7,835 research outputs found
Study of extremely reddened AGB stars in the Galactic bulge
Context. Extremely reddened AGB stars lose mass at high rates of >10^-5
Msun/yr. This is the very last stage of AGB evolution, in which stars in the
mass range 2.0--4.0 Msun (for solar metallicity) should have been converted to
C stars already. The extremely reddened AGB stars in the Galactic bulge are
however predominantly O-rich, implying that they might be either low-mass stars
or stars at the upper end of the AGB mass range. Aims. To determine the mass
range of the most reddened AGB stars in the Galactic bulge. Methods. Using
Virtual Observatory tools, we constructed spectral energy distributions of a
sample of 37 evolved stars in the Galactic bulge with extremely red IRAS
colours. We fitted DUSTY models to the observational data to infer the
bolometric fluxes. Applying individual corrections for interstellar extinction
and adopting a common distance, we determined luminosities and mass-loss rates,
and inferred the progenitor mass range from comparisons with AGB evolutionary
models. Results. The observed spectral energy distributions are consistent with
a classification as reddened AGB stars, except for two stars, which are
proto-planetary nebula candidates. For the AGB stars, we found luminosities in
the range 3000--30,000 Lsun and mass-loss rates 10^-5--3x10^-4 Msun/yr. The
corresponding mass range is 1.1--6.0 Msun assuming solar metallicity.
Conclusions. Contrary to the predictions of the evolutionary models, the
luminosity distribution is continuous, with many O-rich AGB stars in the mass
range in which they should have been converted into C stars already. We suspect
that bulge AGB stars have higher than solar metallicity and therefore may avoid
the conversion to C-rich. The presence of low-mass stars in the sample shows
that their termination of the AGB evolution also occurs during a final phase of
very high mass-loss rate, leading to optically thick circumstellar shells
Self-existing objects and auto-generated information in chronology-violating space-times : a philosophical discussion
Consistency demands an harmony between local and global affairs that excludes grandfather-like paradoxes. However, self-existing objects trapped in CTCs are not seemingly avoided by the standard interpretation of this principle, usually constrained to a dynamical framework. In this paper we discuss whether we are committed to accept an ontology with self-existing objects if CTCs actually occur in the universe. In addition, the epistemological status of the Principle of SelfConsistency is analyzed and a discussion on the information flux through CTCs is presented.Fil: Romero, Gustavo Esteban. Provincia de Buenos Aires. GobernaciĂłn. ComisiĂłn de Investigaciones CientĂficas. Instituto Argentino de RadioastronomĂa. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto Argentino de RadioastronomĂa; ArgentinaFil: Torres, Diego F.. Provincia de Buenos Aires. GobernaciĂłn. ComisiĂłn de Investigaciones CientĂficas. Instituto Argentino de RadioastronomĂa. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto Argentino de RadioastronomĂa; Argentin
Does Harboring Terrorists Have Economic Costs?
The literature on conflict and terrorism has paid little attention to the economic costs of terrorism for the perpetrators of terror attacks. Our research fills that gap by examining the economic costs of harboring suicide terror attacks. We combine data on Palestinian suicide terrorists with data from the Palestinian Labor Force Survey, to identify and quantify the impact of a successful attack on unemployment and wages. We find robust evidence that terror attacks have important economic costs. They cause a significant increase in unemployment and a significant decrease in wages and on the number of Palestinians working in Israel. Importantly, these effects are persistent and last for at least six months after the attack.
Do Poor Economic Conditions Affect Terrorism?
While the existing empirical literature shows that poverty and economic conditions are not correlated with the quantity of terror, theory predicts that poverty and poor economic conditions may affect the quality of terror. Poor economic conditions may lead more able individuals to participate in terror attacks, allowing terror organizations to send betterqualified terrorists to more complex, high-impact terror missions. Using data on Palestinian suicideterrorists, we provide evidence of the correlation between economic conditions, the characteristics of suicide terrorists, and the targets they attack.
Does Terrorism Work?
This paper examines whether terrorism is an effective tool to achieve political goals. By exploiting variation in terror attacks over time and across locations in Israel from 1984 to 2006, we show that local terror attacks cause Israelis to be: (i) more willing to grant territorial concessions to the Palestinians; (ii) more willing to accept a Palestinian state; (iii) less likely to identify oneself as being right-wing; and (iv) more likely to have a favorable opinion of Arabs. These effects are especially pronounced for individuals from particular demographic groups which are typically right-wing in their political views. In addition, we show that terror induces Israelis to vote increasingly for right-wing parties. This pattern of results demonstrates that right-wing parties are becoming more accommodating to Palestinian demands for territorial concessions. Hence, this paper shows that terrorism appears to be an effective strategy in terms of shifting the entire Israeli political landscape to the left. These findings may shed light on the causes underlying the spread of global terrorism in the last few decades.
Rapid internationalization and long-term performance: The knowledge link
Drawing on the knowledge-based view and organizational learning theory, we develop and test a set of hypotheses to provide a first attempt at analyzing the effect of speed of internationalization on long-term performance. Using a panel-data sample of Spanish listed firms (1986-2010), we find that there is an inverted U-shaped relationship between speed of internationalization and long-term performance. We also find that whereas technological knowledge steepens this relationship, the diversity of prior international experience flattens it. Our results contribute to the existing IB literature on the performance of FDI, cross-country knowledge transferability, and nonsequential entry
Stellar clusters in the inner Galaxy and their correlation with cold dust emission
Stars are born within dense clumps of giant molecular clouds, constituting
young stellar agglomerates known as embedded clusters, which only evolve into
bound open clusters under special conditions. We statistically study all
embedded clusters (ECs) and open clusters (OCs) known so far in the inner
Galaxy, investigating particularly their interaction with the surrounding
molecular environment and the differences in their evolution. We first compiled
a merged list of 3904 clusters from optical and infrared clusters catalogs in
the literature, including 75 new (mostly embedded) clusters discovered by us in
the GLIMPSE survey. From this list, 695 clusters are within the Galactic range
|l| < 60 deg and |b| < 1.5 deg covered by the ATLASGAL survey, which was used
to search for correlations with submm dust continuum emission tracing dense
molecular gas. We defined an evolutionary sequence of five morphological types:
deeply embedded cluster (EC1), partially embedded cluster (EC2), emerging open
cluster (OC0), OC still associated with a submm clump in the vicinity (OC1),
and OC without correlation with ATLASGAL emission (OC2). Together with this
process, we performed a thorough literature survey of these 695 clusters,
compiling a considerable number of physical and observational properties in a
catalog that is publicly available. We found that an OC defined observationally
as OC0, OC1, or OC2 and confirmed as a real cluster is equivalent to the
physical concept of OC (a bound exposed cluster) for ages in excess of ~16 Myr.
Some observed OCs younger than this limit can actually be unbound associations.
We found that our OC and EC samples are roughly complete up to ~1 kpc and ~1.8
kpc from the Sun, respectively, beyond which the completeness decays
exponentially. Using available age estimates for a few ECs, we derived an upper
limit of 3 Myr for the duration of the embedded phase... (Abridged)Comment: 39 pages, 9 figures. Accepted for publication in A&A on Sept 16,
2013. The catalog will be available at the CDS after official publication of
the articl
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