Transport of high-temperature superconductors in the normal state

The impurity mechanism proposed earlier is used to interpret the transport properties of high-temperature superconductors in the normal state. Temperature and impurity concentration dependences of the resistance and the Seebeck and Hall coefficients are discussed. An explanation for the sharp drop in the Seebeck and Hall coefficients with impurity concentration and reducing them to zero in La_2–x Sr _x CuO₄ at the maximumx at which superconductivity exists is put foward.     

Theory of spin fluctuations in striped phases of doped antiferromagnetic cuprates

We study the properties of generalized striped phases of doped cuprate planar quantum antiferromagnets. We invoke an effective, spatially anisotropic, nonlinear sigma model in two space dimensions. Our theoretical predictions are inquantitative agreement with recent experiments in La_{2-x}Sr_xCuO₄ with 0≤ x ≤ 0.018. We focus on (i) the magnetic correlation length, (ii) the staggered magnetization at T= 0, and (iii) the Néel temperature, as functions of doping, using parameters determined previously and independently for this system. These results support the proposal that the low doping (antiferromagnetic) phase of the cuprates has a striped configuration.     

ESR studies of superconducting cuprates: Low magnetic field effects at X-band and 300 MHz

Low field microwave absorption in cuprate superconductors belowT _c is reported in a range of materials using ESR spectrometers operating at X-band and 300 MHz. The radiofrequency apparatus facilitated a detailed study of the 0–100G region where the absorption is most intense and we include here a brief discussion of the effects of incident microwave power and sample temperature on the intensity and position of the signal.     

CsI(Tl)晶体发光均匀性的研究

本文对Tl分布、几何形状以及表面条件对大尺寸锥形CsI（Tl）晶体的闪烁发光均匀性的影响进行了研究,提出了改善大尺寸锥形CsI（Tl）晶体的发光均匀性的措施.     

Preparation of High - Purity Tl(1223) Ceramics

The influence of changes in the nominal composition and preparation conditions on the formation of Tl(1223) under a high isostatic gas pressure was studied. Optimization of the cation substitution allowed to increase the phase purity, whereas substitution of small amounts of oxygen by fluorine decreased the formation temperature of the Tl(1223) phase and extended the temperature range favorable for grain growth. A two-step reaction involving substantial melting produced well shaped, plate-like grains.     

Preparation and properties of Tl2Ba2CaCu2O8 thin films

Anex situ process has been developed to produce thin superconducting Tl₂Ba₂CaCu₂O₈ films. The properties of films grown on different substrates using different annealing regimes were studied. Critical temperatures of 103–107 K were measured on films prepared in a broad range of annealing temperatures on SrTiO₃, LaAlO₃, and Y-ZrO₂ substrates. A critical current density,J _c, of 2×10⁶ A/cm² at 77 K was measured on LaAlO₃. Film morphology was studied by SEM, AFM, and STM.     

Symmetry, mechanism of the pairing, and the isotope effect in the cuprates

This paper is concerned mainly with the problem of the origin of highT _c .s-Wave vs.d-wave pairing, the isotope effect, and the strong coupling of the carriers to low-frequency optical phonon modes are discussed. This latter strong coupling is sufficient to provide highT _c .The work of VZK was sponsored by the U.S. Office of Naval Research Contract No. N00014-92-F0006.     

Ultralow-concentration Sm codoping in CsI:Tl scintillator: A case of little things can make a big difference

CsI:Tl scintillators were hindered from computer tomography and high-speed imaging applications by a serious afterglow problem. In this study, the effects of ultralow-concentration Sm codoping on the scintillation characteristics of CsI:Tl were investigated. Pulsed X-ray excited afterglow after 50 ms in 0.005 mol% Sm-codoped CsI:Tl was lowered by over one order of magnitude in comparison with Sm-free one. The beneficial effects of ultralow-concentration Sm codoping also appeared to be maintaining the light yield and energy resolution. The light yield and energy resolution after 0.005 mol% Sm codoping were 71,700 ± 6000 photons/MeV and 6.9% at 662 keV, respectively.     

Combinatorial solid state chemistry by multitarget laser ablation: a way for the elaboration of new superconducting cuprates thin films?

Laser ablation by varying the number of consecutive laser pulses upon two targets, one superconducting YBa₂Cu₃O₇, the other insulating MCuO₂ (M=Sr, Ca), is used to build thin films of tuneable average compositions. Most of the samples are found to display high-T_c superconductivity with critical temperature generally higher than the 60 K of the ‘Cava phase’, the prototypic structure with two consecutive conducting CuO₂ planes and containing same types of atoms. The properties of the samples are not linearly dependent on the concentration of species coming from the insulating target. In addition, they depend not only on the ratio of the number of pulses on each target, but also on the number of consecutive pulses on each target. Thin films are characterized by temperature-dependent DC conductivity, X-ray diffraction, Castaing microprobe and infrared reflectivity spectroscopy. Present results suggest the robustness of high-T_c superconductivity, possibly related to a ‘Cava-phase-like’ skeleton.     

Electronic structure of Nd2CuO4 and its physical properties

In order to clarify the electronic structure of the electron-doped superconducting material Nd_2–xM_xCuO₄, we have performed a first-principle band structure calculation for the matrix material Nd₂CuO₄. We find that doped electrons can be accommodated in both the Cu 4s and 4p _z conduction bands provided that the Cu 3dx²–y ² band splits into two bands, i.e., the upper and lower Hubbard bands by the strong correlation. Based on this electronic structure, we have calculated the Hall coefficient of the Nd system and have shown for the first time that the sign of the Hall coefficient is negative, coinciding with the experimental result in the low-concentration case. In the overdoped region above x=0.18, the dopant electrons occupy not only 4s and 4p _z bands but also the upper Hubbarddx ²–y ² so that the Hall coefficient changes its sign from negative to positive.     

Thermoelectric properties of p-type PbSe nanowires

The thermoelectric properties of individual solution-phase synthesized p-type PbSe nanowires have been examined. The nanowires showed near degenerately doped charge carrier concentrations. Compared to the bulk, the PbSe nanowires exhibited a similar Seebeck coefficient and a significant reduction in thermal conductivity in the temperature range 20 K to 300 K. Thermal annealing of the PbSe nanowires allowed their thermoelectric properties to be controllably tuned by increasing their carrier concentration or hole mobility. After optimal annealing, single PbSe nanowires exhibited a thermoelectric figure of merit (ZT) of 0.12 at room temperature.      

The Transport of Choline

ABSTRACT

Choline has many physiological functions throughout the body that are dependent on its available local supply. However, since choline is a charged hydrophilic cation, transport mechanisms are required for it to cross biological membranes. Choline transport is required for cellular membrane construction and is the rate-limiting step for acetylcholine production. Transport mechanisms include: (1) sodium-dependent high-affinity uptake mechanism in synaptosomes, (2) sodium-independent low-affinity mechanism on cellular membranes, and (3) unique choline uptake mechanisms (e.g., blood–brain barrier choline transport). A comprehensive overview of choline transport studies is provided. This review article examines landmark and current choline transport studies, molecular mapping, and molecular identification of these carriers. Information regarding the choline-binding site is presented by reviewing choline structural analog (hemicholinium-3 and 15, and other nitrogen/methyl-hydroxyl compounds) inhibition studies. Choline transport in Alzheimer's disease, brain ischemic events, and aging is also discussed. Emphasis throughout the article is placed on targeting the choline transporter in disease and use of this carrier as a drug delivery vector.     

Galvanomagnetic properties of plastically deformed InSb single crystals

The dc Hall effect, dc conductivity and mobility have been studied on deformed and undeformed samples ofn-type InSb from liquid nitrogen temperature to room temperature. These studies have shown that the Hall coefficient values of deformed samples do not differ much from undeformed sample, but a considerable amount of change was observed in mobility, suggesting that equal number of donor and acceptor type dislocations are introduced during the deformation process. In addition the mobility variation of the deformed samples with temperature has shown a peak in 170–300°K range. The dislocation mobility (μ _D) is deduced from the observed mobilities of deformed and undeformed samples. The plotμ _D vs T has two regions, region 1 being independent of temperature and region 2 having a linear increase with temperature. Theβ factor obtained from region 2 is found to be almost equal to the one calculated from Dexter and Seitz model. The dislocation densities at room temperature are also calculated for the deformed samples using the above model.     

Hg1-xMnxTe晶片电学参数的测量及分析

采用范德堡法分别在77K和室温下对多个Hg1-xMnxTe晶片的电学性能进行了测量,发现部分晶片在77K下的导电类型为p型,而在室温下却为n型.通过理论分析对此现象进行了解释.分析表明:Hg1-xMnxTe晶片中电子迁移率与空穴迁移率的比值较大和Hg1-xMnxTe的禁带较窄是造成晶片导电类型转变的主要原因.对所测其它电学参数的理论分析表明范德堡法不适合用于Hg1-xMnxTe晶片室温时的载流子浓度和迁移率的测量,但仍可用其对晶片室温时的电阻率和霍尔系数进行测量.     

Van Hove model of pseudogaps and stripes in the uederdoped cuprates

Recent photoemission and thermodynamic experiments on underdoped cuprates strikingly confirm the prediction that the pseudogap is driven by a splitting of the degeneracy of the Van Hove singularity. The doping dependence of the pseudogap can be understood in terms of a crossover from magnetic to charge-dominated behavior (including strong electron-phonon coupling). The crossover is accompanied by a nanoscale phase separation (striped phase), which is shown to be driven by Van Hove nesting.     

现代物流中商品运输包装动力可靠性

由于复杂的流通环境条件、产品运输包装缓冲结构几何参数等都具有随机特征,影响着整个商品运输包装的可靠性,重点论述了计算商品运输包装动力可靠性的现有的技术方法和应用以及其研究发展方向.     

玩具的包装设计与运输安全

玩具的科技含量越来越高,应该重视玩具的包装设计。对于高档的电子玩具的包装,除了考虑外包装盒对玩具的外观保护、装饰、说明作用,还要了解玩具的流通环境,了解玩具本身的结构特点,设计合理的内部衬垫,以保证玩具在运输、装卸过程中的安全。     

物流链中的运输包装优化问题

文章在分析了众多影响物流包装成本的因素的基础上,提出了物流链中包装优化的可行性方案,指出了降低物流包装总成本的途径,最后列出物流运输包装优化程序的流程图.实例证明,从包装材料成本与运输空间利用率两方面努力,可以获得比较好的优化效果.