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  • 251.
    Landén, Camilla
    KTH, Superseded Departments, Mathematics.
    Spot price realizations of futures price term structures2000In: AMS Scand 2000: First AMS-Scandinavian International Mathematics Meeting, XXIII Scandinavian Congress of Mathematicians, June 13-16, WMY 2000, Odense, Denmark : Abstracts., Odense: Syddansk Universitet , 2000Conference paper (Other academic)
  • 252.
    Landén, Camilla
    et al.
    KTH, Superseded Departments, Mathematics.
    Björk, Tomas
    On the construction of finite dimensional realizations for nonlinear forward rate models2002In: Finance and Stochastics, ISSN 0949-2984, E-ISSN 1432-1122, Vol. 6, no 3, p. 303-331Article in journal (Refereed)
    Abstract [en]

    We consider interest rate models of Heath-Jarrow-Morton type where the forward rates are driven by a multidimensional Wiener process, and where the volatility structure is allowed to be a smooth functional of the present forward rate curve. In a recent paper [3], Björk and Svensson give necessary and sufficient conditions for the existence of a finite dimensional Markovian state space realization (FDR) for such a forward rate model, and in the present paper we provide a general method for the actual construction of an FDR. We illustrate the method by constructing FDR:s for a number of concrete models. These FDR:s generalize previous results by allowing for a more general volatility structure. Furthermore the dimension of the realizations obtained by using our method is typically smaller than that of the corresponding previously known realizations.

  • 253.
    Landén, Camilla
    et al.
    KTH, Superseded Departments, Mathematics.
    Björk, Tomas
    On the Term Structure of Futures and Forward Prices2002In: Mathematical Finance - Bachelier Congress 2000 / [ed] Geman, Helyette, Madan, Dilip, Pliska, Stanley, Vorst, Ton, Springer-Verlag , 2002, p. 111-150Conference paper (Other academic)
    Abstract [en]

    We investigate the term structure of forward and futures prices for models where the price processes are allowed to be driven by a general marked point process as well as by a multidimensional Wiener process. Within an infinite dimensional HJM-type model for futures and forwards we study the properties of futures and forward convenience yield rates. For finite dimensional factor models, we develop a theory of affine term structures, which is shown to include almost all previously known models. We also derive two general pricing formulas for futures options. Finally we present an easily applicable sufficient condition for the possibility of fitting a finite dimensional futures price model to an arbitrary initial futures price curve, by introducing a time dependent function in the drift term.

  • 254.
    Laptev, Ari
    KTH, Superseded Departments, Mathematics.
    The negative spectrum of a class of two-dimensional Schrodinger operators with potentials depending only on radius2000In: Functional analysis and its applications, ISSN 0016-2663, E-ISSN 1573-8485, Vol. 34, no 4, p. 305-307Article in journal (Refereed)
  • 255.
    Laptev, Ari
    et al.
    KTH, Superseded Departments, Mathematics.
    Naboko, S.
    Safronov, O.
    On new relations between spectral properties of Jacobi matrices and their coefficients2003In: Communications in Mathematical Physics, ISSN 0010-3616, E-ISSN 1432-0916, Vol. 241, no 1, p. 91-110Article in journal (Refereed)
    Abstract [en]

    We study the spectral properties of Jacobi matrices. By using ``higher order'' trace formulae we obtain a result relating the properties of the elements of Jacobi matrices and the corresponding spectral measures. Complicated expressions for traces of some operators can be magically simplified allowing us to apply induction arguments. Our theorems are generalizations of a recent result of R. Killip and B. Simon [17].

  • 256.
    Laptev, Ari
    et al.
    KTH, Superseded Departments, Mathematics.
    Sigal, I. M.
    Global Fourier integral operators and semiclassical asymptotics2000In: Reviews in Mathematical Physics, ISSN 0129-055X, Vol. 12, no 5, p. 749-766Article, review/survey (Refereed)
    Abstract [en]

    In this paper we introduce a class of semiclassical Fourier integral operators with global complex phases approximating the fundamental solutions (propagators) for time-dependent Schrodinger equations. Our construction is elementary, it is inspired by the joint work of the first author with Yu. Safarov and D. Vasiliev. We consider several simple but basic examples.

  • 257.
    Laptev, Ari
    et al.
    KTH, Superseded Departments, Mathematics.
    Weidl, T.
    Sharp Lieb-Thirring inequalities in high dimensions2000In: Acta Mathematica, ISSN 0001-5962, E-ISSN 1871-2509, Vol. 184, no 1, p. 87-111Article in journal (Refereed)
  • 258. Lee, K. A.
    et al.
    Shahgholian, Henrik
    KTH, Superseded Departments, Mathematics.
    Regularity of a free boundary for viscosity solutions of nonlinear elliptic equations2001In: Communications on Pure and Applied Mathematics, ISSN 0010-3640, E-ISSN 1097-0312, Vol. 54, no 1, p. 43-56Article in journal (Refereed)
    Abstract [en]

    Our objective in this paper is to analyze the regularity of the boundary of a set Omega2 that admits a solution u to the following overdetermined problem: F(D(2)u) = chi (Omega) in B, u = \ delu \ = 0 in B \ Omega. Here F is a convex, uniformly elliptic operator of homogeneity one, B is the unit ball in R-n, and the equation is satisfied in the viscosity sense. We also consider the case of concave F in R-2.

  • 259. Lee, K.
    et al.
    Shahgholian, Henrik
    KTH, Superseded Departments, Mathematics.
    Hausdorff measure and stability for the p-obstacle problem (2 < p 2003In: Journal of Differential Equations, ISSN 0022-0396, E-ISSN 1090-2732, Vol. 195, no 1, p. 14-24Article in journal (Refereed)
    Abstract [en]

    In this paper we analyze the free boundary for the inhomogeneous obstacle problem with zero obstacle governed by the degenerate operator div(A/(delu)) = fchi({u>0}), where f is a positive, Lipschitz function, and A(delu) is of the p-Laplacian type, i.e., A(delu) approximate to \delu\(p-2)delu, (2

  • 260.
    Lindell, Andreas
    KTH, Superseded Departments, Mathematics.
    Numerical investigations of the distributions of the longest excursions in tied down simple random walks and brownian bridges2000Licentiate thesis, monograph (Other scientific)
  • 261.
    Lindquist, Anders
    KTH, Superseded Departments, Mathematics.
    A covariance extension approach to identification of time series2000In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 36, no 3, p. 379-398Article in journal (Refereed)
    Abstract [en]

    In this paper we consider a three-step procedure far identification of time series, based on covariance extension and model reduction, and we present a complete analysis of its statistical convergence properties. A partial covariance sequence is estimated from statistical data. Then a high-order maximum-entropy model is determined, which is finally approximated by a lower-order model by stochastically balanced model reduction. Such procedures have been studied before, in various combinations, but an overall convergence analysis comprising all three steps has been lacking. Supposing the data is generated from a true finite-dimensional system which is minimum phase, it is shown that the transfer function of the estimated system tends in H-infinity to the true transfer function as the data length tends to infinity, if the covariance extension and the model reduction is done properly. The proposed identification procedure, and some variations of it, are evaluated by simulations.

  • 262.
    Lindquist, Anders
    KTH, Superseded Departments, Mathematics.
    A new approach to spectral estimation: A tunable high-resolution spectral estimator2000In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 48, no 11, p. 3189-3205Article in journal (Refereed)
    Abstract [en]

    Traditional maximum entropy spectral estimation determines a power spectrum from covariance estimates. Here, we present a new approach to spectral estimation, which is based on the use of filter banks as a means of obtaining spectral interpolation data, Such data replaces standard covariance estimates, A computational procedure for obtaining suitable pole-zero (ARMA) models from such data is presented. The choice of the zeros (MA-part) of the model is completely arbitrary. By suitably choices of filterbank poles and spectral zeros, the estimator can be tuned to exhibit high resolution in targeted regions of the spectrum.

  • 263.
    Lindquist, Anders
    KTH, Superseded Departments, Mathematics.
    Generalized entropy criterion for Nevanlinna-Pick interpolation with degree constraint2001In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 46, no 6, p. 822-839Article in journal (Refereed)
    Abstract [en]

    In this paper, we present a generalized entropy criterion for solving the rational Nevanlinna-Pick problem for n + 1 interpolating conditions and the degree of interpolants bounded by n, The primal problem of maximizing this entropy gain has a very well-behaved dual problem. This dual is a convex optimization problem in a finite-dimensional space and gives rise to an algorithm for finding all interpolants which are positive real and rational of degree at most n, The criterion requires a selection of a monic Schur polynomial of degree n, It follows that this class of monic polynomials completely parameterizes all such rational interpolants, and it therefore provides a set of design parameters for specifying such interpolants. The algorithm is implemented in state-space form and applied to several illustrative problems in systems and control, namely sensitivity minimization, maximal power transfer and spectral estimation.

  • 264.
    Lindquist, Anders
    KTH, Superseded Departments, Mathematics.
    On the duality between filtering and Nevanlinna-Pick interpolation2000In: SIAM Journal of Control and Optimization, ISSN 0363-0129, E-ISSN 1095-7138, Vol. 39, no 3, p. 757-775Article in journal (Refereed)
    Abstract [en]

    Positive real rational functions play a central role in both deterministic and stochastic linear systems theory, as well as in circuit synthesis, spectral analysis, and speech processing. For this reason, results about positive real transfer functions and their realizations typically have many applications and manifestations. In this paper, we study certain manifolds and submanifolds of positive real transfer functions, describing a fundamental geometric duality between filtering and Nevanlinna Pick interpolation. Not surprisingly, then, this duality, while interesting in its own right, has several corollaries which provide solutions and insight into some very interesting and intensely researched problems. One of these is the problem of parameterizing all rational solutions of bounded degree of the Nevanlinna-Pick interpolation problem, which plays a central role in robust control, and for which the duality theorem yields a complete solution. In this paper, we shall describe the duality theorem, which we motivate in terms of both the interpolation problem and a fast algorithm for Kalman filtering, viewed as a nonlinear dynamical system on the space of positive real transfer functions. We also outline a new proof of the recent solution to the rational Nevanlinna Pick interpolation problem, using an algebraic topological generalization of Hadamard's global inverse function theorem.

  • 265.
    Maakestad, Helge
    KTH, Superseded Departments, Mathematics.
    Principal Parts on P^1 and Chow-groups of the classical discriminants.2000Doctoral thesis, monograph (Other scientific)
  • 266. Manfredi, J.
    et al.
    Petrosyan, A.
    Shahgholian, Henrik
    KTH, Superseded Departments, Mathematics.
    A free boundary problem for infinity-Laplace equation2002In: Calculus of Variations and Partial Differential Equations, ISSN 0944-2669, E-ISSN 1432-0835, Vol. 14, no 3, p. 359-384Article in journal (Refereed)
    Abstract [en]

    We consider a free boundary problem for the p-Laplacian Delta(mu)u = div(\delu\(p-2)delu), describing nonlinear potential flow past a convex profile K with prescribed pressure \delu(x)\ = a(x) on the free stream line. The main purpose of this paper is to study the limit as p --> infinity of the classical solutions of the problem above, existing under certain convexity assumptions on a(x). We show, as one can expect, that the limit solves the corresponding potential flow problem for the infinity-Laplacian Deltax u = del(2) u delu . delu. in a certain weak sense, strong enough however, to guarantee uniqueness. We show also that in the special case a(x) = a(0) > 0 the limit is given by the distance function.

  • 267.
    Mari, Jorge
    KTH, Superseded Departments, Mathematics.
    Rational modeling of time series and applications of geometric control1998Doctoral thesis, monograph (Other scientific)
  • 268.
    Matevosyan, Norayr
    KTH, Superseded Departments, Mathematics.
    Tangential Touch Between Free And Fixed Boundaries2003Doctoral thesis, comprehensive summary (Other scientific)
  • 269.
    Mattila, Kirsti
    KTH, Superseded Departments, Mathematics.
    Restrictions of relatively Tauberian operators2003In: Journal of Mathematical Analysis and Applications, ISSN 0022-247X, E-ISSN 1096-0813, Vol. 287, no 2, p. 494-503Article in journal (Refereed)
    Abstract [en]

    For operators T with the property TX1 subset of T X which in addition satisfy a spectral condition we consider conditions under which the restriction of T to a closed invariant subspace also satisfies the same inclusion on the subspace.

  • 270.
    Mazo, Manuel
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Speranzon, Alberto
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Johansson, Karl Henrik
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Hu, Xiaoming
    KTH, Superseded Departments, Mathematics.
    Multi-robot tracking of a moving object using directional sensors2004In: 2004 IEEE INTERNATIONAL CONFERENCE ON ROBOTICS AND AUTOMATION, VOLS 1- 5, PROCEEDINGS, 2004, p. 1103-1108Conference paper (Refereed)
    Abstract [en]

    The problem of estimating and tracking the motion of a moving target by a team of mobile robots is studied in this paper. Each robot is assumed to have a directional sensor with limited range, thus more than one robot (sensor) is needed for solving the problem. A sensor fusion scheme based on inter-robot communication is proposed in order to obtain accurate real-time information of the target's position and motion. Accordingly a hierarchical control scheme is applied, in which a consecutive set of desired formations is planned through a discrete model and low-level continuous-time controls are executed to track the resulting references. The algorithm is illustrated through simulations and on an experimental platform.

  • 271. Meyer, F. G.
    et al.
    Averbuch, A. Z.
    Strömberg, Jan-Olov
    KTH, Superseded Departments, Mathematics.
    Fast adaptive wavelet packet image compression2000In: IEEE Transactions on Image Processing, ISSN 1057-7149, E-ISSN 1941-0042, Vol. 9, no 5, p. 792-800Article in journal (Refereed)
    Abstract [en]

    Wavelets are ill-suited to represent oscillatory patterns: rapid variations of intensity can only be described by the small scale wavelet coefficients, which are often quantized to zero, even at high bit rates. Our goal in this paper is to provide a fast numerical implementation of the best wavelet packet algorithm [1] in order to demonstrate that an advantage can be gained by constructing a basis adapted to a target image. Emphasis in this paper has been placed on developing algorithms that are computationally efficient. We developed a new fast two-dimensional (2-D) convolution-decimation algorithm with factorized nonseparable 2-D filters. The algorithm is four times faster than a standard convolution-decimation, An extensive evaluation of the algorithm was performed on a large class of textured images. Because of its ability to reproduce textures so well, the wavelet packet coder significantly out performs one of the best wavelet coder [2] on images such as Barbara and fingerprints, both visually and in term of PSNR.

  • 272.
    Nagamune, Ryozo
    KTH, Superseded Departments, Mathematics.
    Robust Control with Complexity Constraint: A Nevanlinna-Pick Interpolation Approach2002Doctoral thesis, comprehensive summary (Other scientific)
  • 273.
    Nagnibeda, Tatiana
    KTH, Superseded Departments, Mathematics.
    Random walks, spectral radii, and Ramanujan graphs2004In: Random Walks And Geometry / [ed] Kaimanovich, VA, BERLIN 30: WALTER DE GRUYTER & CO , 2004, p. 487-500Conference paper (Refereed)
    Abstract [en]

    We investigate properties of random walks on trees with finitely many cone types and apply our results to get estimates on spectral radii of groups and to check whether a given finite graph is Ramanujan.

  • 274.
    Nordin, Mattias
    KTH, Superseded Departments, Mathematics.
    Nonlinear backlash compensation for speed controlled elastic systems2000Doctoral thesis, monograph (Other scientific)
  • 275.
    Nåsell, Ingemar
    KTH, Superseded Departments, Mathematics.
    An extension of the moment closure method2003In: Theoretical Population Biology, ISSN 0040-5809, E-ISSN 1096-0325, Vol. 64, no 2, p. 233-239Article in journal (Refereed)
    Abstract [en]

    The moment closure method was recently shown in Nasell (Theor. Popul. Biol. 63 (2) (2003a) 159) to give asymptotic approximations of the first few cumulants for the stochastic logistic model. A slight extension of the method is introduced. It is shown to be robust with regard to the specific distributional assumption that is used to achieve moment closure. The phenomenon of spurious solutions is shown to be related to the domain of attraction of the non-spurious critical point.

  • 276.
    Nåsell, Ingemar
    KTH, Superseded Departments, Mathematics.
    Moment closure and the stochastic logistic model2003In: Theoretical Population Biology, ISSN 0040-5809, E-ISSN 1096-0325, Vol. 63, no 2, p. 159-168Article in journal (Refereed)
    Abstract [en]

    The quasi-stationary distribution of the stochastic logistic model is studied in the parameter region where its body is approximately normal. Improved asymptotic approximations of its first three cumulants are derived. It is shown that the same results can be derived with the aid of the moment closure method. This indicates that the moment closure method leads to expressions for the cumulants that are asymptotic approximations of the cumulants of the quasi-stationary distribution.

  • 277.
    Nåsell, Ingemar
    KTH, Superseded Departments, Mathematics.
    Stochastic models of some endemic infections2002In: Mathematical Biosciences, ISSN 0025-5564, E-ISSN 1879-3134, Vol. 179, no 1, p. 1-19Article in journal (Refereed)
    Abstract [en]

    Stochastic models are established and studied for several endemic infections with demography. Approximations of quasi-stationary distributions and of times to extinction are derived for stochastic versions of SI, SIS, SIR, and SIRS models. The approximations are valid for sufficiently large population sizes. Conditions for validity of the approximations are given for each of the models. These are also conditions for validity of the corresponding deterministic model. It is noted that some deterministic models are unacceptable approximations of the stochastic models for a large range of realistic parameter values.

  • 278.
    Nõu, Andreas
    KTH, Superseded Departments, Mathematics.
    Large scale combinatorial optimization with transportation science applications1997Doctoral thesis, monograph (Other scientific)
  • 279.
    Olivecrona, Henrik
    et al.
    Karolinska Institute, Department of Molecular Medicine and Surgery.
    Weidenhielm, Lars
    Karolinska Institute, Department of Molecular Medicine and Surgery.
    Olivecrona, Lotta
    Karolinska Institutet, Department of Clinical Science, Intervention and Technology, Division of Radiology.
    Beckman, M. O.
    Stark, Andreas
    Karolinska Institute, Department of Molecular Medicine and Surgery.
    Noz, Marilyn E.
    New York University, Department of Radiology.
    Maguire Jr., Gerald Q.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Zeleznik, Michael P.
    RAHD Oncology Products, St. Loius MO, USA.
    Svensson, Lars E.
    KTH, Superseded Departments, Mathematics.
    Jonson, T.
    A new CT method for measuring cup orientation after total hip arthroplasty: A study of 10 patients2004In: Acta Orthopaedica Scandinavica, ISSN 0001-6470, Vol. 75, no 3, p. 252-260Article in journal (Refereed)
    Abstract [en]

    Background It is difficult to assess the orientation of the acetabular component on routine radiographs. We present a method for determining the spatial orientation of the acetabular component after total hip arthroplasty (THA) using computed tomography. Patients and methods Two CT-scans, 10 min apart, were obtained from each of 10 patients after THA. Using locally developed software, two independent examiners measured the orientation of the acetabular component in relation to the pelvis. The measurements were repeated after one week. To be independent of the patient position during scanning, the method involved two steps. Firstly, a 3D volumetric image of the pelvis was brought into a standard pelvic orientation, then the orientation of the acetabular component was measured. The orientation of the acetabular component was expressed as operative anteversion and inclination relative to an internal pelvic reference coordinate system. To evaluate precision, we compared measurements across pairs of CT volumes between observers and trials. Results Mean absolute interobserver angle error was 2.3degrees for anteversion (range 0-6.6degrees), and 1.1degrees for inclination (range 0-4.6degrees). For interobserver measurements, the precision, defined as one standard deviation, was 2.9degrees for anteversion, and 1.5degrees for inclination. A Student's West showed that the overall differences between the examiners, trials, and cases were not significant. Data were normally distributed and were not dependent on examiner or trial. Interpretation We conclude that the implant angles of the acetabular component in relation to the pelvis could be detected repeatedly using CT, independently of patient positioning.

  • 280.
    Petrosyan, Arshak
    KTH, Superseded Departments, Mathematics.
    Convex configurations in free boundary problems2000Doctoral thesis, comprehensive summary (Other scientific)
  • 281.
    Philip, Johan
    KTH, Superseded Departments, Mathematics.
    The area and perimeter of a random spherical triangleManuscript (preprint) (Other academic)
    Abstract [en]

    We determine the distribution functions for the area and the perimeter of a random spherical triangle. We consider two natural ‘polar’ ways of generating the random triangle. It turnsout that the distribution for the area in the first way is closely related to the distribution of the perimeter in the second way, and vice versa.

  • 282.
    Prytz, Mikael
    KTH, Superseded Departments, Mathematics.
    On Optimization in Design of Telecommunications Networks with Multicast and Unicast Traffic2002Doctoral thesis, comprehensive summary (Other scientific)
  • 283. Przytycki, F
    et al.
    Rivera-Letelier, J
    Smirnov, Stanislav
    KTH, Superseded Departments, Mathematics.
    Equality of pressures for rational functions2004In: Ergodic Theory and Dynamical Systems, ISSN 0143-3857, E-ISSN 1469-4417, Vol. 24, p. 891-914Article in journal (Refereed)
    Abstract [en]

    We prove that for all rational functions f on the Riemann sphere and potential -t ln \f'\ t greater than or equal to 0 all the notions of pressure introduced in Przytycki (Proc. Amer Math. Soc. 351(5) (1999), 2081-2099) coincide. In particular, we get a new simple proof of the equality between the hyperbolic Hausdorff dimension and the minimal exponent of conformal measure on a Julia set. We prove that these pressures are equal to the pressure defined with the use of periodic orbits under an assumption that there are not many periodic orbits with Lyapunov exponent close to 1 moving close together, in particular under the Topological Collet-Eckmann condition. In Appendix A, we discuss the case t < 0.

  • 284.
    Raab, Mikael
    KTH, Superseded Departments, Mathematics.
    On the number of exceedances in gaussian and related sequences1997Doctoral thesis, monograph (Other scientific)
  • 285.
    Rehbinder, Henrik
    KTH, Superseded Departments, Mathematics.
    State Estimation and Limited Communication Control for Nonlinear Robotic Systems2001Doctoral thesis, comprehensive summary (Other scientific)
  • 286.
    Rehbinder, Henrik
    et al.
    KTH, Superseded Departments, Mathematics.
    Sanfridson, Martin
    KTH, Superseded Departments, Machine Design.
    Scheduling of a limited communication channel for optimal control2004In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 40, no 3, p. 491-500Article in journal (Refereed)
    Abstract [en]

    In this paper a method for optimal off-line scheduling of a limited resource used for control purposes is presented. For various reasons, real-time communication channels are prone to have-limited bandwidth. To overcome this obstacle, the rate of actions must be chosen accordingly at design time, both with respect to the limitation of the resource and to control performance. A resulting off-line schedule implements the rate of actions as a repetitive sequence of communication instants. Periodic control theory is used to define a cost functional for LQ-control, that measures the performance of a sampled-data system in relation to a desired continuous time performance. In contrast to uniform sampling, the communication sequence is here allowed to be time-varying. This approach results in a complex combinatorial optimization problem, whose solution gives the optimal off-line schedule, i.e., the sequence in which the actions should take place. The optimization problem is solved by a neighborhood search method where a heuristic method is used to generate initial guesses close to the optimum. The optimal schedule is typically such that the sampling is non-uniform, but the resulting LQ-control law is time-varying and takes this non-uniform sampling into account.

  • 287.
    Ridderström, Christian
    et al.
    KTH, Superseded Departments, Machine Design.
    Ingvast, Johan
    KTH, Superseded Departments, Machine Design.
    Hardarson, Freyr
    KTH, Superseded Departments, Machine Design.
    Gudmundsson, Mats
    KTH, Superseded Departments, Machine Design.
    Hellgren, Mikael
    KTH, Superseded Departments, Machine Design.
    Wikander, Jan
    KTH, Superseded Departments, Machine Design.
    Wadden, Tom
    KTH, Superseded Departments, Machine Design.
    Rehbinder, Henrik
    KTH, Superseded Departments, Mathematics.
    The basic design of the quadruped robot WARP12000In: International Conference on Climbing and Walking RobotsArticle in journal (Refereed)
    Abstract [en]

    This paper presents the basic design of a walking robot platform, in terms of its mechanics,electronics and control. The four-legged robot weighs about 60 kilograms, has three actuatorsin each leg and uses a distributed control system over six CAN busses. Basic strength and speedis demonstrated by experiments where the robot performs walking motions and goes down onits knees and then up again. A brief discussion of experiences from designing and implementingthe platform is included.

  • 288.
    Ringh, Axel
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Karlsson, Johan
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Engineering Sciences (SCI), Centres, Center for Industrial and Applied Mathematics, CIAM.
    Lindquist, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Engineering Sciences (SCI), Centres, Center for Industrial and Applied Mathematics, CIAM. KTH, Superseded Departments (pre-2005), Mathematics. Department of Automation, Shanghai Jiao Tong University, Shanghai, China.
    Multidimensional rational covariance extensionManuscript (preprint) (Other academic)
    Abstract [en]

    The rational covariance extension problem (RCEP) is an important problem in systems and control occurring in such diverse fields as control, estimation, system identification, and signal and image processing, leading to many fundamental theoretical questions. In fact, this inverse problem is a key component in many identification and signal processing techniques and plays a fundamental role in prediction, analysis, and modeling of systems and signals. It is well-known that the RCEP can be reformulated as a (truncated) trigonometric moment problem subject to a rationality condition. In this paper we consider the more general multidimensional trigonometric moment problem with a similar rationality constraint. This generalization creates many interesting new mathematical questions and also provides new insights into the original one-dimensional problem. A key concept in this approach is the complete smooth parametrization of all solutions, allowing solutions to be tuned to satisfy additional design specifications without violating the complexity constraints. As an illustration of the potential of this approach we apply our results to multidimensional spectral estimation, Wiener system identification, and image compression.

  • 289.
    Ringström, Hans
    KTH, Superseded Departments, Mathematics.
    Curvature blow up in Bianchi VIII and IX vacuum spacetimes2000In: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 17, no 4, p. 713-731Article in journal (Refereed)
    Abstract [en]

    The maximal globally hyperbolic development of non-Taub-NUT Bianchi IX vacuum initial data and of non-NUT Bianchi VIII vacuum initial data is C-2-inextendible. Furthermore, a curvature invariant is unbounded in the incomplete directions of inextendible causal geodesics.

  • 290.
    Ringström, Hans
    KTH, Superseded Departments, Mathematics.
    On the asymptotics of Bianchi class A spacetimes2000Doctoral thesis, monograph (Other scientific)
  • 291.
    Rosenlund, Magnus
    KTH, Superseded Departments, Mathematics.
    Radical operations in rings and topological spaces2004Doctoral thesis, monograph (Other scientific)
  • 292.
    Ryd, Gustav
    KTH, Superseded Departments, Mathematics.
    Iterations of one parameter families of complex polynomials1997Doctoral thesis, monograph (Other scientific)
  • 293.
    Safron, O.
    KTH, Superseded Departments, Mathematics.
    The discrete spectrum in gaps of the continous one under perturbation of variable sign1997Doctoral thesis, comprehensive summary (Other scientific)
  • 294.
    Safronov, Oleg
    KTH, Superseded Departments, Mathematics.
    The amount of discrete spectrum of a perturbed periodic Schrodinger operator inside a fixed interval (lambda(1),lambda(2))2004In: International mathematics research notices, ISSN 1073-7928, E-ISSN 1687-0247, no 9, p. 411-423Article in journal (Refereed)
    Abstract [en]

    Let A be a periodic Schrödinger operator and let V ≥ 0 be a decaying potential. We study the number of the eigenvalues of the operator A(α)=A−α V inside a fixed interval (λ12). We obtain an asymptotic formula for as α → ∞. In this paper we extend the results of Safronov (2001) for a more general class of perturbations.

  • 295.
    Safronov, Oleg
    KTH, Superseded Departments, Mathematics.
    The spectral measure of a Jacobi matrix in terms of the Fourier transform of the perturbation2004In: Arkiv för matematik, ISSN 0004-2080, E-ISSN 1871-2487, Vol. 42, no 2, p. 363-377Article in journal (Refereed)
    Abstract [en]

    We study the spectral properties of Jacobi matrices. By combining Killip's technique [12] with the technique of Killip and Simon [13] we obtain a result relating the properties of the elements of Jacobi matrices and the corresponding spectral measures. This theorem is a natural extension of a recent result of Laptev-Naboko-Safronov [17].

  • 296.
    Saprykina, Maria
    KTH, Superseded Departments, Mathematics.
    Analytic nonlinearizable uniquely ergodic diffeomorphisms on T-22003In: Ergodic Theory and Dynamical Systems, ISSN 0143-3857, E-ISSN 1469-4417, Vol. 23, p. 935-955Article in journal (Refereed)
    Abstract [en]

    In this paper we study the behavior of diffeomorphisms, contained in the closure (A) over bar (alpha) (in the inductive limit topology) of the set A(alpha) of real-analytic diffeomorphisms of the torus T-2, which are conjugated to the rotation R-alpha : (x, y) hooked right arrow (x+alpha, y) by an analytic measure-preserving transformation. We show that for a generic alpha is an element of [0, 1], (A) over bar (alpha) contains a dense set of uniquely ergodic diffeomorphisms. We also prove that (A) over bar (alpha) contains a dense set of diffeomorphisms that are minimal and non-ergodic.

  • 297.
    Saprykina, Maria
    KTH, Superseded Departments, Mathematics.
    Non-linearizability, unique ergodicity and weak mixing in dynamics2003Doctoral thesis, comprehensive summary (Other scientific)
  • 298.
    Saprykina, Maria
    et al.
    KTH, Superseded Departments, Mathematics.
    Fayad, B
    Weakly mixing diffeomorphisms on the torus, annulus and discArticle in journal (Other academic)
  • 299.
    Selander, Göran
    KTH, Superseded Departments, Mathematics.
    Two deterministic growth models related to diffusion-limited aggregation1999Doctoral thesis, monograph (Other scientific)
  • 300.
    Shahgholian, Henrik
    KTH, Superseded Departments, Mathematics.
    Analysis of the free boundary for the p-parabolic variational problem (p >= 2)2003In: Revista matemática iberoamericana, ISSN 0213-2230, E-ISSN 2235-0616, Vol. 19, no 3, p. 797-812Article in journal (Refereed)
    Abstract [en]

    Variational inequalities (free boundaries), governed by the p-parabolic equation (p : 2), are the objects of investigation in this paper. Using intrinsic scaling we establish the behavior of solutions near the free boundary. A consequence of this is that the time levels of the free boundary are porous (in N-dimension) and therefore its Hausdorff dimension is less than N. In particular the N-Lebesgue measure of the free boundary is zero for each t-level.

34567 251 - 300 of 334
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