4,238 research outputs found
Isabel\u27s Silent Partners: Seasonal and Secular Sea Level Change
Tidal conditions fail to explain a paradoxical similarity in water level extremes induced by Hurricane Isabel on 18 September 2003, and the 23 August 1933 storm of record at Hampton Roads, Virginia. Storm surge peaks occurred near astronomical high tide during both storms, but Isabel arrived during neap tides while tides during the 1933 storm were nearer to spring. In addition, Isabel produced a lesser storm surge, yet she yielded a storm tide, or high-water mark, roughly equal to that of the 1933 hurricane. The answer to the paradox lies in observed sea level—water level measured relative to the land—and its movement during the 70 years between these events. Water level analysis shows that the sea level change observed can be divided into three categories at three different time scales: daily (astronomical tides), monthly (seasonal change), and yearly (secular trend in sea level). At Hampton Roads, a secular rise rate of 4.25 mm⋅yr-1 (1.39 ft/century) predicted an increase of 29.8 cm in 70 years; mean sea level for the month of September stood an additional 21.9 cm above the annual mean for 2003. These numbers are comparable to the mean semirange of tide (37.0 cm) at Hampton Roads. Thus seasonal and secular change are both factors of key importance in evaluating storm tide risk at time scales attributable to major hurricanes (100 years). Adoption of a new vertical reference, projected monthly mean sea level, is proposed to facilitate their inclusion in storm tide predictions at decadal time scales.https://scholarworks.wm.edu/vimsbooks/1002/thumbnail.jp
A microscopic approach to nonlinear Reaction-Diffusion: the case of morphogen gradient formation
We develop a microscopic theory for reaction-difusion (R-D) processes based
on a generalization of Einstein's master equation with a reactive term and we
show how the mean field formulation leads to a generalized R-D equation with
non-classical solutions. For the -th order annihilation reaction
, we obtain a nonlinear reaction-diffusion equation
for which we discuss scaling and non-scaling formulations. We find steady
states with either solutions exhibiting long range power law behavior (for
) showing the relative dominance of sub-diffusion over reaction
effects in constrained systems, or conversely solutions (for )
with finite support of the concentration distribution describing situations
where diffusion is slow and extinction is fast. Theoretical results are
compared with experimental data for morphogen gradient formation.Comment: Article, 10 pages, 5 figure
State detection using coherent Raman repumping and two-color Raman transfers
We demonstrate state detection based on coherent Raman repumping and a
two-color Raman state transfer. The Raman coupling during detection selectively
eliminates unwanted dark states in the fluorescence cycle without compromising
the immunity of the desired dark state to off-resonant scattering. We
demonstrate this technique using where a combination of
Raman coupling and optical pumping leaves the
metastable state optically dark and immune to off-resonant scattering. All
other states are strongly coupled to the upper levels. We achieve a
single shot state-detection efficiency of in a
integration time, limited almost entirely by technical imperfections. Shelving
to the state before detection is performed via a two-color
Raman transfer with a fidelity of
Lattice gas with ``interaction potential''
We present an extension of a simple automaton model to incorporate non-local
interactions extending over a spatial range in lattice gases. {}From the
viewpoint of Statistical Mechanics, the lattice gas with interaction range may
serve as a prototype for non-ideal gas behavior. {}From the density
fluctuations correlation function, we obtain a quantity which is identified as
a potential of mean force. Equilibrium and transport properties are computed
theoretically and by numerical simulations to establish the validity of the
model at macroscopic scale.Comment: 12 pages LaTeX, figures available on demand ([email protected]
Finite Temperature Spectral Densities of Momentum and R-Charge Correlators in Yang Mills Theory
We compute spectral densities of momentum and R-charge correlators in thermal
Yang Mills at strong coupling using the AdS/CFT correspondence. For
and smaller, the spectral density differs markedly from
perturbation theory; there is no kinetic theory peak. For large , the
spectral density oscillates around the zero-temperature result with an
exponentially decreasing amplitude. Contrast this with QCD where the spectral
density of the current-current correlator approaches the zero temperature
result like . Despite these marked differences with perturbation
theory, in Euclidean space-time the correlators differ by only from
the free result. The implications for Lattice QCD measurements of transport are
discussed.Comment: 18 pages, 3 figure
Transport properties of dense dissipitive hard-sphere fluids for arbitrary energy loss models
The revised Enskog approximation for a fluid of hard spheres which lose
energy upon collision is discussed for the case that the energy is lost from
the normal component of the velocity at collision but is otherwise arbitrary.
Granular fluids with a velocity-dependent coefficient of restitution are an
important special case covered by this model. A normal solution to the Enskog
equation is developed using the Chapman-Enskog expansion. The lowest order
solution describes the general homogeneous cooling state and a generating
function formalism is introduced for the determination of the distribution
function. The first order solution, evaluated in the lowest Sonine
approximation, provides estimates for the transport coefficients for the
Navier-Stokes hydrodynamic description. All calculations are performed in an
arbitrary number of dimensions.Comment: 27 pages + 1 figur
Breakdown of Hydrodynamic Transport Theory in the Ordered Phase of Helimagnets
It is shown that strong fluctuations preclude a hydrodynamic description of
transport phenomena in helimagnets, such as MnSi, at T>0. This breakdown of
hydrodynamics is analogous to the one in chiral liquid crystals. Mode-mode
coupling effects lead to infinite renormalizations of various transport
coefficients, and the actual macroscopic description is nonlocal. At T=0 these
effects are weakened due to the fluctuation-dissipation theorem, and the
renormalizations remain finite. Observable consequences of these results, as
manifested in the neutron scattering cross-section, are discussedComment: 4pp., 1 eps figur
Dynamic correlations in stochastic rotation dynamics
The dynamic structure factor, vorticity and entropy density dynamic
correlation functions are measured for Stochastic Rotation Dynamics (SRD), a
particle based algorithm for fluctuating fluids. This allows us to obtain
unbiased values for the longitudinal transport coefficients such as thermal
diffusivity and bulk viscosity. The results are in good agreement with earlier
numerical and theoretical results, and it is shown for the first time that the
bulk viscosity is indeed zero for this algorithm. In addition, corrections to
the self-diffusion coefficient and shear viscosity arising from the breakdown
of the molecular chaos approximation at small mean free paths are analyzed. In
addition to deriving the form of the leading correlation corrections to these
transport coefficients, the probabilities that two and three particles remain
collision partners for consecutive time steps are derived analytically in the
limit of small mean free path. The results of this paper verify that we have an
excellent understanding of the SRD algorithm at the kinetic level and that
analytic expressions for the transport coefficients derived elsewhere do indeed
provide a very accurate description of the SRD fluid.Comment: 33 pages including 16 figure
Macroscopic evidence of microscopic dynamics in the Fermi-Pasta-Ulam oscillator chain from nonlinear time series analysis
The problem of detecting specific features of microscopic dynamics in the
macroscopic behavior of a many-degrees-of-freedom system is investigated by
analyzing the position and momentum time series of a heavy impurity embedded in
a chain of nearest-neighbor anharmonic Fermi-Pasta-Ulam oscillators. Results
obtained in a previous work [M. Romero-Bastida, Phys. Rev. E {\bf69}, 056204
(2004)] suggest that the impurity does not contribute significantly to the
dynamics of the chain and can be considered as a probe for the dynamics of the
system to which the impurity is coupled. The () entropy, which measures
the amount of information generated by unit time at different scales of
time and of the observable, is numerically computed by methods of nonlinear
time-series analysis using the position and momentum signals of the heavy
impurity for various values of the energy density (energy per degree
of freedom) of the system and some values of the impurity mass . Results
obtained from these two time series are compared and discussed.Comment: 7 pages, 5 figures, RevTeX4 PRE format; to be published in Phys. Rev.
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