458.The ability to obtain polymer cholesteric film on a single substrate by use of the procedure that we have developed suggests that a closely spaced etalon with a large free spectral range can be implemented by use of PCLC (polymer cholesteric liquid crystal) mirrors.
459.This program is designed to give a minimal understanding of radiation use and effects in medicine to assist in optimizing the techniques used.
460.Fascinated by Hertz’s discovery of radio waves, Marconi realized that it could be used for receiving and sending the telegraph messages, referring to it as wireless telegraphs Marconi’s station situated in Massachusetts carried greetings between King Edward YII and Theodore Roosevelt.
461.Natural gas, in addition to being burned to heat water for steam, can also be burned to produce hot combustion gases that pass directly through a turbine, spinning the blades of the turbine to generate electricity.
462.After having the board installed and correctly reported by the operating system, with sensor cables attached, the user is ready to start using the sensor.
463.By constructing artificial intelligence systems that have structural features similar to ours, we may be more likely to create robots that can ape human abilities.
464.While constructing a railway in 1936 near Baghdad, workers uncovered what appeared to be a prehistoric battery, also known as the Parthian Battery.
465.While experimenting with their own uranium-containing ore, Pierre Curie and Marie Curie came up with the term "radioactivity" to describe the spontaneous emissions that they studied.
466.By varying the characteristics of a radio wave—frequency, amplitude, or phase—these waves can be made to communicate information of many types, including audio, video, and data.
467.The absence of the electron's negative charge can be thought of as creating a positively charged hole.
468.Westinghouse AC Networks was winning, but the ultra competitive Edison made a last attempt to defeat his rival by hiring an outside engineer named Harold P. Brown to perform a public demonstration of animals being electrocuted by AC power. This demonstration led to the invention of the electric chair to execute condemned prisoners.
469.By banning the classic light bulb, power savings could total more than 18 billion dollars every year, equivalent to the electric bill of the entire state of Texas for one year, which translates in about 100 million tons of carbon dioxide gas prevented from being emitted by the electric power plants.
470.Unless coil resistance is substantial, the core flux waveform over time will be just as sinusoidal as the voltage waveform, because without resistance to drop voltage, the relationship between voltage and flux is described by the following formula, the rate-of-change of a perfect sine wave being a perfect cosine wave.
471.If the location of the source matches the location of a primary user, the source is considered to be a primary user. Otherwise it is considered to be an attacker trying to emulate a primary user.
472.The big idea behind the methodology of combining multiple copies of the transmitted signal to obtain a better signal is that if we have multiple copies, probably at least one must be in good condition, and we have more chance of a better decoding!
473.If the device is not designed to be removed while the system is running, it is recommended that you notify the operating system in advance to avoid problems.
474.Even if the wires are perfectly stripped and the wires clean, the contact resistance is unlikely to be exactly equal, even at rest.
475.If a magnet is placed within a magnetic field, it is acted upon by magnetic forces.
476.If you had told me when I was in college that I would have a map in my car that spoke to me I would have thought you were crazy!
477.Should the engine run too fast, the governor will reduce the current being applied to the motor, causing the return spring to pull back and close the throttle.
478.No one could have dreamed that the transistor would have the broad social consequences it has had.
479.If you have not yet read through this document we suggest reading this whole page so nothing is missed.
480.If you had some way to see them, you would find that there are literally thousands of different radio waves (in the form of sine waves) around you right now —TV broadcasts, AM and FM radio broadcasts, police and fire radios, satellite TV transmissions, cell phone conversations, GPS signals, and so on.
481.If you looked at the top of this beach ball, you would see the ping-pong balls floating in the liquid, and the beach ball would appear white.
482.Voltage can be thought of as the force that pushes electrons through a conductor and the greater the voltage the greater is its ability to “push” the electrons through a given circuit.
483.Given the relationship between wavelength and frequency — the higher the frequency, the shorter the wavelength — it follows that short wavelengths are more energetic than long wavelengths.
484.Italian physicist Alessandro Volta discovered that particular chemical reactions could produce electricity, and in 1800 he constructed the voltaic pile (an early electric battery) that produced a steady electric current, and so he was the first person to create a steady flow of electrical charge.
485.One of the first to discover and publish a link between man-made electric current and magnetism was Romagnosi, who in 1802 noticed that connecting a wire across a voltaic pile deflected a nearby compass needle.
486.It was not until the end of the 19th century that this "something" was found to consist of negative electricity, known today as electrons.
487.The first LED – a diode emitting yellow light – was developed by Henry Joseph Round in 1907. This early version was too dim to be useful, however, and it was not until 1968 that visible red light was emitted through a diode.
488.The greater the current in the wire, or the greater the magnetic field, the faster the wire moves because of the greater force created. If the wire sits parallel with the magnetic field, there will be no force on the wire.
489.Davenport has the honor of being the first of thousands of engineers who received a patent for an electric motor. But he is neither their inventor nor did his designs have had any significant influence on the further development of electric motors.
490.Circuit protection would be unnecessary if overloads and short circuits could be eliminated. Unfortunately, overloads and short circuits do occur.
491.When buying a satellite radio receiver from a company other than the provider itself, do make certain the device will work with the service you have chosen.
492.While investigating the properties of fluorescent minerals, it was Becquerel who discovered that certain types of atoms disintegrate by themselves.
493.Fiber has been around for a while, but what’s new is that it is now being widely installed in business offices.
494.For the vast majority of jobs, however, it is the individual workers who are primarily affected, suffering discomfort, injuries.
495.It is the first time that scientists have succeeded in this way in realizing robust electronics with dimensions that can compete with commercial technology.
496.But it wasn’t long before word got out that Tesla’s AC motor was worth investing in, and the Western Union Company put Tesla to work in a lab not far from Edison’s office, where he designed AC power systems that are still used around the world.
497.It is the voltage in the secondary turns which, when applied to heating elements, creates the energy to heat or melt metals.
498.Vacuum tubes were found to have several built-in problems. Although the tubes were lightweight, associated components and chassis were quite heavy. It was not uncommon for such chassis to weigh 40 to 50 pounds.
499.As a result of this amazing revolution in semiconductor technology, it is not unusual for modern integrated circuits to contain over 10 million switching elements (i.e., transistors) packed into a chip area as large as 500 mm2.
500.Not only will you find highlights of important technological contributions, you will also learn about the tribulations and excitement that accompany the discoveries of these early masters. Included are nearly 100 rare photographs from museums around the world.
 Натан Стаблфилд (1860 –1928)
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 Романьози (1761—1835)
Дата: 2018-11-18, просмотров: 350.