Time-dependent versus static quantum transport simulations beyond linear response

To explore whether the density-functional theory non-equilibrium Green's function formalism (DFT-NEGF) provides a rigorous framework for quantum transport, we carried out time-dependent density functional theory (TDDFT) calculations of the transient current through two realistic molecular devices, a carbon chain and a benzenediol molecule inbetween two aluminum electrodes. The TDDFT simulations for the steady state current exactly reproduce the results of fully self-consistent DFT-NEGF calculations even beyond linear response. In contrast, sizable differences are found with respect to an equilibrium, non-self-consistent treatment which are related here to differences in the Kohn-Sham and fully interacting susceptibility of the device region. Moreover, earlier analytical conjectures on the equivalence of static and time-dependent approaches in the low bias regime are confirmed with high numerical precision.Comment: 4 pages, 4 figure

Problematik der Grenzüberschreitenden Zusammenarbeit in der Europäischen Union am Beispiel der Euroregion Neisse-Nisa-Nysa und der Euroregion Bayerischer Wald-Böhmerwald-Untere Inn

In der Arbeit wurden bestehende Problemfelder grenzüberschreitender Zusammenarbeit in den Euroregionen Bayerischer Wald-Böhmerwald-Untere Inn und Neisse-Nisa-Nysa herausgearbeitet und Lösungsvorschläge entwickelt. Die ablaufenden Kooperationsprozesse wurde an Hand des Multi Level Governance Ansatzes erläutert. Als Problemfelder wurden vor allem rechtliche Hindernisse, finanzielle Barrieren, wirtschaftliche Disparitäten sowie unterschiedliche Einflussmöglichkeiten der grenzüberschreitenden Einrichtungen identifiziert. Die ambitionierten Ziele und Strategien konnten nur zum Teil verwirklicht werden, weil Entscheidungs- und Machtkonflikte sowie Konkurrenzdenken die Herausbildung eines gemeinsamen Kooperations- und Lebensraums erschwerten. Sinnvolle Maßnahmen zur Reduzierung bestehender Hindernisse wären insbesondere die Erarbeitung gemeinsamer Entwicklungsstrategien, Stärkung der euroregionalen Einflussmöglichkeiten und realistische Zielsetzung. The Ph.D. examines existing problems of cross-border cooperation in the two Euroregions Bavarian Forest - Bohemian Forest - Lower Inn as well as Neisse-Nisa-Nysa and generates suggestions for improvement. The cooperation processes is analysed and illustrated by means of the multi-level governance approach. Identified problem areas are in particular regulatory barriers, financial barriers, economic disparities and insufficiently aligned organisational structures in the abut countries. The aspired implementation of the ambitious goals and strategies had only been partly successful in the past years. The creation of a joint cooperation and living space were impeded by decision making conflicts, power struggles and rivalry. Meaningful measures to reduce existing barriers would be particularly implementing joint development strategies, strengthening the Euroregional influence and setting realistic goals taking all existing obstacles into account

Dynamical generalization of a solvable family of two-electron model atoms with general interparticle repulsion

Holas, Howard and March [Phys. Lett. A {\bf 310}, 451 (2003)] have obtained analytic solutions for ground-state properties of a whole family of two-electron spin-compensated harmonically confined model atoms whose different members are characterized by a specific interparticle potential energy u($r_{12}$). Here, we make a start on the dynamic generalization of the harmonic external potential, the motivation being the serious criticism levelled recently against the foundations of time-dependent density-functional theory (e.g. [J. Schirmer and A. Dreuw, Phys. Rev. A {\bf 75}, 022513 (2007)]). In this context, we derive a simplified expression for the time-dependent electron density for arbitrary interparticle interaction, which is fully determined by an one-dimensional non-interacting Hamiltonian. Moreover, a closed solution for the momentum space density in the Moshinsky model is obtained.Comment: 5 pages, submitted to J. Phys.

Optical collisions of cold, metastable helium atoms

We have studied the optical collisions of cold, metastable helium atoms in a magneto-optical trap. We have detected the rate of Penning and associative ionization of two metastable helium atoms at a temperature of 1 mK with and without nearly resonant light. We find that the associative ionization rate is increased with more than a factor 20 due to the presence of the light field. The absolute ionization rate near resonance of (1.9±0.8)×10^(-9) cm3/s for the optical collision differs two orders of magnitude with the rate reported by Bardou et al. (Europhys. Lett. 20, 681 (1992)). Our experimental findings are in good agreement with theory. We present a simple, semi-classical model, which accounts for all the observed features

Polypeptides, Nucleic Acid Molecules, and Methods for Synthesis of Triterpenes

This application relates to the polypeptides, nucleic acid molecules, vectors, transfected cells, and methods for synthesis of triterpenes, including botryococcene

Method and System for Producing Triterpenes

A method and system are provided for the production of triterpene including methylated triterpenes. The method and system include isolated nucleic acid sequences encoding triterpene methyltransferases such as triterpene methyltransferases 1, 2, 3. Advantageously, the method and system includes transgenic plant cells via an expression vector for triterpene methyltransferase and optionally various triterpene synthase and prenyltransferase all with tags directing these enzymes to the chloroplast of the transgenic plant cells for using the chloroplast methyl erythritol phosphate (MEP) pathway in the triterpene biogenesis

Photo induced collisions with laser cooled He* atoms

This paper presents an experimental investigation of cold collisions between metastable Helium atoms in an optical trap at 1mK. Penning (PI) and associative (AI) ionization reactions are distinguished using a mass spectrometer and studied under influence of near resonant laser light. Sensitive behavior of the ion rate is observed when the laser is tuned close to resonance. Experimental ?ndings are well described, on an absolute scale, by a semi-classical model we have developed for optical collisions and by a modi?ed Julienne-Vigu´e model

Quasiparticle energies for large molecules: a tight-binding GW approach

We present a tight-binding based GW approach for the calculation of quasiparticle energy levels in confined systems such as molecules. Key quantities in the GW formalism like the microscopic dielectric function or the screened Coulomb interaction are expressed in a minimal basis of spherically averaged atomic orbitals. All necessary integrals are either precalculated or approximated without resorting to empirical data. The method is validated against first principles results for benzene and anthracene, where good agreement is found for levels close to the frontier orbitals. Further, the size dependence of the quasiparticle gap is studied for conformers of the polyacenes ($C_{4n+2}H_{2n+4}$) up to n = 30.Comment: 10 pages, 5 eps figures submitted to Phys. Rev.