The eighth virial coefficient of four- and five-dimensional hard hyperspheres

The eighth virial coefficient for hard hyperspheres is calculated by Monte Carlo techniques. It is found that B8/B(7)2=0.000 274+/-0.000 014 and -0.000 115+/-0.000 012 in four and five dimensions, respectively. The results are in good agreement with the findings of Clisby and McCoy (e-print arXiv:cond-mat0410511), and confirm that B8 is negative in five dimensions.     

Analytical Chemistry of Phases of Variable Composition and the Principles of Stoichiographic Determination of Such Phases in Multielement Multiphase Samples

The general problems of determining the stoichiometry and content of solid phases of variable composition in multielement multiphase substances are discussed. The possibilities and conditions of application of a reference-free stoichiographic method based on the differential dissolution (DD) of components for the analysis of samples containing spatially homogeneous and inhomogeneous phases are considered. The results of mathematical modeling of the DD process for a mixture of phases of constant and variable composition are presented. These data substantiate the use of the stoichiogram affinity criterion for the identification of spatially inhomogeneous phases of variable composition. Examples of applying the DD method to the phase analysis of various substances containing phases of variable composition are given.     

Ammoxidation of methylpyrazine over phosphorus-modified vanadium-titanium catalysts

Vanadium-titanium catalysts modified with phosphorus additives (1-15 wt.% of P₂O₅) have been studied in methylpyrazine ammoxidation. Introduction of high amounts of the additive (≥ 10 wt.% of P₂O₅) results in a decrease in activity and selectivity of the catalysts due to formation of low active phase - a ternary compound with the component ratio V : P : Ti ≈ 1 : 1 : 1 with only one type of slightly distorted tetrahedral vanadium (5+) bound via oxygen to phosphorus (5+). The nature of the active sites of the samples modified with 1-5 wt.% of P₂O₅, similarly to that in the V-Ti-O catalyst, was found to include the V⁵⁺ cations strongly bound with TiO₂ and located in the significantly distorted octahedral oxygen environment. This revised version was published online in June 2006 with corrections to the Cover Date.     

Electronic tongue for quality assessment of ethanol, vodka and eau-de-vie

Rapid quality assessment of alcoholic beverages, including brand identification and detection of products of unacceptable quality or counterfeits is an important practical task. In the present work the multisensor electronic tongue system (ET), based on array of potentiometric chemical sensors was applied to recognition and classification of spirits such as vodka and ethanol used for vodka production and also for eau-de-vie in cognac production. The ET system was capable of detecting presence of contaminant substances in vodka in concentrations exceeding allowed levels as well as of distinguishing vodka complying and not complying with state quality standards. Ten brands of vodka produced at the same distillery using water and ethanol of different purity and various taste additives were discriminated using the instrument. The ET could distinguish synthetic and alimentary grain ethanol as well as alimentary ethanol of different grades (i.e. different degree of purification). A feasibility study was run on several eau-de-vie samples, which included fresh and aged eau-de-vie as well as samples produced using different distillation technology and samples kept in contact with different kinds of oak. The electronic tongue showed a promise as an analytical instrument for rapid quality assessment of spirits.     

Phase transformations in pentagonal nanocrystals

The kinetics of phase transformations in pentagonal nanocrystals with a logarithmic coordinate dependence of the internal stress fields is considered. Such a dependence makes it possible to obtain an exact analytical solution to the problems of diffusion kinetics.     

Sorbents based on transition metal salts for the retention of low molecular weight N-, O- and S-containing organic compounds from the air flow

1. Download : Download high-res image (168KB)
2. Download : Download full-size image