| 释义 |
ultra-ˈshort, a.
Also ultrashort.
[ultra- 3.]
a. Radio. Applied to radio waves significantly shorter than the usual ‘short waves’: in mod. use, shorter than 10 metres, corresponding to a frequency greater than 30 MHz (i.e. in the VHF range).
1926E. V. Appleton in Proc. Cambridge Philos. Soc. XXIII. 155 (heading) On the diurnal variation of ultra⁓short wave wireless transmission. [Note] The term ‘ultra⁓short’ is here applied to wave-lengths less than the critical band indicated by the magneto-ionic theory (i.e. about 200 meters). It seems desirable, for historical reasons, to retain the term ‘short waves’ for the broadcasting wave-lengths 200–600 metres. 1935Discovery Sept. 278/1 A difficulty is..the limited range of these ultra-short wave⁓lengths, as we are dependent upon the direct waves propagated more or less parallel to the earth's surface. 1947Nature 4 Jan. 16/1 The electrical interference from motor⁓car ignition systems..is a serious factor in the reception of ultra-short waves. 1974Radio Engin. & Electronic Physics Dec. 20 (heading) Multiple diffractor amplification of ultrashort waves.
b. gen. Extremely short (in length or duration).
1962R. H. Smythe Anat. Dog Breeding 29 An ultra⁓short loin. 1975Bio Systems VII. 45 Accordingly, we may introduce an ultrashort time scale. 1977Jrnl. R. Soc. Arts CXXV. 766/1 The same lasers can be used to generate ultra-short light pulses. |