Preparation of YBa2Cu3O7–x high-Tcceramic superconductors from melt

Fabrication of high-T _c ceramic superconductor in the system Y₂O₃-BaO-CuO by melting a mixture of component oxides has been investigated. The compositions of the resulting specimens and the effects of heat treatment have been investigated. It was determined that molten material was composed of phases including BaCuO₂, CuO, Y₂O₃, and Y₂BaCuO₅. A subsequent heat treatment in air produced a nominal amount of the high-T _c phase, while heat treatment in an O₂ atmosphere resulted in a significantly large percentage of the superconducting phase.     

On the feasibility of high spatial resolution superconducting X-ray detectors

We discuss a class of superconducting particle/radiation detectors in which the readout is by magnetic means. Even a small energy deposition can change the state of a superconductor, leading to a drastic change of its electromagnetic properties. To increase the detector sensitivity, a highly granulated superconducting medium is used. Millions of physically separated sensors are read out in parallel by only a few channels of very sensitive D.C.-SQUID based electronics. We present the mathematical formulation of the problem and discuss how the excellent signal-to-noise ratio obtained using SQUIDs permits us to determine particle/photon localization.     

Kic Transition-temperature behavior of A517-F Steel

Linear-elastic fracture mechanics has been widely used to obtain K_ic values on very-high-strength steels (yield strengths > 200 ksi) that generally do not exhibit a ductue-to-brittie transition in failure mode as a function of temperature. However, as the use of the K_ic test approach is extended to those steels that do exhibit a ductile-to-brittle transition, information on the K_ic transition-temperature behavior of steels is required. Therefore, to establish general relations between K_ic and Charpy test results, slow-bend K_ic fracture tests and various Charpy tests were conducted on A517-F steel at temperatures between −320 and +80°F.

The results indicated that a plane-strain K_ic température transition does exist for A517-F steel. Furthermore, this transition occurred in the same temperature range (−150 to −50°F) as the transition denned by slow-bend Charpy test results for fatigue-cracked specimens. In both the K_ic tests and the Charpy tests, the transition-temperature behavior appeared to be related to a gradual change in the microscopic fracture mechanism. The upper shelf, as denned by slow-bend Charpy tests, appeared to be a region in which K_ic values cannot be obtained, regardless of specimen geometry, because of general yielding and crack blunting.

A procedure is proposed in which the dynamic K_ic behavior of a material can be predicted from static K_ic test data by shifting the static K_ic values along the temperature axis by the same amount as the static Charpy energy values are shifted by impact testing.

In general, the results of this investigation have demonstrated that a transition in K_ic behavior of A517-F steel does exist as a fution of temperature and that that transition is independent of the K_ic to K_c stress-state transition.     

On the limiting factors of the critical current density in high-Tc superconducting ceramics

The temperature dependence of the critical current density at high temperatures and in weak applied magnetic field for YBa₂Cu₃O_7–y ceramic samples with a pronounced granular character is analyzed. The experimental results can be explained in terms of thermally activated motion of the intergrain Josephson vortices at grain boundaries, which may be an indication that the actual limiting factor for the critical current density in ceramic samples results from a weak pinning force density for the intergrain vortices rather than from the weak-link quenching.     

Consequences of Orbital Degeneracy in Insulating and Doped Manganites

We derive a spin-orbital model for manganites which includes the complete e _g and t _2g superexchange of S=2 spins at Mn³⁺ ions and predicts that the same type of antiferromagnetic and orbital ordering is stabilized in insulating La₃Mn₂O₇ as in LaMnO₃ by a purely electronic mechanism dominated by the e _g-superexchange. At finite doping we consider a model of t–J variety which describes a metal–insulator transition due to a competition between lattice polarons and kinetic energy in the metallic ferromagnetic ground state.     

计算沉积层古厚度的逐层恢复法

油气勘探实践证明,绝大多数油气聚集存在于含油气盆地之中,因此,油气田的调查和勘探必须着眼于含油气盆地的研究,研究盆地的沉积史,构造发展史,有机物质演化史以及流体(石油和天然气)的运移和聚集史。在盆地全部地质演化史的研究中,沉积层的厚度是一个极其重要的参数,然而,各个地史时期沉积层的厚度不应该是一个常数,随着它自身埋藏深度的增加而逐渐减薄,这是一个众所周知的客观事实。但是,目前利用厚度法进行地质分析时都运用沉积层的现厚度(或称今厚度)代替各地史时期沉积层的古厚度,这样分析的结果必然产生一定的误差。     

硼-羟丙基瓜胶交联体系高温压裂液配方的室内研究

介绍了高温硼交联剂和用高温硼交联剂交联羟丙基瓜胶体系的压裂液配方，以及该体系压裂液的室内性能评价。该压裂液具有伤害率低、破胶化水彻底等特点，适用于深层低渗油气藏，可以满足小于150℃油气层压裂施工的需要。     

裂缝性气藏不同完井方式渗流场分析

地层模型中具有多条不规则天然裂缝,有的裂缝直达井壁,有的裂缝相互贯通,造成渗流规律复杂,运用常规的解析算法很难对其进行计算求解。采用有限元方法,基于ANSYS软件进行建模,模型中对地层和裂缝采用同一种材料,通过引入裂缝放大系数来区分并描述裂缝对流体导流能力的增大。模型中考虑了钻井液入侵造成的井壁和裂缝污染带,通过引入污染系数来描述污染带的渗透率下降。通过模拟计算得出2种模型的渗流压力场分布、渗流速度场分布以及全井流量,并进行对比分析,为完井方式的选择提供较为直观的理论依据。     

Recent advances in hydrogel-based anti-infective coatings

Bacterial infections associated with biomedical devices and implants have posed a great challenge to global healthcare systems.These infections are mainly caused by bacterial biofilm formed on the surface of biomaterials,protecting the encapsulated bacteria from conventional antibiotic treatment and attack of the immune system.As the bacterial biofilm is difficult to eradicate,bactericidal and antifouling coatings have emerged as promising strategies to prevent biofilm formation and subsequent infections.Hydrogels with three-dimensional crosslinked hydrophilic networks,tunable mechanical property and large drug-loading capacity are desirable coating materials,which can kill bacteria and/or prevent bacterial adhesion on the surface,inhibiting biofilm formation.Herein,we review recent developments of hydrogels as anti-infective coatings.Particularly,we highlight two chemical approaches(graft-from and graft-to),which have been used to immobilize hydrogels on surfaces,and present advances in the development of bactericidal(contact-killing and antimicrobial-releasing),antifouling(hydrophilic polymer network)and bifunctional hydrogel coatings with both bactericidal and antifouling activities.In addition,the challenges of hydrogel coatings for clinical applications are discussed,and future research directions of anti-infective hydrogel coatings are proposed.     

Thermal activation on calcium silicate slag from high-alumina fly ash: a technical report

The fly ash with alumina composition from 45 to 55 % has been found in China in last 10 years, which attracts great attention from Chinese government and related alumina industry. Chinese government and its state-owned enterprises have successfully extracted the Al as alloy product from the high-alumina fly ash. However, to recycle the calcium silicate slag as residue from the Al industry is still undetermined. In this report, an innovative process is introduced to achieve the regional sustainability for the high-alumina fly ash industry, and it is found that the cementitious material composed of calcium silicate slag met with the mechanical requirements of 32.5 cement for road pavement. The chemical and mineral analysis show that the calcium silicate slag has high CaO content, which reaches up to 48.64 %. C₂S and C₃A are the dominant mineral phases by XRD analysis indicating its potential pozzolanic activity during the hydration process. Thermal activation from 200 to 900 °C was applied to enhance its pozzolanic activity for the calcium silicate slag and it proved that 600 °C is the optimal calcination temperature due to the decomposition of calcite and clay minerals. Also the mineral phase amorphization was also observed during the XRD analysis, which might also contribute to the enhanced pozzolanic properties at 600 °C. Although the designed cementitious material contains a large quantity of solid waste, none of the hazardous heavy metals exceed the EPA limits. This short article originally reported a promising direction for managing solid waste for Al industry and enhancing utilization efficiency for the enterprise internal solid wastes.