20,385 research outputs found
Fully Automatic Expression-Invariant Face Correspondence
We consider the problem of computing accurate point-to-point correspondences
among a set of human face scans with varying expressions. Our fully automatic
approach does not require any manually placed markers on the scan. Instead, the
approach learns the locations of a set of landmarks present in a database and
uses this knowledge to automatically predict the locations of these landmarks
on a newly available scan. The predicted landmarks are then used to compute
point-to-point correspondences between a template model and the newly available
scan. To accurately fit the expression of the template to the expression of the
scan, we use as template a blendshape model. Our algorithm was tested on a
database of human faces of different ethnic groups with strongly varying
expressions. Experimental results show that the obtained point-to-point
correspondence is both highly accurate and consistent for most of the tested 3D
face models
Mass inventory of the giant-planet formation zone in a solar nebula analog
The initial mass distribution in the solar nebula is a critical input to
planet formation models that seek to reproduce today's Solar System.
Traditionally, constraints on the gas mass distribution are derived from
observations of the dust emission from disks, but this approach suffers from
large uncertainties in grain growth and gas-to-dust ratio. On the other hand,
previous observations of gas tracers only probe surface layers above the bulk
mass reservoir. Here we present the first partially spatially resolved
observations of the CO J=3-2 line emission in the closest
protoplanetary disk, TW Hya, a gas tracer that probes the bulk mass
distribution. Combining it with the CO J=3-2 emission and the previously
detected HD J=1-0 flux, we directly constrain the mid-plane temperature and
optical depths of gas and dust emission. We report a gas mass distribution of
13(R/20.5AU) g cm in the
expected formation zone of gas and ice giants (5-21AU). We find the total
gas/millimeter-sized dust mass ratio is 140 in this region, suggesting that at
least 2.4M_earth of dust aggregates have grown to >centimeter sizes (and
perhaps much larger). The radial distribution of gas mass is consistent with a
self-similar viscous disk profile but much flatter than the posterior
extrapolation of mass distribution in our own and extrasolar planetary systems.Comment: Definitive version of the manuscript is published in Nature
Astronomy, 10.1038/s41550-017-0130. This is the authors' versio
Partial-volume Bayesian classification of material mixtures in MR volume data using voxel histograms
The authors present a new algorithm for identifying the distribution of different material types in volumetric datasets such as those produced with magnetic resonance imaging (MRI) or computed tomography (CT). Because the authors allow for mixtures of materials and treat voxels as regions, their technique reduces errors that other classification techniques can create along boundaries between materials and is particularly useful for creating accurate geometric models and renderings from volume data. It also has the potential to make volume measurements more accurately and classifies noisy, low-resolution data well. There are two unusual aspects to the authors' approach. First, they assume that, due to partial-volume effects, or blurring, voxels can contain more than one material, e.g., both muscle and fat; the authors compute the relative proportion of each material in the voxels. Second, they incorporate information from neighboring voxels into the classification process by reconstructing a continuous function, Ï(x), from the samples and then looking at the distribution of values that Ï(x) takes on within the region of a voxel. This distribution of values is represented by a histogram taken over the region of the voxel; the mixture of materials that those values measure is identified within the voxel using a probabilistic Bayesian approach that matches the histogram by finding the mixture of materials within each voxel most likely to have created the histogram. The size of regions that the authors classify is chosen to match the sparing of the samples because the spacing is intrinsically related to the minimum feature size that the reconstructed continuous function can represent
The Dark Matter Radial Profile in the Core of the Relaxed Cluster A2589
We present an analysis of a Chandra--ACIS observation of the galaxy cluster
A2589 to constrain the radial distribution of the total gravitating matter and
the dark matter in the core of the cluster. A2589 is especially well-suited for
this analysis because the hot gas in its core region (r < ~0.1 Rvir) is
undisturbed by interactions with a central radio source. From the largest
radius probed (r=0.07 Rvir) down to r ~0.02 Rvir dark matter dominates the
gravitating mass. Over this region the radial profiles of the gravitating and
dark matter are fitted well by the NFW and Hernquist profiles predicted by CDM.
The density profiles are also described well by power laws, rho ~r^{-alpha},
where alpha=1.37 +/- 0.14 for the gravitating matter and alpha=1.35 +/- 0.21
for the dark matter. These values are consistent with profiles of CDM halos but
are significantly larger than alpha ~0.5 found in LSB galaxies and expected
from self-interacting dark matter models.Comment: 10 pages, 6 figures, To Appear in The Astrophysical Journal, March 20
issue, a few very minor changes to match copyedited versio
A multipole-Taylor expansion for the potential of gravitational lens MG J0414+0534
We employ a multipole-Taylor expansion to investigate how tightly the
gravitational potential of the quadruple-image lens MG J0414+0534 is
constrained by recent VLBI observations. These observations revealed that each
of the four images of the background radio source contains four distinct
components, thereby providing more numerous and more precise constraints on the
lens potential than were previously available. We expand the two-dimensional
lens potential using multipoles for the angular coordinate and a modified
Taylor series for the radial coordinate. After discussing the physical
significance of each term, we compute models of MG J0414+0534 using only VLBI
positions as constraints. The best-fit model has both interior and exterior
quadrupole moments as well as exterior m=3 and m=4 multipole moments. The
deflector centroid in the models matches the optical galaxy position, and the
quadrupoles are aligned with the optical isophotes. The radial distribution of
mass could not be well constrained. We discuss the implications of these models
for the deflector mass distribution and for the predicted time delays between
lensed components.Comment: 44 pages, 5 figures, 11 tables, accepted for publication in Ap
GEMS: Galaxy Evolution from Morphologies and SEDs
GEMS, Galaxy Evolution from Morphologies and SEDs, is a large-area (800
arcmin2) two-color (F606W and F850LP) imaging survey with the Advanced Camera
for Surveys on HST. Centered on the Chandra Deep Field South, it covers an area
of ~28'x28', or about 120 Hubble Deep Field areas, to a depth of
m_AB(F606W)=28.3 (5sigma and m_AB(F850LP)=27.1 (5sigma) for compact sources. In
its central ~1/4, GEMS incorporates ACS imaging from the GOODS project.
Focusing on the redshift range 0.2<=z<=1.1, GEMS provides morphologies and
structural parameters for nearly 10,000 galaxies where redshift estimates,
luminosities and SEDs exist from COMBO-17. At the same time, GEMS contains
detectable host galaxy images for several hundred faint AGN. This paper
provides an overview of the science goals, the experiment design, the data
reduction and the science analysis plan for GEMS.Comment: 24 pages, TeX with 6 eps Figures; to appear in ApJ Supplement. Low
resolution figures only. Full resolution at
http://zwicky.as.arizona.edu/~rix/Misc/GEMS.ps.g
ROAM: a Radial-basis-function Optimization Approximation Method for diagnosing the three-dimensional coronal magnetic field
The Coronal Multichannel Polarimeter (CoMP) routinely performs coronal
polarimetric measurements using the Fe XIII 10747 and 10798 lines,
which are sensitive to the coronal magnetic field. However, inverting such
polarimetric measurements into magnetic field data is a difficult task because
the corona is optically thin at these wavelengths and the observed signal is
therefore the integrated emission of all the plasma along the line of sight. To
overcome this difficulty, we take on a new approach that combines a
parameterized 3D magnetic field model with forward modeling of the polarization
signal. For that purpose, we develop a new, fast and efficient, optimization
method for model-data fitting: the Radial-basis-functions Optimization
Approximation Method (ROAM). Model-data fitting is achieved by optimizing a
user-specified log-likelihood function that quantifies the differences between
the observed polarization signal and its synthetic/predicted analogue. Speed
and efficiency are obtained by combining sparse evaluation of the magnetic
model with radial-basis-function (RBF) decomposition of the log-likelihood
function. The RBF decomposition provides an analytical expression for the
log-likelihood function that is used to inexpensively estimate the set of
parameter values optimizing it. We test and validate ROAM on a synthetic test
bed of a coronal magnetic flux rope and show that it performs well with a
significantly sparse sample of the parameter space. We conclude that our
optimization method is well-suited for fast and efficient model-data fitting
and can be exploited for converting coronal polarimetric measurements, such as
the ones provided by CoMP, into coronal magnetic field data.Comment: 23 pages, 12 figures, accepted in Frontiers in Astronomy and Space
Science
3D reconstruction of ribcage geometry from biplanar radiographs using a statistical parametric model approach
Rib cage 3D reconstruction is an important prerequisite for thoracic spine modelling, particularly for studies of the deformed thorax in adolescent idiopathic scoliosis. This study proposes a new method for rib cage 3D reconstruction from biplanar radiographs, using a statistical parametric model approach. Simplified parametric models were defined at the hierarchical levels of rib cage surface, rib midline and rib surface, and applied on a database of 86 trunks. The resulting parameter database served to statistical models learning which were used to quickly provide a first estimate of the reconstruction from identifications on both radiographs. This solution was then refined by manual adjustments in order to improve the matching between model and image. Accuracy was assessed by comparison with 29 rib cages from CT scans in terms of geometrical parameter differences and in terms of line-to-line error distance between the rib midlines. Intra and inter-observer reproducibility were determined regarding 20 scoliotic patients. The first estimate (mean reconstruction time of 2â30) was sufficient to extract the main rib cage global parameters with a 95% confidence interval lower than 7%, 8%, 2% and 4° for rib cage volume, antero-posterior and lateral maximal diameters and maximal rib hump, respectively. The mean error distance was 5.4 mm (max 35mm) down to 3.6 mm (max 24 mm) after the manual adjustment step (+3â30). The proposed method will improve developments of rib cage finite element modeling and evaluation of clinical outcomes.This work was funded by Paris Tech BiomecAM chair on subject specific muscular skeletal modeling, and we express our acknowledgments to the chair founders: Cotrel foundation, SociĂ©tĂ© gĂ©nĂ©rale, ProtĂ©or Company and COVEA consortium. We extend your acknowledgements to Alina Badina for medical imaging data, Alexandre JournĂ© for his advices, and Thomas Joubert for his technical support
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