On Tutte polynomial uniqueness of twisted wheels

A graph G is called T-unique if any other graph having the same Tutte polynomial as G is isomorphic to G. Recently, there has been much interest in determining T-unique graphs and matroids. For example, de Mier and Noy [A. de Mier, M. Noy, On graphs determined by their Tutte polynomials, Graphs Combin. 20 (2004) 105-119; A. de Mier, M. Noy, Tutte uniqueness of line graphs, Discrete Math. 301 (2005) 57-65] showed that wheels, ladders, Möbius ladders, square of cycles, hypercubes, and certain class of line graphs are all T-unique. In this paper, we prove that the twisted wheels are also T-unique.     

X射线荧光光谱法测定中低合金钢中的各元素

通过对标准样品和仪器条件的选择,元素条件及组条件的编辑、回归分析、工作曲线的制作、准确度和精密度的试验,建立了X射线荧光光谱法测定中低合金钢中Si、Mn、Cr、Ni、Mo、V、W、Ti、Cu和P元素质量分数的分析方法。方法的精密度和准确度满足国家标准要求。     

极限下限分析的正交基无单元Galerkin法

基于极限分析的下限定理,建立了用正交基无单元Galerkin法进行理想弹塑性结构极 限分析的整套求解算法．下限分析所需的虚拟弹性应力场可由正交基无单元Galerkin法直接 得到,所需的自平衡应力场由一组带有待定系数的自平衡应力场基矢量的线性组合进行模 拟．这些自平衡应力场基矢量可由弹塑性增量分析中的平衡迭代得到．通过对自平衡应力场 子空间的不断修正,整个问题的求解将化为一系列非线性数学规划子问题,并通过复合形法 进行求解．算例表明该方法有效地克服了维数障碍问题,使计算效率得到了充分的提高,是 切实可行的．     

P2P网络的研究与进展(下)

本文归纳总结了国内外近期对P2P网络的一些研究内容和成果.首先,按拓扑结构和发展顺序分类介绍了P2P网络的背景知识;接着,针对国外的近期研究工作,着重系统地介绍了斯坦福大学的相关研究,简略介绍了美国国家科学基金会资助的IRIS计划和SUN公司的JXTA平台;然后,介绍了国内大学、研究机构的近期研究,包括北京大学、中国科学院、上海交通大学、中国科技大学、复旦大学等.通过这些研究分析,可以更好地了解国内外P2P网络的研究热点和发展趋势.     

一种基于基线力的平面几何非线性余能原理有限元模型

以基线力为状态变量,构造几何非线性问题单元的余能,该余能包括变形部分和转动部分．利用高玉臣提出的弹性大变形余能原理,以Lagrange乘子法松弛单元域内的平衡条件,得到了一个以基线力表达的修正的余能原理．在假设平面单元每一个边上的力为均匀分布的条件下,推导出一种几何非线性平面4节点有限元模型．运用MATLAB语言编制出相应的非线性有限元分析程序．数值算例结果表明该模型具有良好的性能．     

Post-Assembly Modification of Homochiral Titanium–Organic Cages for Recognition and Separation of Molecular Isomers

A chiral metal–organic cage (MOC) was extended and fixed into a porous framework using a post-assembly modification strategy, which made it easier to study the host–guest chemistry of the solid-state MOC using a single-crystal diffraction technique. Anionic Ti₄L₆ (L=embonate) cage can be used as a 4-connecting crystal engineering tecton, and its optical resolution was achieved, thus homochiral ΔΔΔΔ- and ΛΛΛΛ-[Ti₄L₆] cages were obtained. Accordingly, a pair of homochiral cage-based microporous frameworks ( PTC-236(Δ) and PTC-236(Λ) ) were easily prepared by a post-assembly reaction. PTC-236 has rich recognition sites provided by the Ti₄L₆ moieties, chiral channels and high framework stability, affording a single-crystal-to-single-crystal transformation for guest structure analyses. Thus it was successfully utilized for the recognition and separation of isomeric molecules. This study provides a new approach for the orderly combination of well-defined MOCs into functional porous frameworks.