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Search Results: 1 - 10 of 27879 matches for " Martin;Koch "
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Quality Visualization of Microarray Datasets Using Circos
Martin Koch,Michael Wiese
Microarrays , 2012, DOI: 10.3390/microarrays1020084
Abstract: Quality control and normalization is considered the most important step in the analysis of microarray data. At present there are various methods available for quality assessments of microarray datasets. However there seems to be no standard visualization routine, which also depicts individual microarray quality. Here we present a convenient method for visualizing the results of standard quality control tests using Circos plots. In these plots various quality measurements are drawn in a circular fashion, thus allowing for visualization of the quality and all outliers of each distinct array within a microarray dataset. The proposed method is intended for use with the Affymetrix Human Genome platform ( i.e., GPL 96, GPL570 and GPL571). Circos quality measurement plots are a convenient way for the initial quality estimate of Affymetrix datasets that are stored in publicly available databases.
The Bretton Woods Institutions and the Environment: Organizational Learning within the World Bank and the International Monetary Fund (IMF)
Alexandra Lindenthal,Martin Koch
Administrative Sciences , 2013, DOI: 10.3390/admsci3040166
Abstract: Due to a growing public awareness, in the last 40 years environmental impacts of development projects financed and supported by the World Bank and the International Monetary Fund (IMF) have come into view. Since then, the member states have pressured both organizations to implement environmental concerns. We analyze the reactions of the World Bank and the IMF’s bureaucracies towards their principals’ demands. To reveal if, and to what extent, the observed reactions of both bureaucracies towards environmental integration can be assessed as organizational learning, we develop in a first step a heuristic model that allows for a distinction between different levels of learning (compliant and non-compliant, single-loop and double-loop). In a second step we describe the efforts of the bureaucracies of the World Bank (from the 1970s until today) and the IMF (from the 1990s until today) to integrate environmental protection into their activities. Due to our interest in the quality of the organizational changes, we finally analyze if and to what extent the bureaucracies’ reactions to the new external demand qualify as organizational learning. Furthermore, we discuss which factors helped or hindered organizational learning.
First Order Calculation of the Inclusive Cross Section pp to ZZ by Graviton Exchange in Large Extra Dimensions
Kober, Martin;Koch, Benjamin;Bleicher, Marcus
High Energy Physics - Phenomenology , 2007, DOI: 10.1103/PhysRevD.76.125001
Abstract: We calculate the inclusive cross section of double Z-boson production within large extra dimensions at the Large Hadron Collider (LHC). Using perturbatively quantized gravity in the ADD model we perform a first order calculation of the graviton mediated contribution to the pp to ZZ cross section. At low energies (e.g. Tevatron) this additional contribution is very small, making it virtually unobservable, for a fundamental mass scale above 2500 GeV. At LHC energies however, the calculation indicates that the ZZ-production rate within the ADD model should differ significantly from the Standard Model if the new fundamental mass scale would be below 15000 GeV. A comparison with the observed production rate at the LHC might therefore provide direct hints on the number and structure of the extra dimensions.
Path Dependence in Decision-Making Processes: Exploring the Impact of Complexity under Increasing Returns
Jochen Koch,Martin Eisend,Arne Petermann
BuR : Business Research , 2009,
Abstract: The development of path-dependent processes basically refers to positive feedback in terms of increasing returns as the main driving forces of such processes. Furthermore, path dependence can be affected by context factors, such as different degrees of complexity. Up to now, it has been unclear whether and how different settings of complexity impact path-dependent processes and the probability of lock-in. In this paper we investigate the relationship between environmental complexity and path dependence by means of an experimental study. By focusing on the mode of information load and decision quality in chronological sequences, the study explores the impact of complexity on decision-making processes. The results contribute to both the development of path-dependence theory and a better understanding of decision-making behavior under conditions of positive feedback. Since previous path research has mostly applied qualitative case-study research and (to a minor part) simulations, this paper makes a further contribution by establishing an experimental approach for research on path dependence.
Mott-Hubbard insulators for systems with orbital degeneracy
Olle Gunnarsson,Erik Koch,Richard M. Martin
Physics , 1997, DOI: 10.1103/PhysRevB.56.1146
Abstract: We study how the electron hopping reduces the Mott-Hubbard band gap in the limit of a large Coulomb interaction U and as a function of the orbital degeneracy N. The results support the conclusion that the hopping contribution grows as roughly \sqrt{N}W, where W is the one-particle band width, but in certain models a crossover to a \sim NW behavior is found for a sufficiently large N.
Dielectric screening in doped Fullerides
Erik Koch,Olle Gunnarsson,Richard M. Martin
Physics , 1998, DOI: 10.1063/1.56505
Abstract: For conventional superconductors the electron-electron interaction is strongly reduced by retardation effects, making the formation of Cooper pairs possible. In the alkali-doped Fullerides, however, there are no strong retardation effects. But dielectric screening can reduce the electron-electron interaction sufficiently, if we assume that the random-phase approximation (RPA) is valid. It is not clear, however, if this assumption holds, since the alkali-doped Fullerides are strongly correlated systems close to a Mott transition. To test the validity of the RPA for these systems we have calculated the screening of a test charge using quantum Monte Carlo.
Quantum Monte Carlo calculations for integer-doped Fullerides
Erik Koch,Olle Gunnarsson,Richard M. Martin
Physics , 1998,
Abstract: The doped Fullerides can be well described by a Hubbard model, which comprises the partly filled, threefold-degenerate t_1u orbital and the on-site Coulomb interaction U. The orbital degeneracy is known to shift the critical ratio U_c/W for the Mott-Hubbard transition towards larger values. This puts the half-filled alkali-doped Fullerides A_3 C_60 on the metallic side of the transition. Prompted by the recent synthesis of isostructural families of integer-doped Fullerides with different fillings, we investigate how the orbital degeneracy affects the Mott transition at integer fillings different from 3. The calculations are done by fixed-node diffusion Monte Carlo, using a trial function, which permits us to systematically vary the magnetic character of the system.
Screening of a point charge: a fixed-node diffusion Monte Carlo study
Erik Koch,Olle Gunnarsson,Richard M. Martin
Physics , 1999,
Abstract: We study the static screening in a Hubbard-like model using fixed-node diffusion Monte Carlo. We find that the random phase approximation is surprisingly accurate even for metallic systems close to the Mott transition. As a specific application we discuss the implications of the efficient screening for the superconductivity in the doped Fullerenes. In the Monte Carlo calculations we use trial functions with two Gutzwiller-type parameters. To deal with such trial functions, we introduce a method for efficiently optimizing the Gutzwiller parameters, both in variational and in fixed-node diffusion Monte Carlo.
Mott Transition in Degenerate Hubbard Models: Application to Doped Fullerenes
Olle Gunnarsson,Erik Koch,Richard M. Martin
Physics , 1996, DOI: 10.1103/PhysRevB.54.R11026
Abstract: The Mott-Hubbard transition is studied for a Hubbard model with orbital degeneracy N, using a diffusion Monte-Carlo method. Based on general arguments, we conjecture that the Mott-Hubbard transition takes place for U/W \propto \sqrt{N}, where U is the Coulomb interaction and W is the band width. This is supported by exact diagonalization and Monte-Carlo calculations. Realistic parameters for the doped fullerenes lead to the conclusion that stoichiometric A_3 C_60 (A=K, Rb) are near the Mott-Hubbard transition, in a correlated metallic state.
Fixed-node DMC for Fermions on a lattice: Application to the doped Fullerides
Erik Koch,Olle Gunnarsson,Richard M. Martin
Physics , 1998,
Abstract: Fullerides are crystals made from C60 molecules. When doped with alkali metals the valence electrons of the alkali atoms are transfered to the C60 molecules. We show how to set up a model Hamiltonian to describe the correlated hopping of these electrons between C60 molecules. Then we discuss Monte Carlo methods for such lattice Hamiltonians, putting special emphasis on the optimization of Gutzwiller wavefunctions both in variational and fixed-node diffusion Monte Carlo. As application of these methods we analyze the metal-insulator transition in the integer-doped Fullerides.
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