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821.
822.
R. Grac M. Pugnet J.H. Collet B. Lambert C. De Matos H. L'Haridon A. Le Corre J.O. White 《Superlattices and Microstructures》1997,22(4):505-509
We report new results on the diffraction properties of photoinduced gratings in InGaAs/InGaAsP MQW structures. The original feature of this device is that the QWs are enclosed in an asymmetric Fabry–Perot microcavity in order to increase the diffraction efficiency. We observe oscillations in the diffraction efficiency due to resonant effects in the microcavity. The experimental spectra are compared with theory. Diffraction efficiency at 1.55 μm attains a maximum value of 2.7% at a write beam fluence of 260 μ J cm−2, and then decreases at higher fluences. We explain this phenomenon by an absorption saturation at high excitation. 相似文献
823.
The Modeling of Velocity Enhancement in Polymer Flooding 总被引:1,自引:0,他引:1
In single-phase polymer flooding experiments it has repeatedly been observed that the average velocity of the polymer molecules is higher than the average velocity of the water molecules. This effect is incorporated in many conventional Enhanced Oil Recovery (EOR) simulators by the introduction of a constant velocity enhancement factor. In this paper we show that, in absence of dispersion, a constant enhancement factor in the mathematical model for two-phase polymer flow (Buckley--Leverett displacement) leads to ill-posedness of the model equations. We propose a saturation dependent enhancement factor, derived from a model based on percolation concepts, for which this problem does not occur. 相似文献
824.
In the nineteenth century, field theory brilliantly resolveda number of questions that had taxed mathematicians for centuries;for example, The circle cannot be squared by straightedge and compass, and solving polynomial equations by radicalsis not always possible. These successes have continued to beheld up as superb examples of the power of mathematical thought,and are demonstrated at an undergraduate level. The purposeof this article is to provide another such natural example whichleads to a concrete realisation of the free group on 2 generators. 相似文献
825.
V. D. Dyachenko S. G. Krivokolysko Yu. A. Sharanin V. P. Litvinov 《Chemistry of Heterocyclic Compounds》1997,33(7):793-798
Ammonium 6-amino-4-aryl-3,5-dicyano-1,4-dihydropyridine-2-thiolates were synthesized by recyclization of 4-aryl-2,6-diamino-3,5-dicyano-4H-thiopyranes in the presence of organic bases. On acidification of the products, the corresponding substituted 3,4-dihydropyridine-2(1H)-thiones were obtained which were used in the synthesis of 2-alkylthio-1,4-dihydropyridines, bis-(pyridyl-2)disulfides and thieno[2,3-b]pyridines.Deceased.T. G. Shevchenko Lugansk State Pedagogical Institute, Lugansk 348011. N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 909–914, July, 1997. 相似文献
826.
827.
828.
Let G be either a split SO(2n+2), or a split adjoint group of type En, (n=6,7,8), over a p-adic field. In this article we study correspondences arising by restricting the minimal representation of G to various dual pairs in G. 相似文献
829.
The magnetic properties of existing amorphous iron based materials, i.e., Fe--metalloid, Fe--early transition metals and Fe--rare
earth alloys, are briefly discussed for some representative alloys. The spin orientation of amorphous Fe--metalloid alloys
has been determined by the angular dependence of hyperfine interactions. It is shown that in iron--early transition metals
ferromagnetic order is not long-ranged, but determined by magnetic clusters. The magnetic hyperfine field distributions of
Fe-rich iron--early transition metals consist of a high and a low field tail. The magnetic structure has been investigated
for two representative Fe--RE (RE = Er, Ce) amorphous alloys. For the first time, the magnetic coupling phenomenon in amorphous/crystalline
multilayers has been discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
830.