965 research outputs found
How healthy are survey respondents compared with the general population? Using survey-linked death records to compare mortality outcomes
Background: National surveys are used to capture US health trends and set clinical guidelines, yet the sampling frame often includes those in non-institutional households, potentially missing those most vulnerable for poor health. Declining response rates in national surveys also represent a challenge, and existing inputs to survey weights have limitations. We compared mortality rates between those who respond to surveys and the general population over time.
Methods: Survey respondents from twenty waves of the National Health Interview Survey from 1990 through 2009 who have been linked to death records through 31 December 2011 were included. For each cohort in the survey, we estimated their mortality rates along with that cohort's mortality rate in the census population using vital statistics records and differences were examined using Poisson models.
Results: In all years, survey respondents had lower mortality rates compared with the general population, when data were both weighted and unweighted. Among men, survey respondents in the weighted sample had 0.86 (95% C.I. 0.853-0.868) times the mortality rate of the general population (among women, RR=0.887; 95% C.I. 0.879-0.895). Differences in mortality are evident along all points of the life course. Differences have remained relatively stable over time.
Conclusion: Survey respondents have lower death rates than the general US population, suggesting that they are a systematically healthier source population. Incorporating non-household samples and revised weighting strategies to account for sample frame exclusion and non-response may allow for more rigorous estimation of the US population's health
Resident Corneal Cells Communicate with Neutrophils Leading to the Production of IP-10 during the Primary Inflammatory Response to HSV-1 Infection
In this study we show that murine and human neutrophils are capable of secreting IP-10 in response to communication from the HSV-1 infected cornea and that they do so in a time frame associated with the recruitment of CD8+ T cells and CXCR3-expressing cells. Cellular markers were used to establish that neutrophil influx corresponded in time to peak IP-10 production, and cellular depletion confirmed neutrophils to be a significant source of IP-10 during HSV-1 corneal infection in mice. A novel ex vivo model for human corneal tissue infection with HSV-1 was used to confirm that cells resident in the cornea are also capable of stimulating neutrophils to secrete IP-10. Our results support the hypothesis that neutrophils play a key role in T-cell recruitment and control of viral replication during HSV-1 corneal infection through the production of the T-cell recruiting chemokine IP-10
Efficiency of Electron-Positron Pair Productionby Neutrino Flux from Accretion Disk of a Kerr Black Hole
Dominant processes of neutrino production and neutrino-induced \ep-pair
production are examined in the model of a disk hyper-accreting onto a Kerr
black hole. The efficiency of plasma production by a neutrino flux from the
disk, obtained for the both cases of presence and absence of a magnetic field,
is found to be no more than several tenths of percent and, therefore, not
enough for the origin of cosmological gamma-ray bursts.Comment: 8 pages, 1 figur
Implications of the metallicity dependence of Wolf-Rayet winds
Aims: Recent theoretical predictions for the winds of Wolf-Rayet stars
indicate that their mass-loss rates scale with the initial stellar metallicity
in the local Universe.We aim to investigate how this predicted dependence
affects the models of Wolf-Rayet stars and their progeny in different chemical
environments. Methods: We compute models of stellar structure and evolution for
Wolf-Rayet stars for different initial metallicities, and investigate how the
scaling of the Wolf-Rayet mass-loss rates affects the final masses, the
lifetimes of the WN and WC subtypes, and how the ratio of the two populations
vary with metallicity. Results: We find significant effects of metallicity
dependent mass-loss rates for Wolf-Rayet stars. For models that include the
scaling of the mass-loss rate with initial metallicity, all WR stars become
neutron stars rather than black holes at twice the solar metallicity; at lower
, black holes have larger masses. We also show that our models that include
the mass-loss metallicity scaling closely reproduce the observed decrease of
the relative population of WC over WN stars at low metallicities.Comment: 8 pages, 9 figures, accepted by Astronomy & Astrophysic
Swift monitoring of Cygnus X-2: investigating the NUV-X-ray connection
The neutron star X-ray binary (NSXRB) Cygnus X-2 was observed by the Swift
satellite 51 times over a 4 month period in 2008 with the XRT, UVOT, and BAT
instruments. During this campaign, we observed Cyg X-2 in all three branches of
the Z track (horizontal, normal, and flaring branches). We find that the NUV
emission is uncorrelated with the soft X-ray flux detected with the XRT, and is
anticorrelated with the BAT X-ray flux and the hard X-ray color. The observed
anticorrelation is inconsistent with simple models of reprocessing as the
source of the NUV emission. The anticorrelation may be a consequence of the
high inclination angle of Cyg X-2, where NUV emission is preferentially
scattered by a corona that expands as the disk is radiatively heated.
Alternatively, if the accretion disk thickens as Cyg X-2 goes down the normal
branch toward the flaring branch, this may be able to explain the observed
anticorrelation. In these models the NUV emission may not be a good proxy for
in the system. We also discuss the implications of using Swift/XRT to
perform spectral modeling of the continuum emission of NSXRBs.Comment: 10 pages, 8 figures. ApJ Accepte
Theorising social class and its application to the study of health inequalities
The literature on health inequalities often uses measures of socio-economic position pragmatically to rank the population to describe inequalities in health rather than to understand social and economic relationships between groups. Theoretical considerations about the meaning of different measures, the social processes they describe, and how these might link to health are often limited. This paper builds upon Wright’s synthesis of social class theories to propose a new integrated model for understanding social class as applied to health. This model incorporates several social class mechanisms: social background and early years’ circumstances; Bourdieu’s habitus and distinction; social closure and opportunity hoarding; Marxist conflict over production (domination and exploitation); and Weberian conflict over distribution. The importance of discrimination and prejudice in determining the opportunities for groups is also explicitly recognised, as is the relationship with health behaviours. In linking the different social class processes we have created an integrated theory of how and why social class causes inequalities in health. Further work is required to test this approach, to promote greater understanding of researchers of the social processes underlying different measures, and to understand how better and more comprehensive data on the range of social class processes these might be collected in the future
On the angular momentum evolution of merged white dwarfs
We study the angular momentum evolution of binaries containing two white
dwarfs which merge and become cool helium-rich supergiants. Our object is to
compare predicted rotation velocities with observations of highly evolved stars
believed to have formed from such a merger, including RCrB and extreme helium
stars. The principal study involves a binary containing a 0.6 solar mass CO
white dwarf, and a 0.3 solar mass He white dwarf. The initial condition for the
angular momentum distribution is defined where the secondary fills its Roche
Lobe. We assume conservation of angular momentum to compute the angular
momentum distribution in a collisionless disk and subsequently in the giant
envelope. At the end of shell-helium burning, the giant contracts to form a
white dwarf. We derive the surface rotation velocity during this contraction.
The calculation is repeated for a range of initial mass ratios, and also for
the case of mergers between two helium white dwarfs; the latter will contract
to the helium main-sequence rather than the white dwarf sequence. Assuming
complete conservation of angular momentum, we predict acceptable angular
rotation rates for cool giants and during the initial subsequent contraction.
However such stars will only survive spin-up to reach the white dwarf sequence
(CO+He merger) if the initial mass ratio is close to unity. He+He merger
products must lose angular momentum in order to reach the helium main sequence.
Minimum observed rotation velocities in extreme helium stars are lower than our
predictions by at least one half, indicating that CO+He mergers must lose at
least one half of their angular momentum.Comment: 11 pages, 11 figures, MNRAS in pres
The X-ray eclipse of the dwarf nova HT CAS observed by the XMM-Newton satellite: spectral and timing analysis
A cataclysmic variable is a binary system consisting of a white dwarf that
accretes material from a secondary object via the Roche-lobe mechanism. In the
case of long enough observation, a detailed temporal analysis can be performed,
allowing the physical properties of the binary system to be determined. We
present an XMM-Newton observation of the dwarf nova HT Cas acquired to resolve
the binary system eclipses and constrain the origin of the X-rays observed. We
also compare our results with previous ROSAT and ASCA data. After the spectral
analysis of the three EPIC camera signals, the observed X-ray light curve was
studied with well known techniques and the eclipse contact points obtained.
The X-ray spectrum can be described by thermal bremsstrahlung of temperature
keV plus a black-body component (upper limit) with
temperature eV. Neglecting the black-body, the bolometric
absorption corrected flux is erg
s cm, which, for a distance of HT Cas of 131 pc, corresponds to a
bolometric luminosity of erg s.
The study of the eclipse in the EPIC light curve permits us to constrain the
size and location of the X-ray emitting region, which turns out to be close to
the white dwarf radius. We measure an X-ray eclipse somewhat smaller (but only
at a level of ) than the corresponding optical one. If this
is the case, we have possibly identified the signature of either high latitude
emission or a layer of X-ray emitting material partially obscured by an
accretion disk.Comment: Accepted for publication on Astronomy and Astrophysics, 200
Causal Viscosity in Accretion Disc Boundary Layers
The structure of the boundary layer region between the disc and a
comparatively slowly rotating star is studied using a causal prescription for
viscosity. The vertically integrated viscous stress relaxes towards its
equilibrium value on a relaxation timescale , which naturally yields a
finite speed of propagation for viscous information. For a standard alpha
prescription with alpha in the range 0.1-0.01, and ratio of viscous speed to
sound speed in the range 0.02-0.5, details in the boundary layer are strongly
affected by the causality constraint. We study both steady state polytropic
models and time dependent models, taking into account energy dissipation and
transport. Steady state solutions are always subviscous with a variety of
profiles which may exhibit near discontinuities. For alpha =0.01 and
small viscous speeds, the boundary layer adjusted to a near steady state. A
long wavelength oscillation generated by viscous overstability could be seen at
times near the outer boundary. Being confined there, the boundary layer
remained almost stationary. However, for alpha =0.1 and large viscous speeds,
short wavelength disturbances were seen throughout which could significantly
affect the power output in the boundary layer. This could be potentially
important in producing time dependent behaviour in accreting systems such as
CVs and protostars.Comment: 10 LateX pages, requires lamuphys.sty and psfig.sty, 3 figures
included, to appear in the Proceedings of the EARA Workshop on Accretion
Disks (Garching, Oct. 96), Lecture Notes in Physic
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