Photoinduced centers in the optically transparent ceramic PLZT 8/65/35

The photoinduced centers in the nominally pure, optically transparent ceramic PLZT 8/65/35 and samples doped with Cu, Mn, Fe, and Co (0.1 and 0.01%) are investigated by ESR at 24 K. Photoinduced ESR signals are observed with g _eff=1.995 and 1.94, caused by Pb³⁺ and Ti³⁺ ions, respectively, and with g _eff=2.015, which can be assigned to an F center, i.e., an electron in an oxygen vacancy. The influence of heating and doping of the samples on the intensity of the ESR signals is studied. An analysis of the results obtained corroborates models of the photoinduced centers and a scheme of their local electronic levels. Fiz. Tverd. Tela (St. Petersburg) 39, 1833–1837 (October 1997)     

Parametric analysis of kinetic models, 10. Catalytic oscillator with a diffustion step

A mechanism of catalytic reaction suggested allows self-oscillations when a step of diffusion exchange is added: Z₁X₁, X₁Y₁, 2X₁+Y₁3Z₁, X₁+Z₂Z₁ +X₂. For the corresponding kinetic model parametric portraits are built and regions with unique unstable steady states (st. s.) are revealed.     

Silicon nitride nanofibers produced by the pyrolysis of SiCl<Subscript>4</Subscript> in H<Subscript>2</Subscript> and N<Subscript>2</Subscript> media

The synthesis of fibrous Si₃N₄ nanostructures by gas-phase chemical deposition during the pyrolysis of silicon tetrachloride in a hydrogen and nitrogen atmosphere was investigated. It was shown that the products contained both amorphous Si₃N₄ nanofibers and their α and β phases both with and without a silicon coating. In addition to the Si₃N₄ nanofibers the products also contained nanoribbons. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 2, pp. 81–84, March–April, 2007.     

Quantum-chemical investigation of the dependence of pK a on the calculated energy of proton removal for certain derivatives of indole and phenol

The total energies of derivatives of N-hydroxyindole, indole, and phenol, and of their corresponding anions have been estimated with the aid of ab initio calculations on the 3-21G basis. The energies of proton removal were calculated from the difference in total energies of the appropriate anions and molecules. By comparing the calculated energies of proton removal with experimental values of pK_a (acidity characteristic) a practically linear dependence was shown for the acidity characteristic on the energy of proton removal for the series of compounds investigated. An empirical formula has been proposed expressing the dependence of pK_a on the energy of proton removal, which makes it possible to predict pK_a in this series by carrying out calculations of the energy of proton removal (transfer). __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 47–50, January, 2006.     

Steady states of three-step heterogeneous reactions on a decaying catalyst

A slow decay of the catalyst's activity may lead to qualitative changes in the phase pattern of the reaction, depending on the reversibility of steps involved in the reaction mechanism.

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Regulation of the spatial organization of DNA molecules in particles of liquid-crystalline dispersions by means of biologically active compounds

Using the “structural conflict” method based on differences in the spatial organization of a liquid-crystalline dispersion (LCD) of DNA-polycation complexes and the DNA cholesteric LCD, it was shown that in a solvent with specific properties, the spatial structure of the LCD of DNA-polycation complexes can be controlled by biologically active compounds (BAC) that cause either dissociation of the DNA-polycation complex or destruction of the polycation molecules. In both cases, the cholesteric structure of LCD typical of the initial uncomplexed DNA molecules is recovered. The recovery of cholesteric LCD of DNA was proved by circular dichroism spectroscopy and confirmed by X-ray diffraction and polarization microscopy. The fact that spatial restructuring of LCD of the DNA-polycation complexes is induced by BAC in low concentrations opens up the possibility for using particles of these dispersions as sensing elements (sandwich-type biosensing units) of biosensor devices. A new method for determination of heparin based on the use of LCD of the DNA-polyconidine complexes was developed. The minimum heparin concentration determined in the sample equals ∼ 0.4–0.5 μg mL⁻¹. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2405–2412, December, 2007.     

A Calorimetric Study of Alloy Formation in Au-Cu and Au-In Systems

A calorimetric study of alloy formation in Au-Cu and Au-In systems was carried out. The heats of mixing, ΔH _mix, were measured at 1380,1484 and 1604 K for Au-Cu and at 1387, 1449 and 1505 K for Au-In in the full concentration range. The results of experiments were described by approximating equations. Observed values of ΔH _mix were discussed using the phase diagrams of the systems. It was shown that the systems become closer to the ideal state with increasing temperature. From the experimental data, the dependencies of the enthalpies of the systems on the composition and temperature were estimated. The simultaneous effects of composition and temperature on enthalpy are represented in 3D diagrams. The specific heats of the alloys, in the temperature range of experiments, were derived from the slopes of enthalpy planes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Scanning tunnelling microscopic investigation of fullerene monolayers

C₆₀ fullerene monolayers have been investigated by scanning tunnelling microscopy/spectroscopy. Single C₆₀ molecules have been resolved and a regular surface lattice structure of fullerene – in – surfactant is observed. Tunnel electron spectroscopic measurements results in typical I(V) curves which are interpreted in terms of the two-junction Coulomb blockade effect.     

On a diffusion model of a catalytic reaction

A model to describe a catalytic reaction with simultaneous diffusion is analyzed. The possibility of formation of periodic structures in space is shown.

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