1,438 research outputs found
An Introduction to Breakdown Phenomena in Disordered Systems
The rupture of a medium under stress typifies breakdown phenomena. More
generally, the latter encompass the dynamics of systems of many interacting
elements governed by the interplay of a driving force with a pinning disorder,
resulting in a macroscopic transition. A simple mean-field formalism
incorporating these features is presented and applied to systems representative
of fracture phenomena, social dilemmas, and magnets out of equilibrium. The
similarities and differences in the corresponding mathematical structures are
emphasized. The solutions are best obtained from a graphical method, from which
very general conclusions may be drawn. In particular, the various classes of
disorder distribution are treated without reference to a particular analytical
or numerical form, and are found to lead to qualitatively different
transitions. Finally, the notion of effective (or phenomenological) theory is
introduced and illustrated for non-equilibrium disordered magnets.Comment: Pedagogical article published as part of a special issue on
thermodynamics and statistical physics; 20 page
The effect of polydispersity on the ordering transition of adsorbed self-assembled rigid rods
Extensive Monte Carlo simulations were carried out to investigate the nature
of the ordering transition of a model of adsorbed self-assembled rigid rods on
the bonds of a square lattice [Tavares et. al., Phys. Rev E 79, 021505 (2009)].
The polydisperse rods undergo a continuous ordering transition that is found to
be in the two-dimensional Ising universality class, as in models where the rods
are monodisperse. This finding is in sharp contrast with the recent claim that
equilibrium polydispersity changes the nature of the phase transition in this
class of models [L`opez et. al., Phys. Rev E 80, 040105(R)(2009)].Comment: 19 pages, 5 figure
The influence of strong magnetic field on photon-neutrino reactions
The two-photon two-neutrino interaction induced by magnetic field is
investigated. In particular the processes and
are studied in the presence of strong magnetic
field. An effective Lagrangian and partial amplitudes of the processes are
presented. Neutrino emissivities due to the reactions and are calculated taking into
account of the photon dispersion and large radiative corrections. A comparison
of the results obtained with previous estimations and another inducing
mechanisms of the processes under consideration is made.Comment: 16 pages, LATEX, 3 EPS figures, based on the talk presented at XXXI
ITEP Winter School of Physics, Moscow, Russia, February 18 - 26, 200
Electron--phonon coupling and anharmonic effects in metal clusters
The periods of the harmonic oscillations of the ion core of charged sodium
clusters around the equilibrium shapes are considered. It is found that these
periods are of the order of magnitude of the experimentally measured relaxation
times of the plasmons, which suggests the importance of the electron-ion
coupling and stresses the role played by the electron-phonon interaction in the
dissipation of the plasmon energy. The relation of the process to fission is
briefly discussed.Comment: 6 pages, no figures, to appear in EPLetter
Pathways to folding, nucleation events and native geometry
We perform extensive Monte Carlo simulations of a lattice model and the Go
potential to investigate the existence of folding pathways at the level of
contact cluster formation for two native structures with markedly different
geometries. Our analysis of folding pathways revealed a common underlying
folding mechanism, based on nucleation phenomena, for both protein models.
However, folding to the more complex geometry (i.e. that with more non-local
contacts) is driven by a folding nucleus whose geometric traits more closely
resemble those of the native fold. For this geometry folding is clearly a more
cooperative process.Comment: Accepted in J. Chem. Phy
Application of the zero-range potential model to positron annihilation on molecules
In this paper we use a zero-range potential (ZRP) method to model positron
interaction with molecules. This allows us to investigate the effect of
molecular vibrations on positron-molecule annihilation using the van der Waals
dimer Kr2 as an example. We also use the ZRP to explore positron binding to
polyatomics and examine the dependence of the binding energy on the size of the
molecule for alkanes. We find that a second bound state appears for a molecule
with ten carbons, similar to recent experimental evidence for such a state
emerging in alkanes with twelve carbons.Comment: 14 pages, 6 figures, to be published in Nuclear Instruments and
Methods
Native geometry and the dynamics of protein folding
In this paper we investigate the role of native geometry on the kinetics of
protein folding based on simple lattice models and Monte Carlo simulations.
Results obtained within the scope of the Miyazawa-Jernigan indicate the
existence of two dynamical folding regimes depending on the protein chain
length. For chains larger than 80 amino acids the folding performance is
sensitive to the native state's conformation. Smaller chains, with less than 80
amino acids, fold via two-state kinetics and exhibit a significant correlation
between the contact order parameter and the logarithmic folding times. In
particular, chains with N=48 amino acids were found to belong to two broad
classes of folding, characterized by different cooperativity, depending on the
contact order parameter. Preliminary results based on the G\={o} model show
that the effect of long range contact interaction strength in the folding
kinetics is largely dependent on the native state's geometry.Comment: Proceedings of the BIFI 2004 - I International Conference, Zaragoza
(Spain) Biology after the genome: a physical view. To appear in Biophysical
Chemistr
Adiabatic Condition and Quantum Geometric Potential
In this paper, we present a U(1)-invariant expansion theory of the adiabatic
process. As its application, we propose and discuss new sufficient adiabatic
approximation conditions. In the new conditions, we find a new invariant
quantity referred as quantum geometric potential (QGP) contained in all
time-dependent processes. Furthermore, we also give detailed discussion and
analysis on the properties and effects of QGP.Comment: 5 pages, 1 figur
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