The structure and properties of a new type of nanostructured composite Si/C electrodes for lithium ion accumulators

The results obtained in studies of the structure and electrochemical properties of film electrodes prepared by magnetron plasma sputtering of silicon and graphite and working under the conditions of lithium injection and extraction are generalized. Composite silicon-carbon electrodes synthesized by depositing silicon and carbon nanolayers with the use of a magnetron plasma were films 100–500 nm thick. Part of them exhibited highly uniform nanogranular structure based on a carbon matrix with inserted silicon clusters of size below 6 nm. The nanogranular structure of Si/C composites was observed for the first time; such a morphology was not characteristic of not structured silicon layers deposited under equal conditions. The factors that determined the electrochemical charging-discharging behavior of new composites were the degree of uniformity of the nanogranular structure, the ratio between the silicon and carbon components, and film thickness. For two thin films, the initial composite capacitance was higher than that corresponding to the Li_4.4Si stoichiometry for the silicon component and LiC₆ stoichiometry for the carbon component, which was related to the special nanostructured state of silicon and carbon. The effects (luminescence band and absorption bands in the visible range) characteristic of nanosized silicon particles were observed.     

Coupling of mixed finite elements and boundary elements

The symmetric coupling of mixed finite element and boundaryelement methods is analysed for a model interface problem withthe Laplacian. The coupling involves a further continuous ansatzfunction on the interface to link the discontinuous displacementfield to the necessarily continuous boundary ansatz function.Quasi-optimal a priori error estimates and sharp a posteriorierror estimates are established which justify adaptive mesh-refiningalgorithms. Numerical experiments prove the adaptive couplingas an efficient tool for the numerical treatment of transmissionproblems.     

Spectral-luminescent parameters of the amniotic fluid

Absorption and luminescence excitation and emission spectra of the amniotic fluid from females with a normal course of pregnancy and with fetation anomalies are investigated. It is shown that the amniotic fluid manifests, in addition to an intense UV luminescence, a luminescence in the range of 380–650 nm. The first luminescence peak with λ_max = 430–450 nm is most likely due to the presence of NADH₂ and hormones in the amniotic fluid, whereas the peak located at longer wavelengths with λ_max = 520–540 nm is due to pigments (bilirubin, etc.). Differences in absorption spectra of the amniotic fluid in the case of the normal course of pregnancy and upon its pathologies are established. Luminescence emission and excitation spectra of the amniotic fluid in cases of intrauterine fetation pathologies are shifted toward the longwave region compared to normal pregnancy cases. It is concluded that the spectral-luminescent analysis of the amniotic fluid can be used as an additional rapid test for monitoring of intrauterine fetal pathologies. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 939–942, November–December, 1998.     

Solid-state polymerization of diacetylenes under the action of outside forces on crystalline monomer lattice

The polymerization of crystalline diacetylenes TS and DCH with different lattice structure was studied under high hydrostatic pressures (up to 4 kbar). It was shown that pressure increases the deformation of chain growing in monomer crystal. The features of such deformation depend on lattice structure that governs the influence of pressure on polymerization rate. We studied also polymerization of diacetylene HD crystals obtained in the pores of stretched polymer (PP). The field of polymer matrix influences the crystal state and the rate of polymerization. It was shown that the interaction of monomer crystals with the matrix leads to growth of more strained chains in these crystals.