| 释义 |
▪ I. parametric, a.1|pærəˈmɛtrɪk|
[f. as parametral a. + -ic.]
a. Math. Of or pertaining to a parameter. parametric curve, a curve obtained by keeping constant one of the parameters in the parametric equations of a surface; parametric equation, one of a set of equations each of which expresses one of the co-ordinates of a curve or surface as a function of one or more parameters (parameter 2 d).
This, rather than parametral or parametrical, is the usual adj. (except in Cryst.: cf. parametral a.).
1864Cayley in Coll. Math. Papers V. 552, µ is the parametric order, ν the parametric class, of the system. 1873G. Salmon Higher Plane Curves 65 When the variable curve depends on a parametric point moving on a given parametric curve. 1900Trans. Amer. Math. Soc. I. 461 (heading) Parametric representation of the fundamental quadric. 1909L. P. Eisenhart Treat. Differential Geom. Curves & Surfaces i. 1 (heading) Parametric equations of a curve. Ibid. ii. 55 Upon a surface (2) there lie an infinity of curves whose equations are given by equations (2), when u is constant, each constant value of v determining a curve... In a similar way, there is an infinite family of curves v = const. The curves of these two families are called the parametric curves for the given equations of the surface. 1942C. H. Lehmann Analytic Geom. xi. 229 The parametric equations of a specific locus are not unique. Ibid. 230 Find the rectangular equation of the curve whose parametric equations are x = 2 + 3 tan θ, y = 1 + 4 sec θ. 1969J. J. Stoker Differential Geom. ii. 14 Many important results in differential geometry can often be made direct and easy to achieve once a special parametric representation has been tactfully chosen.
b. Electronics. Applied to devices and processes in which amplification or frequency conversion is obtained by applying a signal to a non-linear device that is modulated by a pumping frequency, so that there is a transfer of power from the latter to the output, which in general can include the sum and difference frequencies.
So called because the action of the pumping frequency is to modulate the parameters of the non-linear device.
1957RCA Rev. XVIII. 578 (heading) Theory of parametric amplification using nonlinear reactances. Ibid. 579 In this paper the parametric amplifier is analyzed in terms of an equivalent circuit using a nonlinear inductance. 1961Guardian 14 Feb. 24/1 The so-called ‘parametric amplifiers’..can increase the sensitivity of radio reception over great distances. 1968Angelakos & Everhart Microwave Communications iv. 82 A parametric amplifier converts power at one frequency (from a source generally called the pump) into power at another frequency, the signal frequency... The pump voltage is mixed with the signal voltage by a nonlinear reactance, which in microwave systems is generally a varactor diode. 1971Physics Bull. Aug. 464/3 Parametric conversions of waves to other frequencies are familiar in the field of non⁓linear optics. 1972Sci. Amer. Sept. 136/3 In present-day satellite-communication terminals the maser amplifier has given way to the cooled parametric amplifier, which combines low-noise performance with an even wider bandwidth. 1972Zernike & Midwinter Appl. Non⁓linear Optics (1973) vii. 153 The parametric up-converter is a special case of sum-frequency generation. Similarly, the parametric amplifier and the parametric oscillator are special cases of difference-frequency generation.
Also paraˈmetrical a.
1887R. A. Roberts Integr. Calc. I. 301 These angles belong to different parametrical systems.
▪ II. parametric, a.2 Anat. and Path.|pærəˈmiːtrɪk|
[f. Gr. παρά beside + µήτρα womb, matrix + -ic: cf. mod.L. parametrium the organic tissue beside the uterus.]
Situated beside or near the uterus, or affecting the parts so situated.
1889J. M. Duncan Lect. Dis. Women viii. (ed. 4) 44 The parametric cellular tissue. Ibid. xiv. 101 The inflammatory disease is generally parametric. |