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...materials that are modified when exposed to radiation (either in the form of visible, ultraviolet, or X-ray photons or in the form of energetic electron beams). A photoresist typically contains a photoactive compound (PAC) and an alkaline-soluble resin. The PAC, mixed into the resin, renders it insoluble. This mixture is coated onto the semiconductor wafer and is then exposed to radiation......

Life on Earth is dependent on the conversion of solar energy to cellular energy by the process of photosynthesis. The general process of photosynthesis makes use of pigments called chlorophylls that absorb light energy from the Sun and release an electron with a higher energy level. This electron is passed through an electron transport chain, with the generation of energy by formation of a......

Life on Earth is dependent on the conversion of solar energy to cellular energy by the process of photosynthesis. The general process of photosynthesis makes use of pigments called chlorophylls that absorb light energy from the Sun and release an electron with a higher energy level. This electron is passed through an electron transport chain, with the generation of energy by formation of a......

Life on Earth is dependent on the conversion of solar energy to cellular energy by the process of photosynthesis. The general process of photosynthesis makes use of pigments called chlorophylls that absorb light energy from the Sun and release an electron with a higher energy level. This electron is passed through an electron transport chain, with the generation of energy by formation of a.........

...about by the contraction and expansion of melanophores, or pigment granules. Expansion of the melanophores cuts off the light, whereas contraction allows light to pass through. The well-known flashlight fishes (Photoblepharon) of Indonesia possess large light organs beneath the eyes. The light is extinguished when a fold of black skin is drawn upward over the organ....

an element of a photoelectric cell that emits electrons when struck by light, making possible the flow of electric current through the device. A substance often used for photocathodes is a partially oxidized silver–cesium alloy. ...

A photocell may be lowered into the ocean to measure light intensity at discrete depths and to determine light reduction from the surface value or from the previous depth value. The photocell may sense all available wavelengths or may be equipped with filters that pass only certain wavelengths of light. Since Iz and I0 are known, changing light......

fundamental principle relating to chemical reactions induced by light, which states that for every quantum of radiation that is absorbed, one molecule of the substance reacts. A quantum is a unit of electromagnetic radiation with energy equal to the product of a constant (Planck’s constant, h) and the frequency of the radiation, symbolized by the...

PCM is an extension of CHM that uses a series of photographic and chemical etching techniques to produce components and devices in a wide range of metals, especially stainless steel....

a chemical reaction initiated by the absorption of energy in the form of light. The consequence of molecules’ absorbing light is the creation of transient excited states whose chemical and physical properties differ greatly from the original molecules. These new chemical species can fall apart, change to new structures, combine with e...

Photochemical smog, which occurs most prominently in urban areas that have large numbers of automobiles, requires neither smoke nor fog. This type of smog has its origin in the nitrogen oxides and hydrocarbon vapours emitted by automobiles and other sources, which then undergo photochemical reactions in the lower atmosphere. The highly toxic gas ozone arises from the reaction of nitrogen oxides......

There are two “laws” of photochemistry. The first, the Grotthuss–Draper law (named for the chemists Christian J.D.T. von Grotthuss and John W. Draper), is simply: for light to produce an effect upon matter it must be absorbed. The second, or Stark–Einstein law (for the physicists Johannes Stark and Albert Einstein), in its most modern form is: one resultant primary......

...step above the threshold, a point comes when the subject states that it is coloured, and the difference between the threshold for light appreciation and this, the chromatic threshold, is called the photochromatic interval. This suggests that the rods give only achromatic, or colourless, vision, and that it is the cones that permit wavelength discrimination. The photochromatic interval for long....

...hand-coloured woodcuts had a great tradition and labour was cheap, some firms from the 1870s onward sold photographs of scenic views and daily life that had been delicately hand-tinted. In the 1880s photochromes, colour prints made from hand-coloured photographs, became fashionable, and they remained popular until they were gradually replaced in the first decades of the 20th century by......

Traditional photochromic eyeglasses are generally alkali boroaluminosilicates with 0.01 to 0.1 percent silver halide and a small amount of copper. Upon absorption of light, the silver ion reduces to metallic silver, which nucleates to form colloids about 120 angstroms in size. This is small enough to keep the glass transparent, but the colloids are dense enough to make the glass look gray or......

Certain dyelike substances can exist in a colourless and a coloured state. They are called photochromic compounds. The coloured state is formed by exposure to radiations of a certain wavelength. The compound reverts to its colourless state either in the dark or on treatment with radiation of a different wavelength. This reversibility is a primary characteristic of photochromism, and it is an......

Prevention or control of diabetic retinopathy relies on control of blood glucose levels. Various types of laser photocoagulation of the retina are used in certain forms of diabetic retinopathy in an attempt to halt or slow its progression. In cases of retinal detachment or persistent or recurrent hemorrhage within the vitreous gel, more extensive surgical treatments are employed. Glaucoma......

photomechanical printing process that gives accurate reproduction because no halftone screen is employed to break the images into dots. In the process, a plate (aluminum, glass, cellophane, etc.) is coated with a light-sensitive gelatin solution and exposed to light through a photographic negative. The gelatin is hardened in exposed areas and is then soaked in glycerin, which is absorbed most in t...

method of assembling or setting type by photographing characters on film from which printing plates are made. The characters are developed as photographic positives on film or light-sensitive paper from a negative master containing all the characters; the film, carrying the completed text, is then used for making a plate for letterpress, gravure, or lithographic printing by a photomechanical proce...

A photocell may be lowered into the ocean to measure light intensity at discrete depths and to determine light reduction from the surface value or from the previous depth value. The photocell may sense all available wavelengths or may be equipped with filters that pass only certain wavelengths of light. Since Iz and I0 are known, changing light......

...the combination of aperture and shutter speed) for film of a specific sensitivity. Modern instruments are of two basic types: the self-generating, or photovoltaic, and the variable resistance, or photoconductive....

the increase in the electrical conductivity of semiconductors and insulators when they are exposed to light of sufficient energy. Photoconductivity serves as a tool to understand the internal processes in these materials, and it is also widely used to detect the presence of light and measure its intensity in light-sensitive devices....

any device for producing copies of text or graphic material by the use of light, heat, chemicals, or electrostatic charges. The need for a process other than wet photographic reproduction for copying documents stimulated the invention of various techniques, notably the diffusion-transfer and dye-line processes, during the early 1950s. In the diffusion-transfer process a master c...

any device for producing copies of text or graphic material by the use of light, heat, chemicals, or electrostatic charges. The need for a process other than wet photographic reproduction for copying documents stimulated the invention of various techniques, notably the diffusion-transfer and dye-line processes, during the early 1950s. In the diffusion-transfer process a master c...

...matter. In the dark depths of the ocean, for instance, where fish and other marine life forms are extremely scarce and scattered, the chance of encounter is rare indeed. The small angler fish (Photocorynus spiniceps) that cruise around at great depths are most unlikely to meet a member of the opposite sex at a time or place when the female happens to be ready to shed her eggs. As a......

...by the CCITT in 1980. At the transmitter end of a modern Group 3 fax machine, the image of a page to be transmitted is focused on a charge-coupled device (CCD), a solid-state scanner that has 1,728 photosensors in a single row. The photosensors measure the brightness of spots, or pixels, in a line 0.01 inch high across the width of the page. After each line is scanned, the scanner is advanced.....

Alternatively, the light can be measured using a solid-state device known as a photodiode. A device of this type consists of a thin semiconductor wafer that converts the incident light photons into electron-hole pairs. As many as 80 or 90 percent of the light photons will undergo this process, and so the equivalent quantum efficiency is considerably higher than in a photomultiplier tube. There......

in physics, nuclear reaction in which the absorption of high-energy electromagnetic radiation (a gamma-ray photon) causes the absorbing nucleus to change to another species by ejecting a subatomic particle, such as a proton, neutron, or alpha particle. For example, magnesium-25, upon absorbing a photon of sufficient energy, emits a proton and becomes sodium-24. Photodisintegration differs from the...

...the kinetics of fast ion-molecular reactions would prevail. The reactions might reshuffle the original molecules present in the nucleus into new parent species, which would be the ones subsequently photodissociated into observed fragments by solar light. (This complex situation is still far from being completely understood.) In turn, the observed fragments, after having absorbed and reemitted.....

Another form of nonionizing radiation therapy is photodynamic therapy (PDT). This experimental technique involves administering a light-absorbing substance that is selectively retained by the tumour cells. The cells are killed by exposure to intense light, usually laser beams of appropriate wavelengths. Lesions amenable to PDT include tumours of the bronchus, bladder, skin, and peritoneal......

conversion of certain substances in the skin of animals into other substances by the action of light. The resultant compounds may be beneficial (e.g., vitamin D), but in some cases they produce disorders of the skin. The original compound may be present in normal skin; it may be derived from certain foods; it may result from an inherited biochemical de...

the property of some transparent materials, such as glass or plastic, while under stress, to become doubly refracting (i.e., a ray of light will split into two rays at entry). When photoelastic materials are subjected to pressure, internal strains develop that can be observed in polarized light; i.e., light vibrating normally in two planes, which has had one plane...

In this process, the incident X-ray or gamma-ray photon interacts with an atom of the absorbing material, and the photon completely disappears; its energy is transferred to one of the orbital electrons of the atom. Because this energy in general far exceeds the binding energy of the electron in the host atom, the electron is ejected at high velocity. The kinetic energy of this secondary......

an electron tube with a photosensitive cathode that emits electrons when illuminated and an anode for collecting the emitted electrons. Various cathode materials are sensitive to specific spectral regions, such as ultraviolet, infrared, or visible light. The voltage between the anode and cathode causes no current in darkness because no electrons are emitted, but illumination excites electrons that...

...d1/d2, times the known concentration (c1). If a photoelectric cell instead of the eye is used to compare intensities, the instrument is called a photoelectric colorimeter....

the increase in the electrical conductivity of semiconductors and insulators when they are exposed to light of sufficient energy. Photoconductivity serves as a tool to understand the internal processes in these materials, and it is also widely used to detect the presence of light and measure its intensity in light-sensitive devices....

an electron tube with a photosensitive cathode that emits electrons when illuminated and an anode for collecting the emitted electrons. Various cathode materials are sensitive to specific spectral regions, such as ultraviolet, infrared, or visible light. The voltage between the anode and cathode causes no current in darkness because no electrons are emitted, but illumination excites electrons that...

phenomenon in which electrically charged particles are released from or within a material when it absorbs electromagnetic radiation. The effect is often defined as the ejection of electrons from a metal plate when light falls on it. In a broader definition, the radiant energy may be infrared, visible, or...

...now available for most solids; the chief obstacles to the development of such data were the difficulty of preparing clean surfaces and the energy loss of electrons in penetration into vacuum. The photoelectric threshold frequency, symbolized by the Greek letter nu with subscript zero, νにゅー0, is that frequency at which the effect is barely possible; it is given by the ratio of the...

an electron tube with a photosensitive cathode that emits electrons when illuminated and an anode for collecting the emitted electrons. Various cathode materials are sensitive to specific spectral regions, such as ultraviolet, infrared, or visible light. The voltage between the anode and cathode causes no current in darkness because no electrons are emitted, but illumination excites electrons that...

...in quanta of energy equal to Planck’s constant (h) times light frequency, hνにゅー, by electrons, one at a time. A minimum energy symbolized by the Greek letter psi, ψぷさい, called the photoelectric work function of the surface, must be supplied before the electron can be ejected. When a quantum of energy is greater than the work function, photoelectric emission is possi...

4. A fraction of the emerging light photons are converted to charge in a light sensor normally mounted in optical contact with the exit window. This fraction is known as the quantum efficiency of the light sensor. In a silicon photodiode, as many as 80 to 90 percent of the light photons are converted to electron-hole pairs, but in a photomultiplier tube, only about 25 percent of the photons are......

...Therefore, detectors that produce the largest number of carriers per pulse show the best energy resolution. For example, the charge Q from a scintillation detector normally consists of photoelectrons in a photomultiplier tube. The average number produced by a 1-MeV particle is normally no more than a few thousand, and the observed energy resolution is typically 5–10 percent.......

Photoelectron spectroscopy is an extension of the photoelectric effect (see radiation: The photoelectric effect.), first explained by Einstein in 1905, to atoms and molecules in all energy states. The technique involves the bombardment of a sample with radiation from a high-energy monochromatic source and the subsequent determination of the kinetic energies of the ejected electrons. The source......

phenomenon in which electrically charged particles are released from or within a material when it absorbs electromagnetic radiation. The effect is often defined as the ejection of electrons from a metal plate when light falls on it. In a broader definition, the radiant energy may be infrared, visible, or...

any of several processes for producing printing plates by photographic means. In general, a plate coated with a photosensitive substance is exposed to an image, usually on film; the plate is then treated in various ways, depending upon whether it is to be used in a relief (letterpress) or an intaglio (gravure) printing process....

Photofinishing laboratories process most amateur and some professional photographers’ films and prints. In the 1980s, virtually all of the total business of the laboratories in the United States was in colour processing....

...on the particular nucleus being considered. Fission can be induced by exciting the nucleus to an energy equal to or greater than that of the barrier. This can be done by gamma-ray excitation (photofission) or through excitation of the nucleus by the capture of a neutron, proton, or other particle (particle-induced fission). The binding energy of a particular nucleon to a nucleus will......

...astronomy, and physics. He briefly served in Parliament (1833–34) and in 1835 published his first article documenting a photographic discovery, that of the paper negative. These so-called photogenic drawings were basically contact prints on light-sensitive paper, which unfortunately produced dark and spotty images. In 1840 he modified and improved this process and called it the......

shadowlike photographic image made on paper without the use of a negative or a camera. It is made by placing objects between light-sensitive paper or film and a light source. Opaque objects lying directly on the paper produce a solid silhouette; transparent images or images that do not come in direct contact with the paper produce amorphous, mysterious images....

technique that uses photographs for mapmaking and surveying. As early as 1851 the French inventor Aimé Laussedat perceived the possibilities of the application of the newly invented camera to mapping, but it was not until 50 years later that the technique was successfully employed. In the decade before World War I, terrestrial photogrammetry, as it came to be known later...

As a means of visual communication and expression, photography has distinct aesthetic capabilities. In order to understand them, one must first understand the characteristics of the process itself. One of the most important characteristics is immediacy. Usually, but not necessarily, the image that is recorded is formed by a lens in a camera. Upon exposure to the light forming the image, the......

in physical chemistry, mixture of two or more liquids in which one is present as droplets, of microscopic or ultramicroscopic size, distributed throughout the other. Emulsions are formed from the component liquids either spontaneously or, more often, by mechanical means, such as agitation, provided that the liquids that are mixed have no (or a very limited) mutual solubility. Emulsions are stabil...

The most widely used photographic process is the black-and-white negative–positive system (Figure 1). In the camera the lens projects an image of the scene being photographed onto a film coated with light-sensitive silver salts, such as silver bromide. A shutter built into the lens admits light reflected from the scene for a given time to produce an invisible but developable image in the......

in photography, device used to selectively modify the component wavelengths of mixed (e.g., white) light before it strikes the film. Filters may be made of coloured glass, plastic, gelatin, or sometimes a coloured liquid in a glass cell. They are most often placed over the camera lens but can in some cases be placed over the light source with the same effect....

...by a Soviet psychologist (see Bibliography). This man’s exceptional mnemonic ability seemed largely to depend on an outstandingly vivid, detailed, and persistent visual memory, almost certainly eidetic (“photographic”) in nature. “S” also reported an unusual degree of synesthesia, though whether this helped or hindered his feats of memory is not clear. (A pers...

Photographic photometry, by contrast, relies on visual comparisons of images of starlight recorded on photographic plates. It is considerably less accurate than photoelectric photometry because the complex relationships between the size and density of photographic images of stars and the brightness of those optical images are not subject to full control or accurate calibration. Because of this,......

matted or felted sheet, usually made of cellulose fibres, formed on a wire screen from water suspension....

Transparency refers to the preference in East Asian music for chamber-music sound ideals; no matter how large an ensemble may be, the individual instruments are meant to be heard. This differs from the orchestral sound ideal, popular in 19th-century Western music, in which the intention is to merge the sounds of the individual instruments into one musical colour. A transparent texture is a......

The photographic zenith tube (PZT) is a telescope permanently mounted in a precisely vertical position. The light from a star passing almost directly overhead is refracted by the lens, reflected from the perfectly horizontal surface of a pool of mercury, and brought to a focus just beneath the lens. A photographic plate records the images of the star at clock times close to that at which it......

...method of identification, though it remains an excellent means of furnishing a minutely descriptive portrait, valuable to investigators. Bertillon wrote extensively on his method, one work being La Photographie judiciaire (1890). A biography by H.T.F. Rhodes, Alphonse Bertillon: Father of Scientific Detection, was published in 1954....

...stars. The second volume of this work catalogs double stars, variable stars, and various kinds of nonstellar objects, including radio and X-ray sources. The German astronomer Hans Vehrenberg’s Photographischer Stern-Atlas (1962–64), covering the entire sky in 464 sheets, each 12° square, has probably reached wider use than any other photographic atlas because of its ...

method of recording the image of an object through the action of light, or related radiation, on a light-sensitive material. The word, derived from the Greek photos (“light”) and graphein (“to draw”), was first used in the 1830s....

method of recording the image of an object through the action of light, or related radiation, on a light-sensitive material. The word, derived from the Greek photos (“light”) and graphein (“to draw”), was first used in the 1830s.......

equipment, techniques, and processes used in the production of photographs....

...stone, then on a tin plate, in order to engrave it in intaglio, Joseph-Nicephore Niepce in the 1820s established that certain chemical compounds are sensitive to light. This marked the origins of photogravure and led to both the invention of photography (between 1829 and 1838) and the use of photographic processes for the printed reproduction of photographs....

...chemical and equipment technology during the 1980s. These types of adhesive normally consist of a monomer (which also can serve as the solvent) and a low-molecular-weight prepolymer combined with a photoinitiator. Photoinitiators are compounds that break down into free radicals upon exposure to ultraviolet radiation. The radicals induce polymerization of the monomer and prepolymer, thus......

the interaction of electromagnetic radiation with matter resulting in the dissociation of that matter into electrically charged particles. The simplest example, the photoelectric effect , occurs when light shines on a piece of metal, causing the ejection of electrons. Another category of photo-ionization involves the disruption of covalent chemical bonds, producing positively a...

...the retinal has a shape called 11-cis, being somewhat folded, while on conversion to prelumirhodopsin the retinal has a straighter shape called all-trans; the process is called one of photoisomerization, the absorption of light energy causing the molecule to twist into a new shape. Having suffered this alteration in shape, the retinal presumably causes some instability in the......

From the outset, photography served the press. Within weeks after the French government’s announcement of the process in 1839, magazines were publishing woodcuts or lithographs with the byline “from a daguerreotype.” In fact, the two earliest illustrated weeklies—The Illustrated London News, which started in May 1842, and ......

...be photographed. Before the end of the 19th century this circumstance led to consideration of machines for composing headings by photographing the images of the letters in succession. In 1915 the Photoline, a photographic equivalent of the Ludlow, assembled matrices of transparent letters in a composing stick in order to film each line of the heading....

...or just resist, typically dissolves in a high-pH solution after exposure to light (including ultraviolet radiation or X rays), and this process, known as development, is controlled by using a mask. A mask is made by applying a thick deposit of chromium in a particular pattern to a glass plate. The chromium provides a shadow over most of the wafer, allowing “light” to shine......

In order to alter specific locations on a wafer, a photoresist layer is first applied (as described in the section Deposition). Photoresist, or just resist, typically dissolves in a high-pH solution after exposure to light (including ultraviolet radiation or X rays), and this process, known as development, is controlled by using a mask. A mask is made by applying a thick deposit of chromium in......

...Alternatively, organisms may be autotrophs, acquiring their useful free energy from some other source, either from the energy of sunlight, in which case the organism is called a photoautotroph, or from the controlled chemical reaction of inorganic materials, in which case the organism is known as a chemoautotroph. Organisms that use both modes are called photochemoautotrophs....

...Alternatively, organisms may be autotrophs, acquiring their useful free energy from some other source, either from the energy of sunlight, in which case the organism is called a photoautotroph, or from the controlled chemical reaction of inorganic materials, in which case the organism is known as a chemoautotroph. Organisms that use both modes are called photochemoautotrophs....

emission of light from a substance as a result of absorption of electromagnetic radiation; such a substance is called a phosphor, and the emitted light usually has a longer wavelength than the incident radiation. ...

Ultraviolet light, when acting on DNA, can lead to covalent linking of adjacent pyrimidine bases. Such pyrimidine dimerization is mutagenic, but this damage can be repaired by an enzyme called photolyase, which utilizes the energy of longer wavelengths of light to cleave the dimers. However, people with a defect in the gene coding for photolyase develop xeroderma pigmentosum, a condition......

...a proposed 50) plates document the beginnings of photography primarily through studies of art objects and architecture. In 1851 Talbot discovered a way of taking instantaneous photographs, and his “photolyphic engraving” (patented in 1852 and 1858), a method of using printable steel plates and muslin screens to achieve quality middle tones of photographs on printing plates, was th...

chemical process by which molecules are broken down into smaller units through the absorption of light. ...

Near photography to reveal fine texture and detail covers several ranges: (1) close-up photography at image scales between 0.1 and 1 (one-tenth to full natural size); (2) macrophotography between natural size and 10 to 20× magnification, using the camera lens on its own; (3) photomicrography at magnifications above about 20×, combining the camera with a microscope; and (4) electron.....

...create a data file on disk or tape, containing the coordinates of all the lines and other features on the map. On the other hand, aerial photographs can be combined and printed directly to form a photomap. For flat areas this operation requires simply cutting and pasting the photographs together into a mosaic. For greater accuracy the centres of the photographs may be aligned by the use of......

...or just resist, typically dissolves in a high-pH solution after exposure to light (including ultraviolet radiation or X rays), and this process, known as development, is controlled by using a mask. A mask is made by applying a thick deposit of chromium in a particular pattern to a glass plate. The chromium provides a shadow over most of the wafer, allowing “light” to shine......

device that measures the strength of electromagnetic radiation in the range from ultraviolet to infrared and including the visible spectrum. Such devices are generally transducers that convert an electric current into a mechanical indication—e.g., a pointer moving across a dial. The source of the current may be a selenium cell, which generates a current when light falls on it, or it...

...of American survey points with respect to European ones. Much of his early astronomical work for the Survey was done in the Harvard Observatory, in whose Annals (1878) there appeared his Photometric Researches (concerning a more precise determination of the shape of the Milky Way Galaxy)....

in astronomy, the measurement of the brightness of stars and other celestial objects (nebulae, galaxies, planets, etc.). Such measurements can yield large amounts of information on the objects’ structure, temperature, distance, age, etc....

in astronomy, the measurement of the brightness of stars and other celestial objects (nebulae, galaxies, planets, etc.). Such measurements can yield large amounts of information on the objects’ structure, temperature, distance, age, etc.......

photography of objects under a microscope. Such opaque objects as metal and stone may be ground smooth, etched chemically to show their structure, and photographed by reflected light with a metallurgical microscope....

composite photographic image made either by pasting together individual prints or parts of prints, by successively exposing individual images onto a single paper, or by exposing the component images simultaneously through superimposed negatives. In the 1880s the juxtaposition of separate images through successive exposures became fashionable in the “combination print,” especially in...

electron multiplier tube that utilizes the multiplication of electrons by secondary emission to measure low light intensities. It is useful in television camera tubes, in astronomy to measure intensity of faint stars, and in nuclear studies to detect and measure minute flashes of light. The tube utilizes a photosensitive cathode, that is, a cathode that emits electrons when light strikes it, foll...

minute energy packet of electromagnetic radiation. The concept originated (1905) in Einstein’s explanation of the photoelectric effect, in which he proposed the existence of discrete energy packets during the transmission of light. Earlier (1900), the German physicist Max Planck had prepared the way for the concept by explaining that heat radiation is emitted and absorbed...

Photon-Lumitype was the first phototypesetter to introduce the selection and photographing of the character in a rapid circular movement without interrupting continuity....

...of the blades on the photographic shutter, producing 12 characters per second, or 43,200 per hour. The model that succeeded it (1965) is equipped with a drum and is capable of double the output. The Photon-Lumitype 713 (1957) also performs at the rate of 70,000 to 80,000 characters per hour. But at this speed the technique of using a rotary matrix case reaches its limit because of the problems....

Photon-Lumizip is based on a different principle. The performance speed of drum phototypesetters can hardly be increased because of the technical problems posed by the rapid rotation of the drum. To increase speed, the Lumizip abandoned rotary movement. The type matrices are stationary and are aligned in negative on a large-sized plate. There is an individual electronic flash behind each type......

Computers and communications systems have been dominated by electronic technology since their beginnings, but photonic technology is making serious inroads throughout the information movement and management systems with such devices as lasers, light-emitting diodes, photodetecting diodes, optical switches, optical amplifiers, optical modulators, and optical fibres. Indeed, for long-distance......

in physics, nuclear reaction in which the absorption of high-energy electromagnetic radiation (a gamma-ray photon) causes the absorbing nucleus to change to another species by ejecting a subatomic particle, such as a proton, neutron, or alpha particle. For example, magnesium-25, upon absorbing a photon of sufficient energy, emits a proton and becomes sodium-24. Photodisintegration differs from the...

...compound water serving as the ultimate electron donor. Certain photosynthetic bacteria that cannot utilize water as the electron donor and require organic compounds for this purpose are called photoorganotrophs. Animals, according to this classification, are chemoorganotrophs; i.e., they utilize chemical compounds to supply energy and organic compounds as electron donors....

...compound water serving as the ultimate electron donor. Certain photosynthetic bacteria that cannot utilize water as the electron donor and require organic compounds for this purpose are called photoorganotrophs. Animals, according to this classification, are chemoorganotrophs; i.e., they utilize chemical compounds to supply energy and organic compounds as electron donors....

the functional or behavioral response of an organism to changes of duration in daily, seasonal, or yearly cycles of light and darkness. Photoperiodic reactions can be reasonably predicted, but temperature, nutrition, and other environmental factors also modify an organism’s response....

...can irreversibly bleach the visual pigments, as in sun blindness. Numerous pathological conditions of the eye are accompanied by abnormal light sensitivity and pain, a condition that is known as photophobia. The pain appears to be associated with reflex movements of the iris and reflex dilation of the blood vessels of the conjunctiva. Workers exposed to ultraviolet-light sources or to atomic......

...of America (RCA), which had tried to market a sound-on-film system that had been developed in the laboratories of its parent company, General Electric, and had been patented in 1925 as RCA Photophone. In October 1928, RCA therefore acquired the Keith-Albee-Orpheum vaudeville circuit and merged it with Joseph P. Kennedy’s Film Booking Offices of America (FBO) to form RKO Radio Pictures......