22 research outputs found
Single-file diffusion on self-similar substrates
We study the single file diffusion problem on a one-dimensional lattice with
a self-similar distribution of hopping rates. We find that the time dependence
of the mean-square displacement of both a tagged particle and the center of
mass of the system present anomalous power laws modulated by logarithmic
periodic oscillations. The anomalous exponent of a tagged particle is one half
of the exponent of the center of mass, and always smaller than 1/4. Using
heuristic arguments, the exponents and the periods of oscillation are
analytically obtained and confirmed by Monte Carlo simulations.Comment: 12 pages, 6 figure
Intermediate Range Structure in Ion-Conducting Tellurite Glasses
We present ac conductivity spectra of tellurite glasses at several
temperatures. For the first time, we report oscillatory modulations at
frequencies around MHz. This effect is more pronounced the lower the
temperature, and washes out when approaching the glass transition temperature
. We show, by using a minimal model, how this modulation may be attributed
to the fractal structure of the glass at intermediate mesoscopic length scales
Anomalous diffusion with log-periodic modulation in a selected time interval
On certain self-similar substrates the time behavior of a random walk is
modulated by logarithmic periodic oscillations on all time scales. We show that
if disorder is introduced in a way that self-similarity holds only in average,
the modulating oscillations are washed out but subdiffusion remains as in the
perfect self-similar case. Also, if disorder distribution is appropriately
chosen the oscillations are localized in a selected time interval. Both the
overall random walk exponent and the period of the oscillations are
analytically obtained and confirmed by Monte Carlo simulations.Comment: 4 pages, 5 figure
Anisotropic anomalous diffusion modulated by log-periodic oscillations
We introduce finite ramified self-affine substrates in two dimensions with a
set of appropriate hopping rates between nearest-neighbor sites, where the
diffusion of a single random walk presents an anomalous {\it anisotropic}
behavior modulated by log-periodic oscillations. The anisotropy is revealed by
two different random walk exponents, and , in the {\it x} and
{\it y} direction, respectively. The values of these exponents, as well as the
period of the oscillation, are analytically obtained and confirmed by Monte
Carlo simulations.Comment: 7 pages, 7 figure
Log-periodic modulation in one-dimensional random walks
We have studied the diffusion of a single particle on a one-dimensional
lattice. It is shown that, for a self-similar distribution of hopping rates,
the time dependence of the mean-square displacement follows an anomalous power
law modulated by logarithmic periodic oscillations. The origin of this
modulation is traced to the dependence on the length of the diffusion
coefficient. Both the random walk exponent and the period of the modulation are
analytically calculated and confirmed by Monte Carlo simulations.Comment: 6 pages, 7 figure
Quantum diffusion on a cyclic one dimensional lattice
The quantum diffusion of a particle in an initially localized state on a
cyclic lattice with N sites is studied. Diffusion and reconstruction time are
calculated. Strong differences are found for even or odd number of sites and
the limit N->infinit is studied. The predictions of the model could be tested
with micro - and nanotechnology devices.Comment: 17 pages, 5 figure
Mechanistic model for the electrochemical facetting of metals with development of preferred crystallographic orientations
A model for the development of surface profiles of face-centred cubic metals which can be related to the electrochemical facetting with preferred, oriented crystallographic planes, is proposed and simulated by means of the Monte Carlo method. Successive cycles of selective electrodissolution and electrodeposition under a periodic potential are simulated through the withdrawal and attachment of particles to the metal profile according to specified rules which are supported by experimental observations. The model is applied to the development of two different crystallographic faces starting from either perfectly-ordered void-free profiles (single crystal approach) or a rough profile with defects in the bulk (polycrystal approach). The simulation results are in qualitative agreement with electrochemical facetting data, scanning electron microscopy and scanning tunneling microscopy images of various face-centred cubic metals.Instituto de Investigaciones FisicoquÃmicas Teóricas y AplicadasFacultad de Ciencias Exacta
Identical particles are indistinguishable but..
It is shown that quantum systems of identical particles can be treated as if
they were different when they are in well differentiated states. This
simplifying assumption allows the consideration of quantum systems isolated
from the rest of the universe and justifies many intuitive statements about
identical systems. However, it is shown that this simplification may lead to
wrong results in the calculation of the entropy.
Keywords: quantum mechanics, identical systems, entrop