Study of the Hubbard model at half filling

Under the conditions of a strong Coulomb repulsion between electrons at a lattice site, we now study the equations for the self-energy part of the electron Green’s function, which we previously obtained using the generating functional method. These equations have a form close to that corresponding to the self-consistent Born approximation in the weak-coupling theory. In these equations, we omit the dependence of the self-energy on the momentum, which corresponds to the infinite-dimensional space limit. We then numerically solve the integral equations, where all the variables depend only on the frequency, and obtain results consistent with the dynamical mean field theory. In particular, we show that as the Coulomb repulsion increases, the three-peak structure of the quasiparticle spectrum changes into a two-peak structure and the metal–insulator phase transition occurs. The proposed method can be used to study other models of the theory of strongly correlated systems. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 154, No. 1, pp. 63–76, January, 2008.     

Effect of pressure on the structure of composite chitosan films obtained from solutions in carbonic acid

The effect of pressure in solutions of chitosan in carbonic acid with the AgNO₃ precursor on the structure of cast nanocomposite films with silver nanoparticles has been studied for the first time. The size of silver nanoparticles can be controlled by varying pressure in carbonic acid.     

Fast magnetic relaxation, studied by microwave absorption in neutron-irradiated YBa2Cu3O7−x ceramic

A contactless microwave method is used to measure the fast magnetic relaxation of granular ceramic samples of YBa₂Cu₃O_7−x irradiated by neutrons with fluences of 10¹⁶–10¹⁹ cm⁻². An experimental study of the time dependence of the relaxation of high-frequency (rf) absorption (f=100 MHz) after the action of an external magnetic field pulse has shown the magnetic relaxation times τ ₀ to be in the time interval of 0.5–150 ms. The rf-absorption mechanism is discussed in terms of an intergranular system with a thermally activated flux of vortices and their diffusion in the granular medium. Fiz. Tverd. Tela (St. Petersburg) 39, 977–981 (June 1997)     

Synthesis and properties of 3-substituted 3-azabicyclo-[3.3.1]nonan-9-amines

Catalytic hydrogenation of 3-benzyl- and 3-tert-butoxycarbonyl-3-azabicyclo[3.3.1]nonan-9-one oximes over Raney nickel gave the corresponding 3-substituted 3-azabicyclo[3.3.1]nonan-9-amines which were converted into amides via reactions with acetyl and chloroacetyl chlorides and maleic and succinic anhydrides, into Schiff bases by condensation with benzaldehyde and 4-chlorobenzaldehyde, and into isothiocyanates by treatment with thiophosgene in the presence of K₂CO₃. 3-Benzyl- and 3-tert-butoxycarbonyl-3-azabicyclo-[3.3.1]nonan-9-yl isothiocyanates readily reacted with methanol, aniline, and sodium azide to produce methyl thiocarbamate, thiourea, and dihydrotetrazole-5-thione derivatives having a 3-azabicyclo[3.3.1]nonane fragment.     

Laser-Synchrotron Facility of the National Research Centre “Kurchatov Institute”

Crystallography Reports - The laser-synchrotron facility (LSF) of the National Research Centre “Kurchatov Institute” (NRC KI) is a unique research complex that combines unprecedented...     

Biological Xenogenic Vessel Prostheses: Effect of H<Subscript>2</Subscript>O/CO<Subscript>2</Subscript> and EtOH Media on the Structure and Mechanical Properties of the Bovine Jugular Veins

The effect of the H₂O/CO₂ and EtOH/CO₂ media at pressures and temperatures corresponding to the formation of supercritical (sc) carbon dioxide on the structure and mechanical properties of bovine jugular veins was studied for the first time. Treatment of bovine jugular veins in an sc-CO₂ + ethanol or sc-CO₂ + water medium considerably devitalized the tissue and increased the tissue elasticity, which allows considering the treated veins as promising vascular grafts with expected high capacity to suppress calcification and good hemodynamic properties.     

Catalytic properties of SnO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> compositions in total methane oxidation

Tin and titanium dioxides and their compositions were studied as catalysts for the reaction of complete oxidation of methane. The catalytic activity of the test samples was compared in terms of first-order reaction rate constants with reference to the unit surface area of a catalyst. The crystal structures and specific surface areas of the obtained compositions were characterized. The thermal stability of SnO₂ was investigated. Data on the temperature-programmed reduction of SnO₂ and the composition Sn_0.70Ti_0.30O₂ in hydrogen were given.     

Oligosaccharide sequencing by means of mass spectrometry—I: N-phenylosotriazole acetates

Fragmentation of the acetates of the N-phenylosotriazoles of some mono-, di, tri-, tetra- and pentasaccharides under electron-impact (EI) has been studied. The mass spectra of these derivatives can be used for determination of the sequence of monosaccharide units in oligosaccharides (oligosaccharide sequencing), of molecular weight, of the location of the position of the interglycosidic bond in disaccharides and of the position of the methyl group in partially methylated monosaccharides.     

Thermal decomposition of alkylcyclohexane mixtures

Thermal decomposition of model alkylcyclohexane mixtures with different ratios of components has been investigated. The possibility to estimate the yield of reaction products by calculating the relative activities of a group of hydrocarbons is shown.

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