Anisotropic diffusion and traveling waves of toxic proteins in neurodegenerative diseases

Neurodegenerative diseases are closely associated with the amplification and invasion of toxic proteins. In particular Alzheimer's disease is characterized by the systematic progression of amyloid-β and τ-proteins in the brain. These two protein families are coupled and it is believed that their joint presence greatly enhances the resulting damage. Here, we examine a class of coupled chemical kinetics models of healthy and toxic proteins in two spatial dimensions. The anisotropic diffusion expected to take place within the brain along axonal pathways is factored in the models and produces a filamentary, predominantly one-dimensional transmission. Nevertheless, the potential of the anisotropic models towards generating interactions taking advantage of the two-dimensional landscape is showcased. Finally, a reduction of the models into a simpler family of generalized Fisher-Kolmogorov-Petrovskii-Piskunov (FKPP) type systems is examined. It is seen that the latter captures well the qualitative propagation features, although it may somewhat underestimate the concentrations of the toxic proteins.     

The competitive salesman problem on a network: a worst-case approach

We provide a complexity analysis of the problem of optimal routing of a server on a transportation network in the presence of a competing server. The server that reaches a node first gets the profit from the node. The objective is to maximize the worst-case profit.     

旅行推销员问题的凸包收缩法

本提出一种用凸包收缩来解决旅行推销员问题。首先形成一个凸包初始环路。然后，逐个考察凸包内的点，按照增加值从小到大的顺序依次插入，直至考察完所有的点。从而得到一个包含所有点的环路，即旅行推销员问题的一个满意解。     

A composite-neighborhood tabu search approach to the traveling tournament problem

The Traveling Tournament Problem (TTP) is a combinatorial problem that combines features from the traveling salesman problem and the tournament scheduling problem. We propose a family of tabu search solvers for the solution of TTP that make use of complex combination of many neighborhood structures. The different neighborhoods have been thoroughly analyzed and experimentally compared. We evaluate the solvers on three sets of publicly available benchmarks and we show a comparison of their outcomes with previous results presented in the literature. The results show that our algorithm is competitive with those in the literature.     

A note on relatives to the Held and Karp 1-tree problem

We study a class of graph problems which includes as special cases the Held and Karp 1-tree problem, and the minimum spanning tree problem with one degree constraint studied by Glover and Klingman. For another special case, we note a mistake in a paper by Ramesh, Yoon and Karwan.     

The tanh method and a variable separated ODE method for solving double sine-Gordon equation

We use the tanh method and a variable separated ODE method for solving the double sine-Gordon equation and a generalized form of this equation. Several exact travelling wave solutions are formally derived. The two methods provide distinct solutions of different physical structures.     

On the refinement of bounds of heuristic algorithms for the traveling salesman problem

A number of heuristics for the traveling salesman problem (TSP) rely on the assumption that the triangle inequality (TI) is satisfied. When TI does not hold, the paper proposes a transformation such that for the transformed problem the TI holds. Consequently, the bounds obtained for heuristics are valid with appropriate modification. Moreover, for a TSP satisfying TI the same transformation strengthens such bounds. The transformation essentially maps the problem into one that is minimal with respect to the property that TI holds. For the symmetric TSP the transformation is particularly simple. For an application of the transformation in the asymmetric case we need the dual solution of an assignment problem.     

On properties of geometric random problems in the plane

In this paper, we present results dealing with properties of well-known geometric random problems in the plane, together with their motivations. The paper specifically concentrates on the traveling salesman and minimum spanning tree problems, even though most of the results apply to other problems such as the Steiner tree problem and the minimum weight matching problem.     

时滞格微分方程组的行波解

本文利用Schauder不动点定理的方法和上、下解技巧,研究了时滞格微分方程组的行波解,给出了当系统的非线性项满足“拟单调条件”和“指数拟单调条件”时行波解的存在性.