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The cross section of a body that is placed in an airstream to produce a useful aerodynamic force in the most efficient manner possible. The cross sections of wings, helicopter rotor blades (Fig. 1), propeller blades, windmill blades, compressor and…

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) [Fig. 1]. In wrought…

A structural member that is fabricated from metal, reinforced or prestressed concrete, wood, fiber-reinforced plastic, or other construction materials and that resists loads perpendicular to its longitudinal axis. A beam's length is usually much…

Any of several leguminous plants, or their seeds, long utilized as food by humans or livestock. There are more than 40,000 varieties of beans, with only a small number of these being mass-produced for human or animal consumption. In particular,…

A coarse, erect, annual herb plant, Ricinus communis, belonging to the spurge family (Euphorbiaceae). The castor plant (Ricinus communis) is a member of the spurge family (Euphorbiaceae) in the order Malpighiales. The plant varies greatly in height…

Any member of the grass family (Poaceae or Gramineae) that produces edible grains usable as food by humans and livestock. Cereals are important cultivated crops. Common cereals include rice, wheat, barley, oats, maize (corn), sorghum, rye, and…

An evergreen shrub or small tree, particularly Cinnamomum verum, and the spice obtained from the plant's bark. The cinnamon plant (see illustration) is a member of the laurel family (Lauraceae) in the order Laurales. Native to Sri Lanka, the…

Any device connected internally or externally to a computer and used in the transfer of data to or from a computer. A personal computer (PC) processes information. Data (unprocessed information) must get into the computer, and the processed…

The biological study of insects that have a direct influence on humanity. Economic entomology is a subdiscipline of entomology (the biological science that deals with the investigation of insects) and focuses on the effects of insects on human…

A condition in space in the vicinity of an electrically charged body such that the forces due to the charge are detectable. An electric field (or electrostatic field) exists in a region if an electric charge at rest in the region experiences a force…

The segment of horticulture concerned with the commercial production, marketing, and sale of plants grown and used for decorative or display purposes. Floriculture is a branch of horticulture, that is, the art and science of growing plants,…

Any interaction between objects that causes motion. Fundamentally, objects interact through the four known physical forces: gravity, electromagnetism, and the strong and weak nuclear interactions. In practice, however, many of the forces worked with…

The science, art, and practice of managing and using the natural resources that occur on and in association with forested lands. Forestry is the management of forested lands (see illustration). It involves the planning and implementation of…

Plants that have altered genetic material (DNA) through recombinant DNA (rDNA) manipulation. Genetic engineering of plants allows for very specific genetic changes to be made to a plant's deoxyribonucleic acid (DNA), as opposed to the random…

Commercially grown plants that have altered genetic material through artificial recombinant manipulation. Genetic modification is the latest scientific tool for developing improved crop varieties. Such genetically modified (GM) crops can help to…

An organism that has had its genetic material manipulated or altered in a laboratory setting through the use of genetic or genomic engineering techniques. Genetically modified organisms (GMOs) are microorganisms, plants, or animals that have been…

Optical instruments that establish an optical line or axis for the purpose of aiming a weapon. The axis includes the observer's eye, a suitable mark in the instrument, and the target. For a pistol, the traditional iron sights employ a rear notch and…

Electromagnetic radiation whose wavelengths are in the range from about 0.75 micrometer (μm) to 1 millimeter (mm). Infrared radiation (Fig. 1) is outside the range of visible light and cannot be seen with the unaided eye. Infrared radiation was…

The artificial application of water to the soil to produce plant growth. Irrigation also cools the soil and atmosphere, making the environment favorable for plant growth. The use of some form of irrigation (Fig. 1) is well documented throughout the…

That branch of mechanics which deals with the motion of a system of material particles without reference to the forces which act on the system. Kinematics differs from dynamics in that the latter takes these forces into account. Dynamics Mechanics…

A solid or liquid (molten), opaque material with a lustrous surface and good electrical and thermal conductivities. Solid metal is usually crystalline and ductile and can be permanently deformed by shear on crystal planes (Fig. 1); permanent…

The change in the position of an object in a physical space over time. A familiarly encountered phenomenon, motion (see illustration) occurs on all levels of reality, from the constant movements of subatomic particles (conveyed by probabilities of…

The branch of acoustics that deals with the generation of sound by musical instruments, the transmission of sound to the listener, and the perception of musical sound. Musical acoustics has fascinated scientists at least since the time of the Greek…

Weapons that arm warships. Of the wide variety of such weapons, three important categories are exclusively naval: antiship missiles, torpedoes, and mines. Other weapons all correspond to land-based types, but submarine-launched ballistic missiles…

The extraction and refining of nickel from its ores. Nickel's properties of strength, toughness, and resistance to corrosion have been used to advantage in alloys since ancient times. Paktong, similar to modern nickel silver, was used in the…

An annual leafy leguminous vine, Pisum sativum (order Fabales), cultivated for its smooth or wrinkled, round edible seeds, which are borne in dehiscent pods. The garden pea (Fig. 1) is one of the world's oldest cultivated crops. It is a native of…

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…

Concrete in which steel is embedded in such a manner that the two materials act together in resisting forces. Reinforced concrete was invented in the nineteenth century and has now become the most popular construction material (Fig. 1). Many…

An electron microscope that builds up images of samples via the scanning of the sample's surface with a focused electron beam. The idea of the scanning electron microscope (SEM) dates back to the 1930s, with a great deal of the pioneering…

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…

Related terms used to define the intensity of internal reactive forces in a deformed body and associated unit changes of dimension, shape, or volume caused by externally applied forces.Stress is a measure of the internal reaction between elementary…

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 planning and implementation of actions to establish, protect, restore, and maintain trees and forests in cities and smaller communities. When the field of urban forestry began in the 1960s, it focused on individual trees along streets and…

The general term applied to the description of a disturbance which propagates from one point in a medium to other points without giving the medium as a whole any permanent displacement. Waves are a common phenomenon in the natural world and manifest…

Products, such as veneer, plywood, laminate of products, particleboard, waferboard, pulp and paper, hardboard, and fiberboard, made from the stems and branches of coniferous (softwood) and deciduous (hardwood) tree species. The living portion of the…

An early mechanical calculator. The abacus likely originated in Babylonia sometime before 1000 BCE. Over the subsequent centuries, it became a commonplace device in many regions of the world. The abacus is still occasionally used as a cognitive…

A departure of an optical image-forming system from ideal behavior. Ideally, such a system will produce a unique image point corresponding to each object point. In addition, every straight line in the object space will have as its corresponding…

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 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…

The use of a combination of mass spectrometers and an accelerator to measure the natural abundances of very rare radioactive isotopes. These abundances are frequently lower than parts per trillion. The most important applications of accelerator mass…

An instrument that utilizes focused acoustic waves to produce images of surface and subsurface features in materials, and to measure elastic properties on a microscopic scale. It has been used to image and measure local elastic properties in metals,…

Unwanted sound. Noise control is the process of obtaining an acceptable noise environment for people in different situations. These definitions and the words “unwanted” and “acceptable” suggest that criteria need to be established to determine when…

The discipline of acoustic phonetics can be narrowly defined as the study of the acoustic output of the vocal tract for speech, but ultimately it encompasses much more. Acoustic phonetics makes direct contact with, and in many cases is the…

A device to measure the acoustic power or intensity of a sound beam by means of the force or torque that the beam exerts on an inserted object or interface. The underlying theory involves the concept of radiation pressure, which is the…

A discipline that deals generally with the extraction of information from acoustic signals in the presence of noise and uncertainty. Acoustic signal processing has expanded from the improvement of music and speech sounds and a tool to search for oil…

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 software development methods in which requirements and solutions evolve through collaboration between the developers and the customers. Agile methods have significantly changed the practice of software development since their inception…

A branch of meteorology that examines the effects and impacts of weather and climate on crops, rangeland, livestock, and various agricultural operations. Agricultural meteorology, or agrometeorology, addresses topics that often require an…

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 science and study of crops and soils. Agronomy is the umbrella term for a number of technical research and teaching activities (see illustration): crop physiology and management, soil science, plant breeding, and weed management frequently are…

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…

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…

Helium nuclei, which are abundant throughout the universe both as radioactive-decay products and as key participants in stellar fusion reactions. Alpha particles can also be generated in the laboratory, either by ionizing helium or from nuclear…

The analog of linear momentum for rotational motion. A particle with mass m moving with velocity v has linear momentum p = m v (Note: This article follows the convention of using bold, non-italicized variables for vectors and using non-bold,…

A deciduous tree (genus Malus) in the order Rosales, which produces an edible, simple, fleshy, pome-type fruit. Apples (Fig. 1) belong to the family Rosaceae, which includes many other deciduous fruits, including pears, peaches, and cherries. There…

The subfield of computer science concerned with understanding the nature of intelligence and constructing computer systems capable of intelligent behavior. Many activities, such as perception, learning, planning, natural language, and understanding,…

Vegetables that are prevalent in Asian cuisines, but less well known in Western diets. Asian vegetables (Fig. 1), also referred to as Asian greens or oriental vegetables, are very important in Asian countries, but are not as popular in North America…

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…

A large tropical plant of the genus Musa and its edible fruit. The banana belongs to the family Musaceae (order Zingiberales). The banana of commerce (Musa acuminata), which is believed to have originated in the Asian tropics, was one of the…

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…

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 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.…

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…

A binary digit. In the computer, electronics, and communications fields, “bit” is generally understood as a shortened form of “binary digit.” In a numerical binary system, a bit is either a 0 or 1. Bits are generally used to indicate situations that…

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 process in which a liquid phase is converted into a vapor phase. The energy for phase change is generally supplied by the surface on which boiling occurs. Boiling differs from evaporation at predetermined vapor/gas–liquid interfaces because it…

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 constant occurring in practically all statistical formulas and having a numerical value of 1.3807 × 10−23 joule/K. It is represented by the letter k. If the temperature T is measured from absolute zero, the quantity kT has the dimensions of an…

To describe a system consisting of a large number of particles in a physically useful manner, recourse must be had to so-called statistical procedures. If the mechanical laws operating in the system are those of classical mechanics, and if the…

An equation which is used to study the nonequilibrium behavior of a collection of particles. In a state of equilibrium a gas of particles has uniform composition and constant temperature and density. If the gas is subjected to a temperature…

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…

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…

A system that receives and processes television signals, as well as other digital forms of communications such as those related to high-speed Internet connectivity and cable telephony, from various sources and retransmits these signals through…

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…

Desktop or, more often, portable electronic devices that are used to perform arithmetic, statistical, or other, more complex processing operations at the step-by-step direction of the user or by execution of a program (a stored sequence of…

A set of generalized coordinates of a classical dynamical system together with their conjugate momenta, and transformations among these coordinates and momenta that leave the form of Hamilton's equations of motion unchanged. Explanation of some 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 periodic waveform upon which an information-bearing signal is impressed. This process is known as modulation and comprises a variety of forms such as amplitude, phase, and frequency modulation. The most common type of carrier is the sinusoidal…

A biennial umbellifer (Daucus carota) of Asiatic and Mediterranean origin belonging to the plant order Apiales. The carrot (Daucus carota; Fig. 1) is grown for its edible roots, which are eaten raw or cooked. Cultivated forms of the root vegetable…

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…

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…