920 research outputs found
Effective temperature in nonequilibrium steady states of Langevin systems with a tilted periodic potential
We theoretically study Langevin systems with a tilted periodic potential. It
has been known that the ratio of the diffusion constant to the
differential mobility is not equal to the temperature of the environment
(multiplied by the Boltzmann constant), except in the linear response regime,
where the fluctuation dissipation theorem holds. In order to elucidate the
physical meaning of far from equilibrium, we analyze a modulated
system with a slowly varying potential. We derive a large scale description of
the probability density for the modulated system by use of a perturbation
method. The expressions we obtain show that plays the role of the
temperature in the large scale description of the system and that can
be determined directly in experiments, without measurements of the diffusion
constant and the differential mobility
Measurement-based modelling and validation of PV systems
This paper presents the analysis and results of modelling of various photovoltaic (PV) systems. Two general models are discussed and presented: an analytical model and an equivalent circuit model, both formulated for main PV technologies currently available on the market. Analytical model does not require any PV system specific input data or parameter, and is formulated as a generic performance model of a considered PV technology. Equivalent circuit model, however, requires specific input data and adjustment of the model parameters, in order to provide an accurate representation of a modelled PV system. The paper provides direct comparison of models based on manufacturer’s specification data and available measurements, as well as the discussion of obtained results
The order-disorder transition in colloidal suspensions under shear flow
We study the order-disorder transition in colloidal suspensions under shear
flow by performing Brownian dynamics simulations. We characterize the
transition in terms of a statistical property of time-dependent maximum value
of the structure factor. We find that its power spectrum exhibits the power-law
behaviour only in the ordered phase. The power-law exponent is approximately -2
at frequencies greater than the magnitude of the shear rate, while the power
spectrum exhibits the -type fluctuations in the lower frequency regime.Comment: 11 pages, 10 figures, v.2: We have made some small improvements on
presentation
An order parameter equation for the dynamic yield stress in dense colloidal suspensions
We study the dynamic yield stress in dense colloidal suspensions by analyzing
the time evolution of the pair distribution function for colloidal particles
interacting through a Lennard-Jones potential. We find that the equilibrium
pair distribution function is unstable with respect to a certain anisotropic
perturbation in the regime of low temperature and high density. By applying a
bifurcation analysis to a system near the critical state at which the stability
changes, we derive an amplitude equation for the critical mode. This equation
is analogous to order parameter equations used to describe phase transitions.
It is found that this amplitude equation describes the appearance of the
dynamic yield stress, and it gives a value of 2/3 for the shear thinning
exponent. This value is related to the mean field value of the critical
exponent in the Ising model.Comment: 8 pages, 2 figure
Exact transformation of a Langevin equation to a fluctuating response equation
We demonstrate that a Langevin equation that describes the motion of a
Brownian particle under non-equilibrium conditions can be exactly transformed
to a special equation that explicitly exhibits the response of the velocity to
a time dependent perturbation. This transformation is constructed on the basis
of an operator formulation originally used in nonlinear perturbation theory for
differential equations by extending it to stochastic analysis. We find that the
obtained expression is useful for the calculation of fundamental quantities of
the system, and that it provides a physical basis for the decomposition of the
forces in the Langevin description into effective driving, dissipative, and
random forces in a large-scale description.Comment: 14 pages, to appear in J. Phys. A: Math. Ge
A universal form of slow dynamics in zero-temperature random-field Ising model
The zero-temperature Glauber dynamics of the random-field Ising model
describes various ubiquitous phenomena such as avalanches, hysteresis, and
related critical phenomena. Here, for a model on a random graph with a special
initial condition, we derive exactly an evolution equation for an order
parameter. Through a bifurcation analysis of the obtained equation, we reveal a
new class of cooperative slow dynamics with the determination of critical
exponents.Comment: 4 pages, 2 figure
Slow decay of dynamical correlation functions for nonequilibrium quantum states
A property of dynamical correlation functions for nonequilibrium states is
discussed. We consider arbitrary dimensional quantum spin systems with local
interaction and translationally invariant states with nonvanishing current over
them. A correlation function between local charge and local Hamiltonian at
different spacetime points is shown to exhibit slow decay.Comment: typos correcte
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