11,787 research outputs found
Analysis of SPDEs Arising in Path Sampling Part I: The Gaussian Case
In many applications it is important to be able to sample paths of SDEs
conditional on observations of various kinds. This paper studies SPDEs which
solve such sampling problems. The SPDE may be viewed as an infinite dimensional
analogue of the Langevin SDE used in finite dimensional sampling. Here the
theory is developed for conditioned Gaussian processes for which the resulting
SPDE is linear. Applications include the Kalman-Bucy filter/smoother. A
companion paper studies the nonlinear case, building on the linear analysis
provided here
Vortex-glass transition in superconducting Nb/Cu superlattices
Nb/Cu superconducting superlattices have been fabricated by dc magnetron
sputtering. This system shows a vortex glass transition with critical exponents
similar to high temperatures superconductors exponents. The transition
dymensionality is governed by the superconducting coupling regime. The vortex
glass transition shows a pure two dimensional behavior in decoupled
superlattices and a quasi-two dimensional behavior in the superlattice coupling
regime.Comment: 9 pages, 3 figure
Off-Balance Sheet Financing: Current Techniques and Associated Risks
B.S. (Bachelor of Science
Shuttle active thermal control system development testing. Volume 2: Modular radiator system tests
Tests were designed to investigate the validity of the "modular" approach to space radiator system design for space shuttle and future applications by gathering performance data on various systems comprised of different numbers of identical panels, subject to nominal and extreme heat loads and environments. Both one-sided and two-sided radiation was tested, and engineering data was gathered on simulated low a/e coatings and system response to changes in outlet temperature control point. The results of the testing showed system stability throughout nominal orbital transients, unrealistically skewed environments, freeze-thaw transients, and rapid changes in outlet temperature control point. Various alternative panel plumbing arrangements were tested with no significant changes in performance being observed. With the MRS panels arranged to represent the shuttle baseline system, a maximum heat rejection of 76,600 Btu/hr was obtained in segmented tests under the expected worst case design environments. Testing of an alternate smaller two-sided radiation configuration yielded a maximum heat rejection of 52,931 Btu/hr under the maximum design environments
A statistical test of emission from unresolved point sources
We describe a simple test of the spatial uniformity of an ensemble of
discrete events. Given an estimate for the point source luminosity function and
an instrumental point spread function (PSF), a robust upper bound on the
fractional point source contribution to a diffuse signal can be found. We
verify with Monte Carlo tests that the statistic has advantages over the
two-point correlation function for this purpose, and derive analytic estimates
of the statistic's mean and variance as a function of the point source
contribution. As a case study, we apply this statistic to recent gamma-ray data
from the Fermi Large Area Telescope (LAT), and demonstrate that at energies
above 10 GeV, the contribution of unresolved point sources to the diffuse
emission is small in the region relevant for study of the WMAP Haze.Comment: 11 pages, 7 figures. Final version, accepted by Mon. Not. R. Astron.
Soc. The definitive version is available at www.blackwell-synergy.com
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