49,018 research outputs found
Non-gaussian Noise in Quantum Spin Glasses and Interacting Two-level Systems
We study a general model for non-gaussian noise based on an infinite
range quantum Ising spin system in the paramagnetic state, or equivalently,
interacting two-level classical fluctuators. We identify a dilatation
interaction term in the dynamics which survives the thermodynamic limit and
circumvents the central limit theorem to produce non-gaussian noise even when
the equilibrium distribution is that of {\em non-interacting} spins. The
resulting second spectrum (`noise of the noise') itself has a universal
form which we analyze within a dynamical mean field approximation.Comment: 4 pages, 3 figure
Non-linear generation of acoustic noise in the IAR spacecraft
The requirement to produce high level acoustic noise fields with increasing accuracy in environmental test facilities dictates that a more precise understanding is required of the factors controlling nonlinear noise generation. Details are given of various nonlinear effects found in acoustic performance data taken from the IAR Spacecraft Acoustic Chamber. This type of data has enabled the IAR to test large spacecraft to relatively tight acoustic tolerances over a wide frequency range using manually set controls. An analog random noise automatic control system was available and modified to provide automatic selection of the chamber's spectral sound pressure levels. The automatic control system when used to complete a typical qualification test appeared to equal the accuracy of the manual system and had the added advantage that parallel spectra could be easily achieved during preset tests
Applied analytical combustion/emissions research at the NASA Lewis Research Center
Emissions of pollutants from future commercial transports are a significant concern. As a result, the Lewis Research Center (LeRC) is investigating various low emission combustor technologies. As part of this effort, a combustor analysis code development program was pursued to guide the combustor design process, to identify concepts having the greatest promise, and to optimize them at the lowest cost in the minimum time
Jet Fragmentation in Vacuum and Medium with gamma-hadron Correlations in PHENIX
Jet fragmentation in p+p and Au+Au collisions is studied via back-to-back
correlations of direct photons and charged hadrons. The direct photon
correlations are obtained by statical subtraction of the background from decay
photons. Results on the nuclear modification to the associated charged hadron
yields are reviewed. Further studies of jet fragmentation in p+p using isolated
direct photons are also presented. A kT-smeared LO pQCD calculation is used to
interpret the data. The sensitivity of the data to the underlying fragmentation
function is tested and the results are found to be compatible with expectations
of a sample dominated by quark jet fragmentation.Comment: Talk presented at Hot Quarks 2010, June 21-26, La Londe Les Maures,
France. To be published in Journal of Physics: Conference Series (JPCS
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