2,082 research outputs found
Solar-like oscillations in the metal-poor subgiant nu Indi: II. Acoustic spectrum and mode lifetime
Convection in stars excites resonant acoustic waves which depend on the sound
speed inside the star, which in turn depends on properties of the stellar
interior. Therefore, asteroseismology is an unrivaled method to probe the
internal structure of a star. We made a seismic study of the metal-poor
subgiant star nu Indi with the goal of constraining its interior structure. Our
study is based on a time series of 1201 radial velocity measurements spread
over 14 nights obtained from two sites, Siding Spring Observatory in Australia
and ESO La Silla Observatory in Chile. The power spectrum of the high precision
velocity time series clearly presents several identifiable peaks between 200
and 500 uHz showing regularity with a large and small spacing of 25.14 +- 0.09
uHz and 2.96 +- 0.22 uHz at 330 uHz. Thirteen individual modes have been
identified with amplitudes in the range 53 to 173 cm/s. The mode damping time
is estimated to be about 16 days (1-sigma range between 9 and 50 days),
substantially longer than in other stars like the Sun, the alpha Cen system or
the giant xi Hya.Comment: 5 pages, 7 figures, A&A accepte
Pubertal development of penile Nitric Oxide Synthase (NOS)-containing nerve fibers in the rat
Objectives: To evaluate the expression of nitric oxide synthase (NOS)-containing nerve fibers in penile tissue in different age groups in the rat and to measure serum testosterone levels during this developmental process. Material and Methods: Fifteen male Sprague-Dawley (SD) rats divided into 3 equally numbered groups of different age (40 days (d), 54d and 65d) were used in this study. Penile erection was evaluated using cavernous nerve electrostimulation. Before sacrificing the rats, a penile midshaft specimen was taken for nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase staining and blood samples were collected to evaluate the testosterone levels. Results: Electrostimulation of the cavernous nerve revealed no significant difference in the maximal intracavernous pressure in the different age groups (44.9 ± 6.4, 54.8 ± 24.8, 45.9 ± 16.8 cm H2O, respectively; p>0.05), but the latency of the response to electrostimulation was significantly shorter in 54d and 65d than in 40d-old rats (5.4 ± 0.8 and 5.0 ± 0.7 vs. 9.0 ± 5.4 sec., respectively;
Non-radial oscillations in the red giant HR7349 measured by CoRoT
Convection in red giant stars excites resonant acoustic waves whose
frequencies depend on the sound speed inside the star, which in turn depends on
the properties of the stellar interior. Therefore, asteroseismology is the most
robust available method for probing the internal structure of red giant stars.
Solar-like oscillations in the red giant HR7349 are investigated. Our study is
based on a time series of 380760 photometric measurements spread over 5 months
obtained with the CoRoT satellite. Mode parameters were estimated using maximum
likelihood estimation of the power spectrum. The power spectrum of the
high-precision time series clearly exhibits several identifiable peaks between
19 and 40 uHz showing regularity with a mean large and small spacing of Dnu =
3.47+-0.12 uHz and dnu_02 = 0.65+-0.10 uHz. Nineteen individual modes are
identified with amplitudes in the range from 35 to 115 ppm. The mode damping
time is estimated to be 14.7+4.7-2.9 days.Comment: 8 pages, A&A accepte
Atmospheric parameters and chemical properties of red giants in the CoRoT asteroseismology fields
A precise characterisation of the red giants in the seismology fields of the
CoRoT satellite is a prerequisite for further in-depth seismic modelling.
High-resolution FEROS and HARPS spectra were obtained as part of the
ground-based follow-up campaigns for 19 targets holding great asteroseismic
potential. These data are used to accurately estimate their fundamental
parameters and the abundances of 16 chemical species in a self-consistent
manner. Some powerful probes of mixing are investigated (the Li and CNO
abundances, as well as the carbon isotopic ratio in a few cases). The
information provided by the spectroscopic and seismic data is combined to
provide more accurate physical parameters and abundances. The stars in our
sample follow the general abundance trends as a function of the metallicity
observed in stars of the Galactic disk. After an allowance is made for the
chemical evolution of the interstellar medium, the observational signature of
internal mixing phenomena is revealed through the detection at the stellar
surface of the products of the CN cycle. A contamination by NeNa-cycled
material in the most massive stars is also discussed. With the asteroseismic
constraints, these data will pave the way for a detailed theoretical
investigation of the physical processes responsible for the transport of
chemical elements in evolved, low- and intermediate-mass stars.Comment: Accepted for publication in A&A, 25 pages, 13 colour figures (revised
version after language editing
Model-assisted measurements of suspension-feeding flow velocities
Author Posting. © Company of Biologists, 2017. This article is posted here by permission of Company of Biologists for personal use, not for redistribution. The definitive version was published in Journal of Experimental Biology 220 (2017): 2096-2107, doi:10.1242/jeb.147934.Benthic marine suspension feeders provide an important link between benthic and pelagic ecosystems. The strength of this link is determined by suspension-feeding rates. Many studies have measured suspension-feeding rates using indirect clearance-rate methods, which are based on the depletion of suspended particles. Direct methods that measure the flow of water itself are less common, but they can be more broadly applied because, unlike indirect methods, direct methods are not affected by properties of the cleared particles. We present pumping rates for three species of suspension feeders, the clams Mya arenaria and Mercenaria mercenaria and the tunicate Ciona intestinalis, measured using a direct method based on particle image velocimetry (PIV). Past uses of PIV in suspension-feeding studies have been limited by strong laser reflections that interfere with velocity measurements proximate to the siphon. We used a new approach based on fitting PIV-based velocity profile measurements to theoretical profiles from computational fluid dynamic (CFD) models, which allowed us to calculate inhalant siphon Reynolds numbers (Re). We used these inhalant Re and measurements of siphon diameters to calculate exhalant Re, pumping rates, and mean inlet and outlet velocities. For the three species studied, inhalant Re ranged from 8 to 520, and exhalant Re ranged from 15 to 1073. Volumetric pumping rates ranged from 1.7 to 7.4 l h−1 for M. arenaria, 0.3 to 3.6 l h−1 for M. mercenaria and 0.07 to 0.97 l h−1 for C. intestinalis. We also used CFD models based on measured pumping rates to calculate capture regions, which reveal the spatial extent of pumped water. Combining PIV data with CFD models may be a valuable approach for future suspension-feeding studies.This research is part of a collaborative project (National Science Foundation grant OCE-1260232 to P.A.J., and grant OCE-1260199 to J. Crimaldi, University of Colorado). Funding was also provided by NSF grant OIA-1355457 to Maine EPSCoR at the University of Maine (D.C.B.).2018-05-3
Model-assisted measurements of suspension-feeding flow velocities
Benthic marine suspension feeders provide an important link between benthic and pelagic ecosystems. The strength of this link is determined by suspension-feeding rates. Many studies have measured suspension-feeding rates using indirect clearance-rate methods, which are based on the depletion of suspended particles. Direct methods that measure the flow of water itself are less common, but they can be more broadly applied because, unlike indirect methods, direct methods are not affected by properties of the cleared particles. We present pumping rates for three species of suspension feeders, the clams Mya arenaria and Mercenaria mercenaria and the tunicate Ciona intestinalis, measured using a direct method based on particle image velocimetry (PIV). Past uses of PIV in suspension-feeding studies have been limited by strong laser reflections that interfere with velocity measurements proximate to the siphon. We used a new approach based on fitting PIV-based velocity profile measurements to theoretical profiles from computational fluid dynamic (CFD) models, which allowed us to calculate inhalant siphon Reynolds numbers (Re). We used these inhalant Re and measurements of siphon diameters to calculate exhalant Re, pumping rates, and mean inlet and outlet velocities. For the three species studied, inhalant Re ranged from 8−520, and exhalant Re ranged from 15−1073. Volumetric pumping rates ranged from 1.7−7.4 l h−1 for Mya, 0.3−3.6 l h−1 for Mercenaria, and 0.07−0.97 l h−1 for Ciona. We also used CFD models based on measured pumping rates to calculate capture regions, which reveal the spatial extent of pumped water. Combining PIV data with CFD models may be a valuable approach for future suspension-feeding studies
Models of red giants in the CoRoT asteroseismology fields combining asteroseismic and spectroscopic constraints
Context. The availability of asteroseismic constraints for a large sample of
red giant stars from the CoRoT and Kepler missions paves the way for various
statistical studies of the seismic properties of stellar populations.
Aims. We use the first detailed spectroscopic study of 19 CoRoT red-giant
stars (Morel et al 2014) to compare theoretical stellar evolution models to
observations of the open cluster NGC 6633 and field stars.
Methods. In order to explore the effects of rotation-induced mixing and
thermohaline instability, we compare surface abundances of carbon isotopic
ratio and lithium with stellar evolution predictions. These chemicals are
sensitive to extra-mixing on the red-giant branch.
Results. We estimate mass, radius, and distance for each star using the
seismic constraints. We note that the Hipparcos and seismic distances are
different. However, the uncertainties are such that this may not be
significant. Although the seismic distances for the cluster members are self
consistent they are somewhat larger than the Hipparcos distance. This is an
issue that should be considered elsewhere. Models including thermohaline
instability and rotation-induced mixing, together with the seismically
determined masses can explain the chemical properties of red-giants targets.
However, with this sample of stars we cannot perform stringent tests of the
current stellar models. Tighter constraints on the physics of the models would
require the measurement of the core and surface rotation rates, and of the
period spacing of gravity-dominated mixed modes. A larger number of stars with
longer times series, as provided by Kepler or expected with Plato, would help
for ensemble asteroseismology.Comment: Accepted 03/05/201
Core properties of alpha Cen A using asteroseismology
A set of long and nearly continuous observations of alpha Centauri A should
allow us to derive an accurate set of asteroseismic constraints to compare to
models, and make inferences on the internal structure of our closest stellar
neighbour. We intend to improve the knowledge of the interior of alpha Centauri
A by determining the nature of its core. We combined the radial velocity time
series obtained in May 2001 with three spectrographs in Chile and Australia:
CORALIE, UVES, and UCLES. The resulting combined time series has a length of
12.45 days and contains over 10,000 data points and allows to greatly reduce
the daily alias peaks in the power spectral window. We detected 44 frequencies
that are in good overall agreement with previous studies, and found that 14 of
these show possible rotational splittings. New values for the large and small
separations have been derived. A comparison with stellar models indicates that
the asteroseismic constraints determined in this study allows us to set an
upper limit to the amount of convective-core overshooting needed to model stars
of mass and metallicity similar to those of alpha Cen A.Comment: 8 pages, 11 figures, A&A accepte
The analytic structure of 2D Euler flow at short times
Using a very high precision spectral calculation applied to the
incompressible and inviscid flow with initial condition , we find that the width of its analyticity
strip follows a law at short times over eight decades. The
asymptotic equation governing the structure of spatial complex-space
singularities at short times (Frisch, Matsumoto and Bec 2003, J.Stat.Phys. 113,
761--781) is solved by a high-precision expansion method. Strong numerical
evidence is obtained that singularities have infinite vorticity and lie on a
complex manifold which is constructed explicitly as an envelope of analyticity
disks.Comment: 19 pages, 14 figures, published versio
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