Excitonic terahertz absorption in semiconductors with effective-mass anisotropies

A microscopic approach is developed to compute the excitonic properties and the corresponding terahertz response for semiconductors characterized by anisotropic effective masses. The approach is illustrated for the example of germanium where it is shown that the anisotropic electron mass in the L-valley leads to two distinct terahertz absorption resonances separated by 0.8 meV.Comment: 10 pages, 7 figure

Gamma-Deuteron Compton Scattering in Effective Field Theory

The differential cross section for gamma-deuteron Compton scattering is computed to next-to-leading order (NLO) in an effective field theory that describes nucleon-nucleon interactions below the pion production threshold. Contributions at NLO include the nucleon isoscalar electric polarizability from its 1/m_pi behavior in the chiral limit. The parameter free prediction of the gamma-deuteron differential cross section at NLO is in good agreement with data.Comment: 16 pages, 7 figures as 8 eps files, late

Hybrid cluster-expansion and density-functional-theory approach for optical absorption in TiO2

A combined approach of first-principles density-functional calculations and the systematic cluster-expansion scheme is presented. The dipole, quadrupole, and Coulomb matrix elements obtained from ab initio calculations are used as an input to the microscopic many-body theory of the excitonic optical response. To demonstrate the hybrid approach for a nontrivial semiconductor system, the near-bandgap excitonic optical absorption of rutile TiO2 is computed. Comparison with experiments yields strong evidence that the observed near-bandgap features are due to a dipole-forbidden but quadrupole-allowed 1s-exciton state.Comment: 14 pages, 4 figure

Cohomology of the minimal nilpotent orbit

We compute the integral cohomology of the minimal non-trivial nilpotent orbit in a complex simple (or quasi-simple) Lie algebra. We find by a uniform approach that the middle cohomology group is isomorphic to the fundamental group of the sub-root system generated by the long simple roots. The modulo $\ell$ reduction of the Springer correspondent representation involves the sign representation exactly when $\ell$ divides the order of this cohomology group. The primes dividing the torsion of the rest of the cohomology are bad primes.Comment: 29 pages, v2 : Leray-Serre spectral sequence replaced by Gysin sequence only, corrected typo

Geschichten statt Geschichte. : Dieter Fortes erzählerische Aufarbeitung des Bombenkrieges im Kontext der Sebald-Debatte

Nachdem der Autor und Germanist W.G. Sebald Ende der Neunzigerjahre eine öffentliche Debatte bezüglich des Luftkriegs in der deutschen Literatur angeregt hatte, ist der II. Weltkrieg zu einem der beherrschenden Themen in der deutschen Gegenwartsliteratur geworden. Doch schon vorher hatte der Autor D. Forte in einer knapp neunhundertseitigen Romantrilogie gezeigt, welche fundamentale Rolle dem schriftlichen und mündlichen Erzählen über die Vergangenheit zukommt. Der Artikel versucht, anhand dieses Autors die Bedeutung des Erinnerns und des Erzählens und damit auch der Literatur sowohl für individuelle Identitätskonstruktionen, als auch für das kollektive Geschichtsbewusstein herauszuarbeitenAfter the author and germanist W.G. Sebald had inspired, by the end of last century nineties, a public discussion about the bombing warfare in the German literature, the Second World War has become one of the dominating themes in German present-day literature. But much earlier, the author D. Forte had already shown, in a nearly nine hundred pages novelistic trilogy, the fundamental importance of written and oral narrations about the past. Based on this author, the article tries to work out the importance of memory and narration and thus, also of literature as well for individual identity construction, as for collective historical consciousnessDespués de que, a finales de los años noventa, el autor y germanista W.G.Sebald hubiera provocado una discusión pública sobre los bombardeos de las ciudades en la literatura alemana, la Segunda Guerra Mundial ha llegado a convertirse en uno de los temas dominantes de la literatura alemana contemporánea. Pero con anterioridad, el autor D.Forte ya había mostrado en su trilogía novelesca de casi novecientas páginas el papel fundamental que tiene la narración oral y escrita del pasado. El artículo intenta estudiar, basándose en este autor, la importancia de la memoria y la narración y con ello también de la literatura tanto para la construcción de la identidad individual como para la conciencia histórica colectiv

¿Qué enseñamos cuando impartimos clases de lengua extranjera?

Este artículo analiza la cuestión de qué significa enseñar una lengua extranjera, planteando un recorrido por la historia de la filosofía del lenguaje y la lingüística en sus relaciones con una L2. La lengua materna determina nuestro acceso al mundo, fenómeno que no puede dejar de tenerse en cuenta en un tiempo que parece haber apostado por el inglés como lengua franca para el acceso a las ciencias y otras disciplinas. El texto recoge diferentes ejemplos de esta hipótesis para apostar por el multilingüismo desde el que el ser humano accede a la realidad y valorarlo como riqueza que jamás debe olvidarse en la enseñanza de la L2.This article analyses what teaching a foreign language means, and it sets out a tour through the history of language's philosophy and linguistics in their connections with a second language. Mother tongue determines our access to the world, a phenomenon that cannot be forgotten in a time that seems to have bet on English as a lingua franca for the access to sciences and other disciplines. The text collects different examples of this hypothesis to bet on the multilingualism from which human beings access to the reality and value it as a source of wealth that should never be forgotten when teaching a second language

A unified approach on Springer fibers in the hook, two-row and two-column cases

We consider the Springer fiber over a nilpotent endomorphism. Fix a Jordan basis and consider the standard torus relative to this. We deal with the problem to describe the flags fixed by the torus which belong to a given component of the Springer fiber. We solve the problem in the hook, two-row and two-column cases. We provide two main characterizations which are common to the three cases, and which involve dominance relations between Young diagrams and combinatorial algorithms. Then, for these three cases, we deduce topological properties of the components and their intersections.Comment: 42 page