1,042 research outputs found
A Bottom Up Procedure for Text Line Segmentation of Latin Script
In this paper we present a bottom up procedure for segmentation of text lines
written or printed in the Latin script. The proposed method uses a combination
of image morphology, feature extraction and Gaussian mixture model to perform
this task. The experimental results show the validity of the procedure.Comment: Accepted and presented at the IEEE conference "International
Conference on Advances in Computing, Communications and Informatics (ICACCI)
2017
Image morphology: from perception to rendering
Complete image ontology can be obtained by formalising a top-down meta-language wich must address all possibilities, from global message and composition to objects and local surface properties
Resonant Scattering of Emission Lines in Coronal Loops: Effects on Image Morphology and Line Ratios
We have investigated the effects of resonant scattering of emission lines on
the image morphology and intensity from coronal loop structures. It has
previously been shown that line of sight effects in optically thin line
emission can yield loop images that appear uniformly bright at one viewing
angle, but show ``looptop sources'' at other viewing angles. For optically
thick loops where multiple resonant scattering is important, we use a 3D Monte
Carlo radiation transfer code. Our simulations show that the intensity
variation across the image is more uniform than the optically thin simulation
and, depending on viewing angle, the intensity may be lower or higher than that
predicted from optically thin simulations due to scattering out of or into the
line of sight.Comment: Accepted for publication in Ap
Models of gravitational lens candidates from Space Warps CFHTLS
We report modelling follow-up of recently-discovered gravitational-lens
candidates in the Canada France Hawaii Telescope Legacy Survey. Lens modelling
was done by a small group of specially-interested volunteers from the
SpaceWarps citizen-science community who originally found the candidate lenses.
Models are categorised according to seven diagnostics indicating (a) the image
morphology and how clear or indistinct it is, (b) whether the mass map and
synthetic lensed image appear to be plausible, and (c) how the lens-model mass
compares with the stellar mass and the abundance-matched halo mass. The lensing
masses range from ~10^11 Msun to >10^13 Msun. Preliminary estimates of the
stellar masses show a smaller spread in stellar mass (except for two lenses): a
factor of a few below or above ~10^11 Msun. Therefore, we expect the
stellar-to-total mass fraction to decline sharply as lensing mass increases.
The most massive system with a convincing model is J1434+522 (SW05). The two
low-mass outliers are J0206-095 (SW19) and J2217+015 (SW42); if these two are
indeed lenses, they probe an interesting regime of very low star-formation
efficiency. Some improvements to the modelling software (SpaghettiLens), and
discussion of strategies regarding scaling to future surveys with more and
frequent discoveries, are included.Comment: 16 pages, 10 figures, 1 table, online supplement table_1.csv contains
additional detailed numbers shown in table 1 and figure
Evidence for Low Black Hole Spin and Physically Motivated Accretion Models from Millimeter VLBI Observations of Sagittarius A*
Millimeter very-long baseline interferometry (mm-VLBI) provides the novel
capacity to probe the emission region of a handful of supermassive black holes
on sub-horizon scales. For Sagittarius A* (Sgr A*), the supermassive black hole
at the center of the Milky Way, this provides access to the region in the
immediate vicinity of the horizon. Broderick et al. (2009) have already shown
that by leveraging spectral and polarization information as well as accretion
theory, it is possible to extract accretion-model parameters (including black
hole spin) from mm-VLBI experiments containing only a handful of telescopes.
Here we repeat this analysis with the most recent mm-VLBI data, considering a
class of aligned, radiatively inefficient accretion flow (RIAF) models. We find
that the combined data set rules out symmetric models for Sgr A*'s flux
distribution at the 3.9-sigma level, strongly favoring length-to-width ratios
of roughly 2.4:1. More importantly, we find that physically motivated accretion
flow models provide a significantly better fit to the mm-VLBI observations than
phenomenological models, at the 2.9-sigma level. This implies that not only is
mm-VLBI presently capable of distinguishing between potential physical models
for Sgr A*'s emission, but further that it is sensitive to the strong
gravitational lensing associated with the propagation of photons near the black
hole. Based upon this analysis we find that the most probable magnitude,
viewing angle, and position angle for the black hole spin are
a=0.0(+0.64+0.86), theta=68(+5+9)(-20-28) degrees, and xi=-52(+17+33)(-15-24)
east of north, where the errors quoted are the 1-sigma and 2-sigma
uncertainties.Comment: 15 pages, 10 figures, submitted to Ap
ALMA Observations of the Gravitational Lens SDP.9
We present long-baseline ALMA observations of the strong gravitational lens
H-ATLAS J090740.0-004200 (SDP.9), which consists of an elliptical galaxy at
lensing a background submillimeter galaxy into two
extended arcs. The data include Band 6 continuum observations, as well as CO
=65 molecular line observations, from which we measure an updated source
redshift of . The image morphology in the ALMA data is
different from that of the HST data, indicating a spatial offset between the
stellar, gas, and dust component of the source galaxy. We model the lens as an
elliptical power law density profile with external shear using a combination of
archival HST data and conjugate points identified in the ALMA data. Our best
model has an Einstein radius of and a
slightly steeper than isothermal mass profile slope. We search for the central
image of the lens, which can be used constrain the inner mass distribution of
the lens galaxy including the central supermassive black hole, but do not
detect it in the integrated CO image at a 3 rms level of 0.0471 Jy km
s.Comment: Accepted for publication in ApJL; 6 pages, 2 figures, 3 table
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