地铁弹性扣件减振性能的落轴冲击仿真分析

建立地铁弹性扣件轨道的落轴冲击有限元模型,对目前地铁中采用的三种典型扣件:一般弹性扣件、粘结板式弹性扣件和轨道减振器扣件进行落轴冲击响应仿真分析,对比分析了减振性能,并重点分析扣件质量、刚度对减振性能的影响。分析结果表明:在建模时考虑部件质量、刚度能更好的反映钢轨扣件的实际减振性能,为弹性扣件的设计提供参考价值。     

Fatigue life of cold‐expanded fastener holes with interference‐fit fasteners at short edge margins

The fatigue life of 7075‐T6 aluminium specimens with countersunk fastener holes with cold expansion and interference‐fit fasteners with short edge margins was studied. The study was performed experimentally and through finite element analysis. The experiments measured the total fatigue life and crack growth. The results from the finite element analysis consisted of tangential residual stress profiles, which were combined with applied cyclic stresses for fatigue analysis. The experiments showed that the fatigue life improved with interference‐fit fasteners and cold expansion at all edge margins. The fatigue life also increased with increasing edge margin. The finite element results were used to make fatigue life predictions that corresponded reasonably well with the experimental results.     

Stress distribution and performance of threaded bolts in gasketed flange joints

The performance of the flange joint depends on the relaxation of load in bolts. This in turn affects the gasket stress and control of leakage. A finite element model of flange joint with threaded bolt-nut fastener having zero helix angle is developed and analyzed for stress distribution in the threaded bolt. The stress concentration factor at the thread root region is observed to be non-uniform along the circumference due to the bending behavior of the bolt in the flange joint. The maximum stress is observed in the first engaged thread. The variation in bolt load due to internal fluid, thermal and external loads are also investigated for both single and twin-gaskets (two concentric half-sized single gaskets). The gasket material and gasket configuration are observed to be potential factors causing variation in the distribution of load in the flange joint. In a flange joint subjected to external bending load, the maximum stress concentration in the bolt is observed to be in the first thread, instead of the first engaged thread. Under external bending load, the flange joint loses its structural integrity before the traces of leakage occur in the joint.     

Joining of aluminium foams with fasteners and adhesives

This paper describes methods of joining aluminium foams with mechanical fasteners and with adhesives, and characterises the mechanical properties of the resulting joints. Different techniques of joining were investigated under monotonic and cyclic pull-out and bearing loads. The effects of fastener geometry on pull-out and bearing-load failure are modelled. Cyclic loading reduces the maximum load a fastener can carry without failure to 0.35 of the static failure load. Epoxy adhesive joints are stronger than the foam itself in all modes of loading: failure always occurs remote from the joint.     

两种绝热型式低温液体槽车的分析比较

文章从绝热性能、外形尺寸与重量、有效载液容积、制造工艺难度及槽车价格五个方面对真空粉末绝热与高真空多层绝热低温液体槽车进行了比较 ,分析了各自在使用上的优势与不足 ,并对具体运用时槽车的选择提出一些建议     

高性能聚氨酯涂料研制及其在耐磨层中的性能研究

利用邵氏A硬度与吸水率作为评价指标,优选出聚氨酯材料合成的最佳配方,在此配方下聚氨酯的邵氏A硬度达到75,吸水率为0.74%。利用FT-IR、SEM和TG对该材料进行微观表征,分析表明,在最佳配方条件下成功合成了聚氨酯粘结剂,其表面连续、平整性较好、固化反应完全,具有良好的热稳定性。综合评价断裂伸长率和拉伸强度发现填料(SiO₂)的掺量应优选为40%。根据抗滑系数和湿轮磨耗实验确定聚氨酯薄层的胶石比范围为0.25～0.67,在此范围内,聚氨酯耐磨层的抗滑系数和1h浸水磨耗损失均能满足规范要求。     

Quasi-static behaviour of composite joints with countersunk composite and metal fasteners

An experimental study of the quasi-static behaviour of composite joints has been carried out. Composite plates were joined by six fasteners of three different types: composite, titanium Torque-set, and titanium Huck-comp. Specimens were quasi-statically tested to obtain results of the joint tensile and compressive strength. Strain gauge and extensometer measurements were used to investigate the static behaviour of the joints. Strain gauge measurements were carried out to analyse strain distribution and load transfer between bolt rows. Extensometer measurements were done in order to observe bolt-movement behaviour. Generally, composite joints with titanium fasteners have a higher quasi-static strength than that with composite fasteners.     

Characteristics of motorcycle-related hospitalizations: comparing states with different helmet laws

This study compares U.S. motorcycle-related hospitalizations across states with differing helmet laws. Cross-sectional analyses of hospital discharge data from 33 states participating in the Healthcare Cost and Utilization Project in 2001 were conducted. Results revealed that motorcyclists hospitalized from states without universal helmet laws are more likely to die during the hospitalization, sustain severe traumatic brain injury, be discharged to long-term care facilities, and lack private health insurance. This study further illustrates and substantiates the increased burden of hospitalization and long-term care seen in states that lack universal motorcycle helmet use laws.     

永磁式电涡流调谐质量阻尼器的研制与性能试验

为了克服传统的调谐质量阻尼器 (TMD) 阻尼单元存在的易漏油等耐久性问题,研制了一种基于电涡流阻尼耗能的竖向TMD装置。其特点在于：电涡流阻尼无需与结构接触,没有任何摩擦;产生磁场的元件为永磁体,无需外界供电;所有构件都由金属材料制成,不存在老化等现象。此外,通过调整永磁体与导体板的距离,很容易实现TMD阻尼参数的后期调节,且不会影响TMD刚度参数。理论与试验结果研究表明,研制的新型TMD具有优良的阻尼特性,而且当磁场间隙较小时电涡流阻尼理论预测值与试验结果吻合较好。     

Development of a green foaming agent and its performance evaluation

With a view to replace synthetic foaming agents in the production of foam concrete, renewable and naturally available soapnut (SN) fruit has been studied as a foaming agent. Soapnut foaming solutions are prepared in two ways, viz., water soaking for 24 h without heating and with heating of soapnut pericap over a range of temperature (i.e.70 °C–90 °C). The foam generated from the above foaming solutions are studied for properties such as initial foam density and foam stability. However, the use of this foam from soapnut led to cement setting problem, which is caused by the compounds present in soapnut. The setting problem is resolved by using alum as an accelerator. The addition of alum resulted in the formation of additional ettringite and enabled the concrete to set, which is confirmed through powder XRD. The properties of foam concrete produced with water soaked SN with heating is noted to be marginally better compared to those of concrete prepared by water soaked SN without heating. The pore size and shape are analysed using an image analysis technique, which gives good correlations with density and strength of foam concrete.     

不同粒度NiMnCo粉末触媒催化特性及其影响因素的研究

采用扫描电干显微镜(SEM)、X射线光电子能谱(XPS)、差热分析(DAT)研究了不同粒度NiMnCo触媒合成空刚石的催化特性及熔化特性、微观形貌、表面化学状态对其影响，结果表明：320／500目触媒适宜粗颗粒金刚石的合成，150／200目粉末触媒合成的SMD系列金刚石比例较高；比表面积、表面状态和熔化特性直接影响其合成金刚石的效果，比表面积增大，有利于提高空刚石的合成单产；熔化温度降低．可以减少连聚晶的发生；控制粉末触媒表面的氧含量是提高其催化活性的关键。     

Impact of different silkworm dietary supplements on its silk performance

This study aims to evaluate the effect of silkworm larva (Bombyx mori) diet supplementation with two amino acids (threonine and valine) on the cocoon production and on the structural and mechanical properties of the silk produced. Negligible morphological differences were observed in the silk fiber threads from silkworm larvae supplemented with the tested amino acids. Higher production (yield) of silk was obtained using threonine in the diet of the silkworm. The treatments with threonine have increased the limit of proportionality, tensile strength, toughness, and maximum deformation of the thread of silk fibers. No significant increment in these properties was observed due to the increase in the threonine content. The treatments with valine led to lower increase in tensile strength and toughness. The real density of the silk has decreased with the use of supplements. The present study contributes to engineering of advanced silk materials, which should be attractive candidates for multipurpose applications.     

超声及其联用技术的杀菌效果

应用超声作为一种杀菌手段已经引起人们越来越多的关注。尽管单独应用超声作用也有较好杀菌效果,然而要在工业范围内使用超声使其杀菌率接近100%,必然要使用极高的超声功率,消耗大量的能源。这使该技术在工业范围内应用变得非常昂贵。若超声与其它杀菌方法联合使用,如超声分别与热、纳米TiO2、激光、O3、抗生素、紫外线、次氯酸钠、电解方法联合使用,就可以大大提高杀菌效率,而且可以降低超声所消耗的能源。大量实验结果表明,超声与其它杀菌技术联用可以用来有效杀菌,但目前超声及超声与其它技术联合杀菌基本上停留在实验室研究阶段,其处理量很小,故难以用于工业化生产,阻碍了超声联合杀菌的发展。     

Rasch techniques for detecting bias in performance assessments: an example comparing the performance of native and non-native speakers on a test of academic English

The use of common tasks and rating procedures when assessing the communicative skills of students from highly diverse linguistic and cultural backgrounds poses particular measurement challenges, which have thus far received little research attention. If assessment tasks or criteria are found to function differentially for particular subpopulations within a test candidature with the same or a similar level of criterion ability, then the test is open to charges of bias in favour of one or other group. While there have been numerous studies involving dichotomous language test items (see e.g. Chen and Henning, 1985 and more recently Elder, 1996) few studies have considered the issue of bias in relation to performance based tasks which are assessed subjectively, via analytic and holistic rating scales. The paper demonstrates how Rasch analytic procedures can be applied to the investigation of item bias or differential item functioning (DIF) in both dichotomous and scalar items on a test of English for academic purposes. The data were gathered from a pilot English language test administered to a representative sample of undergraduate students (N= 139) enrolled in their first year of study at an English-medium university. The sample included native speakers of English who had completed up to 12 years of secondary schooling in their first language (L1) and immigrant students, mainly from Asian language backgrounds, with varying degrees of prior English language instruction and exposure. The purpose of the test was to diagnose the academic English needs of incoming undergraduates so that additional support could be offered to those deemed at risk of failure in their university study. Some of the tasks included in the assessment procedure involved objectively-scored items (measuring vocabulary knowledge, text-editing skills and reading and listening comprehension) whereas others (i.e. a report and an argumentative writing task) were subjectively-scored. The study models a methodology for estimating bias with both dichotomous and scalar items using the programs Quest (Adams and Khoo, 1993) for the former and ConQuest (Wu, Adams and Wilson, 1998) for the latter. It also offers answers to the practical questions of whether a common set of assessment criteria can, in an academic context such as this one, be meaningfully applied to all subgroups within the candidature and whether analytic criteria are more susceptible to biased ratings than holistic ones. Implications for test fairness and test validity are discussed.     

Comparing the performance of residential fire sprinklers with other life-safety technologies

Residential fire sprinklers have long proven themselves as life-safety technologies to the fire service community. Yet, about 1% of all one- and two-family dwelling fires occur in homes protected by sprinklers. It has been argued that measured sprinkler performance has ignored factors confounding the relationship between sprinkler use and performance. In this analysis, sprinkler performance is measured by comparing ‘like’ structure fires, while conditioning on smoke detection technology and neighborhood housing and socioeconomic conditions, using propensity score matching. Results show that residential fire sprinklers protect occupant and firefighter health and safety, and are comparable to other life-safety technologies.     

The generalized finite element method: an example of its implementation and illustration of its performance

The generalized finite element method (GFEM) was introduced in Reference 1 as a combination of the standard FEM and the partition of unity method. The standard mapped polynomial finite element spaces are augmented by adding special functions which reflect the known information about the boundary value problem and the input data (the geometry of the domain, the loads, and the boundary conditions). The special functions are multiplied with the partition of unity corresponding to the standard linear vertex shape functions and are pasted to the existing finite element basis to construct a conforming approximation. The essential boundary conditions can be imposed exactly as in the standard FEM. Adaptive numerical quadrature is used to ensure that the errors in integration do not affect the accuracy of the approximation. This paper gives an example of how the GFEM can be developed for the Laplacian in domains with multiple elliptical voids and illustrates implementation issues and the superior accuracy of the GFEM versus the standard FEM. Copyright © 2000 John Wiley & Sons, Ltd.     

扩散真空泵性能自动测试系统的研制

本文介绍了一套新研制的扩散真空泵件能的自动测试系统.该系统可以按照国家标准规定的方法自动检测扩散真空泵的极限压力和抽速.系统利用自主开发的光电液位检测方法和元件实现滴管液位的自动读取和记时;利用步进电机驱动针阀实现气体流量和测试罩内压力的自动调节;使用上位PC机和下位单片机的双级控制系统实现对整个测试系统和测试过程的自动控制.     

Preparation and electrochemical performance of nano-scale nickel hydroxide with different shapes

Platelet-like, flake-like, and needle-like nano-scale β-Ni(OH)₂ particles were prepared by coordination homogeneous precipitation method in this paper. X-ray diffraction (XRD), transmission electron microscopy (TEM) and infrared absorption spectra (IR) were used to characterize the microstructure and morphology of the products. The nano-scale Ni(OH)₂ composite electrodes were prepared by mixing 10 wt.% samples with spherical Ni(OH)₂ to carry out charge-discharge test. The results show that the nano-scale Ni(OH)₂ composite electrodes have higher discharge specific capacity, and the nickel hydroxide nanoneedles show a better adulteration performance than the others.     

不同规格磁流变阻尼器的磁学与力学特性

结合试验数据与理论分析,从磁学与力学两种角度,分析了不同规格磁流变阻尼器的特点.研究表明:活塞杆与动密封圈之间的摩擦效应,导致设计具有大可调倍数的小阻尼器的难度远高于设计具有同样可调倍数的大阻尼器;对于一定阻尼力要求的磁流变阻尼器来说,存在着一个最优的直径范围;研究还表明,大吨位阻尼器工作会生成巨大的热量,必须考虑其散热系统.     

Investigating performance of microchannel evaporators with different manifold structures

In this paper, the performances of microchannel evaporators with different manifold structures are experimentally investigated. Eight evaporator samples with 7 different designs of the I/O manifold and 5 different designs of the return manifold are made for this study. The performances of the evaporator samples are tested on a psychometric calorimeter test bench with the refrigerant 134A at a real automotive AC condition. The results on the variations of the cooling capacity and air temperature distribution of the evaporator due to the deflector designs in the I/O manifold and flow hole arrangements in the return manifold are presented and analyzed. By studying the KPI’s for the performance of an evaporator, the design trade-off for an evaporator designer is summarized and discussed.