Specific features of optical properties of helical liquid crystals with a large helix pitch

Light propagation in helical liquid crystals with the helix pitch considerably exceeding the light wavelength is studied. Using a multidimensional analog of the WKB method, the Green function of the electromagnetic field in such a medium is calculated. This function contains terms corresponding to ordinary and extraordinary waves. The behavior of the Green function in the far-field region is analyzed. It is shown that for the extraordinary ray there exists, on the surface of the wave vectors, a forbidden zone, which, due to periodic changes of the refractive index, corresponds to conditions of the beam turn with the formation of a flat wave channel. The extraordinary beam trajectory, both inside and outside the wave channel, determined by the ray vector, is not flat. The asymptotic behavior of the Green function inside and outside the wave channel is substantially different.     

Stabilities of a series of dipyrrin difluoroborates in protic solvents in the ground and electron-excited states

The spectral-luminescent properties of a series of new functionally substituted dipyrrin fluoroborates (BODIPY) in acidified ethanol solutions are studied. The complex stabilities in the ground and excited states are estimated and the quantum yields of phototransformations on exposure to laser radiation are measured.     

Synthesis of 1,3,7-triazapyrene and 1,2,3,7-tetraazapyrene derivatives as a result of anomalous Hoesch reaction

Method for the synthesis of 6,8-diaryl-1,3,7-triazapyrenes and 6,8-diaryl-1,2,3,7-tetraazapyrenes, based on the reaction of 2-R-1H-perimidines and 1H-naphtho[1,8-de][1,2,3]triazine with aromatic nitriles in polyphosphoric acid, has been elaborated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 209–210, January, 2008.     

Chromium interaction with blue-green microalga <Emphasis Type="Italic">Spirulina platensis</Emphasis>

The interaction of different chromium species with blue-green microalga Spirulina platensis was studied by neutron activation analysis (NAA). It was found that, in contrast to other microorganisms, spirulina predominantly assimilates nontoxic, essential Cr(III) species rather than the toxic Cr(VI) species. Photometry and EPR proved the absence of toxic chromium species with high degrees of oxidation in the course of Cr(III) accumulation by S. platensis cells. The relationship between the Cr(III) concentration in the chromium-containing spirulina biomass and the chromium concentration in the nutrient medium was found; it can be used for the determination of Cr(III) concentrations necessary for cell cultivation. The control of the protein composition and cytological status of cells showed that the S. platensis biomass assimilated Cr(III) in necessary concentrations under the selected conditions retained its protein composition and useful natural properties, and, hence, could be used for medical and preventive purposes.     

Photophysics of the analogs of pyrromethene PM 567

The spectral and luminescence properties of a number of pyrromethene (PM) dyes have been investigated. The absorption and luminescence spectra of PM molecules in different solvents are measured. The electronic structure and electronic excited states are calculated by the method of intermediate neglect of differential overlap with special spectroscopic parameterization. The rate constants of photophysical processes are estimated, and the fluorescence quantum yields are calculated. The fluorescence quantum yields of PM I and PM II molecules are found to decrease upon their excitation to the second short-wavelength absorption band. This phenomenon is interpreted.     

The thermodynamic characteristics of point defects and the mechanism of charge transfer in lanthanum cobaltite doped with strontium and nickel

The specific conductivity and thermal electromotive force (EMF) coefficient of lanthanum cobaltite doped with strontium and nickel La_0.9Sr_0.1Co_0.9Ni_0.1O_3−δ were measured over the temperature and pressure ranges 1023–1223 K and 10⁻⁶−1 atm. The oxide was found to exhibit metallic-type conductivity (800 Ω⁻¹ cm⁻¹ ≤ σ ≤ 1150 Ω⁻¹ cm⁻¹) and small positive thermal EMF coefficient values. A joint analysis of the thermodynamic characteristics of formation of point defects and external T and p _{O 2} parameter dependences of conductivity and thermal EMF showed that charge was transferred in the oxide by small-radius polarons according to the hopping mechanism. The role of polarons was played by electrons Me ^′_Co and holes Me ^•_Co localized on 3d transition metals. The isothermal dependences of the concentrations and mobilities of charge carriers on the degree of oxygen nonstoichiometry of the oxide studied were calculated.