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Habituation to a specific practice, such as drinking alcoholic beverages or using drugs (for example, heroin, cocaine, or amphetamines), and disorders characterized by the chronic use of a drug, alcohol, or similar substance. Addiction and addictive…

A disease of the nervous system characterized by a progressive dementia that leads to profound impairment in cognition and behavior. Dementia occurs in a number of brain diseases where the impairment in cognitive abilities represents a decline from…

A neurodevelopmental condition that impairs the way that a person relates to and communicates with other people. Persons with autism have difficulties with social communication and interaction. They also can have unusual behaviors, such as…

The separation of petroleum into fractions and the treating of these fractions to yield marketable products. Petroleum is a mixture of gaseous, liquid, and solid hydrocarbon compounds that occurs in sedimentary rock deposits throughout the world. In…

A theory expressing the idea that life on Earth passed through an era when biological processes were carried out predominantly by ribonucleic acids, without the involvement of deoxyribonucleic acids or proteins. The RNA World theory (or hypothesis)…

The penetration by humans into the reaches of the universe above Earth's atmosphere through the use of crewed vehicles. Human space flight poses significant challenges as an enterprise, given the technical rigors and costs associated with achieving…

An electronic display that allows a user to interact with a computer system by touching an area or areas on the display. Touch-screen displays have been in use for many years in ATMs, checkout registers, and other applications, but gained mass…

The technique of measuring the magnitude and direction of acceleration. Measurement of acceleration (see illustration) includes translational acceleration with tangential and radial components and angular acceleration. Acceleration The May 16, 2011…

A chemical compound, (CH3)2CO; the first member of the homologous series of aliphatic ketones. Acetone (see illustration) is a colorless, volatile, and flammable liquid. Acetone occurs naturally in plants and animals. Its physical properties include…

In the Brönsted classification, an acid is any chemical species, ionic or molecular, capable of donating a proton (hydrogen ion) to another substance; the other substance acts as a base in accepting the proton. For these two interrelated classes of…

One of a large group of organic substances possessing the halocarbonyl group in which X stands for fluorine, chlorine, bromine, or iodine. The terms acyl and aroyl halides refer to aliphatic or aromatic derivatives, respectively.The great inherent…

The ratio of the current to the voltage in an alternating-current circuit.In terms of complex current I and voltageV, the admittance of a circuit is given by Eq. (1), and is related to the impedance of the circuit Z by Eq. (2). Y is a complex number…

The force retarding an airplane, especially in supersonic flight, as a consequence of the formation of shock waves. Although the physical laws governing flight at speeds in excess of the speed of sound are the same as those for subsonic flight, the…

A group of psychiatric conditions, also known as mood disorders, that are characterized by disturbances of affect, emotion, thinking, and behavior. Affective or mood disorders are strong mental disturbances that interfere with daily life (Fig. 1).…

A discipline that combines the means to know the location and heading of an aircraft with respect to some map or coordinate system, with guidance which means steering the aircraft along some desired path toward a destination. The construction of the…

The branch of mathematics dealing with the solution of equations. These equations involve unknowns, or variables, along with fixed numbers from a specified system (Fig. 1). The origins of algebra were based on the need to develop equations that…

The study of zero sets of polynomial equations. Examples of zero sets of polynomial equations studied in algebraic geometry are the parabola y − x2 = 0, thought of as sitting in the (x, y)-plane, and the locus of all points (t, t2, t3, t4), which is…

Any compound having highly basic properties, strong acrid taste, and ability to neutralize acids. Aqueous solutions of alkalies are high in hydroxyl ions, have a pH above 7, and turn litmus paper from red to blue. Caustic alkalies include sodium…

The elements of group 1 in the periodic table. Of the alkali metals, lithium differs most from the rest of the group, and tends to resemble the alkaline-earth metals (group 2 of the periodic table) in many ways. In this respect lithium behaves as do…

Usually calcium, strontium, and barium, the heaviest members of group 2 of the periodic table (excepting radium). Other members of the group are beryllium, magnesium, and radium, sometimes included among the alkaline-earth metals. Beryllium…

A metal product containing two or more elements as a solid solution, as an intermetallic compound, or as a mixture of such metallic and/or nonmetallic phases. This article will describe alloys on the basis of their technical applications. Alloys may…

Substances formed by the addition of one or more elements, usually metals, to aluminum. The principal alloying elements in aluminum-base alloys are magnesium (Mg), silicon (Si), copper (Cu), zinc (Zn), and manganese (Mn). In wrought products, which…

A psychiatric disorder in which a dramatic reduction in caloric intake consequent to excessive dieting leads to significant bodily, physiological, biochemical, emotional, psychological, and behavioral disturbances. Anorexia nervosa is one of three…

A group of distinct psychiatric disorders including generalized anxiety disorder, panic disorder, obsessive-compulsive disorder, social anxiety disorder, specific phobia, and posttraumatic stress disorder. Whereas fear is an adaptive emotion that is…

A nonsteroidal anti-inflammatory drug used to control pain, fever, and inflammation. Aspirin is one of the most prevalent medicines in the world and is used to reduce fever and treat minor aches, pains, and inflammation. Furthermore, it is the only…

The engineering aspects of flight and navigation in space. Astronautical engineering deals with vehicles, instruments, and other equipment used in space (see illustration), but not with the sociological or economic aspects of space flight, except as…

An analytical technique for determining the composition of a sample in terms of the chemical elements present and their quantities or concentrations. Unlike other methods of elemental analysis, however, the sample is decomposed into its constituent…

A weapon that consists of integral rocket propulsion, means of pointing or guiding the weapon's velocity vector to a prescribed orientation at the position and time of rocket engine shutoff or burnout, and a warhead. In certain applications, means…

The study of the hereditary factors that shape behavior. Behavior genetics, that is, the scientific investigation of the hereditary factors that influence behavior, may be studied in animals and humans. Charles Darwin, who originated the theory that…

An organic acid, C6H5COOH; also known as benzene carboxylic acid. Benzoic acid is a crystalline solid, with the structure below. Benzoic acid has a melting point of 122°C, and sublimes at 100°C. Benzoic acid is only slightly soluble in water but is…

A chemical element, chemical symbol Be, atomic number 4, and atomic weight 9.0122. Beryllium is the first element in the group called alkaline-earth metals on the periodic table (Fig. 1). Alkaline-earth metals Atomic number Chemical element Periodic…

A sound-reproducing system in which sound is recorded or transmitted by using two microphones mounted at the ears of a dummy human head. To preserve the binaural effect, the sound must be monitored by a listener wearing a set of earphones…

The application of principles from applied and physical sciences to problems in healthcare and biology. As a field, biomedical engineering draws from a variety of disciplines including mechanical, chemical, electrical, and computer engineering, as…

In glass blowing, a long straight tube on which molten glass is gathered and worked, partly by blowing into the tube. The blowpipe (see illustration) is spun to shape the glass object further by centrifugal force, or by a tool, in which case the…

A pressurized system in which water is vaporized to steam, the desired end product, by heat transferred from a source of higher temperature, usually the products of combustion from burning fuels. Steam thus generated may be used directly as a…

A component of a steam-generating unit that absorbs heat from the products of combustion after they have passed through the steam-generating and superheating sections. The name, accepted through common usage, is indicative of savings in the fuel…

Water supplied to a boiler for the generation of steam. The water is heated to produce steam and acts to cool the heat-absorbing surfaces as it circulates through the boiler. The steam withdrawn from the steam drum is of high purity, and…

Addition of water to a steam-generating unit at a rate commensurate with the removal of steam from the unit. The addition of water to a boiler requires a feedwater pump or some other device that will develop a pressure higher than that of the steam…

A device for detecting and measuring small amounts of thermal radiation. The bolometer is a simple electric circuit, the essential element of which is a slab of material with an electrical property, most often resistance, that changes with…

A cylindrical fastener with an integral head on one end and an external screw thread on the other end designed to be inserted through holes in assembled parts and to mate with an internally threaded block, called a nut, which is turned to tighten or…

An assembly of two or more parts fastened together by inserting bolts through matching clearance holes in the parts and engaging nuts that are then tightened to clamp the assembly. The term bolted joint also colloquially denotes a screwed joint, for…

A method of holding the parts of an object together with or without the aid of an adhesive such as an epoxy or a glue. Composite materials such as fiber-reinforced plastics require strong interfacial bonding between the reinforcement and the matrix.…

A subprocess of welding encompassing a group of process embodiments in which coalescence is produced by heating to suitable temperatures above 450°C and by using a filler metal that must have a liquidus temperature above 450°C and below the solidus…

Assembling an electronic circuit in the most convenient manner on a board or other flat surface, without regard for final locations of components, to prove the feasibility of the circuit and to facilitate changes when necessary. Standard breadboards…

The potential difference at which an electrically stressed gas is tranformed from an insulator to a conductor. In an electrically stressed gas, as the voltage is increased, the free electrons present in the gas gain energy from the electric field.…

A circuit composed of a source and four impedances that is used in the measurement of a wide range of physical quantities. The bridge circuit is useful in measuring impedances (resistors, capacitors, and inductors) and in converting signals from…

Electronic circuits whose primary function is to connect a high-impedance source to a low-impedance load without significant attenuation or distortion of the signal. Thus, the output voltage of a buffer replicates the input voltage without loading…

Unwanted, aggressive behavior that involves a real or perceived power inequity. The behavior of bullying is often chronic and includes actions such as threats, spreading rumors, attacking someone physically or verbally, and purposefully excluding or…

The resultant vertical force exerted on a body by a static fluid in which the body is submerged or floating. Buoyancy is the upward force exerted by a fluid (liquid or gas) on a body that is placed within it (see illustration). The buoyant force FB…

The velocity at which the combustible gases move through a flame in the direction perpendicular to the flame surface defines the burning velocity. The term flame as used here refers to the burning of combustible gases. The process of combustion, or…

An aluminum or copper conductor supported by insulators that interconnects the loads and the sources of electric power in an electric power system. A typical application is the interconnection of the incoming and outgoing transmission lines and…

A removable metal lining, usually in the form of a bearing to carry a shaft. Generally a bushing is a small bearing in the form of a cylinder and is made of soft metal or graphite-filled sintered material. Bushings are also used as cylindrical…

The testing of electric circuits to determine and locate any of the following circuit conditions: (1) an open circuit, (2) a short circuit with another conductor in the same circuit, (3) a ground, which is a short circuit between a conductor and…

The branch of mathematics dealing with two fundamental operations, differentiation and integration, which are carried out on functions. The subject of calculus (Fig. 1), as traditionally developed in college textbooks, is partly an elementary…

A chemical element, Cf, atomic number 98, the ninth member of the actinide series of elements. Its discovery and production have been based upon artificial nuclear transmutation of radioactive isotopes of lighter elements. All isotopes of…

Mercury(I) chloride, Hg2Cl2, a covalent compound which is insoluble in water. The substance sublimes when heated. The formula weight is 472.086 and the specific gravity is 7.16 at 20°C (68°F). The material is a white, impalpable powder consisting of…

A method of gathering best practices for various work processes into coherent groupings to facilitate quality and process improvement. Capability Maturity Models® (CMM®) represent a relatively recent step in the evolution of process improvement…

A broad designation for a class of solid carbon-based materials with high elemental carbon content produced from the thermal decomposition of hydrocarbons. Carbon black can be produced with a range of physical properties tailored to applications.…

A functional group found in organic compounds in which a carbon atom is doubly bonded to an oxygen atom. Depending upon the nature of the other groups attached to carbon, the most common compounds containing the carbonyl group are aldehydes (X…

A cluster compound containing both carbon (C) and boron (B) atoms as well as hydrogen (H) atoms external to the framework of the cluster. A cluster compound is one with insufficient electrons to allow for classical two-center two-electron bonds…

One of a large family of organic substances widely distributed in nature, and characterized by the presence of one or more carboxyl groups (COOH). These groups typically yield protons in aqueous solution.Acid and baseIn the type formula,…

A heart-shaped curve generated by a point of a circle that rolls (without slipping) on a fixed circle of the same diameter. In point-wise construction of the curve, let O be a fixed point of a circle C of diameter a, and Q a variable point of C. Lay…

An amplifier stage consisting of a common-emitter transistor cascaded with a common-base transistor. The common-emitter–common-base (CE-CB) transistor pair constitutes a multiple active device which essentially corresponds to a common-emitter stage…

A theory of mathematical structure in which smooth continuous inputs lead to discontinuous responses. Water suddenly boils, ice melts, a building crashes to the ground, or the earth unexpectedly buckles and quakes. The French mathematician René Thom…

Catenanes are compounds that are made of interlocking macrocycles. The interlocking rings are said to be mechanically rather than chemically bound. Catenanes are named according to the number of interlocking rings. The simplest catenane, containing…

The name given to the electrons originating at the cathodes of gaseous discharge devices. The term has now been extended to include low-pressure devices such as cathode-ray tubes. Furthermore, cathode rays are now used to designate electron beams…

An electron tube in which a beam of electrons can be focused to a small cross section and varied in position and intensity on a display surface. In common usage, the term cathode-ray tube (CRT) is usually reserved for devices in which the display…

A luminescence resulting from the bombardment of a substance with an electron (cathode-ray) beam. The principal applications of cathodoluminescence are in television, computer, radar, and oscilloscope displays. In these a thin layer of luminescent…

The formation of vapor- or gas-filled cavities in liquids. If understood in this broad sense, cavitation includes the familiar phenomenon of bubble formation when water is brought to a boil under constant pressure and the effervescence of champagne…

Cameras in mobile phones or smartphones that can capture images and videos.The cellphone, the world’s favorite must-have gadget, has been with us for nearly a half-century, while experiencing continuous and often phenomenal improvements. Much of the…

Light emitted by a high-speed charged particle when the particle passes through a transparent, nonconducting, solid material at a speed greater than the speed of light in the material. The blue glow observed in the water of a nuclear reactor, close…

A chemical element, Ce, atomic number 58, atomic weight 140.12. It is the most abundant metallic element of the rare-earth group in the periodic table. The naturally occurring element is made up of the isotopes 136Ce, 138Ce, 140Ce, and 142Ce. A…

A chemical element, Cs, with an atomic number of 55 and an atomic weight of 132.905, the heaviest of the alkali metals in group 1 of the periodic table (except for francium, the radioactive member of the alkali metal family). Cesium is a soft,…

A flexible device of connected links used to transmit power. A drive consists of an endless chain which meshes with sprockets located on the shaft of a driving source, such as an electric motor/reducer, and a driven source, such as the head shaft of…

A single-particle detector which in its basic form (Fig. 1) consists of a hollow tube (channel) of either glass or ceramic material with a semiconducting inner surface. The detector responds to one or more primary electron impact events at its…

Semiconductor devices wherein minority charge is stored in a spatially defined depletion region (potential well) at the surface of a semiconductor, and is moved about the surface by transferring this charge to similar adjacent wells. The formation…

Charged particles can be accelerated to high velocities by electromagnetic fields. They are then able to travel through matter (termed an absorber), interacting with it, losing energy, and causing various effects important in many applications. In…

The branch of physics concerned with the motion of charged particles under the influence of electric and magnetic fields. Acceleration of charged particles A positively charged particle that moves in an electric field experiences a force in the…

A chemical manufacturing process in which chemical transformation takes place, that is, the product differs chemically from the starting materials. Most chemical manufacturing processes consist of a sequence of steps, each of which involves making…

A branch of physical chemistry that seeks to explain time-dependent phenomena, such as energy transfer and chemical reaction, in terms of the detailed motion of the nuclei and electrons that constitute the system. As such, chemical dynamics seeks…

The study of ecological interactions mediated by chemicals that organisms produce. Chemical ecology seeks to integrate chemistry and biology in order to provide information about the chemical interactions among organisms and their environment (Fig.…

Atoms with the same atomic number; that is, the same number of protons in their atomic nucleus. Some common elements are oxygen, hydrogen, iron, copper, gold, silver, nitrogen, chlorine, and uranium (see illustration). Most of the elements are…

A useful but obsolescent term for the energy available from elements and compounds when they react, as in a combustion reaction. In precise terminology, there is no such thing as chemical energy, since all energy is stored in matter as either…

In a dynamic or kinetic sense, chemical equilibrium is a condition in which a chemical reaction is occurring at equal rates in its forward and reverse directions, so that the concentrations of the reactant and product substances do not change with…

A branch of physical chemistry that measures the rates of chemical reactions, describes them in terms of elementary steps, and understands them in terms of the fundamental interactions between molecules. Reaction kinetics Although the ultimate state…

A system of principles and rules used to name chemical compounds. Various nomenclature systems are used. Hence, a compound may have several acceptable names. Which name is preferred depends on the context. Each nomenclature type has several dialects…

A process used to purify substances or to isolate them from other substances. In industrial applications, the ultimate goal is the isolation of a product of given purity. Most industrial chemical processes involve a separation stage. This may…

A system of symbols and notation for the chemical elements and the combinations of these elements which form numerous chemical compounds. This system of symbols, devised since about 1800 by chemists, consists of letters, numerals, and marks that are…

The application of thermodynamic principles to systems involving physical and chemical transformations is carried out in order to (1) develop quantitative relationships among the identifiable forms of energy and their conjugate variables, (2)…

The type of luminescence wherein a chemical reaction supplies the energy responsible for the emission of light (ultraviolet, visible, or infrared) in excess of that of a blackbody (thermal radiation) at the same temperature and within the same…

A chemical discipline that uses mathematical and statistical methods to design or select optimal measurement procedures and experiments and to provide maximum chemical information by analyzing chemical data. Chemometrics is actually a collection of…

A law governing space-charge-limited flow of electron current between two plane parallel electrodes in vacuum when the emission velocities of the electrons can be neglected. It is often called the three-halves power law, and is expressed by the…

An inductor that is used to prevent electric signals and energy from being transmitted along undesired paths or into inappropriate parts of an electric circuit or system. Power-supply chokes prevent alternating-current components, inherent to a…

The act of interrupting an electric current, beam of light, or beam of infrared radiation at regular intervals. This can be accomplished mechanically by rotating a vibrating mirror in the path of the beam to deflect it away from its intended source…

A chemical element, Cr, atomic number 24, and atomic weight 51.996, which is the weighted average for several isotopes weighing 50 (4.31%), 52 (83.76%), 53 (9.55%), and 54 (2.38%). The orbital arrangement of the electrons is 1s2, 2s2, 2p6, 3s2, 3p6,…

Any device that measures a time interval. The term is usually restricted to measurements that have a small percentage error. Early time measurements used the human pulse rate or counted the number of swings of a pendulum for small time intervals.…

A large, strongly built watch especially designed for precise timekeeping on ships at sea. The name is sometimes loosely applied to any fine watch. WatchThe features that distinguish a chronometer from a watch are (1) a heavy balance wheel, the axis…

A general term referring to a system or part of a system of conducting parts and their interconnections through which electric currents are intended to flow. A circuit is made up of active and passive elements or parts and their interconnecting…

An interconnection of electronic devices, an electronic device being an entity having terminals which is described at its terminals by electromagnetic laws. Most commonly these are voltage–current laws, but others, such as photovoltaic…

A device to open or close an electric power circuit either during normal power system operation or during abnormal conditions. A circuit breaker serves in the course of normal system operation to energize or deenergize loads. During abnormal…