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  • 2551.
    Uddin, Sheikh Fakhar
    et al.
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Khattak, Ismail Khan
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Spectrum Selection Technique to Satisfy the QoS Requirements in Cognitive Radio Network2012Independent thesis Advanced level (degree of Master (Two Years))Oppgave
    Abstract [en]

    The demand of wireless spectrum is increasing very fast as the field of telecommunication is advancing rapidly. The spectrum was underutilized because of fixed spectrum assignment policy and this valuable spectrum can be utilized efficiently by cognitive radio technology. In this thesis we have studied spectrum selection problems in cognitive radio network. Channel sharing and channel contention problems arise when multiple secondary users tend to select same channel. The thesis work is focused on spectrum selection issue with the aim to minimize the overall system time and to solve the problem of channel contention and channel sharing. The overall system time of secondary connection is an important performance measure to provide quality of service for secondary users in cognitive radio network. We studied two spectrum selection schemes that considerably reduce the overall system time and resolve the problems of channel sharing and channel contention. An analytical model associated with Preemptive Resume Priority (PRP) M/G/1 queuing model has been provided to evaluate the studied spectrum selection scheme. This model also analyzes the effect of multiple handoffs due to arrival of primary users. According to this scheme, the traffic load is distributed among multiple channels to balance the traffic load. Secondary users select the operating channels based on the spectrum selection algorithm. They can intelligently adopt better channel selection scheme by considering traffic statistics and overall transmission time. All simulation scenarios are developed in MATLAB. Based on our result we can conclude that both channel selection schemes considerably reduce the overall transmission time of secondary users in cognitive radio network. The overall transmission time increase with the rise of arrival rate of secondary user. The probability based channel selection scheme perform better with lower arrival rate and sensing based channel selection scheme perform better with higher arrival rate of secondary users. These channel selection schemes help distribute the traffic load of secondary users evenly among multiple channels. Hence, increase the channel utilization and resolve the channel contention problem.

  • 2552.
    Umavathi, Jawali C
    et al.
    Department of Mathematics, Gulbarga University, Gulbarga, Karnataka, India, and Department of Engineering, University of Sannio, Benevento, Italy.
    Vajravelu, Kuppalapalle
    Department of Mathematics, University of Central Florida, Orlando, FL 32816, USA,.
    Metri, Prashant G
    Mälardalens högskola, Akademin för utbildning, kultur och kommunikation, Utbildningsvetenskap och Matematik.
    Silvestrov, Sergei
    Mälardalens högskola, Akademin för utbildning, kultur och kommunikation, Utbildningsvetenskap och Matematik.
    Effect of Time-Periodic Boundary TemperatureModulations on the Onset of Convection in aMaxwell Fluid-Nanofluid Saturated Porous Layer2016Inngår i: Engineering Mathematics I: Electromagnetics, Fluid Mechanics, Material Physics and Financial Engineering / [ed] Sergei Silvestrov, Milica Rančić, Springer, 2016, s. 221-245Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    The linear stability of Maxwell fluid-nanofluid flow in a saturated porous layer is examined theoretically when the walls of the porous layers are subjected to time-periodic temperature modulations. A modified Darcy-Maxwell model is used to describe the fluid motion, and the nanofluid model used includes the effects of the Brownian motion. The thermal conductivity and viscosity are considered to be dependent on the nanoparticle volume fraction. A perturbation method based on a small amplitude of an applied temperature field is used to compute the critical value of the Rayleigh number and the wave number. The stability of the system characterized by a critical Rayleigh number is calculated as a function of the relaxation parameter, the concentration Rayleigh number, the porosity parameter, the Lewis number, the heat capacity ratio, the Vad´asz number, the viscosity parameter, the conductivity variation parameter, and the frequency of modulation. Three types of temperature modulations are considered, and the effects of all three types of modulations are found to destabilize the system as compared to the unmodulated system.

  • 2553.
    Unnikrishnan, Vishnu
    et al.
    Linköpings universitet, Institutionen för systemteknik, Elektroniska Kretsar och System. Linköpings universitet, Tekniska fakulteten.
    Vesterbacka, Mark
    Linköpings universitet, Institutionen för systemteknik, Elektroniska Kretsar och System. Linköpings universitet, Tekniska fakulteten.
    Linearization of VCO-based ADCs using asynchronous sigma-delta modulation2016Inngår i: 2016 IEEE 59TH INTERNATIONAL MIDWEST SYMPOSIUM ON CIRCUITS AND SYSTEMS (MWSCAS), New York: Institute of Electrical and Electronics Engineers , 2016, s. 842-845Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Asynchronous sigma-delta modulation is investigated as an alternative linearization scheme for all-digital voltage controlled oscillator based analog-to-digital converters, which commonly require digital post processing to achieve good linearity. The modulator output, when used to drive a VCO-based converter, causes the oscillator to operate at two fixed frequencies thereby removing the VCO nonlinearity from the transfer function. A circuit is proposed consisting of a digital block and a passive RC circuit operating as an integrator. Spectre simulation of the design synthesized using a 65 nm standard cell library indicate that a harmonic suppression up to -60 dB is feasible.

  • 2554.
    Ushakova, Elena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Norm inequalities of Hardy and Pólya-Knopp types2006Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This PhD thesis consists of an introduction and six papers. All these papers are devoted to Lebesgue norm inequalities with Hardy type integral operators. Three of these papers also deal with so-called Pólya-Knopp type inequalities with geometric mean operators instead of Hardy operators. In the introduction we shortly describe the development and current status of the theory of Hardy type inequalities and put the papers included in this PhD thesis into this frame. The papers are conditionally divided into three parts. The first part consists of three papers, which are devoted to weighted Lebesgue norm inequalities for the Hardy operator with both variable limits of integration. In the first of these papers we characterize this inequality on the cones of non-negative monotone functions with an additional third inner weight function in the definition of the operator. In the second and third papers we find new characterizations for the mentioned inequality and apply the results for characterizing the weighted Lebesgue norm inequality for the corresponding geometric mean operator with both variable limits of integration. The second part consists of two papers, which are connected to operators with monotone kernels. In the first of them we give criteria for boundedness in weighted Lebesgue spaces on the semi-axis of certain integral operators with monotone kernels. In the second one we consider Hardy type inequalities in Lebesgue spaces with general measures for Volterra type integral operators with kernels satisfying some conditions of monotonicity. We establish the equivalence of such inequalities on the cones of non-negative respective non-increasing functions and give some applications. The third part consists of one paper, which is devoted to multi-dimensional Hardy type inequalities. We characterize here some new Hardy type inequalities for operators with Oinarov type kernels and integration over spherical cones in n-dimensional vector space over R. We also obtain some new criteria for a weighted multi-dimensional Hardy inequality (of Sawyer type) to hold with one of two weight functions of product type and give as applications of such results new characterizations of some corresponding n-dimensional weighted Pólya-Knopp inequalities to hold.

  • 2555. Ushakova, Elena
    On the Hardy-type operator with variable limits2006Rapport (Annet vitenskapelig)
  • 2556.
    Ushakova, Elena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Some multi-dimensional Hardy-type integral inequalities2006Rapport (Annet vitenskapelig)
  • 2557.
    Vadeby, Anna
    Linköpings universitet, Matematisk statistik.
    Modelling and inference of relative collision safety in cars1998Licentiatavhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    We propose a new mathematical model for relative collision safety in cars. Our present research is restricted to head-on crashes between two cars and we try to determine how much of the injury risk in a crash that depends on car model. The relative risks include the driver populations of the different car models. When two cars crash they are exposed to the same force, but the damage severity is different depending on various factors such as car mass, change of speed and design of the car. To explore the relative risks between different car models, we build a model where we let car mass, change of speed and design of the car explain the injury outcome in the crashes. The mathematical model we use is a birth process where we let the states correspond to the injury classes. A data base containing police reported traffic accidents and hospital information is used to explore the relationships in our model.

    A bootstrap analysis is made to produce a picture of the uncertainty of the estimates. The uncertainty from the bootstrap analysis is compared to the asymptotic estimate of the uncertainty given by the inverse of an information sub-matrix.

  • 2558.
    Vaicenavicius, Juozas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Analys och sannolikhetsteori.
    Optimal Stopping under Drift Uncertainty2015Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 2559.
    Vaktnäs, Marcus
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Analys och sannolikhetsteori.
    On Singular Integral Operators2018Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
  • 2560.
    Van, Chau
    Linköpings universitet, Institutionen för beteendevetenskap och lärande.
    Gymnasieelevers geometrikunskaper i kursen Matematik 2b-en kvalitativ innehållsanalys av elevers kompetenser och kunskapsnivåer2016Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Studien behandlar kompetenser och kunskapsnivåer hos gymnasieelever inom geometriavsnittet, matematikkurs 2b. Syftet är att undersöka i vilken utsträckning elever behärskar de matematiska kompetenserna och vilken kunskapsnivå inom avsnittet geometri elever uppnår på ett kunskapstest som konstruerats av uppgifter från nationella prov och elevernas läromedelsbok.

    Datainsamlingen genomfördes på en svensk gymnasieskola och omfattar 47 elever från två olika klasser i årskurs 2 på det samhällsvetenskapliga programmet. Samtliga elever har besvarat kunskapstest skriftligt. En innehållsanalys med utgångspunkt från kompetenser och kunskapsnivåer har sedan utförts på elevernas skriftliga svar och resultatet visar att eleverna behärskar algoritmkompetens och att en del elever behärskar begreppskompetens. Resultatet visar också att de flesta av eleverna befinner sig på kunskapsnivå 2 och 3. Många elever saknar således en djupare förståelse för geometrin enligt analysen med kunskapsnivåer. Rekommendationen efter studien är att eleverna behöver mera undervisning om begreppens definitioner för att förbättra de andra kompetenserna såsom resonemangskompetens, modelleringskompetens och kommunikationskompetens.

  • 2561. van der Spoel, David
    et al.
    Hess, Berk
    Stockholms universitet, Naturvetenskapliga fakulteten.
    GROMACS-the road ahead2011Inngår i: WIREs Computational Molecular Science, ISSN 1759-0876, Vol. 1, nr 5, s. 710-715Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Molecular dynamics (MD) simulations form a powerful tool that is complementary to experiments and theory. They allow detailed investigations of both biological and chemical systems at the atomic level at timescales ranging from femtoseconds to milliseconds. Mechanisms and processes not accessible to experimental techniques can be followed in 'real time', and hypotheses based on experiments or theoretical arguments can be tested. Limits on the accuracy of results are mainly due to the physical models, the ratio of the complexity of the problem and the amount of computer time. Here, we review the state of the art in MD simulations with a focus on imminent challenges for the GROMACS (GROningen MAchine for Chemical Simulation) software. New hardware puts new requirements on software, while the breadth of applications and the amount of physical models implemented are increasing rapidly, highlighting shortcomings in the architecture of the programs. We sketch a road map for a popular scientific software package and discuss some of the choices to be made.

  • 2562.
    van Lith, B. S.
    et al.
    Eindhoven University of Technology - P. O. Box 513, NL-5600 MB Eindhoven, The Netherlands.
    Muntean, Adrian
    Eindhoven University of Technology - P. O. Box 513, NL-5600 MB Eindhoven, The Netherlands.
    Storm, C.
    Eindhoven University of Technology - P. O. Box 513, NL-5600 MB Eindhoven, The Netherlands.
    A continuum model for hierarchical fibril assembly2014Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 106, nr 6Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Most of the biological polymers that make up our cells and tissues are hierarchically structured. For biopolymers ranging from collagen, to actin, to fibrin and amyloid fibrils this hierarchy provides vitally important versatility. The structural hierarchy must be encoded in the self-assembly process, from the earliest stages onward, in order to produce the appropriate substructures. In this letter, we explore the kinetics of multistage self-assembly processes in a model system which allows comparison to bulk probes such as light scattering. We apply our model to recent turbidimetry data on the self-assembly of collagen fibrils. Our analysis suggests a connection between diffusion-limited aggregation kinetics and fibril growth, supported by slow, power-law growth at very long time scales.

  • 2563.
    van Meurs, Patrick
    et al.
    Eindhoven University of Technology.
    Muntean, Adrian
    Eindhoven University of Technology.
    Upscaling of the dynamics of dislocation walls2014Inngår i: Advances in Mathematical Sciences and Applications, ISSN 1343-4373, Vol. 24, nr 2, s. 401-414Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We perform the discrete-to-continuum limit passage for a microscopic model describing the time evolution of dislocations in a one dimensional setting. This answers the related open question raised by Geers et al. in [GPPS13]. The proof of the upscaling procedure (i.e. the discrete-to-continuum passage) relies on the gradient flow structure of both the discrete and continuous energies of dislocations set in a suitable evolutionary variational inequality framework. Moreover, the convexity and Γ-convergence of the respective energies are properties of paramount importance for our arguments.

  • 2564.
    van Meurs, Patrick
    et al.
    Eindhoven University of Technology, Netherlands.
    Muntean, Adrian
    Eindhoven University of Technology, Netherlands .
    Peletier, M.A.
    Eindhoven University of Technology, Netherlands.
    Upscaling of dislocation walls in finite domains2014Inngår i: European journal of applied mathematics (Print), ISSN 0956-7925, E-ISSN 1469-4425, Vol. 25, nr 6, s. 749-781Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We wish to understand the macroscopic plastic behaviour of metals by upscaling the micromechanics of dislocations. We consider a highly simplified dislocation network, which allows our discrete model to be a one dimensional particle system, in which the interactions between the particles (dislocation walls) are singular and non-local. As a first step towards treating realistic geometries, we focus on finite-size effects rather than considering an infinite domain as typically discussed in the literature. We derive effective equations for the dislocation density by means of Gamma-convergence on the space of probability measures. Our analysis yields a classification of macroscopic models, in which the size of the domain plays a key role.

  • 2565.
    van Noorden, T.L.
    et al.
    Technische Universiteit Eindhoven, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
    Muntean, Adrian
    Technische Universiteit Eindhoven, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
    Homogenisation of a locally periodic medium with areas of low and high diffusivity2011Inngår i: European journal of applied mathematics (Print), ISSN 0956-7925, E-ISSN 1469-4425, Vol. 22, nr 5, s. 493-516Artikkel i tidsskrift (Fagfellevurdert)
  • 2566. Vary, J. P.
    et al.
    Zhao, X.
    Ilderton, Anton
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Honkanen, H.
    Maris, P.
    Brodsky, S. J.
    Basis light-front quantization: a new approach to non-perturbative scattering and time-dependent production processes2013Inngår i: Acta Physica Polonica B, Proceedings Supplement, ISSN 1899-2358, E-ISSN 2082-7865, Vol. 6, nr 1, s. 257-262Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hamiltonian light-front quantum field theory constitutes a framework for deriving invariant masses, correlated parton amplitudes of self-bound systems and time-dependent scattering amplitudes. By choosing the lightfront gauge and adopting an orthonormal basis function representation, we obtain a large, sparse, Hamiltonian matrix for mass eigenstates that is solvable by adapting ab initio no-core methods of nuclear many-body theory. In the continuum limit, the infinite matrix limit, we recover full covariance. There is considerable freedom in the choice of the orthonormal and complete set of basis functions with key considerations being convenience and convergence properties. We adopt a two-dimensional harmonic oscillator basis for transverse modes that corresponds with eigensolutions of the soft-wall anti-de Sitter/quantum chromodynamics (AdS/QCD) model obtained from light-front holography. We outline our approach and present preliminary results for non-linear Compton scattering, evaluated non-perturbatively, where a strong (possibly time-dependent) laser field excites an electron that emits a photon.

  • 2567.
    Vasiljeva, Polina
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematisk statistik.
    Combining Unsupervised and Supervised Statistical Learning Methods for Currency Exchange Rate Forecasting2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    In this thesis we revisit the challenging problem of forecasting currency exchange rate. We combine machine learning methods such as agglomerative hierarchical clustering and random forest to construct a two-step approach for predicting movements in currency exchange prices of the Swedish krona and the US dollar. We use a data set with over 200 predictors comprised of different financial and macro-economic time series and their transformations. We perform forecasting for one week ahead with different parameterizations and find a hit rate of on average 53%, with some of the parameterizations yielding hit rates as high as 60%. However, there is no clear indicator that there exists a combination of the methods and parameters that outperforms all of the tested cases. In addition, our results indicate that the two-step approach is sensitive to changes in the training set.

    This work has been conducted at the Third Swedish National Pension Fund (AP3) and KTH Royal Institute of Technology.

  • 2568.
    Velasquez, Rafael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    The Implicit Function Theorem2018Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [en]

    In this essay we present an introduction to real analysis, with the purpose of proving the Implicit Function Theorem. Our proof relies on other well-known theorems in set theory and real analysis as the Heine-Borel Covering Theorem and the Inverse Function Theorem.

  • 2569.
    Verdier, Olivier
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.).
    Full affine equivariance and weak natural transformations in numerical analysis—The case of B-series2018Inngår i: Springer Proceedings in Mathematics & statistics, ISSN 2194-1017, E-ISSN 2194-1009, Vol. 267, s. 349-361Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Many algorithms in numerical analysis are affine equivariant: they are immune to changes of affine coordinates. This is because those algorithms are defined using affine invariant constructions. There is, however, a crucial ingredient missing: most algorithms are in fact defined regardless of the underlying dimension. As a result, they are also invariant with respect to non-invertible affine transformation from spaces of different dimensions. We formulate this property precisely: these algorithms fall short of being natural transformations between affine functors. We give a precise definition of what we call a weak natural transformation between functors, and illustrate the point using examples coming from numerical analysis, in particular B-Series.

  • 2570.
    Verlaan, Martin
    Luleå tekniska universitet.
    Classification of binary vectors by maximal predictivity and stochastic complexity1993Rapport (Annet vitenskapelig)
  • 2571. Vicedomini, Riccardo
    et al.
    Vezzi, Francesco
    Scalabrin, Simone
    Arvestad, Lars
    Stockholms universitet, Naturvetenskapliga fakulteten, Numerisk analys och datalogi (NADA).
    Policriti, Alberto
    GAM-NGS: genomic assemblies merger for next generation sequencing2013Inngår i: BMC Bioinformatics, ISSN 1471-2105, E-ISSN 1471-2105, Vol. 14, nr Suppl.7, s. S6-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background: In recent years more than 20 assemblers have been proposed to tackle the hard task of assembling NGS data. A common heuristic when assembling a genome is to use several assemblers and then select the best assembly according to some criteria. However, recent results clearly show that some assemblers lead to better statistics than others on specific regions but are outperformed on other regions or on different evaluation measures. To limit these problems we developed GAM-NGS (Genomic Assemblies Merger for Next Generation Sequencing), whose primary goal is to merge two or more assemblies in order to enhance contiguity and correctness of both. GAM-NGS does not rely on global alignment: regions of the two assemblies representing the same genomic locus (called blocks) are identified through reads' alignments and stored in a weighted graph. The merging phase is carried out with the help of this weighted graph that allows an optimal resolution of local problematic regions. Results: GAM-NGS has been tested on six different datasets and compared to other assembly reconciliation tools. The availability of a reference sequence for three of them allowed us to show how GAM-NGS is a tool able to output an improved reliable set of sequences. GAM-NGS is also a very efficient tool able to merge assemblies using substantially less computational resources than comparable tools. In order to achieve such goals, GAM-NGS avoids global alignment between contigs, making its strategy unique among other assembly reconciliation tools. Conclusions: The difficulty to obtain correct and reliable assemblies using a single assembler is forcing the introduction of new algorithms able to enhance de novo assemblies. GAM-NGS is a tool able to merge two or more assemblies in order to improve contiguity and correctness. It can be used on all NGS-based assembly projects and it shows its full potential with multi-library Illumina-based projects. With more than 20 available assemblers it is hard to select the best tool. In this context we propose a tool that improves assemblies (and, as a by-product, perhaps even assemblers) by merging them and selecting the generating that is most likely to be correct.

  • 2572.
    Vromans, Arthur
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för matematik och datavetenskap (from 2013). Centre for Analysis, Computer Science and Applications (CASA), Department of Mathematics and Computers Science, Eindhoven University of Technology, Eindhoven, the Netherlands.
    A pseudoparabolic reaction-diffusion-mechanics system: Modeling, analysis and simulation2018Licentiatavhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    In this thesis, parabolic-pseudoparabolic equations are derived coupling chemical reactions, diffusion, flow and mechanics in a heterogeneous medium using the framework of mixture theory. The weak solvability in 1-D of the obtained models is studied. Furthermore, it is numerically illustrated that approximate solutions according to the Rothe method exhibit expected realistic behaviour. For a simpler model formulation, the periodic homogenization in higher space dimensions is performed.

  • 2573.
    Vu, Viet Thuy
    et al.
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för elektroteknik.
    Sjogren, Thomas
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för elektroteknik.
    Pettersson, Mats
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för elektroteknik.
    Minardi, Michael
    Studying Csar Systems Using Irf-Csar2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, Impulse Response Function in Circular Synthetic Aperture Radar Imaging (IRF-CSAR), which is a special version of Impulse Response Function in Ultrawideband-Ultrawidebeam Synthetic Aperture Radar Imaging (IRF-USAR), is presented and shown to be valid for representing the CSAR image of a point-like scatterer. IRF-CSAR can therefore be used in studying different CSAR systems such as predicting the pattern of a point-like scatterer illuminated by a CSAR system, estimating resolution achieved by that system. Applying IRF-CSAR to define the image quality assessments for CSAR is also presented in the paper.

  • 2574.
    Vu, Viet Thuy
    et al.
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för matematik och naturvetenskap.
    Sjögren, Thomas
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för matematik och naturvetenskap.
    Pettersson, Mats
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för matematik och naturvetenskap.
    On Synthetic Aperture Radar Spatial Azimuth and Range Resolution Equations2012Inngår i: IEEE Transactions on Aerospace and Electronic Systems, ISSN 0018-9251, E-ISSN 1557-9603, Vol. 48, nr 2, s. 1764-1769Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper discusses spatial resolutions for narrowband narrowbeam (NB) synthetic aperture radar (SAR) as well as for ultrawideband ultrawidebeam (UWB) SAR. The similarity and difference between the impulse response function in NB SAR imaging (IRF-NSAR) - sinc function - and the impulse response function in UWB SAR imaging (IRF-USAR) is investigated and the result of this investigation shows that in the intensity interval from −6 dB to 0 dB, the behavior of IRF-NSAR and IRF-USAR in azimuth and range are similar. This is the basis for a derivation of new spatial resolution equations for UWB SAR based on −3 dB width or half power beamwidth (HPBW). The investigated result also shows that there exists the so-called HPBW narrowing/broadening factor in an IRF-USAR.

  • 2575.
    Vu, Viet Thuy
    et al.
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för elektroteknik.
    Sjögren, Thomas
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för elektroteknik.
    Pettersson, Mats
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för elektroteknik.
    Phase Error Calculation for Fast Time-Domain Bistatic SAR Algorithms2013Inngår i: IEEE Transactions on Aerospace and Electronic Systems, ISSN 0018-9251, E-ISSN 1557-9603, Vol. 49, nr 1, s. 631-639Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In synthetic aperture radar (SAR) processing, there is a trade-off between accuracy and speed. The approximations in an algorithm help to increase the algorithm’s speed but cause deterministic phase errors which directly affect the SAR image quality. This paper discusses the phase error calculations for bistatic fast backprojection (BiFBP) and bistatic fast factorized backprojection (BiFFBP) which are essential for setting their parameters. The phase error calculation principle for bistatic SAR in comparison to monostatic SAR is presented. This principle is used to derive the maximum phase error equation.

  • 2576.
    Waara, Einar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Analys och sannolikhetsteori.
    Gauss and Jacobi Sums and the Congruence Zeta Function2018Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
  • 2577. Wahlberg, Patrik
    A transformation of almost periodic pseudodifferential operators to Fourier multiplier operators with operator-valued symbols2009Inngår i: Rendiconti del Seminario Matematico, ISSN 0373-1243, Vol. 67, nr 2, s. 247-269Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present results for pseudodifferential operators on Rd whose symbol a(·,x)is almost periodic (a.p.) for each x ∈ Rd and belongs to a Hörmander class Smr,d. We studya linear transformation a 7→ U(a) from a symbol a(x,x) to a frequency-dependent matrixU(a)(x)l,l′ , indexed by (l,l′) ∈ L×L where L is a countable set in Rd . The map a 7→ U(a) transforms symbols of a.p. pseudodifferential operators to symbols of Fourier multiplieroperators acting on vector-valued function spaces. We show that the map preserves operatorpositivity and identity, respects operator composition and respects adjoints.

  • 2578.
    Wahlberg, Patrik
    Univ Turin, Dipartimento Matemat, I-10123 Turin, TO, Italy.
    Locally stationary stochastic processes and Weyl symbols of positive operators2011Inngår i: Positivity (Dordrecht), ISSN 1385-1292, E-ISSN 1572-9281, Vol. 15, nr 1, s. 105-134Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The paper treats locally stationary stochastic processes. A connection with the Weyl symbols of positive operators is observed and explored. We derive necessary conditions on the two functions that constitute the covariance function of a locally stationary stochastic process, some of which use this connection to time-frequency analysis and pseudodifferential operators. Finally, we discuss briefly the subclass of Cohen's class of time-frequency representations having separable kernels, which is related to locally stationary stochastic processes.

  • 2579.
    Wahlberg, Patrik
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för matematik (MA).
    Propagation of polynomial phase space singularities for Schrödinger equations with quadratic Hamiltonians2018Inngår i: Mathematica Scandinavica, ISSN 0025-5521, E-ISSN 1903-1807, Vol. 122, nr 1, s. 107-140Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study propagation of phase space singularities for a Schrödinger equation with a Hamiltonian that is the Weyl quantization of a quadratic form with non-negative real part. Phase space singularities are measured by the lack of polynomial decay of given order in open cones in the phase space, which gives a parametrized refinement of the Gabor wave front set. The main result confirms the fundamental role of the singular space associated to the quadratic form for the propagation of phase space singularities. The singularities are contained in the singular space, and propagate in the intersection of the singular space and the initial datum singularities along the flow of the Hamilton vector field associated to the imaginary part of the quadratic form.

  • 2580.
    Wahlberg, Patrik
    Department of Mathematics, University of Turin, Via Carlo Alberto 10, 10123, Turin, Italy.
    Representations of almost periodic pseudodifferential operators and applications in spectral theory2012Inngår i: Journal of Pseudo-Differential Operators and Applications, ISSN 1662-9981, E-ISSN 1662-999X, Vol. 3, nr 1, s. 81-119Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The paper concerns algebras of almost periodic pseudodifferential operators on Rd with symbols in Hörmander classes. We study three representations of such algebras, one of which was introduced by Coburn, Moyer and Singer and the other two inspired by results in probability theory by Gladyshev. Two of the representations are shown to be unitarily equivalent for nonpositive order. We apply the results to spectral theory for almost periodic pseudodifferential operators acting on L 2 and on the Besicovitch Hilbert space of almost periodic functions.

  • 2581.
    Wahlberg, Patrik
    Lund University.
    The random Wigner distribution of Gaussian stochastic processes with covariance in S0(R2d)2005Inngår i: Journal of Function Spaces and Applications, ISSN 0972-6802, E-ISSN 1758-4965, Vol. 3, nr 2, s. 163-181Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The paper treats time-frequency analysis of scalar-valued zero mean Gaussian stochastic processes on ℝd. We prove that if the covariance function belongs to the Feichtinger algebra S0(ℝ2d) then: (i) the Wigner distribution and the ambiguity function of the process exist as finite variance stochastic Riemann integrals, each of which defines a stochastic process on ℝ2d, (ii) these stochastic processes on ℝ2d are Fourier transform pairs in a certain sense, and (iii) Cohen's class, ie convolution of the Wigner process by a deterministic function Φ∈C(ℝ2d), gives a finite variance process, and if Φ∈S0(ℝ2d) then W∗Φ can be expressed multiplicatively in the Fourier domain.

  • 2582.
    Wahlberg, Patrik
    Deparment of Electroscience, Lund university.
    The Wigner distribution of Gaussian weakly harmonizable stochastic processes2006Inngår i: Pseudo-differential operators and related topics operator theory: Advances and Applications / [ed] P. Boggiatto, L. Rodino, J. Toft, M.W. Wong, Basel: Birkhäuser Verlag, 2006, s. 211-226Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    The paper treats the Wigner distribution of scalar-valued stochastic processes defined on ℝd. We show that if the process is Gaussian and weakly harmonizable then a stochastic Wigner distribution is well defined. The special case of stationary processes is studied, in which case the Wigner distribution is weakly stationary in the time variable and the variance is equal to the deterministic Wigner distribution of the covariance function.

  • 2583.
    Wahlberg, Patrik
    The University of Newcastle.
    Vector-valued modulation spaces and localization operators with operator-valued symbols2007Inngår i: Integral equations and operator theory, ISSN 0378-620X, E-ISSN 1420-8989, Vol. 59, nr 1, s. 99-128Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the short-time Fourier transformation, modulation spaces, Gabor representations and time-frequency localization operators, for functions and tempered distributions that have as range space a Banach or a Hilbert space. In the Banach space case the theory of modulation spaces contains some modifications of the scalar-valued theory, depending on the Banach space. In the Hilbert space case the modulation spaces have properties similar to the scalar-valued case and the Gabor frame theory essentially works. For localization operators in this context symbols are operator-valued. We generalize two results from the scalar-valued theory on continuity on certain modulation spaces when the symbol belongs to an L p,q space and M , respectively. The first result is true for any Banach space as range space, and the second result is true for any Hilbert space as range space.

  • 2584.
    Wahlberg, Patrik
    et al.
    Univ Newcastle, Sch Elect Engn & Comp Sci, Callaghan, NSW 2308, Australia.
    Schreier, Peter
    Univ Newcastle, Sch Elect Engn & Comp Sci, Callaghan, NSW 2308, Australia.
    Gabor discretization of the Weyl product for modulation spaces and filtering of nonstationary stochastic processes2009Inngår i: Applied and Computational Harmonic Analysis, ISSN 1063-5203, E-ISSN 1096-603X, Vol. 26, nr 1, s. 97-120Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We discretize the Weyl product acting on symbols of modulation spaces, using a Gabor frame defined by a Gaussian function. With one factor fixed. the Weyl product is equivalent to a matrix multiplication on the Gabor coefficient level. If the fixed factor belongs to the weighted Sjostrand space M omega(infinity,1), then the matrix has polynomial or exponential off-diagonal decay, depending oil the weight omega. Moreover, if its operator is invertible on L(2), the inverse matrix has similar decay properties. The results are applied to the equation for the linear minimum mean square error filter for estimation of a nonstationary second-order stochastic process from a noisy observation. The resulting formula for the Gabor coefficients of the Weyl symbol for the optimal filter may be interpreted as a time-frequency version of the filter for wide-sense stationary processes, known as the noncausal Wiener filter.

  • 2585.
    Wahlström, Dennis
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    The Great Picard Theorem2018Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [en]

    In this essay, we present a proof of the great Picard theorem by showing that a holomorphic function with an essential singularity attains infinitely many complex values in the vicinity of the singularity.

  • 2586.
    Waliullah, Shoyeb
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Minimizers and symmetric minimizers for problems with critical Sobolev exponent2008Rapport (Annet vitenskapelig)
  • 2587.
    Wall, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    A Comparison of homogenization, Hashin-Shtrikman bounds and the Halpin-Tsai Equations1997Inngår i: Applications of Mathematics, ISSN 0862-7940, E-ISSN 1572-9109, Vol. 42, nr 4, s. 245-257Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we study a unidirectional and elastic fiber composite. We use the homogenization method to obtain numerical results of the plane strain bulk modulus and the transverse shear modulus. The results are compared with the Hashin-Shtrikman bounds and are found to be close to the lower bounds in both cases. This indicates that the lower bounds might be used as a first approximation of the plane strain bulk modulus and the transverse shear modulus. We also point out the connection with the Hashin-Shtrikman bounds and the Halpin-Tsai equations. Optimal bounds on the fitting parameters in the Halpin-Tsai equations have been formulated.

  • 2588.
    Wall, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Bounds and estimates on the effective properties for nonlinear composites2000Inngår i: Applications of Mathematics, ISSN 0862-7940, E-ISSN 1572-9109, Vol. 45, nr 6, s. 419-437Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we derive lower bounds and upper bounds on the effective properties for nonlinear heterogeneous systems. The key result to obtain these bounds is to derive a variational principle, which generalizes the variational principle by P. Ponte Castaneda from 1992. In general, when the Ponte Castaneda variational principle is used one only gets either a lower or an upper bound depending on the growth conditions. In this paper we overcome this problem by using our new variational principle together with the bounds presented by Lukkassen, Persson and Wall in 1995. Moreover, we also present some examples where the bounds are so tight that they may be used as a good estimate of the effective behavior.

  • 2589.
    Wall, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Computing effective moduli and local stress variations for periodic composites by the homogenization method1994Inngår i: Proceedings, 1st International Conference on Composites Engineering: ICCE/1 / [ed] David Hui, 1994, s. 1001-1002Konferansepaper (Fagfellevurdert)
  • 2590.
    Wall, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Homogenization of Reynolds equation by two-scale convergence2007Inngår i: Chinese Annals of Mathematics. Series B, ISSN 0252-9599, E-ISSN 1860-6261, Vol. 28, nr 3, s. 363-374Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To increase the hydrodynamic performance in different machine elements, as e.g. journal bearings and thrust bearings, during lubrication it is important to understand the influence of surface roughness. In this connection one encounters homogenization of the incompressible Reynolds equation, where the roughness of the lubricated surface is assumed to be periodic. This problem has recently been studied in more engineering-oriented papers by using the formal method of multiple scale expansion. In this paper, we rigorously prove both homogenization and corrector results by using two-scale convergence, which may be regarded as a justification of the formal multiple scale expansion method described above. Moreover, some numerical illustrations and results are presented.

  • 2591.
    Wall, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Homogenization of some partial differential operators and integral functionals1998Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis is devoted to some problems connected to the theory of homogenization of partial differential operators and integral functionals. The thesis consists of an introduction and three different parts, A-C. In the introduction we give an elementary presentation of the basic ideas in the homogenization theory. Moreover, the introduction also serves as an overview of the field and points out where the results contained in this thesis fit in. The first part, Part A, consists of one paper and a complementary appendix and it deals with the limit behavior of the solutions of a sequence of quasi-linear equations. Part B consists of three papers in which bounds on the homogenized integrand for non-linear problems are developed. Moreover, examples where the bounds are optimal are given. The third part, Part C, consists of four papers which consider some further mathematical and engineering aspects on the homogenization method. Several numerical results are also presented and compared with theoretical results.

  • 2592.
    Wall, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Optimal bounds on the effective properties of multiphase materials by homogenization1994Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 2593.
    Wall, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Optimal bounds on the effective shear moduli for some nonlinear and reiterated problems1999Inngår i: Acta Scientarum Mathematicarum, ISSN 0001-6969, Vol. 65, nr 3, s. 553-566Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we study the effective behavior of composites with a nonlinear material behavior and a special type of microstructure. The microstructure we study is obtained by reiteration, i.e., introducing several local scales. We derive bounds on the effective shear properties and prove that the bounds are sharp when the number of scales tends to infinity.

  • 2594.
    Wall, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Some homogenization and corrector results for nonlinear monotone operators1998Inngår i: Journal of Nonlinear Mathematical Physics, ISSN 1402-9251, E-ISSN 1776-0852, Vol. 5, nr 2, s. 331-348Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper deals with the limit behaviour of the solutions of quasi-linear equations of the form - div (a (x, x/h, Duh)) = fh on with Dirichlet boundary conditions. The sequence (h) tends to 0 and the map a(x, y, ) is periodic in y, monotone in and satisfies suitable continuity conditions. It is proved that uh u weakly in H1,2 0 (), where u is the solution of a homogenized problem - div(b(x, Du)) = f on . We also prove some corrector results, i.e. we find (Ph) such that Duh - Ph(Du) 0 in L2 (, Rn ).

  • 2595.
    Wall, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Koroleva, Yo. U
    Faculty of Mechanics and Mathematics, Moscow State University.
    Tsandzana, Afonso Fernando
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Fabricius, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    On the effects of surface roughness in thin film flow governed by the time dependent Stokes equations2014Inngår i: Doklady. Mathematics, ISSN 1064-5624, E-ISSN 1531-8362, Vol. 90, nr 1, s. 445-449Artikkel i tidsskrift (Fagfellevurdert)
  • 2596.
    Wall, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Lukkassen, Dag
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Meidell, Annette
    Norut Northern Research Institute, Narvik.
    New methods for estimating the torsional rigidity of composite bars2009Inngår i: International Journal of Engineering Science, ISSN 0020-7225, E-ISSN 1879-2197, Vol. 47, nr 4, s. 524-536Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We obtain general bounds on the torsional rigidity and give examples on how these bounds can be used to obtain estimates and simple formulae which yield more accurate information than the classical treatment. Moreover, we use the homogenization theory to estimate the limit of the torsional rigidity when the characteristic length of the composite microstructures decreases.

  • 2597.
    Wall, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Meidell, Annette
    Narvik University College, 8505 Narvik, Norway.
    Lukkassen, Dag
    Bounds on the effective behavior of a homogenized generalized Reynolds equation2007Inngår i: Journal of Function Spaces and Applications, ISSN 0972-6802, E-ISSN 1758-4965, Vol. 5, nr 2, s. 133-150Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study upper and lower bounds for estimating the effective behavior described by homogenizing a problem which is a generalization of the Reynold equation. All cases when these bounds coincide are also found.

  • 2598.
    WANG, MIN
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap.
    Description and Application of Genetic Algorithm2012Independent thesis Advanced level (degree of Master (Two Years))Oppgave
    Abstract [en]

    Genetic Algorithm (GA) as a class of Evolutionary Algorithm (EA) is a search algorithm based on the mechanics of natural selection and natural genetics. This dissertation presents the description, solving procedures and application of GA. The definitions of selection, crossover and mutation operators are given in details and an application based on GA in Time Table Problem (TTP) is performed in a new way. Due to its high capability of overall search, GA is particularly appropriate for solving timetabling and scheduling problems. TTP (Time Table Problem) which belongs to NP-hard problem is a special problem concerning resource management. In this dissertation, a new chromosome coding is designed in order to solve TTP more effectively. And the result presented by MATLAB will converge to a steady condition.

  • 2599.
    Wang, Ning
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Analys och tillämpad matematik.
    Price sensitivity to the exponent in the CEV model2012Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 2600.
    Wang, Peiyu
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Tillämpad matematik och statistik.
    Liquidity Adjusted Value-at-Risk and Its Applications2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
495051525354 2551 - 2600 of 2681
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