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Showing papers presented at "Computational Science and Engineering in 2007"


Journal ArticleDOI
01 May 2007
TL;DR: The IPython project as mentioned in this paper provides an enhanced interactive environment that includes, among other features, support for data visualization and facilities for distributed and parallel computation for interactive work and a comprehensive library on top of which more sophisticated systems can be built.
Abstract: Python offers basic facilities for interactive work and a comprehensive library on top of which more sophisticated systems can be built. The IPython project provides on enhanced interactive environment that includes, among other features, support for data visualization and facilities for distributed and parallel computation

3,355 citations


Journal ArticleDOI
01 Sep 2007
TL;DR: VisTrails is presented, an open source provenance-management system that provides infrastructure for data exploration and visualization that transparently records detailed provenance of exploratory computational tasks and uses this information to simplify the process of exploring data through visualization.
Abstract: The demand for the construction of complex visualizations is growing in many disciplines of science, as users are faced with ever increasing volumes of data to analyze. In this paper, the authors present VisTrails, an open source provenance-management system that provides infrastructure for data exploration and visualization. VisTrails transparently records detailed provenance of exploratory computational tasks and leverages this information beyond just the ability to reproduce and share results. In particular, it uses this information to simplify the process of exploring data through visualization.

150 citations


Journal ArticleDOI
01 May 2007
TL;DR: This paper suggests a new method which is based on the combination of the splitting time interval and the traditional iterative operator splitting, and analyses the local splitting error of the method.
Abstract: The operator-splitting methods are based on splitting of the complex problem into a sequence of simpler tasks. A useful method is the iterative splitting method which ensures a consistent approximation in each step. In our paper, we suggest a new method which is based on the combination of the splitting time interval and the traditional iterative operator splitting. We analyse the local splitting error of the method. Numerical examples are given in order to demonstrate the method.

97 citations


Journal ArticleDOI
01 Mar 2007
TL;DR: The main desiderata for access control systems are discussed and the main characteristics of access control solutions are illustrated.
Abstract: Access control is the process of mediating every request to data and services maintained by a system and determining whether the request should be granted or denied. Expressiveness and flexibility are top requirements for an access control system together with, and usually in conflict with, simplicity and efficiency. In this paper, we discuss the main desiderata for access control systems and illustrate the main characteristics of access control solutions.

76 citations


Journal ArticleDOI
01 Apr 2007
TL;DR: A new 'worst-out' approach is studied and the proposed edge contraction heuristic is shown to have an approximation ratio of at least 1/3 and the results of experimental comparison of the worst-out approach, the well-known best-in algorithm, and modifications for both are included.
Abstract: Given a graph with non-negative edge weights, the MAX CUT problem is to partition the set of vertices into two subsets so that the sum of the weights of edges with endpoints in different subsets is maximised. This classical NP-hard problem finds applications in VLSI design, statistical physics, and classification among other fields. This paper compares the performance of several greedy construction heuristics for MAX-CUT problem. In particular, a new 'worst-out' approach is studied and the proposed edge contraction heuristic is shown to have an approximation ratio of at least 1/3. The results of experimental comparison of the worst-out approach, the well-known best-in algorithm, and modifications for both are also included.

62 citations


Book ChapterDOI
01 Jan 2007
TL;DR: Some new convergence results that show superlinear convergence of the parareal algorithm when used on bounded time intervals, and linear convergence for unbounded intervals are shown.
Abstract: The parareal algorithm is a method to solve time dependent problems parallel in time: it approximates parts of the solution later in time simultaneously to parts of the solution earlier in time. In this paper the relation of the parareal algorithm to space-time multigrid and multiple shooting methods is first briefly discussed. The focus of the paper is on some new convergence results that show superlinear convergence of the algorithm when used on bounded time intervals, and linear convergence for unbounded intervals.

52 citations


Journal ArticleDOI
01 Jul 2007
TL;DR: Simulation modeling provides a means for projecting changes in arctic and subarctic vegetation caused by environmental variations.
Abstract: The arctic is a sensitive system undergoing dramatic changes related to recent warming trends. Vegetation dynamics - increases in the quantity of green vegetation and a northward migration of trees into the arctic tundra - are a component of this change. Although field studies over long time periods can be logistically problematic, simulation modeling provides a means for projecting changes in arctic and subarctic vegetation caused by environmental variations.

46 citations


Journal ArticleDOI
01 Jan 2007
TL;DR: A radial basis function-based interpolation method can help researchers render the surface of human organs by using data sets that contain parallel slices of contours extracted from medical images.
Abstract: A radial basis function-based interpolation method can help researchers render the surface of human organs. Moreover, by using data sets that contain parallel slices of contours extracted from medical images, researchers can also efficiently reconstruct an organ's surface

35 citations


Book ChapterDOI
01 Jan 2007
TL;DR: An optimized Schwarz Waveform Relaxation algorithm for convection-diffusion problems with discontinuous coefficients is presented and an optimized Galerkin method for the time-discretization is used in order to get higher order schemes in time.
Abstract: We present and study an optimized Schwarz Waveform Relaxation algorithm for convection-diffusion problems with discontinuous coefficients. Such analysis is a first step towards the coupling of heterogeneous climatic models. The SWR algorithms are global in time, and thus allow for the use of non conforming space-time discretizations. They are therefore well adapted to coupling models with very different spatial and time scales, as in ocean-atmosphere coupling. As the cost per iteration can be very high, we introduce new transmission conditions in the algorithm which optimize the convergence speed. In order to get higher order schemes in time, we use in each subdomain a discontinuous Galerkin method for the time-discretization. We present numerical results to illustrate this approach, and we analyse numerically the time-discretization error.

35 citations


Journal ArticleDOI
01 Jul 2007
TL;DR: The authors traces how research into the Heider balance has moved forward in the past 10 years, from a sociological problem about group divisions to a computational one, and traces the evolution of the problem from sociological to computational one.
Abstract: This article traces how research into the Heider balance has moved forward in the past 10 years, from a sociological problem about group divisions to a computational one.

33 citations


Journal ArticleDOI
M.A. Gray1
01 Nov 2007
TL;DR: A new entrant in the field of discrete event simulation systems, SimEvents has several desirable system features and is particularly useful for existing Matlab and Simulink users looking to construct complex hybrid systems of discrete/continuous processing.
Abstract: A new entrant in the field of discrete event simulation systems, SimEvents has several desirable system features. It still has some catching up to do in some areas, but SimEvents is particularly useful for existing Matlab and Simulink users looking to construct complex hybrid systems of discrete/continuous processing.

Journal ArticleDOI
01 Apr 2007
TL;DR: This paper presents a branch-and-cut method for two stage Stochastic Mixed-Integer Programming (SMIP) problems with continuous first-stage variables derived based on disjunctive decomposition (D2) for SMIP, an approach in whichdisjunctive programming is used to derive valid inequalities forSMIP.
Abstract: This paper presents a branch-and-cut method for two stage Stochastic Mixed-Integer Programming (SMIP) problems with continuous first-stage variables. This method is derived based on disjunctive decomposition (D2) for SMIP, an approach in which disjunctive programming is used to derive valid inequalities for SMIP. The novelty of the proposed method derives from branching on the first-stage continuous domain while the branch-and-bound process is guided by the disjunction variables in the second-stage. Finite convergence of the algorithm for mixed-binary second stage is established and a numerical example to illustrate the new method is given.

Journal ArticleDOI
01 Sep 2007
TL;DR: The hydraulic spline algorithm generates irregular 2D channel grids from highly accurate cross-sectional survey data at any desired resolution, facilitating its integration with high-density light detection and ranging (lidar) data.
Abstract: The hydraulic spline algorithm generates irregular 2D channel grids from highly accurate cross-sectional survey data at any desired resolution, facilitating its integration with high-density light detection and ranging (lidar) data.

Journal ArticleDOI
01 Mar 2007
TL;DR: The author discusses how to model these uncertainties in integrated supply-chain design models and studies their impacts on optimal supply- chain decisions.
Abstract: A supply chain is a network of facilities and activities that procure, produce, and distribute goods to customers. Many uncertainties within a supply chain can substantially affect its performance. The author discusses how to model these uncertainties in integrated supply-chain design models and studies their impacts on optimal supply-chain decisions

Journal ArticleDOI
01 Jan 2007
TL;DR: Polar remote sensing offers numerous opportunities for computer scientists, including spacecraft design and data processing, the development of algorithms for geophysical product retrieval, operational assistance for aircraft and ship navigation, and database management at national archives.
Abstract: Polar remote sensing offers numerous opportunities for computer scientists, including spacecraft design and data processing, the development of algorithms for geophysical product retrieval, operational assistance for aircraft and ship navigation, and database management at national archives.

Journal ArticleDOI
01 Feb 2007
TL;DR: In this article, an adaptive subdivision method called Incremental Subdivision (IS) was proposed for triangle meshes, where the selected area becomes fine and high resolution while the rest of mesh is coarse.
Abstract: We introduce incremental subdivision as a new adaptive subdivision method for triangle meshes. While regular (global) subdivisions produce a smooth surface from a given polygon mesh by refining all of its faces, adaptive subdivision produces a surface by refining only some selected areas of the mesh. Consequently, the selected area becomes fine and high resolution while the rest of mesh is coarse. Incremental subdivision produces a surface whose subdivided area is identical to when the entire mesh is subdivided regularly. In addition, as a good effect, the resolution of the produced surface gradually increases from coarse to fine. The incremental subdivision method expands the specified area to create a buffer region that is subdivided along with it. This method is efficient and easy to implement. We apply the incremental method to Loop and Butterfly subdivision schemes, and we compare it with other adaptive subdivision methods. We discuss some applications of incremental subdivision.

Journal ArticleDOI
01 Nov 2007
TL;DR: Results on melting sea-ice from a regional coupled ice-ocean model are analyzed and their robustness independent of timescales for surface temperature and salinity relaxation is demonstrated.
Abstract: Models help researchers understand past and present states as well as predict scenarios of environmental change in the Arctic The authors analyze results on melting sea-ice from a regional coupled ice-ocean model and demonstrate their robustness independent of timescales for surface temperature and salinity relaxation

Journal ArticleDOI
01 May 2007
TL;DR: Results from a hierarchy of models of different complexity, their strengths and weaknesses, and how they could help forecast the future state of the ice-ocean system are presented.
Abstract: The authors discuss modeling's role in understanding the ice-ocean system, as well as its importance in predicting the future state of Arctic sea ice. In doing so, this article presents results from a hierarchy of models of different complexity, their strengths and weaknesses, and how they could help forecast the future state of the ice-ocean system.

Journal ArticleDOI
01 Mar 2007
TL;DR: To generate huge databases of stochastic material models, the authors propose using an information-learning algorithm to train a network for statistical outputs.
Abstract: An approach derived from information-theoretic principles can help researchers build stochastic microstructural models. This approach involves extracting topological information from microstructural samples and using this information to build a stochastic model. To generate huge databases of stochastic material models, the authors thus propose using an information-learning algorithm to train a network for statistical outputs

Journal ArticleDOI
01 Mar 2007
TL;DR: This paper argues that with a self-organising, dynamic, and large-scale architecture, instead of traditional distributed computing systems, PDNs should be classified with natural complex systems (such as social networks).
Abstract: A Peer-to-peer Data Network (PDN) is an open and evolving society of peer nodes that assemble into a network to share their data. We argue that with a self-organising, dynamic, and large-scale architecture, instead of traditional distributed computing systems, PDNs should be classified with natural complex systems (such as social networks). The 'complex system theory' is a meta-theory that provides a common modelling framework to study such complex systems under one umbrella. In this paper, for the first time we introduce and apply the complex system theory as a modelling framework to study PDNs.

Journal ArticleDOI
01 May 2007
TL;DR: Python offers a unique capability in the field of geographic information system applications because it helps developers create multipurpose Internet maps, and PDF maps in particular are discussed.
Abstract: Python offers a unique capability in the field of geographic information system applications because it helps developers create multipurpose Internet maps. This article discusses PDF maps in particular.

Journal ArticleDOI
01 Apr 2007
TL;DR: The problem-oriented robustification of the previously proposed Fused Bayesian-Regularization enhanced imaging method is performed to alleviate its ill-poseness due to system-level and model-model uncertainties.
Abstract: We address a new efficient robust optimisation approach to large-scale environmental image reconstruction/enhancement as required for remote sensing imaging with multi-spectral array sensors/SAR. First, the problem-oriented robustification of the previously proposed Fused Bayesian-Regularization (FBR) enhanced imaging method is performed to alleviate its ill-poseness due to system-level and model-model uncertainties. Second, the modification of the Hopfield-type Maximum Entropy Neural Network (MENN) is proposed that enables such MENN to perform numerically the robustified FBR technique via computationally efficient iterative scheme. The efficiency of the aggregated robust regularised MENN technique is verified through simulation studies of enhancement of the real-world environmental images.

Journal ArticleDOI
01 Apr 2007
TL;DR: Two related problems that arise in multicast networks: the tree cache placement and the flow cache placement problems are shown to be NP-hard, and a proof of hardness of approximation using a gap-preserving reduction is given.
Abstract: Multicast networks are used to distribute live content, such as video or audio streams, to a potentially large number of destinations. Streaming caches are deployed in these multicast systems to allow content distribution without network overload. We consider two related problems that arise in multicast networks: the tree cache placement and the flow cache placement problems. These problems are shown to be NP-hard, and we give a proof of hardness of approximation using a gap-preserving reduction. We also present approximation algorithms, as well as special cases where these problems can be solved in polynomial time.

Journal ArticleDOI
01 Nov 2007
TL;DR: From the perspective of a computational scientist who models astrophysical fluid flows, the author describes the successes and frustrations he's had with the development and use of scientific visualization techniques.
Abstract: From the perspective of a computational scientist who models astrophysical fluid flows, the author describes the successes and frustrations he's had with the development and use of scientific visualization techniques. A biased view toward the future is also presented.

Journal ArticleDOI
01 Mar 2007
TL;DR: This paper addresses a natural step in the evolution of P2P: data and information sharing where data is accessed based on its attributes or properties, and proposes three new models for both data distribution and data accesses.
Abstract: Peer-to-Peer (P2P) networks are distributed data sharing systems with no dedicated and centralised infrastructure. While P2P systems have been used so far mainly for file sharing, their true potential lies as a vast, loosely connected worldwide infrastructure for sharing resources, data and information. This paper addresses a natural step in the evolution of P2P: data and information sharing where data is accessed based on its attributes or properties. We have identified diverse applications that can benefit directly from attribute-based access to distributed data over P2P systems. Based on the application requirements, we propose three new models for both data distribution and data accesses.

Journal ArticleDOI
01 Sep 2007
TL;DR: High-performance reconfigurable computing combines the advantages of the coarse- grain parallel processing provided in conventional multiprocessor systems with the fine-grain parallel processing available in field-programmable gate arrays.
Abstract: High-performance reconfigurable computing combines the advantages of the coarse-grain parallel processing provided in conventional multiprocessor systems with the fine-grain parallel processing available in field-programmable gate arrays.

Journal ArticleDOI
01 Jan 2007
TL;DR: A new statistical technique has enabled John Rundle and his team at the University of California to narrow the forecast window to less than three years, and he and his partners plan to automate research-quality forecasts and make them available online.
Abstract: The physical forces that govern seismic events are so complex that scientists have struggled to assemble forecasts on the scale of decades. Now a new statistical technique has enabled John Rundle and his team at the University of California to narrow the forecast window to less than three years. The calculations require a day of supercomputing time, but he and his partners plan to automate research-quality forecasts and make them available online. You can only do this with grid computing. The idea of linking supercomputers into a computational grid to confront big problems isn't a new one, but Rundle and others in Earth science are doing something different. They're linking grids together - effectively, using grids of grids - thanks to a software movement that takes its name from the musical phenomenon known as the mashup


Journal ArticleDOI
01 Feb 2007
TL;DR: The algorithm is not limited to a given polygonisation method, but then its use is possible for all other surface approaches that need a starting point at the beginning.
Abstract: This paper presents an adaptive method for polygonisation of implicit surfaces. The method is based on the shape of triangles and the accuracy of resulting approximation. The main advantages of the triangulation presented are simplicity and the stable features that can be used for the next expansion. The presented algorithm is based on the surface tracking scheme, and it is compared with other algorithms that are based on the similar principle, such as the Marching cubes and the Marching triangles algorithms. Moreover, the technique for detection of more disjoint implicit surfaces in a defined area is also presented. The algorithm is not limited to a given polygonisation method, but then its use is possible for all other surface approaches that need a starting point at the beginning.

Journal ArticleDOI
01 May 2007
TL;DR: This paper applies different operator splittings, based on directional decomposition, to the linearised form of the shallow water equations obtained by the method of small perturbations, which has three types of harmonic wave solutions with known dispersion relations and phase velocities.
Abstract: The shallow water equations describe motions in a shallow, incompressible and nonviscous fluid layer on the rotating Earth. Due to their relative simplicity, they are widely used for testing and analysing new numerical methods developed for weather prediction models. In this paper, we apply different operator splittings, based on directional decomposition, to the linearised form of the shallow water equations obtained by the method of small perturbations. This system has three types of harmonic wave solutions with known dispersion relations and phase velocities. We investigate how the application of operator splitting modifies these important characteristics, and compare the performance of different splitting methods from this point of view.