EPR investigation of a-Si:H aerosol particles formed under silane thermal decomposition

The dangling bond defects were investigated in a-Si:H particles formed under silane thermal decomposition in flow reactor. EPR together with hydrogen evolution method were used. The experimental results allowed us to conclude that there are two kinds of dangling bond defects in a-Si:H aerosol particles. The defects of the first kind are localized on the surface of interconnected microvoids and microchannels (surface dangling bonds) and those of the second kind are embedded in amorphous silicon network (volume dangling bonds). The thermal equilibration of dangling bonds and temperature dependence of equilibrium dangling bond concentration were investigated. It was found that at temperatures > 400 K the dangling bond concentrationNApplied Magnetic Resonance _s reversibly depends on sample temperature. The volume dangling bond concentration increases with temperature increasing (the effective activation energy of dangling bond formationU > 0), and the surface dangling bond concentration decreases with temperature increasing (U < 0). It has been found that EPR line is considerably asymmetric for samples with high hydrogen content and for low hydrogen content the EPR line is weakly asymmetric. A conclusion was drawn that the asymmetry degree depends on amorphous silicon lattice distortions. This conclusion has been confirmed by EPR spectra simulations.     

Spatial distribution of spin-labeled trichogin GA IV in the gram-positive bacterial cell membrane determined from PELDOR data

Trichogin GA IV is one of the shortest acyclic linear polypeptide antibiotics of fungal origin, characterized by the presence of three α-amino isobutyric acid residues, an N-octanoyl group and an amino alcohol at the C terminus. Its antibiotic activity is generally thought to be based on its self-assembling and membrane-modifying properties. The technique of double electron-electron resonance in electron spin echo is used to study the spatial distribution of spin-labeled [TOAC-4]-trichogin GA IV analog bound to the cell membrane of the Gram-positive bacteriumMicrococcus luteus. The intermolecular dipole-dipole spin-spin interaction of TOAC spin labels has been experimentally studied at 77 K in glassy dispersions of the spherical cell particles. It is shown that the nonaggregated peptide molecules are distributed at the cytoplasmic membrane. Two possible distribution models are proposed: (i) the peptide molecules are randomly distributed on both inner and outer membrane surfaces with a distance between the surfaces of 7 nm, (ii) the molecules are randomly distributed in a layer up to 2.4 nm from the external surface of the membrane.     

Selection of a piezoelectric sensor array for detecting volatile organic substances in water

Sensitive coatings for piezoelectric sensors used to assess the presence of anthropogenic volatile organic substances in the equilibrium gas phase over natural water have been selected using an array of measuring elements, and the data have been processed using principal component analysis. Groups of piezoelectric sensors with similar characteristics for substance identification have been determined based on the correlation between piezoelectric sensor responses when vapors of organic substances were detected. The stepby-step optimization of the piezoelectric sensor array has been carried out in order to identify the greatest number of organic compounds (vapors) in the sample. Volatile organic compounds can be identified in their aqueous solutions and natural water using the optimized piezoelectric sensor array.     

Increased sensitivity and localization in microspectral analysis of alloys

Methods of improving the sensitivity and localization are developed, which are based on restricting the discharge area with corundum rings. These two features are shown to be dependent on the shape and initial diameter of the ring, the duration of the discharge, and the parameters of the power supply.     

Registration temperature effect in polymers: Physico-chemical aspects

Registration temperature effect in two different polymers - poly(ethylene terephthalate) (PET) and polypropylene (PP) films - is investigated. Temperature effects on track formation are considered in terms of molecular mobility and relaxation transitions. The track eth rate is measured as a function of irradiation temperature in the range of 77 to 373 K. The obtained results are compared with the radical yields, radiothermoluminescence curves and thermally stimulated currents measured with the aim of detecting changes in the mobility of macromolecules and radiolysis intermediates. It is found that the change of the track etch rate with changing registration temperature correlates with γ- and glass transitions in PP and with β-and glass transitions in PET.     

Stability of equilibria in evolution game models

Translated from Sistemnoe Programmirovanie i Modeli Issledovaniya Operatsii, pp. 174–182, 1993.     

Application of electron spin echo ESR-tomography to study radical diffusion in porous media

ESR-tomography based on electron spin echo was used to study the translational diffusion of stable radical 2,2,6,6-tetramethyl-4-pipyridinoxyl in the solutions filling the pore space of silica gel. The values of the efficient diffusion coefficients were measured for the solution of radicals 2,2,6,6-tetramethyl-4-pipyridinoxyl in methanol and 2-methyl-tetrahydrofuran, depending on the mean size of the silica gel pore. It was shown that the value of the diffusion coefficient decreased as pore size decreased, and furthermore depended on the solvent type. A linear relation between the diffusion coefficient and the spin exchange constant was established within the scope of the quasihomogeneous diffusion model.