120°相带环形绕组圆筒型永磁直线发电机定位力降低的优化设计

圆筒型永磁直线发电机(TPMLG)采用120°相带环型绕组可以提高其功率密度,然而,TPLMG具有较大的定位力,这会引起发电机的振荡甚至使系统不稳定.为了解决这一问题,该文对120°相带环形绕组(120°-TPMLG)的圆筒型永磁直线发电机进行优化设计.首先利用有限元方法研究不同结构参数(定子铁心长度、极弧系数、槽肩宽度、定子齿宽和气隙长度)对定位力的影响.根据分析结果,结合田口方法对发电机进行优化设计,在不损失输出功率的情况下使定位力最小,得到120°-TPMLG的最优结构参数.为了验证优化设计过程的有效性,将优化后的120°-TPMLG与初始发电机的性能进行比较.结果表明,优化后的120°-TPMLG的定位力得到了极大的减小,输出功率也略有增加.因此,该文采用的优化方法对减小120°-TPMLG的定位力是有效的.     

基于IGBT行为模型的有源中点钳位五电平变换器损耗特性分析

有源中点钳位五电平拓扑(5L-ANPC)通常用于中压大容量电能变换领域,同时由于其拓扑结构复杂和各器件有效开关频率不同,使得损耗分析较为困难,并且对计算精度要求较高.该文分析基于载波移相脉宽调制(PS-PWM)的损耗计算方法,根据电压电流关系,详细分析所有器件的导通规律,推导导通损耗计算方法.针对传统的开关损耗计算方法在中压大容量条件下误差较大的问题,详细分析IGBT的开关瞬态过程,提出一种基于行为模型的开关暂态损耗计算方法,并将其运用于5L-ANPC拓扑开关损耗分析.对5L-ANPC拓扑损耗特性进行分析,为散热系统设计奠定了坚实的基础.实验结果表明,该文所提方法提高了损耗计算精度,最大误差为10.4％,最小误差为8.4％,验证了所提损耗计算方法的有效性.     

在工业中采用钛合金的微弧氧化

采用硬度测试，金相显微观察和透射电镜分析等方法，研究了微量稀土Er对高纯铝再结晶行为的影响，结果表明，弥散分布的细小Al3Er质点对位错和亚晶界具有钉扎作用，可以有效抑制再结晶，将高纯铝的再结晶温度提高50左右，同时还能显著细化再结晶晶粒，再结晶形核机制是亚晶聚合和亚昌长大双重机制。     

烷基磺酸钠型砂的质量控制

介绍了控制烷基磺酸钠型砂的混砂工艺、配制要点及保存使用等控制要点，并就实际生产中可能出现的一些问题作了探讨，提出了解决的办法。     

Magnesium technology 2002, part I: Primary production,environmental issues,high-temperature alloys

Conclusion It is expected that the research in high-temperature alloy development will reach a critical mass in about five years. This will not only raise the materials science of magnesium to a higher level but will also increase the confidence of the industry in magnesium as a structural performance material. Currently, applications are being actively pursued in United States Council for Automotive Research power train programs and European Council for Automotive R&D engine block programs to develop the technology for elevated-temperature magnesium. More research is still needed in this interesting materials field.     

Atomic force microscopy study of biaxially oriented polypropylene films

Atomic force microscopy (AFM) uses a very sharp pointed mechanical probe to collect real-space morphological information of solid surfaces. AFM was used in this study to image the surface morphology of a biaxially oriented polypropylene film. The polymer film is characterized by a nanometer-scale, fiberlike network structure, which reflects the drawing process used during the fabrication of the film. AFM was used to study polymer-surface treatment to improve wettability by exposing the polymer to ozone with or without ultraviolet (UV) irradiation. Surface-morphology changes observed by AFM are the result of the surface oxidation induced by the treatment. Due to the topographic features of the polymer film, the fiberlike structure has been used to check the performance of the AFM tip. An AFM image is a mixture of the surface morphology and the shape of the AFM tip. Therefore, it is important to check the performance of a tip to ensure that the AFM image collected reflects the true surface features of the sample, rather than contamination on the AFM tip.     

Comparison of two scaling approaches for the development of biomechanical multi-body human models

Dimensional scaling approaches are widely used to develop multi-body human models in injury biomechanics research. Given the limited experimental data for any particular anthropometry, a validated model can be scaled to different sizes to reflect the biological variance of population and used to characterize the human response. This paper compares two scaling approaches at the whole-body level: one is the conventional mass-based scaling approach which assumes geometric similarity; the other is the structure-based approach which assumes additional structural similarity by using idealized mechanical models to account for the specific anatomy and expected loading conditions. Given the use of exterior body dimensions and a uniform Young’s modulus, the two approaches showed close values of the scaling factors for most body regions, with 1.5 % difference on force scaling factors and 13.5 % difference on moment scaling factors, on average. One exception was on the thoracic modeling, with 19.3 % difference on the scaling factor of the deflection. Two 6-year-old child models were generated from a baseline adult model as application example and were evaluated using recent biomechanical data from cadaveric pediatric experiments. The scaled models predicted similar impact responses of the thorax and lower extremity, which were within the experimental corridors; and suggested further consideration of age-specific structural change of the pelvis. Towards improved scaling methods to develop biofidelic human models, this comparative analysis suggests further investigation on interior anatomical geometry and detailed biological material properties associated with the demographic range of the population.     

k-Multi-preference query over road networks

Nowadays, the road network has gained more and more attention in the research area of databases. Existing works mainly focus on standalone queries, such as k-nearest neighbor queries over a single type of objects (e.g., facility like restaurant or hotel). In this paper, we propose a k-multi-preference (kMP) query over road networks, involving complex query predicates and multiple facilities. In particular, given a query graph, a kMP query retrieves of the top-k groups of vertices (of k facility types) satisfying the label constraints and their aggregate distances are the smallest. A naïve solution to this problem is to enumerate all combinations of vertices with k possible facility types and then select the one with the minimum sum distance. This method, however, incurs rather high computation cost due to exponential possible combinations. In addition, the existing solutions to other standalone queries are for a single type of facilities and cannot be directly used to answer kMP queries. Therefore, in this paper, we propose an efficient approach to process a kMP query, which utilizes an index with bounded space and reduces the computation cost of the shortest path queries. We also design effective pruning techniques to filter out false alarms. Through our extensive experiments, we demonstrate the efficiency and effectiveness of our proposed solutions.