3,673 research outputs found
Transport Properties of a Chain of Anharmonic Oscillators with random flip of velocities
We consider the stationary states of a chain of anharmonic coupled
oscillators, whose deterministic hamiltonian dynamics is perturbed by random
independent sign change of the velocities (a random mechanism that conserve
energy). The extremities are coupled to thermostats at different temperature
and and subject to constant forces and . If
the forces differ the center of mass of the system will
move of a speed inducing a tension gradient inside the system. Our aim is
to see the influence of the tension gradient on the thermal conductivity. We
investigate the entropy production properties of the stationary states, and we
prove the existence of the Onsager matrix defined by Green-kubo formulas
(linear response). We also prove some explicit bounds on the thermal
conductivity, depending on the temperature.Comment: Published version: J Stat Phys (2011) 145:1224-1255 DOI
10.1007/s10955-011-0385-
Center-stabilized Yang-Mills theory: confinement and large volume independence
We examine a double trace deformation of SU(N) Yang-Mills theory which, for
large and large volume, is equivalent to unmodified Yang-Mills theory up to
corrections. In contrast to the unmodified theory, large volume
independence is valid in the deformed theory down to arbitrarily small volumes.
The double trace deformation prevents the spontaneous breaking of center
symmetry which would otherwise disrupt large volume independence in small
volumes. For small values of , if the theory is formulated on with a sufficiently small compactification size , then an analytic
treatment of the non-perturbative dynamics of the deformed theory is possible.
In this regime, we show that the deformed Yang-Mills theory has a mass gap and
exhibits linear confinement. Increasing the circumference or number of
colors decreases the separation of scales on which the analytic treatment
relies. However, there are no order parameters which distinguish the small and
large radius regimes. Consequently, for small the deformed theory provides
a novel example of a locally four-dimensional pure gauge theory in which one
has analytic control over confinement, while for large it provides a simple
fully reduced model for Yang-Mills theory. The construction is easily
generalized to QCD and other QCD-like theories.Comment: 29 pages, expanded discussion of multiple compactified dimension
Relaxation dynamics and colossal magnetocapacitive effect in CdCr2S4
A thorough investigation of the relaxational dynamics in the recently
discovered multiferroic CdCr2S4 showing a colossal magnetocapacitive effect has
been performed. Broadband dielectric measurements without and with external
magnetic fields up to 10 T provide clear evidence that the observed
magnetocapacitive effect stems from enormous changes of the relaxation dynamics
induced by the development of magnetic order.Comment: 4 pages, 4 figure
Frustrated quantum-spin system on a triangle coupled with lattice vibrations - Correspondence to Longuet-Higgins et al.'s Jahn-Teller model -
We investigate the quantum three spin model
of spin on a triangle, in which spins are coupled with
lattice-vibrational modes through the exchange interaction depending on
distances between spin sites. The present model corresponds to the dynamic
Jahn-Teller system proposed by Longuet-Higgins {\it et al.},
Proc.R.Soc.A.{\bf 244},1(1958). This correspondence is revealed by using the
transformation to Nakamura-Bishop's bases proposed in Phys.Rev.Lett.{\bf
54},861(1985). Furthermore, we elucidate the relationship between the behavior
of a chiral order parameter and
that of the electronic orbital angular momentum in vibronic model: The regular oscillatory behavior of the expectation value
. The increase of the additional
anharmonicity(chaoticity) is found to yield a rapidly decaying irregular
oscillation of
Leaf area reduction by trimming, a growing technique to restore the anthocyanins : sugars ratio decoupled by the warming climate
The aim of this work is the evaluation of the leaf area reduction by trimming, as a growing technique to restore the anthocyanins : sugars ratio decoupled by the warming climate. A 3-year period (2010-2012) severe shoot trimming treatment was done after berryset (berry diameter 3-4 mm) and the veraison date was delayed around 20 days. The grapes were picked at the same level of soluble solids in all the treatments. However, for every year, the trim treatment significatively increased the total anthocyanin content between 8 % and 21 % compared to control. Therefore, delaying the berry ripening process trough the decrease of the leaf area to fruit ratio, could partially restore the anthocyanins : sugars ratio disrupted by elevated temperatures. Although it is necessary to study other trimmings intensities as well as other times of intervention, the shoot trimming treatment could be a very simple technique to delay berry ripening and compensate the effects of climate warming.
Thermophoresis of Brownian particles driven by coloured noise
The Brownian motion of microscopic particles is driven by the collisions with
the molecules of the surrounding fluid. The noise associated with these
collisions is not white, but coloured due, e.g., to the presence of
hydrodynamic memory. The noise characteristic time scale is typically of the
same order as the time over which the particle's kinetic energy is lost due to
friction (inertial time scale). We demonstrate theoretically that, in the
presence of a temperature gradient, the interplay between these two
characteristic time scales can have measurable consequences on the particle
long-time behaviour. Using homogenization theory, we analyse the infinitesimal
generator of the stochastic differential equation describing the system in the
limit where the two characteristic times are taken to zero; from this
generator, we derive the thermophoretic transport coefficient, which, we find,
can vary in both magnitude and sign, as observed in experiments. Furthermore,
studying the long-term stationary particle distribution, we show that particles
can accumulate towards the colder (positive thermophoresis) or the warmer
(negative thermophoresis) regions depending on the dependence of their physical
parameters and, in particular, their mobility on the temperature.Comment: 9 pages, 4 figure
Evidence for moving breathers in a layered crystal insulator at 300K
We report the ejection of atoms at a crystal surface caused by energetic
breathers which have travelled more than 10^7 unit cells in atomic chain
directions. The breathers were created by bombardment of a crystal face with
heavy ions. This effect was observed at 300K in the layered crystal muscovite,
which has linear chains of atoms for which the surrounding lattice has C_2
symmetry. The experimental techniques described could be used to study
breathers in other materials and configurations.Comment: 7 pages, 3 figure
Configurational Entropy and its Crisis in Metastable States: Ideal Glass Transition in a Dimer Model as a Paragidm of a Molecular Glass
We discuss the need for discretization to evaluate the configurational
entropy in a general model. We also discuss the prescription using restricted
partition function formalism to study the stationary limit of metastable
states. We introduce a lattice model of dimers as a paradigm of molecular fluid
and study metastability in it to investigate the root cause of glassy behavior.
We demonstrate the existence of the entropy crisis in metastable states, from
which it follows that the entropy crisis is the root cause underlying the ideal
glass transition in systems with particles of all sizes. The orientational
interactions in the model control the nature of the liquid-liquid transition
observed in recent years in molecular glasses.Comment: 36 pages, 9 figure
On a direct approach to quasideterminant solutions of a noncommutative KP equation
A noncommutative version of the KP equation and two families of its solutions
expressed as quasideterminants are discussed. The origin of these solutions is
explained by means of Darboux and binary Darboux transformations. Additionally,
it is shown that these solutions may also be verified directly. This approach
is reminiscent of the wronskian technique used for the Hirota bilinear form of
the regular, commutative KP equation but, in the noncommutative case, no
bilinearising transformation is available.Comment: 11 page
Energy transport through rare collisions
We study a one-dimensional hamiltonian chain of masses perturbed by an energy
conserving noise. The dynamics is such that, according to its hamiltonian part,
particles move freely in cells and interact with their neighbors through
collisions, made possible by a small overlap of size between
near cells. The noise only randomly flips the velocity of the particles. If
, and if time is rescaled by a factor ,
we show that energy evolves autonomously according to a stochastic equation,
which hydrodynamic limit is known in some cases. In particular, if only two
different energies are present, the limiting process coincides with the simple
symmetric exclusion process.Comment: 24 pages, 2 figure
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