Effect of bismuth replacement at barium site in Y-Ba-Cu-O system

X-ray diffraction, electron paramagnetic resonance, microwave absorption and resistivity measurements were carried out on YBa_2−x Bi _x Cu₃O₇ (0≤x≤0·5) superconductors in order to study the effect of bismuth on the structural and superconducting properties. A decrease in sintering temperature increased the amount of impurity phase. Transition from an orthorhombic (superconducting) phase to tetragonal structure produced no significant change in EPR zero-field signal at liquid nitrogen temperature (LNT). The non-resonance signal height decreased on higher concentration of bismuth. Sintered YBa_2−x Bi _x Cu₃O₇ superconductor had a strong EPR zero-field signal at LNT. We have evaluated particle size from XRD and EPR studies. The average particle size was about 0·4μm.     

油酸乙二醇单酯在基础油与水界面上形成吸附膜的研究

以油酸和乙二醇为原料，在酸性催化剂作用下，用硼酸间接酯化法合成了润滑油油性油酸乙二醇单酯，用界面张力仪测定了单酯含量的矿物油的界面张力。用量小二乘法求得油中油酸乙二醇单脂的浓度与油对水界面张力关系的回归方程。依据所求的回归方程和Ｇｉｂｂｓ公式计算出油酸乙二醇单脂在油与水界面上形成吸附膜时的最低浓度。     

Al,Ga取代Bi：DyIG薄膜的磁和磁光特性的研究

本文报道用热分解法在玻璃衬底上制备了Ａｌ和Ｇａ取代的Ｂｉ：ＤＹＩＧ薄膜，对其磁和磁光特性做了详细研究．Ａｌ和Ｇａ取代的薄膜均可获得好的矩形比和高的矫顽力．对于Ｂｉ１．２Ｄｙ１．８Ｆｅ５－ｘＭＸＯ１２（Ｍ＝Ａ１，ＧＺ）薄膜，Ａ１和Ｇ２的最佳替代成份分别为１．０和Ｇ．７；最佳晶化温度分别为７００ｏ℃和６７５℃．在波长５１０ｎｍ附近，法拉第旋转角可达８°／ｕｍ左右．光学吸收和品质因子的研究结果表明，Ａｌ和Ｇａ取代能够影响光学吸收和品质因子，其中Ｇａ取代对光学吸收和品质因子的影响较大．     

Ammonia-water absorption machines for refrigeration: theoretical and real performances

In principle, absorption chillers of the ammonia-water type could work at temperatures well below the usual air-conditioning temperatures, arriving at the range 250–260 K, which can be useful for refrigeration applications. This possibility is studied for an air-cooled machine, comparing the results with the experimental data supplied by a manufacturer that recently commercialized such a refrigerator. The prediction is fair, and the study allows an insight into the internal parameters and into the possible behaviour for more severe conditions than those studied.     

奥钢联板坯连铸计算机系统升级研究

某钢厂板坯连铸过程控制系统采用的奥钢联(VAI)技术,运行数年来,由于模型不透明,维护和调整困难,迫切需要升级改造。改造后的计算机系统充分考虑现有资源和需求,能够达到升级改造的目的。     

X-ray microtomography: Application to microstructure analysis of a cementitious material during leaching process

Leaching of cementitious materials leads to an increase in porosity, which has important consequences on transport and mechanical properties. The present study outlines the characterization of microstructural evolution in a mortar subjected to a chemical attack, by means of a powerful non-intrusive experimental method, namely synchrotron X-ray computed microtomography. This innovative method is used to measure the variation of porosity in a leached mortar. Having described the effects of leaching in mortar (influences on microstructure and on mechanical properties), we present the accelerated leaching process and the microtomographic analysis that have been used to monitor it. We then investigate the capacity of this method to quantify the evolution of porosity during the leaching process. The method is validated by comparison of the results obtained with data available in the literature.     

Quasi-static and dynamic crushing behaviors of aluminum and steel tubes with a cutout

Tubular members are commonly used as an energy absorber in engineering structures and many such members have a cutout. In this study, the crushing behaviors of tubes with a cutout are characterized and the effects of cutout on the energy absorption capabilities of these tubes are quantified. Systematic parametric studies were carried out to study the effect of material properties, including yield and ultimate strength of material, strain rate effect, location of cutout, tube length and impact speed on the crushing behaviors and energy absorption capacity of aluminum and steel tubes. First, a numerical model was constructed with a commercial explicit finite element code. It will be first proven that the numerical simulation can produce sufficiently accurate results in an economic manner. Subsequently, the crushing behavior of aluminum and steel tubes with a cutout was experimentally characterized and their energy absorption capacity was evaluated in terms of mean crushing force, peak crushing force and specific energy absorption (SEA). Tubes of various lengths with a cutout located at different locations, subject to both quasi-static and dynamic impact loadings were considered. For steel tubes, the numerical simulation investigated the influence of the strain rate effect and variation in strain hardening ratio of the material. Empirical equations describing the mean and peak crushing forces of aluminum and steel tubes with a cutout were developed using linear and nonlinear regression methods applied to the results obtained from the numerical and experimental studies.     

Heat transfer enhancement by Marangoni convection in the NH3–H2O absorption process

The objectives of this paper are to quantify the effect of Marangini convection on the absorption performance for the ammonia–water absorption process, and to visualize Marangoni convection that is induced by adding a heat transfer additive, n-octanol. A real-time single-wavelength holographic interferometer is used for the visualization using a He–Ne gas laser. The interface temperature is always the highest due to the absorption heat release near the interface. It was found that the thermal boundary layer (TBL) increased faster than the diffusion boundary layer (DBL), and the DBL thickness increased by adding the heat transfer additive. At 5 s after absorption started, the DBL thickness for 5 mass% NH₃ without and with the heat transfer additive was 3.0 and 4.5 mm, respectively. Marangoni convection was observed near the interface only in the cases with heat transfer additive. The Marangoni convection was very strong just after the absorption started and it weakened as time elapsed. It was concluded that the absorption performance could be improved by increasing the absorption driving potential (x_vb−x_vi) and by increasing the heat transfer additive concentration. The absorption heat transfer was enhanced as high as 3.0–4.6 times by adding the heat transfer additive that generated Marangoni convection.     

Uncertainty in Quantitative Electron Probe Microanalysis

Quantitative electron probe analysis is based on models based on the physics or x-ray generation, empirically adjusted to the analyses of specimens of known composition. Their accuracy can be estimated by applying them to a set of specimens of presumably well-known composition.