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.

Determination of strain fields and composition of self-organized quantum dots using x-ray diffraction

Abstract: We give a detailed account of an x-ray diffraction technique which allows us to determine shape, strain fields, and interdiffusion in semiconductor quantum dots grown in the Stranski\char21{}Krastanov mode. A scattering theory for grazing incidence diffraction is derived for the case of highly strained, uncapped nanostructures. It is shown that strain resolution can be achieved by ``decomposing'' the dots in their iso-strain areas. For a selected iso-strain area, it is explained how lateral extent, height above the substrate and radius of curvature can be determined from the intensity distribution around a surface Bragg reflection. The comparison of intensities from strong and weak reflections reveals the mean material composition for each strain state. The combination of all these strain resolved functional dependences yields tomographic images of the dots showing strain field and material composition.

The Size and Development of the Shadow Economies of 22 Transition and 21 OECD Countries

Abstract: Using the currency demand and DYMIMIC approaches estimates are presented about the size of the shadow economy in 22 Transition and 21 OECD countries. Over 2001/2002 in 21 OECD countries is the average size of the shadow economy (in percent of official GDP) 16.7% of "official" GDP and of 22 Transition countries 38.0%. The average size of the shadow economy labor force (in percent of the population of working age) of the year 1998/99 in 7 OECD-countries is 15.3% and in 22 Transition countries is 30.2%. An increasing burden of taxation and social security contributions combined with rising state regulatory activities are the driving forces for the growth and size of the shadow economy (labor force).

The complete generating function for Gessel walks is algebraic

Abstract: Gessel walks are lattice walks in the quarter plane $\set N^2$ which start at the origin $(0,0)\in\set N^2$ and consist only of steps chosen from the set $\{\leftarrow,\swarrow, earrow,\to\}$. We prove that if $g(n;i,j)$ denotes the number of Gessel walks of length $n$ which end at the point $(i,j)\in\set N^2$, then the trivariate generating series $G(t;x,y)=\sum_{n,i,j\geq 0} g(n;i,j)x^i y^j t^n$ is an algebraic function.

Simplifying Multiple Sums in Difference Fields

Abstract: In this survey article we present difference field algorithms for symbolic summation. Special emphasize is put on new aspects in how the summation problems are rephrased in terms of difference fields, how the problems are solved there, and how the derived results in the given difference field can be reinterpreted as solutions of the input problem. The algorithms are illustrated with the Mathematica package Sigma by discovering and proving new harmonic number identities extending those from Paule and Schneider, 2003. In addition, the newly developed package EvaluateMultiSums is introduced that combines the presented tools. In this way, large scale summation problems for the evaluation of Feynman diagrams in QCD (Quantum ChromoDynamics) can be solved completely automatically.