Graphs with only caterpillars as spanning trees

A connected graph G is caterpillar-pure if each spanning tree of G is a caterpillar. The caterpillar-pure graphs are fully characterized. Loosely speaking they are strings or necklaces of so-called pearls, except for a number of small exceptional cases. An upper bound for the number of edges in terms of the order is given for caterpillar-pure graphs, and those which attain the upper bound are characterized.     

On the nonexistence of finite time bubble trees in symmetric harmonic map heat flows from the disk to the 2-sphere

Let and be the unit disk and the unit sphere, and let be a radially symmetric harmonic map heat flow, whose singularities coincide with downward energy jumps. Then its finite time singularities are simple in the sense that precisely one harmonic sphere separates at a time.     

A Heuristic for Moment-Matching Scenario Generation

In stochastic programming models we always face the problem of how to represent the random variables. This is particularly difficult with multidimensional distributions. We present an algorithm that produces a discrete joint distribution consistent with specified values of the first four marginal moments and correlations. The joint distribution is constructed by decomposing the multivariate problem into univariate ones, and using an iterative procedure that combines simulation, Cholesky decomposition and various transformations to achieve the correct correlations without changing the marginal moments.With the algorithm, we can generate 1000 one-period scenarios for 12 random variables in 16 seconds, and for 20 random variables in 48 seconds, on a Pentium III machine.     

The non-approximability of bicriteria network design problems

Let G be an undirected graph with two edge costs (c-cost and d-cost). We want to minimize the diameter of a spanning subgraph S (under d-cost) subject to the constraint that the total cost of the edges in S (with respect to c) does not exceed a given budget. We prove that this problem is non-approximable, even in some special cases. Similar results are proved if the stretch factor or the root stretch factor is considered instead of the diameter.     

5-桥图F(2,a,a,b,c)的色等价刻画

设P(G，λ)是图G关于变量λ的色多项式，P(G，λ)=P(H，λ)，称G和H色等价，由连接两个顶点的S条内部不交的路组成的图叫S-桥图。本讨论了5-桥图F(2,a,a,b,c)(c≥b≥a 1，a≥2)的色性，完整刻画了这类图的色等价图。     

子图识别的层分解方法

子图识别问题(SRP)就是在一个图G中确定并寻找是否存在和另一个图H相同构的子图．本文将引入图的层分解概念，并以此为基础建立识别图的同构子图的算法．该算法的复杂性为O(n(△-1)^k-1)，其中△是图G的度，即G中点的最大度，n，k分别是图G，H的阶．     

软体操作器结构设计及植入式光纤传感方法

为解决微创手术软体机器人的形状实时监测问题,将刻有三个光纤布拉格光栅的单根光纤植入软体操作器中,利用其研究柔性硅胶软体操作器光纤传感和三维形状重构方法。进行了软体操作器的结构设计及模型建立,并对光纤光栅波长漂移量和软体操作器弯曲曲率之间的关系进行了理论分析;通过实验验证了软体操作器结构设计及其模型建立的有效性,测试了软体操作器不同弯曲状态下三个FBG传感器的反射谱特征及其变化规律;通过分析三个FBG传感器的中心波长漂移量,利用线性插值算法计算出软体操作器在不同弯曲状态下的曲率等参数,并结合曲线拟合方法实现软体操作器的三维形状重构。实验结果表明:植入式光纤光栅传感方法可以实现硅胶软体手术操作器的三维形状传感,在微创外科手术领域具有广阔的应用前景。     

Experimental investigation of the quality of lensless super-resolution ghost imaging via sparsity constraints

Ghost imaging via sparsity constraints (GISC) can nonlocally realize super-resolution imaging. Factors influencing the quality of lensless super-resolution GISC are investigated and the experimental results show that, the quality of GISC is enhanced as the object?s sparse ratio in the representation basis or the spatial transverse coherence lengths on the object plane are decreased. The differences between ghost imaging (GI) and GISC are also discussed.     

First-principles study of the (0 0 1) surface of cubic SrZrO3

Density functional calculations have been used to investigate the (0 0 1) surface of cubic SrZrO₃ with both SrO and ZrO₂ termination. Surface structure and electronic structure have been obtained. The SrO surface is found to be similar to its counterpart in SrTiO₃, while there are marked differences between the ZrO₂ and TiO₂ terminations in SrZrO₃ and SrTiO₃, respectively, concerning surface relaxation and rumpling. For the ZrO₂-terminated surface of SrZrO₃, the covalency of the interaction between the outmost Zr and the O beneath is enhanced as a result of their bond contraction. The band gap reduction and the presence of the surface states are also discussed in relation with the behavior of the electrostatic potential.     

一种正交二视角光学层析重建算法

提出了一种基于最大熵原理的正交二视角重建算法,该算法能够较好地重建多峰非对称待测场,且只需两个正交方向的投影数据。算法中融合了含有轴对称因子的先验知识,该先验知识可由两个正交方向的投影数据迭代算出,并分析了正交投影方向这个因素对重建结果的影响。通过计算机数值模拟,结果表明,融合先验知识的正交二视角重建算法与没有融合先验知识的正交二视角重建算法相比重建精度全面超出。其中,在两峰随机余弦高斯模拟待测场的情况下均方根误差减少了73％。在三峰随机高斯模拟待测场的情况下均方根误差减少了47％。该算法充分显示了在重建多峰非对称待测场时的优越性。同时,由于只需要两个正交方向的投影数据,可使实验系统得到简化。