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  • 251.
    Alfredsson, Stefan
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science.
    Del Giudice, Giacomo
    Politecnico di Bari, Italy.
    Garcia, Johan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science.
    Brunstrom, Anna
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science.
    De Cicco, Luca
    Ecole superieure d'Electricite, France; Politecnico di Bari, Italy.
    Mascolo, Saverio
    Politecnico di Bari, Italy.
    Observations of Bufferbloat in Swedish Cellular Networks2013In: Proceedings of the 9th Swedish National Computer Networking Workshop (SNCNW 2013) / [ed] Bengt Ahlgren, 2013Conference paper (Refereed)
  • 252.
    Algervik, Robert
    Karlstad University, Faculty of Technology and Science, Avdelningen för matematik.
    Embedding Theorems for Mixed Norm Spaces and Applications2010Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This thesis is devoted to the study of mixed norm spaces that arise in connection with embeddings of Sobolev and Besov type spaces. We study different structural, integrability, and smoothness properties of functions satisfying certain mixed norm conditions. Conditions of this type are determined by the behaviour of linear sections of functions. The work in this direction originates in a paper due to Gagliardo (1958), and was further developed by Fournier (1988), by Blei and Fournier (1989), and by Kolyada (2005).

    Here we continue these studies. We obtain some refinements of known embeddings for certain mixed norm spaces introduced by Gagliardo, and we study general properties of these spaces. In connection with these results, we consider a scale of intermediate mixed norm spaces, and prove intrinsic embeddings in this scale.

    We also consider more general, fully anisotropic, mixed norm spaces. Our main theorem states an embedding of these spaces to Lorentz spaces. Applying this result, we obtain sharp embedding theorems for anisotropic Sobolev-Besov spaces, and anisotropic fractional Sobolev spaces. The methods used are based on non-increasing rearrangements, and on estimates of sections of functions and sections of sets. We also study limiting relations between embeddings of spaces of different type. More exactly, mixed norm estimates enable us to get embedding constants with sharp asymptotic behaviour. This gives an extension of the results obtained for isotropic Besov spaces by Bourgain, Brezis, and Mironescu, and for anisotropic Besov spaces by Kolyada.

    We study also some basic properties (in particular the approximation properties) of special weak type spaces that play an important role in the construction of mixed norm spaces, and in the description of Sobolev type embeddings.

    In the last chapter, we study mixed norm spaces consisting of functions that have smooth sections. We prove embeddings of these spaces to Lorentz spaces. From this result, known properties of Sobolev-Liouville spaces follow.

  • 253.
    Algervik, Robert
    Karlstad University, Faculty of Technology and Science, Avdelningen för matematik.
    Embedding Theorems for Mixed Norm Spaces and Applications2008Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    This thesis is devoted to the study of mixed norm spaces that arise in connection with embeddings of Sobolev and Besov type spaces. The work in this direction originates in a paper due to Gagliardo (1958), and was continued by Fournier (1988) and by Kolyada (2005).

    We consider fully anisotropic mixed norm spaces. Our main theorem states an embedding of these spaces into Lorentz spaces. Applying this result, we obtain sharp embedding theorems for anisotropic fractional Sobolev spaces and anisotropic Sobolev-Besov spaces. The methods used are based on non-increasing rearrangements and on estimates of sections of functions and sections of sets. We also study limiting relations between embeddings of spaces of different type. More exactly, mixed norm estimates enable us to get embedding constants with sharp asymptotic behaviour. This gives an extension of the results obtained for isotropic Besov spaces $B_p^\alpha$ by Bourgain, Brezis, and Mironescu, and for Besov spaces $B^{\alpha_1,\dots,\alpha_n}_p$ by Kolyada.

    We study also some basic properties (in particular the approximation properties) of special weak type spaces that play an important role in the construction of mixed norm spaces and in the description of Sobolev type embeddings.

  • 254.
    Algervik, Robert
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Mathematics.
    Kolyada, Viktor
    Karlstad University, Faculty of Technology and Science, Department of Mathematics.
    On Fournier-Gagliardo mixed norm spaces2011In: Annales Academiae Scientiarum Fennicae Mathematica, ISSN 1239-629X, Vol. 36, p. 493-508Article in journal (Refereed)
    Abstract [en]

    We study mixed norm spaces

    V (Rn)

    that arise in connection with embeddings of

    Sobolev spaces

    W

    1

    1

    (Rn). We prove embeddings of V (Rn)

    into Lorentz type spaces defined in terms

    of iterative rearrangements. Basing on these results, we introduce the scale of mixed norm spaces

    V

    p

    (Rn). We prove that V ½ V p

    and we discuss some questions related to this embedding.

  • 255.
    Alho, Artur
    et al.
    Univ Lisbon, Ctr Math Anal Geometry & Dynam Syst, Inst Super Tecn, Av Rovisco Pais, P-1049001 Lisbon, Portugal..
    Carloni, Sante
    Univ Lisbon, Ctr Multidisciplinar Astrofis CENTRA, Inst Super Tecn, Av Rovisco Pais, P-1049001 Lisbon, Portugal..
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    On dynamical systems approaches and methods in f (R) cosmology2016In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 8, article id 064Article in journal (Refereed)
    Abstract [en]

    We discuss dynamical systems approaches and methods applied to flat Robertson Walker models in f(R)-gravity. We argue that a complete description of the solution space of a model requires a global state space analysis that motivates globally covering state space adapted variables. This is shown explicitly by an illustrative example, f(R) = R + alpha R-2, alpha > 0, for which we introduce new regular dynamical systems on global compactly extended state spaces for the Jordan and Einstein frames. This example also allows us to illustrate several local and global dynamical systems techniques involving, e.g., blow ups of nilpotent fixed points, center manifold analysis, averaging, and use of monotone functions. As a result of applying dynamical systems methods to globally state space adapted dynamical systems formulations, we obtain pictures of the entire solution spaces in both the Jordan and the Einstein frames. This shows, e.g., that due to the domain of the conformal transformation between the Jordan and Einstein frames, not all the solutions in the Jordan frame are completely contained in the Einstein frame. We also make comparisons with previous dynamical systems approaches to f (R) cosmology and discuss their advantages and disadvantages.

  • 256.
    Alho, Artur
    et al.
    University of Lisbon, Portugal.
    Hell, Juliette
    Free University Berlin, Germany.
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Global dynamics and asymptotics for monomial scalar field potentials and perfect fluids2015In: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 32, no 14, article id 145005Article in journal (Refereed)
    Abstract [en]

    We consider a minimally coupled scalar field with a monomial potential and a perfect fluid in flat Friedmann-Lemaitre-Robertson-Walker cosmology. We apply local and global dynamical systems techniques to a new three-dimensional dynamical systems reformulation of the field equations on a compact state space. This leads to a visual global description of the solution space and asymptotic behavior. At late times we employ averaging techniques to prove statements about how the relationship between the equation of state of the fluid and the monomial exponent of the scalar field affects asymptotic source dominance and asymptotic manifest self-similarity breaking. We also situate the ’attractor’ solution in the three-dimensional state space and show that it corresponds to the one-dimensional unstable center manifold of a de Sitter fixed point, located on an unphysical boundary associated with the dynamics at early times. By deriving a center manifold expansion we obtain approximate expressions for the attractor solution. We subsequently improve the accuracy and range of the approximation by means of Pade approximants and compare with the slow-roll approximation. 

  • 257.
    Alho, Artur
    et al.
    Technical University of Lisbon, Portugal.
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Global dynamics and inflationary center manifold and slow-roll approximants2015In: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 56, no 1, article id 012502Article in journal (Refereed)
    Abstract [en]

    We consider the familiar problem of a minimally coupled scalar field with quadratic potential in flat Friedmann-Lemaître-Robertson-Walker cosmology to illustrate a number of techniques and tools, which can be applied to a wide range of scalar field potentials and problems in, e.g., modified gravity. We present a global and regular dynamical systems description that yields a global understanding of the solution space, including asymptotic features. We introduce dynamical systems techniques such as center manifold expansions and use Padé approximants to obtain improved approximations for the “attractor solution” at early times. We also show that future asymptotic behavior is associated with a limit cycle, which shows that manifest self-similarity is asymptotically broken toward the future and gives approximate expressions for this behavior. We then combine these results to obtain global approximations for the attractor solution, which, e.g., might be used in the context of global measures. In addition, we elucidate the connection between slow-roll based approximations and the attractor solution, and compare these approximations with the center manifold based approximants.

  • 258.
    Alho, Artur
    et al.
    Center for Mathematical Analysis, Geometry and Dynamical Systems, Instituto Superior Técnico, Universidade de Lisboa, Portugal.
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Inflationary alpha-attractor cosmology: A global dynamical systems perspective2017In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 95, no 8, article id 083517Article in journal (Refereed)
    Abstract [en]

    We study flat Friedmann-Lemaitre-Robertson-Walker alpha-attractor E- and T-models by introducing a dynamical systems framework that yields regularized unconstrained field equations on two-dimensional compact state spaces. This results in both illustrative figures and a complete description of the entire solution spaces of these models, including asymptotics. In particular, it is shown that observational viability, which requires a sufficient number of e-folds, is associated with a particular solution given by a one-dimensional center manifold of a past asymptotic de Sitter state, where the center manifold structure also explains why nearby solutions are attracted to this "inflationary attractor solution." A center manifold expansion yields a description of the inflationary regime with arbitrary analytic accuracy, where the slow-roll approximation asymptotically describes the tangency condition of the center manifold at the asymptotic de Sitter state.

  • 259.
    Alho, Artur
    et al.
    Univ Lisbon, Inst Super Tecn, Ctr Math Anal Geometry & Dynam Syst, P-1049001 Lisbon, Portugal..
    Uggla, Claes
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Scalar field deformations of Lambda CDM cosmology2015In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 92, no 10, article id 103502Article in journal (Refereed)
    Abstract [en]

    This paper treats nonrelativistic matter and a scalar field phi with a monotonically decreasing potential minimally coupled to gravity in flat Friedmann-Lemaitre-Robertson-Walker cosmology. The field equations are reformulated as a three-dimensional dynamical system on an extended compact state space, complemented with cosmographic diagrams. A dynamical systems analysis provides global dynamical results describing possible asymptotic behavior. It is shown that one should impose global and asymptotic bounds on lambda = -V-1 dV/d phi to obtain viable cosmological models that continuously deform Lambda CDM cosmology. In particular we introduce a regularized inverse power-law potential as a simple specific example.

  • 260. Ali, A
    et al.
    Hoagg, J. B
    Mossberg, Magnus
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Bernstein, D. S
    Growing window recursive quadratic optimization with variable regularization2010Conference paper (Refereed)
  • 261.
    Ali, Asad A.
    et al.
    Univ Michigan, Dept Aerosp Engn, Ann Arbor, MI 48109 USA..
    Hoagg, Jesse B.
    Univ Kentucky, Dept Mech Engn, 151 Ralph G Anderson Bldg, Lexington, KY 40507 USA..
    Mossberg, Magnus
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Bernstein, Dennis S.
    Univ Michigan, Dept Aerosp Engn, Ann Arbor, MI 48109 USA..
    On the stability and convergence of a sliding-window variable-regularization recursive-least-squares algorithm2016In: International journal of adaptive control and signal processing (Print), ISSN 0890-6327, E-ISSN 1099-1115, Vol. 30, no 5, p. 715-735Article in journal (Refereed)
    Abstract [en]

    A sliding-window variable-regularization recursive-least-squares algorithm is derived, and its convergence properties, computational complexity, and numerical stability are analyzed. The algorithm operates on a finite data window and allows for time-varying regularization in the weighting and the difference between estimates. Numerical examples are provided to compare the performance of this technique with the least mean squares and affine projection algorithms. Copyright (c) 2015 John Wiley & Sons, Ltd.

  • 262.
    Ali, Nour
    et al.
    Brunel University, London, UK.
    Baker, Sean
    University of Limerick, Ireland.
    O’Crowley, Ross
    Red Orkid Limited, Dublin, Ireland.
    Herold, Sebastian
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Buckley, Jim
    University of Limerick, Ireland.
    Architecture consistency: State of the practice, challenges and requirements2018In: Journal of Empirical Software Engineering, ISSN 1382-3256, E-ISSN 1573-7616, Vol. 23, no 1, p. 224-258Article in journal (Refereed)
    Abstract [en]

    Architecture Consistency (AC) aims to align implemented systems with their intended architectures. Several AC approaches and tools have been proposed and empirically evaluated, suggesting favourable results. In this paper, we empirically examine the state of practice with respect to Architecture Consistency, through interviews with nineteen experienced software engineers. Our goal is to identify 1) any practises that the companies these architects work for, currently undertake to achieve AC; 2) any barriers to undertaking explicit AC approaches in these companies; 3) software development situations where practitioners perceive AC approaches would be useful, and 4) AC tool needs, as perceived by practitioners. We also assess current commercial AC tool offerings in terms of these perceived needs. The study reveals that many practitioners apply informal AC approaches as there are barriers for adopting more formal and explicit approaches. These barriers are: 1) Difficulty in quantifying architectural inconsistency effects, and thus justifying the allocation of resources to fix them to senior management, 2) The near invisibility of architectural inconsistency to customers, 3) Practitioners’ reluctance towards fixing architectural inconsistencies, and 4) Practitioners perception that huge effort is required to map the system to the architecture when using more formal AC approaches and tools. Practitioners still believe that AC would be useful in supporting several of the software development activities such as auditing, evolution and ensuring quality attributes. After reviewing several commercial tools, we posit that AC tool vendors need to work on their ability to support analysis of systems made up of different technologies, that AC tools need to enhance their capabilities with respect to artefacts such as services and meta-data, and to focus more on non-maintainability architectural concerns.

  • 263.
    Ali, Nour
    et al.
    Brunel University, London, UK.
    Baker, Sean
    University of Limerick, Ireland.
    O'Crowley, Ross
    Red Orkid Limited, Dublin, Ireland.
    Herold, Sebastian
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Buckley, Jim
    University of Limerick, Ireland.
    Architecture consistency: State of the practice, challenges and requirements (vol 23, pg 224, 2018)2018In: Journal of Empirical Software Engineering, ISSN 1382-3256, E-ISSN 1573-7616, Vol. 23, no 3, p. 1868-1869Article in journal (Refereed)
  • 264. Ali Yahiya, Tara
    et al.
    Chaouchi, Hakima
    Kassler, Andreas
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science. Karlstad University, Faculty of Economic Sciences, Communication and IT, Centre for HumanIT.
    Pujolle, Guy
    Seamless Interworking of WLAN and WMAN Wireless Networks2006Conference paper (Refereed)
    Abstract [en]

    Future network environments will be heterogeneous and mobile terminals will have the opportunity to dynamically select among many different access technologies. Therefore, it is important to provide service continuity in case of vertical handovers when terminals change the access technology. Two important wireless access technologies are WLAN (Wireless Local Access Networks) and WMAN (Wireless Metropolitan Access Networks) networks. In this paper, we address several challenges related to a seamless integration of those technologies. We highlight important aspects for designing a WLAN/WMAN interworking architecture and we address important Quality of Service (QoS) issues for such interworked systems like degree of QoS support provided by the technologies, QoS mapping and signalling for vertical handover. By formulating several interworking scenarios, where WLAN users with ongoing voice, video and data sessions hand over to WMAN, we study QoS and performance issues and analyse feasibility of seamless session continuity through simulations

  • 265.
    Alizadeh Noghani, Kyoomars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Towards Seamless Live Migration in SDN-Based Data Centers2018Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Live migration of Virtual Machines (VMs) has significantly improved the flexibility of modern Data Centers (DCs). Ideally, live migration ought to be seamless which in turn raises challenges on how to minimize service disruption and avoid performance degradation. To address these challenges, a comprehensive support from the underlying network is required. However, legacy DC networks fall short to help as they take a reactive approach to live migration procedure. Moreover, the complexity and inflexibility of legacy DC networks make it difficult to deploy, manage, and improve network technologies that DC providers may need to use for migration.

    In this thesis, we explore the application of Software Defined Networking (SDN) paradigm for making live VM migration more seamless. Exploiting the characteristics of SDN such as its centralized view on network states, we contribute to the body of knowledge by enhancing the quality of intra- and inter-DC live migration. Firstly, for intra-DC migration, we provide an SDN-based solution which minimizes the service disruption by employing OpenFlow-based resiliency mechanisms to prepare a DC network for migration proactively. Secondly, we improve the inter-DC live migration by accelerating the network convergence through announcing the migration in the control plane using MP-BGP protocol. Further, our proposed framework resolves the sub-optimal routing problem by conducting the gateway functionality at the SDN controller. Finally, with the ultimate goal of improving the inter-DC migration, we develop an SDN-based framework which automates the deployment, improves the management, enhances the performance, and increases the scalability of interconnections among DCs.

  • 266.
    Alizadeh Noghani, Kyoomars
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Ghazzai, Hakim
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Kassler, Andreas
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    A Generic Framework for Task Offloading in mmWave MEC Backhaul Networks2018In: 2018 IEEE Global Communications Conference (GLOBECOM), 2018, p. 1-7Conference paper (Refereed)
    Abstract [en]

    With the emergence of millimeter-Wave (mmWave) communication technology, the capacity of mobile backhaul networks can be significantly increased. On the other hand, Mobile Edge Computing (MEC) provides an appropriate infrastructure to offload latency-sensitive tasks. However, the amount of resources in MEC servers is typically limited. Therefore, it is important to intelligently manage the MEC task offloading by optimizing the backhaul bandwidth and edge server resource allocation in order to decrease the overall latency of the offloaded tasks. This paper investigates the task allocation problem in MEC environment, where the mmWave technology is used in the backhaul network. We formulate a Mixed Integer NonLinear Programming (MINLP) problem with the goal to minimize the total task serving time. Its objective is to determine an optimized network topology, identify which server is used to process a given offloaded task, find the path of each user task, and determine the allocated bandwidth to each task on mmWave backhaul links. Because the problem is difficult to solve, we develop a two-step approach. First, a Mixed Integer Linear Program (MILP) determining the network topology and the routing paths is optimally solved. Then, the fractions of bandwidth allocated to each user task are optimized by solving a quasi-convex problem. Numerical results illustrate the obtained topology and routing paths for selected scenarios and show that optimizing the bandwidth allocation significantly improves the total serving time, particularly for bandwidth-intensive tasks.

  • 267.
    Alizadeh Noghani, Kyoomars
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Hernandez Benet, Cristian
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Kassler, Andreas
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Marotta, Antonio
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Jestin, Patrick
    Ericsson AB, Sweden.
    Srivastava, Vivek V.
    Ericsson AB, Sweden.
    Automating Ethernet VPN deployment in SDN-based Data Centers2017In: 2017 Fourth International Conference on Software Defined Systems (SDS)., IEEE, 2017, p. 61-66Conference paper (Refereed)
    Abstract [en]

    Layer 2 Virtual Private Network (L2VPN) is widely deployed in both service provider networks and enterprises. However, legacy L2VPN solutions have scalability limitations in the context of Data Center (DC) interconnection and networking which require new approaches that address the requirements of service providers for virtual private cloud services. Recently, Ethernet VPN (EVPN) has been proposed to address many of those concerns and vendors started to deploy EVPN based solutions in DC edge routers. However, manual configuration leads to a time-consuming, error-prone configuration and high operational costs. Automating the EVPN deployment from cloud platforms such as OpenStack enhances both the deployment and flexibility of EVPN Instances (EVIs). This paper proposes a Software Defined Network (SDN) based framework that automates the EVPN deployment and management inside SDN-based DCs using OpenStack and OpenDaylight (ODL). We implemented and extended several modules inside ODL controller to manage and interact with EVIs and an interface to OpenStack that allows the deployment and configuration of EVIs. We conclude with scalability analysis of our solution.

  • 268.
    Alizadeh Noghani, Kyoomars
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Hernandez Benet, Cristian
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Taheri, Javid
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    SDN helps volume in Big Data2018In: Big Data and Software Defined Networks / [ed] Javid Taheri, London: The Institution of Engineering and Technology , 2018, 1, p. 185-206Chapter in book (Refereed)
    Abstract [en]

    Both Big Data and SDN are described in detail in previous chapters. This chapter investigates how SDN architecture can leverage its unique features to mitigate the challenges of Big Data volume. Accordingly, first, we provide an overview of Big Data volume, its effects on the underlying network, and mention some potential SDN solutions to address the corresponding challenges. Second, we elaborate more on the network-monitoring, traffic-engineering, and fault-tolerant mechanisms which we believe they may help to address the challenges of Big Data volume. Finally, this chapter is concluded with some open issues.

  • 269.
    Alizadeh Noghani, Kyoomars
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Kassler, Andreas
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    SDN Enhanced Ethernet VPN for Data Center Interconnect2017In: 2017 IEEE 6th International Conference on Cloud Networking (CloudNet) / [ed] Maga, D, IEEE, 2017, p. 77-82Conference paper (Refereed)
    Abstract [en]

    Ethernet Virtual Private Network (EVPN) is an emerging technology that addresses the networking challenges presented by geo-distributed Data Centers (DCs). One of the major advantages of EVPN over legacy layer 2 VPN solutions is providing All-Active (A-A) mode of operation so that the traffic can truly be multi-homed on Provider Edge (PE) routers. However, A-A mode of operation introduces new challenges. In the case where the Customer Edge (CE) router is multi-homed to one or more PE routers, it is necessary that only one of the PE routers should forward Broadcast, Unknown unicast, and Multicast (BUM) traffic into the DC. The PE router that assumes the primary role for forwarding BUM traffic to the CE device is called the Designated Forwarder (DF). The proposed solution to select the DF in the EVPN standard is based on a distributed algorithm which has a number of drawbacks such as unfairness and intermittent behavior. In this paper, we introduce a Software-Defined Networking (SDN) based architecture for EVPN support, where the SDN controller interacts with EVPN control plane. We demonstrate how our solution mitigates existing problems for DF selection which leads to improved EVPN performance.

  • 270.
    Alizadeh Noghani, Kyoomars
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Kassler, Andreas
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Sankar Gopannan, Prem
    Ericsson, USA.
    EVPN/SDN Assisted Live VM Migration between Geo-Distributed Data Centers2018In: 4th IEEE Conference on Network Softwarization (NetSoft), 2018, p. 105-113Conference paper (Refereed)
    Abstract [en]

    Live Virtual Machine (VM) migration has significantly improved the flexibility of modern Data Centers (DC). However, seamless live migration of a VM between geo-distributed DCs faces several challenges due to difficulties in preserving the network configuration after the migration paired with a large network convergence time. Although SDN-based approaches can speed up network convergence time, these techniques have two limitations. First, they typically react to the new topology by installing new flow rules once the migration is finished. Second, because the WAN is typically not under SDN control, they result in sub-optimal routing thus severely degrading the network performance once the VM is attached at the new location.

    In this paper, we identify networking challenges for VM migration across geo-distributed DCs. Based on those observations, we design a novel long-haul VM migration scheme that overcomes those limitations. First, instead of reactively restoring connectivity after the migration, our SDN-based approach proactively restores flows across the WAN towards the new location with the help of EVPN and VXLAN overlay technologies. Second, the SDN controller accelerates the network convergence by announcing the migration to other controllers using MP-BGP control plane messages. Finally, the SDN controller resolves the sub-optimal routing problem that arises as a result of migration implementing a distributed anycast gateway. We implement our approach as extensions to the OpenDaylight controller. Our evaluation shows that our approach outperforms existing approaches in reducing the downtime by 400 ms and increasing the application performance up to 12 times.

  • 271. All, Rainar
    et al.
    Harrami, Omar
    Postgård, Ulrika
    Strömgren, Mattias
    Karlstad University, Faculty of Social and Life Sciences, Department of Health and Environmental Sciences.
    Olyckor, riskanalyser och säkerhetsarbete: Några olika perspektiv inom Räddningsverket2006Other (Other (popular science, discussion, etc.))
    Abstract [sv]

    Sammanfattning

    Syftet med denna kartläggning har varit att ge en nulägesbild över hur riskanalyser, riskbedömningar och riskvärderingar sker i Räddningsverkets arbete med skydd mot olyckor. Ett syfte har också varit att beskriva de olika strategier för säkerhetsarbete som tillämpas i myndigheten.



    Kartläggningen har utförts genom gruppintervjuer under perioden oktober 2004 mars 2005 och har följts upp med hjälp av två seminarier i november 2005. Analysgruppen har bestått av medarbetare vid Räddningsverkets sekretariat för forskning och analys.

    Resultaten visar bland annat att:

    - verkets arbete utgår från en kompott av olyckor, skador och händelser, var och en med sin egen logik baserad på tradition, lagstiftning och politisk inriktning

    - arbetet bedrivs utifrån en mångfald av strategier som i många fall inte är produkten av genomtänkta analyser och medvetna val

    - verkets olika roller behöver närmare analyseras och kopplas till tydligare

    strategier och metoder för arbetet med skydd mot olyckor

    - säkerhetsarbete och riskhantering är inte synonyma begrepp i myndigheten

    - det saknas myndighetsgemensamma begreppsdefinitioner inom det kartlagda

    området

    - det råder en brist i myndigheten på djupare diskussioner och reflektioner kring värdegrunder och principer för riskvärdering.



    Rapporten behandlar många olika frågor som på olika sätt är relevanta för Räddningsverkets arbete på kort och lång sikt. I rapporten ges ett tiotal förslag till fortsatt arbete. Några förslag är att:

    - utarbeta en begreppspolicy för myndigheten

    - utarbeta information till privatpersoner som lagenliga skyldigheter inom det olycksförebyggande området

    - satsa på kompetensutveckling internt

    - starta ett utvecklingsarbete inom riskvärdering

    - utveckla analysförmåga för framtidens olycksrisk

    - starta en idéverkstad för framtida säkerhetsarbete



    Kartläggningen ska ligga till grund för fortsatt utvecklingsarbete inom Räddningsverket. Delar av materialet kan också komma att utgöra underlag för

    utveckling av läromedel för verkets utbildningsverksamhet. Rapporten utgör också en möjlig källa för fortsatt forskning och analys inom området

  • 272. Allman, Mark
    et al.
    Avrachenkov, Konstatin
    Ayesta, Urtzi
    Blanton, Josh
    Hurtig, Per
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science.
    Early Retransmit for TCP and SCTP2008Other (Other (popular science, discussion, etc.))
    Abstract [en]

    This document proposes a new mechanism for TCP and SCTP that can be used to recover lost segments when a connection's congestion window is small. The "Early Retransmit" mechanism allows the transport to reduce, in certain special circumstances, the number of duplicate acknowledgments required to trigger a fast retransmission. This allows the transport to use fast retransmit to recover packet losses that would otherwise require a lengthy retransmission timeout.

  • 273.
    Allvin, Michael
    Sociologiska institutionen, Uppsala universitet.
    Recension av Ola Bergström, Kristina Håkansson, Tommy Isidorsson och Lars Walter, Den nya arbetsmarknaden: Bemanningsbranschens etablering i Sverige (Academia Adacta, Lund 2007).2008In: Arbetsmarknad & Arbetsliv, ISSN 1400-9692, Vol. 14, no 2, p. 71-74Article in journal (Other (popular science, discussion, etc.))
  • 274.
    Allvin, Michael
    et al.
    Uppsala universitet.
    Mellner, Christin
    Stockholms universitet.
    Movitz, Fredrik
    Stockholms universitet.
    Aronsson, Gunnar
    Stockholms universitet.
    Den utbredda flexibiliteten: Ett försök att beräkna förekomsten av lågreglerade arbetsvillkor2012In: Arbetsmarknad & Arbetsliv, ISSN 1400-9692, Vol. 18, no 1, p. 9-24Article in journal (Refereed)
    Abstract [sv]

    Nästan 30 år efter det att begreppet flexibilitet i arbetslivet kom i bruk råder det fortfarande stor osäkerhet om vad begreppet innebär och hur vanligt det egentligen är. I artikeln diskuteras flexibilitet utifrån en representativ studie av den svenska arbetskraften. I studien konstateras att både traditionellt organiserade och helt fria arbeten är relativt ovanliga. Däremot är flexibla arbetsvillkor desto mer vanligt förekommande och spridda i varierande grad bland den svenska arbetskraften.

  • 275.
    Allvin, Michael
    et al.
    Uppsala universitet.
    Movitz, Fredrik
    Stockholms universitet.
    "Självständiga lärosäten": Om de förändrade villkoren för högre utbildning och universitetens normalisering2011In: Arbetsmarknad & Arbetsliv, ISSN 1400-9692, Vol. 17, no 2, p. 59-73Article in journal (Refereed)
    Abstract [sv]

    När den högre utbildningen avregleras får universitet  och högskolor själva bestämma hur de ska organisera sin verksamhet. Det sker även i den övriga västvärlden, liksom i den övriga svenska offentliga sektorn. Frågan är dock vad ett sådant självbestämmande egentligen är värt. Avregleringen lämnar nämligen lärosätena att konkurrera med varandra på en allt snävare och alltmer standardiserad spelplan, vilket i sin tur tvingar dem till långtgående rationaliseringar och prioriteringar.

  • 276.
    Alm, Maria
    Karlstad University, Faculty of Arts and Education, Department of Education.
    Teaching materials and students with mental retardation2008Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    Teaching materials and students with mental retardation



    From a socio-cultural perspective, teaching materials can be regarded as mediating tools for transferring culturally based knowledge, norms, values and traditions. While literature on teaching materials in general is substantial, few investigations have been conducted on teaching materials for students with mental retardation.



    In this paper I will present parts of an ongoing project in which this issue is focused. The study includes about twenty students in two training school classes and one class for students with mild mental retardation, covering the grades 7 10 in the compulsory school.



    Teaching materials in this study are defined as cultural tools used in education and serving a pedagogical function in programs for students with mental retardation (särskolan). My preliminary findings indicate predominance for everyday skills in teaching material activities. Reading or mathematical development in teaching material activities are of low priority. The activities often imply dilemmas the teacher have to master.

  • 277.
    Alm, Maria
    et al.
    Karlstad University, Faculty of Arts and Education, Department of Education.
    Berthén, Diana
    Bladini, Kerstin
    Karlstad University, Faculty of Arts and Education, Department of Education.
    Johansson, Iréne
    Komplicerad skolsituation - elever med utvecklingstörning och deras lärare2001Report (Other academic)
  • 278.
    Almang, Jan
    Gothenburg University, Sweden.
    A NOTE ON SHAPES2015In: Journal of Philosophical Research (JPR), ISSN 1053-8364, E-ISSN 2153-7984, Vol. 40, p. 469-471Article in journal (Refereed)
    Abstract [en]

    It has recently been argued that the Special Theory of Relativity entails that shapes are not intrinsic properties of objects. Rather, they are properties an object has only relative to an inertial frame. In this discussion note I argue that this position, while correct, is incomplete. Objects have frame-dependent shapes because they have an intrinsic property that is the same in all inertial frames.

  • 279.
    Almang, Jan
    University of Gothenburg, Sweden.
    Affordances and the Nature of Perceptual Content2008In: International journal of philosophical studies (Print), ISSN 0967-2559, E-ISSN 1466-4542, Vol. 16, no 2, p. 161-177Article in journal (Refereed)
    Abstract [en]

    According to John McDowell, representational perceptual content is conceptual through and through. This paper criticizes this view by claiming that there is a certain kind of representational and non-conceptual perceptual content that is sensitive to bodily skills. After a brief introduction to McDowell's position, Merleau-Ponty's notion of body schema and Gibson's notion of affordance are presented. It is argued that affordances are constitutive of representational perceptual content, and that at least some affordances, the so-called 'conditional affordances', are essentially related to the body schema. This means that the perceptual content depends upon the nature of the body schema. Since the body schema does not pertain to the domain that our conceptual faculties operate upon, it is argued that this kind of perceptual content cannot be conceptual. At least some of that content is representational, yet it cannot feature as non-demonstrative conceptual content. It is argued that if it features as demonstrative conceptual content, it has to be captured by private concepts. Since McDowell's theory does not allow for the existence of a private language, it is concluded that at least some representational perceptual content is non-conceptual.

  • 280.
    Almang, Jan
    Arvika, Sweden.
    An Argument for Shape Internalism2017In: Erkenntnis, ISSN 0165-0106, E-ISSN 1572-8420, Vol. 82, no 4, p. 819-836Article in journal (Refereed)
    Abstract [en]

    This paper is a defense of an internalist view of the perception of shapes. A basic assumption of the paper is that perceptual experiences have certain parts which account both for the phenomenal character associated with perceiving shapes-phenomenal shapes-and for the intentional content presenting shapes-intentional shapes. Internalism about perceptions of shapes is defined as the claim that phenomenal shapes determine the intentional shapes. Externalism is defined as the claim that perceptual experiences represent whatever shape the phenomenal shape reliably tracks. The argument against externalism proceeds in three steps. First, it is argued that phenomenal shapes are modality specific, such that a phenomenal shape that features in a visual perceptual experience cannot feature in a haptic perceptual experience, and vice versa. Second, it is argued that intentional shapes are amodal. Third, it is argued that externalism is incompatible with the fact that phenomenal shapes are modality specific and intentional shapes amodal.

  • 281.
    Almang, Jan
    Gothenburg University, Sweden.
    Perceiving Exploding Tropes2016In: Grazer Philosophische Studien, ISSN 0165-9227, E-ISSN 1875-6735, Vol. 93, no 1, p. 42-62Article in journal (Refereed)
    Abstract [en]

    The topic of this paper is the perception of properties. It is argued that the perception of properties allows for a distinction between the sense of the identity and the sense of the qualitative nature of a property. So, for example, we might perceive a property as being identical over time even though it is presented as more and more determinate. Thus, you might see an object first as red and then as crimson red. In this case, the property is perceived as identical over time, even though the sense of the qualitative nature ( the redness, the crimson redness) of the property is changing. The distinction between the sense of identity and the sense of quality is explicated in terms of perceiving a particular property, a trope, and perceiving it as an instance of a universal. It is subsequently argued that the perceived tropes cannot constitute the phenomenal character of the perceptual experience.

  • 282.
    Almang, Jan
    Gothenburg University, Göteborg, Sweden.
    Perceptual Transparency and Perceptual Constancy2014In: Husserl Studies, ISSN 0167-9848, E-ISSN 1572-8501, Vol. 30, no 1, p. 1-19Article in journal (Refereed)
    Abstract [en]

    A central topic in discussions about qualia concerns their purported transparency. According to transparency theorists, an experience is transparent in the sense that the subject having the experience is aware of nothing but the intended object of the experience. In this paper this notion is criticized for failing to account for the dynamical aspects of perception. A key assumption in the paper is that perceptual content has a certain temporal depth, in the sense that each act of perception can present an object as extended in time and that objects can be perceived as persisting through time. An object that is seen as persisting through time is often seen as constant and unchanging, even though the presentation of it is changing. In this paper it is argued that in order to account for these cases of perceptual constancy, we must distinguish between the awareness of having perceived that an object has a property at a certain point in time, and perceptually intending that it has that property at that point in time. Consequently, we must in at least some instances be aware of something more than the object of the experience. But precisely this distinction is rejected by the transparency theory.

  • 283.
    Almang, Jan
    Gothenburg, University.
    TENSE AS A FEATURE OF PERCEPTUAL CONTENT2014In: Journal of Philosophy, ISSN 0022-362X, E-ISSN 1939-8549, Vol. 111, no 7, p. 361-378Article in journal (Refereed)
  • 284.
    Almang, Jan
    Gothenburg University, Sweden.
    The Causal Self-Referential Theory of Perception Revisited2013In: Dialectica, ISSN 0012-2017, E-ISSN 1746-8361, Vol. 67, no 1, p. 29-53Article in journal (Refereed)
    Abstract [en]

    This is a paper about The Causal Self-Referential Theory of Perception. According to The Causal Self-Referential Theory as developed by above all John Searle and David Woodruff Smith, perceptual content is satisfied by an object only if the object in question has caused the perceptual experience. I argue initially that Searle's account cannot explain the distinction between hallucination and illusion since it requires that the state of affairs that is presented in the perceptual experience must exist in order for the perception to be veridical. Smith's account is interestingly different in that the descriptive content, i.e. the content that presents the perceptual object as having certain properties, does not determine the object of the experience. His account consequently does not require that the state of affairs that is presented in perception exists in order for the perception to have an object. Smith argues instead that perceptual reference is determined by a specific kind of demonstrative content. In this paper it is argued that Smith's account of demonstrative content is too indeterminate and in certain circumstances prescribes the wrong object. It is subsequently argued that the theory of demonstrative content can be modified so as to avoid these consequences. This modification involves deriving the conditions of satisfaction of seeing an object from the conditions of satisfaction of seeing the shape of the object, where the shape of the object is conceived of as a particularized property, what is also called a trope'.

  • 285.
    Almang, Jan
    University West, Trollhättan, Sweden; University of Gothenburg, Gothenburg, Sweden.
    Time, Mode and Perceptual Content2012In: Acta Analytica, ISSN 0353-5150, E-ISSN 1874-6349, Vol. 27, no 4, p. 425-439Article in journal (Refereed)
    Abstract [en]

    Francois Recanati has recently argued that each perceptual state has two distinct kinds of content, complete and explicit content. According to Recanati, the former is a function of the latter and the psychological mode of perception. Furthermore, he has argued that explicit content is temporally neutral and that time-consciousness is a feature of psychological mode. In this paper it is argued, pace Recanati, that explicit content is not temporally neutral. Recanati's position is initially presented. Three desiderata for a theory of time-consciousness are subsequently introduced. It is then argued that a theory locating time-consciousness as a feature of psychological mode will fail to satisfy these desiderata. In the last section the intentionality of memories is discussed. Using the notion of shiftable indexical, it is argued that memories have the same explicit content as perceptions, but that they nevertheless can have different conditions of satisfaction since they are entertained in different modes.

  • 286.
    Almang, Jan
    Gothenburg University, Sweden.
    Two Kinds of Time-Consciousness and Three Kinds of Content2013In: Axiomathes, ISSN 1122-1151, E-ISSN 1572-8390, Vol. 23, no 1, p. 61-80Article in journal (Refereed)
    Abstract [en]

    This paper explores the distinction between perceiving an object as extended in time, and experiencing a sequence of perceptions. I argue that this distinction cannot be adequately described by any present theory of time-consciousness and that in order to solve the puzzle, we need to consider perceptual content as having three distinct constituents: Explicit content, which has a particular phenomenal character, modal content, or the kind of content that is contributed by the psychological mode, and implicit content, which lacks phenomenal character. These notions are then further clarified and related to each other.

  • 287.
    Almang, Jan
    Karlstad University, Faculty of Arts and Social Sciences (starting 2013), Department of Educational Studies (from 2013).
    War, vagueness and hybrid war2019In: Defence Studies, ISSN 1470-2436, E-ISSN 1743-9698, Vol. 19, no 2, p. 189-204Article in journal (Refereed)
    Abstract [en]

    It has frequently been observed in the literature on hybrid wars that there is a grey zone between peace and war, and that hybrid wars are conflicts which are not clear cases of war. In this paper, I attempt to illuminate this grey zone and the concept and nature of war from the philosophical discussions of vagueness and institutional facts. Vague terms are characterized by the fact that there is no non-arbitrary boundary between entities which lie in their extension, and entities which do not lie in their extension. I apply a theory of vagueness to notions such as “war” and “peace” and go on to suggest that the exact boundary for what counts as a war or not is arbitrary. However, the context in which the conflict occurs determines a range of possible locations for this boundary. The most important contextual parameter is in this respect how the parties to the conflict themselves conceptualize the conflict. I suggest that this can in various ways help us understand grey-zone conflicts.

  • 288.
    Almani, T.
    et al.
    UT Austin, Ctr Subsurface Modeling, ICES, Austin, TX 78712 USA.;Saudi Arabian Oil Co, Dhahran, Saudi Arabia..
    Kumar, Kundan
    Univ Bergen, Math Inst, N-5020 Bergen, Norway..
    Dogru, A.
    Saudi Arabian Oil Co, Dhahran, Saudi Arabia..
    Singh, G.
    UT Austin, Ctr Subsurface Modeling, ICES, Austin, TX 78712 USA..
    Wheeler, M. F.
    UT Austin, Ctr Subsurface Modeling, ICES, Austin, TX 78712 USA..
    Convergence analysis of multirate fixed-stress split iterative schemes for coupling flow with geomechanics2016In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 311, p. 180-207Article in journal (Refereed)
    Abstract [en]

    We consider multirate iterative schemes for the Biot system modeling coupled flow and geomechanics in a poro-elastic medium. The multirate iterative coupling scheme exploits the different time scales for the mechanics and flow problems by taking multiple finer time steps for flow within one coarse mechanics time step. We adapt the fixed stress split algorithm that decouples the flow and mechanics equations for the multirate case and perform an iteration between the two problems until convergence. We provide a fully discrete scheme that uses Backward Euler time discretization and mixed spaces for flow and conformal Galerkin for mechanics. Our analysis is based on studying the equations satisfied by the difference of iterates and using Banach contraction argument to prove that the corresponding scheme is a fixed point contraction. The analysis provides the value of an adjustable coefficient used in the proposed iterative coupling algorithms. Furthermore, we show that the converged quantities satisfy the variational weak form for the coupled discrete system. (C) 2016 Elsevier B.V. All rights reserved.

  • 289.
    Almani, T.
    et al.
    Austin, USA.
    Kumar, Kundan
    University of Bergen, Norway.
    Singh, G.
    Austin, USA.
    Wheeler, M. F.
    Austin, USA.
    Stability of multirate explicit coupling of geomechanics with flow in a poroelastic medium2019In: Computers and Mathematics with Applications, ISSN 0898-1221, E-ISSN 1873-7668Article in journal (Refereed)
    Abstract [en]

    We consider single rate and multirate explicit schemes for the Biot system modeling coupled flow and geomechanics in a poro-elastic medium. These schemes are widely used in practice that follows a sequential procedure in which the flow and mechanics problems are fully decoupled. In such a scheme, the flow problem is solved first with time-lagging the displacement term followed by the mechanics solve. The multirate explicit coupling scheme exploits the different time scales for the mechanics and flow problems by taking multiple finer time steps for flow within one coarse mechanics time step. We provide fully discrete schemes for both the single and multirate approaches that use Backward Euler time discretization and mixed spaces for flow and conformal Galerkin for mechanics. We perform a rigorous stability analysis and derive the conditions on reservoir parameters and the number of finer flow solves to ensure stability for both schemes. Furthermore, we investigate the computational time savings for explicit coupling schemes against iterative coupling schemes.

  • 290.
    Almani, T.
    et al.
    Center for Subsurface Modeling, ICES, UT-Austin, Austin, USA; Saudi Arabian Oil Company (Aramco), Dhahran, Saudi Arabia.
    Kumar, Kundan
    Mathematics Institute, University of Bergen, Bergen, Norway.
    Wheeler, M. F.
    Center for Subsurface Modeling, ICES, UT-Austin, Austin, USA.
    Convergence and error analysis of fully discrete iterative coupling schemes for coupling flow with geomechanics2017In: Computational Geosciences, ISSN 1420-0597, E-ISSN 1573-1499, Vol. 21, no 5-6, p. 1157-1172Article in journal (Refereed)
    Abstract [en]

    In this paper, we consider an iterative coupling scheme for solving a fully discretized Biot system based on the fixed-stress split coupling algorithm. Specifically, we derive a priori error estimates for quantifying the error between the solution obtained at any iterate and the true solution. Our approach is based on studying the equations satisfied by the difference of iterates and utilizing a Banach contraction argument to show that the corresponding scheme is a fixed point iteration. Obtained contraction results are then used to derive theoretical convergence error estimates for the single rate iterative coupling scheme. We compare our numerical computations against the theoretically derived contraction estimates and show a good agreement with theory.

  • 291.
    Almasri, Abdullah
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Economics and Statistics.
    A Approach for Analysing the Fractional Difference Processes2006Conference paper (Refereed)
  • 292.
    Almasri, Abdullah
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Economics and Statistics.
    Some aspects of wavelet analysis in time series2000Licentiate thesis, monograph (Other academic)
  • 293.
    Almasri, Abdullah
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Economics and Statistics.
    Testing for Periodicity and Trend in Long-Memory Processes2003Doctoral thesis, monograph (Other academic)
  • 294.
    Almasri, Abdullah
    et al.
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Economics and Statistics.
    Andersson, Eva M
    Barregård, Lars
    A study of residential radon in Sweden using multilevel analysis2008In: Health Physics Journal, to appear 2008Article in journal (Refereed)
    Abstract [en]

    A Swedish radon data set, consisting of more than 8000 measurements of residential radon levels in about 50% of the Swedish municipalities were analysed using a multilevel approach.

    The results were compared with those of a single-level analysis. We found that there was a significant variability between municipalities. The point estimates of the population mean radon levels were similar (geometric mean 60 Bq/m3 and arithmetic mean 106 Bq/m3).

    The analysis shows the advantages of multilevel modeling compared with a single-level OLS model.

    A single-level model results in too optimistic standard errors, about 25% of those of the multilevel

    model which can lead to erroneous conclusions.

    In a multilevel model including house type as a fixed effect (single-family house, row house, or apartment in multi-family house), the estimates of the fixed effect of house type were similar for the single-level and the multi-level models

  • 295.
    Almasri, Abdullah
    et al.
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Economics and Statistics.
    Hussain, S
    Holmquist, B
    Impact of the Periodicity and Trend on the FD Parameter Estimation2007In: Journal of Statistical Computation and Simulation. 2007, 77, 79-87Article in journal (Refereed)
  • 296.
    Almasri, Abdullah
    et al.
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Economics and Statistics.
    Locking, Håkan
    Shukur, Ghazi
    Testing for climate warming in Sweden during 1850-1999, using wavelets analysis2008In: Journal of Applied Statistics, 2008, vol. 35, issue 4, pages 431-443Article in journal (Refereed)
    Abstract [en]

    This paper describes an alternative approach for testing for the existence of trend among time series. The test method has been constructed using wavelet analysis which has the ability of decomposing a time series into low frequencies (trend) and high-frequency (noise) components. Under the normality assumption, the test is distributed as F. However, using generated empirical critical values, the properties of the test statistic have been investigated under different conditions and different types of wavelet. The Harr wavelet has shown to exhibit the highest power among the other wavelet types. The methodology here has been applied to real temperature data in Sweden for the period 1850-1999. The results indicate a significant increasing trend which agrees with the 'global warming' hypothesis during the last 100 years.

  • 297.
    Almasri, Abdullah
    et al.
    Karlstad University, Faculty of Arts and Social Sciences (starting 2013), Karlstad Business School (from 2013).
    Mansson, K.
    Gothenburg Univ, Dept Econ & Stat, Gothenburg, Sweden.;Jonkoping Int Business Sch, Dept Econ Finance & Stat, Jonkoping, Sweden..
    Sjolander, P.
    Jonkoping Int Business Sch, Dept Econ Finance & Stat, Jonkoping, Sweden..
    Shukur, G.
    Jonkoping Int Business Sch, Dept Econ Finance & Stat, Jonkoping, Sweden.;Linnaeus Univ, Dept Econ & Stat, Vaxjo, Sweden..
    A wavelet-based panel unit-root test in the presence of an unknown structural break and cross-sectional dependency, with an application of purchasing power parity theory in developing countries2017In: Applied Economics, ISSN 0003-6846, E-ISSN 1466-4283, Vol. 49, no 21, p. 2096-2105Article in journal (Refereed)
    Abstract [en]

    This article introduces two different non-parametric wavelet-based panel unit-root tests in the presence of unknown structural breaks and cross-sectional dependencies in the data. These tests are compared with a previously suggested non-parametric wavelet test, the parameteric Im-Pesaran and Shin (IPS) test and a Wald type of test. The results from the Monte Carlo simulations clearly show that the new wavelet-ratio tests are superior to the traditional tests both in terms of size and power in panel unit-root tests because of its robustness to cross-section dependency and structural breaks. Based on an empirical Central American panel application, we can, in contrast to previous research (where bias due to structural breaks is simply disregarded), find strong, clear-cut support for purchasing power parity (PPP) in this developing region.

  • 298.
    Almasri, Abdullah
    et al.
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Economics and Statistics.
    Shukur, G.
    An Illustration of the Causality Relation between Government Spending and Revenue Using Wavelets Analysis on Finish Data2003In: Journal of Applied Statistics, 2003, 30, 571-584Article in journal (Refereed)
    Abstract [en]

    Quarterly data for the period 1960:1 to 1997:2, conventional tests, a bootstrap simulation approach and a multivariate Rao's F-test have been used to investigate if the causality between government spending and revenue in Finland was changed at the beginning of 1990 due to future plans to create the European Monetary Union (EMU). The results indicate that during the period before 1990, the government revenue Granger-caused spending, while the opposite happened after 1990, which agrees better with Barro's tax smoothing hypothesis. However, when using monthly data instead of quarterly data for almost the same sample period, totally different results have been noted. The general conclusion is that the relationship between spending and revenue in Finland is still not completely understood. The ambiguity of these results may well be due to the fact that there are several time scales involved in the relationship, and that the conventional analyses may be inadequate to separate out the time scale structured relationships between these variables. Therefore, to investigate empirically the relation between these variables we attempt to use the wavelets analysis that enables us to separate out different time scales of variation in the data. We find that time scale decomposition is important for analysing these economic variables.

  • 299.
    Almasri, Abdullah
    et al.
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Economics and Statistics.
    Shukur, G
    Testing the Causal Relation between Sunspots and Temperature Using Wavelets Analysis2005In: Journal of Modern Applied Statistical Methods, 2005, 4, 134-139Article in journal (Refereed)
  • 300.
    Almasri, Abdullah
    et al.
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Economics and Statistics.
    Shukur, Ghazi
    Clustering Using Wavelet Transformation2008In: Handbook of Research on Cluster Theory / [ed] Charlie Karlsson, Edward Elgar , 2008Chapter in book (Refereed)
3456789 251 - 300 of 22000
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