Plasma expansion and band-gap renormalization in CdTe and GaP

Detailed experimental and theoretical investigations, based on direct excite and probe experiments and on line-shape analysis, on the influence of many-body interaction, polar interaction, and transport effects on the energetic position and shape of the electron-hole plasma (EHP) emmission are reported. The comparison of optical EHP properties in an indirect (GaP) and a direct (CdTe) semiconductor of similar polarity offers the possibility of a separation of drift effects and polar effects with respect to band-gap renormalization. Direct evidence of a fast plasma drift in CdTe is obtained by thickness sensitive optical excite and probe experiments.     

Competitive transport of alkali metal ions from aqueous media into toluene solutions of 2-(sym-dibenzo-16-crown-5-oxy)-decanoic acid. A comparative study

Competitive permeation of alkali metal ions from an alkaline source phase into or through a toluene phase facilitated by the lipophilic crown ether carboxylic acid 2-(symdibenzo-16-crown-5-oxy)-decanoic acid is studied in liquid—liquid extraction, bulk liquid membrane transport, and emulsion liquid membrane transport. Most rapid transport was obtained in emulsion liquid membrane experiments. Some differences in selectivity orders for alkali metal permeation were observed for the three separation techniques.     

Die keimbildungskinetik im glasigen selen mit der beimischung des jods

The rate of crystallization of vitreous selenium containing 2 at.% of iodine was studied by calorimetric method in the temperature range 60–90°C. The obtained results satisfy an equation of Avrami. It was found that the exponential parameter z in this equation decreases as the temperature of crystallization increases. It was assumed in the discussion that the parameter z does not depend on the number of all processes occurring during nucleation. It depends only on slowly occurring processes. The increase of temperature probably causes a decrease of the number of slow processes and thus the value of the parameter z is diminished.The activation energy of crystallization is equal to $\text{E}{}_{\mathrm{kr}}\text{= 80}\text{kJ}\text{mol}$ with the standard deviation $\text{s}{}_{\mathrm{E}}\text{= 5.0}\text{kJ}\text{mol}$.     

X-ray microanalysis of 1.5-10 μm particles in metallurgical research

The importance of particle X-ray microanalysis for contemporary metallurgical research has been accentuated. Corrections in the formulae for the geometric modelling method and simplifications in the calculation procedure are introduced. Conditions for successful application of the peak to background ratio method were outlined. Besides these two methods related to isolated particles a new extrapolation method for matrix embedded particles is developed and comments to the particle weight fraction estimation method for the same kind of particles are given.     

Polyethylene/poly(styrene-co-divinylbenzene) sodium sulphonate membranes : Part 1. Synthesis and properties

Transport properties of cation-exchange membranes have been studied. The self-diffusion coefficients of sodium and chloride ions, the transport numbers of sodium ions and water, and the conductivities were measured in 0.1 M sodium chloride at 25°C. The concentration potentials were determined in the system 0.05/0.15 M sodium chloride.The membranes were prepared by sulphonation of oriented polyethylene (PE) film modified with 30 wt % of styrene—divinylbenzene copolymer (poly(St-co-DVB)). The copolymer was introduced by interpolymerization of the monomers within the film without its dissolution. A sequence of membranes having similar ion-exchange capacity but differing in water content was then obtained from sheets of normal PE/poly(St-co-DVB)SO₃Na membranes by expanding them by heating in water followed by a thermal treatment in air.The deviations of the measured transport properties from the behaviour of homogeneous membranes and the analysis of the Kedem—Katchalsky relationships for composite membranes have led to the conclusion that in PE/poly(St-co-DVB)SO₃Na membranes a structure prevails with a series arrangement of layers with different properties.     

Die einwirkung der struktur auf die kristallisationskinetik des glasigen selens

By means of a calorimetric method the rate of crystallization of vitreous selenium samples remelted at various temperatures t_U (225–3502C) was studied at a temperature of 90.0°C. To describe the kinetics the Avrami equation was used. The samples remelted at t_U < 260°C crystallized in one stage, A. For the samples remelted at t_U ? 260°C two stages, A and B, were observed. The rate constants k_Kr = z(L · c_Kr)$\text{1}\text{2}$ and the coefficients z were calculated from the Avrami equation. For the samples remelted at t_U = 225, 250 and 330°C, the activation energy e_kr was determined.The values of z, k_Kr and z · E_Kr were found to decrease as the temperature t_U increased. The kinetics of crystallization probably depend upon the structure of vitreous selenium (i.e. on the number of crystalline regions and on content of the small rings), which in turn is dependent on the temperature _U. This supposition was confirmed mathematically.     

Effect of temperature on spectroscopic features relevant to laser performance of YVO4:Tm3+, GdVO4:Tm3+, and LuVO4:Tm3+ crystals

Optical spectra and luminescence decay curves were measured for thulium-doped YVO(4), GdVO(4), and LuVO(4) single crystals as a function of temperature in the 300-670 K temperature region. In spite of structural similarity, the three systems studied display significantly different transition intensities and nonradiative relaxation rates. It was found, in particular, that the peak value of the pump band absorption intensity diminishes by about 30% for Tm:YVO(4) and Tm:GdVO(4), and the effective emission cross section for the laser transition of Tm(3+) diminishes by a factor of 2 roughly when temperature increases from 300 to 500 K. An unusually small quantum efficiency of the upper laser level in Tm:LuVO(4) has been derived from the analysis of luminescence decay curves.     

Compact pseudo-Riemannian manifolds with parallel Weyl tensor

It is shown that in every dimension n = 3j + 2, j = 1, 2, 3, . . ., there exist compact pseudo-Riemannian manifolds with parallel Weyl tensor, which are Ricci-recurrent, but neither conformally flat nor locally symmetric, and represent all indefinite metric signatures. The manifolds in question are diffeomorphic to nontrivial torus bundles over the circle. They all arise from a construction that a priori yields bundles over the circle, having as the fibre either a torus, or a 2-step nilmanifold with a complete flat torsionfree connection; our argument only realizes the torus case.     

Thermally stimulated currents as a measure of degradation of zinc oxide varistors

ZnO varistor degradation phenomena was studied using thermally stimulated current (TSC) method. It is believed that asymmetrical degradation of V-I characteristics caused by DC biasing is due to charge accumulation on the reverse biased side of ZnO grain barrier. The TSCs' measuring system and cryostat apparatus used in experiment were described. The thermally stimulated currents observed in this study for varistor samples doped with different amounts of Co, due to their recovery from asymmetrical electric stress, could not be controlled by movement of Zn interstitials with activation energy 0.55 v eV, as it is widely believed, for the TSC activation energy determined in this experiment was 0.39 v eV.