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An efficient method was developed for the synthesis of the ketoamino acid 2, a key intermediate in the synthesis of the novel sweet compound, monatin 1. Preparation of 2 entails coupling of a suitably protected indole acetate anion to an aspartic acid derivative. 相似文献
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An efficient synthesis of dicarbonyl(η5—cyclopentadienyl)iron—(II)—complexes of 2,3—dihydrofuran and 3,4—dihydro—2H—pyran from 3—bromo—2—methoxytetrahydrofuran and—pyran, respectively, is described. 相似文献
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Rate equations for the density of excited atoms in a He-Ne discharge are solved for the steady state. The atomistic parameters in the theoretical treatment are replaced by experimental values. Hence inversion density and single pass gain can be calculated as a function of gas mixture, pressure, discharge current and the geometry of the discharge tube. Conditions for maximum inversion density and single pass gain were calculated and compared with experimentally determined values. Good agreement was found for the maximum single pass gain and the related values of discharge current, gas mixture and pressure. 相似文献
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This paper reports the observation of an isostructural electronic phase transition in CeAl2 near 77 Kbar pressure at ambient temperature. The present volume compression data obtained under truly hydrostatic pressure
conditions gives a clear indication of the first order nature of this phase transformation. 相似文献
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E. Arushanov S. Levcenko G. Fuchs B. Holzapfel S.-L. Drechsler L. Schultz 《Physica C: Superconductivity and its Applications》2011,471(7-8):237-241
We show that the zero-field normal-state resistivity of temperature-dependent resistivity ρ(T) of SrFe2?xNixAs2 can be reproduced by the expression ρ(T) = ρ0 + c T exp(?2Δ/T). ρ(T) can be scaled using both this expression where the energy scale Δ, c and the residual resistivity ρ0 are scaling parameters and a recently proposed model-independent scaling method (H.G. Luo, Y.H. Su, T. Xiang, Phys. Rev. B 77 (2008) 014529). The scaling parameters have been calculated and the compositional variation of 2Δ(x) has been determined. This dependence show almost a linear decreasing in the underdoped regime similar to that reported for cuprates. The existence of a universal metallic ρ(T) curve in a wide temperature range which, however, is restricted for the underdoped compounds to temperatures above a structural and anitiferromagnetic transition is interpreted as an indication of a single mechanism which dominates the scattering of the charge carriers in SrFe2?xNixAs2 (x = 0–0.3). 相似文献