135,362 research outputs found
Modified faceplate assembly for stud-welding gun
Ventilated barrel assembly aids installation of studs on narrow uneven weld lands. The modified faceplate permits proper aligning of the percussion stud-welding gun in any position and on a smaller surface, and it maintains gap setting without any other adjustment
Charged particle modification of surfaces in the outer solar system
Voyager reflectance spectra data have indicated clear leading/trailing differences in the albedo of the icy Galilean and Saturian satellites. For the Galilean satellites, these have been analyzed by Nelson, et al. and, more recently, by McEwen. They have described the longitudinal dependence of this data and attempted to interpret this in terms of plasma and meteorite modification of the surface. Primary attention has been paid to Europa at which the leading/trailing differences are the largest. This data was reanalyzed extracting the single grain albedo (w) and constructing the Espat-function, W = (1-w)/w from this. Because w is near unity, W is approximately 2(alpha)D where alpha is the absorption coefficient and D is the grain size. In doing so, a direct comparison to the longitudinal plasma bombardment flux was found for the first time. This occurs primarily in the UV and is probably due to an absorption associated with implanted S, as the UV band of Voyager overlaps the IUE data of Lane et al. The relative importance of grain size effects and implant impurity effects can now be studied
Lagrangian circulation study near Cape Henry, Virginia
A study of the circulation near Cape Henry, Virginia, was made using surface and seabed drifters and radar tracked surface buoys coupled to subsurface drag plates. Drifter releases were conducted on a line normal to the beach just south of Cape Henry. Surface drifter recoveries were few; wind effects were strongly noted. Seabed drifter recoveries all exhibited onshore motion into Chesapeake Bay. Strong winds also affected seabed recoveries, tending to move them farther before recovery. Buoy trajectories in the vicinity of Cape Henry appeared to be of an irrotational nature, showing a clockwise rotary tide motion. Nearest the cape, the buoy motion elongated to almost parallel depth contours around the cape. Buoy motion under the action of strong winds showed that currents to at least the depth of the drag plates substantially are altered from those of low wind conditions near the Bay mouth. Only partial evidence could be found to support the presence of a clockwise nontidal eddy at Virginia Beach, south of Cape Henry
Charged-particle induced alterations of surfaces in the outer solar system
Researchers calculated the plasma bombardment profiles of the surfaces of the icy Saturnian satellites in order to interpret reflection spectra and the effect of charged particles on the surfaces (mantles) of Pluto and of comets in the Oort cloud. Pluto's exposure to cosmic rays results in a slow alteration of the reflectance if the methane condensed on its surface. The UV absorbed in the atmosphere can produce precipitates. The researchers showed that, depending on the rates of the competing regolith processes and rates for replenishment of the methane, the surface can appear bright, red, or dark. Using laboratory data, they showed that the amount of darkening occurring in one orbit is small. Therefore, transport, burial, and re-exposure of organic sediments must control the reflectance, and the average reflectance is established by the radiation altered species accumulated over many orbits with the observed spatial, and possible temporal, differences in albedo due to transport. The cosmic rays, although producing changes in reflectance slowly, do so inevitably. Therefore, the fact that the surface is not dark everywhere implies that it is active and the exposure rates vs. depth into the surface of Pluto can be used to constrain turnover rates. Comets in the Oort cloud experience similar rates
Drogue performance evaluation. Part 1: Data acquisition
Surface buoy/subsurface drogue drag coupling was investigated. Data acquisition methods and techniques derived from several experimental cruises on the Chesapeake Bay are presented. Four buoys were utilized: three coupled to steel plates rigidly attached to each other at right angles and at various depths; and one spar type that did not require drag plates. Data from these surface floats and the drogue depth combinations were processed. Errors in tracking the surface buoys are discussed
Collapse and revival dynamics of superfluids of ultracold atoms in optical lattices
Recent experiments have shown a remarkable number of collapse-and-revival
oscillations of the matter-wave coherence of ultracold atoms in optical
lattices [Will et al., Nature 465, 197 (2010)]. Using a mean-field
approximation to the Bose-Hubbard model, we show that the visibility of
collapse-and-revival interference patterns reveal number squeezing of the
initial superfluid state. To describe the dynamics, we use an effective
Hamiltonian that incorporates the intrinsic two-body and induced three-body
interactions, and we analyze in detail the resulting complex pattern of
collapse-and-revival frequencies generated by virtual transitions to higher
bands, as a function of lattice parameters and mean-atom number. Our work shows
that a combined analysis of both the multiband, non-stationary dynamics in the
final deep lattice, and the number-squeezing of the initial superfluid state,
explains important characteristics of optical lattice collapse-and-revival
physics. Finally, by treating the two- and three-body interaction strengths,
and the coefficients describing the initial superposition of number states, as
free parameters in a fit to the experimental data it should be possible to go
beyond some of the limitations of our model and obtain insight into the
breakdown of the mean-field theory for the initial state or the role of
nonperturbative effects in the final state dynamics.Comment: 5 pages, 5 figures. This is the updated version published June 201
Orbital stability of periodic waves in the class of reduced Ostrovsky equations
Periodic travelling waves are considered in the class of reduced Ostrovsky
equations that describe low-frequency internal waves in the presence of
rotation. The reduced Ostrovsky equations with either quadratic or cubic
nonlinearities can be transformed to integrable equations of the Klein--Gordon
type by means of a change of coordinates. By using the conserved momentum and
energy as well as an additional conserved quantity due to integrability, we
prove that small-amplitude periodic waves are orbitally stable with respect to
subharmonic perturbations, with period equal to an integer multiple of the
period of the wave. The proof is based on construction of a Lyapunov
functional, which is convex at the periodic wave and is conserved in the time
evolution. We also show numerically that convexity of the Lyapunov functional
holds for periodic waves of arbitrary amplitudes.Comment: 34 page
Laboratory studies of the interaction of ions with condensed gases: Planetary applications
The work described is concerned with laboratory studies of the processes that produce the ejection of molecules from the surfaces of condensed gas solids, the change in the chemistry of the surface materials, and the relationship of these results to processes occurring in the solar system. Included is a discussion of the experimental techniques employed in making these laboratory measurements
The braiding for representations of q-deformed affine
We compute the braiding for the `principal gradation' of for from first principles, starting from the idea of a rigid
braided tensor category. It is not necessary to assume either the crossing or
the unitarity condition from S-matrix theory. We demonstrate the uniqueness of
the normalisation of the braiding under certain analyticity assumptions, and
show that its convergence is critically dependent on the number-theoretic
properties of the number in the deformation parameter . We also examine the convergence using probability, assuming a uniform
distribution for on the unit circle.Comment: LaTeX, 10 pages with 2 figs, uses epsfi
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