286 research outputs found
Final report of comprehensive testing program for concrete at elevated temperatures
The objective of this program was to define the variations in physical (thermal) and mechanical (strength) properties of limestone aggregate concrete and lightweight insulating concrete exposed to elevated temperatures that could occur as a result of a postulated large sodium spill in a lined LMFBR equipment cell. To meet this objective, five test series were conducted: (1) unconfined compression, (2) shear, (3) rebar bond, (4) sustained loading (creep), and (5) thermal properties. Mechanical property results are presented for concretes subjected to temperature up to 621{sup 0}C (1150{sup 0}F)
The off-shell electromagnetic form factors of pions and kaons in chiral perturbation theory
The off-shell electromagnetic vertex of a (pseudo-) scalar particle contains,
in general, two form factors F and G which depend, in addition to the squared
momentum transfer, on the invariant masses associated with the initial and
final legs of the vertex. Chiral perturbation theory to one loop is used to
calculate the off-shell form factors of pions and kaons. The formalism of
Gasser and Leutwyler, which was previously used to calculate the on-shell limit
of the form factor F, is extended to accommodate the most general form for
off-shell Green's functions in the pseudoscalar meson sector. We find that
chiral symmetry predicts that the form factors F of the charged pions and kaons
go off-shell in the same way, i.e., the off-shell slope at the real photon
point is given by the same new phenomenological constant .
Furthermore, it is shown that at order the form factor F of the
does not show any off-shell dependence. The form factors G are all related to
the form factors F in the correct fashion as required by the Ward-Takahashi
identity. Numerical results for different off-shell kinematics are presented.Comment: TRIUMF preprint TRI-PP-94-4, 25 pages in LaTeX + 10 figures
(uufile'd, compressed PostScript file appended at end, hardcopy available
from authors
Antiproton-nucleus electromagnetic annihilation as a way to access the proton timelike form factors
Contrary to the reaction pbar + p --> e+ e- with a high momentum incident
antiproton on a free target proton at rest, in which the invariant mass M of
the (e+ e-) pair is necessarily much larger than the (pbar p) mass, in the
reaction pbar + d --> n e+ e- the value of M can take values near or below the
(pbar p) mass. In the antiproton-deuteron electromagnetic annihilation, this
allows to access the proton electromagnetic form factors in the time-like
region of q^2 near the (pbar p) threshold. We estimate the cross section
dsigma(pbar +d --> e+ e- n)/dM for an antiproton beam momentum of 1.5 GeV/c. We
find that near the (pbar p) threshold this cross section is about 1 pb/MeV. The
case of heavy nuclei target is also discussed. Elements of experimental
feasibility are presented for the process pbar + d --> n e+ e- in the context
of the Panda project.Comment: 14 pages, 11 figures. submitted to EPJ
The Role of Final State Interactions in Quasielastic Fe Reactions at large
A relativistic finite nucleus calculation using a Dirac optical potential is
used to investigate the importance of final state interactions [FSI] at large
momentum transfers in inclusive quasielastic electronuclear reactions. The
optical potential is derived from first-order multiple scattering theory and
then is used to calculate the FSI in a nonspectral Green's function doorway
approach. At intermediate momentum transfers excellent predictions of the
quasielastic Fe experimental data for the longitudinal response
function are obtained. In comparisons with recent measurements at ~GeV/c the theoretical calculations of give good agreement for
the quasielastic peak shape and amplitude, but place the position of the peak
at an energy transfer of about ~MeV higher than the data.Comment: 13 pages typeset using revtex 3.0 with 6 postscript figures in
accompanying uuencoded file; submitted to Phys. Rev.
Gauge-invariant tree-level photoproduction amplitudes with form factors
We show how the gauge-invariance formulation given by Haberzettl is
implemented in practice for photoproduction amplitudes at the tree level with
form factors describing composite nucleons. We demonstrate that, in contrast to
Ohta's gauge-invariance prescription, this formalism allows electric current
contributions to be multiplied by a form factor, i.e., it does not require that
they be treated like bare currents. While different in detail, this
nevertheless lends support to previous ad hoc approaches which multiply the
Born amplitudes by an overall form factor. Numerical results for kaon
photoproduction off the nucleon are given. They show that the gauge procedure
by Haberzettl leads to much improved values as compared to Ohta's
prescription.Comment: 5 pages, RevTeX, two eps figure
Radiative Corrections to Electron-Proton Scattering
The radiative corrections to elastic electron-proton scattering are analyzed
in a hadronic model including the finite size of the nucleon. For initial
electron energies above 8 GeV and large scattering angles, the proton vertex
correction in this model increases by at least two percent the overall factor
by which the one-photon exchange (Rosenbluth) cross section must be multiplied.
The contribution of soft photon emission is calculated exactly. Comparison is
made with the generally used expressions previously obtained by Mo and Tsai.
Results are presented for some kinematics at high momentum transfer.Comment: 31 pages, 4 figure
A Gauge Invariant Unitary Theory for Pion Photoproduction
A covariant, unitary and gauge invariant theory for pion photoproduction on a
single nucleon is presented. To achieve gauge invariance at the operator level
one needs to include both the and thresholds. The final
amplitude can be written in terms of a distorted wave in the final
channel provided one includes additional diagrams to the standard Born term in
which the photon is coupled to the final state pion and nucleon. These
additional diagrams are required in order to satisfy gauge invariance.Comment: 4 pages, LaTeX, 1 figure as a separate uuencoded compressed tar fil
Neutral Pion Photoproduction on Nuclei in Baryon Chiral Perturbation Theory
Threshold neutral pion photoproduction on light nuclei is studied in the
framework of baryon chiral perturbation theory. We obtain a general formula for
the electric dipole amplitude in the special case of neutral pion
photoproduction on a nucleus. To third order in small momenta, the amplitude is
a sum of 2- and 3-body interactions with no undetermined parameters. With
reasonable input from the single nucleon sector, our result for neutral pion
photoproduction on the deuteron is in agreement with experiment.Comment: 24 pages, 4 uuencoded postscript figures, uses LaTex and epsf.tex.
Added footnote and references. Minor changes in text and forma
Atmospheric CO2 inversion reveals the Amazon as a minor carbon source caused by fire emissions, with forest uptake offsetting about half of these emissions
Compactification near and on the light front
We address problems associated with compactification near and on the light
front. In perturbative scalar field theory we illustrate and clarify the
relationships among three approaches: (1) quantization on a space-like surface
close to a light front; (2) infinite momentum frame calculations; and (3)
quantization on the light front. Our examples emphasize the difference between
zero modes in space-like quantization and those in light front quantization. In
particular, in perturbative calculations of scalar field theory using
discretized light cone quantization there are well-known ``zero-mode induced''
interaction terms. However, we show that they decouple in the continuum limit
and covariant answers are reproduced. Thus compactification of a light-like
surface is feasible and defines a consistent field theory.Comment: 24 pages, 4 figure
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