10,924 research outputs found
Gas side heat transfer: 2-D flow
Significant progress was made in advancing the idea of establishing a unified approach for predicting airfoil heat transfer for a wide range of operating conditions and geometries. Preliminary results are encouraging and further mixing length (ml) turbulence modeling ideas will be explored, concentrating on transition behavior. The capability of available modeling techniques to predict airfoil surface heat transfer distributions in a two-dimensional flow field was assessed, experimental data as required for model verification were acquired, and improvements in the analytic models was made and verified
An Accounting of the Sources of Steller Sea Lion, Eumetopias jubatus, Mortality
During 1991–2000, the west-are additional mortalities that fueled the ern stock of Steller sea lions, Eumetopias decline. We tabulated the levels of reported jubatus, declined at 5.03% (SE = 0.25%) anthropogenic sources of mortality (sub-
per year, statistically significant rates (P 8.2% partition the various sources of “additional” per year). Using a published correction mortalities as anthropogenic and as addifactor, we estimated the total non-pup pop-tional mortality including some predation. ulation size in Alaska of the western stock We classified 436 anthropogenic mortalities of Steller sea lions to be about 33,000 ani-and 769 anthropogenic plus some predation mals. Based on a published life table and mortalities as “mortality above replace-the current rate of decline, we estimate that ment”; this accounted for 26% and 46% of the total number of mortalities of non-pup the estimated total level of “mortality above Steller sea lions during 1991–2000 was replacement”, respectively. The remaining about 6,383 animals; of those, 4,718 (74%) mortality (74% and 54%, respectively) was are mortalities that would have occurred if not attributed to a specific cause and may be the population were stable, and 1,666 (26%) the result of nutritional stress
Dynamical evolution of unstable self-gravitating scalar solitons
Recently, static and spherically symmetric configurations of globally regular
self-gravitating scalar solitons were found. These configurations are unstable
with respect to radial linear perturbations. In this paper we study the
dynamical evolution of such configurations and show that, depending on the sign
of the initial perturbation, the solitons either collapse to a Schwarzschild
black hole or else ``explode'' into an outward moving domain wall.Comment: 11 pages, 16 figures, submitted to Phys. Rev.
Uniqueness and Non-uniqueness in the Einstein Constraints
The conformal thin sandwich (CTS) equations are a set of four of the Einstein
equations, which generalize the Laplace-Poisson equation of Newton's theory. We
examine numerically solutions of the CTS equations describing perturbed
Minkowski space, and find only one solution. However, we find {\em two}
distinct solutions, one even containing a black hole, when the lapse is
determined by a fifth elliptic equation through specification of the mean
curvature. While the relationship of the two systems and their solutions is a
fundamental property of general relativity, this fairly simple example of an
elliptic system with non-unique solutions is also of broader interest.Comment: 4 pages, 4 figures; abstract and introduction rewritte
Decoherence induced CPT violation and entangled neutral mesons
We discuss two classes of semi-microscopic theoretical models of stochastic
space-time foam in quantum gravity and the associated effects on entangled
states of neutral mesons, signalling an intrinsic breakdown of CPT invariance.
One class of models deals with a specific model of foam, initially constructed
in the context of non-critical (Liouville) string theory, but viewed here in
the more general context of effective quantum-gravity models. The relevant
Hamiltonian perturbation, describing the interaction of the meson with the foam
medium, consists of off-diagonal stochastic metric fluctuations, connecting
distinct mass eigenstates (or the appropriate generalisation thereof in the
case of K-mesons), and it is proportional to the relevant momentum transfer
(along the direction of motion of the meson pair). There are two kinds of
CPT-violating effects in this case, which can be experimentally disentangled:
one (termed ``omega-effect'') is associated with the failure of the
indistinguishability between the neutral meson and its antiparticle, and
affects certain symmetry properties of the initial state of the two-meson
system; the second effect is generated by the time evolution of the system in
the medium of the space-time foam, and can result in time-dependent
contributions of the $omega-effect type in the time profile of the two meson
state. Estimates of both effects are given, which show that, at least in
certain models, such effects are not far from the sensitivity of experimental
facilities available currently or in the near future. The other class of
quantum gravity models involves a medium of gravitational fluctuations which
behaves like a ``thermal bath''. In this model both of the above-mentioned
intrinsic CPT violation effects are not valid.Comment: 16 pages revtex, no figure
An axisymmetric generalized harmonic evolution code
We describe the first axisymmetric numerical code based on the generalized
harmonic formulation of the Einstein equations which is regular at the axis. We
test the code by investigating gravitational collapse of distributions of
complex scalar field in a Kaluza-Klein spacetime. One of the key issues of the
harmonic formulation is the choice of the gauge source functions, and we
conclude that a damped wave gauge is remarkably robust in this case. Our
preliminary study indicates that evolution of regular initial data leads to
formation both of black holes with spherical and cylindrical horizon
topologies. Intriguingly, we find evidence that near threshold for black hole
formation the number of outcomes proliferates. Specifically, the collapsing
matter splits into individual pulses, two of which travel in the opposite
directions along the compact dimension and one which is ejected radially from
the axis. Depending on the initial conditions, a curvature singularity develops
inside the pulses.Comment: 21 page, 18 figures. v2: minor corrections, added references, new
Fig. 9; journal version
Action and Energy of the Gravitational Field
We present a detailed examination of the variational principle for metric
general relativity as applied to a ``quasilocal'' spacetime region \M (that
is, a region that is both spatially and temporally bounded). Our analysis
relies on the Hamiltonian formulation of general relativity, and thereby
assumes a foliation of \M into spacelike hypersurfaces . We allow for
near complete generality in the choice of foliation. Using a field--theoretic
generalization of Hamilton--Jacobi theory, we define the quasilocal
stress-energy-momentum of the gravitational field by varying the action with
respect to the metric on the boundary \partial\M. The gravitational
stress-energy-momentum is defined for a two--surface spanned by a spacelike
hypersurface in spacetime. We examine the behavior of the gravitational
stress-energy-momentum under boosts of the spanning hypersurface. The boost
relations are derived from the geometrical and invariance properties of the
gravitational action and Hamiltonian. Finally, we present several new examples
of quasilocal energy--momentum, including a novel discussion of quasilocal
energy--momentum in the large-sphere limit towards spatial infinity.Comment: To be published in Annals of Physics. This final version includes two
new sections, one giving examples of quasilocal energy and the other
containing a discussion of energy at spatial infinity. References have been
added to papers by Bose and Dadhich, Anco and Tun
Canonical Quasilocal Energy and Small Spheres
Consider the definition E of quasilocal energy stemming from the
Hamilton-Jacobi method as applied to the canonical form of the gravitational
action. We examine E in the standard "small-sphere limit," first considered by
Horowitz and Schmidt in their examination of Hawking's quasilocal mass. By the
term "small sphere" we mean a cut S(r), level in an affine radius r, of the
lightcone belonging to a generic spacetime point. As a power series in r, we
compute the energy E of the gravitational and matter fields on a spacelike
hypersurface spanning S(r). Much of our analysis concerns conceptual and
technical issues associated with assigning the zero-point of the energy. For
the small-sphere limit, we argue that the correct zero-point is obtained via a
"lightcone reference," which stems from a certain isometric embedding of S(r)
into a genuine lightcone of Minkowski spacetime. Choosing this zero-point, we
find agreement with Hawking's quasilocal mass expression, up to and including
the first non-trivial order in the affine radius. The vacuum limit relates the
quasilocal energy directly to the Bel-Robinson tensor.Comment: revtex, 22 p, uses amssymb option (can be removed
Conformal ``thin sandwich'' data for the initial-value problem of general relativity
The initial-value problem is posed by giving a conformal three-metric on each
of two nearby spacelike hypersurfaces, their proper-time separation up to a
multiplier to be determined, and the mean (extrinsic) curvature of one slice.
The resulting equations have the {\it same} elliptic form as does the
one-hypersurface formulation. The metrical roots of this form are revealed by a
conformal ``thin sandwich'' viewpoint coupled with the transformation
properties of the lapse function.Comment: 7 pages, RevTe
The Holographic Interpretation of Hawking Radiation
Holography gives us a tool to view the Hawking effect from a new, classical
perspective. In the context of Randall-Sundrum braneworld models, we show that
the basic features of four-dimensional evaporating solutions are nicely
translated into classical five-dimensional language. This includes the dual
bulk description of particles tunneling through the horizon.Comment: 10 pages, 1 figure, Honorable Mention in the Gravity Research
Foundation Essay Competition 200
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