259,730 research outputs found
Testing Gravity Theories In The Radiative Regime Using Pulsar Timing Arrays
General relativity has predicted the existence of gravitational waves (GW),
which are waves of the distortions of space-time with two degrees of
polarization and the propagation speed of light. Alternative theories predict
more polarizations, up to a maximum of six, and possible deviation of
propagation speed from the light speed. The present paper reviews recent
proposals to test the gravity theories in the radiation regime by observing GWs
using pulsar timing arrays.Comment: 4 pages, 2 figures, PULSAR CONFERENCE 2010, Chia Laguna Resort,
Sardinia, Italy, 10-15 October, 201
Effect of Diethylenetriamine and Triethylamine sensitization on the critical diameter of Nitromethane
In this work, the critical diameter for detonation was measured for Nitromethane (NM) sensitized with two different amines: Diethylenetriamine (DETA) and Triethylamine (TEA). The critical diameter in glass and polyvinylchloride tubes is found to decrease rapidly as the amount of sensitizer is increased, then increase past a critical amount of sensitizer. Thus the critical diameter reaches a minimum at a critical concentration of sensitizer. It was also found that the critical diameter is lower with DETA than with TEA
Dirty quantum Hall ferromagnets and quantum Hall spin glasses
We study quantum Hall ferromagnets in the presence of a random electrostatic
impurity potential, within the framework of a classical non-linear sigma model.
We discuss the behaviour of the system using a heuristic picture for the
competition between exchange and screening, and test our conclusions with
extensive numerical simulations. We obtain a phase diagram for the system as a
function of disorder strength and deviation of the average Landau level filling
factor from unity. Screening of an impurity potential requires distortions of
the spin configuration. In the absence of Zeeman coupling there is a
disorder-driven, zero-temperature phase transition from a ferromagnet at weak
disorder and small deviation from integer filling to a spin glass at stronger
disorder or large charge deviation. We characterise the spin glass phase in
terms of its magnetic and charge response, as well as its ac conductivity.Comment: 12 pages, 6 figures, REVTEX
An infrared proper motion study of the Orion bullets
We report the first IR proper motion measurements of the Herbig-Haro objects
in the Orion Molecular Cloud--One using a four-year time baseline. The [Fe II]
emitting bullets are moving of order 0.08 arcsec per year, or at about 170
\kms. The direction of motion is similar to that inferred from their
morphology. The proper motions of \h2 emitting wakes behind the [Fe II]
bullets, and of newly found \h2 bullets, are also measured. \h2 bullets have
smaller proper motion than [Fe II] bullets, while \h2 wakes with leading [Fe
II] bullets appear to move at similar speeds to their associated bullets. A few
instances of variability in the emission can be attributed to dense, stationary
clumps in the ambient cloud being overrun, setting up a reverse--oriented
bullet. Differential motion between [Fe II] bullets and their trailing \h2
wakes is not observed, suggesting that these are not separating, and also that
they have reached a steady--state configuration over at least 100 years. The
most distant bullets have, on average, larger proper motions, but are not
consistent with free expansion. Nevertheless an impulsive, or short--lived
( 1,000 years) duration for their origin seems likely.Comment: 9 pages, 8 figure
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