20,500 research outputs found
Nucleon spin structure at very high-x
Dyson-Schwinger equation treatments of the strong interaction show that the
presence and importance of nonpointlike diquark correlations within the nucleon
are a natural consequence of dynamical chiral symmetry breaking. Using this
foundation, we deduce a collection of simple formulae, expressed in terms of
diquark appearance and mixing probabilities, from which one may compute ratios
of longitudinal-spin-dependent u- and d-quark parton distribution functions on
the domain x =1. A comparison with predictions from other approaches plus a
consideration of extant and planned experiments shows that the measurement of
nucleon longitudinal spin asymmetries on x =1 can add considerably to our
capacity for discriminating between contemporary pictures of nucleon structure.Comment: 6 pages, 1 table, 3 figures. To appear in Phys. Lett.
Gamma-ray bursts during neutron star formation. Gamma-ray bursts and transient X-ray sources
Discussions are presented of the associations between cosmic gamma ray bursts and transient X-ray sources, and the release of gravitational binding energy during the formation of neutron stars. The model for studying the associations is described along with the release of neutrinos during the collapse of white dwarfs
PKS1932-46: a radio source in an interacting group?
We present the results of a multiwavelength study of the z=0.23 radio source
PKS1932-46. VIMOS IFU spectroscopy is used to study the morphology, kinematics
and ionisation state of the EELR surrounding this source, and also a companion
galaxy at a similar redshift. Near- and far-IR imaging observations obtained
using the NTT and SPITZER are used to analyse the underlying galaxy
morphologies and the nature of the AGN. The host galaxy is identified as an ~M*
elliptical. Combining Spitzer mid-IR with X-ray, optical and near-IR imaging
observations of this source, we conclude that its AGN is underluminous for a
radio source of this type, despite its status as a BLRG. However, given its
relatively large [OIII] luminosity it is likely that the AGN was substantially
more luminous in the recent past (<10^4 years ago). The EELR is remarkably
extensive and complex, reminiscent of the systems observed around sources at
higher redshifts/radio powers, and the gas is predominantly ionised by a
mixture of AGN photoionisation and emission from young stars. We confirm the
presence of a series of star-forming knots extending N-S from the host galaxy,
with more prodigious star formation occuring in the merging companion galaxy to
the northeast, which has sufficient luminosity at mid- to far-IR wavelengths to
be classified as a LIRG. The most plausible explanation of our observations is
that PKS1932-46 is a member of an interacting galaxy group, and that the
impressive EELR is populated by star-forming, tidal debris. We suggest that the
AGN itself may currently be fuelled by material associated either with the
current interaction, or with a previous merger event. Surprisingly, it is the
companion object, rather than the radio source host galaxy, which is undergoing
the bulk of the star formation activity within the group.Comment: 15 pages, 14 figures (compressed for astro-ph, 1 colour). Accepted
for publication in MNRAS. Abstract abridge
Millstone Hill Thomson Scatter Results for 1972
During 1972, the vertically directed incoherent scatter radar at Millstone Hill (42.6°N, 71.5°W) was employed to measure electron density, electron and ion temperatures, and vertical ion velocity in the F-region over periods of 24 hours, one or two times per month. The observations spanned the height interval 200 to 900 km, approximately, and achieved a time resolution of about 30 minutes. This report presents the results of these measurements in a set of contour diagrams.
For a number of the days, the spectra of the signals gathered at altitudes between 450 and 1125 km have been the subject of further analysis in an effort to determine the percentage of H[superscript +] ions present over Millstone. The results suggest that H[superscript +] ions are escaping from the F-region to the magnetosphere at a value close to the theoretical limiting flux during the daytime in all seasons. At night the flux becomes downward commencing near midnight in winter, but may remain upward throughout the night in summer
Systematic review of brucellosis in the Middle East: disease frequency in ruminants and humans and risk factors for human infection
This paper considers the problem of finding global states incoming to a specified global state in a Boolean network, which may be useful for pre-processing of finding a sequence of control actions for a Boolean network and for identifying the basin of attraction for a given attractor, We show that this problem is NP-hard in general along with related theoretical results, On the other hand, we present algorithms that are much faster than the naive exhaustive search-based algorithm. ©2007 IEEE.link_to_subscribed_fulltex
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