69 research outputs found
Three-Dimensional FDTD Simulation of Biomaterial Exposure to Electromagnetic Nanopulses
Ultra-wideband (UWB) electromagnetic pulses of nanosecond duration, or
nanopulses, have been recently approved by the Federal Communications
Commission for a number of various applications. They are also being explored
for applications in biotechnology and medicine. The simulation of the
propagation of a nanopulse through biological matter, previously performed
using a two-dimensional finite difference-time domain method (FDTD), has been
extended here into a full three-dimensional computation. To account for the UWB
frequency range, a geometrical resolution of the exposed sample was ,
and the dielectric properties of biological matter were accurately described in
terms of the Debye model. The results obtained from three-dimensional
computation support the previously obtained results: the electromagnetic field
inside a biological tissue depends on the incident pulse rise time and width,
with increased importance of the rise time as the conductivity increases; no
thermal effects are possible for the low pulse repetition rates, supported by
recent experiments. New results show that the dielectric sample exposed to
nanopulses behaves as a dielectric resonator. For a sample in a cuvette, we
obtained the dominant resonant frequency and the -factor of the resonator.Comment: 15 pages, 8 figure
Measurement of the Proton's Neutral Weak Magnetic Form Factor
We report the first measurement of the parity-violating asymmetry in elastic
electron scattering from the proton. The asymmetry depends on the neutral weak
magnetic form factor of the proton which contains new information on the
contribution of strange quark-antiquark pairs to the magnetic moment of the
proton. We obtain the value n.m. at
(GeV/c).Comment: 4 pages TEX, text available at
http://www.krl.caltech.edu/preprints/OAP.htm
Qweak: A Precision Measurement of the Proton's Weak Charge
The Qweak experiment at Jefferson Lab aims to make a 4% measurement of the
parity-violating asymmetry in elastic scattering at very low of a
longitudinally polarized electron beam on a proton target. The experiment will
measure the weak charge of the proton, and thus the weak mixing angle at low
energy scale, providing a precision test of the Standard Model. Since the value
of the weak mixing angle is approximately 1/4, the weak charge of the proton
is suppressed in the Standard Model, making it
especially sensitive to the value of the mixing angle and also to possible new
physics. The experiment is approved to run at JLab, and the construction plan
calls for the hardware to be ready to install in Hall C in 2007. The
theoretical context of the experiment and the status of its design are
discussed.Comment: 5 pages, 2 figures, LaTeX2e, to be published in CIPANP 2003
proceeding
Strange Quark Contributions to Parity-Violating Asymmetries in the Backward Angle G0 Electron Scattering Experiment
We have measured parity-violating asymmetries in elastic electron-proton and
quasi-elastic electron-deuteron scattering at Q^2 = 0.22 and 0.63 GeV^2. They
are sensitive to strange quark contributions to currents in the nucleon, and to
the nucleon axial current. The results indicate strange quark contributions of
< 10% of the charge and magnetic nucleon form factors at these four-momentum
transfers. We also present the first measurement of anapole moment effects in
the axial current at these four-momentum transfers.Comment: 5 pages, 2 figures, changed references, typo, and conten
Transverse Beam Spin Asymmetries at Backward Angles in Elastic Electron-Proton and Quasi-elastic Electron-Deuteron Scattering
We have measured the beam-normal single-spin asymmetries in elastic
scattering of transversely polarized electrons from the proton, and performed
the first measurement in quasi-elastic scattering on the deuteron, at backward
angles (lab scattering angle of 108 degrees) for Q2 = 0.22 GeV^2/c^2 and 0.63
GeV^2/c^2 at beam energies of 362 MeV and 687 MeV, respectively. The asymmetry
arises due to the imaginary part of the interference of the two-photon exchange
amplitude with that of single photon exchange. Results for the proton are
consistent with a model calculation which includes inelastic intermediate
hadronic (piN) states. An estimate of the beam-normal single-spin asymmetry for
the scattering from the neutron is made using a quasi-static deuterium
approximation, and is also in agreement with theory
Transverse Beam Spin Asymmetries in Forward-Angle Elastic Electron-Proton Scattering
We have measured the beam-normal single-spin asymmetry in elastic scattering
of transversely-polarized 3 GeV electrons from unpolarized protons at Q^2 =
0.15, 0.25 (GeV/c)^2. The results are inconsistent with calculations solely
using the elastic nucleon intermediate state, and generally agree with
calculations with significant inelastic hadronic intermediate state
contributions. A_n provides a direct probe of the imaginary component of the
2-gamma exchange amplitude, the complete description of which is important in
the interpretation of data from precision electron-scattering experiments.Comment: 5 pages, 3 figures, submitted to Physical Review Letters; shortened
to meet PRL length limit, clarified some text after referee's comment
Measurement of the Electric Form Factor of the Neutron at Q^2=0.5 and 1.0 (GeV/c)^2
The electric form factor of the neutron was determined from measurements of
the \vec{d}(\vec{e},e' n)p reaction for quasielastic kinematics. Polarized
electrons were scattered off a polarized deuterated ammonia target in which the
deuteron polarization was perpendicular to the momentum transfer. The scattered
electrons were detected in a magnetic spectrometer in coincidence with neutrons
in a large solid angle detector. We find G_E^n = 0.0526 +/- 0.0033 (stat) +/-
0.0026 (sys) and 0.0454 +/- 0.0054 +/- 0.0037 at Q^2 = 0.5 and 1.0 (GeV/c)^2,
respectively.Comment: 5 pages, 2 figures, as publishe
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