3,434 research outputs found
Cluster size entropy in the Axelrod model of social influence: small-world networks and mass media
We study the Axelrod's cultural adaptation model using the concept of cluster
size entropy, that gives information on the variability of the cultural
cluster size present in the system. Using networks of different topologies,
from regular to random, we find that the critical point of the well-known
nonequilibrium monocultural-multicultural (order-disorder) transition of the
Axelrod model is unambiguously given by the maximum of the
distributions. The width of the cluster entropy distributions can be used to
qualitatively determine whether the transition is first- or second-order. By
scaling the cluster entropy distributions we were able to obtain a relationship
between the critical cultural trait and the number of cultural
features in regular networks. We also analyze the effect of the mass media
(external field) on social systems within the Axelrod model in a square
network. We find a new partially ordered phase whose largest cultural cluster
is not aligned with the external field, in contrast with a recent suggestion
that this type of phase cannot be formed in regular networks. We draw a new
phase diagram for the Axelrod model in regular networks.Comment: 21 pages, 7 figure
Quartic Horndeski Cartan theories in a FLRW Universe
We consider the Quartic Horndeski theory with torsion on a FLRW background in
the second order formalism. We show that there is a one parameter family of
Quartic Horndeski Cartan Lagrangians and all such theories only modify the
dispersion relations of the graviton and the scalar perturbation that are
usually found in the standard Horndeski theory on a torsionless spacetime. In
other words, for the theories in this class torsion does not induce new degrees
of freedom but it only modifies the propagation. We also show that for most
Lagrangians within the family of Quartic Horndeski Cartan theories the
dispersion relation of the scalar mode is radically modified. We find only one
theory within the family whose scalar mode has a regular wave-like dispersion
relation
Stability of nonsingular Cosmologies in Galileons with Torsion. A No-Go for eternal subluminality
Generic models in Galileons or Horndeski theory do not have cosmological
solutions that are free of instabilities and singularities in the entire time
of evolution. We extend this No-Go theorem to a spacetime with torsion. On this
more general geometry the No-Go argument now holds provided the additional
hypothesis that the graviton is also subluminal throughout the entire
evolution. Thus, critically different for Galileons' stability on a torsionful
spacetime, an arguably unphysical although arbitrarily short (deep UV) phase
occurring at an arbitrary time, when the speed of gravity is slighlty
higher than luminal , and by at least an amount , can lead to an all-time (linearly) stable and nonsingular cosmology. As a
proof of principle we build a stable model for a cosmological bounce that is
almost always subluminal, where the short-lived superluminal phase occurs
before the bounce and that transits to General Relativity in the asymptotic
past and future.Comment: 7 pages, 4 figure
Mechanism for flux guidance by micrometric antidot arrays in superconducting films
A study of magnetic flux penetration in a superconducting film patterned with
arrays of micron sized antidots (microholes) is reported. Magneto-optical
imaging (MOI) of a YBCO film shaped as a long strip with perpendicular antidot
arrays revealed both strong guidance of flux, and at the same time large
perturbations of the overall flux penetration and flow of current. These
results are compared with a numerical flux creep simulation of a thin
superconductor with the same antidot pattern. To perform calculations on such a
complex geometry, an efficient numerical scheme for handling the boundary
conditions of the antidots and the nonlocal electrodynamics was developed. The
simulations reproduce essentially all features of the MOI results. In addition,
the numerical results give insight into all other key quantities, e.g., the
electrical field, which becomes extremely large in the narrow channels
connecting the antidots.Comment: 8 pages, 7 figure
Improvement of Academic Analytics Processes Through the Identification of the Main Variables Affecting Early Dropout of First-Year Students in Technical Degrees. A Case Study
The field of research on the phenomenon of university dropout and the factors that promote it is of the utmost relevance, especially in the current context of the Covid-19 pandemic. Students who have started degrees in the last two years have completed their university studies in periods of lockdown and unlike traditional education, this has often involved taking online classes. In this scenario, the students' motivation and the way they are able to cope with the difficulties of the first year of a university course are very relevant, especially in technical
degrees. Previous studies show that a large number of undergraduate students drop out prematurely. In order to act to reduce dropout rates, schools, especially technical schools, should be able to map the entry profile of students and identify the factors that promote early dropout. This paper focuses on identifying, categorizing and evaluating a number of indicators according to the perception of tutors and the field of study, based on the application of quantitative and qualitative techniques. The results support the approach taken, as they show how tutors can identify students at risk of dropping out at the beginning of the course and act proactively to monitor and motivate them
Lattice effects and current reversal in superconducting ratchets
Competition between the vortex lattice and a lattice of asymmetric artificial
defects is shown to play a crucial role in ratchet experiments in
superconducting films. We present a novel and collective mechanism for current
reversal based on a reconfiguration of the vortex lattice. In contrast to
previous models of vortex current reversal, the mechanism is based on the
global response of the vortex lattice to external forces.Comment: 12 pages, 7 figure
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