What is a DVD-ROM

A Digital Versatile Disc — Read Only Memory, or DVD-ROM, is a media storage disk that closely resembles a CD or compact disk. The major difference is that the DVD-ROM is formatted to hold far more data. A CD commonly has a capacity of 650 megabytes, while the smallest capacity DVD can store about seven times more data, or 4.38 gigabytes (GB). 

There are various kinds of DVDs, but the DVD-ROM refers to a read-only disc, or a disc that cannot be written over. If you purchase a DVD movie from the local video store, you have a good example of a DVD-ROM. Blank DVDs with designations like "DVD-R" and "DVD+R" are formatted, recordable DVDs. The —R and +R refer to competing format standards, but both will record movies, audio or other data.

A DVD-ROM encodes data in the form of a spiraling trail of pits and lands separated by mere nanometers. The trail starts at the center of the DVD-ROM and winds around countless times until it reaches the outer edge. In the case of a double layer disk, the trail continues on a second layer of material. If the disc is also double-sided, the trail of pits and lands extends to side two. 

A laser beam in the DVD player tracks the beam as the disc spins, while a special device reads the intensity of the reflection as it bounces off the pits and lands. The reflective variance gets translated to bits of data which form bytes. Hence, DVDs, including the DVD-ROM, can vary in capacity as follows:

1. Single-sided single-layer disc — 4.38 GB
2. Single-sided double-layer disc — 7.95 GB
3. Double-sided single-layer disc — 8.75 GB
4. Double-sided double-layer disc — 15.9 GB

The DVD-ROM has replaced the videocassette, being far more efficient and superior in all respects. For one, a DVD-ROM stores data in digital form, while the videocassette uses less precise analog technology. A DVD-ROM, under normal conditions, remains error free and consistent, regardless of the amount of times it is viewed, while a video cassette stretches with wear and eventually needs replacement. The DVD-ROM can also hold more information in a higher format, and one can skip to specific scenes without the need for fast-forwarding or rewinding. Finally, the DVD-ROM is much more compact and easier to store, and DVD players can double as CD players.

If purchasing a DVD player, be sure to get one that can play all DVD-ROM formats, including double-sided, double-layered discs. For home theater systems look for models equipped with a 192 kilohertz (kHz), 24-bit digital/analog converter (DAC) for true Dolby theater quality. By comparison, standard DVD players use 96 kHz, 24-bit DACs. This is still a big improvement over CDs, however, which use 44.1 kHz, 16-bit sampling to produce audio. For this reason, people are moving towards DVDs to store music. An audio DVD can hold just over an hour of multi-channel music at 192 kHz, the highest bit rate; about two hours at 96 kHz; and close to seven hours at the standard CD sampling rate of 44.1 kHz. 

While cassettes, videocassettes and laser diskc have become legacy technologies, the DVD-ROM appears to be here to stay. Recordable DVDs are available wherever music and movies are sold, including department stores, office supply chains and discount marts.

What Is CDMA

CDMA stands for Code Division Multiple Access. It is a technique used for digital communication, and wireless technology in particular, that involves multiplexing. Whereas conventional communication systems use constant frequencies, CDMA uses multiple access, or multiplexing. Accomplished through the specific type known as spread spectrum in this case, multiplexing uses varied frequencies to transmit audio signals. This, coupled with code division, which requires a certain code to send and receive the frequency, further protects CDMA communications from interference.

Radio systems, one of the earliest forms of telecommunication, required users to communicate on distinct frequencies. Frequency Division Multiple Access (FDMA), one form of early wireless communication, only allowed users to operate on a single frequency. When tuning in to a radio to get sound, for instance, the listener must select one frequency or another, and must tune the frequency to filter out noise in the spectrum. Another form of early radio communication was Time Division Multiple Access (TDMA). In this case, users could not share a frequency, and each user had to coordinate his or her turn on that frequency in order to communicate.

Both FDMA and TDMA posed restrictions for early users, particularly the military. As early as World War II, militaries recognized the high value in using wireless technology to communicate across vast distances. Military communication units did not always have the time to wait their turn to transmit sound, or to find the right frequency. 

Some telecommunication systems allowed military communication units to transmit sound into the same spectrum their adversaries used. Military signals needed a unique identification through a distinct code to avoid interference from enemy communication. The receiver of that message on the other end could then retrieve the message based on its unique code in the spectrum. 

Just as the radio moved from military use to commercial use, so too was the case with the wireless technology. CDMA became the early choice for personal communication because it could allow multiple users to communicate within the spectrum, avoiding interference or blocking among users. In 1999, CDMA became the standard technology for the telecommunications industry for its growing wireless systems. Since there are large numbers of users in the system communicating at the same time, code division ensures that each user’s signal remains separate in the spectrum.

What Is a Power Inverter

A power inverter is a device that converts DC power (also known as direct current), to standard AC power (alternating current). Inverters are used to operate electrical equipment from the power produced by a car or boat battery or renewable energy sources, like solar panels or wind turbines. DC power is what batteries store, while AC power is what most electrical appliances need to run so an inverter is necessary to convert the power into a usable form. For example, when a cell phone is plugged into a car cigarette lighter to recharge, it supplies DC power; this must be converted to the required AC power by a power inverter to charge the phone.

How Inverters Work

DC power is steady and continuous, with an electrical charge that flows in only one direction. When the output of DC power is represented on a graph, the result would be a straight line. AC power, on the other hand, flows back and forth in alternating directions so that, when represented on a graph, it appears as a sine wave, with smooth and regular peaks and valleys. A power inverter uses electronic circuits to cause the DC power flow to change directions, making it alternate like AC power. These oscillations are rough and tend to create a square waveform rather than a rounded one, so filters are required to smooth out the wave, allowing it to be used by more electronic devices.

Most electronic devices require AC power to work correctly because they are designed to be plugged into a standard wall outlet, which supplies AC power. These devices need a specific amount of low, regulated voltage in order to operate. AC power is easier to step up or down, or change from one voltage to another, than DC and easier to regulate. In many cases, when a power inverter is in use, DC power is being converted to AC power, which is then stepped down and turned back into DC power inside the device.

Types of Inverters

Most modern power inverters produce either modified square (or modified sine) waves, or pure sine (or true sine) waves. Modified square wave inverters don't provide the smooth peaks and valleys that AC power from a home's electrical outlet does, but it can deliver power that is consistent and efficient enough to run most devices. This type of inverter is relatively inexpensive, and probably the most popular type.

Pure sine wave inverters are the most expensive, but they also deliver the smoothest and most even wave output. Any device will run on a pure sine wave, but some sensitive equipment, like certain medical equipment and variable speed or rechargeable tools, requires this type of inverter to operate correctly. Radios, for example, work better with pure sine wave inverters because the modified square wave inverter's less-smooth waves disrupt the radio's reception, causing static and other noise.

Inverter Uses

Basic power inverters are often small, rectangular devices that plug directly into the cigarette lighter or DC outlet on the dashboard of a car or other vehicle. This size inverter is usually sufficient to run a laptop, a small television, a portable DVD player, or similar equipment. These devices don’t draw a lot of power and can be used continuously while the vehicle is running; they may even be used for a half-hour to an hour while the engine is off, such as while camping or during a power outage at home.

Other power inverters come with jumper-like cables so they can be connected directly to a battery. This type is required to run more powerful equipment, such as power tools at a remote work site or a larger TV. Inverters can also be hard-wired into a battery to make them easier to use with larger pieces of equipment.

Larger inverters are used to convert solar or wind energy into AC power that can be used in a home. Called a grid-tie inverter, this device links into the utility grid to allow power to be delivered along the same wires that supply energy from a electric utility. It even allows any excess power produced to be fed back into the grid, where it can be sold to the utility company.

Inverter Capacity

Different models of power inverters vary in how many watts of power they can supply. The capacity of an inverter should equal the total number of watts required by each device, plus at least a 50% addition to account for peaks or spikes in the power draw. For example, if a DVD player draws 100 watts and a small TV another 100 watts, a minimum 300-watt inverter is recommended. Getting an inverter with more capacity than what is immediately needed is a good idea for many people, as it means that different or new devices can be added without the need for a new power inverter.

Safety

When using a power inverter continuously inside a vehicle that is not turned on, the engine should be started at least once an hour for 10 to 15 minutes to keep the battery from running down. A vehicle should never be started in a closed garage, as the carbon monoxide in the exhaust is fatal. 

Power inverters should only be used with batteries that are in good condition and fully charged. A weak battery will be drained easily if demand is too high. If used in a car, this could leave a driver stranded, so the battery's condition should be checked before using an inverter in a stationary vehicle. If the inverter is being used while the vehicle is running, as in the case of a road trip, there should be no problem with the extra draw as long as the battery is in good condition.

Working with large batteries can be dangerous, and when not done properly, can result in serious injury. Improper use of a power inverter can even lead to electrocution. For safety reasons, someone attempting to hook an inverter directly to a battery should be sure to read and follow any and all safety precautions listed in the inverter's instruction booklet.

It is important for people to always use a power inverter that is rated high enough for the device that needs to be run. If a heavy-duty power saw is plugged into a cigarette lighter, for example, the lightweight inverter might overheat and cause a fire in the dashboard. Adapters that allow more outlets than the unit is designed to accommodate should be avoided, and proper ventilation around the inverter is required to prevent overheating.

What is a Hydrogen Bomb

A hydrogen bomb is, by far, the most destructive weapon that mankind has ever invented. It is the most powerful type of nuclear bomb, as much as 25,000 times the yield of the nuclear bombs dropped on Hiroshima and Nagasaki, Japan. Unlike conventional atom bombs (also known as A-bombs), which release energy by fissioning (breaking apart) heavy atomic nuclei like uranium and plutonium, a hydrogen bomb releases energy by fusing together light nuclei like tritium or deuterium, converting even more matter into energy. When Truman authorized the dropping of the A-bomb on Hiroshima and Nagasaki, he said that the weapons used the same power that the Sun did, but that wasn't actually true -- the Sun uses nuclear fusion, not nuclear fission. Thus, a hydrogen bomb really does release the power that fuels the Sun.

The largest nuclear bombs, and the backbone of the nuclear arsenal of the United States and Russia, are hydrogen bombs. These bombs work using a two-stage design whereby a fission bomb "primary" is detonated using the conventional implosion method, which then compresses a fusion fuel "secondary" and ignites a uranium "spark plug" which fissions and subjects the fusion fuel to the heat necessary to begin a chain reaction -- about 20 million degrees F. The light nuclei fuse together into heavier elements, releasing tremendous energy from the strong nuclear force that binds their constituent particles together.

As a result of using fusion rather than fission, the bomb yield is much higher. In fission bombs, approximately 0.1% of the mass of the fuel is converted directly into energy, while in fusion bombs, this ratio is slightly improved, on the order of 0.3%. The first time the principle of a hydrogen bomb was tested was on 9 May 1951 by the United States military, during the George shot of Operation Greenhouse at the Pacific Proving Grounds. Most of the yield of this test came from fission fuel, but it tested the idea that a fission bomb could be used as a stepping stone to something even more destructive. A similar test, Item, took place on 25 May 1951.

The first true hydrogen bomb test, Ivy Mike, was on 1 November 1952, detonated at Enewetak Atoll in the Pacific, as part of Operation Ivy. The bomb exploded with a force equivalent to 10.4 megatons of TNT (over 450 times more powerful than the atomic bomb dropped on Nagasaki during WWII). Using liquid deuterium as fuel, this hydrogen bomb required 18 tonnes of refrigeration equipment to keep the deuterium in liquid form. A later test, Castle Bravo, used solid lithium deuteride instead, decreasing the weight of the device and making it a practical weapon. The Castle Bravo shot is the most powerful nuclear weapon ever tested by the United States, with a yield of 15 megatons.

Today, all of humanity is still put at risk by a nuclear winter initiated by hydrogen bombs.

How Can I Play the Music on my Computer Through my Stereo

Music files have revolutionized the way people listen to and archive music. Soft MP3 players, or software designed to play music files, have made it easy and convenient to build ad-hoc playlists for any occasion or mood. Although programmable compact disk (CD) players allowed some flexibility to create playlists, the ease of clicking to add tunes to a software interface makes other forms of programming feel downright archaic and restrictive by comparison. It’s no wonder then that people want the option of using soft MP3 players to listen to music files through the main stereo system or entertainment center. Luckily, it’s an easy thing to do, and it can be done wired or wirelessly.

The most common and least expensive way to route music from your computer to your stereo system is to run an RCA audio cable from the sound card on the computer to the stereo receiver. All sound cards are made with at least one Line Out jack, used to power computer speakers. The jack is normally a 3.5mm mini phone plug. An inexpensive adapter that features a 3.5mm stereo jack at one end, and two female RCA jacks at the other will work well here. This will connect to a standard RCA stereo cable. The opposite end of the cable will plug into the stereo or surround sound receiver. Here you’ll need an available Audio Line In RCA port, which may be marked Aux for auxiliary. 

After the connection is made, set the volume down before powering up the receiver. Change the receiver mode to auxiliary (rather than tuner, CD, DVD, TV, etc.), and slowly turn the volume up. You may need to boost the volume control of soft MP3 player as well. 

Advanced sound cards might also have other Line Out options, such as Digital Out. The instructions are the same, substituting a digital cable for the RCA cable. The receiver will also need a Digital Audio-In port.

Though wired methods are inexpensive, they have the disadvantage of requiring a physical cable to run from the computer to the stereo system. If the computer is a desktop located in a different room from the stereo or entertainment center, this can be impractical. A laptop provides a good mobile medium for music libraries, as it can be set rather close to the stereo system to simplify things and keep wires out of walkways.

When hard wiring your music connection isn’t practical, another method is to go wireless. In this case a small transmitter is connected to the Line Out port of the sound card, and a matching receiver is connected to the Audio Line In port of the receiver. Music from the computer is silently broadcast via radio waves from the transmitter to the receiver. The receiver interprets the radio signals and translates them back into an audible signal to play through the speakers of the entertainment center. 

Wireless stereo transmitters vary in design and pricing and a few models are expressly designed for iTunes music. Others include composite video ports to send not just audio, but video signals between the computer and entertainment center. Cables might be included or sold separately. For more information check your local electronics stores or your favorite online retailers. 

What Is Teflon®

Teflon® is a brand of polytetrafluoroethylene (PTFE), a solid polymer that is considered to be one of the world's most slippery substances. Accidentally invented in 1938 a laboratory in Deepwater, New Jersey, in the United States, Teflon® has applications in a wide range of areas, including household goods, the aerospace industry, electronics and industrial processes. Teflon® is produced by E.I. du Pont de Nemours and Company, also known as DuPont.

History

PTFE is a fluorocarbon, a compound made up of carbon and fluorine, and it has the molecular formula (C₂F₄)n. A chemist named Roy Plunkett accidentally invented PTFE while trying to create a new chlorofluorocarbon in a New Jersey laboratory operated by Kinetic Chemicals Inc., a company that was co-founded by DuPont and General Motors. Plunkett discovered that the white, wax-like substance that was created during one of his experiments was extremely slippery and water-resistant. The substance was patented in 1941, and the Teflon® trademark was registered in 1945.

Qualities

Teflon® has a coefficient of friction against polished steel of 0.05 to 0.1, which is one of the lowest for any solid that has been measured. This makes it suitable for use in applications that require reduced friction between two solids, such as gears or sliding parts. It also is hydrophobic, which means that it repels water instead of getting wet. Among PTFE's other qualities that make it beneficial for many uses are its high melting point and its electrical insulating properties.

Uses

In the 21st century, in addition to its widespread use in manufacturing and industry, PTFE is used on all sorts of everyday items. Many people are familiar with non-stick cooking pots and pans that have been coated with Teflon®. Automobile wiper blades also are commonly coated with PTFE, which helps keep the blades from squeaking as they pass back and forth across the windshield. PTFE also is used as a carpet or fabric protector because it repels liquids, allowing spills to be wiped up without leaving a stain. It has been used on all-weather clothing, to coat eyeglass lenses, as a fingernail protector and even in a line of haircare products.

Safety

There has been some concern about the safety of PTFE, especially in cookware. In the U.S., the Environmental Protection Agency (EPA) and Food and Drug Administration (FDA) have stated that the use of this coating on cookware and other items commonly used by people does not pose a concern. DuPont has said that Teflon® coatings do begin to deteriorate at or above 500° Fahrenheit (260° Celsius), a temperature higher than that at which most foods are cooked. Teflon®-coated pans are not recommended for cooking techniques that require very high temperatures, such as broiling.

What is an Embryo

An embryo is an organism in the early stages of development which cannot survive on its own. The precise definition of an embryo varies; in humans, for example, a fertilized egg may be considered an embryo until around the eighth week of pregnancy, at which point it is termed a fetus. The study of embryos is known as embryology, and it makes up part of a larger branch of science which is interested in reproduction and development.

The term “embryo” is only used to refer to eukaryote organisms, otherwise known as multicellur organisms. Typically, people use the term specifically to refer to diploid eukaryotes, meaning that the embryo has a complete set of genetic material from two donors. This genetic material takes the form of haploid sperm and eggs; a haploid cell only contains half a set of chromosomes, meaning that it cannot develop into anything unless it is combined with another haploid cell. As an embryo matures, it starts to turn into a recognizable form, at which point people may start referring to it as a fetus, especially in humans.

The formation of an embryo starts at fertilization. When eggs and sperm meet, they form what is known as a zygote. A zygote is a single diploid cell, created through the merging of two haploid cells. After fertilization, the zygote starts to divide, laying the groundwork for the mature organism which will eventually be born, hatched, or grown. When division begins, a zygote turns into an embryo.

Embryos cannot survive independently because they lack the tissues, body structure, organs, and so forth needed to do so. The parent of an embryo must feed it and watch out for it until it reaches viability. In mammals, this is accomplished by incubating the embryo inside the body and nourishing it with nutrients from the parents. Plants and egg laying animals provide the embryo with a rich layer of nutrients encased in a hard shell which will protect it until it is ready to be born.

The status of embryos is rather complex. Some people feel that an embryo is a life form, since it represents the potential of a living organism. Others do not regard embryos as lives, since they cannot survive on their own, and in the early stages they do not resemble anything familiar. This debate has led to conflict in some parts of the world, especially when it comes to human embryos and the choice to terminate a pregnancy.