

Now, imagine a radio station that can broadcast its signal from more than 22,000 miles (35,000 kilometers) away and then come through on your car radio with complete clarity. You could drive from Tacoma, Wash., to Washington, D.C., without ever having to change the radio station! Not only would you never hear static interfering with your favorite tunes, but the music would be interrupted by few or no commercials.

XM Satellite Radio and Sirius Satellite Radio both launched such a service at the beginning of the 21st century. Satellite radio, also called digital radio, offers uninterrupted, near CD-quality music beamed to your radio from space.

In February 2007, XM Radio and Sirius Radio announced that they planned to merge into a single satellite radio company. XM and Sirius are both in debt, and a merger could quickly solve that problem. The merger could also lead to lower prices and more programming choices for consumers. Some people are skeptical about the two companies joining, though, fearing a monopoly would only reduce competition, raise prices and affect consumers poorly. XM and Sirius currently must convince the FCC that a merger wouldn't violate anti-trust laws.

Even though XM and Sirius have had financial trouble, satellite radio still has a fairly strong fan base. About 8 million people subscribe to XM Radio, and more than 6 million people tune into Sirius Radio. Car manufacturers have been installing satellite radio receivers in some models for a few years now, and several models of portable satellite radio receivers are available from a variety of electronics companies. In this article, you'll learn what separates satellite radio from conventional radio and what you need to pick up satellite radio signals.

The Basics

Satellite radio is an idea over a decade in the making. In 1992, the U.S. Federal Communications Commission (FCC) allocated a spectrum in the "S" band (2.3 GHz) for nationwide broadcasting of satellite-based Digital Audio Radio Service (DARS). Only four companies applied for a license to broadcast over that band. The FCC gave licenses to two of these companies in 1997. CD Radio (now Sirius Satellite Radio) and American Mobile Radio (now XM Satellite Radio) paid more than $80 million each to use space in the S-band for digital satellite transmission.

At this time, there are three space-based radio broadcasters:

Sirius Satellite Radio
XM Satellite Radio
WorldSpace

Satellite radio companies are comparing the significance of their service to the impact that cable TV had on television 30 years ago. Listeners won't be able to pick up local stations using satellite radio services, but they will have access to hundreds of stations offering a variety of music genres. Each company has a different plan for its broadcasting system, but the systems do share similarities. Here are the key components of the three satellite radio systems:

Satellites
Ground repeaters
Radio receivers

Satellite radio works a lot like satellite TV -- you purchase a receiver and pay a monthly subscription fee for a certain number of channels. For the moment, there are slight variances in the three satellite radio companies' systems. In the next three sections, we will profile each of the companies and their current satellite radio services.

The XM/Sirius Merger
Both XM and Sirius offer about 100 channels under their current plans. If both the FCC and the Department of Justice approve their proposed merger, though, things might change a little. According to the two companies, the merged company will offer a few options. You could subscribe to 50 channels from either XM or Sirius for $6.99, or you could get a "best-of" package of 100 channels selected from both networks for $14.99. If you're already an XM or Sirius customer, you wouldn’t have to replace your old radio. However, if you wanted to pick and choose your own channels from both networks, you would have to pay a little extra and purchase a new receiver. This all depends on whether the merger is approved, and as of October 2007 there have been no decisions.

XM Satellite Radio

XM Radio uses two Boeing HS 702 satellites, appropriately dubbed "Rock" and "Roll," placed in parallel geostationary orbit, one at 85 degrees west longitude and the other at 115 degrees west longitude. Geostationary Earth orbit (GEO) is about 22,223 miles (35,764 km) above Earth, and is the type of orbit most commonly used for communications satellites. The first XM satellite, "Rock," was launched on March 18, 2001, with "Roll" following on May 8. XM Radio has a third HS-702 satellite on the ground ready to be launched in case one of the two orbiting satellites fails.

Photo courtesy XM Satellite Radio
This graphic illustrates how the XM Radio system works.

XM Radio's ground station transmits a signal to its two GEO satellites, which bounce the signals back down to radio receivers on the ground. The radio receivers are programmed to receive and unscramble the digital data signal, which contains up to 100 channels of digital audio. In addition to the encoded sound, the signal contains information about the broadcast. The song title, artist and genre of music are all displayed on the radio. In urban areas, where buildings can block out the satellite signal, XM's broadcasting system is supplemented by ground transmitters.

Photo courtesy XM Satellite Radio
An XM Satellite Radio receiver

Each receiver contains a proprietary chipset. XM began delivering chipsets to its XM radio manufacturing partners in October 2000. The chipset consists of two custom integrated circuits designed by STMicroelectronics. XM has partnered with Pioneer, Alpine, Clarion, Delphi Delco, Sony and Motorola to manufacture XM car radios. Each satellite radio receiver uses a small, car-phone-sized antenna to receive the XM signal. General Motors has invested about $100 million in XM, and Honda has also signed an agreement to use XM radios in its cars. GM began installing XM satellite radio receivers in selected models in early 2001.

Currently, subscribers can receive the XM signal for $12.95 per month. For that price, listeners get up to 100 channels of music, talk and news. They also get access to XM Radio online, a streaming audio service with over 70 channels. Many of the channels have no commercials, with none of the channels having more than seven minutes of ads per hour. XM's content providers include USA Today, BBC, CNN, Sports Illustrated and The Weather Channel. The service bolsters that lineup with its own music channels.

Sirius Satellite Radio

Sirius originally used three SS/L-1300 satellites, instead of GEO satellites, to form an inclined elliptical satellite constellation. Sirius says the elliptical path of its satellite constellation ensures that each satellite spends about 16 hours a day over the continental United States, with at least one satellite over the country at all times. Sirius completed its three-satellite constellation on Nov. 30, 2000. A fourth satellite will remain on the ground, ready to be launched if any of the three active satellites encounters transmission problems. In 2006, Sirius purchased a GEO satellite because of its superior signal delivery. The GEO satellite will supplement the elliptical satellites, not replace them. It is currently under construction, and a launch is planned for fall 2008.

The Sirius system is similar to that of XM. Programs are beamed to one of the three Sirius satellites -- the satellites then transmit the signal to the ground, where your radio receiver picks up one of the channels within the signal. Signals are also be beamed to ground repeaters for listeners in urban areas where the satellite signal can be interrupted.

Just like XM Radio, Sirius currently offers a monthly subscription for $12.95 per month. Sirius produces car radios and home entertainment systems, as well as car and home kits for portable use. The Sirius receiver includes two parts: the antenna module and the receiver module. The antenna module picks up signals from the ground repeaters or the satellite, amplifies the signal and filters out any interference. The signal is then passed on to the receiver module. Inside the receiver module is a chipset consisting of eight chips. The chipset converts the signals from 2.3 gigahertz (GHz) to a lower intermediate frequency. Sirius also offers an adapter that allows conventional car radios to receive satellite signals.

WorldSpace

So far, WorldSpace has been the farthest-reaching company in the satellite radio industry. It put two of its three satellites, AfriStar and AsiaStar, in geostationary orbit before either of the other two companies launched one. AfriStar and AsiaStar were launched in October 1998 and March 2000, respectively. AmeriStar, which will offer service to South America and parts of Mexico, has not yet been launched. Each satellite transmits three signal beams, carrying more than 40 channels of programming, to three overlapping coverage areas of about 5.4 million square miles (14 million square km) each. Each of the WorldSpace satellites' three beams can deliver over 50 channels of crystal-clear audio and multimedia programming via the 1,467- to 1,492-megahertz (MHz) segment of the L-Band spectrum, which is allocated for digital audio broadcasting.

The United States is not currently part of WorldSpace's coverage area, although the company has invested in XM Radio and has an agreement with XM to share any technological developments. WorldSpace is going beyond one nation and eyeing world domination of the radio market. That might be overstating the company's intent a bit, but WorldSpace does plan to reach the corners of our world that most radio stations can't. There are millions of people living in WorldSpace's projected listening area who can't pick up a signal from a conventional radio station. WorldSpace says it has a potential audience of about 4.6 billion listeners spanning five continents.

Photo courtesy WorldSpace
WorldSpace will be able to broadcast to the majority of the world's population when its AmeriStar satellite is launched.

WorldSpace broadcasters uplink their signal to one of the three satellites through a centralized hub site or an individual feeder link station located within the global uplink beam. The satellite then transmits the signal in one, two or all three beams on each satellite. Receivers on the ground then pick up the signal and provide CD-quality sound through a detachable antenna.

Photo courtesy WorldSpace
Two of the WorldSpace satellite radio receivers

WorldSpace satellite receivers are capable of receiving data at a rate of 128 kilobits per second (Kbps). The receivers use the proprietary StarMan chipset, manufactured by STMicroelectronics, to receive digital signals from the satellites.

Alcatraz

2008-07-03T22:20:00.006+07:00

Surrounded by strong currents and fortified by steel and concrete, Alcatraz federal prison was meant to be the highest-security prison in America, a place no one could escape from. The island on which it rests shuns even plant life. Alcatraz is essentially a rock surrounded by water -- hence its forbidding nickname, "The Rock." The only creatures that don't mind being around are the great white sharks that troll the chilly water. Beyond the prison's security measures, the island itself provided a strong deterrent to escape.

Paul Giamou/Aurora/Getty Images
Welcome to Alcatraz

The name Alcatraz at one time represented the worst side of American life, home of the hardest criminals guilty of the worst crimes. It gained such mystique that some gangsters actually wanted to go there to enhance their reputation among other criminals.

The mystique grew further when Hollywood got hold of it. Movies depicted Alcatraz as haunted, dramatized life inside the prison and glorified the criminals that were sent there, giving Alcatraz a larger-than-life image. Escapees, kingpins and the most famous inmate of all, the Birdman of Alcatraz, continued to inflate the prison's reputation in the public eye.

Reality at the prison was sometimes stranger than fiction -- there were several daring escapes, complete with a few missing bodies and an account of chipping away at walls with spoons. In general, however, the story was often more mundane, because conditions at Alcatraz probably weren't much worse than at other prisons at the time.

Alcatraz has a history much greater than the almost 30 years it spent as a federal penitentiary. As a fort, a lighthouse, the site of a Native American occupation and a national park, Alcatraz has changed through the centuries, often reflecting changes in American society. In this article, we'll learn about the infamous federal prison, some of the notable people who were sent there and famous incidents in the prison's history. We'll also find out how Alcatraz became a prison and why it's an important location in the movement for greater Native American rights.

The Escape-proof Alcatraz Prison

Alcatraz Island is actually the top of a mountain, a rough spit of sandstone jutting from San Francisco Bay. The bay was once a valley, but at some point tens of thousands of years ago, sea levels rose and the valley filled in with water. Very little soil covers the island, and as a result, very little plant life grows there naturally (some trees and bushes were brought there by construction crews in the past).

The waters around Alcatraz are especially treacherous. They're usually very cold, below 60 degrees Fahrenheit (16 degrees Celsius), and the currents are strong. When the tide recedes, the current tends to draw out toward the Pacific Ocean, rather than toward San Francisco. To make matters worse, let's not forget the great whites.

Perched on this island rock is a concrete and steel prison. It was first built as a military prison in 1912. In 1934, it was completely remodeled, making it the most high-tech prison in the U.S. at the time.

Juan Silva/Iconica/Getty Images
An aerial view of Alcatraz Island

The prison was built to accommodate about 600 prisoners, although as a federal prison, Alcatraz only held a maximum of 300 inmates (some of the cell blocks from the military prison era were closed off with wire grating). The initial 1912 design was innovative -- the island provided one barrier to escape, and the thick concrete walls and barred windows of the prison building created another. Within the prison building were cell blocks, rows of iron cells that had no point of contact with any outer walls. Each cell block was like a prison inside a prison. The 1934 remodeling replaced all the iron bars with hardened steel, called "tool-resistant" steel because it could withstand cutting with a hacksaw. It cost more to install the new steel bars in 1934 than it cost to build the entire prison in 1912: more than $200,000 [source: Barter].

New steel wasn't the only new technology on the island. A mechanical locking system that allowed guards to open certain cell doors or groups of cell doors remotely, by pulling levers at a control panel, replaced the old system of a single key for each cell. Metal detectors, a relatively new technology in 1934, were also placed on prison grounds.

Justin Sullivan/Getty Images
A re-creation of the cell once occupied by Alcatraz escapee Frank Morris

There were three cell blocks, A, B and C, all running parallel to each other. A Block was the shortest, while B and C ran the length of most of the main building. Each cell block was three tiers high. Each cell was 5 feet (1.5 m) wide by 9 feet (2.7 m) deep, and contained a bed, a sink, a toilet and a small desk for writing. Two shelves for personal items ran along the back wall. Three of the cell walls were solid concrete, while the front "wall" was made of the hardened steel bars. Only one prisoner lived in each cell.

Next, we'll see what life was like inside Alcatraz.

D Block
What do you do when inmates in a jail misbehave? Put them in a more restrictive part of the jail. At Alcatraz, this purpose was served by D Block, where prisoners spent almost every minute in their cells, with only one hour per week for exercise. Repeat rule breakers might end up in "the Hole," one of five special cells with an iron door that blocked all light. One final cell was for the worst of the worst. It had no toilet, just a hole in the floor. Prisoners were often left in this cell naked and without any blankets, and the food was meager.

Prior to D Block's construction, troublesome prisoners were sent to "the dungeon," a series of old cells in the basement, left over from the original building upon whose foundation the prison was built.

Life on Alcatraz Island

For the prisoners living in Alcatraz prison, life was similar to life in other American prisoners of the era. That is to say, not especially pleasant, but neither was Alcatraz the brutal hellhole many blockbuster films make it out to be. In the mornings, each prisoner swept his cell clean, dressed and stood ready for a head count. Then they all marched to the mess hall for breakfast before moving on to work at the docks, in the laundry area or at one of the industrial buildings on the island. They could also spend time studying in the library. After dinner, inmates returned to their cells -- "lights out" was at 9:30 p.m.

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A National Park Service ranger walks down "Broadway."

The prisoners nicknamed the long concrete walkways between the cell blocks. The central walkway was Broadway, and the others were named Park Avenue and Michigan Avenue. The area in between the mess hall and the cell blocks was called Times Square. At either end of the main cell block area was a "gun gallery," a multilevel walkway enclosed in bars and mesh and patrolled by armed guards who had a clear view (and a straight shot) at any point on the cell block.

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An empty guard house near the prison recreation yard as the sun sets on Alcatraz

There were some key differences at Alcatraz, however. The first warden, James Johnston, upheld absolute discipline and a very rigid routine. For the first few years of operation, the prisoners weren't allowed to talk at all except for brief periods, even at meals. Speaking out loud resulted in a stay in the dungeon or on D Block. This enforced silence was one aspect of life at Alcatraz that really grated on the inmates. Eventually, they began talking out en masse, realizing that there weren't enough isolation cells to hold them all, and the talking ban was relaxed [source: Barter].

It's true that the treatment of prisoners in the isolation cells was inhumane, and there were protests regarding prisoner treatment at Alcatraz at the time. These led to gradual reforms that removed some of the harshest punishments. On the other hand, many Alcatraz prisoners were happy to be there instead of another prison. The intense discipline and routine meant the prison was kept very clean, and it was relatively safe compared to other places.

Convicts weren't the only ones living on the island. The guards and their families lived there too. The children took a boat off the island to attend school every day. In fact, nothing was produced or grown on the island, so a boat ride was required for every shopping trip. The island did have a movie theater and other recreational opportunities. But life was also a bit strange. Children weren't allowed to have toy guns, because a prisoner could get a hold of one and use it to bluff a guard and escape. Magazines had to be carefully destroyed, because the prisoners weren't allowed to receive news of the outside world and definitely weren't allowed to read about sex or crime. Razors, knives and silverware had to be thrown into the bay [source: Babyak].

Next: inmates who tried to escape the escape-proof prison.

No Special Treatment Here

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Robert Stroud, the Birdman of Alcatraz

All inmates at Alcatraz were treated the same, even if they were famous. Crime boss Al Capone, who had it easy at his prior prison and ran his criminal empire from behind bars, came to Alcatraz expecting the same deal. He received no special treatment and spent most of his time at Alcatraz sick with syphilis.

The legendary Birdman of Alcatraz, Robert Stroud, was known for breeding and studying dozens of birds in his cell at his former prison. No birds were allowed in his cell at Alcatraz, despite his growing fame outside prison walls. In fact, when his own biography was published, he wasn't allowed to read it because it had chapters about his criminal life [source: Oliver].

Escape from Alcatraz

Despite the intense security, things didn't always run smoothly at Alcatraz Federal Penitentiary. There were several escape attempts from the escape-proof prison, including one that might have been successful.

Nat Farbman/Time Life Pictures/Getty Images
Alcatraz may not have been escape-proof, but that doesn't mean it was easy to break out.

Joseph Bowers was shot and killed while climbing a fence in 1936. Two prisoners managed to escape in 1937, but it's generally believed that they drowned, although their bodies were never found. The next year, three inmates attacked and killed a guard during an escape attempt. One was killed by another guard, a second was wounded and the third gave up.

A 1939 escape attempt was the seed of a fictionalized film,"Murder in the First," starring Kevin Bacon as Henri Young. In real life, Young tried to escape along with three others. They were found on the beach, where one escapee was shot and killed, another wounded, while Young and Rufus McCain were nearly incapacitated by the cold water. A year later, Young stabbed McCain to death in the prison workshop. Young's trial brought attention to the miserable conditions of the solitary confinement cells, where he was kept for extended periods. This eventually resulted in a conviction on a reduced charge, but Young wasn't quite the sympathetic character portrayed in the movie.

It's a 1962 escape that is perhaps the most famous. Brothers Clarence and John Anglin and Frank Morris spent long months patiently working at their plan. They chipped away with spoons at the rotted concrete around the ventilation grates in their cells, using cardboard painted to look like the original grate to disguise the work. When the holes were large enough, they could move into an open maintenance space, reserved for pipes and conduits. There, they constructed life vests and a raft out of raincoats they accumulated. Their absence from their cells at night was disguised by clever papier-mâché heads left on each pillow. Finally, the trio climbed ventilation shafts to the roof, hopped a fence and escaped into San Francisco Bay. Later, some personal items belonging to one of the Anglin brothers were found floating in a plastic bag, leading prison officials to declare the men drowned. They were never seen or heard from again, but the legend persists that they successfully made their way to nearby Angel Island or were picked up by a waiting boat.

In the first season of the TV show MythBusters, the show's crew tested the Anglin/Morris escape strategy, attempting to paddle across the bay on a similar makeshift raft. They successfully made it to shore after a difficult, unpleasant journey. While the experiment doesn't prove that the 1962 escape succeeded, it shows that such an escape was technically possible.

Charles E. Steinheimer/Time & Life Pictures/Getty Images
Alcatraz during the prison riots of May 1946

There were also several riots and protests by prisoners at Alcatraz, many due to the general conditions in the prison. In the 1950s, racist white prisoners rioted because of the presence of black prisoners in the same cell blocks. But the bloodiest incident in Alcatraz history happened in 1946. A band of six prisoners overpowered a guard and launched an effort to take over the entire prison. Several more guards were locked up (and later shot). Guards from nearby San Quentin prison joined with military troops to retake Alcatraz by force. Two guards were killed and three of the prisoners who had started the incident also died. Two of the surviving three were later killed in San Quentin's gas chamber.

In the next section, we'll find out how a nondescript island became a notorious prison.

The Worst of the Worst
Alcatraz's status as a federal prison led to the presence of some inmates who weren't the hardened crooks one might imagine. The concept of a federal prison was relatively new, and anyone convicted of a federal offense might be sent there. As a result, some of the cons at Alcatraz were convicted of lesser crimes, like shoplifting from a store that had a post office branch inside it or transporting bootlegged alcohol into another state.

History of Alcatraz

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Alcatraz: for the birds

We don't know much about the early days of Alcatraz Island, because no one called it home. There is speculation that Native Americans used it as a place of exile for those who broke tribal law. More likely, local tribes visited the island to gather eggs, since birds were the only creatures who lived there. In fact, the name Alcatraz comes from a Spanish word for gannets or pelicans: alcatraces.

In 1847, the first official survey of the island took place. Lieutenant William H. Warner of the U.S. Army noted that the island overlooks the entrance to San Francisco Bay and would make a perfect location for a fortification to guard the area [source: Oliver]. The army built a dock and reshaped the island to construct defensive positions. Several buildings had been constructed by the 1860s, when dozens of artillery pieces were placed to help defend against possible Confederate incursions during the Civil War. A large building called the Citadel was erected to house the troops stationed there -- the prison at Alcatraz would later be built on the Citadel's foundations.

No major military events occurred at Alcatraz, although the island's guns were fired several times, always due to a misunderstanding or misidentification of a ship. As the years passed, the military began shipping prisoners to the island, usually soldiers who had deserted or committed other crimes. The commanding officers would stick these prisoners wherever they would fit (in the Citadel's basement, at first), building new places for them almost haphazardly. At the end of the Civil War, it was decided officially to convert the island into a military prison. The Citadel was converted and expanded in the 1870s.

By the dawning of the 20th century, the old military prison was overflowing and outdated. The massive earthquake that struck San Francisco in 1906 shunted almost 200 city prisoners to Alcatraz, proving once and for all that a modern prison was needed. The Citadel was torn down, and the United States Military Prison, Pacific Branch, Alcatraz Island was completed in 1912.

By the 1930s, military officials had begun to question the need for a prison like Alcatraz. The military wasn't in the business of running prisons, and it was creating a drain on their budget. At the same time, Prohibition and other factors had led a high crime rate nationwide. J. Edgar Hoover, head of the FBI, was spearheading efforts to crack down on criminals. He needed a fearsome prison to send criminals to, and Alcatraz fit the bill. The change of ownership and renovation of the prison took place between 1933 and 1934, when the first prisoners arrived under a shroud of secrecy.

Jon Brenneis/Time Life Pictures/
Getty Images
Sioux tribesmen staking claim to live and farm on Alcatraz.

Alcatraz's life as a federal prison ended for many of the same reasons it stopped being a military prison. Everything on Alcatraz had to be shipped in -- every meal, magazine and pack of cigarettes -- which made running Alcatraz far more expensive than a mainland prison. In addition, the old concrete building was deteriorating due to the constant contact with saltwater. It would cost millions to repair. The final nail in the coffin was the escape of 1962. If the prison wasn't truly escape-proof, what purpose did it serve? In 1963, it was closed down permanently.

The history of Alcatraz wasn't over, however. In the late 1960s and 1970s, the island was occupied by a band of Native Americans from several tribes who demanded that they be given ownership of the island. Ultimately, their demands weren't met and the takeover failed, but it brought a great deal of attention to the inequalities suffered by Native Americans. In the aftermath, government policies changed to allow tribes to determine their own fates and exist as political and commercial entities [source: Johnson].

In 1973, Alcatraz Island became part of Golden Gate National Recreation Area. The prison still stands, and millions of visitors have taken tour boats to the island to experience a small piece of U.S. history.

For more articles on prisons and other history stuff you might like, try the next page.

What was the Prison Project?

2008-07-03T22:13:00.002+07:00

Back in the early 1990s, most of us weren't yet savvy Internet surfers. We still got all our news from the paper rather than Web sites, and e-mail hadn't yet taken over faxes and letters in our business and personal lives. Many of us were still years away from learning about the possibilities of the Internet -- that is, if we'd heard of it at all. However, Bill Burrall, a computer instructor for Moundville Junior High School in West Virginia, was ahead of us. He'd already been steeped in the Internet world for over a decade, and was not only thoroughly familiar with it, but recognized its educational potential for students.

iStockPhoto/Tom Mc Nemar
Burrall's prison project coordinated with several inmates inside this facility, the West Virginia State Penitentiary.

Using the AT&T Learning Network, a worldwide educational Internet community, Burrall and his middle school classes participated in a valuable telecommunications project where kids got the chance to correspond with other classes from around the country and around the world. After realizing the success of these projects, Burrall decided to take advantage of the same system in a new way that later put him in the national spotlight.

As it happened, Moundsville Junior High was situated merely a few blocks from West Virginia's State Penitentiary. Where most teachers would have found this close proximity a source of concern, Burrall saw opportunity. The school would serve as a focal point for Burrall's revolutionary prison project, which used telecommunications to connect kids from around the world to the prison's inmates. After a year of struggle to get his idea approved by the school board and eventually the governor, Burrall was finally able to launch his prison project in 1992, later known as the "Inmates and Alternatives Project."

Read the next page to find out how Burrall used telecommunications to offer students life-altering experiences.

Another Look Inside
In a vastly different approach to gain inmate insight, Bill Geerhart, a pop-culture historian, mailed letters to notorious murderers posing as a conflicted 10 year old with questions about whether to stay in school. He later published what he claimed were actual responses from such people as Charles Manson, Richard Ramirez and Ted Kacynski -- some disturbing, some unintelligible [Source: RADAR].

Prison Pen Pals: How the Prison Project Worked

As an authority on educational telecommunications, Burrall had the advantage of being one of eight coordinators in the AT&T Learning Network, which consisted of 50,000 students in 22 foreign countries [source: Burrall]. This helped him orchestrate a system where he could communicate with other middle-school teachers from such places as Louisiana, Alaska and the Netherlands.

Meanwhile, Burrall partnered with the education department at the West Virginia State Penitentiary. There, several inmates volunteered to become "pen pals" (pun intended) with students. Of the twelve participants, six were "lifers," meaning they had been sentenced to life in prison. To kick things off, Burrall asked these inmates to assume pseudonyms (fake names) and write short biographies of themselves. Taking names from the J.R.R. Tolkien Lord of the Rings trilogy, such as "Frodo" and "Pippin," many listed their hobbies and described their families and what life was like before prison.

The inmates would submit their letters to the prison's electronic bulletin board, known as the "Play Pen." The educational director at the prison, who would read over them, then sent them to Burrall at Moundsville. Burrall would look them over before disseminating them to the appropriate schools.

Burrall assigned one inmate to each of the participating schools including his own, so that each class could serve as a consistent pen pal to a particular inmate. After reading the inmate's biography, the teacher helped students to come up with a set of 10 questions for their pen pal having to do with "society's problems." Students submitted these questions onto an electronic bulletin board (anonymously) under the teachers' supervision. They commonly asked about the inmate's relationship with his family or what life was like in prison. The inmates responded to these questions, and the kids were then allowed to ask more questions. This correspondence went on for about 15 weeks.

iStockPhoto/Andrejs Zemdega
For the prison project, inmates received a printout of the children's questions so that they could respond.

Although there was concern about the prisoners' responses, the inmates' answers were better than even Burrall hoped. Amazingly, Burrall asserts that neither he nor the prison's educational director ever needed to censor inappropriate material in the inmates' letters [source: Burrall]. Instead, the prisoners were quick to warn the students about how easy it is to go down the wrong path and described the despair they felt in prison. Burrall claims that the "virtual bond" formed during the correspondence challenged the students' misconceptions [source: Burrall]. Prisoners also showed their appreciation of the project, claiming that it helped them to gain personal insight [source: Burrall].

After a few successful semesters of working with many different schools, the project ended -- partly because the prison closed, and partly because Burrall was chosen as IBM's National Teacher of the Year for Technology and as a result of this honor took several years to tour the country and give talks about the project to other educators. The project has even been given the distinction of being archived in the Smithsonian.

Since then, some educators have been able to replicate the project, such as one known as the Harlem Valley Project in New York, which also ran for a few semesters.

For more information on prison life and telecommunications technology, explore the links on the next page.

Prison Project vs. "Scared Straight"
Although they are often compared, Bill Burrall's Prison Project is drastically different from "Scared Straight" programs, where adolescents personally visit prisons to learn about life inside. For instance, Burrall's program let kids in remote areas (such as the kids in one Alaskan school) have the opportunity to connect with prisoners. In addition, the anonymity allowed inmates to open up more, ensuring the emotional efficacy of the program, as well as the safety of the kids.

evolution

2008-05-16T19:15:00.002+07:00

The theory of evolution is one of the best-known scientific theories around. Try to make it through a day without using or hearing the word "evolution" and you'll see just how widespread this theory is.

Evolution is fascinating because it attempts to answer one of the most basic human questions: Where did life, and human beings, come from? The theory of evolution proposes that life and humans arose through a natural process. A very large number of people do not believe this, which is something that keeps evolution in the news.

In this article, we will explore the theory of evolution and how it works. We will also examine several important areas that show holes in the current theory -- places where scientific research will be working in the coming years in order to complete the theory. The holes are considered by many to be proof that the theory of evolution should be overthrown. As a result, quite a bit of controversy has surrounded evolution ever since it was first proposed.

Let's start off by taking a look at the basic principles of the theory of evolution, look at some examples and then examine the holes.

The Basic Process of Evolution

The basic theory of evolution is surprisingly simple. It has three essential parts:

It is possible for the DNA of an organism to occasionally change, or mutate. A mutation changes the DNA of an organism in a way that affects its offspring, either immediately or several generations down the line.
The change brought about by a mutation is either beneficial, harmful or neutral. If the change is harmful, then it is unlikely that the offspring will survive to reproduce, so the mutation dies out and goes nowhere. If the change is beneficial, then it is likely that the offspring will do better than other offspring and so will reproduce more. Through reproduction, the beneficial mutation spreads. The process of culling bad mutations and spreading good mutations is called natural selection.
As mutations occur and spread over long periods of time, they cause new species to form. Over the course of many millions of years, the processes of mutation and natural selection have created every species of life that we see in the world today, from the simplest bacteria to humans and everything in between.

Billions of years ago, according to the theory of evolution, chemicals randomly organized themselves into a self-replicating molecule. This spark of life was the seed of every living thing we see today (as well as those we no longer see, like dinosaurs). That simplest life form, through the processes of mutation and natural selection, has been shaped into every living species on the planet.

Can such a simple theory explain all of life as we know it today? Let's start by understanding how life works and then look at some examples.

How Life Works: DNA and Enzymes

Evolution can be seen in its purest form in the daily evolution of bacteria. If you have read How Cells Work, then you are familiar with the inner workings of the E. coli bacteria and can skip this section. Here's a quick summary to highlight the most important points in How Cells Work:

A bacterium is a small, single-celled organism. In the case of E. coli, the bacteria are about one-hundredth the size of a typical human cell. You can think of the bacteria as a cell wall (think of the cell wall as a tiny plastic bag) filled with various proteins, enzymes and other molecules, plus a long strand of DNA, all floating in water.
The DNA strand in E. coli contains about 4 million base pairs, and these base pairs are organized into about 1,000 genes. A gene is simply a template for a protein, and often these proteins are enzymes.
An enzyme is a protein that speeds up a particular chemical reaction. For example, one of the 1,000 enzymes in an E. coli's DNA might know how to break a maltose molecule (a simple sugar) into its two glucose molecules. That is all that that particular enzyme can do, but that action is important when an E. coli is eating maltose. Once the maltose is broken into glucose, other enzymes act on the glucose molecules to turn them into energy for the cell to use.
To make an enzyme that it needs, the chemical mechanisms inside an E. coli cell make a copy of a gene from the DNA strand and use this template to form the enzyme. The E. coli might have thousands of copies of some enzymes floating around inside it, and only a few copies of others. The collection of 1,000 or so different types of enzymes floating in the cell makes all of the cell's chemistry possible. This chemistry makes the cell "alive" -- it allows the E. coli to sense food, move around, eat and reproduce. See How Cells Work for more details.

You can see that, in any living cell, DNA helps create enzymes, and enzymes create the chemical reactions that are "life."

In the next section, we'll discuss how bacteria reproduce.

How Life Works: Asexual Reproduction

Bacteria reproduce asexually. This means that, when a bacteria cell splits, both halves of the split are identical -- they contain exactly the same DNA. The offspring is a clone of the parent.

As explained in How Human Reproduction Works, higher organisms like plants, insects and animals reproduce sexually, and this process makes the actions of evolution more interesting. Sexual reproduction can create a tremendous amount of variation within a species. For example, if two parents have multiple children, all of the children can be remarkably different. Two brothers can have different hair color, different heights, different blood types and so on. Here's why that happens:

Instead of a long loop of DNA like a bacterium, cells of plants and animals have chromosomes that hold the DNA strands. Humans have 23 pairs of chromosomes, for a total of 46 chromosomes. Fruit flies have five pairs. Dogs have 39 pairs, and some plants have as many as 100.

The human chromosomes hold the DNA of the human genome. Each parent contributes 23 chromosomes.
Chromosomes come in pairs. Each chromosome is a tightly packed strand of DNA. There are two strands of DNA joined together at the centromere to form an X-shaped structure. One strand comes from the mother and one from the father.
Because there are two strands of DNA, it means that animals have two copies of every gene, rather than one copy as in an E. coli cell.

Photo courtesy U.S. DOE, Human Genome Project
When a female creates an egg or a male creates a sperm, the two strands of DNA must combine into a single strand. The sperm and egg from the mother and father each contribute one copy of each chromosome. They meet to give the new child two copies of each gene.
To form the single strand in the sperm or egg, one or the other copy of each gene is randomly chosen. One or the other gene from the pair of genes in each chromosome gets passed on to the child.

Because of the random nature of gene selection, each child gets a different mix of genes from the DNA of the mother and father. This is why children from the same parents can have so many differences.

A gene is nothing but a template for creating an enzyme. This means that, in any plant or animal, there are actually two templates for every enzyme. In some cases, the two templates are the same (homozygous), but in many cases the two templates are different (heterozygous).

Here is a well-known example from pea plants that helps understand how pairs of genes can interact. Peas can be tall or short. The difference comes, according to Carol Deppe in the book "Breed your own Vegetable Varieties":

...in the synthesis of a plant hormone called gibberellin. The "tall" version of the gene is normally the form that is found in the wild. The "short" version, in many cases, has a less active form of one of the enzymes involved in the synthesis of the hormone, so the plants are shorter. We refer to two genes as alleles of each other when they are inherited as alternatives to each other. In molecular terms, alleles are different forms of the same gene. There can be more than two alleles of a gene in a population of organisms. But any given organism has only two alleles at the most. Shorter plants usually cannot compete with the taller forms in the wild. A short mutant in a patch of tall plants would be shaded out. That problem isn't relevant when a human plants a patch or field with nothing but short plants. And short plants may be earlier than tall ones, or less subject to lodging (falling over) in the rain or wind. They also may have a higher proportion of grain to the rest of the plant. So shorter plants can be advantageous as cultivated crops. Specific mutations or alleles are not good or bad in and of themselves, but only within a certain context. An allele that promotes better growth in hot weather may promote inferior growth in cold weather, for example.

One thing to notice in Deppe's quote is that a mutation in a single gene may have no effect on an organism, or its offspring, or its offspring's offspring. For example, imagine an animal that has two identical copies of a gene in one allele. A mutation changes one of the two genes in a harmful way. Assume that a child receives this mutant gene from the father. The mother contributes a normal gene, so it may have no effect on the child (as in the case of the "short" pea gene). The mutant gene might persist through many generations and never be noticed until, at some point, both parents of a child contribute a copy of the mutant gene. At that point, taking the example from Deppe's quote, you might get a short pea plant because the plant does not form the normal amount of gibberellin.

Another thing to notice is that many different forms of a gene can be floating around in a species. The combination of all of the versions of all of the genes in a species is called the gene pool of the species. The gene pool increases when a mutation changes a gene and the mutation survives. The gene pool decreases when a gene dies out.

One of the simplest examples of evolution can be witnessed in an E. coli cell. To get a better grip on the process, we'll take a look at what happens in this cell.

The Simplest Example of Evolution

The process of evolution acts on an E. coli cell by creating a mutation in the DNA. It is not uncommon for the DNA strand in an E. coli bacterium to get corrupted. An X-ray, a cosmic ray or a stray chemical reaction can change or damage the DNA strand. In most cases, a particular E. coli cell with mutated DNA will either die, fix the damage in the strand or fail to reproduce. In other words, most mutations go nowhere. But every so often, a mutation will actually survive and the cell will reproduce.

Imagine, for example, a bunch of identical E. coli cells that are living in a petri dish. With plenty of food and the right temperature, they can double every 20 minutes. That is, each E. coli cell can duplicate its DNA strand and split into two new cells in 20 minutes.

Now, imagine that someone pours an antibiotic into the petri dish. Many antibiotics kill bacteria by gumming up one of the enzymes that the bacteria needs to live. For example, one common antibiotic gums up the enzyme process that builds the cell wall. Without the ability to add to the cell wall, the bacteria cannot reproduce, and eventually they die.

When the antibiotic enters the dish, all of the bacteria should die. But imagine that, among the many millions of bacteria living in the dish, one of them acquires a mutation that makes its cell-wall-building enzyme different from the norm. Because of the difference, the antibiotic molecule does not attach properly to the enzyme, and therefore does not affect it. That one E. coli cell will survive, and since all of its neighbors are dead, it can reproduce and take over the petri dish. There is now a strain of E. coli that is immune to that particular antibiotic.

In this example, you can see evolution at work. A random DNA mutation created an E. coli cell that is unique. The cell is unaffected by the antibiotic that kills all of its neighbors. This unique cell, in the environment of that petri dish, is able to survive.

E. coli are about as simple as living organisms can get, and because they reproduce so rapidly you can actually see evolution's effects on a normal time scale. In the past several decades, many different types of bacteria have become immune to antibiotics. In a similar way, insects become immune to insecticides because they breed so quickly. For example, DDT-resistant mosquitoes evolved from normal mosquitoes.

In most cases, evolution is a much slower process.

The Speed of Mutations

As mentioned in the previous section, many things can cause a DNA mutation, including:

X-rays
Cosmic rays
Nuclear radiation
Random chemical reactions in the cell

Therefore, mutations are fairly common. Mutations happen at a steady rate in any population, but the location and type of every mutation is completely random. According to Carl Sagan in "The Dragons of Eden":

Large organisms such as human beings average about one mutation per ten gametes [a gamete is a sex cell, either sperm or egg] -- that is, there is a 10 percent chance that any given sperm or egg cell produced will have a new and inheritable change in the genetic instructions that make up the next generation. These mutations occur at random and are almost uniformly harmful -- it is rare that a precision machine is improved by a random change in the instructions for making it.

According to "Molecular Biology of the Cell":

Only about one nucleotide pair in a thousand is randomly changed every 200,000 years. Even so, in a population of 10,000 individuals, every possible nucleotide substitution will have been "tried out" on about 50 occasions in the course of a million years, which is a short span of time in relation to the evolution of species. Much of the variation created in this way will be disadvantageous to the organism and will be selected against in the population. When a rare variant sequence is advantageous, however, it will be rapidly propagated by natural selection. Consequently, it can be expected that in any given species the functions of most genes will have been optimized by random point mutation and selection.

According to the book "Evolution," by Ruth Moore, it is possible to speed up mutations with radiation:

So Muller put hundreds of fruit flies in gelatin capsules and bombarded them with X-rays. The irradiated flies were then bred to untreated ones. In 10 days thousands of their offspring were buzzing around their banana-mash feed, and Muller was looking upon an unprecedented outburst of man-made mutations. There were flies with bulging eyes, flat eyes, purple, yellow and brown eyes. Some had curly bristles, some no bristles...

Mutations fuel the process of evolution by providing new genes in the gene pool of a species.

Then, natural selection takes over.

Natural Selection

As you saw in the previous section, mutations are a random and constant process. As mutations occur, natural selection decides which mutations will live on and which ones will die out. If the mutation is harmful, the mutated organism has a much decreased chance of surviving and reproducing. If the mutation is beneficial, the mutated organism survives to reproduce, and the mutation gets passed on to its offspring. In this way, natural selection guides the evolutionary process to incorporate only the good mutations into the species, and expunge the bad mutations.

The book "Extinct Humans," by Ian Tattersall and Jeffrey Schwartz, puts it this way:

...in every generation, many more individuals are produced than ever survive to maturity and to reproduce themselves. Those that succeed -- the "fittest" -- carry heritable features that not only promote their own survival but are also passed along preferentially to their offspring. In this view, natural selection is no more than the sum of all those factors that act to promote the reproductive success of some individuals (and its lack in others). Add the dimension of time, and over the generations natural selection will act to change the complexion of each evolving lineage, as advantageous variations become common in the population at the expense of those less advantageous.

Let's look at an example of natural selection from How Whales Work.

The ancestors of whales lived on land -- there is evidence of the evolution of the whale from life on land to life in the sea (read How Whales Work for details), but how and why did this happen? The "why" is commonly attributed to the abundance of food in the sea. Basically, whales went where the food was. The "how" is a bit more perplexing: Whales are mammals, like humans are, and like humans, they lived and walked on solid ground, breathing air into their lungs. How did whales become sea creatures? One aspect of this evolution, according to Tom Harris, author of How Whales Work, is explained as follows:

To make this transition, whales had to overcome a number of obstacles. First of all, they had to contend with reduced access to breathable air. This led to a number of remarkable adaptations. The whale's "nose" moved from the face to the top of the head. This blowhole makes it easy for whales to breathe in air without fully surfacing. Instead, a whale swims near the surface, arches its body so its back briefly emerges and then flexes its tail, propelling it quickly to lower depths.

Photo courtesy Sea World Orlando

Odd as it seems that the whale's "nose" actually changed positions, the theory of evolution explains this phenomenon as a long process that occurs over perhaps millions of years:

Random mutation resulted in at least one whale whose genetic information placed its "nose" farther back on its head.
The whales with this mutation were more suited to the sea environment (where the food was) than "normal" whales, so they thrived and reproduced, passing on this genetic mutation to their offspring: Natural selection "chose" this trait as favorable.
In successive generations, further mutations placed the nose farther back on the head because the whales with this mutation were more likely to reproduce and pass on their altered DNA. Eventually, the whale's nose reached the position we see today.

Natural selection selects those genetic mutations that make the organism most suited to its environment and therefore more likely to survive and reproduce. In this way, animals of the same species who end up in different environments can evolve in completely different ways.

Creating a New Species

Imagine that you take a group of Saint Bernards and put them on one island, and on another island you put a group of Chihuahuas. Saint Bernards and Chihuahuas are both members of the species "dog" right now -- a Saint Bernard can mate with a Chihuahua (probably through artificial insemination) and create normal puppies. They will be odd-looking puppies, but normal puppies nonetheless.

Given enough time, it is possible to see how speciation -- the development of a new species through evolution -- could occur among the Saint Bernards and the Chihuahuas on their respective islands. What would happen is that the Saint Bernard gene pool would acquire random mutations shared by all of the Saint Bernards on the island (through interbreeding), and the Chihuahuas would acquire a completely different set of random mutations shared by all of the Chihuahuas on their island. These two gene pools would eventually become incompatible with one another, to the point where the two breeds could no longer interbreed. At that point, you have two distinct species.

Because of the huge size difference between a Saint Bernard and a Chihuahua, it would be possible to put both types of dogs on the same island and have the exact same process occur. The Saint Bernards would naturally breed with only the Saint Bernards and the Chihuahuas would naturally breed with only the Chihuahuas, so speciation would still occur.

If you put two groups of Chihuahuas on two separate islands, the process would also occur. The two groups of Chihuahuas would accumulate different collections of mutations in their gene pools and eventually become different species that could not interbreed.

The theory of evolution proposes that the process that might create a separate Chihuahua-type species and Saint Bernard-type species is the same process that has created all of the species we see today. When a species gets split into two (or more) distinct subsets, for example by a mountain range, an ocean or a size difference, the subsets pick up different mutations, create different gene pools and eventually form distinct species.

Is this truly how all of the different species we see today have formed? Most people agree that bacteria evolve in small ways (microevolution), but there is some controversy around the idea of speciation (macroevolution). Let's take a look at where the controversy comes from.

Holes in the Theory

The theory of evolution is just that -- a theory. According to "The American Heritage Dictionary," a theory is:

A set of statements or principles devised to explain a group of facts or phenomena, especially one that has been repeatedly tested or is widely accepted and can be used to make predictions about natural phenomena.

Evolution is a set of principles that tries to explain how life, in all its various forms, appeared on Earth. The theory of evolution succeeds in explaining why we see bacteria and mosquitoes becoming resistant to antibiotics and insecticides. It also successfully predicted, for example, that X-ray exposure would lead to thousands of mutations in fruit flies.

Many theories are works in progress, and evolution is one of them. There are several big questions that the theory of evolution cannot answer right now. This is not unusual. Newtonian physics worked really well for hundreds of years, and it still works well today for many types of problems. However, it does not explain lots of things that were eventually answered by Einstein and his theories of relativity. People create new theories and modify existing ones to explain the unexplained.

In answering the open questions that still remain unsolved, the theory of evolution will either become complete or it will be replaced by a new theory that better explains the phenomena we see in nature. That is how the scientific process works.

Here are three common questions that are asked about the current theory of evolution:

How does evolution add information to a genome to create progressively more complicated organisms?
How is evolution able to bring about drastic changes so quickly?
How could the first living cell arise spontaneously to get evolution started?

Let's look at each of these questions briefly in the following sections.

Question 1: How Does Evolution Add Information?

The theory of evolution explains how strands of DNA change. An X-ray, cosmic ray, chemical reaction or similar mechanism can modify a base pair in the DNA strand to create a mutation, and this modification can lead to the creation of a new protein or enzyme.

The theory of evolution further proposes that billions of these mutations created all of the life forms we see today. An initial self-replicating molecule spontaneously formed. It evolved into single-cell organisms. These evolved into multi-cell organisms, which evolved into vertebrates like fish, and so on. In the process, DNA structures evolved from the asexual single-strand format found in bacteria today into the dual-strand chromosomal format found in all higher life forms. The number of chromosomes also proliferated. For example, fruit flies have five chromosomes, mice have 20, humans have 23 and dogs have 39.

Evolution's mutation mechanism does not explain how growth of a genome is possible. How can point mutations create new chromosomes or lengthen a strand of DNA? It is interesting to note that, in all of the selective breeding in dogs, there has been no change to the basic dog genome. All breeds of dog can still mate with one another. People have not seen any increase in dog's DNA, but have simply selected different genes from the existing dog gene pool to create the different breeds.

One line of research in this area focuses on transposons, or transposable elements, also referred to as "jumping genes." A transposon is a gene that is able to move or copy itself from one chromosome to another. The book "Molecular Biology of the Cell" puts it this way:

Transposable elements have also contributed to genome diversity in another way. When two transposable elements that are recognized by the same site-specific recombination enzyme (transposase) integrate into neighboring chromosomal sites, the DNA between them can become subject to transposition by the transposase. Because this provides a particularly effective pathway for the duplication and movement of exons (exon shuffling), these elements can help create new genes.

Another area of research involves polyploidy. Through the process of polyploidy, the total number of chromosomes can double, or a single chromosome can duplicate itself. This process is fairly common in plants, and explains why some plants can have as many as 100 chromosomes.

The amount of research in this area is truly remarkable and is teaching scientists amazing things about DNA. The following links give you a taste of that research, and are interesting if you would like to learn more about these topics:

you create a very large cage and put a group of mice into it. You let the mice live and breed in this cage freely, without disturbance. If you were to come back after five years and look into this cage, you would find mice. Five years of breeding would cause no change in the mice in that cage -- they would not evolve in any noticeable way. You could leave the cage alone for a hundred years and look in again and what you would find in the cage is mice. After several hundred years, you would look into the cage and find not 15 new species, but mice.

The point is that evolution in general is an extremely slow process. When two mice breed, the offspring is a mouse. When that offspring breeds, its offspring is a mouse. When that offspring breeds... And the process continues. Point mutations do not change this fact in any significant way over the short haul.

Carl Sagan, in "The Dragons of Eden," put it this way:

The time scale for evolutionary or genetic change is very long. A characteristic period for the emergence of one advanced species from another is perhaps a hundred thousand years; and very often the difference in behavior between closely related species -- say, lions and tigers -- does not seem very great. An example of recent evolution of organ systems in humans is our toes. The big toe plays an important function in balance while walking; the other toes have much less obvious utility. They are clearly evolved from fingerlike appendages for grasping and swinging, like those of arboreal apes and monkeys. This evolution constitutes a respecialization -- the adaptation of an organ system originally evolved for one function to another and quite different function -- which required about ten million years to emerge.

The fact that it takes evolution 100,000 or 10 million years to make relatively minor changes in existing structures shows just how slow evolution really is. The creation of a new species is time consuming.

On the other hand, we know that evolution can move extremely quickly to create a new species. One example of the speed of evolution involves the progress mammals have made. You have probably heard that, about 65 million years ago, all of the dinosaurs died out quite suddenly. One theory for this massive extinction is an asteroid strike. For dinosaurs, the day of the asteroid strike was a bad one, but for mammals it was a good day. The disappearance of the dinosaurs cleared the playing field of most predators. Mammals began to thrive and differentiate.

Example: The Evolution of Mammals
65 million years ago, mammals were much simpler than they are today. A representative mammal of the time was the species Didelphodon, a smallish, four-legged creature similar to today's opossum.

In 65 million years, according to the theory of evolution, every mammal that we see today (over 4,000 species) evolved from small, four-legged creatures like Didelphodon. Through random mutations and natural selection, evolution has produced mammals of striking diversity from that humble starting point:

Humans
Dogs
Moles
Bats
Whales
Elephants
Giraffes
Panda bears
Horses

Evolution has created thousands of different species that range in size and shape from a small brown bat that weighs a few grams to a blue whale that is nearly 100 feet (30.5 m) long.

Let's take Carl Sagan's statement that "A characteristic period for the emergence of one advanced species from another is perhaps a hundred thousand years, and very often the difference in behavior between closely related species -- say, lions and tigers -- does not seem very great." In 65 million years, there are only 650 periods of 100,000 years -- that's 650 "ticks" of the evolutionary clock.

Imagine trying to start with an opossum and get to an elephant in 650 increments or less, even if every increment were perfect. An elephant's brain is hundreds of times bigger than an opossum's, containing hundreds of times more neurons, all perfectly wired. An elephant's trunk is a perfectly formed prehensile appendage containing 150,000 muscle elements (reference). Starting with a snout like that of an opossum, evolution used random mutations to design the elephant's snout in only 650 ticks. Imagine trying to get from an opossum to a brown bat in 650 increments. Or from an opossum to a whale. Whales have no pelvis, have flukes, have very weird skulls (especially the sperm whale), have blow holes up top, have temperature control that allows them to swim in arctic waters and they consume salt water rather than fresh. It is difficult for many people to imagine that sort of speed given the current theory.

Example: The Evolution of the Human Brain
Here is another example of the speed problem. Current fossil evidence indicates that modern humans evolved from a species called Homo erectus. Homo erectus appeared about 2 million years ago. Looking at the skull of Homo erectus, we know that its brain size was on the order of 800 or 900 cubic centimeters (CCs).

Modern human brain size averages about 1,500 CCs or so. In other words, in about 2 million years, evolution roughly doubled the size of the Homo erectus brain to create the human brain that we have today. Our brains contain approximately 100 billion neurons today, so in 2 million years, evolution added 50 billion neurons to the Homo erectus brain (while at the same time redesigning the skull to accommodate all of those neurons and redesigning the female pelvis to let the larger skull through during birth, etc.).

Let's assume that Homo erectus was able to reproduce every 10 years. That means that, in 2 million years, there were 200,000 generations of Homo erectus possible. There are four possible explanations for where the 50 billion new neurons came from in 200,000 generations:

Every generation, 250,000 new neurons were added to the Homo erectus brain (250,000 * 200,000 = 50 billion).
Every 100,000 years, 2.5 billion new neurons were added to the Homo erectus brain (2,500,000,000 * 20 = 50 billion).
Perhaps 500,000 years ago, there was a spurt of 20 or so closely-spaced generations that added 2.5 billion neurons per generation.
One day, spontaneously, 50 billion new neurons were added to the Homo erectus brain to create the Homo sapiens brain.

* In an absolutely fascinating experiment first reported in July 2002, scientists modified a single mouse gene and created mice with brains 50% larger than normal. This experiment shows that a point mutation can, in fact, have an immense effect on brain size. It is still unknown whether the larger brains make the mice smarter or not, but it is easy to imagine later mutations refining the wiring of these millions of new neurons.

In another fascinating study, researches have identified minimal changes in an amino acid on a single gene that have a profound effect on speech processing in humans.

It does appear that tiny changes in single genes can have very large effects on the species.

None of these scenarios is particularly comfortable. We see no evidence that evolution is randomly adding 250,000 neurons to each child born today, so that explanation is hard to swallow. The thought of adding a large package of something like 2.5 billion neurons in one step is difficult to imagine, because there is no way to explain how the neurons would wire themselves in. What sort of point mutation would occur in a DNA molecule that would suddenly create billions of new neurons and wire them correctly?* The current theory of evolution does not predict how this could happen.

One line of current research is looking at the effect of very small changes in DNA patterns during embryonic development. Any new animal, be it a mouse or a human, starts life as a single cell. That cell differentiates and develops into the complete animal. A tremendous amount of signaling happens between cells during the development process to ensure that everything ends up in the right place. Tiny changes in these signaling processes can have very large effects on the resulting animal. This is how the human genome, with at most 60,000 or so genes, is able to specify the creation of a human body containing trillions of cells, billions of carefully wired neurons and hundreds of different cell types all brilliantly sculpted into organs as diverse as the heart and the eyes. The book "Molecular Biology of the Cell" puts it this way:

Humans, as a genus distinct from the great apes, have existed for only a few million years. Each human gene has therefore had the chance to accumulate relatively few nucleotide changes since our inception, and most of these have been eliminated by natural selection. A comparison of humans and monkeys, for example, shows that their cytochrome-c molecules differ in about 1 percent and their hemoglobins in about 4 percent of their amino acid positions. Clearly, a great deal of our genetic heritage must have been formed long before Homo sapiens appeared, during the evolution of mammals (which started about 300 million years ago) and even earlier. Because the proteins of mammals as different as whales and humans are very similar, the evolutionary changes that have produced such striking morphological differences must involve relatively few changes in molecules from which we are made. Instead, it is thought that the morphological differences arise from differences in the temporal and spatial pattern of gene expression during embryonic development, which then determine the size, shape and other characteristics of the adult.

In other words, there just are not that many differences in the DNA of a human and a whale, yet humans and whales look totally different. Small collections of DNA mutations can have a very big effect on the final result.

Right now, the signaling mechanisms that wire up the 100 billion cells in the human brain are something of a mystery. How can the mere 60,000 genes in the human genome tell 100 billion neurons how to precisely wire themselves in the human brain? No one right now has a clear understanding of how so few genes can meticulously wire so many neurons. In a developing fetus in the womb, DNA is correctly creating and wiring up millions of cells per minute. Given that DNA does wire up a working human brain every time a baby is born, it may be the case that DNA has special properties that make evolution work more efficiently. As the mechanisms become better understood, the effects of DNA mutations during development will become better understood as well.

Question 3: Where Did the First Living Cell Come From?

In order for the principles of mutation and natural selection in the theory of evolution to work, there have to be living things for them to work on. Life must exist before it can to start diversifying. Life had to come from somewhere, and the theory of evolution proposes that it arose spontaneously out of the inert chemicals of planet Earth perhaps 4 billion years ago.

Could life arise spontaneously? If you read How Cells Work, you can see that even a primitive cell like an E. coli bacteria -- one of the simplest life forms in existence today -- is amazingly complex. Following the E. coli model, a cell would have to contain at an absolute minimum:

A cell wall of some sort to contain the cell
A genetic blueprint for the cell (in the form of DNA)
An enzyme capable of copying information out of the genetic blueprint to manufacture new proteins and enzymes
An enzyme capable of manufacturing new enzymes, along with all of the building blocks for those enzymes
An enzyme that can build cell walls
An enzyme able to copy the genetic material in preparation for cell splitting (reproduction)
An enzyme or enzymes able to take care of all of the other operations of splitting one cell into two to implement reproduction (For example, something has to get the second copy of the genetic material separated from the first, and then the cell wall has to split and seal over in the two new cells.)
Enzymes able to manufacture energy molecules to power all of the previously mentioned enzymes

Obviously, the E. coli cell itself is the product of billions of years of evolution, so it is complex and intricate -- much more complex than the first living cells. Even so, the first living cells had to possess:

A cell wall
The ability to maintain and expand the cell wall (grow)
The ability to process "food" (other molecules floating outside the cell) to create energy
The ability to split itself to reproduce

Otherwise, it is not really a cell and it is not really alive. To try to imagine a primordial cell with these capabilities spontaneously creating itself, it is helpful to consider some simplifying assumptions. For example:

Perhaps the original energy molecule was very different from the mechanism found in living cells today, and the energy molecules happened to be abundant and free-floating in the environment. Therefore, the original cell would not have had to manufacture them.
Perhaps the chemical composition of the Earth was conducive to the spontaneous production of protein chains, so the oceans were filled with unimaginable numbers of random chains and enzymes.
Perhaps the first cell walls were naturally forming lipid spheres, and these spheres randomly entrapped different combinations of chemicals.
Perhaps the first genetic blueprint was something other than DNA.

These examples do simplify the requirements for the "original cell," but it is still a long way to spontaneous generation of life. Perhaps the first living cells were completely different from what we see today, and no one has yet imagined what they might have been like. Speaking in general terms, life can only have come from one of two possible places:

Spontaneous creation - Random chemical processes created the first living cell.
Supernatural creation - God or some other supernatural power created the first living cell.

And it doesn't really matter if aliens or meteorites brought the first living cell to earth, because the aliens would have come into existence through either spontaneous creation or supernatural creation at some point -- something had to create the first alien cells.

Most likely, it will be many years before research can completely answer any of the three questions mentioned here. Given that DNA was not discovered until the 1950s, the research on this complicated molecule is still in its infancy, and we have much to learn.

The Future of Evolution

One exciting thing about the theory of evolution is that we can see its effects both today and in the past. For example, the book "Evolution" mentions this:

The earliest known reptiles are so amphibian-like that their assignment to one category or the other is largely a matter of opinion. In this area of life, however, there was no missing link; all the gradations from amphibian to reptile exist with a clarity seldom equaled in paleontology.

In other words, there is plenty of evidence, past and present, for some sort of evolutionary process. We see it in bacteria and insects today, and we see it in the fossil record through the development of millions of species over millions of years.

After thinking about questions like the three mentioned in the previous sections, different people come to different conclusions. In the future, there are three possible scenarios for the theory of evolution:

Scientists will come to a complete understanding of DNA and show how mutations and natural selection explain every part of the development of life on this planet.
Scientists will develop a new theory that answers the questions posed above to almost everyone's satisfaction, and it will replace the theory of evolution that we have today.
Scientists will observe a completely new phenomenon that accounts for the diversity of life that we see today. For example, many people believe in creationism. In this theory, God or some other supernatural power intervenes to create all of the life that we see around us. The fossil record indicates that hundreds of millions of new species have been created over hundreds of millions of years -- Species creation is an intense and constant process with an extremely long history. If scientists were to observe the creation process occurring the next time a major new species comes into existence, they could document it and understand how it works.

Let's assume that the theory of evolution as currently stated is the process that did bring about all of the life that we see today. One compelling question is: "What happens next?" Evolution must be at work right now. Our species, Homo sapiens, only appeared about 40,000 years ago. What does evolution have in store for human beings, and how will the change manifest itself?

Will a child appear one day whose brain is twice as big as any normal human brain? If so, what will be the capabilities of that brain, and how will it differ from the brain seen today? Or are our brains slowly evolving right now?
Will children appear one day who have more than 23 chromosomes? If so, what will be the effects of the new chromosomes?
Will man learn how to control or accelerate evolution through genetic engineering? Once we completely understand different genomes, will we be able to engineer evolutionary steps that lead to new species on a much faster schedule? What would those species look like? What would we design them to do?

These are all fascinating questions to think about. They reveal just how big an effect evolution can have. Given enough time, evolution could completely alter life on this planet by disposing of the species we see today and creating new ones.

Car Engines Work

2008-05-04T13:08:00.002+07:00

Have you ever opened the hood of your car and wondered what was going on in there? A car engine can look like a big confusing jumble of metal, tubes and wires to the uninitiated.

Car Engine Image Gallery

Photo courtesy DaimlerChrysler
Jeep® Grand Cherokee Engine.
See more pictures of car engines.

You might want to know what's going on simply out of curiosity. Or perhaps you are buying a new car, and you hear things like "3.0 liter V-6" and "dual overhead cams" and "tuned port fuel injection." What does all of that mean?

In this article, we'll discuss the basic idea behind an engine and then go into detail about how all the pieces fit together, what can go wrong and how to increase performance.

The purpose of a gasoline car engine is to convert gasoline into motion so that your car can move. Currently the easiest way to create motion from gasoline is to burn the gasoline inside an engine. Therefore, a car engine is an internal combustion engine -- combustion takes place internally. Two things to note:

There are different kinds of internal combustion engines. Diesel engines are one form and gas turbine engines are another. See also the articles on HEMI engines, rotary engines and two-stroke engines. Each has its own advantages and disadvantages.
There is such a thing as an external combustion engine. A steam engine in old-fashioned trains and steam boats is the best example of an external combustion engine. The fuel (coal, wood, oil, whatever) in a steam engine burns outside the engine to create steam, and the steam creates motion inside the engine. Internal combustion is a lot more efficient (takes less fuel per mile) than external combustion, plus an internal combustion engine is a lot smaller than an equivalent external combustion engine. This explains why we don't see any cars from Ford and GM using steam engines.

Let's look at the internal combustion process in more detail in the next section.

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Internal Combustion

The potato cannon uses the basic principle behind any reciprocating internal combustion engine: If you put a tiny amount of high-energy fuel (like gasoline) in a small, enclosed space and ignite it, an incredible amount of energy is released in the form of expanding gas. You can use that energy to propel a potato 500 feet. In this case, the energy is translated into potato motion. You can also use it for more interesting purposes. For example, if you can create a cycle that allows you to set off explosions like this hundreds of times per minute, and if you can harness that energy in a useful way, what you have is the core of a car engine!

Figure 1

Almost all cars currently use what is called a four-stroke combustion cycle to convert gasoline into motion. The four-stroke approach is also known as the Otto cycle, in honor of Nikolaus Otto, who invented it in 1867. The four strokes are illustrated in Figure 1. They are:

Intake stroke
Compression stroke
Combustion stroke
Exhaust stroke

You can see in the figure that a device called a piston replaces the potato in the potato cannon. The piston is connected to the crankshaft by a connecting rod. As the crankshaft revolves, it has the effect of "resetting the cannon." Here's what happens as the engine goes through its cycle:

The piston starts at the top, the intake valve opens, and the piston moves down to let the engine take in a cylinder-full of air and gasoline. This is the intake stroke. Only the tiniest drop of gasoline needs to be mixed into the air for this to work. (Part 1 of the figure)
Then the piston moves back up to compress this fuel/air mixture. Compression makes the explosion more powerful. (Part 2 of the figure)
When the piston reaches the top of its stroke, the spark plug emits a spark to ignite the gasoline. The gasoline charge in the cylinder explodes, driving the piston down. (Part 3 of the figure)
Once the piston hits the bottom of its stroke, the exhaust valve opens and the exhaust leaves the cylinder to go out the tailpipe. (Part 4 of the figure)

Now the engine is ready for the next cycle, so it intakes another charge of air and gas.

Notice that the motion that comes out of an internal combustion engine is rotational, while the motion produced by a potato cannon is linear (straight line). In an engine the linear motion of the pistons is converted into rotational motion by the crankshaft. The rotational motion is nice because we plan to turn (rotate) the car's wheels with it anyway.

Now let's look at all the parts that work together to make this happen, starting with the cylinders.

Basic Engine Parts

The core of the engine is the cylinder, with the piston moving up and down inside the cylinder. The engine described above has one cylinder. That is typical of most lawn mowers, but most cars have more than one cylinder (four, six and eight cylinders are common). In a multi-cylinder engine, the cylinders usually are arranged in one of three ways: inline, V or flat (also known as horizontally opposed or boxer), as shown in the following figures.

Figure 2. Inline - The cylinders are arranged in a line in a single bank.

Figure 3. V - The cylinders are arranged in two banks set at an angle to one another.

Figure 4. Flat - The cylinders are arranged in two banks on opposite sides of the engine.

Different configurations have different advantages and disadvantages in terms of smoothness, manufacturing cost and shape characteristics. These advantages and disadvantages make them more suitable for certain vehicles.

Let's look at some key engine parts in more detail.

Spark plug
The spark plug supplies the spark that ignites the air/fuel mixture so that combustion can occur. The spark must happen at just the right moment for things to work properly.

Valves
The intake and exhaust valves open at the proper time to let in air and fuel and to let out exhaust. Note that both valves are closed during compression and combustion so that the combustion chamber is sealed.

Piston
A piston is a cylindrical piece of metal that moves up and down inside the cylinder.

Piston rings
Piston rings provide a sliding seal between the outer edge of the piston and the inner edge of the cylinder. The rings serve two purposes:

They prevent the fuel/air mixture and exhaust in the combustion chamber from leaking into the sump during compression and combustion.
They keep oil in the sump from leaking into the combustion area, where it would be burned and lost.

Most cars that "burn oil" and have to have a quart added every 1,000 miles are burning it because the engine is old and the rings no longer seal things properly.

Connecting rod
The connecting rod connects the piston to the crankshaft. It can rotate at both ends so that its angle can change as the piston moves and the crankshaft rotates.

Crankshaft
The crankshaft turns the piston's up and down motion into circular motion just like a crank on a jack-in-the-box does.

Sump
The sump surrounds the crankshaft. It contains some amount of oil, which collects in the bottom of the sump (the oil pan).

Next, we'll learn what can go wrong with engines.

Engine Problems

So you go out one morning and your engine will turn over but it won't start... What could be wrong? Now that you know how an engine works, you can understand the basic things that can keep an engine from running. Three fundamental things can happen: a bad fuel mix, lack of compression or lack of spark. Beyond that, thousands of minor things can create problems, but these are the "big three." Based on the simple engine we have been discussing, here is a quick rundown on how these problems affect your engine:

Bad fuel mix - A bad fuel mix can occur in several ways:

You are out of gas, so the engine is getting air but no fuel.
The air intake might be clogged, so there is fuel but not enough air.
The fuel system might be supplying too much or too little fuel to the mix, meaning that combustion does not occur properly.
There might be an impurity in the fuel (like water in your gas tank) that makes the fuel not burn.

Lack of compression - If the charge of air and fuel cannot be compressed properly, the combustion process will not work like it should. Lack of compression might occur for these reasons:

Your piston rings are worn (allowing air/fuel to leak past the piston during compression).
The intake or exhaust valves are not sealing properly, again allowing a leak during compression.
There is a hole in the cylinder.

The most common "hole" in a cylinder occurs where the top of the cylinder (holding the valves and spark plug and also known as the cylinder head) attaches to the cylinder itself. Generally, the cylinder and the cylinder head bolt together with a thin gasket pressed between them to ensure a good seal. If the gasket breaks down, small holes develop between the cylinder and the cylinder head, and these holes cause leaks.

Lack of spark - The spark might be nonexistent or weak for a number of reasons:

If your spark plug or the wire leading to it is worn out, the spark will be weak.
If the wire is cut or missing, or if the system that sends a spark down the wire is not working properly, there will be no spark.
If the spark occurs either too early or too late in the cycle (i.e. if the ignition timing is off), the fuel will not ignite at the right time, and this can cause all sorts of problems.

Many other things can go wrong. For example:

If the battery is dead, you cannot turn over the engine to start it.
If the bearings that allow the crankshaft to turn freely are worn out, the crankshaft cannot turn so the engine cannot run.
If the valves do not open and close at the right time or at all, air cannot get in and exhaust cannot get out, so the engine cannot run.
If someone sticks a potato up your tailpipe, exhaust cannot exit the cylinder so the engine will not run.
If you run out of oil, the piston cannot move up and down freely in the cylinder, and the engine will seize.

In a properly running engine, all of these factors are within tolerance.

As you can see, an engine has a number of systems that help it do its job of converting fuel into motion. We'll look at the different subsystems used in engines in the next few sections.

Engine Valve Train and Ignition Systems

Most engine subsystems can be implemented using different technologies, and better technologies can improve the performance of the engine. Let's look at all of the different subsystems used in modern engines, beginning with the valve train.

The valve train consists of the valves and a mechanism that opens and closes them. The opening and closing system is called a camshaft. The camshaft has lobes on it that move the valves up and down, as shown in Figure 5.

Figure 5. The camshaft

Most modern engines have what are called overhead cams. This means that the camshaft is located above the valves, as you see in Figure 5. The cams on the shaft activate the valves directly or through a very short linkage. Older engines used a camshaft located in the sump near the crankshaft. Rods linked the cam below to valve lifters above the valves. This approach has more moving parts and also causes more lag between the cam's activation of the valve and the valve's subsequent motion. A timing belt or timing chain links the crankshaft to the camshaft so that the valves are in sync with the pistons. The camshaft is geared to turn at one-half the rate of the crankshaft. Many high-performance engines have four valves per cylinder (two for intake, two for exhaust), and this arrangement requires two camshafts per bank of cylinders, hence the phrase "dual overhead cams." See How Camshafts Work for details.

The ignition system (Figure 6) produces a high-voltage electrical charge and transmits it to the spark plugs via ignition wires. The charge first flows to a distributor, which you can easily find under the hood of most cars. The distributor has one wire going in the center and four, six, or eight wires (depending on the number of cylinders) coming out of it. These ignition wires send the charge to each spark plug. The engine is timed so that only one cylinder receives a spark from the distributor at a time. This approach provides maximum smoothness. See How Automobile Ignition Systems Work for more details.

Figure 6. The ignition system

We'll look at how your car's engine starts, cools and circulates air in the next section.

Engine Cooling, Air-intake and Starting Systems

The cooling system in most cars consists of the radiator and water pump. Water circulates through passages around the cylinders and then travels through the radiator to cool it off. In a few cars (most notably Volkswagen Beetles), as well as most motorcycles and lawn mowers, the engine is air-cooled instead (You can tell an air-cooled engine by the fins adorning the outside of each cylinder to help dissipate heat.). Air-cooling makes the engine lighter but hotter, generally decreasing engine life and overall performance. See How Car Cooling Systems Work for details.

Diagram of a cooling system showing how all the plumbing is connected

So now you know how and why your engine stays cool. But why is air circulation so important? Most cars are normally aspirated, which means that air flows through an air filter and directly into the cylinders. High-performance engines are either turbocharged or supercharged, which means that air coming into the engine is first pressurized (so that more air/fuel mixture can be squeezed into each cylinder) to increase performance. The amount of pressurization is called boost. A turbocharger uses a small turbine attached to the exhaust pipe to spin a compressing turbine in the incoming air stream. A supercharger is attached directly to the engine to spin the compressor.

Photo courtesy Garrett

See How Turbochargers Work for details.

Increasing your engine's performance is great, but what exactly happens when you turn the key to start it? The starting system consists of an electric starter motor and a starter solenoid. When you turn the ignition key, the starter motor spins the engine a few revolutions so that the combustion process can start. It takes a powerful motor to spin a cold engine. The starter motor must overcome:

All of the internal friction caused by the piston rings
The compression pressure of any cylinder(s) that happens to be in the compression stroke
The energy needed to open and close valves with the camshaft
All of the "other" things directly attached to the engine, like the water pump, oil pump, alternator, etc.

Because so much energy is needed and because a car uses a 12-volt electrical system, hundreds of amps of electricity must flow into the starter motor. The starter solenoid is essentially a large electronic switch that can handle that much current. When you turn the ignition key, it activates the solenoid to power the motor.

Next, we'll look at the engine subsystems that maintain what goes in (oil and fuel) and what comes out (exhaust and emissions).

Engine Lubrication, Fuel, Exhaust and Electrical Systems

When it comes to day-to-day car maintenance, your first concern is probably the amount of gas in your car. How does the gas that you put in power the cylinders? The engine's fuel system pumps gas from the gas tank and mixes it with air so that the proper air/fuel mixture can flow into the cylinders. Fuel is delivered in three common ways: carburetion, port fuel injection and direct fuel injection.

In carburetion, a device called a carburetor mixes gas into air as the air flows into the engine.
In a fuel-injected engine, the right amount of fuel is injected individually into each cylinder either right above the intake valve (port fuel injection) or directly into the cylinder (direct fuel injection).

See How Fuel Injection Systems Work for more details.

Oil also plays an important part. The lubrication system makes sure that every moving part in the engine gets oil so that it can move easily. The two main parts needing oil are the pistons (so they can slide easily in their cylinders) and any bearings that allow things like the crankshaft and camshafts to rotate freely. In most cars, oil is sucked out of the oil pan by the oil pump, run through the oil filter to remove any grit, and then squirted under high pressure onto bearings and the cylinder walls. The oil then trickles down into the sump, where it is collected again and the cycle repeats.

Now that you know about some of the stuff that you put in your car, let's look at some of the stuff that comes out of it. The exhaust system includes the exhaust pipe and the muffler. Without a muffler, what you would hear is the sound of thousands of small explosions coming out your tailpipe. A muffler dampens the sound. The exhaust system also includes a catalytic converter. See How Catalytic Converters Work for details.

The emission control system in modern cars consists of a catalytic converter, a collection of sensors and actuators, and a computer to monitor and adjust everything. For example, the catalytic converter uses a catalyst and oxygen to burn off any unused fuel and certain other chemicals in the exhaust. An oxygen sensor in the exhaust stream makes sure there is enough oxygen available for the catalyst to work and adjusts things if necessary.

Besides gas, what else powers your car? The electrical system consists of a battery and an alternator. The alternator is connected to the engine by a belt and generates electricity to recharge the battery. The battery makes 12-volt power available to everything in the car needing electricity (the ignition system, radio, headlights, windshield wipers, power windows and seats, computers, etc.) through the vehicle's wiring.

Now that you know all about the main engine subsystems, let's look at ways that you can boost engine performance.

Producing More Engine Power

Horsepower For a complete explanation of what horsepower is and what horsepower means, check out How Horsepower Works.

Using all of this information, you can begin to see that there are lots of different ways to make an engine perform better. Car manufacturers are constantly playing with all of the following variables to make an engine more powerful and/or more fuel efficient.

Increase displacement - More displacement means more power because you can burn more gas during each revolution of the engine. You can increase displacement by making the cylinders bigger or by adding more cylinders. Twelve cylinders seems to be the practical limit.

Increase the compression ratio - Higher compression ratios produce more power, up to a point. The more you compress the air/fuel mixture, however, the more likely it is to spontaneously burst into flame (before the spark plug ignites it). Higher-octane gasolines prevent this sort of early combustion. That is why high-performance cars generally need high-octane gasoline -- their engines are using higher compression ratios to get more power.

Stuff more into each cylinder - If you can cram more air (and therefore fuel) into a cylinder of a given size, you can get more power from the cylinder (in the same way that you would by increasing the size of the cylinder). Turbochargers and superchargers pressurize the incoming air to effectively cram more air into a cylinder. See How Turbochargers Work for details.

Cool the incoming air - Compressing air raises its temperature. However, you would like to have the coolest air possible in the cylinder because the hotter the air is, the less it will expand when combustion takes place. Therefore, many turbocharged and supercharged cars have an intercooler. An intercooler is a special radiator through which the compressed air passes to cool it off before it enters the cylinder. See How Car Cooling Systems Work for details.

Let air come in more easily - As a piston moves down in the intake stroke, air resistance can rob power from the engine. Air resistance can be lessened dramatically by putting two intake valves in each cylinder. Some newer cars are also using polished intake manifolds to eliminate air resistance there. Bigger air filters can also improve air flow.

Let exhaust exit more easily - If air resistance makes it hard for exhaust to exit a cylinder, it robs the engine of power. Air resistance can be lessened by adding a second exhaust valve to each cylinder (a car with two intake and two exhaust valves has four valves per cylinder, which improves performance -- when you hear a car ad tell you the car has four cylinders and 16 valves, what the ad is saying is that the engine has four valves per cylinder). If the exhaust pipe is too small or the muffler has a lot of air resistance, this can cause back-pressure, which has the same effect. High-performance exhaust systems use headers, big tail pipes and free-flowing mufflers to eliminate back-pressure in the exhaust system. When you hear that a car has "dual exhaust," the goal is to improve the flow of exhaust by having two exhaust pipes instead of one.

Make everything lighter - Lightweight parts help the engine perform better. Each time a piston changes direction, it uses up energy to stop the travel in one direction and start it in another. The lighter the piston, the less energy it takes.

Inject the fuel - Fuel injection allows very precise metering of fuel to each cylinder. This improves performance and fuel economy. See How Fuel Injection Systems Work for details.

In the next sections, we'll answer some common engine-related questions submitted by readers.

Engine Questions and Answers

Here is a set of engine-related questions from readers and their answers:

What is the difference between a gasoline engine and a diesel engine? In a diesel engine, there is no spark plug. Instead, diesel fuel is injected into the cylinder, and the heat and pressure of the compression stroke cause the fuel to ignite. Diesel fuel has a higher energy density than gasoline, so a diesel engine gets better mileage. See How Diesel Engines Work for more information.
What is the difference between a two-stroke and a four-stroke engine? Most chain saws and boat motors use two-stroke engines. A two-stroke engine has no moving valves, and the spark plug fires each time the piston hits the top of its cycle. A hole in the lower part of the cylinder wall lets in gas and air. As the piston moves up it is compressed, the spark plug ignites combustion, and exhaust exits through another hole in the cylinder. You have to mix oil into the gas in a two-stroke engine because the holes in the cylinder wall prevent the use of rings to seal the combustion chamber. Generally, a two-stroke engine produces a lot of power for its size because there are twice as many combustion cycles occurring per rotation. However, a two-stroke engine uses more gasoline and burns lots of oil, so it is far more polluting. See How Two-stroke Engines Work for more information.
You mentioned steam engines in this article -- are there any advantages to steam engines and other external combustion engines? The main advantage of a steam engine is that you can use anything that burns as the fuel. For example, a steam engine can use coal, newspaper or wood for the fuel, while an internal combustion engine needs pure, high-quality liquid or gaseous fuel. See How Steam Engines Work for more information.
Are there any other cycles besides the Otto cycle used in car engines? The two-stroke engine cycle is different, as is the diesel cycle described above. The engine in the Mazda Millenia uses a modification of the Otto cycle called the Miller cycle. Gas turbine engines use the Brayton cycle. Wankel rotary engines use the Otto cycle, but they do it in a very different way than four-stroke piston engines.
Why have eight cylinders in an engine? Why not have one big cylinder of the same displacement of the eight cylinders instead? There are a couple of reasons why a big 4.0-liter engine has eight half-liter cylinders rather than one big 4-liter cylinder. The main reason is smoothness. A V-8 engine is much smoother because it has eight evenly spaced explosions instead of one big explosion. Another reason is starting torque. When you start a V-8 engine, you are only driving two cylinders (1 liter) through their compression strokes, but with one big cylinder you would have to compress 4 liters instead.

How Are 4-Cylinder and V6 Engines Different?

The number of cylinders that an engine contains is an important factor in the overall performance of the engine. Each cylinder contains a piston that pumps inside of it and those pistons connect to and turn the crankshaft. The more pistons there are pumping, the more combustive events are taking place during any given moment. That means that more power can be generated in less time.

4-Cylinder engines commonly come in “straight” or “inline” configurations while 6-cylinder engines are usually configured in the more compact “V” shape, and thus are referred to as V6 engines. V6 engines have been the engine of choice for American automakers because they’re powerful and quiet but still light and compact enough to fit into most car designs.

Historically, American auto consumers turned their noses up at 4-cylinder engines, believing them to be slow, weak, unbalanced and short on acceleration. However, when Japanese auto makers, such as Honda and Toyota, began installing highly-efficient 4-cylinder engines in their cars in the 1980s and 90s, Americans found a new appreciation for the compact engine. Even though Japanese models, such as the Toyota Camry, began quickly outselling comparable American models, U.S. automakers, believing that American drivers were more concerned with power and performance, continued to produce cars with V6 engines. Today, with rising gas prices and greater public environmental awareness, Detroit seems to be reevaluating the 4-cylinder engine for its fuel efficiency and lower emissions.

As for the future of the V6, in recent years the disparity between 4-cylinder and V6 engines has lessened considerably. In order to keep up with the demand for high gas-mileage and lower emission levels, automakers have worked diligently to improve the overall performance of V6 engines. Many current V6 models come close to matching the gas-mileage and emissions standards of the smaller, 4-cylinder engines. So, with the performance and efficiency gaps between the two engines lessening, the decision to buy a 4-cylinder or V6 may just come down to cost. In models that are available with either type of engine, the 4-cylinder version can run up to $1000 cheaper than the V6. So, regardless of what kind of performance you’re looking to get out of your car, the 4-cylinder will always be the budget buy.

One final note: It’s not a good idea to try to install a V6 engine into a car model that comes with a standard 4-cylinder. Retrofitting a 4-cylinder car to handle a V6 engine could cost more than simply buying a new car.

Elevators

2008-04-23T18:21:00.002+07:00

Elevators have been around for over 150 years.

In the 1800s, new iron and steel production processes revolutionized the world of construction. With sturdy metal beams as their building blocks, architects and engineers could erect monumental skyscrapers hundreds of feet in the air.

But these towers would have been basically unusable if it weren't for another technological innovation that came along around the same time. Modern elevators are the crucial element that makes it practical to live and work dozens of stories above ground. High-rise cities like New York absolutely depend on elevators. Even in smaller multi-story buildings, elevators are essential for making offices and apartments accessible to handicapped people.

In this article, we'll find out how these ubiquitous machines move you from floor to floor. We'll also look at the control systems that decide where the elevator goes and the safety systems that prevent catastrophes.

Hydraulic Elevators

The concept of an elevator is incredibly simple -- it's just a compartment attached to a lifting system. Tie a piece of rope to a box, and you've got a basic elevator.

Of course, modern passenger and freight elevators are a lot more elaborate than this. They need advanced mechanical systems to handle the substantial weight of the elevator car and its cargo. Additionally, they need control mechanisms so passengers can operate the elevator, and they need safety devices to keep everything running smoothly.

There are two major elevator designs in common use today: hydraulic elevators and roped elevators.

Hydraulic elevator systems lift a car using a hydraulic ram, a fluid-driven piston mounted inside a cylinder. You can see how this system works in the diagram below.

The cylinder is connected to a fluid-pumping system (typically, hydraulic systems like this use oil, but other incompressible fluids would also work). The hydraulic system has three parts:

A tank (the fluid reservoir)
A pump, powered by an electric motor
A valve between the cylinder and the reservoir

The pump forces fluid from the tank into a pipe leading to the cylinder. When the valve is opened, the pressurized fluid will take the path of least resistance and return to the fluid reservoir. But when the valve is closed, the pressurized fluid has nowhere to go except into the cylinder. As the fluid collects in the cylinder, it pushes the piston up, lifting the elevator car.

When the car approaches the correct floor, the control system sends a signal to the electric motor to gradually shut off the pump. With the pump off, there is no more fluid flowing into the cylinder, but the fluid that is already in the cylinder cannot escape (it can't flow backward through the pump, and the valve is still closed). The piston rests on the fluid, and the car stays where it is.

To lower the car, the elevator control system sends a signal to the valve. The valve is operated electrically by a basic solenoid switch (check out How Electromagnets Work for information on solenoids). When the solenoid opens the valve, the fluid that has collected in the cylinder can flow out into the fluid reservoir. The weight of the car and the cargo pushes down on the piston, which drives the fluid into the reservoir. The car gradually descends. To stop the car at a lower floor, the control system closes the valve again.

This system is incredibly simple and highly effective, but it does have some drawbacks. In the next section, we'll look at the main disadvantages of using hydraulics.

Pros and Cons of Hydraulics

The main advantage of hydraulic systems is they can easily multiply the relatively weak force of the pump to generate the stronger force needed to lift the elevator car (see How Hydraulic Machines Work to find out how).

But these systems suffer from two major disadvantages. The main problem is the size of the equipment. In order for the elevator car to be able to reach higher floors, you have to make the piston longer. The cylinder has to be a little bit longer than the piston, of course, since the piston needs to be able to collapse all the way when the car is at the bottom floor. In short, more stories means a longer cylinder.

The problem is that the entire cylinder structure must be buried below the bottom elevator stop. This means you have to dig deeper as you build higher. This is an expensive project with buildings over a few stories tall. To install a hydraulic elevator in a 10-story building, for example, you would need to dig at least nine stories deep! (Some hydraulic elevators don't require quite as much digging. Check out this site to learn about these systems.)

The other disadvantage of hydraulic elevators is that they're fairly inefficient. It takes a lot of energy to raise an elevator car several stories, and in a standard hydraulic elevator, there is no way to store this energy. The energy of position (potential energy) only works to push the fluid back into the reservoir. To raise the elevator car again, the hydraulic system has to generate the energy all over again.

The roped elevator design gets around both of these problems. In the next section, we'll see how this system works.

The Cable System

The most popular elevator design is the roped elevator. In roped elevators, the car is raised and lowered by traction steel ropes rather than pushed from below.

The ropes are attached to the elevator car, and looped around a sheave (3). A sheave is just a pulley with a grooves around the circumference. The sheave grips the hoist ropes, so when you rotate the sheave, the ropes move too.

The sheave is connected to an electric motor (2). When the motor turns one way, the sheave raises the elevator; when the motor turns the other way, the sheave lowers the elevator. In gearless elevators, the motor rotates the sheaves directly. In geared elevators, the motor turns a gear train that rotates the sheave. Typically, the sheave, the motor and the control system (1) are all housed in a machine room above the elevator shaft.

The ropes that lift the car are also connected to a counterweight (4), which hangs on the other side of the sheave. The counterweight weighs about the same as the car filled to 40-percent capacity. In other words, when the car is 40 percent full (an average amount), the counterweight and the car are perfectly balanced.

The purpose of this balance is to conserve energy. With equal loads on each side of the sheave, it only takes a little bit of force to tip the balance one way or the other. Basically, the motor only has to overcome friction -- the weight on the other side does most of the work. To put it another way, the balance maintains a near constant potential energy level in the system as a whole. Using up the potential energy in the elevator car (letting it descend to the ground) builds up the potential energy in the weight (the weight rises to the top of the shaft). The same thing happens in reverse when the elevator goes up. The system is just like a see-saw that has an equally heavy kid on each end.

Both the elevator car and the counterweight ride on guide rails (5) along the sides of the elevator shaft. The rails keep the car and counterweight from swaying back and forth, and they also work with the safety system to stop the car in an emergency.

Roped elevators are much more versatile than hydraulic elevators, as well as more efficient. Typically, they also have more safety systems. In the next section, we'll see how these elements work to keep you from plummeting to the ground if something goes wrong.

Safety Systems

In the world of Hollywood action movies, hoist ropes are never far from snapping in two, sending the car and its passengers hurdling down the shaft. In actuality, there is very little chance of this happening. Elevators are built with several redundant safety systems that keep them in position.

The first line of defense is the rope system itself. Each elevator rope is made from several lengths of steel material wound around one another. With this sturdy structure, one rope can support the weight of the elevator car and the counterweight on its own. But elevators are built with multiple ropes (between four and eight, typically). In the unlikely event that one of the ropes snaps, the rest will hold the elevator up.

Even if all of the ropes were to break, or the sheave system were to release them, it is unlikely that an elevator car would fall to the bottom of the shaft. Roped elevator cars have built-in braking systems, or safeties, that grab onto the rail when the car moves too fast.

In the next section, we'll examine a built-in braking system.

Safety Systems: Safeties

Safeties are activated by a governor when the elevator moves too quickly. Most governor systems are built around a sheave positioned at the top of the elevator shaft. The governor rope is looped around the governor sheave and another weighted sheave at the bottom of the shaft. The rope is also connected to the elevator car, so it moves when the car goes up or down. As the car speeds up, so does the governor. The diagram below shows one representative governor design.

In this governor, the sheave is outfitted with two hooked flyweights (weighted metal arms) that pivot on pins. The flyweights are attached in such a way that they can swing freely back and forth on the governor. But most of the time, they are kept in position by a high-tension spring.

As the rotary movement of the governor builds up, centrifugal force moves the flyweights outward, pushing against the spring. If the elevator car falls fast enough, the centrifugal force will be strong enough to push the ends of the flyweights all the way to the outer edges of the governor. Spinning in this position, the hooked ends of the flyweights catch hold of ratchets mounted to a stationary cylinder surrounding the sheave. This works to stop the governor.

The governor ropes are connected to the elevator car via a movable actuator arm attached to a lever linkage. When the governor ropes can move freely, the arm stays in the same position relative to the elevator car (it is held in place by tension springs). But when the governor sheave locks itself, the governor ropes jerk the actuator arm up. This moves the lever linkage, which operates the brakes.

In this design, the linkage pulls up on a wedge-shaped safety, which sits in a stationary wedge guide. As the wedge moves up, it is pushed into the guide rails by the slanted surface of the guide. This gradually brings the elevator car to a stop.

Safety Systems: More Backups

Elevators also have electromagnetic brakes that engage when the car comes to a stop. The electromagnets actually keep the brakes in the open position, instead of closing them. With this design, the brakes will automatically clamp shut if the elevator loses power.

Elevators also have automatic braking systems near the top and the bottom of the elevator shaft. If the elevator car moves too far in either direction, the brake brings it to a stop.

If all else fails, and the elevator does fall down the shaft, there is one final safety measure that will probably save the passengers. The bottom of the shaft has a heavy-duty shock absorber system -- typically a piston mounted in an oil-filled cylinder. The shock absorber works like a giant cushion to soften the elevator car's landing.

In addition to these elaborate emergency systems, elevators need a lot of machinery just to make their stops. In the next section, we'll find out how an elevator operates under normal conditions.

Making the Rounds

Many modern elevators are controlled by a computer. The computer's job is to process all of the relevant information about the elevator and turn the motor the correct amount to put the elevator car where it needs to be. In order to do this, the computer needs to know at least three things.

Where people want to go
Where each floor is
Where the elevator car is

Finding out where people want to go is very easy. The buttons in the elevator car and the buttons on each floor are all wired to the computer. When you press one of these buttons, the computer logs this request.

There are lots of ways to figure out where the elevator car is. In one common system, a light sensor or magnetic sensor on the side of the car reads a series of holes on a long vertical tape in the shaft. By counting the holes speeding by, the computer knows exactly where the car is in the shaft. The computer varies the motor speed so that the car slows down gradually as it reaches each floor. This keeps the ride smooth for the passengers.

In a building with many floors, the computer has to have some sort of strategy to keep the cars running as efficiently as possible. In older systems, the strategy is to avoid reversing the elevator's direction. That is, an elevator car will keep moving up as long as there are people on the floors above that want to go up. The car will only answer "down calls" after it has taken care of all the "up calls." But once it starts down, it won't pick up anybody who wants to go up until there are no more down calls on lower floors. This program does a pretty good job of getting everybody to their floor as fast as possible, but it is highly inflexible.

More advanced programs take passenger traffic patterns into account. They know which floors have the highest demand, at what time of day, and direct the elevator cars accordingly. In a multiple car system, the elevator will direct individual cars based on the location of other cars.

In one cutting-edge system, the elevator lobby works like a train station. Instead of simply pressing up or down, people waiting for an elevator can enter a request for a specific floor. Based on the location and course of all the cars, the computer tells the passengers which car will get them to their destinations the fastest.

Most systems also have a load sensor in the car floor. The load sensor tells the computer how full the car is. If the car is near capacity, the computer won't make any more pick-up stops until some people have gotten off. Load sensors are also a good safety feature. If the car is overloaded, the computer will not close the doors until some of the weight is removed.

In the next section, we'll look at one of the coolest components in an elevator: the automatic doors.

Doors

The automatic doors at grocery stores and office buildings are mainly there for convenience and as an aid for handicapped people. The automatic doors in an elevator, on the other hand, are absolutely essential. They are there to keep people from falling down an open shaft.

Elevators use two different sets of doors: doors on the cars and doors opening into the elevator shaft. The doors on the cars are operated by an electric motor, which is hooked up to the elevator computer. You can see how a typical door-opener system works in the diagram below.

The electric motor turns a wheel, which is attached to a long metal arm. The metal arm is linked to another arm, which is attached to the door. The door can slide back and forth on a metal rail.

When the motor turns the wheel, it rotates the first metal arm, which pulls the second metal arm and the attached door to the left. The door is made of two panels that close in on each other when the door opens and extend out when the door closes. The computer turns the motor to open the doors when the car arrives at a floor and close the doors before the car starts moving again. Many elevators have a motion sensor system that keeps the doors from closing if somebody is between them.

The car doors have a clutch mechanism that unlocks the outer doors at each floor and pulls them open. In this way, the outer doors will only open if there is a car at that floor (or if they are forced open). This keeps the outer doors from opening up into an empty elevator shaft.

In a relatively short period of time, elevators have become an essential machine. As people continue to erect monumental skyscrapers and more small buildings are made handicap-accessible, elevators will become an even more pervasive element in society. It is truly one of the most important machines in the modern era, as well as one of the coolest.

How Caching Works

2008-04-22T16:30:00.002+07:00

If you have been shopping for a computer, then you have heard the word "cache." Modern computers have both L1 and L2 caches, and many now also have L3 cache. You may also have gotten advice on the topic from well-meaning friends, perhaps something like "Don't buy that Celeron chip, it doesn't have any cache in it!"

It turns out that caching is an important computer-science process that appears on every computer in a variety of forms. There are memory caches, hardware and software disk caches, page caches and more. Virtual memory is even a form of caching. In this article, we will explore caching so you can understand why it is so important.

A Simple Example: Before Cache

Caching is a technology based on the memory subsystem of your computer. The main purpose of a cache is to accelerate your computer while keeping the price of the computer low. Caching allows you to do your computer tasks more rapidly.

To understand the basic idea behind a cache system, let's start with a super-simple example that uses a librarian to demonstrate caching concepts. Let's imagine a librarian behind his desk. He is there to give you the books you ask for. For the sake of simplicity, let's say you can't get the books yourself -- you have to ask the librarian for any book you want to read, and he fetches it for you from a set of stacks in a storeroom (the library of congress in Washington, D.C., is set up this way). First, let's start with a librarian without cache.

The first customer arrives. He asks for the book Moby Dick. The librarian goes into the storeroom, gets the book, returns to the counter and gives the book to the customer. Later, the client comes back to return the book. The librarian takes the book and returns it to the storeroom. He then returns to his counter waiting for another customer. Let's say the next customer asks for Moby Dick (you saw it coming...). The librarian then has to return to the storeroom to get the book he recently handled and give it to the client. Under this model, the librarian has to make a complete round trip to fetch every book -- even very popular ones that are requested frequently. Is there a way to improve the performance of the librarian?

Yes, there's a way -- we can put a cache on the librarian. In the next section, we'll look at this same example but this time, the librarian will use a caching system.

A Simple Example: After Cache

Let's give the librarian a backpack into which he will be able to store 10 books (in computer terms, the librarian now has a 10-book cache). In this backpack, he will put the books the clients return to him, up to a maximum of 10. Let's use the prior example, but now with our new-and-improved caching librarian.

The day starts. The backpack of the librarian is empty. Our first client arrives and asks for Moby Dick. No magic here -- the librarian has to go to the storeroom to get the book. He gives it to the client. Later, the client returns and gives the book back to the librarian. Instead of returning to the storeroom to return the book, the librarian puts the book in his backpack and stands there (he checks first to see if the bag is full -- more on that later). Another client arrives and asks for Moby Dick. Before going to the storeroom, the librarian checks to see if this title is in his backpack. He finds it! All he has to do is take the book from the backpack and give it to the client. There's no journey into the storeroom, so the client is served more efficiently.

What if the client asked for a title not in the cache (the backpack)? In this case, the librarian is less efficient with a cache than without one, because the librarian takes the time to look for the book in his backpack first. One of the challenges of cache design is to minimize the impact of cache searches, and modern hardware has reduced this time delay to practically zero. Even in our simple librarian example, the latency time (the waiting time) of searching the cache is so small compared to the time to walk back to the storeroom that it is irrelevant. The cache is small (10 books), and the time it takes to notice a miss is only a tiny fraction of the time that a journey to the storeroom takes.

From this example you can see several important facts about caching:

Cache technology is the use of a faster but smaller memory type to accelerate a slower but larger memory type.
When using a cache, you must check the cache to see if an item is in there. If it is there, it's called a cache hit. If not, it is called a cache miss and the computer must wait for a round trip from the larger, slower memory area.
A cache has some maximum size that is much smaller than the larger storage area.
It is possible to have multiple layers of cache. With our librarian example, the smaller but faster memory type is the backpack, and the storeroom represents the larger and slower memory type. This is a one-level cache. There might be another layer of cache consisting of a shelf that can hold 100 books behind the counter. The librarian can check the backpack, then the shelf and then the storeroom. This would be a two-level cache.

Computer Caches

A computer is a machine in which we measure time in very small increments. When the microprocessor accesses the main memory (RAM), it does it in about 60 nanoseconds (60 billionths of a second). That's pretty fast, but it is much slower than the typical microprocessor. Microprocessors can have cycle times as short as 2 nanoseconds, so to a microprocessor 60 nanoseconds seems like an eternity.

What if we build a special memory bank in the motherboard, small but very fast (around 30 nanoseconds)? That's already two times faster than the main memory access. That's called a level 2 cache or an L2 cache. What if we build an even smaller but faster memory system directly into the microprocessor's chip? That way, this memory will be accessed at the speed of the microprocessor and not the speed of the memory bus. That's an L1 cache, which on a 233-megahertz (MHz) Pentium is 3.5 times faster than the L2 cache, which is two times faster than the access to main memory.

Some microprocessors have two levels of cache built right into the chip. In this case, the motherboard cache -- the cache that exists between the microprocessor and main system memory -- becomes level 3, or L3 cache.

There are a lot of subsystems in a computer; you can put cache between many of them to improve performance. Here's an example. We have the microprocessor (the fastest thing in the computer). Then there's the L1 cache that caches the L2 cache that caches the main memory which can be used (and is often used) as a cache for even slower peripherals like hard disks and CD-ROMs. The hard disks are also used to cache an even slower medium -- your Internet connection.

Caching Subsystems

Your Internet connection is the slowest link in your computer. So your browser (Internet Explorer, Netscape, Opera, etc.) uses the hard disk to store HTML pages, putting them into a special folder on your disk. The first time you ask for an HTML page, your browser renders it and a copy of it is also stored on your disk. The next time you request access to this page, your browser checks if the date of the file on the Internet is newer than the one cached. If the date is the same, your browser uses the one on your hard disk instead of downloading it from Internet. In this case, the smaller but faster memory system is your hard disk and the larger and slower one is the Internet.

Cache can also be built directly on peripherals. Modern hard disks come with fast memory, around 512 kilobytes, hardwired to the hard disk. The computer doesn't directly use this memory -- the hard-disk controller does. For the computer, these memory chips are the disk itself. When the computer asks for data from the hard disk, the hard-disk controller checks into this memory before moving the mechanical parts of the hard disk (which is very slow compared to memory). If it finds the data that the computer asked for in the cache, it will return the data stored in the cache without actually accessing data on the disk itself, saving a lot of time.

Here's an experiment you can try. Your computer caches your floppy drive with main memory, and you can actually see it happening. Access a large file from your floppy -- for example, open a 300-kilobyte text file in a text editor. The first time, you will see the light on your floppy turning on, and you will wait. The floppy disk is extremely slow, so it will take 20 seconds to load the file. Now, close the editor and open the same file again. The second time (don't wait 30 minutes or do a lot of disk access between the two tries) you won't see the light turning on, and you won't wait. The operating system checked into its memory cache for the floppy disk and found what it was looking for. So instead of waiting 20 seconds, the data was found in a memory subsystem much faster than when you first tried it (one access to the floppy disk takes 120 milliseconds, while one access to the main memory takes around 60 nanoseconds -- that's a lot faster). You could have run the same test on your hard disk, but it's more evident on the floppy drive because it's so slow.

To give you the big picture of it all, here's a list of a normal caching system:

L1 cache - Memory accesses at full microprocessor speed (10 nanoseconds, 4 kilobytes to 16 kilobytes in size)
L2 cache - Memory access of type SRAM (around 20 to 30 nanoseconds, 128 kilobytes to 512 kilobytes in size)
Main memory - Memory access of type RAM (around 60 nanoseconds, 32 megabytes to 128 megabytes in size)
Hard disk - Mechanical, slow (around 12 milliseconds, 1 gigabyte to 10 gigabytes in size)
Internet - Incredibly slow (between 1 second and 3 days, unlimited size)

As you can see, the L1 cache caches the L2 cache, which caches the main memory, which can be used to cache the disk subsystems, and so on.

Cache Technology

One common question asked at this point is, "Why not make all of the computer's memory run at the same speed as the L1 cache, so no caching would be required?" That would work, but it would be incredibly expensive. The idea behind caching is to use a small amount of expensive memory to speed up a large amount of slower, less-expensive memory.

In designing a computer, the goal is to allow the microprocessor to run at its full speed as inexpensively as possible. A 500-MHz chip goes through 500 million cycles in one second (one cycle every two nanoseconds). Without L1 and L2 caches, an access to the main memory takes 60 nanoseconds, or about 30 wasted cycles accessing memory.

When you think about it, it is kind of incredible that such relatively tiny amounts of memory can maximize the use of much larger amounts of memory. Think about a 256-kilobyte L2 cache that caches 64 megabytes of RAM. In this case, 256,000 bytes efficiently caches 64,000,000 bytes. Why does that work?

In computer science, we have a theoretical concept called locality of reference. It means that in a fairly large program, only small portions are ever used at any one time. As strange as it may seem, locality of reference works for the huge majority of programs. Even if the executable is 10 megabytes in size, only a handful of bytes from that program are in use at any one time, and their rate of repetition is very high. On the next page, you'll learn more about locality of reference.

Locality of Reference

Let's take a look at the following pseudo-code to see why locality of reference works (see How C Programming Works to really get into it):

Output to screen « Enter a number  between 1 and 100 »
Read input from user
Put value from user in variable X
Put value 100 in variable Y
Put value 1 in variable Z
Loop Y number of time
  Divide Z by X
  If the remainder of the division = 0
     then output « Z is a multiple of X »
  Add 1 to Z
Return to loop
End

This small program asks the user to enter a number between 1 and 100. It reads the value entered by the user. Then, the program divides every number between 1 and 100 by the number entered by the user. It checks if the remainder is 0 (modulo division). If so, the program outputs "Z is a multiple of X" (for example, 12 is a multiple of 6), for every number between 1 and 100. Then the program ends.

Even if you don't know much about computer programming, it is easy to understand that in the 11 lines of this program, the loop part (lines 7 to 9) are executed 100 times. All of the other lines are executed only once. Lines 7 to 9 will run significantly faster because of caching.

This program is very small and can easily fit entirely in the smallest of L1 caches, but let's say this program is huge. The result remains the same. When you program, a lot of action takes place inside loops. A word processor spends 95 percent of the time waiting for your input and displaying it on the screen. This part of the word-processor program is in the cache.

This 95%-to-5% ratio (approximately) is what we call the locality of reference, and it's why a cache works so efficiently. This is also why such a small cache can efficiently cache such a large memory system. You can see why it's not worth it to construct a computer with the fastest memory everywhere. We can deliver 95 percent of this effectiveness for a fraction of the cost.

Classic Airplanes

2008-04-22T16:03:00.002+07:00

In a sense, all airplanes are classic airplanes, because each one represents the very best its designer and builder could do, given the talent, materials, and time available at the moment. No development group ever set out to make a second-best airplane. Instead, every aircraft, and especially every classic aircraft described and pictured within these pages, was the product of the loving care of an intelligent design team.

Classic Airplane Image Gallery

French fighter pilots who were seriously challenged by top-rank German airplanes during World War I welcomed the rugged SPAD VII. See more classic airplane pictures.

The following pages in this article provide links to profiles of classic airplanes built over the last century. You'll begin with classic airplanes of the Early Years, including the Wright Flyers first successful flight. Learn about the military fighter airplanes of World War I and World War II, and explore the aircraft built during the Golden Age of Flight. Then fast-forward to the present day Jet Age and see how much classic airplanes have progressed over the last 100 years.

Lockheed's immortal P-38 Lightning was a multi-role fighter-bomber that was a scourge of the Axis, particularly the Japanese, during World War II.

Each and every one of these classic airplanes was manufactured by skilled and motivated people who worked long hours -- often at their own expense -- to turn out a world-beater. Each was flown by test pilots who risked their lives to make the designers' dreams come true. Each was flown in war or for commerce by equally dedicated pilots who wanted only to use it in the most effective manner. And each was maintained by loyal workers, often unappreciated, who were responsible for the lives of all who piloted and flew in the craft.

In truth, classic airplanes are no more than mirrors in which we find reflected the human beings who created and used them. See the next page for links to profiles of classic airplanes built between 1903 to 1913.

The Early Years, 1903-1913

The collaborative genius of Orville and Wilbur Wright completely transcended the efforts of all of their predecessors in the field of aviation. Not only had they leaped beyond the most advanced innovator of the day, Otto Lilienthal, they corrected the errors they had found in his mathematical tables.

In 1909, Louis Bleriot flew his Bleriot XI monoplane above the Notre-Dame de Paris.

On December 17, 1903, the Wright brothers' four flights carried them into the record books as the first to make a controlled powered flight, and established them as being far ahead of all competitors in Europe.

The links below provide details and specifications for early classic airplanes:

The Wright Flyers: 1903, 1905, and 1908
Learn about the Wright brothers' first powered flight, which took place on December 17, 1903. Their first airplane, the Kitty Hawk Flyer, was the world's first military aircraft.

Bleriot XI
The need for speed and the powerful engines of the Bleriot XI led to the tragic deaths of many famous pilots, including America's first licensed female pilot. Get the details here.

Curtiss Golden Flyer
Sometimes called the Gold Bug, this classic airplane was built by Glenn Hammond Curtiss and was inspired by the Wright Flyer. Spot the differences and similarities between the Golden Flyer and the Wright Flyer in this article.

The Wright brothers would demonstrate their leadership in the next five years, only to lose it suddenly and dramatically to new ideas from abroad. Follow links to classic European airplanes of World War I on the next page.

World War I, 1914-1918

World War I had a tremendous effect upon the development of aviation, creating an entirely new military arm, one only dimly foreseen in the past, but immediately important. Huge industries sprang up to produce the aircraft, engines, and components required for the new and extremely expensive service. Because the stalemated war in the trenches was so horrible, the war in the air was given a sense of chivalry and honor by the press and public.

Above, the Red Baron (red plane) is shown closing on the Sopwith Camel of Canadian Lt. Wilfred May, unaware that Capt. Roy Brown has slid into position behind him.

Each new aircraft was carefully examined and the men who won five victories to become aces were regarded as popular heroes.

Below are links to some of the classic airplanes that these brave soldiers flew:

Curtiss JN-4
Nicknamed "the Jenny," this classic airplane was originally mass-produced for the American effort in World War I but was also used as a crop duster, a stunt plane, and an entertainment aircraft after the war. Learn more here.

Nieuport 17
Learn about this extremely influential classic airplane, also known as "Bebe." Copies of the Nieuport 17 were eventually produced at other companies around the world -- some with fatal results.

Gotha G.V
Because of the Gothas' weight and balance problems, more of these German fighter planes were lost due to pilot mishap and accidents than enemy fighters. Learn about this long-range heavy bomber.

Albatros D. Va
Even though the German Albatros was handsome and well built, it didn't prove successful in the German air effort during World War I. Read about this classic fighter plane.

Sopwith Camel F.1
The most famous of all fighter planes, the British Camel brought down more enemies than any other Allied plane during World War I. Find out how this classic airplane was also lethal to its own pilots.

Fokker Dr I Triplane
In an effort to remedy the problems of the Albatros, the Germans built the Fokker Dr I Triplane, which showed promise until a flawed wing design caused a series of fatal crashes.

SPAD VII & SPAD XIII
This classic airplane's name is an acronym for Societe pour Aaviation et ses Derives, which was a firm under the control of Louis Bleriot. Get more details here.

De Havilland DH-4
When the U.S. entered World War I, the Air Service decided to produce the British D. H.4s with American Liberty engines. Learn about this classic airplane's role in World War I.

The years between World War I and World War II were known as the Golden Age of Flight. Discover the aircraft built across the globe on the next page.

The Golden Age of Flight, 1919-1938

The first two decades after World War I, known as the Golden Age of Flight, saw the appearance of some of the most beautiful and most efficient aircraft in history. All over the world, regardless of their country's size or its relative wealth, aircraft designers were busy producing the very best aircraft they could conceive.

The excitement and infinite promise of flight during the Golden Age was exemplified by the Ryan NYP Spirit of St. Louis, piloted famously in 1927 by Charles Lindbergh.

The Golden Age of Flight was a time when much could be done with relatively small resources, as when the Granville brothers designed an aircraft in an abandoned dance hall, and witnessed it suddenly become a world-beater.

Follow these links to classic airplanes of the Golden Age:

Polikarpov I-16
Find out how this classic airplane, considered the Rodney Dangerfield of fighter planes, surprised the German Luftwaffes and the rest of the world during World War II.

Martin B-10
The American Martin B-10 bomber plane is held as the most important and beautiful contributions to the Golden Age of Flight. Learn why in this article.

Ford Tri-Motor
Henry Ford, a name commonly associated with classic cars, turned his talents toward classic airplanes in 1924. Read all about the Ford "Tin Goose" Tri-Motor.

Ryan NYP Spirit of St. Louis
In 1927, Charles Lindbergh and the Spirit of St. Louis successfully flew the first non-stop solo flight across the Atlantic. Learn about the legend here.

Lockheed Vega
"Aviatrix" Amelia Earhart shared many firsts with the Lockheed Vega, including the first successful flight from Hawaii to California. Find out why she chose this classic airplane for her flying adventures.

Hawker Hart
An effective light bomber, a trainer and a seaplane, the Hawker Hart was a classic airplane with many accomplishments. Explore the many sides of the Hawker Hart.

Piper J-3 Cub
With its economical price, the Piper J-3 Cub helped democratize civil aviation. Read about the classic airplane that earned its place as "an American classic in peace and war."

Beech Staggerwing
See specifications for the Beech Model 17, a classic airplane launched at the very depth of the Depression and which got its nickname from the reverse stagger of its wings.

Granville Brothers Gee Bee Super Sportster R-1
The Gee Bee was built for the 1932 air-racing season and, flown by pilot Jimmy Doolittle, quickly became America's sweetheart. Get a closer look into the adventures of this classic airplane.

Martin Model 130 China Clipper
With the ability to make saltwater landings in exotic places, the "flying boat" took passengers throughout the Pacific for attractive scenery. Discover the glamor of this classic airplane.

By the time World War II began, the progress of aviation had taken many great leaps forward. Move on to the next page for links to classic World War II fighter airplanes.

World War II, 1939-1945

World War II accelerated the pace of aviation at an even faster rate than World War I, and on a far greater scale. Aviation was in its infancy prior to the First World War, and almost all of the progress in establishing an aviation industry and in determining the uses of air power took place as the war was going on.

A carrier-based F4U Corsair bears down relentlessly on a pair of J apanese Zeros in a heated moment during the Pacific air war.

Aviation progress had a running start beginning in 1939, so it was possible for aviation to make great strides not only in aircraft performance but also in many new disciplines required to fight an air war. The field saw advancements in navigation, radar, communications and improved ordnance.

Follow the links below for more details of classic World War II fighter planes:

Douglas C-47
This classic airplane started life as the best-selling airliner of its day, placing the U.S. in the lead in commercial aviation. Learn how the C-47 became one of the most effective warplanes in history.

Lockheed P-38 Lightning
The P-38 was the only U.S. fighter plane that was produced prewar and continued to be produced when the war ended. Find out what made this classic plane so intriguing.

Focke Wulf Fw 190
Read about a classic German airplane that was beautiful, versatile, and considered one of the best fighter airplanes of World War II.

Boeing B-29 Superfortress
The most famous B-29 was the Enola Gay, which dropped an atomic bomb on Hiroshima and forced Japan to surrender, bringing World War II to an end.

Junkers Ju 87 Stuka
Although slow, the Stuka proved incredibly effective as a German dive-bomber during World War II. Discover how this classic airplane fought bravely until the very end.

Supermarine Spitfire
The Spitfire was a superior plane built by the Supermarine Company for the British Royal Air Force. Get details on this handsome hero of World War II.

Boeing B-17
Learn about the four-engine "Flying Fortress," aptly named for its ability to survive damage during bombing missions and still return safely.

Grumman F4F Wildcat
The Wildcat started as an underdog and ended a champion, successfully taking down inferior Japanese bombers. See photos and specs in this article.

Messerschmitt Bf 109
German engineers succeeded with their attempt to fit an enormous engine in a small airframe, resulting in the Bf 109 and 100 more variants of the original design.

Douglas SBD Dauntless
A supreme dive-bomber of the Pacific War, the Dauntless is known for its efforts during the Battle of Midway -- sinking Japanese carriers and reversing the course of World War II.

North American B-25 Mitchell
Explore the details of the classic airplane flown by Lt. Col. Jimmy Doolittle during the first bombing raid against Tokyo in April 1942.

Curtiss P-40 Warhawk
The P-40 served in all theaters of World War II, including the Pacific, Alaska, Africa, and Russia, and is famous for its performance with the AVG Flying Tigers.

Consolidated B-24 Liberator
The Liberator was vital to the American effort in World War II -- its many roles included bombing, special operations, and carrying cargo and passengers. Learn more here.

Mitsubishi A6M Zero
Read about the Japanese Zero, a symbol of Imperial Japan that succeeded early on in the war only to be surpassed by continually improving American aircrafts and pilots.

Grumman F6F Hellcat
The Hellcat's first appearance in World War II battle was during the U.S. attack against the Japanese on Marcus Island in September 1943.

Yakovlev Yak-9
Yak-9s were flown bravely by the Soviets against German fighters. Learn why this classic plane proved faster and more maneuverable than German Bf 109s.

Chance Vought F4U Corsair
Also called the "Bent-wing Bird," the F4U Corsair dominated Japanese enemies in World War II and went on to serve in the Korean War.

North American P-51 Mustang
The Mustang classic airplane had the ability to defeat every Axis fighter it encountered. Learn about it's history and the many restored models that still fly today.

Messerschmitt Me 262
If the production of the German Me 262 had not been delayed, the outcome of World War II might have changed drastically. Learn how this classic airplane could have altered history.

The classic fighter planes of World War II will always be remembered as brave warriors, but the arrival of the Jet Age changed the way we see aircraft. Follow the links on the next page for more details.

The Jet Age, 1946-Present

Jet power in the raw: A double threat of well-armed Douglas AE-4 Skyhawks streaks from the clouds, superbly piloted and ready to take on all challengers.

The end of World War II found the victorious Allies with thousands of fighter planes, all but a few of which were obsolete because the Jet Age had arrived. Although peacetime budgets were cut to a minimum, military and civil leaders poured as much money as possible into research and development.

The result was a series of ever more powerful and reliable jet engines, as well as new and increasingly radical airframes. The growth in jet power was paralleled by a revolution in electronics.

This, plus the combination of new engines, new airframes, and advanced avionics resulted in aircraft of superb performance and amazing longevity.

Below you'll find links to profiles, specifications and photos of these classic airplanes of the Jet Age:

Grumman EA-6B Prowler
The Prowler serves the U.S. Navy, Marines and Air Force with its high-performance electronic capabilities. Learn more here.

Boeing 747
The Boeing 747's size amazed the public and had many people wondering if it would even be able to fly. Read about the largest airliner in history.

Mcdonnell Douglas F-4 Phantom II
Get details on the classic airplane that served as the United States' principal fighter in Vietnam and dominated combat aviation with its versatility and speed.

Lockheed F-117A Nighthawk Stealth Fighter
The sharp, angular frame of the F-117A Stealth gave the classic airplane a modern look, but its main feature made it almost "invisible." Learn more about the F-117A's ability to deflect incoming radar beams here.

Mikoyan-Guryevich MiG-15
The Soviet-built MiG-15 fighter appeared in combat during the Korean War and, by 1953, was abandoned by the Soviets as a front-line fighter.

North American F-86 Sabre
Many pilots view the Sabre as the last "pure" fighter plane. Find out what made this classic airplane so special and versatile.

Douglas A-4 Skyhawk
With more than 29 variants used by the U.S. Navy and Marines, the lightweight Skyhawk was truly a remarkable classic combat airplane, remaining in production for 25 years.

Boeing B-52 Stratofortress
The B-52, also known as the Buff, has proven successful in Vietnam, the Persian Gulf War and other important missions. Learn the Buff's many roles.

Mikoyan-Guryevich MiG-21
This Soviet aircraft was one of the greatest jets of its time with different versions serving in nearly 40 air forces across the globe. Get the details here.

Boeing 707
The creation of the 707 was a huge step for globalization, making international travel easier for the public. Read more about this landmark in aviation history.

Lockheed SR-71 Blackbird
The Blackbird was named for its heat-resistant black paint and remains one of the world's fastest, highest-flying aircraft since its first flight in 1964.

McDonnell Douglas F-15 Eagle
The F-15 Eagle was created after the Vietnam War when pilots felt the need for a new fighter plane that would dominate the sky. Take a closer look at this classic airplane in this article.

General Dynamics F-16 Fighting Falcon
Often referred to as the "Electric Jet" rather than the "Fighting Falcon," the F-16 is fully equipped with the latest radars, night vision equipment and missiles. See specifications and photos here.

Northrop Grumman B-2 Spirit
The B-2's unusual appearance and high cost -- approximately $2.2 billion per copy -- prove just how much classic airplanes have evolved over the century.

do you know SMS Works ?

2008-04-22T15:30:00.002+07:00

Just when we're finally used to seeing everybody constantly talking on their cell phones, it suddenly seems like no one is talking at all. Instead, they're typing away on tiny numerical pads, using their cell phones to send quick messages. SMS, or text messaging, has replaced talking on the phone for a new "thumb generation" of texters.

In this article, we'll find out how text messaging works, explore its uses and learn why it sometimes takes a while for your text message to get to its recipient.

SMS stands for short message service. Simply put, it is a method of communication that sends text between cell phones, or from a PC or handheld to a cell phone. The "short" part refers to the maximum size of the text messages: 160 characters (letters, numbers or symbols in the Latin alphabet). For other alphabets, such as Chinese, the maximum SMS size is 70 characters.

SMS Attacks Recently it has been suggested that SMS messages could be used to attack a cell phone system. The basic idea is very simple. If a large number of SMS messages were sent by computers to phones in a small geographical area (like a city), these messages would overwhelm the control channels and make it impossible for the cell phone system to set up calls. Now that cell phone providers know about the possibility of this threat, they can design systems to throttle messages coming from the SMSC onto the network.

But how do SMS messages actually get to your phone? If you have read How Cell Phones Work, you can actually see what is happening.

Even if you are not talking on your cell phone, your phone is constantly sending and receiving information. It is talking to its cell phone tower over a pathway called a control channel. The reason for this chatter is so that the cell phone system knows which cell your phone is in, and so that your phone can change cells as you move around. Every so often, your phone and the tower will exchange a packet of data that lets both of them know that everything is OK.

Your phone also uses the control channel for call setup. When someone tries to call you, the tower sends your phone a message over the control channel that tells your phone to play its ringtone. The tower also gives your phone a pair of voice channel frequencies to use for the call.

The control channel also provides the pathway for SMS messages. When a friend sends you an SMS message, the message flows through the SMSC, then to the tower, and the tower sends the message to your phone as a little packet of data on the control channel. In the same way, when you send a message, your phone sends it to the tower on the control channel and it goes from the tower to the SMSC and from there to its destination.

The actual data format for the message includes things like the length of the message, a time stamp, the destination phone number, the format, etc. For a complete byte-by-byte breakdown of the message format, see this page.

Why 160 Characters? SMS was designed to deliver short bursts of data such as numerical pages. To avoid overloading the system with more than the standard forward-and-response operation, the inventors of SMS agreed on a 160-character maximum message size.

But the 160-character limit is not absolute. Length limitations may vary depending on the network, phone model and wireless carrier. Some phones don't allow you to keep typing once the 160-character limit is reached. You must send your message before continuing. However, some services will automatically break any message you send into chunks of 160 characters or less. So, you can type and send a long message, but it will be delivered as several messages.

Advantages of SMS

SMS has several advantages. It is more discreet than a phone conversation, making it the ideal form for communicating when you don't want to be overheard. It is often less time-consuming to send a text message than to make a phone call or send an e-mail. SMS doesn't require you to be at your computer like e-mail and instant messaging (IM) do -- although some phones are equipped for mobile e-mail and IM services. SMS is also a convenient way for deaf and hearing-impaired people to communicate.

SMS is a store-and-forward service, meaning that when you send a text message to a friend, the message does not go directly to your friend's cell phone. The advantage of this method is that your friend's cell phone doesn't have to be active or in range for you to send a message. The message is stored in the SMSC (for days if necessary) until your friend turns his cell phone on or moves into range, at which point the message is delivered. The message will remain stored on your friend's SIM card until he deletes it.

In addition to person-to-person messages, SMS can be used to send a message to a large number of people at a time, either from a list of contacts or to all the users within a particular area. This service is called broadcasting and is used by companies to contact groups of employees or by online services to distribute news and other information to subscribers.

In a 2004 University of Plymouth study on the psychology of SMS users, researchers found that mobile phone users were primarily either "texters" or "talkers" [ref]. Compared to the talkers, the texters sent nearly double the number of SMS messages and made less than half as many voice calls per month. The texters preferred SMS to voice calls for its convenience as well as for the ability to review a message before sending it.

Companies have come up with many uses for the service beyond just your typical person-to-person message. Because SMS doesn't overload the network as much as phone calls, it is frequently used by TV shows to let viewers vote on a poll topic or for a contestant. As a promotional tool, wireless carriers put up giant screens at concerts and other large-scale events to display text messages from people in the audience.

SMS History SMS was created during the late 1980s to work with a digital technology called GSM (global system for mobile communications), which is the basis for most modern cell phones. The Norwegian engineers who invented it wanted a very simple messaging system that worked when users' mobile phones were turned off or out of signal range. Most sources agree that the first SMS message was sent in the UK in 1992.

As SMS was born in Europe, it's not surprising that it took a little longer to make its way to the United States. Even today, texting enjoys much greater popularity in Europe, though its stateside use is on the rise. A July 2005 study found that 37 percent of U.S. mobile phone owners had sent or received at least one text message in the previous month [ref].

You can use text messaging subscription services to get medication reminders sent to your phone, along with weather alerts, news headlines or even novels broken into 160-character "chapters." Internet search engines such as Yahoo! and Google have short messaging services that enable users to get information such as driving directions, movie showtimes or local business listings just by texting a query to the search engine's phone number. Social networking services such as Dodgeball use SMS to alert people who live in big cities when their friends or crushes are nearby. The possibilities for integrating SMS into your lifestyle seem endless.

Next, we'll discuss the disadvantages of SMS and look at some alternative communication technologies.

SMS Criticism and Alternatives

SMS in the News Because of the impersonal nature of SMS, it raises certain questions of etiquette -- namely, what kind of information is OK to send in a text instead of delivering it in person? Recently, several people have sought legal action after they were fired or notified of divorce proceedings via SMS.

Broadcast text messages have been used to rally political activists in Beijing and to mobilize young people for riots in Belfast. Recently, a contest pitted the efficiency of SMS against Morse code (the Morse coders won).

Despite their popularity, short messaging services have received some criticism. Here are a few of the disadvantages of SMS:

You have to pay for it. Most wireless plans charge for a certain number of text messages a month. Some only charge for user-originated messages, while others charge for incoming messages as well. If you exceed your message allowance, you may be charged 10 cents per message, and those little charges can add up.
Speedy message delivery is not guaranteed. During periods of high traffic, it might be minutes or even hours before a message gets through.
It's strictly for sending text messages. SMS does not support sending pictures, video or music files.

Alternatives to SMS
Alternative messaging services allow for more elaborate types of messages. With EMS (Enhanced Messaging Service), you can send formatted text, sound effects, small pictures and icons. MMS (Multimedia Messaging Service) allows you to send animations, audio and video files in addition to text. If your mobile phone is EMS- or MMS-enabled, you can use these standards just as you would SMS. However, the cost per message will be higher.

Another alternative to using SMS is using an instant messaging program, such as AOL IM, on your cell phone. This can be in the form of software that's pre-installed on your phone, or you can use WAP (Wireless Application Protocol) to access the Internet and sign into your IM account. WAP is a protocol that gives you small, simplified versions of web pages that are easily navigable on your mobile phone or PDA (check out How WAP Works for more information). You can use it to send instant messages or actual e-mails from your phone.

A common complaint about SMS is its inefficient delivery structure -- when the message center is backed up, messages take longer to reach their destination. To make message delivery faster, networks are using more new next-generation technologies such as GPRS (General Packet Radio Service).

To learn more about SMS and other forms of mobile communication, check out the links on the following page.

Why is the Google algorithm so important?

2008-04-20T23:16:00.001+07:00

Finding useful information on the World Wide Web is something many of us take for granted. According to the Internet research firm Netcraft, there are nearly 150,000,000 active Web sites on the Internet today [source: Netcraft]. The task of sifting through all those sites to find helpful information is monumental. That's why search engines use complex algorithms -- mathematical instructions that tell computers how to complete assigned tasks.

Google's search engine gets more traffic than any
other Web site. So what's the company's secret
algorithm? No one can be sure.

Google's algorithm does the work for you by searching out Web pages that contain the keywords you used to search, then assigning a rank to each page based several factors, including how many times the keywords appear on the page. Higher ranked pages appear further up in Google's search engine results page (SERP), meaning that the best links relating to your search query are theoretically the first ones Google lists.

For Web page administrators, being listed prominently on Google can result in a big boost in site traffic and visibility. In 2007, Google surpassed Microsoft as the most visited site on the Web [source: The San Francisco Chronicle]. With that much traffic, getting a good spot on a Google SERP could mean a huge boost in the number of site visitors.

Are You Down with ODP?The Open Directory Project (ODP) is a Web directory maintained by a large staff of volunteers. Each volunteer oversees a category, and together volunteers list and categorize Web sites into a huge, comprehensive directory. Because a real person evaluates and categorizes each page within the directory, search engines like Google use the ODP as a database for search results. Getting a site listed on the ODP often means it will show up on Google.

Google's keyword search function is similar to other search engines. Automated programs called spiders or crawlers travel the Web, moving from link to link and building up an index page that includes certain keywords. Google references this index when a user enters a search query. The search engine lists the pages that contain the same keywords that were in the user's search terms. Google's spiders may also have some more advanced functions, such as being able to determine the difference between Web pages with actual content and redirect sites -- pages that exist only to redirect traffic to a different Web page.

Keyword placement plays a part in how Google finds sites. Google looks for keywords throughout each Web page, but some sections are more important than others. Including the keyword in the Web page's title is a good idea, for example. Google also searches for keywords in headings. Headings come in a range of sizes, and keywords in larger headings are more valuable than if they are in smaller headings. Keyword dispersal is also important. Webmasters should avoid overusing keywords, but many people recommend using them regularly throughout a page.

Video Gallery: AlgorithmsHaile is a robotic percussionist that analyzes live players' music in real time and plays back an improvised beat. It is designed to combine the computational power and algorithmic music with the richness and expression of acoustic performance. Watch the robotic percussionist in concert in this video from Georgia Tech.

In the next section, we'll learn about Google's patented PageRank system.

Google's PageRank System

The Google algorithm's most important feature is arguably the PageRank system, a patented automated process that determines where each search result appears on Google's search engine return page. Most users tend to concentrate on the first few search results, so getting a spot at the top of the list usually means more user traffic.

This Google SERP shows the results of a search
for HowStuffWorks.

So how does Google determine search results standings? Many people have taken a stab at figuring out the exact formula, but Google keeps the official algorithm a secret. What we do know is this:

PageRank assigns a rank or score to every search result. The higher the page's score, the further up the search results list it will appear.
Scores are partially determined by the number of other Web pages that link to the target page. Each link is counted as a vote for the target. The logic behind this is that pages with high quality content will be linked to more often than mediocre pages.
Not all votes are equal. Votes from a high-ranking Web page count more than votes from low-ranking sites. You can't really boost one Web page's rank by making a bunch of empty Web sites linking back to the target page.
The more links a Web page sends out, the more diluted its voting power becomes. In other words, if a high-ranking page links to hundreds of other pages, each individual vote won't count as much as it would if the page only linked to a few sites.
Other factors that might affect scoring include the how long the site has been around, the strength of the domain name, how and where the keywords appear on the site and the age of the links going to and from the site. Google tends to place more value on sites that have been around for a while.
Some people claim that Google uses a group of human testers to evaluate search returns, manually sorting through results to hand pick the best links. Google denies this and says that while it does employ a network of people to test updated search formulas, it doesn't rely on human beings to sort and rank search results.

Google's strategy works well. By focusing on the links going to and from a Web page, the search engine can organize results in a useful way. While there are a few tricks webmasters can use to improve Google standings, the best way to get a top spot is to consistently provide top quality content, which gives other people the incentive to link back to their pages.

Can't Buy Me (Google) LoveGoogle says that it won't sell prime search results spots. Every site you see in the results section on a Google SERP is there because of the PageRank system. Google does sell space for sponsored links above and next to the search results, but it uses shaded boxes and borders to alert users to the difference between normal search results and sponsored links.

To learn more about search engines and related topics, follow the links on the next page.

the Node Explorer Works

2008-04-19T16:36:00.001+07:00

Imagine taking a trip to a battlefield memorial and spending the day walking from monument to monument, reading signs about historical events. To a lot of people, this sounds educational, but not exciting. But suppose that instead of reading signs, you watch reenactments and interviews on a portable media player. As part of an interactive tour, the player also shows you maps and timelines. Also, what you see and hear changes depending on where you are within the park.

Photo courtesy Node

This location-based media player, called the Explorer, changes your walk in the park into an interactive learning experience. Node, a British media company, created the Explorer for use in museums, historical sites and other cultural centers. People have compared it to the "Hitchhiker's Guide to the Galaxy" and the Marauder's Map from the "Harry Potter" series. It uses global positioning system (GPS) technology to determine where someone is within a site and presents interactive information based on that location.

The Explorer's presentations are interactive, and they can include guided tours, images, maps, videos and sound clips. In this article, we'll look at the Explorer's hardware and software and see how its use can affect the tourism industry.

Hardware

Like a portable media center, the Explorer is essentially a handheld computer. It uses a Linux operating system, and it processes and stores interactive presentations using:

An AMD Alchemy 800 mhz processor
256 MB of RAM
At least 2 GB of storage space

It then plays them using a trans-reflective, high resolution touch screen and 3-D stereo headphones. Its most remarkable feature it is that it uses GPS "Fast Fix" technology to choose which items to play based the visitor's location within the site. It can also mark the visitor's location on an on-screen map.

The Explorer unit is just one part of the wireless Node network, which also includes:

Recharging and data collection docks
A central server
Web-enabled computers, which staff members use to access Node software

In the next section, we'll look at the Node software in more detail.

Location-Based Services Companies are using location-based services to deliver traffic reports, driving directions, coupons, movie listings and other information to people depending on where they are. These services are a blend of three types of technology:

Mobile devices, like PDAs, cell phones or laptop computers

Wireless communication systems, like cell phone networks or wireless network connections

Positioning technology, like GPS receivers

Software

The Node software package uses three components to manage everything from content creation to unit rental. The applications that manage the Explorer from behind the scenes are the Admin and Editor programs. The HirePoint interface controls Explorer rental.

Photo courtesy MorgueFile
A Node Explorer would make this museum visit even more interesting.

Each program is responsible for a specific set of instructions and information:

Admin allows staff members to set up their Explorer units and manage their accounts. The Explorers themselves gather data about where visitors go in the site and how they explore the exhibits. Admin creates reports based on the collected data.
Editor manages the actual content of the Explorer presentations. Using Editor, staff can designate the hot spots, or areas that will activate an interactive portion of the presentation.
HirePoint manages unit rental and security. It collects information about the people who rent the units, including a small, passport-style photo.

Staff members use a web browser to access each of the three programs and can make real-time content updates. This means that they can adjust what visitors see based on the season, the time of day or the weather. For example, if it starts to rain, the Explorers can display the location of the nearest shelter. People can also send and receive messages through the unit.

Next, we'll look at how the Explorer affects operations at a cultural site.

The Explorer and Research In addition to providing data on how people interact with museum exhibits, the Explorer can collect important information for researchers and urban planners. Node is participating in a University of Bath research project called Cityware, which will study how people interact with urban environments.

Guiding Visitors -- and Staff

Robot Tour Guides Media players aren't the only innovation in museum interpretation. TOURBOT hopes to develop robot tour guides that are both mobile and interactive.

Human tour guides have been an important part of museums, historical sites, cultural attractions and zoos. Funding at these kinds of attractions can be scarce, so many have used recorded audio tours supplement their staff. Audio recordings don't have the interactive quality of a human guide, though, and they can't report back on which exhibits visitors liked best.

The Explorer's interactive presentations make up for some of the lack of the human element in most recorded tours. Its data collection capabilities allow the staff to evaluate how visitors are using the site and use this information to improve the facility. The Explorer's location-aware technology can also warn visitors when they are leaving established paths, helping control visitors' impact on the environment and wildlife in outdoor attractions.

Photo courtesy MorgueFile
Antenna Audio's extensive client list includes
the island prison Alcatraz.

Currently, several British attractions use the Explorer and its software. Node has also signed an agreement with Antenna Audio, which creates and distributes audio tours for museums and cultural sites around the world. Their combined unit will be called the XPvision, and its use will likely become widespread the near future.

To learn more about Node Explorer and related topics, check out the links on the following page.

Upcoming Projects from Node One of Node's current projects involves a "Jane Austen experience," in which the Pride and Prejudice character Darcy will lead walking tours of Bath, England. Node also hopes to develop location-based services for spectator sports.

iPod

2008-04-10T22:51:00.002+07:00

Introduction to How iPods Work

Shopping for an iPod? Compare iPod prices at Consumer Guide Products before you buy.

In 2001, Apple introduced the iPod, an MP3 player with the unheard-of storage capacity of 5 gigabytes. Six iPod generations later, the iPod plays songs, movies, games and photo slideshows, and you can store up to 160 GB of any type of file you want. The evolution has been a lesson in consumer electronics marketing and development: Millions of people are so hooked on the iPod, they continue to buy it and its coordinating Apple products despite quick battery death and difficult repairs.

iPod Image Gallery

Photo courtesy Apple
The sixth-generation iPod Classic
See more iPod pictures.

The 2007 iPod release, the sixth-generation iPod classic, is a digital audio player, video player, photo viewer and portable hard drive, making it a full-fledged portable media center. It's available in 80-GB and 160-GB capacities and has a color LCD screen. In addition to the iPod classic, there are several other devices in the current generation of iPod players:

iPod touch, announced in September 2007, is a touch-screen iPod with an 8-GB or 16-GB capacity. It looks a lot like an iPhone, and it uses the iPhone's multi-touch user interface. You can learn all about the technology in How the iPhone Works.
iPod shuffle, with a 1-GB capacity, plays only songs and has no display.
iPod nano plays digital audio, displays digital photos and comes in 4- and 8-GB capacities. It has a 2-inch display screen and a smaller form factor than the iPod video.

Photo courtesy Apple
The newer iPod nano model has a larger screen.

In this article, we'll be focusing on iPods with audio and video capabilities. We'll dissect a fifth-generation iPod video to find out how it works, check out what type of software is available to enhance its functionality, and find out why so many people buy iPod after iPod.

iPod Basics

Although the iPod is an Apple product, it works with both Mac and Windows machines. Since it's the top-selling media player in the United States, probably the big question is: What makes it different from any other digital media player? The answer will differ depending on who you ask. Some might say it's the form factor -- the 80-GB iPod classic is less than half an inch (1.4 centimeters) deep and weighs about 4.9 ounces (140 grams) [source: Apple]. For comparison, the Zen Portable Media Center from Creative is 1.06 inches (2.7 centimeters) deep, weighs 12 ounces (340 grams) and has only 20 GB of hard drive space [source: Creative].

Other people might tell you it's the Apple Click Wheel, a touch-sensitive wheel that makes it incredibly easy to navigate through the various menus and options with just a thumb. According to Apple CEO Steve Jobs in a Newsweek interview, "It was developed out of necessity for the Mini, because there wasn't enough room [for the buttons]. But the minute we experienced it we just thought, 'My God, why didn't we think of this sooner?'" And then, some might tell you the greatest thing in the world is the super-tight iPod/iTunes integration (which, ironically, others will curse until the day they die).

iTunes interface

iTunes is the integrated jukebox/media-player software that comes with an iPod. It lives on your computer, and you use it for organizing, playing, converting and downloading files from an external source to your computer and from your computer to an iPod. This is really no different from the software than comes with any other portable media player. The thing that makes iTunes a brilliant invention from a consumer-electronics standpoint is the built-in iTunes Store that keeps iPod users coming back to Apple on a regular basis. Anyone who owns an iPhone or an iPod touch can also shop at the iTunes store using a WiFi connection.

Thank You Thanks to Daniel Guzman for his assistance with this article.

The iTunes Store lets iPod users purchase music, movies, podcasts, audiobooks and music videos with a click -- it's an integral part of the iTunes software. You can watch or listen to the files through iTunes on your computer and download them to your iPod. And you don't even have to drag and drop: The iTunes software autosyncs with iPod whenever it's connected to your computer through a USB 2.0 port (you can use FireWire for charging, but not for syncing). Just plug it in, and the iPod automatically downloads every new file that you added to your iTunes jukebox since the last time it was connected. It also uploads to iTunes all new data that you added to your iPod since last the two conversed, like playlists and song ratings.

iPod Myths

If I use iPod as my digital-media player, I can only download music from the iTunes Store.
Not true. You can download music from other sites (as long as the site doesn't use Windows Media DRM -- iPod isn't compatible with that encoding).

If I use iPod as my digital-media player, I can only use the iTunes software as my jukebox.
Not true. While iPod is made to work with the iTunes software, there are other jukeboxes out there that you can use with your iPod.

If I download MP3 or WAV files to my iPod, they'll be converted into a proprietary audio format.
Not true. Downloading files to an iPod doesn't change the format. iPod can play MP3, WAV, AAC, AIFF, Apple Lossless and Audible audio files.

iPod Features

In addition to the iTunes integration and autosync, the Click Wheel (more on this in the hardware section) and the slim form factor, some of iPod's more notable features include:

Audio
The 160-GB iPod stores up to 40,000 songs (20,000 for the 80-GB model). The search function lets you type in keywords (song name, artist, album) using the Click Wheel to locate a song on the iPod hard drive. It supports MP3, WAV, AAC, AIFF, Apple Lossless and Audible audio files. You can download songs from the iTunes Store, from a different MP3 download site or rip them from your CDs into the iTunes software. You need to go through the iTunes software to download files to the iPod (unless you download a hack that lets you bypass iTunes -- more on hacks in the Software section). You can listen to audio books at various speeds -- normal, faster or slower -- without seriously distorting the sound, and connect your iPod to your home stereo through a mini-to-RCA jack. The device comes with equalizer presets for different music styles.

Photo courtesy Apple
The iPod touch foregoes the standard Click Wheel in favor of
multi-touch sensing.

Video The 80-GB version holds up to 100 hours of video, and the 160-GB version holds up to 200 hours. It supports H.264 and MPEG-4 files as well as MOV files converted to iPod-friendly video through the iTunes software. You can play video podcasts, music videos, feature films and TV shows on the iPod, plus your own DVDs and home videos that you encode using QuickTime Pro and download to your player through iTunes.
Photos
The player holds up to 25,000 photos. It supports files converted from JPEG, BMP, GIF, TIFF, PNG and PSD. You can download your photos to the iPod from Mac iPhoto or Windows Adobe Photoshop Elements/Album. Using an RCA or S-video connection (S-video through the dock accessory), you can connect the iPod to your home-theater TV to watch photo slideshows (complete with soundtrack) or video on a larger screen.
External hard drive
The iPod can function as portable hard drive, carrying all file types between computers. Just choose "enable disk usage" in the iTunes software, and you can load whatever you want onto the player's hard disk.
Calendar/contacts syncing
iPod automatically downloads all new contact/calendar data added to Mac iCal or Microsoft Outlook/Outlook Express since the last time iPod was connected to your computer.
Games
iPod comes with pre-loaded games. You can also download games from the iTunes store, from third-party companies or even create your own (see the "iPod Software" section).
Car integration
If you have an iPod and you're in the market for a new car or a new head unit receiver, you can get one that fully integrates your player into the sound system. There are manufacturer-built car stereos that support iPod integration to the level that you can control the device through the head-unit or steering-wheel controls.

For a full list of iPod features, see Apple: iPod. Now let's get inside a 30-GB, fifth-generation iPod video to find out what hardware it uses to accomplish these tasks.

iPod Hardware

In addition to a cracked LCD, the iPod we're dissecting is nice and scratched.

Before we take apart our iPod video, there are a couple of things you should know. First, the screen on this iPod is cracked. Since no one at HowStuffWorks volunteered their perfect little iPod as a subject for this author's screwdriver, we turned to eBay to find a damaged unit we could take apart with good conscience. Which brings us to the second thing you should know: iPods are almost as valuable broken as they are in mint condition. After several last-minute outbids, we found out we had to pay about $200 for a 30-GB iPod video with a cracked LCD -- this was the typical ending price for this type of unit. And a brand-new, sixth-generation one costs $249 and has more storage space. We were left shaking our heads. Are hundreds of people writing articles that incorporate an iPod dissection? Are hundreds of people that addicted to tinkering with high-priced electronics? Are iPods really so hard to get fixed by Apple once the one-year warranty runs out? The New York Times article "Good Luck With That Broken iPod" (February 4, 2006) would suggest the latter, although it's really anybody's guess.

That said, let's pry this baby apart.

For most of the iPod video's functionality, we're dealing with seven primary components:

Hard drive - 30-GB Toshiba 1.8-inch hard drive
Battery - rechargeable lithium-ion (700 mAh, 3.7V)
Click Wheel - navigation via touch-sensitive wheel and mechanical buttons
Display - 2.5-inch TFT LCD
Microprocessor - PortalPlayer PP5021C with dual ARM7TDMI cores
Video chip - Broadcom BCM2722
Audio chip - Wolfson Microelectronics WM8758 codec

The case actually isn't that difficult to get into -- we used a 6-inch metal putty knife to pry apart the seam. Once you see that you need to get the knife under the thin edge of one side of the casing (instead of driving it straight down), it comes apart pretty quickly. Here's what we saw when we pulled it apart:

This iPod video uses a 30-GB Toshiba 1.8-inch hard drive (model MK3008GAL), featuring 4200 rpm and a USB interface. It weighs 1.7 ounces (48 grams) and fits 30 GB onto a single platter, squeezing in 93.5 gigabits per square inch. To fit so much into so little space, the drive uses smaller and lighter sliders (which keep the right spacing between the read/write heads and the recording surface) and a more sensitive thin-film technology on the heads and the platter. The increased sensitivity allows for a greater number of recorded bits per square inch.

When you remove the front casing, you're looking at the LCD, the motherboard and the Click Wheel:

The Click Wheel is a section unto itself, and we'll deal with that technology on the next page. Let's start here with the iPod video display.

The display is a 2.5-inch, 16-bit, TFT LCD. It has a 320x240-pixel resolution and a 0.156 dot pitch. The screen is incredibly thin -- just 0.125 inches (3.175 mm) deep.

The connectors used in the iPod are miniscule. Instead of the plastic connectors you find in larger devices, the ends of the wires that connect the various components of the iPod are coated in a film that stiffens them to create a viable input. Here you can see where the LCD connects to the back side of the motherboard (with a U.S. dime for reference):

All of the chips and memory devices that make an iPod run are situated on the motherboard. Here's the front:

And here's the back:

In the image above, you can see the Click Wheel controller. A "mixed-signal array" is a chip that can deal with both analog and digital data. In the case of the Click Wheel, the controller has to accept analog data generated by the movement of a finger over the surface of the wheel and turn it into digital data the microprocessor can understand. Let's find out how it does that.

The Thing About the Battery iPod's battery is completely built-in -- you can't just pop in a couple of new AA batteries when it stops charging. This built-in battery has been a headache both for iPod owners and for Apple.

Originally, the iPod battery was not only non-user-replaceable, but it was also very expensive to replace via Apple. When your battery died (sometimes within a year of buying the iPod), you had to send your iPod to Apple for a replacement, and the new battery cost $100. A lot of bad press and a class-action lawsuit later, Apple's iPod battery-replacement program costs $59. The class-action suit was settled, and iPod owners listed in the suit were compensated with $50 vouchers and partial refunds for their $100 battery replacement.

Apple defends the use of a non-user-replaceable battery by explaining that the built-in battery allows for the ultra-slim form factor for which the iPod is known.

There are ways for you to replace the battery without sending your iPod to Apple. See iPod Battery FAQ to learn more.

iPod Click Wheel

The Click Wheel is a touch-sensitive ring that you use to navigate through all of iPod's menus and control all of its features. It provides two ways to input commands: by sliding your finger around the wheel and by pressing buttons located under and in the middle of the wheel.

Under the plastic surface of the Click Wheel, there are four mechanical buttons (Menu, back, forward, play/pause), and there's one button in the center (select).

Click Wheel face

Behind the Click Wheel face (left) and Click Wheel contacts on the motherboard

You've got five buttons and five corresponding contacts on the motherboard. When you press, say, the right side of the wheel while you're listening to a song, the wheel pushes down the forward button. The underside of each rubber button is metal, so pressing it completes the corresponding circuit on the motherboard. The motherboard tells the processor this circuit is complete, and the processor tells the operating system to fast-forward through the song.

The Click Wheel's touch-sensitive function lets you move through lists, adjust volume and fast forward through a song by moving your finger around the stationary wheel. It works a lot like a laptop touchpad. In fact, the company that supplied the Click Wheel for the 4G iPod was Synaptics, most widely known for making laptop touchpads. For the 5G, Apple created its own proprietary Click Wheel design based on the same capacitive sensing principle as the previous Synaptics-designed Click Wheel.

Under the plastic cover of the Click Wheel, there is a membrane embedded with metallic channels. Where the channels intersect, a positional address is created, like coordinates on a graph.

At its most basic, a capacitive-sensing system works like this: The system controller supplies an electrical current to the grid. The metal channels that form the grid are conductors -- they conduct electricity. When another conductor -- say, your finger -- gets close to the grid, the current wants to flow to your finger to complete the circuit. But there's a piece of nonconductive plastic in the way -- the Click Wheel cover. So the charge builds up at the point of the grid that's closest to your finger. This build-up of an electrical charge between two conductors is called capacitance. The closer the two conductors are without touching, the greater the capacitance.

Front of membrane: Here you can see the conductive grid

Back of membrane: Here you can see the Click Wheel controller.

The "sensing" part of the system comes in with the controller. The Click Wheel controller (see above) is programmed to measure changes in capacitance. The greater the change in capacitance at any given point, the closer your finger must be to that point. When the controller detects a certain change in capacitance, it sends a signal to the microprocessor. As you move your finger around the wheel, the charge build-up moves around the wheel with it. Every time the controller senses capacitance at a given point, it sends a signal. That's how the Click Wheel can detect speed of motion -- the faster you move your finger around the wheel, the more compacted the stream of signals it sends out. And as the microprocessor receives the signals, it performs the corresponding action -- increasing the volume, for instance. When your finger stops moving around the wheel, the controller stops detecting changes in capacitance and stops sending signals, and the microprocessor stops increasing the volume.

Now, in discussing the workings of the Click Wheel, a particularly curious HowStuffWorks staffer raised the following question: If your finger controls the Click Wheel because your finger is a conductor, why can't you control the Click Wheel with a paper clip?

While we scratched our heads, we embarked on a experiment.

Experiment: How About an Apple? What can you use to control the touch-sensitive Click Wheel? Here's an abbreviated list of what we tested:

Finger: Yes

Orange: Yes

Apple: Yes

Plastic pen cap: No

Silly Putty: No

Paper clip: No

Tip of Cold Heat soldering tool: No

Prongs from iPod charger: No

The yesses are easily explainable -- fruit and flesh can conduct electricity. The no's, however, are a bit more mysterious. The pen cap and the Silly Putty are not conductors, end of story. But what about the tip of the soldering tool, the paper clip and the charger prongs? Those are conductors! To solve this riddle, we contacted an expert in the electronics field, who recommended the following action: Wrap your finger in aluminum foil and try to work the Scroll Wheel. Our expert was thinking "surface area." This finger-wrapped-in-foil input worked perfectly.

Can it be that the surface area of the paper clip is not enough to trigger the conductive grid? To investigate this hypothesis, we tried to work the Scroll Wheel using the blunt end of a dinner knife (approx. 0.75 in x 0.5 in). It worked. We concluded that surface area matters.

But there's another factor, too, because holding the dinner knife between two plastic pens and moving it around the Scroll Wheel doesn't work. Same with the apple and the orange. You need to be touching the knife or the orange in order for the Scroll Wheel to detect it. The determining factor, then, is you -- the human body is a very big conductor, providing a very big neutral area for a charge to jump to. The charge difference between your body and the Click Wheel's electrodes provides the voltage -- or electrical "pressure" -- that activates the Click Wheel system.

Now that we've checked out the iPod hardware, let's take a look at the software it's supporting.

iPod Software and Hacks

Photo courtesy Apple
iPod video main menu

While Apple is very tight-lipped about its iPod software, most reports have the iPod 5G runs on the Pixo OS 2.1 operating system along with PortalPlayer's Digital Media Platform. The PortalPlayer platform is an all-in-one "system on a chip" that provides some of the hardware we already looked at, including the two ARM7TDMI microprocessor cores. The developer package includes audio-decoder support, customizable firmware (with support for DRM-system development) and software-development tools. The iPod user-interface is reportedly based on the Pixo Toolbox software that was available when Apple was creating the device (Pixo is now part of Sun Microsystems).

In addition to the user-interface and operating-system software, the iPod's video coding and decoding happens at the software level. The Broadcom video chip we looked at in the last section handles processing at the hardware level but has a corresponding piece of software to run the video codec.

As far as operating-system requirements, iPod video is compatible with Mac OS X v10.3.9 or later, Windows 2000 (with Service Pack 4 or later) and Windows XP Home and Professional (with Service Pack 2 or later).

Where iPod software starts getting really interesting is in the third-party software and "hacks" that have sprung up in response to iPod's popularity. iPod third-party software consists of programs that use or build on current iPod functions without changing the way the device is supposed to work. This includes downloadable iPod games, programs that convert a bunch of DVDs to iPod-friendly video files in one shot, programs that convert PDA data and PowerPoint presentations to iPod-compatible files and software that lets you create your own text-based iPod games.

iPod hacks are programs written to give iPods new (non-Apple-intended) functionality. You know how we talked about things you can't do with an iPod, like sync via FireWire? Well, you can hack an iPod to sync via FireWire. Unless you're a programmer, "hacking an iPod" just means you download a chunk of code that alters your iPod's functionality at the software level. If you're a programmer, it means developing that code. iPod hackers are publishing all sorts of programs that alter the way an iPod works -- some of the software is free, and some of it is for purchase. Some currently available hacks let you:

Make an iPod work with Linux machines and run Linux applications
Remove volume caps (iPods sold in Europe cap the volume at 100 decibels; uncapped iPods can reach more than 115 decibels.)
Turn your iPod into a universal remote
Attach an external hard drive to your iPod to increase the storage capacity
Change your iPod's font and graphics
Watch movies on your iPod in full-screen mode
Plug your iPod into any computer (even without iTunes) and listen to music from the hard drive
Transfer photos to iPod without using iTunes
Replace iTunes all together as the iPod's main jukebox
Use an iPod with a Windows 98 machine

iPod Accessories

Between the built-in applications and the outside iPod software, this little device offers a lot of functionality. Add in the slew of iPod accessories out there, and you start to see why some people's daily lives revolve around an iPod.

Apple
iPod Hi-Fi system

The iPod has become so ubiquitous that you'll regularly hear people refer to MP3 players as "iPods," even if they're not talking about Apple's device. An entire genre of broadcasting has evolved to take advantage of the iPod -- you can download "podcasts" to any type of MP3 player (or computer), but these home-made broadcasts originally popped up as an iPod application.

The extensive list of accessories available for the iPod, both Apple and third-party products, builds on the iPod's hardware and software to place it at the center of a "digital-media experience." From Apple, just some of the accessories you can purchase to outfit your iPod include:

Microphone for recording voice memos
External digital voice recorders
Universal dock for charging, syncing or connecting to external A/V equipment
Remote control compatible with universal dock
Camera connector for downloading photos directly from a digital camera to an iPod
Armbands for portability, cases to protect the shiny exterior, and skins to personalize the appearance of the iPod
Car audio adapters, in-car iPod holders
Portable, desktop and wireless speakers
iPod Hi-Fi speaker system
Car chargers and power adapters
Radio transmitters

HSW Shopper
Tavo iPod Gloves

Other companies besides Apple are developing some pretty cool accessories for the iPod. Numerous car-stereo manufacturers have come out with iPod-compatible head units. Tavo has created "Click Wheel-friendly" gloves for people who use their iPods outside in cold weather. The material of the gloves' index and thumb has silver-alloy-coated nylon strands running through it to make your fingertips warm but still conductive. DesignMobel's iPod-compatible bed has an iPod dock built in and comes with an optional Bose sound system, and Atech's iLounge is a combination iPod dock, speaker system and toilet-paper dispenser. The GeekPod 100 from BatteryGeek.net is an external battery that powers an iPod up to 100 hours on a single charge. Yes, 100 hours of listening pleasure. Which brings us to a potential problem that has become an iPod controversy: People who listen to their iPod at full volume for extended periods of time may experience hearing loss.

The possibility of long-term hearing loss for people who have their earbuds in whenever they leave the house has created a nice talking point in the press. The issue is mostly about the iPod's ability to produce sound at volumes greater than 115 decibels. Some experts believe that repeated exposure to this volume, especially via in-ear headphones ("ear buds") can cause "tinnitus and loss of hearing in later life" [ref]. In Europe, Apple has capped the iPod's volume at 100 decibels in response to a French law requiring it, but units sold in the United States don't have the volume cap.

In early 2006, a man in Louisiana filed a lawsuit against Apple related to the potential for hearing loss. He claims the iPod is "inherently defective in design" and does not appropriately warn its users of the potential damage to their hearing. See BBC News: Man sues over iPod 'hearing risk' to learn more.

In view of the bad press and the lawsuit, it's possible that Apple will decide to include volume caps on all new iPods with the release of the next generation. For the time being, Apple has released a volume-cap software update for iPod video and iPod nano (see iPod Updater 2006-03-23). Regardless of whether the volume gets turned down, it looks like the spread of the iPod will continue. The release of the first iTunes cell phone in 2005 marked the start of what might turn out to be the increasing integration of iPod functionality into other portable devices. The iPod's Broadcom video processor also supports digital camera functions, so that's a possible utility to look for in future iPods. Recent Apple patents include drawings of a touch screen sporting what looks like a virtual Click Wheel, leading some to infer that the next iPod will have a graphical, entirely touch-sensitive interface.

iPod Hacks Work

2008-04-10T22:33:00.001+07:00

iPod Hacks Work

Photo courtesy Consumer Guide Products
Shopping for an iPod? Compare iPod prices at Consumer Guide Products before you buy.

Right out of the box, an iPod can hold, organize and play most people's entire music collection. It can also act like a calendar and a clock, and newer models can play videos and a few simple games. But some people want more from their iPods.

Intrepid technophiles have found ways to hack iPods, giving them the ability to do much more than play music. In this article, we'll explore why iPods can be hacked, which hacks are our favorites and where to go to learn more.

We'll start by looking at what it means to hack an iPod. An iPod is a lot like a tiny computer. A fifth-generation (5g) iPod Video has:

A screen
A hard drive
A processor
Memory, including ROM and RAM
Video and audio chips
An input device (a click wheel)
A power source (a rechargeable battery)

A motherboard connects all of these components together, and external ports provide a place to connect a power cable, headphones and accessories. An iPod also has an operating system and software that allow it to read, store and access files. Firmware – software that tells the iPod how to behave and how to communicate with its software – resides in the device's read-only memory.

Warning: Some Cars Not for Use
with Some Sets There's one important thing to keep in mind if you're thinking about hacking your iPod. Most hacks will void your warranty. In other words, if you decide to change your iPod's hardware or software, the folks at your local Apple Store's Genius Bar won't be able to help you if something goes wrong. In addition, some hacks only work with specific iPod models – a hack meant for a third-generation device might cause problems for a later model.

These components are like smaller versions of what you can find inside a computer or a laptop. But apart from size, there's one big difference between an iPod and a computer. When you buy a computer, you can also buy software and hardware to upgrade its capabilities. In some ways, computers even encourage you to do this. They have cases that you can open with simple tools and CD-ROM or disk drives that let you install software that you buy at the store. With an Internet connection, you can also legally purchase and download software from the Web.

An iPod, on the other hand, is a closed system. You can't get inside it without a special tool to pry the front and rear portions of the case apart. You can't go to a computer store and buy new iPod software. Just about anything you do to modify your iPod voids its warranty. For these reasons, modifications to an iPod's inner workings are known as hacks. When you hack an iPod, you're changing its hardware, software, firmware or operating system, something you're technically not supposed to do.

Numerous iPod hacks rely on one fundamental change – the addition of the open-source operating system Linux. The iPodLinux Project has worked out how to port Linux to an iPod and has developed a Linux user interface called podzilla. Installing Linux allows an iPod to play musical files that it does not normally support, like Ogg files. You can also download:

Image courtesy iPodLinux.org
Linux on the iPod

Schemes, which change the appearance of podzilla
Modules, which are essentially applications for use with the iPodLinux operating system

With the addition of Linux, an iPod becomes less like an MP3 player and more like a PDA or handheld computer.

Currently, iPodLinux has been tested on first-, second- and third-generation iPods. Some users who have developed hacks for newer iPods report that it also works on fourth- and fifth-generation models. But regardless of whether it has been tested, installing Linux on an iPod unquestionably voids its warranty.

Getting your iPod to run Linux is really the ultimate hack. It's the foundation for using your iPod in an entirely new way, and it opens the door for limitless applications. For a lot of users, the addition of Linux adds enough options for applications and functions that the benefits outweigh the inherent risks of tampering with the iPod's programming.

We'll look at what Linux modules and other hacks can do in the next section.

Favorite iPod Hacks

Image courtesy File Front
iDoom for the iPod

Most iPod hacks either enhance an iPod's capabilities or get rid of functions that users find annoying. Here are some of our favorites.

iPod Games
One of the most notable Linux modules is iDoom, which lets you play Doom on your iPod. The game currently does not have sound, but it does have color when played on color iPods. It has some of the same features that the full-scale game does, like the ability to save games and customize the game controls.

iDoom is only one of many ports of popular Linux-based iPod games. Others are:

iGems, an iPod version of Bejeweled
Invaders, which replicates Space Invaders
Magic 8-Ball
iPod MAME, a version of Pac-Man
Pod Pod Revolution, a version of Dance Dance Revolution
Sudoku

Customized Graphics

Image courtesy Phillip Torrone
Hello Kitty customized iPod graphic

Some people find the bit flashing "No" symbol that appears whenever you synch your iPod to be annoying. Engadget explains how to replace it with something else. To do it, you need an iPod, a PC and a Windows application called iPodWizard. You can change the "Do Not Disconnect" graphic to virtually anything you want. iPodWizard also lets you change the iPod's other icons and fonts.

iPod Remote Control
O'Reilly Digital Media explains how to turn an iPod into a universal remote control. The hack combines an infrared (IR) device that plugs into the headphone port with software running on a PC. Essentially, you record the IR pulses from your remote controls and play them back from your iPod.

"Lost" Countdown
As soon as the survivors of Oceanic flight 815 learned about "pushing the button" on "Lost," people created screen savers that replicated the process. You can get a similar"Lost" countdown for your iPod. Using it requires iPodLinux.

Word Processing
You probably wouldn't want to write a novel or a dissertation on your iPod. But being able to keep track of a few notes or a grocery list is a handy feature. An iPodLinux word processing module lets you use your iPod to create and save text files.

Expanded Nano Storage
According to Multiarcade, you can give a 4 GB iPod Nano a storage capacity of 8 GB. The process is fairly simple – you remove the memory chip from a broken Nano and install it in a working Nano. While the resulting player still pales in comparison to a 60 GB iPod Video, it has twice its original storage capacity in the same tiny physical space.

Audible Menus
Rockbox completely replaces an iPod's firmware with an open-source alternative. One of Rockbox's most interesting features is that it can read menu options and album, track and artist names aloud. This makes it possible for visually impaired people to use an iPod.

Enhanced Mac Security
Podsmith turns your iPod into a key to unlock the screen, files or applications on your Macintosh computer. This can protect your data and the privacy of your personal information if your Mac is stolen.

Integrated Car Console
Many new cars come with connections for iPods or other MP3 players built in. But not everyone is ready to trade in their car. O'Reilly Digital Media explains how to modify a car's console to provide a permanent iPod connection. This is more of a car hack than an iPod hack, and the process requires some dangerous chemicals, so exercise caution.

Software Options

Image courtesy Version Tracker
TrailRunner

Making changes to operating systems and firmware isn't for everyone. A low-risk way to add more functionality to your iPod is to install software on your computer that takes advantage of the device's existing features. This isn't technically a hack, since you're not changing your iPod's hardware or software - you're simply using software on your computer that produces files the iPod can use. For example:

TrailRunner is an application that lets you map out jogging or biking routes and create exercise plans. TrailRunner is a Mac OS X application, and it exports files as iPod notes.
VoodooPad is another OS X application, and it's like a sketchbook, notepad and organizer rolled together. Like TrailRunner, it exports documents to an iPod-compatible format.
Apollo is a video converter for Windows. It optimizes video for playback on an iPod.

Low-risk Personalization
If you want to personalize your iPod and buying a new case isn't dramatic enough for your taste, you have some other options. These don't involve changing software or firmware, so they're really mods rather than hacks, and they're unlikely to damage your iPod's ability to play music.

Image courtesy Skinpod.it
An iPod skin

The cheapest way to change your iPod's appearance is to download and print a skin. Sites like SkinPod let you browse, print and use skins for free. The best thing about these skins is that they completely cover the scratches that most iPod models are susceptible to. You just print your selected design onto adhesive paper, cut it out and stick it to your iPod. It's a good idea to use a spray fixative to keep the colors from smearing. Keep in mind, though, that if you ever want to remove your iPod skin, you'll probably have leftover adhesive to deal with in addition to the scratches.

If you want something that's a little more permanent and a little less prone to sticky residue, some companies offer custom iPod painting. ColorEnvy can paint iPods and other electronic devices in a range of colors. The company also offers professional scratch removal as well as a product called E-juice that you can use to remove iPod scratches at home.

If you're interested in finding out about using Linux on your iPod or finding other hacks, check out the following links:

You can also read Hadley Stern's iPod & iTunes Hacks, published by O'Reilly Digital Media.

See the links on the next page for lots more information on iPods, Linux and related topics.

Autofocus Cameras

2008-02-26T12:18:00.002+07:00

Autofocus is that great time saver that is found in one form or another on most cameras today. In most cases, it helps improve the quality of the pictures we take.

Photo courtesy Panasonic and Matsushita Electric Corporation of America

In this article, you will learn about the two most common forms of autofocus, and find out how to determine which type of autofocus your camera uses. You will also learn some valuable tips about preventing the main causes of blurred pictures when using an autofocus camera.

What is Autofocus?

Autofocus (AF) really could be called power-focus, as it often uses a computer to run a miniature motor that focuses the lens for you. Focusing is the moving of the lens in and out until the sharpest possible image of the subject is projected onto the film. Depending on the distance of the subject from the camera, the lens has to be a certain distance from the film to form a clear image. StuffGuide.com for more information. -->

In most modern cameras, autofocus is one of a suite of automatic features that work together to make picture-taking as easy as possible. These features include:

Automatic film advance
Automatic flash
Automatic exposure

There are two types of autofocus systems: active and passive. Some cameras may have a combination of both types, depending on the price of the camera. In general, less expensive point-and-shoot cameras use an active system, while more expensive SLR (single-lens reflex) cameras with interchangeable lenses use the passive system.

Active Autofocus

In 1986, the Polaroid Corporation used a form of sound navigation ranging (SONAR), like a submarine uses underwater, to bounce a sound wave off the subject. The Polaroid camera used an ultra-high-frequency sound emitter and then listened for the echo (see How Radar Works for details). The Polaroid Spectra and later SX-70 models computed the amount of time it took for the reflected ultrasonic sound wave to reach the camera and then adjusted the lens position accordingly. This use of sound has its limitations -- for example, if you try taking a picture from inside a tour bus with the windows closed, the sound waves will bounce off of the window instead of the subject and so focus the lens incorrectly.

This Polaroid system is a classic active system. It is called "active" because the camera emits something (in this case, sound waves) in order to detect the distance of the subject from the camera.

Active autofocus on today's cameras uses an infrared signal instead of sound waves, and is great for subjects within 20 feet (6 m) or so of the camera. Infrared systems use a variety of techniques to judge the distance. Typical systems might use:

Triangulation
Amount of infrared light reflected from the subject
Time

For example, this patent describes a system that reflects an infrared pulse of light off the subject and looks at the intensity of the reflected light to judge the distance. Infrared is active because the autofocus system is always sending out invisible infrared light energy in pulses when in focus mode.

StuffGuide.com for more information. --> It is not hard to imagine a system in which the camera sends out pulses of infrared light just like the Polaroid camera sends out pulses of sound. The subject reflects the invisible infrared light back to the camera, and the camera's microprocessor computes the time difference between the time the outbound infrared light pulses are sent and the inbound infrared pulses are received. Using this difference, the microprocessor circuit tells the focus motor which way to move the lens and how far to move it. This focus process repeats over and over while the camera user presses the shutter release button down half-way. The only difference between this system and the ultrasound system is the speed of the pulse. Ultrasound waves move at hundreds of miles per hour, while infrared waves move at hundreds of thousands of miles per second.

Infrared sensing can have problems. For example:

A source of infrared light from an open flame (birthday cake candles, for instance) can confuse the infrared sensor.
A black subject surface may absorb the outbound infrared beam.
The infrared beam can bounce off of something in front of the subject rather than making it to the subject.

One advantage of an active autofocus system is that it works in the dark, making flash photography much easier.

On any camera using an infrared system, you can see both the infrared emitter and the receiver on the front of the camera, normally near the viewfinder.

To use infrared focusing effectively, be sure the emitter and the sensor have a clear path to and from your subject, and are not blocked by a nearby fence or bars at a zoo cage. If your subject is not exactly in the middle, the beam can go right past the subject and bounce off an undesired subject in the distance, so be sure the subject is centered. Very bright subjects or bright lights can make it difficult for the camera to "see" the reflected infrared beam -- avoid these subjects when possible.

This patent, this patent, and this patent each show a different form of infrared sensing.

Passive Autofocus

Passive autofocus, commonly found on single-lens reflex (SLR) autofocus cameras, determines the distance to the subject by computer analysis of the image itself. The camera actually looks at the scene and drives the lens back and forth searching for the best focus.

A typical autofocus sensor is a charge-coupled device (CCD) that provides input to algorithms that compute the contrast of the actual picture elements. The CCD is typically a single strip of 100 or 200 pixels. Light from the scene hits this strip and the microprocessor looks at the values from each pixel. The following images help you understand what the camera sees:

Out-of-focus scene

Out-of-focus pixel strip

In-focus scene

In-focus pixel strip

The microprocessor in the camera looks at the strip of pixels and looks at the difference in intensity among the adjacent pixels. If the scene is out of focus, adjacent pixels have very similar intensities. The microprocessor moves the lens, looks at the CCD's pixels again and sees if the difference in intensity between adjacent pixels improved or got worse. The microprocessor then searches for the point where there is maximum intensity difference between adjacent pixels -- that's the point of best focus. Look at the difference in the pixels in the two red boxes above: In the upper box, the difference in intensity between adjacent pixels is very slight, while in the bottom box it is much greater. That is what the microprocessor is looking for as it drives the lens back and forth.

Passive autofocus must have light and image contrast in order to do its job. The image needs to have some detail in it that provides contrast. If you try to take a picture of a blank wall or a large object of uniform color, the camera cannot compare adjacent pixels so it cannot focus.

There is no distance-to-subject limitation with passive autofocus like there is with the infrared beam of an active autofocus system. Passive autofocus also works fine through a window, since the system "sees" the subject through the window just like you do.

Passive autofocus systems usually react to vertical detail. When you hold the camera in the horizontal position, the passive autofocus system will have a hard time with a boat on the horizon but no problem with a flagpole or any other vertical detail. If you are holding the camera in the usual horizontal mode, focus on the vertical edge of the face. If you are holding the camera in the vertical mode, focus on a horizontal detail.

Newer, more expensive camera designs have combinations of vertical and horizontal sensors to solve this problem. But it's still the camera user's job to keep the camera's sensors from being confused on objects of uniform color.

You can see how much area your camera's autofocus sensors cover by looking through the viewfinder at a small picture or a light switch on a blank wall. Move the camera from left to right and see at which point the autofocus system becomes confused.

How Do I Know Which Autofocus System My Camera Has?

Look at the type of camera you have:

If it is an under-$50 point-and-shoot camera or one of the single-use, disposable cameras, it is definitely a fixed-focus camera with no focusing system of any kind. This type of lens has its focus set at the factory, and it typically works best with a subject distance of about 8 feet. Four feet is about as close as you can get to the subject with a fixed-focus camera. When you look through a fixed-focus camera, you typically do not see the square brackets or circles found in an autofocus camera. However, you may see a "flash ready" indicator.
SLR cameras with interchangeable lenses typically use the passive autofocus system.
Cameras without interchangeable lenses typically use active infrared, and you can see the emitter and the sensor on the front of the camera.

Here's a quick test to tell which autofocus system is in use in your camera (some cameras may have both systems):

Go outdoors and aim the viewfinder at an area of the sky with no clouds, power lines or tree limbs. Press the shutter button halfway down.
If you get a "focus okay" indication, it's an active autofocus system.
If you get a "focus not okay" indication, it's a passive autofocus system. The CCD cannot find any contrast in a blue sky, so it gives up.

Is Autofocus Always Accurate and Faster?

It is really up to the person using the camera to determine if the subject is in focus. The camera merely assists you in making this decision. The two main causes of blurred pictures taken via autofocus cameras are:

Mistakenly focusing on the background
Moving the camera while pressing the shutter button

Your eye has a fast autofocus! Try this simple experiment: Hold your hand up near your face and focus on it, and then quickly look at something past your hand in the distance. The distant item will be clear, and your hand will not be as clear. Look back at your hand. It will be clear, while out of the corner of your eye the same distant item will not be as clear. Your camera is not nearly this quick or this precise, so you often have to help it.

Focus Lock: The Key to Great Autofocus Pictures

The camera user can often fool the autofocus system. A pose of two people centered in the picture may be unclear if the focus area (the area between the two square brackets) is in the middle of the two people. Why? The camera's autofocus system actually focuses on the landscape in the background, which is what it "sees" between the two people.

The solution is to move your subjects off-center and use the focus-lock feature of your camera. Typically, focus lock works by depressing the shutter button part-way and holding it while you compose the picture. The steps are:

Compose the picture so that the subject is either in the left third or the right third of the picture. (This makes for pleasing pictures.) You will come back to this position.

Move the camera right or left so the square brackets in the center of the viewfinder are over the actual subject.

Press and hold the shutter button halfway down so the camera focuses on the subject. Keep your finger on the button.
Slowly move your camera back to where you composed the picture in step 1. Press (squeeze) the shutter button all the way down. It may take some practice to do it right, but the results will be great!

You may also use the above procedure in the vertical direction, say when taking a picture with mountains or the shore in the background.

When Should I Use Manual Focus?

Manual focus rings are still available on most SLR cameras. When taking a picture of an animal behind bars in a zoo, the autofocus camera might focus on the cage bars instead of the animal. On most consumer-grade autofocus cameras, use manual focus when:

You have a zoom lens on an active autofocus camera, and your subject is more than 25 feet away.
You have a passive autofocus camera and the subject has little or no detail, like a white shirt with no tie.
You have a passive autofocus camera and the subject is not well lit or very bright and more than 25 feet away.

Autofocus Video Cameras

Autofocus in a video camera is a passive system that also uses the central portion of the image. Though very convenient for fast shooting, autofocus has some problems:

It can be slow to respond.
It may search back and forth, vainly seeking a subject to focus on.
It has trouble in low light levels.
It mis-focuses when the intended subject is not in the center of the image.
It changes focus when something passes between the subject and the lens.

Autofocus video cameras work best in bright light. Switch to manual focus in low light.

How to "See" Infrared With Your Camcorder You can sometimes "see" infrared via this simple experiment, using a camcorder with a TV monitor attached. Point the camera toward a TV remote control. Push some buttons on the TV remote control and the camera should "see" invisible infrared light from the remote control. Camcorders typically use CCD imaging chips. These chips are sensitive to infrared light. That's why your camera shows a white spot where the remote's infrared source is located. A "spy" can take pictures in complete darkness if they illuminate the scene with bright infrared light.

do you know PCI Express Works ?

2008-01-05T20:49:00.000+07:00

Introduction to How PCI Express Works

Peripheral Component Interconnect (PCI) slots are such an integral part of a computer's architecture that most people take them for granted. For years, PCI has been a versatile, functional way to connect sound, video and network cards to a motherboard.

But PCI has some shortcomings. As processors, video cards, sound cards and networks have gotten faster and more powerful, PCI has stayed the same. It has a fixed width of 32 bits and can handle only 5 devices at a time. The newer, 64-bit PCI-X bus provides more bandwidth, but its greater width compounds some of PCI's other issues.

Your Browser Does Not Support iFrames

A new protocol called PCI Express (PCIe) eliminates a lot of these shortcomings, provides more bandwidth and is compatible with existing operating systems. In this article, we'll examine what makes PCIe different from PCI. We'll also look at how PCI Express makes a computer faster, can potentially add graphics performance, and can replace the AGP slot.

Photo courtesy Consumer Guide Products

Thank You Thanks to Joshua Senecal for his assistance with this article.

High-Speed Serial Connection
In the early days of computing, a vast amount of data moved over serial connections. Computers separated data into packets and then moved the packets from one place to another one at a time. Serial connections were reliable but slow, so manufacturers began using parallel connections to send multiple pieces of data simultaneously.

It turns out that parallel connections have their own problems as speeds get higher and higher -- for example, wires can interfere with each other electromagnetically -- so now the pendulum is swinging back toward highly-optimized serial connections. Improvements to hardware and to the process of dividing, labeling and reassembling packets have led to much faster serial connections, such as USB 2.0 and FireWire.

Sizing Up Smaller PCIe cards will fit into larger PCIe slots. The computer simply ignores the extra connections. For example, a x4 card can plug into a x16 slot. A x16 card, however, would be too big for a x4 slot.

PCI Express is a serial connection that operates more like a network than a bus. Instead of one bus that handles data from multiple sources, PCIe has a switch that controls several point-to-point serial connections. (See How LAN Switches Work for details.) These connections fan out from the switch, leading directly to the devices where the data needs to go. Every device has its own dedicated connection, so devices no longer share bandwidth like they do on a normal bus. We'll look at how this happens in the next section.

PCI Express Lanes

When the computer starts up, PCIe determines which devices are plugged into the motherboard. It then identifies the links between the devices, creating a map of where traffic will go and negotiating the width of each link. This identification of devices and connections is the same protocol PCI uses, so PCIe does not require any changes to software or operating systems.

Each lane of a PCI Express connection contains two pairs of wires -- one to send and one to receive. Packets of data move across the lane at a rate of one bit per cycle. A x1 connection, the smallest PCIe connection, has one lane made up of four wires. It carries one bit per cycle in each direction. A x2 link contains eight wires and transmits two bits at once, a x4 link transmits four bits, and so on. Other configurations are x12, x16 and x32.

Scalable PCI Express slots.

PCI Express is available for desktop and laptop PCs. Its use may lead to lower cost of motherboard production, since its connections contain fewer pins than PCI connections do. It also has the potential to support many devices, including Ethernet cards, USB 2 and video cards.

Two by Two The "x" in an "x16" connection stands for "by." PCIe connections are scalable by one, by two, by four, and so on.

But how can one serial connection be faster than the 32 wires of PCI or the 64 wires of PCIx? In the next section, we'll look at how PCIe is able to provide a vast amount of bandwidth in a serial format.

PCI Express Connection Speeds

The 32-bit PCI bus has a maximum speed of 33 MHz, which allows a maximum of 133 MB of data to pass through the bus per second. The 64-bit PCI-X bus has twice the bus width of PCI. Different PCI-X specifications allow different rates of data transfer, anywhere from 512 MB to 1 GB of data per second.

Devices using PCI share a common bus, but each device using PCI Express has its own dedicated connection to the switch.

A single PCI Express lane, however, can handle 200 MB of traffic in each direction per second. A x16 PCIe connector can move an amazing 6.4 GB of data per second in each direction. At these speeds, a x1 connection can easily handle a gigabit Ethernet connection as well as audio and storage applications. A x16 connection can easily handle powerful graphics adapters.

How is this possible? A few simple advances have contributed to this massive jump in serial connection speed:

Prioritization of data, which allows the system to move the most important data first and helps prevent bottlenecks
Time-dependent (real-time) data transfers
Improvements in the physical materials used to make the connections
Better handshaking and error detection
Better methods for breaking data into packets and putting the packets together again. Also, since each device has its own dedicated, point-to-point connection to the switch, signals from multiple sources no longer have to work their way through the same bus.

Slowing the Bus Interference and signal degradation are common in parallel connections. Poor materials and crossover signal from nearby wires translate into noise, which slows the connection down. The additional bandwidth of the PCI-X bus means it can carry more data that can generate even more noise. The PCI protocol also does not prioritize data, so more important data can get caught in the bottleneck. Using the Accelerated Graphics Port (AGP) slot for video cards removes a substantial amount of traffic, but not enough to compensate for faster processors and I/O devices.

PCI Express and Advanced Graphics

We've established that PCIe can eliminate the need for an AGP connection. A x16 PCIe slot can accommodate far more data per second than current AGP 8x connections allow. In addition, a x16 PCIe slot can supply 75 watts of power to the video card, as opposed to the 25watt/42 watt AGP 8x connection. But PCIe has even more impressive potential in store for the future of graphics technology.

Photo courtesy Consumer Guide Products
PCI Express video card

Photo courtesy Consumer Guide Products
AGP 8x video card

With the right hardware, a motherboard with two x16 PCIe connections can support two graphics adapters at the same time. Several manufacturers are developing and releasing systems to take advantage of this feature:

NVIDIA Scalable Link Interface (SLI): With an SLI-certified motherboard, two SLI graphics cards and an SLI connector, a user can put two video cards into the same system. The cards work together by splitting the screen in half. Each card controls half of the screen, and the connector makes sure that everything stays synchronized.

Photo courtesy NVIDIA
NVIDIA SLI link card
ATI CrossFire: Two ATI Radeon® video cards, one with a "compositing engine" chip, plug into a compatible motherboard. ATI's technology focuses on image quality and does not require identical video cards, although high-performance systems must have identical cards. Crossfire divides up the work of rendering in one of three ways:
- splitting the screen in half and assigning one half to each card (called "scissoring")
- dividing up the screen into tiles (like a checkerboard) and having one card render the "white" tiles and the other render the "black" tiles
- having each card render alternate frames
Alienware Video Array: Two off-the-shelf video cards combine with a Video Merger Hub and proprietary software. This system will use specialized cooling and power systems to handle all the extra heat and energy from the video cards. Alienware's technology may eventually support as many as four video cards.

Photo courtesy NVIDIA
Two video cards running parallel

Since PCI, PCI-X and PCI Express are all compatible, all three can coexist indefinitely. So far, video cards have made the fastest transition to the PCIe format. Network and sound adapters, as well as other peripherals, have been slower in development. But since PCIe is compatible with current operating systems and can provide faster speeds, it is likely that it will eventually replace PCI as a PC standard. Gradually, PCI-based cards will become obsolete.

For more information about PCI Express and related topics, check out the links on the next page.

do you know magnet works ?

2008-01-03T22:23:00.000+07:00

Introduction to How Magnets Work

It all started when we went shopping for a magnet for a demonstration on liquid body armor. We wanted to show that a magnetic field could cause certain liquids to behave as solids. Along with the petri dishes and iron filings we needed, the Steve Spangler Science catalog had a neodymium magnet it described as "super strong." We ordered our supplies, hoping that the magnet would be powerful enough to create an effect we could capture on film.

Our homemade ferrofluid before and after exposure to a magnetic field

The magnet didn't just transform our iron-and-oil fluid into a solid -- sometimes, its pull on the fluid cracked the petri dish holding it. Once, the magnet unexpectedly flew out of a videographer's hand and into a dish full of dry filings, which required considerable ingenuity to remove. It also adhered itself so firmly to the underside of a metal table that we had to use a pair of locking pliers to retrieve it. When we decided it would be safer to keep the magnet in a pocket between takes, people wound up momentarily stuck to the table, a ladder and the studio door.

Magnetic Poles A magnet can have multiple north and south poles, and these poles always occur in pairs. There can be no north pole without a corresponding south pole, no south pole without a corresponding north.

Around the office, the magnet became an object of curiosity and the subject of impromptu experiments. Its uncanny strength and its tendency to suddenly and noisily jump from unwary grips to the nearest metal surface got us thinking. We all knew the basics of magnets and magnetism -- magnets attract specific metals, and they have north and south poles. Opposite poles attract each other while like poles repel. Magnetic and electrical fields are related, and magnetism, along with gravity and strong and weak atomic forces, is one of the four fundamental forces in the universe.

But none of those facts led to an answer to our most basic question. What exactly makes a magnet stick to certain metals? By extension, why don't they stick to other metals? Why do they attract or repel each other, depending on their positioning? And what makes neodymium magnets so much stronger than the ceramic magnets we played with as children?

Iron filings (right) align along the magnetic field lines of a cylindrical neodymium magnet.

To understand the answers to these questions, it helps to have a basic definition of a magnet. Magnets are objects that produce magnetic fields and attract metals like iron, nickel and cobalt. The magnetic field's lines of force exit the magnet from its north pole and enter its south pole. Permanent or hard magnets create their own magnetic field all the time. Temporary or soft magnets produce magnetic fields while in the presence of a magnetic field and for a short while after exiting the field. Electromagnets produce magnetic fields only when electricity travels through their wire coils.

Iron filings (right) align along the magnetic field lines of a cubical neodymium magnet.

Until recently, all magnets were made from metal elements or alloys. These materials produced magnets of different strengths. For example:

Ceramic magnets, like the ones used in refrigerator magnets and elementary-school science experiments, contain iron oxide in a ceramic composite. Most ceramic magnets, sometimes known as ferric magnets, aren't particularly strong.
Alnico magnets are made from aluminum, nickel and cobalt. They're stronger than ceramic magnets, but not as strong as the ones that incorporate a class of elements known as rare-earth metals.
Neodymium magnets contain iron, boron and the rare-earth element neodymium.
Samarium cobalt magnets combine cobalt with the rare-earth element samarium. In the past few years, scientists have also discovered magnetic polymers, or plastic magnets. Some of these are flexible and moldable. However, some work only at extremely low temperatures, and others pick up only very lightweight materials, like iron filings.

It takes a little effort for these materials to become magnets. We'll look at how it happens in the next section.

Making Magnets: The Basics

Many of today's electronic devices require magnets to function. This reliance on magnets is relatively recent, primarily because most modern devices require magnets that are stronger than the ones found in nature. Lodestone, a form of magnetite, is the strongest naturally-occurring magnet. It can attract small objects, like paper clips and staples.

By the 12th century, people had discovered that they could use lodestone to magnetize pieces of iron, creating a compass. Repeatedly rubbing lodestone along an iron needle in one direction magnetized the needle. It would then align itself in a north-south direction when suspended. Eventually, scientist William Gilbert explained that this north-south alignment of magnetized needles was due to the Earth behaving like an enormous magnet with north and south poles.

A compass needle isn't nearly as strong as many of the permanent magnets used today. But the physical process that magnetizes compass needles and chunks of neodymium alloy is essentially the same. It relies on microscopic regions known as magnetic domains, which are part of the physical structure of ferromagnetic materials, like iron, cobalt and nickel. Each domain is essentially a tiny, self-contained magnet with a north and south pole. In an unmagnetized ferromagnetic material, each of the north poles points in a random direction. Magnetic domains that are oriented in opposite directions cancel one another out, so the material does not produce a net magnetic field.

In an unmagnetized ferromagnetic material, domains point in random directions.

In magnets, on the other hand, most or all of the magnetic domains point in the same direction. Rather than canceling one another out, the microscopic magnetic fields combine to create one large magnetic field. The more domains point in the same direction, the stronger the overall field. Each domain's magnetic field extends from its north pole into the south pole of the domain ahead of it.

In a magnet, most or all of the domains point in the same direction.

This explains why breaking a magnet in half creates two smaller magnets with north and south poles. It also explains why opposite poles attract -- the field lines leave the north pole of one magnet and naturally enter the south pole of another, essentially creating one larger magnet. Like poles repel each other because their lines of force are traveling in opposite directions, clashing with each other rather than moving together.

Connecting the north pole of one magnet to the south pole of another magnet essentially creates one larger magnet.

Making Magnets: The Details

To make a magnet, all you have to do is encourage the magnetic domains in a piece of metal to point in the same direction. That's what happens when you rub a needle with a magnet -- the exposure to the magnetic field encourages the domains to align. Other ways to align magnetic domains in a piece of metal include:

Placing it a strong magnetic field in a north-south direction
Holding it in a north-south direction and repeatedly striking it with a hammer, physically jarring the domains into a weak alignment
Passing an electrical current through it

Two of these methods are among scientific theories about how lodestone forms in nature. Some scientists speculate magnetite becomes magnetic when struck by lightning. Others theorize that pieces of magnetite became magnets when the Earth was first formed. The domains aligned with the Earth's magnetic field while iron oxide was molten and flexible.

Iron filings line up along the magnetic fields of four small magnets. After removing the magnet, the filings will continue to have their own weak magnetic fields.

The most common method of making magnets today involves placing metal in a magnetic field. The field exerts torque on the material, encouraging the domains to align. There's a slight delay, known as hysteresis, between the application of the field and the change in domains -- it takes a few moments for the domains to start to move. Here's what happens:

The magnetic domains rotate, allowing them to line up along the north-south lines of the magnetic field.
Domains that already pointed in the north-south direction become bigger as the domains around them get smaller.
Domain walls, or borders between the neighboring domains, physically move to accommodate domain growth. In a very strong field, some walls disappear entirely.

The resulting magnet's strength depends on the amount of force used to move the domains. Its permanence, or retentivity, depends on how difficult it was to encourage the domains to align. Materials that are hard to magnetize generally retain their magnetism for longer periods, while materials that are easy to magnetize often revert to their original nonmagnetic state.

You can reduce a magnet's strength or demagnetize it entirely by exposing it to a magnetic field that is aligned in the opposite direction. You can also demagnetize a material by heating it above its Curie point, or the temperature at which it loses its magnetism. The heat distorts the material and excites the magnetic particles, causing the domains to fall out of alignment.

Next, we'll take a look at why magnetized materials attract specific metals.

Shipping Magnets Large, powerful magnets have numerous industrial uses, from writing data to inducing current in wires. But shipping and installing huge magnets can be difficult and dangerous. Not only can magnets damage other items in transit, they can be difficult or impossible to install upon their arrival. In addition, magnets tend to collect an array of ferromagnetic debris, which is hard to remove and can even be dangerous.

For this reason, facilities that use very large magnets often have equipment on site that lets them turn ferromagnetic materials into magnets. Often, the device is essentially an electromagnet.

Why Magnets Stick

If you've read How Electromagnets Work, you know that an electrical current moving through a wire creates a magnetic field. Moving electrical charges are responsible for the magnetic field in permanent magnets as well. But a magnet's field doesn't come from a large current traveling through a wire -- it comes from the movement of electrons.

Many people imagine electrons as tiny particles that orbit an atom's nucleus the way planets orbit a sun. As quantum physicists currently explain it, the movement of electrons is a little more complicated than that. Essentially, electrons fill an atom's shell-like orbitals, where they behave as both particles and waves. The electrons have a charge and a mass, as well as a movement that physicists describe as spin in an upward or downward direction. You can learn more about electrons in How Atoms Work.

A simplified view of an atom, with a nucleus and orbiting electrons

Generally, electrons fill the atom's orbitals in pairs. If one of the electrons in a pair spins upward, the other spins downward. It's impossible for both of the electrons in a pair to spin in the same direction. This is part of a quantum-mechanical principle known as the Pauli Exclusion Principle.

Even though an atom's electrons don't move very far, their movement is enough to create a tiny magnetic field. Since paired electrons spin in opposite directions, their magnetic fields cancel one another out. Atoms of ferromagnetic elements, on the other hand, have several unpaired electrons that have the same spin. Iron, for example, has four unpaired electrons with the same spin. Because they have no opposing fields to cancel their effects, these electrons have an orbital magnetic moment. The magnetic moment is a vector -- it has a magnitude and a direction. It's related to both the magnetic field strength and the torque that the field exerts. A whole magnet's magnetic moments come from the moments of all of its atoms.

An iron atom and its four unpaired electrons

In metals like iron, the orbital magnetic moment encourages nearby atoms to align along the same north-south field lines. Iron and other ferromagnetic materials are crystalline. As they cool from a molten state, groups of atoms with parallel orbital spin line up within the crystal structure. This forms the magnetic domains discussed in the previous section.

You may have noticed that the materials that make good magnets are the same as the materials magnets attract. This is because magnets attract materials that have unpaired electrons that spin in the same direction. In other words, the quality that turns a metal into a magnet also attracts the metal to magnets. Many other elements are diamagnetic -- their unpaired atoms create a field that weakly repels a magnet. A few materials don't react with magnets at all.

This explanation and its underlying quantum physics are fairly complicated, and without them the idea of magnetic attraction can be mystifying. So it's not surprising that people have viewed magnetic materials with suspicion for much of history. In the next section, we'll take a look at the powers ascribed to magnets, as well as what they can and can't do.

Measuring Magnets You can measure magnetic fields using instruments like gauss meters, and you can describe and explain them using numerous equations. Here are some of the basics:

Magnetic lines of force, or flux, are measured in Webers (Wb). In electromagnetic systems, the flux relates to the current.

A field's strength, or the density of the flux, is measured in Tesla (T) or gauss (G). One Tesla is equal to 10,000 gauss. You can also measure the field strength in Webers per square meter. In equations, the symbol B represents field strength.

The field's magnitude is measured in amperes per meter or oersted. The symbol H represents it in equations

Magnet Myths

Every time you use a computer, you're using magnets. A hard drive relies on magnets to store data, and some monitors use magnets to create images on the screen. If your home has a doorbell, it probably uses an electromagnet to drive a noisemaker. Magnets are also vital components in CRT televisions, speakers, microphones, generators, transformers, electric motors, burglar alarms, cassette tapes, compasses and car speedometers.

In addition to their practical uses, magnets have numerous amazing properties. They can induce current in wire and supply torque for electric motors. A strong enough magnetic field can levitate small objects or even small animals. Maglev trains use magnetic propulsion to travel at high speeds, and magnetic fluids help fill rocket engines with fuel. The Earth's magnetic field, known as the magnetosphere, protects it from the solar wind. According to Wired magazine, some people even implant tiny neodymium magnets in their fingers, allowing them to detect electromagnetic fields [Source: Wired].

Image used under GNU Free Documentation License
Transrapid train at the Emsland, Germany test facility

Magnetic Resonance Imaging (MRI) machines use magnetic fields to allow doctors to examine patients' internal organs. Doctors also use pulsed electromagnetic fields to treat broken bones that have not healed correctly. This method, approved by the United States Food and Drug Administration in the 1970s, can mend bones that have not responded to other treatment. Similar pulses of electromagnetic energy may help prevent bone and muscle loss in astronauts who are in zero-gravity environments for extended periods.

Magnets can also protect the health of animals. Cows are susceptible to a condition called traumatic reticulopericarditis, or hardware disease, which comes from swallowing metal objects. Swallowed objects can puncture a cow's stomach and damage its diaphragm or heart. Magnets are instrumental to preventing this condition. One practice involves passing a magnet over the cows' food to remove metal objects. Another is to feed magnets to the cows. Long, narrow alnico magnets, known as cow magnets, can attract pieces of metal and help prevent them from injuring the cow's stomach. The ingested magnets help protect the cows, but it's still a good idea to keep feeding areas free of metal debris. People, on the other hand, should never eat magnets, since they can stick together through a person's intestinal walls, blocking blood flow and killing tissue. In humans, swallowed magnets often require surgery to remove.

Photo courtesy Amazon
Cow magnets

Some people advocate the use of magnet therapy to treat a wide variety of diseases and conditions. According to practitioners, magnetic insoles, bracelets, necklaces, mattress pads and pillows can cure or alleviate everything from arthritis to cancer. Some advocates also suggest that consuming magnetized drinking water can treat or prevent various ailments. Americans spend an estimated $500 million per year on magnetic treatments, and people worldwide spend about $5 billion. [Source: Winemiller via NCCAM].

Proponents offer several explanations for how this works. One is that the magnet attracts the iron found in hemoglobin in the blood, improving circulation to a specific area. Another is that the magnetic field somehow changes the structure of nearby cells. However, scientific studies have not confirmed that the use of static magnets has any effect on pain or illness. Clinical trials suggest that the positive benefits attributed to magnets may actually come from the passage of time, additional cushioning in magnetic insoles or the placebo effect. In addition, drinking water does not typically contain elements that can be magnetized, making the idea of magnetic drinking water questionable.

Some proponents also suggest the use of magnets to reduce hard water in homes. According to product manufacturers, large magnets can reduce the level of hard water scale by eliminating ferromagnetic hard-water minerals. However, the minerals that generally cause hard water are not ferromagnetic. A two-year Consumer Reports study also suggests that treating incoming water with magnets does not change the amount of scale buildup in a household water heater.

Even though magnets aren't likely to end chronic pain or eliminate cancer, they are still fascinating to study. To learn more about them, check out the links on the next page.

Santa Claus

2007-12-15T16:02:00.000+07:00

Introduction to How Santa Claus Works

When Virginia O'Hanlon, an 8-year-old girl from New York City, sent a letter addressed to the newspaper The Sun in 1897, she asked a very simple question: "Please tell me the truth; is there a Santa Claus?" In what must have been a surprise to her, the question was answered quite frankly. After calling out Virginia's "little friends" for doubting the existence of Santa Claus and being clouded by an age of skepticism, the writer of the article, Francis Pharcellus Church, gave his straightforward reply, "Yes, Virginia, there is a Santa Claus."

Christmas Tree Image Gallery

Timothy A. Clary/AFP/Getty Images
A sample of a letter received by the United States Postal Service is put on display at a news conference at the James A. Farley Post Office in New York. (See Christmas tree images.)

Today, children all over the world are still asking the same question as Virginia did. So who exactly is this Santa Claus guy, and why would he cause so much skepticism among boys and girls? Is he some kind of magical figure? How could one person cause so much excitement, doubt and even concern?

Ho, Ho, Ho
More Christmas-related articles
How Christmas Works
How Santa's Elves Work
How Santa's Sleigh Work
Christmas Channel

This Santa Claus guy appears to be pretty secretive about his operations. Along with Mrs. Claus, elves and a certain reindeer with a glowing, red nose, Santa is reputed to live at the North Pole, an impressive feat since the temperature almost never rises above freezing.

Because the North Pole isn't the most hospitable place for people to visit, it would be difficult for most people to withstand the harsh weather and rough terrain in order to gain any serious intel on Santa. And although no one may ever know for sure just how Santa operates, we at HowStuffWorks have what we think are the most logical explanations for how the big guy accomplishes all that he does: science and technology.

To find out more about Santa, the gear he might use and his possible connection to mall Santas, read on.

Video Gallery: Year-round Santa
Watch this video about "Santa House," a place where Filipino children can visit Santa year-round.

Naughty or Nice?

Santa Claus is one of the most popular and recognizable figures on Earth. He's been depicted in dozens of holiday-themed shows, from the 1947 film "Miracle on 34th Street" to the 1964 television special "Rudolph the Red-nosed Reindeer" to more recent films like "Elf" in 2003. Many countries have different names for him -- although he's Santa Claus in North America, he goes by Father Christmas in the United Kingdom, Père Noël in France, Babbo Natale in Italy and Sinterklaas in Holland, where he's associated with the Dec. 6 St. Nicholas Day celebration.

Karen Bleier/AFP/Getty Images
Santa waves as he water-skis on the Potomac River in Washington, D.C.

Whether you call him St. Nicholas, St. Nick or Santa Claus, though, the man represents the same thing to nearly everyone who celebrates Christmas and the holiday season -- he's known as a benevolent soul, a giver of gifts and a spreader of Christmas cheer.

According to Christmas folklore, Santa's main concern is making toys and distributing them in a timely and orderly fashion to children all over the world. This has garnered him quite a following. After all, children like toys, and Santa gives toys away -- therefore, children like Santa Claus.

Santa not only gives toys away, but he does it in style, too. He rides in his very own sleigh led by a team of reindeer, but it isn't just any old sleigh -- this one flies and rumor has it that it can make it around the world in just one night. It's also thought by some that Santa doesn't simply pass by your house and leave a few presents on your doorstep -- he lands on top of your roof, climbs down your chimney and puts presents both in your stockings and around your Christmas tree.

But where does Santa get all of these toys? Certainly one couldn't make or buy all of that merchandise by himself. That's where Santa's elves come in. It's possible that these little workers possess a drive and energy even the smallest of nanorobots couldn't match, so Santa would never have to worry too much about being behind in production.

There's a catch to Santa's good will, however. According to the classic Christmas song "Santa Claus is Coming to Town," Santa's always watching: "He's making a list / he's checking it twice / he's gonna find out who's naughty or nice." A big part of his job is to keep an eye on your behavior over the course of the year -- if you've behaved well, there's a good chance you'll get what you want for Christmas. If your behavior was less than satisfactory, however, you risk getting nothing but a lump of coal in your stocking. How does he do this? Our best bet is that he's using something similar to Google Earth. Think of that, then fast-forward into the future a few hundred years.

In the next section, we'll explore what Santa might look like in person and we'll ponder some of the special gadgets and technologies he might use.

Santa's Appearance and Santa Gear

If you've ever paid attention to the floats during the Macy's Thanksgiving Day Parade, you'll notice one constant from year to year -- Santa Claus is always the big finale, the last one to pass through the streets of New York City. We'd have to assume that this is his only major official public appearance during the year, since he would be incredibly busy organizing wish lists and keeping tabs on elf productivity.

Getty Images
Santa Claus scales a building to deliver presents.

That brief glimpse, however, is enough to let us know that all those songs, poems, stories and movies about Santa Claus could be fairly accurate in their visual representations. Whether Santa is portrayed on film in live-action or in stop-motion animation, Hollywood has his image down pretty well -- he's a large, rather plump older man with white hair and a long, white beard, and most of the time he's wearing his trademark red suit and red stocking cap. His cheeks are almost always a rose-colored hue, and it may not be because he's been drinking too much eggnog. As we mentioned earlier, the weather is very cold in the North Pole, so his skin could become easily chapped.

Our best estimations are that Santa must use some serious gear to deliver presents:

The Sleigh - In addition to being outfitted with flying reindeer, Santa's sleigh must be a highly advanced flying machine that performs faster and more efficiently than any spaceship currently used by NASA. The vehicle would have to be equipped with a special Antimatter Propulsion Unit that allows Santa to skip from one roof to the next in less than 24 hours and make it home to the North Pole in time for a nap and Christmas dinner. The sleigh would probably be outfitted with an iPod player and a hot cocoa maker, allowing maximum comfort during Santa's trip around the Earth.

The Suit - The traditional red suit Santa wears would have to be a bit more complex than it looks. First, it would be made out of a protective, lead-free material that blocks any radiation from Santa's engine -- antimatter rockets produce dangerous gamma radiation, so it's important for Santa to keep safe up in the sky. Second, the suit would also be threaded with carbon nanotubes, allowing the suit to shrink with Santa if he ever changes his size.

The Belt - For climbing up and down chimneys, Santa would need a little support. We assume he's taken some rock climbing lessons, and his belt comes with all the necessary hooks, grapples, bells and whistles to get him in and out of your living room before you even have a chance to spot him.

In the next section, we'll examine whether there's any connection to Santa and the mall Santas you might spy while you do your holiday shopping.

What's on Santa's Playlist?
The staff at HowStuffWorks would like to think that Santa's iPod, has a pretty eclectic Christmas playlist. Here's what we like to imagine him listening to as he cruises through the sky:

"Santa Baby" - Eartha Kitt
"Santa Claus Is Coming to Town" - Bruce Springsteen
"Have Yourself a Merry Little Christmas" - Judy Garland
"Sleigh Ride" - Ella Fitzgerald
"Skating" - Vince Guaraldi Trio
"Deck the Halls" - John Denver and The Muppets
"Little Saint Nick" - The Beach Boys
"The Christmas Song (Chestnuts Roasting on an Open Fire)" - Nat King Cole
"Get Behind Me, Santa!" - Sufjan Stevens
"White Christmas" - Bing Crosby
"Baby It's Cold Outside" - Ella Fitzgerald and Louis Jordan
"Christmas Time Is Here" - Vince Guaraldi Trio

Mall Santas and Letters to Santa

If you're ever strolling through your local mall after Thanksgiving, you might notice Santa Claus in the middle of the mall. There's probably an unbearably long line of children waiting for the chance to talk to Santa and tell him what they really want this year for Christmas presents. Perhaps you smile and wave, and Santa will smile and wave right back, laughing his deep, trademark "Ho, ho, ho!" and you'll move on.

Peter Macdiarmid/Getty Images
Professional Father Christmas performers gather for an annual Santa School in London.

Shortly thereafter, you might mosey on over to the other local mall, the one that's across the street. Wandering around from store to store, you might notice yet another Santa Claus, slightly different from the one you just saw at the other mall. How could this be? Is the mall some kind of portal between parallel universes? Is one the real Santa and the other a fake? Or are they both impostors?

First things first: These Santas probably don't consider themselves to be "fake," and they may not appreciate the word "impostor." If anything, you might call them "messengers." Like Santa's elves, we believe that the most logical explanation is that they're an extension of the Santa's Helpers Alliance, aka, mall Santas.

Mall Santas are people just like you and me, but they must pass a few specifications in order to carry out their seasonal duties. They must be of similar build to Santa Claus. They must be in the appropriate age range of 50 to 60 years old, and they must sport an acceptable beard. Mall Santas must also graduate from a special Santa School, where they'll learn to laugh like Santa, eat like Santa and keep a snow-white beard like Santa [source: LA Times]. Could it be that Santa drew up the curriculum himself?

Alexander Hassenstein/Getty Images
Letters addressed to Santa Claus at the post office in Lapland, Finland.

A mall Santa's job is simple -- he must ask children want they want for Christmas, make sure they've behaved this year, and then send detailed e-mail reports back to Santa Claus. A mall Santa's work accounts for about 33 percent of all gift requests, making them an important part of Santa's team -- the other 67 percent of Christmas wishes are sent directly to the North Pole by mail, of course. Nearly 100,000 letters make it out every holiday season to Santa's address at the North Pole.

Why would Santa need an alliance of Mall Santas? Even though he might make it around the world in one night, he couldn't be in lots of different places all at the same time. We'll have to assume that he's not quite there yet with the technology. For the moment, he has to settle with a complex but efficient way of collecting Christmas wish information.