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  • 51.
    Lennerstad, Håkan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Local Linear Time Convergence of a Primal-Dual Energy Minimization Algorithm for Parallel Processing2014Conference paper (Refereed)
    Abstract [en]

    We consider energy minimization by speed-scaling of an open shop multiprocessor with n jobs and m machines. The paper studies the complexity of a primal-dual solution algorithm of [4], which was an open question in that paper.We prove that in a neighbourhood of the solution the complexity of the algorithm is O(mn log(1/ε) if n and m are not equal and ε is the roundoff error of the computer. The paper demonstrates how linearization can be used to investigate the complexity of an algorithm close to the optimum. An estimate of the size of the neighbourhood where the linearization error is smaller than the computer’s roundoff error is also given.

  • 52.
    Lennerstad, Håkan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Spectrums of knowledge types: mathematics, mathematics education and praxis knowledge2008In: Proceedings of MADIF6, Swedish Society for Research in Mathematics Education , 2008Conference paper (Refereed)
    Abstract [en]

    Knowledge in different research paradigms is discussed: mathematics, mathematics education and a paradigm of practical knowledge. I argue that the three paradigms as highly distinct, different and important. They try to cope with entirely different types of knowledge, all highly relevant for mathematics teachers.

    While mathematics is deductive and mathematical education is evidence based, practical knowledge is a type of knowledge that professionals in any profession develop by experience and by exchange with other professionals. It is based on experience more than on written text. It is well known that it to a large extent is difficult to articulate. Such knowledge is also essential in important types of mathematical knowledge. We discuss the role played by vagueness in mathematics. We also discuss linguistic mathematics knowledge which typically is present but mostly unformulated, as the mother tongue.

    I argue that mathematics, pedagogy and mathematics education suffers from drawbacks by being strongly rooted in the positivist tradition, in which knowledge can always be expressed in words – otherwise it is not knowledge. Central aspects of teacher’s day-to-day profession are too complicated to be captured in words. However, work has been done to allow such practical knowledge to be formulated among professionals. I would like to sketch a more fluent cooperation between the paradigms, in which the advantages of all the different knowledge types may interact and become increasingly useful to each other.

    For such an idea to reach reality, an efficient meeting form is needed. The Dialogue Seminar is developed precisely to study and communicate difficult-to-articulate practical knowledge among experienced professionals from different areas, using analogue and metaphor as catalysts. This offers mathematicians, mathematics education researchers, mathematics teachers and teacher students, and others, an excellent opportunity to listen in depth to each other, and to have a dialogue. 

  • 53.
    Lennerstad, Håkan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    The n -dimensional Stern-Brocot tree2019In: International Journal of Number Theory, ISSN 1793-0421Article in journal (Refereed)
    Abstract [en]

    This paper generalizes the Stern-Brocot tree to a tree that consists of all sequences of n coprime positive integers. As for n = 2, each sequence P is the sum of a specific set of other coprime sequences, its Stern-Brocot set B(P), where |B(P)| is the degree of P. With an orthonormal base as the root, the tree defines a fast iterative structure on the set of distinct directions in ℤ+n and a multiresolution partition of S+n-1. Basic proofs rely on a matrix representation of each coprime sequence, where the Stern-Brocot set forms the matrix columns. This induces a finitely generated submonoid SB(n, ℕ) of SL(n, ℕ), and a unimodular multidimensional continued fraction algorithm, also generalizing n = 2. It turns out that the n-dimensional subtree starting with a sequence P is isomorphic to the entire |B(P)|-dimensional tree. This allows basic combinatorial properties to be established. It turns out that also in this multidimensional version, Fibonacci-type sequences have maximal sequence sum in each generation. © 2019 World Scientific Publishing Company.

  • 54.
    Lennerstad, Håkan
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Eriksson, Mattias
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    List graphs and distance-consistent node labelings2018In: Electronic Journal of Graph Theory and Applications, ISSN 2338-2287, Vol. 6, no 1, p. 152-165Article in journal (Refereed)
    Abstract [en]

    In this paper we consider node labelings c of an undirected connected graph G = (V,E) with labels (1, 2, ...,|V|), which induce a list distance c(u, v) = |c(v) - c(u)| besides the usual graph distance d(u, v). Our main aim is to find a labeling c so c(u; v) is as close to d(u, v) as possible. For any graph we specify algorithms to find a distance-consistent labeling, which is a labeling c that minimize Σ u,vεV (c(u, v) - d(u, v))2. Such labeliings may provide structure for very large graphs. Furthermore, we define a labeling c fulfilling d(u1, v1) < d(u2, v2) ) c(u1, v1) ⇒ c(u2, v2) for all node pairs u1; v1 and u2; v2 as a list labeling, and a graph that has a list labeling is a list graph. We prove that list graphs exist for all n = |V| and all k = |E|: n - 1 ≤ k ≤ n(n - 1)/2, and establish basic properties. List graphs are Hamiltonian, and show weak versions of properties of path graphs. © 2018 Indonesian Combinatorics Society.

  • 55.
    Lennerstad, Håkan
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Ljungblad, Ann-Louise
    Matematik och respekt: matematikens mångfald och lyssnandets konst2012Book (Other (popular science, discussion, etc.))
  • 56.
    Lindberg, Terese
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Health.
    Bohman, Doris M.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Health.
    Elmstahl, Solve
    Lund Univ, Dept Hlth Sci, Lund, Sweden..
    Jogreus, Claes
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Berglund, Johan Sanmartin
    Blekinge Institute of Technology, Faculty of Engineering, Department of Health.
    Prevalence of unknown and untreated arrhythmias in an older outpatient population screened by wireless long-term recording ECG2016In: Clinical Interventions in Aging, ISSN 1176-9092, E-ISSN 1178-1998, Vol. 11, p. 1083-1090Article in journal (Refereed)
    Abstract [en]

    Purpose: With longer life expectancies, the prevalence of arrhythmias is increasing; thus, there is a need for new methods to screen the older outpatient population. This population-based study describes the prevalence of arrhythmias in 200 outpatients aged. 66 years. We also investigated the feasibility of wireless long-term recording (LTR) using the ECG-BodyKom (R). Methods: Two hundred elderly persons aged 66-93 years were recruited from the Swedish National Study on Aging and Care in 2010-2013, and data were collected via wireless LTR ECG-BodyKom. Results: Screening with the LTR ECG revealed that persistent atrial fibrillation (AF) occurred in 10% of the outpatient population aged. 66 years. Paroxysmal AF occurred in 5.5% of the population, with no difference between younger (60-80 years) and older (>80 years) elderly participants. Furthermore, all patients with paroxysmal AF had a CHA(2)DS(2)VASc score of >= 2 and were therefore potential candidates for follow-up and medical examination. LTR ECG-BodyKom can be considered a feasible method to screen for arrhythmias in older outpatient populations. This simple method requires little of the user, and there was high satisfaction with the equipment and a good overall experience wearing it. Conclusion: The increasing occurrence of arrhythmias in the older population, as well as the high number of untreated cases of arrhythmias such as persistent AF and paroxysmal AF, poses a challenge for health care. Therefore, it is essential to develop effective strategies for their prevention and treatment.

  • 57.
    Lundberg, Lars
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science.
    Lennerstad, Håkan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Boeva, Veselka
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science.
    García Martín, Eva
    Handling non-linear relations in support vector machines through hyperplane folding2019In: ACM International Conference Proceeding Series, Association for Computing Machinery , 2019, p. 137-141Conference paper (Refereed)
    Abstract [en]

    We present a new method, called hyperplane folding, that increases the margin in Support Vector Machines (SVMs). Based on the location of the support vectors, the method splits the dataset into two parts, rotates one part of the dataset and then merges the two parts again. This procedure increases the margin as long as the margin is smaller than half of the shortest distance between any pair of data points from the two different classes. We provide an algorithm for the general case with n-dimensional data points. A small experiment with three folding iterations on 3-dimensional data points with non-linear relations shows that the margin does indeed increase and that the accuracy improves with a larger margin. The method can use any standard SVM implementation plus some basic manipulation of the data points, i.e., splitting, rotating and merging. Hyperplane folding also increases the interpretability of the data. © 2019 Association for Computing Machinery.

  • 58.
    Lännström, Daniel
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Chain conditions for epsilon-strongly graded rings with applications to Leavitt path algebrasManuscript (preprint) (Other academic)
    Abstract [en]

    Let $G$ be a group with neutral element $e$ and let $S=\bigoplus_{g \in G}S_g$ be a $G$-graded ring. A necessary condition for $S$ to be noetherian is that the principal component $S_e$ is noetherian. The following partial converse is well-known: If $S$ is strongly-graded and $G$ is a polycyclic-by-finite group, then $S_e$ being noetherian implies that $S$ is noetherian. We will generalize the noetherianity result to the recently introduced class of epsilon-strongly graded rings. We will also provide results on the artinianity of epsilon-strongly graded rings.

    As our main application we obtain characterizations of noetherian and artinian Leavitt path algebras with coefficients in a general unital ring. This extends a recent characterization by Steinberg for Leavitt path algebras with coefficients in a commutative unital ring and previous characterizations by Abrams, Aranda Pino and Siles Molina for Leavitt path algebras with coefficients in a field. Secondly, we obtain characterizations of noetherian and artinian unital partial crossed products.

  • 59.
    Lännström, Daniel
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Induced quotient group gradings of epsilon-strongly graded ringsManuscript (preprint) (Other academic)
    Abstract [en]

    Let $G$ be a group and let $S=\bigoplus_{g \in G} S_g$ be a $G$-graded ring. Given a normal subgroup $N$ of $G$, there is a naturally induced $G/N$-grading of $S$. It is well-known that if $S$ is strongly $G$-graded, then the induced $G/N$-grading is strong for any $N$. The class of epsilon-strongly graded rings was recently introduced by Nystedt, Öinert and Pinedo as a generalization of unital strongly graded rings. We give an example of an epsilon-strongly graded partial skew group ring such that the induced quotient group grading is not epsilon-strong. Moreover, we give necessary and sufficient conditions for the induced $G/N$-grading of an epsilon-strongly $G$-graded ring to be epsilon-strong. Our method involves relating different types of rings equipped with local units (s-unital rings, rings with sets of local units, rings with enough idempotents) with generalized epsilon-strongly graded rings. 

  • 60.
    Lännström, Daniel
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    The graded structure of algebraic Cuntz-Pimsner ringsManuscript (preprint) (Other academic)
    Abstract [en]

    The algebraic Cuntz-Pimsner rings are naturally $\mathbb{Z}$-graded rings that generalize both Leavitt path algebras and unperforated $\mathbb{Z}$-graded Steinberg algebras. We  classify strongly, epsilon-strongly and nearly epsilon-strongly graded algebraic Cuntz-Pimsner rings up to graded isomorphism. As an application, we characterize noetherian and artinian fractional skew monoid rings by a single corner automorphism.

  • 61.
    Lännström, Daniel
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    The structure of epsilon-strongly graded rings with applications to Leavitt path algebras and Cuntz-Pimsner rings2019Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The research field of graded ring theory is a rich area of mathematics with many connections to e.g. the field of operator algebras. In the last 15 years, algebraists and operator algebraists have defined algebraic analogues of important operator algebras. Some of those analogues are rings that come equipped with a group grading. We want to reach a better understanding of the graded structure of those analogue rings. Among group graded rings, the strongly graded rings stand out as being especially well-behaved. The development of the general theory of strongly graded rings was initiated by Dade in the 1980s and since then numerous structural results have been established for strongly graded rings.

     In this thesis, we study the class of epsilon-strongly graded rings which was recently introduced by Nystedt, Öinert and Pinedo. This class is a natural generalization of the well-studied class of unital strongly graded rings. Our aim is to lay the foundation for a general theory of epsilon-strongly graded rings generalizing the theory of strongly graded rings. This thesis is based on three articles. The first two articles mainly concern structural properties of epsilon-strongly graded rings. In the first article, we investigate a functorial construction called the induced quotient group grading. In the second article, using results from the first article, we generalize the Hilbert Basis Theorem for strongly graded rings to epsilon-strongly graded rings and apply it to Leavitt path algebras.  In the third article, we study the graded structure of algebraic Cuntz-Pimsner rings. In particular, we obtain a partial classification of unital strongly, epsilon-strongly and nearly epsilon-strongly graded Cuntz-Pimsner rings up to graded isomorphism.

  • 62.
    Machado, Renato
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Pettersson, Mats I.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Vu, Viet Thuy
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Dammert, Patrik
    Hellsten, Hans
    EMPIRICAL-STATISTICAL ANALYSIS OF AMPLITUDE SAR IMAGES FOR CHANGE DETECTION ALGORITHMS2015In: 2015 IEEE INTERNATIONAL GEOSCIENCE AND REMOTE SENSING SYMPOSIUM (IGARSS), 2015, p. 365-368Conference paper (Refereed)
    Abstract [en]

    This paper presents an analysis of pre-filtered clutter VHF SAR images. The image data are reorganized into sub-vectors based on the observation of the image-pair magnitude samples. Based on this approach, we present a statistical description of the SAR clutter obtained by the subtraction between two real SAR images. The statistical analysis based on bivariate distribution data organized into different intervals of magnitude can be an important tool to further understand the properties of the backscattered signal, which can be a valuable premise for change detection processing.

  • 63.
    Mai Hoang, Bien
    et al.
    University of Science, VNM.
    Öinert, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Quasi-duo differential polynomial rings2018In: Journal of Algebra and its Applications, ISSN 0219-4988, E-ISSN 1793-6829, Vol. 17, no 4, article id 1850072Article in journal (Refereed)
    Abstract [en]

    In this article we give a characterization of left (right) quasi-duo differential polynomial rings. We provide non-trivial examples of such rings and give a complete description of the maximal ideals of an arbitrary quasi-duo differential polynomial ring. Moreover, we show that there is no left (right) quasi-duo differential polynomial ring in several indeterminates.

  • 64.
    Molin, R.D.
    et al.
    Federal University of Santa Maria, Brazil.
    Fabrin, A.C.F.
    Federal University of Santa Maria, Brazil.
    Sperotto, P.
    Federal University of Santa Maria, Brazil.
    Alves, D.I.
    Federal University of Santa Maria, Brazil.
    Bayer, F.M.
    Federal University of Santa Maria, Brazil.
    Machado, Renato
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Pettersson, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Dammert, P.
    Saab AB, SWE.
    Hellsten, H.
    Saab AB, SWE.
    Ulander, L
    Totalförsvarets Forskningsinstitut, SWE.
    Iterative Change Detection Algorithm for Low-Frequency UWB SAR2016Conference paper (Refereed)
  • 65.
    Natanael, Rodrigues Gomes
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Viet Thuy, Vu
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Mats, Pettersson
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Patrik, Dammert
    SAAB EDS, SWE.
    Hans, Hellsten
    SAAB EDS, SWE.
    Likelihood ratio test for incoherent wavelength-resolution SAR change detection2016Conference paper (Refereed)
  • 66. Niyizamwiyitira, C.
    et al.
    Lundberg, Lars
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    Lennerstad, Håkan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Utilization-Based Schedulability Test of Real-Time Systems on Virtual Multiprocessors2015In: 2015 44TH INTERNATIONAL CONFERENCE ON PARALLEL PROCESSING WORKSHOPS, IEEE Computer Society, 2015, Vol. 2015-January, p. 267-276Conference paper (Refereed)
    Abstract [en]

    The number of applications that use virtual systems is growing, and one would like to use this kind of systems also for real-time applications with hard deadlines. Virtual machines with many cores are interesting since the underlying physical infrastructure usually contains many cores. We consider hard real-time tasks that execute on a virtual machine with m cores. Tasks are scheduled globally on the cores using fixed-priority preemptive scheduling. This means that a task can execute on different virtual cores at different instances in time. In order to avoid Dhall’s effect, which may cause task sets with even very low utilization to miss deadlines, we classify tasks into two priority classes, namely heavy and light tasks. Heavy tasks have higher priority than light tasks. For light tasks we use rate monotonic priority assignment. In this paper we propose a utilization-based test that shows if a task set is schedulable or not. If the task set is schedulable the test provides the priority for each task. The input to the test is the task set, the number of cores in the virtual machine (m), a period for the virtual machine with m cores, and the blocking time when a virtual machine does not have access to the underlying hardware in each period. © 2015 IEEE.

  • 67.
    Niyizamwiyitira, Christine
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    Niyizamwiyitira, Christine
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    Lennestad, Håkan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    A Utilization-based Schedulability Test of Real-time Systems Running on a Multiprocessor Virtual MachineIn: The Computer JournalArticle in journal (Refereed)
    Abstract [en]

    Virtualization  makes it possible  to  run  multiple  operating  systems  and  applications  on  the  same  physical  hardware  at  the same timeusing Virtual Machines (VMs). Real-time applications with hard deadlineswould also like tobenefit from using VMs. The underlying physical infrastructure usually contains many cores.  In this paper, we consider a hard real-time applicationthat executeson a VM with multiple virtual cores. Tasks are scheduled globally on the multiprocessor VMusing fixed-priority preemptive scheduling. This means that a task can execute on different virtual coresat different instances in time. In order to avoid Dhall’s effect, which may cause task sets with even very low utilization to miss deadlines, we classify tasks into two priority classes, namely heavy and light tasks. Heavy tasks have higher priority than light tasks. For light tasks we use rate monotonic priority assignment. In this paper we propose a utilization-based test that shows if a task set is schedulable or not. If the task set is schedulable, the test also provides an assignment of priorities to tasks. The input to the test is the taskset, the number of cores (processors)in the VM, the period for the multiprocessor VM,the VM’s deadline, the execution time, and the blocking time when theVMdoes not have access to the underlying hardware in each  period.This  work  generalizes  previous  workby  introducing the  VM’sdeadline as  a  parameter.  We  validate  our  study  by simulation, the results show that the priority assignment used by our algorithm scheduleshigher number of task setsthanthose using rate monotonic (RM)priority assignment.

  • 68.
    Nystedt, Patrik
    et al.
    University West, Sweden.
    Öinert, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Simple graded rings, non-associative crossed products and Cayley-Dickson doublingsManuscript (preprint) (Other academic)
    Abstract [en]

    We show that if a non-associative unital ring is graded by a hypercentral group, then the ring is simple if and only if it is graded simple and the center of the ring is a field. Thereby, we extend a result by Jespers from the associative case to the non-associative situation. By applying this result to non-associative crossed products, we obtain non-associative analogues of results by Bell, Jordan and Voskoglou. We also apply this result to Cayley-Dickson doublings, thereby obtaining a new proof of a classical result by McCrimmon.

  • 69.
    Nystedt, Patrik
    et al.
    University West, SWE.
    Öinert, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Pinedo, Héctor
    Industrial University of Santander, COL.
    Artinian and noetherian partial skew groupoid rings2018In: Journal of Algebra, ISSN 0021-8693, E-ISSN 1090-266X, Vol. 503, p. 433-452Article in journal (Refereed)
    Abstract [en]

    Let α={α_g : R_{g^{−1}}→R_g}_{g∈mor(G)} be a partial action of a groupoid G on a (not necessarily associative) ring R and let S=R⋆G be the associated partial skew groupoid ring. We show that if α is global and unital, then S is left (right) artinian if and only if R is left (right) artinian and R_g={0}, for all but finitely many g∈mor(G). We use this result to prove that if α is unital and R is alternative, then S is left (right) artinian if and only if R is left (right) artinian and R_g={0}, for all but finitely many g∈mor(G). This result applies to partial skew group rings, in particular. Both of the above results generalize a theorem by J. K. Park for classical skew group rings, i.e. the case when R is unital and associative, and G is a group which acts globally on R. We provide two additional applications of our main results. Firstly, we generalize I. G. Connell's classical result for group rings by giving a characterization of artinian (not necessarily associative) groupoid rings. This result is in turn applied to partial group algebras. Secondly, we give a characterization of artinian Leavitt path algebras. At the end of the article, we relate noetherian and artinian properties of partial skew groupoid rings to those of global skew groupoid rings, as well as establish two Maschke-type results, thereby generalizing results by M. Ferrero and J. Lazzarin for partial skew group rings to the case of partial skew groupoid rings.

  • 70.
    Nystedt, Patrik
    et al.
    University West, SWE.
    Öinert, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Pinedo, Héctor
    Industrial University of Santander, COL.
    Epsilon-strongly graded rings, separability and semisimplicity2018In: Journal of Algebra, ISSN 0021-8693, E-ISSN 1090-266X, Vol. 514, no Nov., p. 1-24Article in journal (Refereed)
    Abstract [en]

    We introduce the class of epsilon-strongly graded rings and show that it properly contains both the collection of strongly graded rings and the family of unital partial crossed products. We determine when epsilon-strongly graded rings are separable over their principal components. Thereby, we simultaneously generalize a result for strongly group-graded rings by Nastasescu, Van den Bergh and Van Oystaeyen, and a result for unital partial crossed products by Bagio, Lazzarin and Paques. We also show that the family of unital partial crossed products appear in the class of epsilon-strongly graded rings in a fashion similar to how the classical crossed products present themselves in the family of strongly graded rings. Thereby, we obtain, in the special case of unital partial crossed products, a short proof of a general result by Dokuchaev, Exel and Simon concerning when graded rings can be presented as partial crossed products.

  • 71.
    Nystedt, Patrik
    et al.
    Högskolan Väst, SWE.
    Öinert, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences. Blekinge Inst Technol, Dept Math & Nat Sci, SE-37179 Karlskrona, Sweden..
    Richter, Johan
    Mälardalens högskola, SWE.
    NON-ASSOCIATIVE ORE EXTENSIONS2018In: Israel Journal of Mathematics, ISSN 0021-2172, E-ISSN 1565-8511, Vol. 224, no 1, p. 263-292Article in journal (Refereed)
    Abstract [en]

    We introduce non-associative Ore extensions, S = R[X; sigma, delta], for any non-ssociative unital ring R and any additive maps sigma, delta : R -> R satisfying sigma(1) = 1 and delta(1) = 0. In the special case when delta is either left or right R-delta-linear, where R-delta = ker(delta), and R is delta-simple, i.e. {0} and R are the only delta-invariant ideals of R, we determine the ideal structure of the non-associative differential polynomial ring D = R[X; id(R),delta]. Namely, in that case, we show that all non-zero ideals of D are generated by monic polynomials in the center Z(D) of D. We also show that Z(D) = R-delta[p] for a monic p is an element of R-delta [X], unique up to addition of elements from Z(R)(delta) . Thereby, we generalize classical results by Amitsur on differential polynomial rings defined by derivations on associative and simple rings. Furthermore, we use the ideal structure of D to show that D is simple if and only if R is delta-simple and Z(D) equals the field R-delta boolean AND Z(R). This provides us with a non-associative generalization of a result by Oinert, Richter and Silve-strov. This result is in turn used to show a non-associative version of a classical result by Jordan concerning simplicity of D in the cases when the characteristic of the field R-delta boolean AND Z(R) is either zero or a prime. We use our findings to show simplicity results for both non-associative versions of Weyl algebras and non-associative differential polynomial rings defined by monoid/group actions on compact Hausdorff spaces.

  • 72.
    Nystedt, Patrik
    et al.
    Högskolan Väst, SWE.
    Öinert, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Richter, Johan
    Mälardalens högskola, SWE.
    Simplicity of Ore monoid rings2019In: Journal of Algebra, ISSN 0021-8693, E-ISSN 1090-266X, Vol. 530, p. 69-85Article in journal (Refereed)
    Abstract [en]

    Given a non-associative unital ring R, a monoid G and a set π of additive maps R→R, we introduce the Ore monoid ring R[π;G], and, in a special case, the differential monoid ring. We show that these structures generalize, in a natural way, not only the classical Ore extensions and differential polynomial rings, but also the constructions, introduced by Cojuhari, defined by so-called D-structures π. Moreover, for commutative monoids, we give necessary and sufficient conditions for differential monoid rings to be simple. We use this in a special case to obtain new and shorter proofs of classical simplicity results for differential polynomial rings in several variables previously obtained by Voskoglou and Malm by other means. We also give examples of new Ore-like structures defined by finite commutative monoids. © 2019 Elsevier Inc.

  • 73. Oloumi, Daniel
    et al.
    Pettersson, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Mousavi, P.
    Rambabu, K.
    Imaging of oil-well perforations using UWB synthetic aperture radar2015In: IEEE Transactions on Geoscience and Remote Sensing, ISSN 0196-2892, E-ISSN 1558-0644, Vol. 53, no 8, p. 4510-4520Article in journal (Refereed)
    Abstract [en]

    Ultrawideband (UWB) synthetic aperture radar (SAR) as a tool for oil well perforation monitoring is experimentally investigated in this paper. Experiments are conducted on a lab prototype that emulates the small section of an oil well. Oil well perforations are scanned using the designed UWB radar system for different experimental conditions. High-resolution images in both down-range and cross-range are obtained by using UWB pulses and signal processing. High-quality images are constructed using SAR processing algorithm with the proposed modifications. Experiments are carried out for different perforation conditions such as open, partially clogged and fully clogged cases. It is shown by the experiments that the proposed radar technique and the data processing methods are capable of providing more revealing high-quality images. This approach can be applied effectively to monitor the oil well medium and detect well impairment locations.

  • 74.
    Palm, Bruna
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Alves, Dimas
    Universidade Federal do Pampa, BRA.
    Vu, Viet Thuy
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Pettersson, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Bayer, Fabio
    Universidade Federal de Santa Maria, BRA.
    Cintra, Renato
    Universidade Federal de Pernambuco, BRA.
    MacHado, Renato
    Instituto Tecnologico de Aeronautica, BRA.
    Dammert, Patrik
    Saab Electronic Defense Systems, SWE.
    Hellsten, Hans
    Saab Electronic Defense Systems, SWE.
    Autoregressive model for multi-pass SAR change detection based on image stacks2018In: Proceedings of SPIE - The International Society for Optical Engineering / [ed] Bovolo F.,Bruzzone L., SPIE , 2018, Vol. 10789, article id 1078916Conference paper (Refereed)
    Abstract [en]

    Change detection is an important synthetic aperture radar (SAR) application, usually used to detect changes on the ground scene measurements in different moments in time. Traditionally, change detection algorithm (CDA) is mainly designed for two synthetic aperture radar (SAR) images retrieved at different instants. However, more images can be used to improve the algorithms performance, witch emerges as a research topic on SAR change detection. Image stack information can be treated as a data series over time and can be modeled by autoregressive (AR) models. Thus, we present some initial findings on SAR change detection based on image stack considering AR models. Applying AR model for each pixel position in the image stack, we obtained an estimated image of the ground scene which can be used as a reference image for CDA. The experimental results reveal that ground scene estimates by the AR models is accurate and can be used for change detection applications. © 2018 SPIE.

  • 75.
    Palm, Bruna
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Bayer, Fabio
    Universidade Federal de Santa Maria, BRA.
    Cintra, Renato
    Universidade Federal de Per nambuco, BRA.
    Pettersson, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Machado, Renato
    Aeronautics Institute of Technology (ITA), BRA.
    Rayleigh Regression Model for Ground Type Detection in SAR Imagery2019In: IEEE Geoscience and Remote Sensing Letters, ISSN 1545-598X, E-ISSN 1558-0571Article in journal (Refereed)
    Abstract [en]

    This letter proposes a regression model for nonnegative signals. The proposed regression estimates the mean of Rayleigh distributed signals by a structure which includes a set of regressors and a link function. For the proposed model, we present: 1) parameter estimation; 2) large data record results; and 3) a detection technique. In this letter, we present closed-form expressions for the score vector and Fisher information matrix. The proposed model is submitted to extensive Monte Carlo simulations and to the measured data. The Monte Carlo simulations are used to evaluate the performance of maximum likelihood estimators. Also, an application is performed comparing the detection results of the proposed model with Gaussian-, Gamma-, and Weibull-based regression models in synthetic aperture radar (SAR) images.

  • 76.
    Pettersson, Mats
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Sjögren, Thomas K.
    Vu, Viet T.
    Performance of Moving Target Parameter Estimation Using SAR2015In: IEEE Transactions on Aerospace and Electronic Systems, ISSN 0018-9251, E-ISSN 1557-9603, Vol. 51, no 2, p. 1191-1202Article in journal (Refereed)
    Abstract [en]

    Synthetic aperture radar (SAR) gives not only the opportunity to image targets with high resolution but also to measure their position and velocity. Without acceleration (constant speed), the position and velocity both in range and azimuth can be estimated using a multichannel SAR system. This paper introduces a method to find the lower bound on variance of estimate of position and velocity for targets. The method is based on the assumptions needed for the Cramer-Rao lower bound (CRLB). The method works for both narrowband (NB) and ultrawideband (UWB) SAR systems. For demonstration, a monostatic single-channel UWB SAR system operating at low frequency is used. Thus, only lower bounds for estimate variance of azimuth, range, and relative speed are derived.

  • 77.
    Pettersson, Mats
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Vu, Viet Thuy
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Gomes, Natanael Rodrigues
    Universidade Federal de Santa Maria, BRA.
    Dammert, Patrik
    Saab Electronic Defense Systems, SWE.
    Hellsten, Hans
    Saab Electronic Defense Systems, SWE.
    Incoherent detection of man-made objects obscured by foliage in forest area2017In: International Geoscience and Remote Sensing Symposium (IGARSS), Institute of Electrical and Electronics Engineers Inc. , 2017, p. 1892-1895Conference paper (Refereed)
    Abstract [en]

    The paper introduces a new likelihood ratio test (LRT) for incoherent detection of man-made objects obscured by foliage in forest area. The test is performed to detect changes between a reference image and a surveillance image. The method is developed for change detection in high resolution Synthetic Aperture Radar (SAR). For simplicity and lack of more appropriate models, the new LRT is still based on simple and efficient models. If there is no man-made object, the statistical model for clutter and noise of two images will be a bivariate Rayleigh distribution. In contrary, a joint distribution of Rayleigh and uniform is used to model for target, clutter, and noise. The proposed LRT is evaluated using radar data acquired by CARABAS in northern Sweden. The probability of detection is up to 96% with much less than one false alarm per square kilometer. © 2017 IEEE.

  • 78.
    Rakus-Andersson, Elisabeth
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Complex Control Models with Parametric Families of Fuzzy Constrains in Evaluation of Resort Management System2014In: Journal of Advanced Computational Intelligence and Intelligent Informatics, ISSN 1883-8014, Vol. 18, no 3, p. 271-279Article in journal (Refereed)
    Abstract [en]

    In this paper we propose a complex system, involving two control algorithms, to provide a final estimation of Resort Management System (RMS). This distinct RMS quality value depends on some individual appreciations, assigned by customers to basic services. In order to improve the qualities of control actions, we intend to add parametric membership functions of fuzzy sets to the fuzzification part. Another modification considers the newly designed technique of determining some essential estimates in the processing part of control to employ all entry data in the result of final decision.

  • 79.
    Rakus-Andersson, Elisabeth
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Fuzzy decision-making model with qualitative states and fuzzified outcomes2018In: Proceedia Computer Science: Knowledge-Based and Intelligent Information & Engineering Systems: Proceedings of the 22nd International Conference, KES-2018 / [ed] Robert J. Howlett, Carlos Toro, Yulia Hicks, Lakhmi C. Jain, Elsevier, 2018, Vol. 126, p. 2030-2039, article id k18is-162Conference paper (Refereed)
    Abstract [en]

    The classical fuzzy decision-making model is now tested for qualitative compound states-symptoms to select the most efficacious medicine, acting on all symptoms. Instead of terminating the decision procedure in the way comparing values of total utilities of decisions-treatments, we test the aggregated utility values in utility levels. This activity lets us assign a verbally verified utility to each medicine.

  • 80.
    Rakus-Andersson, Elisabeth
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    The new approach to the construction of parametric membership functions for fuzzy sets with unequal supports2017In: Knowledge-Based and Intelligent Information & Engineering Systems: Proceedings of the 21st International Conference, KES-20176-8 September 2017, Marseille, France / [ed] Cecilia Zanni-Merk, Claudia Frydman, Carlos Toro, Yulia Hicks, Robert J. Howlett, Lakhmi C. Jain, Elsevier, 2017, Vol. 112, p. 2057-2065, article id kes17-155Conference paper (Refereed)
    Abstract [en]

    The current research is devoted to developing methods of a novel mathematical interpretation of term-sets of linguistic variables. To the term-sets of the linguistic variables fuzzy sets are assigned. We intend to adopt the π-functions and the π-functions to derive formulas of membership functions of these sets. The fuzzy sets are divided in three families in the case of an odd number of the term-sets. To each family, we assign only one parametric formula, which depends on two parameters: the width of a non-fuzzy set, which contains all supports of the fuzzy sets being representatives of the term-sets, and a number of the term-sets. Provided that the supports of fuzzy sets will be unequal, the membership function of the set, belonging to one of the families, is computed by means of a functional modifier, inserted in the common equation typical of this family. Medical examples explain how to use cumulated membership functions practically. The procedure can be easily computerized.

  • 81.
    Rakus-Andersson, Elisabeth
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Frey, Janusz
    Blekinge Sjukhus, Karlskrona.
    Finite Fuzzy Sets in the Medication Decision Concerning the Retreat of Symptoms in Radiation Cystitis2015In: The Proceedings of the International Conference eHEALTH 2015 / [ed] Mario Macedo, Claire Genzenta, Guo Chao Peng, Miguel Baptista Nunes, IADIS PRESS , 2015, p. 55-62Conference paper (Refereed)
    Abstract [en]

    Radiation cystitis is a rare disease, appearing as the result of radiation of pelvic tumors. We support mathematically the recognition of the most efficacious treatments, which reduce the impact of symptoms typical of the illness. To permute the therapies in the ordering, commencing with the optimal therapy, we apply the fuzzy decision making model furnished with finite fuzzy sets. These act as measures of the treatment effectiveness-utility. In the solution, we adopt the older operations on fuzzy sets of type 1, which make the model simple to be easily converted into a computer program.

  • 82.
    Rakus-Andersson, Elisabeth
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Frey, Janusz
    Blekinge Sjukhuset, Blekinge County Hospital.
    Fuzzy One-Decision Making Model with Fuzzified Outcomes in the Treatment of Necrotizing Fasciitis2016In: Proceedings of eTELEMED 2016 : The Eighth International Conference on eHealth, Telemedicine, and Social Medicine / [ed] Marike Hettinga et al., International Academy, Research and Industry Association (IARIA), 2016, p. 145-152Conference paper (Refereed)
    Abstract [en]

    By proposing a new approach to fuzzy decision making, we try to support the medical decision, concerning recommendations for the treatment with hyperbaric oxygen (HBO). This treatment can be used for patients, suffering from necrotizing fasciitis. Due to the disease rarity, it sometimes is difficult for a physician to determine, if a single patient needs the treatment with HBO. We thus identify the decision with a linguistic variable, equipped with treatment recommendation levels. The choice of the appropriate level is based on values of clinical symptoms, found in the patient. To extract the optimal recommendation level for the treatment with HBO, we involve fuzzy set techniques in the decision model. In the paper, we mainly concentrate on designs of fuzzy sets, standing for clinical symptoms and recommendation levels. The levels act as the outcomes, dependent on the cumulative input of the patient’s clinical markers. Since the focus is laid on a parametric structure of the outcomes, then we can categorize the model as robust approach to algorithmic modeling of outcomes, being part of eHealth data records.

  • 83.
    Rakus-Andersson, Elisabeth
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Frey, Janusz
    Örebro University Hospital, Department of Urology.
    Similarity coefficients of normal distributions in selecting the optimal treatments2016In: Proccedings of the International e-HEALTH Conference 2016. Part of Proceedings of the Multi-Conference of Computer Science and Information Systems 2016 / [ed] Mario Macedo, IADIS Press, 2016, p. 115-122, article id 13Conference paper (Refereed)
    Abstract [en]

    In the current research, we aim to define a new form of the similarity coefficient to compare the resemblance grade of two Gaussian density functions. We aim to assess the method utility on a theoretical model. The density functions are stated for a biological marker “survival length”, observed in three groups of patients, suffering from a hypothetical disease. The first group consists of patients who are not treated, whereas we recommend 2 possible treatment methods for the second and the third group, respectively. All the “survival length” assumptions of the model (mean values and standard deviations) are made to exclude the equivocal conclusion, regarding a selection of the better treatment. At the first stage, we apply the measure of similarity to populations: survival among untreated patients contra survival among patients after Treatment 1. Another similarity coefficient estimates a relation between populations: survival among untreated patients versus survival among patients after Treatment 2. The lower value of the coefficient points out the more effective treatment. In order to simplify calculations, proposed in the definition of a similarity coefficient, we approximate the Gaussian curve by a specially designed polynomial, known as the p-function.

  • 84.
    Rakus-Andersson, Elisabeth
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Frey, Janusz
    The Choquet Integral Applied to Ranking Therapies in Radiation Cystitis2015In: INTELLIGENT SYSTEMS'2014, VOL 2: TOOLS, ARCHITECTURES, SYSTEMS, APPLICATIONS, Warzawa: Springer , 2015, Vol. 323, p. 443-452Conference paper (Refereed)
    Abstract [en]

    Radiation cystitis is in general rarely occurring, which makes it very difficult to study in a large group of clinical trials. Most available data about radiation cystitis treatment come from a small number of descriptive studies or from expert opinions. As clinical data are considered to have low quality then physicians, who are still facing patients with a disease hugely influencing quality of life, mostly base on their own experience. We thus want to test fuzzy decision-making model, regarded as a valuable tool, to help in selecting a patient-tailored treatment in radiation cystitis. Theoretical fuzzy decision-making models, possessing the utility matrix filled with distinct utilities of pairs (decision, object-state), give rise to own trials of successfully accomplished applications concerning the item of medication. After interpreting pairs (decision, object-state) as (therapy, symptom), we intend to prove decision-making based on the Choquet integral to extract the optimal treatment in radiation cystitis.

  • 85.
    Rakus-Andersson, Elisabeth
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Frey, Janusz
    Blekinge County Hospital, Karlskrona, Sweden.
    Rutkowska, Danuta
    Czestochowa Uniwersity of Technology, Czestochowa, Poland.
    The Fuzzified Quasi-perceptron in Decision Making Concerning Treatments in Necrotizing Fasciitis2015In: Artificial Intelligence and Soft Computing LNAI 9120: Proceedings of the 14th International Conference ICAISC 2015 / [ed] L. Rutkowski, M. Korytkowski, R. Scherer, R. Tadeusiewicz, L.A. Zadeh, J.M. Zurada, Cham Heidelberg New York Dortrecht London: Springer, 2015, Vol. II, p. 130-141Conference paper (Refereed)
    Abstract [en]

    In the current paper we mathematically try to support the decision concerning the treatment with hyperbaric oxygen for patients, suffering from necrotizing fasciitis. To accomplish the task, we involve the fuzzified model of a quasi-perceptron, which is our modification of the classical artificial simple neuron. By means of the fuzzification of input signals and output decision levels, we wish to distinguish between decisions “treatment without recommended hyperbaric oxygen” versus “treatment with hyperbaric oxygen”. The number of decision levels can be arbitrary in order to extend the decision scale.

  • 86.
    Rakus-Andersson, Elisabeth
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Frey, Janusz
    Blekinge Cty Hosp, Dept Surg & Urol, S-37185 Karlskrona, Sweden..
    Rutkowska, Danuta
    Czestochowa Tech Univ, Inst Comp & Informat Sci, PL-42201 Czestochowa, Poland..
    The Fuzzified Quasi-Perceptron in Decision Making Concerning Treatments in Necrotizing Fasciitis2015In: ARTIFICIAL INTELLIGENCE AND SOFT COMPUTING, PT II (ICAISC 2015), Springer, 2015, p. 130-141Conference paper (Refereed)
    Abstract [en]

    In the current paper we mathematically try to support the decision concerning the treatment with hyperbaric oxygen for patients, suffering from necrotizing fasciitis. To accomplish the task, we involve the fuzzified model of a quasi-perceptron, which is our modification of the classical artificial simple neuron. By means of the fuzzification of input signals and output decision levels, we wish to distinguish between decisions "treatment without recommended hyperbaric oxygen" versus "treatment with hyperbaric oxygen". The number of decision levels can be arbitrary in order to extend the decision scale.

  • 87.
    Rameez, Muhammad
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Dahl, Mattias
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Pettersson, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Adaptive digital beamforming for interference suppression in automotive FMCW radars2018In: 2018 IEEE Radar Conference, (RadarConf 2018), Institute of Electrical and Electronics Engineers Inc. , 2018, p. 252-256Conference paper (Refereed)
    Abstract [en]

    This paper addresses the problem of mutual interference between automotive radars. This problem is getting more attention with an increase in the number of radar systems used in traffic. An adaptive digital beamforming technique is presented here which suppresses the interference without the exact knowledge of the interfering signal's Direction of Arrival (DoA). The proposed technique is robust and does not rely on any calibration for the interference cancellation. The adaptive interference suppression method is evaluated using a simulated scenario. Up to about 20-23 dB improvement in the target Signal to Interference and Noise Ratio (SINR) is measured in the simulation and a better detection performance is achieved using the proposed interference suppression technique. © 2018 IEEE.

  • 88.
    Renato, Machado
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Vu, Viet Thuy
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Pettersson, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Dammert, Patrik
    Saab Electronic Defense Systems, SWE.
    Hellsten, Hans
    Saab Electronic Defense Systems, SWE.
    The stability of UWB low-frequency SAR images2016In: IEEE Geoscience and Remote Sensing Letters, ISSN 1545-598X, E-ISSN 1558-0571, Vol. 13, no 8, p. 1114-1118Article in journal (Refereed)
    Abstract [en]

    This letter presents an analysis of prefiltered clutter ultrawideband (UWB) very high frequency synthetic aperture radar (SAR) images. The image data are reorganized into subvectors based on the observation of the image-pair magnitude samples. Based on this approach, we present a statistical description of the SAR clutter obtained by the subtraction between two real SAR images. The statistical analysis based on bivariate distribution data organized into different intervals of magnitude can be an important tool to further understand the properties of the backscattered signal for low-frequency SAR images. In this letter, it is found that, for “good” image pairs, the subtracted image has Gaussian distributed clutter backscattering and that the noise mainly consists of the thermal noise and, therefore, speckle noise does not have to be considered. This is a consequence of the stable backscattering for a UWB low-frequency SAR system.

  • 89. Schlosser, Edson R.
    et al.
    Farias, Roger L.
    Heckler, Marcos V. T.
    Machado, Renato
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Optimization of switched-beam arrays for communication systems2014In: 2014 11TH INTERNATIONAL SYMPOSIUM ON WIRELESS COMMUNICATIONS SYSTEMS (ISWCS), IEEE , 2014, p. 579-583Conference paper (Refereed)
    Abstract [en]

    This paper presents the application of optimization methods for the synthesis of a linear array for communication systems. By means of suitably beam switching, the array should provide coverage of a given angular area in azimuth and should allow controlling the sidelobe level simultaneously. For this purpose, two optimization methods have been used to calculate the excitation coefficient for each desired beam. The synthesis technique is demonstrated for arrays composed of isotropic and microstrip elements. By comparing the results obtained for both arrays, the need of consideration of the array element pattern during the synthesis process is demonstrated.

  • 90.
    Schwieger, Kay
    et al.
    Iteratec GmbH, GER.
    Wagner, Stefan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Part III, Free Actions of Compact Quantum Groups on C*-Algebras2017In: SIGMA. Symmetry, Integrability and Geometry, ISSN 1815-0659, E-ISSN 1815-0659, Vol. 13, article id 62Article in journal (Refereed)
    Abstract [en]

    We study and classify free actions of compact quantum groups on unital C*-algebras in terms of generalized factor systems. Moreover, we use these factor systems to show that all finite coverings of irrational rotation C*-algebras are cleft.

  • 91.
    Sidorova, Yulia
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    Sköld, Lars
    Telenor, SWE.
    Lennerstad, Håkan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Lundberg, Lars
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    The Use of Fuzzy Logic in Creating a Visual Data Summary of a Telecom Operator’s Customer Base2019In: Communications in Computer and Information Science, Springer Verlag , 2019, Vol. 932, p. 301-312Conference paper (Refereed)
    Abstract [en]

    As pointed out by Zadeh, the mission of fuzzy logic in the era of big data is to create a relevant summary of huge amounts of data and facilitate decision-making. In this study, elements of fuzzy set theory are used to create a visual summary of telecom data, which gives a comprehensive idea concerning the desirability of boosting an operator’s presence in different neighborhoods and regions. The data used for validation cover historical mobility in a region of Sweden during a week. Fuzzy logic allows us to model inherently relative characteristics, such as “a tall man” or “a beautiful woman”, and importantly it also defines “anchors”, the situations (characterized with the value of the membership function for the characteristic) under which the relative notion receives a unique crisp interpretation. We propose color coding of the membership value for the relative notions such as “the desirability of boosting operator’s presence in the neighborhood” and “how well the operator is doing in the region”. The corresponding regions on the map (e.g., postcode zones or larger groupings) are colored in different shades passing from green (1) though yellow (0.5) to red (0). The color hues pass a clear intuitive message making the summary easy to grasp. © 2019, Springer Nature Singapore Pte Ltd.

  • 92.
    Sievert, Thomas
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    GNSS Radio Occultation Inversion Methods and Reflection Observations in the Lower Troposphere2019Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    GNSS Radio Occultation (GNSS-RO) is an opportunistic Earth sensing technique where GNSS signals passing through the atmosphere are received in low Earth orbit and processed to extract meteorological parameters. As signals are received along an orbit, the measured Doppler shift is transformed to a bending angle profile (commonly referred to as bending angle retrieval), which, in turn, is inverted to a refractivity profile. Thanks to its high vertical resolution and SI traceability, GNSS-RO is an important complement to other Earth sensing endeavors. In the lower troposphere, GNSS-RO measurements often get degraded and biased due to sharp refractive gradients and other complex structures. The main objective of this thesis is to explore contemporary retrieval methods such as phase matching and full spectrum inversion to improve their performance in these conditions. To avoid the bias caused by the standard inversion, we attempt to derive additional information from the amplitude output of the examined retrieval operators. While simulations indicate that such information could be found, it is not immediately straightforward how to achieve this with real measurements. The approach chosen is to examine reflected signal components and their effect on the amplitude output.

  • 93.
    Sievert, Thomas
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Rasch, Joel
    Molflow, SWE.
    Anders, Carlström
    RUAG Space AB, SWE.
    Pettersson, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Vu, Viet Thuy
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Determining the refractivity at the bottom of the atmosphere using radio occultation2017In: 2017 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), IEEE, 2017, p. 4433-4436Conference paper (Refereed)
    Abstract [en]

    High accuracy of impact height is important to get reliableRadio Occultation (RO) measurements of the atmosphere refractivity.We have made an investigation on how accuratelywe can measure the impact height at ground level using waveoptics simulations, realistic refractivity profiles, a realisticsimulator for an advanced RO instrument including noise,and using phase matching for the inversion. The idea of theinvestigation is to increase the measurement accuracy of impactheight at low altitudes and to give reliable measurementseven in cases of super-refractive layers. We present statisticson the accuracy and precision of the determination of theimpact height at ground, as well as the resulting accuracy andprecision in the measured refractivity.

  • 94.
    Sievert, Thomas
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Rasch, Joel
    Molflow, Gothenburg, SWE.
    Carlström, Anders
    RUAG Space AB, SWE.
    Pettersson, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Analysis of reflections in GNSS radio occultation measurements using the phase matching amplitude2018In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 11, no 1, p. 569-580Article in journal (Refereed)
    Abstract [en]

    It is well-known that in the presence of super-refractive layers in the lower-tropospheric inversion of GNSSradio occultation (RO) measurements using the Abel trans-form yields biased refractivity profiles. As such it is problem-atic to reconstruct the true refractivity from the RO signal.Additional information about this lower region of the atmo-sphere might be embedded in reflected parts of the signal. Toretrieve the bending angle, the phase matching operator canbe used. This operator produces a complex function of theimpact parameter, and from its phase we can calculate thebending angle. Instead of looking at the phase, in this paperwe focus on the function’s amplitude. The results in this pa-per show that the signatures of surface reflections in GNSSRO measurements can be significantly enhanced when usingthe phase matching method by processing only an appropri-ately selected segment of the received signal. This signatureenhancement is demonstrated by simulations and confirmedwith 10 hand-picked MetOp-A occultations with reflectedcomponents. To validate that these events show signs of re-flections, radio holographic images are generated. Our resultssuggest that the phase matching amplitude carries informa-tion that can improve the interpretation of radio occultationmeasurements in the lower troposphere.

  • 95.
    Sievert, Thomas
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Rasch, Joel
    Molflow, SWE.
    Carlström, Anders
    RUAG Space AB, SWE.
    Pettersson, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Vu, Viet Thuy
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Comparing reflection signatures in radio occultation measurements using the full spectrum inversion and phase matching methods2018In: PROCEEDINGS VOLUME 10786; Remote Sensing of Clouds and the Atmosphere XXIII / [ed] Comeron A.,Kassianov E.,Picard R.H.,Schafer K.,Weber K., SPIE - International Society for Optical Engineering, 2018, article id 107860AConference paper (Refereed)
    Abstract [en]

    Global Navigation Satellite System Radio Occultation (GNSS-RO) is an important technique used to sound the Earth's atmosphere and provide data products to numerical weather prediction (NWP) systems as well as toclimate research. It provides a high vertical resolution and SI-traceability that are both valuable complements toother Earth observation systems. In addition to direct components refracted in the atmosphere, many received RO signals contain reflected components thanks to the specular and relatively smooth characteristics of the ocean. These reflected components can interfere the retrieval of the direct part of the signal, and can also contain meteorological information of their own, e.g., information about the refractivity at the Earth's surface. While the conventional method to detect such reflections is by using radio-holographic methods, it has been shown that it is possible to see reflections using wave optics inversion, specically while inspecting the amplitude of the output of phase matching (PM). The primary objective of this paper is to analyze the appearance of these reflections in the amplitude output from another wave optics algorithm, namely the much faster full spectrum inversion (FSI). PM and FSI are closely related algorithms - they both use the method of stationary phase to derive the bending angle from a measured signal. We apply our own implementation of FSI to the same GNSS-RO measurements that PM was previously applied to and show that the amplitudes of the outputs again indicate reflection in the surface of the ocean. Our results show that the amplitudes output from the FSI and PM algorithms are practically identical and that the reflection signatures thus appear equally well.

  • 96.
    Sinaian, Pouya
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Application of Ibragimov's method and Noether's theorem for constructing conservation laws of the linear elasticity model2014Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    In this thesis, conservation laws of the Lame equation describing linear elasticity have been constructed. This has been done by the implementation of two theorems for constructing conservation laws: the new theorem suggested by N H.Ibragimov, and the classical theorem presented by E.Noether. As a result one can see that the Ibragimov method provides more conservation laws than the Noether theorem, which may suggest the better efficiency of the Ibragimov method.

  • 97.
    Sjogren, Thomas
    et al.
    nsoSwedish Def Res Agcy FOI, SWE.
    Vu, Viet
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Detection of slow and fast moving targets using hybrid CD-DMTF SAR GMTI mode2015In: 2015 IEEE 5TH ASIA-PACIFIC CONFERENCE ON SYNTHETIC APERTURE RADAR (APSAR), IEEE , 2015, p. 818-821Conference paper (Refereed)
    Abstract [en]

    TerraSAR-X and TanDEM-X has since 2014 been flying in the monostatic pursuit mode. This mode consists of a formation flying with the satellites having identic orbit, but with a displacement in along-track of a distance corresponding to 10 s delay. Such formation gives e.g. the ability to detect movements of very slow targets or targets standing still and moving between measurements. Depending on the integration time for each satellite and the time separation between the satellites, the clutter may behave as stationary or non-stationary. This allows for the possibility to apply either coherent or incoherent change detection algorithms. As has been proved earlier, the potential of coherent change detection has very good abilities but has proven difficult to obtain on X-band. In the case of very high resolution SAR, there will also be a target smearing effect due to the target movement within the coherent processing interval (CPI). The target defocusing effect may also be used for detection of moving targets in the scene using the so-called Detection of Moving Targets by Focusing (DMTF) technique. This is since an estimate or hypothesis test for target movements can be used to reprocess the SAR image and obtain a Signal-To-Clutter-Noise (SCNR) gain, thus increase chances for moving target detection. Therefore, a combination of DMTF and change detection over short times is promising. As such, this paper investigates the potential of the monostatic pursuit mode for GMTI.

  • 98. Thern, Emelie
    et al.
    Sjögren Forss, Katarina
    Blekinge Institute of Technology, Faculty of Health Sciences, Department of Health.
    Jogreus, Claes
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Stjernberg, Louise
    Blekinge Institute of Technology, Faculty of Health Sciences, Department of Health.
    Exercise and factors associated with active commuting2014Conference paper (Refereed)
    Abstract [en]

    Background: In order to increase the current levels of physical activity new strategies have been suggested where it is incorporated into daily routines, such as commuting to and from school/work. Active commuting i.e. cycling or walking to and from school/work is an excellent strategy to increase the overall activity levels. Even though the health benefits of active commuting are well documented, non-active modes of transportation (i.e. cars, bus, train) remain the main mode of transportation. The purpose of the present study is to examine the prevalence and what factors are influencing participation in active commuting in the municipality of Karlskrona, Sweden. Method: A cross-sectional study, including base-line data from parents-to- be was carried out, including 432 participants. Questionnaires were filled in and data collection was conducted during a year in 2008 and 2009. The results were calculated using multivariate logistic regression with odds ratios (OR) and 95% confidence interval (CI). Results: The main mode of commuting was motorised vehicle (63.0%), whilst active commuters were a minority (8.3%). The regression model demonstrated a negative association between being Swedish and AC; as such immigrants were more likely to be active commuters (CI 0.08-0.80). The variable mostly associated with AC was the type of residential area. Participants living in an urban area had 5.4 times higher odds of AC compared to participants living in a rural area (CI 1.51-18.54). Being surrounded by a green-space environment decreased the probability of engaging in AC compared to being surrounded by buildings the majority of time (CI 0.07-0.60). Another important variable was outdoor recreational PA, were engaging resulted in 3.9 times higher odds of AC compared to those not engaging in outdoor recreational PA (CI 1.31-11.71). Although the variable pet-ownership remained in the last step of the model non-significant, it explains some of the variance in the model (0.10-1.24). Conclusions: The number of people being active are modest and are instead using other modes of transportation. This study found several factors both facilitating and impeding active commuting, signifying the importance of applying a broad health promotional approach to active commuting.

  • 99. Thern, Emelie
    et al.
    Sjögren Forss, Katarina
    Blekinge Institute of Technology, Faculty of Health Sciences, Department of Health.
    Jogreus, Claes
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Stjernberg, Louise
    Blekinge Institute of Technology, Faculty of Health Sciences, Department of Health.
    Factors associated with active commuting among parents-to-be in Karlskrona, Sweden2015In: Scandinavian Journal of Public Health, ISSN 1403-4948, E-ISSN 1651-1905, Vol. 43, no 1, p. 59-65Article in journal (Refereed)
    Abstract [en]

    Aim: The purpose of the present study is to examine the prevalence of active commuting and factors associated with participation in active commuting in the municipality of Karlskrona, Sweden. Active commuting is defined here as walking or cycling to and from school/work for at least 15 min one-way. Method: A cross-sectional study was carried out, which included baseline data from parents-to-be. Pregnant females and their partners were invited to participate in the study when they contacted either of the municipality’s two antenatal clinics. Data collection ran from March 2008 to February 2009. When completing the questionnaire, the participants were asked to reflect on their situation one month before the female became pregnant. The final sample consisted of 432 participants (response rate 51.9% for females and 85.0% for males). Results: The main mode of commuting was motor vehicle (63.0%), with active commuters forming a minority (8.3%). The main facilitating factor for active commuting was living in an urban as opposed to a rural area. Regular participation in outdoor recreational physical activity was significantly positively associated with active commuting. Being Swedish and being surrounded by a green space environment were significantly negatively associated with active commuting. Conclusions: This study found that the number of people who are active commuters is modest and other modes of transportation are preferred. Several facilitating and impeding factors associated with active commuting were also found, indicating the importance of applying a broad health-promoting approach to encouraging active commuting.

  • 100.
    Thomas, Sjögren
    et al.
    Totalforsvarets forskningsinstitut, SWE.
    Vu, Viet Thuy
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Pettersson, Mats
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Experimental result for SAR GMTI using monostatic pursuit mode of TerraSAR-X and TanDEM-X on staring spotlight images2016In: Proceedings of EUSAR 2016: 11th European Conference on Synthetic Aperture Radar, IEEE, 2016, p. 207-210, article id 7559278Conference paper (Refereed)
    Abstract [en]

    TerraSAR-X and TanDEM-X is able to fly in monostatic pursuit mode, a formation with the satellites in identic orbit displaced in along-Track of a distance corresponding to 10 s delay. Such formation gives e.g. The ability to detect very slow targets or targets moving only between measurements. This can be performed using Change Detection (CD) and/or the Detection of Moving Targets by Focusing (DMTF) technique. A combination of DMTF and CD is promising. To investigate the applicability of the methods for moving target detection, an experiment was performed with TerraSAR-X and TanDEM-X in monostatic pursuit mode and several deployed targets. © VDE VERLAG GMBH · Berlin · Offenbach.

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