TGSA-Flex: Extending the capabilities of the Topo-Geometrical Superposition Algorithm to handle flexible molecules

In this work, an extension of the already studied Topo-Geometrical Superposition Approach (TGSA) is presented. TGSA, a general-purpose, fast, automatic, and user-intuitive three-dimensional molecular alignment procedure, was originally designed to superpose rigid molecules simply based on atomic numbers, molecular coordinates, and connectivity. The algorithm is further developed to enable handling rotations around single bonds; in this way, common structural features, which were not properly aligned due to conformational causes, can be brought together, thus improving the molecular similarity picture of the final alignment. The present procedure, implemented in Fortran 90 and named TGSA-Flex, is deeply detailed and tested over four molecular sets: amino acids, nordihydroguaiaretic acid (NDGA) derivatives, HIV-1 protease inhibitors, and 1-[2-hydroxyethoxy)methyl]-6-(phenylthio)thymine (HEPT) derivatives. TGSA-Flex performance is evaluated by means of computational time, number of superposed atoms (also comparing it with respect to the rigid approach), and index of fit between the compared structures.     

Semiclassical $$\bar \partial $$ -Method: Generating Equations for Dispersionless Integrable Hierarchies

We use the semiclassical -dressing method to derive compact generating equations for dispersionless hierarchies. The considered illustrative examples are the dispersionless Kadomtsev–Petviashvili and two-dimensional Toda lattice hierarchies.     

The P\bar 1 space group changes in journal of crystallographic and spectroscopic research and in journal of chemical crystallography

The crystal structures of seven compounds, originally described in the centrosymmetric triclinic space group (No. 2), have been revised to centered monoclinic. Six are now described in space group No. 15 (C2/c or I2/a) and one in space group No. 12 (C2/m). Three structures (TADTEX, VICHIY, YAWZUR) have been re-refined in the correct space group. For six instances the decrease in symmetry results in only minor adjustments and the structure is essentially correct as it is expected when the original and the revised space groups are both centrosymmetric. However, in one instance (VICHIY) the reformulation in the higher space group changes (unexpectedly) the molecular dimension as much as 0.12 Å, even if the space group change is between two centrosymmetric space groups (from to C2/c). This was attributed to the easy decomposition of the crystal. The percentage of revised crystal structures was found to be 1.71%, namely 8 on a total of 467 analyzed structures. A low value if compared to the 3% value found by Marsh and Spek for C2 space group.     

Thermal flexibility of aromatic polymide chains in solution from viscometric analysis

Intrinsic viscosities of poly(p-phenylene terephthalamide) (PPTA) and poly(m-phenylene isophthalamide) (PMIA) samples of the same molecular weight are determined in 90%, 96% and 100% sulfuric acid at temperatures from 0 to 130°C. Conditions are established under which the degree of coiling of PPTA molecule is close to that for PMIA. Experimental data are compared with the results of theoretical calculations of the Kuhn segment length. In the light of this comparison, some quantitative characteristics of the deformational flexibility mechanism for aromatic polyamide chains and the hindrance to intramolecular rotation are discussed. © 1993 John Wiley & Sons, Inc.     

半绝对离差证券组合投资模型

提出“半绝对离差”这一新的风险度量工具，并与证券收益率的半方差、绝对离差进行比较，给出了基于半绝对离差的证券组合投资模型，该模型采用半绝对离差作为风险的度量工具，综合了半方差的向下风险和绝对离差的一阶矩在的优点，利用“上证30指数”中的30种成分股票作为样本对该模型进行实证研究，结果表明，在与Markowit模型和绝对离差模型的定性、定量比较中，半绝对离差模型能求解出更优的投资组合，是一种更有效的组合投资模型。     

自聚焦棒干涉仪的设计原理及其应用研究

本文分析并研究了用自聚焦棒做成的干涉仪。并用偏振滤波的方法有效地减少噪声,大幅度提高接收光强,使干涉条纹清晰可见,方便了检测系统。并对其应用作了一些初步的探讨和实验。     

一体化条形码库存MIS的设计思想

根据物料库存管理的特点，本文从预测、管理．订货策略各个方面，以一体化系统设计的观点优化库存管理结构，提出了相应的库存管理信息系统的设计思想，并在微机上做了初步实现．在系统的实现过程中，条形码技术的应相使库存数据的采装集更为方便．     

The de rham homotopy theory of complex algebraic varieties I

In this paper we use Chen's iterated integrals to put a mixed Hodge structure on the homotopy Lie algebra of an arbitrary complex algebraic variety, generalizing work of Deligne and Morgan. Similar techniques are used to put a mixed Hodge structure on other topological invariants associated with varieties that are accessible to rational homotopy theory such as the cohomology of the free loopspace of a simply connected variety.Supported in part by the National Science Foundation through grants MCS-8201642, DMS-8401175 and MCS-8108814(A04).     

复合材料大层数层压矩形截面杆的扭转问题分析

本文根据有效弹性模量理论［１］，采用三维八节点等参数有限元和整体—局部方法，对复合材料大层数矩形厚截面层压杆的扭转问题及其自由边缘效应进行了分析研究，通过算例计算给出了剪切应力在横截面内的分布规律、杆的扭转变形及其在自由边缘区域层间应力的分布情况·由于本文的分析方法可根据需要仅在应力梯度较大的局部区域，按单层逐层划分单元或在单层内再细化单元，以求得单层内精确的应力场和位移场，因此能显著节约计算量与机时，为具有大层数层压杆的扭转强度计算提供了一种有效的方法·