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排序方式: 共有113条查询结果,搜索用时 15 毫秒
31.
The synthesis of tBU2MeCCOOH, which is among the most sterically hindered known acjds is described. Only Newman's sequence via tBU2CO, tBu2MeCOH, tBu2CCH2, tBu2CHCH2OH, tBu2CHCOOH, tBU2CHCOCI and tBu2CCO, which has been optimized in this work by a direct access to tBu2CHCOOH, permits the preparation of tBu2MeCCOOH. The condensation of the corresponding chloride with a Grignard reagent yields new highly-hindered ketones tBu2MeCCOR which by alkylation give more substituted structures. The limitations of each method have been studied in this work. 相似文献
32.
Alexander Lion Nico Diercks Julien Caillard 《International Journal of Solids and Structures》2013,50(14-15):2518-2526
In order to represent process-induced anisotropies in continuum mechanics or to transfer one-dimensional material models to three spatial dimensions the directional approach is a helpful technique. Since the essential equations are defined in the orientation space it is also denoted as microsphere approach. In the current article, the relation for the directional stress tensor of the second Piola–Kirchhoff type is motivated using the volumetric/isochoric split of the deformation gradient and the Clausius–Duhem inequality. Owing to inherent nonlinearities, numerical discretisation techniques are usually applied to calculate the total stress by averaging the directional stress tensors over the unit sphere. In order to investigate the accuracy of such simulations, the availability of exact solutions in closed form is essential. To this end, the tension/compression behaviour which belongs to a certain direction in the orientation space is modelled by an elasticity relation of the Mooney Rivlin type. The exact solutions are calculated, visualized and discussed for uniaxial tension and compression as well as for equibiaxial tension. 相似文献
33.
A measuring system for the determination of the intrinsic permeability of highly porous materials is presented. The evaluation of the measurements is conducted on the basis of the Theory of Porous Media (TPM). By adjusting the calculation to the measurement results achieved with polyethylenglycol (PEG) 300 and open-cell aluminium foam, the intrinsic permeability of the metal foam is determined. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
34.
35.
Chip electrospray mass spectrometry for carbohydrate analysis 总被引:1,自引:0,他引:1
Zamfir AD Bindila L Lion N Allen M Girault HH Peter-Katalinić J 《Electrophoresis》2005,26(19):3650-3673
Currently two types of chip systems are used in conjunction with MS: out-of-plane devices, where hundreds of nozzles, nanospray emitters are integrated onto a single silicon substrate from which electrospray is established perpendicular to the substrate, and planar microchips, embedding a microchannel at the end of which electrospray is generated in-plane, on the edge of the microchip. In the last two years, carbohydrate research greatly benefited from the introduction and implementation of the chip-based MS. In two laboratories the advantages of the chip electrospray in terms of ionization efficiency, sensitivity, reproducibility, quality of data in combination with high mass accuracy, and resolution of detection were systematically explored for several carbohydrate classes: O- and N-glycopeptides, oligosaccharides, gangliosides and glycoprotein-derived O- and N-glycans, and glycopeptides. The current state-of-the-art in interfacing the chip electrospray devices to high-performance MS for carbohydrate analysis, and the particular requirements for method optimization in both positive and negative ion modes are reviewed here. The recent applications of these miniaturized devices and their general potential for glycomic-based surveys are highlighted. 相似文献
36.
Mounir Maafi Jean-Jacques Aaron Claude Lion 《Journal of inclusion phenomena and macrocyclic chemistry》1998,30(3):227-241
The valence photoisomerization of four aromatic norbornadiene (NBD)derivatives has been studied in ethanol and in 0.01 M -cyclodextrin(-CD) water–ethanol (v/v, 99/1) solution (WECD). Observedfirst-order rate constants are found to be of the same order of magnitude inethanol and WECD, ranging between 0.1 and 0.28 s-1, accordingto the compound. These photoisomerization kinetic properties are attributedto the formation of inclusion complexes between NBDs and -CD. Thestoichiometry is 1 : 1, and association constants ranging between 310 and390 M-1 have been determined fluorimetrically, usingBenesi–Hildebrand plots and a nonlinear regression method. Thestructure of the inclusion complexes is discussed on the basis of AMIsemiempirical dimension calculations and photophysical properties. 相似文献
37.
Abstract— The photolysis (Δ < 220 nm) of thymidine-5'-monophosphate was studied by electron-spin resonance (ESR) in acidic and alkaline phases. In both cases, the H–addition radical at the C6 position is detected at 77°K. At 225°K, a triplet 1:2:1 is observed, which suggests a H abstraction radical from the CH3 group. When oxygen is present during irradiation, a peroxide–type radical is observed, which results partly from a reaction like R + O2 → ROO and partly from an energy transfer from thymidine-5'-monophosphate to oxygen, probably in the 1 π0 state. 相似文献
38.
Un critère de Darboux d'existence d'intégrale première pour les 1-formes différentielles analytiques
Jean-Marie Lion 《Bulletin of the Brazilian Mathematical Society》2000,31(2):145-153
Resumé On considère une 1-forme analytique définie sur un ouvert borné de
n
et qui s'étend au voisinage de l'adhérence de cet ouvert. On montre que si elle possède une infinité de feuilles contenues dans des hypersurfaces algébriques différentes et de degrés bornés alors elle admet une intégrale première méromorphe. Si de plus l'origine est dans l'adhérence de chacune de ces feuilles alors la 1-forme admet une intégrale première méromorphe de graphe algébrique. Des exemples illustrent l'optimalité de ces résultats.
Consider a germ of analytic differential one form and suppose there exists infinitely separatrix in algebraic surfaces of bounded degree. The conclusion is that there exists an algebraic first integral. We give a list of examples wich explain the necessity of the hypotheses.
Financements: CNRS et réseau européen TMR Sing. Eq. Diff. et Feuilletages 相似文献
39.
α,α-Disubstituted ketones result from the reaction of organolithium compounds with substituted 4,4-dimethyl-2-oxazolines, 4, after hydrolysis of the intermediate enamine. Alkylation of the latter also permits the synthesis of α,α,α-trisubstituted ketones. α,α-Disubstituted ketones have been prepared by addition of organometallic reagents to 4,4-dimethyl-2-oxazolinium salts, 6. The efficiency of this method has been compared to that of other currently used methods. 相似文献
40.
Like many other materials used in mechanical and civil engineering, wood shows a pronounced history-dependent mechanical material behaviour. Due to its anisotropy its rheological behaviour is strongly dependent on the direction. In this research project, the material behaviour is represented with a phenomenological theory of anisotropic fractional viscoelasticity. In order to identify the material functions and parameters, the time-dependent creep compliances are measured in three orthogonal directions under tension and shear. As a result of the developed constitutive approach, the experimentally observed creep data is described by several power functions. In the second part of the presentation, some differences between classical models of viscoelasticity which are based on Kelvin-Voigt or Maxwell elements and the fractional approach are presented. The assets and drawbacks with respect to wood are discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献