11,121 research outputs found
Transport and Entanglement Generation in the Bose-Hubbard Model
We study entanglement generation via particle transport across a
one-dimensional system described by the Bose-Hubbard Hamiltonian. We analyze
how the competition between interactions and tunneling affects transport
properties and the creation of entanglement in the occupation number basis.
Alternatively, we propose to use spatially delocalized quantum bits, where a
quantum bit is defined by the presence of a particle either in a site or in the
adjacent one. Our results can serve as a guidance for future experiments to
characterize entanglement of ultracold gases in one-dimensional optical
lattices.Comment: 14 pages, 6 figure
Perfect and broadband acoustic absorption by critically coupled sub-wavelength resonators
International audiencePerfect absorption is an interdisciplinary topic with a large number of applications, the challenge of which consists of broadening its inherently narrow frequency-band performance. We experimentally and analytically report perfect and broadband absorption for audible sound, by the mechanism of critical coupling, with a sub-wavelength multi-resonant scatterer (SMRS) made of a plate-resonator/ closed waveguide structure. In order to introduce the role of the key parameters, we first present the case of a single resonant scatterer (SRS) made of a Helmholtz resonator/closed waveguide structure. In both cases the controlled balance between the energy leakage of the several resonances and the inherent losses of the system leads to perfect absorption peaks. In the case of the SMRS we show that systems with large inherent losses can be critically coupled using resonances with large leakage. In particular, we show that in the SMRS system, with a thickness of λ/12 and diameter of λ/7, several perfect absorption peaks overlap to produce absorption bigger than 93% for frequencies that extend over a factor of 2 in audible frequencies. The reported concepts and methodology provide guidelines for the design of broadband perfect absorbers which could contribute to solve the major issue of noise reduction
Overall evaluation of Skylab imagery for mapping of Latin America
The author has identified the following significant results. Skylab imagery is both desired and needed by the Latin American catographic agencies. The imagery is cost beneficial for the production of new mapping and maintenance of existing maps at national topographic series scales. If this information was available on a near time routine coverage basis, it would provide an excellent additional data base to the Latin American cartographic community, specifically Argentina, Bolivia, Chile, Colombia, Dominican Republic, Guatemala, Paraguay, and Venezuela
Neuronal Metabolism and Neuroprotection: Neuroprotective Effect of Fingolimod on Menadione-Induced Mitochondrial Damage
Imbalance in the oxidative status in neurons, along with mitochondrial damage, are common characteristics in some neurodegenerative diseases. The maintenance in energy production is crucial to face and recover from oxidative damage, and the preservation of different sources of energy production is essential to preserve neuronal function. Fingolimod phosphate is a drug with neuroprotective and antioxidant actions, used in the treatment of multiple sclerosis. This work was performed in a model of oxidative damage on neuronal cell cultures exposed to menadione in the presence or absence of fingolimod phosphate. We studied the mitochondrial function, antioxidant enzymes, protein nitrosylation, and several pathways related with glucose metabolism and glycolytic and pentose phosphate in neuronal cells cultures. Our results showed that menadione produces a decrease in mitochondrial function, an imbalance in antioxidant enzymes, and an increase in nitrosylated proteins with a decrease in glycolysis and glucose-6-phosphate dehydrogenase. All these effects were counteracted when fingolimod phosphate was present in the incubation media. These effects were mediated, at least in part, by the interaction of this drug with its specific S1P receptors. These actions would make this drug a potential tool in the treatment of neurodegenerative processes, either to slow progression or alleviate symptoms
Analysis of the wave propagation properties of a periodic array of rigid cylinders perpendicular to a finite impedance surface
The effect of the presence of a finite impedance surface on the wave
propagation properties of a two-dimensional periodic array of rigid cylinders
with their axes perpendicular to the surface is both numerically and
experimentally analyzed in this work. In this realistic situation both the
incident and the scattered waves interact with these two elements, the surface
and the array. The interaction between the excess attenuation effect, due to
the destructive interference produced by the superposition of the incident wave
and the reflected one by the surface, and the bandgap, due to the periodicity
of the array, is fundamental for the design of devices to control the
transmission of waves based on periodic arrays. The most obvious application is
perhaps the design of Sonic Crystals Noise Barriers. Two different finite
impedance surfaces have been analyzed in the work in order to observe the
dependence of the wave propagation properties on the impedance of the surface
Theoretical and experimental evidence of level repulsion states and evanescent modes in sonic crystal stubbed waveguides
The complex band structures calculated using the Extended Plane Wave
Expansion (EPWE) reveal the presence of evanescent modes in periodic systems,
never predicted by the classical \omega(\vec{k}) methods, providing novel
interpretations of several phenomena as well as a complete picture of the
system. In this work we theoretically and experimentally observe that in the
ranges of frequencies where a deaf band is traditionally predicted, an
evanescent mode with the excitable symmetry appears changing drastically the
interpretation of the transmission properties. On the other hand, the
simplicity of the sonic crystals in which only the longitudinal polarization
can be excited, is used to interpret, without loss of generality, the level
repulsion between symmetric and antisymmetric bands in sonic crystals as the
presence of an evanescent mode connecting both repelled bands. These evanescent
modes, obtained using EPWE, explain both the attenuation produced in this range
of frequencies and the transfer of symmetry from one band to the other in good
agreement with both experimental results and multiple scattering predictions.
Thus, the evanescent properties of the periodic system have been revealed
necessary for the design of new acoustic and electromagnetic applications based
on periodicity
Efficient quantum state transfer in spin chains via adiabatic passage
We propose a method for quantum state transfer in spin chains using an
adiabatic passage technique. Modifying even and odd nearest-neighbour couplings
in time allows to achieve transfer fidelities arbitrarily close to one, without
the need for a precise control of coupling strengths and timing. We study in
detail transfer by adiabatic passage in a spin-1 chain governed by a
generalized Heisenberg Hamiltonian. We consider optimization of the transfer
process applying optimal control techniques. We discuss a realistic
experimental implementation using cold atomic gases confined in deep optical
lattices.Comment: 14 pages, 6 figures, to be published in New J. Phy
A multilayer service data acquisition and operation system for oceanographic ships and instrumentation networks
A new Data Acquisition and Operation System for Oceanographic ships
and Instrumentation Networks has been developed by the Marine Technology Unit
of the Spanish Research Vessels for their networked remote acquisition platforms.
The new system built over LABVIR project background follows a Service Oriented Architecture
to allow expandable access to acquired data in real time and to archived
data. Several Data layers are implemented to allow data access from the more common
tools and formats used in marine sciences.Peer Reviewe
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