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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 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…

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…

The closest spiral galaxy to the Milky Way Galaxy. The name of the Andromeda Galaxy (Fig. 1) derives from its appearance in the constellation of Andromeda. The galaxy is also known as M31 and NGC 224, based on its entries in two widely used…

Any living organism taxonomically assigned to the classification kingdom known as Animalia. Members of the kingdom Animalia—that is, animals (see illustration)—possess certain characteristics that distinguish them from organisms belonging to the…

An order of leeches (subclass Hirudinida) characterized by the absence of a protrusible proboscis and including both blood-feeding and macrophagous (predatory) varieties. Most notorious among the blood-feeding leeches in the Arhynchobdellida is the…

A class of the asterozoan group of the phylum Echinodermata, often known as sea stars or starfish. Members of the class Asteroidea, that is, asteroids, are notable echinoderms with a star-shaped body plan (Fig. 1). Unlike members of their sister…

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 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…

One of the main extant classes in the phylum Mollusca. Members of the molluscan class Bivalvia (formerly, Pelecypoda) are known commonly as bivalves and include clams, oysters, mussels, and scallops. All bivalves are aquatic, living at all depths of…

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…

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 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 cellular automaton is a hypothetical computer constructed of a regular array of cells that interact with neighboring cells according to a set of simple rules. Though conceptually simple, cellular automata can produce complex and surprising…

An aquatic mammalian order comprising approximately 90 living species of whales, dolphins, and porpoises and their fossil relatives. Like all other mammals, members of the order Cetacea (cetaceans) nurse their young with milk produced by the mother,…

The common name for numerous species of small to medium-sized lizards that comprise the family Chamaeleonidae (also Chamaeleontidae). Chameleons (see illustration) are members of the family Chamaeleonidae (also Chamaeleontidae) in the order Squamata…

An order of the class Reptilia, including the turtles, terrapins, and tortoises; also termed Testudines. The order Chelonia (often referred to as Testudines) comprises one of the oldest groups of reptiles on Earth. Members of the Chelonia…

An electrical transmission line comprising an inner, central conductor surrounded by a tubular outer conductor. The two conductors are separated by an electrically insulating medium which supports the inner conductor and keeps it concentric with the…

A cable that transmits information signals between geographically separated points. The heart of a communications cable is the transmission medium, which may be optical fibers, coaxial conductors, or twisted wire pairs. A mechanical structure…

A means for ensuring the privacy of voice, data, and video transmissions. While analog techniques were commonly utilized to perform such functions in the past for voice and video, when signals were transmitted in analog form, these techniques are…

The protection of wire and optical communications systems equipment and service from electrical disturbances. This includes the electrical protection of lines, terminal equipment, and switching centers, and inductive coordination, or the protection…

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 (Fig. 1) was originally developed as a music carrier providing high fidelity, random…

The process of protecting against threats to computing systems. A threat is an event that can cause harm to computers, data or programs, or computations (Fig. 1). A failure of computer security occurs because of a vulnerability or weakness in a…

Complex systems in which computers play a major role. While complex physical systems and sophisticated software systems can help people to lead healthier and more enjoyable lives, reliance on these systems can also result in loss of money, time, and…

A large, tawny brown wild cat, Puma concolor (family Felidae), once widespread over most of the Americas; also known as catamount, mountain lion, painter, and puma. The cougar (Puma concolor; see illustration) is a carnivorous member of the family…

Interference in a communications channel (disturbed channel) caused by activity in other communications channels (disturbing channels). The term was originally used to denote the presence in a telephone receiver of unwanted speech signals from other…

The various mechanisms for data confidentiality, data authentication, and nonrepudiation (that is, the property to prevent the denial of previous commitments or actions). Cryptography, with a long history of being an art of secret writing, has…

A class of the phylum Cnidaria, comprising the box jellyfish. Members of the Cubozoa are commonly known as box jellyfish or cubozoans. These cnidarian invertebrates are good swimmers, and their distribution is mostly tropical and subtropical. There…

A multidisciplinary field for analyzing large amounts of data—current and past (historical)—which are processed using tools and methods from statistics, applied mathematics, artificial intelligence, and computer programming, with the object of…

A device that recovers from a transmitted signal information that has been embedded in the signal by a process of modulation. The modification of a usually sinusoidal electrical carrier signal (or simply carrier) for the purpose of transmitting…

An order of nematodes in which the variable stoma may or may not be armed with a dorsal tooth that may or may not be opposed by subventral denticles. The variable amphids (anterior sensory receptors) range from reniform to elongate loops to simple…

An order of nematodes in which the taxa are readily recognized by their conspicuous body annulation. The annuli of members of the order Desmoscolecida may be covered with concretion rings, or the cuticle may be ornamented with scales, warts, or…

An order of sea urchins (class Echinoidea) possessing an aulodont Aristotle's lantern (jaw apparatus) with unkeeled teeth that are U-shaped in cross section, and with the apophyses not meeting at the top of the lantern. In Diadematoida, the…

A large group of flukes (parasitic flatworms) within the class Trematoda, with some thousands of described and probably many thousands of not yet described species. The Digenea range from about 0.2 mm (0.008 in.) to over 1 m (3.3 ft) in length. They…

A four-port waveguide device (Fig. 1) in which an incoming wave at any one port (for example, A) appears at two others (C and D), but not at the fourth (B). This device has numerous applications in wave-guide networks such as microwave waveguides,…

A distributed system consists of a collection of autonomous computers linked by a computer network and equipped with distributed system software. This software enables computers to coordinate their activities and to share the resources of the system…

Programmable computers integrated with electrically powered machines that perform household chores. Domestic robots, also known as home or service robots, are essentially programmable computers integrated with electrically powered machines that…

A transmission network used to selectively modify the components of a signal according to their frequencies. In most cases a filter is used to enhance signals of desired frequencies while suppressing signals of undesired frequencies. An ideal filter…

That branch of electrical engineering dealing with the transmission and reception of information. Information can be transmitted over many different types of pathways, such as satellite channels, underwater acoustic channels, telephone cables, and…

Disturbance to the normal or expected operation of electrical or electronic devices, equipment, and systems. Electrical interference is sometimes called radio-frequency interference (RFI) or electromagnetic interference (EMI). Such disturbances may…

The connection of a specific circuit (called the load) to another circuit. Illustrationa shows a source of electrical energy (S), a coupling circuit (C), and a load (L). In power transmission, S is the generator of the power plant, C represents…

Interfering and unwanted currents or voltages in an electrical device or system. Electrical noise, or simply noise, has a significant effect on the design and operation of almost all electrical and optical systems which are used to communicate or…

A device that produces electrical noise for use in electrical measurements. Electrical noise generators are commonly employed to measure the noise figure or noise temperature of radio receivers. They are also used in various other tests in radar and…

The imposition of a metal or composite barrier between one or more sources of electrical noise and their victims with the objective of reducing or eliminating electrical interference. Examples of the barrier are the case or housing of equipment;…

The situation in which electrical and electronic de­vices and systems work as intended, both within themselves and in their electromagnetic environment.Electromagnetic interference (EMI) is said to exist when unwanted voltages or currents are…

Devices which are used to capture the sound waves of conversation originating in an ostensibly private setting in a form, usually as a magnetic tape recording, which can be used against the target by adverse interests.There are two kinds of…

The asynchronous transmission of messages by using computers and data-communication networks. Historically, electronic mail (or e-mail) referred to any of a number of technologies that allowed people to send documents to one another through…

The art and science of preserving the use of the electromagnetic spectrum for friendly forces while denying its use to the enemy. This is accomplished via use of techniques, devices, and equipment by an adversary to deny or counteract an enemy's use…

Computer systems that cannot be programmed by the user because they are preprogrammed for a specific task and are buried within the equipment they serve. The term derives from the military, where computer systems are generally activated by the flip…

A peculiar order of silk-spinning, orthopteroid insects, commonly called the embiids or web spinners, which are related to termites. The order Embioptera (also known as Embiidina or Embiodea) comprises about 300–400 described species, which are…