1,737 research outputs found
Negative response to an excessive bias by a mixed population of voters
We study an outcome of a vote in a population of voters exposed to an
externally applied bias in favour of one of two potential candidates. The
population consists of ordinary individuals, that are in majority and tend to
align their opinion with the external bias, and some number of contrarians ---
individuals who are always hostile to the bias but are not in a conflict with
ordinary voters. The voters interact among themselves, all with all, trying to
find an opinion reached by the community as a whole. We demonstrate that for a
sufficiently weak external bias, the opinion of ordinary individuals is always
decisive and the outcome of the vote is in favour of the preferential
candidate. On the contrary, for an excessively strong bias, the contrarians
dominate in the population's opinion, producing overall a negative response to
the imposed bias. We also show that for sufficiently strong interactions within
the community, either of two subgroups can abruptly change an opinion of the
other group.Comment: 11 pages, 6 figure
Nonequilibrium dynamics of a stochastic model of anomalous heat transport: numerical analysis
We study heat transport in a chain of harmonic oscillators with random
elastic collisions between nearest-neighbours. The equations of motion of the
covariance matrix are numerically solved for free and fixed boundary
conditions. In the thermodynamic limit, the shape of the temperature profile
and the value of the stationary heat flux depend on the choice of boundary
conditions. For free boundary conditions, they also depend on the coupling
strength with the heat baths. Moreover, we find a strong violation of local
equilibrium at the chain edges that determine two boundary layers of size
(where is the chain length), that are characterized by a
different scaling behaviour from the bulk. Finally, we investigate the
relaxation towards the stationary state, finding two long time scales: the
first corresponds to the relaxation of the hydrodynamic modes; the second is a
manifestation of the finiteness of the system.Comment: Submitted to Journal of Physics A, Mathematical and Theoretica
Memory Effects in Nonequilibrium Transport for Deterministic Hamiltonian Systems
We consider nonequilibrium transport in a simple chain of identical
mechanical cells in which particles move around. In each cell, there is a
rotating disc, with which these particles interact, and this is the only
interaction in the model. It was shown in \cite{eckmann-young} that when the
cells are weakly coupled, to a good approximation, the jump rates of particles
and the energy-exchange rates from cell to cell follow linear profiles. Here,
we refine that study by analyzing higher-order effects which are induced by the
presence of external gradients for situations in which memory effects, typical
of Hamiltonian dynamics, cannot be neglected. For the steady state we propose a
set of balance equations for the particle number and energy in terms of the
reflection probabilities of the cell and solve it phenomenologically. Using
this approximate theory we explain how these asymmetries affect various aspects
of heat and particle transport in systems of the general type described above
and obtain in the infinite volume limit the deviation from the theory in
\cite{eckmann-young} to first-order. We verify our assumptions with extensive
numerical simulations.Comment: Several change
Nonequilibrium dynamics of a stochastic model of anomalous heat transport
We study the dynamics of covariances in a chain of harmonic oscillators with
conservative noise in contact with two stochastic Langevin heat baths. The
noise amounts to random collisions between nearest-neighbour oscillators that
exchange their momenta. In a recent paper, [S Lepri et al. J. Phys. A: Math.
Theor. 42 (2009) 025001], we have studied the stationary state of this system
with fixed boundary conditions, finding analytical exact expressions for the
temperature profile and the heat current in the thermodynamic (continuum)
limit. In this paper we extend the analysis to the evolution of the covariance
matrix and to generic boundary conditions. Our main purpose is to construct a
hydrodynamic description of the relaxation to the stationary state, starting
from the exact equations governing the evolution of the correlation matrix. We
identify and adiabatically eliminate the fast variables, arriving at a
continuity equation for the temperature profile T(y,t), complemented by an
ordinary equation that accounts for the evolution in the bulk. Altogether, we
find that the evolution of T(y,t) is the result of fractional diffusion.Comment: Submitted to Journal of Physics A, Mathematical and Theoretica
Optimal estimates of the diffusion coefficient of a single Brownian trajectory
Modern developments in microscopy and image processing are revolutionizing
areas of physics, chemistry and biology as nanoscale objects can be tracked
with unprecedented accuracy. The goal of single particle tracking is to
determine the interaction between the particle and its environment. The price
paid for having a direct visualization of a single particle is a consequent
lack of statistics. Here we address the optimal way of extracting diffusion
constants from single trajectories for pure Brownian motion. It is shown that
the maximum likelihood estimator is much more efficient than the commonly used
least squares estimate. Furthermore we investigate the effect of disorder on
the distribution of estimated diffusion constants and show that it increases
the probability of observing estimates much smaller than the true (average)
value.Comment: 8 pages, 5 figure
First passages in bounded domains: When is the mean first passage time meaningful?
We study the first passage statistics to adsorbing boundaries of a Brownian
motion in bounded two-dimensional domains of different shapes and
configurations of the adsorbing and reflecting boundaries. From extensive
numerical analysis we obtain the probability P(\omega) distribution of the
random variable \omega=\tau_1/(\tau_1+\tau_2), which is a measure for how
similar the first passage times \tau_1 and \tau_2 are of two independent
realisations of a Brownian walk starting at the same location. We construct a
chart for each domain, determining whether P(\omega) represents a unimodal,
bell-shaped form, or a bimodal, M-shaped behaviour. While in the former case
the mean first passage time (MFPT) is a valid characteristic of the first
passage behaviour, in the latter case it is an insufficient measure for the
process. Strikingly we find a distinct turnover between the two modes of
P(\omega), characteristic for the domain shape and the respective location of
absorbing and reflective boundaries. Our results demonstrate that large
fluctuations of the first passage times may occur frequently in two-dimensional
domains, rendering quite vague the general use of the MFPT as a robust measure
of the actual behaviour even in bounded domains, in which all moments of the
first passage distribution exist.Comment: 9 pages, 6 figure
Design of a highly-birefringent microstructured photonic crystal fiber for pressure monitoring
We present the design of an air hole microstructured photonic crystal fiber for pressure sensing applications. The air-hole photonic crystal lattices were designed to produce a large intrinsic birefringence of 1.16x10-3. The impact of the surrounding air holes for pressure sensing to the propagation mode profiles and indices were studied and improved, which ensures single mode propagation in the fiber core defined by the photonic crystal lattice. An air hole matrix and a practical chemical etching process during the fiber perform preparation stage is proposed to produce an optical fiber with a birefringence-pressure coefficient of 43.89×10-6MPa-1 or a fiber Bragg grating pressure responsivity of 44.15 pm/MPa, which is a 17 times improvement over previous photonic crystal fiber designs. © 2010 Optical Society of America
A stochastic model of anomalous heat transport: analytical solution of the steady state
We consider a one-dimensional harmonic crystal with conservative noise, in
contact with two stochastic Langevin heat baths at different temperatures. The
noise term consists of collisions between neighbouring oscillators that
exchange their momenta, with a rate . The stationary equations for the
covariance matrix are exactly solved in the thermodynamic limit ().
In particular, we derive an analytical expression for the temperature profile,
which turns out to be independent of . Moreover, we obtain an exact
expression for the leading term of the energy current, which scales as
. Our theoretical results are finally found to be consistent
with the numerical solutions of the covariance matrix for finite .Comment: Minor changes in the text. To appear in Journal of Physics
Gender Violence in the University: The Role of Higher Education Institutions in its Prevention
Talking about gender-based violence and sexual harassment at the Ecuadorian university has been considered by many as an uncomfortable subject, and for some years it has been silenced. It is only recently that this situation has become an essential topic to investigate, so that currently several universities have struggled to explore through studies the problems of gender violence, discrimination and sexual harassment in the university context. In this sense, the present study has tried to develop a review of all the investigations that have been carried out to identify cases or situations of gender violence in universities at international, national and local level, as well as to determine the role of education institutions superior in the prevention and eradication of this problem.
Keywords: gender violence, sexual harassment, university.
Resumen
Hablar de violencia de género y acoso sexual en la universidad ecuatoriana ha sido considerado por muchos como un tema incómodo por lo que durante algunos años ha permanecido silenciado. No es sino hace poco que esta situación se ha vuelto una temática imprescindible de investigar, por lo que actualmente varias universidades se han esforzado en explorar a través de estudios los problemas de violencia de género, discriminación y acoso sexual en el contexto universitario. En este sentido, el presente estudio ha pretendido desarrollar una revisión de todas las investigaciones que se han realizado para identificar los casos o situaciones de violencia de género en universidades a nivel internacional, nacional y local, así como determinar el rol de las instituciones de educación superior en la prevención y erradicación de esta problemática.
Palabras clave: violencia de género, acoso sexual, universidad
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