14,360 research outputs found
Surface scattering analysis of phonon transport in the quantum limit using an elastic model
We have investigated the effect on phonon energy transport in mesoscopic
systems and the reduction in the thermal conductance in the quantum limit due
to phonon scattering by surface roughness using full 3-dimensional elasticity
theory for an elastic beam with a rectangular cross-section. At low frequencies
we find power laws for the scattering coefficients that are strongly mode
dependent, and different from the dependence, deriving from
Rayleigh scattering of scalar waves, that is often assumed. The scattering
gives contributions to the reduction in thermal conductance with the same power
laws. At higher frequencies the scattering coefficients becomes large at the
onset frequency of each mode due to the flat dispersion here. We use our
results to attempt a quantitative understanding of the suppression of the
thermal conductance from the universal value observed in experiment.Comment: 27 pages, 13 figure
Domain Coarsening in Systems Far from Equilibrium
The growth of domains of stripes evolving from random initial conditions is
studied in numerical simulations of models of systems far from equilibrium such
as Rayleigh-Benard convection. The scaling of the size of the domains deduced
from the inverse width of the Fourier spectrum is studied for both potential
and nonpotential models. The morphology of the domains and the defect
structures are however quite different in the two cases, and evidence is
presented for a second length scale in the nonpotential case.Comment: 11 pages, RevTeX; 3 uufiles encoded postscript figures appende
Defect Dynamics for Spiral Chaos in Rayleigh-Benard Convection
A theory of the novel spiral chaos state recently observed in Rayleigh-Benard
convection is proposed in terms of the importance of invasive defects i.e
defects that through their intrinsic dynamics expand to take over the system.
The motion of the spiral defects is shown to be dominated by wave vector
frustration, rather than a rotational motion driven by a vertical vorticity
field. This leads to a continuum of spiral frequencies, and a spiral may rotate
in either sense depending on the wave vector of its local environment. Results
of extensive numerical work on equations modelling the convection system
provide some confirmation of these ideas.Comment: Revtex (15 pages) with 4 encoded Postscript figures appende
Antiferromagnetic phase transition in a nonequilibrium lattice of Rydberg atoms
We study a driven-dissipative system of atoms in the presence of laser
excitation to a Rydberg state and spontaneous emission. The atoms interact via
the blockade effect, whereby an atom in the Rydberg state shifts the Rydberg
level of neighboring atoms. We use mean-field theory to study how the Rydberg
population varies in space. As the laser frequency changes, there is a
continuous transition between the uniform and antiferromagnetic phases. The
nonequilibrium nature also leads to a novel oscillatory phase and bistability
between the uniform and antiferromagnetic phases.Comment: 4 pages + appendi
Pinning control of spatiotemporal chaos
Linear control theory is used to develop an improved localized control scheme for spatially extended chaotic systems, which is applied to a coupled map lattice as an example. The optimal arrangement of the control sites is shown to depend on the symmetry properties of the system, while their minimal density depends on the strength of noise in the system. The method is shown to work in any region of parameter space and requires a significantly smaller number of controllers compared to the method proposed earlier by Hu and Qu [Phys. Rev. Lett. 72, 68 (1994)]. A nonlinear generalization of the method for a 1D lattice is also presented
Scattering of a Baseball by a Bat
A ball can be hit faster if it is projected without spin but it can be hit
farther if it is projected with backspin. Measurements are presented in this
paper of the tradeoff between speed and spin for a baseball impacting a
baseball bat. The results are inconsistent with a collision model in which the
ball rolls off the bat and instead imply tangential compliance in the ball, the
bat, or both. If the results are extrapolated to the higher speeds that are
typical of the game of baseball, they suggest that a curveball can be hit with
greater backspin than a fastball, but by an amount that is less than would be
the case in the absence of tangential compliance.Comment: Accepted for publication in American Journal of Physic
OPPORTUNITY COSTS, SHARE LEASING, AND PREVENTED PLANTING CLAIMS IN CROP INSURANCE
This paper determines whether the opportunity costs of share leasing and the share amounts of farmers/tenants affect the likelihood of submitting a prevented planting claim. Results from our probit analysis shows that lower opportunity costs of share leasing and higher farmer/tenant share amount can increase the probability of submitting a prevented planting. These results have potential implications for setting prevented planting buy-up rates and crop insurance compliance procedures.Risk and Uncertainty,
Spatiotemporal dynamics of quantum jumps with Rydberg atoms
We study the nonequilibrium dynamics of quantum jumps in a one-dimensional
chain of atoms. Each atom is driven on a strong transition to a short-lived
state and on a weak transition to a metastable state. We choose the metastable
state to be a Rydberg state so that when an atom jumps to the Rydberg state, it
inhibits or enhances jumps in the neighboring atoms. This leads to rich
spatiotemporal dynamics that are visible in the fluorescence of the strong
transition.Comment: 10 page
Comment on ``The linear instability of magnetic Taylor-Couette flow with Hall effect''
In the paper we comment on (R\"udiger & Shalybkov, Phys. Rev. E. 69, 016303
(2004) (RS)), the instability of the Taylor--Couette flow interacting with a
homogeneous background field subject to Hall effect is studied. We correct a
falsely generalizing interpretation of results presented there which could be
taken to disprove the existence of the Hall--drift induced magnetic instability
described in Rheinhardt and Geppert, Phys. Rev. Lett. 88, 101103. It is shown
that in contrast to what is suggested by RS, no additional shear flow is
necessary to enable such an instability with a non--potential magnetic
background field, whereas for a curl--free one it is. In the latter case, the
instabilities found in RS in situations where neither a hydrodynamic nor a
magneto--rotational instability exists are demonstrated to be most likely
magnetic instead of magnetohydrodynamic. Further, some minor inaccuracies are
clarified.Comment: 3 pages, 1 figure; accepted by Physical Review
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