4,702 research outputs found
Linear Response and Fluctuation Dissipation Theorem for non-Poissonian Renewal Processes
The Continuous Time Random Walk (CTRW) formalism is used to model the
non-Poisson relaxation of a system response to perturbation. Two mechanisms to
perturb the system are analyzed: a first in which the perturbation, seen as a
potential gradient, simply introduces a bias in the hopping probability of the
walker from on site to the other but leaves unchanged the occurrence times of
the attempted jumps ("events") and a second in which the occurrence times of
the events are perturbed. The system response is calculated analytically in
both cases in a non-ergodic condition, i.e. for a diverging first moment in
time. Two different Fluctuation-Dissipation Theorems (FDTs), one for each kind
of mechanism, are derived and discussed
Aproximative solutions to the neutrino oscillation problem in matter
We present approximative solutions to the neutrino evolution equation
calculated by different methods. In a two neutrino framework, using the
physical parameters which gives the main effects to neutrino oscillations from
nu{e} to another flavors for L=3000Km and E=1GeV, the results for the
transition probability calculated by using series solutions, by to take the
neutrino evolution operator as a product of ordered partial operators and by
numerical methods, for a linearly and sinusoidally varying matter density are
compared. The extension to an arbitrary density profile is discussed and the
evolution operator as a product of partial operators in the three neutrino case
is obtained.Comment: 12 pages, 5 figure
Bayesian analysis of 210Pb dating
In many studies of environmental change of the past few centuries, 210Pb
dating is used to obtain chronologies for sedimentary sequences. One of the
most commonly used approaches to estimate the ages of depths in a sequence is
to assume a constant rate of supply (CRS) or influx of `unsupported' 210Pb from
the atmosphere, together with a constant or varying amount of `supported'
210Pb. Current 210Pb dating models do not use a proper statistical framework
and thus provide poor estimates of errors. Here we develop a new model for
210Pb dating, where both ages and values of supported and unsupported 210Pb
form part of the parameters. We apply our model to a case study from Canada as
well as to some simulated examples. Our model can extend beyond the current CRS
approach, deal with asymmetric errors and mix 210Pb with other types of dating,
thus obtaining more robust, realistic and statistically better defined
estimates.Comment: 22 Pages, 4 Figure
Kovacs Effect in a Fragile Glass Model
The Kovacs protocol, based on the temperature shift experiment originally
conceived by A.J. Kovacs for glassy polymers, is implemented in an exactly
solvable dynamical model. This model is characterized by interacting fast and
slow modes represented respectively by spherical spins and harmonic oscillator
variables. Due to this fundamental property, the model reproduces the
characteristic non-monotonic evolution known as the ``Kovacs effect'', observed
in polymers, in granular materials and models of molecular liquids, when
similar experimental protocols are implemented.Comment: 8 pages, 6 figure
Memory Effects in the Standard Model for Glasses
The standard model of glasses is an ensemble of two-level systems interacting
with a thermal bath. The general origin of memory effects in this model is a
quasi-stationary but non-equilibrium state of a single two-level system, which
is realized due to a finite-rate cooling and very slow thermally activated
relaxation. We show that single particle memory effects, such as negativity of
the specific heat under reheating, vanish for a sufficiently disordered
ensemble. In contrast, a disordered ensemble displays a collective memory
effect [similar to that described by Kovacs for glassy polymers], where
non-equilibrium features of the ensemble are monitored via a macroscopic
observable. An experimental realization of the effect can be used to further
assess the consistency of the model.Comment: 4 pages, 6 figure
Absorption and Emission in the non-Poisson case
This letter adresses the challenging problems posed to the Kubo-Anderson (KA)
theory by the discovery of intermittent resonant fluorescence with a
non-exponential distribution of waiting times. We show how to extend the KA
theory from aged to aging systems, aging for a very extended time period or
even forever, being a crucial consequence of non-Poisson statistics.Comment: 4 pages 3 figures. accepted for publication on Physical Review
Letter
Thermal treatment of superconductor thin film of the BSCCO system using domestic microwave oven
In this work, we report the preparation of a superconductor thin film of the
BSCCO system using a good quality powder with nominal composition
Bi_{1.8}Pb_{0.4}Sr_2CaCu_2O_x which was thermally treated using a domestic
microwave oven (2.45 GHz, 800 W). This film was grew on a single crystal of
LaAlO_3(100) substrate and exhibited a crystalline structure with the c-axis
perpendicular to the plane of the substrate. An onset superconducting
transition temperature was measured at 80 K.Comment: 4 pages, 5 figure
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