| 释义 |
commutator|ˈkɒmjuːteɪtə(r)|
[Agent-n. from L. commūtāre.]
1. a. He who or that which commutes or exchanges. spec. A contrivance in an electric machine or telegraph instrument for altering the direction or course of the electric current.
1839Grove Contrib. Sc. in Corr. Phys. Forces 253 A commutator might be easily arranged..for effecting the alternation. 1881Q. Rev. 446 The commutator..used in all direct current machines..was invented in Italy in 1860.
b. Electr. An attachment, usually consisting of a ring of copper segments separated by insulating strips, connected with the armature of a dynamo, which, by revolving in contact with the brushes, directs and makes continuous the current produced in the armature coils of the machine. Also attrib.
1880J. W. Urquhart Electr. Lt. 58 He placed the magnet vertically and revolved the coils about a horizontal axis, and added a commutator to make the currents flow in one direction. 1884[see aperiodic a.] 1884S. P. Thompson Dyn.-Electr. Mach. 133 The only other dynamo in which a commutator at all resembling that of the Brush machine is used is Newton's dynamo. 1896Ibid. (ed. 5) 395 One of these commutator coils. 1909Installation News III. 62/1 High speed tends to undue friction and wear of the commutator surface. 1916Standardization Rules Amer. Inst. Electr. Engin. 47 Brush friction of commutator and collector rings. 1959Which? Aug. 86/2 Eleven machines had induction motors... The remaining 15 machines had commutator motors.
2. Algebra.
a. Of the elements a, b of a group, the quantity a–1 b–1 ab. Also attrib.
1908H. Hilton Introd. Theory Groups i. 4 The commutator of a and b. 1964W. R. Scott Group Theory iii. 58 [H, K] will denote the subgroup generated by the set of all commutators [h, k] with h {elem} H and k {elem} K... The commutator subgroup..of G is the subgroup [G, G].
b. Of the matrices or operators A, B, the quantity AB—BA. Also attrib.
1935Condon & Shortley Theory of Atomic Spectra ii. 25 We shall use the notation [A, B] for the simple commutator A B—B A. 1939V. Rojansky Introd. Quantum Mech. ix. 326 The matrix αβ—αβ is the commutator of α and β. 1965Biedenharn & Van Dam Quantum Theory of Angular Momentum 8 By commutator algebra..they derived all the matrix elements for..the complete Racah co-efficient. |