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  • 2551.
    Zackrisson, Ella
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematisk statistik.
    Evaluation of Hedging Strategies of Asian Options on Electricity at Nord Pool2015Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This thesis empirically evaluates a geometric Brownian motion and a stochastic volatility model for modeling futures prices and hedging Asian call options on the electricity spot price. Estimation of parameters for the models is done based on historical futures prices of futures contracts with a one month delivery period using nonlinear regression and Maximum Likelihood techniques. The models are tested on 2014 data and tracking error for each model is presented. The tracking error is investigated through the median value, the spread between minimum and maximum value along with value at risk at a 95% level.

    In addition, a third model for modeling spot and futures prices is presented theoretically. It is an exponential additive model with the advantage that it models the future price process from the spot price, instead of modeling the future price process immediately. This bypasses the issue of no information about the future price process during the delivery period, when there is no prices of the futures contracts.

    The aim of this thesis is to compare the simpler geometric Brownian motion to the more complex stochastic volatility model. It is found that the stochastic volatility model performs better when tested on out-of-sample data. The geometric Brownian motion tends to underestimate the electricity prices, despite that 2014 had low pricest compared to the other years in the data sample. In addition, the approximation of the distribution of the future price process under the geometric Brownian motion model gave a bad fit and led to difficulties when estimating the parameters. The stochastic volatility model produced more stable results and gave a better fit for the distribution.

  • 2552.
    Zavareh, Alireza
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap.
    Analytical and Numerical methods for a Mean curvature flow equation with applications to financial Mathematics and image processing2012Independent thesis Advanced level (degree of Master (Two Years))Oppgave
    Abstract [en]

    This thesis provides an analytical and two numerical methods for solving a parabolic equation of two-dimensional mean curvature flow with some applications. In analytical method, this equation is solved by Lie group analysis method, and in numerical method, two algorithms are implemented in MATLAB for solving this equation. A geometric algorithm and a step-wise algorithm; both are based on a deterministic game theoretic representation for parabolic partial differential equations, originally proposed in the genial work of Kohn-Serfaty [1].

  • 2553.
    Zemskov, E. P.
    et al.
    Brandeis Univ, Dept Chem, Waltham, MA 02454 USA; Russian Acad Sci, Ctr Comp, Moscow 119333, Russia.
    Epstein, I. R.
    Brandeis Univ, Dept Chem, Waltham, MA 02454 USA; Russian Acad Sci, Ctr Comp, Moscow 119333, Russia.
    Muntean, Adrian
    Technische Universiteit Eindhoven.
    Oscillatory pulses in FitzHugh-Nagumo type systems with cross-diffusion2011Inngår i: Mathematical Medicine and Biology, ISSN 1477-8599, E-ISSN 1477-8602, Vol. 28, nr 2, s. 217-226Artikkel i tidsskrift (Fagfellevurdert)
  • 2554. Zhang, Changyong
    Stochastic Differential Equations Driven by Levy Processes: Numerical Weak Approximation2011Bok (Annet vitenskapelig)
  • 2555.
    Zhang, Chi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Analys och sannolikhetsteori.
    Fast Fourier Transforms in IMEX-schemes to price options under Bates model2014Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 2556. Zhang, Jiangbo
    et al.
    Hong, Yiguang
    Hu, Xiaoming
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    MULTIAGENT OPINION DYNAMICS OF BOUNDED CONFIDENCE WITH NONLOCAL AGGREGATIVE INTERACTION2017Inngår i: SIAM Journal of Control and Optimization, ISSN 0363-0129, E-ISSN 1095-7138, Vol. 2017, nr 55, s. -2573, artikkel-id 4Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we propose nonlocal aggregative opinion interactions for a bounded-confidence opinion model to demonstrate the fluctuation mechanism, and then study this opinion fluctuation mechanism by both theoretical analyses and numerical simulations. In this proposed agent-based opinion model, there are stubborn agents and regular agents: while each stubborn agent never changes its opinion, a regular agent updates his/her opinion based on selected agents' opinion values and his/her confidence bound. At first, we show that the global fluctuation for opinions of regular agents occurs almost surely if and only if the confidence bound of regular agents is larger than a critical value. Next, we give an estimated probability bound of the local fluctuation for regular agent opinions when the confidence bound is sufficiently small. Finally, we provide upper and lower bounds on the fluctuation strength and the regular agent opinion mean in the case when the global fluctuation occurs almost surely.

  • 2557.
    Zhang, Lai
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Pedersen, Michael
    Lin, Zhigui
    Stability patterns for a size-structured population model and its stage-structured counterpart2015Inngår i: Mathematical Biosciences, ISSN 0025-5564, E-ISSN 1879-3134, Vol. 267, s. 109-123Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we compare a general size-structured population model, where a size-structured consumer feeds upon an unstructured resource, to its simplified stage-structured counterpart in terms of equilibrium stability. Stability of the size-structured model is understood in terms of an equivalent delayed system consisting of a renewal equation for the consumer population birth rate and a delayed differential equation for the resource. Results show that the size- and stage-structured models differ considerably with respect to equilibrium stability, although the two models have completely identical equilibrium solutions. First, when adult consumers are superior foragers to juveniles, the size-structured model is more stable than the stagestructured model while the opposite occurs when juveniles are the superior foragers. Second, relatively large juvenile (adult) mortality tends to stabilise (destabilise) the size-structured model but destabilise (stabilise) the stage-structured model. Third, the stability pattern is sensitive to the adult-offspring size ratio in the sizestructured model but much less sensitive in the stage-structured model. Finally, unless the adult-offspring size ratio is sufficiently small, the stage-structured model cannot satisfactorily capture the dynamics of the size-structured model. We conclude that caution must be taken when the stage-structured population model is applied, although it can consistently translate individual life history and stage-specific differences to the population level.

  • 2558.
    Zhang, Ye
    et al.
    Örebro universitet, Institutionen för naturvetenskap och teknik.
    Lukyanenko, Dmitry V.
    Department of Mathematics, Faculty of Physics, M. V. Lomonosov Moscow State University, Moscow, Russian Federation.
    Yagola, Anatoly G.
    Department of Mathematics, Faculty of Physics, M. V. Lomonosov Moscow State University, Moscow, Russian Federation.
    An optimal regularization method for convolution equations on the sourcewise represented set2015Inngår i: Journal of Inverse and Ill-Posed Problems, ISSN 0928-0219, E-ISSN 1569-3945, Vol. 23, nr 5, s. 465-475Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this article, we consider an inverse problem for the integral equation of the convolution typein a multidimensional case. This problem is severely ill-posed. To deal with this problem, using a prioriinformation (sourcewise representation) based on optimal recovery theory we propose a new method. Theregularization and optimization properties of this method are proved. An optimal minimal a priori error ofthe problem is found. Moreover, a so-called optimal regularized approximate solution and its correspondingerror estimation are considered. Eciency and applicability of this method are demonstrated in a numericalexample of the image deblurring problem with noisy data.

  • 2559.
    Zhelezov, Dmitry
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Yamshchikov, Ivan
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Liquidity and optimal consumption with random income2011Independent thesis Advanced level (degree of Master (One Year)), 10 poäng / 15 hpOppgave
    Abstract [en]

    In the first part of our work we focus on the model of the optimal consumption with a random income. We provide the three dimensional equation for this model, demonstrate the reduction to the two dimensional case and provide for two different utility functions the full point-symmetries' analysis of the equations. We also demonstrate that for the logarithmic utility there exists a unique and smooth viscosity solution the existence of which as far as we know was never demonstrated before.

    In the second part of our work we develop the concept of the empirical liquidity measure. We provide the retrospective view of the works on this issue, discuss the proposed definitions and develop our own empirical measure based on the intuitive mathematical model and comprising several features of the definitions that existed before. Then we verify the measure provided on the real data from the market and demonstrate the advantages of the proposed value for measuring the illiquidity.

  • 2560.
    Zhou, Long
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Analys och tillämpad matematik.
    Irregularly-Spaced Financial High-Frequency Data Simulation Using Multi-Dimensional Hawkes Processes: Estimation, Prediction And Corresponding Trading Strategy2012Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 2561.
    Zhou, Yang
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematisk statistik.
    Modelling Swedish Inflation Using Market Data2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This study is an attempt to model Swedish CPI inflation using ARIMA and variations of distributed lag model with market data as explanatory variables. The model will be constructed on the CPI subcomponents level and the results are aggregated to the CPI. Three approaches are tested in this report. In the first approach, only ARIMA model is used to model each of the subcomponents. In the second approach we use a distributed lag model (DLM) on subcomponents with significant correlation to the market data, the residual of the DLM is then modelled using ARIMA. In the third approach we use an restricted finite distributed lag model (RFDLM) instead of DLM. The study found that RFDLM was the best approach to model inflation with 20% RMSE compared to 32% of the naive forecast. However, there is little forecast potential using this approach due to the short lag of market data used as input. The model would be most useful in testing CPI inflation scenarios using predictions or assumptions of market data as input.

  • 2562.
    Zorina, I. A.
    et al.
    Volgograd State University, Russia.
    Tkachev, Vladimir
    Volgograd State University, Russia.
    On entire solutions of quasilinear equations with a quadratic principal part2008Inngår i: Vestn. Samar. Gos. Univ. Estestvennonauchn. Ser., ISSN 1810-5378, s. 108-123Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We establish the existence of a countable family of entire solutions for a class of quasilinear equations including Simon's equation. In particular, we show that all obtained solutions have a polynomial growth and their topological structure is similar to that of harmonic polynomials.

  • 2563.
    Åberg, Hans
    Luleå tekniska universitet.
    General relativistic quantum mechanics: intrinsic spin theory1993Rapport (Annet vitenskapelig)
    Abstract [en]

    On a Lorentz-manifold, a mathematically intrinsic spin-theory (meaning that the spin-operators and spin-fields themselves are tensors) is constructed (for arbitrary spin), the reason being that this is what you need in order to compute the generalization of the Einstein equation in general relativity, for particles with spin. Some of the corresponding (total) metric variations are also described, and from those, one can see that it gives rise to stress-energy tensors with positive statistical energy-densities, the latter being necessary in order to create a quantum field theory. This spin-theory only exists, in its completeness, in a four-dimensional Lorentz metric space, since it depends on the fact that the square of the Hodge star operator is minus one when acting on two-forms.

  • 2564.
    Åhag, Per
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Cegrell, Urban
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Czyz, Rafal
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Vector spaces of delta-plurisubharmonic functions and extensions of the complex Monge-Ampere operator2015Inngår i: Journal of Mathematical Analysis and Applications, ISSN 0022-247X, E-ISSN 1096-0813, Vol. 422, nr 2, s. 960-980Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we shall consider two types of vector ordering on the vector space of differences of negative plurisubharmonic functions, and the problem whether it is possible to construct supremum and infimum. Then we consider two different approaches to define the complex Monge-Ampere operator on these vector spaces, and we solve some Dirichlet problems. We end this paper by stating and discussing some open problems.

  • 2565.
    Åhag, Per
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Cegrell, Urban
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Phạm, Hoàng Hiệp
    Monge-Ampère measures on subvarieties2015Inngår i: Journal of Mathematical Analysis and Applications, ISSN 0022-247X, E-ISSN 1096-0813, Vol. 423, s. 94-105Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this article we address the question whether the complex Monge-Ampere equation is solvable for measures with large singular part. We prove that under some conditions there is no solution when the right-hand side is carried by a smooth subvariety in C-n of dimension k < n.

  • 2566.
    Åhag, Per
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Czyz, Rafal
    Kolodziej's subsolution theorem for unbounded pseudoconvex domains2012Inngår i: Universitatis Iagellonicae Acta Mathematica, ISSN 0083-4386, 2084-3828, Vol. 50, s. 7-23Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we generalize Kolodziej's subsolution theorem to bounded and unbounded pseudoconvex domains, and in that way we are able to solve complex Monge-Ampère equations on general pseudoconvex domains. We then give a negative answer to a question of Cegrell and Kolodziej by constructing a compactly supported Radon measure µ that vanishes on all pluripolar sets in Cn such that µ(Cn) = (2π)n, and forwhich there is no function u in L+ such that (ddcu)=µ. We end this paper by solving a Monge-Ampère type equation. Furthermore, we proveuniqueness and stability of the solution.

  • 2567.
    Åhag, Per
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Czyz, Rafal
    On the Blocki-Zwonek conjectures2015Inngår i: Complex Variables and Elliptic Equations, ISSN 1747-6933, E-ISSN 1747-6941, Vol. 60, nr 9, s. 1270-1276Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Let Omega be a bounded pseudoconvex domain in C-n, and let g(Omega) (z, a) be the pluricomplex Green function with pole at a in Omega. It was conjectured by Blocki and Zwonek that the function given by beta = beta(Omega),(a) : (-infinity, 0) (sic) t -> beta(t) = log (lambda(n)({z is an element of Omega g(Omega) (z, a) < t})) is convex. Here.n is the Lebesgue measure in Cn. In this note we give an affirmative answer to this conjecture when Omega is biholomorphic to the unit ball or to the polydisc in C-n, n >= 1.

  • 2568.
    Åhag, Per
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Czyz, Rafal
    Lundow, Per-Håkan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    A counterexample to a conjecture by Blocki-Zwonek2018Inngår i: Experimental Mathematics, ISSN 1058-6458, E-ISSN 1944-950X, Vol. 27, nr 1, s. 119-124Artikkel i tidsskrift (Fagfellevurdert)
  • 2569.
    Åhag, Per
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Czyz, Rafal
    Persson, Leif
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Radially symmetric plurisubharmonic functions2012Inngår i: Annales Polonici Mathematici, ISSN 0066-2216, E-ISSN 1730-6272, Vol. 106, s. 1-17Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this note we consider radially symmetric plurisubharmonic functions and the complex Monge–Ampère operator. We prove among other things a complete characterization of unitary invariant measures for which there exists a solution of the complex Monge–Ampère equation in the set of radially symmetric plurisubharmonic functions. Furthermore, we prove in contrast to the general case that the complex Monge–Ampère operator is continuous on the set of radially symmetric plurisubharmonic functions. Finally we characterize radially symmetric plurisubharmonic functions among the subharmonic ones using merely the laplacian.

  • 2570.
    Åhag, Per
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Czyż, Rafał
    On the Blocki-Zwonek conjectures and beyond2015Inngår i: Archiv der Mathematik, ISSN 0003-889X, E-ISSN 1420-8938, Vol. 105, nr 4, s. 371-380Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Let \({\Omega}\) be a bounded pseudoconvex domain in \({\mathbb{C}^n}\), and let \({g_{\Omega}(z,a)}\) be the pluricomplex Green function with pole at a in \({\Omega}\). Błocki and Zwonek conjectured that the function given by $$\begin{array}{ll}\alpha = \alpha_{\Omega}, a: (- \infty, 0) \ni t \mapsto \alpha (t) = e^{-2nt} \lambda_n \left( \{z \in \Omega: g_{\Omega}(z, a) < t \} \right)\end{array}$$ is nondecreasing, and that the function given by $$\begin{array}{ll}\beta = \beta_{\Omega}, a: (-\infty, 0) \ni t \to \beta(t)= \log \left(\lambda_n \left(\{z \in \Omega: g_{\Omega}(z,a)< t\}\right)\right)\end{array}$$ is convex. Here \({\lambda_{n}}\) is the Lebesgue measure in \({\mathbb{C}^n}\). In this note we give an affirmative answer to these conjectures when \({\Omega}\) is biholomorphic to a bounded, balanced, and pseudoconvex domain in \({\mathbb{C}^n}\), \({n\geq 1}\). The aim of this note is to consider generalizations of the functions \({\alpha}\), \({\beta}\) defined by the Green function with two poles in \({\mathbb{D}\subset\mathbb{C}}\). We prove that \({\alpha}\) is not nondecreasing, and \({\beta}\) is not convex. By using the product property for pluricomplex Green functions, we then generalize this to n-dimensions. Finally, we end this note by considering two other possibilities generalizing the Błocki–Zwonek conjectures.

  • 2571.
    Åkerblad, Niklas
    Högskolan i Skövde, Institutionen för kommunikation och information.
    Animationsarbete till spelet Colosseum: Code of Hammurabi: en studie i hur man skapar animationer till ett spel utifrån dess kontext och spelsystem utan att kunna testa dessa i en prototyp.2007Independent thesis Basic level (degree of Bachelor), 20 poäng / 30 hpOppgave
    Abstract [sv]

    Denna rapport behandlar det animationsarbete som jag gått igenom för att försöka skapa så trovärdiga och dynamiska animationer som möjligt till spelet Colosseum: Code of Hammurabi och dess nya omarbetade stridssystem. Jag har utgått från ett relativt sparsmakat designdokument som i princip bara förklarar kortfattat hur spelmekaniken ska fungera på en grundläggande nivå samt en animationslista på animationer som ska finnas i spelet. Spelet ska i slutändan innehålla 3 olika vapenstilar men på grund av tidsbrist har jag valt att fokusera på en av dess, nämligen kampstilen för strid med tvåhandssvärd. Först har jag analyserat det gamla stridssystemet för att ha en grund att stå på, för att bland annat se vilka brister mitt tidigare arbete präglats av. Utifrån diverse referenser som behandlar medeltida stridkonst inom nyss nämnda kampstil har jag hämtat det mesta av inspirationen och följaktligen kryddat dessa jordnära anvisningar med mina egna idéer samt ett antal fightingspel med spektakulära kontexter och även försökt dra nytta av det material som finns i kampsportsfilmer. Mycket av arbetet har cirkulerat kring att lära sig hur animationer implementeras i ett stridssystem och vilka tekniska samt programmerarmässiga relationer man måste ta hänsyn till. Jag har även försökt ha Disneys 12 animationsprinciper i bakhuvudet för att ha en teoretisk källa till hur animation ska se ut och fungera.

  • 2572.
    Åström, Freddie
    Linköpings universitet, Institutionen för systemteknik, Datorseende. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Tekniska högskolan.
    Variational Tensor-Based Models for Image Diffusion in Non-Linear Domains2015Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    This dissertation addresses the problem of adaptive image filtering.

    Although the topic has a long history in the image processing community, researchers continuously present novel methods to obtain ever better image restoration results.

    With an expanding market for individuals who wish to share their everyday life on social media, imaging techniques such as compact cameras and smart phones are important factors. Naturally, every producer of imaging equipment desires to exploit cheap camera components while supplying high quality images. One step in this pipeline is to use sophisticated imaging software including, e.g., noise reduction to reduce manufacturing costs, while maintaining image quality.

    This thesis is based on traditional formulations such as isotropic and tensor-based anisotropic diffusion for image denoising. The difference from main-stream denoising methods is that this thesis explores the effects of introducing contextual information as prior knowledge for image denoising into the filtering schemes. To achieve this, the adaptive filtering theory is formulated from an energy minimization standpoint. The core contributions of this work is the introduction of a novel tensor-based functional which unifies and generalises standard diffusion methods. Additionally, the explicit Euler-Lagrange equation is derived which, if solved, yield the stationary point for the minimization problem. Several aspects of the functional are presented in detail which include, but are not limited to, tensor symmetry constraints and convexity. Also, the classical problem of finding a variational formulation to a given tensor-based partial differential equation is studied.

    The presented framework is applied in problem formulation that includes non-linear domain transformation, e.g., visualization of medical images.

    Additionally, the framework is also used to exploit locally estimated probability density functions or the channel representation to drive the filtering process.

    Furthermore, one of the first truly tensor-based formulations of total variation is presented. The key to the formulation is the gradient energy tensor, which does not require spatial regularization of its tensor components. It is shown empirically in several computer vision applications, such as corner detection and optical flow, that the gradient energy tensor is a viable replacement for the commonly used structure tensor. Moreover, the gradient energy tensor is used in the traditional tensor-based anisotropic diffusion scheme. This approach results in significant improvements in computational speed when the scheme is implemented on a graphical processing unit compared to using the commonly used structure tensor.

  • 2573.
    Åström, Kalle
    et al.
    Centre for Mathematical Sciences, Lund University.
    Persson, Lars-ErikLuleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.Silvestrov, Sergei D.Division of Applied Mathematics, Mälardalen University.
    Analysis for science, engineering and beyond: the tribute workshop in honour of Gunnar Sparr held in Lund, May 8-9, 20082012Collection/Antologi (Annet vitenskapelig)
  • 2574.
    Åström, Karl
    et al.
    Lund university.
    Persson, Lars-ErikLuleå university.Silvestrov, SergeiMälardalens högskola, Akademin för utbildning, kultur och kommunikation.
    Analysis for Science, Engineering and Beyond The Tribute Workshop in Honour of Gunnar Sparr held in Lund, May 8-9, 20082012Collection/Antologi (Fagfellevurdert)
  • 2575.
    Öberg, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen.
    Algorithms for approximation of invariant measures for IFS2005Inngår i: Manuscripta mathematica, ISSN 0025-2611, E-ISSN 1432-1785, Vol. 116, nr 1, s. 31-55Artikkel i tidsskrift (Fagfellevurdert)
  • 2576.
    Öberg, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Matematik I-5.
    Approximation of invariant measures for random iterations2006Inngår i: Rocky Mountain Journal of Mathematics, ISSN 0035-7596, E-ISSN 1945-3795, Vol. 36, nr 1, s. 273-301Artikkel i tidsskrift (Fagfellevurdert)
  • 2577.
    Öberg, Anders
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Matematik I-5.
    Strichartz, Robert S.
    Yingst, Andrew Q.
    Level sets of harmonic functions on the Sierpinski gasket2002Inngår i: Arkiv för matematik, ISSN 0004-2080, E-ISSN 1871-2487, Vol. 40, nr 2, s. 335-362Artikkel i tidsskrift (Fagfellevurdert)
  • 2578.
    Ödling, Per
    et al.
    Luleå tekniska universitet.
    Koski, Timo
    Luleå tekniska universitet.
    Börjesson, Per Ola
    Luleå tekniska universitet.
    A reduced complexity viterbi equalizer used in conjunction with a pulse shaping method1992Inngår i: Proceedings of Nordic Radio Symposium: NRS 92 : wave propagation, personal, mobile and satellite communications / in co-operation with AUC - Aalborg University / [ed] Chr. Christensen, Aalborg: Aalborg University , 1992, s. 91-94Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The complexity of the Viterbi algorithm can be reduced by linear pre-equalization. We introduce a linear preprocessor using the weighted least squares filtering of [10]. The geometric technique of L.Barbosa [3] is evoked for analytical representation of the complexity reduction by pre-equalization, and for evaluation of error performance. We give results on the bit error rate of the WLS preprocessor and of the linear preprocessor of Falconer and Magee [6].

  • 2579.
    Öhman, Eric
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematisk statistik.
    Analys av bostadsrättspriser medmultipel linjär regression ochprissättning i praktiken2014Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Syftet med denna rapport är att undersöka de faktorer som påverkar priset på bostadsrätter i Stockholms innerstad och hur mycket dessa faktorer påverkar priset med multipel linjär regression.  Resultaten från regressionsanalysen används för att skapa en modell för att prissätta bostadsrätter i Stockholms innerstad.  Denna modell jämförs med de metoder som byggnationsföretag vars verksamhet riktar sig mot försäljning av nybyggda bostadsrätter direkt till kund för att se om de metoder som används idag går att förbättra.  Arbetet resulterade i en modell som kan ge en indikation på hur mycket olika faktorer påverkar priset samt en grund för bostadsrättsvärdering i Stockholms innerstad.  De metoder som används idag visade sig inte kunna förbättras med de resultat som togs fram i denna rapport då fördelarna med dessa metoder är dess anpassningsbarhet efter ett projekts unika egenskaper samt avgränsningar till relevanta marknader.

  • 2580.
    Öktem, Ozan
    Sidec, Kista, Sweden.
    Reconstruction methods in electron tomography2008Inngår i: Mathematical Methods in Biomedical Imaging and Intensity-Modulated Radiation Therapy (IMRT) / [ed] Y. Censor, Jiang M., and Louis A. K., Springer Berlin/Heidelberg, 2008, s. 289-320Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    Already in 1968 one recognized that the transmission electron micro- scope could be used in a tomographic setting as a tool for structure determination of macromolecules. However, its usage in mainstream structural biology has been limited and one reason is the devastating combination of noisy data and incomplete data problems that leads to severe ill-posedness of the inverse problem. Despite these issues, the importance of electron tomography is beginning to increase, espe- cially in drug discovery. This review begins with a brief introduction to the model for image formation, i.e. the forward operator. Next, we state the difficulties and review some of the various attempts at overcoming those in solving the inverse problem.

  • 2581.
    Öktem, Ozan
    et al.
    Sidec AB, Kista, Sweden.
    Fanelli, Duccio
    University of Florens.
    Electron tomography: A short overview with an emphasis on the absorption potential model for the forward problem2008Inngår i: Inverse Problems, ISSN 0266-5611, E-ISSN 1361-6420, Vol. 24, nr 1, s. 013001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This review of the development and current status of electron tomography deals mainly with the mathematical and algorithmic aspects. After a very brief description of the role of electron tomography in structural biology, we turn our attention to the derivation of the forward operator. Starting from the Schrodinger equation, the electron - specimen interaction is modelled as a diffraction tomography problem and the picture is completed by adding a description of the optical system of the transmission electron microscope. The first- order Born approximation enables one to explicitly express the intensity for any finite wavenumber in terms of the propagation operator acting on the specimen convolved with a point spread function, derived from the optics in the transmission electron microscope. Next, we focus on the difficulties that cause the reconstruction problem to be quite challenging. Special emphasis is put on explaining the extremely low signal- to- noise ratio in the data combined with the incomplete data problems, which lead to severe ill- posedness. The next step is to derive the standard phase contrast model used in the electron tomography community. The above- mentioned expression for the intensity generalizes the standard phase contrast model which can be obtained by replacing the propagation operator by its high- energy limit, the x- ray transform, as the wavenumber tends to infinity. The importance of more carefully including the wave nature of the electron - specimen interaction is supported by performing an asymptotic analysis of the intensity as the wavenumber tends to infinity. Next we provide an overview of the various reconstruction methods that have been employed in electron tomography and we conclude by mentioning a number of open problems. Besides providing an introduction to electron tomography written in the 'language of inverse problems', the authors hope to raise interest among experts in integral geometry and regularization theory for the mathematical and algorithmic difficulties that are encountered in electron tomography.

  • 2582.
    Öktem, Ozan
    et al.
    Sidec, Kista, Sweden.
    Quinto, Eric Todd
    Tufts University.
    Inversion of the X-ray transform from limited angle parallel beam region of interest data with applications to electron tomography2007Inngår i: Proceedings in Applied Mathematics and Mechanics: PAMM, ISSN 1617-7061, E-ISSN 1617-7061, Vol. 7, nr 1, s. 1050301-1050302Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a new local tomographic algorithm applicable to electron microscopy tomography. Our algorithm applies to the standard data acquisition method, single-axis tilting, as well as for more arbitrary acquisition methods. Using microlocal analysis we put the reconstructions in a mathematical context, explaining which singularities are stably visible from the limited data given by the data collection protocol in the electron microscope.

  • 2583.
    Öktem, Ozan
    et al.
    Sidec Technologies, Kista, Sweden.
    Quinto, Eric Todd
    Tufts University.
    Local tomography in electron microscopy2008Inngår i: SIAM Journal on Applied Mathematics, ISSN 0036-1399, E-ISSN 1095-712X, Vol. 68, nr 5, s. 1282-1303Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a new local tomographic algorithm applicable to electron microscope tomography. Our algorithm applies to the standard data acquisition method, single-axis tilting, as well as to more arbitrary acquisition methods including double axis and conical tilt. Using microlocal analysis we put the reconstructions in a mathematical context, explaining which singularities are stably visible from the limited data given by the data collection protocol in the electron microscope. Finally, we provide reconstructions of real specimens from electron tomography data.

  • 2584.
    Öktem, Ozan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematik (Avd.). KTH, Skolan för teknikvetenskap (SCI), Centra, Strategiskt centrum för industriell och tillämpad matematik, CIAM.
    Quinto, Eric Todd
    Tufts University.
    Skoglund, Ulf
    Okinawa Institute of Science and Technology.
    Electron Lambda-tomography2009Inngår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 106, nr 51, s. 21842-21847Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Filtered back-projection and weighted back-projection have long been the methods of choice within the electron microscopy com- munity for reconstructing the structure of macromolecular assem- blies from electron tomography data. Here, we describe electron lambda-tomography, a reconstruction method that enjoys the ben- efits of the above mentioned methods, namely speed and ease of implementation, but also addresses some of their shortcomings. In particular, compared to these standard methods, electron lambda- tomography is less sensitive to artifacts that come from structures outside the region that is being reconstructed, and it can sharpen boundaries.

  • 2585.
    Öktem, Ozan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematik (Avd.).
    Rullgård, Hans
    Stockholm University.
    Skoglund, Ulf
    Karolinska Institutet.
    A component-wise iterated relative entropy regularization method with updated prior and regularization parameter2007Inngår i: Inverse Problems, ISSN 0266-5611, E-ISSN 1361-6420, Vol. 23, nr 5, s. 2121-2139Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a componentwise iterated relative entropy regularization method (COMET) where the prior and regularization parameter could be updated in the iterates. Such a reconstruction method could be useful for multicomponent inverse problems, such as the one occurring in electron tomography. The paper also contains a brief introduction to regularization theory with emphasis on variational based regularization methods, and we rigorously prove that the tolerance-based entropy reconstruction method that occurs in the COMET iterates is a regularization method. We conclude by showing examples of COMET applied to electron tomography data.

  • 2586. Agarwal, R.P.
    Persson, Lars-Erik
    Zafer, A.
    Selected papers of the international workshop on difference and differential inequalities, Gebze, Kocaeli, Turkey, July 3--7, 19961998Inngår i: Mathematical Inequalities & Applications, ISSN 1331-4343, E-ISSN 1848-9966, Vol. 1, nr 3, s. 347-461Artikkel i tidsskrift (Fagfellevurdert)
49505152 2551 - 2586 of 2586
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