Structures of lanthanum and yttrium aluminosilicate glasses determined by X-ray and neutron diffraction

We have measured the structures of lanthanum and yttrium aluminosilicate glasses by X-ray and neutron diffraction and determined the interatomic distances and nearest-neighbor coordination numbers. The results obtained with the two techniques are in good agreement with each other and with recent NMR studies. The Si-O and Al-O coordination numbers are found to be 4 and 4.5, respectively. All the glasses show pronounced intermediate-range order that exhibits a reduced length scale with increasing La or Y content.     

A method and an algorithm for computing the electromagnetic field in a stratified medium with a local nonhomogeneity in an arbitrary layer

Translated from Metody Matematicheskogo Modelirovaniya i Vychislitel'noi Diagnostiki, pp. 133–142, Izd. Moskovskogo Universiteta, Moscow, 1990.     

Synthesis of pyrrolo[3,2-f]quinolines via reaction of 2,5-dimethyl- or 1,2,5-trimethyl-6-aminoindoles with β-ketoesters

The reaction of 2,5-dimethyl- or 1,2,5-trimethyl-6-aminoindoles with β-ketoesters (methyl and ethyl acetoacetates, diethyl oxaloacetate) was found to proceed chemoselectively via the interaction between an amino group of indole and the carbonyl function of ketoester, leading to the formation of enamines. In contrast to enamines synthesized from similar aminoindoles and β-diketones, enamines obtained from β-ketoesters can easily undergo thermal cyclization, furnishing pyrrolo[3,2-f]quinolines with an angular catenation of rings.     

Mathematical modeling of random coupling between polarization modes in single-mode optical fibers: XVI. Depolarization and repolarization of polychromatic radiation in single-mode optical fibers with random inhomogeneities

The dependences of the degree of polarization of polychromatic radiation on the length of a single-mode optical fiber (SMF) with random inhomogeneities have been obtained by mathematical modeling. The case is considered where radiation having both polarization modes excited with equal weights of linear polarization is first introduced into a depolarizer of polychromatic radiation (a SMF segment with high linear birefringence) and arrives at an SMF with low linear birefringence. It is shown that the degree of polarization of radiation after transmission through the first segment becomes significantly suppressed and remains almost constant upon propagation through the second segment, after which it begins to sharply increase at some length; i.e., repolarization of radiation occurs. It is shown that repolarization of radiation depends weakly on the angle made by the axes of unperturbed linear birefringence of the first and second segments. The conditions for the length of the first segment (depolarizer) under which the degree of polarization remains minimum throughout the second segment are determined.     

Linear Transformation of the Polarization Modes in Coiled Optical Spun-Fibers with Strong Unperturbed Linear Birefringence. I. Nonresonant Transformation

A linear transformation of orthogonal polarization modes in coiled optical spun-fibers with strong unperturbed linear birefringence, which causes the emergence of the dependences of the integrated elliptical birefringence and the ellipticity and azimuth of the major axis of the ellipse, as well as the polarization state of radiation (PSR), on the length of optical fiber has been considered. Optical spun-fibers are subjected to a strong mechanical twisting, which is frozen into the structure of the optical fiber upon cooling, in the process of being drawn out from the workpiece. Since the values of the local polarization parameters of coiled spunwaveguides vary according to a rather complex law, the calculations were carried out by numerical modeling of the parameters of the Jones matrices. Since the rotation speed of the axes of the birefringence is constant on a relatively short segment of a coiled optical spun-fiber in the accompanying torsion (helical) coordinate system, the so-called “Ginzburg helical polarization modes” (GHPMs)—two mutually orthogonal ellipses with the opposite directions of traversal, the axis of which rotate relative to the fixed coordinate system uniformly and unidirectionally—are approximately the local normal polarization modes of such optical fiber. It has been shown that, despite the fact that the unperturbed linear birefringence of the spun-fibers significantly exceeds the linear birefringence, which is caused by the winding on a coil, the integral birefringence of an extended segment of such a fiber coincides in order of magnitude with the linear birefringence, which is caused by the winding on the coil, and the integral polarization modes tend asymptotically to circular ones. It has been also shown that the values of the circular birefringence of twisted single-mode fibers, which were calculated in a nonrotating and torsion helical coordinate systems, differ significantly. It has been shown that the polarization phenomena occur in the process of linear transformation of local polarization modes, which lead to small quasi-harmonic oscillations of the birefringence integral parameters of the optical spun-fibers, which depend on their length, and the period of these oscillations is approximately equal to half of the effective period of polarization beating.     

Reduction of nitrogen oxides with ammonia over complex vanadium and chromium oxides

Catalytic properties of -Al₂O₃ -supported complex vanadium and chromium oxides V_2–x Cr _x O_5– (0 < × s 1.3), amorphous to X-rays, in the reduction of nitrogen oxides with ammonia were studied. Vanadium exists in these catalysts mostly in a pentavalent state and chromium exists as Cr³⁺ and Cr⁶⁺. As the content of chromium in the catalysts increases, the optimal temperature of the process decreases, and the degree of conversion of nitrogen oxides increases.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 339–342, February, 1996.     

Crystal structure of the Nd,Gd, and Dy sandwich complexes involving 8-membered macrocyclic phenylsiloxanolate ligands

An X-ray structural investigation of the interaction products of anhydrous trivalent neodymium, gadolynium, and dysprosium chlorides with sodium phenylsiloxanolate was carried out. The synthesized compounds with the general formula Na₆[PhSiO₂]₈M₄(₄-O)[O₂SiPh]₈ · 10EtOH · 8H₂O (M = Nd, Gd, Dy) were found to be isomorphous isostructural sandwich complexes. The macrocyclic octaphenyloctasiloxanolate ligands in the complexes have anall-cis-configuration and are arranged in co-axial antiparallel pairs and coordinate the square planar groups of the four Nd³⁺, Gd³⁺, or Dy³⁺ ions stabilized by an additional central ₄-bridging O^2– ligand. Six Na⁺ counterions form the outer coordination sphere of the complexes such that four of them coordinate the siloxane macrocycle O atoms in pairs in analogy with crown-ether complexes.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 193–198, January, 1993.