18,084 research outputs found
Neural-network selection of high-redshift radio quasars, and the luminosity function at z~4
We obtain a sample of 87 radio-loud QSOs in the redshift range 3.6<z<4.4 by
cross-correlating sources in the FIRST radio survey S{1.4GHz} > 1 mJy with
star-like objects having r <20.2 in SDSS Data Release 7. Of these 87 QSOs, 80
are spectroscopically classified in previous work (mainly SDSS), and form the
training set for a search for additional such sources. We apply our selection
to 2,916 FIRST-DR7 pairs and find 15 likely candidates. Seven of these are
confirmed as high-redshift quasars, bringing the total to 87. The candidates
were selected using a neural-network, which yields 97% completeness (fraction
of actual high-z QSOs selected as such) and an efficiency (fraction of
candidates which are high-z QSOs) in the range of 47 to 60%. We use this sample
to estimate the binned optical luminosity function of radio-loud QSOs at , and also the LF of the total QSO population and its comoving density. Our
results suggest that the radio-loud fraction (RLF) at high z is similar to that
at low-z and that other authors may be underestimating the fraction at high-z.
Finally, we determine the slope of the optical luminosity function and obtain
results consistent with previous studies of radio-loud QSOs and of the whole
population of QSOs. The evolution of the luminosity function with redshift was
for many years interpreted as a flattening of the bright end slope, but has
recently been re-interpreted as strong evolution of the break luminosity for
high-z QSOs, and our results, for the radio-loud population, are consistent
with this.Comment: 20 pages. Accepted for publication in MNRAS on 3 March 201
The Effect of Alternative Nutrition Menu Labels on Childrenâs Meals Purchases and Parent-Child Decision-Making
Children are one subpopulation that have seen a threefold increase in obesity over the last two decades but have received no attention in the menu labeling literature. The purpose of this study is to explore the effects of different menu labeling formats on purchases of childrenâs meals and parent-child decision-making at a family-oriented restaurant. The intervention consists of five childrenâs menus featuring six bundled, nutritionally diverse, and equally priced combinations that are implemented over about a year. Accompanying each menu is a survey postcard collecting information on the parent-child decision process in choosing the item. This is ongoing research and all data is not in but at this point, the very early evidence points toward child-menu labeling having very little impact on food choices and caloric intake. This result is likely due to low parental involvement in the decision process given that children are the main ones deciding what to eat.Consumer/Household Economics, Food Consumption/Nutrition/Food Safety,
Vacuum decay in an interacting multiverse
We examine a new multiverse scenario in which the component universes
interact. We focus our attention to the process of "true" vacuum nucleation in
the false vacuum within one single element of the multiverse. It is shown that
the interactions lead to a collective behaviour that might lead, under specific
conditions, to a pre-inflationary phase and ensued distinguishable imprints in
the comic microwave background radiation.Comment: 9 pages, 5 figure
The Economic Impact of Migration â Productivity Analysis for Spain and the UK
As a consequence of increased internationalization over the past 20 years labour has become increasingly mobile, and yet the implications for firm and industry performance have been largely ignored. This paper explores the direct economic consequences of immigration on host nationsâ productivity performance at a sectoral level. We consider its impact in two very different European countries, Spain and the UK. Whilst the UK has traditionally had a substantial in-flow of migration, for Spain, the phenomenon is much more recent. The paper provides an overview of the role played by immigration on per capita income, highlighting the importance of demographic differences. We then go on to analyze the role of migration on productivity using two different approaches: i) growth accounting methodology and ii) econometric estimation of a production function. Our findings indicate that migration has had very different implications for Spain and the UK, migrants being more productive than natives in the UK but less productive than natives in Spain. This may in part be a function of different immigration policies, particularly related to the skill requirements on entry, but also in part a feature of the host nationsâ ability to âabsorbâ foreign labour.Migration, productivity
Use of neural networks for the identification of new z>=3.6 QSOs from FIRST-SDSS DR5
We aim to obtain a complete sample of redshift > 3.6 radio QSOs from FIRST
sources having star-like counterparts in the SDSS DR5 photometric survey
(r<=20.2). We found that simple supervised neural networks, trained on sources
with SDSS spectra, and using optical photometry and radio data, are very
effective for identifying high-z QSOs without spectra. The technique yields a
completeness of 96 per cent and an efficiency of 62 per cent. Applying the
trained networks to 4415 sources without DR5 spectra we found 58 z>=3.6 QSO
candidates. We obtained spectra of 27 of them, and 17 are confirmed as high-z
QSOs. Spectra of 13 additional candidates from the literature and from SDSS DR6
revealed 7 more z>=3.6 QSOs, giving and overall efficiency of 60 per cent. None
of the non-candidates with spectra from NED or DR6 is a z>=3.6 QSO,
consistently with a high completeness. The initial sample of z>=3.6 QSOs is
increased from 52 to 76, i.e. by a factor 1.46. From the new identifications
and candidates we estimate an incompleteness of SDSS for the spectroscopic
classification of FIRST 3.6<=z<=4.6 QSOs of 15 percent for r<=20.2.Comment: 16 pages, 9 figures accepted for publication in MNRA
Rho meson form factors in a confining Nambu--Jona-Lasinio model
Elastic electromagnetic form factors for the meson are calculated in
a Nambu--Jona-Lasinio model which incorporates quark confinement through the
use of the proper-time regularization scheme. A comparison is made with recent
lattice QCD results and previous quark model calculations for static quantities
and the Sachs form factors. The results are qualitatively in good agreement
with the lattice QCD calculations, with the exception of the quadrupole moment
and corresponding form factor, which may be related to a lack of spherical
symmetry on the lattice.Comment: 8 pages, 11 figure
Baryon Octet Electromagnetic Form Factors in a confining NJL model
Electromagnetic form factors of the baryon octet are studied using a
Nambu--Jona-Lasinio model which utilizes the proper-time regularization scheme
to simulate aspects of colour confinement. In addition, the model also
incorporates corrections to the dressed quarks from vector meson correlations
in the t-channel and the pion cloud. Comparison with recent chiral
extrapolations of lattice QCD results shows a remarkable level of consistency.
For the charge radii we find the surprising result
and , whereas the magnetic radii have a pattern
largely consistent with a naive expectation based on the dressed quark masses.Comment: 7 pages, 4 figure
Immunology and Genetic of Preeclampsia
Preeclampsia is a disease characterized by hypertension and proteinuria in the third trimester of pregnancy. Preeclampsia is a major cause of maternal mortality, and fetal death, especially in developing countries, but its aetiology remains unclear. Key findings support a causal role of superficial placentation driven by immune mal maladaptation, which then lead to reduced concentrations of angiogenic growth factors and to an increase in placental debris in the maternal circulation resulting in a maternal inflammatory response. Epidemiological research has consistently demonstrated a substantial familial predisposition to preeclampsia. Unfortunately, the conquest of the genes explaining such a individual susceptibility has been proved to be a hard task. However, genetics will also inform us about causality of environmental factors, and then serve as a tool to prioritize therapeutic targets for preventive strategies
- âŠ