Intermolecular interactions in rifabutin–2-hydroxypropyl-β-cyclodextrin–water solutions,according to solubility data

The formulations of rifabutin (RB) and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD), obtained using different preparation techniques, are studied by means of differential scanning calorimetry and molecular spectroscopy (FTIR, NMR, Raman scattering, and photon correlation light scattering). It is established that molecules of RB do not form inclusion complexes with the molecules of HP-β-CD, and an increase in the solubility of RB determined earlier is caused by the formation of weak intermolecular associates.     

Anisotropy of the heat capacity of a mixed-state superconducting Nd<Subscript>1.85</Subscript>Ce<Subscript>0.15</Subscript>CuO<Subscript>4</Subscript> single crystal for various magnetic field orientations with respect to the crystallographic axes

The anisotropy in the superconducting properties of single-crystal Nd_1.85Ce_0.15CuO₄ was studied from measurements of the heat capacity within the temperature interval 2–40 K in zero magnetic field and in a magnetic field of 8 T. We report on the first observation of heat capacity jumps occurring at the superconducting transition for various magnetic field orientations with respect to the crystallographic axes and on a strong anisotropy of the magnetic contribution to heat capacity in magnetic fields oriented in the a-b plane and perpendicular to it. These measurements yielded the anisotropy in the electronic heat capacity coefficient γ_n(H) and in the superconducting transition temperature T_c(H). The angular dependence of the Sommerfeld coefficient γ_n in the a-b plane observed in a magnetic field of 8 T exhibits four-lobe symmetry and zero gap direction of the order parameter. A comparison of the results obtained on the Nd_1.85Ce_0.15CuO₄ single crystal with the data available for La_1.85Sr_0.15CuO₄ permits one to conclude that the mechanisms of superconductivity in the electron-and hole-doped superconductors are similar.     

Prebreakdown condition in selenium rectifiers

This paper reports data from an experimental investigation of the prebreakdown and breakdown conditions of factory production selenium rectifiers in the temperature range from 100 ° to –196 ° C when a unit voltage pulse with steep leading edge (rise time about 10^–8 sec) is applied to the rectifier in the non-conducting direction. Change in voltage across the rectifier and in current through it were recorded by a two-channel high-speed electronic oscilloscope. On the basis of this test data, the variation of discharge rise-time in the selenium p-n junction as a function of overvoltage and temperature was determined, the formation of current pulses was detected in the junction, both before and during breakdown in the temperature range from 100 ° to –196 ° C, and it was also established that breakdowns of selenium rectifier p-n junctions are due to joint action of the Zener effect and impact ionization.We are indebted to Prof. Kh. I. Amirkhanov for his constant interest in this work.     

Microporous and mesoporous carbon nanostructures with the inverse opal lattice

The conditions for porous structure formation in carbon nanostructures with the inverse opal lattice have been studied. The characteristics of the porous structure have been determined by means of the gas adsorption-desorption. The morphology and structure of samples have been examined using high-resolution transmission electron microscopy.     

Synthesis of α -SiC nanocrystals by carbothermal reduction of spherical nanoparticles of amorphous silicon dioxide

The method for carbothermal reduction of spherical particles of amorphous silicon dioxide is developed, and hexagonal α-SiC polytype nanocrystals are synthesized. The prepared samples are characterized by X-ray diffraction, Raman spectroscopy, photoluminescence spectroscopy, and electron microscopy. The silicon carbide nanocrystals prepared have sizes in the range 5–50 nm depending on the diameter of initial silicon dioxide particles. A detailed analysis of the positions of the lines in the Raman spectra, their broadening, and shift makes it possible to reliably establish that the samples under investigation predominantly contain the 6H and 4H silicon carbide polytypes and insignificant amounts of the 2H and 3C phases. The 15R and 21R polytypes in the samples are absent. It is noted that the samples are characterized by a substantial size effect: the luminescence intensity of small silicon carbide nanocrystals is more than three times higher than that of large SiC nanocrystals.     

On Reasons for Anomalies of Properties in a Series of Mixed K2CoxNi1–x(SO4)2 · 6H2O Crystals

The microhardness and thermal stability of mixed K₂Co_xNi_1–x(SO₄)₂ · 6H₂O crystals have been studied for the {110} and {001} growth sectors. Maxima of the onset temperature of dehydration have been found at x ≈ 0.1 and x ≈ 0.9. The structure of the {110} and {001} growth sectors has been studied. The observed changes in the properties have been attributed to the degree of imperfection of crystals depending on their sectoral inhomogeneity.

     

Study of the Fracture Toughness of K2NixCo(1 – x)(SO4)2 · 6H2O Crystals in Dependence of the Growth Direction and Rate

Crystallography Reports - K2Ni(SO4)2 · 6H2O (KNSH), K2Co(SO4)2 · 6H2O (KCSH), and K2NixCo(1&nbsp;–&nbsp;x)(SO4)2 · 6H2O (KCNSH) crystals have been grown by traditional...     

Synthesis of a periodic SiC/C nanostructure

Highly porous periodic structures consisting of a three-dimensional replica of pores in the initial opal lattice have been synthesized by high-temperature thermochemical treatment of opal matrices filled with carbon compounds, followed by dissolution of silicon dioxide. It has been shown that the main phases of the composite are carbon and silicon carbide. Based on the X-ray diffraction, Raman, and IR spectroscopy data, it has been assumed that the composite contains fragments of hexagonal diamond. The photoluminescence and optical reflection spectra of the composites have been measured.     

Parametric transformation and spectral shaping of supercontinuum by high-intensity femtosecond laser pulses

The cascaded nonlinear-optical transformation of high-power ultrashort light pulses in an ionizing gas medium involving supercontinuum generation, followed by a frequency conversion of this radiation in the field of femtosecond laser pulses with an intensity of 10¹⁴–10¹⁵ W/cm² has been demonstrated. Parametric four-wave mixing is shown to allow a highly efficient spectral transformation and shaping of supercontinuum radiation. The maximum efficiency of a parametric frequency conversion of femtosecond laser pulses in an ionizing gas medium achieved under the conditions of our experiments is estimated as 1%.