10,371 research outputs found
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
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