897 research outputs found
Self-correction of 3D reconstruction from multi-view stereo images
We present a self-correction approach to improving the
3D reconstruction of a multi-view 3D photogrammetry system.
The self-correction approach has been able to repair
the reconstructed 3D surface damaged by depth discontinuities.
Due to self-occlusion, multi-view range images
have to be acquired and integrated into a watertight nonredundant
mesh model in order to cover the extended surface
of an imaged object. The integrated surface often suffers
from âdentâ artifacts produced by depth discontinuities
in the multi-view range images. In this paper we propose
a novel approach to correcting the 3D integrated surface
such that the dent artifacts can be repaired automatically.
We show examples of 3D reconstruction to demonstrate the
improvement that can be achieved by the self-correction
approach. This self-correction approach can be extended
to integrate range images obtained from alternative range
capture devices
Applying mesh conformation on shape analysis with missing data
A mesh conformation approach that makes use of deformable generic meshes has been applied to establishing correspondences between 3D shapes with missing data. Given a group of shapes with correspondences, we can build up a statistical shape model by applying principal component analysis (PCA). The conformation at first globally maps the generic mesh to the 3D shape based on manually located corresponding landmarks, and then locally deforms the generic mesh to clone the 3D shape. The local deformation is constrained by minimizing the energy of an elastic model. An algorithm was also embedded in the conformation process to fill missing surface data of the shapes. Using synthetic data, we demonstrate that the conformation preserves the configuration of the generic mesh and hence it helps to establish good correspondences for shape analysis. Case studies of the principal component analysis of shapes were presented to illustrate the successes and advantages of our approach
Normal families and fixed points of iterates
Let F be a family of holomorphic functions and let K be a constant less than
4. Suppose that for all f in F the second iterate of f does not have fixed
points for which the modulus of the multiplier is greater than K. We show that
then F is normal. This is deduced from a result about the multipliers of
iterated polynomials.Comment: 5 page
Multi-frequency investigation of the parsec- and kilo-parsec-scale radio structures in high-redshift quasar PKS 1402+044
We investigate the frequency-dependent radio properties of the jet of the
luminous high-redshift (z = 3.2) radio quasar PKS 1402+044 (J1405+0415) by
means of radio interferometric observations. The observational data were
obtained with the VLBI Space Observatory Programme (VSOP) at 1.6 and 5 GHz,
supplemented by other multi-frequency observations with the Very Long Baseline
Array (VLBA; 2.3, 8.4, and 15 GHz) and the Very Large Array (VLA; 1.4, 5, 15,
and 43 GHz). The observations span a period of 7 years. We find that the
luminous high-redshift quasar PKS 1402+044 has a pronounced "core-jet"
morphology from the parsec to the kilo-parsec scales. The jet shows a steeper
spectral index and lower brightness temperature with increasing distance from
the jet core. The variation of brightness temperature agrees well with the
shock-in-jet model. Assuming that the jet is collimated by the ambient magnetic
field, we estimate the mass of the central object as ~10^9 M_sun. The upper
limit of the jet proper motion of PKS 1402+044 is 0.03 mas/yr (~3c) in the
east-west direction.Comment: 9 pages, 6 figures
Galactic kinematics with modified Newtonian dynamics
We look for observational signatures that could discriminate between
Newtonian and modified Newtonian (MOND) dynamics in the Milky Way, in view of
the advent of large astrometric and spectroscopic surveys. Indeed, a typical
signature of MOND is an apparent disk of "phantom" dark matter, which is
uniquely correlated with the visible disk-density distribution. Due to this
phantom dark disk, Newtonian models with a spherical halo have different
signatures from MOND models close to the Galactic plane. The models can thus be
differentiated by measuring dynamically (within Newtonian dynamics) the disk
surface density at the solar radius, the radial mass gradient within the disk,
or the velocity ellipsoid tilt angle above the Galactic plane. Using the most
realistic possible baryonic mass model for the Milky Way, we predict that, if
MOND applies, the local surface density measured by a Newtonist will be
approximately 78 Msun/pc2 within 1.1 kpc of the Galactic plane, the dynamically
measured disk scale-length will be enhanced by a factor of 1.25 with respect to
the visible disk scale-length, and the local vertical tilt of the velocity
ellipsoid at 1 kpc above the plane will be approximately 6 degrees. None of
these tests can be conclusive for the present-day accuracy of Milky Way data,
but they will be of prime interest with the advent of large surveys such as
GAIA.Comment: 5 page
Framework for Evidence Assessment Based on Grade and Application to HPV Vaccination in Males in the European Health Care Context
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Swope Supernova Survey 2017a (SSS17a), the Optical Counterpart to a Gravitational Wave Source
On 2017 August 17, the Laser Interferometer Gravitational-wave Observatory
(LIGO) and the Virgo interferometer detected gravitational waves emanating from
a binary neutron star merger, GW170817. Nearly simultaneously, the Fermi and
INTEGRAL telescopes detected a gamma-ray transient, GRB 170817A. 10.9 hours
after the gravitational wave trigger, we discovered a transient and fading
optical source, Swope Supernova Survey 2017a (SSS17a), coincident with
GW170817. SSS17a is located in NGC 4993, an S0 galaxy at a distance of 40
megaparsecs. The precise location of GW170817 provides an opportunity to probe
the nature of these cataclysmic events by combining electromagnetic and
gravitational-wave observations.Comment: 25 pages, 10 figures, 2 tables, published today in Scienc
The Old Host-Galaxy Environment of SSS17a, the First Electromagnetic Counterpart to a Gravitational Wave Source
We present an analysis of the host-galaxy environment of Swope Supernova
Survey 2017a (SSS17a), the discovery of an electromagnetic counterpart to a
gravitational wave source, GW170817. SSS17a occurred 1.9 kpc (in projection;
10.2") from the nucleus of NGC 4993, an S0 galaxy at a distance of 40 Mpc. We
present a Hubble Space Telescope (HST) pre-trigger image of NGC 4993, Magellan
optical spectroscopy of the nucleus of NGC 4993 and the location of SSS17a, and
broad-band UV through IR photometry of NGC 4993. The spectrum and broad-band
spectral-energy distribution indicate that NGC 4993 has a stellar mass of log
(M/M_solar) = 10.49^{+0.08}_{-0.20} and star formation rate of 0.003
M_solar/yr, and the progenitor system of SSS17a likely had an age of >2.8 Gyr.
There is no counterpart at the position of SSS17a in the HST pre-trigger image,
indicating that the progenitor system had an absolute magnitude M_V > -5.8 mag.
We detect dust lanes extending out to almost the position of SSS17a and >100
likely globular clusters associated with NGC 4993. The offset of SSS17a is
similar to many short gamma-ray burst offsets, and its progenitor system was
likely bound to NGC 4993. The environment of SSS17a is consistent with an old
progenitor system such as a binary neutron star system.Comment: ApJL in pres
Detections of Diffuse Interstellar Bands in the SDSS Low-resolution Spectra
Diffuse interstellar bands (DIBs) have been discovered for almost a century,
but their nature remains one of the most challenging problems in astronomical
spectroscopy. Most recent work to identify and investigate the properties and
carriers of DIBs concentrates on high-resolution spectroscopy of selected
sight-lines. In this paper, we report detections of DIBs in the Sloan Digital
Sky Survey (SDSS) low-resolution spectra of a large sample of Galactic stars.
Using a template subtraction method, we have successfully identified the DIBs
5780, 6283 in the SDSS spectra of a sample of about 2,000
stars and measured their strengths and radial velocities. The sample is by far
the largest ever assembled. The targets span a large range of reddening, E(B-V)
~ 0.2 -- 1.0, and are distributed over a large sky area and involve a wide
range of stellar parameters (effective temperature, surface gravity and
metallicity), confirming that the carriers of DIBs are ubiquitous in the
diffuse interstellar medium (ISM). The sample is used to investigate relations
between strengths of DIBs and magnitudes of line-of-sight extinction, yielding
results (i.e., EW(5780)= 0.61 x E(B-V) and EW(6283) = 1.26 x E(B-V)) consistent
with previous studies. DIB features have also been detected in the
commissioning spectra of the Guoshoujing Telescope (LAMOST) of resolving power
similar to that of SDSS. Detections of DIBs towards hundreds of thousands of
stars are expected from the on-going and up-coming large scale spectroscopic
surveys such as RAVE, SDSS III and LAMOST, particularly from the LAMOST Digital
Sky Survey of the Galactic Anti-center (DSS-GAC). Such a huge database will
provide an unprecedented opportunity to study the demographical distribution
and nature of DIBs as well as using DIBs to probe the distribution and
properties of the ISM and the dust extinction.Comment: 10 pages, 5 figures, accepted for publication in MNRA
Building the cosmic distance scale: from Hipparcos to Gaia
Hipparcos, the first ever experiment of global astrometry, was launched by
ESA in 1989 and its results published in 1997 (Perryman et al., Astron.
Astrophys. 323, L49, 1997; Perryman & ESA (eds), The Hipparcos and Tycho
catalogues, ESA SP-1200, 1997). A new reduction was later performed using an
improved satellite attitude reconstruction leading to an improved accuracy for
stars brighter than 9th magnitude (van Leeuwen & Fantino, Astron. Astrophys.
439, 791, 2005; van Leeuwen, Astron. Astrophys. 474, 653, 2007).
The Hipparcos Catalogue provided an extended dataset of very accurate
astrometric data (positions, trigonometric parallaxes and proper motions),
enlarging by two orders of magnitude the quantity and quality of distance
determinations and luminosity calibrations. The availability of more than 20000
stars with a trigonometric parallax known to better than 10% opened the way to
a drastic revision of our 3-D knowledge of the solar neighbourhood and to a
renewal of the calibration of many distance indicators and age estimations. The
prospects opened by Gaia, the next ESA cornerstone, planned for launch in June
2013 (Perryman et al., Astron. Astrophys. 369, 339, 2001), are still much more
dramatic: a billion objects with systematic and quasi simultaneous astrometric,
spectrophotometric and spectroscopic observations, about 150 million stars with
expected distances to better than 10%, all over the Galaxy. All stellar
distance indicators, in very large numbers, will be directly measured,
providing a direct calibration of their luminosity and making possible detailed
studies of the impacts of various effects linked to chemical element
abundances, age or cluster membership. With the help of simulations of the data
expected from Gaia, obtained from the mission simulator developed by DPAC, we
will illustrate what Gaia can provide with some selected examples.Comment: 16 pages, 16 figures, Conference "The Fundamental Cosmic Distance
scale: State of the Art and the Gaia perspective, 3-6 May 2011, INAF,
Osservatorio Astronomico di Capodimonte, Naples. Accepted for publication in
Astrophysics & Space Scienc
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