Scattering properties of weakly bound dimers of fermionic atoms

We consider weakly bound diatomic molecules (dimers) formed in a two-component atomic Fermi gas with a large positive scattering length for the interspecies interaction. We develop a theoretical approach for calculating atom-dimer and dimer-dimer elastic scattering and for analyzing the inelastic collisional relaxation of the molecules into deep bound states. This approach is based on the single-channel zero range approximation, and we find that it is applicable in the vicinity of a wide two-body Feshbach resonance. Our results draw prospects for various interesting manipulations of weakly bound dimers of fermionic atoms.Comment: extended version of cond-mat/030901

Crystalline phase of strongly interacting Fermi mixtures

We show that the system of weakly bound molecules of heavy and light fermionic atoms is characterized by a long-range intermolecular repulsion and can undergo a gas-crystal quantum transition if the mass ratio exceeds a critical value. For the critical mass ratio above 100 obtained in our calculations, this crystalline order can be observed as a superlattice in an optical lattice for heavy atoms with a small filling factor. We also find that this novel system is sufficiently stable with respect to molecular relaxation into deep bound states and to the process of trimer formation.Comment: 4 pages, 1 color figure, published versio

A discrete-pulse optimal control algorithm with an application to spin systems

This article is aimed at extending the framework of optimal control techniques to the situation where the control field values are restricted to a finite set. We propose a generalization of the standard GRAPE algorithm suited to this constraint. We test the validity and the efficiency of this approach for the inversion of an inhomogeneous ensemble of spin systems with different offset frequencies. It is shown that a remarkable efficiency can be achieved even for a very limited number of discrete values. Some applications in Nuclear Magnetic Resonance are discussed

STRUCTURE OF FARMING UNDER FREER TRADE AMONG NAFTA COUNTRIES

International Relations/Trade,

Le Parc naturel urbain en Suisse : une utopie? Approche philosophique pour dépasser l'opposition ville/nature

Cet article examine le rapport ville/nature par le prisme de la politique des parcs naturels en Suisse. Partant d’une approche philosophique de l’idée de nature, il s’efforce de montrer que la création du Parc national suisse en 1914 s’inscrit dans une opposition sous-jacente entre l’homme et la nature. Avec l’évolution ultérieure de la législation en 2006, cette dichotomie subsiste dans la relation ville/nature. La discussion sur la catégorie de parc naturel urbain permet ensuite de proposer un dépassement de cette opposition en s’appuyant sur la phénoménologie et la pensée critique telles que développées par G. Böhme, A. Berque et V. Plumwood. Un tel dépassement se traduit par une conception intégrative de la nature en ville. Notre proposition s’articule ainsi autour de l’idée d’une nature en relation d’intériorité ou en relation d’identification avec la ville. Pour les acteurs impliqués dans la définition des parcs naturels en Suisse, elle suppose un décentrement autorisant un regard moins hostile sur la ville.Dieser Artikel untersucht das Verhältnis zwischen Stadt und Natur anhand der schweizerischen Gesetzgebung der Naturparks. Der philosophische Ansatz ist der Begriff Natur. Damit wird gezeigt, dass die Schaffung des ersten Naturparks Europas in 1914 – der Schweizerische Nationalpark – auf einen Gegensatz zwischen Mensch und Natur beruht. Mit der Weiterentwicklung der Gesetzgebung besteht jedoch die Entgegensetzung in der Form Stadt/Natur weiter. Die Debatte über die Kategorie des städtischen Naturparks ermöglicht dann mit Hilfe der Phänomenologie und der kritischen Philosophie, wie sie von G. Böhme, A. Berque und V. Plumwood vertreten werden, diesen Gegensatz zu überwinden. Eine solche Überwindung geschieht aber erst durch eine integrative Auffassung der Natur innerhalb der Stadt. Unser Vorschlag basiert auf der Idee einer Natur in innerer Beziehung oder in identifizierender Beziehung zur Stadt. Für die Akteure, die in der Definition der Naturparks involviert sind, bedeutet dies eine Dezentrierung, die einen weniger feindlichen Blick auf die Stadt erlaubt.This paper examines the city/nature relationship through the lens of the policy of natural parks in Switzerland. Using a philosophical approach of the idea of nature, it shows that the creation of the Swiss National Park was linked with an underlying opposition between human and nature. After the evolution of the legal framework in 2006, this dichotomy remains vivid in the city/nature relationship. Discussing the category of urban natural park, our proposition intends to exceed this dichotomy using philosophical concepts of phenomenoly and critical thought as elaborated by G. Böhme, A. Berque and V. Plumwood. Our proposal is thereby structured around the idea of nature in interiority relationship or in relation of identification with the city. Such approaches allow an integrative conception of nature and city. It implies, for the actors involved in defining the natural parks in Switzerland, a decentering allowing a less hostile view of the city

Le Parc naturel urbain en Suisse : une utopie? Approche philosophique pour dépasser l'opposition ville/nature

This paper examines the city/nature relationship through the lens of the policy of natural parks in Switzerland. Using a philosophical approach of the idea of nature, it shows that the creation of the Swiss National Park was linked with an underlying opposition between human and nature. After the evolution of the legal framework in 2006, this dichotomy remains vivid in the city/nature relationship. Discussing the category of urban natural park, our proposition intends to exceed this dichotomy using philosophical concepts of phenomenoly and critical thought as elaborated by G. Böhme, A. Berque and V. Plumwood. Our proposal is thereby structured around the idea of nature in interiority relationship or in relation of identification with the city. Such approaches allow an integrative conception of nature and city. It implies, for the actors involved in defining the natural parks in Switzerland, a decentering allowing a less hostile view of the city

A quasi-pure Bose-Einstein condensate immersed in a Fermi sea

We report the observation of co-existing Bose-Einstein condensate and Fermi gas in a magnetic trap. With a very small fraction of thermal atoms, the 7Li condensate is quasi-pure and in thermal contact with a 6Li Fermi gas. The lowest common temperature is 0.28 muK = 0.2(1) T_C = 0.2(1) T_F where T_C is the BEC critical temperature and T_F the Fermi temperature. Behaving as an ideal gas in the radial trap dimension, the condensate is one-dimensional.Comment: 4 pages, 5 figure

Production of Long-Lived Ultracold Li2 Molecules from a Fermi gas

We create weakly-bound Li2 molecules from a degenerate two component Fermi gas by sweeping a magnetic field across a Feshbach resonance. The atom-molecule transfer efficiency can reach 85% and is studied as a function of magnetic field and initial temperature. The bosonic molecules remain trapped for 0.5 s and their temperature is within a factor of 2 from the Bose-Einstein condensation temperature. A thermodynamical model reproduces qualitatively the experimental findings