spectroscopy: Infrared instrumentation: Thermal detection of infrared radiation is based on the conversion of a temperature change, resulting from such radiation falling on a suitable material, into a measurable signal. A Golay detector employs the reflection of light from a thermally distortable reflecting film onto a photoelectric cell,…

gas: Diffusion and thermal diffusion: Both of these properties present difficulties for the simple mean free path version of kinetic theory. In the case of diffusion it must be argued that collisions of the molecules of species 1 with other species 1 molecules do not inhibit the interdiffusion…

industrial glass: Thermal expansion: …shock is known as the thermal endurance of a glass; it is inversely related to the thermal-expansion coefficient and the thickness of the piece. The thermal expansion coefficients of various oxide glasses are shown in the table of properties of oxide glasses.

thermal energy, internal energy present in a system in a state of thermodynamic equilibrium by virtue of its temperature. Thermal energy cannot be converted to useful work as easily as the energy of systems that are not in states of thermodynamic equilibrium. A flowing fluid or a moving solid, for

thermodynamics: …two systems are each in thermal equilibrium with a third system, the first two systems are in thermal equilibrium with each other. This property makes it meaningful to use thermometers as the “third system” and to define a temperature scale. The first law of thermodynamics, or the law of conservation…

thermal expansion, the general increase in the volume of a material as its temperature is increased. It is usually expressed as a fractional change in length or volume per unit temperature change; a linear expansion coefficient is usually employed in describing the expansion of a solid, while a

combustion: Thermal explosions: Thermal explosion theory is based on the idea that progressive heating raises the rate at which heat is released by the reaction until it exceeds the rate of heat loss from the area. At a given composition of the mixture and a given…

gas meter: In thermal-type gas meters a heater (such as an electrical heating coil) is placed in the gas stream, and thermometers are installed on its upstream and downstream sides. Gas flow is measured in relation to either the temperature rise of the gas stream or the amount…

metamorphic rock: Temperature: …in Earth, known as the geothermal gradient, is the increase in temperature per unit distance of depth; it is given by the tangent to the local geotherm. The magnitude of the geothermal gradient thus varies with the shape of the geotherm. In regions with high surface heat flow, such as…

thermoreception: Thermoreceptors and pain reception: …spatially interlaced; this so-called “thermal grill illusion” mimics the burning sensation associated with painful cold (usually reported at temperatures below 15 °C [59 °F]). The thermal grill demonstrates that there is a central neural mechanism for the cold inhibition of pain. The cold bars in the grill (below 20…

wastewater treatment: Digestion: …two-stage anaerobic digestion process is thermal hydrolysis, or the breaking down of the large molecules by heat. This is done in a separate step before digestion. In a typical case, the process begins with a sludge that has been dewatered to a DS content of some 15 percent. The sludge…

mass spectrometry: Thermal ionization: Atoms with low ionization potentials can be ionized by contact with the heated surface of a metal, generally a filament, having a high work function (the energy required to remove an electron from its surface) in a process called thermal, or surface, ionization.…

Saha equation, mathematical relationship between the observed spectra of stars and their temperatures. The equation was stated first in 1920 by the Indian astrophysicist Meghnad N. Saha. It expresses how the state of ionization of any particular element in a star changes with varying temperatures

dating: Technical advances: …the use of highly sensitive thermal ionization mass spectrometers is replacing the counting techniques employed in some disequilibrium dating. Not only has this led to a reduction in sample size and measurement errors, but it also has permitted a whole new range of problems to be investigated. Certain parent-daughter isotopes…

thermocouple, a temperature-measuring device consisting of two wires of different metals joined at each end. One junction is placed where the temperature is to be measured, and the other is kept at a constant lower temperature. A measuring instrument is connected in the circuit. The temperature

climate change: Thermal maxima: Many parts of the globe experienced higher temperatures than today some time during the early to mid-Holocene. In some cases the increased temperatures were accompanied by decreased moisture availability. Although the thermal maximum has been referred to in North America and elsewhere as…

climate change: Thermal maxima: Many parts of the globe experienced higher temperatures than today some time during the early to mid-Holocene. In some cases the increased temperatures were accompanied by decreased moisture availability. Although the thermal maximum has been referred to in North America and elsewhere as…

natural gas: The biological stage: Often significant amounts of thermal methane gas are generated along with the oil. Below 2,900 metres (9,500 feet), primarily wet gas (gas containing liquid hydrocarbons) is formed.

asteroid: Size and albedo: By using a so-called thermal model to balance the measured intensity of infrared radiation with that of radiation at visual wavelengths, investigators are able to derive the diameter of the asteroid. Other remote-sensing techniques—for example, polarimetry, radar, and adaptive optics (techniques for minimizing the distorting effects of Earth’s atmosphere)—also…

weather modification: Changes in the radiation balance near the ground: …is known as the “thermal mountain effect.”

thermal neutron, any free neutron (one that is not bound within an atomic nucleus) that has an average energy of motion (kinetic energy) corresponding to the average energy of the particles of the ambient materials. Relatively slow and of low energy, thermal neutrons exhibit properties, such as

Harry Nyquist: …explanation of the unexpectedly strong thermal noise studied by J.B. Johnson. The understanding of noise is of critical importance for communications systems. Thermal noise is sometimes called Johnson noise or Nyquist noise because of their pioneering work in this field.

integrated circuit: Chemical methods: …are electrodeposition (or electroplating) and thermal oxidation. In the former the substrate is given an electrically conducting coating and placed in a liquid solution (electrolyte) containing metal ions, such as gold, copper, or nickel. A wide range of film thicknesses can be built. In thermal oxidation the substrate is heated…

thermoperiodicity, the growth or flowering responses of plants to alternation of warm and cool periods. Daily temperature fluctuations produce dramatic effects on the growth or flowering of most plants. The lack of lower night temperatures frequently results in poor growth, as can be observed in

whirlwind: Dust devils: …leads to the formation of thermal plumes (large parcels of hot air rising from the surface). A dust devil draws on this stored energy to develop and then maintain itself. A light wind is required to start rotation in the rising plume. When dissipative forces, such as surface friction and…

river: Environmental problems attendant on river use: Such heated water can alter the existing ecology, sometimes sufficiently to drive out or kill desirable species of fish. It also may cause rapid depletion of the oxygen supply by promoting algal blooms.

Brazil: Power: …has given lower priority to thermal power generation because of the poor quality of Brazilian coal. The opening of a gas pipeline from Bolivia in 1999 has led to a program for construction of gas-fired thermoelectric generating plants, chiefly in the Southeast. The opening of a Bolivia-Brazil natural gas pipeline…

water supply system: Thermal processes: Distillation, a thermal process that includes heating, evaporation, and condensation, is the oldest and most widely used of desalination technologies. Modern methods for the distillation of large quantities of salt water rely on the fact that the boiling temperature of water is lowered…

food preservation: Thermal processing: Thermal processing is defined as the combination of temperature and time required to eliminate a desired number of microorganisms from a food product.

thermal radiation, process by which energy, in the form of electromagnetic radiation, is emitted by a heated surface in all directions and travels directly to its point of absorption at the speed of light; thermal radiation does not require an intervening medium to carry it. Thermal radiation

asteroid: Size and albedo: …solar system) is that of thermal radiometry. That technique exploits the fact that the infrared radiation (heat) emitted by an asteroid must balance the solar radiation it absorbs. By using a so-called thermal model to balance the measured intensity of infrared radiation with that of radiation at visual wavelengths, investigators…

petroleum refining: Naphtha reforming: The initial process, thermal reforming, was developed in the late 1920s. Thermal reforming employed temperatures of 510–565 °C (950–1,050 °F) at moderate pressures—about 40 bars (4 MPa), or 600 psi—to obtain gasolines (petrols) with octane numbers of 70 to 80 from heavy naphthas with octane numbers of less…

thermodynamics: The second law of thermodynamics: …essential point is that the heat reservoir is assumed to have a well-defined temperature that does not change as a result of the process being considered.

thermistor, electrical-resistance element made of a semiconducting material consisting of a mixture of oxides of manganese and nickel; its resistance varies with temperature. Thermistors (temperature-sensitive, or thermal, resistors) are used as temperature-measuring devices and in electrical

refractory: Properties: …also must be resistant to thermal shock. Thermal shock occurs when an object is rapidly cooled from high temperature. The surface layers contract against the inner layers, leading to the development of tensile stress and the propagation of cracks. Ceramics, in spite of their well-known brittleness, can be made resistant…

hot spring, spring with water at temperatures substantially higher than the air temperature of the surrounding region. Most hot springs discharge groundwater that is heated by shallow intrusions of magma (molten rock) in volcanic areas. Some thermal springs, however, are not related to volcanic

radiation: Surface effects: Yet another mechanism is prompt thermal sputtering, in which energized atoms in thermal spikes created close to the surface escape through the surface before annealing occurs. Certain materials (e.g., crystalline alkali halides) are prone to electronic sputtering, in which energy associated with electronic excitations induced by the incident ion is…

mechanics of solids: Thermal strains: Temperature change can also cause strain. In an isotropic material the thermally induced extensional strains are equal in all directions, and there are no shear strains. In the simplest cases, these thermal strains can be treated as being linear in the temperature change…

gas: Thermal transpiration: Suppose that two containers of the same gas but at different temperatures are connected by a tiny hole and that the gas is brought to a steady state. If the hole is small enough and the gas density is low enough that only…

heat-treating, changing the properties of materials such as metals or glass by processes involving heating. It is used to harden, soften, or modify other properties of materials that have different crystal structures at low and high temperatures. The type of transformation depends on the

Diocletian window, semicircular window or opening divided into three compartments by two vertical mullions. Diocletian windows were named for those windows found in the Thermae, or Baths, of Diocletian (now the church of Santa Maria degli Angeli) in Rome. The variant name, thermal window, also

chromatography: Gas chromatographic detectors: Thermal-conductivity detectors compare the heat-conducting ability of the exit gas stream to that of a reference stream of pure carrier gas. To accomplish this, the gas streams are passed over heated filaments in thermal-conductivity cells. Measured changes in filament resistance of the cells reflect temperature…

thermal-heat recovery, use of heat energy that is released from some industrial processes and that would otherwise dissipate into the immediate environment unused. Given the prevalence of heat-generating processes in energy systems, such as those found in household heating and cooling systems and

gliding: …basic method of soaring, called thermaling, is to find and use rising currents of warm air, such as those above a sunlit field of ripened grain, to lift the glider. Thermals can rise very rapidly, which allows the sailplane, if deftly piloted, to attain substantial increases in altitude. Slope soaring…

Peter Zumthor: A commission to design the Therme Vals (1996) in Vals, Switzerland, presented Zumthor with a prime opportunity to create a series of varied spatial experiences. The structure, appearing like an enormous geometric rock carved within the hillside, is made from local quartz and concrete. The building’s entry is a dark…

thermocouple, a temperature-measuring device consisting of two wires of different metals joined at each end. One junction is placed where the temperature is to be measured, and the other is kept at a constant lower temperature. A measuring instrument is connected in the circuit. The temperature

Gustav Tammann: …developed a method known as thermic analysis for determining the chemical composition of a compound from its cooling curve, which enabled him to explain systems of mixed crystals. Tammann conducted much research on the mechanical properties of metals during coldworking and found that changes in such properties resulted from a…

human nutrition: BMR and REE: energy balance: This phenomenon, known as the thermic effect of food (or diet-induced thermogenesis), accounts for about 10 percent of daily energy expenditure, varying somewhat with the composition of the diet and prior dietary practices. Adaptive thermogenesis, another small but important component of energy expenditure, reflects alterations in metabolism due to changes…

Thermidor, the name given during the French Revolution to the eleventh month of the year in the republican calendar. The month fell in the hottest season of the year, beginning on July 19 or 20 and ending on August 18 or 19, according to the year. As in all the other months of the republican

Elsie de Wolfe: …Frohman’s production of Victorien Sardou’s Thermidor (1891) and toured with the production for two years. In 1894 she became a regular member of Frohman’s company. In 1901 she formed her own company and presented Clyde Fitch’s The Way of the World on Broadway and in a two-year tour. She retired…

Thermidorian Reaction, in the French Revolution, the parliamentary revolt initiated on 9 Thermidor, year II (July 27, 1794), which resulted in the fall of Maximilien Robespierre and the collapse of revolutionary fervour and the Reign of Terror in France. By June 1794 France had become fully weary

thermionic emission, discharge of electrons from heated materials, widely used as a source of electrons in conventional electron tubes (e.g., television picture tubes) in the fields of electronics and communications. The phenomenon was first observed (1883) by Thomas A. Edison as a passage of

thermionic power converter, any of a class of devices that convert heat directly into electricity using thermionic emission rather than first changing it to some other form of energy. A thermionic power converter has two electrodes. One of these is raised to a sufficiently high temperature to

thermionic power converter, any of a class of devices that convert heat directly into electricity using thermionic emission rather than first changing it to some other form of energy. A thermionic power converter has two electrodes. One of these is raised to a sufficiently high temperature to

thermionic power converter, any of a class of devices that convert heat directly into electricity using thermionic emission rather than first changing it to some other form of energy. A thermionic power converter has two electrodes. One of these is raised to a sufficiently high temperature to

electronics: The vacuum tube era: Coolidge and Fleming’s thermionic valve (a two-electrode vacuum tube) for use in radio receivers. The detection of a radio signal, which is a very high-frequency alternating current (AC), requires that the signal be rectified; i.e., the alternating current must be converted into a direct current (DC) by a…

electronics: The vacuum tube era: Coolidge and Fleming’s thermionic valve (a two-electrode vacuum tube) for use in radio receivers. The detection of a radio signal, which is a very high-frequency alternating current (AC), requires that the signal be rectified; i.e., the alternating current must be converted into a direct current (DC) by a…

electronic work function: …a heated platinum filament (thermionic work function) differs slightly from that required to eject an electron from platinum that is struck by light (photoelectric work function). Typical values for metals range from two to five electron volts.

thermistor, electrical-resistance element made of a semiconducting material consisting of a mixture of oxides of manganese and nickel; its resistance varies with temperature. Thermistors (temperature-sensitive, or thermal, resistors) are used as temperature-measuring devices and in electrical

Thermit, powdered mixture used in incendiary bombs, in the reduction of metals from their oxides, and as a source of heat in welding iron and steel and in foundry work. The powder consists of aluminum and the oxide of a metal such as iron. When ignited or heated, it gives off an enormous amount of

Thermit, powdered mixture used in incendiary bombs, in the reduction of metals from their oxides, and as a source of heat in welding iron and steel and in foundry work. The powder consists of aluminum and the oxide of a metal such as iron. When ignited or heated, it gives off an enormous amount of

firebrat, (Thermobia domestica), stout-bodied quick-moving wingless insect. The firebrat is worldwide in distribution and is commonly found indoors, typically lingering in warm locations, such as near fireplaces, furnaces, and water heaters. It feeds on starches and thus can cause damage to books,

nitride: Sulfur nitrides: … + 12NH4Cl Tetrasulfur tetranitride forms thermochromic crystals, which are crystals that change colour with temperature. They are red at temperatures above 100 °C (210 °F), orange at 25 °C (80 °F), and colourless at −190 °C (−310 °F). The crystals are stable in air but will explode in response to…

thermocline, oceanic water layer in which water temperature decreases rapidly with increasing depth. A widespread permanent thermocline exists beneath the relatively warm, well-mixed surface layer, from depths of about 200 m (660 feet) to about 1,000 m (3,000 feet), in which interval temperatures

thermocouple, a temperature-measuring device consisting of two wires of different metals joined at each end. One junction is placed where the temperature is to be measured, and the other is kept at a constant lower temperature. A measuring instrument is connected in the circuit. The temperature

vacuum technology: Thermal conductivity gauges: …gauges, the Pirani and the thermocouple, determine pressure by the rate at which heat is dissipated from a hot filament. The Pirani gauge basically is a Wheatstone bridge with one arm in the form of a heated filament placed in the vacuum system. The resistance of the filament depends on…

pyrometer: Thermocouple pyrometers measure the output of a thermocouple (q.v.) placed in contact with the hot body; by proper calibration, this output yields temperature. Pyrometers are closely akin to the bolometer and the thermistor and are used in thermometry.

thermodynamic equilibrium, condition or state of a thermodynamic system, the properties of which do not change with time and that can be changed to another condition only at the expense of effects on other systems. For a thermodynamic equilibrium system with given energy, the entropy is greater

thermodynamics: Temperature: …Celsius scale is called the Kelvin (K) scale, and that related to the Fahrenheit scale is called the Rankine (°R) scale. These scales are related by the equations K = °C + 273.15, °R = °F + 459.67, and °R = 1.8 K. Zero in both the Kelvin and Rankine…

thermodynamics, science of the relationship between heat, work, temperature, and energy. In broad terms, thermodynamics deals with the transfer of energy from one place to another and from one form to another. The key concept is that heat is a form of energy corresponding to a definite amount of

Gilbert N. Lewis: Chemical thermodynamics: …1923 in the publication of Thermodynamics and the Free Energy of Chemical Substances, written in collaboration with chemist Merle Randall.

first law of thermodynamics, thermodynamic relation stating that, within an isolated system, the total energy of the system is constant, even if energy has been converted from one form to another. This law is another way of stating the law of conservation of energy. It is one of four relations

Lars Onsager: …has been described as the “fourth law of thermodynamics.”

second law of thermodynamics, statement describing the amount of useful work that can be done from a process that exchanges or transfers heat. The second law of thermodynamics can be precisely stated in the following two forms, as originally formulated in the 19th century by the Scottish physicist

Walther Nernst: Third law of thermodynamics: In 1905 Nernst was appointed professor and director of the Second Chemical Institute at the University of Berlin and a permanent member of the Prussian Academy of Sciences. The next year he announced his heat theorem, or third law of thermodynamics.…

thermodynamics: laws of thermodynamics are:

Walter Schottky: In his book Thermodynamik (1929), he was one of the first to point out the existence of electron “holes” in the valence-band structure of semiconductors. In 1935 he noticed that a vacancy in a crystal lattice results when an ion from that site is displaced to the crystal’s…

thermoelectricity, direct conversion of heat into electricity or electricity into heat through two related mechanisms, the Seebeck effect and the Peltier effect. When two metals are placed in electric contact, electrons flow out of the one in which the electrons are less bound and into the other.

thermionic power converter, any of a class of devices that convert heat directly into electricity using thermionic emission rather than first changing it to some other form of energy. A thermionic power converter has two electrodes. One of these is raised to a sufficiently high temperature to

thermoelectric power generator, any of a class of solid-state devices that either convert heat directly into electricity or transform electrical energy into thermal power for heating or cooling. Such devices are based on thermoelectric effects involving interactions between the flow of heat and of

thermoelectric power generator: This reversibility distinguishes thermoelectric energy converters from many other conversion systems, such as thermionic power converters. Electrical input power can be directly converted to pumped thermal power for heating or refrigerating, or thermal input power can be converted directly to electrical power for lighting, operating electrical equipment, and…

thermoelectric power generator, any of a class of solid-state devices that either convert heat directly into electricity or transform electrical energy into thermal power for heating or cooling. Such devices are based on thermoelectric effects involving interactions between the flow of heat and of

electricity: Thermoelectricity: …colder and act as a refrigerator. Peltier refrigerators are used to cool small bodies; they are compact, have no moving mechanical parts, and can be regulated to maintain precise and stable temperatures. They are employed in numerous applications, as, for example, to keep the temperature of a sample constant while…

thermocouple, a temperature-measuring device consisting of two wires of different metals joined at each end. One junction is placed where the temperature is to be measured, and the other is kept at a constant lower temperature. A measuring instrument is connected in the circuit. The temperature

thermoelectricity, direct conversion of heat into electricity or electricity into heat through two related mechanisms, the Seebeck effect and the Peltier effect. When two metals are placed in electric contact, electrons flow out of the one in which the electrons are less bound and into the other.

plastic: Thermoforming and cold molding: When a sheet of thermoplastic is heated above its Tg or Tm, it may be capable of forming a free, flexible membrane as long as the molecular weight is high enough to support the stretching. In this heated state, the sheet…

brown adipose tissue: …cause a protein known as thermogenin (also called uncoupling protein 1, UCP1) to become active. Thermogenin effectively uncouples electron transport in the mitochondrion from the production of chemical energy in the form of adenosine triphosphate (ATP). The resulting change in the balance of electrons and protons across the mitochondrial membrane…

thermometer: …mapped, using a technique called thermography that provides a graphic or visual representation of the temperature conditions on the surface of an object or land area.

copier: In this process, sometimes called thermography, sensitized copy paper is placed in contact with the original and both are exposed to infrared rays. The original absorbs the rays in areas darkened by print or by the lines and shades of an illustration and thereby transfers the impressions to the surface…

thermometer: …mapped, using a technique called thermography that provides a graphic or visual representation of the temperature conditions on the surface of an object or land area.

thermohaline circulation (THC), the component of general oceanic circulation controlled by horizontal differences in temperature and salinity. It continually replaces seawater at depth with water from the surface and slowly replaces surface water elsewhere with water rising from deeper depths.

thermokarst, land surface configuration that results from the melting of ground ice in a region underlain by permafrost. In areas that have appreciable amounts of ice, when the ice melts and the ground settles unevenly, small pits, mounds, sinkholes, tunnels, caverns, valleys, steep-walled ravines,

lamp: …as 1784, and a “thermolampe” using gas distilled from wood was patented in 1799. Although coal gas was denounced as unsafe, it won increasing favour for street lighting, and by early in the 19th century most cities in the United States and Europe had gaslighted streets and increasing numbers…

thermoluminescence, emission of light from some minerals and certain other crystalline materials. The light energy released is derived from electron displacements within the crystal lattice of such a substance caused by previous exposure to high-energy radiation. Heating the substance at

dosimeter: Thermoluminescent dosimeters are nonmetallic crystalline solids that trap electrons when exposed to ionizing radiation and can be mounted and calibrated to give a reading of radiation level. The ion-chamber dosimeter, like the thermoluminescent one, is reusable, but it is self-reading for immediate determination of exposure.

thermometer, instrument for measuring the temperature of a system. Temperature measurement is important to a wide range of activities, including manufacturing, scientific research, and medical practice. The invention of the thermometer is generally credited to the Italian mathematician-physicist

cricket: The snowy tree cricket (Oecanthus fultoni) is popularly known as the thermometer cricket because the approximate temperature (Fahrenheit) can be estimated by counting the number of chirps in 15 seconds and adding 40. Tree- and bush-inhabiting crickets usually sing at night, whereas weed-inhabiting crickets sing both…

undersea exploration: Water sampling for temperature and salinity: A mercury thermometer fastened to the bottle records the temperature at the specified depth. The design of the device is such that, when it is inverted, its mercury column breaks. The amount of mercury remaining in the graduated capillary portion of the thermometer indicates the temperature at…

gas: Thermal transpiration: …steady-state result is called the thermomolecular pressure difference. These results follow simply from the effusion formula if the ideal gas law is used to replace N/V with p/T;

thermonatrite, a carbonate mineral, hydrated sodium carbonate (Na2CO3·H2O), found near saline lakes as an evaporation product or on arid soil as an efflorescence. It is usually associated with natron (Na2CO3·10H2O) and trona, which alter to it upon partial dehydration; many reported deposits of