Dehydrogenation of propane on aluminoplatinum catalysts modified with Re,Zr, Sc,and Sn

The effect of addition of Re, Zr, Sc, and Sn on an aluminoplatinum catalyst in the reaction of dehydrogenation of propane was investigated. It was shown that addition of 0.2–0.5% Zr, Sc, or Re virtually does not alter the catalytic properties of the aluminoplatinum catalyst (APC); addition of 0.2% Sn increases the activity, selectivity, and stability of Pt/Al₂O₃. The amount of coke deposited on the APC after the first 5 min of work decreases by three times in the presence of Sn. The coke is more enriched with hydrogen than the other systems formed on the surface of Pt-Sn/Al₂O₃.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 765–771, April, 1991.     

Crystal structure of methylbis(chloromethyl)phosphine oxide

In the crystal structure of (CH₂C1)₂P(O)CH₃ and the isomorphous crystal structures of (CH₂Br)₂P(O)CH₃ and (CH₂I)₂P(O)CH₃, the molecules of the methylbis(halomethyl)phosphine oxide have an identical trans, gauche conformation.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1526–1528, July, 1991.     

A criterion for the uniform distribution of sequences in compact metric spaces

LetX be a compact metric space, le μ be a non-negative normalized Borel measure onX and letf be a measurable bounded real-valued function defined onX such thatf is μ-almost everywhere continuous and different from zero. It is proved that a sequence (x _n ),n=1,2, … of points inX is μ-uniformly distributed if and only if for every Borel setE?X with μ(Bd(E))=0 we have \(\mathop {\lim }\limits_{N \to \infty } \frac{1}{N}\sum\limits_{n = 1}^N {f(x_n )} 1_E (x_n ) = \int\limits_E {f(x)d\mu (x)} ,\) where 1 _E denotes the characteristic function ofE andbdE the boundary ofE. Furthermore some quantitative aspects and generalizations of this theorem are discussed.     

Nonlinear plane-symmetric perturbations of a spatial-plane Friedman universe filled with an ideal dust

The general solution of Einstein's equations with the energy-momentum tensor of an ideal dust in the plane-symmetric case is used to obtain the generalization of the solutions for scalar perturbations in a spatial-plane Friedman universe. It is shown that, in order for plane accumulations of matter with a density much greater than the mean density of the matter in the Universe to exist in the Universe at the present time, perturbations of the density are necessary at the time of recombination, (/)p 10^–4.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 20–24, December, 1987.     

Beryllium diffusion across GaAs/(Al,Ga)As heterojunctions and GaAs/AlAs superlattices during MBE growth

Beryllium diffusion during MBE growth of (Al, Ga)As layers, (Al, Ga)As/GaAs heterojunctions and GaAs/AlAs superlattices has been studied by electrochemical C-V and secondary ion mass spectrometry (SIMS) concentration profiling, in conjunction with transmission electron microscopy. Diffusion times were comparatively short since they were limited to part of the growth sequence, so non-equilibrium effects had a significant influence. The results are consistent with an interstitial-substitutional mechanism in which lattice site incorporation becomes more difficult with increasing band gap enthalpy. Incorporation involves a kick-out reaction which leads to the observed disordering of the superlattices.     

Simulating the diffraction pattern in the focal plane of a lens-axicon system

Laser beam concentration into a narrow ring with a lens and axicon is considered, as there are applications in working surfaces, cutting wafers and slices, and in welding or soldering tubes to heat-exchanger plates. A model is constructed and a working formula is derived for the diffraction pattern in the focal plane of such a system when the axicon is illuminated by a plane wave. For large h/, where h is axicon height and is wavelength, a formula is obtained that passes asymptotically into the approximate Belanger and Rioux ones.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 36–41, December, 1987.     

Electron emission from Al,Pt, Ag,and Au surfaces under the action of resonant photons with λ=2537 and 1850 Å

An original variant of an electronic device is described, which can be used for gamma-process selection under ionized gas conditions. The device is based on a Hanley and Schaffernicht electron gun. Selection of photons and metastable atoms is performed by a quartz tube located in axial symmetry with the primary electron gun. The desired signal is measured from the flow of secondary electrons emitted from Al, Pt, Ag, and Au surfaces under the action of resonant photons radiated from the levels Hg(6³P₁) and Hg(6¹P₁). For =2537 Å the following values were obtained for _ph 9.1, 3.8, 1.1, 0.25. Analogous values of _ph for =1850 Å were equal to 45.5, 10.8, 6.5, 3.2. The _ph values are in units of 10^–4.Translated from Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 68–74, December, 1987.     

Using “quasiphotons” to compute wave fields in an elastic medium

Quasiphoton solutions are constructed for longitudinal and transversal waves in an elastic medium. The quasiphotons are then applied to determine the fields of nonstationary high-frequency point sources in a medium with parameters dependent on two Euclidean coordinates.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 148, pp. 89–103, 1985.