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941.
A facile and efficient nucleophilic difluoromethylation of primary alkyl halides has been disclosed through a novel nucleophilic substitution-reductive desulfonylation strategy, using difluoromethyl phenyl sulfone as a difluoromethyl anion ("CF(2)H(-)") equivalent. 相似文献
942.
N-(phenylthio)-epsilon-caprolactam (1) has been applied as a new promoter for the activation of thioglycosides. This proceeds by the reaction of 1 with trifluoromethansulfonic anhydride, which subsequently activates the thioglycoside for glycosidic bond formation. Notably, the reaction proceeds efficiently at room temperature and is adaptable to our reactivity-based one-pot oligosaccharide synthesis. [reaction: see text] 相似文献
943.
[structure: see text] A lanthanide luminescent probe that was functionalized with quinoline-alkylated diaza-18-crown-6 showed dual-component recognition of concentrations of H+ and K+ at four independent pH ranges, including in the physiological pH window. Moreover, it exhibited pH- and [K+]-independent long-lived lanthanide luminescent lifetimes in aqueous solution. 相似文献
944.
A new methodology for the synthesis of heparin building blocks has been developed. We describe novel efficient routes to both L-iduronic acid and D-glucuronic acid acceptors. Glycosylation with thioglycosides donors gave corresponding disaccharides in a regio- and stereoselective fashion. An improved approach to synthesizing azido-glucose thioglycoside donor to render azido-sugar from mannose via nucleophilic substitution is described. [reaction: see text] 相似文献
945.
946.
Let X be a locally compact Hausdorff space and C
0(X) the Banach space of continuous functions on X vanishing at infinity. In this paper, we shall study unbounded disjointness preserving linear functionals on C
0(X). They arise from prime ideals of C
0(X), and we translate it into the cozero set ideal setting. In particular, every unbounded disjointness preserving linear functional of c
0 can be constructed explicitly through an ultrafilter on complementary to a cozero set ideal. This ultrafilter method can be extended to produce many, but in general not all, such functionals on C
0(X) for arbitrary X. We also make some remarks where C
0(X) is replaced by a non-commutative C*-algebra. 相似文献
947.
IP Wai-Cheung WONG Heung XIE Zhongjie & LUAN YihuiDepartment of Applied Mathematics Hong Kong Polytechnic University Hong Kong China Department of Probability Statistics Peking University Beijing China 《中国科学A辑(英文版)》2004,47(1):52-64
The main purpose of this paper is to investigate the detection of jump points of a discontinuous function in the presence of a noise by the wavelet approach. A computing algorithm of our method is proposed and then applied to the daily exchange rate of US Dollar against Deutsche Mark. All the points detected by our method reflect very strong economic and political impacts. Other statistical methods to detect jump points have also been applied to the same exchange rate data. Our proposed method has produced more convincing empirical results than others. 相似文献
948.
We consider the following system of discrete equations
. Criteria for the existence of three constant-sign solutions of the system will be developed. To illustrate the generality of the results obtained, we include applications to several well-known boundary value problems. Parallel results are also established for a system on {0,1,...}
. 相似文献
949.
Mukherjee M Kellerbauer A Beck D Blaum K Bollen G Carrel F Delahaye P Dilling J George S Guénaut C Herfurth F Herlert A Kluge HJ Köster U Lunney D Schwarz S Schweikhard L Yazidjian C 《Physical review letters》2004,93(15):150801
Mass measurements with a relative precision of better than 1.5 x 10(-8) were performed on 22Mg and its reaction partners 21Na and 22Na with the ISOLTRAP Penning trap mass spectrometer at CERN, yielding the mass excesses D(22Mg)=-399.92(27) keV, D(21Na)=-2184.71(21) keV, and D(22Na)=-5181.56(16) keV. The importance of these results is twofold. First, a comparative half-life (Ft value) has been obtained for the superallowed beta decay of 22Mg to further test the conserved-vector-current hypothesis. Second, the resonance energy for the 21Na proton capture reaction has been independently determined, allowing direct comparisons of observable gamma radiation in nova explosions with the yield expected from models. 相似文献
950.
The total cross sections of the helium dimer, trimer, and tetramer for scattering from Kr atoms have been measured for cluster beam velocities between 250 and 820 m/s. The dimer cross section is twice that of the atom within 5% indicating that the Kr atoms scatter from the He atoms independently, which is consistent with the large dimer bond distance of about 50 A. The trimer and tetramer cross sections are somewhat larger and can be described by an impulse approximation with a multiple "eclipse" correction, extending ideas of Glauber for high energy collisions with the deuteron. 相似文献