| 释义 |
theta|ˈθiːtə|
[a. Gr. θῆτα: see def.]
1. a. The eighth letter of the Greek alphabet, θ, θ (see th).
In ancient Greece, on the ballots used in voting upon a sentence of life or death, θ stood for θάνατος, death; hence in allusive use.
1603Daniel Def. Ryme H iv, Setting his Theta or marke of condemnation vppon them. 1616–61B. Holyday Persius iv. 317 And the black theta, signe of deadly shame, Thou can'st prefix 'fore an offenders name. 1682Sir T. Browne Chr. Mor. i. §22 At the Tribunal..wherein iniquities have their natural Theta's, and no nocent is absolved by the verdict of himself. 1789M. Madan tr. Persius (1795) 103 Able to fix the black theta to vice.
b. attrib. and Comb., as theta-sounding adj.; theta-function, in Math., a name for two different functions: (a) the sum of a series from n = - ∞ to n = + ∞ of terms denoted by exp(n2a + 2na); also extended to a similar function of several variables; (b) a function occurring in probabilities, expressed by the integral ∫exp(-t2)dt; theta-phi diagram, the temperature-entropy diagram, which represents the heat-units converted into work per pound of working fluid (θ = absolute temperature, and ϕ = entropy).
1871M. Collins Mrq. & Merch. III. iii. 88 You [English] are a theta-sounding people. 1879Cayley Coll. Math. Papers X. 475 We have thus an addition-with-subtraction theorem for the double theta-functions. 1901Pract. Engineer Pocket Bk. 166 The temperature-entropy diagram is usually called the θϕ (theta-phi) diagram.
2. Biol. Used to designate rhythmic activity of the brain recorded by an electroencephalograph and having a frequency of between four and seven cycles per second.
1944Walter & Dovey in Jrnl. Neurol., Neurosurg., & Psychiatry VII. 64/1 In the case of the 4–7 c/s. waves the term we suggest is ‘theta’. Ibid. 65/1 It is suggested that rhythms at about 6 c/s. should be termed ‘theta’ rhythms and that such rhythms are characteristic of the resting, immature or isolated parieto-temporal complex. 1953Brit. Jrnl. Psychol. XLIV. 320 The excessive theta rhythm..found in some aggressive psychopaths. 1961Lancet 26 Aug. 465/1 An E.E.G. recorded when fasting showed some abnormality, with rhythmic 6 c.p.s. theta activity in the resting tracing. 1972Sci. Amer. Feb. 85/3 Subjects with a great deal of experience in meditation showed other changes: the alpha waves slowed..and rhythmical theta waves at six to seven cycles per second appeared. 1975J. Taylor Superminds vii. 121 In states of extreme emotion, theta waves of four to seven cycles and up to thirty microvolts occur.
3. In Scientology: creative energy or spirit. Also ˈthetan, the embodiment of this spirit in the individual. (See quots. 1965.)
1951L. R. Hubbard Handbk. for Preclears 77/1 Theta. The mathematical symbol for the static of thought. By theta is meant the static itself. 1952― Scientology: 8–80, 83 The thetan, or theta being, takes over a body only a few days or a week before birth. 1957J. F. Horner Summary of Scientol. iv. 56 In Scientology, the specialized term, ‘theta’, is used to refer to thought and spirit. The term, ‘Thetan’, refers to the single unit of beingness which each person is. 1965L. R. Hubbard Scientol. Abridged Dict. 33 Theta, energy peculiar to life or a thetan which acts upon material in the physical universe. Ibid., Thetan, the person himself..; that which is aware of being aware; the identity that is the individual. 1971[see Scientology]. 1977C. McFadden Serial (1978) xxvii. 60/2 Marlene said Theta taught you how to overcome Specific Negatives. 1977Times Lit. Suppl. 13 May 582/5 The gnosis centres on the ‘thetan’, the true self... The core task of the cult ought to be to cleanse and return the thetan to its immortal, pristine, form.
4. Chem. theta (or θ, θ) temperature, the temperature of a polymer solution at which it behaves ideally as regards its osmotic pressure; so theta condition, theta solvent, etc.
1953P. J. Flory Princ. Polymer Chem. xii. 523 Frequently it is preferred to use as a parameter the ‘ideal’ temperature θ... At the temperature T = θ, the chemical potential due to segment-solvent interactions is zero... Hence the temperature θ is that at which the excess chemical potential is zero and deviations from ideality vanish. Ibid. xiv. 612 An ideal solvent, or θ-solvent. Ibid., The intrinsic viscosity usually changes rapidly with temperature in the vicinity of the θ-point. 1966Brandrup & Immergut Polymer Handbk. iv. 163 Theta-solvents (θ-solvents) are solvents in which, at a given temperature, a polymer molecule is in the so-called theta-state, where it behaves like an ideal statistical coil. 1973J. M. G. Cowie Polymers vii. 138 Above the theta temperature expansion of the coil takes place, caused by interactions with the solvent, whereas below θ the polymer segments attract one another, the excluded volume is negative, and eventual phase separation occurs. 1974Sci. Amer. Dec. 60/2 At that temperature, which varies for different polymers and solvents, the measured properties of the polymer can be usefully compared with those of other polymers at their theta temperature.
5. Particle Physics. Freq. written θ. A meson that decays into two pions, now identified with the kaon. Also theta meson.
1954Physical Rev. XCIV. 1732/1 A large fraction of these V0 decays are consistent with the decay scheme θ0→π{pm} + π{pm} (or µ∓). 1955, etc. [see tau].
6. theta pinch (Nucl. Physics): a toroidal pinch (pinch n. 13) in which the magnetic field follows the axis of the plasma and the current-carrying coils encircle it. [θ, the symbol of the angle of the radius vector of the circular path of the current.]
1959Nucleonics Oct. 82/2 The conference topic that aroused greatest interest was the theta pinch. 1967New Scientist 9 Nov. 369/1 The simplicity of the theta pinch as a means of achieving that sought after goal of power from thermonuclear reactions had led to considerable studies of its real effectiveness in confining and heating up a plasma. 1974Nature 20 Sept. 193/2 In the theta-pinch design, the compression coils are not superconducting and no special measures are taken to reduce neutron heating. |