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Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 66-67).

Thesis (M. Phil.)--University of Hong Kong, 1994. / Typescript. Includes bibliographical references (leaves 92-94).

It is generally assumed that the temperature in the inner part of the primordial nebula was too high to form and agglomerate ice bodies. Yet, water is present in most of the terrestrial planets of our solar system. To investigate the reason for this we concentrate on comets as a potential water deliverer to the inner planets. The data for this work is taken from 3D simulations of comet trajectories inside a gas-dust disk with embedded planet embryos. We have developed a MATLAB code that could read data files from these simulations containing orbital elements of the comets and planetary embryos. Comets experience inward migration due to friction with the remains of the disk. We study comets of four different sizes.      We find that smaller comets migrate faster and therefore spend less time in the inner solar system. Smaller comets are numerous and are therefore destroyed in greater numbers than the larger comets. Larger comets on the other hand slow their migration and spending much more time among inner planets they are more massive and produce more massive collisions with the inner planets than the smaller comets. Therefore are larger comets a more promising source of water delivery to the inner planets. In Studying individual collisions we observe that a typical interaction involves regular close encounters with the same embryo during periods of 100000 years or more before the two orbits intersect. This also tells us that with a large number of comets expected at this stage of solar system evolution the collective effect of comets on low-mass planetary embryos may be significant.

Thesis (Ph.D.) from the Dept. of Physics, University of Adelaide, 1973.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1989. / Cover title. Includes bibliographical references (p. 253-256).

Hubble Space Telescope images of the Orion nebula taken with the Wide-Field Camera have revealed subarcsecond structure in several dozen objects which are apparently ionized externally from nearby stars. We have obtained near-IR images and IR polarimetry of the Orion region to search for correlations with the WFC objects. We find that all of the ultracompact WFC objects are associated with IR features of some sort, and that some are associated with strongly polarized IR emission. The object with strongest polarization also shows small IR "lobes". In addition, we find some previously unreported sources, showing polarized IR emission, outside the field of the HST images, which we believe may be the same sorts of object. We note that the object with strongest polarization has a double-lobed appearance in the K band image.

Gamma-ray astronomy is generally viewed as an adjunct to cosmic ray physics. As such, the observation of very high energy gamma-rays will allow a new and complementary means of examining the origin and evolution of cosmic rays. However, at present the atmospheric Cerenkov technique (the technique by which very high energy gamma-rays are observed) is seriously hampered by limited flux sensitivity. Monte Carlo simulations suggest that the application of imaging to the atmospheric Cerenkov technique will provide a much needed increase in sensitivity. The successful application of imaging to very high energy gamma-ray observations of the Crab nebula will be discussed, as will improved techniques for calibration and noise rejection. These observations permit an improved estimate of the nebular magnetic field strength.

Thesis (Ph. D.)--University of Chicago, Dept. of Astronomy & Astrophysics, August 2001. / Includes bibliographical references. Also available on the Internet.

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