2,841 research outputs found
Error estimates for variational regularization of inverse problems with general noise models for data and operator
No full textSigrid Blömeke/Thorsten Bohl/Ludwig Haag/ Gregor Lang-Wojtasik/Werner Sacher (Hrsg.): Handbuch Schule. Theorie – Organisation – Entwicklung. Bad Heilbrunn: Klinkhardt 2009, 608 S. [Rezension]
No full textRezension zu: Sigrid Blömeke/Thorsten Bohl/Ludwig Haag/ Gregor Lang-Wojtasik/Werner Sacher (Hrsg.): Handbuch Schule. Theorie – Organisation – Entwicklung. Bad Heilbrunn: Klinkhardt 2009, 608 S
Iteratively regularized Newton-type methods for general data misfit functionals and applications to Poisson data
No full textWe study Newton type methods for inverse problems described by nonlinear operator equations F(u)=g in Banach spaces where the Newton equations F′(un;un+1−un)=g−F(un) are regularized variationally using a general data misfit functional and a convex regularization term. This generalizes the well-known iteratively regularized Gauss–Newton method (IRGNM). We prove convergence and convergence rates as the noise level tends to 0 both for an a priori stopping rule and for a Lepskiĭ-type a posteriori stopping rule. Our analysis includes previous order optimal convergence rate results for the IRGNM as special cases. The main focus of this paper is on inverse problems with Poisson data where the natural data misfit functional is given by the Kullback–Leibler divergence. Two examples of such problems are discussed in detail: an inverse obstacle scattering problem with amplitude data of the far-field pattern and a phase retrieval problem. The performance of the proposed method for these problems is illustrated in numerical examples
Convergence rates in expectation for Tikhonov-type regularization of Inverse Problems with Poisson data
No full textWerner Helsper / Rolf-Thorsten Kramer / Merle Hummrich / Susann Busse: Jugend zwischen Familie und Schule. Eine Studie zu pädagogischen Generationsbeziehungen. Wiesbaden: VS Verlag für Sozialwissenschaften 2009 (440 S.) [Rezension]
No full textRezension von: Werner Helsper / Rolf-Thorsten Kramer / Merle Hummrich / Susann Busse: Jugend zwischen Familie und Schule. Eine Studie zu pädagogischen Generationsbeziehungen. Wiesbaden: VS Verlag für Sozialwissenschaften 2009 (440 S.; ISBN 978-3-531-16574-5; 39,90 EUR)
Inverse problems with Poisson data: Statistical regularization theory, applications and algorithms.
No full textInverse problems with Poisson data arise in many photonic imaging modalities in medicine, engineering and astronomy. The design of regularization methods and estimators for such problems has been studied intensively over the last two decades. In this review we give an overview of statistical regularization theory for such problems, the most important applications, and the most widely used algorithms. The focus is on variational regularization methods in the form of penalized maximum likelihood estimators, which can be analyzed in a general setup. Complementing a number of recent convergence rate results we will establish consistency results. Moreover, we discuss estimators based on a wavelet-vaguelette decomposition of the (necessarily linear) forward operator. As most prominent applications we briefly introduce Positron emission tomography, inverse problems in fluorescence microscopy, and phase retrieval problems. The computation of a penalized maximum likelihood estimator involves the solution of a (typically convex) minimization problem. We also review several efficient algorithms which have been proposed for such problems over the last five years
Financial crises in Japan during the 20th century
No full textI have two aims with this paper. Firstly, I would like to extract lessons for theory and policy from Japan’s experience with banking crises. As such, this paper falls into the body of research on banking crises, recent works within which include Caprio and Klingebiel (1996), Caprio et al. (2005), Demirgüç-Kunt and Detragiache (2005), Werner (2005), Beck et al. (2006), and Reinhart and Rogoff (2008). Secondly, I aim to gain insights into the link between the banking sector and the economy (which are again of importance for both theory and policy). This is an important topic that has slowly but steadily grown to a substantial body of literature. Many authors recognise that banks are ‘special’ in some way (Fama, 1985, Bossone, 1999, James and Smith, 2000, Ashcraft, 2005), and that the link between the banking sector and the economy is of great importance (King and Levine, 1996, Levine, 1997). However, the precise details of just what makes banks special, as well as the precise nature of their link to the economy have remained unclear or at least disputed. Analysing crises may help elucidate these issues
Convergence rates for exponentially ill-posed inverse problems with impulsive noise.
No full textThis paper is concerned with exponentially ill-posed operator equations with additive impulsive noise on the right-hand side, i.e., the noise is large on a small part of the domain and small or zero outside. It is well known that Tikhonov regularization with an data fidelity term outperforms Tikhonov regularization with an fidelity term in this case. This effect has recently been explained and quantified for the case of finitely smoothing operators. Here we extend this analysis to the case of infinitely smoothing forward operators under standard Sobolev smoothness assumptions on the solution, i.e., exponentially ill-posed inverse problems. It turns out that high order polynomial rates of convergence in the size of the support of large noise can be achieved rather than the poor logarithmic convergence rates typical for exponentially ill-posed problems. The main tools of our analysis are Banach spaces of analytic functions and interpolation-type inequalities for such spaces. We discuss two examples, the (periodic) backward heat equation and an inverse problem in gradiometry
Identiteter och världsbild : "hårdkokt" skriftbruk i Thorsten Jonssons noveller
No full textidentity and worldview – “hard-boiled” writing in Thorsten Jonsson’s short storiesThis article deals with the Swedish author Thorsten Jonsson (1910–50) and his first short story collection Som det brukar vara (1939) [‘As it usually is’]. The nar- rative represents a new modernistic literary trend in Swedish prose in the 1930s. i take my starting point in Burgess & ivanič’s (2010) theories of the act of writing involving many different identities, and particularly what Burgess & ivanič iden- tify as the discursive self. By contemporary readers and critics the discursive self in the short story collection was often connected with an American hard-boiled literary ideal, often linked to ernest Hemingway’s writings. in this article i dis- cuss the common textual features of the two authors’ first collections, but also the differences that emerge when looking through the linguistic surface. The analysis shows that Thorsten Jonsson’s discursive self is based upon a northern Swedish culture, Hemingway’s on an urban American one. </p
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