912 research outputs found
Consensus formation on adaptive networks
The structure of a network can significantly influence the properties of the
dynamical processes which take place on them. While many studies have been
devoted to this influence, much less attention has been devoted to the
interplay and feedback mechanisms between dynamical processes and network
topology on adaptive networks. Adaptive rewiring of links can happen in real
life systems such as acquaintance networks where people are more likely to
maintain a social connection if their views and values are similar. In our
study, we consider different variants of a model for consensus formation. Our
investigations reveal that the adaptation of the network topology fosters
cluster formation by enhancing communication between agents of similar opinion,
though it also promotes the division of these clusters. The temporal behavior
is also strongly affected by adaptivity: while, on static networks, it is
influenced by percolation properties, on adaptive networks, both the early and
late time evolution of the system are determined by the rewiring process. The
investigation of a variant of the model reveals that the scenarios of
transitions between consensus and polarized states are more robust on adaptive
networks.Comment: 11 pages, 14 figure
Synchronization in Weighted Uncorrelated Complex Networks in a Noisy Environment: Optimization and Connections with Transport Efficiency
Motivated by synchronization problems in noisy environments, we study the
Edwards-Wilkinson process on weighted uncorrelated scale-free networks. We
consider a specific form of the weights, where the strength (and the associated
cost) of a link is proportional to with and
being the degrees of the nodes connected by the link. Subject to the
constraint that the total network cost is fixed, we find that in the mean-field
approximation on uncorrelated scale-free graphs, synchronization is optimal at
-1. Numerical results, based on exact numerical diagonalization
of the corresponding network Laplacian, confirm the mean-field results, with
small corrections to the optimal value of . Employing our recent
connections between the Edwards-Wilkinson process and resistor networks, and
some well-known connections between random walks and resistor networks, we also
pursue a naturally related problem of optimizing performance in queue-limited
communication networks utilizing local weighted routing schemes.Comment: Papers on related research can be found at
http://www.rpi.edu/~korniss/Research
Supernova 1998bw - The final phases
The probable association with GRB 980425 immediately put SN 1998bw at the
forefront of supernova research. Here, we present revised late-time BVRI light
curves of the supernova, based on template images taken at the VLT. To follow
the supernova to the very last observable phases we have used HST/STIS. Deep
images taken in June and November 2000 are compared to images taken in August
2001. The identification of the supernova is firmly established. This allows us
to measure the light curve to about 1000 days past explosion. The main features
are a rapid decline up to more than 500 days after explosion, with no sign of
complete positron trapping from the Cobolt-56 decay. Thereafter, the light
curve flattens out significantly. One possible explanation is powering by more
long lived radioactive isotopes, if they are abundantly formed in this
energetic supernova.Comment: 13 pages, 5 figures, A&A, In pres
Projected Images of Major Chinese Outbound Destinations
This study aimed to explore the projected images of major outbound destinations based on popular travel magazines in China. Travel articles on Hong Kong, Macau, Japan, South Korea, Vietnam and Taiwan from 2006 to 2008 were content analyzed. Japan was reported on most, and the projected images of the six destinations are dominated by leisure and recreation, and culture, history and art. Correspondence analysis was used to examine relationships between destinations and popular image attributes. The results showed that South Korea and Macau had distinct projected images, whereas Japan, Taiwan, Hong Kong and Vietnam shared many similar image attributes. Practical implications for destination marketing organizations are provided
Spectra of supernovae in the nebular phase
When supernovae enter the nebular phase after a few months, they reveal
spectral fingerprints of their deep interiors, glowing by radioactivity
produced in the explosion. We are given a unique opportunity to see what an
exploded star looks like inside. The line profiles and luminosities encode
information about physical conditions, explosive and hydrostatic
nucleosynthesis, and ejecta morphology, which link to the progenitor properties
and the explosion mechanism. Here, the fundamental properties of spectral
formation of supernovae in the nebular phase are reviewed. The formalism
between ejecta morphology and line profile shapes is derived, including effects
of scattering and absorption. Line luminosity expressions are derived in
various physical limits, with examples of applications from the literature. The
physical processes at work in the supernova ejecta, including gamma-ray
deposition, non-thermal electron degradation, ionization and excitation, and
radiative transfer are described and linked to the computation and application
of advanced spectral models. Some of the results derived so far from
nebular-phase supernova analysis are discussed.Comment: Book chapter for 'Handbook of Supernovae,' edited by Alsabti and
Murdin, Springer. 51 pages, 14 figure
Constraining the physical properties of Type II-P supernovae using nebular phase spectra
We present a study of the nebular phase spectra of a sample of Type
II-Plateau supernovae with identified progenitors or restrictive limits. The
evolution of line fluxes, shapes, and velocities are compared within the
sample, and interpreted by the use of a spectral synthesis code. The small
diversity within the dataset can be explained by strong mixing occurring during
the explosion, and by recognising that most lines have significant
contributions from primordial metals in the H envelope, which dominates the
total ejecta mass in these type of objects. In particular, when using the [O I]
6300, 6364 Angstrom doublet for estimating the core mass of the star, care has
to be taken to account for emission from primordial O in the envelope. Finally,
a correlation between the H-alpha line width and the mass of 56Ni is presented,
suggesting that higher energy explosions are associated with higher 56Ni
production.Comment: 18 pages, 15 figures, accepted for publication in MNRA
Lack of consensus in social systems
We propose an exactly solvable model for the dynamics of voters in a
two-party system. The opinion formation process is modeled on a random network
of agents. The dynamical nature of interpersonal relations is also reflected in
the model, as the connections in the network evolve with the dynamics of the
voters. In the infinite time limit, an exact solution predicts the emergence of
consensus, for arbitrary initial conditions. However, before consensus is
reached, two different metastable states can persist for exponentially long
times. One state reflects a perfect balancing of opinions, the other reflects a
completely static situation. An estimate of the associated lifetimes suggests
that lack of consensus is typical for large systems.Comment: 4 pages, 6 figures, submitted to Phys. Rev. Let
Coevolution of Glauber-like Ising dynamics on typical networks
We consider coevolution of site status and link structures from two different
initial networks: a one dimensional Ising chain and a scale free network. The
dynamics is governed by a preassigned stability parameter , and a rewiring
factor , that determines whether the Ising spin at the chosen site flips
or whether the node gets rewired to another node in the system. This dynamics
has also been studied with Ising spins distributed randomly among nodes which
lie on a network with preferential attachment. We have observed the steady
state average stability and magnetisation for both kinds of systems to have an
idea about the effect of initial network topology. Although the average
stability shows almost similar behaviour, the magnetisation depends on the
initial condition we start from. Apart from the local dynamics, the global
effect on the dynamics has also been studied. These parameters show interesting
variations for different values of and , which helps in determining
the steady-state condition for a given substrate.Comment: 8 pages, 10 figure
The Naming Game in Social Networks: Community Formation and Consensus Engineering
We study the dynamics of the Naming Game [Baronchelli et al., (2006) J. Stat.
Mech.: Theory Exp. P06014] in empirical social networks. This stylized
agent-based model captures essential features of agreement dynamics in a
network of autonomous agents, corresponding to the development of shared
classification schemes in a network of artificial agents or opinion spreading
and social dynamics in social networks. Our study focuses on the impact that
communities in the underlying social graphs have on the outcome of the
agreement process. We find that networks with strong community structure hinder
the system from reaching global agreement; the evolution of the Naming Game in
these networks maintains clusters of coexisting opinions indefinitely. Further,
we investigate agent-based network strategies to facilitate convergence to
global consensus.Comment: The original publication is available at
http://www.springerlink.com/content/70370l311m1u0ng3
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