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in law, the rules that govern the obtaining of legal redress. This article deals only with civil procedure in Anglo-American law (for criminal procedure, see criminal law).
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Any one of a number of related integral quantities which serve as the basis for general formulations of the dynamics of both classical and quantum-mechanical systems. The term has been associated with four quantities: the fundamental action S, for general paths of a dynamical system; the classical action SC, for the actual path; the modified action S′, for paths restricted to a particular energy; and action variables, for periodic motions.
A dynamical system can be described in terms of some number N of coordinate degrees of freedom that specify its configuration. As the vector q whose components are the degrees of freedom q1, q2, …, qN varies with time t, it traces a path q(t) in an N-dimensional space. The fundamental action S is the integral of the lagrangian of the system taken along any path q(t), actual or virtual, starting from a specified configuration q1 at a specified time t1, and ending similarly at configuration q2 and time t2. The value of this action S[q(t)] depends on the particular path q(t). The actual path qC(t) which is traversed when the system moves according to newtonian classical mechanics gives an extremum value of S, usually a minimum, relative to the other paths. This is Hamilton's least-action principle. The extremum value depends only on the end points and is called the classical action SC(q1, q2; t1, t2).
An important variant of Hamilton's principle applies when the virtual paths q(t) are restricted to motions all of the same energy E, but no longer to a specific time interval, t1 - t2. The modified action S′ = S - E(t1 - t2) obeys a modified least-action principle, usually called Maupertuis' principle, namely, that the classical path gives again an extremal value of S′ relative to all paths of that energy. Maupertuis' principle is closely related to Fermat's principle of least time in classical optics for the path of light rays of a definite frequency through a region of inhomogeneous refractive index. See Hamilton's principle, Minimal principles
In quantum mechanics, as originally formulated by E. Schrödinger, the state of particles is described by wave functions which obey the Schrödinger wave equation. States of definite energy in, say, atoms are described by stationary wave functions, which do not move in space. Nonstationary wave functions describe transitory processes such as the scattering of particles, in which the state changes. Both stationary and nonstationary state wave functions are determined, in principle, once the Schrödinger wave propagator (also called the Green function) between any two points q1 and q2 is known. In a fundamental restatement of quantum mechanics, R. Feynman showed that all paths from q1 to q2, including the virtual paths, contribute to the wave propagator. Each path contributes a complex phase-term exp i (&phgr;[q(t)]), where the phase &phgr; is proportional to the action for that path. The resulting sum over paths, appropriately defined, is the path integral (or functional integral) representation of the Schrödinger wave propagator. The path integral has become the general starting point for most formulations of quantum theories of particles and fields. The classical path qC(t) of least action now plays the role in the wave function as being the path of stationary phase. See Propagator (field theory)
- any unit or sequence of social activity or behaviour, e.g. the action of a trade union or state, as well as the action of an individual.
- (in contrast with BEHAVIOUR; see also BEHAVIOURISM) any unit or sequence of individual social activity which is intentional or purposive and involves conscious deliberation rather than merely being the result of a biological reflex.
Sociologists are divided as to whether social reality is better explained with reference to individual purposive action (see ACTION THEORY, AGENCY, METHODOLOGICAL INDIVIDUALISM, MEANINGFUL UNDERSTANDING AND EXPLANATION) or as the outcome of SOCIAL STRUCTURE (see also STRUCTURALISM). There are also those sociologists (see SOCIAL PHENOMENOLOGY, ETHNOMETHODOLOGY, SCHUTZ, GARFINKEL) who argue that action theorists as well as structuralists have failed to show how actors' meanings are actually constituted.
The debate about social action in these terms is one of the most central in modern sociological theory. Various attempts have been made to reconcile action theory and structuralist perspectives (see PARSONS, STRUCTURATION THEORY, STRUCTURE AND AGENCY, GIDDENS). While no consensus exists that these attempts are entirely successful, there is an increasing recognition that sociological explanations must include reference to both action and structure (see DUALITY OF STRUCTURE).
in the theater, an important means of expression in the actor’s art. A role is realized through the actions of a performer in a play, concert, or rehearsal; these actions reveal the goal and consequently the inner world of the character being portrayed. An important element in the art of the actor is the verbal action (dramatic speech) that is directed toward the audience and the other actors.