>Magister Scientiae - MSc / Most stable and extremely low abundance neutron deficient nuclei with Z ≥ 34 are referred to as p-nuclei. Nearly all p-nuclei with A < 110 are most likely produced in the rp-process while almost all A > 110 are thought to be produced by the photodisintegration of s- and r- process seed nuclei. However, for some nuclear systems, these processes are not sufficient to explain their observed solar abundance. Results from calculations in ¹⁸ᴼTa generally provoke debates since several processes are able, sometimes exclusively, to reproduce the observed ¹⁸ᴼTa abundance in the cosmos, making it a unique case study. Some of the main sources of errors in the predicted reaction rates of ¹⁸ᴼTa arise due to the absence of nuclear data or due to large uncertainties in the nuclear properties such as the nuclear level densities (NLD) and gamma-ray strength functions (γSF) of ¹⁸ᴼ,¹⁸¹Ta. The NLD and γSF are primary ingredients for astrophysical reaction rate calculations based on the Hauser-Feshbach approach. These parameters need to be well understood to improve our understanding of ¹⁸ᴼTa production in astrophysical environments. In this thesis, new experimental data for the low-energy part of the γSF and NLD in ¹⁸ᴼ,¹⁸¹Ta were extracted, using the so-called Oslo method. An experiment was performed and the NaI(Tl) gamma-ray array and silicon particle telescopes at the Oslo cyclotron laboratory were utilized to measure particle-γ coincidence events from which the NLDs and γSFs are extracted below the neutron separation energy threshold Sn. A beam of ³He was used to populate excited states in ¹⁸ᴼ,¹⁸¹Ta through the inelastic scattering (³He,³He’𝛾) and the transfer reaction (³He,𝜶𝛾). Based on results from this measurements, the Maxwellian averaged (n, 𝛾) cross sections for the 179Ta(n, γ) and ¹⁸ᴼTa(n, 𝛾) reactions, at the s-process thermal energy of kT = 30 keV (i.e. a temperature of T = 3.5 × 10⁸ K) and p-process thermal energy of 215 keV (T = 2.5 × 10⁹ K), respectively, were computed with the TALYS reaction code. These results can be used to place the nuclear physics aspects of the large network abundance calculations on a solid footing and have potential to improve our understanding of the astrophysical processes and sites involved in the production of nature’s rarest isotope ¹⁸ᴼTa. / National Research Foundation (NRF)

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A technique which employs a laser-excited optical resonator has been developed to measure the electron density distribution, both temporal and spatial, in the collapse stage of a fast Z-pinch discharge. The resonator device has an experimentally determined time resolution of better than 0.05 µsec and is suitable for measuring electron densities in excess of 5 • 10¹⁶ /Lʎ cm⁻³, where L is the length of the plasma in cm and ʎ is the wavelength of the laser in microns. A novel feature of this instrument is the use of an unstable optical resonator. The technique is applied to a discharge in argon at filling pressures of 100 and 1000 µHg. The temporal and radial electron density distributions obtained exhibit several interesting features which are discussed from the point of view of the collapse process. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This study was designed to investigate the mechanism(s) underlying the hypercatabolism of high density lipoprotein in Tangier disease (TD). Initially, the metabolism of normal HDL incubated in Tangier plasma in vitro was examined. Sufficient normal human HDL was added to TD plasma to raise the concentration of HDL-cholesterol to within normal levels. During incubation the concentration of HDL-cholesterol in the TD plasma fell by up to 50% in a time dependent manner. This was not seen in control samples treated in a similar manner. The loss of HDL-cholesterol in the TD could be completely accounted for by the loss of HDL-cholesteryl ester and was accompanied by a 2.3-fold increase in the concentration of HDL-triglyceride. These observations could not be accounted for by lecithin: cholesterol acytransferase activity, cholesteryl ester hydrolysis, or the triglyceride level in the TD plasma. However, preliminary evidence suggested that the activity of cholesteryl ester transfer protein in TD plasma is responsible for the changes in HDL-lipid composition. The resulting triglyceride-rich, cholesteryl-poor HDL was shown to have a normal affinity for the human skin fibroblast HDL receptor. However, this finding does not exclude other pathways of HDL catabolism that may contribute to the rapid turnover of modified HDL in TD plasma. The metabolism of normal HDL by TD fibroblasts and monocytes in vitro was also studied in an attempt to identify a cellular defect of HDL metabolism in TD. However, both TD fibroblasts and monocytes were normal with respect to their ability to bind/internalize and degrade normal HDL invitro. It is concluded that the hypercatabolism of normal HDL in TD involves alterations of HDL-lipid and protein composition prior to removal from the plasma component. Thus, these studies support the hypothesis that the defect in TD resides in the plasma and not in the cells of these patients. / Medicine, Faculty of / Pathology and Laboratory Medicine, Department of / Graduate

X-ray densitometry was used to investigate some environmental and genetic influences on wood formation in young Douglas-fir trees growing in the Pacific Northwest. Sampling methods were determined from sectional analyses of even-aged stems and eleven growth-ring width and density variables were measured in several trials to elucidate' some of the causes of variation. Breast height increment core samples were shown to giveve a good representation of stand properties and juvenile-mature correlations for a 40-year-old crop confirmed the validity of determining intra-ring density parameters on young material. Increment core samples from the Co-operative Douglas-fir Provenance Test (5 locations; 5 provenances/location) were used for both gravimetric and densi-tometric analyses. The major components of variation were found to be stand location and the individual tree effect. Provenances consistently accounted for less than 5% of the total variation. Genotype-environment interaction was shown to be small for all properties measured with the exception of the intra-ring density range. Between sites, earlywood widths were more variable than latewood widths, but latewood density properties (mean latewood and ring maximum densities) were more variable than those for earlywood (mean earlywood and ring minimum densities). Earlywood and latewood parameters varied independently of one another. It was suggested that genetic control was weak at the provenance level but strong for individual trees. Regression analyses using growth-ring components and monthly weather data for the outer five rings at each site uncovered some highly significant effects which helped to explain the observed year-to-year variation. Density variables were less affected by weather conditions than earlywood and latewood widths. An examination of eight ramets from each of ten 13-year-old clones revealed highly significant differences in all eleven intra-ring parameters. Heritability estimates for individual growth rings showed a regular increase with tree age, and latewood properties (width, density and ring maximum density) were found to be under strong genetic control. On a clone-mean basis, density was not related significantly to growth rate, so that vigour and density properties could be selected for independently. Crown phenology (flushing and shoot growth characteristics) was not strongly correlated with growth-ring parameters, although there was an indication that early flushing may be associated with higher latewood density. A study of four parent trees and their control-pollinated progeny proved unsatisfactory due to lack of adequate replication and atypical stand conditions, but nevertheless provided a vehicle for discussion of problems involved in assessing plus-tree wood quality and narrow-sense heritabilities. The combined results were discussed in terms of the genecology of Douglas fir and the implications for forest management and utilization. / Forestry, Faculty of / Graduate

Rock density is critical for determining the tonnage of an orebody and therefore impacts on the total resource of a deposit. Density is defined as the concentration of matter, and is expressed as mass per unit volume (g/cc; g/cm3 or t/m3). The density that is calculated will depend on the nature of the rock, and whether the volume calculated includes the open and/or closed pore volume of the rock. The pore volume will depend on the rock’s internal and external characteristics. This study looks at two methods commonly used to determine the rock density of samples taken from boreholes drilled for platinum mines on the North Eastern limb of the Bushveld Complex, South Africa. The first method is a gas pycnometer, which is almost exclusively used by laboratories. A Grabner Minidens air gas pycnometer was used. The second method is a hydrostatic immersion method, using water as the Archimedean fluid. An adapted Snowrex NH – 3 scale that can weigh a rock sample in air and in water was used. The first part of the study investigates the possible differences between conducting rock density measurements on finely milled core in the Grabner Minidens air gas pycnometer or on solid halved core samples using a hydrostatic immersion method, and the implications thereof. The second part of the study, not only investigates the differences between conducting density measurements on solid core samples or on milled core samples, but also looks at how the type of method used and how location affects the density measurement obtained. The location is important because changes in temperature and atmospheric pressure have been shown to produce small, but measurable changes in density. The density of pure water at 4 °C is approximately 1 g/cm3, increases or decreases in temperature will marginally decrease the density of water. The density of pure water at room temperature (21 °C) is 0.998 g/cm 3. Changes in atmospheric pressure have been shown to have a negligible effect on the density of most solids. The diamond drill core samples were taken from boreholes targeting the platinum group element (PGE) rich Merensky reef (MR) and Upper Group 2 (UG2) chromitite layer of the Upper Critical Zone. Samples were taken from the hangingwall (HW), reef and footwall (FW) of the MR and UG2. These rocks are made up of closely interlocking minerals, typical of cumulates. There are generally no visible pore spaces apart from highly fractured and altered samples. In part one of the study, 18,430 samples were used. The halved core samples were first measured using the hydrostatic immersion method at the exploration offices close to where the boreholes were drilled, referred to as the “Driekop” method. The samples were then sent to a laboratory in Johannesburg. Each sample was first milled to a fine powder (40 μm), and then a small portion of the milled sample (4 cm3) measured using the Grabner Minidens air gas pycnometer, referred to as the “Grabner Milled” method. For quality control, 811 of the remaining halved core samples were re-measured using the hydrostatic immersion method.The Grabner Milled results were found to be consistently higher than the Driekop results, with a mean average relative difference (AVRD) of approximately 5 % for all stratigraphic units. The difference observed can be accounted for, from the way in which the sample is prepared and the type of density that is measured. The Driekop method calculates the bulk density of the solid halved core sample, which includes all the open and closed pores of the rock. The Grabner Milled method calculates the true density of the finely milled sample, which through comminution, has excluded all open and closed pores that were in the rock. The quality control repeat measurements on the remaining halved core samples showed a good correlation with the original measurements, with a mean AVRD of only 0.33 %. In part two of the study, 82 randomly selected samples were used. The density of each solid sample was first determined using the hydrostatic immersion method. The same hydrostatic immersion method used in part one was applied at the same location; therefore it is also referred to as the “Driekop” method. The same hydrostatic method was then conducted on the samples at the laboratory in Johannesburg, referred to as “Lab water solid”. The gas pycnometer method was only conducted at the laboratory. The samples were first measured as a solid, referred to as “Grabner solid”. The samples were then milled to 40 μm and remeasured in the Grabner Minidens, referred to as “Grabner Milled”. The three solid methods results showed good correlation, with an average AVRD of only 0.01 % for the two hydrostatic immersion methods. On the other hand, there was a marked difference in results between the solid methods and the Grabner Milled method, the most significant difference being between the Grabner Milled and Grabner solid method (AVRD = 3.42 %). The resource model parameters for a project within the study area were used to illustrate the effect of density on resource planning. The average density used in the resource calculation will depend on what density method is used. The AVRD between the two methods for the mining cut density was approximately 5 %. The resource calculation showed that the difference in tonnage and 4E ounces between the two methods was also approximately 5 %. Changes in density result in equal changes in tonnage and metal content (4E ounces). Increases in dilution or overbreak from 10 to 30 cm above the optimal mining cut showed increases in tonnage and decreases in metal content. Due to similarities in rock composition between the HW, reef and FW of the MR, further dilution caused only a marginal decrease in density. The UG2 was found to be much more sensitive to dilution because of the distinct differences in rock composition between the reef, which is a chromitite layer and the HW and FW, which are both made up of plagioclase pyroxenite. Emphasis is commonly placed on the effect of dilution on grade; however this shows that the effect of density can be as important. The hydrostatic method of density determination is a very practical way of determining rock density at a remote exploration site. The whole sample can be measured and it is not restricted by the size or shape of the sample. Modern gas pycnometers have a higher degree of accuracy and precision, but need to be operated in a laboratory controlled environment, and are only capable of measuring a small amount of sample. With the correct application of quality control, both are suitable methods of density determination. The selection will depend on what type of density is required, the nature of the rock and whether the method must include or exclude pore spaces in the rock. Copyright / Dissertation (MSc)--University of Pretoria, 2012. / Geology / unrestricted

Thesis advisor: Udayan Mohanty / Thesis advisor: Dunwei Wang / With the fast development of society, the demand for batteries has been increasing dramatically over the years. To satisfy the ever-increasing demand for high energy density, different chemistries were explored. From the first-generation lead–acid batteries to the state-of-the-art LIBs (lithium ion batteries), the energy density has been improved from 40 to over 200 Wh kg⁻¹. However, the development of LIBs has approached the upper limit. Electrode materials based on insertion chemistry generally deliver a low capacity of no more than 400 mAh/g. To break the bottleneck of current battery technologies, new chemistries are needed. Moving from the intercalation chemistry to conversion chemistry is a trend. The conversion electrode materials feature much higher capacity than the conventional intercalation-type materials, especially for the O₂ cathode and Li metal anode. The combination of these two can bring about a ten-folds of energy density increase to the current LIBs. Moreover, to satisfy the safety requirements, either using non-flammable electrolytes to reduce the safety risk of Li metal anode or switch to dendrite-free Mg anode is a good strategy toward high energy density batteries. First, to enable the conversion-type O₂ cathode, a wood-derived, free-standing porous carbon electrode was demonstrated and successfully be applied as a cathode in Li-O₂ batteries. The spontaneously formed hierarchical porous structure exhibits good performance in facilitating the mass transport and hosting the discharge products of Li₂O₂. Heteroatom (N) doping further improves the catalytic activity of the carbon cathode with lower overpotential and higher capacity. Next, to solve the irreversible Li plating/stripping and safety issues related with Li metal anode, we introduced O₂ as additives to enable Li metal anode operation in non-flammable triethyl phosphate (TEP) electrolyte. The electrochemically induced chemical reaction between O₂- derived species and TEP solvent molecules facilitated the beneficial SEI components formation and effectively suppressed the TEP decomposition. The promise of safe TEP electrolyte was also demonstrated in Li-O₂ battery and Li-LFP battery. If we think beyond Li chemistries, Mg anode with dendrite-free property can be a promising candidate to further reduce the safety concerns while remaining the high energy density advantage. Toward the end of this thesis, we developed a thin film metal–organic framework (MOF) for selective Mg²⁺ transport to solve the incompatibility issues between the anode and the cathode chemistry for Mg batteries. / Thesis (PhD) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Thesis (Master of Agriculture)--Cape Peninsula University of Technology, 2020 / Grain yield and its components are very important and complicated in barley (Hordeum vulgare L.) and are highly influenced by environmental factors and agronomic management practices. For 2018 growing season, a study was designed under rainfed conditions to evaluate the effects of nitrogen (N) fertilizer rate (0, 10, 20, 30 and 40 kg ha-1 of N) and planting density (120, 140, 160, and 180 to 200 seeds m-2) on the agronomic performance of three barley cultivars (Elim, Hessekwa and S16). A randomized complete block design with 3 replications was used. Combined analysis of variance showed significant (p<0.1) differences among cultivars, N rates and planting densities. The main objective of this study was to determine the effects of planting density and different fertilizer application strategies on barley grain yield and quality. The results showed that biggest increases on yield and yield components were observed at 180 seeds m-2 and 80kg ha-1 N rate. Higher N rates generally reduced kernel size. Kernel size was both increased and decreased by increasing planting density as well as N rate. Increasing planting density from 180 to 200 seeds m–2 generally provided slight reductions in grain N concentration and reduced kernel size. The three cultivars expressed a significant effect on kernel plumpness and N content of grain. The most beneficial agronomic practices for malting barley production in Western Cape were application of N fertilizer at optimum rate depending on cultivar, locality and rainfall and planting seeds at a rate of 160-180 seeds m-2 depending on cultivar. A planting density of 160-180 seeds m-2 at a rate of 80 kg N ha-1 is recommended for planting barley under dry land in the Western Cape.

ABSTRACT CuZn Alloy- Based Electrocatalyst for CO2 Reduction Amira Alazmi Carbon dioxide (CO2) is one of the major greenhouse gases and its emission is a significant threat to global economy and sustainability. Efficient CO2 conversion leads to utilization of CO2 as a carbon feedstock, but activating the most stable carbon-based molecule, CO2, is a challenging task. Electrochemical conversion of CO2 is considered to be the beneficial approach to generate carbon-containing fuels directly from CO2, especially when the electronic energy is derived from renewable energies, such as solar, wind, geo-thermal and tidal. To achieve this goal, the development of an efficient electrocatalyst for CO2 reduction is essential. In this thesis, studies on CuZn alloys with heat treatments at different temperatures have been evaluated as electrocatalysts for CO2 reduction. It was found that the catalytic activity of these electrodes was strongly dependent on the thermal oxidation temperature before their use for electrochemical measurements. The polycrystalline CuZn electrode without thermal treatment shows the Faradaic efficiency for CO formation of only 30% at applied potential ~−1.0 V vs. RHE with current density of ~−2.55 mA cm−2. In contrast, the reduction of oxide-based CuZn alloy electrode exhibits 65% Faradaic efficiency for CO at lower applied potential about −1.0 V vs. RHE with current density of −2.55 mA cm−2. Furthermore, stable activity was achieved over several hours of the reduction reaction at the modified electrodes. Based on electrokinetic studies, this improvement could be attributed to further stabilization of the CO2•− on the oxide-based Cu-Zn alloy surface.

Szemere´di’s Regularity Lemma [32, 33] is an important tool in combinatorics, with numerous appli- cations in combinatorial number theory, discrete geometry, extremal graph theory, and theoretical computer science. The Regularity Lemma hinges on the following concepts. Let G = (V, E) be a graph and let ∅ /= X, Y ⊂ V be a pair of disjoint vertex subsets. We define the density of the pair (X, Y ) by dG(X, Y ) = |E[X, Y ]|/(|X||Y |) where E[X, Y ] denotes the set of edges {x, y} ∈ E with x ∈ X and y ∈ Y . We say the pair (X, Y ) is ε-regular if all subsets XI ⊆ X and Y I ⊆ Y satisfying |XI| > ε|X| and |Y I| > ε|Y | also satisfy |dG(XI, Y I) − dG(X, Y )| < ε. The Regularity Lemma states that, for all ε > 0, all large n-vertex graphs G = (V, E) admit a partition V = V1 ∪ · · · ∪ Vt, where t = t(ε) depends on ε but not on n, so that all but εt2 pairs (Vi, Vj), 1 ≤ i < j ≤ t, are ε-regular. While Szemere´di’s original proof demonstrates the existence of such a partition, it gave no method for (efficiently) constructing such partitions. Alon, Duke, Lefmann, Ro¨dl, and Yuster [1, 2] showed that such partitions can be constructed in time O(M (n)), where M (n) is the time needed to multiply two n × n {0, 1}-matrices over the integers. Kohayakawa, Ro¨dl, and Thoma [17, 18] improved this time to O(n2). The Regularity Lemma can be extended to k-uniform hypergraphs, as can algorithmic for- mulations thereof. The most straightforward of these extends the concepts above to k-uniform hypergraphs H = (V, E) in a nearly verbatim way. Let ∅ /= X1, . . . , Xk ⊂ V be pairwise disjoint subsets, and let E[X1, . . . , Xk] denote the set of k-tuples {x1, . . . , xk} ∈ E satisfying x1 ∈ X1, . . . , xk ∈ Xk. We define the density of (X1, . . . , Xk) as dH(X1, . . . , Xk) = |E[X1, . . . , Xk]| / |X1| · · · |Xk|. We say that (X1, . . . , Xk) is ε-regular if all subsets XiI ⊆ Xi, 1 ≤ i ≤ k, satisfying |XiI| > ε|Xi| also satisfy |dH (X1I , . . . , XkI ) − dH (X1, . . . , Xk)| < ε. With these concepts, Szemeredi’s original proof can be applied to give that, for all integers k ≥ 2 and for all ε > 0, all n-vertex k-uniform hypergraphs H = (V, E) admit a partition V = V1 ∪· · ∪ Vt, where t = t(k, ε) is independent of n, so that all but εtk many k-tuples (Vi1 , . . . , Vik) are ε-regular, where 1 ≤ i1 < · · · < ik ≤ t. Czygrinow and Ro¨dl [4] gave an algorithm for such a regularity lemma, which in the context above, runs in time O(n2k−1 log5 n). In this dissertation, we consider regularity lemmas for 3-uniform hypergraphs. In this setting, our first main result improves the algorithm of Czygrinow and Ro¨dl to run in time O(n3), which is optimal in its order of magnitude. Our second main result shows that this algorithm gives a stronger notion of regularity than what is described above, where this stronger notion is described in the course of this dissertation. Finally, we discuss some ongoing applications of our constructive regularity lemmas to some classical algorithmic hypergraph problems.