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141.
142.
Dalençon S Youcef RA Pipelier M Maisonneuve V Dubreuil D Huet F Legoupy S 《The Journal of organic chemistry》2011,76(19):8059-8063
The asymmetric synthesis of novel cyclohexene nucleoside analogues 12 and 15 is described. An enantiospecific Diels-Alder reaction between (E,E)-diene 2 and (+)-5-(d-mentyloxy)-2(5H)-furanone 3 provided the cycloadduct isomer 4. Three additional steps yielded amine 8 allowing the constructions of the thymine and adenine moieties to afford intermediates 11 and 14, respectively. Amination or cyclization and removal of the protecting groups occurred in one step in the presence of ammonia, giving the target six-membered ring nucleosides. 相似文献
143.
Muriel Behra Stephan Schmidt Jürgen Hartmann Dmitry V. Volodkin Laura Hartmann 《Macromolecular rapid communications》2012,33(12):1049-1054
Porous poly(ethylene glycol) (PEG) microgels of both 17.6 and 8.3 μm in diameter are synthesized via hard templating with calcium carbonate (CaCO3) microparticles. The synthesis is performed in three steps: loading of PEG macromonomers into CaCO3 microparticles, crosslinking via photopolymerization, and removal of the CaCO3 template under acidic conditions. The resulting porous PEG microgels are inverse replicates of their templates as indicated by light microscopy, cryo‐scanning electron microscopy (cryo‐SEM), and permeability studies. Thus this process allows for the straightforward and highly reproducible synthesis of porous hydrogel particles of two different diameters and porosities that show great potential as carriers for drugs or nanomaterials. 相似文献
144.
A. Muriel 《Physics letters. A》2013,377(16-17):1161-1165
From a time evolution equation for the single particle distribution function derived from the N-particle distribution function (A. Muriel, M. Dresden, Physica D 101 (1997) 297), an exact solution for the 3D Navier–Stokes equation – an old problem – has been found (A. Muriel, Results Phys. 1 (2011) 2). In this Letter, a second exact conclusion from the above-mentioned work is presented. We analyze the time symmetry properties of a formal, exact solution for the single-particle distribution function contracted from the many-body Liouville equation. This analysis must be done because group theoretic results on time reversal symmetry of the full Liouville equation (E.C.G. Sudarshan, N. Mukunda, Classical Mechanics: A Modern Perspective, Wiley, 1974). no longer applies automatically to the single particle distribution function contracted from the formal solution of the N-body Liouville equation. We find the following result: if the initial momentum distribution is even in the momentum, the single particle distribution is reversible. If there is any asymmetry in the initial momentum distribution, no matter how small, the system is irreversible. 相似文献
145.
We experimentally demonstrate that imaging of the degree of polarization (DOP) can be achieved from a single intensity image acquired under coherent illumination. This computational technique is based on the analysis of the speckle characteristics in a statistically homogeneous neighborhood of the pixel. Over a variety of samples obtained experimentally, we show that a simple calibration step allows this method to quickly and simply provide correct estimated values of the DOP, with precision in agreement with theoretical predictions. It is shown that unlike linear polarimetric contrast imaging, this method remains valid on birefringent samples. 相似文献
146.
147.
Is the critical Reynolds number universal? 总被引:2,自引:0,他引:2
This paper is devoted to checking whether the critical Reynolds number is universal in identical conditions for the flow of different fluids. The laminar-turbulent transition in a circular pipe flow has been tested experimentally. The flows of inert gases (He, Ne, Ar, Kr, Xe), molecular gases (N2, CO, CO2, SF6), and two similar liquids (H2O, D2O) have been tested. A considerable, up to 40%, difference in critical Reynolds numbers was observed. The possible reasons for nonuniversality of the critical Reynolds number are discussed. 相似文献
148.
Jos a Capmany Jos a Enriquez Miguel A. Muriel David Selviah John E. Midwinter 《Fiber and Integrated Optics》1992,11(1):1-24
This article presents a simulation technique for the analysis of all-optical coherent code division multiple-access asynchronous networks, Graphical results are given showing the signal evolution at different parts of the network, and the various sources of noise that degrade the overall performance are pointed out, including the influence of fiber dispersion, laser biasing, and chirp. 相似文献
149.
Methoxycarbonyl groups in racemic biphenyls show separation of the methyl proton magnetic resonance signals in the presence of large amounts of chiral shift reagents. 相似文献
150.