5,065 research outputs found
Ion Beams in Multi-Species Plasma
Argon and xenon ion velocity distribution functions are measured in Ar-He, Ar-Xe, and Xe-He expanding helicon plasmas to determine if ion beam velocity is enhanced by the presence of lighter ions. Contrary to observations in mixed gas sheath experiments, we find that adding a lighter ion does not increase the ion beam speed. The predominant effect is a reduction of ion beam velocity consistent with increased drag arising from increased gas pressure under all conditions: constant total gas pressure, equal plasma densities of different ions, and very different plasma densities of different ions. These results suggest that the physics responsible for the acceleration of multiple ion species in simple sheaths is not responsible for the ion acceleration observed in expanding helicon plasmas
On the Superradiance of Spin-1 Waves in an Equatorial Wedge around a Kerr Hole
Recently Van Putten has suggested that superradiance of magnetosonic waves in
a toroidal magnetosphere around a Kerr black hole may play a role in the
central engine of gamma-ray bursts. In this context, he computed (in the WKB
approximation) the superradiant amplification of scalar waves confined to a
thin equatorial wedge around a Kerr hole and found that the superradiance is
higher than for radiation incident over all angles. This paper presents
calculations of both spin-0 (scalar) superradiance (integrating the radial
equation rather than using the WKB method) and and spin-1
(electromagnetic/magnetosonic) superradiance, in Van Putten's wedge geometry.
In contrast to the scalar case, spin-1 superradiance decreases in the wedge
geometry, decreasing the likelihood of its astrophysical importance.Comment: Submitted to The Astrophysical Journal Letter
Type-II super-Backlund transformation and integrable defects for the N=1 super sinh-Gordon model
A new super-Backlund transformation for the N=1 supersymmetric sinh-Gordon
equation is constructed. Based on this construction we propose a type-II
integrable defect for the supersymmetric sinh-Gordon model consistent with this
new transformation through the Lagrangian formalism. Explicit expressions for
the modified conserved energy, momentum and supercharges are also computed. In
addition, we show for the model that the type-II defect can also been regarded
as a pair of fused defects of a previously introduced type. The explicit
derivation of the associated defect matrices is also presented as a necessary
condition for the integrability of the model.Comment: Latex 31 pages. Version accepted for publicatio
The missing metals problem. III How many metals are expelled from galaxies?
[Abridged] We revisit the metal budget at z~2. In the first two papers of
this series, we already showed that ~30% (to <60% if extrapolating the LF) of
the metals are observed in all z~2.5 galaxies detected in current surveys.
Here, we extend our analysis to the metals outside galaxies, i.e. in
intergalactic medium (IGM), using observational data and analytical
calculations. Our results for the two are strikingly similar: (1)
Observationally, we find that, besides the small (5%) contribution of DLAs, the
forest and sub-DLAs contribute subtantially to make <30--45% of the metal
budget, but neither of these appear to be sufficient to close the metal budget.
The forest accounts for 15--30% depending on the UV background, and sub-DLAs
for >2% to <17% depending on the ionization fraction. Together, the `missing
metals' problem is substantially eased. (2) We perform analytical calculations
based on the effective yield--mass relation. At z=2, we find that the method
predicts that 2$--50% of the metals have been ejected from galaxies into the
IGM, consistent with the observations. The metal ejection is predominantly by
L<1/3L_B^*(z=2) galaxies, which are responsible for 90% the metal enrichment,
while the 50 percentile is at L~1/10L^*_B(z=2). As a consequence, if indeed 50%
of the metals have been ejected from galaxies, 3--5 bursts of star formation
are required per galaxy prior to z=2. The ratio between the mass of metals
outside galaxies to those in stars has changed from z=2 to z=0: it was 2:1 or
1:1 and is now 1:8 or 1:9. This evolution implies that a significant fraction
of the IGM metals will cool and fall back into galaxies.Comment: 18pages, MNRAS, in press; small changes to match proofs; extended
version with summary tabl
N=1 super sinh-Gordon model with defects revisited
The Lax pair formalism is considered to discuss the integrability of the N=1
supersymmetric sinh-Gordon model with a defect. We derive associated defect
matrix for the model and construct the generating functions of the modified
conserved quantities. The corresponding defect contributions for the modified
energy and momentum of the model are explicitly computed.Comment: Latex 26 page
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