The group gave a presentation outlining their findings at a recent meeting of the American Geophysical Union. Earth scientists have concluded that approximately 85 percent of the Earth's core is made of iron while nickel makes up an additional 10 percent—but the final 5 percent has been a bit of a mystery. In this new effort, the researchers conducted lab experiments that gave results suggesting that the final ingredient is silicon. To figure out which elements exist in the Earth's core, researchers have been building virtual Earths in labs and then subjecting them to real-life conditions such as heat and pressure.
The vacuum tube era Theoretical and experimental studies of electricity during the 18th and 19th centuries led to the development of the first electrical machines and the beginning of the widespread use of electricity. The history of electronics began to evolve separately from that of electricity late in the 19th century with the identification of the electron by the English physicist Sir Joseph John Thomson and the measurement of its electric charge by the American physicist Robert A.
Edison had observed a bluish glow in some of his early lightbulbs under certain conditions and found that a current would flow from one electrode in the lamp to another if the second one anode were made positively charged with respect to the first cathode.
Work by Thomson and his students and by the English engineer John Ambrose Fleming revealed that this so-called Edison effect was the result of the emission of electrons from the cathode, the hot filament in the lamp.
The motion of the electrons to the anode, a metal plate, constituted an electric current that would not exist if the anode were negatively charged. This discovery provided impetus for the development of electron tubes, including an improved X-ray tube by the American engineer William D.
The detection of a radio signal, which is a very high-frequency alternating current ACrequires that the signal be rectified; i. These devices were undependable, lacked sufficient sensitivity, and required constant adjustment of the whisker-to-crystal contact to produce the desired result.
The fact that crystal rectifiers worked at all encouraged scientists to continue studying them and gradually to obtain the fundamental understanding of the electrical properties of semiconducting materials necessary to permit the invention of the transistor.
In Lee De Forestan American engineer, developed a type of vacuum tube that was capable of amplifying radio signals.
De Forest added a grid of fine wire between the cathode and anode of the two-electrode thermionic valve constructed by Fleming. The new device, which De Forest dubbed the Audion patented inwas thus a three-electrode vacuum tube.
In operation, the anode in such a vacuum tube is given a positive potential positively biased with respect to the cathode, while the grid is negatively biased.
A large negative bias on the grid prevents any electrons emitted from the cathode from reaching the anode; however, because the grid is largely open space, a less negative bias permits some electrons to pass through it and reach the anode.
Small variations in the grid potential can thus control large amounts of anode current. The vacuum tube permitted the development of radio broadcasting, long-distance telephony, television, and the first electronic digital computers.
These early electronic computers were, in fact, the largest vacuum-tube systems ever built. The special requirements of the many different applications of vacuum tubes led to numerous improvements, enabling them to handle large amounts of power, operate at very high frequencies, have greater than average reliability, or be made very compact the size of a thimble.
The cathode-ray tubeoriginally developed for displaying electrical waveforms on a screen for engineering measurements, evolved into the television picture tube.
Such tubes operate by forming the electrons emitted from the cathode into a thin beam that impinges on a fluorescent screen at the end of the tube.
The screen emits light that can be viewed from outside the tube. Deflecting the electron beam causes patterns of light to be produced on the screen, creating the desired optical images.
Notwithstanding the remarkable success of solid-state devices in most electronic applications, there are certain specialized functions that only vacuum tubes can perform. These usually involve operation at extremes of power or frequency. Vacuum tubes are fragile and ultimately wear out in service.
Failure occurs in normal usage either from the effects of repeated heating and cooling as equipment is switched on and off thermal fatiguewhich ultimately causes a physical fracture in some part of the interior structure of the tube, or from degradation of the properties of the cathode by residual gases in the tube.
These shortcomings motivated scientists at Bell Laboratories to seek an alternative to the vacuum tube and led to the development of the transistor. The semiconductor revolution Invention of the transistor The invention of the transistor in by John BardeenWalter H. Brattainand William B.Electronics: Electronics, branch of physics and electrical engineering that deals with the emission, behaviour, and effects of electrons and with electronic devices.
Electronics encompasses an exceptionally broad range of technology.
The term originally was applied to the study . Every single photograph was, not surprisingly, dominated by rocks based on silicon and it was a powerful reminder of the fact that silicon is the second most abundant element in the earth's crust, beaten to first place by oxygen, the element with which it invariable entangled.
For most of the world, the terms "Silicon Valley" and "startup" are synonymous. Indeed, Silicon Valley is home to a disproportionate number of companies that have grown from garage startups into global giants.
Biology Dictionary - P to QUOTIDIAN: Meanings of biology terminology and abbreviations starting with the letters P or Q. Another important use of silicon is the use of highly refined silicon in electronics, often as semiconductors for discrete devices and integrated circuits.
This text provides general information. A lack of consensus persists regarding the origin of photoluminescence in silicon nanocrystals. Here we report pressure-dependences of X-ray diffraction and photoluminescence from alkane-terminated colloidal particles.