2,885 research outputs found
Poisson process Fock space representation, chaos expansion and covariance inequalities
We consider a Poisson process on an arbitrary measurable space with an
arbitrary sigma-finite intensity measure. We establish an explicit Fock space
representation of square integrable functions of . As a consequence we
identify explicitly, in terms of iterated difference operators, the integrands
in the Wiener-Ito chaos expansion. We apply these results to extend well-known
variance inequalities for homogeneous Poisson processes on the line to the
general Poisson case. The Poincare inequality is a special case. Further
applications are covariance identities for Poisson processes on (strictly)
ordered spaces and Harris-FKG-inequalities for monotone functions of .Comment: 25 page
Gravitational Waves from Compact Objects Accreting onto Active Galactic Nuclei
We consider a model in which massive stars form in a self-gravitating
accretion disk around an active galactic nucleus. These stars may evolve and
collapse to form compact objects on a time scale shorter than the accretion
time, thus producing an important family of sources for LISA. Assuming the
compact object formation/inspiral rate is proportional to the steady-state gas
accretion rate, we use the observed extra-galactic X-ray luminosity function to
estimate expected event rates and signal strengths. We find that these sources
will produce a continuous low-frequency background detectable by LISA if more
than >~ 1% of the accreted matter is in the form of compact objects. For
compact objects with m >~ 10 Msun, the last stages of the inspiral events
should be resolvable above a few mHz, at a rate of ~10-100 per year.Comment: 7 pages, to appear in Proceedings of Sixth International LISA
Symposiu
Effect of the Centrifugal Force on Domain Chaos in Rayleigh-B\'enard convection
Experiments and simulations from a variety of sample sizes indicated that the
centrifugal force significantly affects rotating Rayleigh-B\'enard
convection-patterns. In a large-aspect-ratio sample, we observed a hybrid state
consisting of domain chaos close to the sample center, surrounded by an annulus
of nearly-stationary nearly-radial rolls populated by occasional defects
reminiscent of undulation chaos. Although the Coriolis force is responsible for
domain chaos, by comparing experiment and simulation we show that the
centrifugal force is responsible for the radial rolls. Furthermore, simulations
of the Boussinesq equations for smaller aspect ratios neglecting the
centrifugal force yielded a domain precession-frequency
with as predicted by the amplitude-equation model for domain
chaos, but contradicted by previous experiment. Additionally the simulations
gave a domain size that was larger than in the experiment. When the centrifugal
force was included in the simulation, and the domain size closely agreed
with experiment.Comment: 8 pages, 11 figure
Integer Point Sets Minimizing Average Pairwise L1-Distance: What is the Optimal Shape of a Town?
An n-town, for a natural number n, is a group of n buildings, each occupying
a distinct position on a 2-dimensional integer grid. If we measure the distance
between two buildings along the axis-parallel street grid, then an n-town has
optimal shape if the sum of all pairwise Manhattan distances is minimized. This
problem has been studied for cities, i.e., the limiting case of very large n.
For cities, it is known that the optimal shape can be described by a
differential equation, for which no closed-form is known. We show that optimal
n-towns can be computed in O(n^7.5) time. This is also practically useful, as
it allows us to compute optimal solutions up to n=80.Comment: 26 pages, 6 figures, to appear in Computational Geometry: Theory and
Application
Enhanced heat transport by turbulent two-phase Rayleigh-B\'enard convection
We report measurements of turbulent heat-transport in samples of ethane
(CH) heated from below while the applied temperature difference straddled the liquid-vapor co-existance curve . When the sample
top temperature decreased below , droplet condensation occurred
and the latent heat of vaporization provided an additional heat-transport
mechanism.The effective conductivity increased linearly with
decreasing , and reached a maximum value that was an
order of magnitude larger than the single-phase . As
approached the critical pressure, increased dramatically even
though vanished. We attribute this phenomenon to an enhanced
droplet-nucleation rate as the critical point is approached.Comment: 4 gages, 6 figure
Inverted spin polarization of Heusler alloys for new spintronic devices
A new magnetic logic overcomes the major limitations of field programmable
gate arrays while having a 50% smaller unit cell than conventional designs
utilizing magnetic tunnel junctions with one Heusler alloy electrode. These
show positive and negative TMR values at different bias voltages at room
temperature which generally adds an additional degree of freedom to all
spintronic devices
The DoF-Box project: An educational kit for configurable robots
China: Shanghai. AirportCNAC is the China National Aviation Corporation. The Shanghai Longhua Airport.GrayscaleForman Nitrate Negatives, Box 2
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