| 单词 | angstrom unit |
| 释义 | > as lemmasangstrom unit A unit of length equal to one hundred-millionth of a centimetre (10−8 cm), used mainly to express wavelengths of electromagnetic radiation and dimensions on an atomic or molecular scale. Also (and in earliest use) angstrom unit. Symbol Å, ÅU (also AU).The International Ångström (I.Å.) was defined in 1907 in terms of the wavelength of a red line in the emission spectrum of cadmium which in standard conditions is 6438·4696 I.Å. When the metre was defined in terms of the wavelength of a line in the spectrum of krypton in 1960 the angstrom became exactly equal to 10−10 m (0.1 nanometres). ΘΚΠ the world > relative properties > measurement > measurement of length > [noun] > the measure of length > specific London measure1647 quincupedal1656 sextula1656 Paris point1781 rack1831 angstrom1881 submicron1927 the world > matter > physics > atomic physics > decomposition of light, spectrum > study of spectra > [noun] > measurements angstrom unit1881 Fresnel1939 1877 Amer. Jrnl. Sci. 114 141 Vogel using Zöllner's reversion spectroscope obtained a displacement of from .08 to 0.15 of one of Angström's units.] 1881 Amer. Jrnl. Sci. 122 137 The middle band..showed three fine, bright lines upon it, one just at the lower edge of the band, and the other two at distances of about 30 Ångstrom units. 1906 Trans. Internat. Union Solar Res. 1 viii. 230 The wave-length of a suitable spectroscopic line shall be taken as the primary standard of wave-length. The number which defines the wave-length of this line shall be fixed permanently and thereby define the unit in which all wave-lengths are to be measured. This unit shall differ as little as possible from 10−10 metres and be called the Ångström. 1925 Chambers's Jrnl. July 421/1 The ångström is so small that ten thousand million of them are needed to make one metre. 1951 Engineering 18 May 589/1 Dr. J. S. Courtney-Pratt has used interferometric methods to study the uniformity and thickness of thin films... He was able to measure the thickness correct to the nearest Ångstrom. 1981 Sci. Amer. Dec. 44/2 The enclosed particles, which are about 500 angstrom units across, are referred to as magnetosomes. 2001 B. Ehrenreich Nickel & Dimed (2002) iii. 147 On the drive home along the interstate, a guy doing over eighty passes me on the right at a few angstroms' distance. 2015 Proc. National Acad. Sci. U.S.A. 112 13147 (caption) Distances are shown in units of angstroms (Å). < as lemmas |
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