5,210 research outputs found
Logarithmic roughening in a growth process with edge evaporation
Roughening transitions are often characterized by unusual scaling properties.
As an example we investigate the roughening transition in a solid-on-solid
growth process with edge evaporation [Phys. Rev. Lett. 76, 2746 (1996)], where
the interface is known to roughen logarithmically with time. Performing
high-precision simulations we find appropriate scaling forms for various
quantities. Moreover we present a simple approximation explaining why the
interface roughens logarithmically.Comment: revtex, 6 pages, 7 eps figure
Replica field theory for a polymer in random media
In this paper we revisit the problem of a (non self-avoiding) polymer chain
in a random medium which was previously investigated by Edwards and Muthukumar
(EM). As noticed by Cates and Ball (CB) there is a discrepancy between the
predictions of the replica calculation of EM and the expectation that in an
infinite medium the quenched and annealed results should coincide (for a chain
that is free to move) and a long polymer should always collapse. CB argued that
only in a finite volume one might see a ``localization transition'' (or
crossover) from a stretched to a collapsed chain in three spatial dimensions.
Here we carry out the replica calculation in the presence of an additional
confining harmonic potential that mimics the effect of a finite volume. Using a
variational scheme with five variational parameters we derive analytically for
d<4 the result R~(g |ln \mu|)^{-1/(4-d)} ~(g lnV)^{-1/(4-d)}, where R is the
radius of gyration, g is the strength of the disorder, \mu is the spring
constant associated with the confining potential and V is the associated
effective volume of the system. Thus the EM result is recovered with their
constant replaced by ln(V) as argued by CB. We see that in the strict infinite
volume limit the polymer always collapses, but for finite volume a transition
from a stretched to a collapsed form might be observed as a function of the
strength of the disorder. For d<2 and for large
V>V'~exp[g^(2/(2-d))L^((4-d)/(2-d))] the annealed results are recovered and
R~(Lg)^(1/(d-2)), where L is the length of the polymer. Hence the polymer also
collapses in the large L limit. The 1-step replica symmetry breaking solution
is crucial for obtaining the above results.Comment: Revtex, 32 page
Energy Spectrum and Turbulent Scales in a Plane Air Jet
The energy spectra and longitudinal length scales measured in a free plane jet are presented. The actual convective velocity was used in determining the scales. The results show a universal spectral distribution along the axis but no obvious similarity in the large scale motion off the axis. The results are limited to x/D \u3c 60. The measured scales suggest a noticeable increase of the microscale along the lateral coordinate but an essentially constant value along the axis. However the macroscales, increasing linearly along the axis do not show any similarity off the axis
Implementation of the strongly pronounced non-linear viscoelasticity of an incompressible filled rubber
Filled rubber materials regularly show a pronounced non-linear viscoelasticity with very long relaxation times. In this contribution, a phenomenological description for an incompressible carbon black-filled EPDM (ethylene propylene diene monomer) is given, which also shows the abovementioned characteristic behaviour. In order to represent the non-linear viscoelastic material, the relaxation times of the model are chosen not as constant material parameters but as process-dependent functions.
This contribution presents two different realisations of the model’s implementation. At first, this work provides an implementation of the material model, which is able to describe complex geometries and loading conditions. In this realisation, the three-dimensional model is implemented in the open source finite element library deal.II for finite deformations. Hence, real applications can be represented. In an alternative numerical solution, the model is reduced to the single case of uniaxial tension. The model is simplified to scalar equations, which are quite easy to handle for the implementation. This procedure provides a more simple identification process, but it presents the roblem that the model character is extremely restricted for the individual case of uniaxial tension.
For the numerical realisation, at first, special attention has to be turned on the determination of the inelastic part of the kinematics. A detailed evaluation of the necessary evolution equations is provided in this contribution. Finally, he results of the different implementations are compared with respect to different loading conditions, like relaxation tests or cyclic loading
The Stellar Populations and Evolution of Lyman Break Galaxies
Using deep near-IR and optical observations of the HDF-N from the HST NICMOS
and WFPC2 and from the ground, we examine the spectral energy distributions
(SEDs) of Lyman break galaxies (LBGs) at 2.0 < z < 3.5. The UV-to-optical
rest-frame SEDs of the galaxies are much bluer than those of present-day spiral
and elliptical galaxies, and are generally similar to those of local starburst
galaxies with modest amounts of reddening. We use stellar population synthesis
models to study the properties of the stars that dominate the light from LBGs.
Under the assumption that the star-formation rate is continuous or decreasing
with time, the best-fitting models provide a lower bound on the LBG mass
estimates. LBGs with ``L*'' UV luminosities are estimated to have minimum
stellar masses ~ 10^10 solar masses, or roughly 1/10th that of a present-day L*
galaxy. By considering the effects of a second component of maximally-old
stars, we set an upper bound on the stellar masses that is ~ 3-8 times the
minimum estimate. We find only loose constraints on the individual galaxy ages,
extinction, metallicities, initial mass functions, and prior star-formation
histories. We find no galaxies whose SEDs are consistent with young (< 10^8
yr), dust-free objects, which suggests that LBGs are not dominated by ``first
generation'' stars, and that such objects are rare at these redshifts. We also
find that the typical ages for the observed star-formation events are
significantly younger than the time interval covered by this redshift range (~
1.5 Gyr). From this, and from the relative absence of candidates for quiescent,
non-star-forming galaxies at these redshifts in the NICMOS data, we suggest
that star formation in LBGs may be recurrent, with short duty cycles and a
timescale between star-formation events of < 1 Gyr. [Abridged]Comment: LaTeX, 37 pages, 21 figures. Accepted for publication in the
Astrophysical Journa
Lorentz and CPT Invariance Violation In High-Energy Neutrinos
High-energy neutrino astronomy will be capable of observing particles at both
extremely high energies and over extremely long baselines. These features make
such experiments highly sensitive to the effects of CPT and Lorentz violation.
In this article, we review the theoretical foundation and motivation for CPT
and Lorentz violating effects, and then go on to discuss the related
phenomenology within the neutrino sector. We describe several signatures which
might be used to identify the presence of CPT or Lorentz violation in next
generation neutrino telescopes and cosmic ray experiments. In many cases,
high-energy neutrino experiments can test for CPT and Lorentz violation effects
with much greater precision than other techniques.Comment: 27 pages, 8 figure
Localization of a polymer in random media: Relation to the localization of a quantum particle
In this paper we consider in detail the connection between the problem of a
polymer in a random medium and that of a quantum particle in a random
potential. We are interested in a system of finite volume where the polymer is
known to be {\it localized} inside a low minimum of the potential. We show how
the end-to-end distance of a polymer which is free to move can be obtained from
the density of states of the quantum particle using extreme value statistics.
We give a physical interpretation to the recently discovered one-step
replica-symmetry-breaking solution for the polymer (Phys. Rev. E{\bf 61}, 1729
(2000)) in terms of the statistics of localized tail states. Numerical
solutions of the variational equations for chains of different length are
performed and compared with quenched averages computed directly by using the
eigenfunctions and eigenenergies of the Schr\"odinger equation for a particle
in a one-dimensional random potential. The quantities investigated are the
radius of gyration of a free gaussian chain, its mean square distance from the
origin and the end-to-end distance of a tethered chain. The probability
distribution for the position of the chain is also investigated. The glassiness
of the system is explained and is estimated from the variance of the measured
quantities.Comment: RevTex, 44 pages, 13 figure
Magnetism and local distortions near carbon impurity in -iron
Local perturbations of crystal and magnetic structure of -iron near
carbon interstitial impurity is investigated by {\it ab initio} electronic
structure calculations. It is shown that the carbon impurity creates locally a
region of ferromagnetic ordering with substantial tetragonal distortions.
Exchange integrals and solution enthalpy are calculated, the latter being in a
very good agreement with experimental data. Effect of the local distortions on
the carbon-carbon interactions in -iron is discussed.Comment: 4 pages 3 figures. Final version, accepted to Phys.Rev. Let
Enhancing image contrast using coherent states and photon number resolving detectors
We experimentally map the transverse profile of diffraction-limited beams
using photon-number-resolving detectors. We observe strong compression of
diffracted beam profiles for high detected photon number. This effect leads to
higher contrast than a conventional irradiance profile between two Airy
disk-beams separated by the Rayleigh criterion.Comment: 7 pages, 3 figures, accepted for publication in Optics Expres
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