21,442 research outputs found
A semi-analytic approach to the self induced motion of vortex sheets
The rolling up of the trailing vortex sheet produced by a wing of finite span was calculated as a series expansion in time. For a vorticity distribution corresponding to a wing with cusped tips, the shape of the sheet was found by summing the series using Pade approximants. The sheet remains analytic for some time but ultimately develops an exponential spiral at the tips. The centroid of vorticity was conserved to high accuracy
On the pressure field of nonlinear standing water waves
The pressure field produced by two dimensional nonlinear time and space periodic standing waves was calculated as a series expansion in the wave height. The high order series was summed by the use of Pade approximants. Calculations included the pressure variation at great depth, which was considered to be a likely cause of microseismic activity, and the pressure distribution on a vertical barrier or breakwater
A piezoelectrically actuated ball valve
Bimorph strip composed of two layers of poled piezoelectric ceramic material closes and opens valve. Strip performs like capacitator, allowing initial inrush of current when valve is energized and then only small leakage current flows as valve remains energized
You\u27re Just An Old Fashioned Girlie : Like Your Mother Used to Be
https://digitalcommons.library.umaine.edu/mmb-vp/2504/thumbnail.jp
In The Land Where The Shamrock Grows
https://digitalcommons.library.umaine.edu/mmb-vp/1875/thumbnail.jp
SCD Patterns Have Singular Diffraction
Among the many families of nonperiodic tilings known so far, SCD tilings are
still a bit mysterious. Here, we determine the diffraction spectra of point
sets derived from SCD tilings and show that they have no absolutely continuous
part, that they have a uniformly discrete pure point part on the z-axis, and
that they are otherwise supported on a set of concentric cylinder surfaces
around this axis. For SCD tilings with additional properties, more detailed
results are given.Comment: 11 pages, 2 figures; Accepted for Journal of Mathematical Physic
Photon rockets and gravitational radiation
The absence of gravitational radiation in Kinnersley's ``photon rocket''
solution of Einstein's equations is clarified by studying the mathematically
well-defined problem of point-like photon rockets in Minkowski space (i.e.
massive particles emitting null fluid anisotro\-pically and accelerating
because of the recoil). We explicitly compute the (uniquely defined) {\it
linearized} retarded gravitational waves emitted by such objects, which are the
coherent superposition of the gravitational waves generated by the motion of
the massive point-like rocket and of those generated by the energy-momentum
distribution of the photon fluid. In the special case (corresponding to
Kinnersley's solution) where the anisotropy of the photon emission is purely
dipolar we find that the gravitational wave amplitude generated by the
energy-momentum of the photons exactly cancels the usual gravitational
wave amplitude generated by the accelerated motion of the rocket. More general
photon anisotropies would, however, generate genuine gravitational radiation at
infinity. Our explicit calculations show the compatibility between the
non-radiative character of Kinnersley's solution and the currently used
gravitational wave generation formalisms based on post-Minkowskian perturbation
theory.Comment: 21 pages, LATEX, submitted to Class. Quant. Gra
Convergence of CI single center calculations of positron-atom interactions
The Configuration Interaction (CI) method using orbitals centered on the
nucleus has recently been applied to calculate the interactions of positrons
interacting with atoms. Computational investigations of the convergence
properties of binding energy, phase shift and annihilation rate with respect to
the maximum angular momentum of the orbital basis for the e^+Cu and PsH bound
states, and the e^+-H scattering system were completed. The annihilation rates
converge very slowly with angular momentum, and moreover the convergence with
radial basis dimension appears to be slower for high angular momentum. A number
of methods of completing the partial wave sum are compared, an approach based
on a Delta X_J = a/(J + 1/2)^n + b/(J + 1/2)^(n+1) form (with n = 4 for phase
shift (or energy) and n = 2 for the annihilation rate) seems to be preferred on
considerations of utility and underlying physical justification.Comment: 23 pages preprint RevTeX, 11 figures, submitted to PR
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