Filters

2013 - 2014295

More filters

2019295
Reset filters

Settings

End date: 2020 × Start date: 2019 × End date: 2014 × Start date: 2013 × Publisher: Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik ×

Search Results

Now showing 1 - 10 of 295
  • Thumbnail Image
    Item
    Modeling and simulations of beam stabilization in edge-emitting broad area semiconductor devices
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2013) Radziunas, Mindaugas; Cˇ iegis, Raimondas
    A 2+1 dimensional PDE traveling wave model describing spatial-lateral dynamics of edge-emitting broad area semiconductor devices is considered. A numerical scheme based on a split-step Fourier method is presented and implemented on a parallel compute cluster. Simulations of the model equations are used for optimizing of existing devices with respect to the emitted beam quality, as well as for creating and testing of novel device design concepts
  • Thumbnail Image
    Item
    Bistability and hysteresis in an optically injected two-section semiconductor laser
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2014) Pimenov, Alexander; Viktorov, Evgeniy A.; Hegarty, Stephen P.; Habruseva, Tatiana; Huyet, Guillaume; Rachinskii, Dmitrii; Vladimirov, Andrei G.
    The effect of coherent single frequency injection on two-section semiconductor lasers is studied numerically using a model based on a set of delay differential equations. The existence of bistability between different CW and non-stationary regimes of operation is demonstrated in the case of sufficiently large linewidth enhancement factors.
  • Thumbnail Image
    Item
    On multivariate chi-square distributions and their applications in testing multiple hypotheses
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2014) Dickhaus, Thorsten; Royen, Thomas
    We are considered with three different types of multivariate chi-square distributions. Their members play important roles as limiting distributions of vectors of test statistics in several applications of multiple hypotheses testing. We explain these applications and provide formulas for computing multiplicity-adjusted p-values under the respective global hypothesis.
  • Thumbnail Image
    Item
    Optimal control of elastic vector-valued AllenCahn variational inequalities
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2013) Farshbaf-Shaker, Mohammad Hassan; Hecht, Claudia
    In this paper we consider a elastic vector-valued AllenCahn MPCC (Mathematical Programs with Complementarity Constraints) problem. We use a regularization approach to get the optimality system for the subproblems. By passing to the limit in the optimality conditions for the regularized subproblems, we derive certain generalized first-order necessary optimality conditions for the original problem.
  • Thumbnail Image
    Item
    Equilibrium shapes of poly-crystalline silicon nanodots
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2013) Korzec, Maciek D.; Roczen, Maurizio; Schade, Martin; Wagner, Barbara; Rech, Bernd
    This study is concerned with the topography of nanostructures consisting of arrays of poly-crystalline nanodots. Guided by transmission electron microscopy (TEM) measurements of crystalline Si (c-Si) nanodots that evolved from a dewetting process of an amorphous Si (a-Si) layer from a SiO2 coated substrate, we investigate appropriate formulations for the surface energy density and transitions of energy density states at grain boundaries. We introduce a new numerical minimization formulation that allows to account for adhesion energy from an underlying substrate. We demonstrate our approach first for the free standing case, where the solutions can be compared to well-known Wulff constructions, before we treat the general case for interfacial energy settings that support partial wetting. We then use our method to predict the morphologies of poly-crystalline silicon nanodots.
  • Thumbnail Image
    Item
    Femtosecond filamentation by intensity clamping at a Freeman resonance
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2014) Hofmann, Michael; Brée, Carsten
    [no abstract available]
  • Thumbnail Image
    Item
    An adaptive SUPG method for evolutionary convection-diffusion equations
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2013) de Frutos, Javier; García-Archilla, Bosco; John, Volker; Novo, Julia
    An adaptive algorithm for the numerical simulation of time-dependent convectiondiffusion-reaction equations will be proposed and studied. The algorithm allows the use of the natural extension of any error estimator for the steady-state problem for controlling local refinement and coarsening. The main idea consists in considering the SUPG solution of the evolutionary problem as the SUPG solution of a particular steady-state convectiondiffusion problem with data depending on the computed solution. The application of the error estimator is based on a heuristic argument by considering a certain term to be of higher order. This argument is supported in the one-dimensional case by numerical analysis. In the numerical studies, particularly the residual-based error estimator from [18] will be applied, which has proved to be robust in the SUPG norm. The effectivity of this error estimator will be studied and the numerical results (accuracy of the solution, fineness of the meshes) will be compared with results obtained by utilizing the adaptive algorithm proposed in [6]
  • Thumbnail Image
    Item
    Dynamics of micro-integrated external-cavity diode lasers: Simulations, analysis and experiments
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2014) Radziunas, Mindaugas; Tronciu, Vasile Z.; Luvsandamdin, Erdenetsetseg; Kürbis, Christian; Wicht, Andreas; Wenzel, Hans
    This paper reports the results of numerical and experimental investigations of the dynamics of an external cavity diode laser device composed of a semiconductor laser and a distant Bragg grating, which provides an optical feedback. Due to the influence of the feedback, this system can operate at different dynamic regimes. The traveling wave model is used for simulations and analysis of the nonlinear dynamics in the considered laser device. Based on this model, a detailed analysis of the optical modes is performed, and the stability of the stationary states is discussed. It is shown, that the results obtained from the simulation and analysis of the device are in good agreement with experimental findings.
  • Thumbnail Image
    Item
    Adaptive smoothing as inference strategy: More specificity for unequally sized or neighboring regions
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2013) Welvaert, Marijke; Tabelow, Karsten; Seurinck, Ruth; Rosseel, Yves
    Although spatial smoothing of fMRI data can serve multiple purposes, increasing the sensitivity of activation detection is probably its greatest benefit. However, this increased detection power comes with a loss of specificity when non-adaptive smoothing (i.e. the standard in most software packages) is used. Simulation studies and analysis of experimental data was performed using the R packages neu-Rosim and fmri. In these studies, we systematically investigated the effect of spatial smoothing on the power and number of false positives in two particular cases that are often encountered in fMRI research: (1) Single condition activation detection for regions that differ in size, and (2) multiple condition activation detection for neighbouring regions. Our results demonstrate that adaptive smoothing is superior in both cases because less false positives are introduced by the spatial smoothing process compared to standard Gaussian smoothing or FDR inference of unsmoothed data.
  • Thumbnail Image
    Item
    Balanced viscosity (BV) solutions to infinite-dimensional rate-independent systems
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2013) Mielke, Alexander; Rossi, Riccarda; Savaré, Giuseppe
    Balanced Viscosity solutions to rate-independent systems arise as limits of regularized rate-independent flows by adding a superlinear vanishing-viscosity dissipation. We address the main issue of proving the existence of such limits for infinite-dimensional systems and of characterizing them by a couple of variational properties that combine a local stability condition and a balanced energy-dissipation identity. A careful description of the jump behavior of the solutions, of their differentiability properties, and of their equivalent representation by time rescaling is also presented. Our techniques rely on a suitable chain-rule inequality for functions of bounded variation in Banach spaces, on refined lower semicontinuity-compactness arguments, and on new BV-estimates that are of independent interest.