In this thesis we make a new measurement of the primordial deuterium abundance, and analyse five other systems selected as possible D/H candidates. We also undertake an investigation of systematic errors in a system where an existing deuterium measurement has been made. We measure the number of hydrogen components and their velocity distributions in a moderate and high redshift sample of Lyman limit systems in one Angstrom resolution spectra. We present a new measurement of the deuterium-to-hydrogen ratio, D/H, at z=3.2560 in a newly-discovered low metallicity absorption system towards the quasar PG1937-1009. We attempt to account for any systematic effects that could influence the D/H measurement. We find a 1 sigma range for D/H*1e5 of 1.6 (+0.25) (-0.30). Using high resolution spectra from the Hubble Space Telescope and the Very Large Telescope, we assess the suitability of five D/H candidate absorption systems. These systems were selected as candidates using lower resolution spectra. We measure the neutral hydrogen column density, identify metal lines and analyse the velocity structure of each system, and show them to be unsuitable for measuring D/H. We also investigate the systematic errors in the absorber at z=0.701 towards quasar PG1718-4801 that was initially thought to show a high primordial D/H value. We analyse the dependence of the putative deuterium line's parameters on wavelength calibration errors in the HST spectra and present a revised deuterium measurement. We examine the velocity widths of two samples of one Angstrom resolution quasar spectra showing Lyman limit absorption systems. The first sample is at high redshifts, taken from the Sloan quasar data release 3 catalogue. The second is at intermediate redshifts, compiled from a survey for UV quasar absorption systems taken with the Hubble Space Telescope. We use a modified version of the Voigt profile fitting program, VPFIT, to estimate the number of hydrogen velocity components and column density in the Lyman limit systems. We compare the velocity distributions of the higher and lower redshift samples. We find the distributions are consistent with other measures of the velocity spread in absorption systems, and find no compelling evidence for evolution between the redshift samples.

Thesis (M. A.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Thesis (M. A.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Thesis (M. A.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Thesis (M. Sc.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 50-51).

Thesis (M. Sc.)--University of Hong Kong, 1967. / Mimeographed.

Thesis (M. Phil.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 134-145).

No description available.

The design and characterization of both electromagnetic bandgap (EBG) and inter-coupled split-ring resonator (SRR) structures utilized in microwave frequencies were proposed and studied. A new double-stopband EBG structure with a passband region of 14 to 18 GHz was initially constructed by determining the critical structural ratios. To reduce the size of EBG structure, a novel tapered array pattern was introduced. The structural period, the number of slot, and the length of slot were examined and a strong correlation was found between the lowpass cutoff frequency and the center slot length. Non-linearly tapered configuration was applied to enhance the filter performance and its size was only 57% of the conventional EBG structure. Inter-coupled SRR was also examined and utilized as a bandpass filter when it is implemented on the microstrip line for the first time. It was found that the proposed structure can provide a fractional bandwidth of over 68% with an insertion loss of 0.81 dB in the passband region with a device size of 15.5 mm. / Chemical bath deposited Cadmium Sulfide (CdS) thin film was applied to the microwave structures to construct switchable filters. The illumination-sensitive CdS thin film's sheet resistance has been demonstrated to be able to switch from 300 to 109 O/square. With the proposed "conductive-islands" implementation, switching of EBG structure's transmission coefficient (S21) was achieved from 31.3 dB to 5.6 dB at 13 GHz. The inter-coupled SRR structure also showed a S21 switching response from 19 dB to 1.5 dB at 5 GHz. Therefore, optically controlled microwave filters were successfully constructed and realized. / Critical contributions in the field of microwave periodic structures are the characterization and the construction of double-stopband structure, linearly and non-linearly tapered array structures, and inter-coupled SRR structures. Vital characteristics and advantages discovered include wide stopband, reduced size, and large fractional bandwidth. Chemical bath deposited CdS thin films were studied to achieve an ultra low sheet resistance and high photosensitivity. Important applications associated with these structures are microwave lowpass/bandpass filters and optically controlled filters.

No description available.