| 释义 |
orientable, a.|ˈɔərɪəntəb(ə)l|
[f. orient v. + -able.]
Capable of being oriented; in Math. [tr. G. orientierbar], applied to a surface for which it is possible, if each point is regarded as surrounded by a small closed curve, to assign a sense (clockwise or anticlockwise) to each curve so that they are the same for all points sufficiently close together; not non-orientable; also used analogously of spaces of higher dimension.
1935A. P. Herbert What a Word! iii. 85 One of our great motor-manufacturers advertises ‘A very neat orientable anti-glare visor.’ 1949S. Lefschetz Introd. Topology ii. 82 Two orientable connected closed surfaces are homeomorphic if they have the same genus. 1952P. Nemenyi tr. Hilbert & Cohn-Vossen's Geom. & Imagination vi. 306 It can be demonstrated that all two-sided surfaces are orientable. 1960L. Picken Organization of Cells vii. 265 Cleveland's material suggests only that in hypermastigine flagellates the centrioles utilize all orientable material. 1965tr. Lietzmann's Visual Topology 120 A one-sided surface is not orientable. 1968A. H. Wallace Differential Topology vi. 79 The sphere is orientable but the projective plane is not. 1975W. M. Boothby Introd. Differentiable Manifolds v. 215 A manifold M is orientable if and only if it has a covering..of coherently oriented coordinate neighborhoods.
Hence ˌorientaˈbility, the property of being orientable.
1949S. Lefschetz Introd. Topology ii. 76 Orientability implies that the triangles of K may be ‘oriented’ (in an intuitive sense) so that adjacent triangles always have their orientations disposed as in Fig. 37. 1956E. M. Patterson Topology i. 9 The idea of orientability is derived from the physical idea of two-sidedness. 1972Nature 13 Oct. 387/1 Within general relativity it is necessary to impose time orientability on the E4 manifold such that the arrows placed on timelike world lines agree in sign. |