613 research outputs found
Kovacs effect in facilitated spin models of strong and fragile glasses
We investigate the Kovacs (or crossover) effect in facilitated -spin
models of glassy dynamics. Although the Kovacs hump shows a behavior
qualitatively similar for all cases we have examined (irrespective of the
facilitation parameter and the spatial dimension ), we find that the
dependence of the Kovacs peak time on the temperature of the second quench
allows to distinguish among different microscopic mechanisms responsible for
the glassy relaxation (e.g. cooperative vs defect diffusion). We also analyze
the inherent structure dynamics underlying the Kovacs protocol, and find that
the class of facilitated spin models with and shows features
resembling those obtained recently in a realistic model of fragile glass
forming liquid.Comment: 7 pages, final version to appear in EPJB, new results and an extended
discussio
Asymmetric exclusion processes with constrained dynamics
Asymmetric exclusion processes with locally reversible kinetic constraints
are introduced to investigate the effect of non-conservative driving forces in
athermal systems. At high density they generally exhibit rheological-like
behavior, negative differential resistance, two-step structural relaxation,
dynamical heterogeneity and, possibly, a jamming transition driven by the
external field.Comment: 4 pages, 4 figures; revised version: minor changes, added references;
to be publishe
Inherent structures and non-equilibrium dynamics of 1D constrained kinetic models: a comparison study
e discuss the relevance of the Stillinger and Weber approach to the glass
transition investigating the non-equilibrium behavior of models with
non-trivial dynamics, but with simple equilibrium properties. We consider a
family of 1D constrained kinetic models, which interpolates between the
asymmetric chain introduced by Eisinger and J\"ackle [Z. Phys. {\bf B84}, 115
(1991)] and the symmetric chain introduced by Fredrickson and Andersen [Phys.
Rev. Lett {\bf 53}, 1244 (1984)], and the 1D version of the Backgammon model
[Phys. Rev. Lett. {\bf 75}, 1190 (1995)]. We show that the configurational
entropy obtained from the inherent structures is the same for all models
irrespective of their different microscopic dynamics. We present a detailed
study of the coarsening behavior of these models, including the relation
between fluctuations and response. Our results suggest that any approach to the
glass transition inspired by mean-field ideas and resting on the definition of
a configurational entropy must rely on the absence of any growing
characteristic coarsening pattern.Comment: 32 pages, 28 figures, RevTe
Out-of-equilibrium dynamical fluctuations in glassy systems
In this paper we extend the earlier treatment of out-of-equilibrium
mesoscopic fluctuations in glassy systems in several significant ways. First,
via extensive simulations, we demonstrate that models of glassy behavior
without quenched disorder display scalings of the probability of local two-time
correlators that are qualitatively similar to that of models with short-ranged
quenched interactions. The key ingredient for such scaling properties is shown
to be the development of a critical-like dynamical correlation length, and not
other microscopic details. This robust data collapse may be described in terms
of a time-evolving Gumbel-like distribution. We develop a theory to describe
both the form and evolution of these distributions based on a effective
sigma-model approach.Comment: 20 pages, RevTex, 9 figure
Free-volume kinetic models of granular matter
We show that the main dynamical features of granular media can be understood
by means of simple models of fragile-glass forming liquid provided that gravity
alone is taken into account. In such lattice-gas models of cohesionless and
frictionless particles, the compaction and segregation phenomena appear as
purely non-equilibrium effects unrelated to the Boltzmann-Gibbs measure which
in this case is trivial. They provide a natural framework in which slow
relaxation phenomena in granular and glassy systems can be explained in terms
of a common microscopic mechanism given by a free-volume kinetic constraint.Comment: 4 pages, 6 figure
Spin-Glass Model for Inverse Freezing
We analyze the Blume-Emery-Griffiths model with disordered magnetic
interaction displaying the inverse freezing phenomenon. The behaviour of this
spin-1 model in crystal field is studied throughout the phase diagram and the
transition and spinodal lines for the model are computed using the Full Replica
Symmetry Breaking Ansatz that always yelds a thermodynamically stable phase. We
compare the results both with the quenched disordered model with Ising spins on
lattice gas - where no reentrance takes place - and with the model with
generalized spin variables recently introduced by Schupper and Shnerb [Phys.
Rev. Lett. 93, 037202 (2004)]. The simplest version of all these models, known
as Ghatak-Sherrington model, turns out to hold all the general features
characterizing an inverse transition to an amorphous phase, including the right
thermodynamic behavior.Comment: 6 pages, 4 figures, to appear in the Proceeding for the X
International Workshop on Disordered Systems (2006), Molveno, Ital
Nonlocal and nonlinear effects in hyperbolic heat transfer in a two-temperature model
AbstractThe correct analysis of heat transport at nanoscale is one of the main reasons of new developments in physics and nonequilibrium thermodynamic theories beyond the classical Fourier law. In this paper, we provide a two-temperature model which allows to describe the different regimes which electrons and phonons can undergo in the heat transfer phenomenon. The physical admissibility of that model is showed in view of second law of thermodynamics. The above model is applied to study the propagation of heat waves in order to point out the special role played by nonlocal and nonlinear effects
Inverse Freezing in Mean-Field Models of Fragile Glasses
A disordered spin model suitable for studying inverse freezing in fragile
glass-forming systems is introduced. The model is a microscopic realization of
the ``random-first order'' scenario in which the glass transition can be either
continuous or discontinuous in thermodynamic sense. The phase diagram exhibits
a first-order transition line between two fluid phases terminating at a
critical point. When the interacting degrees of freedom are entropically
favoured an inverse static glass transition and a double inverse dynamic
freezing appear.Comment: 4 pages, 4 figure
Fibreglass wind turbine blades: Damage tolerant design and verification
This paper presents the damage tolerant design and verification of a composite materials wind turbine blade expected to be manufactured with the manufacturing process named OneShot Blade® technology. This technology allows the production of wind turbine blades without adhesives and/or bonding processes, leading to a significant reduction in labour hours, costs and materials. Here, the OneShot Blade® oriented design of a 10-meter long fibreglass blade is introduced. Two different configurations (conventional and lightened) have been investigated highlighting their damage tolerant characteristics. Structural performances have been evaluated to verify that the structure complies with the IEC 61400-2 and Germanischer-Lloyd (GL) regulations by considering several loading conditions. Finally, comparisons against a similar wind turbine blade, manufactured by means of a standard process, has been presented, to highlight the advantages of the proposed technology
Investigating the thermo-mechanical behavior of a ceramic matrix composite wing leading edge by sub-modeling based numerical analyses
The thermo-structural design of the wing leading edge of hypersonic vehicles is a very challenging task as high gradients in thermal field, and hence high thermal stresses, are expected. Indeed, when employing passive hot structures based thermal protection systems, very high temperatures (e.g., 1400 °C) are expected on the external surface of the wing leading edge, while the internal structural components are required to not exceed a few hundred degrees Celsius (e.g., 400 °C) at the interface with the internal cold structure. Hence, ceramic matrix composites (CMC) are usually adopted for the manufacturing of the external surface of the wing leading edge since they are characterized by good mechanical properties at very high temperatures (up to 1900 °C) together with an excellent thermal shock resistance. Furthermore, the orthotropic behavior of these materials together with the possibility to tailor their lamination sequence to minimize the heat transferred to internal components, make them very attractive for hot structure based thermal protection systems applications. However, the numerical predictions of the thermo-mechanical behavior of such materials, taking into account the influence of each ply (whose thickness generally ranges between 0.2 and 0.3 mm), can be very expensive from a computational point of view. To overcome this limitation, usually, sub-models are adopted, able to focus on specific and critical areas of the structure where very detailed thermo-mechanical analyses can be performed without significantly affecting the computational efficiency of the global model. In the present work, sub-modeling numerical approaches have been adopted for the analysis of the thermo-mechanical behavior of a ceramic matrix composite wing leading edge of a hypersonic vehicle. The main aim is to investigate the feasibility, in terms of computational efficiency and accuracy of results, in using sub-models for dimensioning complex ceramic matrix components. Hence, a comprehensive study on the size of sub-models and on the choice of their boundaries has been carried out in order to assess the advantages and the limitations in approximating the thermo-mechanical behavior of the investigated global ceramic matrix composite component
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