36,477 research outputs found
The Levi-Civita spacetime as a limiting case of the Gamma spacetime
It is shown that the Levi-Civita metric can be obtained from a family of the
Weyl metric, the Gamma metric, by taking the limit when the length of its
Newtonian image source tends to infinity. In this process a relationship
appears between two fundamental parameters of both metrics.Comment: LaTeX2e 17 page
Unified line profiles for hydrogen perturbed by collisions with protons: satellites and asymmetries
We present new calculations of unified line profiles for hydrogen perturbed
by collisions with protons. We report on new calculations of the potential
energies and dipole moments which allow the evaluation of profiles for the
lines of the Lyman series up to Lyman and the Balmer series up to
Balmer10. Unified calculations only existed for the lines Lyman to
Lyman and Balmer including the H quasi-molecule. These
data are available as online material accompanying this paper and should be
included in atmosphere models, in place of the Stark effect of protons, since
the quasi-molecular contributions cause not only satellites, but large
asymmetries that are unaccounted for in models that assume Stark broadening of
electrons and protons are equal.Comment: 13 pages, 25 figures. Accepted for publication in MNRA
Spatial Coherence Resonance near Pattern-Forming Instabilities
The analogue of temporal coherence resonance for spatial degrees of freedom
is reported. Specifically, we show that spatiotemporal noise is able to
optimally extract an intrinsic spatial scale in nonlinear media close to (but
before) a pattern-forming instability. This effect is observed in a model of
pattern-forming chemical reaction and in the Swift-Hohenberg model of fluid
convection. In the latter case, the phenomenon is described analytically via an
approximate approach.Comment: 4 pages, 4 figure
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