published_or_final_version / abstract / Physics / Master / Master of Philosophy

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The recombination rate coefficient for molecular helium ions has been measured in a pulsed afterglow at 1.86 Torr as a function of electron temperature and electron density without making a priori assumptions about the functional dependence. The concentrations of the molecular ions and electrons were measured and the source terms for the molecular ions were included in the rate equation.

Call number: LD2668 .T4 1958 F79 / Master of Science

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, 24 May 2014. / The Sunyaev-Zel'dovich e ect (hereafter SZE), i.e. the distortion of the cosmic microwave background (CMB) spectrum due to inverse Compton scattering of CMB photons o energetic electrons in cosmic structures, is a relevant inves- tigation tool for astrophysical and cosmological studies. Since the SZE is an interaction between photons and electrons, polarization arises as a natural out- come and then provides the SZE with an important complementary component as an astrophysical and cosmological probe. This thesis is an extensive study on the SZE in non-relativistic and relativistic regime including polarization. We rst perform a study on a set of galaxy clusters hosting radio halos where we constrain the non-thermal pressure present in these structures using multifre- quency data such as SZE, radio and X-ray. We found that the average ratio between non-thermal to thermal pressure is 0:5. We then derive, in the full relativistic regime, a general formulation of the properties of the SZE, and we further derive the Stokes parameters, Q and U, of the polarized SZE. This is done in a general case by solving the polarized Boltzmann collisional integral in the Thomson limit that allows us to extract the Stokes parameters for arbitrary electron distribution functions. We further discuss the spectral features of the SZE polarization as produced by other additional e ects occurring in the clus- ter atmospheres, like nite optical depth e ects and transverse plasma motions. We nally apply the results of our study to di erent cosmic structures (e.g. galaxy clusters and radio galaxies) and we discuss the relevance of SZE polar- ization in the study of extragalactic astrophysical plasmas and for cosmological applications.

As an additional study, effect of tyrosine nitration on the BCD of protonated and metalated peptides was investigated. Some fragment ions that were inhibited in the ECD of protonated peptides were liberated in the ECD of metalated peptides. By theoretical calculation of the cation-pi and cation-nitro group coordination using the metal ions nitrated phenol complex as a model, it is found that the metal ions might favor coordinating with the nitro group of the nitrated tyrosine residue in the peptides. / In order to improve the performance of the electron capture dissociation (BCD) mass spectrometry for structural analysis of peptides/proteins, BCD of peptides cationized with various transition metal ions was investigated. It was found that peptides adducted with different divalent transition metal ions generated different BCD tandem mass spectra. For Mn2+and Zn2+, the incoming low-energy electron would not favor being trapped by the metal ions and instead trigger the usual BCD dissociation channel(s) via "hot-hydrogen" or "superbase" intermediates to form a series of c-/z·- fragments. For other first row transition metal ions, including Fe2+, Co2+, Ni 2+and Cu2+, reduction of the metal ions occurs preferentially during the electron capture event and lead to the formation of usual "slow-heating" type of fragment ions, i.e. metalated a-/y-fragments & metalated b-/y- fragments. / To further compare the behavior of metal ions with the same electronic configuration, BCD of Group IIB metal ions adducted peptides were investigated. In contrast to the ECD behavior of Zn2+ adducted peptides, peptide radical cations (M+· ) and fragment ions corresponding to losses of neutral side chain from M+· were observed in the ECD spectra of Hg2+ and Cd2+ adducted peptides. The experimental observations appeared to depend on the balance of the ionization energy of peptide and the solvation modulated ionization energies of the metal atom. The reduction of divalent metal ions by the electron capture event could induce spontaneous electron transfer from the peptide moiety to the monovalent metal centre and generate hydrogen-deficient M +· species. / Chen, Xiangfeng. / Adviser: T.-W. Dominic Chan. / Source: Dissertation Abstracts International, Volume: 73-06, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 131-139). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

by Siu-Chung Wong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1988. / Bibliography: leaves 98-102.

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