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41.
In this Letter, the dynamic plane elasticity problems of 2D quasicrystals is considered. By use of the Fourier transform and matrix transformations the system is reduced to uncoupled ordinary differential equations. Fourier images of Green's functions for dynamic plane elasticity problems of 2D dodecagonal, pentagonal and decagonal quasicrystals are obtained explicitly by the suggested method. 相似文献
42.
Huali Yu Zhengbiao Zhang Zhenping Cheng Jian Zhu Nianchen Zhou Wei Zhang Xiulin Zhu 《Journal of polymer science. Part A, Polymer chemistry》2012,50(11):2182-2187
In this work, zero‐valent iron (Fe(0)) (powder or wire) and elemental bromine (Br2) were used as the catalysts for atom transfer radical polymerization (ATRP) of styrene (St) without any additional initiator at 110 °C. The polymerizations happened with controlled evidence at appropriate molar ratio of Fe(0) to Br2: a remarkable increase of molecular weights with St conversions, the narrow molecular weight distributions and living polymer chains end‐capped by Br. More Br2 or less Fe(0) led to a slow polymerization rate but an improved control over molecular weights. After examining the polymer chain ends by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, it was concluded that the polymerization was initiated by thermal self‐initiation, and regulated by the in situ generated FeIIIBr3. The results suggested that the Fe(0)/Br2 catalyzing polymerization was a classical ATRP process with easier operation and more economical components. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
43.
Uma Maheswara Rao Kunda 《Phosphorus, sulfur, and silicon and the related elements》2017,192(3):276-282
The dimeric assembly of 5,11,17,23-tetrabromo-25,26,27,28-tetrahydroxy thiacalix[4]arene (2) was constructed with several interesting noncovalent interactions such as halogen bonding, sulfur···sulfur (S···S), C=O···π, and hydrogen bonding which were also supported by DFT calculations. In addition, we studied the conformational preferences of 2 using variable temperature NMR experiments. The results revealed that the compound exists in various conformations in a solution state and in a partial cone conformation in a solid state. 相似文献
44.
An VK-Z-Rohren zur Herstellung von Polyamid wurden Verweilzeitspektren mit der Methode der radioaktiven Markierung und der Methode der Indikatoraktivierungsanalyse gemessen. Die nach den beiden Methoden ermittelten Verweilzeitspektren werden miteinander verglichen. Die Übereinstimmung der Verweilzeitspektren wird durch Gegenüberstellung der statistischen Momente und durch einen Test nach Kolmogoroff-Smirnov geprüft. Es wird der experimentelle Aufwand beider Verfahren diskutiert und eine Fehlerabschätzung durchgeführt. 相似文献
45.
D. Chattopadhyay 《Applied Physics A: Materials Science & Processing》1991,53(1):35-42
Transport properties of the electrons itinerant two dimensionality in a square quantum well of In0.53Ga0.47As are studied in the framework of Fermi-Dirac statistics including the relevant scattering mechanisms. An iterative solution of the Boltzmann equation shows that the ohmic mobility is controlled by LO phonon scattering at room temperature, but below 130 K alloy scattering is predominant. The calculated mobilities with a suitable value of the alloy scattering potential agree with the experimental results over a range of lattice temperature. For lattice temperatures below 25 K where the carrier energy loss is governed by the deformation potential acoustic scattering, the warm electron coefficient is found to be negative. Its magnitude decreases with increasing lattice temperature and is greater for larger channel widths. Values of the small-signal AC mobility of hot electrons at a lattice temperature of 4.2 K are obtained for different sheet carrier densities and channel widths. Cut-off frequencies around 100 GHz are indicated.Dedicated to H.-J. Queisser on the occasion of his 60th birthday 相似文献
46.
Formation of Compounds in the Quasi-binary Systems AcX4? MX2 (Ac = Th, U; M = Ca, Sr, Ba, Eu, Ge, Sn, Pb; X = Br, I) T,x-phase diagrams of the systems ThI4? SnI2, ThI4? PbI2, ThI4? CaI2, and ThI4? SrI2 were established using thermoanalysis and x-ray methods. The only ternary compounds have a 1:1 composition. Further AcMX6 compounds (Ac: Th, U; M: Ca, Sr, Ba, Eu, Ge, Sn, Pb; X: Br, I) were synthesized and their structures investigated. Four structure types are found depending on the temperature and the Ac/M combinations. The structures of γ-ThSnI6 and β-ThSnI6 were determined with single crystal methods as representatives of a whole series of isotypic compounds. 相似文献
47.
Comparative study of spectroscopic properties of Er^3+/Yb^3+-codoped tellurite glass and fibres under 980nm excitation*
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A tellurite fibre of TeO_{2}-ZnO-La_{2}O_{3}-Li_{2}O glass codoped with 20000 ppm ytterbium and 5000 ppm erbium was fabricated by the suction casting and rod-in-tube technologies. The absorption spectrum of Er^{3+}/Yb^{3+} -codoped bulk glass has been measured. From the Judd-Ofelt intensity parameters, the spontaneous emission probability and radiative lifetime τ_{rad} of Er^{3+}:{}^{4}I_{13/2}→{}^{4}I_{15/2} transition for the bulk glass have been calculated. The emission fluorescence spectra and lifetimes around 1.5μm, and subsequent upconversion fluorescence in the range of 500-700nm were measured in fibres and compared with those in bulk glass. The changes in amplified spontaneous emission with fibre length and pumping power was also measured. It was found that the emission spectrum from erbium in fibres is almost twice as broad as the corresponding spectrum in bulk glass when pumped at 980nm. 相似文献
48.
本文主要研究了3-溴-N-乙基吩噻嗪(Br-P)在各种酸度、增敏溶剂、感光效应等条件下的荧光变换现象,并确定了最佳的发光体系。方法简单、准确可靠,其线性范围为1×10 相似文献
49.
Gerardo G. Naumis A. Bazán M. Torres R. Quintero-Torres 《Physica B: Condensed Matter》2008,403(18):3179-3184
One of the few examples in which the physical properties of an incommensurable system reflect an underlying higher dimensionality is presented. Specifically, we show that the reflectivity distribution of an incommensurable one-dimensional cavity is given by the density of states of a tight-binding Hamiltonian in a two-dimensional triangular lattice. Such effect is due to an independent phase decoupling of the scattered waves, produced by the incommensurable nature of the system, which mimics a random noise generator. This principle can be applied to design a cavity that avoids resonant reflections for almost any incident wave. An optical analogy, by using three mirrors with incommensurable distances between them, is also presented. Such array produces a countable infinite fractal set of reflections, a phenomena which is opposite to the effect of optical invisibility. 相似文献
50.
Linear alkylbenzene sulfonic acid, the largest-volume synthetic surfactant, in addition to its excellent performance, is important
due to its biodegradable environmental friendliness, as it has a straight chain and is prepared by the sulphonation of linear
alkylbenzenes (LAB). To ensure environmental protection, the commercial benzene alkylation catalysts HF or AlCl3 are replaced and we have developed a clean LAB production process using a pillared clay catalyst capable of not only replacing
the conventional homogeneous catalysts, but also having high selectivity for the best biodegradable 2-phenyl LAB isomer. Pillared
clay catalysts having high Br?nsted acidity show efficient conversion in gas phase alkylation of benzene with 1-octene with
a good 2-phenyl octane selectivity. 相似文献