5,481 research outputs found
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
Anderson localization of matter waves in tailored disordered potentials
We show that, in contrast to immediate intuition, Anderson localization of
noninteracting particles induced by a disordered potential in free space can
increase (i.e., the localization length can decrease) when the particle energy
increases, for appropriately tailored disorder correlations. We predict the
effect in one, two, and three dimensions, and propose a simple method to
observe it using ultracold atoms placed in optical disorder. The increase of
localization with the particle energy can serve to discriminate quantum versus
classical localization
Exponential splitting of bound states in a waveguide with a pair of distant windows
We consider Laplacian in a straight planar strip with Dirichlet boundary
which has two Neumann ``windows'' of the same length the centers of which are
apart, and study the asymptotic behaviour of the discrete spectrum as
. It is shown that there are pairs of eigenvalues around each
isolated eigenvalue of a single-window strip and their distances vanish
exponentially in the limit . We derive an asymptotic expansion also
in the case where a single window gives rise to a threshold resonance which the
presence of the other window turns into a single isolated eigenvalue
International shipping of fumonisins from maize extracts on C\u3csub\u3e18\u3c/sub\u3e sorbent
Fumonisins are mycotoxins found in maize. In developing countries, the resources required for analysis are often lacking, and the shipping of maize between countries can be difficult since the importation of plant materials requires permits/ inspection to prevent the entry of pests that frequently infest maize. A simple, safe and legal method for shipping maize extracts to the USA was needed to conduct a survey of fumonisins in Central America. The objective was to develop a method for isolating and shipping maize extracts for fumonisin analysis so as to facilitate a survey of fumonisin exposure. The results indicate that fumonisins in acetonitrile:water extracts of maize can be isolated on C18 cartridges, held for at least 3 days at 22 °C and then an additional 4 days at 4 °C before elution and analysis with no losses. This method allows the importation and analysis of maize samples from foreign locations without complications from international safety concerns
Quasi-localization and quasi-mobility edge for light atoms mixed with heavy ones
A mixture of light and heavy atoms is considered. We study the kinetics of
the light atoms, scattered by the heavy ones, the latter undergoing slow
diffusive motion. In three-dimensional space we claim the existence of a
crossover region (in energy), which separates the states of the light atoms
with fast diffusion and the states with slow diffusion; the latter is
determined by the dephasing time. For the two dimensional case we have a
transition between weak localization, observed when the dephasing length is
less than the localization length (calculated for static scatterers), and
strong localization observed in the opposite case.Comment: LaTeX, 5 pages, 3 figures. The manuscript has been changed following
the Referees' constructive criticism and is accepted for publication in EPJ
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
Toughening and asymmetry in peeling of heterogeneous adhesives
The effective adhesive properties of heterogeneous thin films are
characterized through a combined experimental and theoretical investigation. By
bridging scales, we show how variations of elastic or adhesive properties at
the microscale can significantly affect the effective peeling behavior of the
adhesive at the macroscale. Our study reveals three elementary mechanisms in
heterogeneous systems involving front propagation: (i) patterning the elastic
bending stiffness of the film produces fluctuations of the driving force
resulting in dramatically enhanced resistance to peeling; (ii) optimized
arrangements of pinning sites with large adhesion energy are shown to control
the effective system resistance, allowing the design of highly anisotropic and
asymmetric adhesives; (iii) heterogeneities of both types result in front
motion instabilities producing sudden energy releases that increase the overall
adhesion energy. These findings open potentially new avenues for the design of
thin films with improved adhesion properties, and motivate new investigation of
other phenomena involving front propagation.Comment: Physical Review Letters (2012)
On Random Field Induced Ordering in the Classical XY Model
Consider the classical XY model in a weak random external field pointing
along the axis with strength . We study the behavior of this
model as the range of the interaction is varied. We prove that in any dimension
and for all sufficiently small, there is a range
so that whenever the inverse temperature is larger than
some , there is strong residual ordering along the
direction.Comment: 30 page
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