18,424 research outputs found
Edge Currents and Vertex Operators for Chern-Simons Gravity
We apply elementary canonical methods for the quantization of 2+1 dimensional
gravity, where the dynamics is given by E. Witten's Chern-Simons
action. As in a previous work, our approach does not involve choice of gauge or
clever manipulations of functional integrals. Instead, we just require the
Gauss law constraint for gravity to be first class and also to be everywhere
differentiable. When the spatial slice is a disc, the gravitational fields can
either be unconstrained or constrained at the boundary of the disc. The
unconstrained fields correspond to edge currents which carry a representation
of the Kac-Moody algebra. Unitary representations for such an
algebra have been found using the method of induced representations. In the
case of constrained fields, we can classify all possible boundary conditions.
For several different boundary conditions, the field content of the theory
reduces precisely to that of 1+1 dimensional gravity theories. We extend the
above formalism to include sources. The sources take into account self-
interactions. This is done by punching holes in the disc, and erecting an
Kac-Moody algebra on the boundary of each hole. If the hole is
originally sourceless, a source can be created via the action of a vertex
operator . We give an explicit expression for . We shall show that when
actingComment: 42 pages, UAHEP 925, SU-4240-508, INFN-NA-IV-92/1
The Chern-Simons Source as a Conformal Family and Its Vertex Operators
In a previous work, a straightforward canonical approach to the source-free
quantum Chern-Simons dynamics was developed. It makes use of neither gauge
conditions nor functional integrals and needs only ideas known from QCD and
quantum gravity. It gives Witten's conformal edge states in a simple way when
the spatial slice is a disc. Here we extend the formalism by including sources
as well. The quantum states of a source with a fixed spatial location are shown
to be those of a conformal family, a result also discovered first by Witten.
The internal states of a source are not thus associated with just a single ray
of a Hilbert space. Vertex operators for both abelian and nonabelian sources
are constructed. The regularized abelian Wilson line is proved to be a vertex
operator. We also argue in favor of a similar nonabelian result. The
spin-statistics theorem is established for Chern-Simons dynamics even though
the sources are not described by relativistic quantum fields. The proof employs
geometrical methods which we find are strikingly transparent and pleasing. It
is based on the research of European physicists about ``fields localized on
cones.'
2+1 Einstein Gravity as a Deformed Chern-Simons Theory
The usual description of 2+1 dimensional Einstein gravity as a Chern-Simons
(CS) theory is extended to a one parameter family of descriptions of 2+1
Einstein gravity. This is done by replacing the Poincare' gauge group symmetry
by a q-deformed Poincare' gauge group symmetry, with the former recovered when
q-> 1. As a result, we obtain a one parameter family of Hamiltonian
formulations for 2+1 gravity. Although formulated in terms of noncommuting
dreibeins and spin-connection fields, our expression for the action and our
field equations, appropriately ordered, are identical in form to the ordinary
ones. Moreover, starting with a properly defined metric tensor, the usual
metric theory can be built; the Christoffel symbols and space-time curvature
having the usual expressions in terms of the metric tensor, and being
represented by c-numbers. In this article, we also couple the theory to
particle sources, and find that these sources carry exotic angular momentum.
Finally, problems related to the introduction of a cosmological constant are
discussed.Comment: Latex file, 26 pages, no figure
Insulator interface effects in sputterâdeposited NbN/MgO/NbN (superconductorâinsulatorâsuperconductor) tunnel junctions
All refractory, NbN/MgO/NbN (superconductorâinsulatorâsuperconductor) tunnel junctions have been fabricated by in situ sputter deposition. The influence of MgO thickness (0.8â6.0 nm) deposited under different sputtering ambients at various deposition rates on currentâvoltage (IâV) characteristics of smallâarea (30Ă30 ÎŒm) tunnel junctions is studied. The NbN/MgO/NbN trilayer is deposited in situ by dc reactive magnetron (NbN), and rf magnetron (MgO) sputtering, followed by thermal evaporation of a protective Au cap. Subsequent photolithography, reactive ion etching, planarization, and top contact (Pb/Ag) deposition completes the junction structure. Normal resistance of the junctions with MgO deposited in Ar or Ar and N2 mixture shows good exponential dependence on the MgO thickness indicating formation of a pinâholeâfree uniform barrier layer. Further, a postdeposition in situ oxygen plasma treatment of the MgO layer increases the junction resistance sharply, and reduces the subgap leakage. A possible enrichment of the MgO layer stoichiometry by the oxygen plasma treatment is suggested. A sumgap as high as 5.7 mV is observed for such a junctio
Dual Instantons
We show how to map the Belavin-Polyakov instantons of the O(3)-nonlinear
model to a dual theory where they then appear as nontopological
solitons. They are stationary points of the Euclidean action in the dual
theory, and moreover, the dual action and the O(3)-nonlinear model
action agree on shell.Comment: 13 page
ON THE GEOMETRY OF THE X-RAY EMITTING REGION IN SEYFERT GALAXIES
For the first time, detailed radiative transfer calculations of Comptonized
X-ray and gamma-ray radiation in a hot pair plasma above a cold accretion disk
are performed using two independent codes and methods. The simulations include
both energy and pair balance as well as reprocessing of the X- and gamma-rays
by the cold disk. We study both plane-parallel coronae as well as active
dissipation regions having shapes of hemispheres and pill boxes located on the
disk surface. It is shown, contrary to earlier claims, that plane-parallel
coronae in pair balance have difficulties in selfconsistently reproducing the
ranges of 2-20 keV spectral slopes, high energy cutoffs, and compactnesses
inferred from observations of type 1 Seyfert galaxies. Instead, the
observations are consistent with the X-rays coming from a number of individual
active regions located on the surface of the disk.
A number of effects such as anisotropic Compton scattering, the reflection
hump, feedback to the soft photon source by reprocessing, and an active region
in pair equilibrium all conspire to produce the observed ranges of X-ray
slopes, high energy cutoffs, and compactnesses. The spread in spectral X-ray
slopes can be due to a spread in the properties of the active regions such as
their compactnesses and their elevations above the disk surface. Simplified
models invoking isotropic Comptonization in spherical clouds are no longer
sufficient when interpreting the data.Comment: 9 pages, 3 postscript figures, figures can be obtained from the
authors via e-mail: [email protected]
Organizational Design for Spill Containment in Deepwater Drilling Operations in the Gulf of Mexico: Assessment of the Marine Well Containment Company (MWCC)
The Deepwater Horizon oil spill in the Gulf of Mexico in April 2010 led to the deaths of 11 workers, a six-month moratorium on deepwater drilling in the Gulf, and nearly three months of massive engineering and logistics efforts to stop the spill. The series of failures before the well was finally capped and the spill contained revealed an inability to deal effectively with a well in deepwater and ultradeepwater. Ensuring that containment capabilities are adequate for drilling operations at these depths is therefore a salient challenge for government and industry. In this paper we assess the Marine Well Containment Company (MWCC), a consortium aimed at designing and building a system capable of containing future deepwater spills in the Gulf. We also consider alternatives for long-term readiness for deepwater spill containment. We focus on the roles of liability and regulation as determinants of readiness and the adequacy of incentives for technological innovation in oil spill containment technology to keep pace with advances in deepwater drilling capability. Liability and regulation can significantly influence the strength of these incentives. In addition, we discuss appropriate governance structure as a major determinant of the effectiveness of MWCC.oil spill, containment, industry R&D, liability, regulation, governance, innovation
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