Crystallization of alkyl-aromatic polyimides (polyalkanimides)

Polyalkane imides based on 3,3′,4,4′-diphenyloxidetetracarboxylic, pyromellitic and 1,4,5,8-naphthalenetetracaboxylic acids, and aliphatic diamines containing 4, 6, 8, 10, or 12 methylene groups have been studied. Relations governing the effect of structure on solubility, heat resistance, density, and crystallizability have been established. Conformation analysis has been carried out and models of the macromolecules have been constructed. The morphology of the crystalline polymers has been studied. For the polymers of the given class, crystallization capability is shown to be associated with the conformational flexibility of the macromolecular unit determining a given acid moiety by the number of methylene groups in the diamine unit.     

Current Trends in Laser Separation of Isotopes in Monatomic Vapors

A comparative analysis of the techniques of laser isotope separation in monatomic vapors is presented. The restraints inherent in the conventional isotope separation technique AVLIS (atomic vapor laser isotope separation) are discussed as applied to the large-scale production of various isotopes. The requirements that should be met by the chemical reactions are formulated for the use of these reactions in isotope separation. The photochemical technique was shown to be quite competitive with the AVLIS.     

Observation of the flux line lattice in high Tc-superconductor Bi2.2Sr2CaCu2OX and Ti2Ba2CaCu2OX single crystals

The flux-line lattice (FLL) has been observed on the (001) face of high T_c Bi_2.2Sr₂CaCu₂O_X and Ti₂Ba₂CaCu₂O_X single cristals using the technique of decorating the sample with small ferromagnetic particles. Strong pinning of the Abrikosov vortices by plane defects along (100) and (010) planes has been found out on Bi_2.2Sr₂CaCu₂O_X. The triangular FLL with a long-range order has been observed on the perfect Ti₂Ba₂CaCu₂O_X single crystal. The penetration depth for a magnetic field parallel to (001) axis has been evaluated as ≤0.2μm at 4.2K for both materials.     

Mass-spectrometric study of isomeric 5-amino-1,2,3-thiadiazoles and 5-mercapto-1,2,3-triazoles

The behavior of the isomeric 5-amino-1,2,3-thiadiazoles and 5-mercapto-1,2,3-triazoles under electron impact was studied. It was shown that mass spectrometry can serve as a rapid and reliable method for the identification of these compounds. Key factors in the assignment of a compound to one or the other class are the peaks of the [M-N₂]⁺ ions, which are more intense in the case of the thiadiazoles, and the ions determined by the decomposition of the prototropic forms of the triazoles. The compositions of the ions were determined by the high-resolution mass spectra.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 681–689, May, 1987.     

Numerical study of the rutile band structure by the Hartree–Fock–Roothaan method in the CO LCAO approximation using the cyclic cluster model

The technique for calculatingmaterial characteristicswith the aid of theHartree–Fock–Roothaan method in the CO LCAO approximation using the cyclic clustermodel is considered. The results of the numerical study are verified for the TiO₂ system. The band gap minimum (2.9 eV) is calculated for the system under consideration.     

Singularities of the boundary of fundamental systems,flat points of projective curves,and Schubert cells

The paper studies the bifurcations of the flat points of projective curves and describes the singularities of the boundaries of the regions where typical three-parameter families of curves have no flat points. A flat-point-preserving transformation group of projective curves is introduced. Finite determinacy and versality theorems are proved for this group. A duality theorem is proved and some results concerning the connection of this problem with other problems of singularity theory are presented.Translated from Itogi Nauki i Tekhniki, Seriya Sovermennye Problemy Matematiki, Noveishie Dostizheniya, Vol. 33, pp. 215–232, 1988.     

Prospects of Employing Metal-Vapor Pulsed Lasers for TV Picture Projection on Large Screens

The possibility of using metal-vapor lasers and picture brightness enhancers for improving the sharpness of TV picture projection on a large screen is demonstrated.     

Boundary Mobility and Energy Anisotropy Effects on Microstructural Evolution During Grain Growth

We have performed mesoscopic simulations of microstructural evolution during curvature driven grain growth in two-dimensions using anisotropic grain boundary properties obtained from atomistic simulations. Molecular dynamics simulations were employed to determine the energies and mobilities of grain boundaries as a function of boundary misorientation. The mesoscopic simulations were performed both with the Monte Carlo Potts model and the phase field model. The Monte Carlo Potts model and phase field model simulation predictions are in excellent agreement. While the atomistic simulations demonstrate strong anisotropies in both the boundary energy and mobility, both types of microstructural evolution simulations demonstrate that anisotropy in boundary mobility plays little role in the stochastic evolution of the microstructure (other than perhaps setting the overall rate of the evolution. On the other hand, anisotropy in the grain boundary energy strongly modifies both the topology of the polycrystalline microstructure the kinetic law that describes the temporal evolution of the mean grain size. The underlying reasons behind the strongly differing effects of the two types of anisotropy considered here can be understood based largely on geometric and topological arguments.