Climate has a selective influence on nasal cavity morphology. Due to the constraints of cranial integration, naturally selected changes in one structure necessitate changes in others in order to maintain structural and functional cohesion. The relationships between climate and skull/nasal cavity morphology have been explored, but the integrative role of nasal variability within the skull as a whole has not. This thesis presents two hypotheses: 1) patterns of craniofacial integration observed in 2D can be reproduced using 3D geometric morphometric techniques; 2) the nasal cavity exhibits a higher level of covariation with the lateral cranial base than with other parts of the skull, since differences in nasal morphology and basicranial breadth have both been linked to climatic variables. The results support the former hypothesis, but not the latter; covariation observed between the nasal cavity and other cranial modules may suggest that these relationships are characterized by a unique integrative relationship. / February 2016

Thesis (MSc (Physics))--University of Stellenbosch, 2009. / In the presented study a diode laser was characterised and used for spec- troscopy, measuring the resonance lines of atomic rubidium. The characteristics of diode lasers and external cavity diode lasers (ECDL) for the purposes of ab- sorption spectroscopy were investigated and an experimental setup for tunable diode laser spectroscopy using an ECDL was developed. In external cavity diode lasers, the advantages of low cost, small size and e ciency of a diode laser is combined with tunability and a narrow frequency bandwidth. The ECDL was applied in experimental setups for absorption spectroscopy and saturated ab- sorption spectroscopy. Measurement of the absorption of atomic rubidium's D2 line near 780 nm is discussed. The Doppler broadened, as well as the Doppler free spectrum of the ne and hyper ne structure of the D2 line were measured and is discussed. Finer control of the ECDL's stability and frequency, using a servo circuit, were investigated and tested. An overview is given of laser cool- ing and trapping of neutral rubidium atoms, which is the main application the ECDL were developed for.

Silicon Photonics has been a major success story in the last decade, with many photonic devices having been successfully demonstrated. The only missing component is the light source, however, as making an efficient light source in silicon is challenging due to the material's indirect bandgap. The development of a silicon light source would enable us to make an all-silicon chip, which would find many practical applications. The most notable among these applications are on-chip communications and sensing applications. In this PhD project, I have worked on enhancing silicon light emission by combining material processing and device engineering methods. Regarding materials processing, the emission level was increased by taking three routes. In all the three cases the emission was further enhanced by coupling it with a photonic crystal (PhC) cavity via Purcell effect. The three different approaches taken in this PhD project are listed below. 1. The first approach involves incorporation of optically active defects into the silicon lattice by hydrogen plasma treatment or ion implantation. This process results in broad luminescence bands centered at 1300 and 1500 nm. By coupling these emission bands with the photonic crystal cavity, I was able to demonstrate a narrowband silicon light emitting diode at room temperature. This silicon nano light emitting diode has a tunable emission line in the 1300-1600 nm range. 2. In the second approach, a narrow emission line at 1.28µm was created by carbon ion implantation, termed “G-line” emission. The possibility of enhancing the emission intensity of this line via the Purcell effect was investigated, but only with limited success. Different proposals for future work are presented in this regard. 3. The third approach is deposition of a thin film of an erbium disilicate on top of a PhC cavity. The erbium emission is enhanced by the PhC cavity. Using this method, an optically pumped light source emitting at 1.54 µm and operating at room temperature is demonstrated. A practical application of silicon light source developed in this project in gas sensing is also demonstrated. As a first step, I show refractive index sensing, which is a simple application for our source and demonstrates its capabilities, especially relating to the lack of fiber coupling schemes. I also discuss several proposals for extending applications into on-chip biological sensing.

published_or_final_version / Dentistry / Master / Master of Dental Surgery

published_or_final_version / abstract / Dentistry / Master / Master of Dental Surgery

Novel integral-equation methods for efficiently solving electromagnetic problems that involve more than a single length scale of interest in complex backgrounds are presented. Such multi-scale electromagnetic problems arise because of the interplay of two distinct factors: the structure under study and the background medium. Both can contain material properties (wavelengths/skin depths) and geometrical features at different length scales, which gives rise to four types of multi-scale problems: (1) twoscale, (2) multi-scale structure, (3) multi-scale background, and (4) multi-scale-squared problems, where a single-scale structure resides in a different single-scale background, a multi-scale structure resides in a single-scale background, a single-scale structure resides in a multi-scale background, and a multi-scale structure resides in a multi-scale background, respectively. Electromagnetic problems can be further categorized in terms of the relative values of the length scales that characterize the structure and the background medium as (a) high-frequency, (b) low-frequency, and (c) mixed-frequency problems, where the wavelengths/skin depths in the background medium, the structure’s geometrical features or internal wavelengths/skin depths, and a combination of these three factors dictate the field variations on/in the structure, respectively. This dissertation presents several problems arising from geophysical exploration and microwave chemistry that demonstrate the different types of multi-scale problems encountered in electromagnetic analysis and the computational challenges they pose. It also presents novel frequency-domain integral-equation methods with proper Green function kernels for solving these multi-scale problems. These methods avoid meshing the background medium and finding fields in an extended computational domain outside the structure, thereby resolving important complications encountered in type 3 and 4 multi-scale problems that limit alternative methods. Nevertheless, they have been of limited practical use because of their high computational costs and because most of the existing ‘fast integral-equation algorithms’ are not applicable to complex Green function kernels. This dissertation introduces novel FFT, multigrid, and FFT-truncated multigrid algorithms that reduce the computational costs of frequency-domain integral-equation methods for complex backgrounds and enable the solution of unprecedented type 3 and 4 multi-scale problems. The proposed algorithms are formulated in detail, their computational costs are analyzed theoretically, and their features are demonstrated by solving benchmark and challenging multi-scale problems. / text

Lightweight building materials are now commonly employed in many countries in preference to heavyweight materials. This has lead to extensive research into the sound transmission loss of double leaf wall systems. These studies have shown that the wall cavity and sound absorption material placed within the cavity play a crucial role in the sound transmission through these systems. However, the influence of the wall cavity on the sound transmission loss is not fully understood. The purpose of this research is to obtain a comprehensive understanding of the role played by the wall cavity and any associated sound absorption material on the sound transmission loss through double leaf wall systems. The research was justified by the fact that some of the existing prediction models do not agree with some observed experimental trends. Gösele’s theory is expanded and used in the creation of an infinite and finite vibrating strip model in order to acquire the desired understanding. The sound transmission loss, radiated sound pressure and directivity of double leaf systems composed of gypsum boards and glass have been calculated using the developed model. A method for calculating the forced radiation efficiency has also been proposed. Predictions are compared to well established theories and to reported experimental results. This work also provides a physical explanation for the under-prediction of the sound transmission loss in London’s model; explains why Sharp’s model corresponds to Davy’s with a limiting angle of 61° and gives an explanation for Rindel’s directivity and sound transmission loss measurements through double glazed windows. The investigation also revealed that a wide variety of conclusions were obtained by different researchers concerning the role of the cavity and the properties of any associated sound absorption material on the sound transmission loss through double wall systems. Consequently recommendations about the ways in which sound transmission through cavity systems can be improved should always be qualified with regard to the specific frequency range of interest, type of sound absorption material, wall panel and stud characteristics.

This dissertation is on the development of a laser system for the generation of femtosecond frequency combs in the vacuum-ultraviolet (VUV) via intracavity high-harmonic generation (HHG). The HHG process yields coherent vacuum ultraviolet (VUV) light resulting from the ionization of noble gases driven by intense near-IR femtosecond frequency combs in an optical enhancement cavity. An injection locked amplification cavity (fsAC) was developed in order to generate a high power femtosecond frequency combs based on a Ti:Sapphire oscillator. Detailed amplifier performance was investigated in order to evaluate the coherence of the pulse amplification process. A passive power enhancement cavity for fs pulses (fsEC) was designed for intracavity high harmonic generation. For maximum power enhancement and conversion efficiency, the intracavity dispersion was compensated and various design layouts tested. A careful analysis of the phase matching conditions was performed, taking into account the effect of reabsorption of the generated high harmonic light, to compare different cavity geometries and determine which would produce the most efficient harmonic yield. Numerical simulations were also performed to determine the level of intra-cavity ionization that could be sustained before disrupting the pulse enhancement process. Based on the results of these simulations and calculations, it was determined that for a xenon gas target, a moderate peak intensity of the order of ~ 5×10¹³W/cm² produces harmonics most efficiently.

No description available.

Inconel alloys are commonly used as structural materials in nuclear reactors. One of these alloys, the Inconel X-750, is a γ’ Ni3(Al, Ti) strengthened superalloy extensively used in the cores of reactors, such as spacers in CANada Deuterium Uranium (CANDU) fuel channels. Prior to their application in commercial reactors, accelerated irradiation tests had been conducted in liquid metal fast reactors. Results did not indicate any problem stemming from significant fast neutron irradiation. However, recently it has been found that the ex-service CANDU Inconel X-750 spacers became severely brittle after a lengthy exposure to reactor environment. The underlying mechanism remains unclear and thus forms the focus of this current investigation, predominantly through transmission electron microscopy (TEM). This dissertation unfolds with the literature review in Chapter 2, followed by presentation of novel techniques in Chapter 3 on the preparation of TEM samples from small reactor components, namely the spacers. Chapter 4 presents TEM characterizations of ex-service spacers removed from the reactors. To simulate neutron irradiation over wide temperature range in an effort to understand the damage mechanisms, heavy ion irradiations were conducted and reported in Chapter 5 and 6. Irradiations are found to significantly alter the stability of the primary strengthening phase γ’, a systematic experimental study of which is presented in Chapter 7. To fully understand the effects of transmutation produced helium on irradiation induced cavity and dislocation microstructures, TEM in-situ heavy ion irradiations with hot/cold pre-injected helium were conducted and reported in Chapter 8 and 9. Helium was found to play an important role in the irradiation-induced instability of γ’ in nickel-based superalloys, the discussion of which is presented in Chapter 10. As one of the most important defect structures induced from irradiation, the stacking-fault-tetrahedra, were dynamically observed and are described in a journal manuscript in Appendix A. In addition to broadening current understanding of material degradation mechanism for in-service CANDU spacer, this study also provides comprehensive information on irradiation damage in nickel based superalloys, irradiation induced lattice defects and phase instability in face centered cubic alloys, as well as helium’s effects on cavity formation, dislocation evolution, and phase transformation. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2013-09-06 15:21:02.334