249 research outputs found
Hierarchical Model for the Evolution of Cloud Complexes
The structure of cloud complexes appears to be well described by a "tree
structure" representation when the image is partitioned into "clouds". In this
representation, the parent-child relationships are assigned according to
containment. Based on this picture, a hierarchical model for the evolution of
Cloud Complexes, including star formation, is constructed, that follows the
mass evolution of each sub-structure by computing its mass exchange
(evaporation or condensation) with its parent and children, which depends on
the radiation density at the interphase. For the set of parameters used as a
reference model, the system produces IMFs with a maximum at too high mass (~2
M_sun) and the characteristic times for evolution seem too long. We show that
these properties can be improved by adjusting model parameters. However, the
emphasis here is to illustrate some general properties of this nonlinear model
for the star formation process. Notwithstanding the simplifications involved,
the model reveals an essential feature that will likely remain if additional
physical processes are included. That is: the detailed behavior of the system
is very sensitive to variations on the initial and external conditions,
suggesting that a "universal" IMF is very unlikely. When an ensemble of IMFs
corresponding to a variety of initial or external conditions is examined, the
slope of the IMF at high masses shows variations comparable to the range
derived from observational data. (Abridged)Comment: Latex, 29 pages, 13 figures, accepted for publication in Ap
Field evidence of social influence in the expression of political preferences: the case of secessionist flags in Barcelona
Different models of social influence have explored the dynamics of social
contagion, imitation, and diffusion of different types of traits, opinions, and
conducts. However, few behavioral data indicating social influence dynamics
have been obtained from direct observation in `natural' social contexts. The
present research provides that kind of evidence in the case of the public
expression of political preferences in the city of Barcelona, where thousands
of citizens supporting the secession of Catalonia from Spain have placed a
Catalan flag in their balconies. We present two different studies. 1) In July
2013 we registered the number of flags in 26% of the the city. We find that
there is a large dispersion in the density of flags in districts with similar
density of pro-independence voters. However, we find that the density of flags
tends to be fostered in those electoral district where there is a clear
majority of pro-independence vote, while it is inhibited in the opposite cases.
2) During 17 days around Catalonia's 2013 National Holiday we observed the
position at balcony resolution of the flags displayed in the facades of 82
blocks. We compare the clustering of flags on the facades observed each day to
equivalent random distributions and find that successive hangings of flags are
not independent events but that a local influence mechanism is favoring their
clustering. We also find that except for the National Holiday day the density
of flags tends to be fostered in those facades where there is a clear majority
of pro-independence vote.Comment: 27 pages, 13 figures, 2 table
Bounded Confidence under Preferential Flip: A Coupled Dynamics of Structural Balance and Opinions
In this work we study the coupled dynamics of social balance and opinion
formation. We propose a model where agents form opinions under bounded
confidence, but only considering the opinions of their friends. The signs of
social ties -friendships and enmities- evolve seeking for social balance,
taking into account how similar agents' opinions are. We consider both the case
where opinions have one and two dimensions. We find that our dynamics produces
the segregation of agents into two cliques, with the opinions of agents in one
clique differing from those in the other. Depending on the level of bounded
confidence, the dynamics can produce either consensus of opinions within each
clique or the coexistence of several opinion clusters in a clique. For the
uni-dimensional case, the opinions in one clique are all below the opinions in
the other clique, hence defining a "left clique" and a "right clique". In the
two-dimensional case, our numerical results suggest that the two cliques are
separated by a hyperplane in the opinion space. We also show that the
phenomenon of unidimensional opinions identified by DeMarzo, Vayanos and
Zwiebel (Q J Econ 2003) extends partially to our dynamics. Finally, in the
context of politics, we comment about the possible relation of our results to
the fragmentation of an ideology and the emergence of new political parties.Comment: 8 figures, PLoS ONE 11(10): e0164323, 201
Dynamics of Coupling Functions in Globally Coupled Maps: Size, Periodicity and Stability of Clusters
It is shown how different globally coupled map systems can be analyzed under
a common framework by focusing on the dynamics of their respective global
coupling functions. We investigate how the functional form of the coupling
determines the formation of clusters in a globally coupled map system and the
resulting periodicity of the global interaction. The allowed distributions of
elements among periodic clusters is also found to depend on the functional form
of the coupling. Through the analogy between globally coupled maps and a single
driven map, the clustering behavior of the former systems can be characterized.
By using this analogy, the dynamics of periodic clusters in systems displaying
a constant global coupling are predicted; and for a particular family of
coupling functions, it is shown that the stability condition of these clustered
states can straightforwardly be derived.Comment: 12 pp, 5 figs, to appear in PR
Emergence of patterns in driven and in autonomous spatiotemporal systems
The relationship between a driven extended system and an autonomous
spatiotemporal system is investigated in the context of coupled map lattice
models. Specifically, a locally coupled map lattice subjected to an external
drive is compared to a coupled map system with similar local couplings plus a
global interaction. It is shown that, under some conditions, the emergent
patterns in both systems are analogous. Based on the knowledge of the dynamical
responses of the driven lattice, we present a method that allows the prediction
of parameter values for the emergence of ordered spatiotemporal patterns in a
class of coupled map systems having local coupling and general forms of global
interactions.Comment: 7 pages, 3 figs, submitted to PRE (2002
Gaslike model of social motility
We propose a model to represent the motility of social elements. The model is
completely deterministic, possesses a small number of parameters, and exhibits
a series of properties that are reminiscent of the behavior of comunities in
social-ecological competition; these are: (i) similar individuals attract each
other; (ii) individuals can form stable groups; (iii) a group of similar
individuals breaks into subgroups if it reaches a critical size; (iv)
interaction between groups can modify the distribution of the elements as a
result of fusion, fission, or pursuit; (v) individuals can change their
internal state by interaction with their neighbors. The simplicity of the model
and its richness of emergent behaviors, such as, for example, pursuit between
groups, make it a useful toy model to explore a diversity of situations by
changing the rule by which the internal state of individuals is modified by the
interactions with the environment.Comment: 11 pages, 4 figures, accepted in PR
On the Thermal Instability in a Contracting Gas Cloud and Formation of a Bound Cluster
We perform linear analysis of thermal instability in a contracting large
cloud filled with warm HI gas and investigate the effect of metallicity and
radiation flux. When the cloud reaches critical density n_f, the cloud
fragments into cool, dense condensations because of thermal instability. For a
lower metallicity gas cloud, the value of n_f is high. Collision between
condensations will produce self-gravitating clumps and stars thereafter. From
the result of calculation, we suggest that high star formation efficiency and
bound cluster formation are realized in low-metallicity and/or strong-radiation
environments.Comment: 7 pages, including 7 figures, LaTeX2e(emulateapj5.sty) To appear in
ApJ, Jun 10, 200
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