磷酸铝分子筛骨架结构及其稳定性的模拟计算(Ⅱ)──骨架结构中各类键长、键角的取值及其分布

应用晶格能极小化技术计算了19种磷酸铝分子筛的骨架晶格能. 从计算结果发现这些磷酸铝分子筛彼此间的晶格能相差很小,而与磷酸铝致密相块磷铝矿(Berlinite)相差48～127kJ/mol. 据此可以解释磷酸铝分子筛骨架结构的多样性和相似性. XRD数据表明在它们的结构中包含很短的AI－O键(0. 1478nm)、P－O键(0. 1348nm)和很长的AI－O键(0. 1942nm)、P－O键(0. 1678nm),O－T－O键角有大的分布范围(O－AI－O键角为98. 62°～122. 27°和O－P一O键角为92. 36°～122. 86°),平均AI-O一P键角在153°左右,并且具有更大的分布范围(114°～180°). 量子化学AMI计算结果表明,在AI-O一P键角由114°变化至180°而引起的能量改变很小(仅22. 97kJ/mol),当AI一O一P键角为137. 74°时能量最低.     

Spectral decomposition of the compliance fourth-rank tensor for orthotropic materials

Summary The compliance tensor related to orthotropic media is spectrally decomposed and its characteristic values are determined. Further, its idempotent tensors are estimated, giving rise to energy orthogonal states of stress and strain, thus decomposing the elastic potential in discrete elements. It is proven that the essential parameters, required for a complete characterisation of the elastic properties of an orthotropic medium, are the six eigenvalues of the compliance tensor, together with a set of three dimensionless parameters, the eigenangles θ, ϕ and ω. In addition, the intervals of variation of these eigenangles with respect to different values of the elastic constants are presented. Furthermore, bounds on Poisson's ratios are obtained by imposing the thermodynamical constraint on the eigenvalues to be strictly positive, as specified from the positive-definite character of the elastic potential. Finally, the conditions are investigated under which a family of orthotropic media behaves like a transversely isotropic or an isotropic one. Received 5 January 1999; accepted for publication 22 June 1999     

Ag_2O胶体粒子的自组装单层膜和多层膜

本文制备了Ａｇ２Ｏ胶体粒子的自组装单层膜和多层膜。运用接触角测量、红外吸收光谱和紫外可见吸收光谱等手段证实了Ａｇ２Ｏ胶体粒子能够组装在具有羧基的基底上,在有１,１８ 十八烷基二羧酸做为交联剂的情况下还可形成自组装多层膜     

Protein Folding with a Reduced Model and Inaccurate Short‐Range Restraints

Summary: A reduced high‐coordination lattice protein model and the Replica Exchange Monte Carlo sampling were employed in de novo folding simulations of a set of representative small proteins. Three distinct situations were analyzed. In the first series of simulations, the folding was controlled purely by the generic force field of the model. In the second, a bias was introduced towards the theoretically predicted secondary structure. Finally, we superimposed soft restraints towards the native‐like local conformation of the backbone. The short‐range restraints used in these simulations are based on approximate values of ϕ and ψ dihedral angles, which may simulate restraints derived from inaccurate experimental measurements. Incorporating such data into the reduced model required developing a procedure, which transforms the ϕ and ψ coordinates into coordinates of the protein alpha carbon trace. It has been shown that such limited data are sufficient for de novo determination of three‐dimensional structures of small and topologically not too complex proteins.

Protein folding based on secondary structure prediction and simulated torsion angles data.     

Domain of mixing angles in three flavor neutrino oscillations

We clarify the domain needed for the mixing angles in three flavor neutrino oscillations. By comparing the ranges of the transition probabilities as functions of the domains of the mixing angles, we show that it is necessary and sufficient to let all mixing angles be in . This holds irrespectively of any assumptions on the neutrino mass squared differences.     

Approximations for Multi-Class Departure Processes

The exact analysis of a network of queues with multiple products is, in general, prohibited because of the non-renewal structure of the arrival and departure processes. Two-moment approximations (decomposition methods, Whitt [9] ) have been successfully used to study these systems. The performance of these methods, however, strongly depends on the quality of the approximations used to compute the squared coefficient variation (CV) of the different streams of products.In this paper, an approximation method for computing the squared coefficient of variation of the departure stream from a multi-class queueing system is presented. In particular, we generalize the results of Bitran and Tirupati [3] and Whitt [11] related to the interference effect.     

Model of Deformation of Monotropic Plastic Foams Parallel to the Foam Rise Direction Based on the Volume-Deformation Hypothesis

The deformation properties of monotropic plastic foams under uniaxial deformation (compression or tension) parallel to the foam rise direction is considered. The theoretical results are obtained in the case where the volume-deformation hypothesis is assumed. The validity of neglecting the fluctuation component in calculations of the effective volume strains of foams is substantiated. A tie condition permitting the sought-for semiaxes to vary not obligatorily equally is derived. The values of Young's modulus and Poisson coefficients are obtained for a wide range of model cell stretch ratios and foam space-filling coefficients. A comparison of the theoretical results with the experimental data available is performed.     

高负荷穷尽循环网络系统的收敛极限

用概率测度弱收敛的理论对高负荷穷尽循环网络系统进行了研究,获得了其系统中的网输入过程,离运过程和队长过程的收敛极限。     

靶场目标三维姿态测量结果自动修正方法

中轴线法是靶场试验中常用的目标三维姿态测量方法,但该方法求出的俯仰角和偏航角所描述的目标姿态可能与目标实际情况相异,必须进行人工修正。提出一种自动对姿态判读结果进行修正的方法,将目标共线方程与中轴线方程联立求解,可快速地求出角度修正量。实验证明该方法可对中轴线法求解结果进行自动修正,得到正确的目标三维姿态角,提高了姿态判读的速度和可靠性。