Knowledge by Narratives: On the Methodology of Stump’s Defence

Eleonore Stump claims in her book "Wandering in Darkness" that the problem of evil can be solved best by the help of narratives. This - so Stump - is due to the fact that narratives allow one to get a general view about relevant parts of the discussion of suffering. In this context she distinguishes the more detailed view of the discussion from a more general one by two different modes of cognition: the mode of gathering "knowledge that" and that one of gathering "knowledge how". Knowledge by narratives is a subcategory of the last-mentioned one. In the paper I argue for the thesis that this distinction is not really crucial for Stump's argumentation and that in fact only "knowledge that" is relevant for her proposed solution

Reply to a Comment on ``Projective Quantum Monte Carlo Method for the Anderson Impurity Model and its Application to Dynamical Mean Field Theory''

In our reply, we show that the objections put forward in cond-mat/0508763 concerning our paper, Phys. Rev. Lett. 93, 136405 (2004), are not valid: (i) There is no orthogonality catastrophe (OC) for our calculations, and it is also generally not ``unpractical'' to avoid it. (ii) The OC does not affect our results.Comment: 1 page, 1 figure, Phys. Rev. Lett. in print; also note cond-mat/050944

Comment on "Projective Quantum Monte Carlo Method for the Anderson Impurity Model and its Application to Dynamical Mean Field Theory"

A comment about importance of Anderson's orthogonality catastrophe for projective Quantum Monte Carlo methods.Comment: Replaced by final versio

Pressure-induced metal-insulator transition in LaMnO3 is not of Mott-Hubbard type

Calculations employing the local density approximation combined with static and dynamical mean-field theories (LDA+U and LDA+DMFT) indicate that the metal-insulator transition observed at 32 GPa in paramagnetic LaMnO3 at room temperature is not a Mott-Hubbard transition, but is caused by orbital splitting of the majority-spin eg bands. For LaMnO3 to be insulating at pressures below 32 GPa, both on-site Coulomb repulsion and Jahn-Teller distortion are needed.Comment: 4 pages, 3 figure

Single-hole dynamics in the half-filled two-dimensional Kondo-Hubbard model

We consider the Kondo lattice model in two dimensions at half filling. In addition to the fermionic hopping integral $t$ and the superexchange coupling $J$ the role of a Coulomb repulsion $U$ in the conduction band is investigated. We find the model to display a magnetic order-disorder transition in the U-J plane with a critical value of J_c which is decreasing as a function of U. The single particle spectral function A(k,w) is computed across this transition. For all values of J > 0, and apart from shadow features present in the ordered state, A(k,w) remains insensitive to the magnetic phase transition with the first low-energy hole states residing at momenta k = (\pm \pi, \pm \pi). As J -> 0 the model maps onto the Hubbard Hamiltonian. Only in this limit, the low-energy spectral weight at k = (\pm \pi, \pm \pi) vanishes with first electron removal-states emerging at wave vectors on the magnetic Brillouin zone boundary. Thus, we conclude that (i) the local screening of impurity spins determines the low energy behavior of the spectral function and (ii) one cannot deform continuously the spectral function of the Mott-Hubbard insulator at J=0 to that of the Kondo insulator at J > J_c. Our results are based on both, T=0 Quantum Monte-Carlo simulations and a bond-operator mean-field theory.Comment: 8 pages, 7 figures. Submitted to PR

Efficient calculation of imaginary time displaced correlation functions in the projector auxiliary field quantum Monte-Carlo algorithm

The calculation of imaginary time displaced correlation functions with the auxiliary field projector quantum Monte-Carlo algorithm provides valuable insight (such as spin and charge gaps) in the model under consideration. One of the authors and M. Imada [F.F. Assaad and M. Imada, J. Phys. Soc. Jpn. 65 189 (1996).] have proposed a numerically stable method to compute those quantities. Although precise this method is expensive in CPU time. Here, we present an alternative approach which is an order of magnitude quicker, just as precise, and very simple to implement. The method is based on the observation that for a given auxiliary field the equal time Green function matrix, $G$, is a projector: $G^2 = G$.Comment: 4 papes, 1 figure in eps forma

Projective Quantum Monte Carlo Method for the Anderson Impurity Model and its Application to Dynamical Mean Field Theory

We develop a projective quantum Monte Carlo algorithm of the Hirsch-Fye type for obtaining ground state properties of the Anderson impurity model. This method is employed to solve the self-consistency equations of dynamical mean field theory. It is shown that the approach converges rapidly to the ground state so that reliable zero-temperature results are obtained. As a first application, we study the Mott-Hubbard metal-insulator transition of the one-band Hubbard model, reconfirming the numerical renormalization group results.Comment: 4 pages, 4 figure

6sterreichische Wasser- und Abfallwirtschaft / Integrierte gew\ue4sser\uf6kologische Modellans\ue4tze zur Beurteilung von Gew\ue4sservernetzungsvarianten am Beispiel der Unteren Lobau

Weltweit z\ue4hlen Flie fgew\ue4ssersysteme und Auenlandschaften zu den gef\ue4hrdetsten 6kosystemen. Flussregulierungs- und Verbauungsma fnahmen haben diese Systeme von ihren nat\ufcrlichen Wasserstandsschwankungen bzw. dem Wasseraustausch mit dem Fluss entkoppelt und f\ufchren damit zu einer Verlandung ehemaliger hochdynamischer Habitate. Gezielte Managementma fnahmen k\uf6nnen diesen Entwicklungen entgegenwirken, m\ufcssen vor Umsetzung aber auf ihre Auswirkungen hin \ufcberpr\ufcft werden. Grunds\ue4tzlich initiieren alle Restaurationsma fnahmen grundlegende Prozesse im Fluss-Auensystem, auf die Arten mit unterschiedlichen Habitatanspr\ufcchen und unterschiedlichem Schutzstatus verschieden reagieren k\uf6nnen. Eine M\uf6glichkeit einer wissenschaftlich fundierten Prognose von hydrologischen Managementma fnahmen wird in diesem Artikel am Beispiel der Verwendung von Habitatmodellen f\ufcr eine Studie in der Unteren Lobau vorgestellt. Die Untere Lobau ist eine Auenlandschaft im Osten von Wien, n\uf6rdlich der Donau. Sie ist Teil des Nationalparks Donau-Auen und gesch\ufctzter FFH-Lebensraum. Vor der Donauregulierung Ende des 19. Jahrhunderts war die Untere Lobau ein dynamisches Auengebiet, aber die heute vorherrschenden Verlandungsprozesse bedrohen dieses in Europa selten gewordene 6kosystem. F\ufcr dieses Gebiet wurden drei Managementvarianten untersucht: 1) Nullvariante \u2013 Das Ausbleiben jeglicher Ma fnahmen mit einer Fortsetzung der Verlandungsprozesse; 2) Dotation \u2013 Die Zufuhr einer gerade ausreichenden Menge an Wasser, um Wasserfl\ue4chen gem\ue4 f dem Status quo zu erhalten; 3) Anbindung \u2013 Das Herstellen einer stromaufw\ue4rtigen Verbindung zum Hauptstrom der Donau, was eine Rheophilisierung des Systems und zumindest eine Ann\ue4herung an historische Verh\ue4ltnisse darstellt. Auf Basis modellierter Umweltdaten und Habitatpr\ue4ferenzen wurden mittels bin\ue4r-logistischer Regressionen von ausgew\ue4hlten Arten verschiedenster Gruppen potenzielle Habitatfl\ue4chen (Weighted Usable Areas) berechnet. Die Qualit\ue4t der Modellergebnisse konnte unterstreichen, dass die Modellierungen die hydrologischen Ma fnahmen mit ihrem Einfluss auf die Bioz\uf6nose gut beschreiben und damit eine wertvolle Hilfe in der Entscheidungsfindung im Gew\ue4ssermanagement sein k\uf6nnen.Floodplains and wetlands are among the most endangered ecosystems worldwide. River-regulation and flood protection measures cut off these formerly highly dynamic systems from their natural water level fluctuations and water exchange conditions leading to siltation processes. Restoration measures to counteract these developments need to be assessed for the effect on currently established habitats and communities in order to estimate their effects, as species with different habitat preferences and different protection status do react distinctly different. This article will present how habitat modelling was used in a case study of the Untere Lobau to assess and predict the effects of potential management measures. The Untere Lobau is a wetland ecosystem of the Danube east of Vienna. It is part of the national park Donau-Auen and a protected area according to the EU habitat-directive. Prior to the river regulation, at the end of the 19th century, the Untere Lobau was a dynamic floodplain. Today, siltation processes endanger especially the status of the aquatic habitats. Three management options were investigated: 1) business as usual \u2013 No implementation of additional hydrological measures, thus siltation processes are not mitigated; 2) a water enhancement scheme \u2013 A small amount of water is supplied to preserve the water bodies at the current status quo; 3) partly reconnection \u2013 An upstream reconnection of the floodplain to the main channel of the Danube, leading to a more rheophilic characteristic of the system moving towards conditions prior regulation. Based on a model approach and calculating habitat preferences via binary logistic regressions of selected species from different organism groups, an increase or decrease of available suitable habitat area (weighted usable areas) could be estimated. This study proofed clearly that models can assess the effects of hydrological management measures on the biocenosis and that they are a valuable tool for supporting the decision taking process in wetland management