2,896 research outputs found
Continuous Forest Fire Propagation in a Local Small World Network Model
This paper presents the development of a new continuous forest fire model
implemented as a weighted local small-world network approach. This new approach
was designed to simulate fire patterns in real, heterogeneous landscapes. The
wildland fire spread is simulated on a square lattice in which each cell
represents an area of the land's surface. The interaction between burning and
non-burning cells, in the present work induced by flame radiation, may be
extended well beyond nearest neighbors. It depends on local conditions of
topography and vegetation types. An approach based on a solid flame model is
used to predict the radiative heat flux from the flame generated by the burning
of each site towards its neighbors. The weighting procedure takes into account
the self-degradation of the tree and the ignition processes of a combustible
cell through time. The model is tested on a field presenting a range of slopes
and with data collected from a real wildfire scenario. The critical behavior of
the spreading process is investigated
Bouncing localized structures in a liquid-crystal light-valve experiment
Experimental evidence of bouncing localized structures in a nonlinear optical
system is reported.Comment: 4 page
Introduction: Localized Structures in Dissipative Media: From Optics to Plant Ecology
Localised structures in dissipative appears in various fields of natural
science such as biology, chemistry, plant ecology, optics and laser physics.
The proposed theme issue is to gather specialists from various fields of
non-linear science toward a cross-fertilisation among active areas of research.
This is a cross-disciplinary area of research dominated by the nonlinear optics
due to potential applications for all-optical control of light, optical
storage, and information processing. This theme issue contains contributions
from 18 active groups involved in localized structures field and have all made
significant contributions in recent years.Comment: 14 pages, 0 figure, submitted to Phi. Trasaction Royal Societ
The Professor Who Changed My Life: A Sesquicentennial Celebration of Educational Interaction at University of the Pacific
https://scholarlycommons.pacific.edu/pacific-pubs/1004/thumbnail.jp
Towards a Better Understanding of the Local Attractor in Particle Swarm Optimization: Speed and Solution Quality
Particle Swarm Optimization (PSO) is a popular nature-inspired meta-heuristic
for solving continuous optimization problems. Although this technique is widely
used, the understanding of the mechanisms that make swarms so successful is
still limited. We present the first substantial experimental investigation of
the influence of the local attractor on the quality of exploration and
exploitation. We compare in detail classical PSO with the social-only variant
where local attractors are ignored. To measure the exploration capabilities, we
determine how frequently both variants return results in the neighborhood of
the global optimum. We measure the quality of exploitation by considering only
function values from runs that reached a search point sufficiently close to the
global optimum and then comparing in how many digits such values still deviate
from the global minimum value. It turns out that the local attractor
significantly improves the exploration, but sometimes reduces the quality of
the exploitation. As a compromise, we propose and evaluate a hybrid PSO which
switches off its local attractors at a certain point in time. The effects
mentioned can also be observed by measuring the potential of the swarm
X-ray AGN in the XMM-LSS galaxy clusters: no evidence of AGN suppression
We present a study of the overdensity of X-ray selected AGN in 33 galaxy
clusters in the XMM-LSS field, up to redhift z=1.05. Previous studies have
shown that the presence of X-ray selected AGN in rich galaxy clusters is
suppressed. In the current study we investigate the occurrence of X-ray
selected AGN in low and moderate X-ray luminosity galaxy clusters. Due to the
wide contiguous XMM-LSS survey area we are able to extend the study to the
cluster outskirts. We therefore determine the projected overdensity of X-ray
point-like sources out to 6r_{500} radius. To provide robust statistical
results we also use a stacking analysis of the cluster projected overdensities.
We investigate whether the observed X-ray overdensities are to be expected by
estimating also the corresponding optical galaxy overdensities. We find a
positive X-ray projected overdensity at the first radial bin, which is however
of the same amplitude as that of optical galaxies. Therefore, no suppression of
X-ray AGN activity with respect to the field is found, implying that the
mechanisms responsible for the suppression are not so effective in lower
density environments. After a drop to roughly the background level between 2
and 3r_{500}, the X-ray overdensity exhibits a rise at larger radii,
significantly larger than the corresponding optical overdensity. Finally, using
redshift information of all optical counterparts, we derive the spatial
overdensity profile of the clusters. We find that the agreement between X-ray
and optical overdensities in the first radial bin is also suggested in the
3-dimensional analysis. However, we argue that the X-ray overdensity "bump" at
larger radial distance is probably a result of flux boosting by gravitational
lensing of background QSOs. For high redshift clusters an enhancement of X-ray
AGN activity in their outskirts is still possible.Comment: 16 pages. Accepted for publication in A&
Universal shape law of stochastic supercritical bifurcations: Theory and experiments
A universal law for the supercritical bifurcation shape of transverse
one-dimensional (1D) systems in presence of additive noise is given. The
stochastic Langevin equation of such systems is solved by using a Fokker-Planck
equation leading to the expression for the most probable amplitude of the
critical mode. From this universal expression, the shape of the bifurcation,
its location and its evolution with the noise level are completely defined.
Experimental results obtained for a 1D transverse Kerr-like slice subjected to
optical feedback are in excellent agreement.Comment: 5 pages, 5 figure
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