1,625 research outputs found
Composition of the nuclear periphery from antiproton absorption
Thirteen targets with mass numbers from 58 to 238 were irradiated with the
antiproton beam from the Low Energy Antiproton Ring facility at CERN leading to
the formation of antiprotonic atoms of these heavy elements. The antiproton
capture at the end of an atomic cascade results in the production of more or
less excited residual nuclei. The targets were selected with the criterion that
both reaction products with one nucleon less than the proton and neutron number
of the target be radioactive. The yield of these radioactive products after
stopped-antiproton annihilation was determined using gamma-ray spectroscopy
techniques. This yield is related to the proton and neutron density in the
target nucleus at a radial distance corresponding to the antiproton
annihilation site. The experimental data clearly indicate the existence of a
neutron-rich nuclear periphery, a "neutron halo", strongly correlated with the
target neutron separation energy Bn and observed for targets with Bn < 10 MeV.
For two-target nuclei 106Cd and 144Sm, with larger neutron binding energies, a
proton-rich nuclear periphery was observed. Most of the experimental data are
in reasonable agreement with calculations based on current antiproton-nucleus
and pion-nucleus interaction potentials and on nuclear densities deduced with
the help of the Hartree-Fock-Bogoliubov approach. This approach was, however,
unable to account for the 106Cd and 144Sm results.Comment: Latex (RevTeX,aps style), 13 pages + 12 Postscript figure
Gold fragmentation induced by stopped antiprotons
A natural gold target was irradiated with the antiproton beam from the Low
Energy Antiproton Ring at CERN. Antiprotons of 200 MeV/c momentum were stopped
in a thick target, products of their annihilations on Au nuclei were detected
using the off-line gamma-ray spectroscopy method. In total, yields for 114
residual nuclei were determined, providing a data set to deduce the complete
mass and charge distribution of all products with A > 20 from a fitting
procedure. The contribution of evaporation and fission decay modes to the total
reaction cross section as well as the mean mass loss were estimated. The
fission probability for Au absorbing antiprotons at rest was determined to be
equal to (3.8+-0.5)%, in good agreement with an estimation derived using other
techniques. The mass-charge yield distribution was compared with the results
obtained for proton and pion induced gold fragmentation. On the average, the
energy released in pbar annihilation is similar to that introduced by ~ 1 GeV
protons. However, compared to proton bombardment products, the yield
distribution of antiproton absorption residues in the N-Z plane is clearly
distinct. The data for antiprotons exhibit also a substantial influence of
odd-even and shell effects.Comment: 14 pages, 9 figures, Revtex 4, to be published in Physical Review
Hereditary Cancer in Clinical Practice transfers to BioMed Central
We are proud to announce the re-launch of Hereditary Cancer in Clinical Practice (HCCP). Moving from a classical printed journal, first published in 2003, to the open access, online format of BioMed Central will allow for a quicker and much wider distribution of published articles. Further improving exposure of articles, the journal has also been accepted for indexing by PubMed, and is now on track to receive it's first Impact Factor in 2010 after being accepted for inclusion in Thomson Reuters' Science Citation Index Expanded and the Journal Citation Reports. In addition, the Editorial Board of the journal has been expanded in acknowledgement of the continuing growth of the field of clinical cancer genetics
The Second INTEGRAL AGN Catalogue
The INTEGRAL mission provides a large data set for studying the hard X-ray
properties of AGN and allows testing of the unified scheme for AGN. We present
analysis of INTEGRAL IBIS/ISGRI, JEM-X, and OMC data for 199 AGN supposedly
detected by INTEGRAL above 20 keV. The data analysed here allow a significant
spectral extraction on 148 objects and an optical variability study of 57 AGN.
The slopes of the hard X-ray spectra of Seyfert 1 and Seyfert~2 galaxies are
found to be consistent within the uncertainties, whereas higher cut-off
energies and lower luminosities are measured for the more absorbed / type 2
AGN. The intermediate Seyfert 1.5 objects exhibit hard X-ray spectra consistent
with those of Seyfert 1. When applying a Compton reflection model, the
underlying continua appear the same in Seyfert 1 and 2 with photon index 2, and
the reflection strength is about R = 1, when assuming different inclination
angles. A significant correlation is found between the hard X-ray and optical
luminosity and the mass of the central black hole in the sense that the more
luminous objects appear to be more massive. There is also a general trend
toward the absorbed sources and type 2 AGN having lower Eddington ratios. The
black holemass appears to form a fundamental plane together with the optical
and X-ray luminosity of the form Lv being proportional to Lx^0.6 M^0.2, similar
to that found between radio luminosity Lr, Lx, and M. The unified model for
Seyfert galaxies seems to hold, showing in hard X-rays that the central engine
is the same in Seyfert 1 and 2, but seen under different inclination angles and
absorption. (Abridged)Comment: 26 pages, 16 figures, accepted for publication in A&A. Corrections by
language editor included in version
Long-term variability of AGN at hard X-rays
Variability at all observed wavelengths is a distinctive property of AGN.
Hard X-rays provide us with a view of the innermost regions of AGN, mostly
unbiased by absorption along the line of sight. Swift/BAT offers the unique
opportunity to follow, on time scales of days to years and with a regular
sampling, the 14-195 keV emission of the largest AGN sample available up to
date for this kind of investigation. We study the amplitude of the variations,
and their dependence on sub-class and on energy, for a sample of 110 radio
quiet and radio loud AGN selected from the BAT 58-month survey. About 80% of
the AGN in the sample are found to exhibit significant variability on months to
years time scales, radio loud sources being the most variable. The amplitude of
the variations and their energy dependence are incompatible with variability
being driven at hard X-rays by changes of the absorption column density. In
general, the variations in the 14-24 and 35-100 keV bands are well correlated,
suggesting a common origin of the variability across the BAT energy band.
However, radio quiet AGN display on average 10% larger variations at 14-24 keV
than at 35-100 keV and a softer-when-brighter behavior for most of the Seyfert
galaxies with detectable spectral variability on month time scale. In addition,
sources with harder spectra are found to be more variable than softer ones.
These properties are generally consistent with a variable power law continuum,
in flux and shape, pivoting at energies >~ 50 keV, to which a constant
reflection component is superposed. When the same time scales are considered,
the timing properties of AGN at hard X-rays are comparable to those at lower
energies, with at least some of the differences possibly ascribable to
components contributing differently in the two energy domains (e.g.,
reflection, absorption).Comment: 17 pages, 11 figures, accepted for publication in A&
Thank you to all our manuscript reviewers in 2015
The editors of Hereditary Cancer in Clinical Practice would like to thank all our reviewers who have contributed to the journal in 2015. Without the participation of skilful reviewers, no academic journal could succeed, and we are grateful to the committed individuals who have given their time and expertise to the peer review of manuscripts for Hereditary Cancer in Clinical Practice. We look forward to your continued support in 2016
Sex differences in mathematics and reading achievement are inversely related: within- and across-nation assessment of 10 years of PISA data
We analyzed one decade of data collected by the Programme for International Student Assessment (PISA), including the mathematics and reading performance of nearly 1.5 million 15 year olds in 75 countries. Across nations, boys scored higher than girls in mathematics, but lower than girls in reading. The sex difference in reading was three times as large as in mathematics. There was considerable variation in the extent of the sex differences between nations. There are countries without a sex difference in mathematics performance, and in some countries girls scored higher than boys. Boys scored lower in reading in all nations in all four PISA assessments (2000, 2003, 2006, 2009). Contrary to several previous studies, we found no evidence that the sex differences were related to nations’ gender equality indicators. Further, paradoxically, sex differences in mathematics were consistently and strongly inversely correlated with sex differences in reading: Countries with a smaller sex difference in mathematics had a larger sex difference in reading and vice versa. We demonstrate that this was not merely a between-nation, but also a within-nation effect. This effect is related to relative changes in these sex differences across the performance continuum: We did not find a sex difference in mathematics among the lowest performing students, but this is where the sex difference in reading was largest. In contrast, the sex difference in mathematics was largest among the higher performing students, and this is where the sex difference in reading was smallest. The implication is that if policy makers decide that changes in these sex differences are desired, different approaches will be needed to achieve this for reading and mathematics. Interventions that focus on high-achieving girls in mathematics and on low achieving boys in reading are likely to yield the strongest educational benefits
Information on antiprotonic atoms and the nuclear periphery from the PS209 experiment
In the PS209 experiments at CERN two kinds of measurements were performed:
the in-beam measurement of X-rays from antiprotonic atoms and the
radiochemical, off-line determination of the yield of annihilation products
with mass number A_t -1 (less by 1 than the target mass). Both methods give
observables which allows to study the peripheral matter density composition and
distribution.Comment: LaTeX (espcrc1 style), 6 pages, 3 EPS figures, 1 table, Proceedings
of the Sixth Biennal Conference on Low-Energy Antiproton Physics LEAP 2000,
Venice, Ital
Multiwavelength campaign on Mrk 509: testing realistic comptonization models
Mrk 509 was observed by XMM-Newton and INTEGRAL in October/November 2009, with one observation every four days for a total of ten observations. Each observation has been fitted with a realistic thermal Comptonization model for the continuum emission. Prompted by the correlation between the UV and soft X-ray flux, we used a thermal Comptonization component for the soft X-ray excess. The UV to X-ray/gamma-ray emission of Mrk 509 can be well fitted by these components, pointing to the existence of a hot (kT ∼ 100 keV), optically-thin (τ ∼ 0.5) corona producing the primary continuum. In contrast, the soft X-ray component requires a warm (kT ∼ 1 keV), optically-thick (τ ∼ 10-20) plasma. Estimates of the amplification ratio for this warm plasma support a configuration relatively close to the “theoretical” configuration of a slab corona above a passive disk. This plasma could be the warm upper layer of the accretion disk. In contrast, the hot corona has a more photon-starved geometry. The high temperature (∼ 100 eV) of the soft-photon field entering and cooling it favors a localization of the hot corona in the inner flow. This soft-photon field could be part of the comptonized emission produced by the warm plasma
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