2,760 research outputs found
High angular resolution imaging and infrared spectroscopy of CoRoT candidates
Studies of transiting extrasolar planets are of key importance for
understanding the nature of planets outside our solar system because their
masses, diameters, and bulk densities can be measured. An important part of
transit-search programmes is the removal of false-positives. The critical
question is how many of the candidates that passed all previous tests are false
positives. For our study we selected 25 CoRoT candidates that have already been
screened against false-positives using detailed analysis of the light curves
and seeing-limited imaging, which has transits that are between 0.7 and 0.05%
deep. We observed 20 candidates with the adaptive optics imager NaCo and 18
with the high-resolution infrared spectrograph CRIRES. We found previously
unknown stars within 2 arcsec of the targets in seven of the candidates. All of
these are too faint and too close to the targets to have been previously
detected with seeing-limited telescopes in the optical. Our study thus leads to
the surprising results that if we remove all candidates excluded by the
sophisticated analysis of the light-curve, as well as carrying out deep imaging
with seeing-limited telescopes, still 28-35% of the remaining candidates are
found to possess companions that are bright enough to be false-positives. Given
that the companion-candidates cluster around the targets and that the J-K
colours are consistent with physical companions, we conclude that the
companion-candidates are more likely to be physical companions rather than
unrelated field stars.Comment: 12 pages, 12 figures, A&A in pres
Sequence structure emission in The Red Rectangle Bands
We report high resolution (R~37,000) integral field spectroscopy of the
central region (r<14arcsec) of the Red Rectangle nebula surrounding HD44179.
The observations focus on the 5800A emission feature, the bluest of the
yellow/red emission bands in the Red Rectangle. We propose that the emission
feature, widely believed to be a molecular emission band, is not a molecular
rotation contour, but a vibrational contour caused by overlapping sequence
bands from a molecule with an extended chromophore. We model the feature as
arising in a Polycyclic Aromatic Hydrocarbon (PAH) with 45-100 carbon atoms.Comment: 13 pages, 9 figures, accepted for publication in ApJ. A version of
the paper with full resolution figures is available at:
http://www.aao.gov.au/local/www/rgs/Sequence-Structure
Asymptotic expansion for reversible A + B <-> C reaction-diffusion process
We study long-time properties of reversible reaction-diffusion systems of
type A + B C by means of perturbation expansion in powers of 1/t (inverse
of time). For the case of equal diffusion coefficients we present exact
formulas for the asymptotic forms of reactant concentrations and a complete,
recursive expression for an arbitrary term of the expansions. Taking an
appropriate limit we show that by studying reversible reactions one can obtain
"singular" solutions typical of irreversible reactions.Comment: 6 pages, no figures, to appear in PR
First experimental results of very high accuracy centroiding measurements for the neat astrometric mission
NEAT is an astrometric mission proposed to ESA with the objectives of
detecting Earth-like exoplanets in the habitable zone of nearby solar-type
stars. NEAT requires the capability to measure stellar centroids at the
precision of 5e-6 pixel. Current state-of-the-art methods for centroid
estimation have reached a precision of about 2e-5 pixel at two times Nyquist
sampling, this was shown at the JPL by the VESTA experiment. A metrology system
was used to calibrate intra and inter pixel quantum efficiency variations in
order to correct pixelation errors. The European part of the NEAT consortium is
building a testbed in vacuum in order to achieve 5e-6 pixel precision for the
centroid estimation. The goal is to provide a proof of concept for the
precision requirement of the NEAT spacecraft. In this paper we present the
metrology and the pseudo stellar sources sub-systems, we present a performance
model and an error budget of the experiment and we report the present status of
the demonstration. Finally we also present our first results: the experiment
had its first light in July 2013 and a first set of data was taken in air. The
analysis of this first set of data showed that we can already measure the pixel
positions with an accuracy of about 1e-4 pixel.Comment: SPIE conference proceeding
A detector interferometric calibration experiment for high precision astrometry
Context: Exoplanet science has made staggering progress in the last two
decades, due to the relentless exploration of new detection methods and
refinement of existing ones. Yet astrometry offers a unique and untapped
potential of discovery of habitable-zone low-mass planets around all the
solar-like stars of the solar neighborhood. To fulfill this goal, astrometry
must be paired with high precision calibration of the detector.
Aims: We present a way to calibrate a detector for high accuracy astrometry.
An experimental testbed combining an astrometric simulator and an
interferometric calibration system is used to validate both the hardware needed
for the calibration and the signal processing methods. The objective is an
accuracy of 5e-6 pixel on the location of a Nyquist sampled polychromatic point
spread function.
Methods: The interferometric calibration system produced modulated Young
fringes on the detector. The Young fringes were parametrized as products of
time and space dependent functions, based on various pixel parameters. The
minimization of func- tion parameters was done iteratively, until convergence
was obtained, revealing the pixel information needed for the calibration of
astrometric measurements.
Results: The calibration system yielded the pixel positions to an accuracy
estimated at 4e-4 pixel. After including the pixel position information, an
astrometric accuracy of 6e-5 pixel was obtained, for a PSF motion over more
than five pixels. In the static mode (small jitter motion of less than 1e-3
pixel), a photon noise limited precision of 3e-5 pixel was reached
Precision is in the Eye of the Beholder: Application of Eye Fixation-Related Potentials to Information Systems Research
This is the final version. Available from Association for Information Systems via the DOI in this recordThis paper introduces the eye-fixation related potential (EFRP) method to IS research. The EFRP method allows one to synchronize eye tracking with electroencephalographic (EEG) recording to precisely capture users’ neural activity at the exact time at which they start to cognitively process a stimulus (e.g., event on the screen). This complements and overcomes some of the shortcomings of the traditional event related potential (ERP) method, which can only stamp the time at which a stimulus is presented to a user. Thus, we propose a method conjecture of the superiority of EFRP over ERP for capturing the cognitive processing of a stimulus when such cognitive processing is not necessarily synchronized with the time at which the stimulus appears. We illustrate the EFRP method with an experiment in a natural IS use context in which we asked users to read an industry report while email pop-up notifications arrived on their screen. The results support our proposed hypotheses and show three distinct neural processes associated with 1) the attentional reaction to email pop-up notification, 2) the cognitive processing of the email pop-up notification, and 3) the motor planning activity involved in opening or not the email. Furthermore, further analyses of the data gathered in the experiment serve to validate our method conjecture about the superiority of the EFRP method over the ERP in natural IS use contexts. In addition to the experiment, our study discusses important IS research questions that could be pursued with the aid of EFRP, and describes a set of guidelines to help IS researchers use this method.Social Sciences and Humanities Research Council of Canada (SSHRC)Natural Sciences and Engineering Research Council of CanadaFonds Québécois pour la Recherche sur la Société et la Culture (FQRSC)Fonds de recherche Nature et Technologies (FQRNT
Molecular ions in L1544. II. The ionization degree
The maps presented in Paper I are here used to infer the variation of the
column densities of HCO+, DCO+, N2H+, and N2D+ as a function of distance from
the dust peak. These results are interpreted with the aid of a crude chemical
model which predicts the abundances of these species as a function of radius in
a spherically symmetric model with radial density distribution inferred from
the observations of dust emission at millimeter wavelengths and dust absorption
in the infrared. Our main observational finding is that the N(N2D+)/N(N2H+)
column density ratio is of order 0.2 towards the L1544 dust peak as compared to
N(DCO+)/N(HCO+) = 0.04. We conclude that this result as well as the general
finding that N2H+ and N2D+ correlate well with the dust is caused by CO being
depleted to a much higher degree than molecular nitrogen in the high density
core of L1544. Depletion also favors deuterium enhancement and thus N2D+, which
traces the dense and highly CO-depleted core nucleus, is much more enhanced
than DCO+. Our models do not uniquely define the chemistry in the high density
depleted nucleus of L1544 but they do suggest that the ionization degree is a
few times 10^{-9} and that the ambipolar diffusion time scale is locally
similar to the free fall time. It seems likely that the lower limit which one
obtains to ionization degree by summing all observable molecular ions is not a
great underestimate of the true ionization degree. We predict that atomic
oxygen is abundant in the dense core and, if so, H3O+ may be the main ion in
the central highly depleted region of the core.Comment: 31 pages, 8 figures, to be published in Ap
The Thermal Structure of Gas in Pre-Stellar Cores: A Case Study of Barnard 68
We present a direct comparison of a chemical/physical model to
multitransitional observations of C18O and 13CO towards the Barnard 68
pre-stellar core. These observations provide a sensitive test for models of low
UV field photodissociation regions and offer the best constraint on the gas
temperature of a pre-stellar core. We find that the gas temperature of this
object is surprisingly low (~7-8 K), and significantly below the dust
temperature, in the outer layers (Av < 5 mag) that are traced by C18O and 13CO
emission. As shown previously, the inner layers (Av > 5 mag) exhibit
significant freeze-out of CO onto grain surfaces. Because the dust and gas are
not fully coupled, depletion of key coolants in the densest layers raises the
core (gas) temperature, but only by ~1 K. The gas temperature in layers not
traced by C18O and 13CO emission can be probed by NH3 emission, with a
previously estimated temperature of ~10-11 K. To reach these temperatures in
the inner core requires an order of magnitude reduction in the gas to dust
coupling rate. This potentially argues for a lack of small grains in the
densest gas, presumably due to grain coagulation.Comment: 33 pages, 11 figures, accepted by Astrophysical Journa
Challenges and improvement needs in the care of patients with central diabetes insipidus
Central diabetes insipidus (CDI) is a rare condition, with significant impact on patient health and well-being. It is a chronic condition which usually requires meticulous long-term care. It can affect both children and adults. There is limited literature considering the needs and challenges inherent in providing high quality care to patients with CDI, across the care pathway. This paper seeks to address this gap by providing a unique and well-rounded understanding of clinical and healthcare systems-related challenges. It draws on insights from the literature, from direct clinical experience contributed by five clinicians as co-authors (providing insights from France, Ireland, Italy, Spain and the United Kingdom), and from patient perspectives provided through interviews with patient representatives from three patient organisations. We identify clinical challenges related to the diagnosis of CDI, including differentiating between other similar conditions and determining the underlying aetiology. Treatment is challenging, given the need to tailor medication to each patient’s needs and ongoing management is required to ensure that patients continue to respond adequately to treatment. Ongoing support is required when patients switch between formulations. We also identify healthcare systems challenges related to limited awareness of CDI amongst primary care physicians and general paediatricians, and the need for highly skilled specialist care and appropriate workforce capacity. There is also a significant need for raising awareness and for the education of both healthcare professionals and patients about different aspects of CDI, with the aim of supporting improved care and effective patient engagement with healthcare professionals. We reflect on this information and highlight improvement opportunities. These relate to developing guidance to support patients, carers, primary care physicians and general paediatricians to identify clinical features earlier, and to consider CDI as a possible diagnosis when a patient presents with suggestive symptom
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