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151.
Horowitz HS McLain SJ Sleight AW Druliner JD Gai PL Vankavelaar MJ Wagner JL Biggs BD Poon SJ 《Science (New York, N.Y.)》1989,243(4887):66-69
Evidence suggests that superconducting, orthorhombic YBa(2)Cu(3)O(6+x)+ (x greater, similar 0.5) is always produced by oxidation of the oxygen-deficient, tetragonal form (x less, similar 0.5) of this phase (commonly referred to as 123). A synthetic route whereby solution-derived, carbon-free precursors are decomposed at 650 degrees to 700 degrees C in inert atmosphere to yield tetragonal 123 is now available. Appropriate precursors include hydrated oxides derived from the hydrolysis of organometallic solutions and aqueous solution-derived hyponitrites. Subsequent oxidation of the tetragonal phase at 400 degrees C results in submicrometer particles of orthorhombic 123. Superconductivity (T(c) onset approximately 87 K) has been confirmed in these materials by both Meissner effect and specific-heat measurements. 相似文献
152.
By utilizing the vapor pressure difference between high-salinity and lowsalinity wvater, one can obtain power from the gradients of salinity. This scheme eliminates the major problems associated with conversion methods in which membranes are used. The method we tested gave higher conversion efficiencies than membrane methods. Furthermore, hardware and techniques being developed for ocean thermal energy conversion may be applied to this approach to salinity gradient energy conversion. 相似文献
153.
McLeod JD 《Science (New York, N.Y.)》1978,200(4343):771-773
An abundant, previously problematic fossil from the Lower Ordovician (Canadian) Black Rock limestone of the Ozark Uplift area is an undescribed dianulitid bryozoan. It is believed to be the oldest unquestionable bryozoan known. The growth morphology varies widely and is believed to be environmentally influenced. 相似文献
154.
Pressure of 40,000 atmospheres at 25 degrees C induces a phase transformation in ytterbium metal; the face-centered cubic structure changes to body-centered cubic. The radius of the atom changes from 1.82 to 1.75 A. At the same time the atom's volume decreases by 11 percent and the volume, observed macroscopically, decreases 3.2 percent. 相似文献
155.
156.
Simultaneous x-ray diffraction and electrical resistance measurements on barium establish, with certainty, that Bridgman's 78-kb resistance transition is identical with his 59-kb volumetransition. During this transition, the bodycentered cubic structure changes to hexagonalclose packed. Lattice parameters for the latter structure at 62 kb (volume scale) are: a = 3.90 A, c = 6.15 A, and c/a = 1.58. Compression (AV/Vo) at 62 kb is 0.359 + 0.005 compared to 0.345 previously reported by Bridgman. Below the transition, at 49 kb, compression is 0.300 +/- 0.005 compared to Bridgman's 0.288. Bridgman's 17-kb volume transition was not detected by x-ray diffraction. 相似文献
157.
Significantly improved values of the zonal gravity harmonic coefficients J(39) J(4), and J(6) of Jupiter have been obtained from a preliminary analysis of Pioneer 11 spacecraft Doppler data taken while the spacecraft was near Jupiter. The new results, which will have an important application as boundary conditions for theoretical models of Jupiter's interior. are consistent with a planet in hydrostatic equilibrium. 相似文献
158.
The scent-gland secretion of the rice stink bug Oebalus pugnax (F.) is composed of a liquid two-phase system. The saturated hydrocarbon n-tridecane accounts for 60 percent of the secretion. In the other phase, the major organoleptic compound is the trans form of 2-heptenal. 相似文献
159.
160.
Sonnenburg JL Xu J Leip DD Chen CH Westover BP Weatherford J Buhler JD Gordon JI 《Science (New York, N.Y.)》2005,307(5717):1955-1959