We study the Bjorken x dependence of the virtual photon spin asymmetry in polarized deep inelastic scattering of electrons from hadrons. We use an exactly solved relativistic potential model of the ...hadron, treating the constituents as independent massless Dirac particles bound to an infinitely massive force center. The potential is chosen to have spin symmetry and a linear radial dependence with spherical symmetry. The effect of interactions of the struck constituent with the remainder of the target on the longitudinal photon asymmetry is demonstrated. In particular, the small-x suppression of the photon asymmetry observed in polarized deep inelastic scattering from the proton is shown to be a consequence of these interactions. The effect of p-wave components of the Dirac wave function, long known to give an important contribution to the spin of hadrons, is explicitly demonstrated through their interference with the s-wave term.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
We compare the elastic-scattering cross sections for electrons and positrons from {sup 208}Pb and {sup 12}C. The results demonstrate that the electron-nucleus interaction can be described to good ...accuracy as a single hard-photon exchange process, and validate the theoretical framework used to interpret electron-scattering data in terms of ground-state charge densities of nuclei.
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The neutron charge form factor G{sub En}(q) is determined from an analysis of the deuteron quadrupole form factor F{sub C2}(q) data. Recent calculations, based on a variety of different model ...interactions and currents, indicate that the contributions associated with the uncertain two-body operators of shorter range are relatively small for F{sub C2}(q), even at large momentum transfer q. Hence, G{sub En}(q) can be extracted from F{sub C2}(q) at large q{sup 2} without undue systematic uncertainties from theory.
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We have perfromed high-precision measurements of {sup 3}He charge and magnetic form factors up to {ital Q}{sup 2}=1 (GeV/{ital c}){sup 2}. These measurements combined with previous data on {sup 3}He ...and {sup 3}H allow us to separate the three-nucleon isospin charge and magnetic form factors up to {ital Q}{sup 2}=1 (GeV/{ital c}){sup 2}. A large discrepancy between experiment and theory occurs for the {ital T}=1 charge form factor.
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Measurements were made at SLAC of the cross section for scattering 29 GeV electrons from carbon at a laboratory angle of 4.5 degrees, corresponding to 0.03
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IJS, IMTLJ, KILJ, KISLJ, NUK, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We address the problem of including Coulomb distortion effects in inclusive quasielastic
(
e
,
e
′
)
reactions using the eikonal approximation. Our results indicate that Coulomb corrections may ...become large for heavy nuclei for certain kinematical regions. The issues of our model are presented in detail and the results are compared to calculations of the Ohio group, where Dirac wave functions were used both for electrons and nucleons. Our results are in good agreement with those obtained by exact calculations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The synthesis of exopolysaccharides as biofilm matrix components by pathogens is a crucial factor for chronic infections and antibiotic resistance. Many periplasmic proteins involved in polymer ...processing and secretion in Gram-negative synthase dependent exopolysaccharide biosynthetic systems have been individually characterized. The operons responsible for the production of PNAG, alginate, cellulose and the Pel polysaccharide each contain a gene that encodes an outer membrane associated tetratricopeptide repeat (TPR) domain containing protein. While the TPR domain has been shown to bind other periplasmic proteins, the functional consequences of these interactions for the polymer remain poorly understood. Herein, we show that the C-terminal TPR region of PgaA interacts with the de-N-acetylase domain of PgaB, and increases its deacetylase activity. Additionally, we found that when the two proteins form a complex, the glycoside hydrolase activity of PgaB is also increased. To better understand structure-function relationships we determined the crystal structure of a stable TPR module, which has a conserved groove formed by three repeat motifs. Tryptophan quenching, mass spectrometry analysis and molecular dynamics simulation studies suggest that the crystallized TPR module can bind PNAG/dPNAG via its electronegative groove on the concave surface, and potentially guide the polymer through the periplasm towards the porin for export. Our results suggest a scaffolding role for the TPR domain that combines PNAG/dPNAG translocation with the modulation of its chemical structure by PgaB.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Measurements were made at SLAC of the cross section for scattering 29 GeV electrons from carbon at a laboratory angle of 4.5°, corresponding to 0.03<
x<0.1 and 1.3<
Q
2<2.7 GeV
2. Values of
R=
σ
L
/
...σ
T
were extracted in this kinematic range by comparing these data to cross sections measured at a higher beam energy by the NMC collaboration. The results are in reasonable agreement with pQCD calculations and with extrapolations of the
R1990 parameterization of previous data. A new fit is made including these data and other recent results.
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IJS, IMTLJ, KILJ, KISLJ, NUK, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We describe an instrument for a fast determination of the beam position of a rastered high-energy electron beam with an intensity as low as 10
nA. Two arrays of stripes of thin metal foils, one in ...the horizontal and one in the vertical direction, are inserted into the beam. They work as a position-sensitive Secondary Emission Monitor (SEM) with a resolution of 1
mm. The charges from the stripes are amplified and converted into position signals using electronics providing a low vibration sensitivity and a fast beam position measurement. At a beam intensity of 10
nA a measurement can be carried out with an integration time of only 130
μs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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