Thesis (M.Sc. (Horticulture)) -- University of Limpopo, 2022 / The purpose of this study was to assess the impact of pre-harvest bagging materials on maturity indices and post-harvest quality of cherry tomatoes. At pre-harvest, fruit were bagged with blue and transparent plastic bags of 0.075- and 0.025-mm thickness, respectively. The non-bagged fruit were considered as control treatment. The experiment was carried out in a randomized complete block design arranged in a 2 × 3 factorial arrangement with three replications. Physical quality parameters such as; colour changes (L*, a*, b*, C*, h˚, and ΔE), firmness, weight loss and size were assessed. Physico-chemical parameters such as pH, total soluble solids, and total titratable acidity were also evaluated. Bagging had a significant effect on the quality of both cherry tomato cultivars. The results showed that bagging cherry tomatoes at 1.5 cm diameter with blue and transparent plastic bags accelerated maturity. Moreover, bagging with transparent plastic bags enhanced exocarp colour, reduced weight loss, retained larger size, increased pH and TTA, with an increase in TSS when compared with blue plastic bags and control, respectively at 12 days of shelf-life. In conclusion, the findings demonstrate that pre-harvest bagging has the potential to improve maturity indices and post-harvest quality of cherry tomatoes. Therefore, pre-harvest bagging can be used as an alternative method to enhance cherry tomato fruit quality and shelf-life. / NRF

Theoretical and computational methods have been used to study nonlinear effects in the mechanical response of materials at the nano and macro scales. These methods include, acoustoelastic theory, molecular dynamics and finite element models. The nonlinear indentation response of Ni thin films of thicknesses in the nano scale was studied using molecular dynamics simulations with embedded atom method (EAM) interatomic potentials. The study included both single crystal films and films containing low angle grain boundaries perpendicular to the film surface. The simulation results for single crystal films show that as film thickness decreases, larger forces are required for similar indentation depths but the contact stress necessary to emit the first dislocation under the indenter is nearly independent of film thickness. The presence of grain boundaries in the films leads to the emission of dislocations at a lower applied stress. For a single crystal Ni thin film of a thickness of 20 nm a direct comparison of simulation and experimental results is presented, showing excellent agreement in hardness values. The effects of using different interatomic potentials and indentation rates for the simulations are also discussed. Dynamic indentation of the Ni thin film was also carried out for different frequencies. It has been found that there is a 12% increase in dislocations compared to quasi static indentation and the results are consistent with experiments. Acoustoelastic theory was used to study how nonlinear elastic properties of unidirectional graphite/epoxy (gr/ep) effect the energy flux deviation due to an applied shear stress. It was found that the quasi-transverse wave (QT) exhibits more flux deviation compared to the quasi-longitudinal (QL) or the pure transverse (PT) due to an applied shear stress. The flux shift in QT wave due to an applied shear stress is higher than that for an applied normal stress along laminate stacking direction for the same magnitude. The QT wave has energy flux deviation due to shear stress at 0o and 90o fiber orientations as compared to normal stress case where the flux deviation is zero. It was found that the energy flux shift of QT wave in gr/ep varies linearly with applied shear stress. The Finite element model of the equations of motion combined with the Newmark method in time was used to confirm the flux shift predicted by theory. / Ph. D.

The research work described in this thesis, the environmentally friendly novel "Microwave Assisted Sub-Critical water (MASCW)" technology for particle engineering of active pharmaceutical ingredients and excipients was developed. The present novel technology MASCW process is described as green technology as water is used as the solvent medium and microwave energy as external source of heat energy for generation of a particle with different morphological and chemical properties. In MASCW process supersaturated solution of APIs is prepared by dissolving solute in water at high temperature and pressure conditions. Upon rapid and controlled cooling, based on the aqueous solubility of solute, solute/solvent concentration and dielectric constant of water rapid precipitation of API with narrow particle size distribution occurs. Using paracetamol (pca) as API moiety understanding of the mechanism of MASCW crystallisation process was investigated. The effect of different process and experimental parameters on crystallisation pathway and end product attributes were analysed. Correlation between the degree of supersaturation concentration of pca solution against temperature and pressure parameters was explained by generating binary phase diagram. Determination of polymorphic transformation pathway of pca from form I (stable) to form II metastable polymorphs in solution was analysed using Raman spectroscopy. The difference between conventional heating and subcritical treatment was explored by determining the change in the solvent dielectric constant and solubility of hydrophobic API molecule. Based on the process understanding results, this technology was further implemented to explore its application in generating phase pure stable and metastable cocrystal phase. Based on the solubility of API and cocrystal former congruent (CBZ/SAC, SMT/SAC, SMZ/SAC) and incongruent (CAF/4HBA) cocrystal pairs were selected. For the first time generation of anhydrous phase of CAF: 4HBA cocrystal in 1:1 stoichiometric ration was reported and generation of metastable cocrystal phase of CA CBZ: SAC form II was reported. The application of this technology was explored in generating phase pure metastable polymorph of paracetamol which retain higher compressibility and dissolution rate. The potential of MASCW micronisation process, theophylline is used as the model component to produce micro sized particles for pulmonary drug delivery system via dry powder inhaler (Foradil inhaler). The results demonstrate that the THF particles generated using MASCW process displayed greater aerodynamic performance compared to conventional spray-dried THF sample. In the final chapter, synthesis of inorganic biomaterial (nano crystalline hydroxyapatite) was reported for the first time and the prospects of combining API like ibuprofen (IBU) with a biologically active component like nano-crystalline hydroxyapatite (HA) through hydrogen bonding was mechanistically explained using X-ray diffractometer and spectroscopic techniques.

This research was designed to investigate the effect of cations on activated sludge characteristics and also to determine their influence on digestion performance. For this purpose, cations in solution and in floc were evaluated along with various activated sludge characteristics and the collected waste activated sludge underwent both anaerobic and aerobic digestion. It was found that large amounts of biopolymer (protein + polysaccharide) remained in the effluent of WWTP that received high influent sodium but had low iron and aluminum in floc. However, sludges from plants with high sodium and high iron and aluminum dewatered well and produced high quality effluents, suggesting that iron and aluminum have significant positive effects on floc properties. Following anaerobic digestion, a significant increase in solution protein occurred and correlations between solution protein, ammonium production, percentile volatile solids reduction and iron in floc were obtained. These data indicate that iron-linked protein is released to solution when iron is reduced and its degradation is responsible for volatile solids reduction in anaerobic digestion. In aerobic digestion, polysaccharide in solution increased along with calcium, magnesium and inorganic nitrogen. This implies that divalent cation-bound biopolymer might be the primary organic fraction that is degraded under aerobic digestion. Combined (anaerobic/aerobic) digestion was performed and produced further volatile solids destruction with discrete cation and biopolymer response during each phase of digestion. These results support the theory that two types of organic matter with different cation bindings are present in floc and each type is degraded under different digestion processes. / Master of Science

MPH / Department of Public Health / See the attached abstract below

The present thesis is on the error estimates of different energy based quasicontinuum (QC) methods, which are a class of computational methods for the coupling of atomistic and continuum models for micro- or nano-scale materials. The thesis consists of two parts. The first part considers the a priori error estimates of three energy based QC methods. The second part deals with the a posteriori error estimates of a specific energy based QC method which was recently developed. In the first part, we develop a unified framework for the a priori error estimates and present a new and simpler proof based on negative-norm estimates, which essentially extends previous results. In the second part, we establish the a posteriori error estimates for the newly developed energy based QC method for an energy norm and for the total energy. The analysis is based on a posteriori residual and stability estimates. Adaptive mesh refinement algorithms based on these error estimators are formulated. In both parts, numerical experiments are presented to illustrate the results of our analysis and indicate the optimal convergence rates. The thesis is accompanied by a thorough introduction to the development of the QC methods and its numerical analysis, as well as an outlook of the future work in the conclusion.

No description available.

Didžiausiais paviršinių nuotekų teršalais laikomi naftos produktai ir skendinčiosios medžiagos. Pastarąsias galima nesunkiai pašalinti taikant tradicinius paviršinių nuotekų valymo metodus, tokius kaip nusodinimas, o naftos produktų šalinimui reikalingas antrinis nuotekų valymas. Vienas efektyviausių NP šalinimo iš nuotekų būdas yra filtravimas pro sorbuojančiosios medžiagos filtrą. Nors šiuo būdu valant nuotekas galima pasiekti didelio teršalų šalinimo efektyvumo, praktiškai dažnai susiduriama su problema, kai į eksploatuojamuosius valymo įrenginius nuotekos atiteka dideliais greičiais ir teršalai nėra iki galo pašalinami. Todėl šiame darbe buvo atliktas trijų skirtingų sintetinių sorbentų („Fibroil, „Duck“, „Reo-dry“) efektyvumo šalinti iš paviršinių nuotekų naftos produktus ekstremaliomis sąlygomis (esant dideliems greičiams) eksperimentinis tyrimas. Atlikus bandymus su dirbtinėmis ir realiomis paviršinėmis nuotekomis laboratoriniame stende, nustatyta, kad visų trijų sorbentų efektyvumas šalinti NP yra panašus ir skendinčiosios medžiagos bei nuotekų drumstumas neturi įtakos NP šalinimo efektyvumui. Tačiau „Fibroil“ sorbentą naudojant kaip filtro užpildą, 30 m/h greitį galima išlaikyti gerokai ilgiau nei su sorbentais „Duck“ ir „Reo-dry“ ir šį sorbentą naudoti ekonomiškiausia. Darbą sudaro 8 dalys: įvadas, darbo aktualumo aprašymas, literatūros apžvalga, tiriamojo darbo metodikos aprašymas, eksperimeto rezultatai, rekomendacijos ir išvados bei literatūros sąrašas. Darbo... [toliau žr. visą tekstą] / Suspended solids and oil products are considered as the most important pollutants in the storm water. As suspended solids can be easily retained from storm water by simple sedimentation, for oil products it is usually needed to have a secondary treatment: filtration through sorbents media. Although storm water filtration through a sorbent filter gives high treatment efficiency, it is usually impossible to ensure the right speed of storm water coming to the treatment facilities (it is usually too high to ensure an efficient sorption). For this reason the research and analysis of three different synthetic sorbents („Fibroil“, „Duck“, „Reo-dry“) were performed with artificial and real storm water in the laboratory under extreme conditions (filtration speed 30 m/h). According to the results of the experiment, all three sorbents have similar treatment efficiency and suspended solids and turbidity has no impact on oil products removal efficiency. But it is more efficient to use “Fibroil” and it is suitable for filtration under 30 m/h speed much longer than sorbents “Duck” and “Reo-dry”. Structure: introduction, relevance, methodology, results of the experiment, recomedations conclusions and references. Thesis consist of: 55 p. text without appendixes, 21 pictures, 8 tables, 39 bibliographical entries.

In a proposed design for a concentrated solar power tower, sand is irradiated by solar energy and transfers its energy to another fluid stream by means of a finned tube heat exchanger. To maximize heat transfer and minimize potential damage to the heat exchanger, it is desired to have a very uniform flow through the heat exchanger. However, performing full scale flow tests can be expensive, impractical, and depending upon the specific quantities of interest, unsuitable for revealing the details of what it happening inside of the flow stream. Thus, the discrete element method has been used to simulate and study particulate flows. In this project, the flow of small glass beads through a square pyramid shaped hopper and a wedge shaped hopper were studied at the lab scale. These flows were also simulated using computers running two versions of discrete element modeling software – EDEM and LIGGGHTS. The simulated results were compared against the lab scale flows and against each other. They show that, in general, the discrete element method can be used to simulate lab scale particulate flows as long as certain material properties are well known, especially the friction properties of the material. The potential for increasing the accuracy of the simulations, such as using better material property data, non-uniform particle size distributions, and non-spherical particle shapes, as well as simulating heat transfer within a granular flow are also discussed.

Capillaries in tumours are often severely buckled (in a plane perpendicular to the axis) and / or chaotic in their direction. We develop a model of these phenomena using nonlinear solid mechanics. Our model focusses on the immediate surrounding of a capillary. The vessel and surrounding tissue are modelled as concentric annulii. The growth is dependent on the concentration of a nutrient (oxygen) diffusing from the vessel into the tumour interstitium. The stress is modelled using a multiplicative decomposition of the deformation gradient F=F_e F_g. The stress is determined by substituting the elastic deformation gradient F_e (which gives the deformation gradient from the hypothetical configuration to the current configuration) into a hyperelastic constitutive model as per classical solid mechanics. We use a Blatz-Ko model, parameterised using uniaxial compression experiments. The entire system is in quasi-static equilibrium, with the divergence of the stress tensor equal to zero. We determine the onset of buckling using a linear stability analysis. We then investigate the postbuckling behaviour by introducing higher order perturbations in the deformation and growth before using the Fredholm Alternative to obtain the magnitude of the buckle. Our results demonstrate that the growth-induced stresses are sufficient for the capillary to buckle in the absence of external loading and / or constraints. Planar buckling usually occurs after 2-5 times the cellular proliferation timescale. Buckles with axial variation almost always go unstable after planar buckles. Buckles of fine wavelength are initially preferred by the system, but over time buckles of large wavelength become energetically more favourable. The tumoural hoop stress T_{ThetaTheta} is the most invariant (Eulerian) variable at the time of buckling: it is typically of the order of the tumoural Young's Modulus when this occurs.