转换反射中光自旋霍尔效应的自旋堆积方向

从理论上和实验上研究了转换反射中光自旋霍尔效应的自旋堆积方向的方法,建立了描述光束在空气-棱镜界面反射的自旋堆积模型,揭示了横移与光束入射偏振角的定性关系.研究发现,当入射角小于布儒斯特角时,随着入射偏振角的逐渐增大,自旋堆积的方向发生反转.而当入射角大于布儒斯特角时,自旋堆积的方向不再随入射偏振角的变化而反转.结果表明,在光束入射角为确定值且小于布儒斯特角的情况下,可以通过调控光束的入射偏振角转换自旋堆积的方向.转换自旋堆积方向的研究为有效调控光自旋霍尔效应提供了新的途径.     

Liquid 2-oxazolidones. I. Dielectric constants,viscosities, and other physical properties of several liquid 2-oxazolidones

Eight derivatives of 2-oxazolidone,, have been synthesized by the Homeyer method and purified by fractional freezing or fractional distillation to obtain low-conducting liquids. Dielectric constants, viscosities, densities, and refractive indices of these 2-oxazolidones have been determined at several temperatures within the range 25 to 75°C. Values for activation energies of viscous flow also have been calculated. The isomeric 3-methyl and 5-methyl derivatives of 2-oxazolidone have high dielectric constants which differ only slightly from that of water. The 3-substituted (or N-substituted) 2-oxazolidones exhibit the most favorable combination of physical properties, stability, and ease of purification and appear to have excellent potential as new nonaqueous solvents.Based on a portion of the Ph. D. dissertation of H. L. Huffman, Jr., University of Kentucky, 1972. Presented in major part at the 21 st Southeastern Regional Meeting of the American Chemical Society, Richmond, Virginia, 1969.     

Physical Properties of Sol-Gel Coatings

One of the most important applications of sol-gel technology is the fabrication of coatings. This is because of the possibility of applying oxide coatings with practically all types of chemical compositions at low ambient temperatures on many substrates of various shapes through the use of liquid solutions. Both oxides and different types of organic-inorganic hybrid coatings have been reported. Both oxides and hybrid coatings are usually amorphous at ambient temperatures but some oxides can be converted to the crystalline phase with heating. Regardless of the intended applications of the coatings their physical properties are always of importance. For instance, an anti-reflective coating for an automobile mirror is of little practical value unless it is fairly scratch-resistant. In this review which covers published information in the past fifteen years, some of the more important results of physical properties of sol-gel derived coatings are discussed firstly for oxides and then for organic-inorganic hybrids. It appears that properties such as the hardness of oxide coatings are inadequate unless the heat-treatment temperatures are in excess of about 400°C. The hybrid coatings, especially when they contain a dispersed phase of a hard solid like colloidal silica, can be processed at temperatures below about 150°C and can improve the performance of organic plastics such as the polycarbonates. There is insufficient scientific understanding of the relationship between physical properties and other interdependent variables such as processing conditions, chemistry and coating thickness. More research in this area will undoubtedly contribute to the availability of better and new coatings via the sol-gel approach.     

多补钙对儿童发钙及生长发育的作用

为研究多补钙对儿童体内钙含量的影响和对生长发育的促进作用,给202名6个月至7岁的儿童服用多补钙1年,在服用前后测量体重、身高、坐高、头围、胸围、臂围和发钙,对儿童形态指标先做等级评价后,应用配对设计差值的符号秩和检验(Wilcoxon配对法)进行统计分析,发钙采用配对设计差值t检验分析。结果表明,服用多补钙1年后儿童发钙平均增加113×10-6,身高、坐高、头围、胸围和臂围的发育水平有显著提高。提示多补钙能有效地提高儿童发钙含量,对儿童的生长发育有明显促进作用。     

Thermoplastic elastomer gels. I. Effects of composition and processing on morphology and gel behavior

Thermoplastic elastomer gels (TPEGs) composed of a poly[styrene-b-(ethylene-co-butylene)-b-styrene] triblock copolymer and a low-volatility, midblock-compatible mineral oil have been investigated at different oil concentrations to ascertain the effect of composition on TPEG morphology and mechanical properties. The impact of thermal processing is also examined by comparing gels thermally quenched to 0°C or slowly cooled to ambient temperature. Transmission electron micrographs reveal that gels with 70 to 90 wt % oil exhibit styrenic micelles measuring ca. 24 nm in diameter. Variation in composition or cooling rate does not have any perceivable effect on micelle size or shape, whereas the rate at which the gels are cooled influences the extent of microstructural order and the time to rupture (t_R) at constant strain. Dynamic rheological testing confirms the presence of a physically crosslinked network at TPEG compositions ranging from 70 to 90 wt % oil, independent of cooling rate. Results presented here suggest that the dynamic elastic shear modulus (G′) scales as t^α_R where α varies from 0.41 to 0.59, depending on cooling rate. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2379–2391, 1998     

Enthalpy relaxation in a partially cured epoxy resin

The enthalpy relaxation of a partially cured (70%) epoxy resin, derived from diglycidyl ether of bisphenol-A cured by methyl-tetrahydrophthalic anhydride with accelerator, has been investigated. The key parameters of the structural relaxation (the apparent activation energy Δh*, the nonlinearity parameter x, and the nonexponentiality parameter β) are compared with those of the fully cured epoxy resin. The aging rates, characterized by the dependences of the enthalpy loss and peak temperature on log(annealing time), are greater in the partially cured epoxy than they are in the fully cured resin at an equivalent aging temperature (T_a = T_g − 20°C). There is a significant reduction in Δh*, from 1100 kJ mol⁻¹ for the fully cured system to 615 kJ mol⁻¹, as the degree of cure is reduced. The parameter x determined by the peak-shift method appears essentially independent of the degree of cure (x = 0.41 ± 0.03 for the partially cured resin compared with 0.42 ± 0.03 obtained previously for the fully cured resin), and does not follow the usually observed correlation of increasing x as Δh* decreases. This invariability of the parameter x seems to indicate that it is determined essentially by the local chemical structure of the backbone chain, and rather little by the supramolecular structure. On the other hand, the estimated nonexponentiality parameter β lies between 0.3 and 0.456, which is significantly lower than in the fully cured epoxy (β ≅ 0.5), indicative of a broadening of the distribution of relaxation times as the degree of cross-linking is reduced. Like the parameter x, this also does not follow the usual correlation with Δh*. These results are discussed in the framework of strong and fragile behavior of glass-forming systems, but it is difficult to reconcile these results in any simple way with the concept of strength and fragility. © 1996 John Wiley & Sons, Inc.     

Qualitative estimation of the dependence of the number of energetic compounds on their oxygen coefficient

The ratio between the numbers of structural formulas of C,H,N,O-containing energetic compounds belonging to the classes of fuels (low values of the oxygen coefficientA), explosives (mediumA), and oxidants (highA values) was studied by a computer generation procedure. The number of the theoretically possible structural formulas was found to decrease rapidly on going from fuels to explosives and then to oxidants; this observation agrees with the data on the numbers of various energetic compounds currently used and proposed. The strategy of the search for new compounds with the specified properties is described in brief, and its applicability to the search for explosives and oxidants with a small (up to 12) number of atoms in a molecule is evaluated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1304–1310, July, 1998.     

Preparation of VPS and PVD coatings for metallographic and TEM investigations

The aim of the first part of the paper is to give some advice for the faultless metallographic preparation of vacuum plasma sprayed coatings. Several coating/substrate combinations using metals, alloys and ceramics were investigated to derive some general rules. The second part deals with a preparation technique for cross-sections- of physical vapour deposition coatings. This technique was optimized for TiN and Ti(C, N) coatings on hardmetals which were examined in an analytical transmission electron microscope.