Noncollinear magnetic order in quasicrystals

Based on Monte-Carlo simulations, the stable magnetization configurations of an antiferromagnet on a quasiperiodic tiling are derived theoretically. The exchange coupling is assumed to decrease exponentially with the distance between magnetic moments. It is demonstrated that the superposition of geometric frustration with the quasiperiodic ordering leads to a three-dimensional noncollinear antiferromagnetic spin structure. The structure can be divided into several ordered interpenetrating magnetic supertilings of different energy and characteristic wave vector. The number and the symmetry of subtilings depend on the quasiperiodic ordering of atoms.Comment: RevTeX, 4 pages, 5 low-resolution color figures (due to size restrictions); to appear in Physical Review Letter

Spectrum of a duality-twisted Ising quantum chain

The Ising quantum chain with a peculiar twisted boundary condition is considered. This boundary condition, first introduced in the framework of the spin-1/2 XXZ Heisenberg quantum chain, is related to the duality transformation, which becomes a symmetry of the model at the critical point. Thus, at the critical point, the Ising quantum chain with the duality-twisted boundary is translationally invariant, similar as in the case of the usual periodic or antiperiodic boundary conditions. The complete energy spectrum of the Ising quantum chain is calculated analytically for finite systems, and the conformal properties of the scaling limit are investigated. This provides an explicit example of a conformal twisted boundary condition and a corresponding generalised twisted partition function.Comment: LaTeX, 7 pages, using IOP style

Financing SMEs: a model for optimising the capital structure

This paper argues that the existing finance literature is inadequate with respect to its cov-erage of capital structure of small and medium sized enterprises (SMEs). In particular it is argued that the cost of equity (being both conceptually ill defined and empirically non quantifiable) is not applicable to the capital structure decisions for a large proportion of SMEs and the optimal capital structure depends only on the mix of short and long term debt. The paper then presents a model for optimising the debt mix and demonstrates its practical application using an Italian firm’s debt structure as a case study

Hot-spot tectonics of Eistla Regio, Venus: Results from Magellan images and Pioneer Venus gravity

Eistla Regio (ER) is a broad, low, discontinuous topographic rise striking roughly EW at low northern latitudes of Venus. Some 2000 x 7000 km in dimensions, it is the third largest rise in planform on Venus after Aphrodite Terra and Beta Phoebe Regiones. These rises are the key physiographic elements in a hot spot model of global tectonics including transient plume behavior. Since ER is the first such rise viewed by Magellan and the latitude is very favorable for Pioneer Venus gravity studies, some of the predictions of a time dependent hot spot model are tested. Western ER is defined as the rise including Gula and Sif Mons and central ER as that including Sappho Patera. Superior conjunction prevented Magellan from returning data on eastern ER (Pavlova) during the first mapping cycle. It is concluded that the western and central portions of ER, while part of the same broad topographic rise and tectonic framework, have distinctly different surface ages and gravity signatures. The western rise, including Gula and Sif Mons, is the expression of deep seated uplift with volcanism limited to the individual large shields. The eastern portion has been widely resurfaced more recently by thermal anomalies in the mantle

Light Transmission Through Metallic-Mean Quasiperiodic Stacks with Oblique Incidence

The propagation of s- and p-polarized light through quasiperiodic multilayers, consisting of layers with different refractive indices, is studied by the transfer matrix method. In particular, we focus on the transmission coefficient of the systems in dependency on the incidence angle and on the ratio of the refractive indices. We obtain additional bands with almost complete transmission in the quasiperiodic systems at frequencies in the range of the photonic band gap of a system with a periodic alignment of the two materials for both types of light polarization. With increasing incidence angle these bands bend towards higher frequencies, where the curvature of the transmission bands in the quasiperiodic stack depends on the metallic mean of the construction rule. Additionally, in the quasiperiodic systems for p-polarized light the bands show almost complete transmission near the Brewster's angle in contrast to the results for s-polarized light. Further, we present results for the influence of the refractive indices at the midgap frequency of the periodic stack, where the quasiperiodicity was found to be most effective.Comment: 10 pages, 7 figure

Probing Phases and Quantum Criticality using Deviations from the Local Fluctuation-Dissipation Theorem

Introduction Cold atomic gases in optical lattices are emerging as excellent laboratories for testing models of strongly interacting particles in condensed matter physics. Currently, one of the major open questions is how to obtain the finite temperature phase diagram of a given quantum Hamiltonian directly from experiments. Previous work in this direction required quantum Monte Carlo simulations to directly model the experimental situation in order to extract quantitative information, clearly defeating the purpose of an optical lattice emulator. Here we propose a new method that utilizes deviations from a local fluctuation dissipation theorem to construct a finite temperature phase diagram, for the first time, from local observables accessible by in situ experimental observations. Our approach extends the utility of the fluctuation-dissipation theorem from thermometry to the identification of quantum phases, associated energy scales and the quantum critical region. We test our ideas using state-of-the-art large-scale quantum Monte Carlo simulations of the two-dimensional Bose Hubbard model.Comment: 7 pages; 4 figures; also see supplementary material of 7 pages with 3 figure

Interpretation of the northern boundary of Ishtar Terra from Magellan images and altimetry

Part of the controversy on the origin of western Ishtar Terra (IT) concerns the nature of Uorsar Rupes (UR), the northern boundary of IT. In the hypothesis of lithospheric convergence and underthrusting, UR is held to be the main boundary thrust fault at the toe of an accretionary wedge. A topographic rise parallel to the scarp was interpreted as a flexural bulge similar to those of terrestrial subduction zones, and quantitative models of this feature seemed broadly consistent with the expected lithospheric structure of Venus. In the alternative mantle upwelling hypothesis for western IT, the outer margins of the highland are thought to be collapsing, and UR has been interpreted as a normal fault. Herein, Magellan images and altimetry are interpreted for this region and the hypothesis that a flexural signature can be distinguished is reassessed. The Magellan images of IT show evidence of crustal shortening adjacent to UR, but extension and burial dominate northwards. Altimetric profiles display the same long wavelength trends visible in Venera data, but no clear evidence of the lithospheric flexure. A model of regional extension and burial is herein favored, but regional compression cannot be ruled out

"Nichts ist widerlicher als eine sogenannte Dichterlesung." : deutsche Autorenlesungen zwischen Marketing und Selbstpräsentation

Dichterlesungen boomen. Man muss nur in das Tagesangebot der Zeitungen schauen, man muss nur in Buchhandlungen gehen, in Volkshochschulen, in Stadtbüchereien: überall sieht man Plakate und Programme, die Lesungen zeitgenössischer Autoren anbieten. Das ist umso verwunderlicher, weil im Allgemeinen Dichterlesungen nicht allzu beliebt sind, auch bei vielen Autoren nicht. Das einschlägige Motto „Nichts ist widerlicher als eine sogenannte Dichterlesung“ stammt aus Thomas Bernhards Schimpfroman „Alte Meister“, in dem der 82jährige Musikkritiker Reger seinen typischen Wiener Schmäh über fast die gesamte österreichische Kunst, Literatur und Musik, in seitenlangen Monologen ausgießt

"Die Macht des Gesanges" : Loreleys Verführungskünste in Opern des 19. Jahrhunderts

Das im ‚Biedermeier’ verbreitete Frauenbild bevorzugte introvertierte, sanfte und tugendhafte Frauen, häusliche, in der Familienpflege aufgehende Geschöpfe, die neben einer zahlreichen Kinderschar auch für den außer Hause arbeitenden Gatten zu sorgen hatte. Die vom Mutter- und Gattinnentypus abweichende Frau geriet leicht in den Ruf der Außenseiterin. Suffragetten waren wenig geschätzt, die männliche Phantasie liebte mehr das Exotische oder das Zauberhafte. Nichtbürgerliche Frauen waren Elfentypen, zarte Wesen der Lüfte oder des Wassers, Feen und Nixen. Die Literatur des 19. Jahrhundert wimmelt von solchen Wasserfrauen, Melusinen und Undinen bis zur schönen Lau. Oder sie waren Unholdinnen, Hexen aller Art, wie man sie von Shakespeare her kannte, meist hässlichen Aussehens, geschmückt mit Warzen und Krallenfingern, und ausgestattet mit fataler Zauberkraft. Ludwig Richter, der durch seine Illustrationen von Ludwig Bechsteins Märchen besondere Popularität erlangte, hat drei solcher Zauberfrauen prototypisch fixiert: die „alte schlimme Hexe“, die Zauberin und die Nixe. [...] Es wäre sonderbar, wenn Opernkomponisten nicht nach diesem dankbaren Stoff gegriffen hätten. Hatte bereits die Antike in der Gestalt Kirkes eine veritable Zauberin, und lieferte Ariost mit seinem „Rasenden Roland“ auch eine brauchbare Vorlage für Händels Oper „Alcina“, so boomten insbesondere im 18. Jahrhundert Zauberstücke und auch Zauberopern. Hier konnte die geheimnisvoll-magische Macht weiblicher Verführung auf die Bühne gestellt werden und die Männer als letzten Endes genasführtes schwaches Geschlecht entlarvt werden. Gehört nicht etwa auch Mozarts „Zauberflöte“, in der Magie und Zauberei eine große Rolle spielen, noch zu den Ausläufern dieses Typus

"Der Kranz des Patrioten" : Nachahmungspraxis und Originalitätsideal bei Herder

Das Thema von Literaturnachahmung und Eigenständigkeit stellt sich für die deutsche Literatur des 18. Jahrhunderts in ganz anderem Maße als für die Barockliteratur. Soziale und wissenschaftliche Gründe - Formierung eines selbstbewußten Bürgertums und Aufstieg der naturwissenschaftlichen Disziplinen - bewirken eine gravierende Verschiebung. Zunächst tritt die Relativierung des Kanons ein. An die Stelle der unbesehen übernommenen Tradition rückt die urteilende Vernunft und der gute Geschmack. Mit der Aufwertung der Natur und des rationalen Denkens verkehrt sich die traditionelle Hierarchie von imitatio und Mimesis. An die Stelle eines "blinden" Nachahmens von Vorbildern tritt die Orientierung an der Vernunftnatur