13,271 research outputs found
Relaxation to magnetohydrodynamics equilibria via collision brackets
Metriplectic dynamics is applied to compute equilibria of fluid dynamical
systems. The result is a relaxation method in which Hamiltonian dynamics
(symplectic structure) is combined with dissipative mechanisms (metric
structure) that relaxes the system to the desired equilibrium point. The
specific metric operator, which is considered in this work, is formally
analogous to the Landau collision operator. These ideas are illustrated by
means of case studies. The considered physical models are the Euler equations
in vorticity form, the Grad-Shafranov equation, and force-free MHD equilibria.Comment: Conference Proceeding (Theory of Fusions Plasmas, 2018), 9 pages, 8
figure
Gravitational Field of Spherical Branes
The warped solution of Einstein's equations corresponding to the spherical
brane in five-dimensional AdS is considered. This metric represents interiors
of black holes on both sides of the brane and can provide gravitational
trapping of physical fields on the shell. It is found the analytic form of the
coordinate transformations from the Schwartschild to co-moving frame that
exists only in five dimensions. It is shown that in the static coordinates
active gravitational mass of the spherical brane, in agreement with Tolman's
formula, is negative, i.e. such objects are gravitationally repulsive.Comment: Minor corrections, 8 pages, the version accepted by Mod. Phys. Lett.
The optical polarization of Epsilon Aurigae through the 1982-84 eclipse
About 350 nights observations on the 61-cm telescope at Pine Mt. Observatory were made of the variable polarization of Eps. Aurigae during 1982-85, in the U, B, and V color bands. The V data are the most complete and are shown. In terms of the overall features the curves in all three colors are quite similar. The typical errors per nightly point in the V curves are about 0.015% for either of the two normalized, equatorial Stokes parameters Q and U. Note that there is a large background or constant component of some 2.5%, position angle around 135 deg. This is presumably largely interstellar, and the intrinsic polarization probably does not much exceed the amplitude of the variable component, approx. 0.5%. A few field-star polarizations were measured but a very clear pattern was not obtained in this part of the sky
Detection of new eruptions in the Magellanic Clouds LBVs R 40 and R 110
We performed a spectroscopic and photometric analysis to study new eruptions
in two luminous blue variables (LBVs) in the Magellanic Clouds. We detected a
strong new eruption in the LBV R40 that reached in 2016, which is
around mag brighter than the minimum registered in 1985. During this new
eruption, the star changed from an A-type to a late F-type spectrum. Based on
photometric and spectroscopic empirical calibrations and synthetic spectral
modeling, we determine that R\,40 reached ~K
during this new eruption. This object is thereby probably one of the coolest
identified LBVs. We could also identify an enrichment of nitrogen and r- and
s-process elements. We detected a weak eruption in the LBV R 110 with a maximum
of mag in 2011, that is, around mag brighter than in the
quiescent phase. On the other hand, this new eruption is about mag
fainter than the first eruption detected in 1990, but the temperature did not
decrease below 8500 K. Spitzer spectra show indications of cool dust in the
circumstellar environment of both stars, but no hot or warm dust was present,
except by the probable presence of PAHs in R\,110. We also discuss a possible
post-red supergiant nature for both stars
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