Experimental investigation of friction coefficient in tube hydroforming

The friction coefficient between tube and die in guide zone of tube hydroforming was obtained. In hydroforming, the tube is expanded by an internal pressure against the tool wall. By pushing the tube through tool, a friction force at the contact surface between the tube and the tool occurs. In guiding zone, the friction coefficients between tube and die can be estimated from the measured axial feeding forces. In expansion zone, the friction coefficients between tube and die can be evaluated from the measured geometries of expanded tubes and FE analysis.     

Effect of Microwave and Conventional Cooking on the Nutritive Value of Colossus Peas (Vigna uniguiculata)

The effect of microwave and conventional cooking methods, designed to simulate those used in home meal preparation, upon nutrient retention in Colossus Peas (Vigna uniguiculata) was studied. Neither method resulted in significant changes in the fat, protein, β-carotene and ascorbic acid content of the peas. Microwave cooking resulted in significantly greater losses of several ammo acids, but resulted in significantly greater retention of thiamin and riboflavin than the conventional treatment. Although each of the mineral components exhibited different magnitudes of loss by the two cooking methods, different due to method of cooking were not significant. Both Fe and Cu were completely retained in the peas cooked by both methods. Both cooking methods (15-60 min cooking) resulted in 92-97% loss of trypsin inhibitor.     

螺栓连接的冷成型钢结构的结构性能

本文介绍了一系列螺栓连接的冷成型钢结构的结构性能的试验和理论研究。首先,研究了搭接剪切试验中冷成型钢条之间螺栓连接的基本变形特性,并采用了包含实体单元和接触单元的高等有限元建模作为对比。其次,介绍了带有螺栓抗弯连接的搭接Z型截面的结构性能,对搭接Z型截面的强度和刚度做了解析方法和数值方法的评估。最后,采用数值方法对双跨搭接Z型檩条的结构性能进行了研究,考察了跨越内部支座的搭接Z型截面对于沿檩条构件内力分布的影响。本文意在提供分析和设计方法,以便于结构工程师理解,使他们能够设计和建造出结构性能更好的冷成型钢结构房屋。     

LACTOBACILLUS CURVATUS PRODUCES A BACTERIOCIN-LIKE AGENT ACTIVE AGAINST GRAM-NEGATIVE PATHOGENIC BACTERIA

Isolates from fermented foods were screened for antimicrobial activity against gram‐negative bacteria. The most active isolate was identified as a Lactobacillus curvatus by biochemical analysis and ribotyping, and the isolate was designated as OSY‐HJC6. Lactobacillus curvatus OSY‐HJC6 was further tested for intracellular and extracellular production of antimicrobial agents. A reduction of > 8 log₁₀ cfu/mL was observed when cell suspensions of Salmonella enterica serovar Enteritidis and Escherichia coli O157:H7 were treated with equal volumes of Lb. curvatus culture supernatant. Gram‐positive bacteria were not sensitive to the culture supernatant, but antimicrobial activity was detected when the cell extract was tested against several gram‐positive and gram‐negative bacteria. Culture supernatant and cell extract retained the antimicrobial activity after heating at 60–100C for 10 min but not after protease treatment. The cell extract of Lb. curvatus retarded the growth of E. coli p220 in broth medium and food extracts (i.e., bacteriostatic action) but showed bactericidal activity against the bacterium in phosphate buffer.     

Partial Lipid Extraction of Egg Yolk Powder: Effects on Emulsifying Properties and Soluble Protein Fraction

Egg yolk powder was partly defatted using hexane, 95% ethanol, isopropanol, chloroform-methanol (2:1, v:v) hexane-isopropanol (77:23, w:w) and hexane-ethanol (77:23, w:w). Hexane-isopropanol was most efficient, extracting more than 50% of the lipid. Protein solubility and emulsifying activity of the extracted powder decreased after extraction. Hexane-isopropanol reduced emulsifying activity about 14% and protein solubility to 13.8% from 15.7%. Extraction with other solvents resulted in up to 41% loss of emulsifying activity; protein solubility decreased to as low as 3%. Ovalbumin in the water-soluble fraction of extracted egg yolk powder reduced its emulsifying effectiveness.     

暂态稳定约束下期望收益最大的断面输电极限

基于机会约束规划理论,提出了暂态稳定约束下断面输电极限计算的随机模型。对给定的置信水平,模型中概率暂态稳定约束被转化为最小临界切除时间代数约束,结合泛函最优控制原理,上述随机模型被变换为线性不等式约束的数学规划模型。最后应用风险决策中的期望值准则,对不同置信水平下系统的收益损失进行综合评估,得到了系统在暂态稳定约束下期望收益最大的运行方案。39节点新英格兰系统上的仿真结果说明了所提方法的有效性和实用性。     

Experimental Investigation of Aerodynamic Performance due to Blade Tip Clearance in a Gas Turbine Rotor Cascade

This study examines how the complex flow structure within a gas turbine rotor affects aerodynamic loss. An unshrouded linear turbine cascade was built, and velocity and pressure fields were measured using a 5-hole probe. In order to elucidate the effect of tip clearance, the overall aerodynamic loss was evaluated by varying the tip clearance and examining the total pressure field for each case. The tip clearance was varied from 0% to 4.2% of blade span and the chord length based Reynolds number was fixed at 2×10⁵. For the case without tip clearance, a wake downstream of the blade trailing edge is observed, along with hub and tip passage vortices. These flow structures result in profile loss at the center of the blade span, and passage vortex related losses towards the hub and tip. As the tip clearance increases, a tip leakage vortex is formed, and it becomes stronger and eventually alters the tip passage vortex. Because of the interference of the secondary tip leakage flow with the main flow, the streamwise velocity decreases while the total pressure loss increases significantly by tenfold in the last 30% blade span region towards the tip for the 4.2% tip clearance case. It was additionally observed that the overall aerodynamic loss increases linearly with tip clearance.     

娱乐场所的噪声——香港酒吧的情况

许多城市居民喜欢在酒吧等娱乐场所享受快乐时光。但是，他们暴露在可能造成健康危害的娱乐场所环境中。这是因为人们逗留在酒吧时，会受到昏暗的灯光、二手烟和高噪声的影响。回顾了有关酒吧噪声的文献，并在香港的六家酒吧进行了噪声测量。分析结果显示，在欢乐时间即在5：00 pm和9：00 pm之间，酒吧声音水平（L_eq，10-min）介于66.5~79.9 dB （A）之间，酒吧声音水平在繁忙时间即10：00 pm至11：30 pm介于69.5~97.0 dB （A）之间。在欢乐时间，最高噪音水平（L_max）介于78.5~96.5 dB （A）之间，在繁忙时间介于80.9~107.8 dB （A）之间。分析发现，酒吧内的声音水平可以通过L_eq，10-min测量，酒吧内的背景噪音则可以通过L₉₀测量。     

A COMBINED FINE-COARSE MESH METHOD FOR THE TRANSMISSION LINE MODELLING OF DIFFUSION

An improved combined fine-coarse mesh (CFCM) method for two transmission line models of diffusion is described. The method allows regular cells of different sizes to be connected and solved simultaneously. The CFCM method is applied to (a) a finite difference algorithm, (b) a conventional transmission line model and (c) a lossy transmission line model. The latter model is shown to be the most accurate. The proposed CFCM method is also compared with the graded mesh and the multigrid techniques.