Oxidation behavior of ytterbium silicide

Si-rich ytterbium silicide was fabricated by through an arc-melting technique for applying use as a bond coat material in an environmental barrier coating system. Evaluation of its potential was accomplished through oxidation tests in dry air and an inert atmosphere. The experimental results showed that the changes in weight and morphologies of ytterbium silicide observed after the tests depended on the oxygen partial pressure. Extensive oxidation and weight gain occurred after oxidation in air. In order to apply this material for hot structures, improvement of the oxidation resistance is needed.     

Heat flux from the catalyst layer of a fuel cell

We report exact solutions to the problem of heat transport in the catalyst layer (CL) of a fuel cell. The solutions are obtained for the low- and high-current regimes of CL operation. The approximate equation for the heat flux from the CL valid for the whole range of current densities is suggested. This equation is suitable for CFD calculations of heat transport in cells and stacks. Heat fluxes from the catalyst layers of PEMFC, HT-PEMFC and DMFC are discussed.     

Velocity measurements inside the concentration boundary layer during copper-magneto-electrolysis using a novel laser Doppler profile sensor

The evolution of the velocity boundary layer during the initial phase of copper electrolysis under the influence of a magnetic field is studied by using particle image velocimetry and a novel laser Doppler velocity profile sensor. With this new sensor, time-resolved velocity measurements within 400 μm of a vertically aligned cathode in an aqueous 0.05 M CuSO₄-solution are presented. In this way, the complex interaction of Lorentz force and opposing buoyancy-driven convection was studied by measuring the resulting velocity profile inside the concentration boundary layer with a spatial resolution of 15 μm. It is shown that the Lorentz force-driven convection only dominates the velocity boundary layer during the early phase of electrolysis and induces a linear velocity profile near the cathode. The linear relationship between the velocity gradient and Lorentz force is determined. With the onset of the opposing buoyancy-driven convection at the cathode, a duplex structure of the boundary layer appears. Its characteristic quantities, given by the horizontal distances, δ_max and δv=0, where the velocity reaches the maximum and where it is equal to zero, remain nearly unchanged, while the maximum velocity, vmax, in spite of the counteracting Lorentz force, increases faster as compared to pure natural convection, depending on the current density.     

Reflection and transmission of ultrasound by a region of damaged material

Reflection and transmission of ultrasonic waves by a layer-like region of distributed microcracks in a bulk material has been investigated. It has been assumed that for sufficiently low frequencies and far away from the damaged layer, the reflected and transmitted waves are plane waves. By applying the Betti reciprocal theorem to a cell containingN cracks, and by choosing one elastodynamic state as the actual wave state and the other as a suitably chosen auxiliary wave state, the reflection and transmission coefficients have been expressed in terms of integrals over theN cracks. Simple expressions have been obtained for the case that all cracks are identical and parallel to each other. For the case that the cracks do not interact with each other, numerical results for the reflection and transmission coefficients are presented for a distribution of penny-shaped cracks. The variation of these coefficients with frequency, relative layer thickness and angle of incidence has been displayed in graphs.     

大庆油田开发的实践和展望

本文回顾了大庆田油开发30年的实践,总结了早期内部注水,分层保持油层压力;不断认识储层属性,用接替稳产方式进行开发调整;分阶段搞好开发试验,注重实践经验,指导开发部署的基本做法,成功地开发了大庆油田。文章还指出了大庆油田在高含水后期进一步挖掘潜力,改善开发效果的工作方向。     

341—115A封隔器设计

３４１—１１５Ａ新型封隔器是对原有旧式封隔器基础上进行了多处结构改造研制而成,该封隔器易于制造、密封好、防渗漏,能实现多级封隔器串联使用,可用于多层分级注水作业．座封时不用水泥车,只靠注水管线的压力就可进行座封,解决了油田急需．     

Influence of the metallic absorption layer on the quality of thermal conductivity measurements by the transient thermo-reflectance method

This work investigates numerically the influence of a metallic absorption layer on the laser-based measurements of the thermal conductivity of dielectric (SiO₂) and semiconductor (Si) electronic materials. The validity of the approach and the obtained results are assessed by comparison with experimental measurements obtained for gold-covered silicon dioxide samples. The results reveal the presence of behaviors associated with thermally thin and thermally thick absorption layers, depending on the ratio between the thickness of the absorption layer and the heat penetration depth. Optimal performance of the transient thermo-reflectance method was found to exist for thicknesses of metal layers falling between the identified thermally thin and thermally thick layers.     

Analytical Solutions for Bending Curved Beams with Different Moduli in Tension and Compression

When materials that exhibit different mechanical behaviors in tension and compression must be analyzed, Ambartsumyan's bimodular model for isotropic materials can be adopted. It deals with the principal stress state in a point, which is particularly important in the analysis and design of structures. In this article, an equivalent section method is used to transform the bimodular curved beam into a classical one with singular modulus; consequently, the simplified solution for bending stresses may be easily determined only by changing a few parameters relating to section characteristics. For the determination of the unknown neutral layer, a perturbation method is used to obtain the explicit expression. Based on the known neutral layer, a stress function method is used to obtain the elasticity solution for stresses and displacements via boundary conditions and continuity conditions. Based on the elasticity solution, an initial stresses problem in a bimodular multiply-connected body is considered. The comparison between two solutions shows that the simplified solution agrees very well with the elasticity one. Moreover, the inclusion of shear stress and the application of the equivalent section method in reinforced-concrete curved beams are also discussed. The results indicate that the bimodularity of materials has definite influences on the bending behavior of a bimodular curved beam.     

连铸结晶器铜板及表面处理技术进展

结晶器是钢坯连续铸造的关键设备,其设计和制造的优劣直接影响到连铸生产的正常与稳定.本文就目前连铸结晶器采用的铜板材料及铜板材料表面处理技术的发展现状进行了总结和分析.指出针对板坯结晶器窄面铜板易高温变形、磨损的情况,采用高强度、高导热率的弥散强化铜材料,进而延长结晶器的维修周期,提高生产效率.同时针对现有结晶器铜板表面...     

Improving secret key generation for wireless communications in FDD mode

Most recent research on channel‐based key generation oriented to time division duplex system because the channel reciprocity feature is applied directly for secret key generation. Most of commercial cellular systems depend on frequency division duplex (FDD) systems. In this paper, we investigate the impact of uplink and downlink of FDD systems for the generation of shared secret keys between two parties in the presents of passive eavesdropper. In addition, we are considering improving the rate of the secret key for wireless communication in FDD mode. The main idea is to use the fading coefficient of the channels between the relay and other parties as an additional random common source for the secret key generation. Also, explore the using of channel estimation techniques to reduce the channel training sequence and study its effect on the generation of shared key for wireless communications in FDD mode. We derive the upper bound of the generated shared key rate for four scenarios and give numerical examples to reveal the performance of our suggested improvement approaches.