837 research outputs found
Corticosterone, inflammation, immune status and telomere length in frigatebird nestlings facing a severe herpesvirus infection
Herpesvirus outbreaks are common in natural animal populations, but little is known about factors that favour the infection and its consequences for the organism. In this study, we examined the pathophysiological consequences of a disease probably attributable to herpesvirus infection for several markers of immune function, corticosterone, telomere length and inflammation. In addition, we assessed whether any markers used in this study might be associated with the occurrence of visible clinical signs of the disease and its impact on short-term survival perspectives. To address our questions, in spring 2015, we collected blood samples from nestlings of the magnificent frigatebird (Fregata magnificens) that were free of any clinical signs or showed visible signs of the disease. We found that the plasma concentration of haptoglobin was strongly associated with the infection status and could predict probabilities of survival. We also found that nestlings with clinical signs had lower baseline corticosterone concentrations and similar telomere length compared with healthy nestlings, whereas we did not find any association of the infection status with innate immune defenses or with nitric oxide concentration. Overall, our results suggest that the plasma concentration of haptoglobin might be a valuable tool to assess survival probabilities of frigatebird nestlings facing a herpesvirus outbreak
Efficient Model Learning for Human-Robot Collaborative Tasks
We present a framework for learning human user models from joint-action
demonstrations that enables the robot to compute a robust policy for a
collaborative task with a human. The learning takes place completely
automatically, without any human intervention. First, we describe the
clustering of demonstrated action sequences into different human types using an
unsupervised learning algorithm. These demonstrated sequences are also used by
the robot to learn a reward function that is representative for each type,
through the employment of an inverse reinforcement learning algorithm. The
learned model is then used as part of a Mixed Observability Markov Decision
Process formulation, wherein the human type is a partially observable variable.
With this framework, we can infer, either offline or online, the human type of
a new user that was not included in the training set, and can compute a policy
for the robot that will be aligned to the preference of this new user and will
be robust to deviations of the human actions from prior demonstrations. Finally
we validate the approach using data collected in human subject experiments, and
conduct proof-of-concept demonstrations in which a person performs a
collaborative task with a small industrial robot
Taking the lead on climate change: Modelling and monitoring the fate of an Amazonian frog
Climate change is expected to have important impacts on biodiversity. However, cases showing explicit links between species decline and climate are scarce, mostly because of a lack of baseline data. Tropical ectotherms with narrow altitudinal ranges are particularly sensitive to climate change; for example the frog Pristimantis espedeus may be at risk, with only nine populations known to date in French Guiana, all on isolated massifs. Ecological niche modelling indicated that these populations could disappear by 2070. To facilitate testing of this prediction we conducted a study to design an efficient, cost-effective monitoring protocol, combining occupancy rate estimations using passive acoustic recorders, and abundance estimations using acoustic repeated counts and capture-mark-recapture. We found the passive recorders to be effective, with a detection probability of 0.8. Two recording sessions were sufficient to estimate occupancy rates reliably. A minimum of 57 surveyed sites were required to detect a decline of 15% in occupancy between two consecutive monitoring events. Acoustic repeated counts and capture-mark-recapture yielded similar density estimates (1.6 and 1.8 calling males per 100 m2, respectively). Based on these results we present a protocol based on passive acoustic recording and abundance monitoring to monitor P. espedeus populations
Electron-Ion Recombination on Grains and Polycyclic Aromatic Hydrocarbons
With the high-resolution spectroscopy now available in the optical and
satellite UV, it is possible to determine the neutral/ionized column density
ratios for several different elements in a single cloud. Assuming ionization
equilibrium for each element, one can make several independent determinations
of the electron density. For the clouds for which such an analysis has been
carried out, these different estimates disagree by large factors, suggesting
that some process (or processes) besides photoionization and radiative
recombination might play an important role in the ionization balance. One
candidate process is collisions of ions with dust grains.
Making use of recent work quantifying the abundances of polycyclic aromatic
hydrocarbon molecules and other grains in the interstellar medium, as well as
recent models for grain charging, we estimate the grain-assisted ion
recombination rates for several astrophysically important elements. We find
that these rates are comparable to the rates for radiative recombination for
conditions typical of the cold neutral medium. Including grain-assisted ion
recombination in the ionization equilibrium analysis leads to increased
consistency in the various electron density estimates for the gas along the
line of sight to 23 Orionis. However, not all of the discrepancies can be
eliminated in this way; we speculate on some other processes that might play a
role. We also note that grain-assisted recombination of H+ and He+ leads to
significantly lower electron fractions than usually assumed for the cold
neutral medium.Comment: LaTeX(12 pages, 8 figures, uses emulateapj5.sty, apjfonts.sty);
submitted to ApJ; corrected typo
Turbulent molecular gas and star formation in the shocked intergalactic medium of Stephan's Quintet
We report on single-dish radio CO observations towards the inter-galactic
medium (IGM) of the Stephan's Quintet (SQ) group of galaxies. Extremely bright
mid-IR H2 rotational line emission from warm molecular gas has been detected by
Spitzer in the kpc-scale shock created by a galaxy collision. We detect in the
IGM CO(1-0), (2-1) and (3-2) line emission with complex profiles, spanning a
velocity range of 1000 km/s. The spectra exhibit the pre-shock recession
velocities of the two colliding gas systems (5700 and 6700 km/s), but also
intermediate velocities. This shows that much of the molecular gas has formed
out of diffuse gas accelerated by the galaxy-tidal arm collision. A total H2
mass of 5x10^9 Msun is detected in the shock. The molecular gas carries a large
fraction of the gas kinetic energy involved in the collision, meaning that this
energy has not been thermalized yet. The turbulent kinetic energy of the H2 gas
is at least a factor of 5 greater than the thermal energy of the hot plasma
heated by the collision. The ratio between the warm H2 mass derived from
Spitzer IRS spectroscopy and the H2 mass derived from CO fluxes is ~0.3 in the
IGM of SQ, which is 10-100 times higher than in star-forming galaxies. In the
shocked region, the ratio of the PAH-to-CO surface luminosities, commonly used
to measure the star formation efficiency of the H2 gas, is lower (up to a
factor 75) than the observed values in star-forming galaxies. We suggest that
turbulence fed by the galaxy-tidal arm collision maintains a high heating rate
within the H2 gas. This interpretation implies that the velocity dispersion on
the scale of giant molecular clouds in SQ is one order of magnitude larger than
the Galactic value. The high amplitude of turbulence may explain why this gas
is not forming stars efficiently. [abridged version]Comment: Revised abstract and small editing to match published version. 15
pages, 5 figures. Accepted for publication in Ap
The XMM-Newton serendipitous ultraviolet source survey catalogue
The XMM-Newton Serendipitous Ultraviolet Source Survey (XMM-SUSS) is a
catalogue of ultraviolet (UV) sources detected serendipitously by the Optical
Monitor (XMM-OM) on-board the XMM-Newton observatory. The catalogue contains
ultraviolet-detected sources collected from 2,417 XMM-OM observations in 1-6
broad band UV and optical filters, made between 24 February 2000 and 29 March
2007. The primary contents of the catalogue are source positions, magnitudes
and fluxes in 1 to 6 passbands, and these are accompanied by profile
diagnostics and variability statistics. The XMM-SUSS is populated by 753,578 UV
source detections above a 3 sigma signal-to-noise threshold limit which relate
to 624,049 unique objects. Taking account of substantial overlaps between
observations, the net sky area covered is 29-54 square degrees, depending on UV
filter. The magnitude distributions peak at 20.2, 20.9 and 21.2 in UVW2, UVM2
and UVW1 respectively. More than 10 per cent of sources have been visited more
than once using the same filter during XMM-Newton operation, and > 20 per cent
of sources are observed more than once per filter during an individual visit.
Consequently, the scope for science based on temporal source variability on
timescales of hours to years is broad. By comparison with other astrophysical
catalogues we test the accuracy of the source measurements and define the
nature of the serendipitous UV XMM-OM source sample. The distributions of
source colours in the UV and optical filters are shown together with the
expected loci of stars and galaxies, and indicate that sources which are
detected in multiple UV bands are predominantly star-forming galaxies and stars
of type G or earlier.Comment: Accepted for publication in MNRA
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