Comparative analysis of the frequency noise in two distributed circuits of semiconductor self-excited oscillators

Kuibyshev State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 2, pp. 242–245, February, 1989.     

Diffusive motion of iron microcrystals studied by Mössbauer spectroscopy

A new model is presented which explains well the dramatic decrease of the Mössbauer line intensities with raising temperatures for freely dispersed iron microscrystals. In contrast to other theories which consider mainly vibration to be responsible we discuss here the decrease in terms of large amplitude diffusive rotational or translational jumps of the particles. Such diffusive jumps lead — in agreement with the observation — to a strong reduction of the Mössbauer-intensity without broadening the line width in a noticeable way. The typical potential well for a diffusing particle in an equilibrium position is derived quantitatively to be 13 meV. The model might be important also for a new understanding of the dynamics of catalytic clusters either in contact with each other or with larger solid surfaces.Part of this work was supported by the DFG Sonderforschungsbereich 306, Konstanz     

Corn stover fractions and bioenergy

Information is presented on structure, composition, and response to enzymes of corn stover related to barriers for bioconversion to ethanol. Aromatic compounds occurred in most tissue cell walls. Ferulic acid esterase treatment before cellulase treatment significantly improved dry weight loss and release of phenolic acids and sugars in most fractions over cellulase alone. Leaf fractions were considerably higher in dry weight loss and released sugars with esterase treatment, but stem pith cells gave up the most phenolic acids. Results help identify plant fractions more appropriate for coproducts and bioconversion and those more suitable as residues for soil erosion control.     

Nonstoichiometry and low-temperature magnetic properties of FeSi crystals

The results of experimental and theoretical studies of the low-temperature properties of FeSi crystals are presented. The specific features of the magnetic susceptibility are shown to be related to the superparamagnetic behavior of impurity clusters. The thermomagnetic hysteresis phenomena observed are explained using the model of exchange-coupled clusters.     

Use of random numbers in computer simulation of magnetic resonance signals

The proton magnetic resonance spectra of water molecules diffusing over regular sites in natrolite are numerically simulated. Experimental data and the results of simulation are found to be in good agreement in a wide temperature interval including the transition range, where the magnetic resonance spectrum is a superposition of a wide unaveraged spectrum and a spectrum averaged by the motion of molecules. The simulation uses generators of pseudorandom-number Markovian sequences. For a binary Markovian process, it is shown, in particular, that the time within which a physical quantity remains constant is described by an exponentially distributed random number.     

Thermal treatment on composite γ-zirconium phosphate-silica

The prepared amorphous γ-ZrP\SiO₂ composite had a complicated composition, since a part of γ-ZrP is converted to α-form during the exfoliation of it. The γ-ZrP\SiO₂ composite have specific surface area of 421 m²g^–1. The acidic P–OH groups of the lamellae species placed on the surface (it is ≈1.0 meq g^–1), do not destroy until the temperature of 1030 K. During the thermal treatment the total mass loss of 7.79% was found. This value corresponds to 0.42 mole of H₂O per molecule unit. The water loss process was found very slow, because of the placing of bilamellar species in the composite.