480 research outputs found
Sublethal toxicant effects with dynamic energy budget theory: application to mussel outplants
We investigate the effectiveness of a sublethal toxic effect model embedded in Dynamic Energy Budget (DEB) theory for the analysis of field data. We analyze the performance of two species of mussels, Mytilus galloprovincialis and M. californianus, near a diffuser discharging produced water in the Southern California Bight, California. Produced water is a byproduct of oil production consisting of fossil water together with compounds added during the extraction process, and generally contains highly elevated levels of pollutants relative to sea water. Produced water negatively affects the production of somatic and reproductive biomass in both mussel species; we show that these negative effects can be quantified with our DEB-based modeling framework through the estimation of toxic effect scaling parameters. Our analyses reveal that the toxic impact of produced water on growth and reproduction of M. californianus is substantially higher than for M. galloprovincialis. Projections of the expected lifetime production of gonad biomass indicate that the environmental impact of produced water can be as large as 100%, whereas short-term assessment without the use of DEB theory projects a maximum effect of only 30%
The Parkes HI Survey of the Magellanic System
We present the first fully and uniformly sampled, spatially complete HI
survey of the entire Magellanic System with high velocity resolution, performed
with the Parkes Telescope. The final data-cubes have an rms noise of sigma ~
0.05 K and an effective angular resolution of 16 arcmin. The Large Magellanic
Cloud (LMC) and the Small Magellanic Cloud (SMC) are associated with huge
gaseous features with a total HI mass of M(HI) = 4.87 10^8 M_sun [d/55 kpc]^2,
if all HI gas is at the same distance of 55 kpc. Approximately two thirds of
this HI gas is located close to the Magellanic Clouds (Magellanic Bridge and
Interface Region), and 25% of the HI gas is associated with the Magellanic
Stream. The Leading Arm has a four times lower HI mass than the Magellanic
Stream, corresponding to 6% of the total HI mass of the gaseous features. We
have analyzed the velocity field of the Magellanic Clouds and their
neighborhood introducing a LMC-standard-of-rest frame. The HI in the Magellanic
Bridge shows low velocities relative to the Magellanic Clouds suggesting an
almost parallel motion, while the gas in the Interface Region has significantly
higher relative velocities indicating that this gas is leaving the Magellanic
Bridge building up a new section of the Magellanic Stream. The clouds in the
Magellanic Stream and the Leading Arm show significant differences, both in the
column density distribution and in the shapes of the line profiles. The HI gas
in the Magellanic Stream is more smoothly distributed than the gas in the
Leading Arm. These morphological differences can be explained if the Leading
Arm is at considerably lower z-heights and embedded in a higher pressure
ambient medium.Comment: 23 pages, 18 figures, accepted for publication in A&
Vocal signals facilitate cooperative hunting in wild chimpanzees
Cooperation and communication likely co-evolved in humans. However, the evolutionary roots of this interdependence remain unclear. We address this issue by investigating the role of vocal signals in facilitating a group cooperative behavior in an ape species: hunting in wild chimpanzees. First, we show that bark vocalizations produced before hunt initiation are reliable signals of behavioral motivation, with barkers being most likely to participate in the hunt. Next, we find that barks are associated with greater hunter recruitment and more effective hunting, with shorter latencies to hunting initiation and prey capture. Our results indicate that the co-evolutionary relationship between vocal communication and group-level cooperation is not unique to humans in the ape lineage, and is likely to have been present in our last common ancestor with chimpanzees
Supernova Remnants and Star Formation in the Large Magellanic Cloud
It has often been suggested that supernova remnants (SNRs) can trigger star
formation. To investigate the relationship between SNRs and star formation, we
have examined the known sample of 45 SNRs in the Large Magellanic Cloud to
search for associated young stellar objects (YSOs) and molecular clouds. We
find seven SNRs associated with both YSOs and molecular clouds, three SNRs
associated with YSOs but not molecular clouds, and eight SNRs near molecular
clouds but not associated with YSOs. Among the 10 SNRs associated with YSOs,
the association between the YSOs and SNRs can be either rejected or cannot be
convincingly established for eight cases. Only two SNRs have YSOs closely
aligned along their rims; however, the time elapsed since the SNR began to
interact with the YSOs' natal clouds is much shorter than the contraction
timescales of the YSOs, and thus we do not see any evidence of SNR-triggered
star formation in the LMC. The 15 SNRs that are near molecular clouds may
trigger star formation in the future when the SNR shocks have slowed down to
<45 km/s. We discuss how SNRs can alter the physical properties and abundances
of YSOs.Comment: 24 pages, 5 figures, 1 table, Accepted for publication in the August
2010 edition of the Astronomical Journa
The CO-to-H2 Conversion Factor From Infrared Dust Emission Across the Local Group
We estimate the conversion factor relating CO emission to H2 mass, alpha_CO,
in five Local Group galaxies that span approximately an order of magnitude in
metallicity - M31, M 33, the Large Magellanic Cloud (LMC), NGC 6822, and the
Small Magellanic Cloud (SMC). We model the dust mass along the line of sight
from infrared (IR) emission and then solve for the alpha_CO that best allows a
single gas-to-dust ratio (delta_GDR) to describe each system. This approach
remains sensitive to CO-dark envelopes of H2 surrounding molecular clouds. In M
31, M 33, and the LMC we find alpha_CO \approx 3-9 M_sun pc^-2 (K km s^-1)^-1,
consistent with the Milky Way value within the uncertainties. The two lowest
metallicity galaxies in our sample, NGC 6822 and the SMC (12 + log(O/H) \approx
8.2 and 8.0), exhibit a much higher alpha_CO. Our best estimates are
\alpha_NGC6822 \approx 30 M_sun/pc^-2 (K km s^-1)^-1 and \alpha_SMC \approx 70
M_sun/pc^-2 (K km s-1)-1. These results are consistent with the conversion
factor becoming CO a strong function of metallicity around 12 + log(O/H) \sim
8.4 - 8.2. We favor an interpretation where decreased dust-shielding leads to
the dominance of CO-free envelopes around molecular clouds below this
metallicity.Comment: Accepted for publication in the Astrophysical Journal, 15 pages, 7
figure
Sub-millimeter Observations of Giant Molecular Clouds in the Large Magellanic Cloud: Temperature and Density as Determined from J=3-2 and J=1-0 transitions of CO
We have carried out sub-mm 12CO(J=3-2) observations of 6 giant molecular
clouds (GMCs) in the Large Magellanic Cloud (LMC) with the ASTE 10m sub-mm
telescope at a spatial resolution of 5 pc and very high sensitivity. We have
identified 32 molecular clumps in the GMCs and revealed significant details of
the warm and dense molecular gas with n(H2) 10 cm and
Tkin 60 K. These data are combined with 12CO(J=1-0) and 13CO(J=1-0)
results and compared with LVG calculations. We found that the ratio of
12CO(J=3-2) to 12CO(J=1-0) emission is sensitive to and is well correlated with
the local Halpha flux. We interpret that differences of clump propeties
represent an evolutionary sequence of GMCs in terms of density increase leading
to star formation.Type I and II GMCs (starless GMCs and GMCs with HII regions
only, respectively) are at the young phase of star formation where density does
not yet become high enough to show active star formation and Type III GMCs
(GMCs with HII regions and young star clusters) represents the later phase
where the average density is increased and the GMCs are forming massive stars.
The high kinetic temperature correlated with \Halpha flux suggests that FUV
heating is dominant in the molecular gas of the LMC.Comment: 74 pages, including 41 figures, accepted for publication in ApJ
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