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171.
172.
We consider the effects of a hierarchical, multiple layered system of fractures on the flow of a single-phase, slightly compressible fluid through a porous medium. A microscopic flow model is first defined which describes precisely the physics of the flow and the geometry of the fracture system and porous matrix, all of which depends on a positive parameter that determines the scale of the various fracture-level thicknesses. We then show by a rigorous mathematical argument that the unique solution of this microscopic problem converges as 0 to the solution of a double-porosity model of the global macroscopic flow. Our techniques make use of the concept of reiterated homogenization and essentially consist of an adaptation of the methods of extension and dilation operators to the reiterated-homogenization context. We show how the porosities and permeability tensor of the porous medium are determined in a precise way by certain physical and geometric features of the microscopic fracture domain, the microscopic matrix blocks, and the interface between them. 相似文献
173.
A short formal stereoselective synthesis of (-)-swainsonine (1) is described. Our synthesis started with the versatile building block (R)-3-benzyloxyglutarimide 5. Through controlled regioselective reduction, Ley's-sulfone chemistry (N-α-sulfonylation and ZnCl2-catalyzed N-α-amidovinylation), an RCM reaction, and an amide reduction, the synthesis of unsaturated indolizidine (8R,8aS)-3 has been achieved in five steps. The indolizidine (8R,8aS)-3 is an advanced intermediate toward the synthesis of (-)-swainsonine (1). 相似文献
174.
175.
Two methods for measuring the parallelism error of gauge blocks are discussed. The first method makes use of contact probes, sampling the gauge thickness at fixed locations; the parallelism error is given by the difference between maximum and minimum thickness over the sampled area. The second method is based on interferometry, producing the height maps of the opposing surfaces with respect to one another; the parallelism error is obtained after processing of the interferometric data. The two methods have been implemented in different laboratories, and compared by measuring five different gauge blocks. The results are reported, showing that the first method is more straightforward and simple, but requires prior calibration and provides information only on a limited number of sample points. The second method is more demanding in terms of equipment and measuring procedure, but in principle it is an absolute method, and provides information over a large number of data points. 相似文献
176.
Attahiru Sule Alfa 《Annals of Operations Research》2006,141(1):51-66
In this paper, we show that the discrete GI/G/1 system with Bernoulli retrials can be analyzed as a level-dependent QBD process with infinite blocks; these blocks are finite when both the inter-arrival and service times have finite supports.
The resulting QBD has a special structure which makes it convenient to analyze by the Matrix-analytic method (MAM). By representing both the
inter-arrival and service times using a Markov chain based approach we are able to use the tools for phase type distributions
in our model. Secondly, the resulting phase type distributions have additional structures which we exploit in the development
of the algorithmic approach. The final working model approximates the level-dependent Markov chain with a level independent
Markov chain that has a large set of boundaries. This allows us to use the modified matrix-geometric method to analyze the
problem. A key task is selecting the level at which this level independence should begin. A procedure for this selection process
is presented and then the distribution of the number of jobs in the orbit is obtained. Numerical examples are presented to
demonstrate how this method works. 相似文献
177.
178.
Michel D. Meijer Arjan W. Kleij Martin Lutz Anthony L. Spek Gerard van Koten 《Journal of organometallic chemistry》2001,640(1-2):166-169
Treatment of the diaminobenzene [C6H4{CH2NMe2}2-1,3] (NCN-H, 1) with one or two equivalents of cis-PtCl2(DMSO)2 leads to exclusive formation of the doubly cycloplatinated species [C6H4{CH2NMe2}2-1,5-{PtCl(DMSO)}2-2,4] (3), which upon addition of triphenylphosphine yields the bisphosphine adduct [C6H4{CH2NMe2}2-1,5-{PtCl(PPh3)}2-2,4] (4). The X-ray molecular structure of 4 revealed the presence of highly distorted square planar Pt(II) centers which is caused by close proximity of the two phosphine donor ligands. Complexes of type 3 can be regarded as suitable starting materials for the directional build-up of larger macromolecular structures. 相似文献
179.
Parthasarathi Majumdar 《Pramana》2000,55(4):511-527
This survey intends to cover recent approaches to black hole entropy which attempt to go beyond the standard semiclassical
perspective. Quantum corrections to the semiclassical Bekenstein-Hawking area law for black hole entropy, obtained within
the quantum geometry framework, are treated in some detail. Their ramification for the holographic entropy bound for bounded
stationary spacetimes is discussed. Four dimensional supersymmetric extremal black holes in string-based N=2 supergravity are also discussed, albeit more briefly. 相似文献
180.
《Journal of Coordination Chemistry》2012,65(7):1133-1140
A 2-D nickel(II) mixed-ligand metal–organic framework [Ni(NPTA)(4,4′-bipy)(H2O)]n (1) was synthesized by reaction of 3-nitrophthalic acid (H2NPTA) and 4,4′-bipyridine (4,4′-bipy) with Ni(II) under hydrothermal condition and characterized by elemental analysis, infrared spectroscopy, and single-crystal X-ray diffraction analysis. Compound 1 possesses a 2-D layer structure constructed from dinuclear nickel(II) building blocks in which two crystallographically equivalent Ni ions are bridged by two NPTA ligands. Furthermore, the layers are connected into 3-D supramolecular network by hydrogen bonds. The magnetism and antibacterial activity of 1 were investigated. 相似文献