Scattering (Physics)

The present research is a targeted endeavor to study the underlying characteristics and novel applications of millimeter (mm) wave through terahertz (THz) spectrum of electromagnetic (EM) energy. Focused thereof are the following specific tasks broadly considered pertinent to the said EM spectral range: (i) To elucidate the material characteristics vis-à-vis the interaction with EM energy at the test frequencies; (ii) to identify biomedical applications based on the material characteristics studied and applied to biomedia; and (iii) to model the wireless communication channels supporting EM waves at the test frequency bands of interest. Commensurate with the scope as above, the objectives of the research are as follows:

Expressions are developed for the near and far field
angular intensity distributions of TM mode scattering of a
plane wave by a glass-enclosed plasma cylinder. Numerical
computations for a simple collisionless plasma model are
made in order to study the effect of the free electron
density structure on intensity distributions. The inverse
problem is briefly considered.

Many acoustic targets of interest contain features that are periodic in space. This thesis demonstrates that a chirp waveform, 2 kHz to 12 kHz, can detect repetitive structures with periods in the range of 0.125 m to 0.75 m. As aspect angle increases from 0 deg to 90 deg, a frequency shift in the range of 830 Hz to 4800 Hz will occur as the period decreases from 0.75 to 0.125 m. It follows that, spectral analysis can aid in target identification. A sonar propagation model has been developed to simulate the acoustic backscattered energy of a target with periodic characteristics in the presence of seafloor scattering. Examining the spectral components, with appropriate time gating, can achieve a gain of 7 dB at 3100 m.

This work is a simulation of the Accretion-Induced Collapse of a 1.37 solar mass white dwarf into a neutron star and the subsequent generation of a neutrino-driven wind, with an examination as to whether the event is a candidate for r-process nucleosynthesis. The simulation utilizes a new radiation hydrodynamic code, RadHyd, to model the AIC event. We examine the process of Accretion-Induced Collapse utilizing two sets of neutrino-scattering and absorption rates: The first, and simpler of the two has been in use since they were first introduced in 1985. The second includes a more accurate implementation of neutrino-nucleon scattering and nucleon bremsstrahlung. The improved nue - nue-nucleon scattering rate now permits energy to be exchanged between neutrinos and matter by this process, and is therefore important for the numu's and nutau's, as their only channels for exchanging energy in the standard rates was by the relatively weak NES and pair processes. Neutrino-nucleon bremmsstrahlung is also important for numu's and nutau's as this opens another channel (beside pair process) for their production. Both simulations show a neutrino-driven wind being generated after core bounce and shock propagation. We examine the conditions in these winds to ascertain whether the requisite conditions are attained for an r-process. In neither case are these achieved during the time of the simulations (i.e. 2 seconds). However, these simulations need to be carried out at least an order of magnitude longer before firm conclusions can be drawn about the applicability of this site for the r-process.