953 research outputs found
Studies on the zoogeography and ecology of palaearctic Coccidae I-III
The study of Coccidae has been restricted mainly to description
of species and control of those forms which are injurious. Species of
which the life-history is well known are very limited even in number.
It is only recently that this extremely interesting group of insects
has been studied by VayssiĂšre, Balachowsky, and the writer in
connection with the problems of zoogeography and ecology. The
following pages aim to extend our knowledge in these respects.Peer reviewe
Formation of giant planets in disks with different metallicities
We present the first results from simulations of processes leading to planet
formation in protoplanetary disks with different metallicities. For a given
metallicity, we construct a two-dimensional grid of disk models with different
initial masses and radii (, ). For each disk, we follow the evolution
of gas and solids from an early evolutionary stage, when all solids are in the
form of small dust grains, to the stage when most solids have condensed into
planetesimals. Then, based on the core accretion - gas capture scenario, we
estimate the planet-bearing capability of the environment defined by the final
planetesimal swarm and the still evolving gaseous component of the disk. We
define the probability of planet-formation, , as the normalized fractional
area in the (, ) plane populated by disks that have formed
planets inside 5 AU. With such a definition, and under the assumption that the
population of planets discovered at 5 AU is not significantly
contaminated by planets that have migrated from 5 AU, our results agree
fairly well with the observed dependence between the probability that a star
harbors a planet and the star's metal content. The agreement holds for the disk
viscosity parameter ranging from to , and it
becomes much poorer when the redistribution of solids relative to the gas is
not allowed for during the evolution of model disks.Comment: Accepted for publication in A&A. 6 pages, 6 figure
Moving from evidence-based medicine to evidence-based health.
While evidence-based medicine (EBM) has advanced medical practice, the health care system has been inconsistent in translating EBM into improvements in health. Disparities in health and health care play out through patients' limited ability to incorporate the advances of EBM into their daily lives. Assisting patients to self-manage their chronic conditions and paying attention to unhealthy community factors could be added to EBM to create a broader paradigm of evidence-based health. A perspective of evidence-based health may encourage physicians to consider their role in upstream efforts to combat socially patterned chronic disease
An alternative look at the snowline in protoplanetary disks
We have calculated an evolution of protoplanetary disk from an extensive set
of initial conditions using a time-dependent model capable of simultaneously
keeping track of the global evolution of gas and water-ice. A number of
simplifications and idealizations allows for an embodiment of gas-particle
coupling, coagulation, sedimentation, and evaporation/condensation processes.
We have shown that, when the evolution of ice is explicitly included, the
location of the snowline has to be calculated directly as the inner edge of the
region where ice is present and not as the radius where disk's temperature
equals the evaporation temperature of water-ice. The final location of the
snowline is set by an interplay between all involved processes and is farther
from the star than implied by the location of the evaporation temperature
radius. The evolution process naturally leads to an order of magnitude
enhancement in surface density of icy material.Comment: Accepted for publication in A&A. 8 pages, 4 figure
A qualitative study of unmet needs and interactions with primary care among cancer survivors
INTRODUCTION: Despite increasing numbers, there is little research investigating the long-term needs of cancer survivors. The aim of this study is to explore the experiences of individuals who have survived at least 5 years following a cancer diagnosis, and to describe perceived unmet needs and interactions with primary care. METHODS: Forty long-term survivors of breast, colorectal and prostate cancer were purposively selected for an in-depth qualitative study. We aimed for a maximum variation sample according to cancer site, gender, time since diagnosis, cancer needs, anxiety and depression. Interviews were audio recorded and transcribed verbatim. Transcripts were coded thematically using a grounded theory approach. RESULTS: Analysis of the interview data is presented in four subthemes: the role they perceived for the general practitioner (GP), unmet needs, reasons for not using primary care for needs they perceived as cancer related, and ongoing care for cancer-related issues. The majority of cancer survivors did not see a role for their GP in their long-term care related to their cancer diagnosis as most considered that they did not need active follow-up, but some expressed a need for psychological services and information on possible long-term effects. Cancer survivors cited three main reasons for not using GP services in relation to their cancer diagnosis: GPs were seen as non-experts in cancer; they were perceived as too busy; and a lack of continuity within primary care made it difficult to talk about long-term issues. There was a wide variation in schedules and notification of PSA tests among the prostate cancer survivors. DISCUSSION: The results from this project suggest that some cancer survivors have specific emotional and physical needs that could benefit from input from their primary care team, but not all cancer survivors look to their GP for their long-term cancer-related care. Better information care planning is required from specialists in order to identify those who would benefit mos
Relative velocities among accreting planetesimals in binary systems: the circumbinary case
We numerically investigate the possibility of planetesimal accretion in
circumbinary disks, under the coupled influence of both stars' secular
perturbations and friction due to the gaseous component of the protoplanetary
disk. We focus on one crucial parameter: the distribution of encounter
velocities between planetesimals in the 0.5 to 100km size range. An extended
range of binary systems with differing orbital parameters is explored. The
resulting encounter velocities are compared to the threshold velocities below
which the net outcome of a collision is accumulation into a larger body instead
of mass erosion. For each binary configuration, we derive the critical radial
distance from the binary barycenter beyond which planetesimal accretion is
possible. This critical radial distance is smallest for equal-mass binaries on
almost circular orbits. It shifts to larger values for increasing
eccentricities and decreasing mass ratio. The importance of the planetesimals'
orbital alignments of planetesimals due to gas drag effects is discussed.Comment: accepted for publication in MNRA
HD 17156b: A Transiting Planet with a 21.2 Day Period and an Eccentric Orbit
We report the detection of transits by the 3.1 M_Jup companion to the V=8.17
G0V star HD 17156. The transit was observed by three independant observers on
Sept. 9/10, 2007 (two in central Italy and one in the Canary Islands), who
obtained detections at confidence levels of 3.0 sigma, 5.3 sigma, and 7.9
sigma, respectively. The observations were carried out under the auspices of
the Transitsearch.org network, which organizes follow-up photometric transit
searches of known planet-bearing stars during the time intervals when transits
are expected to possibly occur. Analyses of the 7.9 sigma data set indicates a
transit depth d=0.0062+/-0.0004, and a transit duration t=186+/-5 min. These
values are consistent with the transit of a Jupiter-sized planet with an impact
parameter b=a*cos(i)/R_star ~ 0.8. This planet occupies a unique regime among
known transiting extrasolar planets, both as a result of its large orbital
eccentricity (e=0.67) and long orbital period (P=21.2 d). The planet receives a
26-fold variation in insolation during the course of its orbit, which will make
it a useful object for characterization of exoplanetary atmospheric dynamics.Comment: Accepted for publication to A&A, 4 pages, 2 figure
A correlation between the heavy element content of transiting extrasolar planets and the metallicity of their parent stars
Nine extrasolar planets with masses between 110 and 430M are known to transit
their star. The knowledge of their masses and radii allows an estimate of their
composition, but uncertainties on equations of state, opacities and possible
missing energy sources imply that only inaccurate constraints can be derived
when considering each planet separately. Aims: We seek to better understand the
composition of transiting extrasolar planets by considering them as an
ensemble, and by comparing the obtained planetary properties to that of the
parent stars. Methods: We use evolution models and constraints on the stellar
ages to derive the mass of heavy elements present in the planets. Possible
additional energy sources like tidal dissipation due to an inclined orbit or to
downward kinetic energy transport are considered. Results: We show that the
nine transiting planets discovered so far belong to a quite homogeneous
ensemble that is characterized by a mass of heavy elements that is a relatively
steep function of the stellar metallicity, from less than 20 earth masses of
heavy elements around solar composition stars, to up to 100M for three times
the solar metallicity (the precise values being model-dependant). The
correlation is still to be ascertained however. Statistical tests imply a
worst-case 1/3 probability of a false positive. Conclusions: Together with the
observed lack of giant planets in close orbits around metal-poor stars, these
results appear to imply that heavy elements play a key role in the formation of
close-in giant planets. The large masses of heavy elements inferred for planets
orbiting metal rich stars was not anticipated by planet formation models and
shows the need for alternative theories including migration and subsequent
collection of planetesimals.Comment: Astronomy and Astrophysics 0 (2006) in pres
Supernova Remnants in the Magellanic Clouds. VI. The DEML316 Supernova Remnants
The DEML316 system contains two shells, both with the characteristic
signatures of supernova remnants (SNRs). We analyze Chandra and XMM-Newton data
for DEML316, investigating its spatial and spectral X-ray features. Our Chandra
observations resolve the structure of the northeastern SNR (Shell A) as a
bright inner ring and a set of "arcs" surrounded by fainter diffuse emission.
The spectrum is well fit by a thermal plasma model with temperature ~1.4 keV;
we do not find significant spectral differences for different regions of this
SNR. The southwestern SNR (Shell B) exhibits an irregular X-ray outline, with a
brighter interior ring of emission including a bright knot of emission. Overall
the emission of the SNR is well described by a thermal plasma of temperature
~0.6 keV. The Bright Knot, however, is spectrally distinct from the rest of the
SNR, requiring the addition of a high-energy spectral component consistent with
a power-law spectrum of photon index 1.6--1.8.
We confirm the findings of Nishiuchi et al. (2001) that the spectra of these
shells are notably different, with Shell A requiring a high iron abundance for
a good spectral fit, implying a Type Ia origin. We further explicitly compare
abundance ratios to model predictions for Type Ia and Type II supernovae. The
low ratios for Shell A (O/Fe of 1.5 and Ne/Fe of 0.2) and the high ratios for
Shell B (O/Fe of 30--130 and Ne/Fe of 8--16) are consistent with Type Ia and
Type II origins, respectively. The difference between the SNR progenitor types
casts some doubt on the suggestion that these SNRs are interacting with one
another.Comment: Accepted for ApJ v. 635 (December issue
Physicians' view of primary care-based case management for patients with heart failure: a qualitative study
- âŠ