223 research outputs found
Fluctuation-dissipation relations and critical quenches in the transverse field Ising chain
Dynamic correlation and response functions of classical and quantum systems
in thermal equilibrium are connected by fluctuation-dissipation theorems, which
allow an alternative definition of their (unique) temperature. Motivated by
this fundamental property, we revisit the issue of thermalization of closed
many-body quantum systems long after a sudden quench, focussing on the
non-equilibrium dynamics of the Ising chain in a critical transverse field. We
show the emergence of distinct observable-dependent effective temperatures,
which rule out Gibbs thermalization in a strict sense but might still have a
thermodynamic meaning.Comment: 5 pages, 3 figure
Corrections to local scale invariance in the non-equilibrium dynamics of critical systems: numerical evidences
Local scale invariance (LSI) has been recently proposed as a possible
extension of the dynamical scaling in systems at the critical point and during
phase ordering. LSI has been applied inter alia to provide predictions for the
scaling properties of the response function of non-equilibrium critical systems
in the aging regime following a quench from the high-temperature phase to the
critical point. These predictions have been confirmed by Monte Carlo
simulations and analytical results for some specific models, but they are in
disagreement with field-theoretical predictions. By means of Monte Carlo
simulations of the critical two- and three-dimensional Ising model with Glauber
dynamics, we study the intermediate integrated response, finding deviations
from the corresponding LSI predictions that are in qualitative agreement with
the field-theoretical computations. This result casts some doubts on the
general applicability of LSI to critical dynamics.Comment: 4 pages, 2 figures, minor changes, version to appear in Phys. Rev. B
as a Rapid Communicatio
Dynamics of fluctuations in the Gaussian model with dissipative Langevin Dynamics
We study the dynamics of the fluctuations of the variance s of the order parameter of the Gaussian model, following a temperature quench of the thermal bath. At each time t, there is a critical value sc (t) of s such that fluctuations with s > s(c)(t) are realized by condensed configurations of the systems, i.e., a single degree of freedom contributes macroscopically to s. This phenomenon, which is closely related to the usual condensation occurring on average quantities, is usually referred to as condensation of fluctuations. We show that the probability of fluctuations with s < inf(t){[}sc (t)], associated to configurations that never condense, after the quench converges rapidly and in an adiabatic way towards the new equilibrium value. The
probability of fluctuations with s > inf(t){[}sc (t)], instead, displays a slow and more complex behavior, because the macroscopic population of the condensing degree of freedom is involved
Critical Langevin dynamics of the O(N)-Ginzburg-Landau model with correlated noise
We use the perturbative renormalization group to study classical stochastic
processes with memory. We focus on the generalized Langevin dynamics of the
\phi^4 Ginzburg-Landau model with additive noise, the correlations of which are
local in space but decay as a power-law with exponent \alpha in time. These
correlations are assumed to be due to the coupling to an equilibrium thermal
bath. We study both the equilibrium dynamics at the critical point and quenches
towards it, deriving the corresponding scaling forms and the associated
equilibrium and non-equilibrium critical exponents \eta, \nu, z and \theta. We
show that, while the first two retain their equilibrium values independently of
\alpha, the non-Markovian character of the dynamics affects the dynamic
exponents (z and \theta) for \alpha < \alpha_c(D, N) where D is the spatial
dimensionality, N the number of components of the order parameter, and
\alpha_c(x,y) a function which we determine at second order in 4-D. We analyze
the dependence of the asymptotic fluctuation-dissipation ratio on various
parameters, including \alpha. We discuss the implications of our results for
several physical situations
Key economic drivers enabling municipal renewable energy communities’ benefits in the Italian context
Community energy is a buzzword that has historically included various type of experiences. In 2018, the Renewable Energy Directive (RED II) legally defined renewable energy communities (RECs). Based on the first pilot projects and on the Italian legal framework, a possible REC configuration of municipal initiative with a high replicability potential is one in which a photovoltaic system is installed in educational buildings and shares energy with neighbouring residential consumers. This analysis presents an economical evaluation of different possible scenarios depending on variables such as solar radiation, system capacity, fraction of self-consumption within the REC, installation costs and energy prices. All the scenarios identified and analysed show positive economic indexes, although the energy and economic results may significantly vary depending on the variables studied. In the analysed case studies, the Net Present Value (after 20 years) is between kEUR 51 and kEUR 478; the internal rate of return is between 9.5% and 88%; the payback time is between 13.6 years and 1.1 years. The results of this analysis are relevant as they allow us to better understand the critical factors that can enable REC in providing local economic and social benefits to have a real impact on energy poverty or on the provision of local social services
Tunability of Critical Casimir Interactions by Boundary Conditions
We experimentally demonstrate that critical Casimir forces in colloidal
systems can be continuously tuned by the choice of boundary conditions. The
interaction potential of a colloidal particle in a mixture of water and
2,6-lutidine has been measured above a substrate with a gradient in its
preferential adsorption properties for the mixture's components. We find that
the interaction potentials at constant temperature but different positions
relative to the gradient continuously change from attraction to repulsion. This
demonstrates that critical Casimir forces respond not only to minute
temperature changes but also to small changes in the surface properties.Comment: 4 figures;
http://www.iop.org/EJ/article/0295-5075/88/2/26001/epl_88_2_26001.htm
Ageing in the contact process: Scaling behavior and universal features
We investigate some aspects of the ageing behavior observed in the contact
process after a quench from its active phase to the critical point. In
particular we discuss the scaling properties of the two-time response function
and we calculate it and its universal ratio to the two-time correlation
function up to first order in the field-theoretical epsilon-expansion. The
scaling form of the response function does not fit the prediction of the theory
of local scale invariance. Our findings are in good qualitative agreement with
recent numerical results.Comment: 20 pages, 3 figure
Probing non-thermal density fluctuations in the one-dimensional Bose gas
Quantum integrable models display a rich variety of non-thermal excited states with unusual properties. The most common way to probe them is by performing a quantum quench, i.e., by letting a many-body initial state unitarily evolve with an integrable Hamiltonian. At late times these systems are locally described by a generalized Gibbs ensemble with as many effective temperatures as their local conserved quantities. The experimental measurement of this macroscopic number of temperatures remains elusive. Here we show that they can be obtained for the Bose gas in one spatial dimension by probing the dynamical structure factor of the system after the quench and by employing a generalized fluctuation-dissipation theorem that we provide. Our procedure allows us to completely reconstruct the stationary state of a quantum integrable system from state-of-the-art experimental observations
Spreading in narrow channels
We study a lattice model for the spreading of fluid films, which are a few
molecular layers thick, in narrow channels with inert lateral walls. We focus
on systems connected to two particle reservoirs at different chemical
potentials, considering an attractive substrate potential at the bottom,
confining side walls, and hard-core repulsive fluid-fluid interactions. Using
kinetic Monte Carlo simulations we find a diffusive behavior. The corresponding
diffusion coefficient depends on the density and is bounded from below by the
free one-dimensional diffusion coefficient, valid for an inert bottom wall.
These numerical results are rationalized within the corresponding continuum
limit.Comment: 16 pages, 10 figure
Effective temperatures in a simple model of non-equilibrium, non-Markovian dynamics
The concept of effective temperatures in nonequilibrium systems is studied
within an exactly solvable model of non-Markovian diffusion. The system is
coupled to two heat baths which are kept at different temperatures: one
('fast') bath associated with an uncorrelated Gaussian noise and a second
('slow') bath with an exponential memory kernel. Various definitions of
effective temperatures proposed in the literature are evaluated and compared.
The range of validity of these definitions is discussed. It is shown in
particular, that the effective temperature defined from the
fluctuation-dissipation relation mirrors the temperature of the slow bath in
parameter regions corresponding to a separation of time scales. On the
contrary, quasi-static and thermodynamic definitions of an effective
temperature are found to display the temperature of the fast bath in most
parameter regions
- …