Renormalization of the Optical Response of Semiconductors by Electron-Phonon Interaction

In the past five years enormous progress has been made in the ab initio calculations of the optical response of electrons in semiconductors. The calculations include the Coulomb interaction between the excited electron and the hole left behind, as well as local field effects. However, they are performed under the assumption that the atoms occupy fixed equilibrium positions and do not include effects of the interaction of the lattice vibrations with the electronic states (electron-phonon interaction). This interaction shifts and broadens the energies at which structure in the optical spectra is observed, the corresponding shifts being of the order of the accuracy claimed for the ab initio calculations. These shifts and broadenings can be calculated with various degrees of reliability using a number of semiempirical and ab initio techniques, but no full calculations of the optical spectra including electron-phonon interaction are available to date. This article discusses experimental and theoretical aspects of the renormalization of optical response functions by electron-phonon interaction, including both temperature and isotopic mass effects. Some of the theoretical techniques used can also be applied to analyze the renormalization of other response functions, such as the phonon spectral functions, the lattice parameters, and the elastic constants.Comment: Latex 2.09, 28 pages, 13 Figs., 2 Tables, submitted to Phys. Stat. Sol.

Electronic Excitations from a Perturbative LDA+GdW Approach

We discuss an efficient approach to excited electronic states within ab-initio many-body perturbation theory (MBPT). Quasiparticle corrections to density-functional theory result from the difference between metallic and non-metallic dielectric screening. They are evaluated as a small perturbation to the DFT-LDA band structure, rather than fully calculating the self energy and evaluating its difference from the exchange-correlation potential. The dielectric screening is desribed by a model, which applies to bulk crystals, as well as, to systems of reduced dimension, like molecules, surfaces, interfaces, and more. The approach also describes electron-hole interaction. The resulting electronic and optical spectra are slightly less accurate but much faster to calculate than a full MBPT calculation. We discuss results for bulk silicon and argon, for the Si(111)-(2x1) surface, the SiH4 molecule, an argon-aluminum interface, and liquid argon

The Political Economy of Bilateralism and Multilateralism: Institutional Choice in Trade and Taxation

Trade relations are governed by the multilateral GATT, whereas the avoidance of international double taxation rests on a network of around 2000 bilateral treaties. Given the two regimes’ similar economic rationales this difference between bilateralism in international double tax avoidance and multilateralism in the trade regime poses an empirical puzzle. In this paper we develop an answer to this puzzle. Differentiating between different stages of international cooperation, we first describe the institutional form in the bargaining and agreement stages of cooperation. This description shows that the regimes are quite similar in the bargaining stage, both exhibiting a mix of bilateral and multilateral bargaining. However, while agreement is multilateral in the trade regime it is bilateral in taxation. Based on stylized institutional histories of both cases we develop simple game theoretic models incorporating domestic level considerations. Building on these models we then go on to explain the institutional choice between bilateral and multilateral cooperation. We show that state concerns for the distribution of benefits can be best achieved under bilateral bargaining in both regimes. However, in order to lower transaction costs there are also elements of multilateral bargaining. Agreement is multilateral in trade in order to overcome a free-rider problem that results from an interaction of concerns for distribution and enforcement. Since such a problem of free-riding does not exist in taxation, there is no need for binding multilateral agreement.Theories of International Cooperation; International Trade; International Double Taxation; Bilateralism; Multilateralism

The political economy of bilateralism and multilateralism: Institutional choice in international trade and taxation

Trade relations are governed by the multilateral GATT, whereas the avoidance of international double taxation rests on a network of around 2000 bilateral treaties. Given the two regimes similar economic rationales this difference between bilateralism in international double tax avoidance and multilateralism in the trade regime poses an empirical puzzle. In this paper we develop an answer to this puzzle. Differentiating between different stages of international cooperation, we first describe the institutional form in the bargaining and agreement stages of cooperation. This description shows that the regimes are quite similar in the bargaining stage, both exhibiting a mix of bilateral and multilateral bargaining. However, while agreement is multilateral in the trade regime it is bilateral in taxation. Based on stylized institutional histories of both cases we develop simple game theoretic models incorporating domestic level considerations. Building on these models we then go on to explain the institutional choice between bilateral and multilateral cooperation. We show that state concerns for the distribution of benefits can be best achieved under bilateral bargaining in both regimes. However, in order to lower transaction costs there are also elements of multilateral bargaining. Agreement is multilateral in trade in order to overcome a free-rider problem that results from an interaction of concerns for distribution and enforcement. Since such a problem of free-riding does not exist in taxation, there is no need for binding multilateral agreement. -- Während Handelsbeziehungen durch das multilaterale GATT geregelt werden, beruht die Vermeidung internationaler Doppelbesteuerung auf einem Netzwerk von etwa 2000 bilateralen Verträgen. Da beide Regime die gleiche ökonomische Zielsetzung der Marktliberalisierung haben, stellt die unterschiedliche institutionelle Form ein empirisches Puzzle dar, das wir in diesem Papier lösen. Wir unterscheiden zwischen verschiedenen Phasen internationaler Kooperation und beschreiben zunächst die institutionelle Form in der Bargaining- und Agreement-Phase. Es wird gezeigt, dass die Systeme in der Bargaining-Phase sehr ähnlich sind: beide weisen einen Mix bilateraler und multilateraler Elemente auf. In der Agreement-Phase hingegen findet man Multilateralismus im Handelsregime und Bilateralismus im Steuerregime. Im zweiten Teil des Papiers leiten wir aus den nationalen Interessenkonstellationen in der Handels- und Steuerpolitik einfache spieltheoretische Modelle ab, mit deren Hilfe wir die institutionelle Wahl zwischen bilateraler und multilateraler Kooperation in beiden Phasen erklären. Wir zeigen, dass Staaten nach Verteilungsgewinnen streben, was am besten in bilateralen Verhandlungen erreicht werden kann. Bilaterales Verhandeln führt jedoch zu hohen Transaktionskosten, die durch multilaterale Elemente in den Verhandlungen reduziert werden können (Bargaining-Phase). Abkommen in Handelsbeziehungen sind multilateral, um ein free-riding zu vermeiden, das wiederum aus dem Streben nach Verteilungsgewinnen resultiert. Da free-riding im Steuerregime aufgrund der Spielstruktur kein gravierendes Problem ist, gibt es hier keine Notwendigkeit eines multilateralen Abkommens, so dass man hier Bilateralismus vorfindet (Agreement-Phase).

Pirate stealth or inattentional blindness?:the effects of target relevance and sustained attention on security monitoring for experienced and naïve operators

Closed Circuit Television (CCTV) operators are responsible for maintaining security in various applied settings. However, research has largely ignored human factors that may contribute to CCTV operator error. One important source of error is inattentional blindness--the failure to detect unexpected but clearly visible stimuli when attending to a scene. We compared inattentional blindness rates for experienced (84 infantry personnel) and naïve (87 civilians) operators in a CCTV monitoring task. The task-relevance of the unexpected stimulus and the length of the monitoring period were manipulated between participants. Inattentional blindness rates were measured using typical post-event questionnaires, and participants' real-time descriptions of the monitored event. Based on the post-event measure, 66% of the participants failed to detect salient, ongoing stimuli appearing in the spatial field of their attentional focus. The unexpected task-irrelevant stimulus was significantly more likely to go undetected (79%) than the unexpected task-relevant stimulus (55%). Prior task experience did not inoculate operators against inattentional blindness effects. Participants' real-time descriptions revealed similar patterns, ruling out inattentional amnesia accounts

The use of synchrony in parent-child interaction can be measured on a signal-level

In our approach, we aim at an objective measurement of synchrony in multimodal tutoring behavior. The use of signal correlation provides a well formalized method that yields gradual information about the degree of synchrony. For our analysis, we used and extended an algorithm proposed by Hershey & Movellan (2000) that correlates single-pixel values of a video signal with the loudness of the corresponding audio track over time. The results of all pixels are integrated over the video to achieve a scalar estimate of synchrony

Redshift of excitons in carbon nanotubes caused by the environment polarizability

Optical excitations of molecular systems can be modified by their physical environment. We analyze the underlying mechanisms within many-body perturbation theory, which is particularly suited to study non-local polarizability effects on the electronic structure. Here we focus on the example of a semiconducting carbon nanotube, which observes redshifts of its excitons when the tube is touched by another nanotube or other physisorbates. We show that the redshifts mostly result from the polarizability of the attached ad-system. Electronic coupling may enhance the redshifts, but depends very sensitively on the structural details of the contact

Internationalization of Studies and Research – The Example of the Integrated French-German Law Curriculum at the University Paris Ouest Nanterre La Défense

Legal experts of international firms need a sound knowledge of national law systems and international law. In view of decision-making processes that assume a global perspective rather than the perspective of one centralized headquarters, they need appropriate human resources from many countries with employees who can combine legal, technical and economic advice. The requirement is a knowledge of methods to cope with new and unknown law systems. The role of the law faculty is to put students in the position to understand what law is, to train their abilities of being able to identify legal problems and find appropriate solutions to them. Faculties should aim at equipping their students with the tools and methods that will later put them in a position to achieve these goals. Law faculties have to adapt law curriculums to the requirements of education of international legal experts. For this reason, the teaching of intercultural skills and judicial terminology in foreign languages takes an important part in the law curriculum. These special programs begin at an early stage of law [email protected]é Paris Ouest Nanterre La Défens

Exploring "Associative Talk": When German Mothers Instruct Their Two Year Olds about Spatial Tasks

In this study, maternal input was analyzed during a task, in which German mothers instructed their two-year-old children to put two objects together in a particular way. In the setting, the spatial relation (ON and UNDER) and the canonicality of these relations (canonical such as ‘a pot on a table’ and noncanonical like ‘a train on a tunnel’) were varied. Two kinds of discourse strategies are proposed that characterize mothers’ input in this task: bring-in and follow-in. For the analysis, an automatic procedure was developed, in which the amount of words spent on a strategy was related to the overall word amount. The data suggest that the canonicality of the task can change the discourse: Bring-in strategies dominated the discourse in tasks with canonical spatial relations while in more difficult tasks with non-canonical relations, German-speaking mothers used follow-ins significantly more often than in the canonical tasks. Together, the results of this study shed light on the process of an on-line adaptation of the mother to her child and give us insight into how a situated understanding in a task-oriented discourse emerges

The Russian Sonderweg: A Course of Endless Exclusion

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