2,761 research outputs found
Thin-shell wormholes with a generalized Chaplygin gas
In this article, spherically symmetric thin-shell wormholes supported by a
generalized Chaplygin gas are constructed and their stability under
perturbations preserving the symmetry is studied. Wormholes with charge and
with a cosmological constant are analyzed and the results are compared with
those obtained for the original Chaplygin gas, which was considered in a
previous work. For some values of the parameters, one stable configuration is
also present and a new extra unstable solution is found.Comment: 14 pages, 6 figures; v2: typos corrected and minor rewordin
An adaptive non-raster scanning method in atomic force microscopy for simple sample shapes
It is a significant challenge to reduce the scanning time in atomic force microscopy while retaining imaging quality. In this paper, a novel non-raster scanning method for high-speed imaging is presented. The method proposed here is developed for a specimen with the simple shape of a cell. The image is obtained by scanning the boundary of the specimen at successively increasing heights, creating a set of contours. The scanning speed is increased by employing a combined prediction algorithm, using a weighted prediction from the contours scanned earlier, and from the currently scanned contour. In addition, an adaptive change in the height step after each contour scan is suggested. A rigorous simulation test bed recreates the x-y specimen stage dynamics and the cantilever height control dynamics, so that a detailed parametric comparison of the scanning algorithms is possible. The data from different scanning algorithms are compared after the application of an image interpolation algorithm (the Delaunay interpolation algorithm), which can also run on-line.We would like to acknowledge the support of the Engineering
and Physical Sciences Research Council (EPSRC) (grant nos.
EP/I034882/1 & EP/I034831/1)
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plutonium isotopic analysis in the 30 KeV to 210 KeV range
Low-Energy Gamma-ray Spectroscopy (LEGS) is a nondestructive assay (NDA) technique developed in the 1980s. In 1999, it was modified to include a physical-based model for the energy dependent efficiency. It uses the gamma rays in the energy range from approximately 30 keV to 210 keV, except the 100-keV region. This energy region provides intense, well-separated gamma rays from the principal isotopes of plutonium. For applications involving small quantities (mg to g) of freshly separated plutonium in various chemical forms, it is ideally suited for accurate real-time or near real-time isotopic analysis. Since the last modification, LEGS has been incorporated into the FRAM code (Fixed-energy Response-function Analysis with Multiple efficiency), version 4. FRAM v4 is capable of analyzing the peaks in the whole energy range from 30 keV to 1 MeV, including the X-ray region. The new capability of analyzing the peaks in the 100-keV region greatly enhances the plutonium analysis in the 30 keV to 2 10 keV ranges of the traditional LEGS. We now can analyze both the freshly separated and aged plutonium with greater accuracy
Summary of combustion instability research at Princeton University, 1969
Control and causes of combustion instability in rocket engine
Stability of Chaplygin gas thin-shell wormholes
In this paper we construct spherical thin-shell wormholes supported by a
Chaplygin gas. For a rather general class of geometries we introduce a new
approach for the stability analysis of static solutions under perturbations
preserving the symmetry. We apply this to wormholes constructed from
Schwarzschild, Schwarzschild-de Sitter, Schwarzschild-anti de Sitter and
Reissner-Nordstrom metrics. In the last two cases, we find that there are
values of the parameters for which stable static solutions exist.Comment: 14 pages, 5 figures; v2: minor changes and new references added.
Accepted for publication in Physical Review
Strong-field terahertz-optical mixing in excitons
Driving a double-quantum-well excitonic intersubband resonance with a
terahertz (THz) electric field of frequency \omega_{THz} generated terahertz
optical sidebands \omega=\omega_{THz}+\omega_{NIR} on a weak NIR probe. At high
THz intensities, the intersubband dipole energy which coupled two excitons was
comparable to the THz photon energy. In this strong-field regime the sideband
intensity displayed a non-monotonic dependence on the THz field strength. The
oscillating refractive index which gives rise to the sidebands may be
understood by the formation of Floquet states, which oscillate with the same
periodicity as the driving THz field.Comment: 4 pages, 6 figure
Nonlinear Response of a Kondo system: Direct and Alternating Tunneling Currents
Non - equilibrium tunneling current of an Anderson impurity system subject to
both constant and alternating electric fields is studied. A time - dependent
Schrieffer - Wolff transformation maps the time - dependent Anderson
Hamiltonian onto a Kondo one. Perturbation expansion in powers of the Kondo
coupling strength is carried out up to third order, yielding a remarkably
simple analytical expression for the tunneling current. It is found that the
zero - bias anomaly is suppressed by an ac - field. Both dc and the first
harmonic are equally enhanced by the Kondo effect, while the higher harmonics
are relatively small. These results are shown to be valid also below the Kondo
temperature.Comment: 7 pages, RevTeX, 3 PS figures attached, the article has been
significantly developed: time - dependent Schrieffer - Wolff transformation
is presented in the full form, the results are applied to the change in the
direct current induced by an alternating field (2 figures are new
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IMPROVEMENT IN MEASUREMENTS OF PLUTONIUM IN SPENT-FUEL DISSOLVER SOLUTIONS.
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