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991.
In telecommunication networks packets are carried from a source s to a destination t on a path that is determined by the underlying routing protocol. Most routing protocols belong to the class of shortest path routing protocols. In such protocols, the network operator assigns a length to each link. A packet going from s to t follows a shortest path according to these lengths. For better protection and efficiency, one wishes to use multiple (shortest) paths between two nodes. Therefore the routing protocol must determine how the traffic from s to t is distributed among the shortest paths. In the protocol called OSPF-ECMP (for Open Shortest Path First-Equal Cost Multiple Path) the traffic incoming at every node is uniformly balanced on all outgoing links that are on shortest paths. In that context, the operator task is to determine the “best” link lengths, toward a goal such as maximizing the network throughput for given link capacities.In this work, we show that the problem of maximizing even a single commodity flow for the OSPF-ECMP protocol cannot be approximated within any constant factor ratio. Besides this main theorem, we derive some positive results which include polynomial-time approximations and an exponential-time exact algorithm. We also prove that despite their weakness, our approximation and exact algorithms are, in a sense, the best possible. 相似文献
992.
This paper develops the basic analytical theory related to some recently introduced crowd dynamics models.Where well posedness was known only locally in time,it is here extended to all of R+.The result... 相似文献
993.
Hyesuk Lee 《Numerical Methods for Partial Differential Equations》2012,28(5):1667-1695
The aim of this work is to investigate the numerical approximation of a nonlinear, time‐dependent quasi‐Newtonian flow problem formulated in the framework of Arbitrary Lagrangian Eulerian method. We present some stability results and convergence analysis of finite element solutions for semidiscrete and fully discretized problems, respectively. Numerical results supporting the derived error estimate are also presented. © 2011 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2012 相似文献
994.
《Optimization》2012,61(6):879-888
A variant for checking a solvability eriterion for multilevel multisort transportation problem is given. 相似文献
995.
996.
Eiji Onodera 《偏微分方程通讯》2013,38(6):1130-1144
We prove time-global existence of solutions to the initial value problem for a third order dispersive flow into compact locally Hermitian symmetric spaces. The equation under consideration generalizes two-sphere-valued completely integrable systems modeling the motion of vortex filament. Unlike one-dimensional Schrödinger maps, our third order equation is not completely integrable under the curvature condition on the target manifold in general. The idea of our proof is to exploit two conservation laws and an “almost conserved quantity” which prevents the formation of a singularity in finite time. 相似文献
997.
Xuan Hien Nguyen 《偏微分方程通讯》2013,38(3):257-280
In this paper, we describe the construction of new examples of self-translating surfaces under the mean curvature flow. We find the new surfaces by desingularizing the intersection of a grim reaper and a plane to obtain approximate solutions, then we solve a perturbation problem to find the exact solutions. Our work is inspired from Kapoulea' construction of minimal surfaces but differs from it by our more abstract and direct study of the linear operator, via Fredholm operators. 相似文献
998.
In this paper, we first study a class of elliptic equations with anisotropic boundary degeneracy. Besides establishing the existence, uniqueness and comparison principle, we obtain the optimal Hölder estimates for weak solutions by the estimates in the Campanato space. Based on such Hölder estimates, we then investigate subsonic-sonic flows with singularities at the sonic curves in a symmetric convergent nozzle with straight wall for an approximate model of the potential flow equation. It is proved that the perturbation problem of the symmetric subsonic-sonic flow is solvable and the symmetric subsonic-sonic flow is stable. 相似文献
999.
1000.
采用以Shan-Chen多组分模型为基础的格子Boltzmann-伪固体模型对两颗粒间的浮体和浸润横向毛细力展开数值模拟研究,其中流体-固体间的相互作用及颗粒润湿性质在介观层次上采用简单形式得以充分考虑．三维测试表明,与已有理论解相比,成功再现了横向毛细力与颗粒间距的“1/L”关系,并确认了浸润横向毛细力与表面张力间的线性关系．这表明可进一步应用该模型研究横向毛细力作用下的颗粒自聚集等现象. 相似文献