Tackling group-to-tree matching in large scale group communications

As a mechanism to efficiently support group communications, multicasting, faces a serious state scalability problem when there are large numbers of groups in the network. Recently, a novel solution called Aggregated Multicast has been proposed, in which multiple groups can share one delivery tree. A key problem in Aggregated Multicast is group-to-tree matching (i.e., assigning groups to proper trees). In this paper, we formally define this problem, and formulate two versions of the problem: static and dynamic. We analyze the static version and prove that it is NP-complete. To tackle this hard problem, we propose three algorithms: one optimal (using Linear Integer Programming, or ILP), one near-optimal (using Greedy method), and one Pseudo-Dynamic algorithm. For the dynamic version, we present a generic dynamic on-line algorithm. Simulation study has been conducted to evaluate the performance of the algorithms. Our results show that: (1) for the static problem, the Greedy algorithm is a feasible solution and its performance is very close to the optimal ILP solution, while the Pseudo-Dynamic algorithm is a good heuristic for many cases where Greedy does not work well; (2) for the dynamic problem, the generic dynamic on-line algorithm is a very practical solution with promising performance and reasonable computation requirement.     

浅谈C语言中循环结构的教学--回答好循环结构的“三个问题”

循环结构是C语言程序设计中的重难点,其掌握情况对于后续章节的学习效果尤为关键。本文以什么是循环、何时需要使用循环以及如何使用循环三个问题为主线,通过精心选择的教学案例和灵活有效的教学方法来进行解答,以激发学生兴趣,培养编程思想。     

微信公众平台辅助课堂教学实证研究

微信公众平台作为移动通信技术催生的一项新生事物,现在已在营销领域进行得如火如荼。基于该平台的功能及优势,通过创建“教育技术学”公众平台,给关注该平台的学生发送《二维动画设计》课程学习资源。通过分析辅助课堂教学效果及学生访谈．探讨微信公众平台辅助常规课堂教学的可能性和现实性,以期为同行使用微信公众平台促进课堂教学效果作借鉴之用。     

基于角色的访问控制技术在考务管理系统中的应用

访问控制是信息安全的一个重要保障。在介绍RBAC模型的基础上,根据考务管理系统中用户职责,规定用户访问权限,定义考务管理系统中的角色及其对应的权限,阐述RBAC在考务管理系统中的应用,为考务管理系统的访问控制安全提供一种思路。     

Reflectivity measurement technology of special high reflective mirrors and uncertainty analysis of measurement results

In order to meet the reflectivity measurement requirements of any incident angle at different points of the large size special high mirror, a rotating cavity ring-down spectroscopy high reflectivity measurement system was built, in which the rotation function of the resonant cavity was set, and the lifting and parallel travelling mechanism of the measured mirror was added. Furthermore, the uncertainty of the measurement results was analyzed and calculated. The results showed that the reflectivity of a high reflective mirror measured by the system was 99.979 5%, the measurement accuracy reached the order of 10-6, and the combined standard uncertainty of reflectivity measurement was 0.002 8%. Collectively, these results provide a detection guarantee for the maintenance of the large size special high mirror, and provide ideas and methods for the uncertainty analysis of measurement results of similar equipment parameters.     

基于校企合作的通信类实验课程云研究与实践

传统的通信类实验课程教学基本上是相对独立的，学生很难融会贯通。根据企业需求，结合高校实际情况，对通信类实验课程体系进行改革，将传统实验课程进行分类融合，构建多个课程云，实践表明，改革取得较好的效果。     

磷铝分子筛对膨胀阻燃聚丙烯复合材料阻燃与热稳定性能影响

通过水热合成法制备了系列不同结构类型的磷铝分子筛（AlPO⁃n,n=5, 11, 17, 34）,并通过熔融挤出共混,将系列AlPO⁃n分子筛应用到膨胀阻燃聚丙烯（PP/IFR）复合材料中,致力改善其阻燃和热稳定性能。利用极限氧指数仪、水平垂直燃烧仪、锥形量热仪和万能试验机分别测试材料的阻燃性能和力学性能。结果表明,AlPO⁃n分子筛可改善PP/IFR复合材料的相关性能,其中AlPO⁃17（1 %,质量分数,下同）相对其他类型磷铝分子筛能明显改善PP/IFR复合材料的阻燃和热稳定性能,复合材料的极限氧指数和600 ℃的残炭率相对于PP分别提高至34.8 %和14.3 %。     

氨分解制氢催化剂的研究进展

氢能作为二次能源在可再生能源和化石能源发展中将发挥重要的桥梁和纽带作用,但其推广应用受限于氢气储存成本高和运输效率低等因素。采用氨作为储氢载体,其储氢密度高、运输技术成熟,方便分布式现场制氢就地供应,避免氢气储运带来的困扰。氨载氢技术推广应用关键在于氨分解催化剂的发展水平。对近年来用于氨分解的Ru基催化剂、非贵金属催化剂、双金属催化剂和氮化物/碳化物催化剂研究进展进行总结,分析了各种催化剂上氨分解的反应机理以及活性金属、载体、助剂和制备方法对催化剂物化性质和催化性能的影响,指出了不同类型催化剂的优势和不足,并对其未来研究方向进行了展望。     

竹炭对溶液中微量铬离子的吸附研究

研究了竹炭粒径、加入量、pH值、吸附时间、Cr(Ⅵ)初始浓度等因素对竹炭吸附Cr(Ⅵ)的影响。实验结果表明,竹炭对水中微量Cr(Ⅵ)离子有较好的吸附性能。当Cr(Ⅵ)离子初始浓度为100μg/mL时,在50 mL Cr(Ⅵ)离子溶液中加入0.3 g60目竹炭,pH为2.0,吸附振荡温度为25℃,吸附3 h,Cr(Ⅵ)离子吸附率达99.5%。竹炭对Cr(Ⅵ)离子的吸附可较好地符合Freundlich等温吸附模型。