| 释义 |
▪ I. † paraˈcentric, a.1 Kinetics. Obs.
[See para-1 and centric.]
In paracentric motion, rendering motus paracentricus of Leibnitz, used by him to express that motion which, compounded with harmonic circulation, he supposed to make up the actual motion of a planet. Sometimes misunderstood by other writers, and applied to simple motion about a centre.
[1689Leibnitz Tentamen de mot. cælest. causis, Opera 1768, III. 216 Motu duplici, composito ex circulatione harmonica..et motu paracentrico. 1702Gregory Astron. phys. elementa i. lxxvii. 100.] 1704C. Hayes Fluxions 293 Paracentric motion of Impetus is so much as the revolving Body approaches nearer to or recedes farther from the Center of Attraction. 1715tr. Gregory's Astron. i. lxxvii. 175 The other Motion (namely the Paracentric) arises from a double curve, namely the excussory impression of Circulation and the Sun's attraction compounded together. 1797Monthly Mag. III. 128 If a slender rod AC revolve round the point C, as a centre,..the centrifugal force arising from the paracentric velocity of the rod [etc.].
So paraˈcentrical a. ? Obs. = prec.
1718G. Cheyne Philos. Princ. Relig. 32 The Paracentrical Motion is compounded of two others, viz...[that] whereby all Bodies moving in a Curve, endeavour to recede from the Center by the Tangent, and the Attraction of the Sun or the Gravitation of the Planet toward it.
▪ II. paracentric, a.2 Cytology.|pærəˈsɛntrɪk|
[f. para-1: cf. -centric 2.]
Involving only the part of a chromosome at one side of the centromere. Opp. pericentric a. 2.
1938H. J. Muller in Collecting Net XIII. 187/2 If the breaks were to one side of the centromere, the inversion may be termed ‘paracentric’, and it will be noted that the proportions of the two arms, and hence the general shape of the chromosome as seen at mitosis, is not changed. But if the breaks included the centromere between them, being ‘pericentric’, the mitotic chromosome will have the relative sizes of its two arms altered, except in the special case in which the two distal sections are sensibly equal in size. 1957C. P. Swanson Cytol. & Cytogenetics xv. 485 Paracentric inversions are by far the most common type of aberration found in natural populations. 1975Nature 3 July 40/1 Heterozygosity for a paracentric inversion, that is, a structural rearrangement in which a chromosome segment that does not include the centromere is rotated through 180°, results in suppression of recombination in the inversion region. |