Rank-perfect and" weakly rank-perfect graphs

An edge e of a perfect graph G is critical if G−e is imperfect. We would like to decide whether G−e is still “almost perfect” or already “very imperfect”. Via relaxations of the stable set polytope of a graph, we define two superclasses of perfect graphs: rank-perfect and weakly rank-perfect graphs. Membership in those two classes indicates how far an imperfect graph is away from being perfect. We study the cases, when a critical edge is removed from the line graph of a bipartite graph or from the complement of such a graph.     

On rank-perfect subclasses of near-bipartite graphs

Shepherd95 proved that the stable set polytopes of near-bipartite graphs are given by constraints associated with the complete join of antiwebs only. For antiwebs, the facet set reduces to rank constraints associated with single antiwebs by Wagler2004. We extend this result to a larger graph class, the complements of fuzzy circular interval graphs, recently introduced in ChudnovskySeymour2004. Received: November 2004 / Revised version: June 2005     

膜流动电位测试中Ag-AgCl电极的制备及稳定性研究

膜的动电特性研究中,往往采用流动电位方法。该方法中,Ag-Ag Cl测试电极的质量是影响测试准确性的关键要素。本文采用正交试验设计和方差分析,着重考察电解法制备Ag-Ag Cl电极过程中,电流强度(I)、氯化时间(t)、电解质溶液浓度(CHCl)、电极来源(n)、烘烤温度(T)、活化电极溶液浓度(CKCl)等因素对Ag-Ag Cl电极稳定性的影响。得到Ag-Ag Cl电极的最优制备参数为:电流密度3.0m A/cm2,氯化时间50min,盐酸浓度0.1mol·L-1,烘烤温度120℃,活化电极溶液(KCl)浓度0.001mol·L-1;最显著影响因素为电极来源,显著影响因素为氯化时间和烘烤温度。对最优条件组合下制备的AgAg Cl电极,进行了稳定性实验,结果表明:制备的电极具有较好的稳定性,24h内电极电位漂移量小于0.10mv,7天内电极电位漂移量小于0.2mv;在聚偏氟乙烯中空纤维超滤膜流动电位测试中,流动电位与流动压差具有良好的线性和可重复性,回归曲线R20.99,变化规律符合Helmholtz-Smoluehowski公式,可以较好满足膜的流动电位测试要求。     

Disilicon Complexes with Two Hexacoordinate Si Atoms: Paddlewheel‐Shaped Isomers with (ClN4)Si?Si(S4Cl) and (ClN2S2)Si?Si(S2N2Cl) Skeletons

The reaction of 1‐methyl‐3‐trimethylsilylimidazoline‐2‐thione with hexachlorodisilane proceeds toward substitution of four of the disilane Cl atoms during the formation of disilicon complexes with two neighboring hexacoordinate Si atoms. The N,S‐bidentate methimazolide moieties adopt a buttressing role, thus forming paddlewheel‐shaped complexes of the type ClSi(μ‐mt)₄SiCl (mt=methimazolyl). Most interestingly, three isomers (i.e., with (ClN₄)Si? Si(S₄Cl), (ClN₃S)Si? Si(S₃NCl), and (ClN₂S₂)Si? Si(S₂N₂Cl) skeletons as so‐called (4,0), (3,1), and cis‐(2,2) paddlewheels) were detected in solution by using ²⁹Si NMR spectroscopic analysis. Two of these isomers could be isolated as crystalline solids, thus allowing their molecular structures to be analyzed by using X‐ray diffraction studies. In accord with time‐dependent NMR spectroscopy, computational analyses proved the cis‐(2,2) isomer with a (ClN₂S₂)Si? Si(S₂N₂Cl) skeleton to be the most stable. The compounds presented herein are the first examples of crystallographically evidenced disilicon complexes with two Si? Si‐bonded octahedrally coordinated Si atoms and representatives of the still scarcely explored class of Si coordination compounds with sulfur donor atoms.     

4-氨基-7-硝基苯并-2-氧杂-1,3-二唑类衍生物的合成及其对汞离子的识别研究

以4-氯-7-硝基苯并-2-氧杂-1,3-二唑、乙二胺和溴乙酸乙酯等为原料,合成4-氨基-7-硝基苯并-2-氧杂-1,3-二唑类衍生物(NBD-OEt),通过IR、NMR和MS对其进行结构表征。研究NBD-OEt的吸收光谱和荧光光谱性质,探讨其在H2O/EtOH(60/40, V/V) pH 7.40的HEPES缓冲体系中对Hg₂ 的响应,以及NBD-OEt与Hg₂ 的结合模式。结果表明, 随Hg₂ 的不断加入可诱使NBD-OEt在476nm的吸收峰红移至514nm,并有两个等吸收点(347nm、482nm);其荧光发射峰由536nm红移至559nm,且在525nm出现等发射点;通过Job plot法测定NBD-OEt与Hg₂ 以1:1的计量比结合。