Noncentrosymmetric Tetrel Pnictides RuSi4P4 and IrSi3P3: Nonlinear Optical Materials with Outstanding Laser Damage Threshold

Noncentrosymmetric (NCS) tetrel pnictides have recently generated interest as nonlinear optical (NLO) materials due to their second harmonic generation (SHG) activity and large laser damage threshold (LDT). Herein nonmetal-rich silicon phosphides RuSi₄P₄ and IrSi₃P₃ are synthesized and characterized. Their crystal structures are reinvestigated using single crystal X-ray diffraction and ²⁹Si and ³¹P magic angle spinning NMR. In agreement with previous report RuSi₄P₄ crystallizes in NCS space group P1, while IrSi₃P₃ is found to crystallize in NCS space group Cm, in contrast with the previously reported space group C2. A combination of DFT calculations and diffuse reflectance measurements reveals RuSi₄P₄ and IrSi₃P₃ to be wide bandgap (E_g) semiconductors, E_g = 1.9 and 1.8 eV, respectively. RuSi₄P₄ and IrSi₃P₃ outperform the current state-of-the-art infrared SHG material, AgGaS₂, both in SHG activity and laser inducer damage threshold. Due to the combination of high thermal stabilities (up to 1373 K), wide bandgaps (≈2 eV), NCS crystal structures, strong SHG responses, and large LDT values, RuSi₄P₄ and IrSi₃P₃ are promising candidates for longer wavelength NLO materials.     

An Indo-Soviet experiment on anmhd generator test section at the Soviet U-02 facility

This paper summarizes the major results of the joint Indo-Soviet experiment for testing the Indianmhd generator channel section, designed and fabricated at the Bhabha Atomic Research Centre, Bombay, which was carried out at the U-02 facility in Moscow, USSR, in May 1980. The total test duration was 65 hours and included electrophysical tests and life tests under applied electric fields. The main purpose of the tests was to substantiate the physical concepts, computer codes, design features and special processing techniques involved in the development ofmhd generators for the Indian pilot plant at Tiruchirapalli. The experimental observations on the phenomena of heat transfer to the walls, gas dynamics in the channel, electrical characteristics of the generator and near-electrode processes including the analysis of arc spots correlate with the theoretical estimates based on present understanding of the physical processes occuring in similarmhd generators. The post-operational inspection of the channel section and extensive investigation of materials through microscopic analysis, chemical analysis and x-ray analysis are also reported in this paper. The joint test programme has clearly demonstrated the definite operating capability of the test section and has given sufficient information and encouragement for building better and improved channels for the future.     

A parameterized model of heat storage by lake sediments

A model of seasonal heat storage by lake sediments is proposed oriented at applications in climate modeling and at lake parameterization in numerical weather prediction. The computational efficiency is achieved by reformulating of the heat transfer problem as a set of ordinary differential equations for evolution of the temperature wave inside the upper sediment layer. Arising temperature and depth scales completely replace the conductivity of the sediment in the heat transfer equation and can be easily achieved from the lake water temperature observations without any data on the sediment thermal properties. The method is proposed for the scales estimation from the inverse solution of the model equations in special case of the constant water-sediment heat flux in ice-covered lakes. The method is tested on data from sediments of Lake Krasnoye, North-Western Russia. The long-term (1961–2002) modeling of temperature in German lakes Müggelsee and Heiligensee with a coupled one-dimensional model of lake water column and sediments has demonstrated an appreciable effect of the sediment heat storage on near-bottom temperatures in both lakes. Thus, incorporation of the sediment layer into lake temperature models can essentially improve, at low computational costs, the model performance, especially for shallow lakes. In addition, a better forecast of near-bottom temperature evolution on climatic scales can provide a better understanding of the response of lake benthic communities to global warming.     

Interaction of Oxide Melt with External-Trap Zirconium Dioxide Refractories

The results of an investigation of the interaction of zirconium dioxide refractories – ceramic and concrete with iron oxides – are presented. The investigations showed that starting at 1600 K in an argon atmosphere contact of a mixture of iron oxides with refractories gives rise to erosion of the latter. Under isothermal conditions (2270 K), ceramic with 16% porosity completely absorbs a melt with mass 1/7 of the ceramic mass. The concrete confines the same melt mass with a lower temperature 1870 K and, in the process, unlike the ceramic, it loses strength.The results obtained and the published data were used to analyze the operation of a refractory protective layer of an EPR trap.     

Thermal Radiative Properties of Ceramic of Cubic ZrO2Stabilized with Y2O3at High Temperatures

The results are given of the investigation of the normally hemispherical reflectivity of ceramic of cubic zirconia stabilized with 8 mol % yttria for the wavelengths of 0.488, 0.6328, 1.15, and 1.39 m both in the process of its rapid heating in air by CO₂-laser radiation from room temperature to 3200 K and in the process of subsequent cooling after the heating radiation is discontinued. It is demonstrated that, in the entire investigated spectral range under conditions of a layer of melt 250–500 m thick on the surface, an optically infinite layer is realized in the melt, and the reflection is largely defined by the refractive index. This latter layer remains optically infinite even immediately after solidification; however, by the end of the solidification process, its reflectivity somewhat increases due to cracks and pores. Measurements of the reflection under conditions of continuous stepwise heating by fluxes of relatively low intensity and in the course of subsequent cooling have produced data on the reflectivity of the layer under close-to-isothermal conditions. Some estimates are made of the values of the absorption coefficient of the melt.     

Ceramics based on partly stabilized zirconium dioxide: technology,structure, properties,and behavior under dynamic action

Technology is described for manufacturing dense ceramic from very fine powder based on zirconium dioxide partly stabilized with yttrium oxide. Some engineering properties of the manufactured ceramic are defined. Its microstructure and phase composition are studied. Ceramic properties with impact-wave loading are studied, and values of dynamic elastic limit and spalling strength are obtained.     

Shock d eformation diagram of fireclay

A method is proposed for constructing the shock compression and load-relief diagrams of a foam material when a one-dimensional stress-strain is realized in it. The method is based on the mathematical analysis of experimental information. The shock-compression and load-relief diagrams of fireclay (strain rate ε=10² sec⁻¹) are constructed from the experimental data obtained in experiments on the compression of samples of this foam material. 5 figures. 10 references. NITs TIV OIVT RAN. Translated from Atomnaya énergiya, Vol. 88, No. 1, pp. 38–43, January, 2000     

Comparison of isradipine and enalapril effects on regional carotid circulation in patients with hypertension with unilateral internal carotid artery stenosis

This randomized, double-blind, placebo-controlled study was aimed at detecting cerebrovascular effects of isradipine and enalapril in patients with moderate hypertension depending on the presence and grade on unilateral stenosis of internal carotid artery (ICA). We evaluated carotid vascular resistance by using Doppler analysis and regional cerebral blood flow (rCBF) by using 133Xe-clearance technique before and after a single 5-mg oral dose of isradipine, enalapril, or placebo. Their effects were randomly and consecutively tested in 73 patients with essential hypertension subdivided into three groups: without carotid occlusive lesions, with moderate (50-75%), and with severe (76-99%) unilateral asymptomatic ICA stenosis. There were no differences in age, gender, and antihypertensive effects of the drugs between these three subgroups. Three major variants of cerebrovascular drug effects were observed: absence of changes (variant I), decrease in carotid vascular resistance with increase in rCBF and elimination of side-to-side asymmetry (variant II), and increase in carotid vascular resistance with further reduction of rCBF ipsilaterally ICA stenosis, and increased side-to-side asymmetry (variant III). Frequency of variant III was significantly higher in patients with severe ICA stenosis. Enalapril produced variant I of cerebrovascular effects in most patients examined; variant III was observed only in 13% of patients with severe ICA stenosis. Isradipine produced variant I of cerebrovascular effects much less frequently than did enalapril. For this drug, variant II was most typical in patients without ICA stenosis and with moderate ICA stenosis. In 43.5% of patients with severe ICA stenosis, however, isradipine produced reduction of cerebral perfusion. Presumably the presence of ICA stenosis, especially >75%, increases the risk of cerebrovascular disorders in antihypertensive therapy. In patients with severe ICA stenosis, treatment with enalapril appears to be safer than that with isradipine.