150 research outputs found
Formal Assurance for Cognitive Architecture Based Autonomous Agent
Autonomous systems are designed and deployed in different modeling paradigms. These environments focus on specific concepts in designing the system. We focus our effort in the use of cognitive architectures to design autonomous agents to collaborate with humans to accomplish tasks in a mission. Our research focuses on introducing formal assurance methods to verify the behavior of agents designed in Soar, by translating the agent to the formal verification environment Uppaal
Seasonal Variation in Terrestrial Invertebrate Subsidies to Tropical Streams and Implications for the Feeding Ecology of Hart’s Rivulus (Anablepsoides hartii)
Terrestrial invertebrates are important subsidies to fish diets, though their seasonal dynamics and importance to tropical stream consumers are particularly understudied. In this year-round study of terrestrial invertebrate input to two Trinidadian headwater streams with different forest canopy densities, we sought to (a) measure the mass and composition of terrestrial inputs with fall-in traps to evaluate the influences of seasonality, canopy cover, and rainfall intensity, and; (b) compare terrestrial and benthic prey importance to Anablepsoides hartii(Hart’s Rivulus), the dominant invertivorous fish in these streams, by concurrently measuring benthic and drifting invertebrate standing stocks and the volume and composition of invertebrates in Rivulus guts throughout the year. The biomass of terrestrial invertebrate fall-in was 53% higher in the wet versus dry season; in particular, ant input was 320% higher. Ant biomass fall-in also increased with the density of canopy cover among sampling locations within both streams. Greater precipitation correlated with increased ant inputs to the more open-canopied stream and increased inputs of winged insects in the more closed canopy stream. Concurrently, the biomass of benthic invertebrates was reduced by more than half in the wet season in both streams. We detected no differences in the total volume of terrestrial prey in Rivulus diets between seasons, though ants were a greater proportion of their diet in the wet season. In contrast, benthic prey were nearly absent from Rivulus diets in the wet season in both streams. We conclude that terrestrial invertebrates are a substantial year-round prey subsidy for invertivores in tropical stream ecosystems like those we studied, which may contrast to most temperate streams where such terrestrial inputs are significantly reduced in the cold season. Interestingly, the strongest seasonal pattern in these tropical streams was observed in benthic invertebrate biomass which was greatly reduced and almost absent from Rivulus diets during the wet season. This pattern is essentially the inverse of the pattern observed in many temperate streams and highlights the need for additional studies in tropical ecosystems to better understand how spatial and temporal variation in terrestrial subsidies and benthic prey populations combine to influence consumer diets and the structure of tropical stream food webs
The Second Annual William French Smith Memorial Lecture: A Conversation with Justice Clarence Thomas
The stellar kinematics and populations of boxy bulges: cylindrical rotation and vertical gradients
Boxy and peanut-shaped bulges are seen in about half of edge-on disc
galaxies. Comparisons of the photometry and major-axis gas and stellar
kinematics of these bulges to simulations of bar formation and evolution
indicate that they are bars viewed in projection. If the properties of boxy
bulges can be entirely explained by assuming they are bars, then this may imply
that their hosts are pure disc galaxies with no classical bulge. A handful of
these bulges, including that of the Milky Way, have been observed to rotate
cylindrically, i.e. with a mean stellar velocity independent of height above
the disc. In order to assess whether such behaviour is ubiquitous in boxy
bulges, and whether a pure disc interpretation is consistent with their stellar
populations, we have analysed the stellar kinematics and populations of the
boxy or peanut-shaped bulges in a sample of five edge-on galaxies. We placed
slits along the major axis of each galaxy and at three offset but parallel
positions to build up spatial coverage. The boxy bulge of NGC3390 rotates
perfectly cylindrically within the spatial extent and uncertainties of the
data. This is consistent with the metallicity and alpha-element enhancement of
the bulge, which are the same as in the disk. This galaxy is thus a pure disc
galaxy. The boxy bulge of ESO311-G012 also rotates very close to cylindrically.
The boxy bulge of NGC1381 is neither clearly cylindrically nor
non-cylindrically rotating, but it has a negative vertical metallicity gradient
and is alpha-enhanced with respect to its disc, suggesting a composite bulge
comprised of a classical bulge and bar (and possibly a discy pseudobulge)
[abridged] Even this relatively small sample is sufficient to demonstrate that
boxy bulges display a range of rotational and population properties, indicating
that they do not form a homogeneous class of object.Comment: MNRAS accepted. 10 page
Dynamics of barred galaxies: effects of disk height
We study dynamics of bars in models of disk galaxies embeded in realistic
dark matter halos. We find that disk thickness plays an important, if not
dominant, role in the evolution and structure of the bars. We also make
extensive numerical tests of different N-body codes used to study bar dynamics.
Models with thick disks typically used in this type of modeling
(height-to-length ratio hz/Rd=0.2) produce slowly rotating, and very long,
bars. In contrast, more realistic thin disks with the same parameters as in our
Galaxy (hz/Rd= 0.1) produce bars with normal length Rbar approx R_d, which
rotate quickly with the ratio of the corotation radius to the bar radius
1.2-1.4 compatible with observations. Bars in these models do not show a
tendency to slow down, and may lose as little as 2-3 percent of their angular
momentum due to dynamical friction with the dark matter over cosmological time.
We attribute the differences between the models to a combined effect of high
phase-space density and smaller Jeans mass in the thin disk models, which
result in the formation of a dense central bulge. Special attention is paid to
numerical effects such as the accuracy of orbital integration, force and mass
resolution. Using three N-body codes -- Gadget, ART, and Pkdgrav -- we find
that numerical effects are very important and, if not carefully treated, may
produce incorrect and misleading results. Once the simulations are performed
with sufficiently small time-steps and with adequate force and mass resolution,
all the codes produce nearly the same results: we do not find any systematic
deviations between the results obtained with TREE codes (Gadget and Pkdgrav)
and with the Adaptive-Mesh-Refinement (ART) code.Comment: 15 pages, 14 plots, submitted to MNRA
Anatomy of a post-starburst minor merger: a multi-wavelength WFC3 study of NGC 4150
(Abridged) We present a spatially-resolved near-UV/optical study of NGC 4150,
using the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope.
Previous studies of this early-type galaxy (ETG) indicate that it has a large
reservoir of molecular gas, exhibits a kinematically decoupled core (likely
indication of recent merging) and strong, central H_B absorption (indicative of
young stars). The core of NGC 4150 shows ubiquitous near-UV emission and
remarkable dusty substructure. Our analysis shows this galaxy to lie in the
near-UV green valley, and its pixel-by-pixel photometry exhibits a narrow range
of near-UV/optical colours that are similar to those of nearby E+A
(post-starburst) galaxies. We parametrise the properties of the recent star
formation (age, mass fraction, metallicity and internal dust content) in the
NGC 4150 pixels by comparing the observed near-UV/optical photometry to stellar
models. The typical age of the recent star formation (RSF) is around 0.9 Gyrs,
consistent with the similarity of the near-UV colours to post-starburst
systems, while the morphological structure of the young component supports the
proposed merger scenario. The RSF metallicity, representative of the
metallicity of the gas fuelling star formation, is around 0.3 - 0.5 Zsun.
Assuming that this galaxy is a merger and that the gas is sourced mainly from
the infalling companion, these metallicities plausibly indicate the gas-phase
metallicity (GPM) of the accreted satellite. Comparison to the local mass-GPM
relation suggests (crudely) that the mass of the accreted system is around
3x10^8 Msun, making NGC 4150 a 1:20 minor merger. A summation of the pixel RSF
mass fractions indicates that the RSF contributes about 2-3 percent of the
stellar mass. This work reaffirms our hypothesis that minor mergers play a
significant role in the evolution of ETGs at late epochs.Comment: 28 pages, 2 tables, accepted for publication in Ap
The Relation Between Galaxy Morphology and Environment in the Local Universe: An RC3-SDSS Picture
We present an analysis of the z ~ 0 morphology-environment relation for 911
bright (M_B < -19) galaxies, matching classical RC3 morphologies to the
SDSS-based group catalog of Yang et al. We study how the relative fractions of
spirals, lenticulars, and ellipticals depend on halo mass over a range of
10^11.7-10^14.8 h^-1 Msol. We pay particular attention to how morphology
relates to central (most massive) vs satellite galaxy status. The fraction of
galaxies which are elliptical is a strong function of stellar mass; it is also
a strong function of halo mass, but only for central galaxies. We interpret
this in a scenario where elliptical galaxies are formed, probably via mergers,
as central galaxies within their halos; satellite ellipticals are previously
central galaxies accreted onto larger halos. The overall fraction of S0
galaxies increases strongly with halo mass, from ~10% to ~70%. We find striking
differences between the central and satellites: 20+/-2% of central M_* >
10^10.5 Msol galaxies are S0 regardless of halo mass, but satellite S0 galaxies
are only found in massive (> 10^13 h^-1 Msol) halos, where they are 69+/-4% of
the M_* > 10^10.5 Msol satellite population. This suggests two channels for S0
formation: one for central galaxies, and another which transforms lower mass
(M_* <~ 10^11 Msol) accreted spirals into satellite S0 galaxies in massive
halos. Analysis of finer morphological structure (bars and rings in disk
galaxies) shows some trends with stellar mass, but none with halo mass; this is
consistent with other recent studies which indicate that bars are not strongly
influenced by galaxy environment. Radio sources in high-mass central galaxies
are common, similarly so for elliptical and S0 galaxies, with a frequency that
increases with halo mass. Emission-line AGN (mostly LINERs) are more common in
S0s, but show no strong environmental trends (abridged).Comment: Accepted for publication in the Astrophysical Journal (ApJ
Evolutionary properties of the low-luminosity galaxy population in the NGC5044 Group
With this third paper of a series we present Johnson-Gunn B,g,V,r,i,z
multicolour photometry for 79 objects, including a significant fraction of the
faintest galaxies around NGC5044, assessing group membership on the basis of
apparent morphology and low-resolution optical spectroscopy to estimate
redshift for 21 objects. Together, dE's and Im's provide the bulk of the galaxy
luminosity function, around M(g)\sim-18.0, while the S0 and dSph components
dominate, respectively, the bright and faint-end tails of the distribution.
This special mix places the NGC 5044 group just "midway" between the
high-density cosmic aggregation scale typical of galaxy clusters, and the
low-density environment of looser galaxy clumps like our Local Group. The
bright mass of the 136 member galaxies with available photometry and
morphological classification, amounts to a total of 2.3x10^{12}M_sun while
current SFR within the group turns to be about or higher than 23M_sun/yr. In
this regard, a drift toward bluer integrated colours is found to be an issue
for dE's pointing to a moderate but pervasive star-formation activity even
among nominally "quiescent" stellar systems. Through Lick narrow-band index
analysis, dwarf ellipticals are found to share a sub-solar metallicity (-1.0 <
[Fe/H] <-0.5) with a clear decoupling between Iron and alpha elements, as
already established also for high-mass systems. Both dE's and dS0's are
consistent with an old age, about one Hubble time, although a possible bias,
toward higher values of age, may be induced by the gas emission affecting the
Hbeta strength.Comment: 25 pages with 19 figure & 8 tables - To appear in the Monthly Notices
of the Royal Astronomical Society (in press) See
http://www.bo.astro.it/~eps/buz10602/10602.html for a complete overview of
the projec
The Tully-Fisher relations of early-type spiral and S0 galaxies
We demonstrate that the comparison of Tully-Fisher relations (TFRs) derived
from global HI line widths to TFRs derived from the circular velocity profiles
of dynamical models (or stellar kinematic observations corrected for asymmetric
drift) is vulnerable to systematic and uncertain biases introduced by the
different measures of rotation used. We therefore argue that to constrain the
relative locations of the TFRs of spiral and S0 galaxies, the same tracer and
measure must be used for both samples. Using detailed near-infrared imaging and
the circular velocities of axisymmetric Jeans models of 14 nearby edge-on Sa-Sb
spirals and 14 nearby edge-on S0s drawn from a range of environments, we find
that S0s lie on a TFR with the same slope as the spirals, but are on average
0.53+/-0.15 mag fainter at Ks-band at a given rotational velocity. This is a
significantly smaller offset than that measured in earlier studies of the S0
TFR, which we attribute to our elimination of the bias associated with using
different rotation measures and our use of earlier type spirals as a reference.
Since our measurement of the offset avoids systematic biases, it should be
preferred to previous estimates. A spiral stellar population in which star
formation is truncated would take ~1 Gyr to fade by 0.53 mag at Ks-band. If S0s
are the products of a simple truncation of star formation in spirals, then this
finding is difficult to reconcile with the observed evolution of the spiral/S0
fraction with redshift. Recent star formation could explain the observed lack
of fading in S0s, but the offset of the S0 TFR persists as a function of both
stellar and dynamical mass. We show that the offset of the S0 TFR could
therefore be explained by a systematic difference between the total mass
distributions of S0s and spirals, in the sense that S0s need to be smaller or
more concentrated than spirals.Comment: Accepted for publication in MNRAS; 17 pages; v2 incorporates minor
proof corrections and updated reference
Galaxy Zoo: Bar Lengths in Nearby Disk Galaxies
We present an analysis of bar length measurements of 3150 local galaxies in a
volume limited sample of low redshift (z < 0.06) disk galaxies. Barred galaxies
were initially selected from the Galaxy Zoo 2 project, and the lengths and
widths of the bars were manually drawn by members of the Galaxy Zoo community
using a Google Maps interface. Bars were measured independently by different
observers, multiple times per galaxy (>=3), and we find that observers were
able to reproduce their own bar lengths to 3% and each others' to better than
20%. We find a "color bimodality" in our disk galaxy population with bar
length, i.e., longer bars inhabit redder disk galaxies and the bars themselves
are redder, and that the bluest galaxies host the smallest galactic bars (< 5
kpc/h). We also find that bar and disk colors are clearly correlated, and for
galaxies with small bars, the disk is, on average, redder than the bar colors,
while for longer bars the bar then itself is redder, on average, than the disk.
We further find that galaxies with a prominent bulge are more likely to host
longer bars than those without bulges. We categorise our galaxy populations by
how the bar and/or ring are connected to the spiral arms. We find that galaxies
whose bars are directly connected to the spiral arms are preferentially bluer
and that these galaxies host typically shorter bars. Within the scatter, we
find that stronger bars are found in galaxies which host a ring (and only a
ring). The bar length and width measurements used herein are made publicly
available for others to use (http://data.galaxyzoo.org).Comment: 15 pages, 16 figures, accepted in MNRA
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