On the role of relaxation processes in the acoustic mechanism of supramolecular structure formation in nematic liquid crystals

We have for the first time developed and tested a model constructed on the basis of nonequilibrium hydrodynamics and postulating that the structural relaxation processes of a nematic liquid crystal (NLC) in wave fields are important for the formation of supramolecular structures in the form of a system of linear domains in a planar mesophase layer. Distortions in the macrostructure of an NLC layer in the field of longitudinal waves were observed in the frequency range of 0.9–18.9 MHz. The values of the spatial period of domains at the threshold of the effect and the threshold amplitudes of the vibrational speed were determined for 10–300-μm-thick layers in wave fields with different degrees of uniformity for the temperature range where the mesophase exists. The simulation results are compared to experimental data.     

Exploring the Subtle Effect of Aliphatic Ring Size on Minor Actinide-Extraction Properties and Metal Ion Speciation in Bis-1,2,4-Triazine Ligands

The synthesis and evaluation of three novel bis-1,2,4-triazine ligands containing five-membered aliphatic rings are reported. Compared to the more hydrophobic ligands 1 – 3 containing six-membered aliphatic rings, the distribution ratios for relevant f-block metal ions were approximately one order of magnitude lower in each case. Ligand 10 showed an efficient, selective and rapid separation of Am^III and Cm^III from nitric acid. The speciation of the ligands with trivalent f-block metal ions was probed using NMR titrations and competition experiments, time-resolved laser fluorescence spectroscopy and X-ray crystallography. While the tetradentate ligands 8 and 10 formed Ln^III complexes of the same stoichiometry as their more hydrophobic analogues 2 and 3 , significant differences in speciation were observed between the two classes of ligand, with a lower percentage of the extracted 1:2 complexes being formed for ligands 8 and 10 . The structures of the solid state 1:1 and 1:2 complexes formed by 8 and 10 with Y^III, Lu^III and Pr^III are very similar to those formed by 2 and 3 with Ln^III. Ligand 10 forms Cm^III and Eu^III 1:2 complexes that are thermodynamically less stable than those formed by ligand 3 , suggesting that less hydrophobic ligands form less stable An^III complexes. Thus, it has been shown for the first time how tuning the cyclic aliphatic part of these ligands leads to subtle changes in their metal ion speciation, complex stability and metal extraction affinity.     

Domain structure in a nematic layer under oscillatory Couette flow

The formation of a spatially modulated structure (domains) in a homeotropically aligned layer of a nematic liquid crystal (NLC) under an oscillatory Couette flow are described theoretically by using the hydrodynamic equations for an NLC which are linearized with respect to perturbations. The shear frequencies at which the phenomenon is determined by the inertial properties of the medium are considered. It is shown that the domain size is equal to the thickness h of an NLC layer and that the dependence of the threshold value of the shear amplitude u _th on the frequency ω and the layer thickness h is described by the expression u _th = const/(ωh²). The calculated results are compared with the experimental data.     

Synthesis of 3-Substituted Arylpyrazole-4-carboxylic Acids

A method was suggested for preparing previously unknown 3-aryl-substituted pyrazole-4-carboxylic acids, involving Vilsmeier formylation of semicarbazones of 26 available mono- and disubstituted acetophenones and 2-acetylthiophene followed by oxidation of the resulting 3-aryl-substituted pyrazole-4-carboxaldehydes under the action of potassium permanganate. The mechanism of the formylation reaction is discussed. The method successfully works even with acetophenones containing alkyl substituents. In the latter case, an additional stage that involves isolation of pyrazole-4-carboxylic acids as their silyl esters is used.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 5, 2005, pp. 829–835.Original Russian Text Copyright © 2005 by Lebedev, Lebedeva, Sheludyakov, Kovaleva, Ustinova, Kozhevnikov.     

Synchrotron and Undulator Radiation Experiments on the SIRIUS Synchrotron

This paper discusses the main results of synchrotron and undulator radiation experiments performed on the SIRIUS accelerator at Tomsk Polytechnical University. Some examples of the use of the SIRIUS synchrotron as a vacuum UV and soft-x-ray source for investigations in solid-state physics and for applied research are given.     

Simulation of the propagation of a light pulse in a randomly inhomogeneous medium

The propagation of a Gaussian pulse in an inhomogeneous medium is considered. The detected pulse is represented as a series in the scattering multiplicities. The developed approach enables one to describe the passage of a pulse through a randomly inhomogeneous medium in the general case, beyond the framework of the diffusion approximation. The known results of the diffusion approximation are shown to represent limiting cases of the expansion constructed in the scattering multiplicities. The calculations are performed by the Monte Carlo method for cases of singly and multiply scattering media. The agreement between the results of the theoretical analysis and the numerical simulation allows one to use the approach developed in both optical problems and investigation of propagation of waves of other nature, in particular, seismic waves.     

Nucleophilic substitution or dipolar 1,3-cycloaddition in reactions of cyanamide with 4-arylpyrimidine 1-oxides

Pyrimidine 1-oxides with cyanamide afforded 2-ureidopyrimidines as the result of the nucleophilic substitution of hydrogen, whereas the formation of similar 2-trichloroacetylaminopyrimidines occurs as dipolar 1,3-cycloaddition of the same oxides to trichloroacetonitrile under much more drastic conditions and in lower yields.     

Quantum field theory and the new phase of the study of hadron production mechanisms caused by high experimental accuracy

Modern experiment makes it possible to solve many problems of hadron physics both rather old and new ones. In particular, during implementation of the project, mechanisms of production of the light scalar mesons in photon-photon collisions are established; i.e., the question raised thirty years ago is solved.