9,062 research outputs found
Structural instability of nonlinear plates modelling suspension bridges: mathematical answers to some long-standing questions
We model the roadway of a suspension bridge as a thin rectangular plate and
we study in detail its oscillating modes. The plate is assumed to be hinged on
its short edges and free on its long edges. Two different kinds of oscillating
modes are found: longitudinal modes and torsional modes. Then we analyze a
fourth order hyperbolic equation describing the dynamics of the bridge. In
order to emphasize the structural behavior we consider an isolated equation
with no forcing and damping. Due to the nonlinear behavior of the cables and
hangers, a structural instability appears. With a finite dimensional
approximation we prove that the system remains stable at low energies while
numerical results show that for larger energies the system becomes unstable. We
analyze the energy thresholds of instability and we show that the model allows
to give answers to several questions left open by the Tacoma collapse in 1940.Comment: 33 page
Saddle Points Stability in the Replica Approach Off Equilibrium
We study the replica free energy surface for a spin glass model near the
glassy temperature. In this model the simplicity of the equilibrium solution
hides non trivial metastable saddle points. By means of the stability analysis
performed for one and two real replicas constrained, an interpretation for some
of them is achieved.Comment: 10 pages and 3 figures upon request, Univerista` di Roma I preprint
94/100
Partial symmetry and existence of least energy solutions to some nonlinear elliptic equations on Riemannian models
We consider least energy solutions to the nonlinear equation posed on a class of Riemannian models of dimension
which include the classical hyperbolic space as well as manifolds
with unbounded sectional geometry. Partial symmetry and existence of least
energy solutions is proved for quite general nonlinearities , where
denotes the geodesic distance from the pole of
Uniqueness of the thermodynamic limit for driven disordered elastic interfaces
We study the finite size fluctuations at the depinning transition for a
one-dimensional elastic interface of size displacing in a disordered medium
of transverse size with periodic boundary conditions, where
is the depinning roughness exponent and is a finite aspect ratio
parameter. We focus on the crossover from the infinitely narrow () to
the infinitely wide () medium. We find that at the thermodynamic
limit both the value of the critical force and the precise behavior of the
velocity-force characteristics are {\it unique} and -independent. We also
show that the finite size fluctuations of the critical force (bias and
variance) as well as the global width of the interface cross over from a
power-law to a logarithm as a function of . Our results are relevant for
understanding anisotropic size-effects in force-driven and velocity-driven
interfaces.Comment: 10 pages, 12 figure
Long term ordering kinetics of the two dimensional q-state Potts model
We studied the non-equilibrium dynamics of the q-state Potts model in the
square lattice, after a quench to sub-critical temperatures. By means of a
continuous time Monte Carlo algorithm (non-conserved order parameter dynamics)
we analyzed the long term behavior of the energy and relaxation time for a wide
range of quench temperatures and system sizes. For q>4 we found the existence
of different dynamical regimes, according to quench temperature range. At low
(but finite) temperatures and very long times the Lifshitz-Allen-Cahn domain
growth behavior is interrupted with finite probability when the system stuck in
highly symmetric non-equilibrium metastable states, which induce activation in
the domain growth, in agreement with early predictions of Lifshitz [JETP 42,
1354 (1962)]. Moreover, if the temperature is very low, the system always gets
stuck at short times in a highly disordered metastable states with finite life
time, which have been recently identified as glassy states. The finite size
scaling properties of the different relaxation times involved, as well as their
temperature dependency are analyzed in detail.Comment: 10 pages, 17 figure
q-State Potts model metastability study using optimized GPU-based Monte Carlo algorithms
We implemented a GPU based parallel code to perform Monte Carlo simulations
of the two dimensional q-state Potts model. The algorithm is based on a
checkerboard update scheme and assigns independent random numbers generators to
each thread. The implementation allows to simulate systems up to ~10^9 spins
with an average time per spin flip of 0.147ns on the fastest GPU card tested,
representing a speedup up to 155x, compared with an optimized serial code
running on a high-end CPU. The possibility of performing high speed simulations
at large enough system sizes allowed us to provide a positive numerical
evidence about the existence of metastability on very large systems based on
Binder's criterion, namely, on the existence or not of specific heat
singularities at spinodal temperatures different of the transition one.Comment: 30 pages, 7 figures. Accepted in Computer Physics Communications.
code available at:
http://www.famaf.unc.edu.ar/grupos/GPGPU/Potts/CUDAPotts.htm
Short-time dynamics of finite-size mean-field systems
We study the short-time dynamics of a mean-field model with non-conserved
order parameter (Curie-Weiss with Glauber dynamics) by solving the associated
Fokker-Planck equation. We obtain closed-form expressions for the first moments
of the order parameter, near to both the critical and spinodal points, starting
from different initial conditions. This allows us to confirm the validity of
the short-time dynamical scaling hypothesis in both cases. Although the
procedure is illustrated for a particular mean-field model, our results can be
straightforwardly extended to generic models with a single order parameter.Comment: accepted for publication in JSTA
Induction of ovarian maturation by means of dietary hormonal treatment in Austropotamobius pallipes
The freshwater crayfish Austropotamobius pallipes is an annual species with low fecundity and a long embryonic development. Restocking programmes for this species have recently been prompted in many countries in Europe because of its ecological importance in the freshwater ecosystem. The role and interactions of neurotransmitters which intervene in crustacean reproduction have been identified but they are not still completely understood. Ovarian development appears to be under the control of two hormones: the vitellogenesis-inhibiting hormone and the gonad stimulating hormone (Fingermann, 1997)
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