The cylindrical cell approximation in thermal utilization

In solving the neutron diffusion equation in one cell of an infinite lattice, a common procedure is to replace the rectangular (or hexagonal) cell with an equivalent cylindrical cell. In order to estimate the effect of this approximation a new method is presented in which the flux in the entire cell (not the equivalent cylindrical cell) is expanded in a Fourier cosine series. Then the boundary conditions over the cell surface are satisfied exactly. Furthermore, algebraic equations for the expansion coefficients of the flux are obtained because the integrals over the cell can be done in closed form. It is found that truncation of the flux series after 10 terms gives good results. The method is felt to have more general application than to the actual problem treated here since such `mixed geometry' problems frequently arise in reactor physics and in other areas as well.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33375/1/0000773.pd

The 3D Structure of N132D in the LMC: A Late-Stage Young Supernova Remnant

We have used the Wide Field Spectrograph (WiFeS) on the 2.3m telescope at Siding Spring Observatory to map the [O III] 5007{\AA} dynamics of the young oxygen-rich supernova remnant N132D in the Large Magellanic Cloud. From the resultant data cube, we have been able to reconstruct the full 3D structure of the system of [O III] filaments. The majority of the ejecta form a ring of ~12pc in diameter inclined at an angle of 25 degrees to the line of sight. We conclude that SNR N132D is approaching the end of the reverse shock phase before entering the fully thermalized Sedov phase of evolution. We speculate that the ring of oxygen-rich material comes from ejecta in the equatorial plane of a bipolar explosion, and that the overall shape of the SNR is strongly influenced by the pre-supernova mass loss from the progenitor star. We find tantalizing evidence of a polar jet associated with a very fast oxygen-rich knot, and clear evidence that the central star has interacted with one or more dense clouds in the surrounding ISM.Comment: Accepted for Publication in Astrophysics & Space Science, 18pp, 8 figure