377 research outputs found
Trifocal Relative Pose from Lines at Points and its Efficient Solution
We present a new minimal problem for relative pose estimation mixing point
features with lines incident at points observed in three views and its
efficient homotopy continuation solver. We demonstrate the generality of the
approach by analyzing and solving an additional problem with mixed point and
line correspondences in three views. The minimal problems include
correspondences of (i) three points and one line and (ii) three points and two
lines through two of the points which is reported and analyzed here for the
first time. These are difficult to solve, as they have 216 and - as shown here
- 312 solutions, but cover important practical situations when line and point
features appear together, e.g., in urban scenes or when observing curves. We
demonstrate that even such difficult problems can be solved robustly using a
suitable homotopy continuation technique and we provide an implementation
optimized for minimal problems that can be integrated into engineering
applications. Our simulated and real experiments demonstrate our solvers in the
camera geometry computation task in structure from motion. We show that new
solvers allow for reconstructing challenging scenes where the standard two-view
initialization of structure from motion fails.Comment: This material is based upon work supported by the National Science
Foundation under Grant No. DMS-1439786 while most authors were in residence
at Brown University's Institute for Computational and Experimental Research
in Mathematics -- ICERM, in Providence, R
Political Effects on the Discontinuation of Participatory Budgeting in Municipalities
The article analyzes the factors associated with the discontinuation of participatory budgeting (PB) in Brazilian municipalities with more than 50,000 inhabitants between 2000 and 2016. We used econometric models to estimate PB’s discontinuation based on political explanatory variables and people’s local participation. The results indicate that discontinuation is associated: (i) positively with the election of a different local government, regardless of the winning party’s ideology; (ii) positively with the election of a local government with a left-wing ideology’; (iii) negatively with the election of a non-left-wing local government; (iv) positively with the election of a left-wing local government replacing another left-wing government. Changes in local government where other non-left-wing parties replace non-left-wing parties had no significant effect on discontinuation. The results contribute to our knowledge by showing the local and contextual factors that explain the discontinuation of participatory budgeting; this should help guide the design of participatory public policies and allow practitioners to reflect on the mechanisms that could be adopted locally to avoid discontinuation. The article also contributes to the literature by demonstrating the association between discontinuation and changes in left-wing local governments, which may prompt future research, given the unexpected result
VLT + UVES Spectroscopy of the Low-Ionization Intrinsic Absorber in SDSS J001130.56+005550.7
We analyse high-resolution VLT+UVES spectra of the low-ionization intrinsic
absorber observed in the BAL QSO SDSS J001130.56+005550.7. Two narrow
absorption systems at velocities -600 km/s and -22000 km/s are detected. The
low-velocity system is part of the broad absorption line (BAL), while the
high-velocity one is well detached. While most narrow absorption components are
only detected in the high-ionization species, the lowest velocity component is
detected in both high- and low-ionization species, including in the excited
SiII* and CII* lines. From the analysis of doublet lines, we find that the
narrow absorption lines at the low-velocity end of the BAL trough are
completely saturated but do not reach zero flux, their profiles being dominated
by a velocity-dependent covering factor. The covering factor is significantly
smaller for MgII than for SiIV and NV, which demonstrates the intrinsic nature
of absorber. From the analysis of the excited SiII* and CII* lines in the
lowest velocity component, we find an electron density ~ 1000 cm^{-3}. Assuming
photoionization equilibrium, we derive a distance ~ 20 kpc between the
low-ionization region and the quasar core. The correspondence in velocity of
the high- and low-ionization features suggests that all these species must be
closely associated, hence formed at the same distance of ~ 20 kpc, much higher
than the distance usually assumed for BAL absorbers.Comment: Accepted for publication in A&
The Optical Polarisation of the Vela Pulsar revisited
In this work we present a revised measurement of the phase-averaged optical
polarisation of the Vela pulsar (PSR B0833-45), for which only one value has
been published so far (Wagner & Seifert 2000). Our measurement has been
obtained through an accurate reanalysis of archival polarisation observations
obtained with the FORS instrument at the VLT. We have measured a phase-averaged
linear polarisation degree P=9.4% +/- 4% and a position angle 146 +/- 11 deg,
very close to the ones of the axis of symmetry of the X-ray arcs and jets
detected by Chandra and of the pulsar proper motion.We have compared the
measured phase-averaged optical polarisation with the expectations of different
pulsars' magnetosphere models. We have found that all models consistently
predict too large values of the phase-averaged linear polarization with respect
to the observed one. This is probably a consequence of present models'
limitations which neglect the contributions of various depolarisation effects.
Interestingly, for the outer gap model we have found that, assuming synchrotron
radiation for the optical emission, the observed polarisation position angle
also implies an alignment between the pulsar rotational axis and the axis of
symmetry of the X-ray arcs and jets.Comment: 8 pages, 4 figure
Recent trends and developments in pyrolysis-gas chromatography: review
Pyrolysis-gas chromatography (Py-GC) has become well established as a simple, quick and reliable analytical technique for a range of applications including the analysis of polymeric materials. Recent developments in Py-GC technology and instrumentation include laser pyrolysis and non-discriminating pyrolysis. Progress has also been made in the detection of low level polymer additives with the use of novel Py-GC devices. Furthermore, it has been predicted that future advances in separation technology such as the use of comprehensive two-dimensional gas chromatography will further enhance the analytical scope of Py-GC
A supervisory loop approach to fulfill workspace constraints in redundant robots
An approach based on geometric invariance and sliding mode ideas is proposed for redundancy resolution in robotic systems to fulfill configuration and workspace constraints caused by robot mechanical limits, collision avoidance, industrial security, etc. Some interesting features of the proposal are that: (1) it can be interpreted as a limit case of the classical potential field-based approach for collision avoidance which requires using variable structure control concepts, (2) it allows reaching the limit surface of the constraints smoothly, depending on a free design parameter, and (3) it can be easily added as a supervisory block to pre-existing redundancy resolution schemes. The algorithm is evaluated in simulation on a 6R planar robot and on the freely accessible 6R robot model PUMA-560, for which the main features of the method are illustrated.This research is partially supported by DISICOM project PROM-ETEO 2008/088 of Generalitat Valenciana (Spain), research project DPI2011-27845-C02-01 of the Spanish Government (Spain), Technical University of Valencia (Spain), and the Argentinian Government (UNLP 11I127, CONICET PIP 112-200801-0, ANPCyT PICT 2007 00535).Gracia Calandin, LI.; Sala, A.; Garelli, F. (2012). A supervisory loop approach to fulfill workspace constraints in redundant robots. Robotics and Autonomous Systems. 60(1):1-15. https://doi.org/10.1016/j.robot.2011.07.008S11560
Quasars Probing Quasars III: New Clues to Feedback, Quenching, and the Physics of Massive Galaxy Formation
Galaxies hosting z~2 quasars are the high- progenitors of today's massive
`red-and-dead' galaxies. With close pairs of quasars at different redshifts, a
background quasar can be used to study a foreground quasar's halo gas in
absorption, providing a wealth of information about feedback, quenching, and
the physics of massive galaxy formation. We present a Keck/HIRES spectrum of
the bright background quasar in a projected pair with angular separation 13.3"
corresponding to 108kpc at the redshift of the foreground quasar z_fg=2.4360
+/- 0.0005, precisely determined from Gemini/GNIRS near-IR spectroscopy. Our
echelle spectrum reveals optically thick gas (NHI~10^19.7), coincident with the
foreground quasar redshift. The ionic transitions of associated metal-lines
reveal the following properties of the foreground quasar's halo: (1) the
kinematics are extreme with absorption extending to +780km/s relative to z_fg;
(2) the metallicity is nearly solar; (3) the temperature of the predominantly
ionized gas is T<~20,000K; (4) the electron density is n_e~1 cm^-3 indicating a
characteristic size ~10 - 100pc for the absorbing `clouds'; (7) there is a
negligible amount of warm gas 10^5K < T < 10^6K; (8) the gas is unlikely
illuminated by the foreground quasar, implying anisotropic or intermittent
emission. The mass of cold T~10^4K gas implied by our observations is
significant, amounting to a few percent of the total expected baryonic mass
density of the foreground quasar's dark halo at r~100kpc. The origin of this
material is still unclear, and we discuss several possibilities in the context
of current models of feedback and massive galaxy formation.Comment: Accepted to ApJ. 38 pages, 11 figure
Mapping the ionised gas around the luminous QSO HE 1029-1401: Evidence for minor merger events?
We present VIMOS integral field spectroscopy of the brightest radio-quiet QSO
on the southern sky HE 1029-1401 at a redshift of z=0.086. Standard
decomposition techniques for broad-band imaging are extended to integral field
data in order to deblend the QSO and host emission. We perform a tentative
analysis of the stellar continuum finding a young stellar population (<100Myr)
or a featureless continuum embedded in an old stellar population (10Gyr)
typical for a massive elliptical galaxy. The stellar velocity dispersion of
sigma_*=320\pm90 km/s and the estimated black hole mass
log(M_BH/M_sun)=8.7\pm0.3 are consistent with the local M_BH-sigma_* relation
within the errors. For the first time we map the two-dimensional ionised gas
distribution and the gas velocity field around HE 1029-1401. While the stellar
host morphology is purely elliptical we find a highly structured distribution
of ionised gas out to 16 kpc from the QSO. The gas is highly ionised solely by
the QSO radiation and has a significantly lower metallicity than would be
expected for the stellar mass of the host, indicating an external origin of the
gas most likely due to minor mergers. We find a rotating gas disc around the
QSO and a dispersion-dominated non-rotating gas component within the central 3
kpc. At larger distances the velocity field is heavily disturbed, which could
be interpreted as another signature of past minor merger events. Alternatively,
the arc-like structure seen in the ionised gas might also be indicative of a
large-scale expanding bubble, centred on and possibly driven by the active
nucleus.Comment: 13 pages, 13 figures, 1 table, accepted for publication in A&
How functional programming mattered
In 1989 when functional programming was still considered a niche topic, Hughes wrote a visionary paper arguing convincingly ‘why functional programming matters’. More than two decades have passed. Has functional programming really mattered? Our answer is a resounding ‘Yes!’. Functional programming is now at the forefront of a new generation of programming technologies, and enjoying increasing popularity and influence. In this paper, we review the impact of functional programming, focusing on how it has changed the way we may construct programs, the way we may verify programs, and fundamentally the way we may think about programs
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