Dynamics of the 2D two-component plasma near the Kosterlitz-Thouless transition

We study the dynamics of a classical, two-component plasma in two dimensions, in the vicinity of the Kosterlitz-Thouless (KT) transition where the system passes from a dielectric low-temperature phase (consisting of bound pairs) to a conducting phase. We use two ``complementary'' analytical approaches and compare to simulations. The conventional, ``intuitive'' approach is built on the KT picture of independently relaxing, bound pairs. A more formal approach, working with Mori projected dynamic correlation functions, avoids to assume the pair picture from the start. We discuss successes and failures of both approaches, and suggest a way to combine the advantages of both.Comment: 4 pages, LaTeX, 4 eps figures included; to appear in the proceedings of the ``1999 International Conference on Strongly Coupled Coulomb Systems'', 4-11 Sept 1999 in Saint-Malo (France); some typos correcte

Marché électrique libéralisé en Suisse: Vers de nouvelles stratégies de coopération entre collectivités publiques et distributeurs d'électricité?

L’entrée en vigueur de la loi sur l’approvisionnement en électricité (LApEl) au début 2008 et l’ouverture du marché électrique sont en passe de recomposer le paysage énergétique suisse et ses acteurs principaux: les collectivités publiques et les entreprises de production et de distribution. Un séminaire organisé le 18 septembre dernier à l’EPFL par le Centre de Recherches Energétiques et Municipales (CREM), l’Energy Center de l’EPFL et SuisseEnergie pour les communes a tâché d’explorer les différentes opportunités, ainsi que les risques en matière de stratégies de coopération entre les multiples acteurs du secteur électrique suisse.Liberalisierung des Schweizer Strommarkts: hin zu neuen Strategien für die Zusammenarbeit zwischen dem Gemeinwesen und Stromanbietern? Das Stromversorgungsgesetz (StromVG), das Anfang 2008 in Kraft getreten ist, und die Öffnung des Strommarkts werden die Schweizer Energielandschaft und deren Hauptakteure stark prägen: das Gemeinwesen sowie die Stromhersteller und -anbieter. Am 18. September 2008 fand an der ETH Lausanne ein vom Centre de Recherches Energétiques et Municipales (CREM), vom EnergyCenter der ETHL und von Energie Schweiz für die Gemeinden organisiertes Seminar statt, an dem die diversen Chancen, aber auch die Risiken bezüglich der Strategien für die Zusammenarbeit der vielen Akteure des Schweizer Strommarktes erörtert wurden

Pseudogap in the one-electron spectral functions of the attractive Hubbard model

We calculate the one-electron Green's function of the 2D attractive Hubbard model by coupling the electrons to pair fluctuations. The latter are approximated by homogeneous amplitude fluctuations and phase correlations corresponding to the XY-model. The electronic density of states shows a pseudogap at temperatures well above the transition temperature $T_{C}$. For a quasi-3D system, a superconducting gap emerges out of the pseudogap below $T_{C}$.Comment: 2 pages, one major typo corrected, one reference adde

One-Electron Spectral Functions of the Attractive Hubbard Model for Intermediate Coupling

We calculate the one-electron spectral function of the attractive (negative-$U$) Hubbard model. We work in the intermediate coupling and low density regime and obtain the self-energy in an approximate analytical form. The excitation spectrum is found to consist of three branches. The results are obtained in a framework, based on the self-consistent T-matrix approximation, which is compatible with the Mermin-Wagner theorem.Comment: 7 pages, revtex, 7 figures in postscript format, submitted to PR

Energy flows monitoring at the Cantonal level

As an increased number of measures (Swiss or European level) aim at developing more sustainable policies for energy management and reduction of CO2 emissions in particular (for example, the 3x20 policy), very few tools currently exist at the regional/cantonal level to monitor the multiple existing energy flows. Energy issues at local and territorial level have become considerably more complex in the last twenty years for a number of reasons. First, new technologies penetrated the market and now compete with fossil-based conversion systems. In addition, energy systems are evolving to systematically become multi-fluid and multi-services. Finally, local and state authorities have taken up a stronger and broader role in terms of energy policy and have committed to ambitious goals in terms of both increased energy efficiency and implementation of renewables. Within this project, a decision-support and monitoring tool for policy makers has been developed, which includes thorough information on the most prominent energy aspects of the Canton of Vaud, and paves the way for establishing more indicators covering environmental and economic aspects. The development of a web-based tool aimed at visualizing the entire energy chain, from energy sources to end-use sectors at the level of a whole Swiss Canton is thus presented here. This tool provides a unifying structure for all the useful information on energy sources, vectors and final consumptions, this approach thereby giving access to a global overview, understanding and monitoring of the energy supply and demand characteristics of any given Canton (or any equivalent subnational territorial entity). The final goal of this approach is to give access to the direct visualization of all energy flows on the platform, thus translating and broadening the national statistics on the energy chain up to the cantonal (territorial) level. Therefore, this innovative tool will allow quantifying energy profiles, modelling conversion nodes along the energy chain, as well as assessing the overall energy balance per end-use sector. This very innovative platform constitutes a centralized energy data repository as well as a quantitative evaluation tool, encompassing most useful energy sources

MEU – A cartographic-based web-platform for urban energy management and planning

This paper presents MEU (http://meu.epfl.ch) project results: a new GIS-centric web application for energy management and planning of existing or new urban zones. The project has been carried out with the collaboration of four Western Switzerland cities and three energy utilities companies using a “bottom-up” approach. The methodology involves the set-up of a dedicated geodatabase model aimed at structuring all energy-related knowledge of a city. Computation solvers could then be used to design and evaluate future energy scenarios. The ArcGIS Server-based web services are readily usable for cities in terms of data import, management, computation and display. The clear geographical presentation of computation results – for example on buildings' footprints thematic maps - using GIS functionalities and analysis tools facilitates the communication with all stakeholders at the local scale (such as energy utilities, local administrations, local government and the public) and provides figures to guide energy policy and investments. A complementary project on the monitoring of energy flows at a broader territorial level is also presented

Smart cities : la métamorphose

Le concept de « villes intelligentes » est aujourd’hui largement répandu et utilisé, de même que celui de « réseaux intelligents ». Or, dans les villes européennes et suisses, nous sommes pour l’instant dans une situation très éloignée par rapport à ces objectifs de « smart cities », non seulement du point de vue technologique mais aussi, peut-être surtout, du point de vue de leur intégration dans les politiques locales et dans les modèles d’affaires des entreprises énergétiques. En effet, s’il existe sur le marché des compteurs énergétiques permettant de communiquer, ils ne sont installés qu’en très petit nombre dans les villes et, dans la grande majorité des cas, sous-utilisés du point de vue des informations détaillées qu’ils pourraient fournir quant à la dynamique de l’approvisionnement et de la demande énergétiques. D’autre part, les implémentations actuelles de réseaux intelligents considèrent les consommateurs finaux comme des éléments « réactifs », pour utiliser une analogie électrique, et non comme des éléments « actifs », qui disposent de véritables outils afin de participer à la dynamique des réseaux, tant du point de vue de la demande énergétique (shift de consommations, installation de nouveaux appareils moins énergivores, rénovations de bâtiments, etc.) que de l’approvisionnement décentralisé. De même, les utilisateurs peuvent devenir co-créateurs de nouveaux services énergétiques, dans un marché dynamique et novateur. Couplés à des outils de planification énergétique territoriale toujours plus performants, ces nouveaux développements permettront aux villes européennes d’atteindre leurs ambitieux objectifs en matière d’efficacité énergétique accrue

Excitation spectrum of the two-dimensional attractive Hubbard model

We calculate the one-particle spectral functions above the superconducting transition temperature $T_{C}$, in the framework of a functional integral approach. The coupling of the electronic self-energy to pair fluctuations, which are treated by means of a time-dependent Ginzburg-Landau equation, yields a double-peak structure, around the Fermi wavenumber. The peak separation is essentially temperature-independent, but the structure sharpens when $T_{C}$ is approached.Comment: 3 pages, revtex, 3 embedded figures (eps), submitted to Physica