Stable and emergent network topologies: A structural approach

Economic, social and military networks have at least one thing in common: they change over time. For various reasons, nodes form and terminate links, thereby rearranging the network. In this paper, we present a structural network mechanism that formalizes a possible incentive that guides nodes in constructing their local network structure. The mechanism assumes that nodes deliberately form and terminate links as they attempt to gain network advantage and/or an identifiable position in the network. Reiteration of this mechanism, which only uses local network characteristics, results in emergent, stable network topologies. Examples are uni-polar networks, bi-polar networks and cycle-networks. This process illustrates that local, binary decisions shape global network structures. These results may be used to derive some rules of thumb for designing networks.     

On the Asymptotic Behavior of First Passage Time Densities for Stationary Gaussian Processes and Varying Boundaries

Making use of a Rice-like series expansion, for a class of stationary Gaussian processes the asymptotic behavior of the first passage time probability density function through certain time-varying boundaries, including periodic boundaries, is determined. Sufficient conditions are then given such that the density asymptotically exhibits an exponential behavior when the boundary is either asymptotically constant or asymptotically periodic.     

Investigation into the GC separation of enantiomers on a trifluoroacetylated cyclodextrin. I. Effect of analyte structure on stereoselectivity for alcohols

More than 30 enantiomeric alcohols have been analyzed, without prior derivatization, by gas chromatography using a fused silica capillary column coated with octakis(3-O-trifluoro-acetyl-2,6-di-O-n-pentyl)-γ-cyclodextrin. Most were analyzed over a range of isothermal temperatures from 35 to 70°C. Enantiomeric separations were observed for most of the analytes, even at temperatures as low as 35°C. The stereoselectivity of the stationary phase was found to depend on the length of the longest carbon chain attached to the stereogenic centre in 2- and 3-hydroxy alkanes, the relative positions of the methyl and hydroxyl substituents in methylsubstituted alcohols, and the effects of multiple bonds in the analyte molecule. Thermodynamic data calculated from the results suggest that the enantiomers of all the analytes are resolved by a similar process. Retention and thermodynamic data are presented and possible mechanisms discussed.     

Finite element dynamic analysis of unsymmetric composite laminated beams with shear effect and rotary inertia under the action of moving loads

The finite element dynamic response of an unsymmetric composite laminated orthotropic beam, subjected to moving loads, has been studied. One-dimensional finite element based on classical lamination theory, first-order shear deformation theory, and higher-order shear deformation theory having 16, 20 and 24 degrees of freedom, respectively, are developed to study the effects of extension, bending, and transverse shear deformation. The theories also account for the Poisson effect, thus, the lateral strains and curvatures can be expressed in terms of the axial and transverse strains and curvatures and the characteristic couplings (bend–stretch, shear–stretch and bend–twist couplings) are not lost. The dynamic response of symmetric cross-ply and unsymmetric angle-ply laminated beams under the action of a moving load have been compared to the results of an isotropic simple beam. The formulation also has been applied to the static and free vibration analysis.     

Aqueous Capillary Electrophoresis of Peptides Part 2: An Investigation of Quantitative Determinants of Hydration and Solvation Relationships

Summary From the published electrophoretic data for a set of 58 peptides at pH 2.5 we have determined the excess hydration required to correct the deviations of the 31 higher-charged peptides from the Offord plot for the 27 singly-charged peptides. These values of the excess hydration were then used to test physical models by regression analysis. The dominant variable is the total excess positive charge, but the number of excess single positive charges and the number of pairs of positive charges – both at the end and internally – were significant determinants. The effect of acidic side chains was ambiguous throughout the analyses and this was presumed to arise from the ability of carboxy groups to be the sites of additional hydration or to diminish hydration via internal bonding with amino groups. A hydrophobicity index was included in he analysis, but surprisingly this too had little effect. In the last stage of the regressions, we also included coding for secondary structure within the peptides. This increased R² for the plots of the excess hydration versus values calculated from the regression constants (Y) from 0.95 to 0.97. Some solvation relationships were particularly good at modelling the hydration of the smaller, lesser-charged peptides, whilst others excelled in the opposite direction. The final model appeared to deal equally well with both extremes, but is not sufficiently sensitive to allow for all of the variations between peptides. As a result, the excess hydration was modelled very well for many of the peptides (±1–2 waters over the range of excess hydration form 5–276), but poorly for a few (± 100–200%). It was not possible to find another set of peptides that could be independently analysed in a similar fashion and compared. However, the regression constants were applied to an alternative set. Although appearing to fall in a generally reasonable range, various tests of the resultant calculated values indicated that this application was not valid. The second set of peptides were much more hydrophilic and the number of amino acid residues with an extended secondary structure appeared to be a contributing factor.     

锌盐与二甲氧基嘧啶配合物的光谱研究

无水乙醇中回流制得ZnCl_2和ZnSO_4与2-氨基-4,6-二甲氧基嘧啶(AMP)的1:2和1:1固态配合物,用化学分析和元素分析确定它们的组成分别为Zn(AMP)_2Cl_2(A)和Zn(AMP)SO_4(B);用IR,XPS和~1HNMR研究了它们的成键情况。IR光谱分析说明配合物中,配体通过氨基N原子及嘧啶环上一个N原子与Zn~(2 )双齿配位,配合物B中SO_4~(2-)参与了配位;XPS谱证明配合物A中和B中SO_4~(2-)均参与了配位,并且N→Zn~(2 )键中有不同程度的反馈键;~1H NMR说明配合物A中有2个配体参与配位,配合物B中只有1个配体参与了配位。由此推测了它们的可能结构。     

A new method of sensitivity analysis of static responses for finite element systems

This paper is the continuation of Liang et al. J. Comput. Struct. 62 (2) (1997) 243–251. In this paper, a set of explicit formulations of variations for calculating sensitivity of static responses are presented. This method may greatly increase the computational efficiency if used with the M–P inverse topological variation method. By using this method the exact sensitivity can be obtained.     

在小硅化物SiX~m（X＝Be、B、C、N、O、F、Ne，m＝～4－＋2）中分子成键倾向的从头算研究

此文用从头计算法，在ＨＦ、ＭＰ２、ＭＰ３水平下，使用基组６—３１Ｇ、６—３１＋Ｇ对ＳｉＯ的等电子分子ＳｉＸｍ（Ｘ＝Ｂｅ、Ｂ、Ｃ、Ｎ、Ｐ、Ｎｅ，ｍ＝－４～＋２）进行了几何优化，并计算了相应的平衡几何构型下的振动频率，对ＳｉＯ分子，使用ＱＣＩＳＤ（Ｔ）方法考虑了不同水平下的电子相关效应，并考虑了不同基函数６－３１＋Ｇ和６－３１１＋Ｇ的影响。计算结果表明，所有分子的势能曲线都有稳定的极小值，并且键长与频率在ＨＦ、ＭＰ２、ＭＰ３水平上都呈现出明显的规律性，通过与实验上存在的稳定分子ＳｉＯ相比较，可以预言ＮＳＩｉ－和ＳｉＦ＋比其它分子有较明显的成键可能性，所以，ＮＳｉ－和ＳｉＦ＋有可能形成稳定的分子。     

Influence of acid–base properties of cobalt–molybdenum catalysts supported on magnesium orthophosphates in isomerization of 3,3-dimethylbut-1-ene

Synthesis and physico-chemical characterization of a pure magnesium phosphate (MgP) prepared by coprecipitation, and MgP modified by introduction of cobalt–molybdenum (4–12 wt.% of MoO₃ with the Co/Mo ratio fixed at 0.5) have been carried out. The structural properties of these catalysts were characterized by X-ray diffraction, their textural properties were determined by N₂ adsorption–desorption isotherms and the dispersion of cobalt–molybdenum was studied by XPS spectroscopy. Their acid properties have been investigated by in situ FT-IR spectroscopy of adsorbed molecules, often, 2,6-dimethylpyridine (pK_a = 6.7), pyridine (pK_a = 5.3). Co–Mo incorporation leads to a modification in the MgP acid–base properties, especially on the acid sites type and number. Thus, lower loading of cobalt–molybdenum species decreased the number of strong Lewis acid sites whereas higher loading increased it. It was found that Lewis acid sites on magnesium phosphates play an important role in the isomerization of 3,3-dimethylbut-1-ene.The 3,3-dimethylbut-1-ene (33DMB1) conversion increases with the reaction temperature from 493 to 653 K for MgP, but decreases after 573 K for MgP supported by Co–Mo. A linear relationship between both types of acid sites and conversion values was found. The deactivation of the catalysts appears at high reaction temperature (>573 K).     

A computational study of supersonic disk-gap-band parachutes using Large-Eddy Simulation coupled to a structural membrane

Large-scale fluid-structure interaction simulations of compressible flows over flexible supersonic disk-gap-band parachutes are compared with matching experimental results. We utilize adaptive mesh refinement, large-eddy simulation of compressible flow coupled with a thin-shell structural finite-element model. The simulations are carried out in the regime where large canopy-area oscillations are present, around and above Mach 2, where strong nonlinear coupling between the system of bow shocks, turbulent wake and canopy is observed. Comparisons of drag history and its dependence on Mach number are discussed. Furthermore, it is observed that important dynamical features of this coupled system can only be reproduced when sufficient grid resolution is used. Lack of resolution resulted in incorrect flow-physics prediction and, consequently, incorrect fluid-structure interaction coupling.