26,836 research outputs found
Recent developments in Vorton Theory
This article provides a concise overview of recent theoretical results
concerning the theory of vortons, which are defined to be (centrifugally
supported) equilibrium configurations of (current carrying) cosmic string
loops. Following a presentation of the results of work on the dynamical
evolution of small circular string loops, whose minimum energy states are the
simplest examples of vortons, recent order of magnitude estimates of the
cosmological density of vortons produced in various kinds of theoretical
scenario are briefly summarised.Comment: 6 pages Latex. Contribution to 1996 Cosmology Meeting, Peyresq,
Franc
Inclusion Polymerization and Doping in Zeolite Channels. Polyaniline
Aniline has been polymerized in the three-dimensional channel system of zeolite Y. The monomer was diffused into zeolites with different levels of acidity from hexane solution. Subsequent admission of peroxydisulfate or iodate from aqueous solution yielded the intrazeolite polymers, as demonstrated by FT-IR, electronic absorption data and recovery of the included polymer. With S2O82-, the intrazeolite products are a function of the proton content of the zeolite. Polymer is only formed when a sufficient supply of protons is present in the zeolite host. When neutral iodate solution is used, no polymer is formed in NaY and acid zeolites, but at low pH aniline polymerizes in all zeolites. The open pore system of the zeolite host can be accessed by base such that the intrazeolite protonated polymer is transformed into the corresponding neutral polymer.
The polymer chains encapsulated in zeolite hosts represent a new class of low- dimensional electronic materials
On higher dimensional black holes with abelian isometry group
We consider (n+1)--dimensional, stationary, asymptotically flat, or
Kaluza-Klein asymptotically flat black holes, with an abelian --dimensional
subgroup of the isometry group satisfying an orthogonal integrability
condition. Under suitable regularity conditions we prove that the area of the
group orbits is positive on the domain of outer communications, vanishing only
on its boundary and on the "symmetry axis". We further show that the orbits of
the connected component of the isometry group are timelike throughout the
domain of outer communications. Those results provide a starting point for the
classification of such black holes. Finally, we show non-existence of zeros of
static Killing vectors on degenerate Killing horizons, as needed for the
generalisation of the static no-hair theorem to higher dimensions
KIC 2856960: the impossible triple star
KIC 2856960 is a star in the Kepler field which was observed by Kepler for 4
years. It shows the primary and secondary eclipses of a close binary of 0.258d
as well as complex dipping events that last for about 1.5d at a time and recur
on a 204d period. The dips are thought to result when the close binary passes
across the face of a third star. In this paper we present an attempt to model
the dips. Despite the apparent simplicity of the system and strenuous efforts
to find a solution, we find that we cannot match the dips with a triple star
while satisfying Kepler's laws. The problem is that to match the dips the
separation of the close binary has to be larger than possible relative to the
outer orbit given the orbital periods. Quadruple star models can get round this
problem but require the addition of a so-far undetected intermediate period of
order 5 -- 20d that has be a near-perfect integer divisor of the outer 204d
period. Although we have no good explanation for KIC 2856960, using the full
set of Kepler data we are able to update several of its parameters. We also
present a spectrum showing that KIC 2856960 is dominated by light from a K3- or
K4-type star.Comment: 11 pages, 13 figures, accepted for publication in MNRAS August 21,
201
Transonic Elastic Model for Wiggly Goto-Nambu String
The hitherto controversial proposition that a ``wiggly" Goto-Nambu cosmic
string can be effectively represented by an elastic string model of exactly
transonic type (with energy density inversely proportional to its tension
) is shown to have a firm mathematical basis.Comment: 8 pages, plain TeX, no figure
Three approaches to the classification of inland wetlands
In the Dismal Swamp project, seasonal, color-infrared aerial photographs and LANDSAT digital data were interpreted for a detailed analysis of the vegetative communities in a large, highly altered wetland. In Western Tennessee, seasonal high altitude color-infrared aerial photographs provided the hydrologic and vegetative information needed to map inland wetlands, using a classification system developed for the Tennessee Valley Region. In Florida, color-infrared aerial photographs were analyzed to produce wetland maps using three existing classification systems to evaluate the information content and mappability of each system. The methods used in each of the three projects can be extended or modified for use in the mapping of inland wetlands in other parts of the United States
Dynamical Stability of Witten Rings
The dynamical stability of cosmic rings, or vortons, is investigated for the
particular equation of state given by the Witten bosonic model. It is found
that there exists a finite range of the state parameter for which the vorton
states are actually stable against dynamical perturbations. Inclusion of the
electromagnetic self action into the equation of state slightly shrinks the
stability region but otherwise yields no qualitative difference. If the Witten
bosonic model represents a good approximation for more realistic string models,
then the cosmological vorton excess problem can only be solved by assuming
either that strings are formed at low energy scales or that some quantum
instability may develop at a sufficient rate.Comment: 11 pages, LaTeX-ReVTeX (v.3), 2 figures available upon request, DAMTP
R-94/1
Hidden Symmetries of Higher Dimensional Black Holes and Uniqueness of the Kerr-NUT-(A)dS spacetime
We prove that the most general solution of the Einstein equations with the
cosmological constant which admits a principal conformal Killing-Yano tensor is
the Kerr-NUT-(A)dS metric. Even when the Einstein equations are not imposed,
any spacetime admitting such hidden symmetry can be written in a canonical form
which guarantees the following properties: it is of the Petrov type D, it
allows the separation of variables for the Hamilton-Jacobi, Klein-Gordon, and
Dirac equations, the geodesic motion in such a spacetime is completely
integrable. These results naturally generalize the results obtained earlier in
four dimensions.Comment: 5 pages, no figure
Investigation of ground effects on large and small scale models of a three fan V/STOL aircraft configuration
Induced lift of a subsonic, three fan, lift/cruise, V/STOL aircraft configuration was investigated using scale modes of a multimission aircraft whose design incorporates a nose mounted lift fan and two lift/cruise units located over the wing. Configuration effects were assessed for lift improvement devices, lift/cruise nozzle rails, nozzle perimeter plates, and alternate nose fan exit hubs. Tests were conducted at four model heights (H/D = 0.95, 1.53, 3.06 and 6.45, where D is the average nozzle exit diameter equal to 0.997 m.) Results are presented and discussed
Spinning BTZ Black Hole versus Kerr Black Hole : A Closer Look
By applying Newman's algorithm, the AdS_3 rotating black hole solution is
``derived'' from the nonrotating black hole solution of Banados, Teitelboim,
and Zanelli (BTZ). The rotating BTZ solution derived in this fashion is given
in ``Boyer-Lindquist-type'' coordinates whereas the form of the solution
originally given by BTZ is given in a kind of an ``unfamiliar'' coordinates
which are related to each other by a transformation of time coordinate alone.
The relative physical meaning between these two time coordinates is carefully
studied. Since the Kerr-type and Boyer-Lindquist-type coordinates for rotating
BTZ solution are newly found via Newman's algorithm, next, the transformation
to Kerr-Schild-type coordinates is looked for. Indeed, such transformation is
found to exist. And in this Kerr-Schild-type coordinates, truely maximal
extension of its global structure by analytically continuing to ``antigravity
universe'' region is carried out.Comment: 17 pages, 1 figure, Revtex, Accepted for publication in Phys. Rev.
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