1,463 research outputs found
Finite sampling effects on generalized fluctuation-dissipation relations for steady states
We study the effects of the finite number of experimental data on the
computation of a generalized fluctuation-dissipation relation around a
nonequilibrium steady state of a Brownian particle in a toroidal optical trap.
We show that the finite sampling has two different effects, which can give rise
to a poor estimate of the linear response function. The first concerns the
accessibility of the generalized fluctuation-dissipation relation due to the
finite number of actual perturbations imposed to the control parameter. The
second concerns the propagation of the error made at the initial sampling of
the external perturbation of the system. This can be highly enhanced by
introducing an estimator which corrects the error of the initial sampled
condition. When these two effects are taken into account in the data analysis,
the generalized fluctuation-dissipation relation is verified experimentally
Temperature Relaxation in Hot Dense Hydrogen
Temperature equilibration of hydrogen is studied for conditions relevant to
inertial confinement fusion. New molecular-dynamics simulations and results
from quantum many-body theory are compared with Landau-Spitzer (LS) predictions
for temperatures T from 50 eV to 5000 eV, and densities with Wigner-Seitz radii
r_s = 1.0 and 0.5. The relaxation is slower than the LS result, even for
temperatures in the keV range, but converges to agreement in the high-T limit.Comment: 4 pages PRL style, two figure
Rotational and vibrational spectra of quantum rings
One can confine the two-dimensional electron gas in semiconductor
heterostructures electrostatically or by etching techniques such that a small
electron island is formed. These man-made ``artificial atoms'' provide the
experimental realization of a text-book example of many-particle physics: a
finite number of quantum particles in a trap. Much effort was spent on making
such "quantum dots" smaller and going from the mesoscopic to the quantum
regime. Far-reaching analogies to the physics of atoms, nuclei or metal
clusters were obvious from the very beginning: The concepts of shell structure
and Hund's rules were found to apply -- just as in real atoms! In this Letter,
we report the discovery that electrons confined in ring-shaped quantum dots
form rather rigid molecules with antiferromagnetic order in the ground state.
This can be seen best from an analysis of the rotational and vibrational
excitations
Influence of the Barrier Shape on Resonant Activation
The escape of a Brownian particle over a dichotomously fluctuating barrier is
investigated for various shapes of the barrier. The problem of resonant
activation is revisited with the attention on the effect of the barrier shape
on optimal value of the mean escape time in the system. The characteristic
features of resonant behavior are analyzed for barriers switching either
between different heights, or "on" and "off" positions. PACS number(s):
05.10-a, 02.50.-r, 82.20.-wj.Comment: 7 pages, 8 figures, RevTex4. Manuscript has been revised and
enhanced. Pictures have been made more clear and some of them have been
cancelled. Additional references have been added. The paper has been
submitted to Phys. Rev.
Interaction of molecular motors can enhance their efficiency
Particles moving in oscillating potential with broken mirror symmetry are
considered. We calculate their energetic efficiency, when acting as molecular
motors carrying a load against external force. It is shown that interaction
between particles enhances the efficiency in wide range of parameters. Possible
consequences for artificial molecular motors are discussed.Comment: 6 pages, 8 figure
Ground state energies of quantum dots in high magnetic fields: A new approach
We present a new method for calculating ground state properties of quantum
dots in high magnetic fields. It takes into account the equilibrium positions
of electrons in a Wigner cluster to minimize the interaction energy in the high
field limit. Assuming perfect spin alignment the many-body trial function is a
single Slater determinant of overlapping oscillator functions from the lowest
Landau level centered at and near the classical equilibrium positions. We
obtain an analytic expression for the ground state energy and present numerical
results for up to N=40.Comment: 4 pages, including 2 figures, contribution to the Proceedings of
EP2DS-14, submitted to Physica
Surmounting Oscillating Barriers
Thermally activated escape over a potential barrier in the presence of
periodic driving is considered. By means of novel time-dependent path-integral
methods we derive asymptotically exact weak-noise expressions for both the
instantaneous and the time-averaged escape rate. The agreement with accurate
numerical results is excellent over a wide range of driving strengths and
driving frequencies.Comment: 4 pages, 4 figure
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