liu.seSearch for publications in DiVA
Change search
Refine search result
1234 1 - 50 of 155
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • 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.
    Alvbrant, Joakim
    et al.
    Linköping University, Department of Electrical Engineering. Linköping University, Faculty of Science & Engineering.
    Keshmiri, Vahid
    Linköping University, Department of Electrical Engineering, Information Coding. Linköping University, Faculty of Science & Engineering.
    Wikner, Jacob
    Linköping University, Department of Electrical Engineering, Integrated Circuits and Systems. Linköping University, Faculty of Science & Engineering.
    Transfer Characteristics and Bandwidth Limitation in a Linear-Drift Memristor Model2015In: 2015 EUROPEAN CONFERENCE ON CIRCUIT THEORY AND DESIGN (ECCTD), IEEE , 2015, p. 332-335Conference paper (Refereed)
    Abstract [en]

    The linear-drift memristor model, suggested by HP Labs a few years ago, is used in this work together with two window functions. From the equations describing the memristor model, the transfer characteristics of a memristor is formulated and analyzed. A first-order estimation of the cut-off frequency is shown, that illustrates the bandwidth limitation of the memristor and how it varies with some of its physical parameters. The design space is elaborated upon and it is shown that the state speed, the variation of the doped and undoped regions of the memristor, is inversely proportional to the physical length, and depth of the device. The transfer characteristics is simulated for Joglekar-Wolf, and Biolek window functions and the results are analyzed. The Joglekar-Wolf window function causes a distinct behavior in the tranfer characteristics at cut-off frequency. The Biolek window function on the other hand gives a smooth state transfer function, at the cost of loosing the one-to-one mapping between charge and state. We also elaborate on the design constraints derived from the transfer characteristics.

  • 2.
    Andersson, Jonathan
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Asymptotic behavior and effective boundaries forage-structured population models in aperiodically changing environment2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Human activity and other events can cause environmental changes to the habitat of organisms. The environmental changes effect the vital rates for a population. In order to predict the impact of these environmental changes on populations, we use two different models for population dynamics. One simpler linear model that ignores environmental competition between individuals and another model that does not. Our population models take into consideration the age distribution of the population and thus takes into consideration the impact of demographics. This thesis generalize two theorems, one for each model, developed by Sonja Radosavljevic regarding long term upper and lower bounds of a population with periodic birth rate ; see [6] and [5]. The generalisation consist in including the case where the periodic part of the birth rate can be expressed with a finite Fourier series and also infinite Fourier series under some constraints. The old theorems only considers the case when the periodic part of the birth rate can be expressed with one cosine term. From the theorems we discover a connection between the frequency of oscillation and the effect on population growth. From this derived connection we conclude that periodical changing environments can have both positive and negative effects on the population.

  • 3.
    Appelgren, Leif H
    Linköping University, Department of Management and Engineering, Economic Information Systems.
    A note on the Erard & Feinstein tax audit model Manuscript (preprint) (Other academic)
    Abstract [en]

    This paper introduces a new method for the determination of near-optimal audit strategies with the Erard & Feinstein model. It is demonstrated that the solution method presented by Erard & Feinstein does not lead to optimal audit strategies. The new method simulates taxpayer behaviour for a class of audit functions among which the best function is selected. Using a simple class of functions, the resulting strategies are superior to those obtained with the Erard & Feinstein method.

    The simulation method can easily handle variations of the model, for instance with involuntary taxpayer errors as well as with partially discrete true income distributions.

  • 4.
    Appelgren, Leif H.
    Linköping University, Department of Management and Engineering, Economic Information Systems. Linköping University, Faculty of Arts and Sciences.
    Audit strategy for temporary parental benefit2012Report (Other (popular science, discussion, etc.))
    Abstract [en]

    The aim of this project is to study the possibility to apply audit strategies developed for taxation on fraud and involuntary errors in the social benefit sector. The efficiency of different audit strategies is compared using a computer-based optimization algorithm.

    Two types of audit strategies are used in this study. One is to adapt the audit intensity to the propensity for errors and fraud in different segments of the group studied. The other type of audit strategy is based on adaptation of behaviour through information concerning the audit intensity. A model for determination of optimal tax audit strategies of the latter type was developed by Erard & Feinstein in 1994.

    This study is based on data from a large study of temporary parental benefit performed by the Institute for Evaluation of Labour Market and Education Policy (Institutet för arbetsmarknadspolitisk utvärdering, IFAU) in 2006.

    The study has shown that it is possible to apply the Erard & Feinstein model on benefit fraud. However, the solution method developed by Erard & Feinstein has proven to be non-optimal. A new solution method based on simulation has been developed and used in the study.

  • 5.
    Appelgren, Leif H.
    Linköping University, Department of Management and Engineering, Economic Information Systems. Linköping University, Faculty of Arts and Sciences.
    Kontrollstrategi för tillfällig föräldrapenning2011Report (Other (popular science, discussion, etc.))
  • 6.
    Arkin, Esther M
    et al.
    Department of Applied Mathematics and Statistics, Stony Brook University, USA .
    Dieckmann, Claudia
    Institute of Computer Science, Freie Universität Berlin, Germany .
    Knauer, Christian
    Institute of Computer Science, Universität Bayreuth, Germany .
    Mitchell, Joseph SB
    Department of Applied Mathematics and Statistics, Stony Brook University, USA .
    Polishchuk, Valentin
    Helsinki Institute for Information Technology, CS Dept, University of Helsinki, Finland .
    Schlipf, Lena
    Institute of Computer Science, Freie Universität Berlin, Germany .
    Yang, Shang
    Department of Computer Science, Stony Brook University, USA .
    Convex transversals2014In: Computational Geometry, ISSN 0925-7721, Vol. 47, no 2, p. 224-239Article in journal (Refereed)
    Abstract [en]

    We answer the question initially posed by Arik Tamir at the Fourth NYU Computational Geometry Day (March, 1987): “Given a collection of compact sets, can one decide in polynomial time whether there exists a convex body whose boundary intersects every set in the collection?”

    We prove that when the sets are segments in the plane, deciding existence of the convex stabber is NP-hard. The problem remains NP-hard if the sets are regular polygons. We also show that in 3D the stabbing problem is hard when the sets are balls. On the positive side, we give a polynomial-time algorithm to find a convex transversal of a maximum number of pairwise-disjoint segments in 2D if the vertices of the transversal are restricted to a given set of points. Our algorithm also finds a convex stabber of the maximum number of a set of convex pseudodisks in the plane.

    The stabbing problem is related to “convexity” of point sets measured as the minimum distance by which the points must be shifted in order to arrive in convex position; we give a PTAS to find the minimum shift in 2D, and a 2-approximation in any dimension. We also consider stabbing with vertices of a regular polygon – a problem closely related to approximate symmetry detection.

  • 7.
    Arnlind, Joakim
    et al.
    Institut des Hautes Études Scientif iques, Le Bois-Marie, 35, Route de Chartres, 91440 Bures-sur-Yvette, France.
    Hoppe, Jens
    Eidgenössische Technische Hochschule, 8093 Zürich, Switzerland (on leave of absence from Kungliga Tekniska Högskolan, 100 44 Stockholm, Sweden).
    Discrete Minimal Surface Algebras2010In: SIGMA. Symmetry, Integrability and Geometry, ISSN 1815-0659, E-ISSN 1815-0659, Vol. 6, no 042, p. -18Article in journal (Refereed)
    Abstract [en]

    We consider discrete minimal surface algebras (DMSA) as generalized noncommutative analogues of minimal surfaces in higher dimensional spheres. These algebras appear naturally in membrane theory, where sequences of their representations are used as a regularization. After showing that the defining relations of the algebra are consistent, and that one can compute a basis of the enveloping algebra, we give several explicit examples of DMSAs in terms of subsets of sln (any semi-simple Lie algebra providing a trivial example by itself). A special class of DMSAs are Yang-Mills algebras. The representation graph is introduced to study representations of DMSAs of dimension d ≤ 4, and properties of representations are related to properties of graphs. The representation graph of a tensor product is (generically) the Cartesian product of the corresponding graphs. We provide explicit examples of irreducible representations and, for coinciding eigenvalues, classify all the unitary representations of the corresponding algebras.

  • 8.
    Arnlind, Joakim
    et al.
    Max Planck Institute for Gravitational Physics (AEI), Am Mühlenberg 1, D-14476 Golm, Germany.
    Makhlouf, Abdenacer
    Université de Haute Alsace, Laboratoire de Mathématiques, Informatique et Applications, 4, rue des Frères Lumière F-68093 Mulhouse, France .
    Silvestrov, Sergei
    Mälardalen University, Division of Applied Mathematics, The School of Education, Culture and Communication, Box 883, 721 23 Västerås, Sweden och Centre for Mathematical Sciences, Lund University, Box 118, 221 00 Lund, Sweden .
    Construction of n-Lie algebras and n-ary Hom-Nambu-Lie algebras2011In: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 52, article id 123502Article in journal (Refereed)
    Abstract [en]

    As n-ary operations, generalizing Lie and Poisson algebras, arise in many different physical contexts, it is interesting to study general ways of constructing explicit realizations of such multilinear structures. Generically, they describe the dynamics of a physical system, and there is a need of understanding their quantization. Hom-Nambu-Lie algebras provide a framework that might be an appropriate setting in which n-Lie algebras (n-ary Nambu-Lie algebras) can be deformed, and their quantization studied. We present a procedure to construct (n + 1)-ary Hom-Nambu-Lie algebras from n-ary Hom-Nambu-Lie algebras equipped with a generalized trace function. It turns out that the implications of the compatibility conditions, that are necessary for this construction, can be understood in terms of the kernel of the trace function and the range of the twisting maps. Furthermore, we investigate the possibility of defining (n + k)-Lie algebras from n-Lie algebras and a k-form satisfying certain conditions.

  • 9.
    Asekritova, Irina
    et al.
    Linnéuniversitetet, Institutionen för datavetenskap, fysik och matematik, DFM.
    Brudnyi, Yuri
    Technion, Haifa, Israel.
    Interpolation of Multiparameter Approximation Spaces2004In: Journal of Approximation Theory, ISSN 0021-9045, E-ISSN 1096-0430, Vol. 129, no 2, p. 182-206Article in journal (Refereed)
    Abstract [en]

    We prove a general interpolation theorem for linear operators acting simultaneously in several approximation spaces which are defined by multiparametric approximation families. As a consequence, we obtain interpolation results for finite families of Besov spaces of various types including those determined by a given set of mixed differences.

  • 10.
    Asekritova, Irina
    et al.
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Karlovich, Yuri
    University of Autonoma Estado Morelos, Mexico.
    Kruglyak, Natan
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    One-sided invertibility of discrete operators and their applications2018In: Aequationes Mathematicae, ISSN 0001-9054, E-ISSN 1420-8903, Vol. 92, no 1, p. 39-73Article in journal (Refereed)
    Abstract [en]

    For p is an element of [1, infinity], we establish criteria for the one-sided invertibility of binomial discrete difference operators A = aI - bV on the space l(p) = l(p)(Z), where a, b is an element of l(infinity), I is the identity operator and the isometric shift operator V is given on functions f. lp by (Vf)(n) = f (n+ 1) for all n is an element of Z. Applying these criteria, we obtain criteria for the one-sided invertibility of binomial functional operators A = aI - bU(alpha) on the Lebesgue space L-p(R+) for every p is an element of [1, infinity], where a, b is an element of L-infinity (R+), a is an orientation-preserving bi-Lipschitz homeomorphism of [0, +infinity] onto itself with only two fixed points 0 and infinity, and U-alpha is the isometric weighted shift operator on L-p(R+) given by U(alpha)f = (alpha)(1/p)(f circle alpha). Applications of binomial discrete operators to interpolation theory are given.

  • 11.
    Asekritova, Irina
    et al.
    Linnéuniversitetet, Institutionen för datavetenskap, fysik och matematik, DFM.
    Kruglyak, Natan
    Department of Mathematics, Lulea University of Technology, Sweden.
    Real Interpolation of Vector-Valued Spaces in Non-Diagonal Case2004In: Proceedings of the American Mathematical Society, ISSN 0002-9939, E-ISSN 1088-6826, Vol. 133, no 6, p. 1665-1675Article in journal (Refereed)
    Abstract [en]

    It is shown that the formula

    where and is correct under the restrictions and It is also true if we suppose that and the spaces are functional Banach or quasi-Banach lattices on the same measure space

  • 12.
    Asekritova, Irina
    et al.
    Linnéuniversitetet, Institutionen för datavetenskap, fysik och matematik, DFM.
    Kruglyak, Natan
    Department of Mathematics, Luleå University of Technology, Sweden.
    The Besikovitch Covering Theorem and Near Minimizers for the Couple (L2,BV)2010In: Proceedings of the Estonian Academy of Sciences: Physics, Mathematics, ISSN 1406-0086, E-ISSN 2228-0685, Vol. 59, no 1, p. 29-33Article in journal (Refereed)
    Abstract [en]

    Let Ω be a rectangle in R2. A new algorithm for the construction of a near-minimizer for the couple (L2(Ω), BV(Ω)) is presented. The algorithm is based on the Besicovitch covering theorem and analysis of local approximations of the given function f ∈ L2(Ω).

  • 13.
    Asekritova, Irina
    et al.
    Linnéuniversitetet, Institutionen för datavetenskap, fysik och matematik, DFM.
    Kruglyak, Natan
    Department of Mathematics, Yaroslavl' State University, Russia.
    Maligranda, Lech
    Department of Mathematics, Luleå University of Technology, Sweden.
    Persson, Lars-Erik
    Department of Mathematics, Luleå University of Technology, Sweden.
    Distribution and Rearranement Estimates of the Maximal Functions and Interpolation1997In: Studia Mathematica, ISSN 0039-3223, E-ISSN 1730-6337, Vol. 124, no 2, p. 107-132Article in journal (Refereed)
    Abstract [en]

    There are given necessary and sufficient conditions on a measure dμ(x)=w(x)dx under which the key estimates for the distribution and rearrangement of the maximal function due to Riesz, Wiener, Herz and Stein are valid. As a consequence, we obtain the equivalence of the Riesz and Wiener inequalities which seems to be new even for the Lebesgue measure. Our main tools are estimates of the distribution of the averaging function f** and a modified version of the Calderón-Zygmund decomposition. Analogous methods allow us to obtain K-functional formulas in terms of the maximal function for couples of weighted $L_p$-spaces.

  • 14.
    Asekritova, Irina
    et al.
    Linnéuniversitetet, Institutionen för datavetenskap, fysik och matematik, DFM.
    Kruglyak, Natan
    Department of Mathematics Luleå University of Technology, Luleå, Sweden.
    Nikolova, Ludmila
    University of Sofia, Bulgaria.
    Lizorkin-Freitag Formula for Several Weighted Lp Spaces and Vector-Valued Interpolation2005In: Studia Mathematica, ISSN 0039-3223, E-ISSN 1730-6337, Vol. 170, no 3, p. 227-239Article in journal (Refereed)
    Abstract [en]

    A complete description of the real interpolation space L=(Lp0(ω0),…,Lpn(ωn))θ⃗ ,q is given. An interesting feature of the result is that the whole measure space (Ω,μ) can be divided into disjoint pieces Ωi (i∈I) such that L is an lq sum of the restrictions of L to Ωi, and L on each Ωi is a result of interpolation of just two weighted Lp spaces. The proof is based on a generalization of some recent results of the first two authors concerning real interpolation of vector-valued spaces.

  • 15.
    Asekritova, Irina
    et al.
    Linnéuniversitetet, Institutionen för datavetenskap, fysik och matematik, DFM.
    Nikolova, Ludmila
    Sofia University, Sofia, Bulgaria.
    Kruglyak, Natan
    Luleå University of Technology, Luleå, Sweden.
    Maligranda, Lech
    Luleå University of Technology, Luleå, Sweden.
    Persson, Lars-Erik
    Luleå University of Technology, Luleå, Sweden.
    Lions-Peetre Reiteration Formulas for Triples and Their Application2001In: Studia Mathematica, ISSN 0039-3223, E-ISSN 1730-6337, Vol. 145, no 3, p. 219-254Article in journal (Refereed)
    Abstract [en]

    We present, discuss and apply two reiteration theorems for triples of quasi-Banach function lattices. Some interpolation results for block-Lorentz spaces and triples of weighted Lp-spaces are proved. By using these results and a wavelet theory approach we calculate (θ,q)-spaces for triples of smooth function spaces (such as Besov spaces, Sobolev spaces, etc.). In contrast to the case of couples, for which even the scale of Besov spaces is not stable under interpolation, for triples we obtain stability in the frame of Besov spaces based on Lorentz spaces. Moreover, by using the results and ideas of this paper, we can extend the Stein–Weiss interpolation theorem known for Lp(μ)-spaces with change of measures to Lorentz spaces with change of measures. In particular, the results obtained show that for some problems in analysis the three-space real interpolation approach is really more useful than the usual real interpolation between couples.

  • 16.
    Auscher, Pascal
    et al.
    Département de Mathématiques d’Orsay, Université Paris-Sud et UMR 8628 du CNRS, Orsay Cedex, France.
    Rosén, Andreas
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, The Institute of Technology.
    Weighted maximal regularity estimates and solvability of non-smooth elliptic systems, II2012In: Analysis & PDE, ISSN 2157-5045, E-ISSN 1948-206X, Vol. 5, no 5, p. 983-1061Article in journal (Refereed)
    Abstract [en]

    We continue the development, by reduction to a first-order system for the conormal gradient, of L2a priori estimates and solvability for boundary value problems of Dirichlet, regularity, Neumann type for divergence-form second-order complex elliptic systems. We work here on the unit ball and more generally its bi-Lipschitz images, assuming a Carleson condition as introduced by Dahlberg which measures the discrepancy of the coefficients to their boundary trace near the boundary. We sharpen our estimates by proving a general result concerning a priori almost everywhere nontangential convergence at the boundary. Also, compactness of the boundary yields more solvability results using Fredholm theory. Comparison between classes of solutions and uniqueness issues are discussed. As a consequence, we are able to solve a long standing regularity problem for real equations, which may not be true on the upper half-space, justifying a posteriori a separate work on bounded domains.

  • 17.
    Baravdish, George
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Cheng, Yuanji
    Malmö University, Malmö, Sweden.
    Svensson, Olof
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Åström, Freddie
    Heidelberg Collaboratory for Image Processing, Heidelberg University, Heidelberg, Germany.
    Extension of p-Laplace Operator for Image Denoising2016In: 27th IFIP TC 7 Conference, CSMO 2015, Sophia Antipolis, France, June 29 - July 3, 2015, Revised Selected Papers / [ed] Bociu, Lorena; Désidéri, Jean-Antoine; Habbal, Abderrahmane, Springer, 2016, p. 107-116Chapter in book (Refereed)
    Abstract [en]

    In this work we introduce a novel operator $$\displaystyle \varDelta _(p,q)$$ as an extended family of operators that generalize the p-Laplace operator. The operator is derived with an emphasis on image processing applications, and particularly, with a focus on image denoising applications. We propose a non-linear transition function, coupling p and q, which yields a non-linear filtering scheme analogous to adaptive spatially dependent total variation and linear filtering. Well-posedness of the final parabolic PDE is established via pertubation theory and connection to classical results in functional analysis. Numerical results demonstrates the applicability of the novel operator $$\displaystyle \varDelta _(p,q)$$ .

  • 18.
    Baravdish, George
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Svensson, Olof
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Åström, Freddie
    Linköping University, Department of Electrical Engineering, Computer Vision. Linköping University, The Institute of Technology. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    On Backward p(x)-Parabolic Equations for Image Enhancement2015In: Numerical Functional Analysis and Optimization, ISSN 0163-0563, E-ISSN 1532-2467, Vol. 36, no 2, p. 147-168Article in journal (Refereed)
    Abstract [en]

    In this study, we investigate the backward p(x)-parabolic equation as a new methodology to enhance images. We propose a novel iterative regularization procedure for the backward p(x)-parabolic equation based on the nonlinear Landweber method for inverse problems. The proposed scheme can also be extended to the family of iterative regularization methods involving the nonlinear Landweber method. We also investigate the connection between the variable exponent p(x) in the proposed energy functional and the diffusivity function in the corresponding Euler-Lagrange equation. It is well known that the forward problems converges to a constant solution destroying the image. The purpose of the approach of the backward problems is twofold. First, solving the backward problem by a sequence of forward problems we obtain a smooth image which is denoised. Second, by choosing the initial data properly we try to reduce the blurriness of the image. The numerical results for denoising appear to give improvement over standard methods as shown by preliminary results.

  • 19.
    Barletta, Giuseppina
    et al.
    University of Mediterranea Reggio Calabria, Italy.
    Cianchi, Andrea
    University of Florence, Italy.
    Mazya, Vladimir
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering. RUDN University, Russia.
    Quasilinear elliptic equations on noncompact Riemannian manifolds2017In: Journal of Functional Analysis, ISSN 0022-1236, E-ISSN 1096-0783, Vol. 273, no 11, p. 3426-3462Article in journal (Refereed)
    Abstract [en]

    The existence of solutions to a class of quasilinear elliptic problems on noncompact Riemannian manifolds, with finite volume, is investigated. Boundary value problems, with homogeneous Neumann conditions, in possibly irregular Euclidean domains are included as a special instance. A nontrivial solution is shown to exist under an unconventional growth condition on the right-hand side, which depends on the geometry of the underlying manifold. The identification of the critical growth is a crucial step in our analysis, and entails the use of the isocapacitary function of the manifold. A condition involving its isoperimetric function is also provided. (C) 2017 Elsevier Inc. All rights reserved.

  • 20.
    Bartoszek, Krzysztof
    et al.
    Department of Mathematics, Uppsala University, Uppsala, Sweden.
    Bartoszek, Wojciech
    Department of Probability and Biomathematics, Gdańsk University of Technology, Gdańsk, Poland.
    A Noether theorem for stochastic operators on Schatten classes2017In: Journal of Mathematical Analysis and Applications, ISSN 0022-247X, E-ISSN 1096-0813, Vol. 452, no 2, p. 1395-1412Article in journal (Refereed)
    Abstract [en]

    We show that a stochastic (Markov) operator S acting on a Schatten class C-1 satisfies the Noether condition (i.e. S' (A) = A and S' (A(2)) = A(2), where A is an element of C-infinity is a Hermitian and bounded operator on a fixed separable and complex Hilbert space (H, <.,.>)), if and only if S(E-A(G)XEA(G)) = E-A (G)S(X)E-A (G) for any state X is an element of C-1 and all Borel sets G subset of R, where E-A (G) denotes the orthogonal projection coming from the spectral resolution A = integral(sigma(A)) zE(A)(dz). Similar results are obtained for stochastic one-parameter continuous semigroups.

  • 21.
    Bartoszek, Krzysztof
    et al.
    Department of Mathematics, Uppsala University, Uppsala, Sweden.
    Pulka, Malgorzta
    Department of Probability and Biomathematics, Gdańsk University of Technology, Gdańsk, Poland.
    Asymptotic properties of quadratic stochastic operators acting on the L1 space2015In: Nonlinear Analysis, ISSN 0362-546X, E-ISSN 1873-5215, Vol. 114, p. 26-39Article in journal (Refereed)
    Abstract [en]

    Quadratic stochastic operators can exhibit a wide variety of asymptotic behaviours andthese have been introduced and studied recently in the l1 space. It turns out that inprinciple most of the results can be carried over to the L1 space. However, due to topologicalproperties of this space one has to restrict in some situations to kernel quadratic stochasticoperators. In this article we study the uniform and strong asymptotic stability of quadratic stochastic operators acting on the L1 space in terms of convergence of the associated (linear)nonhomogeneous Markov chains.

  • 22.
    Basarab-Horwath, Peter
    et al.
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Gungor, F.
    Istanbul Technical University, Turkey.
    Linearizability for third order evolution equations2017In: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 58, no 8, article id 081507Article in journal (Refereed)
    Abstract [en]

    The problem of linearization for third order evolution equations is considered. Criteria for testing equations for linearity are presented. A class of linearizable equations depending on arbitrary functions is obtained by requiring presence of an infinite-dimensional symmetry group. Linearizing transformations for this class are found using symmetry structure and local conservation laws. A number of special cases as examples are discussed. Their transformation to equations within the same class by differential substitutions and connection with KdV and mKdV equations is also reviewed in this framework. Published by AIP Publishing.

  • 23.
    Bergelin, Victor
    Linköping University, Department of Mathematics. Linköping University, Faculty of Science & Engineering.
    Human Activity Recognition and Behavioral Prediction using Wearable Sensors and Deep Learning2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    When moving into a more connected world together with machines, a mutual understanding will be very important. With the increased availability in wear- able sensors, a better understanding of human needs is suggested. The Dart- mouth Research study at the Psychiatric Research Center has examined the viability of detecting and further on predicting human behaviour and complex tasks. The field of smoking detection was challenged by using the Q-sensor by Affectiva as a prototype. Further more, this study implemented a framework for future research on the basis for developing a low cost, connected, device with Thayer Engineering School at Dartmouth College. With 3 days of data from 10 subjects smoking sessions was detected with just under 90% accuracy using the Conditional Random Field algorithm. However, predicting smoking with Electrodermal Momentary Assessment (EMA) remains an unanswered ques- tion. Hopefully a tool has been provided as a platform for better understanding of habits and behaviour. 

  • 24.
    Berntsson, Fredrik
    et al.
    Linköping University, Department of Mathematics, Computational Mathematics. Linköping University, Faculty of Science & Engineering.
    Orlof, Anna
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Thim, Johan
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Error Estimation for Eigenvalues of Unbounded Linear Operators and an Application to Energy Levels in Graphene Quantum Dots2017In: Numerical Functional Analysis and Optimization, ISSN 0163-0563, E-ISSN 1532-2467, Vol. 38, no 3, p. 293-305Article in journal (Refereed)
    Abstract [en]

    The eigenvalue problem for linear differential operators is important since eigenvalues correspond to the possible energy levels of a physical system. It is also important to have good estimates of the error in the computed eigenvalues. In this work, we use spline interpolation to construct approximate eigenfunctions of a linear operator using the corresponding eigenvectors of a discretized approximation of the operator. We show that an error estimate for the approximate eigenvalues can be obtained by evaluating the residual for an approximate eigenpair. The interpolation scheme is selected in such a way that the residual can be evaluated analytically. To demonstrate that the method gives useful error bounds, we apply it to a problem originating from the study of graphene quantum dots where the goal was to investigate the change in the spectrum from incorporating electron–electron interactions in the potential.

  • 25.
    Björn, Anders
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, The Institute of Technology.
    Boundary regularity and barriers for elliptic and parabolic problems, and sharp capacity estimates for annuli2013Conference paper (Refereed)
  • 26.
    Björn, Anders
    Linköping University, Department of Mathematics, Applied Mathematics. Linköping University, The Institute of Technology.
    Cluster sets for Sobolev functions and quasiminimizers2010In: Journal d'Analyse Mathématique, ISSN 0021-7670, Vol. 112, p. 49-77Article in journal (Refereed)
    Abstract [en]

    In this paper, we study cluster sets and essential cluster sets for Sobolev functions and quasiharmonic functions (i.e., continuous quasiminimizers). We develop their basic theory with a particular emphasis on when they coincide and when they are connected. As a main result, we obtain that if a Sobolev function u on an open set has boundary values f in Sobolev sense and f |∂is continuous at x0 ∈ ∂, then the essential cluster set C(u, x0, Ω) is connected. We characterize precisely in which metric spaces this result holds. Further, we provide some new boundary regularity results for quasiharmonic functions. Most of the results are new also in the Euclidean case.

     

     

     

  • 27.
    Björn, Anders
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, The Institute of Technology.
    The Perron method for p-harmonic functions: new resolutivity and invariance results2012Conference paper (Refereed)
  • 28.
    Björn, Anders
    Linköping University, Department of Mathematics. Linköping University, The Institute of Technology.
    The Perron method for p-harmonic functions: Resolutivity and invariance results2012Conference paper (Refereed)
  • 29.
    Björn, Anders
    et al.
    Linköping University, Department of Mathematics, Applied Mathematics. Linköping University, The Institute of Technology.
    Björn, Jana
    Linköping University, Department of Mathematics, Applied Mathematics. Linköping University, The Institute of Technology.
    First-order Sobolev spaces on metric spaces2009In: Function Spaces, Inequalities and Interpolation (Paseky, 2009) / [ed] Jaroslav Lukes, Lubos Pick, Prague: Matfyzpress , 2009, p. 1-29Conference paper (Refereed)
  • 30.
    Björn, Anders
    et al.
    Linköping University, Department of Mathematics, Applied Mathematics. Linköping University, The Institute of Technology.
    Björn, Jana
    Linköping University, Department of Mathematics, Applied Mathematics. Linköping University, The Institute of Technology.
    Nonlinear Potential Theory on Metric Spaces2011 (ed. 1)Book (Refereed)
    Abstract [en]

    The p-Laplace equation is the main prototype for nonlinear elliptic problems and forms a basis for various applications, such as injection moulding of plastics, nonlinear elasticity theory and image processing. Its solutions, called p-harmonic functions, have been studied in various contexts since the 1960s, first on Euclidean spaces and later on Riemannian manifolds, graphs and Heisenberg groups. Nonlinear potential theory of p-harmonic functions on metric spaces has been developing since the 1990s and generalizes and unites these earlier theories.

    This monograph gives a unified treatment of the subject and covers most of the available results in the field, so far scattered over a large number of research papers. The aim is to serve both as an introduction to the area for an interested reader and as a reference text for an active researcher. The presentation is rather self-contained, but the reader is assumed to know measure theory and functional analysis.

    The first half of the book deals with Sobolev type spaces, so-called Newtonian spaces, based on upper gradients on general metric spaces. In the second half, these spaces are used to study p-harmonic functions on metric spaces and a nonlinear potential theory is developed under some additional, but natural, assumptions on the underlying metric space.

    Each chapter contains historical notes with relevant references and an extensive index is provided at the end of the book.

  • 31.
    Björn, Anders
    et al.
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Björn, Jana
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Gianazza, Ugo
    University of Pavia, Italy.
    The Petrovskii criterion and barriers for degenerate and singular p-parabolic equations2017In: Mathematische Annalen, ISSN 0025-5831, E-ISSN 1432-1807, Vol. 368, no 3-4, p. 885-904Article in journal (Refereed)
    Abstract [en]

    In this paper we obtain sharp Petrovskii criteria for the p-parabolic equation, both in the degenerate case p amp;gt; 2 and the singular case 1 amp;lt; p amp;lt; 2 We also give an example of an irregular boundary point at which there is a barrier, thus showing that regularity cannot be characterized by the existence of just one barrier.

  • 32.
    Björn, Anders
    et al.
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Björn, Jana
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Gill, James T.
    St Louis University, MO 63103 USA.
    Shanmugalingam, Nageswari
    University of Cincinnati, OH 45221 USA.
    Geometric analysis on Cantor sets and trees2017In: Journal für die Reine und Angewandte Mathematik, ISSN 0075-4102, E-ISSN 1435-5345, Vol. 725, p. 63-114Article in journal (Refereed)
    Abstract [en]

    dUsing uniformization, Cantor type sets can be regarded as boundaries of rooted trees. In this setting, we show that the trace of a first-order Sobolev space on the boundary of a regular rooted tree is exactly a Besov space with an explicit smoothness exponent. Further, we study quasisymmetries between the boundaries of two trees, and show that they have rough quasiisometric extensions to the trees. Conversely, we show that every rough quasiisometry between two trees extends as a quasisymmetry between their boundaries. In both directions we give sharp estimates for the involved constants. We use this to obtain quasisymmetric invariance of certain Besov spaces of functions on Cantor type sets.

  • 33.
    Björn, Anders
    et al.
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Björn, Jana
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Korte, Riikka
    Aalto University, Finland.
    Minima of quasisuperminimizers2017In: Nonlinear Analysis, ISSN 0362-546X, E-ISSN 1873-5215, Vol. 155, p. 264-284Article in journal (Refereed)
    Abstract [en]

    We show that, unlike minima of superharmonic functions which are again superharmonic, the same property fails for Q-quasisuperminimizers. More precisely, if u(i) is a Q(i)-quasisuperminimizer, i = 1,2, where 1 amp;lt; Q(1) amp;lt; Q(2), then u = min{u(1), u(2)} is a Q-quasisuperminimizer, but there is an increase in the optimal quasisuperminimizing constant Q. We provide the first examples of this phenomenon, i.e. that Q amp;gt; Q(2). In addition to lower bounds for the optimal quasisuperminimizing constant of u we also improve upon the earlier upper bounds due to Kinnunen and Martio. Moreover, our lower and upper bounds turn out to be quite close. We also study a similar phenomenon in pasting lemmas for quasisuperminimizers, where Q = Q(1)Q(2) turns out to be optimal, and provide results on exact quasiminimizing constants of piecewise linear functions on the real line, which can serve as approximations of more general quasiminimizers. (C) 2017 Elsevier Ltd. All rights reserved.

  • 34.
    Björn, Anders
    et al.
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Björn, Jana
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Latvala, Visa
    University of Eastern Finland, Finland.
    SOBOLEV SPACES, FINE GRADIENTS AND QUASICONTINUITY ON QUASIOPEN SETS2016In: Annales Academiae Scientiarum Fennicae Mathematica, ISSN 1239-629X, E-ISSN 1798-2383, Vol. 41, no 2, p. 551-560Article in journal (Refereed)
    Abstract [en]

    We study different definitions of Sobolev spaces on quasiopen sets in a complete metric space X equipped with a doubling measure supporting a p-Poincare inequality with 1 amp;lt; p amp;lt; infinity, and connect them to the Sobolev theory in R-n. In particular, we show that for quasiopen subsets of R-n the Newtonian functions, which are naturally defined in any metric space, coincide with the quasicontinuous representatives of the Sobolev functions studied by Kilpelainen and Maly in 1992.

  • 35.
    Björn, Anders
    et al.
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Björn, Jana
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Latvala, Visa
    University of Eastern Finland, Finland.
    The Weak Cartan Property for the p-fine Topology on Metric Spaces2015In: Indiana University Mathematics Journal, ISSN 0022-2518, E-ISSN 1943-5258, Vol. 64, no 3, p. 915-941Article in journal (Refereed)
    Abstract [en]

    We study the p-fine topology on complete metric spaces equipped with a doubling measure supporting a p-Poincare inequality, 1 less than p less than infinity. We establish a weak Cartan property, which yields characterizations of the p-thinness and the p-fine continuity, and allows us to show that the p-fine topology is the coarsest topology making all p-superharmonic functions continuous. Our p-harmonic and superharmonic functions are defined by means of scalar-valued upper gradients, and do not rely on a vector-valued differentiable structure.

  • 36.
    Björn, Anders
    et al.
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Björn, Jana
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Lehrback, Juha
    University of Jyvaskyla, Finland.
    Sharp capacity estimates for annuli in weighted R-n and in metric spaces2017In: Mathematische Zeitschrift, ISSN 0025-5874, E-ISSN 1432-1823, Vol. 286, no 3-4, p. 1173-1215Article in journal (Refereed)
    Abstract [en]

    We obtain estimates for the nonlinear variational capacity of annuli in weighted R-n and in metric spaces. We introduce four different (pointwise) exponent sets, show that they all play fundamental roles for capacity estimates, and also demonstrate that whether an end point of an exponent set is attained or not is important. As a consequence of our estimates we obtain, for instance, criteria for points to have zero (resp. positive) capacity. Our discussion holds in rather general metric spaces, including Carnot groups and many manifolds, but it is just as relevant on weighted R-n. Indeed, to illustrate the sharpness of our estimates, we give several examples of radially weighted R-n, which are based on quasiconformality of radial stretchings in R-n.

  • 37.
    Björn, Anders
    et al.
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Björn, Jana
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Lehrback, Juha
    University of Jyväskylä, Finland.
    The annular decay property and capacity estimates for thin annuli2017In: Collectanea Mathematica (Universitat de Barcelona), ISSN 0010-0757, E-ISSN 2038-4815, Vol. 68, no 2, p. 229-241Article in journal (Refereed)
    Abstract [en]

    We obtain upper and lower bounds for the nonlinear variational capacity of thin annuli in weighted and in metric spaces, primarily under the assumptions of an annular decay property and a Poincar, inequality. In particular, if the measure has the 1-annular decay property at and the metric space supports a pointwise 1-Poincar, inequality at , then the upper and lower bounds are comparable and we get a two-sided estimate for thin annuli centred at . This generalizes the known estimate for the usual variational capacity in unweighted . We also characterize the 1-annular decay property and provide examples which illustrate the sharpness of our results.

  • 38.
    Björn, Anders
    et al.
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Björn, Jana
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Maly, Jan
    University of JE Purkyne, Czech Republic.
    Quasiopen and p-Path Open Sets, and Characterizations of Quasicontinuity2017In: Potential Analysis, ISSN 0926-2601, E-ISSN 1572-929X, Vol. 46, no 1, p. 181-199Article in journal (Refereed)
    Abstract [en]

    In this paper we give various characterizations of quasiopen sets and quasicontinuous functions on metric spaces. For complete metric spaces equipped with a doubling measure supporting a p-Poincar, inequality we show that quasiopen and p-path open sets coincide. Under the same assumptions we show that all Newton-Sobolev functions on quasiopen sets are quasicontinuous.

  • 39.
    Björn, Anders
    et al.
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Björn, Jana
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Shanmugalingam, Nageswari
    University of Cincinnati, OH 45221 USA.
    The Mazurkiewicz Distance and Sets that are Finitely Connected at the Boundary2016In: Journal of Geometric Analysis, ISSN 1050-6926, E-ISSN 1559-002X, Vol. 26, no 2, p. 873-897Article in journal (Refereed)
    Abstract [en]

    We study local connectedness, local accessibility and finite connectedness at the boundary, in relation to the compactness of the Mazurkiewicz completion of a bounded domain in a metric space. For countably connected planar domains we obtain a complete characterization. It is also shown exactly which parts of this characterization fail in higher dimensions and in metric spaces.

  • 40.
    Björn, Jana
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, The Institute of Technology.
    De Giorgi's method: in(s) and out(s)2011Conference paper (Refereed)
    Abstract [en]

    One of the main break-throughs in the 20th century mathematics was De Giorgi's proof of Hölder continuity for solutions of elliptic PDEs. His method has since then been used to prove interior regularity in various contexts.It is maybe less known, though not entirely surprising that De Giorgi's method also yields sufficient conditions for boundary regularity. In the talk, I will discuss a recent variation of De Giorgi's method which goes in the opposite direction, leading to a necessary condition for boundary regularity of PDEs and variational integrals.

  • 41.
    Björn, Jana
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, The Institute of Technology.
    Dirichlet problem on bad sets and fine topology2011Conference paper (Refereed)
  • 42.
    Björn, Jana
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, The Institute of Technology.
    Fine topology by means of potential theory on metric spaces2013Conference paper (Refereed)
  • 43.
    Björn, Jana
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, The Institute of Technology.
    Fine topology by means of potential theory on metric spaces2013Conference paper (Refereed)
  • 44.
    Björn, Jana
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, The Institute of Technology.
    Metrics, prime ends and the Dirichlet problem on bad domains2013Conference paper (Refereed)
  • 45.
    Björn, Jana
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, The Institute of Technology.
    Obstacle problems on bad sets, minimal gradients and fine topology2012Conference paper (Refereed)
  • 46.
    Björn, Jana
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, The Institute of Technology.
    Quasiminimizers - BMO, integrability and examples2010Conference paper (Refereed)
  • 47.
    Björn, Jana
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Sharp exponents and a Wiener type condition for boundary regularity of quasiminimizers2016In: Advances in Mathematics, ISSN 0001-8708, E-ISSN 1090-2082, Vol. 301, p. 804-819Article in journal (Refereed)
    Abstract [en]

    We obtain a sufficient condition for boundary regularity of quasiminimirers of the p-energy integral in terms of a Wiener type sum. The exponent in the sum is independent of the dimension and is explicitly expressed in terms of p and the quasiminimizing constant. We also show by an example that the exponent is sharp in a certain sense. (C) 2016 Elsevier Inc. All rights reserved.

  • 48.
    Björn, Jana
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    The Dirichlet problem and boundary regularity for nonlinear parabolic equations2016Conference paper (Other academic)
  • 49.
    Björn, Jana
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, The Institute of Technology.
    The Dirichlet problem on bad domains using metrics and prime ends2014Conference paper (Refereed)
    Abstract [en]

    The Perron{Wiener{Brelot method is a powerful way of solving the Dirichlet problem in general domains. For every boundary data it provides an upper and a lower solution. In the case of the Laplace equation it is well known when these two solutions coincide and resolutive boundary data are characterized by means of the harmonic measure. For the nonlinear p-Laplace equation, the class of resolutive boundary data is not known, but there are some partial results, e.g. that continuous boundary data are resolutive. The invariance under perturbations on sets of capacity zero is also not fully understood in the nonlinear case. In the talk we shall see how some of these questions can be attacked by changing the metric in the domain and by considering new capacities.

  • 50.
    Björn, Jana
    et al.
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, The Institute of Technology.
    Björn, Anders
    Lehrbäck, Juha
    University of Jyväskylä, Finland.
    Sharp capacity estimates for annuli in Rn and in metric spaces2014Conference paper (Refereed)
    Abstract [en]

    We obtain estimates for the nonlinear variational capacity of annuli in weighted Rn and in metric spaces. We introduce four different (pointwise) exponent sets, show that they all play fundamental roles for capacity estimates, and also demonstrate that whether an end point of an exponent set is attained or not is important. As a consequence of our estimates we obtain, for instance, criteria for points to have zero (resp. positive) capacity. Our discussion holds in rather general metric spaces, including Carnot groups and many manifolds, but it is just as relevant on weighted Rn. Indeed, to illustrate the sharpness of our estimates, we give several examples of radially weighted Rn, which are based on quasiconformality of radial stretchings in Rn.

     

1234 1 - 50 of 155
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • 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