60,297 research outputs found
Millimeter-wave antenna system
Parabolic reflectors fabricated from Carbon Fiber Reinforced Plastic (CFRP) composite material will not distort their shape by more than 3 percent of millimeter wavelength, despite large temperature differences on reflector surfaces. CFRP has zero thermal expansion. It is derived from charred polyacrylonitrite plastic filaments that are combined with epoxy resin
Cuspy Dark-Matter Haloes and the Galaxy
The microlensing optical depth to Baade's Window constrains the minimum total
mass in baryonic matter within the Solar circle to be greater than 3.9 x
10^{10} solar masses, assuming the inner Galaxy is barred with viewing angle of
roughly 20 degrees. From the kinematics of solar neighbourhood stars, the local
surface density of dark matter is about 30 +/- 15 solar masses per square
parsec. We construct cuspy haloes normalised to the local dark matter density
and calculate the circular-speed curve of the halo in the inner Galaxy. This is
added in quadrature to the rotation curve provided by the stellar and ISM
discs, together with a bar sufficiently massive so that the baryonic matter in
the inner Galaxy reproduces the microlensing optical depth. Such models violate
the observational constraint provided by the tangent-velocity data in the inner
Galaxy (typically at radii 2-4 kpc). The high baryonic contribution required by
the microlensing is consistent with implications from hydrodynamical modelling
and the pattern speed of the Galactic bar. We conclude that the cuspy haloes
favoured by the Cold Dark Matter cosmology (and its variants) are inconsistent
with the observational data on the Galaxy.Comment: 5 pages, 1 figures, MNRAS (submitted
Jamming transitions and avalanches in the game of Dots-and-Boxes
We study the game of Dots-and-Boxes from a statistical point of view. The
early game can be treated as a case of Random Sequential Adsorption, with a
jamming transition that marks the beginning of the end-game. We derive set of
differential equations to make predictions about the state of the lattice at
the transition, and thus about the distribution of avalanches in the end-game.Comment: 7 pages, 8 figures, revtex
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