Effect of strain in crystal on the forbidden reflections in the resonant diffraction of synchrotron radiation

The effect of strain (either static or caused by long-wavelength acoustic oscillations) on the energy spectrum and the azimuthal dependence of the intensity of “forbidden” reflections in crystals at the energy of incident radiation close to the absorption edge is considered. It is shown that a strain causing a weak change in the unit-cell symmetry may additionally contribute to the tensor atomic factor. Examples of changes in the azimuthal dependence of forbidden-reflection intensity in zinc oxide ZnO and potassium dihydrogen phosphate KH₂PO₄ are considered.     

Isosteviol and some of its derivatives as receptors and carriers of amino acid picrates

The ability of diterpenoid isosteviol 1 (ent-16-oxobeyeran-19-oic acid) and some of its derivatives with ester and amide groups to bind amino acid picrates in the course of their transport through a liquid chloroform membrane was observed for the first time. Isosteviol was very competitive with dibenzo-18-crown-6 and N,N′-bis(isostevioyl)-1,4-phenylenediamine 5 was even more effective in transportation of d,l-tryptophan through a liquid chloroform membrane.     

Peculiarities of electrodialysis processing of mineralized human exometabolites

The possibilities of the electrodialysis method in processing solutions of mineralized human exometabolites, where the dialysate is used for watering plants and the concentrate is subjected to further processing to afford common salt, are considered. The effect of the degree of solution purification from organic compounds on the electrodialysis rate is studied. Solutions are purified on carbon sorbent Sibunit which can be repeatedly recovered. The optimal parameters of the sorption stage of purification, namely, solution pH 2–4; contact time 1.5–2 h, specific consumption of sorbent 300 g/L, are determined. It is shown that the preliminary enzymatic degradation (enzymolysis) of urea by urease and, especially, the sorption cleaning of solution considerably accelerate the transmembrane mass transfer, remove complications of this process (precipitation), and favor both the dialysis with the preset degree of desalination with respect to sodium ions (which inhibit the plant growth) and the formation of the organic-free concentrate that can be used in the further extraction of dietary salt.     

Recyclization of dimedone adduct with 2-(2-oxo-2-phenylethylidene)propanedinitrile in the reaction with N-nucleophiles

Three-component condensation of dimedone with phenylglyoxal hydrate and malononitrile gave a polyfunctional 5,6,7,8-tetrahydro-4H-chromene derivative, 2-amino-4-benzoyl-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile, which reacted with ammonium acetate to produce pyrrolo[3,4-c]quinoline ring system. Reactions of the condensation product with primary and secondary amines and hydroxylamine hydrochloride afforded polysubstituted pyrroles, whereas the reaction with hydrazine hydrate led to 3-amino-6-phenylpyridazine-4-carbonitrile.     

Silver dissolution in acid thiocarbamide solutions containing sulfide ions

Regularities of silver dissolution in acid thiocarbamide electrolytes are studied. The kinetics of the process is shown to be severely affected by the admixture of hydrogen sulfide molecules that form upon inserting sodium sulfide or accumulate in electrolyte with the passage of time elapsed since its preparation. Catalytic effect increases with increasing length of time of the electrode’s contact with solution prior to the beginning of experiment or following an increase in the concentration of sulfide ions. Experiments with the surface renewed in the course of potential scans show that the catalytic effect is connected with the adsorption of sulfide ions on an interface. At large values of the surface coverage with sulfide ions, the dissolution rate increases so much that the dissolution process starts to be limited largely by the process of supply of thiocarbamide molecules toward the electrode surface.     

Mass-spectrometric study of thermodesorption from the surface of rutile successively modified with butylamine and acetic acid

Using the method of mass-spectroscopic thermal analysis, it has been shown that when the surface of rutile is modified with n-butylamine and acetic acid, it is possible for the two substances to interact in the surface layer, with the result that the order in which the amine and the acid are adsorbed affects the structure of the resulting adsorbed layers. The chemisorbed layer on the surface of a sample of TiO₂-AA-BA consists of molecules of both modifiers and the product of their surface reaction. Acetic acid adsorbed on TiO₂-BA displaces the coordinatively bound amine molecules from the surfaces, leading to the formation of butylacetamide and the chemisorption of the acid molecules on unoccupied areas of the TiO₂ surface.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 305–310, February, 1991.     

Resonant X-Ray Diffraction: Forbidden Bragg Reflections Induced by Atomic Displacements

The displacements of atoms from their equilibrium sites with high symmetry are accompanied by the appearance of the additional components of the resonant susceptibility tensor and become a source of additional anisotropy of resonant X-ray scattering. As a result, forbidden Bragg reflections can appear near absorption edges, which are absent far from the edges in a regular crystal. These reflections can be induced by dynamic thermal atomic vibrations or by static displacements because of modulation and point defects. A theoretical approach is suggested that allows the calculation of the susceptibility tensor and a set of forbidden reflections, in the case of small atomic displacements. This approach is based on the calculation of the displacements using the mechanic representation of space groups. The example of a space group Pnma with resonant atoms in 4(c) position is discussed in detail.     

Oscillatory instability of the Couette flow between two unidirectionally rotating cylinders

In the problem of stability of the Couette flow between unidirectionally rotating cylinders, bifurcation points of codimensions 1, 2, and 3 are calculated. These points are interesting because in their small neighborhood the sequences of fluid flow bifurcations, including the development of chaotic regimes, can be studied analytically by completely correct methods. It is found that at large rotation velocities of both cylinders the pattern of the neutral curves corresponding to bifurcation points of codimension 1 changes and various intersections of two and three neutral curves (bifurcation points of codimensions 2 and 3) appear.     

Influence of the material hardening and compressibility on the solution of elastoplastic deformation problems for a space with a cylindrical cavity

The present paper deals with plane deformation problems (ɛ _z = 0) concerned with elastoplastic deformation of a space with a cylindrical cavity in the case where the load is given either at infinity or on the cavity surface. It is assumed that the material obeys the relations of the theory of flow with isotropic hardening and the von Mises plasticity condition. The effects of the elastic compressibility (Poisson’s ratio) and the coefficient of linear hardening on the stress-strain state are studied. The influence of the linear hardening is shown to be small, while that of the elastic compressibility is shown to be quite significant.