基于分层的改进A＊算法在路径规划中的应用

智能交通中的路径诱导系统能够极大地提高人们的出行效率与出行体验。经典A＊算法只注重搜索精度而忽略了搜索效率,在城市道路网络分层的基础上,对高层道路使用的A＊算法进行了改进,对于道路网络中的不同节点,设置估价函数具有不同的权值,同时给定权值的一个上下限阈值,以平衡算法的搜索效率与搜索精度。实验表明,得到的最短路径虽然不是常规的距离最短却是实际行驶时间最优的。     

随机时变路网下的城市应急服务车辆路径分析

针对城市应急服务车辆（110、119、120等）的最优路径选择问题及路网的随机性与时变性,利用鲁棒优化理论,考虑路网在最坏情况下的行程时间,建立了随机时变条件下的应急车辆路径选择模型,并对 Dijkstra算法进行改进,将算法的路阻矩阵进行实时更新,以在时变条件下实现对路径选择模型的求解。经算例分析表明,该模型能有效解决随机时变路网环境下的应急车辆最优路径问题,与基于概率分布的期望行程时间最短的方法相比,该模型拥有更高的鲁棒性和易操作性。     

平盖开孔的有限元分析及其补强方法的探讨

为了使平盖开孔补强结构更为合理、可靠,使用圆形平板的理论解和有限元分析方法,对不同开孔直径的27个平盖模型进行了应力计算和分析比较,进一步探讨了不同的开孔补强方法。结果表明,对于开孔率小于0.5的平盖开孔补强采用均匀增加平盖厚度的方法,不能解决孔边产生的应力集中问题,难以达到补强的效果;而采用外加补强元件的方法,则应明确其补强范围应在2d范围内。     

Stresses of cohesionless granular flows in liquids

We construct constitutive relations for friction stress, slide stress and collision stress of cohesionless granular flows. We propose that the friction stress and slide stress could be neglected when τ_c/τ_e < 0.02, where τ_c represents the interval time experienced by a given particle between two consecutive binary collisions and τ_e the particle relaxation time. We applied these constitutive relations to a simulation of solid-liquid flow in an inclined chute and found the simulation results agree with experimental data.     

一种线性时间复杂度的高效路由保护方法

如何高效快速地应对网络中的故障是设计路由协议的基本要求和主要任务。由于动态路由协议在应对网络中的故障时,在协议动态收敛的过程中将会有大量的报文被丢弃。因此,目前路由器厂商普遍采用路由保护方法来克服网络故障,在众多的路由保护方法中,DC（downstream criterion）规则是一种被普遍认可的方法。然而,已有的实现 DC规则算法的时间复杂度普遍较高,并且复杂度随着网络节点平均度的增加而迅速增加。为了应对上述问题,提出一种线性时间复杂度的高效路由保护方案ERPLR（an efficient routing protection method with linear time complexity）,该方法首先提出了备份下一跳计算规则,然后在已有最短路径树的基础上,根据备份下一跳计算规则为所有的源目的节点对计算备份下一跳。在计算备份下一跳的过程中,每个节点和其邻居最多被访问一次,因此ERPLR的时间复杂度为O（V+E）。实验结果表明,与已有的实现DC规则相比较,ERPLR在故障保护率和路径拉伸度两个度量指标结果相似的情况下,在真实网络拓扑和模拟拓扑中,ERPLR分别降低了大约74.93%和78.91%的计算开销,该方法可以极大地降低DC规则的计算开销。     

无先验地图条件下电力管廊无人机自主巡检方法研究

针对无先验地图条件下电力管廊无人机自主巡检能力不足的问题,本文提出了一种不依赖先验地图的无人机巡检方法。首先,无人机搭载激光雷达,通过SLAM（Simultaneous Localization and Mapping）算法进行实时场景构图,并基于RRT（Rapidly-exploring Random Tree）算法对构建的全局栅格地图进行边界搜索;其次,针对传统RRT算法难以判断环境地图完整性、保障巡检全面性的问题,提出了一种基于数字图像处理的边界检测方法。通过Canny算子对实时构建的地图进行边缘检测,并对地图进行完整性评估。最后,为验证本文提出方法的有效性,在江苏无锡处某220kV电力管廊的仿真模型中进行验证,分别采用RRT算法和本文改进算法进行自主巡检测试,结果表明本文提出的算法相比RRT算法可提升21.8%的巡检覆盖率。     

基于差异路径权重的二部图网络推荐算法

针对二部图网络结构推荐算法中资源分配不合理的现象,同时为了丰富推荐结果多样性和促进冷门物品的推荐,提出了一种利用差异路径权重改变资源传递的二部图网络结构算法。利用用户相似性构造路径权重改变第一阶段资源传递规则,使资源较多地流向与目标用户相似的用户节点。通过物品属性相似的构造路径权重,使第二阶段资源更多地流向与目标用户已购物品具有相似属性的物品。实验结果表明,本算法相对于其他流行网络结构算法提高了推荐的综合性能,并且更好地解决推荐中的相关问题。     

DAMPED OSCILLATIONS IN A BINGHAM PLASTIC FLUID

Stokes' second problem, the propagation and damping of waves into a semi-infinite fluid generated by harmonic oscillations of a flat pate on the surface, is solved for the simple Bingham Theological constitutive model. The solution reveals the existence of “windows” in the distance-time-stress space in which shearing is possible whereas outside these restricted regions no shearing can occur. Within these restricted regions the wave forms developed are exponentially damped, traveling waves which propagate from the excitation plane into the fluid and disappear along definitely prescribed boundaries determined by the yield condition. The most significant consequence of the existence of these “windows” of shear is that even very small yield stresses will radically modify the induced velocity wave patterns from that which would be expected based upon the classical Newtonian fluid solution of Stokes' second problem. At least in this physical setting, it is not necessary for shear to occur globally for motion to occur anywhere, as has been postulated in some recent studies of complex motions. Thus, the motion is consistent with a simple Bingham model which does possess a yield stress.     

Counting maximal independent sets in directed path graphs

The problem of counting maximal independent sets is #P-complete for chordal graphs but solvable in polynomial time for its subclass of interval graphs. This work improves upon both of these results by showing that the problem remains #P-complete when restricted to directed path graphs but that a further restriction to rooted directed path graphs admits a polynomial time solution.     

Betweenness estimation in OLSR-based multi-hop networks for distributed filtering

In traditional networks special efforts are put to secure the perimeter with firewalls: particular routers that analyze and filter the traffic to separate zones with different levels of trust. In wireless multi-hop networks the perimeter is a concept extremely hard to identify, thus, it is much more effective to enforce control on the nodes that will route more traffic. But traffic filtering and traffic analysis are costly activities for the limited resources of mesh nodes, so a trade-off must be reached limiting the number of nodes that enforce them. This work shows how, using the OLSR protocol, the centrality of groups of nodes with reference to traffic can be estimated with high accuracy independently of the network topology or size. We also show how this approach greatly limits the impact of an attack to the network using a number of firewalls that is only a fraction of the available nodes.