Thesis (M.S.)--Naval Postgraduate School, 2002. / Thesis advisor(s): Philip A. Durkee, Douglas L. Westphal. Includes bibliographical references (p. 81-82). Also available online.

The calculation of the physical conditions near the inner rim of a protoplanetary disk using the new computational model Pisco is described. Diagnostic plots illustrate solutions for disk structure, radiation field, chemical composition, and heating and cooling of the disk in a steady-state approximation for both disks with unsettled dust and with settled dust. Disks with unsettled dust are found to have hotter gas temperatures above the disk photosphere and a more pronounced temperature inversion at the disk photosphere. Recommendations are made for the development of Pisco. Pisco has the potential to explore what observed molecular emission can imply about disk structure. / text

ITC/USA 2012 Conference Proceedings / The Forty-Eighth Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2012 / Town and Country Resort & Convention Center, San Diego, California / The extremely large electrical-size and complexity of terrain scene poses great challenge in channel modeling of aeronautic telemetry. It becomes even more difficult if severe multipath and fading present due to scattering and attenuation of ground, terrain objects and precipitation [Rice, 2004]. This is critical in more sophisticated test scenarios involving low flying unmanned air vehicles and helicopters tested over water at high sea states, in hilly terrain, or even over urban environment. Conventional ray tracing and simple Fresnel reflection are not sufficient to characterize such complex channels. Hence, the novel bidirectional analytic ray tracing and radiative transfer (RT²) is proposed for advanced telemetry channel modeling.

No description available.

We developed radiative transfer models to reproduce Titan’s visible and near infrared spectra, to determine the effects of the haze, and retrieve the methane abundances during Titan’s current southern summer. With ground-based high resolution spectra of CH3D absorption at 1.6 μm, we measured the global CH₃D abundance. Combined with observations of 8.6 μm emission of CH₃D and CH₄ that indicate their relative abundances, we thus determined the global CH₄ abundance. We expanded on these ground-based measurements, with improved radiative transfer models based on the Huygens DISR models, and spectra which resolve the spatial variation of the CH₃D lines. The profiles of CH3D thus obtained revealed that the methane abundance on the lowest 10 km of Titan’s atmosphere does not vary by more than 20% over 32°S-32°N. With the extensive coverage of Cassini VIMS observations at 0.35-1.6 μm, we determined the latitudinal variation of the methane at 20-50 km and of the haze. We find an ambiguity between the methane and haze abundances, so their gradients become coupled. At the lower limit of the methane gradient, the spectral variation observed can be reproduced with no methane change, and a haze density increase of 60% between 20°S and 10°S. The largest methane variation allowed by the data, derived assuming no haze variation with latitude, is a drop of 60% over latitudes 27°S to 19°N. Our analysis indicates that the latitudinal variations in Titan’s visible to near-IR albedo, the North/South Asymmetry, result primarily from variations in the thickness of the haze above 80 km altitude. The range of methane latitudinal variations allowed between 27°S to 19°N indicates temperature variations of no more than 1.5 K at 20-30 km, altitudes where the Huygens profile is saturated.

No description available.

Stellar model atmospheres are a fundamental tool for our understanding of stars. Because the chemical composition of stars cannot be measured directly, the inferred stellar parameters are model dependent. In recent years great progress has been made in the modeling of stellar atmospheres, allowing the relaxation of simplifying assumptions made in previous models. The use of new 3D model atmospheres to infer the solar chemical composition has resulted in a decrease of the solar metallicity. This result has caused some controversy and is being challenged. The main aim of this thesis is to ascertain if the new models of stellar atmospheres are realistic and can be trusted to derive the chemical composition of stars in general, and the Sun in particular. Other objectives also include the study of line formation in the Sun at high spatial resolution, and possible implications in the modeling. The Sun is the ideal test-bench for detailed analyses of stellar atmospheres. With the solar surface being resolved in great detail and at different viewing angles, a wealth of information can be gathered that allows for very robust tests of atmosphere models. The testing detailed here addresses several fronts. On one hand, the model�s temperature structure is directly tested with the classical tests of continuum centre-to-limb variations and absolute fluxes. On the other hand, the line formation is tested at different viewing angles and high spatial and spectral resolution. Here the main focus is on oxygen lines, as oxygen has an important contribution for the total solar metallicity. However, other lines are also tested. High quality data were specifically obtained for these line formation tests, using the Swedish 1-m Solar Telescope. For the temperature structure tests we find a surprisingly good agreement between the 3D model and the observations, surpassing even semi-empirical models. The solar 1D non-LTE models have a very similar behaviour to 1D LTE models, confirming that LTE is a good approximation in the solar photosphere. The 3D theoretical model performs consistently better than its 1D counterparts. The oxygen line formation tests are carried out in great detail, with a careful wavelength calibration, revised atomic data, and allowing for departures from LTE. Again we find a reassuring agreement between the 3D model predictions and the observations, both for the centre-to-limb variation of the lines and the line formation at high spatial resolution. The observations at different viewing angles also allowed the empirical determination of the role of hydrogen collisions with oxygen, important when deriving the oxygen abundance. The tests undertaken here show that the 3D model atmospheres are indeed very realistic. Their predicted temperature structure and velocity fields compare very favourably with observations of the Sun. Together with previous tests, this indicates they can be relied upon to derive the chemical composition of the Sun and similar late-type stars.

Thesis (Ph. D.)--University of Washington, 2008. / Vita. Includes bibliographical references (p. 99-102).

Thesis (Ph.D.) - University of St Andrews, March 2007.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (p. 87-94).