772 research outputs found
A meta-analysis of obesity and the risk of pancreatic cancer
Smoking and diabetes are the only established risk factors for pancreatic cancer. Findings from recent studies suggest that obesity may also be associated with an increased risk of pancreatic cancer, but several earlier studies were less conclusive. We examined this relationship in a meta-analysis of published data. Six case-control and eight cohort studies involving 6391 cases of pancreatic cancer were identified from a computer-based literature search from 1966 to 2003. The relative risk per unit increase in body mass index was estimated for each of the studies from the published data. In a random effects model, the summary relative risk per unit increase in body mass index was 1.02 (95% CI: 1.01-1.03). There was some evidence of heterogeneity between the studies' results (P=0.1). The summary relative risk estimates were slightly higher for studies that had adjusted for smoking and for case-control studies that had not used proxy respondents. The estimated per unit increase in body mass index would translate into a relative risk of 1.19 (95% CI: 1.10-1.29) for obese people (30 kg m(-2)) compared to people with a normal body weight (22 kg m(-2)). These results provide evidence that the risk of pancreatic cancer may be weakly associated with obesity. However, the small magnitude of the summary risk means the possibility of confounding cannot be excluded
N-acetyltransferase 2 and bladder cancer: an overview and consideration of the evidence for gene–environment interaction
Genetic polymorphism of the carcinogen metabolizing enzyme N -acetyl transferase 2 (NAT2) may influence susceptibility to bladder cancers related to smoking or to occupational exposure to arylamine carcinogens. This article reviews the results of 21 published case–control studies of NAT2 polymorphism and bladder-cancer risk, with a total of 2700 cases and 3426 controls. The published evidence suggests that NAT2 slow acetylator phenotype or genotype may be associated with a small increase in bladder cancer risk. However, given the possibility of selective publication of results from studies that found an excess risk, the current evidence is not sufficient to conclude that there is a real increase in risk. Only five of the 21 studies reported results separately for the effect of NAT2 on bladder cancer risk in smokers and non-smokers. Although the results suggest that the effect may be greater in smokers than in non-smokers, the possibility of publication bias makes these results difficult to interpret. There was insufficient evidence to assess the joint effect of NAT2 and occupational exposure to arylamines on bladder cancer risk. Even if estimates of the effect of NAT2 from published data are correct, studies with around 3000–5000 cases will be needed to confirm them. © 2000 Cancer Research Campaig
The Hilbert-Schmidt Theorem Formulation of the R-Matrix Theory
Using the Hilbert-Schmidt theorem, we reformulate the R-matrix theory in
terms of a uniformly and absolutely convergent expansion. Term by term
differentiation is possible with this expansion in the neighborhood of the
surface. Methods for improving the convergence are discussed when the
R-function series is truncated for practical applications.Comment: 16 pages, Late
Lower entropy bounds and particle number fluctuations in a Fermi sea
We demonstrate, in an elementary manner, that given a partition of the single
particle Hilbert space into orthogonal subspaces, a Fermi sea may be factored
into pairs of entangled modes, similar to a BCS state. We derive expressions
for the entropy and for the particle number fluctuations of a subspace of a
fermi sea, at zero and finite temperatures, and relate these by a lower bound
on the entropy. As an application we investigate analytically and numerically
these quantities for electrons in the lowest Landau level of a quantum Hall
sample.Comment: shorter version, typos fixe
The discovery of diffuse steep spectrum sources in Abell 2256
Context: Hierarchical galaxy formation models indicate that during their
lifetime galaxy clusters undergo several mergers. Here we report on the
discovery of three diffuse radio sources in the periphery of Abell 2256, using
the GMRT.
Aims: The aim of the observations was to search for diffuse ultra-steep
spectrum radio sources within the galaxy cluster Abell 2256.
Methods: We have carried out GMRT 325 MHz radio continuum observations of
Abell 2256. V, R and I band images of the cluster were taken with the 4.2m WHT.
Results: We have discovered three diffuse elongated radio sources located
about 1 Mpc from the cluster center. Two are located to the west of the cluster
center, and one to the southeast. The sources have a measured physical extent
of 170, 140 and 240 kpc, respectively. The two western sources are also visible
in deep low-resolution 115-165 MHz WSRT images, although they are blended into
a single source. For the combined emission of the blended source we find an
extreme spectral index of -2.05\pm 0.14 between 140 and 351 MHz. The extremely
steep spectral index suggests these two sources are most likely the result of
adiabatic compression of fossil radio plasma due to merger shocks.
Conclusions: The discovery of the steep spectrum sources implies the
existence of a population of faint diffuse radio sources in (merging) clusters
with such steep spectra that they have gone unnoticed in higher frequency
(\gtrsim 1 GHz) observations. An exciting possibility therefore is that such
sources will determine the general appearance of clusters in low-frequency high
resolution radio maps as will be produced by for example LOFAR or LWA.Comment: 5 pages, 2 figures, accepted for publication in A&A on October 16,
200
Development of the preterm gut microbiome in twins at risk of necrotising enterocolitis and sepsis
The preterm gut microbiome is a complex dynamic community influenced by genetic and environmental factors and is implicated in the pathogenesis of necrotising enterocolitis (NEC) and sepsis. We aimed to explore the longitudinal development of the gut microbiome in preterm twins to determine how shared environmental and genetic factors may influence temporal changes and compared this to the expressed breast milk (EBM) microbiome. Stool samples (n = 173) from 27 infants (12 twin pairs and 1 triplet set) and EBM (n = 18) from 4 mothers were collected longitudinally. All samples underwent PCR-DGGE (denaturing gradient gel electrophoresis) analysis and a selected subset underwent 454 pyrosequencing. Stool and EBM shared a core microbiome dominated by Enterobacteriaceae, Enterococcaceae, and Staphylococcaceae. The gut microbiome showed greater similarity between siblings compared to unrelated individuals. Pyrosequencing revealed a reduction in diversity and increasing dominance of Escherichia sp. preceding NEC that was not observed in the healthy twin. Antibiotic treatment had a substantial effect on the gut microbiome, reducing Escherichia sp. and increasing other Enterobacteriaceae.
This study demonstrates related preterm twins share similar gut microbiome development, even within the complex environment of neonatal intensive care. This is likely a result of shared genetic and immunomodulatory factors as well as exposure to the same maternal microbiome during birth, skin contact and exposure to EBM. Environmental factors including antibiotic exposure and feeding are additional significant determinants of community structure, regardless of host genetics
Nitrogen K-shell photoabsorption
Reliable atomic data have been computed for the spectral modeling of the
nitrogen K lines, which may lead to useful astrophysical diagnostics. Data sets
comprise valence and K-vacancy level energies, wavelengths, Einstein
-coefficients, radiative and Auger widths and K-edge photoionization cross
sections. An important issue is the lack of measurements which are usually
employed to fine-tune calculations so as to attain spectroscopic accuracy. In
order to estimate data quality, several atomic structure codes are used and
extensive comparisons with previous theoretical data have been carried out. In
the calculation of K photoabsorption with the Breit--Pauli -matrix method,
both radiation and Auger damping, which cause the smearing of the K edge, are
taken into account. This work is part of a wider project to compute atomic data
in the X-ray regime to be included in the database of the popular {\sc xstar}
modeling code
A Radial Velocity Survey of the Cygnus OB2 Association
We conducted a radial velocity survey of the Cygnus OB2 Association over a 6
year (1999 - 2005) time interval to search for massive close binaries. During
this time we obtained 1139 spectra on 146 OB stars to measure mean systemic
radial velocities and radial velocity variations. We spectroscopically identify
73 new OB stars for the first time, the majority of which are likely to be
Association members. Spectroscopic evidence is also presented for a B3Iae
classification and temperature class variation (B3 - B8) on the order of 1 year
for Cygnus OB2 No. 12. Calculations of the intial mass function with the
current spectroscopic sample yield Gamma = -2.2 +/- 0.1. Of the 120 stars with
the most reliable data, 36 are probable and 9 are possible single-lined
spectroscopic binaries. We also identify 3 new and 8 candidate double-lined
spectroscopic binaries. These data imply a lower limit on the massive binary
fraction of 30% - 42%. The calculated velocity dispersion for Cygnus OB2 is
2.44 +/- km/s, which is typical of open clusters. No runaway OB stars were
found.Comment: 56 pages, 23 figures, 5 tables, accepted for publication in the
Astrophysical Journa
K-shell dielectronic resonances in photoabsorption: differential oscillator strengths for Li-like C IV, O VI, and Fe XXIV
Recently X-ray photoabsorption in KLL resonances of O VI was predicted
[Pradhan, Astrophys.J. Lett. 545, L165 (2000)], and detected by the Chandra
X-ray Observatory [Lee et al, Astrophys. J. {\it Lett.}, submitted].
The required resonance oscillator strengths f_r, are evaluated in terms of
the differential oscillator strength df/de that relates bound and continuum
absorption. We present the f_r values from radiatively damped and undamped
photoionization cross sections for Li-like C,O, and Fe calculated using
relativistic close coupling Breit-Pauli R-matrix method. The KLL resonances of
interest here are: 1s2p (^3P^o) 2s [^4P^o_{1/2,3/2}, ^2P^o_{1/2,3/2}] and 1s2p
(^1P^o) 2s [^2P^o_{1/2,3/2}]. The KLL photoabsorption resonances in Fe XXIV are
fully resolved up to natural autoionization profiles for the first time. It is
demonstrated that the undamped f_r independently yield the resonance radiative
decay rates, and thereby provide a precise check on the resolution of
photoionization calculations in general. The predicted photoabsorption features
should be detectable by the X-ray space observatories and enable column
densities in highly ionized astrophysical plasmas to be determined from the
calculated f_r. The dielectronic satellites may appear as redward broadening of
resonances lines in emission and absorption.Comment: 9 pages, 2 figurs, Phys. Rev. A, Rapid Communication (submitted
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