The chemistry of fullerenes, which are a class of carbon allotropes that can be prepared by vaporization of graphite in an electric arc in a low pressure atmosphere,1 has become a topic of much experimental and theoretical study over the past 25 years.  Herein we present a series of theoretical studies related to recently discovered or studied endohedral metallofullerenes (EMF) and a theory as to the selective stability of certain isomers of EMFs. Computational treatments of the anions of C80 and C94 are presented and compared in an effort to gain an understanding and predictive model for which isomers of each cage size EMF will be most stable.  A model is proposed in which the pentagons of fullerene anions are seen as charge localization centers that repel one another, making the pyracyclene bonding motif much more unstable for fullerene anions than for fullerene neutral cages. Computational treatments are also presented for two newly discovered EMFs, Y2C2@C92 and Gd2@C79N.  Y2C2@C92 is reported to exhibit a previously undiscovered mode of internal cluster rotation, while Gd2@C79N is shown to have unusual stability for an azofullerene with a large spin quantum number (15/2). Finally, computational techniques are employed to predict the thermodynamic feasibility of a chemical reaction replacing one metal atom in a trimetallic-nitride template (TNT) endohedral metallofullerene with different metal atom.  At least two of these are predicted to be thermodynamically practical. / Ph. D.

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We investigate the effect of the substitution of Ni, Ti and Co in MnBi using first principles calculations based on density functional theory (DFT) within the generalized gradient approximation (GGA). We also performed total energy calculations to compare different structures to determine the ground state structures and investigate their magnetic properties. Our calculation shows that the substitution of Ni, Co and Ti lowers the total magnetization of MnBi. We also found that the stable structure of Ni and Ti substitute is to replace Mn atoms in their regular site while the substitute Co is most stable when Co occupies the interstitial site of MnBi unit cell.

Various models of density dependence predicted different evolutionary outcomes for Helicoverpa zea, Diabrotica virgifera, and Ostrinia nubilalis using simple and complex resistance evolution models, different dose assumptions and refuge proportions. Increasing available refuge increased durabilities of pyramided Plant-Incorporated-Protectants (PIPs), especially between 1-5%. For some models of density dependence and pests, additional refuge resulted in faster adaptation rates. Significant considerations should be given to a pest’s intra-specific competition in simple and complex theoretical models when designing insect resistance management plans. Life-history, refuge, and dose characteristics of a PIP had different effects on the adaptation rate of a generic pest of Bt, and unexpected outcomes occurred. Intrinsic growth rate ‘R0’ was the strongest evolutionary force, and large R0’s reduced time to resistance for a high dose PIP to similar levels as projected for a low dose PIP. This was caused by differential density dependent effects in refuge and Bt fields that elevated generational resistance increases beyond those from selection alone. Interactions between density dependence and R0 were always present and further affected the life-time of the PIPs. Varying ‘average dispersal distance’ did not affect evolutionary outcomes; however, increasing the proportion of the population engaging in dispersal often increased the durability of high dose PIPs. When resistance genes spread from a hypothetical hotspot, local resistance phenomena developed in the immediate surroundings. Higher growth rates lead resistance to spread faster through the landscape than lower rates. Increasing available refuges slowed adaptation rates to single PIPs and low dose pyramids, although non-linear trends were possible. Integrated Pest Management (IPM) practices at the onset of PIP commercialization slowed pest adaptation rates. For corn rootworm, interspersing non-selective periods with IPM+IRM delayed resistance evolution, yet crop rotation was the best strategy to delay resistance. For bollworm inclusion of isoline corn as an IPM tool did not increase the life-time of the PIP. A local resistance phenomenon for rootworm was maintained immediately surrounding the hotspot; random selection of mitigatory strategies in the landscape slowed adaptation rates while mitigation in the hotspot alone did not. Mitigation extended the life-time of the pyramid minimally for both corn rootworm and bollworm.

The effects of cultural intensity (operational and intensive) and planting densities (741, 1483, 2224, and 2965 ha-1) on modulus of elasticity (MOE), modulus of rupture (MOR) and specific gravity (SG) of small clear samples obtained from 15 and 16 year-old loblolly pine (Pinus taeda) from the Lower Coastal Plain and Piedmont region of the southeastern United State were examined. Planting density and distance from pith showed a significant (p < 0.0001) and strong main effect on stiffness (MOE) and strength (MOR) for the samples. Regardless of planting density, MOE, MOR and SG of samples increased significantly from pith toward bark. A significant culture × density interaction (p < 0.0001) was observed for the samples obtained from the Lower Coastal Plain. The project also determined the feasibility of measuring microfibril angle (MFA) on solid wood loblolly pine samples using scanning electron microscopy and transmission electron microscopy with the angle analyzed using image analysis. Measurements of MFA revealed minor differences (5⁰) between juvenile wood and mature wood.

In this dissertation, covariant density functional theory has been applied to a variety of nuclear phenomena in the ground and excited states of rotating and non-rotating nuclei. It has been applied for the interpretation of excited superdeformed bands in 154Dy using the effective alignmentmethods. The properties of the predicted hyperdeformed nuclei at high spin in the Z = 40−58 region were investigated and the spins at which such configuration become yrast were defined. The moments of inertia, the role of single-particle energies and necking degree of freedom have also been studied. It also predicted that 107Cd is the best nucleus for its observation. The impact of time-odd mean fields (nuclear magnetism NM) in both non-rotating and rotating frame works, on physical observables has been studied. It is shown that nuclear magnetism always provide additional binding to the binding energies of odd-mass nuclei. Time-odd mean fields affect odd-even mass differences. However, the modifications of the strength of pairing correlations required to compensate for their effects are modest. In contrast, time-odd mean fields have a profound effect on the properties of odd-proton nuclei in the vicinity of the proton drip line. Their presence can modify the half-lives of proton emitters and considerably affect the possibilities of their experimental observation. They also have a profound effect on the dynamic and kinematic moments of inertia, particle number, configuration, and rotational frequency dependencies of their impact on the moments of inertia. The effect of NM on the binding energy and moments of inertia weakly depend on the choice of the RMF parametrization. Fission barriers are studied systematically with the allowence for triaxial deformations, in the actinide and superheavy regions. It is shown that covariant density functional theory is able to describe fission barriers, in actinides, on a level of accuracy comparable with nonrelativistic calculations. Triaxiality in the region of the first saddle plays a crucial role in achieving that. However, in the Z = 112 - 120 superheavy nuclei, the inner fission barriers are not affected by triaxiality. General trends of the evolution of inner fission heights are discussed.

This experiment was conducted to assess the effects of either low or high trailer stocking density (SD) on cattle behavior. British x Continental steers (n = 200; mean BW = 361.53 ± 54.4 kg) were loaded onto one of two truck-towed trailers. Steer behavior and positional orientation were recorded by video camera (8 h). Aggressive behaviors were more frequent (P < 0.0001) in low (178 ± 34.46 kg BW/m2) than high (333 ± 31.84 kg BW/m2) SD. Chin-resting occurred more often (P < 0.05) in low SD, yet there was no difference (P = 0.98) between SD for mounting. There was a SD × trip effect for loss of balance (P < 0.05), ruminating (P < 0.0001), and lying behaviors (P < 0.0001). At both SD, side-left and side-right were the preferred (P < 0.05) standing orientations. These results suggest that SD can affect cattle behavior and orientation en route.

Orbital-free density functional theory requires accurate approximations for the noninteracting kinetic energy as a functional of the ground-state electron den- sity. For explicit functionals in real space, it has proved difficult to supersede the quality of the gradient expansion, truncated at second order. This is partly because the gradient expansion diverges for atomic and molecular densities. In an effort to include information about higher-order terms in the gradient expansion but avoid divergences, we consider resummations for the series using Padé approximants and Meijer-G functions. To regularize terms that appear in the denominator, we consider various damping functions, which introduces parameter(s) that can be fit to atomic data. These results improve upon the second-order truncation, but do not achieve the exquisite accuracy that would be required for practical orbital-free density-functional theory calculations. / Thesis / Master of Science (MSc)

Peat is an accumulation of soil formed from partially decomposed organic matter. Peat can burn, especially in hot, dry weather which is happening more often due to climate change; smouldering releases stored carbon to the atmosphere. Peat that has higher organic bulk density and lower moisture content is more vulnerable to fire: it will burn more severely (more deeply) if ignited. Shallower peat is less able to retain moisture during droughts and is therefore likely more vulnerable to fire; however, mapping peat depths at high spatial resolution is expensive or requires extensive fieldwork. This project uses remote sensing in combination with machine learning to estimate peat depth across a peatland and rock barren landscape. A Random Forest model was used to map peat depths across the landscape at a 1 m spatial resolution using LiDAR data and orthophotography. The resulting map was able to predict peat depths (R2 = 0.73, MAE = 28 cm) and showed that the peat depths which are especially vulnerable to high severity fire are distributed in numerous small patches across the landscape. This project also examined peat bulk density and found that the Von Post scale for peat decomposition can be used as a field method for estimating bulk density (R2 = 0.71). In addition, in this landscape, peat bulk densities at the same depth (within the top 45 cm) are higher in shallower peat because in shallower peat, more decomposed peat was found closer to the surface, and because peat with high mineral content was found close to the bedrock or mineral soil. The findings of this project will be valuable for wildfire managers to determine which areas on the landscape are most vulnerable to fire, allowing them to mobilize resources more rapidly for wildfire suppression. / Thesis / Master of Science (MSc) / Peat is organic soil made from decomposing plant material. Peat can burn, especially in the hot, dry weather which is happening more often due to climate change. Dense, dry peat is more vulnerable to fire: it will burn more deeply. Because it is known that areas with deeper peat can retain moisture better, peat depth can be used as a proxy for vulnerability to fire. Since peat depth is expensive and time consuming to map directly, remotely sensed data such as aerial imagery was used in a model to predict peat depths. The model was able to predict peat depths and displayed that the most vulnerable areas are scattered across the landscape in small patches. This project also found that denser peat is found farther from the surface in deeper peat areas, further supporting the use of peat depth as a proxy for vulnerability to smouldering.

Original published work submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy, August 2019 / Age-at-death estimates in skeletal remains are hampered by observer bias and error, as well as individual and population variation. This study aimed at improving accuracy and reliability of age estimates obtained from applying methods involving the assessment of histomorphometric variables of bone and bone mineral density (BMD). The assessment of osteon population density (OPD) and size (length, surface area and volume) of Haversian systems were investigated in three populations by means of stereology. Bone slides prepared from South African black (n = 99), South African white (n = 94) and Danish white (n = 30) individuals were analysed using MicroBrightField’s StereoInvestigator software. ANCOVA results revealed a statistically significant difference (p < 0.001) between the three groups in terms of OPD. No statistically significant difference was seen in the size of secondary osteons between the groups. Linear regression analysis was used to construct population-specific formulae for age-atdeath estimation in South African white and black individuals. The Danish sample was used as a comparative group for white South African standards established. Age mimicry appeared to play a role in the over-estimation of age in the Danish individuals, after which the problem was corrected by combining the two samples in order to achieve normal age distribution within the larger sample. Secondly, DXA scans of the proximal femur were done for a subgroup of South African black (n = 64) and white (n = 59) individuals for estimation of age-at-death from bone mineral density. Results displayed a significant difference between white and black groups for total and neck BMD. White males and females differed in total and neck BMD, although black males and females differed only in terms of neck BMD. Age could be significantly correlated with BMD in the white population, but not in the black population. Regression analysis was also done for the complete sample (white and black individuals pooled), as ancestry is unknown in some cases. A significant correlation was seen for age versus neck BMD in the total sample and in sex-specific groups. The outcome of this study suggested that the three population samples are somewhat dissimilar in bone microstructure, with differences related to OPD and BMD present between the groups. Based on this outcome, it should be emphasized that age estimation standards should be adapted to accommodate combined groups and create to more generally applicable standards. Further research involving various disciplines is needed to better understand the underlying reason(s) for these differences between these populations. / PH2020