This diploma thesis dealt with the study of interactions of soil organic matter, specifically humic acids with a pollutant, where the surfactant Septonex was used. Humic acids were isolated from two different soils in the work, namely black earth and cambium. The theoretical part describes the formation of humic acids as such, their possible interactions with substances and the characterization of surfactants. The experimental part is devoted to the characteristics of humic acids using elemental analysis, thermogravimetry and then the most important part of the thesis, namely the monitoring of interactions using isothermal titration calorimetry. The experiment showed that the sample of isolated black earth at the surfactant concentration of 0,075 molâdm3 had the best interaction with the surfactant.

Indiana University-Purdue University Indianapolis (IUPUI) / High-temperature alloys have been extensively used in many applications, such as furnace muffles, fuel nozzles, heat-treating fixtures, and fuel nozzles. Due to such conditions, these materials should have resistance to cyclic loading, oxidation, and high heat. Although there are numerous prior experimental and theoretical studies, there is insufficient understanding of application of the unified viscoplasticity theory to finite element software for fatigue life prediction. Therefore, the goal of this research is to develop a procedure to implement unified viscoplasticity theory in finite element (FE) model to model the complex material deformation pertaining to thermomechanical load and implement an incremental damage lifetime rule to predict the thermomechanical fatigue life of high-temperature alloys. The objectives of the thesis are: 1. Develop a simplified integrated approach to model the fatigue creep deformation under the framework of ‘unified viscoplasticity theory’ 2. Implement a physics - based crack growth damage model into the framework 3. Predict the deformation using the unified viscoplastic material model for ferritic cast iron (Fe-3.2C-4.0Si-0.6Mo) SiMo4.06 4. Predict the isothermal low cycle fatigue (LCF) and LCF-Creep life using the damage model In this work, a unified viscoplastic material model is applied in a FE model with a combination of Chaboche non-linear kinematic hardening, Perzyna rate model, and static recovery model to model rate-dependent plasticity, stress relaxation, and creep-fatigue interaction. Also, an incremental damage rule has been successfully implemented in a FE model. The calibrated viscoplastic model is able to correlate deformations pertaining to isothermal LCF, LCF-Creep, and thermal-mechanical fatigue (TMF) experimental deformations. The life predictions from the FE model have been fairly good at room temperature (20°C), 400°C, and 550°C under Isothermal LCF (0.00001/s and 0.003/s) and LCF-Creep tests. The material calibration techniques proposed for calibrating the model parameters resulted in a fairly good correlation of FE model derived hysteresis loops with experimental hysteresis, pertaining to Isothermal LCF (ranging from 0.00001/s to 0.003/s), Isothermal LCF-Creep tests (withhold time) and TMF responses. In summary, the method and models developed in this work are capable of simulating material deformation dependency on temperature, strain rates, hold time, therefore, they are capable of modeling creep-stress relaxation and fatigue interaction in high-temperature alloy design.

Copper is an essential element for all living organisms. However, due to its low redox potential it can be involved in the production of reactive oxygen species; where excess amounts of copper can be exceptionally toxic.1 In humans, malfunctions in copper metabolism are linked to diseases such as Menkes syndrome, Wilson’s disease, prion disease, and Alzheimer’s disease.2 Maintenance of copper homeostasis requires a number of proteins, such as copper transporters and chaperones to deliver copper to the correct protein while limiting free copper in the cell.3 Therefore, understanding the thermodynamics of copper(II) coordination in proteins is critical to our understanding of copper homeostasis. Herein we report human carbonic anhydrase II contains a novel copper binding site with picomolar affinity.4 A full characterization of the structure and thermodynamics associated with the coordination of both Cu atoms into their respective sites is discussed. Techniques including paramagnetic nuclear magnetic resonance spectroscopy (NMR), and x-ray absorption spectroscopy (XAS) techniques provide insight into the high affinity CuA coordination environment. A detailed characterization of this high affinity binding site and related peptide-bound model complexes are included, with the results providing insights into the chemistry and physiological impact of copper binding in human carbonic anhydrase II.

Carbonic anhydrase (CA) is a well-studied, zinc dependent metalloenzyme that catalyzes hydrolysis of carbon dioxide to the bicarbonate ion. In the past, metal binding studies related to CA have continually relied on equilibrium dialysis measurements to ascertain an extremely strong association constant (Ka= approx. 1.2 x 1012) for Zn2+. However, new methodology has allowed us to collect data using isothermal titration calorimetry (ITC), which calls that number and the association constants for many other first row transition metal ions into question. Thermodynamic parameters associated with Zn2+, Cu2+, Ni2+, and Co2+ binding to apoCA are unraveled from a series of complex equilibria associated with the in vitro metal binding event. This in-depth analysis adds clarity to the complex ion chemistry associated with metal ion binding to carbonic anhydrase and validates thermochemical methods that accurately measure association constants and thermodynamic parameters for complex-ion and coordination chemistry observed in vitro. Additionally, the as-isolated and the reconstituted ZnCA and other metalsubstituted CAs were probed using X-ray absorption spectroscopy. Both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses indicate the metal centers in the reconstituted carbonic anhydrases offer new metal binding coordination sites that can be used as models to understand nonheme metal sites in vivo.

The crystallization behavior of bisphenol-A polycarbonate (BAPC) was studied, focusing on the initial stage of crystallization and the secondary stage of crystallization. Bisphenol-A polycarbonate was the polymer chosen for this study because of its slow crystallization rate. With slow crystallization kinetics, the polymer morphology does not change when quenched below its glass transition temperature, enabling the study of different stages of crystallization through the frozen morphology. The study of the initial stages of crystallization pertained to crystallization times prior to the growth of detectable crystallinity. This study employed BAPC because of the long induction period, a direct result of the slow crystallization kinetics. During the induction period of polycarbonate crystallized at 190°C there was no evidence of polymer chain ordering that was seen in literature for other polymers. The length of the induction period determined by differential scanning calorimetry and wide-angle X-ray diffraction varied by over 6 hours because differential scanning calorimetry can detect a smaller amount of crystallinity than wide-angle X-ray diffraction. Signs of pre-ordering in the literature could be a result of experimental sensitivity. The study of the secondary crystallization dealt with the isothermal lamellar thickening of BAPC crystals during annealing, after crystallization for an extended period of time. Small-angle X-ray scattering and differential scanning calorimetry experiments were performed on bisphenol-A polycarbonate samples crystallized near 190°C for 8 days and annealed at either 223°C or 228°C for various times. The Gibbs-Thomson relationship, which can be defined using the experiments mentioned, yielded two thermodynamic constants, the equilibrium melting temperature and the surface free energy. Including data from literature in the determination of the constants, the equilibrium melting temperature and surface free energy of BAPC is 303°C and 36.6mJ/m2, respectively. Comparing the lamellar thickness measurements by small-angle X-ray diffraction with direct measurements by microscopy was difficult because the morphology of the polymer was not easily seen in the bulk using atomic force microscopy or scanning electron microscopy. Etching the sample was the most promising technique for future investigations of revealing the bulk morphology for direct lamellar thickness measurements. Crystallizing thin films of polycarbonate on calcite substrates allowed the measurement of lamellar thickness using scanning electron microscopy because the lamellae grow epitaxially to the substrate. The measurement of the long spacing in thin film samples was comparable to that of bulk samples. / Master of Science

Current improvements in gas turbine engine performance have arisen primarily due to increases in turbine inlet temperature and compressor pressure ratios. However, a maximum possible turbine inlet temperature exits in the form of the adiabatic combustion temperature of the fuel. In addition, thermal limits of turbine blade materials also places an upper bound on turbine inlet temperatures. Thus, the current strategy for improving gas turbine efficiency is inherently limited. Introduction of a new gas turbine, based on an alternative work cycle utilizing isothermal combustion (i.e. combustion within the turbine) affords significant opportunities for improving engine output and/or efficiency. However, implementation of such a scheme presents a number of technological challenges such as holding a flame in high-speed flow. The current research is aimed at determining whether such a combustion scheme is feasible using computational methods. The geometry, a simple 2-D cascade utilizes surface injection within the stator or rotor boundary layers (including the rotor pressure side recirculation zone (a natural flame holder). Computational methods utilized both steady and time accurate calculations with transitional flow as well as laminar and turbulent combustion and species transport. It has been determined that burning within a turbine is possible given a variety of injection schemes using "typical" foil geometries under "typical" operating conditions. Specifically, results indicate that combustion is self-igniting and, hence, self-sustaining given the high temperatures and pressures within a high pressure turbine passage. Deterioration of aerodynamic performance is not pronounced regardless of injection scheme. However, increased thermal loading in the form of higher adiabatic surface temperatures or heat transfer is significant given the injection and burning of the fuel within the boundary layer. This increase in thermal loading is, however, minimized when injection takes place in or near a recirculation zone. The effect of injection location on pattern factors indicates that suction side injection minimizes temperature variation downstream of the injection surface (for rotor injection only). In addition, the most uniform temperature profile (in the flow direction) is achieved by injection fuel and combustion nearest to the source of work extraction. Namely, injection at the rotor produces the most "isothermal" temperature distribution. Finally, a pseudo direct simulation of an isothermal machine is conducted by combining simulation data and assumed processes. The results indicate that isothermal combustion results in an increase in turbine specific work and efficiency over the equivalent Brayton cycle. / Master of Science

This thesis presents the study of organofunctional alkoxysilane coatings to prevent high temperature oxidation of Sm-Co powders. Sm-Co are important permanent magnetic alloys, owing to their high Curie temperature and large values of magnetocrystalline anisotropy. They possess stable magnetic properties in the temperature range -40 to 120 °C which makes them very attractive candidates for automobile’s electric motors. However, the environmental conditions for such applications are a sum of high temperatures, humidity, fuels and salts which provide perfect breeding ground for corrosion. In this study we report the high temperature oxidation resistance of Sm2Co17 powders coated with four common commercially available organofunctional silanes; (3-aminopropyl)trimethoxysilane (APTMS), (3-aminopropyl)triethoxysilane (APTES), methyltrimethoxysilane (MTMS) and (3-glycidyloxypropyl)trimethoxysilane (GPTMS). The as received powder was a multimodal mixture of many sizes and shapes which represented a typical ball milling product. The thermal analyses of the powders suggested that the powders without surface coatings had profound affinity towards oxidation. The thermal properties of sieved uncoated powders revealed that the small powders were more susceptible to oxidation than the large powders due to their large specific surface area. The isothermal properties of coated powders revealed that the powders coated with silanes had at least 10 times higher resistance to oxidation as compared to uncoated powders heated at 400 °C for 10 h. The non-isothermal tests conducted from room temperature to 500 °C also revealed that the uncoated powders gained 6 times more mass as compared to the powders coated with an ideal (MTMS) silane. The microstructural analysis of the uncoated powders heated from 400 °C to 550 °C revealed diffusion of oxygen, instable intermetallic phases which resulted in a redistribution of alloying elements, precipitation of alloying elements and formation of a featureless shell (approximately 20 µm in thickness) that surrounded the unreacted core. The coated powders on the other hand showed homogenous distribution of alloying elements, stable intermetallic phases and limited the shell thickness (1 µm). The thermo-magnetic properties of Sm-Co powders showed that the thermal instability also affected the magnetic properties adversely. It was found that the magnetic properties were deteriorated with a decrease in powder size. The energy dispersive spectroscopic (EDS) analyses showed that the small powders contained higher oxygen content than the large powders. Moreover XRD analysis also revealed that the small powders contain higher residual strains and smaller crystallite size which can play their role in deteriorating magnetic properties. It was found that surface modification by silanization improve the thermo-magnetic properties by effectively shielding the powder surfaces from surface oxidation. The rheological properties Sm-Co/PA12 composites revealed that the viscosity of the composites was increased with decreasing powder size due to the presence of rough surfaces and sharp corners in small powders. The rheological properties of the melts containing coated powders revealed that the silane layer acted as a lubricant and decreased the melt viscosity. It was found that coating the powders with silanes not only improve the rheological properties but also improve the other physical properties such as glass transition temperature the loss modulus by modifying the interfacial layer between the polymer matrix (PA12) and the powder. It results in a decrease in viscosity, a broadening of the glass transition temperature and a change in the damping properties of the composites. The dynamic mechanical properties of Sm-Co/PA12 composites showed that the storage modulus was increased with decreasing powder size. The results were expected as the rough surfaces act as local welding points between the powder and the polymer matrix. It was found that the surface modification improve the storage modulus. It is assumed that the silanes modify the interfacial properties which not only resulted in increasing the storage modulus but also broadened the glass transition temperature, Tg and damping, tanδ peaks. From the thermogravimetric, microstructural, rheological and magnetic analyses it can be concluded that the silanes are the effective coatings in preventing high temperature oxidation, stabilizing microstructure, enhancing mechanical properties, and improving rheological and magnetic properties. / <p>QC 20121205</p>

The aim of the work presented was to investigate the effects of upper bainite on impact toughness in quench and tempered low alloy plate steels. The experimental research included construction of CCT diagrams by dilatometry, verification of phases by optical microscopy (OM), Vickers hardness, scanning electron microscopy (SEM), transmission electron microscopy (TEM) on precipitates extracted by carbon replica and by electrolytic means and finally impact testing of Charpy specimens with mixed bainite:martensite microstructures. Bainite was formed in High Chromium Low Molybdenum (HCrLMo) and in High Molybdenum Low Chromium (HMoLCr) steel samples by isothermal annealing within the bainite C-curve of the respective CCT diagrams. The isothermal kinetics of the upper bainite transformation was modelled with the Johnson Mehl Avrami Kolmogorov (JMAK) model. Avrami exponents of 1.4 and 1.3 were obtained for the HCrLMo and HMoLCr steels respectively which indicated linear growth with a considerable lengthening rate of laths and negligible thickening. The measurably slower growth kinetics in the HMoLCr steel as observed in the JMAK model and the higher hardenability with reference to its CCT diagram, suggested a strong Mo alloying element effect. The stronger effect of Mo compared to Cr was attributed to a solute drag like effect. The effect of upper bainite in a tempered martensitic matrix was investigated for the following amounts of bainite; 0%, 10%, 25%, 60%, 75%, 90% and 100%. The impact toughness of the mixed bainite:martensite samples was evaluated against the toughness of 100% bainite and 100% martensite. It was demonstrated that upper bainite reduces the total absorbed impact energy by an adverse effect on crack nucleation energy and crack propagation energy. / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Materials Science and Metallurgical Engineering / Unrestricted

Acute and chronic sleeping sickness are fatal neglected tropical diseases caused by Trypanosoma brucei rhodesiense and Trypanosoma brucei gambiense respectively (members of the sub-genus Trypanozoon). Accurate diagnostics are needed to guide treatment since the symptoms of disease are non-specific and the drugs that are used for treatment are too toxic to be administered to unconfirmed cases. Tests need to be simple enough to confirm clinical diagnosis of sleeping sickness in poorly-resourced, peripheral health centres and for use as epidemiological tools to detect T. b. rhodesiense in the zoonotic reservoirs of infection. This study focuses upon LAMP (loop-mediated isothermal amplification) as a novel diagnostic for sleeping sickness that may serve to bridge the gap between the need for sensitive, specific molecular diagnostics on the one hand and ‘field-friendly’ diagnostics on the other. Here, two previously published LAMP assays for Trypanozoons were compared to classic PCR based methods for the diagnosis of Trypanozoon infection status in 428 cattle blood samples. The results did not support the use of LAMP as an improved system for surveillance of T. b. rhodesiense in the zoonotic cattle reservoir. T. b. rhodesiense and T. b. gambiense subspecies specific LAMP assays were evaluated against traditional reference subspecies specific PCR tests, using DNA purified from 86 cryopreserved trypanosome isolates. Novel LAMP assays for these subspecies were also designed and evaluated. Both the published and novel assays for T. b. rhodesiense (targeting different regions of the SRA gene) were sensitive, specific and reliable when applied to purified DNAs, but were less consistent on field samples. The novel T. b. gambiense LAMP (targeting TgsGP) was sensitive and specific but this was not the case for the published LAMP assay (targeting the 5.8S rRNA gene). However reliability may be less than optimal for LAMP TgsGP. Finally, simple endpoint readout methods for LAMP were evaluated. The colour change reagent hydroxynaphthol blue was identified as the best currently available method taking cost, ease of use and reliability into consideration. In 2009 the number of reported sleeping sickness cases fell below 10,000 for the first time in 50 years. Improved LAMP diagnostics could facilitate the diagnosis of sleeping sickness and support the continued fight against this neglected, but deadly disease.

A series of phosphotripeptide ligands for the Grb2 SH2 domain was designed and synthesized, each of which derived from the minimal consensus sequence required for binding: Ac-pYXN. The binding affinity and related thermodynamic parameters were determined by isothermal titration calorimetry. Both the size and connectivity of the side-chain was varied. The consequences of incorporating α,α-disubstitution at the pY+1 residue on binding thermodynamics were evaluated, as were the effects of constraining the side-chains in a ring. The series was evaluated from a number of perspectives: (1) increasing size of the pY+1 residue by utilizing various amino acid types: monoalkyl, dialkyl, or cycloalkyl; (2) comparisons between ligands with the same number of carbons (scission control); and (3) by comparing ligands incorporating cyclic pY+1 residues with those incorporating α,α-dialkyl residues with one fewer methylene group (excision control). Inconsistencies in the thermodynamic consequence of constraining the backbone were observed within this set of ligands, which reveal the limitations of our understanding of protein-ligand interactions. Aspects of both the classical and non-classical hydrophobic effect were observed, but the occurance of one over the other could not be explained. / text