1,432 research outputs found
Embodying life-long learning: Transition and capstone experiences
This paper discusses the principle of Transition as it has been conceptualised by the Curriculum Renewal in Legal Education project. The project sought to develop a principled framework for renewing the final year of tertiary legal education in Australia. Capstone experiences were chosen as the most appropriate mechanism for assisting final year students to manage the transition process. Thoughtfully designed capstones assist students to integrate and synthesize their learning over their entire degree program, facilitate closure on the undergraduate experience, and assist students to transition from student to emerging professional. We discuss the importance of addressing final year studentsâ transitional needs and explain how the principle facilitates this process. Although the framework has been developed specifically for legal education in Australia its approach enables transferability across disciplines and institutions. The framework addresses criticisms that universities and law schools are not meeting the needs of final year students by preparing them for the transition to graduate life in a complex and uncertain world
Nitrogen superfractionation in dense cloud cores
We report new calculations of interstellar 15N fractionation. Previously, we
have shown that large enhancements of 15N/14N can occur in cold, dense gas
where CO is frozen out, but that the existence of an NH + N channel in the
dissociative recombination of N2H+ severely curtails the fractionation. In the
light of recent experimental evidence that this channel is in fact negligible,
we have reassessed the 15N chemistry in dense cloud cores. We consider the
effects of temperatures below 10 K, and of the presence of large amounts of
atomic nitrogen. We also show how the temporal evolution of gas-phase isotope
ratios is preserved as spatial heterogeneity in ammonia ice mantles, as
monolayers deposited at different times have different isotopic compositions.
We demonstrate that the upper layers of this ice may have 15N/14N ratios an
order of magnitude larger than the underlying elemental value. Converting our
ratios to delta-values, we obtain delta(15N) > 3,000 per mil in the uppermost
layer, with values as high as 10,000 per mil in some models. We suggest that
this material is the precursor to the 15N `hotspots' recently discovered in
meteorites and IDPsComment: accepted by MNRA
New observations of the extended hydrogen exosphere of the extrasolar planet HD209458b
Atomic hydrogen escaping from the planet HD209458b provides the largest
observational signature ever detected for an extrasolar planet atmosphere.
However, the Space Telescope Imaging Spectrograph (STIS) used in previous
observational studies is no longer available, whereas additional observations
are still needed to better constrain the mechanisms subtending the evaporation
process, and determine the evaporation state of other `hot Jupiters'. Here, we
aim to detect the extended hydrogen exosphere of HD209458b with the Advanced
Camera for Surveys (ACS) on board the Hubble Space Telescope (HST) and to find
evidence for a hydrogen comet-like tail trailing the planet, which size would
depend on the escape rate and the amount of ionizing radiation emitted by the
star. These observations also provide a benchmark for other transiting planets,
in the frame of a comparative study of the evaporation state of close-in giant
planets. Eight HST orbits are used to observe two transits of HD209458b.
Transit light curves are obtained by performing photometry of the unresolved
stellar Lyman-alpha emission line during both transits. Absorption signatures
of exospheric hydrogen during the transit are compared to light curve models
predicting a hydrogen tail. Transit depths of (9.6 +/- 7.0)% and (5.3 +/-
10.0)% are measured on the whole Lyman-alpha line in visits 1 and 2,
respectively. Averaging data from both visits, we find an absorption depth of
(8.0 +/- 5.7)%, in good agreement with previous studies. The extended size of
the exosphere confirms that the planet is likely loosing hydrogen to space.
Yet, the photometric precision achieved does not allow us to better constrain
the hydrogen mass loss rate.Comment: Accepted for publication in Astronomy & Astrophysics. 5 pages, 3
figure
Descartes, corpuscles and reductionism : mechanism and systems in Descartes' physiology
I argue that Descartes explains physiology in terms of whole systems, and not in terms of the size, shape and motion of tiny corpuscles (corpuscular mechanics). It is a standard, entrenched view that Descartesâs proper means of explanation in the natural world is through strict reduction to corpuscular mechanics. This view is bolstered by a handful of corpuscular-mechanical explanations in Descartesâs physics, which have been taken to be representative of his treatment of all natural phenomena. However, Descartesâs explanations of the âprincipal partsâ of physiology do not follow the corpuscularâmechanical pattern. Des Chene (2001) has identified systems in Descartesâs account of physiology, but takes them ultimately to reduce down to the corpuscle level. I argue that they do not. Rather, Descartes maintains entire systems, with components selected from multiple levels of organisation, in order to construct more complete explanations than corpuscular mechanics alone would allow
Transit spectrophotometry of the exoplanet HD189733b. I. Searching for water but finding haze with HST NICMOS
We present Hubble Space Telescope near-infrared transit photometry of the
nearby hot-Jupiter HD189733b. The observations were taken with the NICMOS
instrument during five transits, with three transits executed with a narrowband
filter at 1.87 microns and two performed with a narrowband filter at 1.66
microns. Our observing strategy using narrowband filters is insensitive to the
usual HST intra-orbit and orbit-to-orbit measurement of systematic errors,
allowing us to accurately and robustly measure the near-IR wavelength
dependance of the planetary radius. Our measurements fail to reproduce the
Swain et al. absorption signature of atmospheric water below 2 microns at a
5-sigma confidence level. We measure a planet-to-star radius contrast of
0.15498+/-0.00035 at 1.66 microns and a contrast of 0.15517+/-0.00019 at 1.87
microns. Both of our near-IR planetary radii values are in excellent agreement
with the levels expected from Rayleigh scattering by sub-micron haze particles,
observed at optical wavelengths, indicating that upper-atmospheric haze still
dominates the near-IR transmission spectra over the absorption from gaseous
molecular species at least below 2 microns.Comment: 9 pages, 7 figures. Accepted for publication in A&
FUSE observations of the HI interstellar gas of IZw18
We present the analysis of FUSE observations of the metal-deficient dwarf
galaxy IZw18. We measured column densities of HI, NI, OI, ArI, SiII, and FeII.
The OI/HI ratio (log(OI/HI)=-4.7^{+0.8}_{-0.6}) is consistent with the O/H
ratio observed in the HII regions (all uncertainties are 2-sigma). If the
oxygen is depleted in the HI region compared to the HII regions, the depletion
is at most 0.5dex. This is also consistent with the log(O/H) ratios ~-5
measured with FUSE in the HI regions of other blue compact dwarf galaxies. With
log(NI/OI)=-2.4^{+0.6}_{-0.8}, the measured NI/OI ratio is lower than expected
for primary nitrogen. The determination of the NII column density is needed to
discriminate between a large ionization of NI or a possible nitrogen
deficiency. The neutral argon is also apparently underabundant, indicating that
ionization into ArII is likely important. The column densities of the other
alpha-chain elements SiII and ArI favor the lower edge of the permitted range
of OI column density, log(N(OI))~16.3.Comment: Accepted for publication in A&
A new look at NICMOS transmission spectroscopy of HD189733, GJ-436 and XO-1: no conclusive evidence for molecular features
We present a re-analysis of archival HST/NICMOS transmission spectroscopy of
three exoplanet systems; HD 189733, GJ-436 and XO-1. Detections of several
molecules, including H20, CH4 and CO2, have been claimed for HD 189733 and
XO-1, but similarly sized features are attributed to systematic noise for
GJ-436. The data consist of time-series grism spectra covering a planetary
transit. After extracting light curves in independent wavelength channels, we
use a linear decorrelation technique account for instrumental systematics
(which is becoming standard in the field), and measure the planet-to-star
radius ratio as a function of wavelength. For HD 189733, the uncertainties in
the transmission spectrum are significantly larger than those previously
reported. We also find the transmission spectrum is considerably altered when
using different out-of-transit orbits to remove the systematics, when some
parameters are left out of the decorrelation procedure, or when we perform the
decorrelation with quadratic functions rather than linear functions. Given that
there is no physical reason to believe the baseline flux should be modelled as
a linear function of any particular set of parameters, we interpret this as
evidence that the linear decorrelation technique is not a robust method to
remove systematic effects from the light curves for each wavelength channel.
For XO-1, the parameters measured to decorrelate the light curves would require
extrapolation to the in-transit orbit to remove the systematics, and we cannot
reproduce the previously reported results. We conclude that the resulting
NICMOS transmission spectra are too dependent on the method used to remove
systematics to be considered robust detections of molecular species in
planetary atmospheres, although the presence of these molecules is not ruled
out.Comment: 17 pages, 28 figures, accepted in MNRA
Doppler follow-up of OGLE transiting companions in the Galactic bulge
Two years ago, the OGLE-III survey (Optical Gravitational Lensing Experiment)
announced the detection of 54 short period multi-transiting objects in the
Galactic bulge (Udalski et al., 2002a, 2002b). Some of these objects were
considered to be potential hot Jupiters. In order to determine the true nature
of these objects and to characterize their actual mass, we conducted a radial
velocity follow-up of 18 of the smallest transiting candidates. We describe
here our procedure and report the characterization of 8 low mass star
transiting companions, 2 grazing eclipsing binaries, 2 triple systems, 1
confirmed exoplanet (OGLE-TR-56b), 1 possible exoplanet (OGLE-TR-10b), 1 clear
false positive and 3 unsolved cases. The variety of cases encountered in our
follow-up covers a large part of the possible scenarii occuring in the search
for planetary transits. As a by-product, our program yields precise masses and
radii of low mass stars.Comment: accepted in A&
Learning outcomes from a biomedical research course for second year osteopathic medical students
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