11,025 research outputs found
Scaling approach to glassy stationary states of spin-glasses under chaos effects
Dynamics of spin-glasses subjected to slow continuous changes of working
enviroment such as slow changes of temperature or interaction bonds are studied
based on scaling arguments and numerical simulations of continuous bond
changes. Such perturbations lead to a glassy stationary state where the age or
domain size of the system are pinned to macroscopic but finite values due to
competition between relaxation and chaos effects (rejuvenation).
Flutuation-dissipation relation is also pinned to that of a finite age. The
scenario explains the anomalously weak cooling rate dependece of spin glasses.Comment: Contribution to SPDSA 2004, Hayama, Japa
Radiant Emission Characteristics of Diffuse Conical Cavities
Radiant-energy emission of diffuse conical cavitie
Thermal Radiation Absorption in Rectangular-Groove Cavities
Thermal radiation absorption in rectangular-groove cavitie
Crew procedures and workload of retrofit concepts for microwave landing system
Crew procedures and workload for Microwave Landing Systems (MLS) that could be retrofitted into existing transport aircraft were evaluated. Two MLS receiver concepts were developed. One is capable of capturing a runway centerline and the other is capable of capturing a segmented approach path. Crew procedures were identified and crew task analyses were performed using each concept. Crew workload comparisons were made between the MLS concepts and an ILS baseline using a task-timeline workload model. Workload indexes were obtained for each scenario. The results showed that workload was comparable to the ILS baseline for the MLS centerline capture concept, but significantly higher for the segmented path capture concept
Absorption and Emission Characteristics of Diffuse Spherical Enclosures
The thermal radiation characteristics of spherical cavities are of practical interest in connection with the absorption of radiant energy for both space-vehicle and terrestrial applications. Also, spherical cavities are of potential use as sources of black-body energy. The purpose of this brief paper is to determine both the absorption and emission characteristics of spherical cavities which are diffuse reflectors and emitters
Effect of exchange interaction on superparamagnetic relaxation
We use Langer's approach to calculate the reaction rate of a system of two
(classical) spins interacting via the exchange coupling in a magnetic field
, with uniaxial anisotropy of constant .
We find a particular value of the exchange coupling, that is , where , which separates two regimes
corresponding to a two-stage and one-stage switching.
For the N\'eel-Brown result for the one-spin problem is recovered.Comment: 7 pages, 2 eps figures, fig.1 of better quality can be provided upon
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A streamwise-constant model of turbulent pipe flow
A streamwise-constant model is presented to investigate the basic mechanisms
responsible for the change in mean flow occuring during pipe flow transition.
Using a single forced momentum balance equation, we show that the shape of the
velocity profile is robust to changes in the forcing profile and that both
linear non-normal and nonlinear effects are required to capture the change in
mean flow associated with transition to turbulence. The particularly simple
form of the model allows for the study of the momentum transfer directly by
inspection of the equations. The distribution of the high- and low-speed
streaks over the cross-section of the pipe produced by our model is remarkably
similar to one observed in the velocity field near the trailing edge of the
puff structures present in pipe flow transition. Under stochastic forcing, the
model exhibits a quasi-periodic self-sustaining cycle characterized by the
creation and subsequent decay of "streamwise-constant puffs", so-called due to
the good agreement between the temporal evolution of their velocity field and
the projection of the velocity field associated with three-dimensional puffs in
a frame of reference moving at the bulk velocity. We establish that the flow
dynamics are relatively insensitive to the regeneration mechanisms invoked to
produce near-wall streamwise vortices and that using small, unstructured
background disturbances to regenerate the streamwise vortices is sufficient to
capture the formation of the high- and low-speed streaks and their segregation
leading to the blunting of the velocity profile characteristic of turbulent
pipe flow
Five-Torsion in the Homology of the Matching Complex on 14 Vertices
J. L. Andersen proved that there is 5-torsion in the bottom nonvanishing
homology group of the simplicial complex of graphs of degree at most two on
seven vertices. We use this result to demonstrate that there is 5-torsion also
in the bottom nonvanishing homology group of the matching complex on
14 vertices. Combining our observation with results due to Bouc and to
Shareshian and Wachs, we conclude that the case is exceptional; for all
other , the torsion subgroup of the bottom nonvanishing homology group has
exponent three or is zero. The possibility remains that there is other torsion
than 3-torsion in higher-degree homology groups of when and .Comment: 11 page
Lensing magnification of supernovae in the GOODS-fields
Gravitational lensing of high-redshift supernovae is potentially an important
source of uncertainty when deriving cosmological parameters from the measured
brightness of Type Ia supernovae, especially in deep surveys with scarce
statistics. Photometric and spectroscopic measurements of foreground galaxies
along the lines-of-sight of 33 supernovae discovered with the Hubble Space
Telescope, both core-collapse and Type Ia, are used to model the magnification
probability distributions of the sources. Modelling galaxy halos with SIS or
NFW-profiles and using M/L scaling laws provided by the Faber-Jackson and
Tully-Fisher relations, we find clear evidence for supernovae with lensing
(de)magnification. However, the magnification distribution of the Type Ia
supernovae used to determine cosmological distances matches very well the
expectations for an unbiased sample, i.e.their mean magnification factor is
consistent with unity. Our results show that the lensing distortions of the
supernova brightness can be well understood for the GOODS sample and that
correcting for this effect has a negligible impact on the derived cosmological
parameters.Comment: 22 pages, 9 figures, accepted for publication by Ap
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