Effect of Oxygen Redistribution on the Normal and Superconducting Properties of Yttrium High‐Temperature Superconductors

An anomaly is found in the vicinity of T_max 560$ K on electric resistance versus temperature curves for yttrium hightemperature superconductors of the 123 phase. Xray phase analysis suggests a structural phase transition in the vicinity of T_max due to oxygen redistribution in the mobile sublattice of this compound. Investigation of samples with Y partially replaced by Ca has shown that the structural phase transition does not depend on carrier concentration in the conduction band.     

Selective Formation of Spinel Iron Oxide in Thin Films by Complexing Agent-Assisted Sol-Gel Processing

The structure of iron oxide was controlled by regulating the hydrolytic polymerization of aquo iron complexes with organic polydentate ligands such as diols. Iron oxides were prepared by calcining the precursor polymers obtained from iron nitrate nonahydrate and diols. When the diols were 1,2-pentanediol, 1,2-hexanediol and 1,2-octanediol, α-Fe₂O₃ with corundum structure appeared exclusively or as the main crystalline phase, in spite of the amount of diol used and the calcination temperature. In the case of 1,2-decanediol and 1,2-dodecanediol, when five moles of the diols were used to one mole of iron nitrate and the calcination temperatures were below 400°C, ψ-Fe₂O₃ with spinel structure appeared as the main phase and, when less than five moles of the diols were used, α-Fe₂O₃ appeared exclusively or as the main phase, irrespective of the calcination temperature. This tendency was also observed in thin films. Thus, a transparent magnetic film composed of γ-Fe₂O₃ could be prepared by applying a benzene solution of the iron polymer, obtained with 5 equivalents of 1,2-decanediol, on quartz and calcining the gel film at 350°C.     

Molecular structure of potassium [N,N′-bis(salicylideneamino)nitroguanidonate-N,N′,-O,O′]nickel(ii), the product of condensation of (salicylideneamino)nitroguanidine with salicylaldehyde on a Ni2+ ion template

The crystal structure of the product of the condensation of (salicylideneamino)nitroguanidine with salicylaldehyde on a Ni²⁺ ion template, K[Ni(C₁₅H₁₀N₅O₄)] · DMF, has been studied. It was established that a planar Ni complex, consisting of isolated [NiL]^– anions and solvated [K⁺ · DMF] cations, is formed. The negative charge of the anion is localized mainly on the O atoms of the nitro group. The nitroguanidine fragment of the ligand occurs in the tautomeric form, which was not reported previously.Deceased in 1995Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2273–2277, September, 1996.     

Reversible Full‐Range Color Control of a Cholesteric Liquid‐Crystalline Film by using a Molecular Motor

By using a chiral molecular motor as a dopant in a cholesteric liquid‐crystalline film, fully reversible control of the reflection color of this film across the entire visible spectrum is possible. The large difference in helical twisting power between the two isomeric forms of the motor allows efficient light‐ and heat‐induced switching of the helicity of the cholesteric liquid‐crystal superstructure.     

Analysis of the Micropore Structure of Various Microporous Materials from Nitrogen Adsorption at 77 K

The micropore structure of four microporous materials (two zeolites, ZSM-5 and Y-82; an activated carbon and an alumina pillared clay) and their binary physical mixtures (50-50 wt%) have been examined by nitrogen adsorption at 77 K. Various micropore sizes have been considered from the stages on the micropore filling mechanism in the microporous materials. The application of the Dubinin-Astakhov (DA) equation to characterize and obtain the adsorption potential distributions of the microporous materials is presented.     

Synthesis and structure of 6-chloro-2,3-trimethylene-4-phenylquinoline

An X-ray structural investigation of 6-chloro- 2,3-trimethylene-4- phe nylquinoli ne obtained by the reaction of 2-amino-5-chlorobenzophenone with cyclopentanone was carried out. At 20 °C, a = 23.750,b = 9,242, c = 14.018 A, = 112,68° space group (21c,Z = 8, 2647 reflections,R = 0.047 He five-membered ring has an envelope conformation Conjugation between the quinohne fragment and the phenyl substituent is significantly distorted dm to the rotation of the latter by -62.9°Translated fromIzvestiya Akademii Nauk. Seriva Khimicheskaya, No. 7, pp. 1800–1802, July, 1996.     

老年人彩度对比敏感度函数研究及滤波应用

为研究老年人彩色视觉频率响应特性，获取彩度对比敏感度与空间频率之间的函数关系，本文在LCH均匀颜色空间基础上，固定明度和色调角值，以彩度作为变量，设计人眼彩度对比敏感度实验，进行人眼视觉观察实验。获得彩度对比敏感度与空间频率的关系，并构建指数型对比敏感度函数模型。经分析表明老年人眼彩度对比敏感度随着空间频率的增加，产生先升高再缓慢降低的变化，各色调角下彩度对比度存在差异。经分析人眼对比敏感度差异与人眼视觉辨色特性有很大的相关性。并且，将构建的对比敏感度函数模型用于实现基于人眼视觉系统的滤波处理。     

Crystal Structures and Magnetic Studies of Naphthalene Derivatives Containing Nitronly Nitroxides

Crystal structures of new nitronyl nitroxide derivatives 1, 2 and 3 were determined with X‐ray diffraction analysis: 1, monoclinic, C₂/c, a = 1.2404(5) nm, b = 0.9730(5) um, c = 2.7049(10) ran, β = 98.189(15)°, V = 3.2315(24) nm³, Z = 8; 2, or‐thorhombic, Pbca, a = 0.61262(2) nm, b = 1.11426(6) nm, c = 2.30543(13) nm, V = 1.57373(13) nm³, Z = 4; 3, monoclinic, P2(1)/n, a=0.64253(4) nm, b=2.55003(17) nm, c = 1.15497(6) nm, β = 95.000(3)°, V = 1.8852(2) nm³, Z = 4. Their magnetic properties were measured with SQUID and analyzed based on their crystal structures with simple singlet‐triplet, modified one dimensional antiferromagnetic chain and modified singlet‐triplet models respectively: 1, J/k_b= ?2.5 K; 2, J/k_b = 7.8 K, θ = 2.8 K; 3, J/k_b = ?0.96 K, θ = 0.21 K.     

Enthalpies of mixing of <Emphasis Type="Italic">o</Emphasis>- and <Emphasis Type="Italic">m</Emphasis>-isomers at 298.15 K

Excess enthalpies (H ^E) of 17 binary mixtures of o- and m-isomers of dichlorobenzene, difluorobenzene, methoxymethylbenzene, dimethylbenzene, dimethoxybenzene, aminofluorobenzene, fluoronitrobenzene, diethylbenzene, chlorofluorobenzene, fluoroiodobenzene, bromofluorobenzene, chloromethylbenzene, fluoromethylbenzene, bromomethylbenzene, iodomethylbenzene, fluoromethoxybenzene, dibromobenzene at 298.15 K were measured. All excess enthalpies measured were very small, and those of o-+m-isomers of aminofluorobenzene, dibromobenzene and iodomethylbenzene were negative but 14 other binary mixtures of isomers were positive over the whole range of mole fractions. H ^E of o-+m-isomers of dimethoxybenzene showed the largest enthalpic instability and those of aminofluorobenzene showed the largest enthalpic stability. There was a correlation between dipole–dipole interaction, dipole–induced dipole interaction or entropies of vaporization and excess partial molar enthalpies at infinite dilution.     

Modification of Surface and Structural Properties of Ordered Mesoporous Silicates

Two simple modification methods for ordered mesoporous silicas were examined and compared. MCM-41 molecular sieve was physically coated with 4-cyano-4-biphenyl [4(4-pentenyloxy)]benzoate (CBPB) and chemically modified using trimethylethoxysilane. The structural and surface properties of the obtained materials were characterized using elemental analysis, thermogravimetry and nitrogen adsorption over a wide pressure range.It was shown that the pore size of the MCM-41 material was not decreased significantly after the coating procedure, even for high loadings of CBPB. Moreover, low pressure adsorption measurements indicated that significant fractions of the MCM-41 surface were not covered by CBPB, even for high CBPB loadings, which suggests that the attained coverage may be very nonuniform. The chemical bonding procedure led to a marked decrease in the pore size and change of surface properties.It was demonstrated that nitrogen adsorption measurements provide a means of a thorough characterization of modified MCM-41 materials, allowing to estimate the surface area, pore volume and pore size distribution. Moreover, low pressure adsorption data can be used to qualitatively or semiquantitatively assess the surface coverage of the coated/bonded organic groups, which may be used to estimate the uniformity of the coverage and therefore, the usefulness of the modification procedure.