500 research outputs found
Nucleosynthesis of light element isotopes in evolved stars experiencing extended mixing
We present computations of nucleosynthesis in red giants and asymptotic giant
branch stars of Population I experiencing extended mixing. The assumed physical
cause for mass transport is the buoyancy of magnetized structures, according to
recent suggestions. The peculiar property of such a mechanism is to allow for
both fast and slow mixing phenomena, as required for reproducing the spread in
Li abundances displayed by red giants and as discussed in an accompanying
paper. We explore here the effects of this kind of mass transport on CNO and
intermediatemass nuclei and compare the results with the available evidence
from evolved red giants and from the isotopic composition of presolar grains of
AGB origin. It is found that a good general accord exists between predictions
and measurements; in this framework we also show which type of observational
data best constrains the various parameters. We conclude that magnetic
buoyancy, allowing for mixing at rather different speeds, can be an interesting
scenario to explore for explaining together the abundances of CNO nuclei and of
Li.Comment: 8 pages, 7 figures, proceeding of 'The Origin of the Elements Heavier
than Fe' September 24-28, 2008, Torino, Italy. PASA (accepted for
publication
Extra-Mixing in Luminous Cool Red Giants. Hints from Evolved Stars with and without Li
We present an analysis of Li abundances in low mass stars (LMS) during the
Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) stages, based on a new
determination of their luminosities and evolutionary status. By applying
recently suggested models for extra-mixing, induced by magnetic buoyancy, we
show that both Li-rich and Li-poor stars can be accounted for. The simplest
scenario implies the development of fast instabilities on the RGB, where Li is
produced. When the fields increase in strength, buoyancy slows down and Li is
destroyed. 3He is consumed, at variable rates. The process continues on the
AGB, where however moderate mass circulation rates have little effect on Li due
to the short time available. O-rich and C-rich stars show different histories
of Li production/destruction, possibly indicative of different masses. More
complex transport schemes are allowed by magnetic buoyancy, with larger effects
on Li, but most normal LMS seem to show only the range of Li variation
discussed here.Comment: 8 pages, 6 figures, accepted for publication in PAS
Sizing of integrated solar photovoltaic and electrolysis systems for clean hydrogen production
This work presents a method to design an optimised system that combines electrolysers and solar photovoltaic panels for sustainable hydrogen production. Given the daily and seasonal
variations of the electricity output vs. a stable hydrogen demand, power exchange to/from the electric grid and hydrogen storage systems are considered. The aim is to determine the optimal size of the PV field, the electrolyser, and the storage, for a given hydrogen demand, by minimising the cost of the hydrogen produced
Mid Infrared Photometry of Mass-Losing AGB Stars
We present ground-based mid-infrared imaging for 27 M-, S- and C-type
Asymptotic Giant Branch (AGB) stars. The data are compared with those of the
database available thanks to the IRAS, ISO, MSX and 2MASS catalogues. Our goal
is to establish relations between the IR colors, the effective temperature
, the luminosity and the mass loss rate , for improving
the effectiveness of AGB modelling. Bolometric (absolute) magnitudes are
obtained through distance compilations, and by applying previously-derived
bolometric corrections; the variability is also studied, using data accumulated
since the IRAS epoch. The main results are: i) Values of and for C
stars fit relations previously established by us, with Miras being on average
more evolved and mass losing than Semiregulars. ii) Moderate IR excesses (as
compared to evolutionary tracks) are found for S and M stars in our sample:
they are confirmed to originate from the dusty circumstellar environment. iii)
A larger reddening characterizes C-rich Miras and post-AGBs. In this case, part
of the excess is due to AGB models overestimating for C-stars, as a
consequence of the lack of suitable molecular opacities. This has a large
effect on the colors of C-rich sources and sometimes disentangling the
photospheric and circumstellar contributions is difficult; better model
atmospheres should be used in stellar evolutionary codes for C stars. iv) The
presence of a long-term variability at mid-IR wavelengths seems to be limited
to sources with maximum emission in the 8 -- 20 m region, usually Mira
variables (1/3 of our sample). Most Semiregular and post-AGB stars studied here
remained remarkably constant in mid-IR over the last twenty years.Comment: Accepted for publication in the Astronomical Journal - 35 pages (in
preprint), 9 figures, 5 table
Mass loss in AGB stars from infrared colors
Abstract. We have selected a wide database of mid infrared observations for AGB stars from both ground-based and space-borne observatories, with the aim of characterizing the efficient mass loss mechanisms leading to the formation of their extended dusty envelopes and of planetary nebulae. Our sample includes more than 250 sources in our Galaxy, distributed along the evolutionary sequence that gradually changes the spectral characteristics of M giants, forming MS, S and then C-stars. Thanks to a re-analysis of existing estimates of mass loss at radio frequencies and to improved measurements of distance (often provided by the Hipparcos mission), we compile a homogeneous set of corrected mass loss rates and of mid-infrared colors. We show the existence of clear correlations suggesting that mass loss can be inferred from photometric colors in mid infrared, once these have been suitably calibrated. This provides a tool to predict the efficiency of stellar winds for other less known sources, and is a decisive step in view of the determination of observationally based criteria for including mass loss in stellar models. In this paper we discuss in particular, as an example, our sample of C-rich stars
Structural Performance of Reinforced Concrete Flat Plate Buildings Subjected to Fire
El siguiente artĂculo se propone estudiar la poesĂa de Luis HernĂĄndez a partir de los problemas que surgen al intentar estudiar su obra reunida. Antes que ser valorada como una poesĂa âinacabadaâ, la deliberada asistematicidad de su poĂ©tica debe ser entendida como el resultado de un calculado y consciente ejercicio artĂstico, cuyas fuentes filosĂłficas tradicionalmente han pugnado por una ontologĂa del movimiento frente a una metafĂsica de la permanencia. Bajo esta perspectiva, la obra de HernĂĄndez se revela como un âplano de inmanenciaâ, desde el cual acontece el sentido de su poesĂa en el quehacer de la escritura.The article aims to study Luis HernĂĄndezâ poetry from the point of view of the problems that emerge when trying to analyze his Complete Works. Rather than being assessed as âunfinishedâ, the deliberate and unsystematic appearance of his poetic, should rather be understood as the result of a calculated and conscious artistic practice that stems from philosophical trends which traditionally have fostered an ontology of movement against a metaphysics of permanence. Under this view, HernĂĄndez work shows up as âplane of immanenceâ from where sense becomes an event for the creative writing process.El segĂŒent article es proposa estudiar la poesia de Luis HernĂĄndez a partir dels problemes que sorgeixen al tractar dâestudiar la seva obra reunida. Abans de ser valorada com una poesia âincabadaâ, la deliberada asistematicitat de la seva poĂštica deu ser entesa com el resultat dâun calculat i conscient exercici artĂstic, fonts filosĂČfiques de les quals han pugnat tradicionalment per una ontologia del moviment davant una metafĂsica de la permanĂšncia. Sota aquesta perspectiva, lâobra dâHernĂ ndez es revela com un âpla dâinmanĂšnciaâ, des del qual esdevĂ© el sentit de la seva poesia en el afer de lâescriptura
CSF parvalbumin levels reflect interneuron loss linked with cortical pathology in multiple sclerosis
INTRODUCTION AND METHODS: In order to verify whether parvalbumin (PVALB), a protein specifically expressed by GABAergic interneurons, could be a MS-specific marker of grey matter neurodegeneration, we performed neuropathology/molecular analysis of PVALB expression in motor cortex of 40 post-mortem progressive MS cases, with/without meningeal inflammation, and 10 control cases, in combination with cerebrospinal fluid (CSF) assessment. Analysis of CSF PVALB and neurofilaments (Nf-L) levels combined with physical/cognitive/3TMRI assessment was performed in 110 naïve MS patients and in 32 controls at time of diagnosis. RESULTS: PVALB gene expression was downregulated in MS (fold change = 3.7 ± 1.2, P < 0.001 compared to controls) reflecting the significant reduction of PVALB+ cell density in cortical lesions, to a greater extent in MS patients with high meningeal inflammation (51.8, P < 0.001). Likewise, post-mortem CSF-PVALB levels were higher in MS compared to controls (fold change = 196 ± 36, P < 0.001) and correlated with decreased PVALB+ cell density (r = -0.64, P < 0.001) and increased MHC-II+ microglia density (r = 0.74, P < 0.01), as well as with early age of onset (r = -0.69, P < 0.05), shorter time to wheelchair (r = -0.49, P < 0.05) and early age of death (r = -0.65, P < 0.01). Increased CSF-PVALB levels were detected in MS patients at diagnosis compared to controls (P = 0.002). Significant correlation was found between CSF-PVALB levels and cortical lesion number on MRI (R = 0.28, P = 0.006) and global cortical thickness (R = -0.46, P < 0.001), better than Nf-L levels. CSF-PVALB levels increased in MS patients with severe cognitive impairment (mean ± SEM:25.2 ± 7.5 ng/mL) compared to both cognitively normal (10.9 ± 2.4, P = 0.049) and mild cognitive impaired (10.1 ± 2.9, P = 0.024) patients. CONCLUSIONS: CSF-PVALB levels reflect loss of cortical interneurons in MS patients with more severe disease course and might represent an early, new MS-specific biomarker of cortical neurodegeneration, atrophy, and cognitive decline
The Magnetised Bellows of Betelgeuse
We present calculations for a magnetised hybrid wind model for Betelegeuse
(Orionis). The model is a direct application of our previously
derived theory, combining a canonical Weber-Davis (WD) stellar wind with dust
grains in the envelope of an AGB star \citep[see][]{Thirumalai2010}. The
resulting hybrid picture provides a mechanism for solving the problem of
lifting stellar material up from the photosphere \citep[e.g.][]
{Harper2009,Guandalini2006,Jura1984} and into the circumstellar envelope. It
also predicts wind velocities in agreement with current estimates. Our approach
reveals that magnetic fields in supergiant stars like Betelgeuse
\citep[see][]{Auriere2010}, may play a vital role in determining the nature of
the stellar outflow and consequently, opens a new avenue of investigation in
the field of hybrid stellar winds.Comment: 13 pages, 4 figure
Breast milk butyrate as protective factor against food allergy
Conflicting evidences suggest a role for breast milk as pro-
tective factor against food allergy. The major short chain fatty
acids, butyrate produced by gut microbiota exerts positive effect
on immune system. We aimed to see whether butyrate concen-
tration in human milk is able to prevent food allergy in an animal
model of cow milk allergy.
Mature breast milk butyrate concentration from 40 healthy
women (aged 21â42 yrs) was assessed by gas chromatography. 4-
Week-old female C3H/HeOuJ mice were sensitized by oral route
with -lactoglobulin (BLG, 20 mg) plus cholera toxin (CT, 10 g)
as an adjuvant in the presence or absence of butyrate. Acute aller-
gic skin response,anaphylactic symptom score, body temperature,
intestinal permeability, anti-BLG IgE, IL-4 and IL-10 production
were assessed soon after oral challenge. Mean butyrate concen-
tration in breast milk was 0.75 mM (SD ± 0.15). Based on this
concentration a daily dose of 30 mg/kg body weight was calculated.
The same butyrate concentration was able to significantly prevent
acute allergic skin response, anaphylactic symptom score, body
temperature decrease, intestinal permeability increase, anti-BLG
IgE, IL-4 and IL-10 production in CMA animal model (p < .05).
Our data suggest a pivotal role for butyrate as an effective human
milk component in food allergy prevention
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