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11.
Perfluoroalkanesulfonic anhydrides (RFSO2)2O when mixed with acids decompose into perfluoroalkanesulfonic esters RFSO2ORF, thereby providing a new facile synthesis of these esters from perfluoroalkanesulfonic acids and phosphorus pentoxide. 相似文献
12.
We prove global existence and scattering for a class of quadratic Schrödinger equations in dimension 2 with small and localized data. The proof relies on the idea of space–time resonance. 相似文献
13.
Germain ObameHélène Pellissier Nicolas VanthuyneJean-Bernard Bongui Gérard Audran 《Tetrahedron letters》2011,52(10):1082-1085
The enzymatic desymmetrization of methylenecyclopropane diol or its corresponding diacetate derivative, generated from a [2+1] cycloaddition between dioxepin and methylchlorocarbene, is described. After screening five commercial lipases, the two enantiomers of acetic acid 2-hydroxymethyl-3-methylene-cyclopropylmethyl ester are obtained in high yields and excellent enantioselectivities by using PFL or LPP in organic solvent. The stereostructure of the desymmetrization products was established by X-ray analysis. We also reported a new example with this non racemic chiral building block where the sign of optical rotation is dramatically solvent dependent and inverted. Using these enantiopure building blocks, a synthesis of novel nucleoside analogs is also presented. 相似文献
14.
A simple model is presented which interprets conductivity variations due to crystallization in amorphous layers and allows the determination of the growth rate of crystallization. The validity of this model is demonstrated in the case of germanium. 相似文献
15.
N. D. Nguyen M. Germain M. Schmeits R. Evrard B. Schineller M. Heuken 《Journal of Crystal Growth》2001,230(3-4):596-601
The ac characteristics of GaN : Mg and undoped GaN layers, grown by MOVPE on sapphire substrates, are measured for a wide range of temperature and bias conditions, in order to investigate the effect of the magnesium-related level on the transport properties. Two peaks, whose height and position depend on the measurement temperature, are observed in the admittance curves (G/ω versus frequency) of the Mg-doped samples, whereas only one peak appears in undoped samples. The study of the frequency dependence of the impedance, with a model including the two metallic Au/GaN junctions, the GaN layer itself, shows that, besides the effect of the differential resistance of the layer which plays a role in both sample types, the presence of a Mg-related deep level contributes to the observed variations of the peaks in the admittance curves of the p-doped samples. Results of a theoretical steady-state and small-signal analysis based on numerical modelling of the Au/GaN/Au heterostructure complete our analysis. 相似文献
16.
L Germain R Jacques J D Cheeke 《The Journal of the Acoustical Society of America》1989,86(4):1560-1565
The use of an acoustic microscope as a method for nonlinear characterization of biological media is evaluated. The method consists of measuring the second harmonic signal generated in a sample located at the focus of the acoustic lens. Two experimental configurations were compared: The first is the simple case where the sample is a liquid mixture filling the space between the lens cavity and the receiver; in the second case, the liquid mixture is confined to a thin layer at the focal plane, in order to simulate a real tissue layer. Aqueous solutions of ethylene glycol and methanol were used as liquid samples. Simple theoretical models are presented for each configuration and the predictions show good qualitative agreement with experimental measurements. These results confirm our belief that the acoustic microscope is potentially a good tool for nonlinear B/A imaging of biological systems. 相似文献
17.
Richard Ducray Pascal Boutron Hervé Germain Maryannick Lamorlette Mickael Maudet Georges Pasquet Iain Simpson 《Tetrahedron letters》2010,51(36):4755-4701
A two-step synthesis of 3-(2-chloropyrimidin-4-yl)imidazo[1,2-a]pyridines is presented. The late stage elaboration of the imidazopyridine through a cyclocondensation allows a rapid access to a variety of substitution patterns. The intermediate enol ethers were obtained from inexpensive reagents in a ligand-free Heck coupling. This methodology has been extended to the formation of pyrazolo[1,5-a]pyridines via a formal 1,3-dipolar cycloaddition. 相似文献
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Ohne Zusammenfassung 相似文献
20.
We prove that the action of a countable discrete group on a locally compact invariant space of minimal harmonic functions is ameanable. To cite this article: P. Biane, E. Germain, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 355–358. 相似文献