Relative Discrete Spectrum and Joinings

 A joining characterization of ergodic isometric extensions is given. We also give a simple joining proof of a relative version of the Halmos-von Neumann theorem. Research partly supported by KBN grant 2 P03A 002 14 (1998). Received June 5, 2001; in revised form March 4, 2002     

超市模型的实时动态控制及其数值分析

超市模型是针对大型并行排队网络所进行的 实时动态控制的随机负载平衡策略, 它在计算机网络、云计算、制造系统、交通网络等领域有着重要的实际应用价值. 本文考虑了超市模型中的若干重要问题: 实时动态控制模式; 效率比较; 平均场黑洞; 马氏变动环境; 稳定性; 固定点; 系统性能评价等等. 同时, 本文也通过数值算例研究了上述重要问题, 包括对顾客加入最短队列的超市模型与服务台服务最长队列的超市模型进行了性能比较, 给出了他们效率的优劣分析; 在超市模型中对控制到达过程机制进行了三种情况的对比; 对马氏变动环境下的超市模型进行了性能评价.     

Menger-type theorems with restrictions on path lengths

If the paths of length s, joining two non-adjacent vertices u, υ of a graph cannot be destroyed by deleting less than t vertices, then there are at least t internally vertex-disjoint paths joining u and υ, each having length less than . Some constructions show that using paths of length at least s/t−1^t might be necessary.     

Disjoint shortest paths in graphs

It is an interesting problem that how much connectivity ensures the existence ofn disjoint paths joining givenn pairs of vertices, but to get a sharp bound seems to be very difficult. In this paper, we study how muchgeodetic connectivity ensures the existence ofn disjointgeodesics joining givenn pairs of vertices, where a graph is calledk-geodetically connected if the removal of anyk−1 vertices does not change the distance between any remaining vertices.     

On geodesics in asymptotic Teichm��ller spaces

Let R be a Riemann surface of infinite analytic type, T(R) and AT(R) be the Teichmüller space and asymptotic Teichmüller space on R respectively. The purpose of this paper is to discuss some problems related to geodesics in AT(R). It is proved that uniqueness of geodesics joining two given points [??] and [??] in T (R) dose not imply uniqueness of geodesics joining?[[??]] and [[??]] in AT(R). Furthermore, a Beltrami differential??? is constructed such that there are infinitely many geodesics joining [[0]] and?[[??]] in AT(R), and a sufficient condition to determine the difference of the geodesics [[t?? ₁]] and [[t?? ₂]] (0??? t??? 1) joining [[0]] and?[[??]] in AT(??) is given.     

Hamiltonicity and combinatorial polyhedra

We say that a polyhedron with 0–1 valued vertices is combinatorial if the midpoint of the line joining any pair of nonadjacent vertices is the midpoint of the line joining another pair of vertices. We show that the class of combinatorial polyhedra includes such well-known classes of polyhedra as matching polyhedra, matroid basis polyhedra, node packing or stable set polyhedra and permutation polyhedra. We show the graph of a combinatorial polyhedron is always either a hypercube (i.e., isomorphic to the convex hull of a k-dimension unit cube) or else is hamilton connected (every pair of nodes is the set of terminal nodes of a hamilton path). This implies several earlier results concerning special cases of combinatorial polyhedra.     

网络部分结点最佳连通关系的逐步生成法

提出了一种就现有公路网中 ,在对其部分结间的连通关系进行技术等级升级时 ,生成以连通这些目标结点为目的的最小树生成方法——逐步生成法 .     

Paths and cycles in matroid base graphs

LetG be the base graph of any simple matroid. It is proved thatG is Hamilton-connected, edge-pancyclic, and if for any two vertices ofG there are paths of lengthsm andn joining them,m < n, then there is a path of lengthk joining them for all integersk satisfyingm < k < n. This research was partially supported by the Natural Sciences and Engineering Council of Canada under Grant A-4792.This research was done while the author was a Visiting Scholar at Simon Fraser University.     

Modeling the join curve between two co-axial carbon nanotubes

Making use of an applied mathematical model, we employ a calculus of variations technique to join two co-axial nanotubes. Due to the axial symmetry of the tubes, the three-dimensional problem can be reduced to a problem in two dimensions. The curvature squared for the join region is minimized for a prescribed join length and given tube radii. In this model, a certain non-dimensional parameter B arises, which approximately has the same numerical value when compared with the standard method for the joining between any two carbon nanotubes of different radii. This value occurs in consequence of adopting an angle of inclination of 9.594°, which occurs in the conventional method for joining two carbon nanotubes of different radii and which is necessary to accommodate a single pentagon. The simple calculus of variations model described here provides a general framework to connect nanotubes or other nanostructures.     

On the continuity of the geometric operations in Minkowski planes with parallel classesS 2

Conclusion The continuity of the geometric operations is proved in 2.1, 2.2, 2.6, and 2.9 assuming the continuity of joining. Thus becomes a topological Minkowski plane, which indeed is compact and 4-dimensional.As already mentioned in the introduction there are candidates for 4-dimensional Minkowski planes. Those candidates are in standard representation and it is easy to see that circles are indeed compact. So, with the present theorem, it suffices to verify the geometric axioms of a Minkowski plane for those candidates and the continuity of joining.This research was supported by a Feodor Lynen Fellowship.     

On time graphs

For n points on the real line, joining each pair of points such that their difference is less than a certain positive constant, we have a time graph. In this paper we characterize time graphs and enumerate them.     

Crossing Numbers of Periodic Graphs

A graph is periodic if it can be obtained by joining identical pieces in a cyclic fashion. It is shown that the limit crossing number of a periodic graph is computable. This answers a question of Richter [1, Problem 4.2].     

Heavy fans, cycles and paths in weighted graphs of large connectivity

A set of paths joining a vertex y and a vertex set L is called (y,L)-fan if any two of the paths have only y in common, and its width is the number of paths forming it. In weighted graphs, it is known that the existence of heavy fan is useful to find a heavy cycle containing some specified vertices.In this paper, we show the existence of heavy fans with large width containing some specified vertices in weighted graphs of large connectivity, which is a weighted analogue of Perfect's theorem. Using this, in 3-connected weighted graphs, we can find heavy cycles containing three specified vertices, and also heavy paths joining two specified vertices containing two more specified vertices. These results extend the previous results in 2-connected weighted graphs to 3-connected weighted graphs.     

Asymptotically exact joining conditions at the junction of plates with very different characteristics

The phenomenon of the boundary layer which occurs when plates are joined is studied A procedure for deriving the asymptotically exact joining (transmission) conditions which associate the two-dimensional equations for the deformation of the plates along the joining line Γ is developed using the method of matched asymptotic expansions. Two situations are discussed in which these conditions turn out to be non-standard: the bending moment in Γ must disappear and the deflection can undergo a jump (for real values of the physical parameters, the longitudinal displacements and forces as well as the bending and the shearing force always remain continuous). One of the situations (the joining of “thick, soft” and a “thin, rigid” shells) is characteristic of a moving loudspeaker system. The results of a numerical experiment, which confirm the asymptotic analysis of the problem, are presented.     

Almost sure convergence of the multiple ergodic average for certain weakly mixing systems

The family of pairwise independently determined(PID) systems, i.e., those for which the independent joining is the only self joining with independent 2-marginals, is a class of systems for which the long standing open question by Rokhlin, of whether mixing implies mixing of all orders, has a positive answer. We show that in the class of weakly mixing PID one finds a positive answer for another long-standing open problem, whether the multiple ergodic averages 1/N N-1∑n=0 f_1(T~nx)···f_d(T~(dnx)),N→∞,almost surely converge.     

On the existence of real R-matrices for virtual link invariants

We characterize the virtual link invariants that can be described as partition function of a real-valued R-matrix, by being weakly reflection positive. Weak reflection positivity is defined in terms of joining virtual link diagrams, which is a specialization of joining virtual link diagram tangles. Basic techniques are the first fundamental theorem of invariant theory, the Hanlon–Wales theorem on the decomposition of Brauer algebras, and the Procesi–Schwarz theorem on inequalities for closed orbits.     

关于可拓集合的运算

根据蔡文提出的可拓集合的新定义,给出了可拓集合的包含、并、交、非运算的新定义,并讨论了有关运算性质,进而获得可拓域与稳定域的几个交并运算结果.     

Finding Shortest Paths in a Sequence of Triangles in 3D by the Planar Unfolding

We present an efficient algorithm for finding the shortest path joining two points in a sequence of triangles in three-dimensional space using the concept of funnels associated with common edges along the sequence of triangles and the planar unfolding for each funnel. We show that the unfolded image of a funnel is a simple polygon, it thus is non-overlapping. Therefore, such funnels are determined iteratively to their associated common edges by the planar unfolding and the shortest path joining two points is determined by cusps of these funnels.     

Curves and Surfaces Construction Based on New Basis with Exponential Functions

By incorporating two exponential functions into the cubic Bernstein basis functions, a new class of λμ-Bernstein basis functions is constructed. Based on these λμ-Bernstein basis functions, a kind of λμ-Bézier-like curve with two shape parameters, which include the cubic Bernstein-Bézier curve, is proposed. The C ¹ and C ² continuous conditions for joining two λμ-Bézier-like curves are given. By using tensor product method, a class of rectangular Bézier-like patches with four shape parameters is shown. The G ¹ and G ² continuous conditions for joining two rectangular Bézier-like patches are derived. By incorporating three exponential functions into the cubic Bernstein basis functions over triangular domain, a new class of λμη-Bernstein basis functions over triangular domain is also constructed. Based on the λμη-Bernstein basis functions, a kind of triangular λμη-Bézier-like patch with three shape parameters, which include the triangular Bernstein-Bézier cubic patch, is presented. The conditions for G ¹ continuous smooth joining two triangular λμη-Bézier-like patches are discussed. The shape parameters serve as tension parameters and have a predictable adjusting role on the curves and patches.