18,065 research outputs found
Terrain Database Correlation Assessment Using an Open Source Tool
Configuring networked simulators for training military teams in a distributed
environment requires the usage of a set of terrain databases to represent the
same training area. The results of simulation exercises can be degraded if the
terrain databases are poorly correlated. A number of methodologies for
determining the correlation between terrain databaHowever, there are few
computational tools for this task and most of them were developed to address
government needs, have limited availability, and handle specific digital
formats. The goal of this paper is thus to present a novel open source tool
developed as part of an academic research project.Comment: 12 pages, I/ITSEC 201
Optimal control strategies for tuberculosis treatment: a case study in Angola
We apply optimal control theory to a tuberculosis model given by a system of
ordinary differential equations. Optimal control strategies are proposed to
minimize the cost of interventions. Numerical simulations are given using data
from Angola.Comment: This is a preprint of a paper whose final and definite form will
appear in the international journal Numerical Algebra, Control and
Optimization (NACO). Paper accepted for publication 15-March-201
Blobs in Wolf-Rayet Winds: Random Photometric and Polarimetric Variability
Some isolated Wolf-Rayet stars present random variability in their optical
flux and polarization. We make the assumption that such variability is caused
by the presence of regions of enhanced density, i.e. blobs, in their envelopes.
In order to find the physical characteristics of such regions we have modeled
the stellar emission using a Monte Carlo code to treat the radiative transfer
in an inhomogeneous electron scattering envelope. We are able to treat multiple
scattering in the regions of enhanced density as well as in the envelope
itself. The finite sizes of the source and structures in the wind are also
taken into account. Most of the results presented here are based on a parameter
study of models with a single blob. The effects due to multiple blobs in the
envelope are considered to a more limited extent. Our simulations indicate that
the density enhancements must have a large geometric cross section in order to
produce the observed photopolarimetric variability. The sizes must be of the
order of one stellar radius and the blobs must be located near the base of the
envelope. These sizes are the same inferred from the widths of the sub-peaks in
optical emission lines of Wolf-Rayet stars. Other early-type stars show random
polarimetric fluctuations with characteristics similar to those observed in
Wolf-Rayet stars, which may also be interpreted in terms of a clumpy wind.
Although the origin of such structures is still unclear, the same mechanism may
be working in different types of hot stars envelopes to produce such
inhomogeneities.Comment: Accepted to ApJ. 17 pages + 6 figure
Environment, morphology and stellar populations of bulgeless low surface brightness galaxies
Based on the Sloan Digital Sky Survey DR 7, we investigate the environment,
morphology and stellar population of bulgeless low surface brightness (LSB)
galaxies in a volume-limited sample with redshift ranging from 0.024 to 0.04
and . The local density parameter is used to
trace their environments. We find that, for bulgeless galaxies, the surface
brightness does not depend on the environment. The stellar populations are
compared for bulgeless LSB galaxies in different environments and for bulgeless
LSB galaxies with different morphologies. The stellar populations of LSB
galaxies in low density regions are similar to those of LSB galaxies in high
density regions. Irregular LSB galaxies have more young stars and are more
metal-poor than regular LSB galaxies. These results suggest that the evolution
of LSB galaxies may be driven by their dynamics including mergers rather than
by their large scale environment.Comment: 12 pages, 13 figures, Accepted by A&
Regeneração de espécies silvestres brasileiras de arroz através do cultivo de embrião.
O objetivo deste trabalho foi regenerar os acessos das espécies silvestres de arroz brasileiras através do cultivo de embriões
Ocorrência da murcha de Sclerotium no feijão caupi no estado do Pará.
Edição dos resumos do 44º Congresso Brasileiro de Fitopatologia, 2011, Bento Gonçalves. Resumo 1173
On Matrix Superpotential and Three-Component Normal Modes
We consider the supersymmetric quantum mechanics (SUSY QM) with three-
component normal modes for the Bogomol'nyi-Prasad-Sommerfield (BPS) states. An
explicit form of the SUSY QM matrix superpotential is presented and the
corresponding three-component bosonic zero-mode eigenfunction is investigated.Comment: 17 pages, no figure. Paper accepted for publication in Journal of
Physics A: Mathematical and Theoretica
Random fluctuation leads to forbidden escape of particles
A great number of physical processes are described within the context of
Hamiltonian scattering. Previous studies have rather been focused on
trajectories starting outside invariant structures, since the ones starting
inside are expected to stay trapped there forever. This is true though only for
the deterministic case. We show however that, under finitely small random
fluctuations of the field, trajectories starting inside Arnold-Kolmogorov-Moser
(KAM) islands escape within finite time. The non-hyperbolic dynamics gains then
hyperbolic characteristics due to the effect of the random perturbed field. As
a consequence, trajectories which are started inside KAM curves escape with
hyperbolic-like time decay distribution, and the fractal dimension of a set of
particles that remain in the scattering region approaches that for hyperbolic
systems. We show a universal quadratic power law relating the exponential decay
to the amplitude of noise. We present a random walk model to relate this
distribution to the amplitude of noise, and investigate this phenomena with a
numerical study applying random maps.Comment: 6 pages, 6 figures - Up to date with corrections suggested by
referee
The role of structural evolution on the quantum conductance behavior of gold nanowires during stretching
Gold nanowires generated by mechanical stretching have been shown to adopt
only three kinds of configurations where their atomic arrangements adjust such
that either the [100], [111] or [110] zone axes lie parallel to the elongation
direction. We have analyzed the relationship between structural rearrangements
and electronic transport behavior during the elongation of Au nanowires for
each of the three possibilities. We have used two independent experiments to
tackle this problem, high resolution transmission high resolution electron
microscopy to observe the atomic structure and a mechanically controlled break
junction to measure the transport properties. We have estimated the conductance
of nanowires using a theoretical method based on the extended H\"uckel theory
that takes into account the atom species and their positions. Aided by these
calculations, we have consistently connected both sets of experimental results
and modeled the evolution process of gold nanowires whose conductance lies
within the first and third conductance quanta. We have also presented evidence
that carbon acts as a contaminant, lowering the conductance of one-atom-thick
wires.Comment: 10 page
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