HI in the Outskirts of Nearby Galaxies

The HI in disk galaxies frequently extends beyond the optical image, and can trace the dark matter there. I briefly highlight the history of high spatial resolution HI imaging, the contribution it made to the dark matter problem, and the current tension between several dynamical methods to break the disk-halo degeneracy. I then turn to the flaring problem, which could in principle probe the shape of the dark halo. Instead, however, a lot of attention is now devoted to understanding the role of gas accretion via galactic fountains. The current $\rm \Lambda$ cold dark matter theory has problems on galactic scales, such as the core-cusp problem, which can be addressed with HI observations of dwarf galaxies. For a similar range in rotation velocities, galaxies of type Sd have thin disks, while those of type Im are much thicker. After a few comments on modified Newtonian dynamics and on irregular galaxies, I close with statistics on the HI extent of galaxies.Comment: 38 pages, 17 figures, invited review, book chapter in "Outskirts of Galaxies", Eds. J. H. Knapen, J. C. Lee and A. Gil de Paz, Astrophysics and Space Science Library, Springer, in pres

A Mathematical Model Of The Chemical Distribution In A Disease State: Hypothyroidism

A mathematical model of the fluid and electrolyte distribution in a standard laboratory dog was developed. It adequately predicted measured changes in distribution of various chemical substances following administration of saline and alkaline solutions; however, the measured changes due to acid addition were not as well predicated. A new fluid compartment was added to the standard dog model to simulate hypothyroidism as a result of a hypothesis of body chemistry changes in hypothyroid animals. Although most parameters of the new compartment were determined from the literature, some were chosen numerically to correlate most accurately the model prediction and the chemical data take on hypothyroid dogs following an alkaline chemical infusion. Both hypothyroid and euthyroid dogs received injections of acid solution to provide chemical data for comparing distributional changes in these groups and paring chemical distributional changes in these groups and for validation of the models simulation these states. The results proved statistically the hypothyroid dogs respond differently from normal ones to acid infusion. However, the hypothyroid model, like the normal mode, did not predict these experimental results well. Laboratory technological problems accounted for many of these discrepancies. The results of this research have suggested that additional experiments and other chemical perturbations are necessary to test the biochemical hypotheses formulated in this Memorandum. The ideas explored are applicable to studies of other disease states that exhibit gross fluid and electrolyte abnormalities.U.S. Air Forc