experimentalism See instrumentalism
expert system Computer-based system designed to respond like a human expert in a given field. Expert systems are built on knowledge gathered from human experts, analogous to a database but containing rules that may be applied to solving a specific problem. An interface allows the user to specify symptoms and to clarify a problem by responding to ques¬ tions posed by the system. Software tools exist to help designers build a special-purpose expert system with minimal effort. An outgrowth of work in artificial intelligence, expert systems show promise for an ever-widening range of applications. There are now widely used expert systems in the fields of medicine, personnel screening, and education.
explanation In philosophy, set of statements that makes intelligible the existence or occurrence of an object, event, or state of affairs. Among the most common forms of explanation are causal explanation (see cau¬ sation), deductive-nomological explanation (see covering-law model), which involves subsuming the explanandum under a generalization from which it may be derived in a deductive argument (e.g., “All gases expand when heated; this gas was heated; therefore, this gas expanded”) and sta¬ tistical explanation, which involves subsuming the explanandum under a generalization that gives it inductive support (e.g., “Most people who use tobacco contract cancer; this person used tobacco; therefore, this person contracted cancer”). Explanations of human behaviour typically appeal to the subject’s beliefs and desires, as well as other facts about him, and proceed on the assumption that the behaviour in question is rational (at least to a minimum degree). Thus an explanation of why the subject removed his coat might cite the fact that the subject felt hot, that the sub¬ ject desired to feel cooler, and that the subject believed that he would feel cooler if he took off his coat.
Explorer Any of the largest (55-member) series of unmanned U.S. spacecraft, launched between 1958 and 1975. Explorer 1, the first satellite sent into orbit by the U.S., discovered the innermost Van Allen radiation belt. Other notable craft in this series include Explorer 38 (1968), which measured galactic radio sources and studied low radio frequencies in space, and Explorer 53 (SAS 3; 1975), which investigated X-ray and gamma-ray sources within and beyond the Milky Way Galaxy. See photo on following page.
© 2006 Encyclopaedia Britannica, Inc.
650 i explosive ► extrusion
Explorer 10 satellite undergoing testing in a NASA laboratory prior to being launched in 1961.
NASA
explosive Any substance or device that can produce a volume of rap¬ idly expanding GAS in an extremely brief period. Mechanical explosives, which depend on a physical reaction (e.g., overloading a container with compressed air until it bursts), are little used except in mining. Nuclear explosives (see nuclear weapon) use either nuclear fission or nuclear fusion. Chemical explosives are of two types: detonating (high) explosives (e.g., TNT, dynamite) have extremely rapid decomposition and development of high pressure; deflagrating (low) explosives (e.g., black powder, smoke¬ less powder; see gunpowder) merely burn quickly and produce relatively low pressure. Primary detonating explosives are ignited by a flame, a spark, or an impact; secondary ones require a detonator and sometimes a booster. Modern high explosives use either mixtures of ammonium nitrate and fuel oil or ammonium nitrate-based water gels.
exponential function In mathematics, a function in which a constant base is raised to a variable power. Exponential functions are used to model changes in population size, in the spread of diseases, and in the growth of investments. They can also accurately predict types of decline typified by radioactive decay (see half-life). The essence of exponential growth, and a characteristic of all exponential growth functions, is that they double in size over regular intervals. The most important exponential function is e x , the inverse of the natural logarithmic function (see logarithm).
Export-Import Bank of the United States (Ex-lm Bank) One
of the principal U.S. government agencies in international finance. Origi¬ nally incorporated as the Export-Import Bank of Washington in 1934, its goal is to help finance U.S. exports, principally by lending money to for¬ eign buyers of U.S. goods and services. Such assistance often consists of credits to foreign banks and governments in connection with development projects. See also development bank.
Expressionism In the visual arts, artistic style in which the artist depicts not objective reality but the subjective emotions that objects or events arouse. This aim is accomplished through the distortion and exag¬ geration of shape and the vivid or violent application of colour. Its roots are found in the works of Vincent van Gogh, Edvard Munch, and James Ensor. In 1905 the movement took hold with a group of German artists known as Die Brucke; their works influenced such artists as Georges Rouault, Chaim Soutine, Max Beckmann, Kathe Kollwitz, and Ernst Barlach. The group of artists known as Der Blaue Reiter were also considered Expressionists. Expressionism was the dominant style in Germany after World War I; postwar Expressionists included George Grosz and Otto Dix. Its emotional qualities were adopted by other 20th-century art move¬ ments. See also Abstract Expressionism.
extenuating circumstance or mitigating circumstance In
law, circumstance that diminishes the culpability of one who has com¬ mitted a criminal offense. In many Anglo-American legal systems, provo¬ cation of the accused by the victim can reduce a charge of first-degree murder to second-degree murder or to manslaughter. In Britain, a charge
of murder may be reduced to manslaughter if the accused is found to be suffering diminished capacity (see diminished responsibility). The Italian penal code allows consideration of motives of honour. Extenuating cir¬ cumstances also are a factor in many civil actions.
extinction (of species) Dying out or termination of a species. It occurs when a species can no longer reproduce at replacement levels. Most past extinctions are thought to have resulted from environmental changes that the doomed species was either unable to adapt to or that caused it to adapt so thoroughly that it became a distinctly new species. The effect of humans on the environment, through hunting, collecting, and habitat destruction, has become the principal factor in plant and ani¬ mal extinctions.
extortion Unlawful exaction of money or property through intimida¬ tion or undue exercise of authority. It may include threats of physical harm, criminal prosecution, or public exposure. Some forms of threat, especially those made in writing, are occasionally singled out for sepa¬ rate statutory treatment as blackmail. See also bribery.
extradition Process by which one state, at the request of another, returns a person for trial for a crime punishable by the laws of the request¬ ing state and committed outside the state of refuge. Extradition is regu¬ lated within countries by extradition acts and between countries by treaties. Some principles of extradition are common to many countries. Most decline to surrender their own nationals. Countries also generally recognize the right of political asylum. In view of the solidarity of nations in the repression of crime, however, countries are usually willing to coop¬ erate in bringing criminals to justice.
extrasensory perception (ESP) Perception that involves awareness of information about something (such as a person or event) not gained through the senses and not deducible from previous experience. Classic forms of ESP include telepathy, clairvoyance, and precognition. No con¬ clusive demonstrations of the existence of ESP in any individual have been given, but popular belief in the phenomenon remains widespread, and people who claim to possess ESP are sometimes employed by inves¬ tigative teams searching for missing persons or things. See also parapsy¬ chology.