An elastic strip with multiple cracks and applications to tapered specimens

In this paper an infinite elastic strip containing arbitrarily oriented cracks and subjected to uniform tension and a pair of concentrated forces is formulated in terms of a system of singular integral equations. Even though the technique is sufficiently general to solve any multiple crack problem, with the objective of applying the results to tapered specimens, only a certain symmetric crack geometry and loading conditions are considered. The stress intensity factors are calculated for edge cracks in the strip under uniform tension and for a “compact” and a “slender” tapered specimen (the latter simulating the double cantilever beam) under concentrated forces or crack surface wedge forces.

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Résumé On formule sous forme d'un système d'équation inégrale, le cas d'une bande élastique infinie comportant des fissures orientées de manière quelconque et soumise à traction uniforme et à une paire de forces concentrées. Même si la technique est suffisament générale pour solutionner tout problème de fissures multiples, en vue d'en appliquer les résultats à des éprouvettes à congés, on ne considère ici qu'un certain type de géométrie symétrique de fissures et que certaines conditions de mise en charge. On calcule les facteurs d'intensité de contrainte correspondant à des fissures de bord dans la bande soumise à tension uniforme, et dans des éprouvettes à congé de raccordement de type “compact” ou “élancé” (ce dernier type simulant une poutre double cantilever) soumises à forces concentrées ou à forces émanant d'un coin.

     

基于即时编译的动态污点跟踪优化

动态污点跟踪技术展现了在移动隐私保护方面强大功能,但存在系统性能较低问题.提出了一个基于即时编译的动态污点传播优化方法.首先,将程序逻辑精确抽象为污点传播逻辑,简化污点传播分析复杂性;然后,提出了一个污点传播框架并证明了在该框架下污点传播分析的正确性和有效性;最后,采用消除,替换和移动等方法将冗余低效的污点传播代码转化为高效等价的污点传播代码.实验结果表明经过优化后单条热路径的污点传播代码节省了38%内存占用和指令执行时间,系统整体性能平均提升了6.8%.     

基于Hausdorff距离的插值方法评价

在图像放大处理中通常要将图像进行插值,在Hausdorff测度理论的基础上对Hausdorff距离进行了改进．然后将改进后的Haosdorff距离作为评价图像质量的一种标准，对放大后的图像进行量化评估,并与其他的评价方法进行比较．结果表明用Hausdorff距离作为评价标准得到的结果更接近图像的视觉效果.     

Study of milling force variation in ultrasonic vibration-assisted end milling

Ultrasonic vibration cutting has been proved to be an effective cutting technology for its excellent cutting performance and has been widely applied in turning and drilling process. However, this kind of technology is rarely tried in milling process. In cutting process, cutting force is an important process parameter, which affects surface finish and tool wear. This paper investigates the milling force variation in ultrasonic vibration-assisted end milling process through a series of slot-milling experiments. The main research contents include two parts, one is the effect of the externally excited vibration on milling force in milling process, and the other is the influence of milling and vibrating parameters matching on milling force value. Experimental results show that ultrasonic vibration can change traditional milling conditions, realize separate-type milling, obtain similar pulse-like profiles of cutting forces, reduce average cutting force value; and the peak value of the feed direction cutting force can also be greatly decreased by adopting reasonable vibration amplitude, an optimal combination of machining parameters is of great benefit to achieving small cutting force. According to the experimental findings, ultrasonic vibration-assisted milling is a prospective technology to achieve precision milling of small part.     

Optimization of SC-CO2 extraction of oil from almond pretreated with autoclaving

Supercritical carbon dioxide (SC-CO₂) extraction parameters affecting oil recovery from almond were optimized through response surface methodology (RSM). The optimum extraction conditions were as follows: extraction pressure, 44.1 MPa; extraction temperature, 43.8 °C; dynamic extraction time, 93.6 min; and CO₂ flow rate, 10.1 mL/min. Under these conditions, a mean value of 86.54 ± 0.66 g/100 g (n = 3) was observed, which is well matched with the predicted value of 87.32 g/100 g. Furthermore, the effects of autoclaving pretreatment for the almond particles on the oil recovery, fatty acids' composition, and almond particles' microstructure were also investigated by calculating the percentages of the oil yield, gas chromatograph fitted with a mass spectrometer (GC-MS), and scanning electron microscopy (SEM) analysis, respectively. The results showed that autoclaving pretreatment had minor modifications of the fatty acids' profile of the extracted oil, but greatly promoted the disturbing of almond cell walls, and increased the oil recovery by 6.44%.     

藏南古堆地区煌斑岩地球化学特征及构造环境

藏南古堆地区煌斑岩脉主要发育于隆子-古堆断裂附近,出露于隆子县城-马扎拉一带广大区域,属喜马拉雅造山带后碰撞阶段的产物。在分析该区煌斑岩主量元素、微量元素及稀土元素地球化学特征的基础上,讨论了区内煌斑岩的构造环境及成因,为进一步研究古堆地区地质特征及区内煌斑岩构造特征提供参考。     

P2P网络架构下蚁群算法的应用研究

蚁群算法(ACO)是一种新型的模拟进化算法,是受自然界中蚂蚁搜索食物行为启发而提出的一种智能优化算法。探讨了P2P网络架构下蚁群算法的应用,对在P2P网络架构下怎样使用蚁群算法解决网络服务中的Peer间的通信和路由、服务注册和查找等问题进行了研究。采用的蚁群算法在性能和收敛性速度上优于常规算法。     

Visfatin和A-FABP水平及PPARγ2基因多态性与心脑血管疾病关系研究进展

目前,国内外学者通过检测脂肪细胞型脂肪酸结合蛋白(adipocyte fatty acid binding protein, A-FABP)和内脂素(visfatin)水平,评价其与代谢综合征(metabolic syndrome, MS)的相关性。过氧化物酶体增殖物激活受体(peroxisome proliferator activated receptor gamma 2, PPARγ)可能在肥胖、高血压、脂代谢异常等疾病中发挥着关键作用,是 MS 的重要侯选基因。本文综述了 Visfatin、A-FABP 水平和 PPARγ2基因多态性与心脑血管疾病(cardio-cerebrovascular disease)关系的研究进展,为制定非传染性疾病(non-communicable disease, NCD)预防和控制战略及干预措施提供借鉴。     

Visfatin和A-FABP水平及PPARγ2基因多态性 与心脑血管疾病关系研究进展

目前, 国内外学者通过检测脂肪细胞型脂肪酸结合蛋白(adipocyte fatty acid binding protein, A-FABP)和内脂素(visfatin)水平, 评价其与代谢综合征(metabolic syndrome, MS)的相关性。过氧化物酶体增殖物激活受体(peroxisome proliferator activated receptor gamma 2, PPARγ)可能在肥胖、高血压、脂代谢异常等疾病中发挥着关键作用, 是MS的重要侯选基因。本文综述了Visfatin、A-FABP水平和PPARγ2基因多态性与心脑血管疾病(cardio-cerebrovascular disease)关系的研究进展, 为制定非传染性疾病(non-communicable disease, NCD)预防和控制战略及干预措施提供借鉴。     

无线自组网络中TCP流公平性的分析与改进

研究了TCP(transmission control protocol)流在多跳无线自组网络中的公平性问题,发现IEEE802.11DCF协议在此环境下会导致严重的不公平性,即部分节点垄断了网络带宽而其他节点被饿死.首先,通过仿真分析了产生TCP流不公平性的原因,指出其根源在于MAC(media access and control)协议的不公平性,同时,TCP的超时机制加剧了不公平性的产生;然后,利用概率模型定量分析了TCP不公平性与MAC协议参数之间的关系,发现TCP流的公平性与TCP报文长度直接相关,并且增加MAC协议初始竞争窗口的大小能够有效提高公平性.据此,提出了一种根据TCP报文长度动态调节初始回退窗口大小的自适应回退MAC协议改进算法.理论分析和仿真表明,该算法在很大程度上可以有效缓解不公平性问题的产生,并且不会引起网络吞吐量的严重降低.