Pipeline model of a Fermi-sea electron pump

The use of a band offset between the two leads of an electron pump driven by a local oscillating voltage is shown to increase the pump current dramatically. The structure of the electron transmission suggests the existence of dominant inelastic channels which we call pipelines. This permits the formulation of a simple model that gives a physical account of the numerical results for a realistic device. A spectral analysis reveals the pump current to be carried by scattering states with initial energy deep within the Fermi sea and not at its surface, thereby rendering the effect insensitive to temperature. We show this is compatible with the current flowing near the Fermi surface in the leads.Comment: 6 pages in RevTex4 (beta4), 4 figures; status: accepted for publication reason for replacement: A more detailed discussion of the differences to Ref. [5] has been provided & new reference adde

QCD thermodynamics with effective models

In this talk we extend the Polyakov-quark-meson model to N_f=2+1 quark flavors and study its bulk thermodynamics at finite temperatures in mean-field approximation. Three different Polyakov-loop potentials are considered. Our findings are confronted to recent QCD lattice simulations of the RBC-Bielefeld and HotQCD collaborations. Furthermore, the finite chemical potential expansion of the quark-number susceptibility in a Taylor series around vanishing chemical potential is analyzed. By means of a novel algorithmic differentiation technique, we have calculated Taylor coefficients up to 24th order in the model for the first time. This allows the systematic study of convergence properties of the Taylor series.Comment: [references added]; 10 pages, 5 figures, talk given at the workshop CPOD 2009, June 08 - 12, BNL, US

On the efficient computation of high-order derivatives for implicitly defined functions

Scientific studies often require the precise calculation of derivatives. In many cases an analytical calculation is not feasible and one resorts to evaluating derivatives numerically. These are error-prone, especially for higher-order derivatives. A technique based on algorithmic differentiation is presented which allows for a precise calculation of higher-order derivatives. The method can be widely applied even for the case of only numerically solvable, implicit dependencies which totally hamper a semi-analytical calculation of the derivatives. As a demonstration the method is applied to a quantum field theoretical physical model. The results are compared with standard numerical derivative methods.Comment: 11 pages, 4 figures, to appear in Comput. Phys. Commu

QCD Thermodynamics: Confronting the Polyakov-Quark-Meson Model with Lattice QCD

NJL-type effective models represent a low-energy realization of QCD and incorporate pertinent aspects such as chiral symmetry and its spontaneous breaking, the center symmetry in the heavy-quark limit as well as the axial anomaly. One such model, the Polyakov-quark-meson model for three light quark flavors, is introduced in order to study the phase structure of strongly-interacting matter. With recent high-statistics lattice QCD simulations of the finite-temperature equation of state, a detailed comparison with model results becomes accessible. Such comparisons allow to estimate volume and truncation effects of quantities, obtained on the lattice and provide possible lattice extrapolation procedures to finite chemical potential which are important to locate a critical endpoint in the QCD phase diagram.Comment: 10 pages, 4 figures, contributed to the proceedings of the EMMI Workshop and XXVI Max Born Symposium at 09th-11th of July 2009 in Wroclaw, Polan

Relating geometry descriptions to its derivatives on the web

Sharing building information over the Web is becoming more popular, leading to advances in describing building models in a Semantic Web context. However, those descriptions lack unified approaches for linking geometry descriptions to building elements, derived properties and derived other geometry descriptions. To bridge this gap, we analyse the basic characteristics of geometric dependencies and propose the Ontology for Managing Geometry (OMG) based on this analysis. In this paper, we present our results and show how the OMG provides means to link geometric and non-geometric data in meaningful ways. Thus, exchanging building data, including geometry, on the Web becomes more efficient

Satisfaction not Guaranteed - Institutions and Satisfaction with Democracy in Western Europe

What determines citizens’ satisfaction with the “constitution in operation”? We make two contributions towards an answer to this important policy question. First, we place stronger emphasis than existing studies on quantitative interpretations of the importance of different factors. We use scenario analysis to show that a consensual system generally promotes satisfaction, but affects different types of citizens differently. Second, we focus on informal institutions and rules of the game in European societies. Corporatism and group membership as a measure of social capital are good for satisfaction, and people who live in countries with a high degree of income inequality tend to be less satisfied. The findings for trust and for the rule of law are ambiguous.satisfaction with democracy, political economy, institutions

Including widespread geometry formats in semantic graphs using RDF literals

The exchange of building data involves both geometric and non-geometric data. A promising Linked Data approach is to embed data from existing geometry formats inside Resource Description Framework (RDF) literals. Based on a study of relevant specifications and related work, this toolset-independent approach was found suitable for the exchange of geometric construction data. To implement the approach in practice, the File Ontology for Geometry formats (FOG) and accompanying modelling method is developed. In a proof-of-concept web application that uses FOG, is demonstrated how geometry descriptions of different existing formats are automatically recognised and parsed