2,927 research outputs found
Behaviour of Lq norms of the sincp function
This is the author accepted manuscript. The final version is available from American Mathematical Society via the DOI in this recordAn integral inequality due to Ball involves the Lq norm of the sincp
function; the dependence of this norm on q as q → ∞ is now understood.
By use of recent inequalities involving p−trigonometric functions (1 <
p < ∞) we obtain asymptotic information about the analogue of Ball’s
integral when sin is replaced by sinp
The Origin of the Mass-Metallicity relation: an analytical approach
The existence of a mass-metallicity (MZ) relation in star forming galaxies at
all redshift has been recently established. We aim at studying some possible
physical mechanisms contributing to the MZ relation by adopting analytical
solutions of chemical evolution models including infall and outflow. We explore
the hypotheses of a variable galactic wind rate, infall rate and yield per
stellar generation (i.e. a variation in the IMF), as possible causes for the MZ
relation. By means of analytical models we compute the expected O abundance for
galaxies of a given total baryonic mass and gas mass.The stellar mass is
derived observationally and the gas mass is derived by inverting the Kennicutt
law of star formation, once the star formation rate is known. Then we test how
the parameters describing the outflow, infall and IMF should vary to reproduce
the MZ relation, and we exclude the cases where such a variation leads to
unrealistic situations. We find that a galactic wind rate increasing with
decreasing galactic mass or a variable IMF are both viable solutions for the MZ
relation. A variable infall rate instead is not acceptable. It is difficult to
disentangle among the outflow and IMF solutions only by considering the MZ
relation, and other observational constraints should be taken into account to
select a specific solution. For example, a variable efficiency of star
formation increasing with galactic mass can also reproduce the MZ relation and
explain the downsizing in star formation suggested for ellipticals. The best
solution could be a variable efficiency of star formation coupled with galactic
winds, which are indeed observed in low mass galaxies.Comment: Accepted by A&
Metallicity Evolution of Damped Lyman-Alpha Galaxies
We have reanalyzed the existing data on Zinc abundances in damped Ly-alpha
(DLA) absorbers to investigate whether their mean metallicity evolves with
time. Most models of cosmic chemical evolution predict that the mass- weighted
mean interstellar metallicity of galaxies should rise with time from a low
value ~ 1/30 solar at z ~ 3 to a nearly solar value at z ~ 0. However, several
previous analyses have suggested that there is little or no evolution in the
global metallicity of DLAs. We have used a variety of statistical techniques to
quantify the global metallicity-redshift relation and its uncertainties, taking
into account both measurement and sampling errors. Three new features of our
analysis are: (a) an unbinned N(H I)-weighted nonlinear chi-square fit to an
exponential relation; (b) survival analysis to treat the large number of limits
in the existing data; and (c) a comparison of the data with several models of
cosmic chemical evolution based on an unbinned N(H I)-weighted chi-square. We
find that a wider range of evolutionary rates is allowed by the present data
than claimed in previous studies. The slope of the exponential fit to the N(H
I)-weighted mean Zn metallicity vs. redshift relation is -0.20 plus minus 0.11
counting limits as detections and -0.27 plus minus 0.12 counting limits as
zeros. Similar results are also obtained if the data are binned in redshift,
and if survival analysis is used. These slopes are marginally consistent with
no evolution, but are also consistent with the rates predicted by several
models of cosmic chemical evolution. Finally, we outline some future
measurements necessary to improve the statistics of the global
metallicity-redshift relation.Comment: 25 pages, 1 figure, accepted for publication in the Astrophysical
Journa
The star formation history and chemical evolution of star forming galaxies in the nearby universe
We have determined the O/H and N/O of a sample of 122751 SFGs from the DR7 of
the SDSS. For all these galaxies we have also determined their morphology and
their SFH using the code STARLIGHT. The comparison of the chemical abundance
with the SFH allows us to describe the chemical evolution in the nearby
universe (z < 0.25) in a manner which is consistent with the formation of their
stellar populations and morphologies. A 45% of the SFGs in our sample show an
excess of abundance in nitrogen relative to their metallicity. We also find
this excess to be accompanied by a deficiency of oxygen, which suggests that
this could be the result of effective starburst winds. However, we find no
difference in the mode of star formation of the nitrogen rich and nitrogen poor
SFGs. Our analysis suggests they all form their stars through a succession of
bursts of star formation extended over a few Gyr period. What produces the
chemical differences between these galaxies seems therefore to be the intensity
of the bursts: the galaxies with an excess of nitrogen are those that are
presently experiencing more intense bursts, or have experienced more intense
bursts in their past. We also find evidence relating the chemical evolution
process to the formation of the galaxies: the galaxies with an excess of
nitrogen are more massive, have more massive bulges and earlier morphologies
than those showing no excess. As a possible explanation we propose that the
lost of metals consistent with starburst winds took place during the formation
of the galaxies, when their potential wells were still building up, and
consequently were weaker than today, making starburst winds more efficient and
independent of the final mass of the galaxies. In good agreement with this
interpretation, we also find evidence consistent with downsizing, according to
which the more massive SFGs formed before the less massive ones.Comment: 69 pages, 27 figures, accepted for publication in Ap
Hazard Analysis of Critical Control Points Assessment as a Tool to Respond to Emerging Infectious Disease Outbreaks
Highly pathogenic avian influenza virus (HPAI) strain H5N1 has had direct and indirect economic impacts arising from direct mortality and control programmes in over 50 countries reporting poultry outbreaks. HPAI H5N1 is now reported as the most widespread and expensive zoonotic disease recorded and continues to pose a global health threat. The aim of this research was to assess the potential of utilising Hazard Analysis of Critical Control Points (HACCP) assessments in providing a framework for a rapid response to emerging infectious disease outbreaks. This novel approach applies a scientific process, widely used in food production systems, to assess risks related to a specific emerging health threat within a known zoonotic disease hotspot. We conducted a HACCP assessment for HPAI viruses within Vietnam’s domestic poultry trade and relate our findings to the existing literature. Our HACCP assessment identified poultry flock isolation, transportation, slaughter, preparation and consumption as critical control points for Vietnam’s domestic poultry trade. Introduction of the preventative measures highlighted through this HACCP evaluation would reduce the risks posed by HPAI viruses and pressure on the national economy. We conclude that this HACCP assessment provides compelling evidence for the future potential that HACCP analyses could play in initiating a rapid response to emerging infectious diseases
The serotype distribution among healthy carriers before vaccination is essential for predicting the impact of pneumococcal conjugate vaccine on invasive disease.
Pneumococcal conjugate vaccines (PCVs) have substantially reduced morbidity and mortality of pneumococcal disease. The impact of the 7-valent PCV on all-serotype invasive pneumococcal disease (IPD) among children was reported to vary between high-income countries. We investigate the ability to predict this heterogeneity from pre-vaccination data. We propose a parsimonious model that predicts the impact of PCVs from the odds of vaccine serotype (VT) among carriers and IPD cases in the pre-PCV period, assuming that VT are eliminated in a mature PCV programme, that full serotype replacement occurs in carriage and that invasiveness of the NVT group is unchanged. We test model performance against the reported impact of PCV7 on childhood IPD in high-income countries from a recent meta-analysis. The odds of pre-PCV7 VT IPD, PCV schedule, PCV coverage and whether a catch up campaign was used for introduction was gathered from the same analysis. We conducted a literature review and meta-analysis to obtain the odds of pre-PCV7 VT carriage in the respective settings. The model predicted the reported impact on childhood IPD of mature PCV programmes; the ratio of predicted and observed incidence risk ratios was close to 1 in all settings. In the high income settings studied differences in schedule, coverage, and catch up campaigns were not associated with the observed heterogeneity in impact of PCV7 on childhood all-serotype IPD. The pre-PCV7 proportion of VT IPD alone also had limited predictive value. The pre-PCV7 proportion of VT carriage and IPD are the main determinants for the impact of PCV7 on childhood IPD and can be combined in a simple model to provide predictions of the vaccine preventable burden of IPD
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Direct and indirect effects of rotavirus vaccination: Comparing predictions from transmission dynamic models
Early observations from countries that have introduced rotavirus vaccination suggest that there may be indirect protection for unvaccinated individuals, but it is unclear whether these benefits will extend to the long term. Transmission dynamic models have attempted to quantify the indirect protection that might be expected from rotavirus vaccination in developed countries, but results have varied. To better understand the magnitude and sources of variability in model projections, we undertook a comparative analysis of transmission dynamic models for rotavirus. We fit five models to reported rotavirus gastroenteritis (RVGE) data from England and Wales, and evaluated outcomes for short- and long-term vaccination effects. All of our models reproduced the important features of rotavirus epidemics in England and Wales. Models predicted that during the initial year after vaccine introduction, incidence of severe RVGE would be reduced 1.8-2.9 times more than expected from the direct effects of the vaccine alone (28-50% at 90% coverage), but over a 5-year period following vaccine introduction severe RVGE would be reduced only by 1.1-1.7 times more than expected from the direct effects (54-90% at 90% coverage). Projections for the long-term reduction of severe RVGE ranged from a 55% reduction at full coverage to elimination with at least 80% coverage. Our models predicted short-term reductions in the incidence of RVGE that exceeded estimates of the direct effects, consistent with observations from the United States and other countries. Some of the models predicted that the short-term indirect benefits may be offset by a partial shifting of the burden of RVGE to older unvaccinated individuals. Nonetheless, even when such a shift occurs, the overall reduction in severe RVGE is considerable. Discrepancies among model predictions reflect uncertainties about age variation in the risk and reporting of RVGE, and the duration of natural and vaccine-induced immunity, highlighting important questions for future research
Stony coral populations are more sensitive to changes in vital rates in disturbed environments
The K luminosity-metallicity relation for dwarf galaxies and the tidal dwarf galaxies in the tails of HCG 31
We determine a K-band luminosity-metallicity (K-Z) relation for dwarf
irregular galaxies, over a large range of magnitudes, -20.5 < M_K < -13.5,
using a combination of K photometry from either the 2-micron all sky survey
(2MASS) or the recent study of Vadivescu er al. (2005), and metallicities
derived mainly with the T_e method, from several different studies. We then use
this newly-derived relation, together with published K_s photometry and our new
spectra of objects in the field of HCG 31 to discuss the nature of the possible
tidal dwarf galaxies of this group. We catalogue a new member of HCG 31, namely
"R", situated ~40 kpc north of the group center, composed by a ring of H alpha
knots which coincides with a peak in HI. This object is a deviant point in the
K-Z relation (it has too high metallicity for its luminosity) and its projected
distance to the parent galaxy and large gas reservoir makes it one of the most
promising tidal dwarf galaxy candidates of HCG 31, together with object F. The
subsystems A1, E, F, H and R all have metallicities similar to that of the
galaxies A+C and B, result that is expected in a scenario where those were
formed from material expelled from the central galaxies of HCG 31. While
objects A1, E and H will most probably fall back onto their progenitors, F and
R may survive as tidal dwarf galaxies. We find that two galaxies of HCG 31, G
and Q, have A+em spectral signatures, and are probably evolving toward a
post-starburst phase.Comment: 32 pages, 4 figures - Submitted to AJ - A version of this paper with
full resolution figures can be found at
http://www.astro.iag.usp.br/~eduardo/HCG31-KZrelation.pd
Risk factors for transmission of Ebola or Marburg virus disease: a systematic review and meta-analysis
Background The Ebola virus disease outbreak that started in Western Africa in 2013 was unprecedented because it spread within densely populated urban environments and affected many thousands of people. As a result, previous advice and guidelines need to be critically reviewed, especially with regard to transmission risks in different contexts. Methods Scientific and grey literature were searched for articles about any African filovirus. Articles were screened for information about transmission (prevalence or odds ratios especially). Data were extracted from eligible articles and summarised narratively with partial meta-analysis. Study quality was also evaluated. Results 31 reports were selected from 6552 found in the initial search. Eight papers gave numerical odds for contracting filovirus illness, 23 further articles provided supporting anecdotal observations about how transmission probably occurred for individuals. Many forms of contact (conversation, sharing a meal, sharing a bed, direct or indirect touching) were unlikely to result in disease transmission during incubation or early illness. Amongst household contacts who reported directly touching a case, the attack rate was 32% (95% CI 26-38%). Risk of disease transmission between household members without direct contact was low (1%; 95% CI 0-5%). Caring for a case in the community, especially until death, and participation in traditional funeral rites were strongly associated with acquiring disease, probably due to a high degree of direct physical contact with case or cadaver. Conclusions Transmission of filovirus is unlikely except through close contact, especially during the most severe stages of acute illness. More data are needed about the context, intimacy and timing of contact required to raise the odds of disease transmission. Risk factors specific to urban settings may need to be determined
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