3,218 research outputs found
A Functional Naturalism
I provide two arguments against value-free naturalism. Both are based on considerations concerning biological teleology. Value-free naturalism is the thesis that both (1) everything is, at least in principle, under the purview of the sciences and (2) all scientific facts are purely non-evaluative. First, I advance a counterexample to any analysis on which natural selection is necessary to biological teleology. This should concern the value-free naturalist, since most value-free analyses of biological teleology appeal to natural selection. My counterexample is unique in that it is likely to actually occur. It concerns the creation of synthetic life. Recent developments in synthetic biology suggest scientists will eventually be able to develop synthetic life. Such life, however, would not have any of its traits naturally selected for. Second, I develop a simple argument that biological teleology is a scientific but value-laden notion. Consequently, value-free naturalism is false. I end with some concluding remarks on the implications for naturalism, the thesis that (1). Naturalism may be salvaged only if we reject (2). (2) is a dogma that unnecessarily constrains our conception of the sciences. Only a naturalism that recognizes value-laden notions as scientifically respectable can be true. Such a naturalism is a functional naturalism
Tidal evolution of close-in giant planets : Evidence of Type II migration?
It is well accepted that 'hot Jupiters' did not form in situ, as the
temperature in the protoplanetary disc at the radius at which they now orbit
would have been too high for planet formation to have occurred. These planets,
instead, form at larger radii and then move into the region in which they now
orbit. The exact process that leads to the formation of these close-in planets
is, however, unclear and it seems that there may be more than one mechanism
that can produce these short-period systems. Dynamical interactions in
multiple-planet systems can scatter planets into highly eccentric orbits which,
if the pericentre is sufficiently close to the parent star, can be tidally
circularised by tidal interactions between the planet and star. Furthermore,
systems with distant planetary or stellar companions can undergo Kozai cycles
which can result in a planet orbiting very close to its parent star. However,
the most developed model for the origin of short period planets is one in which
the planet exchanges angular momentum with the surrounding protoplanetary disc
and spirals in towards the central star. In the case of 'hot Jupiters', the
planet is expected to open a gap in the disc and migrate through Type II
.migration. If this is the dominant mechanism for producing `hot Jupiters' then
we would expect the currect properties of observed close-in giant planets to be
consistent with an initial population resulting from Type II migration followed
by evolution due to tidal interactions with the central star. We consider
initial distributions that are consistent with Type II migration and find that
after tidal evolution, the final distributions can be consistent with that
observed. Our results suggest that a modest initial pile-up at a ~ 0.05 au is
required and that the initial eccentricity distribution must peak at e \sim 0.Comment: 10 pages, 15 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Anastomotic complications after tracheal resection: Prognostic factors and management
ObjectiveWe sought to identify risk factors for anastomotic complications after tracheal resection and to describe the management of these patients.MethodsThis was a single-institution, retrospective review of 901 patients who underwent tracheal resection.ResultsThe indications for tracheal resection were postintubation tracheal stenosis in 589 patients, tumor in 208, idiopathic laryngotracheal stenosis in 83, and tracheoesophageal fistula in 21. Anastomotic complications occurred in 81 patients (9%). Eleven patients (1%) died after operation, 6 of anastomotic complications and 5 of other causes (odds ratio 13.0, P = .0001 for risk of death after anastomotic complication). At the end of treatment, 853 patients (95%) had a good result, whereas 37 patients (4%) had an airway maintained by tracheostomy or T-tube. The treatments of patients with an anastomotic complication were as follows: multiple dilations (n = 2), temporary tracheostomy (n = 7), temporary T-tube (n = 16), permanent tracheostomy (n = 14), permanent T-tube (n = 20), and reoperation (n = 16). Stepwise multivariable analysis revealed the following predictors of anastomotic complications: reoperation (odds ratio 3.03, 95% confidence interval 1.69-5.43, P = .002), diabetes (odds ratio 3.32, 95% confidence interval 1.76-6.26, P = .002), lengthy (≥4 cm) resections (odds ratio 2.01, 95% confidence interval 1.21-3.35, P = .007), laryngotracheal resection (odds ratio 1.80, 95% confidence interval 1.07-3.01, P = .03), age 17 years or younger (odds ratio 2.26, 95% confidence interval 1.09-4.68, P = .03), and need for tracheostomy before operation (odds ratio 1.79, 95% confidence interval 1.03-3.14, P = .04).ConclusionsTracheal resection is usually successful and has a low mortality. Anastomotic complications are uncommon, and important risk factors are reoperation, diabetes, lengthy resections, laryngotracheal resections, young age (pediatric patients), and the need for tracheostomy before operation
WASP-50b: a hot Jupiter transiting a moderately active solar-type star
We report the discovery by the WASP transit survey of a giant planet in a
close orbit (0.0295+-0.0009 AU) around a moderately bright (V=11.6, K=10) G9
dwarf (0.89+-0.08 M_sun, 0.84+-0.03 R_sun) in the Southern constellation
Eridanus. Thanks to high-precision follow-up photometry and spectroscopy
obtained by the telescopes TRAPPIST and Euler, the mass and size of this
planet, WASP-50b, are well constrained to 1.47+-0.09 M_jup and 1.15+-0.05
R_jup, respectively. The transit ephemeris is 2455558.6120 (+-0.0002) + N x
1.955096 (+-0.000005) HJD_UTC. The size of the planet is consistent with basic
models of irradiated giant planets. The chromospheric activity (log R'_HK =
-4.67) and rotational period (P_rot = 16.3+-0.5 days) of the host star suggest
an age of 0.8+-0.4 Gy that is discrepant with a stellar-evolution estimate
based on the measured stellar parameters (rho_star = 1.48+-0.10 rho_sun, Teff =
5400+-100 K, [Fe/H]= -0.12+-0.08) which favours an age of 7+-3.5 Gy. This
discrepancy could be explained by the tidal and magnetic influence of the
planet on the star, in good agreement with the observations that stars hosting
hot Jupiters tend to show faster rotation and magnetic activity (Pont 2009;
Hartman 2010). We measure a stellar inclination of 84 (-31,+6) deg,
disfavouring a high stellar obliquity. Thanks to its large irradiation and the
relatively small size of its host star, WASP-50b is a good target for
occultation spectrophotometry, making it able to constrain the relationship
between hot Jupiters' atmospheric thermal profiles and the chromospheric
activity of their host stars proposed by Knutson et al. (2010).Comment: 9 pages, 8 figures. Accepted for publication in Astronomy &
Astrophysic
Rossiter-McLaughlin Effect Measurements for WASP-16, WASP-25 and WASP-31
We present new measurements of the Rossiter-McLaughlin (RM) effect for three
WASP planetary systems, WASP-16, WASP-25 and WASP-31, from a combined analysis
of their complete sets of photometric and spectroscopic data. We find a low
amplitude RM effect for WASP-16 (Teff = 5700 \pm 150K), suggesting that the
star is a slow rotator and thus of an advanced age, and obtain a projected
alignment angle of lambda = -4.2 degrees +11.0 -13.9. For WASP-25 (Teff =
5750\pm100K) we detect a projected spin-orbit angle of lambda = 14.6 degrees
\pm6.7. WASP-31 (Teff = 6300\pm100K) is found to be well-aligned, with a
projected spin-orbit angle of lambda = 2.8degrees \pm3.1. A circular orbit is
consistent with the data for all three systems, in agreement with their
respective discovery papers. We consider the results for these systems in the
context of the ensemble of RM measurements made to date. We find that whilst
WASP-16 fits the hypothesis of Winn et al. (2010) that 'cool' stars (Teff <
6250K) are preferentially aligned, WASP-31 has little impact on the proposed
trend. We bring the total distribution of the true spin-orbit alignment angle,
psi, up to date, noting that recent results have improved the agreement with
the theory of Fabrycky & Tremaine (2007) at mid-range angles. We also suggest a
new test for judging misalignment using the Bayesian Information Criterion,
according to which WASP-25 b's orbit should be considered to be aligned.Comment: 20 pages, 14 tables, 10 figures. Accepted to MNRA
Planetary mass function and planetary systems
With planets orbiting stars, a planetary mass function should not be seen as
a low-mass extension of the stellar mass function, but a proper formalism needs
to take care of the fact that the statistical properties of planet populations
are linked to the properties of their respective host stars. This can be
accounted for by describing planet populations by means of a differential
planetary mass-radius-orbit function, which together with the fraction of stars
with given properties that are orbited by planets and the stellar mass function
allows to derive all statistics for any considered sample. These fundamental
functions provide a framework for comparing statistics that result from
different observing techniques and campaigns which all have their very specific
selection procedures and detection efficiencies. Moreover, recent results both
from gravitational microlensing campaigns and radial-velocity surveys of stars
indicate that planets tend to cluster in systems rather than being the lonely
child of their respective parent star. While planetary multiplicity in an
observed system becomes obvious with the detection of several planets, its
quantitative assessment however comes with the challenge to exclude the
presence of further planets. Current exoplanet samples begin to give us first
hints at the population statistics, whereas pictures of planet parameter space
in its full complexity call for samples that are 2-4 orders of magnitude
larger. In order to derive meaningful statistics however, planet detection
campaigns need to be designed in such a way that well-defined
fully-deterministic target selection, monitoring, and detection criteria are
applied. The probabilistic nature of gravitational microlensing makes this
technique an illustrative example of all the encountered challenges and
uncertainties.Comment: 7 pages, MNRAS accepte
Comparative hemodynamic effects of selective superior mesenteric arterial and peripheral intravenous glucagon infusions
This experiment was designed to determine whether any hemodynamic benefits attend administration of equal pharmacologic doses of glucagon (1 [mu]g/kg/m) by continuous intravenous infusion (Group I, n = 6) versus selective intraarterial infusion (Group II, n = 6) via the superior mesenteric artery (SMA) in dogs. Cardiac output, heart rate, mean arterial pressure, total peripheral resistance, pulmonary vascular resistance, superior mesenteric artery flow (SMAQ), SMA vascular resistance, and portal venous pressure were measured at baseline (BL) and at 5, 15, 30, and 45 min during glucagon infusion. SMAQ virtually doubled at 5 min from a baseline of 570 +/- 60 ml/min to 1158 +/- 146 ml/min in Group I (P P P P < 0.05). Changes in systemic hemodynamic parameters, as well as glucagon and glucose levels were not statistically different between Groups I and II at any time period. Glucagon is a potent mesenteric vasodilator and the resultant profound splanchnic hemodynamic effects are as marked during intravenous administration as during selective SMA infusion.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25582/1/0000126.pd
Resilience and stability of kelp forests: the importance of patch dynamics and environment-engineer feedbacks
Habitat forming ‘ecosystem engineers’ such as kelp species create complex habitats that support biodiverse and productive communities. Studies of the resilience and stability of ecosystem engineers have typically focussed on the role of external factors such as disturbance. However, their population dynamics are also likely to be influenced by internal processes, such that the environmental modifications caused by engineer species feedback to affect their own demography (e.g. recruitment, survivorship). In numerous regions globally, kelp forests are declining and experiencing reductions in patch size and kelp density. To explore how resilience and stability of kelp habitats is influenced by this habitat degradation, we created an array of patch reefs of various sizes and supporting adult Ecklonia radiata kelp transplanted at different densities. This enabled testing of how sub-canopy abiotic conditions change with reductions in patch size and adult kelp density, and how this influenced demographic processes of microscopic and macroscopic juvenile kelp. We found that ecosystem engineering by adult E. radiata modified the environment to reduce sub-canopy water flow, sedimentation, and irradiance. However, the capacity of adult kelp canopy to engineer abiotic change was dependent on patch size, and to a lesser extent, kelp density. Reductions in patch size and kelp density also impaired the recruitment, growth and survivorship of microscopic and macroscopic juvenile E. radiata, and even after the provisioning of established juveniles, demographic processes were impaired in the absence of sufficient adult kelp. These results are consistent with the hypothesis that ecosystem engineering by adult E. radiata facilitates development of juvenile conspecifics. Habitat degradation seems to impair the ability of E. radiata to engineer abiotic change, causing breakdown of positive intraspecific feedback and collapse of demographic functions, and overall, leading to reductions in ecosystem stability and resilience well before local extirpation
Omentum is highly effective in the management of complex cardiothoracic surgical problems
AbstractObjectives: Vascularized, pedicled tissue flaps are often used for cardiothoracic surgical problems complicated by factors that adversely affect healing, such as previous irradiation, established infection, or steroid use. We reviewed our experience with use of the omentum in these situations to provide a yardstick against which results with other vascularized flaps (specifically muscle flaps) could be compared. Methods: A retrospective review was undertaken of 85 consecutive patients in whom omentum was used in the chest. In 47 patients (group I), use of omentum was prophylactic to aid in the healing of closures or anastomoses considered to be at high risk for failure. In 32 patients (group II), omentum was used in the treatment of problems complicated by established infection. In 6 patients (group III), omentum was used for coverage of prosthetic chest wall replacements after extensive chest wall resection. Results: Overall, omental transposition was successful in its prophylactic or therapeutic purpose in 88% of these difficult cases (75/85). Success with omentum was achieved for 89% of patients (42/47) in group I, 91% of patients (29/32) in group II, and 67% of patients (4/6) in group III. Three patients (3.5%) had complications of omental mobilization. Four patients (4.7%) died after the operation as a result of failure of the omentum to manage the problem for which it was used. Conclusions: Results with omental transposition compare favorably with published series of similarly challenging cases managed with muscle transposition. Complications of omental mobilization are rare. We believe that its unique properties render the omentum an excellent choice of vascularized pedicle in the management of the most complex cardiothoracic surgical problems.J Thorac Cardiovasc Surg 2003;125:526-3
The Neon Abundance of Galactic Wolf-Rayet Stars
The fast, dense winds which characterize Wolf-Rayet (WR) stars obscure
their underlying cores, and complicate the verification of evolving
core and nucleosynthesis models. Core evolution can be probed by
measuring abundances of wind-borne nuclear processed elements,
partially overcoming this limitation. Using ground-based mid-infrared
spectroscopy and the 12.81um [NeII] emission line measured in
four Galactic WR stars, we estimate neon abundances and compare to
long-standing predictions from evolved-core models. For the WC star
WR121, this abundance is found to be >~11x the cosmic
value, in good agreement with predictions. For the three less-evolved
WN stars, little neon enhancement above cosmic values is measured, as
expected. We discuss the impact of clumping in WR winds on this
measurement, and the promise of using metal abundance ratios to
eliminate sensitivity to wind density and ionization structure.Comment: Accepted for publication in ApJ; 9 pages, 2 color figures, 4 table
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