Theory of high temperature superconductivity in YBa2Cu3O7_δ

A theory of high temperature superconductivity in YBa₂Cu₃O₇__δ compound has been developed on the basis of the momentum pairing of electrons through the relativistic Darwin interaction. The transport behaviour of electrons is explained in terms of a mechanism of correlated electron transfer arising from the electron-phonon coupling. A model Hamiltonian has been developed to describe the superconducting properties of the system. This gives an energy gap which is higher than the BCS value. Attempts have been made to explain the absence of isotope effect, the linear dependence of specific heat, the presence of larger temperature-independent paramagnetism in the normal phase and the softening of some of the optic phonon modes observed in this system.     

Electrical conductivity in very anisotropic conductors and semiconductors

Summary For very anisotropic metallic and semiconducting systems it is shown that the electrical conductivity in the direction of high effective mass decreases as the number of electrons in the conduction band grows. In the other directions the conductivity behaves normally.

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Riassunto Si mostra che, per sistemi semiconduttori e metallici anisotropi, la conduttività elettrica nella direzione di massa altamente efficace diminuisce all'aumentare del numero di elettroni nella banda di conduzione. Nelle altre direzioni la conduttività si comporta normalmente.

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Резюме Для очень анизотропных металлических и полупроводниковых систем показывается, что электропропроводность в направлении большой эффективной массы уменьшается, когда число электронов в зоне проводимости увеличивается. В других направлениях проводимость ведет себя нормальным образом.

     

Anisotropic transport of charge and complexified duality

Charge transport in two dimensions provides an ideal laboratory for investigating parameter space geometries. The Onsager relations for anisotropic transport in a parity-violating external field endow these spaces with a highly nontrivial complex (and Kähler) structure, which can be given a simple geometrical interpretation. A large class of Coulomb gases exhibiting this structure have a generalized Kramers-Wannier symmetry (complexfield duality) which is contained in the modular group. Knowledge of this symmetry and the degrees of freedom encoded in the Coulomb gas appear to be sufficient to determine the global phase diagram and the renormalization group fixed-point structure, including the critical exponents. This accounts for all the scaling behavior observed so far in the quantum Hall system.     

Assessment of different fixation protocols on the presence of membrane-bound vesicles in Caco-2 cells: A multidimensional view by means of correlative light and 3-D transmission electron microscopy

Herein, we present a comparative analysis of a variety of chemical and physical fixation protocols for the specific visualisation of the membrane-bound vesicles (MBVs) in the Caco-2 colorectal cancer (CRC) cell line. In so doing, we validated the applicability of specific specimen preparation protocols for the preservation and contrasting of membrane-associated vesicles. Next, by employing the best respective chemical (GOT) and physical (SHPF) fixation methods for the application of transmission electron tomography and modelling we were able to characterise MBVs in three-dimensions and at the nanometer scale. In the second part of this study, we employ a correlative light and electron microscopy (CLEM) approach in order to determine which vesicular compartments are implicated in the uptake of FITC-BSA as a model protein drug. In so doing, we provide a solid foundation for future studies investigating chemotherapeutic drug uptake, transport and fate in cancer cell lines.     

Oxide magnetic semiconductors： Materials, properties, and devices

We give a brief introduction to the oxide （ZnO, TiO2, In2O3, SnO2, etc.）-based magnetic semiconductors from fundamental material aspects through fascinating magnetic, transport, and optical properties, particularly at room temperature, to promising device applications. The origin of the observed ferromagnetism is also discussed, with a special focus on first-principles investigations of the exchange interactions between transition metal dopants in oxide-based magnetic semiconductors.     

端基对分子器件整流性质的影响

利用基于非平衡Green函数加密度泛函理论的第一原理方法,研究了以S(Se)为端基的三并苯环分子夹在两半无限长的Au电极之间构成双探针系统的输运特性,发现体系具有较好的整流效应,最大整流系数达到6;用H取代右端同一位置的一个S（Se）,整流行为明显减弱.分析认为,这种整流是由于分子两端与电极的耦合不对称,使正负偏压下分子能级的移动和空间轨道分布不同所致.比较而言,S端基与电极的耦合导致的整流比Se强. 关键词： 电子输运 整流行为 非平衡Green函数方法     

金融街地下交通工程通风系统流动特性分析

采用计算流体力学的方法,对金融街地下交通工程通风系统的流场特性进行了数值分析,研究了各分系统流场的均匀特性、各通风管道内部流场细节和各分系统可靠性.结果表明:排风系统各风口的风速很不均匀,且高速风口处形成明显的气幕效应和旋涡区;在风道内形成明显的低速区.在送风系统中,各风口的风速基本均匀,风机的风压可满足要求;但在风道内也存在了明显的低速区或旋涡区.需要对该通风系统进行等风量设计,并对系统的内部气流组织进行改进设计,以提高通风系统的可靠性并降低能耗.     

Longitudinal and bulk viscosities of binary fluid mixtures

Expressions for zeroth, second and fourth sum rules of longitudinal and bulk stress auto correlation functions have been derived for binary fluid mixtures. Longitudinal and bulk viscosities of an Ar–Kr mixture have been calculated using Mori's memory function formalism coupled with the sum rules of longitudinal and bulk stress auto correlation functions. The results obtained are compared with the molecular dynamics simulation. Mass dependence of the longitudinal and bulk viscosities has been studied for different compositions of an isotopic mixture at different densities and temperatures. For very large mass ratio, the longitudinal and bulk viscosities of the isotopic mixture are more dependent on mole fraction than on mass.     

Correlated electron current and temperature dependence of the conductance of a quantum point contact

We investigate finite temperature corrections to the Landauer formula due to electron–electron interaction within the quantum point contact. When the Fermi level is close to the barrier height, the conducting wavefunctions become peaked on the barrier, enhancing the electron–electron interaction. At the same time, away from the contact the interaction is strongly suppressed by screening. To describe electron transport we formulate and solve a kinetic equation for the density matrix of electrons. The correction to the conductance G is negative and strongly enhanced in the region 0.5 × 2e²/h ≤ G ≤ 1.0 × 2e²/h. Our results for conductance agree with the so-called “0.7 structure” observed in experiments.     

Momentum transfer theory of ion transport under the influence of resonant charge transfer collisions: the case of argon and neon ions in parent gases

Transport properties of ion swarms in presence of Resonant Charge Transfer (RCT) collisions are studied using Momentum Transfer Theory (MTT). It was shown that, not surprisingly, RCT collisions may be represented as a special case of elastic scattering. Using the developed MTT we tested a previously available anisotropic set of cross-sections for Ar+Ar ⁺ collisions by making the comparisons with the available data for the transverse diffusion coefficient. We also developed an anisotropic set of Ne+Ne ⁺ integral cross-sections based on the available data for mobility, longitudinal and transverse diffusion. Anisotropic sets of cross-sections are needed for Monte Carlo simulations of ion transport and plasma models. Received 16 June 2002 / Received in final form 2nd August 2002 Published online 24 September 2002 RID="a" ID="a"e-mail: vrhovac@phy.bg.ac.yu RID="b" ID="b"e-mail: zoran@phy.bg.ac.yu