20,146 research outputs found
Chemical Evolution of the Galaxy Based on the Oscillatory Star Formation History
We model the star formation history (SFH) and the chemical evolution of the
Galactic disk by combining an infall model and a limit-cycle model of the
interstellar medium (ISM). Recent observations have shown that the SFH of the
Galactic disk violently variates or oscillates. We model the oscillatory SFH
based on the limit-cycle behavior of the fractional masses of three components
of the ISM. The observed period of the oscillation ( Gyr) is reproduced
within the natural parameter range. This means that we can interpret the
oscillatory SFH as the limit-cycle behavior of the ISM. We then test the
chemical evolution of stars and gas in the framework of the limit-cycle model,
since the oscillatory behavior of the SFH may cause an oscillatory evolution of
the metallicity. We find however that the oscillatory behavior of metallicity
is not prominent because the metallicity reflects the past integrated SFH. This
indicates that the metallicity cannot be used to distinguish an oscillatory SFH
from one without oscillations.Comment: 21 pages LaTeX, to appear in Ap
HST Survey of Clusters in Nearby Galaxies. II. Statistical Analysis of Cluster Populations
We present a statistical system that can be used in the study of cluster
populations. The basis of our approach is the construction of synthetic cluster
color-magnitude-radius diagrams (CMRDs), which we compare with the observed
data using a maximum likelihood calculation. This approach permits a relatively
easy incorporation of incompleteness (a function of not only magnitude and
color, but also radius), photometry errors and biases, and a variety of other
complex effects into the calculation, instead of the more common procedure of
attempting to correct for those effects.
We then apply this procedure to our NGC 3627 data from Paper I. We find that
we are able to successfully model the observed CMRD and constrain a number of
parameters of the cluster population. We measure a power law mass function
slope of alpha = -1.50 +/- 0.07, and a distribution of core radii centered at
r_c = 1.53 +/- 0.15 pc. Although the extinction distribution is less
constrained, we measured a value for the mean extinction consistent with that
determined in Paper I from the Cepheids.Comment: 21 pages, 3 figures accepted for publication by A
The Dog on the Ship: The "Canis Major Dwarf Galaxy" as an Outlying Part of the Argo Star System
Overdensities in the distribution of low latitude, 2MASS giant stars are
revealed by systematically peeling away from sky maps the bulk of the giant
stars conforming to ``isotropic'' density laws generally accounting for known
Milky Way components. This procedure, combined with a higher resolution
treatment of the sky density of both giants and dust allows us to probe to
lower Galactic latitudes than previous 2MASS giant star studies. While the
results show the swath of excess giants previously associated with the
Monoceros ring system in the second and third Galactic quadrants at distances
of 6-20 kpc, we also find a several times larger overdensity of giants in the
same distance range concentrated in the direction of the ancient constellation
Argo. Isodensity contours of the large structure suggest that it is highly
elongated and inclined by about 3 deg to the disk, although details of the
structure -- including the actual location of highest density, overall extent,
true shape -- and its origin, remain unknown because only a fraction of it lies
outside highly dust-obscured, low latitude regions. Nevertheless, our results
suggest that the 2MASS M giant overdensity previously claimed to represent the
core of a dwarf galaxy in Canis Major (l ~ 240 deg) is an artifact of a dust
extinction window opening to the overall density rise to the more significant
Argo structure centered at larger longitude (l ~ 290 +- 10 deg, b ~ -4 +- 2
deg).Comment: 4 pages, 4 figure
Effective action in DSR1 quantum field theory
We present the one-loop effective action of a quantum scalar field with DSR1
space-time symmetry as a sum over field modes. The effective action has real
and imaginary parts and manifest charge conjugation asymmetry, which provides
an alternative theoretical setting to the study of the particle-antiparticle
asymmetry in nature.Comment: 8 page
The mismatch repair system protects against intergenerational GAA repeat instability in a Friedreich ataxia mouse model
Copyright @ 2012 Elsevier. The article can be accessed from the link below.This article has been made available through the Brunel Open Access Publishing Fund.Friedreich ataxia (FRDA) is an autosomal recessive neurodegenerative disorder caused by a dynamic GAA repeat expansion mutation within intron 1 of the FXN gene. Studies of mouse models for other trinucleotide repeat (TNR) disorders have revealed an important role of mismatch repair (MMR) proteins in TNR instability. To explore the potential role of MMR proteins on intergenerational GAA repeat instability in FRDA, we have analyzed the transmission of unstable GAA repeat expansions from FXN transgenic mice which have been crossed with mice that are deficient for Msh2, Msh3, Msh6 or Pms2. We find in all cases that absence of parental MMR protein not only maintains transmission of GAA expansions and contractions, but also increases GAA repeat mutability (expansions and/or contractions) in the offspring. This indicates that Msh2, Msh3, Msh6 and Pms2 proteins are not the cause of intergenerational GAA expansions or contractions, but act in their canonical MMR capacity to protect against GAA repeat instability. We further identified differential modes of action for the four MMR proteins. Thus, Msh2 and Msh3 protect against GAA repeat contractions, while Msh6 protects against both GAA repeat expansions and contractions, and Pms2 protects against GAA repeat expansions and also promotes contractions. Furthermore, we detected enhanced occupancy of Msh2 and Msh3 proteins downstream of the FXN expanded GAA repeat, suggesting a model in which Msh2/3 dimers are recruited to this region to repair mismatches that would otherwise produce intergenerational GAA contractions. These findings reveal substantial differences in the intergenerational dynamics of expanded GAA repeat sequences compared with expanded CAG/CTG repeats, where Msh2 and Msh3 are thought to actively promote repeat expansions.This study is funded under European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement number 242193/EFACTS. This article is made available through the Brunel Open Access Publishing Fund
Efeito das mudanças climĂĄticas para cana-de-açĂșcar com base no modelo APSIM/Sugarcane.
O objetivo deste trabalho foi avaliar a sensibilidade do modelo Agricultural production simulator - sugarcane (APSIM/Sugarcane) (Keating et al. 1998; Thorburn et al., 2005) quanto aos parĂąmetros climĂĄticos [CO2], temperatura e precipitação, e analisar cenĂĄrios futuros de mudança climĂĄtica para a cultura de cana-de-açĂșcar
Carbon coating of the SPS dipole chambers
The Electron Multipacting (EM) phenomenon is a limiting factor for the
achievement of high luminosity in accelerators for positively charged particles
and for the performance of RF devices. At CERN, the Super Proton Synchrotron
(SPS) must be upgraded in order to feed the Large Hadron Collider (LHC) with 25
ns bunch spaced beams. At such small bunch spacing, EM may limit the
performance of the SPS and consequently that of the LHC. To mitigate this
phenomenon CERN is developing a carbon thin film coating with low Secondary
Electron Yield (SEY) to coat the internal walls of the SPS dipoles beam pipes.
This paper presents the progresses in the coating technology, the performance
of the carbon coatings and the strategy for a large scale production.Comment: 7 pages, contribution to the Joint INFN-CERN-EuCARD-AccNet Workshop
on Electron-Cloud Effects: ECLOUD'12; 5-9 Jun 2012, La Biodola, Isola d'Elba,
Italy; CERN Yellow Report CERN-2013-002, pp.141-14
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