322 research outputs found
Measurement of the Generalized Forward Spin Polarizabilities of the Neutron
The generalized forward spin polarizabilities and of
the neutron have been extracted for the first time in a range from 0.1 to
0.9 GeV. Since is sensitive to nucleon resonances and
is insensitive to the resonance, it is expected that the
pair of forward spin polarizabilities should provide benchmark tests of the
current understanding of the chiral dynamics of QCD. The new results on
show significant disagreement with Chiral Perturbation Theory
calculations, while the data for at low are in good agreement
with a next-to-lead order Relativistic Baryon Chiral Perturbation theory
calculation. The data show good agreement with the phenomenological MAID model.Comment: 5 pages, 2 figures, corrected typo in author name, published in PR
Virtual Compton Scattering and the Generalized Polarizabilities of the Proton at Q^2=0.92 and 1.76 GeV^2
Virtual Compton Scattering (VCS) on the proton has been studied at Jefferson
Lab using the exclusive photon electroproduction reaction (e p --> e p gamma).
This paper gives a detailed account of the analysis which has led to the
determination of the structure functions P_LL-P_TT/epsilon and P_LT, and the
electric and magnetic generalized polarizabilities (GPs) alpha_E(Q^2) and
beta_M(Q^2) at values of the four-momentum transfer squared Q^2= 0.92 and 1.76
GeV^2. These data, together with the results of VCS experiments at lower
momenta, help building a coherent picture of the electric and magnetic GPs of
the proton over the full measured Q^2-range, and point to their non-trivial
behavior.Comment: version 2: modified according to PRC Editor's and Referee's
recommendations. Archival paper for the E93-050 experiment at JLab Hall A. 28
pages, 23 figures, 5 cross-section tables. To be submitted to Phys.Rev.
New Measurement of Parity Violation in Elastic Electron-Proton Scattering and Implications for Strange Form Factors
We have measured the parity-violating electroweak asymmetry in the elastic
scattering of polarized electrons from the proton. The result is A = -15.05 +-
0.98(stat) +- 0.56(syst) ppm at the kinematic point theta_lab = 12.3 degrees
and Q^2 = 0.477 (GeV/c)^2. The measurement implies that the value for the
strange form factor (G_E^s + 0.392 G_M^s) = 0.025 +- 0.020 +- 0.014, where the
first error is experimental and the second arises from the uncertainties in
electromagnetic form factors. This measurement is the first fixed-target parity
violation experiment that used either a `strained' GaAs photocathode to produce
highly polarized electrons or a Compton polarimeter to continuously monitor the
electron beam polarization.Comment: 8 pages, 4 figures, Tex, elsart.cls; revised version as accepted for
Phys. Lett.
Measurement of the Proton and Deuteron Spin Structure Functions g2 and Asymmetry A2
We have measured the spin structure functions g2p and g2d and the virtual
photon asymmetries A2p and A2d over the kinematic range 0.02 < x < 0.8 and 1.0
< Q^2 < 30(GeV/c)^2 by scattering 38.8 GeV longitudinally polarized electrons
from transversely polarized NH3 and 6LiD targets.The absolute value of A2 is
significantly smaller than the sqrt{R} positivity limit over the measured
range, while g2 is consistent with the twist-2 Wandzura-Wilczek calculation. We
obtain results for the twist-3 reduced matrix elements d2p, d2d and d2n. The
Burkhardt-Cottingham sum rule integral - int(g2(x)dx) is reported for the range
0.02 < x < 0.8.Comment: 12 pages, 4 figures, 1 tabl
Q^2 Evolution of the Neutron Spin Structure Moments using a He-3 Target
We have measured the spin structure functions and of He in a
double-spin experiment by inclusively scattering polarized electrons at
energies ranging from 0.862 to 5.07 GeV off a polarized He target at a
15.5 scattering angle. Excitation energies covered the resonance and
the onset of the deep inelastic regions. We have determined for the first time
the evolution of ,
and for the neutron in the range 0.1 GeV 0.9 GeV with good precision. displays a smooth
variation from high to low . The Burkhardt-Cottingham sum rule holds
within uncertainties and is non-zero over the measured range.Comment: 5 pages, 2 figures, submitted to Phys. Rev. Lett.. Updated Hermes
data in Fig. 2 (top panel) and their corresponding reference. Updated the low
x extrapolation error Fig. 2 (middle panel). Corrected references to ChiPT
calculation
Backward electroproduction of pi0 mesons on protons in the region of nucleon resonances at four momentum transfer squared Q**2 = 1.0 GeV**2
Exclusive electroproduction of pi0 mesons on protons in the backward
hemisphere has been studied at Q**2 = 1.0 GeV**2 by detecting protons in the
forward direction in coincidence with scattered electrons from the 4 GeV
electron beam in Jefferson Lab's Hall A. The data span the range of the total
(gamma* p) center-of-mass energy W from the pion production threshold to W =
2.0 GeV. The differential cross sections sigma_T+epsilon*sigma_L, sigma_TL, and
sigma_TT were separated from the azimuthal distribution and are presented
together with the MAID and SAID parametrizations.Comment: 17 pages, 11 figures, information can be found at
http://hallaweb.jlab.org/experiment/E93-050/vcs.html updated content about
SAID analysis updated MAID results following new reference nucl-th/0310041
updated figure
The Q^2 evolution of the generalized Gerasimov-Drell-Hearn integral for the neutron using a He-3 target
We present data on the inclusive scattering of polarized electrons from a
polarized He-3 target at energies from 0.862 to 5.06 GeV, obtained at a
scattering angle of 15.5 degrees. Our data include measurements from the
quasielastic peak, through the resonance region, to the beginning of the deep
inelastic regime, and were used to determine the spin difference in the virtual
photoabsorption cross section. We extract the extended Gerasimov-Drell-Hearn
integral for the neutron in the range of 4-momentum transfer squared Q^2 of
0.1-0.9 GeV.Comment: 14 pages of text when TeXed in preprint format with figures embedded.
RevTeX format. Three eps figure
Bithiazole Inhibitors of Phosphatidylinositol 4-Kinase (PI4KIIIβ) as Broad-Spectrum Antivirals Blocking the Replication of SARS-CoV-2, Zika Virus, and Human Rhinoviruses
Over half a century since the description of the first antiviral drug, “old” re-emerging viruses and “new” emerging viruses still represent a serious threat to global health. Their high mutation rate and rapid selection of resistance toward common antiviral drugs, together with the increasing number of co-infections, make the war against viruses quite challenging. Herein we report a host-targeted approach, based on the inhibition of the lipid kinase PI4KIIIβ, as a promising strategy for inhibiting the replication of multiple viruses hijacking this protein. We show that bithiazole inhibitors of PI4KIIIβ block the replication of human rhinoviruses (hRV), Zika virus (ZIKV) and SARS-CoV-2 at low micromolar and sub-micromolar concentrations. However, while the anti-hRV/ZIKV activity can be directly linked to PI4KIIIβ inhibition, the role of PI4KIIIβ in SARS-CoV-2 entry/replication is debated
FDG uptake by prosthetic arterial grafts in large vessel vasculitis Is not specific for active disease
OBJECTIVES: This study investigated the incidence and clinical significance of arterial graft-associated uptake of fluorodeoxyglucose in large-vessel vasculitis (LVV). BACKGROUND: The role of (18)F-labeled fluorodeoxyglucose-positron emission tomography/computed tomography ([(18)F]FDG-PET/CT) in the management of LVV remains to be defined. Although [(18)F]FDG uptake at arterial graft sites raises concerns regarding active arteritis or infection, its clinical significance in LVV has never been formally studied. METHODS: An observational prospective study sought to identify patients with Takayasu arteritis (TA) undergoing [(18)F]FDG-PET/CT more than 6 months after graft surgery from a large cohort of patients from 2 tertiary referral centers. [(18)F]FDG uptake by the graft and native arteries was scored on a scale of 0 to 3 relative to hepatic uptake, and periprosthetic maximum standardized uptake value (SUVmax) was calculated. Periprosthetic [(18)F]FDG uptake in active disease was compared with that in inactive disease, and arterial progression was assessed by prospective magnetic resonance angiography (MRA). RESULTS: Twenty-six subjects with TA were enrolled. All were afebrile with negative blood culture. Periprosthetic uptake was significant in 23 of 26 patients, and the mean SUVmax was 4.21 ± 1.46. Median periprosthetic [(18)F]FDG uptake score (3; interquartile range [IQR]: 3 to 3) was higher than in native aorta (1; IQR: 0 to 1; p < 0.001). Graft-specific [(18)F]FDG uptake was unrelated to disease activity. Despite the high frequency of graft-associated [(18)F]FDG uptake, sequential MRAs did not reveal arterial progression in 25 of 26 patients; the 1 remaining case showed minor progression limited to native arteries. Nine patients underwent repeated PET/CT scanning without showing changes in graft-specific uptake, despite increased treatment. CONCLUSIONS: Significant [(18)F]FDG uptake that is confined to arterial graft sites in patients with LVV does not reflect clinically relevant disease activity or progression. To minimize exposure to immunosuppression and in the face of negative blood culture, clinically quiescent arteritis, normal or stably raised C-reactive protein levels, we elected not to escalate treatment and monitor progression with MRA
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