9,000 research outputs found
The Origin of Nitrogen on Jupiter and Saturn from the N/N Ratio
The Texas Echelon cross Echelle Spectrograph (TEXES), mounted on NASA's
Infrared Telescope Facility (IRTF), was used to map mid-infrared ammonia
absorption features on both Jupiter and Saturn in February 2013. Ammonia is the
principle reservoir of nitrogen on the giant planets, and the ratio of
isotopologues (N/N) can reveal insights into the molecular
carrier (e.g., as N or NH) of nitrogen to the forming protoplanets, and
hence the source reservoirs from which these worlds accreted. We targeted two
spectral intervals (900 and 960 cm) that were relatively clear of
terrestrial atmospheric contamination and contained close features of
NH and NH, allowing us to derive the ratio from a single
spectrum without ambiguity due to radiometric calibration (the primary source
of uncertainty in this study). We present the first ground-based determination
of Jupiter's N/N ratio (in the range from to
), which is consistent with both previous space-based studies
and with the primordial value of the protosolar nebula. On Saturn, we present
the first upper limit on the N/N ratio of no larger than
for the 900-cm channel and a less stringent
requirement that the ratio be no larger than for the
960-cm channel ( confidence). Specifically, the data rule out
strong N-enrichments such as those observed in Titan's atmosphere and in
cometary nitrogen compounds. To the extent possible with ground-based
radiometric uncertainties, the saturnian and jovian N/N ratios
appear indistinguishable, implying that N-enriched ammonia ices could
not have been a substantial contributor to the bulk nitrogen inventory of
either planet, favouring the accretion of primordial N from the gas phase
or as low-temperature ices.Comment: 33 pages, 19 figures, manuscript accepted for publication in Icaru
Fast ray-tracing algorithm for circumstellar structures (FRACS) I. Algorithm description and parameter-space study for mid-IR interferometry of B[e] stars
The physical interpretation of spectro-interferometric data is strongly
model-dependent. On one hand, models involving elaborate radiative transfer
solvers are too time consuming in general to perform an automatic fitting
procedure and derive astrophysical quantities and their related errors. On the
other hand, using simple geometrical models does not give sufficient insights
into the physics of the object. We propose to stand in between these two
extreme approaches by using a physical but still simple parameterised model for
the object under consideration. Based on this philosophy, we developed a
numerical tool optimised for mid-infrared (mid-IR) interferometry, the fast
ray-tracing algorithm for circumstellar structures (FRACS) which can be used as
a stand-alone model, or as an aid for a more advanced physical description or
even for elaborating observation strategies. FRACS is based on the ray-tracing
technique without scattering, but supplemented with the use of quadtree meshes
and the full symmetries of the axisymmetrical problem to significantly decrease
the necessary computing time to obtain e.g. monochromatic images and
visibilities. We applied FRACS in a theoretical study of the dusty
circumstellar environments (CSEs) of B[e] supergiants (sgB[e]) in order to
determine which information (physical parameters) can be retrieved from present
mid-IR interferometry (flux and visibility). From a set of selected dusty CSE
models typical of sgB[e] stars we show that together with the geometrical
parameters (position angle, inclination, inner radius), the temperature
structure (inner dust temperature and gradient) can be well constrained by the
mid-IR data alone. Our results also indicate that the determination of the
parameters characterising the CSE density structure is more challenging but, in
some cases, upper limits as well as correlations on the parameters
characterising the mass loss can be obtained. Good constraints for the sgB[e]
central continuum emission (central star and inner gas emissions) can be
obtained whenever its contribution to the total mid-IR flux is only as high as
a few percents. Ray-tracing parameterised models such as FRACS are thus well
adapted to prepare and/or interpret long wavelengths (from mid-IR to radio)
observations at present (e.g. VLTI/MIDI) and near-future (e.g. VLTI/MATISSE,
ALMA) interferometers
Bayesian modelling of the cool core galaxy group NGC 4325
We present an X-ray analysis of the radio-quiet cool-core galaxy group NGC
4325 (z=0.026) based on Chandra and ROSAT observations. The Chandra data were
analysed using XSPEC deprojection, 2D spectral mapping and forward-fitting with
parametric models. Additionally, a Markov chain Monte Carlo method was used to
perform a joint Bayesian analysis of the Chandra and ROSAT data. The results of
the various analysis methods are compared, particularly those obtained by
forward-fitting and deprojection. The spectral mapping reveals the presence of
cool gas displaced up to 10 kpc from the group centre. The Chandra X-ray
surface brightness shows the group core to be highly disturbed, and indicates
the presence of two small X-ray cavities within 15 kpc of the group core. The
XSPEC deprojection analysis shows that the group has a particularly steep
entropy profile, suggesting that an AGN outburst may be about to occur. With
the evidence of prior AGN activity, but with no radio emission currently
observed, we suggest that the group in in a pre-outburst state, with the
cavities and displaced gas providing evidence of a previous, weak AGN outburst.Comment: 12 pages, 10 figures; accepted for publication in MNRA
Process algebra modelling styles for biomolecular processes
We investigate how biomolecular processes are modelled in process algebras, focussing on chemical reactions. We consider various modelling styles and how design decisions made in the definition of the process algebra have an impact on how a modelling style can be applied. Our goal is to highlight the often implicit choices that modellers make in choosing a formalism, and illustrate, through the use of examples, how this can affect expressability as well as the type and complexity of the analysis that can be performed
Modelling Reactive Multimedia: Design and Authoring
Multimedia document authoring is a multifaceted activity, and authoring tools tend to concentrate on a restricted set of the activities involved in the creation of a multimedia artifact. In particular, a distinction may be drawn between the design and the implementation of a multimedia artifact.
This paper presents a comparison of three different authoring paradigms, based on the common case study of a simple interactive animation. We present details of its implementation using the three different authoring tools, MCF, Fran and SMIL 2.0, and we discuss the conclusions that may be drawn from our comparison of the three approaches
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