The design and synthesis of stable organic radicals with delocalized spin density distribution and low energy optical and redox processes is central to the development of magneto-conducting materials. Towards this end, a generalized synthetic methodology has been developed allowing for the synthesis of a series of annelated benzonitronyl nitroxide (BNN) radicals. The BNN radicals exhibited remarkably low reduction potentials (~0.0 V vs SCE) and a near-infrared absorption attributed to a HOMO–SOMO charge-transfer excitation. The annelated BNN radicals were found to be less stable than the closely related tetramethyl nitronyl nitroxide radicals, particularly in solution. A series of π-delocalized and heteroaromatic radicals were synthesized to determine if the instability was due to the delocalization of electron density onto the carbon skeleton or the low reduction potential. DFT calculations with the EPR-II basis gave rise to calculated electronic structures that were consistent with EPR spectroscopy and suggested changes in spin density distribution are occurring with perturbation of the annelated ring. Cyclic voltammetry revealed the heteroaromatic and π-delocalized radicals had reduction potentials lower than BNN, with some systems reducing at potentials of 0.2 V vs SCE, comparable to that of 7,7,8,8-tetracyanoquinodimethane. The distribution of spin throughout the molecular framework and the low reduction potential of the annelated nitronyl nitroxide radicals were both found to contribute to the lowered stability of the annelated nitronyl nitroxides relative to the far less redox active tetramethyl nitronyl nitroxides. The low reduction potential of the BNN radicals suggested that incorporation into acceptor–donor (A–D) systems would allow for investigation of the role of charge transfer interactions on the electronic structure and properties of neutral open-shell A–D radicals. Two D–A–D radicals were prepared using metal catalyzed coupling and furoxan condensation methodologies which resulted in incorporation of a second donor in the C5 position of the BNN moiety. The radical D1–A–D2 triads, where D1 = thiophene and D2 = thiophene or phenyl, exhibited three intramolecular charge-transfer excitations (λmax = 550, 580 and 1000 nm) that were investigated by variable temperature absorption spectroscopy. Structural characterization of the triads in the solid state by single crystal and powder X-ray diffraction revealed slipped π stacks that arise from intermolecular π– π and D–A interactions, providing pathways for antiferromagnetic (AFM) and ferromagnetic (FM) exchange. While the phenyl substituted triad (Th–BNN–Ph) exhibited antiferromagnetic interactions and a room temperature conductivity of σRT = 10−7 S cm−1, the thienyl substituted derivative (Th–BNN–Th) exhibited short-range FM interactions and increased conductivity (σRT = 10−5 S cm−1), giving rise to an organic semiconductor exhibiting FM exchange. The differences in conductivity and magnetic behavior were rationalized by the degree of slippage dictated by an interplay between π– π and intermolecular D−A interactions. Finally, a series of BNN–D radicals were investigated where the donor ability of D was systematically varied from Eox = 2.30 V vs SCE (benzene) to 0.32 V vs SCE (tetrathiafulvalene). Calculations of the near-infrared charge transfer excitation suggested that the HOMO–SOMO gap could be significantly decreased with increasing donor ability, consistent with charge transfer theory. A subset of the series of BNN–D radicals with D = anisole, benzo[b]thiophene, N-methylindole, N-ethylcarbazole, and N,Ndiphenylaniline were synthesized. Solution state spectroscopic studies of the series by EPR and electronic absorption spectroscopy revealed spin-delocalized structures with extremely low reduction potentials (~0 V vs SCE). The solid state properties of the BNN–D radicals were investigated by magnetometry and room temperature conductivity measurements. Due to primarily steric interactions, weak D–A coupling was observed, with weak intermolecular interactions in the solid state leading to paramagnetic and insulating behaviour. The BNN-(N,N-diphenylaniline) radical structure was characterized by single crystal XRD and found to exist as well isolated radical moieties with extremely weak intermolecular interactions, consistent with magnetometry and conductivity measurements. / Graduate / 0490 / 0794

M.Sc. (Theoretical Physics) / Please refer to full text to view abstract

M.Sc. / Lightning data are used in various applications from risk management to weather forecasting providing valuable insight to everyday operations. In South Africa, the South African Weather Services (SAWS) commissioned a new lightning detection network in February 2006. The nineteen-sensor network spread across South Africa overcomes previous disadvantages to lightning detection by providing wider coverage, higher detection efficiencies and better spatial resolution. This study investigated the influence of terrain elevation on lightning density in South Africa using data from the SAWS lightning detection network. Data incorporating one year from February 2006 to January 2007 were analysed using Geoinformatic Information System (GIS) programmes. The study incorporated two phases of analysis. The first included an evaluation of lightning climatology and the influence of elevation on lightning density for the whole of South Africa. The second phase, using four sub-regions of South Africa, included evaluation of local influences of elevation, slope and aspect on lightning density, for a period restricted to one month, December, during the peak lightning season. Lightning density was found to be highest over high topographic regions of the Highveld and escarpment regions. Enhanced lightning activity occurs over the eastern coast and over the Indian Ocean adjacent to the KwaZulu Natal coast. Diurnal variations in lightning activity indicate the influence of solar radiation on convective thunderstorm development with peaks occurring during the late afternoon and early evening. Results of the influence of elevation on lightning density over the country of South Africa, indicate that lightning density increases with elevation up to a maximum of 1 800 m decreasing thereafter, in contrast to literature reports indicating maximum activity at 1 200 m elevation. This result was found throughout the year except for winter months where thunderstorms are dominated by frontal activity. Lightning density in all four sub-regions was found to increase with elevation up to approximately 1 500 m and decrease thereafter. Diurnal patterns of lightning activity in all regions indicate the dominance of convective thunderstorms. Slope and aspect was found to be influential in certain regions but mostly as a secondary factor influencing thunderstorm development. Lightning density in South Africa is influenced to a great degree by terrain elevation especially over the highly elevated regions of the Highveld and Escarpment. This work contains the first comprehensive analysis of lightning frequency distributions from the new (2006) SAWS lightning detection network, and the first significant update of lightning distribution over southern Africa since 1975.

No description available.

Density functional theory BLYP (Becke's exchange and Lee-Yang-Parr's correlation functionals), ab initio Hartree-Fock (HF) and hybrid DFT/HF B3LYP calculations were carried out to study the structure and vibrational spectra of quadricyclane. The BLYP/6-31G* and scaled HF/6-31G* frequencies correspond well with each other and with available experimental assignment of the fundamental vibrational modes. Based on conformity between the calculated and experimental results, a plausible assignment of two remaining a1 modes and all non-CH stretching a2, b1, and b2 modes is proposed.

No description available.

No description available.

The likelihood of a given bone fracturing atraumatically is difficult to assess.. A number of factors - age, frequency of falling, cushioning by overlying tissues, protective reactions - as well as bone strength determine fracture risk. The interrelationships between these factors make it hard to evaluate the effect of any one variable in a study. The most common method of assessing bone strength is to use the surrogate method of bone mineral content (BMC) or bone mineral density (BMD). The architectural breakdown of the trabeculae, the mineral "mesh" which makes up bone, is a little-studied factor which may help to better predict fracture. In this thesis, the results of quantitative measurements of trabecular architecture, BMD, and strength of femoral heads scavenged from hip replacement surgery will be presented. This is intended to illuminate the relationships between bone strength, bone density, and trabecular architecture. / Thesis / Master of Science (MSc)

The elusive and nocturnal nature of the ocelot Leopardus pardalis poses difficulty in gaining basic information on demographic parameters needed to better inform conservation. My study used camera trapping data from long-term monitoring of ocelot populations on six different protected areas in Belize over a time span ranging from 1 to 12 years, with 1,700 ocelot detections in 65,157 total trap nights. I used classical and spatially explicit methods, including multi-session robust design, to estimate and compare ocelot density and survival across sites and time. Full likelihood single session models estimated densities ranging from 6.4 - 22.5 individuals/100km2 in the broadleaf forested sites. Robust design models estimated densities from 8.8 - 22.8 individuals/100 km2 and ocelots had high annual survival (71-79%) in 2 broadleaf sites. Contrary to predictions, robust design models had higher precision than full likelihood models less than half the time. Spatially explicit models estimated density ranging between 7.2 – 22.0 individuals/100 km2 in broadleaf sites, and much lower estimates at 0.9 individuals/100 km2 in the pine forest site. Accounting for sex in spatially explicit methods, which directly incorporate locations of captures into the model, increased precision in density estimates by reducing individual heterogeneity in capture probability. The spatial models also demonstrated that males moved larger distances than females and had slightly higher detection rates. Ocelot populations remained relatively stable over time at the long term sites. My study produced methodologically rigorous abundance/density estimates for ocelots in Belize and the first ever ocelot survival estimates. / Master of Science

Madagascar is renowned for its biodiversity, but also for forest loss, fragmentation, and degradation, making it a global conservation priority. With few studies dedicated to Madagascar's carnivores, little is known about their ecology. My objectives were to 1) compare density estimation techniques applicable to enumerating rare and/or elusive carnivores, 2) investigate Malagasy carnivore distributions, abundance and density, and occupancy/use across four sites that vary in forest disturbance, and 3) explore temporal activity patterns of rainforest carnivores. I found the spatially-explicit-capture-recapture models were empirically superior, as they are flexible and account for spatial variation in detection probability and area estimation. I found both endemic and exotic carnivore composition varied among four rainforest sites: Primary, Selectively-logged, Fragments <2.5 km and Fragments >15 km from contiguous-primary rainforest. All endemic carnivores were present in the Primary and Selectively-logged rainforest, while endemic carnivore species richness decreased and exotic carnivore species richness increased in the fragmented forests. Malagasy civet (Fossa fossana) density ± SE was significantly less in the Selectively-logged compared to the Primary rainforest (1.38 ± 0.22, 3.19 ± 0.55 civets/km2, respectively); they were absent from both fragmented forests. Fossa (Cryptoprocta ferox) density ± SE was not different between the Primary and Selectively-logged rainforests (0.12 ± 0.05, 0.09 ± 0.04 adults/km2, respectively); a single animal was detected in the Fragments <2.5 km, while none were detected in the Fragments >15 km. Malagasy carnivores had varied temporal activity overlap (5.8-88.8%). C. ferox preferred crepuscular activity, but overall exhibited a cathemeral activity pattern. / Master of Science