620 research outputs found
Hawks and Doves on Small-World Networks
We explore the Hawk-Dove game on networks with topologies ranging from
regular lattices to random graphs with small-world networks in between. This is
done by means of computer simulations using several update rules for the
population evolutionary dynamics. We find the overall result that cooperation
is sometimes inhibited and sometimes enhanced in those network structures, with
respect to the mixing population case. The differences are due to different
update rules and depend on the gain-to-cost ratio. We analyse and qualitatively
explain this behavior by using local topological arguments.Comment: 12 pages, 8 figure
Denying humanness to victims: How gang members justify violent behavior
The high prevalence of violent offending amongst gang-involved youth has been established in the literature. Yet the underlying psychological mechanisms that enable youth to engage in such acts of violence remain unclear. 189 young people were recruited from areas in London, UK, known for their gang activity. We found that gang members, in comparison to non-gang youth, described the groups they belong to as having recognized leaders, specific rules and codes, initiation rituals, and special clothing. Gang members were also more likely than non-gang youth to engage in violent behavior and endorse moral disengagement strategies (i.e., moral justification, euphemistic language, advantageous comparison, displacement of responsibility, attribution of blame, and dehumanization). Finally, we found that dehumanizing victims partially mediated the relationship between gang membership and violent behavior. These findings highlight the effects of groups at the individual level and an underlying psychological mechanism that explains, in part, how gang members engage in violence
Diffusion Processes on Small-World Networks with Distance-Dependent Random-Links
We considered diffusion-driven processes on small-world networks with
distance-dependent random links. The study of diffusion on such networks is
motivated by transport on randomly folded polymer chains, synchronization
problems in task-completion networks, and gradient driven transport on
networks. Changing the parameters of the distance-dependence, we found a rich
phase diagram, with different transient and recurrent phases in the context of
random walks on networks. We performed the calculations in two limiting cases:
in the annealed case, where the rearrangement of the random links is fast, and
in the quenched case, where the link rearrangement is slow compared to the
motion of the random walker or the surface. It has been well-established that
in a large class of interacting systems, adding an arbitrarily small density
of, possibly long-range, quenched random links to a regular lattice interaction
topology, will give rise to mean-field (or annealed) like behavior. In some
cases, however, mean-field scaling breaks down, such as in diffusion or in the
Edwards-Wilkinson process in "low-dimensional" small-world networks. This
break-down can be understood by treating the random links perturbatively, where
the mean-field (or annealed) prediction appears as the lowest-order term of a
naive perturbation expansion. The asymptotic analytic results are also
confirmed numerically by employing exact numerical diagonalization of the
network Laplacian. Further, we construct a finite-size scaling framework for
the relevant observables, capturing the cross-over behaviors in finite
networks. This work provides a detailed account of the
self-consistent-perturbative and renormalization approaches briefly introduced
in two earlier short reports.Comment: 36 pages, 27 figures. Minor revisions in response to the referee's
comments. Furthermore, some typos were fixed and new references were adde
Efficient Behavior of Small-World Networks
We introduce the concept of efficiency of a network, measuring how
efficiently it exchanges information. By using this simple measure small-world
networks are seen as systems that are both globally and locally efficient. This
allows to give a clear physical meaning to the concept of small-world, and also
to perform a precise quantitative a nalysis of both weighted and unweighted
networks. We study neural networks and man-made communication and
transportation systems and we show that the underlying general principle of
their construction is in fact a small-world principle of high efficiency.Comment: 1 figure, 2 tables. Revised version. Accepted for publication in
Phys. Rev. Let
Unusual percolation in simple small-world networks
We present an exact solution of percolation in a generalized class of
Watts-Strogatz graphs defined on a 1-dimensional underlying lattice. We find a
non-classical critical point in the limit of the number of long-range bonds in
the system going to zero, with a discontinuity in the percolation probability
and a divergence in the mean finite-cluster size. We show that the critical
behavior falls into one of three regimes depending on the proportion of
occupied long-range to unoccupied nearest-neighbor bonds, with each regime
being characterized by different critical exponents. The three regimes can be
united by a single scaling function around the critical point. These results
can be used to identify the number of long-range links necessary to secure
connectivity in a communication or transportation chain. As an example, we can
resolve the communication problem in a game of "telephone".Comment: 10 pages, 4 figures, revtex
Studying the [OIII]5007A emission-line width in a sample of 80 local active galaxies: A surrogate for ?
For a sample of 80 local () Seyfert-1 galaxies
with high-quality long-slit Keck spectra and spatially-resolved
stellar-velocity dispersion () measurements, we study the
profile of the [OIII]5007A emission line to test the validity of using
its width as a surrogate for . Such an approach has often been
used in the literature, since it is difficult to measure for
type-1 active galactic nuclei (AGNs) due to the AGN continuum outshining the
stellar-absorption lines. Fitting the [OIII] line with a single Gaussian or
Gauss-Hermite polynomials overestimates by 50-100%. When line
asymmetries from non-gravitational gas motion are excluded in a double Gaussian
fit, the average ratio between the core [OIII] width () and is 1, but with individual data points
off by up to a factor of two. The resulting black-hole-mass- relation scatters around that of quiescent galaxies and
reverberation-mapped AGNs. However, a direct comparison between
and shows no close correlation, only
that both quantities have the same range, average and standard deviation,
probably because they feel the same gravitational potential. The large scatter
is likely due to the fact that line profiles are a luminosity-weighted average,
dependent on the light distribution and underlying kinematic field. Within the
range probed by our sample (80-260 km s), our results strongly caution
against the use of [OIII] width as a surrogate for on an
individual basis. Even though our sample consists of radio-quiet AGNs, FIRST
radio-detected objects have, on average, a 10% larger [OIII] core width.Comment: 15 pages, 10 figures, 6 tables. Accepted for publication in the
Monthly Notices of the Royal Astronomical Societ
Between overt and covert research: concealment and disclosure in an ethnographic study of commercial hospitality
This article examines the ways in which problems of concealment emerged in an ethnographic study of a suburban bar and considers how disclosure of the research aims, the recruitment of informants, and elicitation of information was negotiated throughout the fieldwork. The case study demonstrates how the social context and the relationships with specific informants determined overtness or covertness in the research. It is argued that the existing literature on covert research and covert methods provides an inappropriate frame of reference with which to understand concealment in fieldwork. The article illustrates why concealment is sometimes necessary, and often unavoidable, and concludes that the criticisms leveled against covert methods should not stop the fieldworker from engaging in research that involves covertness
Maximal planar networks with large clustering coefficient and power-law degree distribution
In this article, we propose a simple rule that generates scale-free networks
with very large clustering coefficient and very small average distance. These
networks are called {\bf Random Apollonian Networks}(RAN) as they can be
considered as a variation of Apollonian networks. We obtain the analytic
results of power-law exponent and clustering coefficient
, which agree very well with the
simulation results. We prove that the increasing tendency of average distance
of RAN is a little slower than the logarithm of the number of nodes in RAN.
Since most real-life networks are both scale-free and small-world networks, RAN
may perform well in mimicking the reality. The RAN possess hierarchical
structure as that in accord with the observations of many
real-life networks. In addition, we prove that RAN are maximal planar networks,
which are of particular practicability for layout of printed circuits and so
on. The percolation and epidemic spreading process are also studies and the
comparison between RAN and Barab\'{a}si-Albert(BA) as well as Newman-Watts(NW)
networks are shown. We find that, when the network order (the total number
of nodes) is relatively small(as ), the performance of RAN under
intentional attack is not sensitive to , while that of BA networks is much
affected by . And the diseases spread slower in RAN than BA networks during
the outbreaks, indicating that the large clustering coefficient may slower the
spreading velocity especially in the outbreaks.Comment: 13 pages, 10 figure
Dietary and Behavioral Interventions Protect against Age Related Activation of Caspase Cascades in the Canine Brain
Lifestyle interventions such as diet, exercise, and cognitive training represent a quietly emerging revolution in the modern approach to counteracting age-related declines in brain health. Previous studies in our laboratory have shown that long-term dietary supplementation with antioxidants and mitochondrial cofactors (AOX) or behavioral enrichment with social, cognitive, and exercise components (ENR), can effectively improve cognitive performance and reduce brain pathology of aged canines, including oxidative damage and Aβ accumulation. In this study, we build on and extend our previous findings by investigating if the interventions reduce caspase activation and ceramide accumulation in the aged frontal cortex, since caspase activation and ceramide accumulation are common convergence points for oxidative damage and Aβ, among other factors associated with the aged and AD brain. Aged beagles were placed into one of four treatment groups: CON – control environment/control diet, AOX– control environment/antioxidant diet, ENR – enriched environment/control diet, AOX/ENR– enriched environment/antioxidant diet for 2.8 years. Following behavioral testing, brains were removed and frontal cortices were analyzed to monitor levels of active caspase 3, active caspase 9 and their respective cleavage products such as tau and semaphorin7a, and ceramides. Our results show that levels of activated caspase-3 were reduced by ENR and AOX interventions with the largest reduction occurring with combined AOX/ENR group. Further, reductions in caspase-3 correlated with reduced errors in a reversal learning task, which depends on frontal cortex function. In addition, animals treated with an AOX arm showed reduced numbers of cells expressing active caspase 9 or its cleavage product semaphorin 7A, while ENR (but not AOX) reduced ceramide levels. Overall, these data demonstrate that lifestyle interventions curtail activation of pro-degenerative pathways to improve cellular health and are the first to show that lifestyle interventions can regulate caspase pathways in a higher animal model of aging
Age and distraction are determinants of performance on a novel visual search task in aged Beagle dogs
Aging has been shown to disrupt performance on tasks that require intact visual search and discrimination abilities in human studies. The goal of the present study was to determine if canines show age-related decline in their ability to perform a novel simultaneous visual search task. Three groups of canines were included: a young group (N = 10; 3 to 4.5 years), an old group (N = 10; 8 to 9.5 years), and a senior group (N = 8; 11 to 15.3 years). Subjects were first tested for their ability to learn a simple two-choice discrimination task, followed by the visual search task. Attentional demands in the task were manipulated by varying the number of distracter items; dogs received an equal number of trials with either zero, one, two, or three distracters. Performance on the two-choice discrimination task varied with age, with senior canines making significantly more errors than the young. Performance accuracy on the visual search task also varied with age; senior animals were significantly impaired compared to both the young and old, and old canines were intermediate in performance between young and senior. Accuracy decreased significantly with added distracters in all age groups. These results suggest that aging impairs the ability of canines to discriminate between task-relevant and -irrelevant stimuli. This is likely to be derived from impairments in cognitive domains such as visual memory and learning and selective attention
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