Meet-Cloud for Secure and Accurate Distribution of Negative Messages in Vehicular Ad hoc Network

Keeping Vehicular Ad hoc Network(VANET) from attacks requires secure and efficient distribution of information about bad entities. Negative messages are pieces of information that define the negative attributes of vehicles. By formally defining the negative message, we observe that accuracy is essential for its efficient distribution. We formally define the coverage percentage and accurate coverage percentage to describe the availability and distribution efficiency of negative message. These two metrics can jointly evaluate the performance of a distribution method. To obtain both high coverage percentage and high accurate coverage percentage, we propose meet-cloud, a scheme based on meet-table and cloud computing to securely and accurately distribute negative messages in VANET. A meet-table in a Road Side Unit(RSU) records the vehicles it encounters. All meettables are sent to cloud service to aggregate a global meet-table. The algorithm for distributing and redistributing negative messages are designed. Security analysis shows that meet-cloud is secure against fake and holding on to negative message attacks. Simulations and analysis demonstrate that meet-cloud is secure under denial of service and fake meet-table attacks. The simulation results also justify that meet-cloud outperforms the RSU broadcast and epidemic model.     

The Difference of the Pulmonary-Artery Pressure of the Migrants from Difference Elevation at the 4636 - 4907 m Altitude

Study Objective： To compare and analyze the changes of the pulmonary-artery pressure of the migrants coming from different elevation in the hypoxic environment of 4636 - 4907 m extreme altitude. To explore the susceptibility to hypoxic pulmonary-artery hypertension （PH） in the subjects from different altitude and profession. Methods： By using Color Doppler Ultmsonography （CDU）, measuring the pulmonary-artery pressure of 207 healthy men, who had continuously being lived and worked at the extreme altitude for more than six months, and then were divided into three groups according to their profession and the altitude of original living place. Results： There was a significant difference in the outcomes of pulmonary-artery pressure from the 3 groups. Conclusions： Altitude of original living place, labor intensity are some of factors that impact the pulmonary-artery pressure of the people who exposure to a hypoxic environment. The pulmonary- artery pressure of person without strenuously physical work experience was more sensitive to hypoxic surroundings than that of labor workers. It was not always the fact at an extreme altitude that the moderate altitude mountaineers were superior to other migrants from a lower altitude or plain. The higher PH was found in the groups of the moderate altitude mountaineers and labor workers. It is unlikely certain that one with PH would surfer from HAPE.     

快速成型技术的典型方法比较

本文介绍了一种当今国内外最新制造技术—快速成型技术。对该技术的四种典型方法进行了较详细的分析和比较，并对快速成型技术的未来发展提出了自己的看法。     

大黄酸抑制脂多糖刺激巨噬细胞升高[Ca2+]i和释放TNFα的作用特征

以正常腹腔巨噬细胞(PMφ)和脂多糖(Lipopolysacharide，LPS)刺激的PM垂为对象，用MTT法和激光共焦扫描显微术检测肿瘤坏死因子α(TNFα)释放量和单细胞[Ca^2 ]i的动态变化，研究了大黄酸(Rhein)的作用特征和机理．结果显示，大黄酸对正常PMφ释放TNFα没有明确的影响，但对LPS刺激的PMφ释放TNFα有显的抑制作用，其抑制作用随浓度增加而增强，10^-4mol／L大黄酸抑制了10μg／mL LPS效应的72％．值得注意的是，大黄酸不但抑制了LPS引发的PMφ[Ca^2 ]i的升高，而且使LPS引发的[Ca^2 ]i由宽平台峰状转变为振荡动力学模式，胞外介质无钙时又转变为更低幅值的峰．以上结果表明，大黄酸降低LPS引发的PM垂的[Ca^2 ]i升高是其抑制TNFα释放的信号传导通路的重要环节，并提示大黄酸在降低胞内钙释放和胞外钙内流的同时又对其动力学进行了类周期性的调制．     

振动钻削加工过程的监控系统

讨论振动钻削监控系统的工作原理．此系统采用８０９８单片机和上位微机通讯方式，通过对振动钻削过程中动态切削力信号的采集和分析，实现对加工过程的在线监测，提出合理的报警条件．通过钻削实验，优化切削参数和振动参数，改善钻头的工作状况，得到最佳的切削效果．     

在生物圈保护区中开展生态旅游的探讨

介绍了生物圈保护区和生态旅游产生的背景和发展，论述了在生物圈保护区中开展生态旅游的可行性以及对其产生的正负影响，提取了应采取的对策。     

一致性测试中的时间约束及测试用例生成算法

针对协议测试理论中的时间约束问题，从不同的一致性测试方法出发对协议测试中的时间参数做了严格的约束，同时给出了基于等待、协调和同步时间的严格约束下的测试用例生成算法．在控制流测试中，先生成引导序列，然后按照测试拓扑环境设置和事件约束对引导序列、测试序列的时间进行约束设置．在数据流测试中，等待时间只需按照需求描述和约束来设定．对边界网关协议进行测试的结果表明，所提算法能适应不同的网络拓扑环境，其生成的测试用例在测试中能够有效降低测试代价．     

基于有限状态机的被动测试错误诊断

针对被动测试错误诊断算法只能推测出被测系统可能存在错误却无法准确定位错误的问题，提出了一种逐步定位系统实现错误的层次递进的方法．先利用测试序列的输入输出信息并结合错误模型生成初始诊断错误集合，再依据测试套上下文使用错误检测算法对该集合进行筛选，最后经连续观察或结合主动测试进行错误区分．实例验证结果表明，所提方法能够对绝大多数有单个实现错误的有限状态机模型进行错误定位．     

Theoretical studies of C36 encapsulated in zigzag single-wall carbon nanotubes

Discovery of carbon nanotubes (CNTs) has attracted considerable attention in the scientific community due to their unique structures and properties. Chemical doping can further modify the electrical properties of CNT. The empty space inside CNT provides t…     

北京大气中痕量烷烃的浓度分析与研究

采用二步深冷浓缩与气相色谱质谱联用（ACIS-GC／MS）对北京大气中痕量烷烃进行长期连续观测，观测数据表明：日变化有双峰和三峰变化，冬、春呈现与交通高峰吻合的双峰变化，即：上午08：00点至10：00和下午17：00前后各出现一个高值；四季日变化中夜间22：00出现第三峰值；夏季变化呈三峰型，最大值在正午前后．季变化峰值出现在夏季，低值出现在冬季．