Particle density and non-local kinetic energy density functional for two-dimensional harmonically confined Fermi vapors

We evaluate analytically some ground state properties of two-dimensional harmonically confined Fermi vapors with isotropy and for an arbitrary number of closed shells. We first derive a differential form of the virial theorem and an expression for the kinetic energy density in terms of the fermion particle density and its low-order derivatives. These results allow an explicit differential equation to be obtained for the particle density. The equation is third-order, linear and homogeneous. We also obtain a relation between the turning points of kinetic energy and particle densities, and an expression of the non-local kinetic energy density functional.Comment: 7 pages, 2 figure

Collisional oscillations of trapped boson-fermion mixtures approaching collapse

We study the collective modes of a confined gaseous cloud of bosons and fermions with mutual attractive interactions at zero temperature. The cloud consists of a Bose-Einstein condensate and a spin-polarized Fermi gas inside a spherical harmonic trap and the coupling between the two species is varied by increasing either the magnitude of the interspecies s-wave scattering length or the number of bosons. The mode frequencies are obtained in the collisional regime by solving the equations of generalized hydrodynamics and are compared with the spectra calculated in the collisionless regime within a random-phase approximation. We find that, as the mixture is driven towards the collapse instability, the frequencies of the modes of fermionic origin show a blue shift which can become very significant for large numbers of bosons. Instead the modes of bosonic origin show a softening, which becomes most pronounced in the very proximity of collapse. Explicit illustrations of these trends are given for the monopolar spectra, but similar trends are found for the dipolar and quadrupolar spectra except for the surface (n=0) modes which are essentially unaffected by the interactions.Comment: 9 pages, 5 figures, revtex

Fully Frustrated Cold Atoms

Fully frustrated Josephson Junction arrays (FF-JJA's) exhibit a subtle compound phase transition in which an Ising transition associated with discrete broken translational symmetry and a Berezinskii-Kosterlitz-Thouless (BKT) transition associated with quasi-long-range phase coherence occur nearly simultaneously. In this Letter we discuss a cold atom realization of the FF-JJA system. We demonstrate that both orders can be studied by standard momentum-distribution-function measurements and present numerical results, based on a successful self-consistent spin-wave approximation, that illustrate the expected behavior of observables.Comment: 5 pages, 3 figures, submitte

Superconducting atomic contacts inductively coupled to a microwave resonator

We describe and characterize a microwave setup to probe the Andreev levels of a superconducting atomic contact. The contact is part of a superconducting loop inductively coupled to a superconducting coplanar resonator. By monitoring the resonator reflection coefficient close to its resonance frequency as a function of both flux through the loop and frequency of a second tone we perform spectroscopy of the transition between two Andreev levels of highly transmitting channels of the contact. The results indicate how to perform coherent manipulation of these states.Comment: 14 pages, 10 figures, to appear in special issue on break-junctions in JOPC

Ag and N acceptors in ZnO: ab initio study of acceptor pairing, doping efficiency, and the role of hydrogen

Efficiency of ZnO doping with Ag and N shallow acceptors, which substitute respectively cations and anions, was investigated. First principles calculations indicate a strong tendency towards formation of nearest neighbor Ag-N pairs and N-Ag-N triangles. Binding of acceptors stems from the formation of quasi-molecular bonds between dopants, and has a universal character in semiconductors. The pairing increases energy levels of impurities, and thus lowers doping efficiency. In the presence of donors, pairing is weaker or even forbidden. However, hydrogen has a tendency to form clusters with Ag and N, which favors the Ag-N aggregation and lowers the acceptor levels of such complexes.Comment: 10 pages, 4 figure

Bovedillas fabricadas con hormigones livianos con la incorporación de residuos de construcción y demolición en sus mezclas

In Argentina, small vaults were introduced by the Italians immigrants during the 19th Century to be used in roofs and floors for housing and public buildings. These vaults were built with bricks put on edge or in sharp ends, giving them the shape of small vaults which rested on iron rafters to cover the expanse of the room. At present, in Argentina´s market we can find a variety of products, such as roof bricks made of different materials like ceramic, concrete and EPS7. These bricks are straight in their lower side and they need to be covered with a ceiling afterwards. The bricks or blocks are supported with thin concrete pre-tense beams; the system is completed with a compression layer of reinforced concrete in-situ. In the construction areas, there is a big amount of arid waste in construction and demolition of buildings that exceed in quantity the circuit reuse. Also, there is discarded material from the packaging of EPS, both wastes are problems because of their volume and, the last one is an environmental contamination agent by drain obstruction. They do not have yet a formal circuit or rooted of reduction or commercialization that could be managed either by the Urban Collectors Cooperatives or by companies. This research work, investigates the applications of concrete mixtures with the incorporations of recycled EPS and crushed rubble, which have been researched and developed at our Center in different small vaults designs in order to develop products that can compete economically with their equivalent in the national market. Thus, optimizing their characteristics in weight, vault’s visible side endings, thermal insulation and safety at work, emulating the image of the traditional brick vaults and recovering memory constructive. In this way, an efficient energetic constructive system is investigated and promoted, by developing an innovative product in technology and quality that represents an environmental improvement, which aims to reduce consumption of natural resources, trying to reduce carbon footprint and the possibility of creating green employment.En Argentina, las bovedillas fueron introducidas por los inmigrantes italianos a mediados del siglo XlX para la construcción de techos y entrepisos de viviendas y edificios públicos. Eran realizadas con ladrillos colocados de canto o de punta, dándole la forma de pequeñas bóvedas, apoyadas sobre vigas de hierro, para cubrir las luces del local. En la actualidad, encontramos en el mercado argentino productos similares ladrillos de techo realizados en diferentes materiales cerámicos, hormigón y EPS8. Dichos ladrillos o bloques son rectos en su cara inferior y necesitan una terminación de cielorraso luego de ser colocados. Son utilizados con viguetas de hormigón pretensadas donde se apoyan las piezas, el sistema se completa con una capa de compresión de hormigón armado in situ. Se cuenta por otra parte, con una cantidad de residuos de áridos de construcción y demolición de obra que exceden en cantidad al circuito de su re uso, como también materiales de descarte proveniente de embalajes de EPS, ambos significan un problema por su volumen y estos últimos son agentes de contaminación ambiental por obstrucción de sumideros, dado que no tienen aún un circuito formal ni arraigado de reducción ni de comercialización por parte de las Cooperativas de Recolectores Urbanos o empresarial. En este trabajo, se investigan las aplicaciones de mezclas de hormigones con incorporación de EPS reciclado y cascotes triturados, ya investigadas y desarrolladas en nuestro Centro, en diferentes diseños de bovedillas con el objetivo de desarrollar productos que puedan competir económicamente con sus equivalentes del mercado nacional, optimizando las características de los mismos, en cuanto a peso, terminaciones en su cara vista, aislación térmica y seguridad para trabajo en obra, emulando la imagen de las bóvedas con ladrillos tradicionales citadas y recuperando la memoria constructiva. De esta manera se investiga y promueve la aplicación de un sistema constructivo energéticamente eficiente, desarrollando un producto innovador en lo tecnológico y de calidad, que represente una mejora en lo ambiental, minimizando el consumo de los recursos naturales, transformando residuos en recursos con la meta de reducir la huella de carbono y con posibilidad de crear empleos verdes

Phase separation in a boson-fermion mixture of Lithium atoms

We use a semiclassical three-fluid model to analyze the conditions for spatial phase separation in a mixture of fermionic Li-6 and a (stable) Bose-Einstein condensate of Li-7 atoms under cylindrical harmonic confinement, both at zero and finite temperature. We show that with the parameters of the Paris experiment [F. Schrek et al., Phys. Rev. Lett. 87 080403 (2001)] an increase of the boson-fermion scattering length by a factor five would be sufficient to enter the phase-separated regime. We give examples of configurations for the density profiles in phase separation and estimate that the transition should persist at temperatures typical of current experiments. For higher values of the boson-fermion coupling we also find a new phase separation between the fermions and the bosonic thermal cloud at finite temperature.Comment: 8 pages, 4 figures, new version of Fig. 4 and typos correcte

Emergence of Wigner molecules in one-dimensional systems of repulsive fermions under harmonic confinement

A Bethe-Ansatz spin-density functional approach is developed to evaluate the ground-state density profile in a system of repulsively interacting spin-1/2 fermions inside a quasi-one-dimensional harmonic well. The approach allows for the formation of antiferromagnetic quasi-order with increasing coupling strength and reproduces with high accuracy the exact solution that is available for the two-fermion system.Comment: 3 pages, 2 figures, submitte

Analysis of Self-Organized Criticality in the Olami-Feder-Christensen model and in real earthquakes

We perform a new analysis on the dissipative Olami-Feder-Christensen model on a small world topology considering avalanche size differences. We show that when criticality appears the Probability Density Functions (PDFs) for the avalanche size differences at different times have fat tails with a q-Gaussian shape. This behaviour does not depend on the time interval adopted and is found also when considering energy differences between real earthquakes. Such a result can be analytically understood if the sizes (released energies) of the avalanches (earthquakes) have no correlations. Our findings support the hypothesis that a self-organized criticality mechanism with long-range interactions is at the origin of seismic events and indicate that it is not possible to predict the magnitude of the next earthquake knowing those of the previous ones.Comment: 5 pages, 3 figures. New version accepted for publication on PRE Rapid Communication