Method of measuring the astigmatic distance of laser diodes

A modification that simplifies the measurement procedure is presented for a microscopic method of measuring the astigmatic distance of laser diodes. The errors of the proposed method are estimated and results are presented of measurements of the astigmatic distance of the commercial laser diodes of type ILPN-102, ILPN-205, and ILPN-210, as well as of laboratory specimens with ridge waveguides.Quantum Radiophysics Division, Kuibyshev Branch. Translation of Preprint No. 198, Lebedev Institute of Physics, Academy of Sciences of the USSR, Moscow, 1990.     

Atomic structure and transport and magnetic properties of the Sm1−x SrxMnO3 system

This is the first study of the temperature dependences of the atomic structure by neutron diffraction, as well as of the resistivity, differential magnetic susceptibility, and magnetoresistance of the ceramic system ¹⁵⁴Sm_1−x Sr_xMnO₃ (x∼0.16–0.4). Samples (x⩾0.3) having an initially orthorhombic structure transfer upon cooling from the insulating to the metallic state and exhibit giant magnetoresistance, which at liquid-helium temperature reaches as high as 90% in magnetic fields up to 30 kOe. At lower doping levels (x⩽0.25), the compound has monoclinic structure. The resistivity of such compounds in zero magnetic field displays insulating behavior upon lowering the temperature to 77 K. Fiz. Tverd. Tela (St. Petersburg) 40, 1271–1276 (July 1998)     

Crystal and electronic structures of magnesium(II), copper(II), and mixed magnesium(II)-copper(II) complexes of the quinoline half of styrylquinoline-type HIV-1 integrase inhibitors

A new target in AIDS therapy development is HIV-1 integrase (IN). It was proven that HIV-1 IN required divalent metal cations to achieve phosphodiester bond cleavage of DNA. Accordingly, all newly investigated potent IN inhibitors contain chemical fragments possessing a high ability to chelate metal cations. One of the promising leads in the polyhydroxylated styrylquinolines (SQLs) series is (E)-8-hydroxy-2-[2-(4,5-dihydroxy-3-methoxyphenyl)-ethenyl]-7-quinoline carboxylic acid (1). The present study focuses on the quinoline-based progenitor (2), which is actually the most probable chelating part of SQLs. Conventional and synchrotron low-temperature X-ray crystallographic studies were used to investigate the chelating power of progenitor 2. Mg2+ and Cu2+ cations were selected for this purpose, and three types of metal complexes of 2 were obtained: Mg(II) complex (4), Cu(II) complex (5) and mixed Mg(II)-Cu(II) complexes (6 and 7). The analysis of the crystal structure of complex 4 indicates that two tridentate ligands coordinate two Mg2+ cations, both in octahedral geometry. The Mg-Mg distance was found equal to 3.221(1) A, in agreement with the metal-metal distance of 3.9 A encountered in the crystal structure of Escherichia coli DNA polymerase I. In 5, the complex is formed by two bidentate ligands coordinating one copper ion in tetrahedral geometry. Both mixed Mg(II)-Cu(II) complexes, 6 and 7 exhibit an original arrangement of four ligands linked to a central heterometallic cluster consisting of three octahedrally coordinated magnesium ions and one tetrahedrally coordinated copper ion. Quantum mechanics calculations were also carried out in order to display the electrostatic potential generated by the dianionic ligand 2 and complex 4 and to quantify the binding energy (BE) during the formation of the magnesium complex of progenitor 2. A comparison of the binding energies of two hypothetical monometallic Mg(II) complexes with that found in the bimetallic magnesium complex 4 was made.     

Selectivity in the photo‐Fenton and photocatalytic hydroxylation of biphenyl‐4‐carboxylic acid and derivatives (viz. 4‐phenylsalicylic acid and 5‐phenylsalicylic acid)

The selectivity of hydroxylation of the distal rings of 4‐phenylbenzoic acid, 4‐phenylsalicylic acid, and 5‐phenylsalicylic acid were determined using partial TiO₂‐mediated photocatalytic degradation and photo‐Fenton conditions. This separation of the binding site from the phenyl group being hydroxylated allows a less‐biased evaluation. The hydroxylation regiochemistry behaves as qualitatively expected for an electrophilic reaction, given the assumption that 4‐carboxyphenyl is a slightly electron‐withdrawing substituent. Selectivity for hydroxylation of the distal phenyl in 4‐ and 5‐phenylsalicylic acid is reversed, due to the reversal of the electronic demand, while adsorption to the TiO₂ surface is assumed to be analogous for the two structures. Copyright © 2011 John Wiley & Sons, Ltd.     

Efficient second harmonic generation of a diode laser using ring cavity with a KNbO<Subscript>3</Subscript> Crystal

The spatial mode and impedance matching of an IR diode laser beam with a ring cavity has been investigated by the example of second-harmonic generation in a KNbO₃ crystal placed in the cavity. The frequency conversion efficiency into blue light is found to be as high as 20%.     

Cooperative behavior between oscillatory and excitable units: the peculiar role of positive coupling-frequency correlations

We study the collective dynamics of noise-driven excitable elements, so-called active rotators. Crucially here, the natural frequencies and the individual coupling strengths are drawn from some joint probability distribution. Combining a mean-field treatment with a Gaussian approximation allows us to find examples where the infinite-dimensional system is reduced to a few ordinary differential equations. Our focus lies in the cooperative behavior in a population consisting of two parts, where one is composed of excitable elements, while the other one contains only self-oscillatory units. Surprisingly, excitable behavior in the whole system sets in only if the excitable elements have a smaller coupling strength than the self-oscillating units. In this way positive local correlations between natural frequencies and couplings shape the global behavior of mixed populations of excitable and oscillatory elements.     

A chiral link between structure and magnetism in MnSi

We consider crystal and magnetic chiral structures for MnSi and isostructural metal silicides, where a complete set of structural and magnetic measurements allows us to define both magnetic and structural chiral configurations. We show that magnetic symmetry inherits chirality from the crystal structure. We derive, with emphasis on symmetry arguments, a new type of magneto-structural relation, namely a symmetrized coupling between structural and magnetic chiralities that provides a structural control on the magnetic chirality.