4,167 research outputs found
Analytic, dust-independent mass-loss rates for red supergiant winds initiated by turbulent pressure
Context. Red supergiants are observed to undergo vigorous mass-loss. However,
to date, no theoretical model has succeeded in explaining the origins of these
objects' winds. This strongly limits our understanding of red supergiant
evolution and Type II-P and II-L supernova progenitor properties.
Aims. We examine the role that vigorous atmospheric turbulence may play in
initiating and determining the mass-loss rates of red supergiant stars.
Methods. We analytically and numerically solve the equations of conservation
of mass and momentum, which we later couple to an atmospheric temperature
structure, to obtain theoretically motivated mass-loss rates. We then compare
these to state-of-the-art empirical mass-loss rate scaling formulae as well as
observationally inferred mass-loss rates of red supergiants.
Results. We find that the pressure due to the characteristic turbulent
velocities inferred for red supergiants is sufficient to explain the mass-loss
rates of these objects in the absence of the normally employed opacity from
circumstellar dust. Motivated by this initial success, we provide a first
theoretical and fully analytic mass-loss rate prescription for red supergiants.
We conclude by highlighting some intriguing possible implications of these
rates for future studies of stellar evolution, especially in light of the lack
of a direct dependence on metallicity.Comment: 14 pages, 9 figures, 2 table
Rapid short-pulses of focused ultrasound and microbubbles deliver a range of agent sizes to the brain
Focused ultrasound and microbubbles can non-invasively and locally deliver therapeutics and imaging agents across the bloodâbrain barrier. Uniform treatment and minimal adverse bioeffects are critical to achieve reliable doses and enable safe routine use of this technique. Towards these aims, we have previously designed a rapid short-pulse ultrasound sequence and used it to deliver a 3 kDa model agent to mouse brains. We observed a homogeneous distribution in delivery and bloodâbrain barrier closing within 10 min. However, many therapeutics and imaging agents are larger than 3 kDa, such as antibody fragments and antisense oligonucleotides. Here, we evaluate the feasibility of using rapid short-pulses to deliver higher-molecular-weight model agents. 3, 10 and 70 kDa dextrans were successfully delivered to mouse brains, with decreasing doses and more heterogeneous distributions with increasing agent size. Minimal extravasation of endogenous albumin (66.5 kDa) was observed, while immunoglobulin (~â150 kDa) and PEGylated liposomes (97.9 nm) were not detected. This study indicates that rapid short-pulses are versatile and, at an acoustic pressure of 0.35 MPa, can deliver therapeutics and imaging agents of sizes up to a hydrodynamic diameter between 8 nm (70 kDa dextran) and 11 nm (immunoglobulin). Increasing the acoustic pressure can extend the use of rapid short-pulses to deliver agents beyond this threshold, with little compromise on safety. This study demonstrates the potential for deliveries of higher-molecular-weight therapeutics and imaging agents using rapid short-pulses
Radio Continuum and Recombination Line Study of UC HII Regions with Extended Envelopes
We have carried out 21 cm radio continuum observations of 16 UC HII regions
using the VLA (D-array) in search of associated extended emission. We have also
observed H76 recombination line towards all the sources and
He76 line at the positions with strong H76 line emission. The
UC HII regions have simple morphologies and large (>10) ratios of single-dish
to VLA fluxes. Extended emission was detected towards all the sources. The
extended emission consists of one to several compact components and a diffuse
extended envelope. All the UC HII regions but two are located in the compact
components, where the UC HII regions always correspond to their peaks. The
compact components with UC HII regions are usually smaller and denser than
those without UC HII regions. Our recombination line observations indicate that
the ultracompact, compact, and extended components are physically associated.
The UC HII regions and their associated compact components are likely to be
ionized by the same sources on the basis of the morphological relations
mentioned above. This suggests that almost all of the observed UC HII regions
are not `real' UC HII regions and that their actual ages are much greater than
their dynamical age (<10000 yr). We find that most of simple UC HII regions
previously known have large ratios of single-dish to VLA fluxes, similar to our
sources. Therefore, the `age problem' of UC HII regions does not seem to be as
serious as earlier studies argued. We present a simple model that explains
extended emission around UC HII regions. Some individual sources are discussed.Comment: 29 pages, 28 postscript figures, Accepted for publication in Ap
Dynamically inflated wind models of classical Wolf-Rayet stars
Vigorous mass loss in the classical Wolf-Rayet (WR) phase is important for
the late evolution and final fate of massive stars. We develop spherically
symmetric time-dependent and steady-state hydrodynamical models of the
radiation-driven wind outflows and associated mass loss from classical WR
stars. The simulations are based on combining the opacities typically used in
static stellar structure and evolution models with a simple parametrised form
for the enhanced line-opacity expected within a supersonic outflow. Our
simulations reveal high mass-loss rates initiated in deep and hot optically
thick layers around T\approx 200kK. The resulting velocity structure is
non-monotonic and can be separated into three phases: i) an initial
acceleration to supersonic speeds ii) stagnation and even deceleration, and
iii) an outer region of rapid re-acceleration. The characteristic structures
seen in converged steady-state simulations agree well with the outflow
properties of our time-dependent models. By directly comparing our dynamic
simulations to corresponding hydrostatic models, we demonstrate explicitly that
the need to invoke extra energy transport in convectively inefficient regions
of stellar structure and evolution models is merely an artefact of enforcing a
hydrostatic outer boundary. Moreover, the "dynamically inflated" inner regions
of our simulations provide a natural explanation for the often-found mismatch
between predicted hydrostatic WR radii and those inferred from spectroscopy.
Finally, we contrast our simulations with alternative recent WR wind models
based on co-moving frame radiative transfer for computing the radiation force.
Since CMF transfer currently cannot handle non-monotonic velocity fields, the
characteristic deceleration regions found here are avoided in such simulations
by invoking an ad-hoc very high degree of clumping.Comment: 15 pages, 9 figure
Generalization of the JTZ model to open plane wakes
The JTZ model [C. Jung, T. T\'el and E. Ziemniak, Chaos {\bf 3}, (1993) 555],
as a theoretical model of a plane wake behind a circular cylinder in a narrow
channel at a moderate Reynolds number, has previously been employed to analyze
phenomena of chaotic scattering. It is extended here to describe an open plane
wake without the confined narrow channel by incorporating a double row of
shedding vortices into the intermediate and far wake. The extended JTZ model is
found in qualitative agreement with both direct numerical simulations and
experimental results in describing streamlines and vorticity contours. To
further validate its applications to particle transport processes, the
interaction between small spherical particles and vortices in an extended JTZ
model flow is studied. It is shown that the particle size has significant
influences on the features of particle trajectories, which have two
characteristic patterns: one is rotating around the vortex centers and the
other accumulating in the exterior of vortices. Numerical results based on the
extended JTZ model are found in qualitative agreement with experimental ones in
the normal range of particle sizes.Comment: 21 pages, 4 figures, 1 tabl
Phase coherence phenomena in superconducting films
Superconducting films subject to an in-plane magnetic field exhibit a gapless
superconducting phase. We explore the quasi-particle spectral properties of the
gapless phase and comment on the transport properties. Of particular interest
is the sensitivity of the quantum interference phenomena in this phase to the
nature of the impurity scattering. We find that films subject to columnar
defects exhibit a `Berry-Robnik' symmetry which changes the fundamental
properties of the system. Furthermore, we explore the integrity of the gapped
phase. As in the magnetic impurity system, we show that optimal fluctuations of
the random impurity potential conspire with the in-plane magnetic field to
induce a band of localized sub-gap states. Finally, we investigate the
interplay of the proximity effect and gapless superconductivity in thin normal
metal-superconductor bi-layers.Comment: 13 pages, 8 figures include
Alcoholic Beverage Preference and Dietary Habits in Elderly across Europe: Analyses within the Consortium on Health and Ageing: Network of Cohorts in Europe and the United States (CHANCES) Project
Introduction: The differential associations of beer, wine, and spirit consumption on cardiovascular risk found in observational studies may be confounded by diet. We described and compared dietary intake and diet quality according to alcoholic beverage preference in European elderly. Methods: From the Consortium on Health and Ageing: Network of Cohorts in Europe and the United States (CHANCES), seven European cohorts were included, i.e. four sub-cohorts from EPIC-Elderly, the SENECA Study, the Zutphen Elderly Study, and the Rotterdam Study. Harmonized data of 29,423 elderly participants from 14 European countries were analyzed. Baseline data on consumption of beer, wine, and spirits, and dietary intake were collected with questionnaires. Diet quality was assessed using the Healthy Diet Indicator (HDI). Intakes and scores across categories of alcoholic beverage preference (beer, wine, spirit, no preference, non-consumers) were adjusted for age, sex, socio-economic status, self-reported prevalent diseases, and lifestyle factors. Cohort-specific mean intakes and scores were calculated as well as weighted means combining all cohorts. Results: In 5 of 7 cohorts, persons with a wine preference formed the largest group. After multivariate adjustment, persons with a wine preference tended to have a higher HDI score and intake of healthy foods in most cohorts, but differences were small. The weighted estimates of all cohorts combined revealed that non-consumers had the highest fruit and vegetable intake, followed by wine consumers. Non-consumers and persons with no specific preference had a higher HDI score, spirit consumers the lowest. However, overall diet quality as measured by HDI did not differ greatly across alcoholic beverage preference categories. Discussion: This study using harmonized data from ~30,000 elderly from 14 European countries showed that, after multivariate adjustment, dietary habits and diet quality did not differ greatly according to alcoholic beverage preference
Nonlinear electrodynamics of p-wave superconductors
We consider the Maxwell-London electrodynamics of three dimensional
superconductors in p-wave pairing states with nodal points or lines in the
energy gap. The current-velocity relation is then nonlinear in the applied
field, cubic for point nodes and quadratic for lines. We obtain explicit
angular and depth dependent expressions for measurable quantities such as the
transverse magnetic moment, and associated torque. These dependences are
different for point and line nodes and can be used to distinguish between
different order parameters. We discuss the experimental feasibility of this
method, and bring forth its advantages, as well as limitations that might be
present.Comment: Fourteen pages RevTex plus four postscript figure
Natriuretic peptides and integrated risk assessment for cardiovascular disease. an individual-participant-data meta-analysis
BACKGROUND: Guidelines for primary prevention of cardiovascular diseases focus on prediction of coronary heart disease and stroke. We assessed whether or not measurement of N-terminal-pro-B-type natriuretic peptide (NT-proBNP) concentration could enable a more integrated approach than at present by predicting heart failure and enhancing coronary heart disease and stroke risk assessment.
METHODS: In this individual-participant-data meta-analysis, we generated and harmonised individual-participant data from relevant prospective studies via both de-novo NT-proBNP concentration measurement of stored samples and collection of data from studies identified through a systematic search of the literature (PubMed, Scientific Citation Index Expanded, and Embase) for articles published up to Sept 4, 2014, using search terms related to natriuretic peptide family members and the primary outcomes, with no language restrictions. We calculated risk ratios and measures of risk discrimination and reclassification across predicted 10 year risk categories (ie, <5%, 5% to <7·5%, and â„7·5%), adding assessment of NT-proBNP concentration to that of conventional risk factors (ie, age, sex, smoking status, systolic blood pressure, history of diabetes, and total and HDL cholesterol concentrations). Primary outcomes were the combination of coronary heart disease and stroke, and the combination of coronary heart disease, stroke, and heart failure.
FINDINGS: We recorded 5500 coronary heart disease, 4002 stroke, and 2212 heart failure outcomes among 95â617 participants without a history of cardiovascular disease in 40 prospective studies. Risk ratios (for a comparison of the top third vs bottom third of NT-proBNP concentrations, adjusted for conventional risk factors) were 1·76 (95% CI 1·56-1·98) for the combination of coronary heart disease and stroke and 2·00 (1·77-2·26) for the combination of coronary heart disease, stroke, and heart failure. Addition of information about NT-proBNP concentration to a model containing conventional risk factors was associated with a C-index increase of 0·012 (0·010-0·014) and a net reclassification improvement of 0·027 (0·019-0·036) for the combination of coronary heart disease and stroke and a C-index increase of 0·019 (0·016-0·022) and a net reclassification improvement of 0·028 (0·019-0·038) for the combination of coronary heart disease, stroke, and heart failure.
INTERPRETATION: In people without baseline cardiovascular disease, NT-proBNP concentration assessment strongly predicted first-onset heart failure and augmented coronary heart disease and stroke prediction, suggesting that NT-proBNP concentration assessment could be used to integrate heart failure into cardiovascular disease primary prevention
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