无线传感网络中拥塞控制与路由的跨层设计:分布式牛顿法

无线传感网络应用广泛, 其性能与路由选择和拥塞控制密切相关. 致力于拥塞控制与多径路由的跨层优化, 以实现在链路容量受限和节点能量受限情况下的无线传感网络效用最大化. 针对对偶次梯度算法具有收敛速度慢与信息交互量大等缺陷, 设计了具有二阶收敛性能的分布式牛顿算法来实现网络效用最大化. 通过矩阵分裂技术, 实现了只需单跳信息交互的牛顿对偶方向的分布式求解方法. 仿真结果表明, 分布式牛顿算法的收敛性能显著优于对偶次梯度算法.     

Methane activation without using oxidants over Mo/HZSM-5 zeolite catalysts

The effect of Mo loading, calcination temperature, reaction temperature and space velocity on the catalytic performance of methane dehydrogenation and aromatization without using oxidants over Mo/HZSM-5 has been studied. The XRD and BET measurements show that Mo species are highly dispersed in the channels of the HZSM-5 zeolite, resulting from the interaction between the Mo species and the zeolite, which also leads to a decrease in its crystallinity. The Brønsted acidity, the channel structure and the state and location of Mo species in the zeolite seem to be crucial factors for its catalytic performance. It was found that 2% Mo/HZSM-5 calcined at 773 K showed the best aromatization activity among the tested catalysts, the methane conversion being 9% at 1013 K with the selectivity to aromatics higher than 90%. The experimental results obtained from the variation of space velocity gave evidence that ethylene is an initial product. On the basis of these results a possible mechanism for methane dehydrogenation and aromatization has been proposed in which both the heterolytic splitting of methane in a solid acid environment and a molybdenum carbene-like complex as an intermediate are of significance.     

Hydrothermal synthesis of flaky crystallized La2Ti2O7 for producing hydrogen from photocatalytic water splitting

Flaky monoclinic La₂Ti₂O₇ was prepared via a hydrothermal method based on the reaction of Ti(SO₄)₂ and La(NO₃)₃. Relative to the solid-state reaction sample, the flaky La₂Ti₂O₇ showed higher surface areas, much smaller crystal size and more efficient light absorption. All these factors led to the higher photoactivity to produce H₂ from water splitting under UV irradiation.     

高压旋喷锚杆在黄土深基坑支护中的模拟研究

为了研究高压旋喷锚杆支护体系在黄土深基坑工程中的工作性状,选取西安某深基坑支护工程为研究对象,运用MIDAS/GTS软件对该支护体系进行了有限元数值模拟,并与二次注浆锚杆支护体系的模拟结果进行了对比分析。结果表明:两种基坑支护方式均可满足该基坑支护的技术要求,但采用高压旋喷锚杆支护时,需要锚杆的总长度为二次注浆锚杆长度的62%,且高压旋喷锚杆筋体可实现回收,降低了锚杆施工对周围土层的干扰,其在黄土地区高边坡及深基坑支护工程中有着广阔的应用前景。     

Highly Efficient Overall Water Splitting Through Optimization of Preparation and Operation Conditions of Layered Perovskite Photocatalysts

The layered perovskite materials were found to give the high photocatalytic activity in water splitting reaction under UV irradiation, where the electronic structure of perovskite slab constructing the layered structure (the total cation valency) was the most crucial factor to the high photocatalytic activity. Both the excessive cation valency and the layered structure were required for active photocatalysts, while the slab thickness of layered perovskites had an insignificant effect on water-splitting activity. In order to identify key variables that affected photocatalytic activity and to optimize the performance of (110) layered perovskite, La₂Ti₂O₇ was modified by various methods. The optimum amount of loaded nickel had a great effect and the amount depended on the surface area of the perovskite phase. When an alkaline-earth element such as Ba, Sr, and Ca was doped on La₂Ti₂O₇, the photocatalytic activity was enhanced markedly. Introduction of an alkaline hydroxide into the reaction system as an external additive enhanced the activity further showing extremely high quantum yields close to 50%.     

利用七宫格的遮挡车辆凹性检测与分割

目的:交通场景中车辆间的距离过近或相互遮挡容易造成识别上的粘连,增加了准确检测目标车辆的难度,因此需要建立有效、可靠的遮挡车辆分割机制。方法:首先在图像分块的基础上确定出车辆区域,根据车辆区域的长宽比和占空比进行多车判断;然后提出了一种基于“七宫格”的凹陷区域检测算法,用以找出车辆间的凹陷区域,通过匹配对应的凹陷区域得到遮挡区域;最后,将遮挡区域内检测出的车辆边缘轮廓作为分割曲线,从而分割遮挡车辆。结果:实验结果表明,在满足实时性的前提下算法具有较高的识别率,且能够按车辆的边缘轮廓准确分割多个相互遮挡的车辆。与其他算法相比,该算法提高了分割成功率和分割精度,查全率和查准率均可达到90%。结论:提出了一种新的遮挡车辆分割方法,有效解决了遮挡车辆不宜分割和分割不准确的问题,具有较强的适应性。     

基于物理的波浪实时模拟方法

为解决广域范围内波浪状态的实时计算和可视化问题,结合无粘滞流体力学的物理模型,提出了一种以三角形为控制单元的有限体积简化算法。该算法的优点在于：以不规则边界区域的非规则三角网格为基础,通过简化通量向量分裂方法获得三角形控制单元的边界数值通量,能快速逼近二维浅水方程的解进而模拟非规则边界浅水的实时流动。实验结果显示,所提方法能在符合现实世界物理规律的前提下较好地实现大规模波浪的实时可视化模拟。     

基于可拆分倒排索引的可搜索加密方案

为快速检索云环境下的加密数据,提出了一种高效的适用于批量数据处理场合的可搜索加密方案。首先,由客户端创建两个倒排索引,分别是存储了文件-关键词映射的文件索引和用于存储关键词-文件映射的空的搜索索引;然后,将这两个索引提交给云服务器。搜索索引是在用户检索过程中由云端根据搜索凭证和文件索引逐渐更新建立的,记录了已被检索关键词的检索结果,该方法将搜索索引的构建时间有效分摊了到了每次检索过程中并节省了存储空间。索引采用基于key-value结构的集合存储方式,支持索引的同时合并和拆分,即在添加和删除文件时,由客户端根据要添加或删除的文件集生成对应的文件索引和搜索索引,然后服务器对索引进行合并和拆分,从而实现文件的快速批量添加和删除。测试结果表明,所提方案极大提高了文件更新的效率,适用于批量数据处理。通过泄露函数证明了该方案能满足自适应动态选择关键词攻击下的不可区分性安全标准。     

带肋钢筋与灌浆料黏结性能试验

为灌浆料在预制装配式结构及加固改造领域提供理论依据,进行了27个带肋钢筋-灌浆料拉拔试验,研究了试件的破坏模式和黏结强度随变量的变化规律,分析了灌浆料开裂、压碎过程及与过程相对应的典型黏结-滑移曲线各阶段.基于试验数据,拟合了灌浆料黏结锚固强度公式、黏结强度对应的滑移值公式和黏结应力-滑移关系式,提出了钢筋在灌浆料中的锚固长度经验值.结果表明:随着保护层厚度增大,试件平均黏结强度不断增大,相比于混凝土,保护层厚度增大相同幅度,灌浆料黏结强度增长慢;随着钢筋直径增大,平均黏结强度减小;随着钢筋锚固长度增加,试件平均黏结强度降低,相比于自密实混凝土,锚固长度增加相同幅度,灌浆料黏结强度增长快;强度等级相同时,灌浆料黏结强度高于普通混凝土;钢筋与灌浆料间黏结性能和钢筋与混凝土间黏结性能有差异.