The charge form factor of 4He has been extracted in the range 29 fm(-2) ≤ Q2 ≤ 77 fm(-2) from elastic electron scattering, detecting 4He recoil nuclei and electrons in coincidence with the high ...resolution spectrometers of the Hall A Facility of Jefferson Lab. The measurements have uncovered a second diffraction minimum for the form factor, which was predicted in the Q2 range of this experiment. The data are in qualitative agreement with theoretical calculations based on realistic interactions and accurate methods to solve the few-body problem.
Schwann cells express the low-affinity neurotrophin receptor (p75), but no role for either the neurotrophins or their cognate receptors in Schwann cell development has been established. We have found ...that Schwann cells isolated from postnatal day 1 (P1) or P2 mice that were p75-deficient exhibited potentiated survival compared to wild-type cells after growth factor and serum withdrawal. There was, however, no disparity in the survival of p75-deficient and wild-type Schwann cells isolated at embryonic day 15, suggesting that the death-inducing effects of p75 are developmentally regulated. A comparable degree of cell death was also observed in the sciatic nerves of both wild-type and p75-deficient mice at P1. However, 24 hr after axotomy, there was a 13-fold increase in the percentage of apoptotic nuclei in the distal nerve stumps of the transected sciatic nerves of neonatal wild-type but not p75-deficient mice. The expression of both the p75 and nerve growth factor (NGF) genes was upregulated after axotomy in neonatal wild-type nerves. Collectively, these results suggest that NGF-mediated activation of p75 is likely to be an important mediator of Schwann cell apoptosis in the context of peripheral nerve injury.
A review of the elastic form factors of the proton and neutron in the space-like region is presented. A summary of the results of the pioneering elastic electron-nucleon scattering experiments and ...their interpretation is given along with a theoretical background. Recent results from Rosenbluth separations and experiments using polarized beams and polarized targets or recoil nucleon polarimeters are summarized. Future prospects for extending or improving the present measurements are outlined.
Crystals of Ha-Ras p21 with caged GTP at the active site have been used to investigate the conformational changes of p21 on GTP hydrolysis. The structure of the short-lived p21.GTP complex was ...determined by Laue diffraction methods. After GTP hydrolysis, substantial structural changes occur in the parts of the molecule implicated in the interaction with GTPase-activating protein. The trigger for this process seems to be a change in coordination of the active-site Mg2+ ion as a result of loss of the gamma-phosphate of GTP.
The spin structure function of the neutron ital gsub 1sup ital n has been determined over the range 0.03ltital xlt0.6 at an average ital Qsup 2 of 2 (GeV/ital c)sup 2 by measuring the asymmetry in ...deep inelastic scattering of polarized electrons from a polarized sup 3He target at energies between 19 and 26 GeV. The integral of the neutron spin structure function is found to be integralsub 0sup 1ital gsub 1sup ital n(ital x)ital dx=minus0.022plus minus0.011. Earlier reported proton results together with the Bjorken sum rule predict integralsub 0sup 1ital gsub 1sup ital n(ital x)ital dx=minus0.059plus minus0.019.
We have measured proton and deuteron virtual photon-nucleon asymmetries A{sup p}{sub 2} and A{sup d}{sub 2} and structure functions g{sup p}{sub 2} and g{sup d}{sub 2} over the range 0.03 < x < 0.8 ...and 1.3 < Q{sup 2} < 10 (GeV/c){sup 2} by inelastically scattering polarized electrons off polarized ammonia targets. Results for A{sub 2} are significantly smaller than the positivity limit (sqrt)R for both targets. Within experimental precision the g{sub 2} data are well described by the twist-2 contribution, g{sup ww}{sub 2}. Twist-3 matrix elements have been extracted and are compared to theoretical predictions.
The purification scheme of chitinase A (ChiA) from S. marcescens has been extensively revised. The pure enzyme crystallizes readily under new crystallization conditions. The ChiA crystal structure ...has been refined to 1.55 Å resolution and the crystal structure of ChiA co‐crystallized with the inhibitor allosamidin has been refined to 1.9 Å resolution. Allosamidin is located in the deep active‐site tunnel of ChiA and interacts with three important residues: Glu315, the proton donor of the catalysis, Asp313, which adopts two conformations in the native structure but is oriented towards Glu315 in the inhibitor complex, and Tyr390, which lies opposite Glu315 in the active‐site tunnel.
The charge and magnetic form factors, F_{C} and F_{M}, respectively, of ^{3}He are extracted in the kinematic range 25 fm^{-2}≤Q^{2}≤61 fm^{-2} from elastic electron scattering by detecting ^{3}He ...recoil nuclei and scattered electrons in coincidence with the two High Resolution Spectrometers of the Hall A Facility at Jefferson Lab. The measurements find evidence for the existence of a second diffraction minimum for the magnetic form factor at Q^{2}=49.3 fm^{-2} and for the charge form factor at Q^{2}=62.0 fm^{-2}. Both minima are predicted to exist in the Q^{2} range accessible by this Jefferson Lab experiment. The data are in qualitative agreement with theoretical calculations based on realistic interactions and accurate methods to solve the three-body nuclear problem.
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 〈
...θ
lab〉=12.3° and 〈
Q
2〉=0.477 (GeV/
c)
2. Both errors are a factor of two smaller than those of the result reported previously. The value for the strange form factor extracted from the data is
(G
s
E+0.392
G
s
M)=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.
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