525 research outputs found
Downwash-Aware Trajectory Planning for Large Quadrotor Teams
We describe a method for formation-change trajectory planning for large
quadrotor teams in obstacle-rich environments. Our method decomposes the
planning problem into two stages: a discrete planner operating on a graph
representation of the workspace, and a continuous refinement that converts the
non-smooth graph plan into a set of C^k-continuous trajectories, locally
optimizing an integral-squared-derivative cost. We account for the downwash
effect, allowing safe flight in dense formations. We demonstrate the
computational efficiency in simulation with up to 200 robots and the physical
plausibility with an experiment with 32 nano-quadrotors. Our approach can
compute safe and smooth trajectories for hundreds of quadrotors in dense
environments with obstacles in a few minutes.Comment: 8 page
Assessing the Prosody of Non-Native Speakers of English: Measures and Feature Sets
In this paper, we describe a new database with audio recordings of non-native (L2) speakers of English, and the perceptual evaluation experiment conducted with native English speakers for assessing the prosody of each recording. These annotations are then used to compute the gold standard using different methods, and a series of regression experiments is conducted to evaluate their impact on the performance of a regression model predicting the degree of Abstract naturalness of L2 speech. Further, we compare the relevance of different feature groups modelling prosody in general (without speech tempo), speech rate and pauses modelling speech tempo (fluency), voice quality, and a variety of spectral features. We also discuss the impact of various fusion strategies on performance.Overall, our results demonstrate that the prosody of non-native speakers of English as L2 can be reliably assessed using supra- segmental audio features; prosodic features seem to be the most important ones
Embedded AGN and star formation in the central 80 pc of IC 3639
[Abridged] Methods: We use interferometric observations in the -band with
VLTI/MIDI to resolve the mid-IR nucleus of IC 3639. The origin of the nuclear
infrared emission is determined from: 1) the comparison of the correlated
fluxes from VLTI/MIDI with the fluxes measured at subarcsec resolution
(VLT/VISIR, VLT/ISAAC); 2) diagnostics based on IR fine-structure line ratios,
the IR continuum emission, IR bands produced by polycyclic aromatic
hydrocarbons (PAH) and silicates; and 3) the high-angular resolution spectral
energy distribution. Results: The unresolved flux of IC 3639 is at , measured with three different baselines in
VLTI (UT1-UT2, UT3-UT4, and UT2-UT3; -), making this the
faintest measurement so far achieved with mid-IR interferometry. The correlated
flux is a factor of - times fainter than the VLT/VISIR total flux
measurement. The observations suggest that most of the mid-IR emission has its
origin on spatial scales between and (-). A composite scenario where the star formation component dominates
over the AGN is favoured by the diagnostics based on ratios of IR
fine-structure emission lines, the shape of the IR continuum, and the PAH and
silicate bands. Conclusions: A composite AGN-starburst scenario is able to
explain both the mid-IR brightness distribution and the IR spectral properties
observed in the nucleus of IC 3639. The nuclear starburst would dominate the
mid-IR emission and the ionisation of low-excitation lines (e.g. [NeII]) with a net contribution of . The AGN accounts for the
remaining of the mid-IR flux, ascribed to the unresolved component
in the MIDI observations, and the ionisation of high-excitation lines (e.g.
[NeV] and [OIV]).Comment: Accepted for publication in A&
A dust-parallax distance of 19 megaparsecs to the supermassive black hole in NGC 4151
The active galaxy NGC 4151 has a crucial role as one of only two active
galactic nuclei for which black hole mass measurements based on emission line
reverberation mapping can be calibrated against other dynamical methods.
Unfortunately, effective calibration requires an accurate distance to NGC 4151,
which is currently not available. Recently reported distances range from 4 to
29 megaparsecs (Mpc). Strong peculiar motions make a redshift-based distance
very uncertain, and the geometry of the galaxy and its nucleus prohibit
accurate measurements using other techniques. Here we report a dust-parallax
distance to NGC 4151 of Mpc. The measurement is
based on an adaptation of a geometric method proposed previously using the
emission line regions of active galaxies. Since this region is too small for
current imaging capabilities, we use instead the ratio of the
physical-to-angular sizes of the more extended hot dust emission as determined
from time-delays and infrared interferometry. This new distance leads to an
approximately 1.4-fold increase in the dynamical black hole mass, implying a
corresponding correction to emission line reverberation masses of black holes
if they are calibrated against the two objects with additional dynamical
masses.Comment: Authors' version of a letter published in Nature (27 November 2014);
8 pages, 5 figures, 1 tabl
The dusty heart of nearby active galaxies. I. High-spatial resolution mid-IR spectro-photometry of Seyfert galaxies
We present 8-13 micron imaging and spectroscopy of 9 type 1 and 10 type 2 AGN
obtained with the VLT/VISIR instrument at spatial resolution <100 pc. The
emission from the host galaxy sources is resolved out in most cases. The
silicate absorption features are moderately deep and emission features are
shallow. We compare the mid-IR luminosities to AGN luminosity tracers and found
that the mid-IR radiation is emitted quite isotropically. In two cases, IC5063
and MCG-3-34-64, we find evidence for extended dust emission in the narrow-line
region. We confirm the correlation between observed silicate feature strength
and Hydrogen column density recently found in Spitzer data. In a further step,
our 3D clumpy torus model has been used to interpret the data. We show that the
strength of the silicate feature and the mid-IR spectral index can be used to
get reasonable constraints on the dust distribution in the torus. The mid-IR
spectral index, alpha, is almost exclusively determined by the radial dust
distribution power-law index, a, and the silicate feature depth is mostly
depending on the average number of clouds, N0, along an equatorial
line-of-sight and the torus inclination. A comparison of model predictions to
our type 1 and type 2 AGN reveals typical average parameters a=-1.0+/-0.5 and
N0=5-8, which means that the radial dust distribution is rather shallow. As a
proof-of-concept of this method, we compared the model parameters derived from
alpha and the silicate feature to more detailed studies of IR SEDs and
interferometry and found that the constraints on a and N0 are consistent.
Finally, we might have found evidence that the radial structure of the torus
changes from low to high AGN luminosities towards steeper dust distributions,
and we discuss implications for the IR size-luminosity relation. (abridged)Comment: 22 pages, 13 figues, 6 tables; Accepted for publication in A&A; Note
that this is the second submitted paper from the series, but we changed paper
order. This one will be referred to as paper I, the previously submitted
arXiv:0909.4539 will become paper I
Some factors affecting the efficiency of potato production, under Al–Ghab plain conditions, Syrian Arab Republic
ArticleData were collected by a field survey of 300 farmers from Al–Ghab region (Syria)
during 2014–2015. The non–parametric Data Envelopment was used in analyzing the Technical
efficiency. The relationship between farm size and production efficiency was considered.
Technical efficiency amounted about 53% and most of farms are operating at low level of
technical efficiency. The relationship between farm size and productivity efficiency is Non–
linear, it decreases from small to medium farm size and then increases as the size increase. Large
farms have the higher net farm income per thousand square metersand are the most efficient
technically followed by small and medium farm size. To disclose that factors causing the
technical efficiency, Two–limit Tobit Regression Model was used. The calculated results showed
that, Household Size, Occupation, Farm Size, Experience in Farming, Seed Type and
Membership are factors that cause the technical inefficiency potato farming at Al–Ghab region.
Therefore, the Syrian Planning Board and Decision Makers should take this results into account
when they draw their plans to improve farmer's skills by allocating more investment in farm
research and extension programmers
Modeling the optical/UV polarization while flying around the tilted outflows of NGC 1068
Recent modeling of multi-waveband spectroscopic and maser observations
suggests that the ionized outflows in the nuclear region of the archetypal
Seyfert-2 galaxy NGC 1068 are inclined with respect to the vertical axis of the
obscuring torus. Based on this suggestion, we build a complex reprocessing
model of NGC 1068 for the optical/UV band. We apply the radiative transfer code
STOKES to compute polarization spectra and images. The effects of electron and
dust scattering and the radiative coupling occurring in the inner regions of
the multi-component object are taken into account and evaluated at different
polar and azimuthal viewing angles. The observed type-1/type-2 polarization
dichotomy of active galactic nuclei is reproduced. At the assumed observer's
inclination toward NGC 1068, the polarization is dominated by scattering in the
polar outflows and therefore it indicates their tilting angle with respect to
the torus axis. While a detailed analysis of our model results is still in
progress, we briefly discuss how they relate to existing polarization
observations of NGC 1068.Comment: To appear in the proceedings of the meeting "The Central Kiloparsec
in Galactic Nuclei" held in Bad Honnef (Germany) from August 29th to
September 2nd 201
High-Spatial Resolution SED of NGC 1068 from Near-IR to Radio. Disentangling the thermal and non-thermal contributions
We investigate the ideas that a sizable fraction of the interferometrically
unresolved infrared emission of the nucleus of NGC 1068 might originate from
other processes than thermal dust emission from the torus. We examine the
contribution of free-free or synchrotron emissions to the central mid- and
near-IR parsec-scale emitting region of NGC 1068. Each mechanism is constrained
with parsec scale radio data available for NGC 1068 in the 10^9 - 10^11 Hz
regime, and compared to the highest-resolution interferometric data available
in the mid-infrared. It is shown that the unresolved emission in the
interferometric observation (<~1pc) is still dominatedd by dust emission and
not by contributions from synchrotron or free-free emission. As recent studies
suggest, the interferometric observations prefer a clumpy structure of the dust
distribution. Extrapolation of the radio free-free or synchrotron emission to
the IR indicates that their contribution is <20% even for the unresolved
fraction of the interferometric flux. The slope of the available radio data is
consistent with a power law exponent alpha = 0.29 +/- 0.07 which we interprete
in terms of either free-free emission or synchrotron radiation from
quasi-monochromatic electrons. We apply emission models for both mechanisms in
order to obtain physical parameters. (abridged)Comment: 8 pages, 3 figures; accepted by A&
- …