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Statistics of nucleation of chiral forms of sodium chlorate from unstirred, achiral solutions was studied. The trimodal distribution of enantiomers was obtained in which apart from the peak for the same probability of the creation of L and D crystals, two other maxima for the large enantiomeric excesses of L and D forms were present. The first nucleated crystals govern the handedness of the secondary crystals and the formation of pure enantiomers and high enantiomeric excesses in crystallization from unstirred, unseeded solutions are caused by the process of chiral symmetry breaking rather than statistical fluctuations. 相似文献
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Investigations made on the etching behaviour of magnesium orthosilicate crystals in hydrochloric acid and melts of potassium and sodium hydroxides are described. It is shown that the morphology and orientation of the etch pits depend upon the concentration, composition and temperature of the etchant used. At low concentrations of HCl acid solution, the boat shaped pits produced are oriented along [100] direction while in concentrated acid, the hexagonal pits produced are oriented along [001] direction. At intermediate concentrations of about 5 N HCl acid the pits are square. KOH melt at 400 °C is found to produce rectangular pits with their longer sides parallel to [100] direction. The effect of a mixture of KOH and NaOH in different proportions in the melt is investigated. It is observed that square pits are obtained in melt of the mixture of KOH and NaOH in the proportion of 6:4 respectively. The mechanism responsible for the change in orientation of etch pits have been explained. The implications are discussed. 相似文献
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Diammonium Hydrogen Citrate single crystals have been grown from aqueous solution. The etch technique for defect studies is applied to these crystals. Propionic acid is shown to be a reliable etchant capable of bringing out dislocations intersecting the (001) face. Various other interesting features observed during etching are also presented and discussed. 相似文献
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The undoped and doped (Si, N, In) GaAs single crystals are grown by horizontal Bridgman technique. The etch pit density (EPD) profiles were measured in transverse direction for each crystal. It was found that the shape of EPD profiles differs in dependence on the used dopant. 相似文献
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The effect of temperature and concentration of HCl aqeous solutions on the etching behaviour on the face {111} of CaF2 single crystals is investigated. It has been observed that the shape and the evolution of etch pits and the values of dissolution rate depend on the etching conditions. From the plots of logarithm of dissolution rate versus inverse of absolute temperature the values of activation energy and the pre-exponential factor for the dissolution process are computed. It has been found that the value of the activation energy and of the pre-exponential factor do not remain constant with acid concentration, but exhibit a minimum for the concentration of 6 N. 相似文献
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Patrick Keller 《Molecular Crystals and Liquid Crystals》2013,570(10):295-305
Esterification of 4-nitrocinnamoyl chloride by new chiral alcohols((d) and (1) 2-butanol; (d) 2-heptanol), followed by reduction of the nitro group by a new reagent(SnC12), gives new chiral 4-aminocinnamates.Condensation of these amines with 4-alkyloxybenzaldehydes or terephthaldehyde gives Schiff bases showing in some cases chiral smectic C phases. A comparative study of the mesomorphism of both these compounds and the compounds of the DOBAMBC family is made, in order to evaluate the effect of the chiral building block structure on the liquid crystalline properties.During this study, a new compound has been prepared, which exhibits the smectic O phase: ((d) 1-methylhexyl)terephthalidene Bis 4-aminocinna-mate. 相似文献
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本文首先利用有限元仿真软件COMSOL计算了二维手性声子晶体的带隙,分析了散射体参数与韧带涂层参数变化对带隙的影响规律。在此基础上,确定手性声子晶体带隙最优设计的有效参数设计空间;然后基于ISIGHT优化设计平台嵌入遗传算法,开展二维手性声子晶体带隙的最优设计。在带隙的最优设计过程中,先以二维手性声子晶体的有效构型参数为设计变量,相对带隙宽度最大为目标,设计手性声子晶体单胞构型。再以此优化单胞构型为初始构型,以手性声子晶体的有效材料参数为设计变量,相对带隙宽度最大为目标,进一步实现二维手性声子晶体带隙的最优设计。本工作极大限度地挖掘了二维手性声子晶体带隙最优设计潜能,为充分发挥手性声子晶体在减振降噪中的作用提供了可靠有效的分析设计方法。 相似文献
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The results of a study of the effect of HgCl2, ZnCl2, PbCl2 and CaCl2 on the surface micro-morphology and kinetics of etching of {100} planes of NaCl crystals in methanol and ethanol are described and discussed. It was found that addition of an impurity to the solvent leads to the formation of contrasting dislocation etch pits, and that the overall dissolution rate in a solvent decreases with an increase in additive concentration. In the case of HgCl2 impurity added to methanol terraced etch pits are observed, but their terracing behaviour diminishes with the increasing impurity concentration. 相似文献
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Abstract In 1989, Chandani et al. showed that the tristable switching, already observed by themselves and by others in 4-(1-methylheptyloxycarbonyl) phenyl 4′-octyloxybiphenyl-4-carboxylate (MHPOBC). 相似文献
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Boštjan Žekš 《Molecular Crystals and Liquid Crystals》2013,570(1-3):259-270
The biquadratic coupling between the tilt and polarization is added to the usual bilinear coupling in the Landau free energy density expansion describing the SmA - SmC* transition. The effect on the temperature dependence of the tilt, spontaneous polarization and the pitch of the helix is studied. The results agree qualitatively with measured data. 相似文献
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The effects of quenching temperature and orientation of Knoop indenter on microhardness of cleavage planes of synthetic sodium nitrate crystals are studied for the range of applied loads (20–160 g) in the high load region. Phenomenological approach was followed to obtain an empirical relation connecting Knoop hardness number, orientation, and quenching temperature. Anisotropic indices are also determined. The implications are discussed. 相似文献
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A.L. Aleksandrovskii I.I. Naumova P. Posmykiewicz 《Crystal Research and Technology》1982,17(5):601-607
The possibility of inducing rotational growth striae with a small period in barium sodium niobate crystals (BSN) is examined. Crystals grown had a period stability up to 1 percent and were suitable material for anisotropic light diffraction by ferroelectric domains. However intense striae were produced only for periods λ > 5 m̈m. With the help of Bragg optical diffraction by growth striae the diffusion coefficient D in solid phase responsible for striae smoothing during annealing was measured. The magnitude D ≈ 10-11 cm2 s-1 at the melting point was obtained. Such D value leads to the vanishing of striae with λ < 5 m̈m in BSN crystals during growth. 相似文献
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Microtopographical studies on habit faces of gel grown crystals (of different habits) of iodates of Ba, Sr, and Ca are illustrated and described. Etch patterns on these faces are illustrated and correlated to the observed growth patterns on the respective faces. Growth mechanism of the crystals is explained in light of the observed surface structures and etch pits suitably produced. 相似文献
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The electro-optic response in planar-aligned chiral nematic liquid crystals in an electric field oriented perpendicular to the helical structure axis is studied as a function of the magnitude and sign of the dielectric anisotropy of liquid crystal in order to understand the mechanism of this electro-optic effect. The main contribution to the electro-optic response is shown to be due to the interaction of the electric field with the dielectric anisotropy. The flexoelectric effect also contributes to the electro-optic response, but its magnitude is much smaller. 相似文献
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Prism face dislocation densities of Czochralski-grown Te single crystals were determined and a new etchant for the basal planes tested, these being prepared by spark-erosive cutting. 相似文献