Structure of Thermal Radio Emission from the Atmosphere in the Middle Part of the Submillimeter Wavelength Range

We present the results of theoretical studies of the structure of thermal radio emission from the Earth's atmosphere in the middle part of the submillimeter wavelength range (wave numbers 1/ 20–50 cm^-1). Absorption spectra of the atmosphere, heights at which the radiation is formed, and other physical factors, which determine the features of the inverse problems of remote sensing in the band considered, are analyzed.     

The effect of microwave pulse duration on the distance distribution function between spin labels obtained by PELDOR data analysis

A method is proposed for obtaining a distance distribution function between spin labels in spin-labeled molecules on the basis of the data of pulsed electron-electron double resonance with regard to the finite duration of microwave (mw) pulses. It is shown that taking into account the finite duration of mw pulses makes it possible to extend the range of the studied distances between spin labels to the region of short distance in which the magnitude of the dipole-dipole interaction becomes comparable to or exceeds the spectrum widths of exciting mw pulses. With frozen glassy solutions of biradicals as model systems with a length between spins of less than 2 nm, the shape for the distance distribution function between labels was obtained, and the value and sign of the exchange interaction were estimated. It is demonstrated that the analysis of the dipole-dipole interaction neglecting the duration of mw pulses can lead to substantial distortions in the shape of the distance distribution function.     

Influence of structural defects on magnetic properties of the submicrometer ceramic Mn3O4

A high-density single-phase submicrometer ceramic Mn₃O₄ with a grain size d ≥ 0.06 μm has been obtained by using spherically converging shock waves. The action of shock waves reduces the unit cell volume and increases the Curie temperature T _C . The shape of the temperature dependences of reciprocal susceptibility x ^?1 of a polycrystal and the submicrometer ceramic at T > T _C is hyperbolic, which is typical of ferrimagnets. It is shown that the susceptibility of the ceramic in the region of short-range order at 78 K ≤ T ≤ 300 K is larger than that of the polycrystal, while the field dependences of the magnetization are nonlinear. The bombardment by electrons with a small dose of Φ = 0.8 × 10¹⁸ cm^?2 increases the susceptibility of the submicrometer ceramic as well as that of the polycrystal. When the fluence increases to Φ = 5 × 10¹⁸ cm^?2, the susceptibility decreases, which can be explained by radiation-induced disordering and a change in the “local” exchange interactions.     

Kinetics of cleansing action of sodium alkylbenzenesulfonate-sodium carbonate binary solutions

Kinetics of cleansing action of sodium alkylbenzenesulfonate-sodium carbonate binary solutions, as the most widely used components of synthetic detergents, is studied using the procedure based on direct determination of the weight fraction of pollutants removed from the fabric. The effective kinetic parameters of the cleansing process are determined.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 11, 2004, pp. 1858–1860.Original Russian Text Copyright © 2004 by Kotomin, Naumov, Yakimchuk.     

Molecular structure of two substituted 2,7-dioxa-1-phosphabicyclo[3.2.0]hept-4-enes

A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Science Center, Russian Academy of Science. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 5, pp. 145–147, September–October, 1992.     

Crystal-chemical analysis of the structures of oxalic acid and its salts M x (C2O4) y ·nH2O (n=0−3)

Crystal-chemical analysis of the structures of oxalic acid and its salts M_x(C₂O₄)y·nH₂O (n=0?3) is carried out. It is shown that the dimensions of oxalate ions play a critical role for closest packing in the structures of the acid and anhydrous and aqueous metal salts. In most compounds, the centers of masses of oxalate ions lie in the planes and form trigonal loops with average bond lengths and angles of 5–6 Å and 60°, respectively. The dimensions and distortions of the nets depend on the proximity of the cations and/or water molecules to the planes. For the structures of one cation, the influence of the quantity of water on the arrangement of oxalate ions is shown. The relationship between the polymorphism and variations of orientations and packings of oxalate ions is discussed. The analysis gives grounds for predicting the structural arrangement of ionic or molecular compounds provided that the structure-forming units have a pseudospherical form.     

Heteroorganic furan derivatives. 62. The molecular and crystal structure and reactivity of 2-furylhydrosilanes

In contrast to reported hydrosilanes with alkyl and aromatic substituents at the silicon atom, 2-furyl-, di(2-furyl)- and tri(2-furyl)silanes undergo dehydrocondensation with water, while di(2-furyl)silane also undergoes this reaction with ethanol in the absence of catalyst. The structures of 2-furyl-, di(2-furyl)- and tri(2-furyl)silane were studied by electron diffraction.For Communication 61, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 25–30, January, 1987.     

Statistical analysis of spectra of single impurity molecules and dynamics of disordered solids: II. Manifestation of interaction of two-level systems with impurity molecules at different distances

Manifestations in the spectra of impurity chromophore molecules in a disordered solid matrix of the interaction of these molecules with two-level systems (TLSs) of the matrix are analyzed. The characteristic distances within the limits of which the interaction between TLSs and an impurity molecule leads, in the main, to either splitting or broadening of the spectrum, as well as the distance beginning with which this interaction is practically undetectable, are determined. Information about the effective value of the minimal distance between impurity molecules and TLSs, which is caused by nonzero sizes of the molecules and the TLSs, is presented. The analysis is performed by a statistical processing of experimental and model spectra of single tetra-tert-butylterrylene molecules in amorphous polyisobutylene at a temperature of 2 K, when the contribution of quasi-local low-frequency vibrational modes of the matrix to these spectra can be neglected.     

Optical dephasing in solid toluene activated by octaethylporphine zinc

The optical dephasing in frozen amorphous toluene doped with octaethylporphine zinc is investigated using the photon echo technique over a wide range of temperatures (0.4–100 K) up to the Debye temperature of solid toluene (T_D=100.7 K). The contributions of different mechanisms to the broadening of the zero-phonon line (ZPL) are reliably separated owing to the measurements performed over such a wide range of temperatures. Analysis of the experimental data demonstrates that, at low temperatures, the main contribution to the optical dephasing is determined by the interaction of impurities with fast tunneling transitions in two-level systems. The temperature dependence of the linewidth exhibits a quasi-linear behavior at temperatures below 3–4 K. At higher temperatures, the dominant contribution to the dephasing is made by the interaction of impurities with quasi-local phonons, which leads to a quasi-exponential temperature dependence of the linewidth. It is shown that the latter contribution can be described in the framework of the soft-potential model allowing for a broad spectrum of low-frequency phonon vibrations in the matrix. The temperature of the crossover between the aforementioned two mechanisms of line broadening is determined.     

Magnetic susceptibility anisotropy and low-dimensional antiferromagnetism of CuO

The anisotropy of the magnetic susceptibility χ and the influence of oxygen vacancies in CuO single crystals on it are investigated. The temperature dependences of χ(T) along the a, b, and c axes in the range 60<T<600 K and the behavior of the field dependence of the magnetization σ(H) above and below the Néel temperature T _N are plotted for a crystal before and after heat treatment. The χ(T) curves have the form characteristic of low-dimensional systems, which become three-dimensional when the temperature is lowered. The character of the χ(T) curves remains unchanged after annealing. Oxygen vacancies have practically no influence on the a-axis magnetic susceptibility, but they alter the absolute values of the b-and c-axis susceptibilities. The significant effects of reducing the oxygen concentration include a decrease in the magnitude of the low-temperature anomaly (increase) in χ and an increase in the minimum value of χ. The results of the calculations of the exchange parameter I/k and the g factor are discussed in terms of the Heisenberg and Ising models for a one-dimensional system. Zh. éksp. Teor. Fiz. 113, 1026–1035 (March 1998)