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The time rate of change of velocity. Acceleration is a physics term that measures the rate of change of velocity per unit of time. Because velocity is a directed or vector quantity involving both magnitude and direction, a velocity may change by a…

The pure and applied science that is concerned with botany and management of crop and ornamental plants for utilization by humankind. As it relates to plants, agricultural science concerns itself with the application of scientific methods to…

The art and science of crop and livestock production. In its broadest sense, agriculture comprises the entire range of technologies associated with the production of useful products from plants and animals, including soil cultivation, crop and…

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…

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 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 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 management and maintenance of colonies of honeybees for human purposes. Beekeeping is an ancient art. Although the commonly known honeybee species (Fig. 1) is native to Europe and Africa, humans have transported them to other continents. The…

The use of parasitoids, predators, and pathogens to reduce injurious pest insect populations and consequently the damage that they cause. Biological insect control (or insect biocontrol) is the regulation of insect populations by biological means.…

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…

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…

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…

An enclosure capable of resounding or resonating and thereby intensifying sound tones or electromagnetic waves. Resonance is the phenomenon which results when the frequency of the impressed driving force is the same as the natural vibration of the…

A set of four numbers used to specify the orientation of a body, or equivalently, the rotation R which produces that orientation, starting from some reference orientation. They can be expressed in terms of the Euler angles ψ, θ, and ϕ, as in Eqs.…

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…

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 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…

A system for data storage in which digitally encoded information in the form of microscopic pits on a rotating disk is accessed by optical readout. The compact disk was originally developed as a music carrier providing high fidelity, random access,…

The principle stating that energy cannot be created or destroyed, although it can be changed from one form to another. The law of conservation of energy has been established by a multitude of meticulous measurements of gains and losses of all known…

The fundamental physical law stating that the momentum of a system is constant if no external forces act upon the system. The principle of conservation of momentum holds generally and is applicable in all fields of physics. In particular, momentum…

An electrostatic potential that exists between samples of two dissimilar electrically conductive materials (metals or semiconductors with different electron work functions) that have been brought into thermal equilibrium with each other, usually…

A conducting disk with concentric inner and outer electrical contacts, which can be placed in a magnetic field parallel to its axis. The disk is named after O. M. Corbino, who in 1911 reported magnetoresistance measurements on several metals by…

The characteristic wavelength dependence of the optical rotatory dispersion curve or the circular dichroism curve or both in the vicinity of an absorption band.When an initially plane-polarized light wave traverses an optically active medium, two…

Nuclear excitation caused by the time-dependent long-ranged electric field acting between colliding nuclei. Theoretically, the Coulomb force between the positively charged colliding nuclei is well understood, and the interaction is exactly…

A process in which a molecule moving with high velocity strikes a solid and the electrons that bond the molecule are torn off rapidly in violent collisions with the electrons of the solid; as a result, the molecule is suddenly transformed into a…

For electrostatics, Coulomb's law states that the direct force F of point charge q1 on point charge q2, when the charges are separated by a distance r in free space, is given by F = k0 q1 q2 r2 , where k0 is a constant of proportionality whose…

A system of two parallel forces of equal magnitude and opposite sense (Fig. 1). Forces P at normal distance P constitute a counterclockwise couple Cz (viewed from +Z) in the OXY plane; forces Q at arm q constitute a clockwise couple Cx (from +X)…

Two or more electric circuits are said to be coupled if energy or signals can transfer electrically or magnetically from one to another. If electric charge, or current, or rate of change of current in one circuit produces electromotive force or…

A solid in which the atoms or molecules are arranged periodically. Within a crystal, many identical parallelepiped unit cells, each containing a group of atoms, are packed together to fill all space (see illustration). In scientific nomenclature,…

The wavelength or energy dependence of the attenuation of electromagnetic radiation as it passes through a crystal, due to its conversion to other forms of energy in the crystal. When atoms are grouped into an ordered array to form a crystal, their…

A device, more correctly described as a crystal detector, that detects ionizing radiations of all types and is adaptable to measuring neutrons. The sensitive element is a single crystal with a dc resistance normally higher than 1012 ohms. The…

Departures of a crystalline solid from a regular array of atoms or ions. A “perfect” crystal of sodium chloride (NaCl), for example, would consist of alternating Na+ and Cl- ions on an infinite three-dimensional simple cubic lattice, and a simple…

The growth of crystals, of which all crystalline solids are composed. This article discusses the processes by which crystal growth occurs, and methods of artificially growing crystals. Growth Processes Crystal growth generally comes about by means…

The study of the propagation of light, and associated phenomena, in crystalline solids.The propagation of light in a solid crystalline material depends upon the atomic spacing, elemental composition, and arrangement of atoms. Crystals with simple…

The arrangement of atoms, ions, or molecules in a crystal. Crystals are defined as solids having, in all three dimensions of space, a regular repeating internal unit of structure. This definition, which dates from early studies of crystals,…

Single crystals that have grown in filamentary form. Such filamentary growths have been known for centuries and can form by a variety of mechanisms. Some grow from their base: either these are extruded to relieve pressure in the base material or…

The branch of science that deals with the geometric forms of crystals. The field of crystallography originated in the prehistoric observation of geometric forms of minerals, such as a collection of quartz (SiO2) crystals (Fig. 1). These crystals…

An apparatus with which force is measured between current-carrying conductors. The purpose of the measurement was to establish the value of the ampere in terms of its International System (SI) definition; therefore the relative locations of the…

A device that measures very accurately an unknown current in terms of a known one. Current comparators are based on Ampère's law, Eq. (1),1where the left side of the equation is the sum of currents, each calculated as the current Ip in a conductor…

A vector quantity equal in magnitude to the instantaneous rate of flow of electric charge, perpendicular to a chosen surface, per unit area per unit time. If a uniform wire of cross-sectional area A carries a current I, the current density J is I/A.…

The measurement of the rate of passage of electric charges in a circuit. The unit of measurement, the ampere (A), is one of the base units of the International System of Units (SI). It is defined as that constant current which, if maintained in two…

Equipment used in the production and processing of milk and milk products, including milking machines, cream separators, coolers, pasteurizers, homogenizers, butter-making equipment, evaporators and dryers, and related items of equipment. The…

A general term for a genus of tall forage grasses, of which the most important species is the deeply rooted perennial Paspalum dilatatum. Dallis grass (see illustration) is widely grown in the southern United States, mostly for pasture, and remains…

A term broadly used to denote either the dissipation of energy in, and the consequent decay of, oscillations of all types or the extent of the dissipation and decay. The energy losses arise from frictional (or analogous) forces which are unavoidable…

Common name for the plant Colocasia esculenta, including the variety antiquorum (taro). Dasheen plants are among the few edible members of the aroid family (Araceae). Native to southeastern Asia and Malaysia, the plants supply local inhabitants with…

The date palm, Phoenix dactylifera, which is one of the oldest cultivated tree crops. The date palm provides a staple food for many populations in the Middle East and North Africa and is also highly valued for feed, fiber, and shelter. Beginning in…

Defoliants are chemicals that cause leaves to drop from plants; defoliation facilitates harvesting. Desiccants are chemicals that kill leaves of plants; the leaves may either drop off or remain attached; in the harvesting process the leaves are…

A transmission line (as nearly dissipationless as possible) or an electric network approximation of it which, if terminated in its characteristic impedance, will reproduce at its output a waveform applied to its input terminals with little…

The division of forestry concerned with taxonomy of trees and other woody plants. The term dendrology is derived from the Ancient Greek: dendron (= tree) and -logia (= study of or science of); the term xylology is used occasionally to denote the…