127 research outputs found
On the time dependence of the -index
The time dependence of the -index is analyzed by considering the average
behaviour of as a function of the academic age for about 1400 Italian
physicists, with career lengths spanning from 3 to 46 years. The individual
-index is strongly correlated with the square root of the total citations
: . For academic ages ranging from 12 to 24
years, the distribution of the time scaled index is
approximately time-independent and it is well described by the Gompertz
function. The time scaled index has an average approximately
equal to 3.8 and a standard deviation approximately equal to 1.6. Finally, the
time scaled index appears to be strongly correlated with the
contemporary -index
Engineering interband transport by time-dependent disorder
We show how the evolution of atoms in a tilted lattice can be changed and
controlled by phase noise on the lattice. Dependent on the characteristic
parameters of the noise, the interband transport can either be suppressed or
enhanced, which is of interest for high precision control in experimental
realization with Bose-Einstein condensates. The effect of the noise on the
survival probability in the ground band is summarized in a scaling plot
stressing the universality of our results
Macroscopic Manifestation of Microscopic Entropy Production: Space-Dependent Intermittence
We study a spatial diffusion process generated by velocity fluctuations of
intermittent nature. We note that intermittence reduces the entropy production
rate while enhancing the diffusion strength. We study a case of space-dependent
intermittence and prove it to result in a deviation from uniform distribution.
This macroscopic effect can be used to measure the relative value of the
trajectory entropy.Comment: 2 postscript figures, enclose
Numerical integration of stochastic differential equations
Numerical algorithms for the integration of stochastic differential equations
in the presence of white noise are introduced and compared. Algorithms for the
integration of stochastic correlated forces are also briefly reviewed. Finally,
a specialised algorithm for two dimensional systems is derived, having in mind
the integration of particles in the liquid state.Comment: ps file; 30 pages including figure
Noise assisted transport in the Wannier-Stark system
We investigated how the presence of an additional lattice potential, driven
by a harmonic noise process, changes the transition rate from the ground band
to the first excited band in a Wannier-Stark system. Alongside numerical
simulations, we present two models that capture the essential features of the
dynamics. The first model uses a noise-driven Landau-Zener approximation and
describes the short time evolution of the full system very well. The second
model assumes that the noise process' correlation time is much larger than the
internal timescale of the system, yet it allows for good estimates of the
observed transition rates and gives a simple interpretation of the dynamics.
One of the central results is that we obtain a way to control the interband
transitions with the help of the second lattice. This could readily be realized
in state-of-the-art experiments using either Bose-Einstein condensates or
optical pulses in engineered potentials
Optimal FPE for non-linear 1d-SDE. I: Additive Gaussian colored noise
Many complex phenomena occurring in physics,chemistry, biology, finance, etc.
can be reduced, by some projection process, to a 1-d stochastic Differential
Equation (SDE) for the variable of interest. Typically, this SDE is both
non-linear and non-markovian, so a Fokker Planck equation (FPE), for the
probability density function (PDF), is generally not obtainable. However, a FPE
is desirable because it is the main tool to obtain relevant analytical
statistical information such as stationary PDF and First Passage Time. This
problem has been addressed by many authors in the past, but due to an incorrect
use of the interaction picture (the standard tool to obtain a reduced FPE)
previous theoretical results were incorrect, as confirmed by direct numerical
simulation of the SDE. We will show, in general, how to address the problem and
we will derived the correct best FPE from a perturbation approach. The method
followed and the results obtained have a general validity beyond the simple
case of exponentially correlated Gaussian driving used here as an example; they
can be applied even to non Gaussian drivings with a generic time correlation.Comment: 23 pages, 13 figure
Linear or Nonlinear Modeling for ENSO Dynamics?
The observed ENSO statistics exhibits a non-Gaussian behavior, which is indicative of the presence of nonlinear processes. In this paper, we use the Recharge Oscillator Model (ROM), a largely used Low-Order Model (LOM) of ENSO, as well as methodologies borrowed from the field of statistical mechanics to identify which aspects of the system may give rise to nonlinearities that are consistent with the observed ENSO statistics. In particular, we are interested in understanding whether the nonlinearities reside in the system dynamics or in the fast atmospheric forcing. Our results indicate that one important dynamical nonlinearity often introduced in the ROM cannot justify a non-Gaussian system behavior, while the nonlinearity in the atmospheric forcing can instead produce a statistics similar to the observed. The implications of the non-Gaussian character of ENSO statistics for the frequency of extreme El Nino events is then examined
Chaotic ratchet dynamics with cold atoms in a pair of pulsed optical lattices
We present a very simple model for realizing directed transport with cold
atoms in a pair of periodically flashed optical lattices. The origin of this
ratchet effect is explained and its robustness demonstrated under imperfections
typical of cold atom experiments. We conclude that our model offers a clear-cut
way to implement directed transport in an atom optical experiment.Comment: 7 pages, 7 figure
Noise-assisted transport in the Wannier-Stark system
We investigated how the presence of an additional lattice potential, driven by a harmonic noise process, changes the transition rate from the ground band to the first excited band in a Wannier-Stark system. Alongside numerical simulations, we present two models that capture the essential features of the dynamics. The first model uses a noise-driven Landau-Zener approximation and describes the short-time evolution of the full system very well. The second model assumes that the noise process correlation time is much larger than the internal timescale of the system, yet it allows for good estimates of the observed transition rates and gives a simple interpretation of the dynamics. One of the central results is that we obtain a way of controlling the interband transitions with the help of the second lattice. This could readily be realized in state-of-the-art experiments using either Bose-Einstein condensates or optical pulses in engineered potentials
Resonant nonlinear quantum transport for a periodically kicked Bose condensate
Our realistic numerical results show that the fundamental and higher-order
quantum resonances of the delta-kicked rotor are observable in state-of-the-art
experiments with a Bose condensate in a shallow harmonic trap, kicked by a
spatially periodic optical lattice. For stronger confinement,
interaction-induced destruction of the resonant motion of the kicked harmonic
oscillator is predicted.Comment: amended version, new Fig.
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