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951.
V. B. Nazarov V. G. Avakyan T. G. Vershinnikova M. V. Alfimov 《Russian Chemical Bulletin》2000,49(10):1699-1706
Fluorescence of the inclusion complexes with different compositions formed by naphthalene-h8, naphthalene-d8, 2,7-dimethylnaphthalene (DMN), and 2-benzylnaphthalene (BN) with β-cyclodextrin (β-CD) in water was studied. Two types of fluorescence are observed, monomer (MF) and excimer (EF_ fluorescence. The excimer fluorescence of the 2∶2 complex emitted by aggregated light-dispersing crystals forming a precipitate, whereas is the MF is concentrations, EF predominates for the resulting complexes. A proposed structure of the inclusion complexes was derived from MNDO/PM3 semiempirical quantum-chemical calculations. The EF is caused by the structure of the complex, in which both naphthalene molecules are separated by a distance of 4.7 Å: they lie in parallel orientation to each other, whereby one ring is displaced from the other by one-fourth of the length of the naphthalene ring. The complexes of 2,7-DMN and 2-benzylnaphthalene with β-CD do not exhibit EF. For the 2∶2 complex of 2,7-DMN with β-CD, this is due to the fact that the aromatic fragments are removed too far from one another 2-Benzylnaphthalene is unable to form an inclusion complex with β-CD, in whose structure the aromatic fragments inside the cavity could be arranged in parallel planes; instead, it forms a 1∶2 complex with β-CD. 相似文献
952.
Mengkai Lü Fanqing Meng Dong Xu Duorong Yuan Quan Ren 《Progress in Crystal Growth and Characterization of Materials》2000,40(1-4):123-132
Based on Molecular Engineering and Crystal Engineering concepts, a new method for designing nonlinear optical (NLO) crystal materials, the Organic Inclusion Complex (OIC) method has been demonstrated. In defining an appropriate optical transparent range with respect to the Molecular Engineering method, small organic molecules containing n-π conjugation were selected as “second order harmonic generation (SHG)-active units”(guests). Together with the Crystal Engineering method, chiral molecules were used as “molecular scaffolding” (hosts) to combine with the “SHG-active units” by hydrogen bonds. The former can provide a nonlinear optical effect. The latter leads to the OIC with a noncentrosymmetric structure and are expected to enhance the macroscopic nonlinearity in a synergistic mode of guest and host by inducing the guest molecular dipole alignment as well as other properties, such as thermal stability, mechanical strength and ease of growth. Here, we report two new inclusion complex crystals, urea-(d)tartaric acid (UDT) and urea-(dl)tartaric acid (UDLT) (here, d means dextral and dl means racemic). UDT and UDLT crystals belong to P2,2,2, and P2, space group, respectively. Bulk size crystals with high optical quality were successfully obtained from aqueous solution by using a temperature-lowering method. The experimental results show that these two crystals demonstrate higher NLO effects and shorter wavelength cutoff. 相似文献
953.
The identification of the stiffness properties of typical laminated composite tubes from dynamic tests is presented. Unknown coefficients are identified by a technique of model updating. The fomulation is based on the minimization of the eigensolution residuals (sensitivity method). Errors of generalized masses are considered. The technique allows for the simultaneous identification of several properties from a single test. Stiffness properties of extension, bending/twisting and transverse shear are identified. Important points of the model updating of tubes in dynamics are addressed: potential energy evaluation, placement of sensors and the problem of multiple eigenvalues. Results obtained by numerical simulation show the efficiency of the proposed method. 相似文献
954.
求解饱和半空间上弹性圆板固结沉降的积分方程 总被引:1,自引:0,他引:1
本文采用解析方法分析了弹性圆板在饮和半空间上的固结沉降。考虑弹性圆板与饮和半空间的接触面上无摩擦力,且饱和半空间表面为全部透水的。运用Biot固结理论和积分方程技术,在Laplace变换域上建立了弹性圆板固结沉降的对偶积分方程,并化此对偶积分方程为第二类Fredholm积分方程。通过对其核函数的有效数值发得到第二类Fredholm积分方程的解,再利用Lapace反演技术获得弹性板在时间域中的固结沉 相似文献
955.
弹性地基板的弯曲问题,尤其是自由边板,一直是学者和工程师们所十分关切的问题。本文用无单元法研究双参数弹性地基板的弯曲问题,由最小二乘法和变分原理导出了双参数弹性地基板的无单元法刚度短阵,编制相应的无单元法计算程序,并给出计算实例。结果表明本方法精度良好,可求出任意荷载作用下板中任一点的挠度、转角、弯矩和扭矩,且有广泛的工程应用前景。 相似文献
956.
A Model of Arterial Adaptation to Alterations in Blood Flow 总被引:3,自引:0,他引:3
Alexander Rachev 《Journal of Elasticity》2000,61(1-3):83-111
Mechanisms of arterial adaptation to changes in blood flow rates were tested by comparing the predictions of a proposed theoretical
model with available experimental data. The artery was modeled as an elastic membrane made of a nonlinear, incompressible,
elastic material. Stimulation of the vascular smooth muscle was modeled through the generation of an active component of circumferential
stress. The muscular tone was modulated by flow-induced shear stress sensed by the arterial endothelium, and is responsible
for the vasomotor adjustment of the deformed arterial diameter in response to changes in blood flow. This study addresses
the hypothesis that the synthetic and proliferative activity of smooth muscle cells, leading to a change in arterial dimensions,
is shear stress dependent and is associated with changes in the contractile state of the smooth muscle cells and changes in
the circumferential wall stress. Remodeling to a step change in flow was formulated as an initial-value problem for a system
of first order autonomous differential equations for the evolution of muscular tone and evolution of arterial geometry. The
governing equations were solved numerically for model parameters identified from experimental data available in the literature.
The model predictions for the time variation of the geometrical dimensions and their asymptotic values were found to be in
qualitative agreement with available experimental data. Experiments for validating the introduced hypotheses and further generalizations
of the model were discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
957.
958.
Anisotropic thermopiezoelectric solids with an elliptic inclusion or a hole under uniform heat flow 总被引:1,自引:0,他引:1
The two-dimensional problem of a thermopiezoelectric material containing an elliptic inclusion or a hole subjected to a remote
uniform heat flow is studied. Based on the extended Lekhnitskii formulation for thermopiezoelectricity, conformal mapping
and Laurent series expansion, the explicit and closed-form solutions are obtained both inside and outside the inclusion (or
hole). For a hole problem, the exact electric boundary conditions on the hole surface are used. The results show that the
electroelastic fields inside the inclusion or the electric field inside the hole are linear functions of the coordinates.
When the elliptic hole degenerates into a slit crack, the electroelastic fields and the intensity factors are obtained. The
effect of the heat flow direction and the dielectric constant of air inside the crack on the thermal electroelastic fields
are discussed. Comparison is made with two special cases of which the closed solutions exist and it is shown that our results
are valid. 相似文献
959.
Theory of water waves in an elastic vessel 总被引:3,自引:0,他引:3
D. Y. Hsieh 《Acta Mechanica Sinica》2000,16(2):97-112
Recent experiments related to the Dragon Wash phenomena showed that axisymmetric capillary waves appear first from excitation,
and circumferential capillary waves appear after increase of the excitation strength. Based on this new finding, a theory
of parametric resonance is developed in detail to explain the on-set of the prominent circumferential capillary waves. Numerical
computation is also carried out and the results agree generally with the experiments. Analysis and numerical computation are
also presented to explain the generation of axisymmetric low-frequency gravity waves by the high-frequency external excitation. 相似文献
960.
Niels Saabye Ottosen Matti Ristinmaa Christer Ljung 《European Journal of Mechanics - A/Solids》2000,19(6):929
Rayleigh waves in a linear elastic couple-stress medium are investigated; the constitutive equations involve a length parameter l that characterizes the microstructure of the material. With
, cT=conventional transversal speed and q=wave number, an explicit expression is derived for the relation between
, lq and Poisson's ratio ν. The Rayleigh speed turns out to be dispersive and always larger than the conventional Rayleigh speed. It is of interest that when lq=1 and ν≥0, it always holds that
. The displacement field is investigated and it is shown that no Rayleigh wave motions exist when lq→∞ and when lq=1, ν≥0. Moreover, a principal change of the displacement field occurs when lq passes unity. The peculiarity that no Rayleigh wave motions exist when lq=1, ν≥0 may support the criticism by Eringen (1968) against the couple-stress theory adopted here as well as in much recent literature. 相似文献