16,693 research outputs found
Lithium factories in the Galaxy: novae and AGB stars
We review the state of the art in modelling lithium production, through the
Cameron-Fowler mechanism, in two stellar sites: during nova explosions and in
the envelopes of massive asymptotic giant branch (AGB) stars. We also show
preliminary results concerning the computation of lithium yields from
super-AGBs, and suggest that super-AGBs of metallicity close to solar may be
the most important galactic lithium producers. Finally, we discuss how lithium
abundances may help to understand the modalities of formation of the "second
generation" stars in globular clusters.Comment: invited review presented at IAU Symposium 267 "Light Elements in the
Universe", Geneva, Switzerland, Nov. 9-13 2009, in pres
Implications of inhomogeneous distribution of concentration polarization for interpretation of pressure-driven
A number of CFD studies have demonstrated that there is a considerable inhomogeneity of extent of Concentration Polarization (CP) over the membrane surface especially in spacer-filled feed channels. However, the consequences of this inhomogeneity for the interpretation of measurements of solute rejection in pressure-driven membrane processes have received little attention.
This study uses a simple model of locally-1D CP combined with a postulated probability distribution of unstirred-layer thickness over the membrane thickness. In this way, we obtain transparent analytical results and can consider qualitative consequences of inhomogeneous distribution of CP over membrane surface. Our analysis shows that disregarding the CP distribution under-estimates the CP of strongly positively-rejected solutes and over-estimates the CP for the negatively-rejected ones. This observation is especially important for the interpretation of ion rejection from multi-ion solutions in nanofiltration where strong positive and pronounced negative rejections can occur simultaneously for solutes of different charges.
We conclude that for reliable interpretation of pressure-driven membrane measurements it is desirable to reduce the inhomogeneity of CP distribution to a minimum in membrane-testing devicesPeer ReviewedPostprint (author's final draft
Robustness-Driven Resilience Evaluation of Self-Adaptive Software Systems
An increasingly important requirement for certain classes of software-intensive systems is the ability to self-adapt their structure and behavior at run-time when reacting to changes that may occur to the system, its environment, or its goals. A major challenge related to self-adaptive software systems is the ability to provide assurances of their resilience when facing changes. Since in these systems, the components that act as controllers of a target system incorporate highly complex software, there is the need to analyze the impact that controller failures might have on the services delivered by the system. In this paper, we present a novel approach for evaluating the resilience of self-adaptive software systems by applying robustness testing techniques to the controller to uncover failures that can affect system resilience. The approach for evaluating resilience, which is based on probabilistic model checking, quantifies the probability of satisfaction of system properties when the target system is subject to controller failures. The feasibility of the proposed approach is evaluated in the context of an industrial middleware system used to monitor and manage highly populated networks of devices, which was implemented using the Rainbow framework for architecture-based self-adaptation
The rotational shear layer inside the early red-giant star KIC 4448777
We present the asteroseismic study of the early red-giant star KIC 4448777,
complementing and integrating a previous work (Di Mauro et al. 2016), aimed at
characterizing the dynamics of its interior by analyzing the overall set of
data collected by the {\it Kepler} satellite during the four years of its first
nominal mission. We adopted the Bayesian inference code DIAMOND (Corsaro \& De
Ridder 2014) for the peak bagging analysis and asteroseismic splitting
inversion methods to derive the internal rotational profile of the star. The
detection of new splittings of mixed modes, more concentrated in the very inner
part of the helium core, allowed us to reconstruct the angular velocity profile
deeper into the interior of the star and to disentangle the details better than
in Paper I: the helium core rotates almost rigidly about 6 times faster than
the convective envelope, while part of the hydrogen shell seems to rotate at a
constant velocity about 1.15 times lower than the He core. In particular, we
studied the internal shear layer between the fast-rotating radiative interior
and the slow convective zone and we found that it lies partially inside the
hydrogen shell above and extends across the core-envelope
boundary. Finally, we theoretically explored the possibility for the future to
sound the convective envelope in the red-giant stars and we concluded that the
inversion of a set of splittings with only low-harmonic degree , even
supposing a very large number of modes, will not allow to resolve the
rotational profile of this region in detail.Comment: accepted for publication on Ap
Evolution of two stellar populations in globular clusters II. Effects of primordial gas expulsion
We investigate the early evolution of two distinct populations of low-mass
stars in globular clusters under the influence of primordial gas expulsion
driven by supernovae to study if this process can increase the fraction of
second generation stars at the level required by observations. We analyse
N-body models that take into account the effect of primordial gas expulsion. We
divide the stars into two populations which mimic the chemical and dynamical
properties of stars in globular clusters so that second generation stars start
with a more centrally concentrated distribution. The main effect of gas
expulsion is to eject preferentially first generation stars while second
generation stars remain bound to the cluster. In the most favourable cases
second generation stars can account for 60% of the bound stars we see today. We
also find that at the end of the gas expulsion phase, the radial distribution
of the two populations is still different, so that long-term evolution will
further increase the fraction of second generation stars. The large fraction of
chemically anomalous stars is readily explainable as a second generation of
stars formed out of the slow winds of rapidly rotating massive stars if
globular clusters suffer explosive residual gas expulsion for a star formation
efficiency of about 0.33.Comment: 11 pages, accepted for publication in A&
ENVIE Co-ordination action on indoor air quality and health effects; WP3 Final report – Characterisation of spaces and source
Human exposure to environmental pollutants occurs via various pathways. For many
pollutants, especially the volatile ones, air exposure is the dominant pathway.
Exposure via air occurs both outdoors and indoors, with diverse types of indoor
spaces playing a role, e.g., home, workplace, and passenger cabins of means of
transportation. In average people spend over 90% of their time indoors, that
percentage being particularly high for some specific groups as new-born,
elderly, disabled or sick people. The global exposure to air contaminants is
therefore drastically determined by indoor conditions. It is now well
established that indoor air pollution contributes significantly to the global
burden of disease of the population. For a majority of indoor air contaminants,
particularly in the presence of common indoor sources, however, indoor
concentrations usually exceed outdoor concentrations, for some pollutants even
with an indoor/outdoor ratio of 10 or 20. Emissions are identified, accordingly
to the EnVIE approach and grouped into four categories: building materials and
related sources, including dampness and moulds; ventilation, natural and
mechanical, including, or not, heating, cooling and humidification/
dehumidification; consumer products, furnishing, cleaning and household
products; and occupant activities. Emission of chemical substances from
construction materials and products in buildings to the indoor air have been
reported and reviewed for a wide range of substances, including those formed
during secondary reactions, causing complaints of irritation and odour. During
the last two decades there has been increasing advances in construction
technology that have caused a much greater use of synthetic building materials.
Whilst these improvements have led to more comfortable buildings, they also
provide indoor environments with contaminants in higher concentrations than are
found outside. Wood and cork are now frequently used as a building product for
floor coverings, because the material is often regarded as “natural” and
“healthy”. However, industrial products, even based on natural raw materials,
may contain a number of artificial ingredients and the chemical emissions will
strongly depend on the type of additives and the manufacturing process. Modern
interior paints are usually based on a polymeric binder. In order to fulfil
requirements on e.g., durability, paint contains various functional chemicals.
Water-borne paints usually also contains small amounts of approved biocides.
Polymeric binders with a very low content of residual monomers have been
developed for paint. Besides the release of substances to the indoor air due to
primary emission, damp building materials may give rise to volatile substances
formed during secondary reactions. Semi-volatile organic compounds (SVOCs) are
now receiving much more attention than heretofore. The HVAC (Heating,
Ventilation and Air Conditioning) systems as providers, among others, of
services of cleaning and dilution of pollutants in the indoor air are also
recognized as potential pollution sources. Several studies have shown that the
prevalence of SBS symptoms is often higher in air conditioned buildings than in
buildings with natural ventilation. 8 The outdoor air introduced indoors through
either ventilation systems or natural means is also an important and not always
controllable source for the intake of some outdoor pollutants. Outdoor air used
for ventilation may also be source of pollution containing particulate matter,
particulates of biological origin (microorganisms, pollen, etc.) and various
gases like NOx and O building structures which is a driving force for the
airflows which will transport to indoors water vapour and gaseous or particulate
contaminants. Volatile organic compounds are emitted from a wide variety of
household and consumer products with emission rates that are strongly dependent
on the type of application and are distributed over several orders of magnitude.
A number of product classes are identified and information on ingredients and
available data on emissions from individual products are presented. Human
activities and the associated use of products encompass a wide range of indoor
sources involving release of inorganic gases, particles and organic compounds as
a consequence of the activity. For some releases such as with air fresheners the
release is a necessary part of the activity to achieve the intended effect
whereas for others, such as the release of combustion fumes from a gas
appliance, the purpose of the action (in this case generation of heat) is
different from the emission. Combustion processes are an important source of a
range of air pollutants as carbon monoxide, nitrogen dioxide, sulphur dioxide,
particulates and associated inorganic and organic chemicals, organic vapours
e.g. formaldehyde, acetaldehyde, and benzene. Sources of these are present in
both ambient and indoor environments. The concentrations present in the ambient
air provide a baseline for the level of pollutant found indoors as this air
enters indoors by processes of infiltration and ventilation. However, the
concentration indoors will be modified by processes of sorption to surfaces and
chemical reaction depending on the chemical and physical properties of the
pollutant and internal surfaces. People themselves are a source of emissions of
chemicals and gases, notably CO range of organic compounds that are referred to
as body odours. The removal of such body odours is a prime objective of
ventilation in order to achieve a satisfactory indoor environment. WP3 aims at
to characterize spaces and sources in order to understand where and how to act
to guarantee good IAQ. From the two strategies for good IAQ, source control and
ventilation, the precautionary principle suggests that first priority shall be
given to source control, avoiding, mitigating or simply managing sources of
emissions. An overview of all policies on IAQ or related to IAQ, existing or in
preparation, directly related to indoor air sources, but also covering outdoor
air and industrial emissions, which could affect indirectly IAQ is made.
Considering the presented it could be concluded that IAQ is yet poorly regulated
at EU level, and in view of that some recommendations are made. The
recommendations on policies have taken into account the existing related to IAQ
policies such as new EU policies on chemicals (REACH; 2006/121/EC), consumer
products (GPSD; 2001/95/EC), construction products (CPD; 89/106/EC) and energy
performance of buildings (EPBD; 2002/91/EC) all refer to IAQ issues - suggesting
that they could, and probably should, contribute to IAQ policy development and
advocate an integrative and comprehensive policy approach centred
Contribuições dos incentivos fiscais: responsabilidade x benefícios
TCC (graduação) - Universidade Federal de Santa Catarina, Centro Sócio Econômico, Curso de Ciências Contábeis.Esse estudo visa verificar se empresas ditas como socialmente responsáveis divulgam os benefícios conseguidos pela redução ou isenção de tributos pelo patrocínio ou doação realizada a projetos sociais, ocasionados pelas leis de incentivos fiscais. O estudo foi desenvolvido analisando 6 empresas que, segundo a reportagem da revista Istoé de 2008, foram as empresas que mais investiram em projetos sociais voltados a cultura por meio da Lei Rouanet no ano de 2007. Tais empresas são a Petrobras, Vale, Telecomunicações de São Paulo (Telesp), Banco do Brasil, Bradesco e Eletrobrás. Os resultados obtidos sugerem que as empresas divulgam o que melhor resultado lhes gerem, neste caso elas enaltecem suas ações, focando no marketing social, melhorando a visão de seus clientes, sem divulgar nada sobre os benefícios com os referidos incentivos. Como conclusão identificou-se então que as empresas da amostra tendem a divulgar somente o que lhe é conveniente, ou seja, as empresas divulgam somente o seu lado socialmente responsável, sem transparecer os benefícios que elas conseguem com tais ações, como por exemplo, a redução dos tributos devidos ou reduzidos por ações de patrocínio
Models for the lithium abundances of multiple populations in globular clusters and the possible role of the Big Bang lithium
Globular cluster stars show chemical abundance patterns typical of hot-CNO
processing. Lithium is easily destroyed by proton capture in stellar
environments, so its abundance may be crucial to discriminate among different
models proposed to account for multiple populations. In order to reproduce the
observed O-Na anticorrelation and other patterns typical of multiple
populations, the formation of second generation stars must occur from the
nuclearly processed stellar ejecta, responsible of the chemical anomalies,
diluted with pristine gas having the composition of first generation stars. The
lithium abundance in the unprocessed gas -which is very likely to be equal to
the lithium abundance emerging from the Big Bang- affects the lithium chemical
patterns among the cluster stars. This paper focuses on a scenario in which
processed gas is provided by asymptotic giant branch (AGB) stars. We examine
the predictions of this scenario for the lithium abundances of multiple
populations. We study the role of the non-negligible lithium abundance in the
ejecta of massive AGB (A(Li)~2), and, at the same time, we explore how our
models can constrain the extremely large ---and very model dependent--- lithium
yields predicted by recent super--AGB models. We show that the super--AGB
yields may be tested by examining the lithium abundances in a large set of blue
main sequence stars in wCen and/or NGC2808. In addition, we examine the
different model results obtained by assuming for the pristine gas either the
Big Bang abundance predicted by the standard models (A(Li)=2.6-2.7), or the
abundance detected at the surface of population II stars (A(Li)=2.2-2.3). Once
a chemical model is well constrained, the O--Li distribution could perhaps be
used to shed light on the primordial lithium abundance
- …