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1.
The paper discusses the investigation of crystallization of metals and alloys by differential thermal analysis (DTA). It was assumed that this method allows determination of the mechanism and kinetics of volumetric crystallization underiso conditions (e.g. anisothermal) on the basis of the parameters of the equation expressing an integral form of the DTA curve. From DTA, a course of eutectic transformation was determined for a technical Zn?Al alloy containing 4wt% Al. Investigations were carried out under continuous cooling at various rates and the kinetics parameters were determined with the KEKAM equation:-ln(1-x)=kl n  相似文献   
2.
Potential difficulties associated with background silver salt clusters during matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) of nonpolar polymers are reported. Silver salt cluster ions were observed from m/z 1500 to 7000 when acidic, polar matrices, such as 2,5-dihydroxybenzoic acid (DHB), all-trans-retinoic acid (RTA) or 2-(4-hydroxyphenylazo)benzoic acid (HABA), were used for the analysis of nonpolar polymers. These background signals could be greatly reduced or eliminated by the use of nonpolar matrices such as anthracene or pyrene. Representative examples of these background interferences are demonstrated during the analysis of low molecular weight nonpolar polymers including polybutadiene and polystyrene. Nonpolar polymers analyzed with acidic, polar matrices (e.g., RTA) and silver cationization reagents can yield lower quality mass spectral results when interferences due to silver clusters are present. Replacing the polar matrices with nonpolar matrices or the silver salts with copper salts substantially improved the quality of the analytical results. In addition, it was found that silver contamination cannot be completely removed from standard stainless steel sample plates, although the presence of silver contamination was greatly reduced after thorough cleaning of the sample plate with aluminum oxide grit. Carry-over silver may cationize polymer samples and complicate the interpretation of data obtained using nonpolar matrices in the absence of added cationization reagents.  相似文献   
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A short and stereoselective synthesis of conduramine F-1 and ent-conduramine E-1 derivatives have been achieved starting from d-mannitol using nucleophilic vinylation on imine. A concise sequence of vinylation at both ends of d-mannitol and followed by RCM allowed us to prepare target compound.  相似文献   
5.
Using the formulation of Hopke and Slattery, upper and lower bounds on the drag coefficient of a sphere moving slowly in Ellis model fluids have been calculated, over wide range of conditions, and compared with the suitable experimental data available in the literature. C D drag coefficient - d diameter of sphere - El Ellis number - Re Reynolds number based on zero-shear viscosity - V terminal falling velocity of a sphere - X drag correction factor - Ellis model parameter - 0 zero-shear viscosity - 1/2 Ellis model parameter  相似文献   
6.
Since Ghosh and Bard [80] first established the field of clay-modified electrodes some 15 years ago, great strides have been made in understanding the nature of the clay structural units and their impact on transport of a variety of electroactive probes (anions, neutrals, small cations, large cations, and compounds with distributed charge). Great strides have also been made in understanding the nature of the layered material in creating access of interlayer sites (size, charge, iron content, pillaring, and organic tailoring). In the last five years several successful applications of clay-modified electrodes have been achieved. Given the explosive growth in tailoring and construction of novel clay structures it seems reasonable to predict further significant advances in applications involving clay-modified electrodes.  相似文献   
7.
A short and efficient strategy for the synthesis of (?)-cytoxazone, (?)-4-epi-cyoxazone and their analogues by using DDQ mediated diastereoselective intermolecular benzylic amination has been described. Immunological evaluation of their cytokine modulating activity revealed that the change of hydroxy methyl to methyl group increased the cellular immunity in in-vitro cultures. Changes in the stereochemistry of oxazolidine haven't influenced the biological activity.  相似文献   
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Fatigue criterion based on the maximum normal stress acting on a fracture plane with random triaxial stress state is related to an equivalent stress state. Probability density function of the equivalent stress state and its associated parameters are obtained. Planes on which the maximum values of the equivalent stress variance occur are assumed to coincide with the sites of fatigue fracture.  相似文献   
10.
An efficient strategy for the synthesis of dihydroxy chiral amino moiety which can be utilized for the synthesis of polyoxamic acid, 1,4-dideoxy-1,4-imino-d-xylitol, and dihydroxy pyrrolidine by using highly diastereoselective nucleophilic addition on chiral imine has been reported.  相似文献   
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