659 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 electron-nucleon cross section in reactions
We examine commonly used approaches to deal with the scattering of electrons
from a bound nucleon. Several prescriptions are shown to be related by gauge
transformations. Nevertheless, due to current non-conservation, they yield
different results. These differences reflect the size of the uncertainty that
persists in the interpretation of experiments.Comment: 6 pp (10 in preprint form), ReVTeX, (+ 4 figures, uuencoded
NDE of Thick and Highly Reinforced Concrete Structures: State of the Art
AbstractThe objective of the report is to present the state-of-the art of non-destructive testing methods and technologies for the inspection of thick, heavily-reinforced structures, (e.g. found in nuclear power plants). Wall thicknesses can be in excess of one meter and the structures often have increased steel reinforcement density. The accessibility for any testing method may be limited due to the presence of liners and other components such as cast-in-place items. Testing methods have to provide solutions for tasks such as locating failure (inclusions, corrosion, voids, delaminations) in the structures or the assessment of the condition of the structure in general
Cognitive Information Processing
Contains reports on three research projects.Joint Services Electronics Program (Contract DAAB07-75-C-1346)National Science Foundation (Grant ENG74-24344
Nuclear currents based on the integral form of the continuity equation
We present an approach to obtain new forms of the nuclear electromagnetic
current, which is based on an integral form of the continuity equation. The
procedure can be used to restore current conservation in model calculations in
which the continuity equation is not verified. Besides, it provides, as a
particular result, the so-called Siegert's form of the nuclear current, first
obtained by Friar and Fallieros by extending Siegert's theorem to arbitrary
values of the momentum transfer. The new currents are explicitly conserved and
permit a straightforward analysis of their behavior at both low and high
momentum transfers. The results are illustrated with a simple nuclear model
which includes a harmonic oscillator mean potential.Comment: 19 pages, revtex, plus 2 PS figure
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Primer on Durability of Nuclear Power Plant Reinforced Concrete Structures - A Review of Pertinent Factors
The objective of this study was to provide a primer on the environmental effects that can affect the durability of nuclear power plant concrete structures. As concrete ages, changes in its properties will occur as a result of continuing microstructural changes (i.e., slow hydration, crystallization of amorphous constituents, and reactions between cement paste and aggregates), as well as environmental influences. These changes do not have to be detrimental to the point that concrete will not be able to meet its performance requirements. Concrete, however, can suffer undesirable changes with time because of improper specifications, a violation of specifications, or adverse performance of its cement paste matrix or aggregate constituents under either physical or chemical attack. Contained in this report is a discussion on concrete durability and the relationship between durability and performance, a review of the historical perspective related to concrete and longevity, a description of the basic materials that comprise reinforced concrete, and information on the environmental factors that can affect the performance of nuclear power plant concrete structures. Commentary is provided on the importance of an aging management program
Are Hospital Efficiency and Quality of Care Affordable without External Revenue?
This qualitative study explored strategies academic research hospital administrators in Ontario, Canada, apply to generate nongovernment revenue to remain sustainable. The participants in the study consisted of senior-level academic research hospital executives with extensive experience in the subject area from major academic research hospitals, ranking the hospitals from highest to lowest in revenue generation. From this study, five themes emerged: working within the fiscal reality, the impact of the political environment, the focus on the mission, nongovernment revenue generation, and opportunities for the Ontario academic research hospitals. Findings from this study may contribute to discussions on implementing change by encouraging hospital executives to adopt a more coordinated and consistent approach to generating nongovernment revenue to support the mission of their hospitals
Deep-ultraviolet cavity ringdown spectroscopy
The sensitive optical detection technique of cavity ringdown spectroscopy is extended to the wavelength range 197-204 nm. A novel design narrowband Fourier-transform-limited laser is used, and the technique is applied to gas-phase extinction measurements in CO2, SF6, and O-2. Further demonstration of the system capabilities is given in high-resolution recordings of the Schumann-Runge (0, 0), (1, 0), and (2, 0) bands in O-2. (C) 2004 Optical Society of America
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