Multifrequency Raman generation in liquid carbon tetrachloride with two-color pumping

The multifrequency parametric Raman generation was carried out in liquid CCl₄ by using the second harmonic of a 30 ps pulsed Nd:YAG laser and its first Stokes in CCl₄ as two-color pumping. Up to 80% energy conversion efficiency of the 50 μJ pump pulse into 10 Raman components covering spectral range from 490 to 640 nm was achieved. A scheme for a multifrequency parametric Raman laser operating with pulse repetition rates up to 0.1 MHz is suggested.     

Picosecond parametric Raman laser based on KGd(WO4)2 crystal

Simultaneous frequency up and down conversion using a biharmonically pumped parametric Raman laser (PRL) based on a KGd(WO₄)₂ (KGW) crystal has been demonstrated experimentally. Collimated beams have been generated for both the 1st anti-Stokes (1AS) at 511 nm and 2nd Stokes (2S) at 579 nm by four-wave parametric Raman interaction. To excite PRL biharmonically, we pumped the KGW crystal with 20 ps pulses at the fundamental 530 nm and its 1st Stokes component at 555 nm. The 1st Stokes pump beam was generated using stimulated Raman scattering in a separate KGW Raman oscillator. The energy conversion efficiencies reached experimentally were 10% for the 2S and 4% for the 1AS.     

Application of Silica Chemically Modified by Sulfur-Containing Groups to the Separation and Determination of Platinum and Rhenium in Catalysts Based on Aluminum Oxide

Adsorbents based on silica chemically modified by sulfur-containing groups (dithiocarbamate, thiodiazolethiol, mercaptophenyl, and aminobenzothiazole) quantitatively extract (recovery ≥99%) platinum( IV) from solutions ranging from 4 M HCl to pH 6. Under the conditions of the adsorption separation of platinum(IV), rhenium(VII) is not extracted and remains in the solution. The subsequent quantitative (98–99%) adsorption of rhenium(VII) is achieved in the presence of a 1000-fold excess of tin(II) chloride. Adsorption on the surface of adsorbents leads to the formation of platinum(II) complexes with sulfur-containing groups, luminescent at 77 K on irradiation with UV light. The luminescence spectra of surface platinum( II) complexes are located in the region of 550–700 nm. In the adsorption of rhenium(III) in the presence of tin(II) chloride, intensely colored brown complexes of rhenium formed on the surface of adsorbents. Electron paramagnetic resonance showed that, in the surface complexes, rhenium is in the oxidation state 2+. Silicas chemically modified by sulfur-containing groups were used in the development of procedures for the sequential isolation and determination of platinum and rhenium in solutions after the decomposition of aluminum–platinum–rhenium catalysts.     

Descendants constructed from matter field in Landau-Ginzburg theories coupled to topological gravity

It is argued that gravitational descendants in the theory of topological gravity coupled to topological Landau-Ginzburg theory (not necessarily conformal) can be constructed from matter fields alone (without metric fields and ghosts). In this sense topological gravity is induced. We discuss the mechanism of this effect (that turns out to be connected with K. Saito's higher residue pairing: Kⁱ(_i(₁),₂)=K⁰(₁,₂)), and demonstrate how it works in a simplest nontrivial example: correlator on a sphere with four marked points. We also discuss some results on k-point correlators on a sphere. From the idea of induced topological gravity it follows that the theory of pure topological gravity (without topological matter) is equivalent to the trivial Landau-Ginzburg theory (with quadratic superpotential).Published in Teoreticheskaya i Matematicheskaya Fizika, Vol. 95, No. 2, pp. 307–316, May, 1993.     

PHOTOREDUCTION OF PROTOCHLOROPHYLL AND ITS DERIVATIVES

Abstract —Photoreduction of protochlorophyll and a series of its derivatives (with gradual simplification of the structure) was studied in ascorbic acid-propanol-pyridine mixtures. Additions were introduced into the solutions to suppress some side processes. Conditions were found for the photoreduction of pigment on the 7,8-linkage, with the formation of corresponding chlorins. Chlorin yields depended on the nature of the metal in the centre of the pigment molecule. The yield of chlorophyll upon photoreduction of protochlorophyll was 30 per cent, and the yields of Zn-derivatives of protochphyll was about 35–80 per cent. Photochemically prepared chlorins were isolated by chromatography. Some differences were discovered between their electronic, infrared, and nuclear magnetic resonance spectra and those of natural chlorins. These differences result from chlorins with a cis arrangement of hydrogen atoms on the 7,8-linkage being selectively formed upon photoreduction, while natural chlorins have the trans arrangement. The mechanism of the photoreduction reaction is discussed.     

Prediction of the dispersity of starch hydrogels prepared under hydroacoustic treatment

The effect of shear stresses on the dispersion process in starch hydrogels under their treatment in a rotary-pulse apparatus was examined.     

Conversion of a Chirp Pulse Into the Second Harmonic in a KDP Crystal

Russian Physics Journal - Results of investigation of conversion of radiation with the wavelength λ = 950 nm and pulse duration of 100 ps into the second harmonic are reported. It is...     

Stability analysis of the zero solution of a relay system of ordinary differential equations with two relays

We consider a relay system of ordinary differential equations whose right-hand sides are sums of linear functions and two discontinuous functions. We analyze the stability of the zero solution of a relay system of this form for the case in which the system parameters satisfy some equality-type constraints.     

Laser-induced photodynamic effects of chlorinse 6 andp 6 on an isolated neuron

Photodynamic effects of chlorins e₆ and p₆ on an isolated mechanoreceptor neuron of a fluvial crayfish are investigated. A He−Ne laser (632.8 nm, 0.3 W/cm²) was used as an excitation source. The impulsive activity of neurons was found to be extremely sensitive to the photodynamic effect of low concentrations of chlorins e₆ and p₆ (0.005–6.000 and 0.05–0.50 μM, respectively). Cell reactions consisted of several phases of acceleration and inhibition of pulsations followed by an irreversible cancellation of nervous pulse generation. The type of reaction depended on the photosensitizer form and concentration. It is supposed that the phases of acceleration of impulsive activity are connected with the photodynamic damage of the cell membrane, and the inhibition phases are connected with the photodynamic effect on intracell organells. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 2, pp. 250–255, March–April, 1999.