2,534 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
Structure-reactivity relationship in pyrolysis of plastics. A comparison with natural polymers
Recent advances in plastics recycling confirm the high potential of pyrolysis technologies to enhance recovery and selectivity rates. Modelling the kinetics of this complex process to stimulate scaling-up opportunities remains a major challenge.This study is an attempt to develop practical quantitative reactivity indices for the pyrolysis of natural and synthetic polymers. Representative samples from both categories (coal and pine vs. PET, PE and PMMA) were selected. Their weight loss during pyrolysis was determined experimentally and analyzed using judicious lumping procedures for its initiation, propagation and termination steps. The combined experimental and theoretical approach allowed us to determine apparent activation energies using the isoconversional Friedman method; and the use of Benson’s group contribution method generated reaction enthalpies for the initiation reactions. Increasing activation energies with conversion in each case indicated that bond scission proceeds in order of increasing bond strength. The greater chemical complexity of natural polymers was reflected in the higher coefficients of variability for activation energy and wider ranges of reaction enthalpies. A structure-reactivity relationship based on the Evans-Polanyi theory was used to test the hypothesis that primary pyrolysis kinetics is controlled by cleavage of weakest chemical bonds. While the results show that this approach is promising, especially if confirmed by extension to a larger data set, they also suggest the need to compare the relative kinetic importance of initiation and propagation steps in the sequence of polymer pyrolysis reactions
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
An Economic Analysis of What Role Monetary Contributions Play in How a Government Representative Will Vote
As a result of polarizing election outcomes, controversial legislative actions, and the general stigma that elected officials are corrupt, many Americans are questioning whether their representatives in government have the best interest of their constituents at heart, or are considering more self-centered motives. One point of contention is that political action committees and lobbyists contribute hundreds of thousands of dollars to legislators\u27 campaigns in return for consideration of their viewpoints. This study seeks to determine exactly how much weight members of the House of Representatives give to monetary contributions when considering how to vote on a bill by using voting records and control variables associated with the Patient Protection and Affordable Care Act. After testing how party, ideology, monetary contributions, constituent income, percent of votes received in the election, and the size of the election margin impacted how each Representative voted on the ACA it was unclear whether any variables had significant impacts on the dependent variable. However, when only the data from the Democrats was considered, it was possible to conclude that both ideology and monetary contributions were major contributing factors for the vote
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;
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
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