1Traceroute及其在网络拓扑发现中的应用

本文分析了Traceroute正确性和完整性两方面存在的问题．设计了相应的改进方案，结合其网络拓扑发现中的应用，详述了防火墙定位的方法．并提出了一种子网发现算法。     

Visibility-driven mesh analysis and visualization through graph cuts

In this paper we present an algorithm that operates on a triangular mesh and classifies each face of a triangle as either inside or outside. We present three example applications of this core algorithm: normal orientation, inside removal, and layer-based visualization. The distinguishing feature of our algorithm is its robustness even if a difficult input model that includes holes, coplanar triangles, intersecting triangles, and lost connectivity is given. Our algorithm works with the original triangles of the input model and uses sampling to construct a visibility graph that is then segmented using graph cut.     

三维网格模型数据流压缩算法研究

当前的网格压缩算法在编码顶点和连通信息之前,需要按照某种顺序遍历网格模型,而且需要构造支持拓扑结构访问的临时数据结构,不利于处理大型网格模型.从根源上抛弃了传统网格数据组织形式,给出了一种新的网格顶点和连通信息交错的网格数据组织方法,提出了以网格数据读入顺序渐进编码算法.实验结果表明,算法的处理速度和所占用的内存空间都优于传统的压缩方法.     

无线网格网的路由与拓扑优化

在无线网格网(Wireless Mesh Network,WMN)节点通过一跳或者多跳连接到网关,网关为节点用户提供接入Internet的入口,如何构建合理并且高效的拓扑结构是提高整个无线mesh性能的关键因素。结合布尔变量来描述WMN节点数据传输无回路,节点到网关的总跳数最少,数据流量符合节点与网关的承载能力这些问题使网络拓扑达到需求,验证利用邻接矩阵来确定网关节点,通过Network Simulator Version2(NS2)验证了满足上述问题的拓扑结构相对最优。     

Automatic mesh generation and transformation for topology optimization methods

This paper presents automatic tools aimed at the generation and adaptation of unstructured tetrahedral meshes in the context of composite or heterogeneous geometry. These tools are primarily intended for applications in the domain of topology optimization methods but the approach introduced presents great potential in a wider context. Indeed, various fields of application can be foreseen for which meshing heterogeneous geometry is required, such as finite element simulations (in the case of heterogeneous materials and assemblies, for example), animation and visualization (medical imaging, for example). Using B-Rep concepts as well as specific adaptations of advancing front mesh generation algorithms, the mesh generation approach presented guarantees, in a simple and natural way, mesh continuity and conformity across interior boundaries when trying to mesh a composite domain. When applied in the context of topology optimization methods, this approach guarantees that design and non-design sub-domains are meshed so that finite elements are tagged as design and non-design elements and so that continuity and conformity are guaranteed at the interface between design and non-design sub-domains. The paper also presents how mesh transformation and mesh smoothing tools can be successfully used when trying to derive a functional shape from raw topology optimization results.     

Query-driven visualization of time-varying adaptive mesh refinement data

The visualization and analysis of AMR-based simulations is integral to the process of obtaining new insight in scientific research. We present a new method for performing query-driven visualization and analysis on AMR data, with specific emphasis on time-varying AMR data. Our work introduces a new method that directly addresses the dynamic spatial and temporal properties of AMR grids that challenge many existing visualization techniques. Further, we present the first implementation of query-driven visualization on the GPU that uses a GPU-based indexing structure to both answer queries and efficiently utilize GPU memory. We apply our method to two different science domains to demonstrate its broad applicability.     

无线mesh网络的拓扑控制算法研究

针对无线mesh网络(WMN)中由于无线信号干扰造成的端到端吞吐量并不是很理想的问题,提出了一种通过以最小化最大冲突负载为策略构造无线mesh网络拓扑的拓扑控制算法.在形成网络拓扑之后,算法通过调整节点的传输功率到一个合理水平来降低干扰,从而提高信道的空间复用度以优化网络的吞吐量.最后以最大冲突域负载作为性能指标的仿真结果表明:通过拓扑控制能够提升无线mesh网络的吞吐量.     

Integrated topology control and routing in wireless optical mesh networks

We study the problem of integrated topology control and routing in Free Space Optical (FSO) mesh backbone networks. FSO links are high-bandwidth, low interference links that can be set-up very fast, making them suitable for mesh networking. FSO networks are highly constrained by interface constraints, i.e., constraints on the number of FSO links a node can establish. We prove the problem to be NP-Hard and propose efficient algorithms for integrated topology control and single-path or multi-path routing.     

Morse complexes for shape segmentation and homological analysis: discrete models and algorithms

Morse theory offers a natural and mathematically‐sound tool for shape analysis and understanding. It allows studying the behavior of a scalar function defined on a manifold. Starting from a Morse function, we can decompose the domain of the function into meaningful regions associated with the critical points of the function. Such decompositions, called Morse complexes, provide a segmentation of a shape and are extensively used in terrain modeling and in scientific visualization. Discrete Morse theory, a combinatorial counterpart of smooth Morse theory defined over cell complexes, provides an excellent basis for computing Morse complexes in a robust and efficient way. Moreover, since a discrete Morse complex computed over a given complex has the same homology as the original one, but fewer cells, discrete Morse theory is a fundamental tool for efficiently detecting holes in shapes through homology and persistent homology. In this survey, we review, classify and analyze algorithms for computing and simplifying Morse complexes in the context of such applications with an emphasis on discrete Morse theory and on algorithms based on it.     

Construction of harmonic map flows through the method of discrete Morse flows

By the method of discrete Morse flows, we construct the Morse flow of harmonic map from a Riemannian manifold with measurable and bounded metric into that with Alexander non-positive curvature. The construction is directly derived without isometrically embedding of the target manifold into Euclidean space. Our method will be in force in the case, as treated in [11], where a target manifold has the bounded positive curvature.     

网络拓扑可视化类库TopVisLibrary的设计与实现

以信息可视化参考模型为基础,分析了网络拓扑可视化过程中的主要操作及数据形态变化,并以此为依据,建立了网络拓扑可视化对象模型,设计实现了网络拓扑可视化类库TopVisLibrary.该库的编程模型和数据接口简单清晰,有助于灵活搭建不同的网络拓扑可视化应用,同时对其它可视化工具的设计实现有一定的借鉴意义.此外,网络拓扑可视化类库的设计方法也可为其它库的设计提供参考.     

Eigenspace compression: dynamic 3D mesh compression by restoring fine geometry to deformed coarse models

Multimedia Tools and Applications - Dynamic 3D mesh compression is of great practical important issues in computer graphics and multimedia applications. In this paper, an efficient compression...     

Computation and visualization of discrete particle systems on gLite-based grid

Three-dimensional simulation of discrete particle systems is performed by the discrete element method (DEM) software on the gLite-based BalticGrid infrastructure. The performance of a parallel algorithm for particles exchanging processors is investigated by using a number of benchmarks. Polydispersed particle systems are visualized by a novel grid e-service VizLitG designed for convenient access and interactive visualization of remote data files located on the grid. Partial dataset transfer from the storage element is implemented in the visualization e-service. The efficiency tests of VizLitG are performed on the datasets of different sizes. Two granular problems associated with triaxial compaction and hopper discharge are solved.     

Optimal topology design of discrete structures resisting degradation effects

In this technical note we treat the problem of finding the optimal topology of a truss, so that stiffness after degradation is maximized. It is shown that for the problem setting at hand, the optimal topology has uniform relative degradation in all bars and the topology is unchanged from the topology for a truss not undergoing degradation. As is well-known such a design can be realized as a fully stressed, statically determinate truss.     

Applications of automatic differentiation in topology optimization

The goal of this article is to demonstrate the applicability and to discuss the advantages and disadvantages of automatic differentiation in topology optimization. The technique makes it possible to wholly or partially automate the evaluation of derivatives for optimization problems and is demonstrated on two separate, previously published types of problems in topology optimization. Two separate software packages for automatic differentiation, CoDiPack and Tapenade are considered, and their performance and usability trade-offs are discussed and compared to a hand coded adjoint gradient evaluation process. Finally, the resulting optimization framework is verified by applying it to a non-trivial unsteady flow topology optimization problem.     

A new scheme for mesh generation and mesh refinement using graph theory

There are an extensive number of algorithms available from graph theory, some of which, for problems with geometric content, make graphs an attractive framework in which to model an object from its geometry to its discretization into a finite element mesh. This paper presents a new scheme for finite element mesh generation and mesh refinement using concepts from graph theory. This new technique, which is suitable for an interactive graphical environment, can also be used efficiently for fully automatic remeshing in association with self-adaptive schemes. Problems of mesh refinement around holes and local mesh refinement are treated. The suitability of the algorithms presented in this paper is demonstrated by some examples.     

A neuron membrane mesh representation for visualization of electrophysiological simulations

We present a process to automatically generate three-dimensional mesh representations of the complex, arborized cell membrane surface of cortical neurons (the principal information processing cells of the brain) from nonuniform morphological measurements. Starting from manually sampled morphological points (3D points and diameters) from neurons in a brain slice preparation, we construct a polygonal mesh representation that realistically represents the continuous membrane surface, closely matching the original experimental data. A mapping between the original morphological points and the newly generated mesh enables simulations of electrophysiolgical activity to be visualized on this new membrane representation. We compare the new mesh representation with the state of the art and present a series of use cases and applications of this technique to visualize simulations of single neurons and networks of multiple neurons.     

Game theory approach to robust topology optimization with uncertain loading

The paper concerns robustness with respect to uncertain loading in topology optimization problems. Using a game theoretic framework we formulate problems, or games, defining generalized Nash equilibria. In each game a set of topology design variables aim to find an optimal topology, while a set of load variables aim to find the worst possible load. Several numerical examples with uncertain loading are solved in 2D and 3D. The games are formulated using global stress, mass and compliance as objective functions or constraints.