1,031 research outputs found
Electromagnetic form factors of the nucleon in effective field theory
We calculate the electromagnetic form factors of the nucleon to third chiral
order in manifestly Lorentz-invariant effective field theory. The rho and omega
mesons as well as the Delta(1232) resonance are included as explicit dynamical
degrees of freedom. To obtain a self-consistent theory with respect to
constraints we consider the proper relations among the couplings of the
effective Lagrangian. For the purpose of generating a systematic power
counting, the extended on-mass-shell renormalization scheme is applied in
combination with the small-scale expansion. The results for the electric and
magnetic Sachs form factors are analyzed in terms of experimental data and
compared to previous findings in the framework of chiral perturbation theory.
The pion-mass dependence of the form factors is briefly discussed.Comment: 26 pages, 9 figure
Polarization transfer in scattering using the Super BigBite Spectrometer
The effects of multi-photon-exchange and other higher-order QED corrections
on elastic electron-proton scattering have been a subject of high experimental
and theoretical interest since the polarization transfer measurements of the
proton electromagnetic form factor ratio at large momentum
transfer conclusively established the strong decrease of this ratio with
for GeV. This result is incompatible with previous
extractions of this quantity from cross section measurements using the
Rosenbluth Separation technique. Much experimental attention has been focused
on extracting the two-photon exchange (TPE) effect through the unpolarized
cross section ratio, but polarization transfer in polarized elastic
scattering can also reveal evidence of hard two-photon exchange. Furthermore,
it has a different sensitivity to the generalized TPE form factors, meaning
that measurements provide new information that cannot be gleaned from
unpolarized scattering alone. Both -dependence of polarization
transfer at fixed , and deviations between electron-proton and
positron-proton scattering are key signatures of hard TPE. A polarized positron
beam at Jefferson Lab would present a unique opportunity to make the first
measurement of positron polarization transfer, and comparison with
electron-scattering data would place valuable constraints on hard TPE. Here, we
propose a measurement program in Hall A that combines the Super BigBite
Spectrometer for measuring recoil proton polarization, with a non-magnetic
calorimetric detector for triggering on elastically scattered positrons. Though
the reduced beam current of the positron beam will restrict the kinematic
reach, this measurement will have very small systematic uncertainties, making
it a clean probe of TPE.Comment: 6 pages, 3 figures. Contribution to the EPJA topical issue, "An
Experimental Program with Positron Beams at Jefferson Lab." arXiv admin note:
substantial text overlap with arXiv:2007.15081, arXiv:1906.0941
The OLYMPUS Internal Hydrogen Target
An internal hydrogen target system was developed for the OLYMPUS experiment
at DESY, in Hamburg, Germany. The target consisted of a long, thin-walled,
tubular cell within an aluminum scattering chamber. Hydrogen entered at the
center of the cell and exited through the ends, where it was removed from the
beamline by a multistage pumping system. A cryogenic coldhead cooled the target
cell to counteract heating from the beam and increase the density of hydrogen
in the target. A fixed collimator protected the cell from synchrotron radiation
and the beam halo. A series of wakefield suppressors reduced heating from beam
wakefields. The target system was installed within the DORIS storage ring and
was successfully operated during the course of the OLYMPUS experiment in 2012.
Information on the design, fabrication, and performance of the target system is
reported.Comment: 9 pages, 13 figure
Evaluation of early and late presentation of patients with ocular mucous membrane pemphigoid to two major tertiary referral hospitals in the United Kingdom
PURPOSE: Ocular mucous membrane pemphigoid (OcMMP) is a sight-threatening autoimmune disease in which referral to specialists units for further management is a common practise. This study aims to describe referral patterns, disease phenotype and management strategies in patients who present with either early or established disease to two large tertiary care hospitals in the United Kingdom.\ud
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PATIENTS AND METHODS: In all, 54 consecutive patients with a documented history of OcMMP were followed for 24 months. Two groups were defined: (i) early-onset disease (EOD:<3 years, n=26, 51 eyes) and (ii) established disease (EstD:>5 years, n=24, 48 eyes). Data were captured at first clinic visit, and at 12 and 24 months follow-up. Information regarding duration, activity and stage of disease, visual acuity (VA), therapeutic strategies and clinical outcome were analysed.\ud
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RESULTS: Patients with EOD were younger and had more severe conjunctival inflammation (76% of inflamed eyes) than the EstD group, who had poorer VA (26.7%=VA<3/60, P<0.01) and more advanced disease. Although 40% of patients were on existing immunosuppression, 48% required initiation or switch to more potent immunotherapy. In all, 28% (14) were referred back to the originating hospitals for continued care. Although inflammation had resolved in 78% (60/77) at 12 months, persistence of inflammation and progression did not differ between the two phenotypes. Importantly, 42% demonstrated disease progression in the absence of clinically detectable inflammation.\ud
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CONCLUSIONS: These data highlight that irrespective of OcMMP phenotype, initiation or escalation of potent immunosuppression is required at tertiary hospitals. Moreover, the conjunctival scarring progresses even when the eye remains clinically quiescent. Early referral to tertiary centres is recommended to optimise immunosuppression and limit long-term ocular damage.\ud
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A Collaborative Filtering Approach for Protein-Protein Docking Scoring Functions
A protein-protein docking procedure traditionally consists in two successive
tasks: a search algorithm generates a large number of candidate conformations
mimicking the complex existing in vivo between two proteins,
and a scoring function is used to rank them in order to extract a native-like
one. We have already shown that using Voronoi constructions and a well chosen
set of parameters, an accurate scoring function could be designed and optimized.
However to be able to perform large-scale in silico exploration
of the interactome, a near-native solution has to be found in the ten
best-ranked solutions. This cannot yet be guaranteed by any of the existing
scoring functions
Proprioceptive isokinetic exercise test
Proprioception, the reception of stimuli within the body that indicates position, is an important mechanism for optimal human performance. People exposed to prolonged bed rest, microgravity, or other deconditioning situations usually experience reduced proprioceptor and kinesthetic stimuli that compromise body balance, posture, and equilibrium. A new proprioceptive test is described that utilizes the computer-driven LIDO isokinetic ergometer. An overview of the computer logic, software, and testing procedure for this proprioceptive test, which can be performed with the arms or legs, is described
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