| 1. |
- Alcorn, J, et al.
(författare)
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Basic instrumentation for Hall A at Jefferson Lab
- 2004
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 522:3, s. 294-346
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Tidskriftsartikel (refereegranskat)abstract
- The instrumentation in Hall A at the Thomas Jefferson National Accelerator Facility was designed to study electro-and photo-induced reactions at very high luminosity and good momentum and angular resolution for at least one of the reaction products. The central components of Hall A are two identical high resolution spectrometers, which allow the vertical drift chambers in the focal plane to provide a momentum resolution of better than 2 x 10(-4). A variety of Cherenkov counters, scintillators and lead-glass calorimeters provide excellent particle identification. The facility has been operated successfully at a luminosity well in excess of 10(38) CM-2 s(-1). The research program is aimed at a variety of subjects, including nucleon structure functions, nucleon form factors and properties of the nuclear medium. (C) 2003 Elsevier B.V. All rights reserved.
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| 2. |
- Wijesooriya, K, et al.
(författare)
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Polarization measurements in high-energy deuteron photodisintegration
- 2001
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 86:14, s. 2975-2979
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Tidskriftsartikel (refereegranskat)abstract
- We present measurements of the recoil proton polarization for the d(γ⃗,p⃗)n reaction at θc.m. = 90° for photon energies up to 2.4 GeV. These are the first data in this reaction for polarization transfer with circularly polarized photons. The induced polarization py vanishes above 1 GeV, contrary to meson-baryon model expectations, in which resonances lead to large polarizations. However, the polarization transfer Cx does not vanish above 1 GeV, inconsistent with hadron helicity conservation. Thus, we show that the scaling behavior observed in the d(γ,p)ncross sections is not a result of perturbative QCD. These data should provide important tests of new nonperturbative calculations in the intermediate energy regime.
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| 3. |
- Schulte, EC, et al.
(författare)
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High energy angular distribution measurements of the exclusive deuteron photodisintegration reaction
- 2002
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Ingår i: Physical Review C (Nuclear Physics). - : American Physical Society. - 0556-2813 .- 1089-490X. ; 66:4
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Tidskriftsartikel (refereegranskat)abstract
- The first complete measurements of the angular distributions of the two-body deuteron photodisintegration differential cross section at photon energies above 1.6 GeV were performed at the Thomas Jefferson National Accelerator Facility. The results show a persistent forward-backward asymmetry up to E-gamma=2.4 GeV, the highest-energy measured in this experiment. The Hard Rescattering and the Quark-Gluon string models are in fair agreement with the results.
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| 4. |
- Wijesooriya, K, et al.
(författare)
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Polarization measurements in neutral pion photoproduction
- 2002
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 66:3
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Tidskriftsartikel (refereegranskat)abstract
- We present measurements of the recoil proton polarization for the H-1((γ) over right arrow,(p) over right arrow)pi(0) reaction for theta(c.m.)(pi) = 60degrees-135degrees and for photon energies up to 4.1 GeV. These are the first data in this reaction for polarization transfer with circularly polarized photons. Various theoretical models are compared with the results. No evidence for hadron helicity conservation is observed. Models that employ factorization are not favored. It appears from the strong angular dependence of the induced polarization at photon energies of 2.5 and 3.1 GeV that a relatively high spin resonance or background amplitude might exist in this energy region.
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| 5. |
- Ulmer, PE, et al.
(författare)
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H-2(e,e ' p)n reaction at high recoil momenta
- 2002
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Ingår i: Physical Review Letters. - 1079-7114. ; 89:6
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Tidskriftsartikel (refereegranskat)abstract
- The 2H(e,e(')p)n cross section was measured in Hall A of the Thomas Jefferson National Accelerator Facility near the top of the quasielastic peak (x(Bj)=0.964) at a four-momentum transfer squared, Q(2)=0.665 (GeV/c) (2) (omega=0.368 GeV, W=2.057 GeV), and for recoil momenta up to 550 MeV/c. The measured cross section deviates by 1-2sigma from a state-of-the-art calculation at low recoil momenta. At high recoil momenta the cross section is well described by the same calculation; however, in this region, final-state interactions and interaction currents are predicted to be large, and alternative choices of nucleon-nucleon potential and nucleon current operator may result in significant spread in the calculations.
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| 6. |
- Wang, S. Y., et al.
(författare)
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High-spin level scheme of Cs-126
- 2004
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Ingår i: Gaoneng wuli yu he wuli. - 0254-3052. ; 28:5, s. 491-494
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Tidskriftsartikel (refereegranskat)abstract
- High-spin states of Cs-126 have been populated via the Cd-116(N-14, 4n) Cs-126 reaction. The experiment was performed at Niels Bohr Institute in Denmark in 1991. After careful data analysis, most of the previously-known bands have been pushed up to much higher spins and 3 new rotational sequences have been identified. Spin, parity and configuration assignments are tentatively proposed for all of the observed bands.
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| 7. |
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| 8. |
- Bruton, Joseph D., et al.
(författare)
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Ryanodine receptors of pancreatic beta-cells mediate a distinct context-dependent signal for insulin secretion
- 2003
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Ingår i: The FASEB Journal. - : Wiley. - 0892-6638 .- 1530-6860. ; 17:2, s. 301-303
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Tidskriftsartikel (refereegranskat)abstract
- The ryanodine (RY) receptors in beta-cells amplify signals by Ca2+-induced Ca2+ release (CICR). The role of CICR in insulin secretion remains unclear in spite of the fact that caffeine is known to stimulate secretion. This effect of caffeine is attributed solely to the inhibition of cAMP-phosphodiesterases (cAMP-PDEs). We demonstrate that stimulation of insulin secretion by caffeine is due to a sensitization of the RY receptors. The dose-response relationship of caffeine-induced inhibition of cAMP-PDEs was not correlated with the stimulation of insulin secretion. Sensitization of the RY receptors stimulated insulin secretion in a context-dependent manner, that is, only in the presence of a high concentration of glucose. This effect of caffeine depended on an increase in [Ca2+]i. Confocal images of beta-cells demonstrated an increase in [Ca2+]i induced by caffeine but not by forskolin. 9-Methyl-7-bromoeudistomin D (MBED), which sensitizes RY receptors, did not inhibit cAMP-PDEs, but it stimulated secretion in a glucose-dependent manner. The stimulation of secretion by caffeine and MBED involved both the first and the second phases of secretion. We conclude that the RY receptors of beta-cells mediate a distinct glucose-dependent signal for insulin secretion and may be a target for developing drugs that will stimulate insulin secretion only in a glucose-dependent manner.
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| 9. |
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| 10. |
- Kocevski, D., et al.
(författare)
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Search for relativistic curvature effects in gamma-ray burst pulses
- 2003
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 596:1, s. 389-400
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Tidskriftsartikel (refereegranskat)abstract
- We analyze the time profiles of individual gamma-ray burst (GRB) pulses that are longer than 2 s by modeling them with analytical functions that are based on physical first principles and well-established empirical descriptions of GRB spectral evolution. These analytical profiles are independent of the emission mechanism and can be used to model both the rise and decay profiles, allowing for the study of the entire pulse light curve. Using this method, we have studied a sample of 77 individual GRB pulses, allowing us to examine the fluence, pulse width, asymmetry, and rise and decay power-law distributions. We find that the rise phase is best modeled with a power law of average index r=1.48+/-0.07 and that the average decay phase has an index of d=2.44+/-0.12. We also find that the ratio between the rise and decay times (the pulse asymmetry) exhibited by the GRB pulse shape has an average value of 0.47, which varies little from pulse to pulse and is independent of pulse duration or intensity. Although this asymmetry is largely uncorrelated to other pulse properties, a statistically significant trend is observed between the pulse asymmetry and the decay power-law index, possibly hinting at the underlying physics. We compare these parameters with those predicted to occur if individual pulse shapes are created purely by relativistic curvature effects in the context of the fireball model, a process that makes specific predictions about the shape of GRB pulses. The decay index distribution obtained from our sample shows that the average GRB pulse fades faster than the value predicted by curvature effects, with only 39% of our sample being consistent with the curvature model. We discuss several refinements of the relativistic curvature scenario that could naturally account for these observed deviations, such as symmetry breaking and varying relative timescales within individual pulses.
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