926 research outputs found
DVCS with CLAS
Generalized parton distributions provide a unifying framework for the
interpretation of exclusive reactions at high . The most promising
reaction for the investigation of these distributions is the hard production of
photons using Deeply Virtual Compton Scattering (DVCS). This reaction can be
accessed experimentally by determining the production asymmetry using polarized
electrons on a proton target. Pioneering experiments with CLAS and HERMES have
produced the first measurements of this asymmetry. We will review the current
experimental program to study DVCS at Jefferson Lab. Recent high statistics
data taken with CLAS at 5.75 GeV allows us to determine this asymmetry at low
- in the valence region (=0.1-0.5) up to a of 4 GeV.Comment: 5 pages, 3 figures, Conference on the Intersections of Particle and
Nuclear Physics, New York City, May 19-24, 200
Review of Recent Jlab Results
High quality polarized electron beams at Jefferson Lab make possible
precision measurements of hadronic properties in the regime of strongly
interacting QCD. We will describe a few programs at Jefferson Lab that are
making measurements that link the basic static properties of hadrons to their
quark sub-structure. For example, parity-violating electron proton elastic
scattering probes the spatial distribution of strange quarks in the nucleon.
The nucleon-Delta transition form factors give us information about the
deformation of nucleons and Deltas. Finally, new high statistics measurements
of photons scattering off proton and deuteron targets are used to set upper
limits on the production of exotic baryons with strangeness S=+1. These
examples will be used to illustrate the capabilities and focus of the
experimental program at JLab.Comment: Contribution to XI International Conference on Hadron Spectroscopy, 4
figure
JLab: Probing Hadronic Physics with Electrons and Photons
Precision measurements of the structure of nucleons and nuclei in the regime
of strong interaction QCD are now possible with the availability of high
current polarized electron beams, polarized targets, and recoil polarimeters,
in conjunction with modern spectrometers and detector instrumentation. The
physics at JLab will be highlighted using two recent measurements of general
interest. The ratio of the proton electric to magnetic form factors indicates
the importance of the role of angular momentum in the structure of the nucleon.
The existence of 5-quark configurations in the ground state wavefunctions of
hadrons is confirmed by a narrow peak attributed to an exotic baryon with
strangeness S=+1. These and other examples will be used to illustrate the
capabilities and focus of the experimental program at JLab.Comment: V Latinamerican Symposium on Nuclear Physics, Santos, Brazil (Sept
1-5, 2003) 4 pages, 4 figure
Quaternary fossil fauna from the Luangwa Valley, Zambia
This paper describes a large collection of Quaternary fossil fauna from the Luangwa rift valley, Zambia. Stone Age artefacts have been recovered from stratified fluvial contexts, but no in situ fossil fauna have yet been recovered. We report on 500 fossil specimens collected from the surface of point bars exposed seasonally along the banks of the main Luangwa river channel. We used non-destructive x-ray fluorescence analysis of the fossils' chemical signatures to determine whether they derive from one or many primary contexts, and the relation between chemical signature and state of preservation. Specimens are identified to taxon (genus) to reconstruct palaeoenvironments and biochronology. A relatively wide range of taxa is identified, including a fossil hominin talus, described here. None of the fossils are positively attributable to extinct species, except a femur of an extinct Theropithecus reported in 2003 (Elton et al., 2003). Although no additional extinct taxa were identified, some of the remains were attributable to genera which are not currently found in this region. The results suggest that the majority of the assemblage derives from sediments which are Middle Pleistocene or later, and that past environments in the Luangwa Valley may have differed from the habitat availability found today
Statistics of Atmospheric Correlations
For a large class of quantum systems the statistical properties of their
spectrum show remarkable agreement with random matrix predictions. Recent
advances show that the scope of random matrix theory is much wider. In this
work, we show that the random matrix approach can be beneficially applied to a
completely different classical domain, namely, to the empirical correlation
matrices obtained from the analysis of the basic atmospheric parameters that
characterise the state of atmosphere. We show that the spectrum of atmospheric
correlation matrices satisfy the random matrix prescription. In particular, the
eigenmodes of the atmospheric empirical correlation matrices that have physical
significance are marked by deviations from the eigenvector distribution.Comment: 8 pages, 9 figs, revtex; To appear in Phys. Rev.
Phase Transitions and Spatio-Temporal Fluctuations in Stochastic Lattice Lotka-Volterra Models
We study the general properties of stochastic two-species models for
predator-prey competition and coexistence with Lotka-Volterra type interactions
defined on a -dimensional lattice. Introducing spatial degrees of freedom
and allowing for stochastic fluctuations generically invalidates the classical,
deterministic mean-field picture. Already within mean-field theory, however,
spatial constraints, modeling locally limited resources, lead to the emergence
of a continuous active-to-absorbing state phase transition. Field-theoretic
arguments, supported by Monte Carlo simulation results, indicate that this
transition, which represents an extinction threshold for the predator
population, is governed by the directed percolation universality class. In the
active state, where predators and prey coexist, the classical center
singularities with associated population cycles are replaced by either nodes or
foci. In the vicinity of the stable nodes, the system is characterized by
essentially stationary localized clusters of predators in a sea of prey. Near
the stable foci, however, the stochastic lattice Lotka-Volterra system displays
complex, correlated spatio-temporal patterns of competing activity fronts.
Correspondingly, the population densities in our numerical simulations turn out
to oscillate irregularly in time, with amplitudes that tend to zero in the
thermodynamic limit. Yet in finite systems these oscillatory fluctuations are
quite persistent, and their features are determined by the intrinsic
interaction rates rather than the initial conditions. We emphasize the
robustness of this scenario with respect to various model perturbations.Comment: 19 pages, 11 figures, 2-column revtex4 format. Minor modifications.
Accepted in the Journal of Statistical Physics. Movies corresponding to
Figures 2 and 3 are available at
http://www.phys.vt.edu/~tauber/PredatorPrey/movies
Intersubject Variability of and Genetic Effects on the Brain's Functional Connectivity during Infancy
Infancy is a period featuring a high level of intersubject variability but the brain basis for such variability and the potential genetic/environmental contributions remain largely unexplored. The assessment of the brain's functional connectivity during infancy by the resting state functional magnetic resonance imaging (rsfMRI) technique (Biswal et al., 1995) provides a unique means to probe the brain basis of intersubject variability during infancy. In this study, an unusually large typically developing human infant sample including 58 singletons, 132 dizygotic twins, and 98 monozygotic twins with rsfMRI scans during the first 2 years of life was recruited to delineate the spatial and temporal developmental patterns of both the intersubject variability of and genetic effects on the brain's functional connectivity. Through systematic voxelwise functional connectivity analyses, our results revealed that the intersubject variability at birth features lower variability in primary functional areas but higher values in association areas. Although the relative pattern remains largely consistent, the magnitude of intersubject variability undergoes an interesting U-shaped growth during the first 2 years of life. Overall, the intersubject variability patterns during infancy show both adult-like and infant-specific characteristics (Mueller et al., 2013). On the other hand, age-dependent genetic effects were observed showing significant but bidirectional relationships with intersubject variability. The temporal and spatial patterns of the intersubject variability of and genetic contributions to the brain's functional connectivity documented in this study shed light on the largely uncharted functional development of the brain during infancy
Women with learning disabilities and access to cervical screening: retrospective cohort study using case control methods
<p>Abstract</p> <p>Background</p> <p>Several studies in the UK have suggested that women with learning disabilities may be less likely to receive cervical screening tests and a previous local study in had found that GPs considered screening unnecessary for women with learning disabilities. This study set out to ascertain whether women with learning disabilities are more likely to be ceased from a cervical screening programme than women without; and to examine the reasons given for ceasing women with learning disabilities. It was carried out in Bury, Heywood-and-Middleton and Rochdale.</p> <p>Methods</p> <p>Carried out using retrospective cohort study methods, women with learning disabilities were identified by Read code; and their cervical screening records were compared with the Call-and-Recall records of women without learning disabilities in order to examine their screening histories. Analysis was carried out using case-control methods – 1:2 (women with learning disabilities: women without learning disabilities), calculating odds ratios.</p> <p>Results</p> <p>267 women's records were compared with the records of 534 women without learning disabilities. Women with learning disabilities had an odds ratio (OR) of 0.48 (Confidence Interval (CI) 0.38 – 0.58; <it>X</it><sup>2</sup>: 72.227; p.value <.001) of receiving a cervical screening test; an OR of 2.05 (CI 1.88 – 2.22; <it>X</it><sup>2</sup>: 24.236; p.value <.001) of being ceased from screening; and an OR of 0.14 (CI 0.001 – 0.28; <it>X</it><sup>2</sup>: 286.341; p.value <0.001 of being a non-responder compared to age and practice-matched women without learning disabilities.</p> <p>Conclusion</p> <p>The reasons given for ceasing and/or not screening suggest that merely being coded as having a learning disability is <b>not </b>the sole reason for these actions. There are training needs among smear takers regarding appropriate reasons not to screen and providing screening for women with learning disabilities.</p
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