58,104 research outputs found
Gravothermal Catastrophe, an Example
This work discusses gravothermal catastrophe in astrophysical systems and
provides an analytic collapse solution which exhibits many of the catastrophe
properties. The system collapses into a trapped surface with outgoing energy
radiated to a future boundary, and provides an example of catastrophic
collapse.Comment: To appear in Phys. Rev.
The Structure of the Outer Halo of the Galaxy and its Relationship to Nearby Large-Scale Structure
We present evidence to support an earlier indication that the Galaxy is
embedded in an extended, highly inclined, triaxial halo outlined by the spatial
distribution of companion galaxies to the Milky Way. Signatures of this spatial
distribution are seen in 1) the angular variation of the radial-velocity
dispersion of the companion galaxies, 2) the spatial distribution of the M~31
sub-group of galaxies, 3) the spatial distribution of the isolated, mainly
dwarf irregular, galaxies of the Local Group, 4) the velocity anisotropy
quadrupole of a sub-group of high-velocity clouds, and 5) the spatial
distribution of galaxies in the Coma-Sculptor cloud. Tidal effects of M~31 and
surrounding galaxies on the Galaxy are not strong enough to have affected the
observed structure. We conclude that this distribution is a reflection of
initial conditions. A simple galaxy formation scenario is proposed which ties
together the results found here with those of Holmberg (1969) and Zaritsky et
al. (1997) on the peculiar distribution of satellites around a large sample of
spiral galaxies.Comment: Accepted for publication in the Astron J., March 2000, 12 pages with
1 figur
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Ontology learning for semantic web services
Semantic Web Services promise automatic service discovery and composition, relying heavily on domain ontology as a core component. With large Web Service repository, manual ontology development is proving a bottleneck (with associated expense and likely errors) to the realisation of a semantic Web of services. Providing the appropriate tools that assist in and automate ontology development is essential for a dynamic service vision to be realised. As a statement of research-in-progress, this paper proposes combining different ontology learning paradigms in Web Services domain, highlighting the need for further research that accommodates the variation in Web Service descriptive and operational sources. A research agenda is proposed that recognises this variation in artefacts as they are selected, pre-processed and analyzed by ontology learning techniques
Bell's inequality and the coincidence-time loophole
This paper analyzes effects of time-dependence in the Bell inequality. A
generalized inequality is derived for the case when coincidence and
non-coincidence [and hence whether or not a pair contributes to the actual
data] is controlled by timing that depends on the detector settings. Needless
to say, this inequality is violated by quantum mechanics and could be violated
by experimental data provided that the loss of measurement pairs through
failure of coincidence is small enough, but the quantitative bound is more
restrictive in this case than in the previously analyzed "efficiency loophole."Comment: revtex4, 3 figures, v2: epl document class, reformatted w slight
change
Inertial frame rotation induced by rotating gravitational waves
We calculate the rotation of the inertial frames within an almost flat
cylindrical region surrounded by a pulse of non-axially-symmetric gravitational
waves that rotate about the axis of our cylindrical polar coordinates. Our
spacetime has only one Killing vector. It is along the z-axis and hypersurface
orthogonal. We solve the Einstein equations to first order in the wave
amplitude and superpose such linearized solutions to form a wave pulse. We then
solve the relevant Einstein equation to second order in the amplitude to find
the rotation of inertial frames produced by the pulse. The rotation is without
time delay. The influence of gravitational wave angular momentum on the
inertial frame demonstrates that Mach's principle can not be expressed in terms
of the influence of the stress-energy-momentum tensor alone but must involve
also influences of gravitational wave energy and angular momentum.Comment: Scheduled to appear in Class. and Quantum Grav. July 2008, "inertial"
added in titl
Bell nonlocality, signal locality and unpredictability (or What Bohr could have told Einstein at Solvay had he known about Bell experiments)
The 1964 theorem of John Bell shows that no model that reproduces the
predictions of quantum mechanics can simultaneously satisfy the assumptions of
locality and determinism. On the other hand, the assumptions of \emph{signal
locality} plus \emph{predictability} are also sufficient to derive Bell
inequalities. This simple theorem, previously noted but published only
relatively recently by Masanes, Acin and Gisin, has fundamental implications
not entirely appreciated. Firstly, nothing can be concluded about the
ontological assumptions of locality or determinism independently of each other
-- it is possible to reproduce quantum mechanics with deterministic models that
violate locality as well as indeterministic models that satisfy locality. On
the other hand, the operational assumption of signal locality is an empirically
testable (and well-tested) consequence of relativity. Thus Bell inequality
violations imply that we can trust that some events are fundamentally
\emph{unpredictable}, even if we cannot trust that they are indeterministic.
This result grounds the quantum-mechanical prohibition of arbitrarily accurate
predictions on the assumption of no superluminal signalling, regardless of any
postulates of quantum mechanics. It also sheds a new light on an early stage of
the historical debate between Einstein and Bohr.Comment: Substantially modified version; added HMW as co-autho
Pseudo-Dirac Neutrino Scenario: Cosmic Neutrinos at Neutrino Telescopes
Within the "pseudo-Dirac" scenario for massive neutrinos the existence of
sterile neutrinos which are almost degenerate in mass with the active ones is
hypothesized. The presence of these sterile neutrinos can affect the flavor
composition of cosmic neutrinos arriving at Earth after traveling large
distances from astrophysical objects. We examine the prospects of neutrino
telescopes such as IceCube to probe the very tiny mass squared differences
10^(-12) eV^2<\Delta m^2<10^(-19) eV^2, by analyzing the ratio of -track
events to shower-like events. Considering various sources of uncertainties
which enter this analysis, we examine the capability of neutrino telescopes to
verify the validity of the pseudo-Dirac neutrino scenario and especially to
discriminate it from the conventional scenario with no sterile neutrino. We
also discuss the robustness of our results with respect to the uncertainties in
the initial flavor ratio of neutrinos at the source.Comment: 24 pages, 5 figure
An inverse method for the aerodynamic design of three-dimensional aircraft engine nacelles
A fast, efficient and user friendly inverse design system for 3-D nacelles was developed. The system is a product of a 2-D inverse design method originally developed at NASA-Langley and the CFL3D analysis code which was also developed at NASA-Langley and modified for nacelle analysis. The design system uses a predictor/corrector design approach in which an analysis code is used to calculate the flow field for an initial geometry, the geometry is then modified based on the difference between the calculated and target pressures. A detailed discussion of the design method, the process of linking it to the modified CFL3D solver and its extension to 3-D is presented. This is followed by a number of examples of the use of the design system for the design of both axisymmetric and 3-D nacelles
Criteria for generalized macroscopic and mesoscopic quantum coherence
We consider macroscopic, mesoscopic and "S-scopic" quantum superpositions of
eigenstates of an observable, and develop some signatures for their existence.
We define the extent, or size of a superposition, with respect to an
observable \hat{x}, as being the range of outcomes of \hat{x} predicted by that
superposition. Such superpositions are referred to as generalized -scopic
superpositions to distinguish them from the extreme superpositions that
superpose only the two states that have a difference in their prediction
for the observable. We also consider generalized -scopic superpositions of
coherent states. We explore the constraints that are placed on the statistics
if we suppose a system to be described by mixtures of superpositions that are
restricted in size. In this way we arrive at experimental criteria that are
sufficient to deduce the existence of a generalized -scopic superposition.
The signatures developed are useful where one is able to demonstrate a degree
of squeezing. We also discuss how the signatures enable a new type of
Einstein-Podolsky-Rosen gedanken experiment.Comment: 15 pages, accepted for publication in Phys. Rev.
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