Homogeneous Catalysis : VII. The catalysis of isoprene hydrosilylation using metal atoms

The catalysis of isoprene hydrosilylation using transition-metal atoms has been investigated. Hydrosilylation by co-condensation of nickel, cobalt, or iron vapour at —196°C with isoprene and triethoxysilane proceeded both regio- and stereo-selectively to afford (Z)-1-triethoxysilyl-2-methyl-2-butene. Nickel, in particular, was a very active catalyst, giving quantitative yields below 0°C. Other first-row transition metals did not cause hydrosilylation, either alone, or in the presence of a co-catalyst, [Et₂AlCl]₂.     

Synthesis of the enantiomers of 4-substituted γ-lactones with known absolute configuration

The highly pure enantiomers of several 4-alkyl (or alkenyl)-γ-lactones of known absolute configuration were synthesized from glutamic acid enantiomers. The key step is selective tosylate displacement rather than ring opening of the lactone tosylate (7→1) by lithium dialkylcuprate or dialkenylcuprate. The enantiomeric purity of synthesized γ-caprolactone was confirmed within the limitations of Pirkle's chiral solvating agent. The enantiomers of synthesized (Z)-6-dodecen-4-olide were used for reference to determine the enantiomeric composition of the pheromone isolated from the black-tailed deer.     

A micro-computer system for potentiometric stripping analysis

In potentiometric stripping analysis, trace metals are first amalgamated into a mercury film electrode and then oxidized back into solution by an oxidant. The potential vs. time curve is recorded. Microcomputer-controlled equipment for automation of the potentiometric stripping analysis is described. The higher resolution of time compared to manual equipment increases the sensitivity of the method. A resident, 3-kB BASIC interpreter with routines for handling the hardware makes the programming simple and the instrumentation flexible for changes in the analytical scheme. Printer and keyboard are incorporated in the equipment which makes the whole analyser compact.     

Elektronenstossinduzierter zerfall von cyclopentadienyl-nitrosyl-chrom-komplexen

The low- and high-resolution mass spectra of CpCr(NO)₂Cl (Cp = cyclopentadienyl) and of Cp₂Cr₂(NO)₂(μ-NO)(μ-X) compounds with X = No, NH₂, NHCH₃, N(OH)-t-C₄H₉, N=CH₂, and N=CH-n-C₃H₇ have been measured; complete fragmentation diagrams have been obtained by detection of metastable decompositions using a linked scan technique. The degradation of the dinuclear complexes is essentially determined by the bridging ligand X. The numerous rearrangements are partially characterized by transfer of the nitrosyl nitrogen onto other ligands with formation of CrO bonds.     

债务治理、地方融资平台期限错配与企业绩效——基于“43号文”的研究

本文利用我国2009~2018年2193家地方融资平台的面板数据,采用基准回归模型和中介效应模型,分析了43号文件对地方融资平台期限错配的治理效应,并进一步分析了债务治理是如何通过缓解地方融资平台期限错配最终改善企业绩效的。结果表明:(1)43号文改善了地方融资平台期限错配问题,并增加了企业绩效,这一结论在稳健性检验中也得到了验证;(2)43号文改善了省及省会(单列市)类地方融资平台的期限错配问题,并相应的改善了企业的绩效;(3)43号文改善了土木工程类和房地产类地方融资平台的期限错配问题,并相应的改善了企业的绩效。     

The condition for applying Slit Island Method

I.IntroductionSinceII]proposedtheSlitIslandMethod(i.e.SIM)inthefractaldimensionmeasurementformetalfaultplane,alotofresearchworkhasbeendoneinthisfield,whichiswidelyusedtosolvetheproblemsinengineeringandphysics.However,manyexperimentalresultsshowthatthetana…     

The Box counting Dimension of Invariant Sets for Iterated Function Systems

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Ultrasonic-assisted eggshell extract-mediated polymorphic transformation of calcium carbonate

This study aimed to evaluate the combined effects of eggshell extract and ultrasonic irradiation on the polymorphic transformation of calcium carbonate (CaCO₃). In this context, XRD, Raman spectroscopy, SEM, AFM, TGA-FTIR, BET, and zeta potential analysis were used to identify and characterize the different polymorphs of CaCO₃ obtained in the absence and presence of eggshell extract in the media with and without ultrasonic irradiation. The morphology and polymorphic nature of the CaCO₃ crystals were observed to change, which indicated that the eggshell extract and ultrasonication influenced the structure and crystallization of CaCO₃. The structural analysis results indicated that the addition of eggshell extract to the media resulted in the full transformation of calcite to the vaterite polymorph. The results also showed that ultrasonic irradiation had a more significant influence on the BET specific surface area of the crystals compared to the eggshell extract media. Furthermore, a Box–Behnken design with response surface methodology was employed to determine the optimal operating conditions for CaCO₃ crystallization. The effects of stirring rate, extract concentration, and ultrasonic power on the BET surface area were investigated. The results show that the data sufficiently fit the second-order polynomial model. Understanding the eggshell extract-mediated polymorphic transformation with ultrasonic irradiation obtained in this study makes it possible to control the polymorphic formation and modify the product characteristics.     

2-piercings via graph theory

We provide a very simple proof for a Helly-type result given by Danzer and Grünbaum on 2-piercings of box families in d-dimensional Euclidean space.     

Filters,Antichains and Towers in Topological Spaces and the Axiom of Choice

We find some characterizations of the Axiom of Choice (AC) in terms of certain families of open sets in T₁ spaces.