6,606 research outputs found
Directed transport of Brownian particles in a double symmetric potential
We investigate the dynamics of Brownian particles in internal state-
dependent symmetric and periodic potentials. Although no space or time symmetry
of the Hamiltonian is broken, we show that directed transport can appear. We
demonstrate that the directed motion is induced by breaking the symmetry of the
transition rates between the potentials when these are spatially shifted.
Finally, we discuss the possibility of realizing our model in a system of cold
particles trapped in optical lattices.Comment: to appear in Physical Review
Phase-control of directed diffusion in a symmetric optical lattice
We demonstrate the phenomenon of directed diffusion in a symmetric periodic
potential. This has been realized with cold atoms in a one-dimensional
dissipative optical lattice. The stochastic process of optical pumping leads to
a diffusive dynamics of the atoms through the periodic structure, while a
zero-mean force which breaks the temporal symmetry of the system is applied by
phase-modulating one of the lattice beams. The atoms are set into directed
motion as a result of the breaking of the temporal symmetry of the system
Rayleigh scattering and atomic dynamics in dissipative optical lattices
We investigate Rayleigh scattering in dissipative optical lattices. In particular, following recent proposals [S. Guibal et al., Phys. Rev. Lett. 78, 4709 (1997); C. Jurczak et al., Phys. Rev. Lett. 77, 1727 (1996)], we study whether the Rayleigh resonance originates from the diffraction on a density grating and is therefore a probe of transport of atoms in optical lattices. It turns out that this is not the case: the Rayleigh line is instead a measure of the cooling rate, while spatial diffusion contributes to the scattering spectrum with a much broader resonance
Localization from quantum interference in one-dimensional disordered potentials
We show that the tails of the asymptotic density distribution of a quantum
wave packet that localizes in the the presence of random or quasiperiodic
disorder can be described by the diagonal term of the projection over the
eingenstates of the disordered potential. This is equivalent of assuming a
phase randomization of the off-diagonal/interference terms. We demonstrate
these results through numerical calculations of the dynamics of ultracold atoms
in the one-dimensional speckle and quasiperiodic potentials used in the recent
experiments that lead to the observation of Anderson localization for matter
waves [Billy et al., Nature 453, 891 (2008); Roati et al., Nature 453, 895
(2008)]. For the quasiperiodic case, we also discuss the implications of using
continuos or discrete models.Comment: 5 pages, 3 figures; minor changes, references update
Banda sonora de la publicidad televisiva española: formas, géneros y estilos musicales.
La presente investigación es
fruto de un anterior trabajo teórico
presentado en esta misma revista en
2009, La música en la comunicación
publicitaria. Ahora, el estudio avanza
presentando los resultados de una investigación
sobre 2.346 anuncios televisivos
en distintas cadenas nacionales
españolas en horario prime-time
durante 2009. En España, 9 de cada
10 espots televisivos cuentan con
algún tipo de componente musical en
su formato final, resultado similar a
estudios realizados en distintos países
y en distintas épocas. Donde existen
sensibles diferencias es en la forma
musical utilizada para comunicar
el producto así como en los estilos y
géneros musicales en los que se basan
dichas formas musicales y su relación
con el tipo de producto y anunciante
Localized and extended states in a disordered trap
We study Anderson localization in a disordered potential combined with an
inhomogeneous trap. We show that the spectrum displays both localized and
extended states, which coexist at intermediate energies. In the region of
coexistence, we find that the extended states result from confinement by the
trap and are weakly affected by the disorder. Conversely, the localized states
correspond to eigenstates of the disordered potential, which are only affected
by the trap via an inhomogeneous energy shift. These results are relevant to
disordered quantum gases and we propose a realistic scheme to observe the
coexistence of localized and extended states in these systems.Comment: Published versio
A model of dispersive transport across sharp interfaces between porous materials
Recent laboratory experiments on solute migration in composite porous columns
have shown an asymmetry in the solute arrival time upon reversal of the flow
direction, which is not explained by current paradigms of transport. In this
work, we propose a definition for the solute flux across sharp interfaces and
explore the underlying microscopic particle dynamics by applying Monte Carlo
simulation. Our results are consistent with previous experimental findings and
explain the observed transport asymmetry. An interpretation of the proposed
physical mechanism in terms of a flux rectification is also provided. The
approach is quite general and can be extended to other situations involving
transport across sharp interfaces.Comment: 4 pages, 4 figure
Inclusive Advertising through the Soundtrack: Insights from People with Visual Impairments
Today’s audiovisual advertising is heard more than seen, as many viewers feel overloaded with visual information or engage in multitasking while viewing. The fact that many viewers are not watching the screen is a problem that should concern the entire advertising industry. Are there technological solutions that enable us to hear what we do not see? Audio description (AD) is an established option in the field of visual impairment, but is it the only option to make advertising accessible to people who are not looking at the images? This study considers these questions, applying a methodology based on Qualitative Data Analysis (QDA) and combining Grounded Theory and the focus group model as a data collection technique. Three focus groups ⎼two comprising people with a visual disability and the third made up of people without one explored the question of whether contemporary advertising has been drifting towards an exclusion of spectators with visual impairment. Participant responses were split between the view that commercials should incorporate AD but with clear improvements that take viewer opinion into account and the belief that advertising should return to its origins and make its soundtrack more explicit, perhaps rendering AD unnecessary
Demonstration of a controllable three-dimensional Brownian motor in symmetric potentials
We demonstrate a Brownian motor, based on cold atoms in optical lattices,
where isotropic random fluctuations are rectified in order to induce controlled
atomic motion in arbitrary directions. In contrast to earlier demonstrations of
ratchet effects, our Brownian motor operates in potentials that are spatially
and temporally symmetric, but where spatiotemporal symmetry is broken by a
phase shift between the potentials and asymmetric transfer rates between them.
The Brownian motor is demonstrated in three dimensions and the noise-induced
drift is controllable in our system.Comment: 5 pages, 4 figure
Tailoring Anderson localization by disorder correlations in 1D speckle potentials
We study Anderson localization of single particles in continuous, correlated,
one-dimensional disordered potentials. We show that tailored correlations can
completely change the energy-dependence of the localization length. By
considering two suitable models of disorder, we explicitly show that disorder
correlations can lead to a nonmonotonic behavior of the localization length
versus energy. Numerical calculations performed within the transfer-matrix
approach and analytical calculations performed within the phase formalism up to
order three show excellent agreement and demonstrate the effect. We finally
show how the nonmonotonic behavior of the localization length with energy can
be observed using expanding ultracold-atom gases
- …