组合星图的最优生成树

文章解决了组合星图生成树的构造问题。首先给出了组合星图的定义及其重要的拓扑性质．然后采用构造方法获得了组合星图的一棵高度为D（Sn，k）的生成树，并给出了相应的算法，其中D（Sn,k）为组合星图的直径。该生成树具有最优的高度，且是一棵贪婪树。     

A mixed integer linear formulation for the minimum label spanning tree problem

In this paper we deal with the minimum label spanning tree problem. This is a relevant problem with applications such as telecommunication networks or electric networks, where each edge is assigned with a label (such as a color) and it is intended to determine a spanning tree with the minimum number of different labels. We introduce some mixed integer formulations for this problem and prove that one of their relaxations always gives the optimal value. Finally we present and discuss the results of computational experiments.     

The Green CTTC model for predicting the air temperature in small urban wooded sites

An analytical model, the Green CTTC (cluster thermal time constant) model, for predicting diurnal air temperature inside an urban wooded site, is the object of this study. The proposed model is based on the same principles as the CTTC model, developed earlier by M.E. Hoffman and colleagues, with the addition of vegetation effects.

It is shown that the tree thermal effect can be evaluated either as the shade effect partly offset by the convection component of the tree radiation balance or, equivalently, as the combined effect of evapotranspiration and the change in the plant heat storage. In this paper, the former approach is adopted.

Simulations for testing the validity of the Green CTTC model were carried out on summer data of 11 small urban wooded sites in the Tel-Aviv metropolitan area near the Mediterranean sea coast. Results show a satisfactory fit, with average root-mean-square-error <0.5 K for all studied sites and time intervals at 09:00, 15:00, and 18:00 h (summer time). The CTTC values and the convection parameters were estimated from the empirical data, using a novel procedure.

The proposed model, which can be enlarged to encompass the cases of groves and lawns, is an appropriate tool for assessment of the climatic impact of trees and other greeneries on urban design alternatives.     

Maximum lifetime broadcast communications in cooperative multihop wireless ad hoc networks: Centralized and distributed approaches

We investigate the problem of broadcast routing in energy constrained stationary wireless ad hoc networks with an aim to maximizing the network lifetime measured as the number of successive broadcast sessions that can be supported. We propose an energy-aware spanning tree construction scheme supporting a broadcast request, considering three different signal transmission schemes in the physical layer: (a) point-to-point, (b) point-to-multipoint, and (c) multipoint-to-point. First we present a centralized algorithm that requires global topology information. Next, we extend this to design an approximate distributed algorithm, assuming the availability of k-hop neighborhood information at each node, with k as a parameter. We prove that the centralized scheme has time complexity polynomial in the number of nodes and the distributed scheme has a message complexity that is linear in the number of nodes. Results of numerical experiments demonstrate significant improvement in network lifetime following our centralized scheme compared to existing prominent non-cooperative broadcasting schemes proposed to solve the same lifetime maximization problem in wireless ad hoc networks. Due to lack of global topology information, the distributed solution does not produce as much advantage as the centralized solution. However, we demonstrate that with increasing value of k, the performance of the distributed scheme also improves significantly.     

面向WTAs的VHR双臂避碰操控算法

针对虚拟仿人机器人（VHR）处理工作空间多目标区域（WTAs）避碰操控问题,先基于齐次变换矩阵和链式相乘法则,建立了VHR双臂机理正向运动学模型,进而推导了两种求解VHR双臂逆运动学的公式（DLS-SVD法和基于链式解耦的解析法）;其次,建立了WTAs的数学模型,并以WTAs位姿为操控目标,提出了融合正向和逆向运动学及其双向快速搜索随机树算法的VHR双臂避碰操控算法;最后,通过三维仿真建立VHR虚拟样机,验证了提出算法的正确性和有效性。     

通信网络扩展的一种优化方法

讨论了目前可靠性评估的常用方法和相应的测度指标,指出了当前可靠性评估技术的缺点和不足。针对以添加链路的形式扩展通信网络的过程,提出了一种基于生成树的通信网络扩展的优化方法,并且利用这种方法进行了某种网络拓扑结构扩展的仿真计算,与现存的其它方法的比较表明,这种基于生成树的优化方法设计合理、计算快速,可以有效地应用于实际的通信网络扩展的优化过程中。     

A new spanning tree-based genetic algorithm for the design of multi-stage supply chain networks with nonlinear transportation costs

The design of configuration and the transportation planning are crucial issues to the effectiveness of multi-stage supply chain networks. The decision makers are interested in the determination the optimal locations of the hubs and the optimal transportation routes to minimize the total costs incurred in the whole system. One may formulate this problem as a 0-1 mixed integer non-linear program though commercial packages are not able to efficiently solve this problem due to its complexity. This study proposes a new spanning tree-based Genetic Algorithm (GA) using determinant encoding for solving this problem. Also, we employ an efficient heuristic that fixes illegal spanning trees existing in the chromosomes obtained from the evolutionary process of the proposed GA. Our numerical experiments demonstrate that the proposed GA outperforms the other previously published GA in the solution quality and convergence rate.     

一种基于累积误差优化分配的多视角拼接方法

多视角三维拼接是三维测量的重要组成部分,为了提高多视角拼接的精度,提出了一种基于累积误差优化分配的多视角拼接方法。根据多视角点云数据的空间位置信息,构建环形拼接生成树,利用设计的环形结构将拼接产生的累积误差分散到各个视角,从而逐步提高整体拼接精度。实验表明,该方法能获得令人满意的拼接精度。     

Stacked Regressions

Stacking regressions is a method for forming linear combinations of different predictors to give improved prediction accuracy. The idea is to use cross-validation data and least squares under non negativity constraints to determine the coefficients in the combination. Its effectiveness is demonstrated in stacking regression trees of different sizes and in a simulation stacking linear subset and ridge regressions. Reasons why this method works are explored. The idea of stacking originated with Wolpert (1992).