3,425 research outputs found
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First ozone reanalysis on Mars using SPICAM data
To further our understanding of important photochemical processes in the Martian atmosphere, a synthesis can be used to investigate the temporal and spatial agreement between model and observations and determine any possible causes of identified differences. In this study [1], we have assimilated, for the first time, total ozone into a Mars Global Circulation model (GCM) to study the ozone cycle
Tapping Thermodynamics of the One Dimensional Ising Model
We analyse the steady state regime of a one dimensional Ising model under a
tapping dynamics recently introduced by analogy with the dynamics of
mechanically perturbed granular media. The idea that the steady state regime
may be described by a flat measure over metastable states of fixed energy is
tested by comparing various steady state time averaged quantities in extensive
numerical simulations with the corresponding ensemble averages computed
analytically with this flat measure. The agreement between the two averages is
excellent in all the cases examined, showing that a static approach is capable
of predicting certain measurable properties of the steady state regime.Comment: 11 pages, 5 figure
Tapping Spin Glasses
We consider a tapping dynamics, analogous to that in experiments on granular
media, on spin glasses and ferromagnets on random thin graphs. Between taps,
zero temperature single spin flip dynamics takes the system to a metastable
state. Tapping, corresponds to flipping simultaneously any spin with
probability . This dynamics leads to a stationary regime with a steady state
energy . We analytically solve this dynamics for the one dimensional
ferromagnet and spin glass. Numerical simulations for spin glasses and
ferromagnets of higher connectivity are carried out, in particular we find a
novel first order transition for the ferromagnetic systems.Comment: 5 pages, 3 figures, RevTe
Metastability in zero-temperature dynamics: Statistics of attractors
The zero-temperature dynamics of simple models such as Ising ferromagnets
provides, as an alternative to the mean-field situation, interesting examples
of dynamical systems with many attractors (absorbing configurations, blocked
configurations, zero-temperature metastable states). After a brief review of
metastability in the mean-field ferromagnet and of the droplet picture, we
focus our attention onto zero-temperature single-spin-flip dynamics of
ferromagnetic Ising models. The situations leading to metastability are
characterized. The statistics and the spatial structure of the attractors thus
obtained are investigated, and put in perspective with uniform a priori
ensembles. We review the vast amount of exact results available in one
dimension, and present original results on the square and honeycomb lattices.Comment: 21 pages, 6 figures. To appear in special issue of JPCM on Granular
Matter edited by M. Nicodem
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Analysis of the Martian ozone cycle by assimilation of SPICAM observations
Observations of ozone, a trace gas on Mars, have the potential to constrain atmospheric dynamical and physical processes. Current Mars Global Circulation Models (MGCMs) are able to represent the photochemistry occuring in the atmosphere, with comparisons to observations used to confine particular species. However, a long term comparison using data assimilation provides a more robust constraint on the model. We have assimilated total-ozone observations from SPICAM into an MGCM to study the Martian ozone cycle. Ozone has never before been assimilated for an extraterrestrial planet. Our aim is to use ozone to provide a preliminary technique for trace gas data assimilation for the analysis of observations from current and future satellite missions (such as ExoMars) which observe the spatial and temporal distribution of trace gases on Mars
Crossover from stationary to aging regime in glassy dynamics
We study the non-equilibrium dynamics of the spherical p-spin models in the
scaling regime near the plateau and derive the corresponding scaling functions
for the correlators. Our main result is that the matching between different
time regimes fixes the aging function in the aging regime to
. The exponent is related to the one giving the
length of the plateau. Interestingly is quickly very small when one
goes away from the dynamic transition temperature in the glassy phase. This
gives new light on the interpretation of experiments and simulations where
simple aging was found to be a reasonable but not perfect approximation, which
could be attributed to the existence of a small but non-zero stretching
exponent.Comment: 7 pages+2 figure
Steady State Behavior of Mechanically Perturbed Spin Glasses and Ferromagnets
A zero temperature dynamics of Ising spin glasses and ferromagnets on random
graphs of finite connectivity is considered, like granular media these systems
have an extensive entropy of metastable states. We consider the problem of what
energy a randomly prepared spin system falls to before becoming stuck in a
metastable state. We then introduce a tapping mechanism, analogous to that of
real experiments on granular media, this tapping, corresponding to flipping
simultaneously any spin with probability , leads to stationary regime with a
steady state energy . We explicitly solve this problem for the one
dimensional ferromagnet and spin glass and carry out extensive
numerical simulations for spin systems of higher connectivity. The link with
the density of metastable states at fixed energy and the idea of Edwards that
one may construct a thermodynamics with a flat measure over metastable states
is discussed. In addition our simulations on the ferromagnetic systems reveal a
novel first order transition, whereas the usual thermodynamic transition on
these graphs is second order.Comment: 11 pages, 7 figure
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