129,186 research outputs found
Investigation of fitness function weight-coefficients for optimization in WMN-PSO simulation system
(c) 2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.With the fast development of wireless technologies, Wireless Mesh Networks (WMNs) are becoming an important networking infrastructure due to their low cost and increased high speed wireless Internet connectivity. In our previous work, we implemented a simulation system based on Particle Swam Optimization for solving node placement problem in wireless mesh networks, called WMN-PSO. In this paper, we use Size of Giant Component (SGC) and Number of Covered Mesh Clients (NCMC) as metrics for optimization. Then, we analyze effects of weight-coefficients for SGC and NCMC. From the simulation results, we found that the best values of the weight-coefficients for SGC and NCMC are 0.7 and 0.3, respectively.Peer ReviewedPostprint (author's final draft
Threshold for the Outbreak of Cascading Failures in Degree-degree Uncorrelated Networks
In complex networks, the failure of one or very few nodes may cause cascading
failures. When this dynamical process stops in steady state, the size of the
giant component formed by remaining un-failed nodes can be used to measure the
severity of cascading failures, which is critically important for estimating
the robustness of networks. In this paper, we provide a cascade of overload
failure model with local load sharing mechanism, and then explore the threshold
of node capacity when the large-scale cascading failures happen and un-failed
nodes in steady state cannot connect to each other to form a large connected
sub-network. We get the theoretical derivation of this threshold in
degree-degree uncorrelated networks, and validate the effectiveness of this
method in simulation. This threshold provide us a guidance to improve the
network robustness under the premise of limited capacity resource when creating
a network and assigning load. Therefore, this threshold is useful and important
to analyze the robustness of networks.Comment: 11 pages, 4 figure
Ramsey games with giants
The classical result in the theory of random graphs, proved by Erdos and
Renyi in 1960, concerns the threshold for the appearance of the giant component
in the random graph process. We consider a variant of this problem, with a
Ramsey flavor. Now, each random edge that arrives in the sequence of rounds
must be colored with one of R colors. The goal can be either to create a giant
component in every color class, or alternatively, to avoid it in every color.
One can analyze the offline or online setting for this problem. In this paper,
we consider all these variants and provide nontrivial upper and lower bounds;
in certain cases (like online avoidance) the obtained bounds are asymptotically
tight.Comment: 29 pages; minor revision
Social Bootstrapping: How Pinterest and Last.fm Social Communities Benefit by Borrowing Links from Facebook
How does one develop a new online community that is highly engaging to each
user and promotes social interaction? A number of websites offer friend-finding
features that help users bootstrap social networks on the website by copying
links from an established network like Facebook or Twitter. This paper
quantifies the extent to which such social bootstrapping is effective in
enhancing a social experience of the website. First, we develop a stylised
analytical model that suggests that copying tends to produce a giant connected
component (i.e., a connected community) quickly and preserves properties such
as reciprocity and clustering, up to a linear multiplicative factor. Second, we
use data from two websites, Pinterest and Last.fm, to empirically compare the
subgraph of links copied from Facebook to links created natively. We find that
the copied subgraph has a giant component, higher reciprocity and clustering,
and confirm that the copied connections see higher social interactions.
However, the need for copying diminishes as users become more active and
influential. Such users tend to create links natively on the website, to users
who are more similar to them than their Facebook friends. Our findings give new
insights into understanding how bootstrapping from established social networks
can help engage new users by enhancing social interactivity.Comment: Proc. 23rd International World Wide Web Conference (WWW), 201
Coarse-graining the dynamics of network evolution: the rise and fall of a networked society
We explore a systematic approach to studying the dynamics of evolving
networks at a coarse-grained, system level. We emphasize the importance of
finding good observables (network properties) in terms of which coarse grained
models can be developed. We illustrate our approach through a particular social
network model: the "rise and fall" of a networked society [1]: we implement our
low-dimensional description computationally using the equation-free approach
and show how it can be used to (a) accelerate simulations and (b) extract
system-level stability/bifurcation information from the detailed dynamic model.
We discuss other system-level tasks that can be enabled through such a
computer-assisted coarse graining approach.Comment: 18 pages, 11 figure
The M81 Group Dwarf Irregular Galaxy DDO 165. I. High Velocity Neutral Gas in a Post-Starburst System
We present new multi-configuration VLA HI spectral line observations of the
M81 group dIrr post-starburst galaxy DDO 165. The HI morphology is complex,
with multiple column density peaks surrounding a large region of very low HI
surface density that is offset from the center of the stellar distribution. The
bulk of the neutral gas is associated with the southern section of the galaxy;
a secondary peak in the north contains ~15% of the total HI mass. These
components appear to be kinematically distinct, suggesting that either tidal
processes or large-scale blowout have recently shaped the ISM of DDO 165. Using
spatially-resolved position-velocity maps, we find multiple localized
high-velocity gas features. Cross-correlating with radius-velocity analyses, we
identify eight shell/hole structures in the ISM with a range of sizes (~400-900
pc) and expansion velocities (~7-11 km/s). These structures are compared with
narrow- and broad-band imaging from KPNO and HST. Using the latter data, recent
works have shown that DDO 165's previous "burst" phase was extended temporally
(>1 Gyr). We thus interpret the high-velocity gas features, HI holes, and
kinematically distinct components of the galaxy in the context of the immediate
effects of "feedback" from recent star formation. In addition to creating HI
holes and shells, extended star formation events are capable of creating
localized high velocity motion of the surrounding interstellar material. A
companion paper connects the energetics from the HI and HST data.Comment: The Astrophysical Journal, in press. Full-resolution version
available on request from the first autho
Maximizing the size of the giant
We consider two classes of random graphs: Poissonian random graphs in
which the vertices in the graph have i.i.d.\ weights distributed as ,
where . Edges are added according to a product measure and
the probability that a vertex of weight shares and edge with a vertex of
weight is given by . A thinned configuration model
in which we create a ground-graph in which the vertices have i.i.d.\
ground-degrees, distributed as , with . The graph of
interest is obtained by deleting edges independently with probability .
In both models the fraction of vertices in the largest connected component
converges in probability to a constant , where depends on or
and .
We investigate for which distributions and with given and ,
is maximized. We show that in the class of Poissonian random graphs,
should have all its mass at 0 and one other real, which can be explicitly
determined. For the thinned configuration model should have all its mass at
0 and two subsequent positive integers
The M81 Group Dwarf Irregular Galaxy DDO 165. II. Connecting Recent Star Formation with ISM Structures and Kinematics
We compare the stellar populations and complex neutral gas dynamics of the
M81 group dIrr galaxy DDO 165 using data from the HST and the VLA. Paper I
identified two kinematically distinct HI components, multiple localized high
velocity gas features, and eight HI holes and shells (the largest of which
spans ~2.2x1.1 kpc). Using the spatial and temporal information from the
stellar populations in DDO 165, we compare the patterns of star formation over
the past 500 Myr with the HI dynamics. We extract localized star formation
histories within 6 of the 8 HI holes identified in Paper I, as well as 23 other
regions that sample a range of stellar densities and neutral gas properties.
From population synthesis modeling, we derive the energy outputs (from stellar
winds and supernovae) of the stellar populations within these regions over the
last 100 Myr, and compare with refined estimates of the energies required to
create the HI holes. In all cases, we find that "feedback" is energetically
capable of creating the observed structures in the ISM. Numerous regions with
significant energy inputs from feedback lack coherent HI structures but show
prominent localized high velocity gas features; this feedback signature is a
natural product of temporally and spatially distributed star formation. In DDO
165, the extended period of heightened star formation activity (lasting more
than 1 Gyr) is energetically capable of creating the observed holes and high
velocity gas features in the neutral ISM.Comment: The Astrophysical Journal, in press. Full-resolution version
available on request from the first autho
Herd Immunity/Herd Infection: Cultural Artifacts of Marginalization and the Dynamics of AIDS
We examine conditions under which high prevalence of infectious disease can become endemic within a community, in effect constituting a state of 'herd infection' inverse to epidemiological herd immunity. For something like AIDS, under such circumstances, a single behavioral lapse or adverse accident will probably be a death sentence
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