Change search
Refine search result
12 1 - 50 of 89
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Amouzgar, Kaveh
    et al.
    University of Skovde, Jonkoping University.
    Strömberg, Niclas
    University West, Department of Engineering Science, Division of Welding Technology. Jonkoping University, Orebro Univ, University University West - Sweden.
    An approach towards generating surrogate models by using RBFN with a priori bias2014In: PROCEEDINGS OF THE ASME INTERNATIONAL DESIGN ENGINEERING TECHNICAL CONFERENCES AND COMPUTERS AND INFORMATION IN ENGINEERING CONFERENCE, 2014, VOL 2B, AMER SOC MECHANICAL ENGINEERS , 2014, Vol. 2BConference paper (Refereed)
    Abstract [en]

    In this paper, an approach to generate surrogate models constructed by radial basis function networks (RBFN) with a priori bias is presented. RBFN as a weighted combination of radial basis functions only, might become singular and no interpolation is found. The standard approach to avoid this is to add a polynomial bias, where the bias is defined by imposing orthogonality conditions between the weights of the radial basis functions and the polynomial basis functions. Here, in the proposed a priori approach, the regression coefficients of the polynomial bias are simply calculated by using the normal equation without any need of the extra orthogonality prerequisite. In addition to the simplicity of this approach, the method has also proven to predict the actual functions more accurately compared to the RBFN with a posteriori bias. Several test functions, including Rosenbrock, Branin-Hoo, Goldstein-Price functions and two mathematical functions (one large scale), are used to evaluate the performance of the proposed method by conducting a comparison study and error analysis between the RBFN with a priori and a posteriori known biases. Furthermore, the aforementioned approaches are applied to an engineering design problem, that is modeling of the material properties of a three phase spherical graphite iron (SGI). The corresponding surrogate models are presented and compared.

  • 2.
    Arvemo, Tobias
    et al.
    University West, School of Business, Economics and IT, Divison of Law, Economics, Statistics and Politics.
    Gråsjö, Urban
    University West, School of Business, Economics and IT, Divison of Law, Economics, Statistics and Politics.
    Employment and Economic Activity in Different Swedish Border Regions2015In: Uddevalla Symposium 2015. Regional Development in an International Context. Regional, National, Cross Border and International Factors for Growth and Development: Revised papers presented at the 18th Uddevalla Symposium, 11-13 June, Sönderborg, Denmark / [ed] Iréne Bernhard, Trollhättan: University West , 2015, p. 45-57Conference paper (Refereed)
    Abstract [en]

    This study investigate how the effect of cross border activities between Sweden and its three Nordic neighbours influence the Swedish local economies along the border using municipal data from 2009. Two measures for the local economies are examined, economic activity (measured by gross pay per inhabitant) and employment rates. The Swedish border regions where divided into four regions: The Swedish border to Finland, The Swedish border to the part of Norway not included in the Oslo labour market, The Swedish border to the Oslo labour market, and the Swedish-Danish border region. The regression models show how the the regions compare to the Swedish average when controlled for market structure and accessibility to population. For Sweden's border regions to Denmark and the Oslo labour market there are significant improvements in both economic activity and employment rates when the border activity is included. The improvement is highest for the Oslo border regions. For the Swedish border to Finland and to the part of Norway not included inte the Olso labour market the border activity has no significant influence on either economic activity or employment rates.

  • 3.
    Arvemo, Tobias
    et al.
    University West, Department of Economics and IT, Division of Law, Politics and Economics.
    Gråsjö, Urban
    University West, Department of Economics and IT, Division of Law, Politics and Economics.
    University Colleges Effect on Municipal Growth in Swedish Middle-sized Municipalities2008In: Uddevalla Symposium 2008: Spatial Dispersed Production and Network Governance: Revised papers presented at the 11th Uddevalla Symposium, 15-17 May, 2008, Kyoto, Japan / [ed] Iréne Bernhard, Trollhättan: University West , 2008, p. 85-98Conference paper (Refereed)
    Abstract [en]

    The main purpose in this paper is to study to what extent accessibility to R&D is an important factor of explaining municipal economic growth. Of special interests is the question whether, the effect of company (private) R&D efforts on economic growth differ if a university college is present in the municipality or not. Therefore the empirical analysis is conducted on a reduced dataset (92 out of 290 municipalities), containing only middle-sized municipalities without traditional ´old´ universities. The idea of the selection process was to find two sets of comparable municipalities with one containing municipalities with university colleges and one with municipalities without university colleges. In the empirical analysis a knowledge production function is estimated with the difference in Gross Municipal Product, GMP, between 1993 and 2001 as the output. In order to account for the importance of proximity, the explanatory variables are expressed as accessibilities to university and company R&D. The total accessibility is then decomposed into local, intra-regional and inter-regional accessibility to R&D. The main results show that local and intra-regional accessibility to company R&D has positive effects on economic growth. On the other hand, local accessibility to university R&D is of no importance, while there are influential effects of intra-regional university R&D. Moreover, the presence of university college R&D activities decreases the importance of the local accessibilitiy to company R&D or put it differently, local accessibility to company R&D is more important in municipalitites without university college activities.

  • 4.
    Björkholdt, Elise
    et al.
    University West, Department of Technology, Mathematics and Computer Science.
    Lundström, Patrik
    University West, Department of Technology, Mathematics and Computer Science.
    Generalizations of the normal basis theorem2004In: Mathematica Scandinavica, ISSN 0025-5521, E-ISSN 1903-1807, Vol. 94, p. 5p. 185-190Article in journal (Refereed)
  • 5.
    Choquet, Isabelle
    et al.
    University West, Department of Engineering Science.
    Lucquin-Desreux, Brigitte
    University Pierre and Marie Curie, Paris, France.
    Non equilibrium ionization in magnetized two-temperature thermal plasma2011In: Kinetic and Related Models, ISSN 1937-5093, E-ISSN 1937-5077, ISSN 1, Vol. 4, no 3, p. 669-700Article in journal (Refereed)
    Abstract [en]

    A thermal plasma is studied accounting for both impact ionization, and an electromagnetic field. This plasma problem is modeled based on a system of Boltzmann type transport equations. Electron-neutral collisions are assumed to be much more frequently elastic than inelastic, to complete previous investigations of thermal plasma . A viscous hydrodynamic/diffusion limit is derived in two stagesdoing an Hilbert expansion and using the  Chapman-Enskog method. The resultant viscous fluid model is characterized by two temperatures, and non equilibrium ionization. Its diffusion coefficients depend on the magnetic field, and can be computed explicitely.

  • 6.
    Edstorp, Marcus
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    A Comparison between Moving Mesh Implementations for Metal Deposition Simulations2006In: Proceedings of the Nordic COMSOL Conference: Lyngby, Denmark, 2006, p. 107-110Conference paper (Other academic)
  • 7.
    Edstorp, Marcus
    University West, Department of Engineering Science, Division of Production Engineering.
    An Investigation of Mesh Moving Methods for Simulating the Deformation of Incompressible Fluid Bodies2009In: COMSOL Conference: 14-16 okt. 2009, Milan, 2009Conference paper (Other academic)
    Abstract [en]

    In this article we apply a finite element method for approximating the geometrical deformation of a two dimensional incompressible fluid body the flow velocity of which is not constrained along its top boundary. As a pressure force is applied on the free boundary, the domain occupied by the fluid deforms. There are several well established methods for treating this type of problem. The purpose of the present work is to investigate the computational efficiency of a number domain-mapping methods, which are akin to many solid mechanical applications involving large deformations, in that they employ a mapping of the initial configuration range onto the current. However, in fluid dynamical applications the deformation of the fluid body may be very large and contain several vortices. When employing domain-mapping methods, the spatial representations of the element domains are attached to the motion, and the Lagrange formulation is therefore inadequate. Instead we wish to find a motion which minimizes the element deformations and the computational complexity of the problem, while satisfying the kinematic constraint along the boundaries.

     

  • 8.
    Edstorp, Marcus
    University West, Department of Engineering Science, Division of Production Engineering.
    Weld Pool Simulations2008Licentiate thesis, monograph (Other academic)
    Abstract [en]

    This investigation is devoted to the study of welding and its effect on the workpiece, focusing on the thermo and fluid dynamical phenomena occuring during a autogenous or nonautogenous arc fusion welding process. Its aim is to simulate the behaviour of the weld pool and analyze the consequence of the solid-liquid phase change, thus obtaining a methodology for predicting the appearance of weld defects related to solidification and cooling. In order to accomplish this, we solve equations governing a number of continuum mechanical and electromagnetical quantities, as well as consider the motion of the freely moving boundary of the weld pool. Since the state of these quantities is strongly influenced by phenomena such as arc and droplet impingement, non-isothermal phase change, surface tension, Marangoni forces and Lorentz forces, much effort is necessarily devoted to the modelling of the corresponding fluxes and sources, as well as to the implementation of computationally efficient techniques for simulating the geometrical deformation of the workpiece, which in our setting is entirely determined by the motion of the weld pool surface.

    Common to all arc fusion welding processes is the employment of a welding arc. Many techniques rely on the arc to clean and shield the workpiece during the process, however in this study we consider it to be its main purpose to cause the local increase of thermal energy that is required for the establishment of the weld pool, and also to exert the mechanical forces that provoke the subsequent fluid flow which enhances heat transfer and facilitates weld penetration. The physics of the welding arc itself is quite intricate, and although the modelling of the arc is not the prime objective of this research project, we conclude that arc forces act on the pool surface, and that the investigation of the arc behaviour is important insofar that it provides input to the pool model and thus enables a more accurate prediction of the quality of the weldment that is created once the pool has solidified

  • 9.
    Eshagh, Mehdi
    Royal Institute of Technology Division of Geodesy .
    On the estimation of variance in unstable condition adjustment models2011In: Acta Geodaetica et Geophysica Hungarica, ISSN 1217-8977, E-ISSN 1587-1037, ISSN 1217-8977, Vol. 46, no 1, p. 71-83Article in journal (Refereed)
    Abstract [en]

    Estimation of variance in an ordinary adjustment model is straightforward, but if the model becomes unstable or ill-conditioned its solution and the variance of the solution will be very sensitive to the errors of observations. This sensitivity can be controlled by stabilizing methods but the results will be distorted due to stabilization. In this paper, stabilizing an unstable condition model using Tikhonov regularization, the estimations of variance of unit weight and variance components are investigated. It will be theoretically proved that the estimator of variance or variance components has not the minimum variance property when the model is stabilized, but unbiased estimation of variance is possible. A simple numerical example is provided to show the performance of the theory.

    |

  • 10.
    Eshagh, Mehdi
    et al.
    University West, Department of Engineering Science, Division of Computer, Electrical and Surveying Engineering. Royal Institute of Technology, Division of Geodesy, Stockholm, Sweden .
    Lars E:, Sjöberg
    Royal Institute of Technology, Division of Geodesy, Stockholm, Sweden .
    The modified best quadratic unbiased non-negative estimator (MBQUNE) of variance components2008In: Studia Geophysica et Geodaetica, ISSN 0039-3169, E-ISSN 1573-1626, Vol. 52, no 3, p. 305-320Article in journal (Refereed)
    Abstract [en]

    Estimated variance components may come out as negative numbers without physical meaning. One way out of this problem is to use non-negative methods. Different approaches have been presented for the solution. Sjöberg presented a method of Best Quadratic Unbiased Non-Negative Estimator (BQUNE) in the Gauss-Helmert model. This estimator does not exist in the general case. Here we present the Modified BQUNE (MBQUNE) obtained by a simple transformation from the misclosures used in the BQUE to residuals. In the Gauss-Markov adjustment model the BQUNE and MBQUNE are identical, and they differ in condition and Gauss-Helmert models only by a simple transformation. If the observations are composed of independent/disjunctive groups the MBQUNE exists in any adjustment model and it carries all the properties of the BQUNE (when it exists). The presented variance component models are tested numerically in some simple examples. It is shown that the MBQUNE works well for disjunctive groups of observations.

  • 11.
    Flensburg, Per
    et al.
    University West, School of Business, Economics and IT, Divison of Informatics.
    Holl, Alfred
    Technische Hochschule Nürnberg Georg Simon Ohm / University Nuremberg, Germany.
    Das älteste gedruckte schwedische Rechenbuch (Aegidius Aurelius, Arithmetica, Uppsala 1614): (Aegidius Aurelius, Arithmetica, Uppsala 1614)2017In: Tagungsband zum wissenschaftlichen Kolloquium vom 21.–23. April 2017 in der Berg- und Adam-Ries-Stadt Annaberg-Buchholz / [ed] Gebhardt, Rainer, Annaberg-Buchholz: Adam-Ries-Bund , 2017, p. 313-326Conference paper (Other academic)
  • 12.
    Gellerstedt, Martin
    University West, School of Business, Economics and IT, Division of Computer Science and Informatics.
    M12: Medicinsk statistik2004 (ed. 1)Book (Other academic)
  • 13.
    Gellerstedt, Martin
    University West, Department of Studies of Work, Economics and Health.
    Statistical issues: significantly important in medical research.2002In: Allergy. European Journal of Allergy and Clinical Immunology, ISSN 0105-4538, E-ISSN 1398-9995, Vol. 57, no 2, p. 76-82Article, review/survey (Other academic)
  • 14.
    Gellerstedt, Martin
    University West, Department of Economics and IT, Division of Computer Science and Informatics.
    Statistiska metoder för kvalitetsutveckling1997 (ed. 1)Book (Other academic)
  • 15.
    Gellerstedt, Martin
    et al.
    University West, School of Business, Economics and IT, Division of Computer Science and Informatics.
    Svensson, Lars
    University West, School of Business, Economics and IT, Division of Computer Science and Informatics.
    Www means win win win in education: some experiences from online courses in applied statistics2010In: OZCOTS 2010 Proceedings of the 7th Australian Conferenceon Teaching Statistics / [ed] Helen MacGillivray & Brian Phillips, Statistical society of Australia , 2010, p. 51-56Conference paper (Refereed)
    Abstract [en]

    This paper reports on the experiences from online courses in applied statistics. The courses were designed with the ambition of making studies in statistics, fun, interesting, useful, not that difficult and directly supported the possibility to combine studies and work. When designing the courses we considered three dimensions: "pedagogies","community" and "structure". Experiences after giving a first-year course three times show that the online course succeeds in attracting new studen ts since 90% of the participants would not be able to follow an on-campus course and 62% worked full time.

    The pedagogies were highly appreciated because focusing on the interpretation of results and using computer analyses really changed the prejudices about statistics. Structure and prompt feedback was experienced as important factors. It was possible to combine online studies with employment, and the student completion rate was (84%, 55% and 61%), with a potential for further improvements.

  • 16.
    Gillerstedt, Monica
    et al.
    University West, Department of Social and Behavioural Studies.
    Isaksson, Anders
    University West, Department of Social and Behavioural Studies, Division for Educational Science and Languages.
    Gymnasielevers problem med procenträkning.2009Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Undersökningen handlar om gymnasieelevers svårigheter med procentavsnittet i matematik. Syftet var att undersöka vilka svårigheter eleverna har att lösa olika sorters räkneuppgifter av procentkaraktär. Vi ville även veta om det skiljer i svårighet att lösa sifferuppgifter respektive textuppgifter samt hur det är med den matematiska begreppsförståelsen. Studien är gjord på två gymnasieskolor i Västsverige och omfattar 68 elever från fyra olika klasser i årskurs 1 på teknikprogrammet. Samtliga elever har svarat på ett skriftligt test i form av ett diagnostiskt prov och av dessa har sedan 19 elever också intervjuats. Den skriftliga diagnosen bestod av uppgifter av följande fem typer: Att räkna ut delen, då det hela och procenttalet är kända. Att räkna ut det hela, då delen och procenttalet är kända. Att räkna ut procenttalet, då delen och det hela är kända. Begreppen procent och procentenheter. Kombinationer och räkning med procent i flera steg. Elevernas svar har granskats och analyserats med utgångspunkt från Kilpatrick, Swafford och Bradfords (2001) samt Mölleheds (2001) forskning vars arbeten lyfter fram olika färdigheter och påverkansfaktorer som har betydelse för elevernas resultat vid problemlösning i matematik. Vi har funnit att de flesta elever inte har så stora problem när det gäller de enklare uppgifterna. De problem som finns här består mest av missförstånd av texten, låg uppmärksamhet och bristande räkneförmåga. De lite mer krävande uppgifterna avslöjar desto fler svårigheter. Både antalet svårigheter och antalet elever med svårigheter ökar. I diagnosen finner vi exempel på osäkerhet kring Kilpatricks et al. (2001) alla matematiska färdigheter samt flera av Mölleheds (2001) påverkansfaktorer. Svårigheterna består i osäkerhet att räkna på rätt sätt och att tolka det uträknade värdet för att kunna svara på den ställda frågan. En textuppgift med helheter och delar som måste byta relation under lösningen av problemet ställer till bekymmer för många. Ingen av de undersökta eleverna har ritat upp och visualiserat i sina uträkningar vilket är en brist då det hade förenklat förståelsen av texten. Vi har även funnit att det finns problem med att på ett korrekt sätt ställa upp det bråk som räknar ut procenttalet, då delen och det hela är kända. En del elever vill gärna ha den stora delen i nämnaren oavsett fråga. Det finns även brister i den matematiska begreppsförståelsen vilken är av stor betydelse för problemlösning. Skillnaden mellan procent och procentenheter är ett sådant exempel. Begreppet procentenheter har gett stora svårigheter för eleverna att tolka och beräkna liksom behandlingen av olika förändringsfaktorer.

  • 17.
    Guevara-Garca, Alfredo
    et al.
    McMaster University, Department of Chemistry and Chemical Biology.
    Echegaray, Eleonora
    Pontificia Universidad Catlica de Chile, Facultad de Qumica, Laboratorio de Qumica Terica Computacional (QTC).
    Toro-Labbe, Alejandro
    Pontificia Universidad Catlica de Chile, Facultad de Qumica, Laboratorio de Qumica Terica Computacional (QTC).
    Jenkins, Samantha
    University West, School of Business, Economics and IT, Division of Computer Science and Informatics.
    Kirk, Steven R.
    University West, School of Business, Economics and IT, Division of Computer Science and Informatics.
    Ayers, Paul W.
    McMaster University, Department of Chemistry and Chemical Biology.
    Pointing the way to the products Comparison of the stress tensor and the second-derivative tensor of the electron density2011In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 134, no 23, p. 234106-Article in journal (Refereed)
    Abstract [en]

    The eigenvectors of the electronic stress tensor can be used to identify where new bond paths form in a chemical reaction. In cases where the eigenvectors of the stress tensor are not available, the gradient-expansion- approximation suggests using the eigenvalues of the second derivative tensor of the electron density instead; this approximation can be made quantitatively accurate by scaling and shifting the second-derivative tensor, but it has a weaker physical basis and less predictive power for chemical reactivity than the stress tensor. These tools provide an extension of the quantum theory of atoms and molecules from the characterization of molecular electronic structure to the prediction of chemical reactivity. © 2011 American Institute of Physics.

  • 18.
    Hansbo, Anita
    et al.
    University West, Department of Technology, Mathematics and Computer Science.
    Hansbo, Peter
    Hansson, Mats G.
    A finite element method on composite grids based on Nitsche's method2002Report (Other (popular science, discussion, etc.))
  • 19.
    Kiamehr, Ramin
    et al.
    Department of Geodesy and Geomatics, Zanjan University, Iran.
    Eshagh, Mehdi
    Royal Institute of Technology, Stockholm, Sweden.
    Estimating variance components of ellipsoidal, orthometric and geoidalheights through the GPS/levelling Network in Iran2008In: Journal of the Earth and Space Physics, Vol. 34, no 3, p. 1-13Article in journal (Refereed)
    Abstract [en]

    The Best Quadratic Unbiased Estimation (BQUE) of variance components in the Gauss-Helmert model is used to combine adjustment of GPS/levelling and geoid to determinethe individual variance components for each of the three height types. Through theresearch, different reasons for achievement of the negative variance components werediscussed and a new modified version of the Best Quadratic Unbiased Non-negativeEstimator (MBQUNE) was successfully developed and applied. This estimation could beuseful for estimating the absolute accuracy level which can be achieved using theGPS/levelling method. A general MATLAB function is presented for numericalestimation of variance components by using the different parametric models. Themodified BQUNE and developed software was successfully applied for estimating thevariance components through the sample GPS/levelling network in Iran. In the followingresearch, we used the 75 outlier free and well distributed GPS/levelling data. Threecorrective surface models based on the 4, 5 and 7 parameter models were used throughthe combined adjustment of the GPS/levelling and geoidal heights. Using the 7-parametermodel, the standard deviation indexes of the geoidal, geodetic and orthometric heights inIran were estimated to be about 27, 39 and 35 cm, respectively.

  • 20.
    Kristiansson, Lilia
    University West, Department of Engineering Science, Division of Mechanical Engineering. University West, Department of Engineering Science, Division of Industrial Engineering and Management, Electrical- and Mechanical Engineering.
    Competence development through Project-based learning in higher education i Sweden and England2012In: 40th annual congress of the Nordic Educational Research association, NPFP/NERA: 8-10 mars, 2012, Copenhagen, Aarhus: Department of Eduation, Aarhus University , 2012, p. 286-Conference paper (Refereed)
    Abstract [en]

    The focus of higher education curricula has been changing from factual knowledge acquisition to developing students competences in response to a changing professional environment in the context of a knowledge economy and labour market globalisation.

    Despite these social changes, existing teaching and learning strategies in Engineering are still mainly lecture-based.

    We investigate competence development using a Project- Based Learning (PrBL) environment on a range of Engineering programmes at Lancaster University, UK and Högskolan Väst, Sweden. We evaluate the PrBL potential to enhance student employability prospects.

    PrBL is an example of collaborative student-focussed learning underpinned by constructivist theory which encourages deeper learning via construction of meaning, connection of ideas and creation of meaningful artefacts. PrBL stimulates collaborative knowledge building among participants and develops a range of skills through creating an informal learning environment. First and second-year students on undergraduate programmes in Engineering departments in both universities with projects as part of their course participated in this study. In the UK the students had to design, build and test two types of robots. The Swedish students were given a project to make calculations for a pump with preset parameters. The projects were designed to help the students acquire competences relevant to their future career. All students worked in small groups. After finishing their projects, the students completed an open-ended questionnaire about their experiences.

    The students evaluated PrBL positively, stating that they developed problem solving and analytical skills and the ability to apply mathematical tools. They highly rated collaboration with peers and emphasised the necessity of developing time management, communication and organisational skills.

    Higher education systems in Europe including Scandinavia are facing new challenges in developing students' employability. We conclude with recommendations for promoting PrBL in university courses as it contributes to competence development and is an efficient tool when administrative resources are limited and when academic staff are faced with large student numbers.

  • 21.
    Lindström, David
    University West, Department of Engineering Science, Division of Mechanical Engineering and Natural Sciences.
    Evaluation of a Surrogate Based Method for Global Optimization2015In: International Journal of Computer, Electrical, Automation, Control and Information Engineering, E-ISSN 1307-6892, Vol. 9, no 7, p. 1636-1642Article in journal (Refereed)
    Abstract [en]

    We evaluate the performance of a numerical method for global optimization of expensive functions. The method is using a response surface to guide the search for the global optimum. This metamodel could be based on radial basis functions, kriging, or a combination of different models. We discuss how to set the cyclic parameters of the optimization method to get a balance between local and global search. We also discuss the eventual problem with Runge oscillations in the response surface.

  • 22.
    Lindström, David
    University West, Department of Engineering Science.
    Robustness analysis of airfoil performance: DETC2010-282612010In: Proceedings of the ASME 2010 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference: August 15-18, 2010, Montreal, Quebec, Canada, ASME, the American Society of Mechanical Engineers , 2010, p. 1-6Conference paper (Refereed)
    Abstract [en]

    We demonstrate a technique to evaluate the aerodynamic robustness of a given blade profile which it is exposed to stochastic geometrical variation. The technique is based on random fields, with geometrical deviations continuously defined over the entire structure, with a prescribed statistical distribution function and a given correlation between these deviations. Control points are defined on the blade surface to model the blade geometry disturbances. At each control point a stochastic deviation is defined, which acts in the normal direction of the blade. By modeling disturbances in the normal direction instead of in the separate Cartesian directions, we automatically reduce the number of stochastic variables by a factor two. The perturbation variables are transformed via Karhunen-Loève eigenvalue decomposition, giving stochastically independent variables. The robustness is finally estimated by a Monte Carlo simulation, where computational fluid dynamic simulations are performed to evaluate the resulting change in blade performance for given geometrical perturbations.

  • 23.
    Lindström, David
    et al.
    University West, Department of Engineering Science, Division of Mechanical Engineering and Natural Sciences.
    Eriksson, Kenneth
    University West, Department of Engineering Science, Division of Mechanical Engineering and Natural Sciences.
    A surrogate model based global optimization method2008In: 38th International Conference on Computers and Industrial Engineering 2008, 2008, p. 226-232Conference paper (Refereed)
    Abstract [en]

    A new surrogate model based algorithm for global optimization is derived. A metamodel such as a kriging model or a radial basis function model is used to build an interpolant of the objective function. Evaluation points are chosen in such a way that local search and global exploration is balanced. Instead of putting the next point exactly where it is most likely to find the global optimum, the new method also prepares for steps to come by minimizing the total uncertainty of the interpolated function within the most interesting areas of the search space.

  • 24.
    Lundström, Patrik
    University West, Department of Technology, Mathematics and Computer Science.
    Brauer group rings2004In: JP Journal of Algebra, Number Theory & Applications, Vol. 4, p. 22p. 465-494Article in journal (Refereed)
  • 25.
    Lundström, Patrik
    University West, Department of Technology.
    Cohomology and Self-dual Normal Bases for Infinite Galois Field Extensions2002In: Journal of Algebra, ISSN 0021-8693, E-ISSN 1090-266X, Vol. 256, p. 531-541Article in journal (Refereed)
    Abstract [en]

    We generalize an injectivity result obtained by Bayer-Fluckiger and Lenstra concerning pointed cohomology sets, defined by norm-one groups of finite-dimensional algebras with involution over fields k of characteristic different from 2, to the case of inverse limits of finite-dimensional k-algebras with involution. We use this generalization to obtain a result about self-dual normal bases for infinite Galois field extensions.

  • 26.
    Lundström, Patrik
    University West, Department of Technology, Mathematics and Computer Science, Division for Mathematics and Sciences.
    Cohomology and the normal basis theorem2007In: Indagationes mathematicae, ISSN 0019-3577, E-ISSN 1872-6100, Vol. 18, p. 69-72Article in journal (Refereed)
  • 27.
    Lundström, Patrik
    University West, Department of Technology, Mathematics and Computer Science.
    Crossed product algebras defined by separable extensions2005In: Journal of Algebra, ISSN 0021-8693, E-ISSN 1090-266X, Vol. 283, p. 14p. 723-737Article in journal (Refereed)
  • 28.
    Lundström, Patrik
    University West, Department of Technology, Mathematics and Computer Science.
    Fuzzified categories of composition graphs2005Report (Other (popular science, discussion, etc.))
    Abstract [en]

    Serving as a generalization of many examples of fuzzy algebraical systems equipped with a binary operation, we introduce fuzzy composition graphs and show that categories formed by such graphs are, in the sense of Wyler [10], top categories. By using this, we investigate projective and injective objects in such categories, and we determine when various limits and colimits, such as terminal and initial objects, products, coproducts, pullbacks, pushouts, equalizers, coequalizers, kernels and cokernels, exist in categories of this type and what they look like. These results are then applied to the categories of fuzzy sets, fuzzy categories, fuzzy groupoids, fuzzy monoids, fuzzy groups and fuzzy abelian groups.

  • 29.
    Lundström, Patrik
    University West, Department of Technology, Mathematics and Computer Science, Division for Mathematics and Sciences.
    Galois Module Structure of Field Extensions2007In: International Electronic Journal of Algebra, ISSN 1306-6048, E-ISSN 1306-6048, Vol. 2, no 8, p. 100-105Article in journal (Refereed)
    Abstract [en]

    We show, in two different ways, that every finite field extension has a basis with the property that the Galois group of the extension acts faithfully on it. We use this to prove a Galois correspondence theorem for general finite field extensions. We also show that if the characteristic of the base field is different from two and the field extension has a normal closure of odd degree, then the extension has a self-dual basis upon which the Galois group acts faithfully.

  • 30.
    Lundström, Patrik
    University West, Department of Technology.
    Generalized Brauer Algebras2002In: Communications in Algebra, ISSN 0092-7872, E-ISSN 1532-4125, Vol. 30, no 5, p. 2229-2270Article in journal (Refereed)
    Abstract [en]

    Using some ideas of Brauer, we introduce what we call generalized Brauer algebras and, as a special case, Brauer orders. We show that many well-known classes of so-called crossed product algebras, and in particular, the well-known crossed product orders, can be obtained as special instances of our construction. We prove several results showing when Brauer orders are Azumaya, maximal, hereditary or Gorenstein.

  • 31.
    Lundström, Patrik
    University West, Department of Engineering Science, Divison of Natural Sciences, Surveying and Mechanical Engineering.
    Good Magma Gradings On Rings2014In: Communications in Algebra, ISSN 0092-7872, E-ISSN 1532-4125, Vol. 42, no 12, p. 5357-5373Article in journal (Refereed)
    Abstract [en]

    Suppose that G and H are magmas and that R is a strongly G-graded ring. We show that there is a bijection between the set of good (zero) H-gradings of R and the set of (zero) magma homomorphisms from G to H. Thereby we generalize a result by Dascalescu, Ion, Nastasescu and Rios Montes from group gradings of matrix rings to strongly magma graded rings. We also show that there is an isomorphism between the preordered set of good (zero) H-filters on R and the preordered set of (zero) submagmas of G \times H. These results are applied to category graded rings and, in particular, to the case when G and H are groupoids. In the latter case, we use this bijection to determine the cardinality of the set of good H-gradings on R.

  • 32.
    Lundström, Patrik
    University West, Department of Engineering Science, Division of Land Surveying and Mathematics.
    Hilbert 90 for Rings with ConjugationManuscript (preprint) (Other academic)
    Abstract [en]

    We show a version of Hilbert 90 that is valid for a large class ofalgebras many of which are not commutative, distributive orassociative. This class contains the n:th iteration of theConway-Smith doubling procedure. We use our version of Hilbert 90 toparametrize all solutions in ordered fields to the norm one equation for such algebras.

  • 33.
    Lundström, Patrik
    University West, Department of Engineering Science, Division of Land Surveying and Mathematics.
    Hilbert 90 for algebras with conjugation2012In: Algebras and Representation Theory, ISSN 1386-923X, E-ISSN 1572-9079, Vol. 15, no 1, p. 119-135Article in journal (Refereed)
    Abstract [en]

    We show a version of Hilbert 90 that is valid for a large class ofalgebras many of which are not commutative, distributive orassociative. This class contains the n:th iteration of theConway-Smith doubling procedure. We use our version of Hilbert 90 toparametrize all solutions in ordered fields to the norm one equation for such algebras.

  • 34.
    Lundström, Patrik
    University West, Department of Technology.
    Normal Bases for Infinite Galois Ring Extensions1999In: Colloquium Mathematicum, ISSN 0010-1354, E-ISSN 1730-6302, Vol. 79, p. 235-240Article in journal (Refereed)
  • 35.
    Lundström, Patrik
    University West, Department of Technology. University West, Department of Engineering Science, Division of Mathematics, Computer and Surveying Engineering.
    Normal Integral Bases for Infinite Abelian Extensions2001In: Acta Arithmetica, ISSN 0065-1036, E-ISSN 1730-6264, Vol. 100, p. 79-83Article in journal (Refereed)
  • 36.
    Lundström, Patrik
    University West, Department of Engineering Science, Division of Land Surveying and Mathematics.
    Pythagoreiska tripplar på sex olika sätt2008In: Normat, ISSN 0801-3500, Vol. 56, no 3, p. 111-119Article in journal (Refereed)
    Abstract [en]

    Six different ways of parametrising Pythagorean triplets are presented, from the elementary arguments supplied by the Greek, via trigonometry to Gaussian integers and applications of Hilbers 90th theorem.

  • 37.
    Lundström, Patrik
    University West, Department of Technology.
    Self-dual Normal Bases for Infinite Galois Field Extensions1998In: Communications in Algebra, ISSN 0092-7872, E-ISSN 1532-4125, Vol. 26, p. 4331-4341Article in journal (Refereed)
  • 38.
    Lundström, Patrik
    University West, Department of Technology, Mathematics and Computer Science.
    Self-dual normal bases for infinite odd abelian Galois ring extensions2006In: Acta Arithmetica, ISSN 0065-1036, E-ISSN 1730-6264, Vol. 123, no 1, p. 1-8Article in journal (Refereed)
  • 39.
    Lundström, Patrik
    University West, Department of Technology, Mathematics and Computer Science.
    Self-dual Normal Integral Bases for Infinite Unramified Extensions2002In: Journal of Number Theory, ISSN 0022-314X, E-ISSN 1096-1658, Vol. 97, no 2, p. 350-367Article in journal (Refereed)
    Abstract [en]

    We prove a generalization to infinite Galois extensions of local fields, of a classical result by Noether on the existence of normal integral bases for finite tamely ramified Galois extensions. We also prove a self-dual normal integral basis theorem for infinite unramified Galois field extensions of local fields with finite residue fields of characteristic different from 2. This generalizes a result by Fainsilber for the finite case. To do this, we obtain an injectivity result concerning pointed cohomology sets, defined by inverse limits of norm-one groups of free finite-dimensional algebras with involution over complete discrete valuation rings.

  • 40.
    Lundström, Patrik
    University West, Department of Technology, Mathematics and Computer Science, Division for Mathematics and Sciences.
    Separable Groupoid Rings2006In: Communications in Algebra, ISSN 0092-7872, E-ISSN 1532-4125, Vol. 34, no 8, p. 3029-3041Article in journal (Refereed)
    Abstract [en]

    We show that groupoid rings are separable over their ring of coefficients if and only if the groupoid is finite and the orders of the associated principal groups are invertible in the ring of coefficients. We use this to show that if we are given a finite groupoid, then the associated groupoid ring is semisimple (or hereditary) if and only if the ring of coefficients is semisimple (or hereditary) and the orders of the principal groups are invertible in the ring of coefficients. To this end, we extend parts of the theory of graded rings and modules from the group graded case to the category graded, and, hence, groupoid graded situation. In particular, we show that strongly groupoid graded rings are separable over their principal components if and only if the image of the trace map contains the identity

  • 41.
    Lundström, Patrik
    University West, Department of Technology, Mathematics and Computer Science.
    Separable groupoid rings2006In: Communications in Algebra, ISSN 0092-7872, E-ISSN 1532-4125, Vol. 34, p. 13p. 3029-3041Article in journal (Other (popular science, discussion, etc.))
  • 42.
    Lundström, Patrik
    University West, Department of Technology, Mathematics and Computer Science.
    The category of groupoid graded modules2004In: Colloquium Mathematicum, ISSN 0010-1354, E-ISSN 1730-6302, Vol. 100, p. 15p. 195-211Article in journal (Refereed)
  • 43.
    Lundström, Patrik
    University West, Department of Technology, Mathematics and Computer Science.
    The Picard Groupoid and Strongly Groupoid Graded Modules2006In: Colloquium Mathematicum, ISSN 0010-1354, E-ISSN 1730-6302, Vol. 106, p. 1-13Article in journal (Refereed)
  • 44.
    Lundström, Patrik
    University West, Department of Engineering Science.
    The Picard Groupoid and Strongly Groupoid Graded Modules2006In: Colloquium Mathematicum, ISSN 0010-1354, E-ISSN 1730-6302, Vol. 106, p. 1-13Article in journal (Refereed)
  • 45.
    Lundström, Patrik
    University West, Department of Technology, Mathematics and Computer Science.
    Von Neumann finite endomorphism rings2003In: Indagationes mathematicae, ISSN 0019-3577, E-ISSN 1872-6100, Vol. 14, p. 9p. 223-232Article in journal (Refereed)
  • 46.
    Lundström, Patrik
    University West, Department of Engineering Science, Division of Land Surveying and Mathematics.
    Weak topological functors2008In: Journal of Generalized Lie Theory and Applications, ISSN 1736-5279, E-ISSN 1736-4337, Vol. 2, no 3, p. 211-215Article in journal (Refereed)
    Abstract [en]

    We introduce weak topological functors and show that they lift and preserve weak limits and weak colimits. We also show that if then the induced functor of Wyler’s top categories and in particular to functor categories of fuzzy maps, fuzzy relations, fuzzy topological spaces and fuzzy measurable spaces. A ! B is a topological functor and J is a category,AJ ! BJ is topological. These results are applied to a generalization

  • 47.
    Lundström, Patrik
    et al.
    University West, Department of Engineering Science, Division of Land Surveying and Mathematics.
    Öinert, Johan
    Commutativity and Ideals in Category Crossed Products2010In: Proceedings of the Estonian Academy of Sciences: Physics, Mathematics, ISSN 1406-0086, E-ISSN 2228-0685, Vol. 59, no 4, p. 338-346Article in journal (Refereed)
  • 48.
    Lundström, Patrik
    et al.
    University West, Department of Engineering Science, Division of Land Surveying and Mathematics.
    Öinert, Johan
    LTH.
    Miyashita Action in Strongly Groupoid Graded RingsManuscript (preprint) (Other academic)
    Abstract [en]

    We determine the commutant of homogeneous subringsin strongly groupoid graded rings in terms of an action on the ring induced by the grading. Thereby we generalize a classical result of Miyashita from the groupgraded case to the groupoid graded situation. In the end of the article we exemplify this result. To this end, we show, by an explicit construction,that given a finite groupoid $G$, equipped with a nonidentitymorphism t : d(t) -> c(t), there is a strongly G-graded ring R with the properties that each R_s, for s in G, is nonzero and R_t is a nonfree left R_c(t)-module.

  • 49.
    Lundström, Patrik
    et al.
    University West, Department of Engineering Science.
    Öinert, Johan
    LTH.
    Miyashita Action in Strongly Groupoid Graded Rings2012In: International Electronic Journal of Algebra, ISSN 1306-6048, E-ISSN 1306-6048, Vol. 11, p. 46-63Article in journal (Refereed)
    Abstract [en]

    We determine the commutant of homogeneous subrings in strongly groupoid graded rings in terms of an action on the ring induced by the grading. Thereby we generalize a classical result of Miyashita from the groupgraded case to the groupoid graded situation. In the end of the article we exemplify this result. To this end, we show, by an explicit construction,that given a finite groupoid $G$, equipped with a nonidentitymorphism t : d(t) -> c(t), there is a strongly G-graded ring R with the properties that each R_s, for s in G, is nonzero and R_t is a nonfree left R_c(t)-module.

  • 50.
    Lundström, Patrik
    et al.
    University West, Department of Engineering Science, Division of Natural Sciences and Electrical and Surveying Engineering.
    Öinert, Johan
    Köpenhamns Universitet.
    Skew category algebras associated with partially defined dynamical systems2012In: International Journal of Mathematics, ISSN 0129-167X, Vol. 23, no 4, p. 16-Article in journal (Refereed)
    Abstract [en]

    We introduce partially defined dynamical systems defined on a topological space. To each such system we associate a functor s from a category G to Top^op and show that it defines what we call a skew category algebra AxG. We study the connection between topological freeness of s and, on the one hand, ideal properties of AxG and, on the other hand, maximal commutativity of A in AxG. In particular, we show that if G is a groupoid and for each e in ob(G) the group of all morphisms from e to e is countable and the topological space s(e) is Tychonoff and Baire, then the following assertions are equivalent: (i) s is topologically free; (ii) A has the ideal intersection property, that is if I is a nonzero ideal of AxG, then I \cap A is not equal to zero; (iii) the ring A is a maximal abelian complex subalgebra of AxG. Thereby, we generalize a result by Svensson, Silvestrov and de Jeu from the additive group of integers to a large class of groupoids.

12 1 - 50 of 89
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf