351 research outputs found
Local gauge invariance implies Siegert's hypothesis
The nonrelativistic Ward-Takahashi identity, a consequence of local gauge
invariance in quantum mechanics, shows the necessity of exchange current
contributions in case of nonlocal and/or isospin-dependent potentials. It also
implies Siegert's hypothesis: in the nonrelativistic limit, two-body charge
densities identically vanish. Neither current conservation, which follows from
global gauge invariance, nor the constraints of (lowest order) relativity are
sufficient to arrive at this result. Furthermore, a low-energy theorem for
exchange contributions is established.Comment: 5 pages, REVTE
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
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Concrete containment aging study
In 1989, IAEA initiated a pilot study on the management of aging of nuclear power plant components. The Phase I and II studies of concrete containment are discussed. With the data base, plant owners will be able to review and enhance their existing programs. IAEA will analyze data provided by participating plants and the report is scheduled to be released by late 1994 (final report release mid-1995)
Electromagnetic form factors of the bound nucleon
We calculate electromagnetic form factors of the proton bound in specified
orbits for several closed shell nuclei. The quark structure of the nucleon and
the shell structure of the finite nuclei are given by the QMC model. We find
that orbital electromagnetic form factors of the bound nucleon deviate
significantly from those of the free nucleon.Comment: 12 pages including 4 ps figure
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)
QCD near the Light Cone
Starting from the QCD Lagrangian, we present the QCD Hamiltonian for near
light cone coordinates. We study the dynamics of the gluonic zero modes of this
Hamiltonian. The strong coupling solutions serve as a basis for the complete
problem. We discuss the importance of zero modes for the confinement mechanism.Comment: 32 pages, ReVTeX, 2 Encapsulated PostScript figure
Assessment of Aging of Nuclear Power Plant Civil Structures
ABSTRACT Research is being conducted by ORNL for the USNRC to address aging of civil structures in light-water reactor plants. The importance and operating experience of nuclear power plant (NPP) civil structures is reviewed. Factors that can lead to age-related degradation of reinforced concrete structures and containment metallic pressure boundaries (i.e., steel containments and liners of reinforced concrete containments) are identified and their manifestations described. Background information and data for improving and developing methods to assess the effects of age-related degradation on structural performance are provided. Techniques for detection of degradation are reviewed and research related to development of methods for inspection of inaccessible regions of the containment pressure boundary presented. Application of structural reliability analysis methods to develop condition assessment tools and guidelines is described
Relativistic Effects in the Electromagnetic Current at GeV Energies
We employ a recent approach to the non-relativistic reduction of the
electromagnetic current operator in calculations of electronuclear reactions.
In contrast to the traditional scheme, where approximations are made for the
transferred momentum, transferred energy and initial momentum of the struck
nucleon in obtaining an on-shell inspired form for the current, we treat the
problem exactly for the transferred energy and transferred momentum. We
calculate response functions for the reaction at CEBAF (TJNAF)
energies and find large relativistic corrections. We also show that in Plane
Wave Impulse Approximation, it is always possible to use the full operator, and
we present a comparison of such a limiting case with the results incorporating
relativistic effects to the first order in the initial momentum of the struck
nucleon.Comment: 31 pages, 8 figures, Revte
Transverse QCD Dynamics Near the Light Cone
Starting from the QCD Hamiltonian in near-light cone coordinates, we study
the dynamics of the gluonic zero modes. Euclidean 2+1 dimensional lattice
simulations show that the gap at strong coupling vanishes at intermediate
coupling. This result opens the possibility to synchronize the continuum limit
with the approach to the light cone.Comment: 15 pages, LaTeX, 3 figures (7 PS files
Strongly linked current flow in polycrystalline forms of the new superconductor MgB2
The discovery of superconductivity at 39 K in MgB2[1] raises many issues. One
of the central questions is whether this new superconductor resembles a
high-temperature-cuprate superconductor or a low-temperature metallic
superconductor in terms of its current carrying characteristics in applied
magnetic fields. In spite of the very high transition temperatures of the
cuprate superconductors, their performance in magnetic fields has several
drawbacks[2]. Their large anisotropy restricts high bulk current densities to
much less than the full magnetic field-temperature (H-T) space over which
superconductivity is found. Further, weak coupling across grain boundaries
makes transport current densities in untextured polycrystalline forms low and
strongly magnetic field sensitive[3,4]. These studies of MgB2 address both
issues. In spite of the multi-phase, untextured, nano-scale sub-divided nature
of our samples, supercurrents flow throughout without the strong sensitivity to
weak magnetic fields characteristic of Josephson-coupled grains[3].
Magnetization measurements over nearly all of the superconducting H-T plane
show good temperature scaling of the flux pinning force, suggestive of a
current density determined by flux pinning. At least two length scales are
suggested by the magnetization and magneto optical (MO) analysis but the cause
of this seems to be phase inhomogeneity, porosity, and minority insulating
phase such as MgO rather than by weakly coupled grain boundaries. Our results
suggest that polycrystalline ceramics of this new class of superconductor will
not be compromised by the weak link problems of the high temperature
superconductors, a conclusion with enormous significance for applications if
higher temperature analogs of this compound can be discovered
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