Critical Transport Properties Near the Superfluid Transition in 3He-4He Mixtures

The renormalization group(RG) functions for the critical dynamics at the λ-transition in ³He–⁴He mixtures (model F^′) have been calculated in two loop order. Comparison is made with the hydrodynamic transport coefficients as functions of the concentration of ³He. Improvement is achieved with respect to an earlier calculation based on a combination of one loop and two loop terms in the field theoretic functions, The non-universal initial values of the flow parameters take values more compatible with the physical expectation. As a corollary we obtain the field theoretic functions of model F describing the critical dynamics of the superfluid transition in pure ⁴He. Comparing with experiments in pure ⁴He improves the background value of the imaginary part of the time scale ratio between the order parameter and the entropy density.     

Critical Currents and Melting Temperature of a Two-Dimensional Vortex Lattice with Periodic Pinning

The critical current and melting temperature of a vortex system are analyzed. Calculations are made for a two-dimensional film at finite temperature with two kinds of periodic pinning: hexagonal and Kagomé. A transport current parallel and perpendicular to the main axis of the pinning arrays is applied and molecular dynamics simulations are used to calculate the vortex velocities to obtain the critical currents. The structure factor and displacements of vortices at zero transport current are used to obtain the melting temperature for both pinning arrays. The critical currents are higher for the hexagonal pinning lattice and anisotropic for both pinning arrays. This anisotropy is stronger with temperature for the hexagonal array. For the Kagomé pinning lattice, our analysis shows a multi stage phase melting; that is, as we increase the temperature, each different dynamic phase melts before reaching the melting temperature. Both the melting temperature and critical currents are larger for the hexagonal lattice, indicating the role for the interstitial vortices in decreasing the pinning strength.     

聚乳酸玻璃化转变行为的分子模拟

采用等温等压(NPT)正则系综,用分子动力学方法研究了聚乳酸的玻璃化转变行为,获得了玻璃化转变温度.在230～440K范围内,通过模拟体系的密度、比体积及相关径向分布函数等参数,最终确定了聚乳酸的玻璃化温度,模拟计算的结果与实验值吻合.     

A Critical Grain Size Concept to Predict the Impact Transition Temperature of Ti-Microalloyed Steels

Based on the assumption that local principal stress remains the same everywhere within a ferrite grain, a critical value of grain size can be determined for a fixed TiN particle size. When the grain size is smaller than the critical size, grain boundary is expected to resist the propagation of a micro-crack that is initiated from a TiN particle. Using this concept, an attempt has been made to predict the local cleavage fracture stress and 27J impact transition temperature (ITT) of different Ti-microalloyed steels, which were subjected to (instrumented) Charpy impact testing.     

硒化温度对铜铟镓硒太阳能电池吸收层性能的影响

用预制膜硒化法制备铜铟硒系太阳能电池的吸收层CIGSe薄膜,用X射线荧光分析(XRF)、扫描电子显微镜(SEM)、X射线衍射分析(XRD)和拉曼谱分析(Raman)以及基于霍尔效应分别测定或观测CIGSe薄膜的成分、表面形貌、结构以及电阻率和少数载流子迁移率,研究了在近玻璃软化点520-560℃区间硒化温度对薄膜成分、表面形貌、结构和电学性能的影响。结果表明:当硒化温度在520-560℃时,CIGSe薄膜的成分和表面形貌保持不变,但是随着硒化温度的升高CIGSe薄膜中有序缺陷相(ODC)和Cu-Se短路相增加,提高了薄膜内的缺陷浓度,使薄膜的少数载流子迁移率降低、电阻率增大。     

Modeling the Combined Effect of Temperature and Composition on the Properties of a Glass Plate

The alkali-metal-ion exchange between glass surfaces and molten salts, widely used to strengthen glass and produce graded materials, is analyzed in terms of relaxation theory. A model is proposed which adequately describes stress development and relaxation in the glass during ion exchange and subsequent heat treatment. The model calculations are compared with the present and earlier experimental data. The model is shown to reflect the salient features of the temperature dependences and depth profiles of glass properties in the modified surface layer, in spite of the relatively small number of model parameters, some of which are derived from experiment.     

Transport in Vortex State of d-Wave Superconductors at Zero Temperature: Wiedemann–Franz Violation

We show that the Wiedemann–Franz law is violated at zero temperature in the vortex state of a d-wave BCS superconductor with isotropic impurity scattering. We use a semiclassical approach to include the Doppler shift experienced by the quasiparticles due to the circulating supercurrents and consider as well the Andreev scattering from an array of vortices assumed to be randomly distributed. We also show that the vertex corrections to the electric conductivity, which can be large when there is significant anisotropy in the impurity scattering, become unimportant as the magnetic field is increased. For the thermal conductivity, the corrections remain negligible as in the absence of a magnetic field.     

温度对核壳胶乳涂膜形成及性能的影响

研究了温度对P(St-co-BA)/P(BA-co-MMA)核壳型复合胶乳的成膜及其性能的影响.通过涂膜干燥速率由线、透光率、吸水率及水蒸汽渗透系数随温度的变化,发现在40℃～90℃内适宜的温度下,可加速膜的形成、提高涂膜的性能.而当在临界温度(90℃)以上成膜或退火时,可使胶膜产生二次相分离,且在膜内产生微裂纹、针孔及空穴等缺陷,但这些针孔不是贯通的.     

Effect of Synthesis Temperature on the Transport Properties of Copper Ferrites

Copper ferrites were prepared from equimolar oxide mixtures at different temperatures, and their electrical conductivity and thermoelectric power were measured. The transport properties of the ferrites were found to vary systematically with the synthesis temperature. A model for charge transport in copper ferrite spinels was proposed. The conductivity and thermoelectric power data, together with earlier Mössbauer results, were used to assess the cation distribution in the ferrites.     

Influence of Interfacial LSMO Nanoparticles/Layer on the Vortex Pinning Properties of YBCO Thin Film

YBa₂Cu₃O_7?δ (YBCO) thin films have been deposited on bare and La_0.67Sr_0.33MnO₃ (LSMO) modified single crystal SrTiO₃ (STO) substrates. The effect of randomly distributed ferromagnetic LSMO nanoparticles and a complete LSMO layer, present at STO/YBCO interface, on the superconducting properties of YBCO thin films has been investigated by temperature dependent magnetization studies. The YBCO thin film on LSMO nanoparticles decorated STO substrate shows significant improvement in the critical current density and pinning force density as compared to the YBCO thin film deposited on bare STO substrate and this improvement is more significant at higher applied magnetic field. However, the LSMO/YBCO bilayer showed the improved flux pinning properties only up to a magnetic field of 1.5 T above which it deteriorates. In the case of LSMO/YBCO bilayer, the underlying LSMO layer gives rise to magnetic inhomogeneities due to domain structure, which leads to improved flux pinning properties limited to lower field. However, in the case of LSMO nanoparticles decorated substrate, the presence of LSMO nanoparticles at YBCO/STO interface seems to introduce magnetic inhomogeneities as well as structural defects, which might be acting as correlated pinning sites leading to improved flux pinning properties of the YBCO thin film over a wide range of applied magnetic field.     

Express Analysis of the Dependence of the Critical Temperature of Superconducting Film on its Thickness

Measurement Techniques - Express analysis of the dependence of the critical temperature of different superconducting films on its thickness was proposed, developed, and tested. The technique is...     

Non-ohmic Electrical Transport Properties Above the Critical Temperature in Optimally and Underdoped Superconducting YBa2Cu3O6+x

The resistivity and the Hall effect as a function of current density and temperature in the normal state of very thin films of YBa₂Cu₃O_6+x are measured with a fast pulsed-current technique. The in-plane longitudinal and transverse (Hall) conductivities are reduced in intense current densities up to several $\mathrm{MA\,cm}^{-2}$ . In optimally-doped samples, this non-ohmic effect is limited to temperatures below 100?K. In a moderately underdoped sample, however, the non-linearity extends to the temperature range from T _c =53?K to ??150?K. The non-linear part of the Hall conductivity does not scale with a critical exponent, thus excluding classical amplitude fluctuations of the superconducting order parameter as possible origin.     

A Note on the Critical Enhancement of Transport Properties and Correlation Length of Fluids

The thermal conductivity and viscosity of fluids are known to exhibit an enhancement due to critical fluctuations. Procedures proposed in the literature for estimating the correlation length determining the magnitude of these enhancements have been reviewed, and a recommendation to reduce complexity and computation time is presented.     

‘Fragile Superconductivity’: A Kinetic Glass Transition in the Vortex Matter of the High-temperature Superconductor YBa2 Cu3O7-δ

Using high-resolution thermal expansion and magnetization measurements, we provide experimental evidence for a kinetic glass transition in the vortex matter of YBa₂Cu₃O_7-δ with some disorder. This transition, which represents the true superconducting transition in a magnetic field, exhibits many of the features of the usual glass transition found in supercooled structural liquids such as window glass. We demonstrate, using both kinetic and thermodynamic criteria, that this vortex matter is the most fragile system known to date, which we argue makes it possible to investigate the behavior very close to the Kauzmann temperature. Vortex matter, we suggest, may be a model system to study glassy behavior in general, which is expected to lead to a better understanding of the strong-fragile behavior in structural glasses.     

Dynamics of a Particle and a Quantized Vortex at Zero Temperature: Self-consistent Calculation

Many experiments for visualizing quantized vortices and normal fluid flow have been performed in superfluid ⁴He. Recently, metastable He₂ excimer molecules have been used as tracer particles. Since their radius is only about 10^?10 m, they hardly perturb the system, thus being a good candidate of tracer particles. In order to understand the interactive motion of He₂ molecules and vortices at zero temperature, we numerically study the trapping diameter by using the self-consistent equations of motions. We calculated the trapping diameter as a function of the initial velocity of the particle. The trapping diameter is almost inversely proportional to the initial velocity of the particle and compared with the observation.     

The Effect of Run Time on the Inter-Unit Uniformity of Aqueous Film Coating Applied to Glass Beads in a Hi-Coater

Abstract

Coating experiments were conducted to assess the inter-unit uniformity using individual weight gains of glass beads. Applying more aqueous film coating and prolonging the film-coating process by diluting the coating suspension did improve the coating variability among glass beads. It appears that run time is an important underlying factor which affecting the inter-unit coating uniformity.     

The Effect of Run Time on the Inter-Unit Uniformity of Aqueous Film Coating Applied to Glass Beads in a Hi-Coater

Coating experiments were conducted to assess the inter-unit uniformity using individual weight gains of glass beads. Applying more aqueous film coating and prolonging the film-coating process by diluting the coating suspension did improve the coating variability among glass beads. It appears that run time is an important underlying factor which affecting the inter-unit coating uniformity.     

Influence of the Injection Molding Process on the Creep Behavior of Semicrystalline PBT During Aging Below its Glass Transition Temperature

Depending on the processing conditions, Polybutylene terepthalate (PBT) exhibits different creep behavior as a result of its thermorheological history during the injection molding process, although the short-term tensile tests do not show any significant differences. With aging time, this effect is more pronounced and the difference is mainly attributed to the differences in frozen-in free volume and the crystallinity content of the material. A higher mold temperature during injection molding produces higher crystallinity and lower free volume leading to reduced creep strain, whereas a longer aging time leads to a reduction in free volume and therefore less creep. The results thus show that apart from crystallinity, free volume also plays an important role in determining the creep behavior of the semicrystalline polymers.