Johannes Kepler University of Linz

About: Johannes Kepler University of Linz is a education organization based out in Linz, Oberösterreich, Austria. It is known for research contribution in the topics: Thin film & Quantum dot. The organization has 6605 authors who have published 19243 publications receiving 385667 citations.

Relations Between Regularization and Diffusion Filtering

Abstract: Regularization may be regarded as diffusion filtering with an implicit time discretization where one single step is used. Thus, iterated regularization with small regularization parameters approximates a diffusion process. The goal of this paper is to analyse relations between noniterated and iterated regularization and diffusion filtering in image processing. In the linear regularization framework, we show that with iterated Tikhonov regularization noise can be better handled than with noniterated. In the nonlinear framework, two filtering strategies are considered: the total variation regularization technique and the diffusion filter technique of Perona and Malik. It is shown that the Perona-Malik equation decreases the total variation during its evolution. While noniterated and iterated total variation regularization is well-posed, one cannot expect to find a minimizing sequence which converges to a minimizer of the corresponding energy functional for the Perona–Malik filter. To overcome this shortcoming, a novel regularization technique of the Perona–Malik process is presented that allows to construct a weakly lower semi-continuous energy functional. In analogy to recently derived results for a well-posed class of regularized Perona–Malik filters, we introduce Lyapunov functionals and convergence results for regularization methods. Experiments on real-world images illustrate that iterated linear regularization performs better than noniterated, while no significant differences between noniterated and iterated total variation regularization have been observed.

Spherical expansion of the vapor plume into ambient gas: an analytical model

Abstract: A simplified model of plume expansion into ambient atmosphere is presented which is based on the laws of mass, momentum, and energy conservation. In the course of expansion, the energy is redistributed between the thermal and kinetic energies of the plume and (internal and external) shock waves (SW). The expansion is described by ordinary differential equations for the characteristic radii (contact surface, position of the SWs). The initial stage is similar to inertial expansion into vacuum, with radius R∝t. Internal SW propagates inwards from the contact surface. Later expansion follows a point-blast model with R∝t2/5. Here the homogenized plume is decelerated and heated because of the counter-pressure of the ambient gas, which forms external SW. At a certain distance from the target, the plume stops (and even contracts), while external SW weakens and detaches from the contact surface. Analytical formulas for the transitional stages of expansion are discussed, and theoretical predictions are compared with experimental results of laser ablation of steel and YBCO in Ar.

Estimating marginal likelihoods for mixture and Markov switching models using bridge sampling techniques

Abstract: Summary This paper discusses the problem of estimating marginal likelihoods for mixture and Markov switching model. Estimation is based on the method of bridge sampling (Meng and Wong 1996; Statistica Sinica 11, 552-86.) where Markov Chain Monte Carlo (MCMC) draws from the posterior density are combined with an i.i.d. sample from an importance density. The importance density is constructed in an unsupervised manner from the MCMC draws using a mixture of complete data posteriors. Whereas the importance sampling estimator as well as the reciprocal importance sampling estimator are sensitive to the tail behaviour of the importance density, we demonstrate that the bridge sampling estimator is far more robust. Our case studies range from computing marginal likelihoods for a mixture of multivariate normal distributions, testing for the inhomogeneity of a discrete time Poisson process, to testing for the presence of Markov switching and order selection in the MSAR model.

Producer Services, Manufacturing Linkages, and Trade

Abstract: Working with a mix of panel data on goods and services trade for the OECD for 1994-2004, combined with social accounts data (i.e. data on intermediate linkages) for 78 countries benchmarked to the panel midpoint, we examine the role of services as inputs in manufacturing, with a particular focus on indirect exports of services through merchandise exports, and also on the related interaction between service sector openness and the overall pattern of manufacturing exports. From the cross-section, we also develop a set of stylized facts linking services to level of development and the density of intermediate linkages. We find significant and strong positive effects from increased business service openness (i.e. greater levels of imports) on industries like machinery, motor vehicles, chemicals and electric equipment, supporting the notion that off-shoring of business services may promote the competitiveness of the most skill and technology intensive industries in the OECD. Conversely, we find evidence of negative general equilibrium effects for sectors that are less service intensive.