Photochemical behaviours of star-like liquid crystal with azobenzene terminal groups

The photochemical behaviours of a new star-like liquid crystal S6 with four hexyloxyazobenzene terminal groups were described in this paper. The molar absorption coefficient, quantum yield, photoisomerization, photo back-isomerization, thermal back-isomerization and activation energy of S6 in solution are studied by UV/Vis absorption spectra. The results indicate that the photochromism, photo and thermal back-isomerization of S6 in chloroform (CHCl₃) and tetrahydrofuran (THF) solutions are in accordance with the first order kinetics. The photochromism rate constants of S6 are 10⁻¹ s⁻¹, it is 10⁷ times larger than that of side-chain liquid crystalline polymers containing the same azobenzene moieties. These results indicate that the star structure does not significantly affect the photoisomerization activity of the azobenzene unit in its periphery. The k_t/k_c of S6 is less than that of azobenzene unit shows that the S6 has better photo-reversibility. So the star-like liquid crystal has many potential applications.     

以硝基为端基的香蕉形液晶的合成与性能

合成了4种以间苯二甲酸、间苯二酚为中心,硝基为端基的芳香酯类香蕉形液晶(M1～M4)。利用红外光谱(IR)、核磁共振谱(1 H NMR)及元素分析对其分子结构进行了表征,通过差示扫描量热(DSC)、偏光显微分析(POM)、热重分析(TG)对其介晶性能、相行为及热稳定性进行了研究。结果表明,所合成的香蕉形化合物(M1～M4)均有液晶性,呈现树叶、马赛克、扇形、球粒及纹影织构;升、降温时的液晶区间分别为32.9～57.2℃(M1除外)与28.4～96.5℃;随着分子刚性增加,它们的tm、ti、tic值明显提高;该类物质热稳定性良好,5%热失重温度均在285℃以上。     

阳离子超支化聚合物电解质的合成及离子传导性能研究

以间苯三酚、1,2,4-偏苯三酸酐和环氧氯丙烷为原料合成不同支化度的超支化聚合物(HBP),利用合成的超支化聚合物外围的氯原子与N-甲基咪唑进行离子化反应,制备含咪唑阳离子的超支化聚合物电解质(HBPE)。利用1H-NMR、FT-IR、DSC、TG和复阻抗谱分析等对HBPE的化学结构,热力学性能和离子传导性能进行了研究,结果表明,该聚合物电解质室温离子电导率可达2.3×10-4S/cm,热稳定性在270℃以上。     

Theoretical investigation of Josephson tunnel junctions with spatially inhomogeneous superconducting electrodes

The microscopic theory of the Josephson effect in tunnel structures with electrodes having spatially inhomogeneous superconducting properties is formulated. Two mechanisms of inhomogeneity are considered. The first is associated with the presence of a thin transition normal layer located near the tunnel barrier, which is relevant for junctions based on refractory superconductors. The second case is the trapping of Abrikosov vortices by junction electrodes. The tunnel current components are calculated numerically in the whole temperature range 0<T<T _c and magnetic field range 0<H<H _c2. It is shown that the tunnel current is extremely sensitive to the type of smearing of the singularities of the classical tunnel theory ateV=2. The results allow experimental determination of the characteristics of real tunnel junctions.     

Theoretical investigation of selective dissolution of alloys

We construct a quantum-chemical cluster model of interaction of α-brass and zinc-aluminum and ironchromium alloys with components of an acid aqueous solution of sodium chloride. We established the priority of an increase in the concentration of ions of zinc and iron as compared with the concentration of ions of other metals. The results of computation show that elastic mechanical deformations activate the process of selective dissolution of the alloys considered, which qualitatively agress with the experimental data. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 6, pp. 67–71, November–December, 1999.     

Theoretical and experimental investigation of electrochemical ballizing

This paper investigates the application of electrochemical ballizing (ECB) in finishing holes which are produced by conventional machining processes. A special test rig has been designed where the electrolyte is pumped through an initial hole of hardened steel workpieces. The front of the tool is of spherical shape, and therefore the electrolyte distribution is regular. A computer implement model is proposed for accurately estimating the thickness of the removed workpiece surface. Experimental results have been found to agree with the estimated values. The surface roughness measurement and scanning electron microscopy indicate the improvement in the surface characteristics of holes.     

基于表面等离激元的偏振不灵敏型电光调制器的理论研究

由于受到表面等离激元(SPP)固有偏振性的影响,基于表面等离激元的波导型调制器只支持横磁模式(TM)传播。本文提出了一种在垂直方向和水平方向上均构建混合(hybrid)波导结构的表面等离激元电光调制器,以实现调制器的低偏振灵敏性。在组合的混合波导中,垂直和水平偏振方向上的表面等离激元被限制在相应的混合波导中。通过调控介质和ITO界面处形成载流子积累层中载流子浓度可实现光吸收调制。在经优化的结构中两个偏振态的消光比差为0.005dB/μm。通过3D-FDTD模拟调制器的光场调控,清楚地显示了传统硅波导与偏振不灵敏调制器间的耦合传输特性。两种偏振态下,偏振不灵敏调制器与硅波导之间的耦合效率均达到了74%以上。此项研究将为表面等离激元电光调制器在偏振不灵敏光集成回路中的应用提供解决方案,为其与具有偏振随机态光纤回路的集成奠定了基础。     

HPLC separation of different generations of poly(amidoamine) dendrimers modified with various terminal groups

Polyamidoamine (PAMAM) dendrimers of different generations with various terminal groups were analyzed, for the first time, using a combination of high-performance liquid chromatography (HPLC), size exclusion chromatography (SEC), and matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) techniques. Separation of amine-terminated dendrimers from generation 1 through generation 9 (G1NH(2)-G9NH(2)) was achieved using reversed-phase HPLC with elution time increasing gradually as the density of terminal amine groups increases as a function of generation. Furthermore, separation of dendrimers with terminal amino, acetamide, hydroxyl, and carboxylate groups was obtained. It has also been shown that HPLC can be used to separate dendrimers based on some structural defects inherent during the syntheses of PAMAM dendrimers. MALDI-TOF mass spectra of G1NH(2) identify the major imperfections present during typical synthesis processes. The absolute molar masses (M(n)) and molar mass distributions of the dendrimers were measured using the SEC system equipped with multiangle laser light scattering and refractive-index detectors. Findings from this study suggest HPLC can be a vital tool for characterization and preparative separation of PAMAM dendrimers.     

Extraction properties of polyfunctional P,N-containing podands with diphenylphosphorylacetamide terminal groups in nitric acid solutions

The extraction of HNO₃ and microamounts of U(VI), Th(IV), Sc(III), and REE(III) nitrates from HNO₃ solutions with dichloroethane solutions of phosphorus-containing podands containing two terminal Ph₂P(O)CH₂C(O)NH groups linked by a di-or triethylene glycol chain was studied, and the stoichiometry of the extractable metal complexes was determined. The compounds extract the metal ions from nitric acid solutions more efficiently than does (dibutylcarbamoylmethyl)diphenylphosphine oxide. With increasing length of the polyethylene glycol chain, the extraction of HNO₃ increases, but the degree of recovery of REE(III) ions from HNO₃ solutions of the concentration exceeding 3 M decreases.     

Theoretical study of charge-induced defects at metal/polymer interface

Conducting polymers have attracted much attention concerning the possibility of their use as active components of electronic and optoelectronic devices. We use a molecular dynamics method with semi-empirical quantum chemistry at CNDO (complete Neglect of differential overlap) level to study the chemical interactions between aluminium atoms and trans-polyacetylene during the interface formation. Our results suggest that aluminium dimer (Al₂) bound to a polymer chain is energetically more favourable than the adsorption of isolated aluminium atoms. In both cases, the compound formation is accompanied by charge transfer between metal and polymer. As a result charge rearrangement among the polyacetylene atoms is induced. We shall describe the charge-induced structural relaxation of the trans-polyacetylene backbone which is accompanied by a local change in the electronic structure of the polymer, commonly called defects.     

Local density of states effects at the metal-molecule interfaces in a molecular device

Clarifying the nature of interactions between metal electrodes and organic molecules still represent one of the challenging problems in molecular electronics that needs to be solved in order to optimize electron transport through a molecular device. For this purpose, electronic properties at metal-molecule interfaces were studied by combining experimental and theoretical methods. Applying a novel electrochemical approach, strictly two-dimensional Pd islands were prepared on top of 4-mercaptopyridine self-assembled monolayers (4MP-SAMs) which, in turn, were deposited on (111)-oriented Au single crystals. Electron spectroscopy together with density functional theory calculations revealed strong interactions between the molecules and the islands due to Pd-N bonds, resulting in a drastically reduced density of states (DOS) at the Fermi level EF for a nearly closed Pd monolayer, and even non-metallic properties for nanometre-sized islands. Similarly, a significantly reduced DOS at EF was observed for the topmost Au layer at the Au-SAM interface due to Au-S interactions, suggesting that these effects are rather general.     

黏滞阻尼器耗能增效减震系统理论及试验研究

鉴于传统消能减震系统在层间位移较小时耗能效率有限,介绍了一种带位移放大装置的黏滞阻尼器增效减震系统,可通过放大阻尼器的相对变形提升系统耗能能力。基于该系统变形受力特性构建了其耗能增效及高阶效应力学模型,发现在阻尼器拉伸和压缩变形过程中存在不对称现象,进一步讨论了模型参数对力学性能的影响规律。设计制作了试验模型,并完成了在正弦荷载的作用下的往复加载试验。通过对比试验结果与理论曲线验证了理论力学模型的正确性,并通过试验探讨了频率相关性与疲劳性能。最后针对某框架?剪力墙减震结构进行地震响应分析,结果表明较少数量的带位移放装置的黏滞阻尼器增效减震系统可实现数倍普通阻尼器的增效减震效果。     

Theoretical investigation of reinforced mutually intersecting cylindrical shells

The state of stress of reinforced radial joints of mutually intersecting cylindrical shells was investigated theoretically by the finite element method. For two design variants of reinforcement, viz., monolithic and by butt straps, the article presents the results of a comparative analysis of their effectiveness when the shells are loaded by internal pressure. The influence of the geometric parameters of the joint and of the reinforcement on the maximal stresses in the shells is shown.Moscow. Translated from Problemy Prochnosti, No. 10, pp. 59–62, October, 1989.     

Theoretical investigation of interaction between psoralen and altretamine with stacked DNA base pairs

The present study is an attempt to have a better understanding of physicochemical interaction between anticancer drugs psoralen and altretamine with stacked DNA base pairs. The isolated structural parameters of the stacked base pairs were taken from the Protein Data Bank (PDB) of A-DNA file. The influence of the intercalators on the stability of stacked base pairs was studied based on the results of the interaction energies, which were calculated by the structures of intercalation complexes of psoralen and altretamine with stacked DNA base pairs. The higher dipole moment and polarizability which account for the dispersion forces play an important role during the intercalation of psoralen and altretamine molecules with the base pairs. The stability of the stacking base pairs and their interaction with the intercalator molecules due to the formation of hydrogen bond have been analyzed by Natural Bond Orbital analysis. It has also been noted that intercalator molecules produce significant changes in the values of the phase angle P of pseudorotation conformation of the sugar ring. The physicochemical properties of the psoralen and altretamine as well as the mechanism by which the drug interacts with DNA base pairs allow the rational design of novel anticancer drugs.     

STM investigation of carbon nanotubes connected by functional groups

Chemical functionalization of carbon nanotubes (CNTs) is essential for many applications. Attachment of functional groups to nanotubes can dramatically increase the solubility of the nanotube material. Sidewall functional groups should react with polymers and improve the mechanical properties of nanocomposites. Tubes interconnected by chemical bonds will have a reduced contact resistance and can be used for interconnection purposes in nanoscale circuits. Carbon nanotubes covered with functional groups attached to their exterior wall were analyzed using scanning tunneling microscopy (STM) and TEM. The functionalization was carried out in three steps: acid treatment in H₂SO₄/HNO₃ (3:1) mixture, reaction with SOCl₂ and reaction with diaminopropanol (DAP). The binding force between the nanotubes connected by functional groups and the mechanical stability of the connection was investigated.