| 释义 |
metastable, a.|mɛtəˈsteɪb(ə)l|
[Irreg. f. meta- + stable a., as tr. of G. metastabil (coined in sense 1 by W. Ostwald, in Lehrb. d. allgemeinen Chem. (1893) II. i. 517).]
1. Of a physical system: persisting (in its existing state) when undisturbed or subject to disturbances smaller than some small or infinitesimal amount, but passing to a more stable state when subject to greater disturbances.
1897Jrnl. Chem. Soc. LXXII. ii. 309 The author gives to the above form of instability, where the change to solid can only be caused by the presence of the solid itself, the name of ‘metastabile’ [sic]. Ibid. 777/1 (Index), Equilibrium, metastable and labile. 1899J. Walker Introd. Physical Chem. xi. 101 A supercooled liquid may be kept for a very long time without any solid appearing, but as soon as the smallest particle of the substance in the more stable solid phase is introduced, the less stable, or, as it has been called, the metastable phase is transformed into it. 1940Glasstone Text-bk. Physical Chem. vi. 459 The term metastable is used to describe a definite equilibrium, which is nevertheless not the most stable equilibrium at the given temperature; a metastable system undergoes spontaneous change on the addition of the stable phase. 1941J. H. Keenan Thermodynamics xxiii. 404 A system is in a state of metastable equilibrium if for all infinitesimal possible variations △S)E S > 0, while for some finite possible variations △S)E > 0, that is, △E)S ‹ 0. A marble at rest at the bottom of the higher of two depressions in a continuous surface is an example of metastable equilibrium. 1954Electronic Engin. XXVI. 60/1 The 11 points a, c, e,{ddd}t, u are the stable positions corresponding to the digits 0, 1, 2,{ddd}9 and the reset point [of the counting tube], whereas the 10 points b, d, f,{ddd}are metastable. Suppose the anode current is at the point corresponding to b and a small disturbance shifts the beam to the left... The beam will then move farther away..and soon reach the point corresponding to c at which it will remain despite any small disturbances. 1968C. G. Kuper Introd. Theory Superconductivity i. 11 Long-lived metastable states cannot be rejected a priori as impossible. Diamond at room temperature shows no tendency to graphitize, nor glass to crystallize. But in all cases like these the excess entropy is frozen in by the immobility of the atoms at low temperatures.
2. Physics. Of an excited state of an atom, nucleus, or other quantum-mechanical system: having an exceptionally long lifetime because the transitions to states of lower energy are forbidden transitions. [Introduced in this sense (in Ger.) by Franck & Knipping 1919, in Physik Zeitschr. XX. 485/2.]
1922A. D. Udden tr. Bohr's Theory of Spectra iii. 86 These experiments showed that the impact of electrons could bring helium into a ‘metastable’ state from which the atom cannot return to its normal state by means of a simple transition. 1942J. D. Stranathan ‘Particles’ of Mod. Physics xi. 455 It seems that certain nuclei can exist for considerable time in an excited state, known as a metastable state. 1961Powell & Crasemann Quantum Mech. xii. 458 The ground state of the orthohelium system..is therefore stable with respect to optical transitions of the usual kind, and has a correspondingly long lifetime. For this reason, it is frequently referred to as a metastable state. 1973Sci. Amer. Feb. 93/2 The singlet and triplet metastable states have long lifetimes because they have no means of radiating their energy. |