Preparation of supported iron-containing catalysts from a FeSo<Subscript>4</Subscript> solution: The effect of the support

The iron compounds resulting from the impregnation of the most common supports—alumina and silica gel-with an aqueous FeSO₄ · 7H₂O solution and subsequent heat treatment in air are identified by thermal analysis and Mössbauer spectroscopy. The state of the active component of the iron-containing catalysts depends strongly on the nature of the support.     

On the minimum of several random variables

For a given sequence of real numbers , we denote the th smallest one by . Let be a class of random variables satisfying certain distribution conditions (the class contains Gaussian random variables). We show that there exist two absolute positive constants and such that for every sequence of real numbers and every , one has

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where are independent random variables from the class . Moreover, if , then the left-hand side estimate does not require independence of the 's. We provide similar estimates for the moments of as well.

     

Electromagnetically induced transparency in high-temperature magnetoactive plasma

We investigate a classical analog of electromagnetically induced transparency (EIT) currently popular in quantum electronics. We consider EIT for electron cyclotron waves in finite-temperature plasma. We derive an expression for the effective refractive index of an electromagnetic wave and study the dispersion and absorption of this wave under EIT conditions. Allowance for thermal motion is shown to radically change the behavior of the dispersion curves for the signal wave in the EIT region compared to the case of cold plasma.     

On the anti-symmetric vierbein in quantum supergravity

We consider the BRS identities for N = 1 supergravity in a covariant gauge. It is shown that, as in the axial gauge, the anti-symmetric part of the vierbein does contribute to the BRS identities, even though one can choose a gauge in which it does not propagate.     

Excitation of nonlinear surface modes by wave beams

We consider the interaction of 2-D and 3-D wave beams with an interface between linear and nonlinear media. The range of parameters of Gaussian beams exciting nonlinear surface waves (NSW) with high efficiency is analytically determined. Different regimes of NSW excitation are numerically studied. Analytical data are in good agreement with numerical results.Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, Nos. 3–4, pp. 246–255, March–April, 1995.     

The Role of Surfactants in the Formation of Highly Dispersed Iron–Zirconium Oxide Composites with Uniform Pores

The effects of the nature and concentration of surfactants and the preparation conditions on the genesis of iron–zirconium composites with a [Fe³⁺]/[Zr⁴⁺] ratio of 0.123 were studied. The effect of surfactants on the physicochemical properties of precipitates is determined by the conditions of synthesis. The amount of surfactants retained by the precipitate at pH 3 is about an order of magnitude greater than at pH 9. The thermolysis of samples synthesized at acidic pH is accompanied by the dehydration and dehydroxylation of iron–zirconium composites as well as by the decomposition and destruction of surfactants. In the latter processes, compounds or their fragments capable of reducing some phases are removed in a stepped-up manner. The specific surface area of oxide systems formed in this way is at most 100–150 m²/g. In the pH range corresponding to the complete precipitation of the components, highly dispersed single-phase and uniformly porous composites are formed. The choice of a surfactant, its fraction, and preparation conditions enables the preparation of oxides with specific surface areas of 100–400 m²/g. The average pore diameter of the samples ranges from 3.0 to 27.0 nm, and the total pore volume ranges from 0.20 to 0.38 cm³/g.     

Mechanochemical Synthesis and Catalytic Properties of the Calcium Ferrite Ca2Fe2O5

The formation of the real structure of calcium ferrite prepared by the calcination of a mechanochemically activated hydroxide mixture at 600–1100°C was studied by X-ray diffraction analysis, electron microscopy, thermal analysis, Moessbauer spectroscopy, IR spectroscopy, small-angle X-ray scattering, and secondary-ion mass spectrometry. It was found that low-temperature calcium ferrite is an anion-modified oxide, in which the ordering of oxygen vacancies was incomplete. Regions with a disordered structure were detected on the surface of crystallites. As the calcination temperature was increased, the brownmillerite crystal structure was improved and the intercrystalline boundaries were formed and then annealed. At the surface, these processes were accompanied by a change in the predominant form of adsorbed NO from nitrosyl to dinitrosyl species. An increase in the specific catalytic activity of samples with calcination temperature can be associated with the perfection of the brownmillerite structure and with a change in the state of adsorption centers.     

Generation of Multipetawatt Laser Pulses with a Small Number of Field Oscillations

Radiophysics and Quantum Electronics - We propose a method for two-stage compression of laser pulses, which makes it possible to shorten laser pulses of tens of picoseconds to an optical period...     

The effect of chemical modification on the chromatographic properties of polymeric adsorbents polysorb-1 and hisep Q and the diatomite carrier chromosorb P NAW

Polytrimethylsilylpropyne with the decomposition temperature 205°C was synthesized and characterized. The effect of chemical modification by polytrimethylsilylpropyne on the gas chromatographic properties of polymeric adsorbents and the diatomite carrier for the selective separation of C₁–C₁₀ hydrocarbons, alcohols and aromatic and sulfur-containing compounds was studied. Original Russian Text ? E.Yu. Yakovleva, V.Yu. Belotserkovskaya, V.P. Fadeeva, G.S. Litvak, E.A. Paukshtis, D.E. Babushkin, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 5, pp. 972–977.