Entropy-driven formation of the gyroid cubic phase

We show, by computer simulation, that tapered or pear-shaped particles, interacting through purely repulsive interactions, can freely self-assemble to form the three-dimensionally periodic, gyroid cubic phase. The Ia3d gyroid cubic phase is formed by these particles both on compression of an isotropic configuration and on expansion of a smectic A bilayer arrangement. For the latter case, it is possible identify the steps by which the topological transformation from non-intersecting planes to fully interpenetrating, periodic networks takes place</p

Galactic Cosmic Rays from Supernova Remnants: II Shock Acceleration of Gas and Dust

This is the second paper (the first was astro-ph/9704267) of a series analysing the Galactic Cosmic Ray (GCR) composition and origin. In this we present a quantitative model of GCR origin and acceleration based on the acceleration of a mixture of interstellar and/or circumstellar gas and dust by supernova remnant blast waves. We present results from a nonlinear shock model which includes (i) the direct acceleration of interstellar gas-phase ions, (ii) a simplified model for the direct acceleration of weakly charged dust grains to energies of order 100keV/amu simultaneously with the gas ions, (iii) frictional energy losses of the grains colliding with the gas, (iv) sputtering of ions of refractory elements from the accelerated grains and (v) the further shock acceleration of the sputtered ions to cosmic ray energies. The calculated GCR composition and spectra are in good agreement with observations.Comment: to appear in ApJ, 51 pages, LaTeX with AAS macros, 9 postscript figures, also available from ftp://wonka.physics.ncsu.edu/pub/elliso

CO and CI maps of the starburst galaxy M82

The first map of an external galaxy in the 3P₁ - 3P0 fine-structure line of atomic carbon (CI) is presented towards the nucleus of the starbuster M82, and compared with the distinction of the CO J = 4 - 3 molecular emission. The CI traces features that are seen in lower transition CO maps, and shows that CI and the CO are well mixed and have similar spatial distributions. There are small differences between the CO J = 4 - 3 line and lower transition CO data towards the NE part of the molecular ring, where the emission is less prominent. The abundance ratio [CI]/[CO] across M82 is very high, with an average value ~ 0.5 across most of the nucleus, a factor at least 5 times that which is typical of dense molecular cloud cores seen in our own Galaxy. This means that on average, CI is overabundant towards M82. This result can be explained using models which provide enhancements to the CI abundance above normal Interstellar Medium values, a result of a greater cosmic ray flux in M82, or where there is substantial mixing of the gas