The Images of the Clique Operator and Its Square are Different

Let be the class of all graphs and K be the clique operator. The validity of the equality has been an open question for several years. A graph in but not in is exhibited here.     

Redox behaviour of thermally activated platinum electrodes with particular reference to operation at elevated temperature

The present work is a continuation of an earlier investigation of the effect of severe thermal pretreatment on the redox properties of platinum electrodes in aqueous media. The most interesting observation was that raising the solution temperature to ca. 75 °C resulted in a dramatic anodic response in the positive sweep at ca. 0.25 V (RHE). Such behaviour was noted earlier at room temperature but only when the thermally pretreated sample was further activated by cathodic polarization. This transition at 0.25 V was partially reversed on the negative sweep, but the cathodic process involved was subject to severe inhibition. There is independent evidence for similar behaviour for gold in aqueous acid solution. The relevance of the present results to the operation of fuel cell anodes is outlined. Received: 2 December 1999 / Accepted: 24 February 2000     

Electric Field Gradients of B in TiO2

We observed the electric quadrupole interaction of ¹²B implanted in the interstitial site of TiO₂ using β-NMR method. The electric field gradients including the direction of the principal axes were determined. The direction agreed well with the theoretical calculation.     

二维晶格上Kadanoff分块及重整化群方法

对二维晶格上的Kadanoff分块进行了全面分析，给出了划分的一般规律，得出元块选择的非任意性和含相同元块选择不惟一等结论，并给出正三角形格子和正方形格子元块中格点数目的允许值。同时，利用重整化群方法对9点，13点元块进行了计算，得到了相应的不动点和各种临界指数，并与其它计算结果进行了比较，结果表明，计算精度有随元块中所含格点数的增加而增加的趋势。     

Studies of two interrelated series of triiridatrithia-cyclohexane and trimetallatrithia (or trioxo)-adamantane rhodium and iridium complexes

From a comparativereview on the two title series of compounds, the first part of the paper describes the most salient structural and reactivity properties of these trimetallic complexes, including metal-metal bond formation, conformational changes, enantio, and diastereomorphism. The second part presentsnew results which extend the comparison to a series of trimetallatrioxo adamantane complexes. The single crystal X-ray diffraction of the parent compound [Rh₃{μ ₃−(OCH₂)₃CCH₃}(CO)₆]—a derivative of the commercially available tripod ligand 1,1,1tris (oxomethyl)ethane—is reported together with its crystal packing which is compared to that of its sulfido analog. The paper includes a discussion of the nucleophilic and electrophilic properties of the trimetalla trioxo adamantane rhodium complexes, based on semi-empirical extended Hückel calculations Dedicated to Professor Yves Jeannin on the occasion of his 65 th birthday.     

含多源损伤的胶接修补结构有限元分析方法

采用有限元法研究含多源损伤结构的胶接修补问题,利用二维三层有限元模型对损伤区进行了数值模拟,并选取典型多源损伤情况中含共线双裂纹铝板结构为算例,详细分析了含多裂纹胶接修补结构中两裂纹相对位置、补片尺寸、铺层和厚度对应力强度因子的影响.结果表明,复合材料胶接修补可明显降低含共线双裂纹母板的应力强度因子;对于确定的裂纹和应力场,应对复合材料补片长度和厚度等参数进行优化设计,以获得最佳的修补效果.     

A Simple,High‐Yield Synthesis of DNA Duplexes Containing a Covalent,Thermally Cleavable Interstrand Cross‐Link at a Defined Location

Interstrand DNA–DNA cross‐links are highly toxic to cells because these lesions block the extraction of information from the genetic material. The pathways by which cells repair cross‐links are important, but not well understood. The preparation of chemically well‐defined cross‐linked DNA substrates represents a significant challenge in the study of cross‐link repair. Here a simple method is reported that employs “post‐synthetic” modifications of commercially available 2′‐deoxyoligonucleotides to install a single cross‐link in high yield at a specified location within a DNA duplex. The cross‐linking process exploits the formation of a hydrazone between a non‐natural N⁴‐amino‐2′‐deoxycytidine nucleobase and the aldehyde residue of an abasic site in duplex DNA. The resulting cross‐link is stable under physiological conditions, but can be readily dissociated and re‐formed through heating–cooling cycles.     

EPR‐Based Approach for the Localization of Paramagnetic Metal Ions in Biomolecules

Metal ions play an important role in the catalysis and folding of proteins and oligonucleotides. Their localization within the three‐dimensional fold of such biomolecules is therefore an important goal in understanding structure–function relationships. A trilateration approach for the localization of metal ions by means of long‐range distance measurements based on electron paramagnetic resonance (EPR) is introduced. The approach is tested on the Cu²⁺ center of azurin, and factors affecting the precision of the method are discussed.     

A two‐dimensional layered CdII coordination polymer with a three‐dimensional supramolecular architecture incorporating mixed multidentate N‐ and O‐donor ligands

The combination of N‐heterocyclic and multicarboxylate ligands is a good choice for the construction of metal–organic frameworks. In the title coordination polymer, poly[bis{μ₂‐1‐[(1H‐benzimidazol‐2‐yl)methyl]‐1H‐tetrazole‐κ²N³:N⁴}(μ₄‐butanedioato‐κ⁴O¹:O^1′:O⁴:O^4′)(μ₂‐butanedioato‐κ²O¹:O⁴)dicadmium], [Cd(C₄H₄O₄)(C₉H₈N₆)]_n, each Cd^II ion exhibits an irregular octahedral CdO₄N₂ coordination geometry and is coordinated by four O atoms from three carboxylate groups of three succinate (butanedioate) ligands and two N atoms from two 1‐[(1H‐benzimidazol‐2‐yl)methyl]‐1H‐tetrazole (bimt) ligands. Cd^II ions are connected by two kinds of crystallographically independent succinate ligands to generate a two‐dimensional layered structure with bimt ligands located on each side of the layer. Adjacent layers are further connected by hydrogen bonding, leading to a three‐dimensional supramolecular architecture in the solid state. Thermogravimetric analysis of the title polymer shows that it is stable up to 529 K and then loses weight from 529 to 918 K, corresponding to the decomposition of the bimt ligands and succinate groups. The polymer exhibits a strong fluorescence emission in the solid state at room temperature.