2,700 research outputs found
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
A new type of carbon resistance thermometer with excellent thermal contact at millikelvin temperatures
Using a new brand of commercially available carbon resistor we built a
cryogenic thermometer with an extremely good thermal contact to its thermal
environment. Because of its superior thermal contact the thermometer is
insensitive to low levels of spurious radio frequency heating. We calibrated
our thermometer down to 5mK using a quartz tuning fork He-3 viscometer and
measured its thermal resistance and thermal response time.Comment: 5 pages, 4 figure
Comparison of Bond Character in Hydrocarbons and Fullerenes
We present a comparison of the bond polarizabilities for carbon-carbon bonds
in hydrocarbons and fullerenes, using two different models for the fullerene
Raman spectrum and the results of Raman measurements on ethane and ethylene. We
find that the polarizabilities for single bonds in fullerenes and hydrocarbons
compare well, while the double bonds in fullerenes have greater polarizability
than in ethylene.Comment: 7 pages, no figures, uses RevTeX. (To appear in Phys. Rev. B.
Reflection, radiation and interference for black holes
Black holes are capable of reflection: there is a finite probability for any
particle that approaches the event horizon to bounce back. The albedo of the
black hole depends on its temperature and the energy of the incoming particle.
The reflection shares its physical origins with the Hawking process of
radiation, both of them arise as consequences of the mixing of the incoming and
outgoing waves that takes place on the event horizon.Comment: 10 pages, 1 figure, Revte
Theory of Melting and the Optical Properties of Gold/DNA Nanocomposites
We describe a simple model for the melting and optical properties of a
DNA/gold nanoparticle aggregate. The optical properties at fixed wavelength
change dramatically at the melting transition, which is found to be higher and
narrower in temperature for larger particles, and much sharper than that of an
isolated DNA link. All these features are in agreement with available
experiments. The aggregate is modeled as a cluster of gold nanoparticles on a
periodic lattice connected by DNA bonds, and the extinction coefficient is
computed using the discrete dipole approximation. Melting takes place as an
increasing number of these bonds break with increasing temperature. The melting
temperature corresponds approximately to the bond percolation threshold.Comment: 5 pages, 4 figure. To be published in Phys. Rev.
Variational principle and a perturbative solution of non-linear string equations in curved space
String dynamics in a curved space-time is studied on the basis of an action
functional including a small parameter of rescaled tension
, where is a metric parametrizing
constant. A rescaled slow worldsheet time is introduced, and
general covariant non-linear string equation are derived.
It is shown that in the first order of an -expansion these
equations are reduced to the known equation for geodesic derivation but
complemented by a string oscillatory term. These equations are solved for the
de Sitter and Friedmann -Robertson-Walker spaces. The primary string
constraints are found to be split into a chain of perturbative constraints and
their conservation and consistency are proved. It is established that in the
proposed realization of the perturbative approach the string dynamics in the de
Sitter space is stable for a large Hubble constant .Comment: 22 pages, LATEX, no figure
Elements of String Cosmology
Aspects of string cosmology for critical and non-critical strings are
discussed emphasizing the necessity to account for the dilaton dynamics for a
proper incorporation of ``large - small" duality. This drastically modifies the
intuition one has with Einstein's gravity. For example winding modes, even
though contribute to energy density, oppose expansion and if not annihilated
will stop the expansion. Moreover we find that the radiation dominated era of
the standard cosmology emerges quite naturally in string cosmology. Our
analysis of non-critical string cosmology provides a reinterpretation of the
(universal cover of the) recently studied two dimensional black hole solution
as a conformal realization of cosmological solutions found previously by
Mueller.Comment: 34 page
Single-atom entropy squeezing for two two-level atoms interacting with a single-mode radiation field
In this paper we consider a system of two two-level atoms interacting with a
single-mode quantized electromagnetic field in a lossless resonant cavity via
-photon-transition mechanism. The field and the atoms are initially prepared
in the coherent state and the excited atomic states, respectively. For this
system we investigate the entropy squeezing, the atomic variances, the von
Neumann entropy and the atomic inversions for the single-atom case. We show
that the more the number of the parties in the system the less the amounts of
the nonclassical effects exhibited in the entropy squeezing.
The entropy squeezing can give information on the corresponding von Neumann
entropy. Also the nonclassical effects obtained form the asymmetric atoms are
greater than those obtained form the symmetric atoms. Finally, the entropy
squeezing gives better information than the atomic variances only for the
asymmetric atoms.Comment: 15 pages, 4 figures, comments are most welcom
Competition of Mesoscales and Crossover to Tricriticality in Polymer Solutions
We show that the approach to asymptotic fluctuation-induced critical behavior
in polymer solutions is governed by a competition between a correlation length
diverging at the critical point and an additional mesoscopic length-scale, the
radius of gyration. Accurate light-scattering experiments on polystyrene
solutions in cyclohexane with polymer molecular weights ranging from 200,000 up
to 11.4 million clearly demonstrate a crossover between two universal regimes:
a regime with Ising asymptotic critical behavior, where the correlation length
prevails, and a regime with tricritical theta-point behavior determined by a
mesoscopic polymer-chain length.Comment: 4 pages in RevTeX with 4 figure
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