Electron Energy-Loss Spectroscopy: A versatile tool for the investigations of plasmonic excitations

The inelastic scattering of electrons is one route to study the vibrational and electronic properties of materials. Such experiments, also called electron energy-loss spectroscopy, are particularly useful for the investigation of the collective excitations in metals, the charge carrier plasmons. These plasmons are characterized by a specific dispersion (energy-momentum relationship), which contains information on the sometimes complex nature of the conduction electrons in topical materials. In this review we highlight the improvements of the electron energy-loss spectrometer in the last years, summarize current possibilities with this technique, and give examples where the investigation of the plasmon dispersion allows insight into the interplay of the conduction electrons with other degrees of freedom

Bribery and Public Procurement - An Experimental Study

A procurement contract is granted by a bureaucrat (the auctioneer) who is interested in a low price and a bribe from the provider. The optimal bids and bribes are derived based on an iid private cost assumption. In the experiment, bribes are negatively framed (betweensubjects treatment) to capture that society is better off if bribes are rare or low. Although bids are lower than predicted, behavior is qualitatively in line with the linear equilibrium prediction. When bribes generate a negative externality, there is a significant increase in the variability of the data.Corruption, Procurement Auctions

Indication of direct acoustical cochlea stimulation in comparison to cochlear implants

AbstractThe new implantable hearing system Codacs™ was designed to close the treatment gap between active middle ear implants and cochlear implants in cases of severe-to-profound mixed hearing loss. The Codacs™ actuator is attached to conventional stapes prosthesis during the implantation and thereby provides acoustical stimulation through a stapedotomy to the cochlea. Cochlear implants (CIs) on the other hand are an established treatment option for profoundly deaf patients including mixed hearing losses that are possible candidates for the Codacs™.In this retrospective study, we compared the clinical outcome of 25 patients with the Codacs™ (≥3 month post-activation) to 54 CI patients (two years post-activation) with comparable pre-operative bone conduction (BC) thresholds that were potential candidates for both categories of devices. The word recognition score (Freiburg monosyllables test) in quiet was significantly (p < 0.05) better in the Codacs™ than in the corresponding CI patients for average pre-operative bone conduction below 60 dB HL and equal in patients with a pre-operative BC PTA between 60 and 70 dB HL. Speech in noise intelligibility (HSM sentences test at +10 dB SNR) was significantly (p < 0.001) better in Codacs™ (80% median) than in CI patients (25% median) in all tested groups.Our results indicate for patients with sufficient cochlear reserve that speech intelligibility in noise with the Codacs™ hearing implant is significantly better than with a CI. Further, results in Codacs™ were better predictable, encouraging the extension of the indication to patients with less cochlear reserve than reported here

Doping dependent plasmon dispersion in 2H-transition metal dichalcogenides

We report the behavior of the charge carrier plasmon of 2H-transition metal dichalcogenides (TMDs) as a function of intercalation with alkali metals. Intercalation and concurrent doping of the TMD layers have a substantial impact on plasmon energy and dispersion. While the plasmon energy shifts are related to the intercalation level as expected within a simple homogeneous electron gas picture, the plasmon dispersion changes in a peculiar manner independent of the intercalant and the TMD materials. Starting from a negative dispersion, the slope of the plasmon dispersion changes sign and grows monotonously upon doping. Quantitatively, the increase of this slope depends on the orbital character (4d or 5d) of the conduction bands, which indicates a decisive role of band structure effects on the plasmon behavior.Peer reviewe

Finite-Size Effects in a Supercooled Liquid

We study the influence of the system size on various static and dynamic properties of a supercooled binary Lennard-Jones liquid via computer simulations. In this way, we demonstrate that the treatment of systems as small as N=65 particles yields relevant results for the understanding of bulk properties. Especially, we find that a system of N=130 particles behaves basically as two non-interacting systems of half the size.Comment: Proceedings of the III Workshop on Non Equilibrium Phenomena in Supercooled Fluids, Glasses and Amorphous Materials, Sep 2002, Pis

Machine Learning gegen Schwerhörigkeit : Vorhersage des Erfolgs bei Cochlea-Implantat-Versorgung

Sogenannte Cochlea-Implantate sind unter Menschen mit Schwerhörigkeit noch nicht sehr weit verbreitet, unter anderem, weil sich das Ausmaß des Sprachverstehens mit dem Implantat vor der Operation schwer einschätzen lässt. Wissenschaftlerinnen und Wissenschaftler der Medizinischen Hochschule Hannover (MHH), der Technischen Universität Braunschweig und des Forschungszentrums L3S wollen in einem von der VW-Stiftung geförderten Projekt Patientendaten auswerten, um den Erfolg von Cochlea-Implantaten besser bestimmen zu können

Universal electronic structure of polar oxide hetero-interfaces

The electronic properties of NdGaO3/SrTiO3, LaGaO3/SrTiO3, and LaAlO3/SrTiO3 interfaces, all showing an insulator-to-metal transition as a function of the overlayer-thickness, are addressed in a comparative study based on x-ray absorption, x-ray photoemission and resonant photoemission spectroscopy. The nature of the charge carriers, their concentration and spatial distribution as well as the interface band alignments and the overall interface band diagrams are studied and quantitatively evaluated. The behavior of the three analyzed heterostructures is found to be remarkably similar. The valence band edge of all the three overlayers aligns to that of bulk SrTiO3. The near-interface SrTiO3 layer is affected, at increasing overlayer thickness, by the building-up of a confining potential. This potential bends both the valence and the conduction band downwards. The latter one crossing the Fermi energy in the proximity of the interface and determines the formation of an interfacial band offset growing as a function of thickness. Quite remarkably, but in agreement with previous reports for LaAlO3/SrTiO3, no electric field is detected inside any of the polar overlayers. The essential phenomenology emerging from our findings is discussed on the base of different alternative scenarios regarding the origin of interface carriers and their interaction with an intense photon beam

Erste Erfahrungen mit TINNELEC, ein Implantat für die Therapie von chronischem Tinnitus [meeting abstract]

Meeting Abstract : 82. Jahresversammlung der Deutschen Gesellschaft für Hals-Nasen-Ohren-Heilkunde, Kopf- und Hals-Chirurgie. Freiburg i. Br., 01.-05.06.2011. Ca. 3 Millionen Erwachsene in der Bundesrepublik Deutschland leiden unter Tinnitus, wobei eine bei jedem dieser Patienten zur Heilung führende Therapie bisher noch nicht existiert. Ansatzpunkt einer neuartigen Therapie ist die Wiederherstellung des normalen elektrischen Entladungsmusters im Hörnerv mittels elektrischer Stimulation. Hiermit berichten wir über unsere ersten Erfahrungen mit dem Tinnelec, einem Implantat mit einer einzelnen Stimulations-Elektrode die in der Rundfensternische platziert wird. Zurzeit haben wir 4 einseitig ertaubten Patienten mit Tinnitus auf dem betroffenen Ohr jeweils ein Tinnelec-System implantiert. Die Dauer des Tinnitus betrug mindestens ein Jahr und gängige Tinnitus-Therapien wie z.B. Infusionstherapie waren erfolglos geblieben. Ein psychogener Tinnitus wurde ausgeschlossen. Der durch den Tinnitus verursachte Leidensdruck wurde anhand einer VAS Scala (Visuelle Analog Scala) und eines Tinnitus-Handicap-Inventory (THI) Fragebogens beurteilt. Die Reizapplikation betrug mind. 4 Stunden täglich. Als Stimulationsparameter wurde eine Reizmusterannäherung an den Tinnitus angestrebt. Bei drei Patienten wurde unter der Stimulation der Tinnitus erträglicher, eine zeitweise komplette Unterdrückung des Tinnitus schon innerhalb der ersten Therapie-Wochen wurde jedoch nur in einem der Fälle berichtet. Diese Ergebnisse wurden auch durch das THI und VAS unterstützt. Die Tinnelec-Implantation erscheint für Tinnitus Erfolg versprechend zu sein. Weitere Studien bei Tinnitus-Patienten ohne zusätzliche Hörbeeinträchtigung sind jedoch notwendig bis endgültige Schlussfolgerungen betreffend dieses Implantats gezogen werden können. In jedem Fall bleibt die Option einer Cochlea-Implantation im selben Ohr, nach Explantation des Tinnelec, bestehen

Stripe order and quasiparticle Nernst effect in cuprate superconductors

After a brief review of current ideas on stripe order in cuprate high-temperature superconductors, we discuss the quasiparticle Nernst effect in the cuprates, with focus on its evolution in non-superconducting stripe and related nematic states. In general, we find the Nernst signal to be strongly enhanced by nearby van-Hove singularities and Lifshitz transitions in the band structure, implying that phases with translation symmetry breaking often lead to a large quasiparticle Nernst effect due to the presence of multiple small Fermi pockets. Open orbits may contribute to the Nernst signal as well, but do so in a strongly anisotropic fashion. We discuss our results in the light of recent proposals for a specific Lifshitz transition in underdoped YBCO and make predictions for the doping dependence of the Nernst signal.Comment: 10 pages, 4 figs, article prepared for a special issue of New J Phy

The potential energy landscape of a model glass former: thermodynamics, anharmonicities, and finite size effects

It is possible to formulate the thermodynamics of a glass forming system in terms of the properties of inherent structures, which correspond to the minima of the potential energy and build up the potential energy landscape in the high-dimensional configuration space. In this work we quantitatively apply this general approach to a simulated model glass-forming system. We systematically vary the system size between N=20 and N=160. This analysis enables us to determine for which temperature range the properties of the glass former are governed by the regions of the configuration space, close to the inherent structures. Furthermore, we obtain detailed information about the nature of anharmonic contributions. Moreover, we can explain the presence of finite size effects in terms of specific properties of the energy landscape. Finally, determination of the total number of inherent structures for very small systems enables us to estimate the Kauzmann temperature