1,159 research outputs found
Distributional extensions of Carollia castanea and Micronycteris minuta from Guatemala, Central America
Field expeditions in 2011 that inventoried the terrestrial vertebrate fauna of two wildlife protected areas in the tropical Caribbean of Guatemala have produced the first confirmed records of two bats for the country: the white-bellied big-eared bat, Micronycteris (Schizonycteris) minuta (Gervais 1856) and the Chesnut short-tailed bat Carollia castanea H. Allen, 1890, both of neotropical distribution and with their current northern limit at Lancetilla, Honduras. The record of M. minuta at Sierra de Caral, Guatemala extends the range of this species 137 km to the west, and the record of C. castanea at Cerro San Gil extends its range 147 km to the west
Metallo-dielectric core-shell nanospheres as building blocks for optical three-dimensional isotropic negative-index metamaterials
Materials showing electromagnetic properties that are not attainable in naturally occurring media, so-called metamaterials, have been lately, and still are, among the most active topics in optical and materials physics and engineering. Among these properties, one of the most attractive ones is the subdiffraction resolving capability predicted for media having an index of refraction of -1. Here, we propose a fully three-dimensional, isotropic metamaterial with strong electric and magnetic responses in the optical regime, based on spherical metallo-dielectric core-shell nanospheres. The magnetic response stems from the lowest, magnetic-dipole resonance of the dielectric shell with a high refractive index, and can be tuned to coincide with the plasmon resonance of the metal core, responsible for the electric response. Since the response does not originate from coupling between structures, no particular periodic arrangement needs to be imposed. Moreover, due to the geometry of the constituents, the metamaterial is intrinsically isotropic and polarization independent. It could be realized with current fabrication techniques with materials such as silver (core) and silicon or germanium (shell). For these particular realistic designs, the metamaterials present a negative index in the range of 1.2-1.55οm. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.The authors acknowledge support from the Spain Ministerio de Ciencia e Innovacion´ through the Consolider-Ingenio project EMET (CSD2008-00066) and NANOPLAS (FIS2009- 11264) and from the Comunidad de Madrid (grant MICROSERES P2009/TIC-1476). RP-D acknowledges support from CSIC through a JAE-Pre grantPeer Reviewe
Fano-like interference of plasmon resonances at a single rod-shaped nanoantenna
Single metallic nanorods acting as half-wave antennas in the optical range
exhibit an asymmetric, multi-resonant scattering spectrum that strongly depends
on both their length and dielectric properties. Here we show that such spectral
features can be easily understood in terms of Fano-like interference between
adjacent plasmon resonances. On the basis of analytical and numerical results
for different geometries, we demonstrate that Fano resonances may appear for
such single-particle nanoantennas provided that interacting resonances overlap
in both spatial and frequency domains.Comment: 18 pages, 9 figure
Noncommutative 6D Gauge Higgs Unification Models
The influence of higher dimensions in noncommutative field theories is
considered. For this purpose, we analyze the bosonic sector of a recently
proposed 6 dimensional SU(3) orbifold model for the electroweak interactions.
The corresponding noncommutative theory is constructed by means of the
Seiberg-Witten map in 6D. We find in the reduced bosonic interactions in 4D
theory, couplings which are new with respect to other known 4D noncommutative
formulations of the Standard Model using the Seiberg-Witten map.
Phenomenological implications due to the noncommutativity of extra dimensions
are explored. In particular, assuming that the commutative model leads to the
standard model values, a bound -5.63 10^{-8} GeV^{-2}< theta <1.06
10^{-7}GeV^{-2} on the corresponding noncommutativity scale is derived from
current experimental constraints on the S and T oblique parameters. This bound
is used to predict a possibly significant impact of noncommutativity effects of
extra dimensions on the rare Higgs boson decay H-> gamma gamma.Comment: Latex file, 11 pages, 1 figur
Effect of disorder on the vortex-lattice melting transition
We use a three dimensional stacked triangular network of Josephson junctions
as a model for the study of vortex structure in the mixed state of high Tc
superconductors. We show that the addition of disorder destroys the first order
melting transition occurring for clean samples. The melting transition splits
in two different (continuous) transitions, ocurring at temperatures Ti and Tp
(>Ti). At Ti the perpendicular-to-field superconductivity is lost, and at Tp
the parallel-to-field superconductivity is lost. These results agree well with
recent experiments in YBaCuO.Comment: 4 pages + 2 figure
Cultural distance and risk perception of Brazil according to the official travel advices
La percepción de riesgo del turista es uno de los elementos que más influyen en la elección del
destino a viajar. Esta percepción puede variar de acuerdo a la cultura del país de quien toma la decisión. En
este trabajo se valora la influencia de las culturas nacionales en la percepción de riesgo de un destino turístico
identificando las dimensiones de riesgo más importantes. Se realiza un análisis de contenido textual de las
recomendaciones de viaje sobre Brasil emitidas por los gobiernos de Australia, España, Estados Unidos y
Reino Unido. Se observa que la percepción de riesgo experimenta importantes diferencias de un país a otro,
tanto en su categoría como en su intensidad. Estas diferencias guardan estrecha relación con la distancia
cultural, países más cercanos culturalmente tienden a ser más tolerantes con el riesgo del país de destino.
Entender estas diferencias e identificar su magnitud es clave para aplicar políticas correctas de promoción
adaptadas al país de procedencia del viajero.The perception of risk is one of the elements with the greatest influence in the choice of destination
to travel. This perception may vary according to the culture of the country where the decision is made. In this
work, we identify the most important risk dimensions in order to assess the influence of national cultures on
the perception of risk of a given tourist destination. Specifically, we conducted a thematic content analysis
of the travel recommendations on Brazil issued by the governments of Australia, Spain, the United States
and the United Kingdom. It is observed that the perception of risk experiences important differences from
one country to another, both in its category and in its intensity. These differences are closely related to
cultural distance; i.e. culturally closer countries tend to be more tolerant of possible risks in the destination.
Understanding these differences and identifying their magnitude are key to applying correct promotion
policies adapted to the country of origin of tourists
Linearizing Control Based on Adaptive Observer for Anaerobic Continuous Sulphate Reducing Bioreactors with Unknown Kinetics
Anaerobic reactors are a typical example of processes that exhibit non-linear behavior and, also time varying parameters; hence their operation is known to be difficult to model and control. In contrast to modeling approaches, in practice linear controllers are widely employed for industrial processes because of their easy implementation and manipulation by plant operators; nevertheless linear approaches are not robust when the operating conditions
change suddenly and/or strong disturbances are present. In order to introduce robust controllers to these processes, this paper addresses the tracking problem for the substrate (sulphate) control in a class of continuous bioreactors. An experimentally corroborated bioreactor model serves as benchmark problem for advanced non-linear analysis and control techniques; taking into account system non-linearities, stability and performance objectives over large operating regions. It is considered that, as it is common in practice,
the rate of substrate consumption exhibits uncertainty. Results show that the proposed controller exhibits better dynamic performance than a classical Proportional-Integral control tuned using the methodology suggested by Internal Model Control
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