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  • 1.
    Aarno, Daniel
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Kragic, Danica
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Christensen, Henrik
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Artificial potential biased probabilistic roadmap method2004In: 2004 IEEE INTERNATIONAL CONFERENCE ON ROBOTICS AND AUTOMATION, VOLS 1- 5, PROCEEDINGS, 2004, p. 461-466Conference paper (Refereed)
    Abstract [en]

    Probabilistic roadmap methods (PRMs) have been successfully used to solve difficult path planning problems but their efficiency is limited when the free space contains narrow passages through which the robot must pass. This paper presents a new sampling scheme that aims to increase the probability of finding paths through narrow passages. Here, a biased sampling scheme is used to increase the distribution of nodes in narrow regions of the free space. A partial computation of the artificial potential field is used to bias the distribution of nodes.

  • 2.
    Abenius, Erik
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Time-Domain Inverse Electromagnetic Scattering using FDTD and Gradient-based Minimization2004Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    The thesis addresses time-domain inverse electromagneticscattering for determining unknown characteristics of an objectfrom observations of the scattered .eld. Applications includenon-destructive characterization of media and optimization ofmaterial properties, for example the design of radar absorbingmaterials.A nother interesting application is the parameteroptimization of subcell models to avoid detailed modeling ofcomplex geometries.

    The inverse problem is formulated as an optimal controlproblem where the cost function to be minimized is thedi.erence between the estimated and observed .elds, and thecontrol parameters are the unknown object characteristics. Theproblem is solved in a deterministic gradient-basedoptimization algorithm using a parallel 2D FDTD scheme for thedirect problem.This approach is computationally intensive sincethe direct problem needs to be solved in every optimizationiteration in order to compute an estimated .eld.H ighlyaccurate analytical gradients are computed from the adjointformulation.In addition to giving better accuracy than .nitedi.erences, the analytical gradients also have the advantage ofonly requiring one direct and one adjoint problem to be solvedregardless of the number of parameters.

    When absorbing boundary conditions are used to truncate thecomputational domain, the equations are non-reversible and theentire time-history of the direct solution needs to be storedfor the gradient computation.Ho wever, using an additionaldirect simulation and a restart procedure it is possible tokeep the storage at an acceptable level.

    The inverse method has been successfully applied to a widerange of industrial problems within the European project,IMPACT (Inverse Methods for Wave Propagation Applications inTime-Domain).T he results presented here includecharacterization of layered dispersive media, determination ofparameters in subcell models for thin sheets and narrow slotsand optimization problems where the observed .eld is given bydesign objectives.

  • 3. Addario-Berry, L
    et al.
    Chor, B
    Hallett, M
    Lagergren, Jens
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Panconesi, A
    Wareham, T
    Ancestral maximum likelihood of evolutionary trees is hard2004In: Journal of Bioinformatics and Computational Biology, ISSN 0219-7200, E-ISSN 1757-6334, Vol. 2, no 2, p. 257-271Article in journal (Refereed)
    Abstract [en]

    Maximum likelihood (ML) (Felsenstein, 1981) is an increasingly popular optimality criterion for selecting evolutionary trees. Finding optimal ML trees appears to be a very hard computational task - in particular, algorithms and heuristics for ML take longer to run than algorithms and heuristics for maximum parsimony (MP). However, while MP has been known to be NP-complete for over 20 years, no such hardness result has been obtained so far for ML. In this work we make a first step in this direction by proving that ancestral maximum likelihood (AML) is NP-complete. The input to this problem is a set of aligned sequences of equal length and the goal is to find a tree and an assignment of ancestral sequences for all of that tree's internal vertices such that the likelihood of generating both the ancestral and contemporary sequences is maximized. Our NP-hardness proof follows that for MP given in (Day, Johnson and Sankoff, 1986) in that we use the same reduction from VERTEX COVER; however, the proof of correctness for this reduction relative to AML is different and substantially more involved.

  • 4.
    Ahsant, Mehran
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Mulmo, Olle
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Basney, Jim
    University of Illinois.
    Grid Delegation Protocol2004In: Workshop on Grid Security Practice and Experience, 2004, p. 81-91Conference paper (Refereed)
    Abstract [en]

    We propose a delegation protocol based on the WS-Trust specification, which is applicablefor a wide range of Grid applications. The protocol is independent of underlying securitymechanisms and is therefore applicable to all security mechanisms of common use in Gridenvironments, such as X.509 proxy certificates, Kerberos based delegation, and SAML assertions.We emphasize that this is work in progress. In this paper, we document our thoughtsand current strategy, and we solicit comments and feedback on our approach.

  • 5. Alimonti, P.
    et al.
    Kann, Viggo
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Some APX-completeness results for cubic graphs2000In: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 237, no 2-Jan, p. 123-134Article in journal (Refereed)
    Abstract [en]

    Four fundamental graph problems, Minimum vertex cover, Maximum independent set, Minimum dominating set and Maximum cut, are shown to be APX-complete even for cubic graphs. Therefore, unless P = NP, these problems do not admit any polynomial time approximation scheme on input graphs of degree bounded by three.

  • 6. Alkema, W. B. L.
    et al.
    Johansson, O.
    Lagergren, Jens
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Wasserman, W. W.
    MSCAN: identification of functional clusters of transcription factor binding sites2004In: Nucleic Acids Research, ISSN 0305-1048, E-ISSN 1362-4962, Vol. 32, p. W195-W198Article in journal (Refereed)
    Abstract [en]

    Identification of functional transcription factor binding sites in genomic sequences is notoriously difficult. The critical problem is the low specificity of predictions, which directly reflects the low target specificity of DNA binding proteins. To overcome the noise produced in predictions of individual binding sites, a new generation of algorithms achieves better predictive specificity by focusing on locally dense clusters of binding sites. MSCAN is a leading method for binding site cluster detection that determines the significance of observed sites while correcting for local compositional bias of sequences. The algorithm is highly flexible, applying any set of input binding models to the analysis of a user-specified sequence. From the user's perspective, a key feature of the system is that no reference data sets of regulatory sequences from co-regulated genes are required to train the algorithm. The output from MSCAN consists of an ordered list of sequence segments that contain potential regulatory modules. We have chosen the features in MSCAN such that sequence and matrix retrieval is highly facilitated, resulting in a web server that is intuitive to use. MSCAN is available at http://mscan.cgb.ki.se/cgi-bin/MSCAN.

  • 7.
    Althaus, Philipp
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Indoor Navigation for Mobile Robots: Control and Representations2003Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    This thesis deals with various aspects of indoor navigationfor mobile robots. For a system that moves around in ahousehold or office environment,two major problems must betackled. First, an appropriate control scheme has to bedesigned in order to navigate the platform. Second, the form ofrepresentations of the environment must be chosen.

    Behaviour based approaches have become the dominantmethodologies for designing control schemes for robotnavigation. One of them is the dynamical systems approach,which is based on the mathematical theory of nonlineardynamics. It provides a sound theoretical framework for bothbehaviour design and behaviour coordination. In the workpresented in this thesis, the approach has been used for thefirst time to construct a navigation system for realistic tasksin large-scale real-world environments. In particular, thecoordination scheme was exploited in order to combinecontinuous sensory signals and discrete events for decisionmaking processes. In addition, this coordination frameworkassures a continuous control signal at all times and permitsthe robot to deal with unexpected events.

    In order to act in the real world, the control system makesuse of representations of the environment. On the one hand,local geometrical representations parameterise the behaviours.On the other hand, context information and a predefined worldmodel enable the coordination scheme to switchbetweensubtasks. These representations constitute symbols, on thebasis of which the system makes decisions. These symbols mustbe anchored in the real world, requiring the capability ofrelating to sensory data. A general framework for theseanchoring processes in hybrid deliberative architectures isproposed. A distinction of anchoring on two different levels ofabstraction reduces the complexity of the problemsignificantly.

    A topological map was chosen as a world model. Through theadvanced behaviour coordination system and a proper choice ofrepresentations,the complexity of this map can be kept at aminimum. This allows the development of simple algorithms forautomatic map acquisition. When the robot is guided through theenvironment, it creates such a map of the area online. Theresulting map is precise enough for subsequent use innavigation.

    In addition, initial studies on navigation in human-robotinteraction tasks are presented. These kinds of tasks posedifferent constraints on a robotic system than, for example,delivery missions. It is shown that the methods developed inthis thesis can easily be applied to interactive navigation.Results show a personal robot maintaining formations with agroup of persons during social interaction.

    Keywords:mobile robots, robot navigation, indoornavigation, behaviour based robotics, hybrid deliberativesystems, dynamical systems approach, topological maps, symbolanchoring, autonomous mapping, human-robot interaction

  • 8.
    Althaus, Philipp
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Ishiguro, H.
    Kanda, T.
    Miyashita, T.
    Christensen, Henrik
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Navigation for human-robot interaction tasks2004In: 2004 IEEE INTERNATIONAL CONFERENCE ON ROBOTICS AND AUTOMATION, VOLS 1- 5, PROCEEDINGS, 2004, p. 1894-1900Conference paper (Refereed)
    Abstract [en]

    One major design goal in human-robot interaction is that the robots behave in an intelligent manner, preferably in a similar way as humans. This constraint must also be taken into consideration when the navigation system for the platform is developed. However, research in human-robot interaction is often restricted to other components of the system including gestures, manipulation, and speech. On the other hand, research for mobile robot navigation focuses primarily on the task of reaching a certain goal point in an environment. We believe that these two problems can not be treated separately for a personal robot that coexists with humans in the same surrounding. Persons move constantly while they are interacting with each other. Hence, also a robot should do that, which poses constraints on the navigation system. This type of navigation is the focus of this paper. Methods have been developed for a robot to join a group of people engaged in a conversation. Preliminary results show that the platform's moving patterns are very similar to the ones of the persons. Moreover, this dynamic interaction has been judged naturally by the test subjects, which greatly increases the perceived intelligence of the robot.

  • 9. Andersson, A.
    et al.
    Hagerup, T.
    Håstad, Johan
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Petersson, O.
    Tight bounds for searching a sorted array of strings2000In: SIAM journal on computing (Print), ISSN 0097-5397, E-ISSN 1095-7111, Vol. 30, no 5, p. 1552-1578Article in journal (Refereed)
    Abstract [en]

    Given a k-character query string and an array of n strings arranged in lexicographical order, computing the rank of the query string among the n strings or deciding whether it occurs in the array requires the inspection [GRAPHICS] characters in the worst case.

  • 10.
    Andersson, Birger
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Bider, I
    Perjons, Erik
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Integration of business process support with knowledge management - A practical perspective2004In: PRACTICAL ASPECTS OF KNOWLEDGE MANAGEMENT, PROCEEDINGS, BERLIN: SPRINGER , 2004, Vol. 3336, p. 227-238Conference paper (Refereed)
    Abstract [en]

    For knowledge management to be of use in an organization, it should be seamlessly incorporated in everyday business activities. Large parts of an organization's activities, especially on the operational level, are structured around business processes. Therefore, knowledge management needs to be integrated with these processes, which means that a computerized system that supports business processes should also support knowledge management. This paper reports on the experiences of implementing an integrated business process support system and knowledge management system into an organization. The implementation is the subject of a research project. The project's objective is to work out techniques for developing integrated process and knowledge management systems, and investigate effects of introducing such a system in operational practice, e.g., effects on productivity, internal cooperation, and democracy in organizational life.

  • 11.
    Andersson, Christer
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Numerical simulation of dendritic solidification using a phase field model2000Licentiate thesis, monograph (Other scientific)
  • 12.
    Andersson, Christer
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Phase-field Simulation of Dendritic Solidification2002Doctoral thesis, comprehensive summary (Other scientific)
  • 13. Andersson, G.
    et al.
    Engebretsen, L.
    Håstad, Johan
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    A new way of using semidefinite programming with applications to linear equations mod p2001In: Journal of Algorithms, ISSN 0196-6774, E-ISSN 1090-2678, Vol. 39, no 2, p. 162-204Article in journal (Refereed)
    Abstract [en]

    We introduce a new method of constructing approximation algorithms for combinatorial optimization problems using semidefinite programming. It consists of expressing each combinatorial object in the original problem as a constellation of vectors in the semidefinite program. When we apply this technique to systems of linear equations mod p with at most two variables in each equation, we can show that the problem is approximable within (1 - kappa (p))p, where kappa (p)> 0 for all p. Using standard techniques we also show that it is NP-hard to approximate the problem within a constant ratio, independent of p.

  • 14.
    Andersson, Gunnar
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Some new randomized approximation algorithms2000Doctoral thesis, monograph (Other scientific)
  • 15.
    Andersson, Mats
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Svärd, Kenneth
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Producer studies: informative web sites from the inside2004In: Proceedings of Interactive Computer Aided Learning (ICL), 2004, p. 1-12Conference paper (Refereed)
    Abstract [en]

    An emerging genre of web sites can be described with the following characteristics: asubject is well defined; the subject is well covered; a publicist takes responsibility forwhat is published; and the publicist has a certain authority within the field of the subject.Such sites can function as teaching tools or as substitutes for the user’s knowledge.In the long run, the user will know more about the subject, i.e. the site supportslifelong learning and learning on-demand. These sites seem to have an informative"mission" and are run by public authorities, corporations or other organizations.Subjects can be medical care, health, tourism, sports etc. This paper presents a studyof how producers work and experience their production of informative content. Theinterviews were conducted in 2004 with people employed at Swedish sites.

  • 16.
    Andersson, Ulf
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Time-Domain Methods for the Maxwell Equations2001Doctoral thesis, monograph (Other scientific)
  • 17.
    Andersson, Ulf
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Ekman, Per
    KTH.
    Öster, Per
    KTH.
    Performance and performance counters on the Itanium 2 - A benchmarking case study2004In: Parallel Computing: Software Technology, Algorithms, Architectures And Applications / [ed] Joubert, G; Nagel, WE; Peters, FJ; Walter, WV, 2004, Vol. 13, p. 517-524Conference paper (Refereed)
    Abstract [en]

    We study the performance of the Itanium 2 processor on a number of benchmarks from computational electromagnetics. In detail, we show how the hardware performance counters of the Itanium 2 can be used to analyze the behavior of a kernel code. Yee_bench, for the FDTD method. We also present performance results for a parallel FDTD code on a cluster of HP rx2600 Intel Itanium 2 based workstations. Finally we give results from a benchmark suite of an industrial time-domain code based on the FDTD method. Ail these results show that the Itanium 2/rx2600 is very well suited to the FDTD method due to its high main memory bandwidth.

  • 18.
    Andrae, Johan
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Edsberg, Lennart
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Numerical studies of wall effects with laminar methane flames2002In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921, Vol. 128, no 1-2, p. 165-180Article in journal (Refereed)
    Abstract [en]

    Wall effects in the combustion of lean methane mixtures have been studied numerically using the CHEMKIN software. To gain a deeper understanding of the flame-wall interaction in lean burn combustion, and in particular the kinetic and thermal effects, we have simulated lean and steady methane/air flames in a boundary layer flow. The gas-phase chemistry is modeled with the GRI mechanism version 1.2. Boundary conditions include an inert wall, a recombination wall and catalytic combustion of methane. Different pressures, wall temperatures and fuel-air ratios are used to address questions such as which part of the wall effects is most important at a given set of conditions. As the results are analyzed it can be seen that the thermal wall effects are more significant at the lower wall temperature (600 K) and the wall can essentially be modeled as chemical inert for the lean mixtures used. At the higher wall temperature (1,200 K), the chemical wall effects become more significant and at the higher pressure (10 atm) the catalytic surface retards homogeneous combustion of methane more than the recombination wall because of product inhibition. This may explain the increased emissions of unburned fuel observed in engine studies, when using catalytic coatings on the cylinder walls. The overall wall effects were more pronounced for the leaner combustion case (phi = 0.2). When the position of the reaction zone obtained from the boundary layer calculations is compared with the results from a one-dimensional premixed flame model, there is a small but significant difference except at the richer combustion case (phi = 0.4) at atmospheric pressure, where the boundary layer model may not predict the flame position for the given initial conditions.

  • 19.
    Aniander, Magnus
    et al.
    KTH, Superseded Departments, Industrial Economics and Management.
    Blomgren, Henrik
    KTH, Superseded Departments, Industrial Economics and Management.
    Handberg, Leif
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Investigating a new production technique: the case of digital printing1997In: Journal of prepress and printing technology, ISSN 1365-7321, Vol. 1, p. 30-38Article in journal (Refereed)
  • 20.
    Appelgren, Ester
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Convergence and divergence in media: different perspectives2004In: ICCC 8th International Conference on Electronic Publishing 2004,Brasilia, Brazil., 2004, p. 237-248Conference paper (Refereed)
    Abstract [en]

    A current issue in the media industry is coping with the effects of convergence. The concept ofconvergence is frequently used both in the academic field and within the media industry to denotethe ongoing restructuring of media companies as well as to describe the latest developments inmedia forms, distribution, and consumption. However, there is currently no generally accepteddefinition of the concept. Depending on the context, the meaning and connotations vary. Someresearchers suggest that convergence is a result of a change toward a more modern media societywhile others treat the concept as denoting the actual process toward a more efficient managementof the media value chain. This paper discusses various definitions of convergence, both in a historicalperspective and as it is used and understood in contemporary media and communications research,one aim being the evaluation of how the meaning of the concept has evolved during the past decade.The study is based on literature research and one conclusion is that convergence is a processdependent on current circumstances within society. The use of the concept has therefore developedfrom being mainly connected with digitalization in media technology to also include elements ofintegration, combination, competition and divergence. This paper suggests that convergence shouldbe seen as an ongoing process of media and media industry development that is dependent on and incontinuous interplay with a contrasting and complementary process, that of media divergence.

  • 21.
    Appelgren, Ester
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Möller, Kristina Sabelström
    Tidningsutgivarna, Stockholm.
    Nordqvist, Stig
    Tidningsutgivarna, Stockholm.
    E-Paper Production Workflow: Adapting Production Workflow Processes for Digital Newsprint2004In: Proceedings of the Technical Association of the Graphic Arts, TAGA, 2004, 2004, p. 181-208Conference paper (Refereed)
    Abstract [en]

    This study focuses on production flow for publishing in generic digital newsprint editions, such as e-paper, PDAs or on-line editions, by analyzing and mapping existing production workflow at three Swedish newspaper publishing companies covering the most common organizational types in the newspaper publishing industry today. Most newspaper publishing companies produce a range of electronic editions, all part of the digital newsprint family. In general, there exists two types of organizational production workflows - the integrated multiple channel workflow, and the separated, where the printed and the electronic workflows are detached, sometimes in totally separate organizations. Using scenarios, the aim is to propose a model for the production workflow of the electronic paper editions in newspaper publishing. The results indicate several possibilities for automation in the workflow. Furthermore, the study points out stages as challenges in the workflow where changes have to be done in order to introduce epaper as a publishing channel for news publishing. We will as an introduction, along with the workflow scenarios in this paper, also present a brief overview of the existing techniques for displaying content on electronic paper terminals.

  • 22.
    Appelgren, Ester
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Nordqvist, S.
    Tidningsutgivarna, Stockholm.
    Evaluating digital TV as a publishing channel for newspapers2003In: Proceedings of the Technical Association of the Graphic Arts, TAGA, 2003, 2003, p. 23-24Conference paper (Refereed)
    Abstract [en]

    Can there be synergies between newspapers and digital TV? What business synergies exist and are the technical formats reliable and flexible enough for cross media publishing? At the end of the 1990's, several Swedish newspapers applied for a license to broadcast digital TV. The major trend among newspapers during this time was to develop websites as a secondary publishing channel, and many companies withdrew their applications. Today, digital TV is again raising expectations. When digital TV broadcasting technology replaces analogue broadcasting, the media landscape will change. The conversion will offer new publishing and business opportunities for newspaper companies. We have studied three Swedish newspaper companies actively working with TV production, three major Nordic television companies, and five television broadcasting operators in Sweden. The objective is to give a wider perspective on the digital TV publishing market today, focusing on technical as well as on economical aspects. In addition, we have evaluated the next steps for newspaper companies interested in establishing themselves in the digital TV medium. The study indicates that among the viable strategies for small and medium sized newspapers are entering the digital TV business through text based services and using cross promotion in order to strengthen the brand.

  • 23.
    Appelö, Daniel
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Non-reflecting Boundary Conditions for Wave Propagation Problems2003Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    We consider two aspects of non-reflecting boundaryconditions for wave propagation problems. First we evaluate aproposed Perfectly Matched Layer (PML) method for thesimulation of advective acoustics. It is shown that theproposed PML becomes unstable for a certain combination ofparameters. A stabilizing procedure is proposed andimplemented. By numerical experiments the performance of thePML for a problem with nonuniform flow is investigated. Furtherthe performance for different types of waves, vorticity andsound waves, are investigated.

    The second aspect concerns spurious waves, which areintroduced by any discretization procedure. We constructdiscrete boundary conditions, that are nonreflecting for bothphysical and spurious waves, when combined with a fourth orderaccurate explicit discretization of one-way wave equations. Theboundary condition is shown to be GKS-stable. The boundaryconditions are extended to hyperbolic systems in two spacedimensions, by combining exact continuous non-reflectingboundary conditions and the one dimensional discretelynon-reflecting boundary condition. The resulting boundarycondition is localized by the standard Pad´eapproximation.

    Numerical experiments reveal that the resulting methodsuffers from boundary instabilities. Analysis of a relatedcontinuous problem suggests that the discrete boundarycondition can be stabilized by adding tangential viscosity atthe boundary. For the lowest order Pad´e approximation weare able to stabilize the discrete boundary condition.

  • 24.
    Appelö, Daniel
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Hagstrom, Thomas
    Construction of stable PMLs for general 2 x 2 symmetric hyperbolic systems2004In: Proceedings of the HYP2004 conference, 2004, p. 1-8Conference paper (Refereed)
    Abstract [en]

    The perfectly matched layer (PML) has emerged as animportant tool for accurately solving certain hyperbolic systems onunbounded domains. An open issue is whether stable PMLs can beconstructed in general. In this work we consider the specializationof our general PML formulation to 2 × 2 symmetric hyperbolicsystems in 2 + 1 dimensions. We show how to choose the layerparameters as functions of the coefficient matrices to guaranteestability.

  • 25.
    Appelö, Daniel
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Kreiss, Gunilla
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Discretely nonreflecting boundary conditions for higher order centered schemes for wave equations2003In: Proceedings of the WAVES-2003 conference, Berlin: Springer Verlag , 2003, p. 130-135Chapter in book (Other academic)
    Abstract [en]

    Using the framework introduced by Rawley and Colonius [2] we construct a nonreflecting boundary condition for the one-way wave equation spatially discretized with a fourth order centered difference scheme. The boundary condition, which can be extended to arbitrary order accuracy, is shown to be well posed. Numerical simulations have been performed showing promising results.

  • 26.
    Arnborg, Stefan
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Robust Bayesianism: Imprecise and Paradoxical Reasoning2004In: Proceedings of the Seventh International Conference on Information Fusion, FUSION 2004, 2004, p. 407-414Conference paper (Refereed)
    Abstract [en]

    We are interested in understanding the relationship between Bayesian inference and evidence theory, in particular imprecise and paradoxical reasoning. The concept of a set of probability distributions is central both in robust Bayesian analysis and in some versions of Dempster-Shafer theory. Most of the literature regards these two theories as incomparable. We interpret imprecise probabilities as imprecise posteriors obtainable from imprecise likelihoods and priors, both of which can be considered as evidence and represented with, e.g., DS-structures. The natural and simple robust combination operator makes all pairwise combinations of elements from the two sets. The DS-structures can represent one particular family of imprecise distributions, Choquet capacities. These are not closed under our combination rule, but can be made so by rounding. The proposed combination operator is unique, and has interesting normative and factual properties. We compare its behavior on Zadeh's example with other proposed fusion rules. We also show how the paradoxical reasoning method appears in the robust framework.

  • 27.
    Arnborg, Stefan
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Artman, Henrik
    Brynielsson, Joel
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Wallenius, Klas
    Information awareness in command and control: precision, quality, utility2000In: FUSION 2000: Proceedings of the Third International Conference on Information Fusion, 2000, p. THB1/25-THB1/32 vol.2Conference paper (Refereed)
    Abstract [en]

    In current command and control system design, the concept of information plays a central role. In order to find architectures for situation and threat databases making full use of all dimensions of information, the concept of information awareness must be understood. We consider and define some information attributes: measures of precision, quality and usability, and suggest some uses of these concepts. The analysis is Bayesian. A critical point is where subjective Bayesian probabilities of decision makers meet the objective sensor related Bayesian assessments of the system. This interface must be designed to avoid credibility problems.

  • 28. Aroyo, L
    et al.
    Dicheva, D
    Brusilovsky, P
    Diaz, P
    Dimitrova, V
    Duval, E
    Greer, J
    Hirashima, T
    Hoppe, U
    Houben, G J
    Ikeda, M
    Kay, J
    Kinshuk,
    Melis, E
    Mitrovic, T
    Naeve, Ambjörn
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Nykanen, O
    Paquette, G
    Retalis, S
    Sampson, D
    Sinitsa, K
    Soller, A
    Staab, S
    Vassileva, J
    Verdejo, F
    Wagner, G
    Workshop on applications of semantic web technologies for E-learning2004In: INTELLIGENT TUTORING SYSTEMS, PROCEEDINGS / [ed] Lester, JC; Vicari, RM; Paraguacu, F, BERLIN: SPRINGER , 2004, Vol. 3220, p. 912-912Conference paper (Refereed)
  • 29.
    Artman, Henrik
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Procurer usability requirements: Negotiations in contract development2002In: NordiCHI '02 Proceedings of the second Nordic conference on Human-computer interaction, 2002, p. 61-70Conference paper (Refereed)
    Abstract [en]

    This article describes a case study that examined one procurer's reasoning about and work with usability-related issues as well as the contractor's response to those requirements. The aim of this study was to examine the procurer's power to direct the system development process according to user-centred principles and indeed to point out its responsibility to use that power. The study elucidated the procurer's and the contractor's differing views of usability. The results suggest that the project leaders from the two organisations examined in this study had differing views of usability and that both approached usability more from a business perspective than from a user perspective. Furthermore, we found that the procurer valued user-centred activities less for their results than for the opportunity they gave to come in contact with the user's point of view and then to visualize the requirements concretely. We conclude this article with an analysis of some contradictions within and between the two organisations from a socio-cultural point of view. We suggest some mundane but nevertheless important requirements that procurers should think of when contracting consultants.

  • 30.
    Arvestad, Lars
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Adapting to nature: some improvements on alignment algorithms in computational biology1997Licentiate thesis, monograph (Other scientific)
  • 31.
    Arvestad, Lars
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Algorithms for biological sequence alignment1999Doctoral thesis, monograph (Other scientific)
  • 32.
    Arvestad, Lars
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Aligning coding DNA in the presence of frame-shift errors1997In: Combinatorial Pattern Matching, 1997, p. 180-190Conference paper (Other academic)
    Abstract [en]

    The problem of aligning two DNA sequences with respect to the fact that they are coding for proteins is discussed. Criteria for a good alignment of coding DNA, together with an algorithm that satisfies them, are presented. The algorithm is robust against frame-shifts and forgiving towards silent substitutions. The important choice of objective function is examined and several variants are proposed.

  • 33.
    Arvestad, Lars
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Berglund, Ann-Charlotte
    Stockholm Bioinformatics Center, Dept. of Biochemistry, Stockholm University.
    Lagergren, Jens
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Sennblad, Bengt
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Gene tree reconstruction and orthology analysis based on an integrated model for duplications and sequence evolution.2004In: Proceedings of the Annual International Conference on Computational Molecular Biology, RECOM, 2004, p. 326-335Conference paper (Refereed)
    Abstract [en]

    Gene tree and species tree reconstruction, orthology analysis and reconciliation, are problems important in multigenome-based comparative genomics and biology in general. In the present paper, we advance the frontier of these areas in several respects and provide important computational tools. First, exact algorithms are given for several probabilistic reconciliation problems with respect to the probabilistic gene evolutionmodel, previously developed by the authors. Until now, those problems were solved by MCMC estimation algorithms. Second, we extend the gene evolution model to the genesequence evolution model, by including sequence evolution. Third, we develop MCMC algorithms for the gene sequence evolution model that, given gene sequence data allows: (1) orthology analysis, reconciliation analysis, and gene tree reconstruction, w.r.t. a species tree, that balances a likely/unlikely reconciliation and a likely/unlikely genetree and (2) species tree reconstruction that balance a likely /unlikely reconciliation and a likely/unlikely gene trees. These MCMC algorithms take advantage of the exact algorithms for the gene evolution model. We have successfully tested our dynamical programming algorithms on real data for a biogeography problem. The MCMC algorithms perform very well both on synthetic and biological data.

  • 34.
    Arvestad, Lars
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Bruno, William
    Los Alamos National Laboratory.
    Estimation of Reversible Substitution Matrices from Multiple Pairs of Sequences1997In: Journal of Molecular Evolution, ISSN 0022-2844, E-ISSN 1432-1432, Vol. 45, no 6, p. 696-703Article in journal (Refereed)
    Abstract [en]

    We present a method for estimating the most general reversible substitution matrix corresponding to a given collection of pairwise aligned DNA sequences. This matrix can then be used to calculate evolutionary distances between pairs of sequences in the collection. If only two sequences are considered, our method is equivalent to that of Lanave et al. (1984). The main novelty of our approach is in combining data from different sequence pairs. We describe a weighting method for pairs of taxa related by a known tree that results in uniform weights for all branches. Our method for estimating the rate matrix results in fast execution times, even on large data sets, and does not require knowledge of the phylogenetic relationships among sequences. In a test case on a primate pseudogene, the matrix we arrived at resembles one obtained using maximum likelihood, and the resulting distance measure is shown to have better linearity than is obtained in a less general model.

  • 35.
    Atle, Andreas
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Numerical approximations of time domain boundary integral equation for wave propagation2003Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    Boundary integral equation techniques are useful in thenumerical simulation of scattering problems for wave equations.Their advantage over methods based on partial di.erentialequations comes from the lack of phase errors in the wavepropagation and from the fact that only the boundary of thescattering object needs to be discretized. Boundary integraltechniques are often applied in frequency domain but recentlyseveral time domain integral equation methods are beingdeveloped.

    We study time domain integral equation methods for thescalar wave equation with a Galerkin discretization of twodi.erent integral formulations for a Dirichlet scatterer. The.rst method uses the Kirchho. formula for the solution of thescalar wave equation. The method is prone to get unstable modesand the method is stabilized using an averaging .lter on thesolution. The second method uses the integral formulations forthe Helmholtz equation in frequency domain, and this method isstable. The Galerkin formulation for a Neumann scattererarising from Helmholtz equation is implemented, but isunstable.

    In the discretizations, integrals are evaluated overtriangles, sectors, segments and circles. Integrals areevaluated analytically and in some cases numerically. Singularintegrands are made .nite, using the Du.y transform.

    The Galerkin discretizations uses constant basis functionsin time and nodal linear elements in space. Numericalcomputations verify that the Dirichlet methods are stable, .rstorder accurate in time and second order accurate in space.Tests are performed with a point source illuminating a plateand a plane wave illuminating a sphere.

    We investigate the On Surface Radiation Condition, which canbe used as a medium to high frequency approximation of theKirchho. formula, for both Dirichlet and Neumann scatterers.Numerical computations are done for a Dirichlet scatterer.

  • 36. Aumann, Y.
    et al.
    Håstad, Johan
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Rabin, M. O.
    Sudan, M.
    Linear-consistency testing2001In: Journal of computer and system sciences (Print), ISSN 0022-0000, E-ISSN 1090-2724, Vol. 62, no 4, p. 589-607Article in journal (Refereed)
    Abstract [en]

    We extend the notion of linearity testing to the task of checking linear consistency of multiple functions. Informally, functions are linear if their graphs form straight lines on the plane. Two such functions are consistent if the lines have the same slope. We propose a variant of a test of M. Blum et al. (J. Comput. System Sci. 47 (1993), 549-595) to check the linear consistency of three functions f(1). f(2). f(3) mapping a finite Abelian group G to an Abelian group H: Pick x, y is an element of G uniformly and independently at random and check if f(1)(x) + f(2)(y) = f(3)(x + y). We analyze this test for two cases: (1) G and H are arbitrary Abelian groups and (2) G = F-2(n) and H = F-2. Questions bearing close relationship to linear-consistency testing seem to hav e been implicitly considered in recent work on the construction of PCPs and in particular in the work of J. Hastad [9] (in Proceedings of the Twenty-Ninth Annual ACM Symposium on Theory of Computing. El Paso. Texas, 4-6 May 1997, pp. 1-10). It is abstracted explicitly for the first time here. As an application of our results we give yet another new and tight characterization of NP. namely For All epsilon > 0, NP = MIP1-epsilon 1/2 [O(log n), 3, 1]. That is, every language in NP has 3-prover 1-round proof systems in which the verifier tosses O(log n) coins and asks each of the three provers one question each. The provers respond with one bit each such that the verifier accepts instance of the language with probability 1 - epsilon and rejects noninstances with probability at least;. Such a result is of some interest in the study of probabilistically checkable proofs.

  • 37.
    Aurell, Erik
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Fanelli, D.
    Gurbatov, S. N.
    Moshkov, A. Y.
    The inner structure of Zeldovich pancakes2003In: Physica D: Non-linear phenomena, ISSN 0167-2789, E-ISSN 1872-8022, Vol. 186, no 04-mar, p. 171-184Article in journal (Refereed)
    Abstract [en]

    The evolution of a planar perturbation in a Einstein-de Sitter Universe is studied using a previously introduced Lagrangian scheme. An approximate discrete dynamical system is derived, which describes the mass agglomeration process. Quantitative predictions for the late-time mean density profile are obtained therefrom, and validated by numerical simulations. A simple but important result is that the characteristic scale of a mass agglomeration is an increasing function of cosmological time t. For one kind of initial conditions we further find a scaling regime for the density profile of a collapsing object. These results are compared with analogous investigations for the adhesion model (Burgers equation with positive viscosity). We further study the mutual motion of two mass agglomerations, and show that they oscillate around each other for long times, like two heavy particles. Individual particles in the two agglomerations do not mix effectively on the time scale of the inter-agglomeration motion.

  • 38.
    Aurell, Erik
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Fanelli, D.
    Muratore-Ginanneschi, P.
    On the dynamics of a self-gravitating medium with random and non-random initial conditions2001In: Physica D: Non-linear phenomena, ISSN 0167-2789, E-ISSN 1872-8022, Vol. 148, no 04-mar, p. 272-288Article in journal (Refereed)
    Abstract [en]

    The dynamics of a 1D self-gravitating medium with initial density almost uniform is studied. Numerical experiments are performed with ordered and with Gaussian random initial conditions. The phase space portraits art shown to be qualitatively similar to shock waves, in particular with initial conditions of Brownian type. The PDF of the mass distribution is investigated.

  • 39.
    Aurell, Erik
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Muratore-Ginnaneschi, Paolo
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Growth-Optimal Strategies with Quadratic Friction Over Finite-Time Investment Horizons2004In: International Journal of Theoretical and Applied Finance, ISSN 0219-0249, Vol. 7, no 5, p. 645-657Article in journal (Refereed)
    Abstract [en]

    We investigate the growth optimal strategy over a finite time horizon for a stock and bond portfolio in an analytically solvable multiplicative Markovian market model. We show that the optimal strategy consists in holding the amount of capital invested in stocks within an interval around an ideal optimal investment. The size of the holding interval is determined by the intensity of the transaction costs and the time horizon.

  • 40.
    Aurell, Erik
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Sneppen, K.
    Epigenetics as a first exit problem2002In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 88, no 4Article in journal (Refereed)
    Abstract [en]

    We develop a framework to discuss the stability of epigenetic states as first exit problems in dynamical systems with noise. We consider in particular the stability of the lysogenic state of the A prophage. The formalism defines a quantitative measure of robustness of inherited states.

  • 41. Babuska, I.
    et al.
    Liu, K. M.
    Tempone, Raul
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Solving stochastic partial differential equations based on the experimental data2003In: Mathematical Models and Methods in Applied Sciences, ISSN 0218-2025, Vol. 13, no 3, p. 415-444Article in journal (Refereed)
    Abstract [en]

    We consider a stochastic linear elliptic boundary value problem whose stochastic coefficient a(x, omega) is expressed by a finite number N-KL of mutually independent random variables, and transform this problem into a deterministic one. We show how to choose a suitable N-KL which should be as low as possible for practical reasons, and we give the a priori estimates for modeling error when a(x, omega) is completely known. When a random function a(x, omega) is selected to fit the experimental data, we address the estimation of the error in this selection due to insufficient experimental data. We present a simple model problem, simulate the experiments, and give the numerical results and error estimates.

  • 42. Babuska, I.
    et al.
    Tempone Olariaga, Raul
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Zouraris, Georgios
    Galerkin finite element approximations of stochastic elliptic partial differential equations2004In: SIAM Journal on Numerical Analysis, ISSN 0036-1429, E-ISSN 1095-7170, Vol. 42, no 2, p. 800-825Article in journal (Refereed)
    Abstract [en]

    We describe and analyze two numerical methods for a linear elliptic problem with stochastic coefficients and homogeneous Dirichlet boundary conditions. Here the aim of the computations is to approximate statistical moments of the solution, and, in particular, we give a priori error estimates for the computation of the expected value of the solution. The first method generates independent identically distributed approximations of the solution by sampling the coefficients of the equation and using a standard Galerkin finite element variational formulation. The Monte Carlo method then uses these approximations to compute corresponding sample averages. The second method is based on a finite dimensional approximation of the stochastic coefficients, turning the original stochastic problem into a deterministic parametric elliptic problem. A Galerkin finite element method, of either the h- or p-version, then approximates the corresponding deterministic solution, yielding approximations of the desired statistics. We present a priori error estimates and include a comparison of the computational work required by each numerical approximation to achieve a given accuracy. This comparison suggests intuitive conditions for an optimal selection of the numerical approximation.

  • 43.
    Bellander, Mats
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Handberg, Leif
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Koulouvari, Panagiota
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Identifying requirements for the implementation of production management systems in graphic arts companies1999In: Proceedings of the 31th conference of the technical association of graphic arts, 1999, p. 36-54Conference paper (Other academic)
  • 44. Bellander, Mats
    et al.
    Handberg, Leif
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Stenberg, Johan
    KTH, School of Computer Science and Communication (CSC), Media technology and interaction design.
    Workflow analyses in commercial printing: methods and results1997In: Proceedings of the 24th conference of the international association of research institutes of the graphic arts industry / [ed] Bristow, J.A., 1997, p. 163-176Conference paper (Refereed)
  • 45. Bem, T.
    et al.
    Cabelguen, J. M.
    Ekeberg, Örjan
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Grillner, S.
    From swimming to walking: a single basic network for two different behaviors2003In: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 88, no 2, p. 79-90Article in journal (Refereed)
    Abstract [en]

    In this paper we consider the hypothesis that the spinal locomotor network controlling trunk movements has remained essentially unchanged during the evolutionary transition from aquatic to terrestrial locomotion. The wider repertoire of axial motor patterns expressed by amphibians would then be explained by the influence from separate limb pattern generators, added during this evolution. This study is based on EMG data recorded in vivo from epaxial musculature in the newt Pleurodeles waltl during unrestrained swimming and walking, and on a simplified model of the lamprey spinal pattern generator for swimming. Using computer simulations, we have examined the output generated by the lamprey model network for different input drives. Two distinct inputs were identified which reproduced the main features of the swimming and walking motor patterns in the newt. The swimming pattern is generated when the network receives tonic excitation with local intensity gradients near the neck and girdle regions. To produce the walking pattern, the network must receive (in addition to a tonic excitation at the girdles) a phasic drive which is out of phase in the neck and tail regions in relation to the middle part of the body. To fit the symmetry of the walking pattern, however, the intersegmental connectivity of the network had to be modified by reversing the direction of the crossed inhibitory pathways in the rostral part of the spinal cord. This study suggests that the 'input drive required for the generation of the distinct walking pattern could, at least partly, be attributed to mechanosensory feedback received by the network directly from the intraspinal stretch-receptor system. Indeed, the input drive required resembles the pattern of activity of stretch receptors sensing the lateral bending of the trunk, as expressed during walking in urodeles. Moreover, our results indicate that a nonuniform distribution of these stretch receptors along the trunk can explain the discontinuities exhibited in the swimming pattern of the newt. Thus, original network controlling axial movements not only through a direct coupling at the central level but also via a mechanical coupling between trunk and limbs, which in turn influences the sensory signals sent back to the network. Taken together, our findings support the hypothesis of a phylogenetic conservatism of the spinal locomotor networks generating axial motor patterns from agnathans to amphibians.

  • 46. Benamou, J. D.
    et al.
    Collino, F.
    Runborg, Olof
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Numerical microlocal analysis of harmonic wavefields2004In: Journal of Computational Physics, ISSN 0021-9991, E-ISSN 1090-2716, Vol. 199, no 2, p. 717-741Article in journal (Refereed)
    Abstract [en]

    We present and test a numerical method which, given an analytical or numerical solution of the Helmholtz equation in a neighborhood of a fixed observation point and assuming that the geometrical optics approximation is relevant, determines at this point the number of crossing rays and computes their directions and associated complex amplitudes.

  • 47.
    Berg, Christer
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    On oracles and circuits1997Doctoral thesis, monograph (Other scientific)
  • 48.
    Berggren, Ulf
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Pappersmodellen som utgångspunkt för utformning av skrivsamar- betsverktyg1999Licentiate thesis, monograph (Other scientific)
  • 49.
    Bergholtz, Maria
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Jayaweera, Prasad M.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Johannesson, Paul
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Wohed, Petia
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Modelling institutional, communicative and physical domains in agent oriented information systems2004In: Lect Notes Artif Intell, 2004, p. 189-205Conference paper (Refereed)
    Abstract [en]

    One role of a business system is to provide a representation of a Universe of Discourse, which reflects its structure and behaviour. An equally important function of the system is to support communication within an organisation, by structuring and co-ordinating the actions performed by the organisation's agents. These two roles of a business system may be represented in terms of business and process models, i.e. separating the declarative aspects from the procedural control flow aspects of the system. Although this separation of concerns has many advantages, the differences in representation techniques and focus of the two model types constitute a problem in itself. Abstracting business semantics out of, for instance, technical messaging protocols poses severe problems for business analysts. The main contribution of this paper is a unified framework based on agent oriented concepts for facilitating analysis and integration of business models and process models in a systematic way. The approach suggested bridges the gap between the declarative and social/ economic aspects of a business model and the procedural and communicative aspects of a process model in a technology independent manner. We illustrate how our approach can simplify business and process models integration, process specification, process pattern interpretation and process choreography.

  • 50. Berman, F.
    et al.
    Chien, A.
    Cooper, K.
    Dongarra, J.
    Foster, I.
    Gannon, D.
    Johnsson, Lennart
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Kennedy, K.
    Kesselman, C.
    Mellor-Crummey, J.
    Reed, D.
    Torczon, L.
    Wolski, R.
    The GrADS project: Software support for high-level grid application development2001In: The international journal of high performance computing applications, ISSN 1094-3420, E-ISSN 1741-2846, Vol. 15, no 4, p. 327-344Article in journal (Refereed)
    Abstract [en]

    Advances in networking technologies will soon make it possible to use the global information infrastructure in a qualitatively different way-as a computational as well as an information resource. As described in the recent book The Grid: Blueprint for a New Computing Infrastructure, this Grid will connect the nation's computers, databases, instruments, and people in a seamless web of computing and distributed intelligence, which can be used in an on demand fashion as a problem-solving resource in many fields of human endeavor-and, in particular, science and engineering. The availability of grid resources will give rise to dramatically new classes of applications, in which computing resources are no longer localized but, rather, distributed, heterogeneous, and dynamic; computation is increasingly sophisticated and multidisciplinary; and computation is integrated into our daily lives and, hence, subject to stricter time constraints than at present. The impact of these new applications will be pervasive, ranging from new systems for scientific inquiry, through computing support for crisis management, to the use of ambient computing to enhance personal mobile computing environments. To realize this vision, significant scientific and technical obstacles must be overcome. Principal among these is usability. The goal of the Grid Application Development Software (GrADS) project is to simplify distributed heterogeneous computing in the same way that the World Wide Web simplified information sharing over the Internet. To that end, the project is exploring the scientific and technical problems that must be solved to make it easier for ordinary scientific users to develop, execute, and tune applications on the Grid. In this paper, the authors describe the vision and strategies underlying the GrADS project, including the base software architecture for grid execution and performance monitoring, strategies and tools for construction of applications from libraries of grid-aware components, and development of innovative new science and engineering applications that can exploit these new technologies to run effectively in grid environments.

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