231 research outputs found
The spin temperature of high-redshift damped Lyman- systems
We report results from a programme aimed at investigating the temperature of
neutral gas in high-redshift damped Lyman- absorbers (DLAs). This
involved (1) HI 21cm absorption studies of a large DLA sample, (2) VLBI studies
to measure the low-frequency quasar core fractions, and (3) optical/ultraviolet
spectroscopy to determine DLA metallicities and velocity widths.
Including literature data, our sample consists of 37 DLAs with estimates of
the spin temperature and the covering factor. We find a strong )
difference between the distributions in high-z (z>2.4) and low-z (z<2.4)
DLA samples. The high-z sample contains more systems with high values,
K. The distributions in DLAs and the Galaxy are also
clearly (~) different, with more high- sightlines in DLAs than in
the Milky Way. The high values in the high-z DLAs of our sample arise due
to low fractions of the cold neutral medium.
For 29 DLAs with metallicity [Z/H] estimates, we confirm the presence of an
anti-correlation between and [Z/H], at significance via a
non-parametric Kendall-tau test. This result was obtained with the assumption
that the DLA covering factor is equal to the core fraction. Monte Carlo
simulations show that the significance of the result is only marginally
decreased if the covering factor and the core fraction are uncorrelated, or if
there is a random error in the inferred covering factor.
We also find evidence for redshift evolution in DLA values even for the
z>1 sub-sample. Since z>1 DLAs have angular diameter distances comparable to or
larger than those of the background quasars, they have similar efficiency in
covering the quasars. Low covering factors in high-z DLAs thus cannot account
for the observed redshift evolution in spin temperatures. (Abstract abridged.)Comment: 37 pages, 22 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Socioeconomic and geographic determinants of survival of patients with digestive cancer in France
Using a multilevel Cox model, the association between socioeconomic and geographical aggregate variables and survival was investigated in 81 268 patients with digestive tract cancer diagnosed in the years 1980–1997 and registered in 12 registries in the French Network of Cancer Registries. This association differed according to cancer site: it was clear for colon (relative risk (RR)=1.10 (1.04–1.16), 1.10 (1.04–1.16) and 1.14 (1.05–1.23), respectively, for distances to nearest reference cancer care centre between 10 and 30, 30 and 50 and more than 90 km, in comparison with distance of less than 10 km; P-trend=0.003) and rectal cancer (RR=1.09 (1.03–1.15), RR=1.08 (1.02–1.14) and RR=1.12 (1.05–1.19), respectively, for distances between 10 and 30 km, 30 and 50 km and 50 and 70 km, P-trend=0.024) (n=28 010 and n=18 080, respectively) but was not significant for gall bladder and biliary tract cancer (n=2893) or small intestine cancer (n=1038). Even though the influence of socioeconomic status on prognosis is modest compared to clinical prognostic factors such as histology or stage at diagnosis, socioeconomic deprivation and distance to nearest cancer centre need to be considered as potential survival predictors in digestive tract cancer
Binding energies of ground and isomeric states in neutron-rich ruthenium isotopes: measurements at JYFLTRAP and comparison to theory
We report on precision mass measurements of Ru performed with
the JYFLTRAP double Penning trap mass spectrometer at the Accelerator
Laboratory of University of Jyv\"askyl\"a. The phase-imaging
ion-cyclotron-resonance technique was used to resolve the ground and isomeric
states in Ru and enabled for the first time a measurement of the
isomer excitation energies, Ru keV and
Ru keV. The ground state of Ru was measured
using the time-of-flight ion-cyclotron-resonance technique. The new mass-excess
value for Ru is around 36 keV lower and 7 times more precise than the
previous literature value. With the more precise ground-state mass values, the
evolution of the two-neutron separation energies is further constrained and a
similar trend as predicted by the BSkG1 model is obtained up to the neutron
number .Comment: 12 pages, 9 figures, submitted to Physical Review
Unexpected high-energy γ emission from decaying exotic nuclei
Abstract The N = 52 Ga 83 β decay was studied at ALTO. The radioactive 83Ga beam was produced through the ISOL photofission technique and collected on a movable tape for the measurement of γ-ray emission following β decay. While β-delayed neutron emission has been measured to be 56–85% of the decay path, in this experiment an unexpected high-energy 5–9 MeV γ-ray yield of 16(4)% was observed, coming from states several MeVs above the neutron separation threshold. This result is compared with cutting-edge QRPA calculations, which show that when neutrons deeply bound in the core of the nucleus decay into protons via a Gamow–Teller transition, they give rise to a dipolar oscillation of nuclear matter in the nucleus. This leads to large electromagnetic transition probabilities which can compete with neutron emission, thus affecting the β-decay path. This process is enhanced by an excess of neutrons on the nuclear surface and may thus be a common feature for very neutron-rich isotopes, challenging the present understanding of decay properties of exotic nuclei
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