Factors affecting the low-dose gamma irradiation of hydrocarbons

The effect of differing conditions on the extent and nature of the damage produced in organic substances by γ-irradiation at low dose rates has been examined by a new chromatographic method which makes detection possible in a region where all other standard techniques fail. Use is made of the fact that certain surface active dyes profoundly affect the shape of a chromatographic band in a manner related to the composition of the material undergoing chromatography.

Taking length of outline per unit area as a measure of the shape of the band on paper impregnated with such dyes, a method of chromatography has been evolved, having a completely standardized development technique for all mixtures which does not require the separation of the components of the mixture.

This outline/area index varies with the temperature according to the nature of the polar groups of the compounds present in the mixture under investigation and with the concentration of the individual components.

It is thus possible to construct a three dimensional diagram having as axes, temperature, concentration and index. The diagram obtained is absolutely characteristic of the composition of a given mixture.     

Potential energy surface and orientational disorder in solid fullerene C60

The polymorphism and molecular disorder in crystalline C₆₀ have been studied by modelling the optimum packing of fullerene molecules by the atom-atomic potential method. The study includes the calculation of minima and saddle points of the potential energy surface with sorting out of the most common space symmetry groups. Two models of intermolecular potential for C₆₀ have been checked, one of which assumes effective charges at the centers of C-C bonds. It has been found that the calculated barrier of reorientations is much lower in the case where the concerted character of rotations of different molecules is taken into account. The model of orientational disorder in the face-centered cubic phase is suggested, which is based on consideration of symmetrically arranged equivalent minima separated by low potential barriers.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1466–1469, August, 1995.The work was financially supported by the Russian Foundation for Basic Research (Project No. 94-03-08895).     

Crossover from quantum to classical transport

Understanding the crossover from quantum to classical transport has become of fundamental importance not only for technological applications due to the creation of sub-10-nm transistors – an important building block of our modern life – but also for elucidating the role played by quantum mechanics in the evolutionary fitness of biological complexes. This article provides a basic introduction into the nature of charge and energy transport in the quantum and classical regimes. It discusses the characteristic transport properties in both limits and demonstrates how they can be connected through the loss of quantum mechanical coherence. The salient features of the crossover physics are identified, and their importance in opening new transport regimes and in understanding efficient and robust energy transport in biological complexes are demonstrated.     

Order–disorder transition and thermal conductivity of (Yb x Nd1− x )2Zr2O7 solid solutions

X-ray diffraction, transmission electron microscopy and a laser-flash method were used to investigate the order–disorder transition and thermal conductivity of (Yb _x Nd_{1? x} )₂Zr₂O₇ (0 ≤ x ≤ 1.00) solid solutions. The structures were found to be pyrochlore-type for 0 ≤ x ≤ 0.25, defect fluorite for 0.45 ≤ x ≤ 1.00 and a mixture of these at 0.30 ≤ x ≤ 0.40. The thermal conductivities of (Yb _x Nd_{1? x} )₂Zr₂O₇ first gradually decrease with increasing temperature, and then increase slightly above 800°C due to the increased radiation contribution. YbNdZr₂O₇ has the lowest thermal conductivity due to the reduced cation mean free path at the compositional combination of equal molar Yb³⁺ and Nd³⁺ cations.     

Density of states and extent of wave function: two crucial factors for small polaron hopping conductivity in 1D

Abstract

We introduce a theoretical model to scrutinize the conductivity of small polarons in 1D disordered systems, focusing on two crucial – as will be demonstrated – factors: the density of states and the spatial extent of the electronic wave function. The investigation is performed for any temperature up to 300 K and under electric field of arbitrary strength up to the polaron dissociation limit. To accomplish this task, we combine analytical work with numerical calculations.     

Ethane Bond Length in 1,2-Diphenylethanes

Crystal structures of 1,2-diphenylethane (1), 1,2-bis(4-dimethoxyphenyl)ethane (3), 1,2-bis(2,3-dimethylphenyl)ethane (4), 1,2-bis(2,4-dimethylphenyl)ethane (5) and 1,2-bis(2,4,6-trimethylphenyl)ethane (6) were determined by X-ray diffraction analysis at various temperatures. An apparent shortening of the ethane bond and its temperature dependence were observed and it was interpreted as an artifact caused by the torsional vibration of the C—Ph bonds in crystals. The extent of the shortening was dependent on the compounds and was explained in terms of the difference in the amplitude of the torsional vibration controlled by ortho methyl groups. In the crystal structures of 1, a so far unrecognized orientational disorder was observed at room temperature and 315 K. The disorder, which disappeared at lower temperatures, proved to be dynamic and was ascribed to a conformational interconversion through a very large amplitude torsional vibration. The disorder might be another reason for the exceptionally short ethane bond in 1.