Crystal Structure of HAsUO6 4H2O

The crystal structure of HAsUO₆ 4H₂O was solved at 295 K by X-ray analysis. Reasons for structural changes due to temperature variation are analyzed.     

Reentrant phase transitions in liquid crystals

A comprehensive review of the recent developments regarding the phenomenon of reentrant phase transitions (RPT) in liquid crystals is presented. In addition to liquid crystals this phenomenon has been observed in amazingly diverse systems. A critical assessment of the experimental investigations concerning single and multiple reentrances is given. A brief account of the theoretical efforts is also given. The article ends with the identification of the factors which impede the proper understanding of the phenomenon.     

Synthesis,spectral and thermal characterization of Bis(diethylammonium) tetrachloromercurate(II)-An nonlinear optical material

A new semiorganic compound, bis(diethylammonium) tetrachloromercurate(II) was grown by slow evaporation solution growth technique at ambient temperature from its aqueous solution. The crystal system and the cell parameters have been identified from the powder X-ray diffraction pattern. The UV–visible absorption of the compound shows absorption at 246 nm and there is absorption observed in the entire visible region indicates that the compound can be used as a nonlinear optical material. The UV–visible transmittance spectrum of grown crystal shows a lower cut-off wavelength at 275 nm and it was found that the crystal is suitable for optoelectronic applications. Thermal studies were carried out to find out the thermal stability and confirm the stoichiometric ratio of the compound. The thermal anomalies in DSC study indicate the occurrence of first order transition in the compound at low temperatures. The FTIR spectrum of the compound characterizes various functional groups. The various kinds of protons and carbons were assigned through NMR (¹H and ¹³C) spectroscopic techniques. The SHG efficiency of the compound was studied by Kurtz-Perry power technique and observed that it has SHG efficiency 1.5 times greater than that of potassium dihydrogen phosphate (KDP). The dielectric constant and dielectric loss of the compound decreases with increase in frequency.     

啁啾脉冲堆积宽带激光的三次谐波产生

针对啁啾脉冲堆积方法获得的宽带激光,分析了其形成机制,并给出了其时间波形和光谱分布。采用KDP晶体Ⅰ/Ⅱ类角度失谐的三倍频方案以及Ⅰ/Ⅱ/Ⅱ晶体级联角度失谐方案,定量分析了啁啾脉冲堆积方式宽带激光三倍频转换效率随入射光强、带宽、以及晶体厚度等因素的变化,并与时间相位调制的宽带激光三倍频的相应结果进行了比较。研究结果表明,采用晶体级联方式可以大幅度提高宽带三倍频转换效率,并且啁啾脉冲堆积宽带激光的三倍频转换效率的提高比时间相位调制宽带激光更为明显。     

Charge distributions on polyatomic ions,and their relationships with cohesive energies of ionic crystals

Some current approaches to the determination of the charge distributions on polyatomic ions are considered. The methods involving cohesive energies of ionic solids on the one hand and those using molecular-orbital calculations on the other hand are compared and discussed. New charge distributions are presented for a series of polyatomic ions.     

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Abstract

Stanford Resources Inc., the leading market research firm specializing in the global electronic display industry, has released its annual study on the flat panel display (FPD) industry - Flat lnformation Displays. Now in its eighth edition, this industry perspective analyses competing FPD technologies in terms of technological development, sales, suppliers and future prospects.     

Guest-Host Type Liquid Crystal Displays

Eight modes of the guest-host cells (GH-cells), in which types of dye, liquid crystal and their alignments are adequately combined, are surveyed, and the color contrast of each mode is calculated.

Three modes among them are of positive type display, that is, colored patterns on the colorless background contrary to the initially proposed fundamental GH-cell. Another three modes are the GH-cells without polarizer, by which bright display can be obtained.

Light stability of dyes are also discussed and lifetimes of various dyes are estimated by accelerated life test. As a result, it is found that diazo-and axomethine-dayes without thiazole groups as well as anthraqunone-dyes have satisfying lifetimes as long as they are used indoors.     

Galvanomagnetic Properties Of Asf5 -Intercalated Highly-Oriented Pyrolytic Graphite (HOPG)

Due to the anisotropy of the conductivity in AsF₅-intercalated HOPG, eddy current methods have to be used for the measurement of transport effects. The measurements yield carrier concentration, mobility and charge transfer for C8nAsF₅ with n=l-4 at temperatures between 4.2K and 300K.     

A Binary System of a Swallow-Tailed and a Double Swallow-Tailed Compound

The geometrical anisotropy in the shape of swallow-tailed ST liquid crystalline molecules results in an extremely strong tendency of an antiparallel order in the short range. Dielectric measurements on a binary system of a ST and a double ST compound show that even at a mole fraction of 0.5 this effect can be observed. The strong deviations from the statistical distribution of the directions of the molecular long axis is caused by the asymmetric repulsive forces and the dipole-dipole interaction.