Up-conversion with resonantly two-photon pumped atomic nonlinear media

The schemes of efficient frequency conversion from infrared (ir) wide band to the visible, as well the generation schemes of 42 new vacuum ultraviolet (VUV) and ultrasoft X-ray wavelengths up to λ = 708 A; are proposed.     

Gain saturation in a cyclotron — Synchronous wave amplifier

Problems of the formation of the electrostatic field of the amplification zone of a cyclotron — synchronous wave amplifier are considered. An analysis of the amplification processes is performed for the case of a variable longitudinal velocity. The expediency of using a non-linear operating mode of the amplifier in order to increase the efficiency is noted. Results of preliminary experiments are presented.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 15, No. 4, pp. 615–624, April, 1972.     

About the limits of existence of α-cluster structure in nuclei

The shape of the d-α coincidence spectrum from the reaction ¹²C(⁶Li, d)¹⁶O(α)¹²C in the region corresponding to the 20.9 MeV 7^? level in ¹⁶O has been measured. Also, measurements of the α-particle elastic scattering excitation functions on ¹²C and ¹⁶O have been made in the regions corresponding to the α-cluster levels found in the (⁶Li, d) reactions. A comparison of the d-α coincidence spectra and excitation functions allows us to draw conclusions about splitting of the α-cluster states and region of their existence.     

Effective upconversion of CO2-laser radiation in sodium vapors

The effective upconversion of CO₂-laser radiation to the uv spectral range has been obtained in sodium vapors, the photon efficiency being 65%, the corresponding power efficiency being 2640%.     

Electronic spectra of XeNe molecules in the range 77100-90100 cm-1 near Xe* (6p, 5d, 6p’, 7s, 7p, 6d) obtained by the (3 + 1) REMPI and (2 + 1) REMPI methods

The electronic spectra of XeNe molecules in the range of 77100-90100 cm^-1 are measured by the method of laser resonance multiphoton ionization in a supersonic jet. The photoionization spectra are obtained upon two- and three-photon excitations of molecules and their ionization by the next photon. In the range of 80300-90100 cm^-1 near Xe*(5d, 6p’, 6d, 7s, and 7p), the spectra are obtained for the first time. A whole number of vibrational systems are measured in this range. The majority of vibrational systems near Xe* (5d, 6d, 7p, and 7s) are located in the red range with respect to their dissociation limits. In the blue range with respect to the dissociation limits, continua corresponding to transitions of molecules from the ground state to repulsive potential curves of excited states are detected. For a number of excited states of XeNe molecules, the vibrational analysis is performed and molecular constants are estimated.     

Stability of the collisional plasma flow in a magnetic field

A collisional plasma flow moving along a magnetic field at a velocity lower than the speed of sound is considered. It has been found that stationary small perturbations increase downstream in the flow. The mechanism of the increase is related to the fact that subsonic ideal-plasma flows respond to external perturbations primarily by a change in the pressure of the plasma. As a result, the pressure under perturbation of the velocity changes so that the stationary flow is decelerated and accelerated if the force is directed along and against the velocity, respectively. This phenomenon can be explained under the assumption that the effective mass of the plasma is negative. If the velocity of the flow is inhomogeneous in the transverse direction, the viscosity force plays a role of the external perturbing force. In this case, the effective transverse viscosity coefficient, which should be treated as negative, can be renormalized instead of the effective mass. The sign of the effective specific heat or the effective transverse thermal conductivity coefficient changes similarly if the velocity of the flow is lower than the speed of sound but is higher than the thermal velocity of ions calculated from the sum of the ion and electron temperatures. A downstream increase in the stationary perturbations is called in this work spatial instability. The downstream growth rate has been determined. The numerical analysis of the evolution of perturbations illustrates the development of the spatial instability of subsonic collisional plasma flows moving along the magnetic field.     

Three-dimensional structure of thymidine phosphorylase from E. coli in complex with 3′-azido-2′-fluoro-2′,3′-dideoxyuridine

The three-dimensional structures of thymidine phosphorylase from E. coli containing the bound sulfate ion in the phosphate-binding site and of the complex of thymidine phosphorylase with sulfate in the phosphate-binding site and the inhibitor 3′-azido-2′-fluoro-2′,3′-dideoxyuridine (N₃F-ddU) in the nucleoside-binding site were determined at 1.55 and 1.50 Å resolution, respectively. The amino-acid residues involved in the ligand binding and the hydrogen-bond network in the active site occupied by a large number of bound water molecules are described. A comparison of the structure of thymidine phosphorylase in complex with N₃F-ddU with the structure of pyrimidine nucleoside phosphorylase from St. Aureus in complex with the natural substrate thymidine (PDB_ID: 3H5Q) shows that the substrate and the inhibitor in the nucleoside-binding pocket have different orientations. It is suggested that the position of N₃F-ddU can be influenced by the presence of the azido group, which prefers a hydrophobic environment. In both structures, the active sites of the subunits are in the open conformation.     

Investigation of superconductivity in a diamond anvil cell by mutual inductance bridge

Abstract

The method for the investigation of the superconductivity under high pressure in a DAC by mutual inductance bridge is proposed. Low frequency magnetic modulation system was used to distinguish signal due to superconducting transition from the temperature dependent background and to increase the sensibility. The sensibility was sufficient to detect the superconductivity of the sample with linear dimensions of 50 microns.     

Microdetermination of titanium on the developed silicon surface using cells made of perfluorinated proton-conducting membranes

A technique for microdetermination of titanium on the developed silicon surface is suggested. In this technique, thin titanium layers are dissolved in an aqueous solution of hydrofluoric acid and then the resulting solutions are analyzed using potentiometric cells made of perfluorinated proton-conducting membranes. The feasibility of estimation of titanium on the silicon surface in amounts of 5 × 10^?7 mol or less is demonstrated.