13,952 research outputs found
Stellar Oscillons
We study the weakly nonlinear evolution of acoustic instability of a plane-
parallel polytrope with thermal dissipation in the form of Newton's law of
cooling. The most unstable horizontal wavenumbers form a band around zero and
this permits the development of a nonlinear pattern theory leading to a complex
Ginzburg-Landau equation (CGLE). Numerical solutions for a subcritical, quintic
CGLE produce vertically oscillating, localized structures that resemble the
oscillons observed in recent experiments of vibrated granular material.Comment: 12 Latex pages using aasms4.sty, 2 postscript figures, submitted to
the proceedings of the Florida Workshop in Nonlinear Astrophysics and Physic
On the Orbits of Low-mass Companions to White Dwarfs and the Fates of the Known Exoplanets
The ultimate fates of binary companions to stars (including whether the
companion survives and the final orbit of the binary) are of interest in light
of an increasing number of recently discovered, low-mass companions to white
dwarfs (WDs). In this Letter, we study the evolution of a two-body system
wherein the orbit adjusts due to structural changes in the primary, dissipation
of orbital energy via tides, and mass loss during the giant phases; previous
studies have not incorporated changes in the primary's spin. For companions
ranging from Jupiter's mass to ~0.3 Msun and primaries ranging from 1-3 Msun,
we determine the minimum initial semimajor axis required for the companion to
avoid engulfment by the primary during post-main-sequence evolution, and
highlight the implications for the ultimate survival of the known exoplanets.
We present regions in secondary mass and orbital period space where an engulfed
companion might be expected to survive the common envelope phase (CEP), and
compare with known M dwarf+WD short-period binaries. Finally, we note that
engulfed Earth-like planets cannot survive a CEP. Detection of a
first-generation terrestrial planet in the white dwarf habitable zone requires
scattering from a several-AU orbit to a high-eccentricity orbit (with a
periastron of ~Rsun) from which it is damped into a circular orbit via tidal
friction, possibly rendering it an uninhabitable, charred ember.Comment: Replaced with version in Journa
An automated system for creep testing
A completely automated data collection system was devised to measure, analyze, and graph creep versus time using a PC, a 16 channel multiplexed analog to digital converter, and low friction potentiometers to measure length. The sampling rate for each experiment can be adjusted in the software to meet the needs of the material tested. Data is collected and stored on a diskette for permanent record and also for later data analysis on a different machine
De derde-benadeelde en de directe actie in het verzekeringsrecht: grensoverschrijdende gevallen
Generation of large-scale winds in horizontally anisotropic convection
We simulate three-dimensional, horizontally periodic Rayleigh-B\'enard
convection between free-slip horizontal plates, rotating about a distant
horizontal axis. When both the temperature difference between the plates and
the rotation rate are sufficiently large, a strong horizontal wind is generated
that is perpendicular to both the rotation vector and the gravity vector. The
wind is turbulent, large-scale, and vertically sheared. Horizontal anisotropy,
engendered here by rotation, appears necessary for such wind generation. Most
of the kinetic energy of the flow resides in the wind, and the vertical
turbulent heat flux is much lower on average than when there is no wind
Climate injustice, criminalisation of land protection and anti-colonial solidarity:Courtroom ethnography in an age of fossil fuel violence
Fossil fuel violence and visual practices on Indigenous land:Watching, witnessing and resisting settler-colonial injustices
Characteristic value determination from small samples
The paper deals with the characteristic value determination from relatively small samples. When the distribution and its parameters of a random variable are known, the characteristic value is deterministic quantity. However, in practical problems the parameters of distribution are unknown and can only be estimated from random samples. Therefore the characteristic value is by itself a random variable. The estimates of characteristic values are strongly dependant on the distribution of random variable. In the paper we show the analytical solution for characteristic value determination from random samples of normal and lognormal random variables. The confirmation of analytical results is accomplished by the use of computer simulations. For Gumbel, and Weibull distribution the characteristic value estimates are obtained numerically by combination of simulations and bisection method. In the paper the numerical results are presented for 5% characteristic values with 75% confidence interval, which is in accord with the majority of European building standards. The proposed approach is demonstrated on the data of experimentally obtained bending strengths of finger jointed wooden beams. (C) 2006 Elsevier Ltd. All rights reserved
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