249 research outputs found
Spectral and electroluminescent properties of coordination compounds of terbium (III) with ibuprofen (in solid form, chloroform solutions, and polyvinylcarbazole films)
Spectral properties of terbium (III) complexes with composition of TbL3DL, where L is an anion of d,l-2-(4-isobutylphenyl)propanoic acid (ibuprofen) and DL is 2,2âČ-dipyridyl (Dipy), 1,10-phenanthroline (Phen), or triphenylphosphine oxide (TPPO), have been studied in a solid form, chloroform solutions, and polyvinylcarbazole (PVC) films. It has been demonstrated that, in PVC films, occupation of the emitting level of terbium (III) involves the participation of polymer. The emission decay lifetimes of terbium in the chloroform solutions and PVC films have been measured. The possibility of the appearance of electroluminescence of complexes in PVC films has been studied
Bioinformatics advances in saliva diagnostics
There is a need recognized by the National Institute of Dental & Craniofacial Research and the National Cancer Institute to advance
basic, translational and clinical saliva research. The goal of the Salivaomics Knowledge Base (SKB) is to create a data management system and web resource constructed to support human salivaomics research. To maximize the utility of the SKB for retrieval,
integration and analysis of data, we have developed the Saliva Ontology and SDxMart. This article reviews the informatics advances in saliva diagnostics made possible by the Saliva Ontology and SDxMart
Search for pentaquark in high statistics measurement of at CLAS
The exclusive reaction was studied in the
photon energy range between 1.6-3.8 GeV searching for evidence of the exotic
baryon . The decay to requires the assignment of
strangeness to any observed resonance. Data were collected with the CLAS
detector at the Thomas Jefferson National Accelerator Facility corresponding to
an integrated luminosity of 70 . No evidence for the
pentaquark was found. Upper limits were set on the production cross section as
function of center-of-mass angle and mass. The 95% CL upper limit on the
total cross section for a narrow resonance at 1540 MeV was found to be 0.8 nb.Comment: Submitted to Physical Review Letter
Measurement of Deeply Virtual Compton Scattering with a Polarized Proton Target
The longitudinal target-spin asymmetry A_UL for the exclusive
electroproduction of high energy photons was measured for the first time in
p(e,e'p\gamma). The data have been accumulated at Jefferson Lab with the CLAS
spectrometer using 5.7 GeV electrons and a longitudinally polarized NH_3
target. A significant azimuthal angular dependence was observed, resulting from
the interference of the Deeply Virtual Compton Scattering and Bethe-Heitler
processes. The amplitude of the sin(phi) moment is 0.252 +/- 0.042(stat) +/-
0.020(sys). Theoretical calculations are in good agreement with the magnitude
and the kinematic dependence of the target-spin asymmetry, which is sensitive
to the generalized parton distributions H and H-tilde.Comment: Modified text slightly, added reference
Light Vector Mesons in the Nuclear Medium
The light vector mesons (, , and ) were produced in
deuterium, carbon, titanium, and iron targets in a search for possible
in-medium modifications to the properties of the meson at normal nuclear
densities and zero temperature. The vector mesons were detected with the CEBAF
Large Acceptance Spectrometer (CLAS) via their decays to . The rare
leptonic decay was chosen to reduce final-state interactions. A combinatorial
background was subtracted from the invariant mass spectra using a
well-established event-mixing technique. The meson mass spectrum was
extracted after the and signals were removed in a nearly
model-independent way. Comparisons were made between the mass spectra
from the heavy targets () with the mass spectrum extracted from the
deuterium target. With respect to the -meson mass, we obtain a small
shift compatible with zero. Also, we measure widths consistent with standard
nuclear many-body effects such as collisional broadening and Fermi motion.Comment: 15 pages, 18 figures, 3 table
Measurement of the Polarized Structure Function for in the Resonance Region
The polarized longitudinal-transverse structure function
has been measured using the reaction in the
resonance region at and 0.65 GeV. No previous
data exist for this reaction channel. The kinematically
complete experiment was performed at Jefferson Lab with the CEBAF Large
Acceptance Spectrometer (CLAS) using longitudinally polarized electrons at an
energy of 1.515 GeV. A partial wave analysis of the data shows generally better
agreement with recent phenomenological models of pion electroproduction
compared to the previously measured channel. A fit to both
and channels using a unitary isobar model suggests the unitarized
Born terms provide a consistent description of the non-resonant background. The
-channel pion pole term is important in the channel through a
rescattering correction, which could be model-dependent.Comment: 6 pages, LaTex, 5 eps figures: Submitted to PRC/Brief Reports v2:
Updated referenc
Search for medium modification of the meson
The photoproduction of vector mesons on various nuclei has been studied using
the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Laboratory. The
vector mesons, , , and , are observed via their decay to
, in order to reduce the effects of final state interactions in the
nucleus. Of particular interest are possible in-medium effects on the
properties of the meson. The spectral function is extracted from
the data on various nuclei, carbon, iron, and titanium, and compared to the
spectrum from liquid deuterium, which is relatively free of nuclear effects. We
observe no significant mass shift for the meson; however, there is some
widening of the resonance in titanium and iron, which is consistent with
expected collisional broadening.Comment: 8 pages, 4 figure
Deeply virtual and exclusive electroproduction of omega mesons
The exclusive omega electroproduction off the proton was studied in a large
kinematical domain above the nucleon resonance region and for the highest
possible photon virtuality (Q2) with the 5.75 GeV beam at CEBAF and the CLAS
spectrometer. Cross sections were measured up to large values of the
four-momentum transfer (-t < 2.7 GeV2) to the proton. The contributions of the
interference terms sigma_TT and sigma_TL to the cross sections, as well as an
analysis of the omega spin density matrix, indicate that helicity is not
conserved in this process. The t-channel pi0 exchange, or more generally the
exchange of the associated Regge trajectory, seems to dominate the reaction
gamma* p -> omega p, even for Q2 as large as 5 GeV2. Contributions of handbag
diagrams, related to Generalized Parton Distributions in the nucleon, are
therefore difficult to extract for this process. Remarkably, the high-t
behaviour of the cross sections is nearly Q2-independent, which may be
interpreted as a coupling of the photon to a point-like object in this
kinematical limit.Comment: 15 pages,19 figure
Q^2 Dependence of the S_{11}(1535) Photocoupling and Evidence for a P-wave resonance in eta electroproduction
New cross sections for the reaction are reported for total
center of mass energy =1.5--2.3 GeV and invariant squared momentum transfer
=0.13--3.3 GeV. This large kinematic range allows extraction of new
information about response functions, photocouplings, and coupling
strengths of baryon resonances. A sharp structure is seen at 1.7 GeV.
The shape of the differential cross section is indicative of the presence of a
-wave resonance that persists to high . Improved values are derived for
the photon coupling amplitude for the (1535) resonance. The new data
greatly expands the range covered and an interpretation of all data with
a consistent parameterization is provided.Comment: 31 pages, 9 figure
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