Scaling properties of ballistic nano-transistors

Recently, we have suggested a scale-invariant model for a nano-transistor. In agreement with experiments a close-to-linear thresh-old trace was found in the calculated ID - VD-traces separating the regimes of classically allowed transport and tunneling transport. In this conference contribution, the relevant physical quantities in our model and its range of applicability are discussed in more detail. Extending the temperature range of our studies it is shown that a close-to-linear thresh-old trace results at room temperatures as well. In qualitative agreement with the experiments the ID - VG-traces for small drain voltages show thermally activated transport below the threshold gate voltage. In contrast, at large drain voltages the gate-voltage dependence is weaker. As can be expected in our relatively simple model, the theoretical drain current is larger than the experimental one by a little less than a decade

Fano regime of transport through open quantum dots

We analyze a quantum dot strongly coupled to the conducting leads via quantum point contacts - Fano regime of transport - and report a variety of resonant states which demonstrate the dominance of the interacting resonances in the scattering process in a low confining potential. There are resonant states similar to the eigenstates of the isolated dot, whose widths increase with increasing the coupling strength to the environment, and hybrid resonant states. The last ones are approximatively obtained as a linear combination of eigenstates with the same parity in the lateral direction, and the corresponding resonances show the phenomena of resonance trapping or level repulsion. The existence of the hybrid modes suggests that the open quantum dot behaves in the Fano regime like an artificial molecule

On Eisenbud's and Wigner's R-matrix: A general approach

The main objective of this paper is to give a rigorous treatment of Wigner's and Eisenbud's $R$-matrix method for scattering matrices of scattering systems consisting of two selfadjoint extensions of the same symmetric operator with finite deficiency indices. In the framework of boundary triplets and associated Weyl functions an abstract generalization of the $R$-matrix method is developed and the results are applied to Schr\"odinger operators on the real axis

Functional dissection of two amino acid substitutions unique to the human FOXP2 protein

The transcription factor forkhead box P2 (FOXP2) is involved in the development of language and speech in humans. Two amino acid substitutions (T303N, N325S) occurred in the human FOXP2 after the divergence from the chimpanzee lineage. It has previously been shown that when they are introduced into the FOXP2 protein of mice they alter striatal synaptic plasticity by increasing long-term depression in medium spiny neurons. Here we introduce each of these amino acid substitutions individually into mice and analyze their effects in the striatum. We find that long-term depression in medium spiny neurons is increased in mice carrying only the T303N substitution to the same extent as in mice carrying both amino acid substitutions. In contrast, the N325S substitution has no discernable effects.journal articl

On Eisenbud's and Wigner's R-matrix: A general approach

The main objective of this paper is to give a rigorous treatment of Wigner's and Eisenbud's R-matrix method for scattering matrices of scattering systems consisting of two selfadjoint extensions of the same symmetric operator with finite deficiency indices. In the framework of boundary triplets and associated Weyl functions an abstract generalization of the R-matrix method is developed and the results are applied to Schrödinger operators on the real axis

Pulse Propagation in Resonant Tunneling

We consider the analytically solvable model of a Gaussian pulse tunneling through a transmission resonance with a Breit-Wigner characteristic. The solution allows for the identification of two opposite pulse propagation regimes: if the resonance is broad compared to the energetic width of the incident Gaussian pulse a weakly deformed and slightly delayed transmitted Gaussian pulse is found. In the opposite limit of a narrow resonance the dying out of the transmitted pulse is dominated by the slow exponential decay characteristic of a quasi-bound state with a long life time (decaying state). We discuss the limitation of the achievable pulse transfer rate resulting from the slow decay. Finally, it is demonstrated that for narrow resonances a small second component is superimposed to the exponential decay which leads to characteristic interference oscillations.Comment: 6 pages, 4 figure

Energiemangel - Rohstoffknappheit: Welche mittelfristigen Perspektiven hat die deutsche Wirtschaft?

Steigende Energiekosten und Rohstoffpreise, Unsicherheit hinsichtlich der Verlässlichkeit der Energielieferungen und Verknappung auf den Rohstoffmärkten - Joachim Wuermeling, Bundesministerium für Wirtschaft und Technologie, sieht die Notwendigkeit einer neue Rohstoffstrategie für Deutschland, die derzeit von der Bundesregierung gemeinsam mit der Wirtschaft entwickelt wird. Wulf H. Bernotat, E.ON AG, unterstreicht, dass die europäischen Länder energiepolitisch nicht mehr allein agieren können, wenn sie zukunftsfähige und effiziente Energiestrukturen in Europa aufbauen wollen. Und Jochen Weise, E.ON AG Ruhrgas, sieht die Politik gefordert. Sie solle die Sicherung der Energieversorgung künftig als eines der zentralen Themen der Außenpolitik verfolgen. Ulrich Grillo, BDI, kann sich eine kapitalstarke "nationale Beteiligungsgesellschaft", die die Rohstoffinteressen bündelt, vorstellen. Nach Meinung von Werner Bohnenschäfer, Institut für Energetik und Umwelt gemeinnützige GmbH, Leipzig, muss sich mittelfristig die Wirtschaft auf ein hohes Preisniveau für Rohstoffe aller Art einstellen. Längerfristig müssten neue Technologien, die neue - rohstoffseitig "unbegrenzt" verfügbare - Verbundwerkstoffe einsetzen, entwickelt werden, um die Wettbewerbsposition absichern.Energieversorgung, Rohstoffreserven, Rohstoffpreis, Rohstoffmarkt, Erdgas, Nachfrage, Wettbewerb, Branche, EU-Binnenmarkt, Deutschland

Sensitivity analysis of effective thermal conductivity of open-cell ceramic foams using a simplified model based on detailed structure

The Effective Thermal Conductivity (ETC) of open-cell porous foams can be predicted from the detailed numerical simulation, considering the complex foam structure obtained from three-dimensional (3D) Computed Tomography (CT)-scan images. An alternative approach could be to consider simplified models for a quick and accurate estimation of the ETC. A model for ETC of open-cell porous foams, using such a simplified approach, has been proposed recently which relies upon a single numerical prediction of the dimensionless ETC under vacuum condition, evaluated using the detailed foam structure obtained from 3D CT-scan information. This model is applied in the present study in order to analyze the influence of different parameters, namely the microscopic porosity within the bulk solid material and the direction of heat transfer, on the ETC of open-cell ceramic foams. The present investigation demonstrates that the considered simplified modeling approach offers reasonable accuracy with reduced computational effort for the sensitivity analysis of ETC to different parameters