230 research outputs found
Iodine sorption study on the proposed use of Viton A in a shuttle galley water accumulator
The installation of a Viton A accumulator in the Shuttle galley has been proposed to prevent overpressurization of the hot water supply system. A laboratory study has been conducted to determine if there would be any interaction between the Viton A material and the iodine used to disinfect the water. Coupons of Viton A were exposed for 24 hours to aqueous iodine solutions similar in quality to the Shuttle's potable water. Changes in the iodine residual were monitored to determine the rate of iodine sorption by the coupon. Total organic carbon (TOC) was monitored to determine the rate of desorption of organic materials from the Viton A. The same coupons were then soaked in reagent-grade water for 24 hours, and iodine was monitored to determine the rate of iodine desorption. The coupons were again exposed to iodine solutions for 24 hours and iodine and TOC were monitored. No significant change in the iodine sorption rate was detected between the first and second exposures. A triangle taste test indicated at a 1 percent confidence level that the water exposed to Viton A had a different taste which was less acceptable to the panelists
Nonsingular global string compactifications
We consider an exotic `compactification' of spacetime in which there are two
infinite extra dimensions, using a global string instead of a domain wall. By
having a negative cosmological constant we prove the existence of a nonsingular
static solution using a dynamical systems argument. A nonsingular solution also
exists in the absence of a cosmological constant with a time-dependent metric.
We compare and contrast this solution with the Randall-Sundrum universe and the
Cohen-Kaplan spacetime, and consider the options of using such a model as a
realistic resolution of the hierarchy problem.Comment: 8 pages revtex, 1 figure : References added and equation correcte
The scalar perturbation of the higher-dimensional rotating black holes
The massless scalar field in the higher-dimensional Kerr black hole (Myers-
Perry solution with a single rotation axis) has been investigated. It has been
shown that the field equation is separable in arbitrary dimensions. The
quasi-normal modes of the scalar field have been searched in five dimensions
using the continued fraction method. The numerical result shows the evidence
for the stability of the scalar perturbation of the five-dimensional Kerr black
holes. The time scale of the resonant oscillation in the rapidly rotating black
hole, in which case the horizon radius becomes small, is characterized by
(black hole mass)^{1/2}(Planck mass)^{-3/2} rather than the light-crossing time
of the horizon.Comment: 16 pages, 7 figures, revised versio
Power-Law Inflation from the Rolling Tachyon
Modeling the potential by an inverse square law in terms of the tachyon field
() we find exact solution for spatially flat isotropic
universe.We show that for the model undergoes power-law
inflation. A way to construct other exact solutions is specified and
exemplified.Comment: References added. Matches the version in print. To appear in PR
BPS Branes in Cosmology
The possibility to study the M/string theory cosmology via 5d bulk & brane
action is investigated. The role of the 4-form field in the theory of BPS
branes in 5d is clarified. We describe arguments suggesting that the effective
4d description of the universe in the ekpyrotic scenario (hep-th/0103239)
should lead to contraction rather than expansion of the universe. To verify
these arguments, we study the full 5d action prior to its integration over the
5th dimension. We show that if one adds the potential V(Y) to the action of the
bulk brane, then the metric ansatz used in the ekpyrotic scenario does not
solve the dilaton and gravitational equations. To find a consistent
cosmological solution one must use a more general metric ansatz and a complete
5d description of the brane interaction instead of simply adding an effective
4d bulk brane potential V(Y).Comment: 18 pages, revte
Born-Infeld Quantum Condensate as Dark Energy in the Universe
Some cosmological implications of ultraviolet quantum effects leading to a
condensation of Born-Infeld matter are considered. It is shown that under very
general conditions the quantum condensate can not act as phantom matter if its
energy density is positive. On the other hand, it behaves as an effective
cosmological constant in the limit where quantum induced contributions to the
energy-momentum tensor dominate over the classical effects.Comment: 9 pages, no figures. Extended discussion, In Press, Physics Letters
Domain Walls of D=8 Gauged Supergravities and their D=11 Origin
Performing a Scherk-Schwarz dimensional reduction of D=11 supergravity on a
three-dimensional group manifold we construct five D=8 gauged maximal
supergravities whose gauge groups are the three-dimensional (non-)compact
subgroups of SL(3,R). These cases include the Salam-Sezgin SO(3) gauged
supergravity. We construct the most general half-supersymmetric domain wall
solutions to these five gauged supergravities. The generic form is a triple
domain wall solution whose truncations lead to double and single domain wall
solutions. We find that one of the single domain wall solutions has zero
potential but nonzero superpotential.
Upon uplifting to 11 dimensions each domain wall becomes a purely
gravitational 1/2 BPS solution. The corresponding metric has a 7+4 split with a
Minkowski 7-metric and a 4-metric that corresponds to a gravitational
instanton. These instantons generalize the SO(3) metric of Belinsky, Gibbons,
Page and Pope (which includes the Eguchi-Hanson metric) to the other Bianchi
types of class A.Comment: 23 pages, 1 figure, minor changes, references adde
Gauging the Full R-Symmetry Group in Five-dimensional, N=2 Yang-Mills/Einstein/tensor Supergravity
We show that certain five dimensional, N=2 Yang-Mills/Einstein supergravity
theories admit the gauging of the full R-symmetry group, SU(2)_R, of the
underlying N=2 Poincare superalgebra. This generalizes the previously studied
Abelian gaugings of U(1)_R subgroup of SU(2)_R and completes the construction
of the most general vector and tensor field coupled five dimensional N=2
supergravity theories with gauge interactions. The gauging of SU(2)_R turns out
to be possible only in special cases, and leads to a new type of scalar
potential. For a large class of these theories the potential does not have any
critical points.Comment: Latex file, 15 pages ; section two is split in two and the discussion
of the critical points is moved into the new section. Version to appear in
Physical Review
Wave function of the radion in the brane background with a massless scalar field and a self-tuning problem
We consider flat solutions in the brane background with a massless scalar
field appearing in 5D . Since there exist bulk singularities or
arises the divergent 4D Planck mass, we should introduce a compact extra
dimension, the size of which is then fixed by brane tension(s) and a bulk
cosmological constant. Inspecting scalar perturbations around the flat
solutions, we find that the flat solutions are stable vacua from the positive
mass spectrum of radion. We show that the massless radion mode is projected out
by the boundary condition arising in cutting off the extra dimension. Thus, the
fixed extra dimension is not alterable, which is not useful toward a
self-tuning of the cosmological constant.Comment: Latex file of 18 pages including 1 eps figur
Born-Infeld Theory and Stringy Causality
Fluctuations around a non-trivial solution of Born-Infeld theory have a
limiting speed given not by the Einstein metric but the Boillat metric. The
Boillat metric is S-duality invariant and conformal to the open string metric.
It also governs the propagation of scalars and spinors in Born-Infeld theory.
We discuss the potential clash between causality determined by the closed
string and open string light cones and find that the latter never lie outside
the former. Both cones touch along the principal null directions of the
background Born-Infeld field. We consider black hole solutions in situations in
which the distinction between bulk and brane is not sharp such as space filling
branes and find that the location of the event horizon and the thermodynamic
properties do not depend on whether one uses the closed or open string metric.
Analogous statements hold in the more general context of non-linear
electrodynamics or effective quantum-corrected metrics. We show how Born-Infeld
action to second order might be obtained from higher-curvature gravity in
Kaluza-Klein theory. Finally we point out some intriguing analogies with
Einstein-Schr\"odinger theory.Comment: 31 pages, 4 figures, LaTex; Some comments and references adde
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