Dissertations / Theses on the topic 'Mineral replacement'

Mineral bone disturbances are common in chronic kidney disease (CKD), and associated with significant risk of mortality and morbidity in patients on renal replacement therapy (RRT). Surrogate biomarkers of bone turnover such as parathyroid hormone (PTH), phosphate, calcium and Vitamin D are used to diagnose, evaluate, and guide treatment. This thesis examines the effect of RRT on mineral bone disturbances, it's association with bone morbidity, and management strategies for phosphate control. Initially the incidence of radiologically proven bone fracture by site, in prevalent RRT groups is quantified and the relationship to associated risk factors studied. In this multicentre observational study of 2096 patients over a 3-year period the risk of fracture is higher in haemodialysis (HD) patients than in transplant patients even when controlling for other risk factors. Exposure to lanthanum and Vitamin D is apparently a protective factor in the HD group. I then examine a thrice-weekly nocturnal in-centre dialysis model in which we attain normal phosphate levels without dietary restriction or supplementation by altering the dialysis prescription and time. This observational trial over a 2-year period with over 2000 sessions of dialysis in 14 patients is associated with reduction of blood pressure medications. Subsequently I investigate the relationship of phosphate to FGF23 in a group of peritoneal dialysis patients. Finally, I study the effect of dialysis on clearances of FGF23 and expand on the knowledge of FGF-23 during a session of dialysis.

Cement replacement materials are by-products used to produce high performance concrete. Published data on the effects of combinations of mineral admixtures in concrete on the microstructural and performance-related properties under different curing regimes are comparatively little. Further the correlation of strength of concrete to its permeability and pore structure is also not clear. The main objective of this research is to study the performance of various combinations of fly ash/silica fume and slag/silica fume concretes under three different curing regimes, viz. continuous moist curing, no moist curing after demolding and air drying after 7-days of initial moist curing. Six different concrete mixes were prepared with ordinary portland cement and a blend of portland cement and combinations of fly ash+silica fume and slag+silica fume The water-to-cementitious materials ratio of all the concrete mixtures was kept constant at 0.45. The properties investigated included workability of the fresh concrete, engineering properties such as cube and modified cube compressive strength, flexural strength, dynamic modulus of elasticity, pulse velocity, shrinkage and swelling, permeability and microstructural properties such as porosity and pore size distribution. The results show that prolonged dry curing results in lower strengths, higher porosity, coarser pore structure and more permeable concretes. It was found that the loss in early age compressive strength due to incorporation of fly ash or slag can be compensated for by the addition of small amounts of silica fume. The engineering and microstructural properties and permeability of concretes containing fly ash or slag appear to be more sensitive to poor curing than the control concrete, with the sensitivity increasing with increasing amounts of fly ash or slag in the mixtures. The incorporation of high volumes of slag in the concrete mixtures refined the pore structure and produced concretes with very low porosity and threshold diameters. The results emphasize that a minimum 7-day wet curing is needed for concrete with mineral admixtures to develop the full potential, and that continued exposure to a drying environment can have adverse effects on the long-term durability of inadequately cured slag or fly ash concretes. The results also confirm that compressive strength alone is not an adequate index to judge the performance of concrete, and the knowledge of the strength, pore structure and permeability are required for this purpose. Slag/silica fume concrete mixtures showed better performance than fly ash/silica fume concrete mixtures as regards the development of engineering and microstructural properties.

The porosity in minerals contributes to enhanced permeability for fluid flow in natural systems and engineering processes. Porosity can be created by fluid-mediated mineral replacement reactions. Such reaction-induced porosity can evolve with time, yet the mechanisms and kinetics of porosity creation and evolution remain poorly understood. This thesis presents experimental investigations on the creation and evolution of mineral porosity in two model replacement reactions, i.e., the replacement of calcite by gypsum and anhydrite with a positive volume change and the replacement of pentlandite by violarite and millerite with a negative volume change. These replacement reactions were conducted under mildly acidic hydrothermal conditions for up to 18 months, and the mineralogy, microstructure and porosity of the reaction products were quantitatively analysed by powder X-ray diffraction, (ultra) small-angle neutron scattering, high resolution scanning electron microscopy, focused-ion beam scanning electron microscopy, and X-ray micro-tomography. The results showed that porosity creation and evolution are highly dependent on mineral systems and reaction conditions. In the calcite-gypsum-anhydrite mineral system, the experiments at 25-60 °C produced intragranular nanopores in gypsum replacing calcite. Because of the positive volume change, gypsum overgrowth also occurred on the grain surface, and the gypsum in the overgrowth region contained intergranular micropores. Porosity coarsening was rapid (a few weeks) in the replacement region, leading to the formation of micro-voids in the core of gypsum grains. The replacement reaction was sensitive to temperature. When the experiments were conducted at a higher temperature of 220 °C, anhydrite was formed instead of gypsum. Porosity evolution in anhydrite was different when compared to gypsum at lower temperatures. In the pentlandite-violarite-millerite mineral system, only replacement occurred, likely because the negative volume change does not require overgrowth for additional space. The replacement was sensitive to temperature and solution pH. The experiments conducted at 125 °C and pH 4 produced permeable nanopores leading to the complete replacement of pentlandite; these nanopores coarsened slowly during the 17 months of experiment and occurred preferentially near the grain surface. However, in experiments conducted at 125 °C and pH 5, violarite became impermeable in partially replaced grains due to hematite precipitation in the pore space, blocking the fluid flow. At a higher temperature of 220 °C and pH 4, the formation of millerite in addition to violarite resulted in faster porosity coarsening and formed micropores within 4 weeks. Fundamentally, these complex porosity creation and evolution phenomena observed in the two model mineral replacement reactions are controlled by the interplay between dissolution, precipitation, epitaxial nucleation, and Ostwald ripening processes which are all sensitive to reaction conditions. This understanding should generally be applicable to other mineral replacement reactions. Finally, a case study of the application of porosity control was presented. The leaching of chalcopyrite is often kinetically inhibited by surface passivation layers, which are formed by the replacement of chalcopyrite during leaching. Common passivation layers are elemental sulphur and jarosite. Our leaching experimental results showed that surface sulphur could be removed by adding sulphur-dissolving solvent tetrachloroethylene (TCE) into the sulfuric acid leaching solution. The removal of surface sulphur significantly improved the leaching rate by almost 6 times compared with TCE-free leaching. At the later stage of leaching, chalcopyrite was replaced by potassium jarosite. The jarosite shell did not passivate TCE-free leaching due to its porous structure. However, the jarosite shell became nearly impermeable in TCE-assisted leaching because elemental sulphur filled the pores in the jarosite. This case study suggests that chalcopyrite leaching can be significantly enhanced by either removing the surface passivating layer or by controlling the porosity and permeability of the surface layers formed on the chalcopyrite surface.

Effects of dietary supplementation with low levels of organic sources of trace minerals in place of normal levels of their inorganic salts and phytase on growth performance and mineral metabolism were evaluated in two studies using pullets of white and brown shell laying strains. The organic sources were proteinates of copper, iron, manganese and zinc and selenium yeast. A corn-soybean meal diet was fed alone, plus inorganic minerals or plus organic minerals, and with or without phytase in a 3 x 2 factorial arrangement. Twelve groups of 16 pullets, 2 weeks old, were used per treatment. Compared with inorganic minerals, feeding no mineral supplement or organic minerals significantly (P<0.05) decreased manure Cu, Fe and Zn for white pullets and Cu, Fe, Mn and Zn for brown pullets. Dietary phytase significantly reduced manure Fe, P and Ca for white pullets and Fe, Mn, Zn, P and Ca for brown pullets. Adding phytase to diets containing inorganic minerals reduced manure Zn concentration for white pullets and manure Fe, Mn, Zn, P and Ca concentrations for brown pullets. These studies indicate manure levels of trace minerals can be decreased by using low levels of organic mineral supplements and phytase in pullet diets.

Pseudomorphic mineral replacement reactions occur in numerous geological processes (e.g. metamorphism, metasomatism, ore deposition, and chemical weathering) and anthropogenic processes (e.g., reservoir acidification, CO2 sequestration, acid mine drainage, materials syntheses, and minerals processing). Therefore, the understanding of the mechanism and kinetics of these reactions is important not only to geosciences but also to industrial applications. These reactions involve the replacement of a primary mineral by a product mineral in the presence of a fluid phase, with the product mineral preserving the external dimension of the primary mineral. In the early years, solid-state diffusion (SSD) was proposed as the main mechanism for such reactions, while over the past 20 years the importance of coupled dissolution-reprecipitation (CDR) mechanism has been recognized, especially at low temperatures when SSD is assumed to be a very slow process. However, it has recently been recognized that in some mineral replacement reactions the rate of solid-state diffusion can be comparable to the rate of dissolution-reprecipitation, and hence complex mineral textures can be produced from a synergy between SSD and fluid-mediated CDR processes. The interplay between SSD and CDR mechanisms has profound implications in our interpretations of petrological and geological observations, yet it has not been adequately studied so far. Also, the role of the bulk hydrothermal fluids in the formation of lamellae textures by solid-state diffusion process in parent phases that are free of fluid inclusions is still not well elucidated. These and other issues were addressed in this present study. Thus, to better understand the interaction between SSD and CDR reactions, the replacement of bornite (Cu5FeS4) by copper sulphides was used as a model system. In the present thesis, a series of experimental studies have been conducted into the mineral replacement reactions of bornite by copper sulphides to obtain an insight into the kinetics and mechanisms of the replacement reactions, as well as the formation and evolution of porosity during the replacement reactions. The outcomes of these sets of experiments are summarised below: In Chapter 2, the hydrothermal dissolution and replacement of bornite by copper sulphides was studied experimentally in pH 1 solutions at three temperatures (160, 180 and 200 °C) under anoxic conditions, and the effects of background additives (Na2SO3, CuSO4, CuCl2 and CuCl) on the replacement pathway were established. The results revealed that the reaction firstly involved the decomposition of bornite to form chalcopyrite (CuFeS2) lamellae and digenite-I (Cu9S5) via fluid-induced solid-state diffusion (FI-SSD) of Fe3+ from bornite structure. As the reaction progresses, chalcopyrite was later replaced by the second generation of digenite (digenite-II). Subsequently, both digenite-I and -II were replaced by covellite (CuS) and/or chalcocite (Cu2S) via the CDR reaction mechanism, depending on the experimental conditions. In addition, nantokite (CuCl) and atacamite (Cu2Cl[OH]3) formed due to the reaction between the dissolved copper with Cl-rich hydrothermal fluids. The observed replacement reactions at the rim and along fractures, the preservation of the external shape of the original bornite grain, and the presence of porosity in the product phase are characteristic features of the CDR mechanism. The first critical finding from this set of experiments is the fluid-induced exsolution of chalcopyrite lamellae and digenite from bornite. This is because the exsolution rate and lamellae size were sensitive to the composition of the fluids, and no exsolution was observed in the heating experiment in the absence of fluid. This FI-SSD mechanism is made possible by the near-identical topology of the crystal structure of bornite, chalcopyrite and digenite. Secondly, the replacement of bornite is multi-step but proceeds via different pathways under the various conditions studied. The interplay between the FI-SSD and CDR mechanisms resulted in complex reactions which cannot be easily predicted empirically. In Chapter 3, a combined kinetic, textural and mineralogical study of the replacement of bornite by copper sulphides under oxic conditions is presented, in order to obtain insights into the competing reactions between FI-SSD and CDR reactions under oxic conditions. The mechanism and kinetic behaviour of the reactions were described by exploring the effects of key variables including pH (1-6), temperature (160, 180 and 200 °C) and time on the reaction kinetics, and on the evolution of mineralogy and sample textures. Like the anoxic experiments, the resulting textures under oxic conditions also revealed the interplay between the FI-SSD and CDR mechanisms during the replacement of bornite. However, the most important distinctive difference from the anoxic conditions is that the ICP-OES results suggests both Cu and Fe removal into the solution at pH 1, and predominantly Cu-removal at pH 2, 3 and 5 during the FI-SSD under oxic conditons as against predominantly Fe-removal under anoxic condtions. The kinetic behaviour shows a complex dependence on various physical and chemical parameters including temperature, pH and contact time. For example, the result revealed that the reaction rate increases with temperature at pH 1 to 3, and decreases with temperature at pH 4 to 6. This change in reaction trend is linked to a change in the rate-limiting step of the reaction. For the effect of pH, the rate decreases with increasing pH from 1 to 6 at 180 and 200 °C, while the results show a complex effect of pH at 160 °C. There are several important findings from Chapter 3: (1) the dissolution and the replacement of bornite under oxic conditions not only changed with pH but also with temperature, (2) bornite is relatively kinetically stable at higher pH 4-6, while pervasive fast replacement/dissolution of bornite was observed at lower pH (1-3), and (3) the exsolution rate and lamellae distribution is dependent on pH, indicating a FI-SSD mechanism. In Chapter 4, the formation and evolution of porosity during the replacement of bornite by copper sulphides under anoxic and oxic conditions were monitored using combined (ultra) small-angle neutron scattering (USANS/SANS) measurements and microscopic textural examinations. The USANS/SANS measurements were carried out under both dry conditions and after filling the open pores with contrast matching D2O-H2O fluid, which made it possible to differentiate open pores from closed pores. The reactions created pores in the product phases, and all samples contained pores with very broad size distributions from nano to micrometre. Nearly all small pores (<20 nm) were closed while larger pores were mostly open. The textures resulted from the FI-SSD process are largely non-porous, while the products from CDR reactions presents high porosity. Porosity generation in the product phase(s) is due to molar volume and relative solubility differences between the parent and the replacing phase. Porosity dropped at the initial stage of the reaction, but increased again with the progressive replacement, reaching a maximum at complete replacement, and then porosity slowly dropped again, showing porosity creation during the replacement and evolution after the replacement reaction. Therefore, this study provides another experimental evidence demonstrating the transient and dynamic nature of porosity during mineral replacement reactions. Porosity coarsening also occurred during and after replacement reactions, likely driven by surface energy minimization via Ostwald ripening. Overall, this experimental study provides new insights into the physical chemistry of bornite replacement in nature. The documented mineralogical and textural differences could be used as one of the paleoproxies of the chemistry (including pH) and temperature of the fluids responsible for the alteration of copper minerals and remobilization of metals in ore deposits. Particularly, this study shows that mineral replacement can proceed via the synergy between SSD and CDR mechanisms; this happens at geologically low temperatures (≤200˚C) in the chalcogenide systems under both anoxic and oxic conditions, and may be used to interpret observations in other mineral systems such as the silicate systems at amphibolite or eclogitic metamorphic grades. This study also provides insights about porosity formation and evolution in copper-iron sulphides interacting with hydrothermal fluids, and how different reaction mechanisms contributes to porosity evolution, suggesting that mineral porosity can evolve and may be annealed out over geological timescale.

Mineral replacement reactions commonly occur during the formation and alteration of ore deposits. In such settings, primary minerals are often dissolved, with new phases forming as products in the presence of a fluid phase. Particularly within carbonate-hosted epigenetic ore deposits, mineral replacement reactions represent a fundamental ore-forming mechanism whereby primary carbonates are replaced by secondary minerals. These replacement processes generate porosity and facilitate ore mineral precipitation. This study compares observations of natural, ore-forming mineral replacement reactions with laboratory-derived hydrothermal replacement experiments to decipher the metasomatic processes of ore formation from the deposit scale to the nanoscale. This thesis presents insights on (i) the ore-forming mechanisms and post-ore alteration of the Artemis Zn-Cu-Au prospect (Chapters 2 and 3), (ii) the pseudomorphic replacement of calcite by siderite (Chapter 4), and (iii) the replacement of bastnaesite by rhabdophane and monazite (Chapter 5). These chapters focus on the mechanisms, porosity formation, and element redistribution of mineral replacement reactions, typically observed in carbonate-hosted mineral deposits. Chapter 2 details the importance of mineral replacement reactions during the formation and post-depositional alteration of a carbonate replacement deposit. The study was carried out on the Artemis Zn-Cu-Au prospect, which is located in the Cloncurry district, NW Queensland, Australia. The high-grade polymetallic mineralization displays a complex association of massive sulfides and carbonates hosted in a vertical marble lens. Petrographic analyses suggested three major stages: (i) pre-ore stage marble; (ii) ore stage mineralization involving the dissolution of calcite from the marble and precipitation of sulfides and secondary carbonates; and (iii) a post-ore alteration stage involving the replacement of sulfides by calcite and garnet. The replacement of Co-rich arsenopyrite (Fe0.75Co0.26As1.13S0.83) by relatively Co-poor arsenopyrite (Fe0.86Co0.15As0.99S0.99) revealed formation temperatures of 650 ± 50 and 450 ± 70 °C, respectively. In the post-ore stage, pyrrhotite Fe(1-x)S, (x = 0.091–0.119) was pervasively replaced by an almandine-spessartine-rich garnet. The microscale investigations of the mineralization processes in the Artemis orebody document the impact of hydrothermal mineral replacement reactions on metal sequestration. Mineral replacement reactions facilitate the formation of ore deposits and subsequent alteration processes, which may lead to the late-stage loss of economic value of the deposit. Chapter 3 discusses the importance of conducting nanoscale investigations of mineral replacement reactions to constrain their physicochemical conditions, exemplified by the suggested replacement of pyrrhotite by garnet at the Zn-Cu-Au Artemis prospect. Nanoscale examinations by transmission electron microscopy (TEM) of the grain boundary between pyrrhotite and garnet reveal textural and compositional complexity at the reaction front. The single crystal of pyrrhotite has a <100 nm thick Bi-rich rim (~2.7 at.% of Bi). The pyrrhotite rim is bounded by a 5–20 nm wide hematite layer, while pores (<10 nm thick) are present between the two phases. The garnet single crystal and the hematite layer are separated by a gap (10–30 nm). These observations indicate that the replacement of pyrrhotite by hematite proceeded via the coupled dissolution reprecipitation (CDR) mechanism, while Bi precipitated from the hydrothermal solution. The newly formed porosity was occupied by subsequent precipitation of garnet. This study highlights the importance of nanoscale characterization for revealing detailed mechanisms of sulfide alteration. Chapter 4 details experiments on the replacement of calcite by siderite in Fe-rich hydrothermal fluids, investigating the effects of temperature (60–200 °C), solution pH (1.8–10), time (2–1680 h), and calcite precursor (marble and Iceland spar). Two contrasting replacement processes were identified: At 60 °C, the replacement was slow at a transformation of 89% after 1680 h for Iceland spar experiments. Siderite precipitated preferentially along the twin boundaries of calcite, and porosity developed in-between the twins. At 200 °C, the reaction was much quicker at a transformation of 94 % after 8 h. Several concentric 5–15 μm thick epitaxial siderite layers, separated by gaps (<15 μm) that were partly occupied by akaganeite [Fe3+O(OH,Cl)], replaced the calcite grains. Two siderite populations were identified: (i) metastable, pristine and Ca-rich siderite-1 and (ii) microporous, Ca-poor siderite-2. With time, siderite-1 equilibrated with the Fe-rich bulk fluid and transformed into siderite-2, marking the second replacement step. The formation of microporosity created permeability as a result of molar volume change between siderite-1 and -2 (-4.8%). The concentric layer formation is interpreted as an “oscillatory” CDR mechanism, which forms due to the interplay of passivation, fluid with nonequilibrium composition at the reaction front, and secondary porosity formation. Both textures may be used to interpret reaction conditions in natural mineral replacement reactions, especially within carbonate-replacement deposits. Chapter 5 focuses on the replacement of the rare earth element (REE) fluorocarbonate mineral bastnaesite (REECO3F), which is frequently affected by fluid-induced alteration processes throughout all crustal levels. The experiments studied the effect of epithermal phosphate-bearing solutions on bastnaesite, which led to its replacement by monazite (REEPO4) and rhabdophane (REEPO4∙nH2O). At 90 °C, fibrous metastable rhabdophane replaced bastnaesite, which was then gradually replaced by monazite. At 220 °C, only monazite formed, and the reaction initiation was much quicker. Spot analyses showed that REE patterns were similar between bastnaesite and monazite. However, rhabdophane preferentially scavenged Nd to Ho. The presented results provide new insights into the formation conditions of rhabdophane and monazite and detail contrasting REE fractionation processes in the epithermal environment, which are critical to our understanding of the genesis of REE deposits.

Thesis (MBA)--Stellenbosch University, 2001.
Some digitised pages may appear illegible due to the condition of the original hard copy
ENGLISH ABSTRACT: The decision to make equipment replacements has a major influence on the competitiveness of any business. A company like Iscor recently spent approximately one billion Rand to modernise its fleet of equipment at various centres. This report presents a holistic approach to the issue of equipment replacement decision-making. It contends that equipment replacement decisions are not isolated incidents that occur by chance. In fact, the whole process is an integral part of the various processes in the business. This ranges from the influence on the strategy, through to issues such as production planning, maintenance, staffing, financial planning and so on. The role of the replacement decision in each of these elements are discussed and elaborated on. The report goes on to review the various models available in the industry and discusses their advantages and disadvantages. Thus ensuring a clear understanding of the differences in the approaches. The report attempted to propose a method that is relatively straight forward and in terms of application lends itself to the practical mining man. The proposed models are then used to complete a relatively simple example. The example was primarily aimed at showing the elements of the application and certainly not the full extent of the model.
AFRIKAANSE OPSOMMING: Die uitvoer van toerusting vervanging_sbesluite kan 'n dramatiese invloed op die mededingendheid van enige besigheid hê. 'n Maatskappy soos Iscor het onlangs 'n bedrag van ongeveer een biljoen Rand gespandeer om hul vloot van toerusting op verskeie sentrums te vervang. Die verslag stel 'n alles omvattende benadering tot die kwessie van toerusting vervangingsbesluitneming voor. Die verslag gaan voort om voor te stel dat die vervangingsbesluit nie iets is wat toevallig geneem moet word nie. Inteendeel dit is 'n integrale deel van al die verskeidenheid besigheidsprosesse. Die verslag bespreek die verskeidenheid modelle beskikbaar en brei uit oor die voor - en- nadele van elk. Die bespreking verseker dat die leser 'n duidelike beeld kry oor die toepaslikheid van die verskeie modelle. Dit gaan voort om 'n praktiese model voor te stel wat redelik maklik is om aan te wend. Die model word dan toegepas op 'n eenvoudige voorbeeld.

La sostituzione totale d’anca è uno degli interventi chirurgici con le più alte percentuali di successo. Esistono due varianti di protesi d’anca che differiscono in base al metodo di ancoraggio all’osso: cementate (fissaggio tramite cemento osseo) e non cementate (fissaggio tramite forzamento). Ad oggi, i chirurghi non hanno indicazioni quantitative di supporto per la scelta fra le due tipologie di impianto, decidendo solo in base alla loro esperienza. Due delle problematiche che interessano le protesi non cementate sono la possibilità di frattura intra-operatoria durante l’inserimento forzato e il riassorbimento osseo nel periodo di tempo successivo all’intervento. A partire da rilevazioni densitometriche effettuate su immagini da TC di pazienti sottoposti a protesi d’anca non cementata, sono stati sviluppati due metodi: 1) per la valutazione del rischio di frattura intra-operatorio tramite analisi agli elementi finiti; 2) per la valutazione della variazione di densità minerale ossea (tridimensionalmente attorno alla protesi) dopo un anno dall’operazione. Un campione di 5 pazienti è stato selezionato per testare le procedure. Ciascuno dei pazienti è stato scansionato tramite TC in tre momenti differenti: una acquisita prima dell’operazione (pre-op), le altre due acquisite 24 ore (post 24h) e 1 anno dopo l’operazione (post 1y). I risultati ottenuti hanno confermato la fattibilità di entrambi i metodi, riuscendo inoltre a distinguere e a quantificare delle differenze fra i vari pazienti. La fattibilità di entrambe le metodologie suggerisce la loro possibilità di impiego in ambito clinico: 1) conoscere la stima del rischio di frattura intra-operatorio può servire come strumento di guida per il chirurgo nella scelta dell’impianto protesico ottimale; 2) conoscere la variazione di densità minerale ossea dopo un anno dall’operazione può essere utilizzato come strumento di monitoraggio post-operatorio del paziente.

Osteoporosis is a condition of reduced bone mineral density (BMD) resulting in an increased susceptibility to bone fractures. The purpose of this study was to determine the effects of 12 months of weight bearing and resistance exercise on BMD, bone formation, measured by serum osteocalcin (OC) and bone resorption, measured by urinary excretion of deoxypyridinoline crosslinks (Dpd), in 2 groups of postmenopausal women who were either taking or not taking hormone replacement therapy (HRT). Secondary aims were to characterize the changes in insulin-like growth factors-l and -2 (IGF-l and -2) and IGF binding protein 3 (IGFBP3) in response to exercise training, and to determine the contribution of these growth factors in predicting changes in bone mineral density in the 2 populations of postmenopausal women. Women who were three to ten years postmenopausal and aged 40-65 years were included in the study. Women in HRT and no HRT groups were randomized into the exercise intervention resulting in four groups: (1) women not taking HRT, not exercising; (2) women taking HRT, not exercising; (3) women exercising, not taking HRT; and (4) women exercising, taking HRT. The number of subjects per group after one year was 27, 21, 25, and 16, respectively. Exercise training and HRT increase BMD similarly at most BMD sites whereas the combination of exercise and HRT produced increases in BMD greater than either treatment alone. Bone remodeling was surpressed in the groups taking HRT regardless of exercise status. The bone remodeling response to exercise training in women not taking HRT was not significantly different from those not exercising but the direction of change suggests an elevation in bone remodeling in response to exercise training. Exercise training does not stimulate a change in IGF-1, IGF-2, IGF-1:IGF-2, and IGFBP3. Markers of bone remodeling and IGF-1 are significant predictors of BMD changes but the overall amount of variation in BMD changes accounted for is low. Exercise and HRT status were significant predictors of changes in BMD even after accounting for variation due to bone remodeling indicating that bone changes are regulated by factors not addressed in this study.

Thesis (M. S.)--Materials Science and Engineering, Georgia Institute of Technology, 2005.
Committee Chair: Kenneth Sandhage; Committee Members: Joe Cochran, Robert Snyder and Tom Sanders. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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Natural loss of estrogen occurring in menopausal process may contribute to various health problems many of them possibly related to oxidative stress. Decrease in circulating estrogen levels and increase in follicle stimulating hormone levels (FSH) in menopausal status are related with decrease in bone mineral density. Hormone replacement therapy (HRT) is the most common treatment to attenuate menopausal disturbances and strontium (Sr) and iron (Fe) have been suggested to influence to bone metabolism. The objectives of this study was to evaluate the influence of HRT on the activity of antioxidant enzymes (SOD, CAT, and GPx) and lipid peroxidation (TBARS) in menopausal women and to determine blood strontium and iron levels and their relationship with bone mineral density and biochemical parameters in pre and postmenopausal women with or without HRT. Blood antioxidant enzyme activities were determined in premenopausal (n=18) and in postmenopausal healthy women without (n=21) or with HRT (n=19) (mean ages: 47, 59, and 57, respectively). Whole blood Sr and Fe levels were determined by spectrometric methods (inductively coupled plasma mass spectrometry - ICP-MS and inductively coupled plasma optical emission spectrometry - ICP-OES, respectively) in premenopausal (n=17) and postmenopausal women without (n=20) or with HRT (n=19) (mean ages: 47, 60 and 57 years, respectively). Bone mineral density (BMD) was evaluated at the lumbar spine (BMD L1-L4) and femoral neck (BMD femur) by dual energy X-ray absorptiometry (DEXA). TBARS, CAT, and GPx activity were not significantly different among the groups of study. However, SOD activity was significantly lower in postmenopausal women without HRT (0.68±0.04 U/mg Hb) when compared both to premenopausal women (0.91±0.04 U/mg Hb) and to postmenopausal women with HRT (0.89±0.07 U/mg Hb). SOD activity was positively correlated to the duration of HRT in the postmenopausal groups (r=0.33, p<0.05). Blood Sr and Fe levels in premenopausal (33.66±3.57 µg L-1 and 502.09±19.90 mg L-1, respectively) and postmenopausal women without (31.47±2.58 µg L-1 and 523.65±9.91 mg L-1, respectively) or with HRT (29.74±3.02 µg L-1 and 540.30±20.24 mg L-1, respectively) were not significantly different among study groups. BMD L1-L4 and BMD femur were significantly higher in premenopausal women (1.05±0.23 and 0.84±0.02 g/cm2, respectively) when compared both to postmenopausal women without (0.90±0.37 and 0.75±0.02 g/cm2, respectively) and to postmenopausal women with HRT (0.94±0.04 and 0.74±0.02 g/cm2, respectively). However, BMD had no relationship with blood metal levels, but was negatively influenced by FSH levels (β=-0.47, p<0.01 for BMD L1-L4 and β=-0.42, p<0.01 for BMD femur) and age (r=-0.48, p<0.01 for BMD L1-L4 and r=-0.38, p<0.01 for BMD femur). We concluded that HRT antagonizes the decrease of SOD activity that occurs after menopause, suggesting that HRT may play a beneficial role in the protection against oxidative stress. It was also shown that the physiologic whole blood Sr and Fe levels had no significant effect in BMD or other biochemical parameters in pre and postmenopausal women. BMD decreased with the increased in FSH levels and with aging.
A redução natural nos níveis de estrogênio, que ocorre na menopausa pode contribuir para vários problemas de saúde muitos deles também possivelmente relacionados ao estresse oxidativo. A diminuição dos níveis circulantes de estrogênio e o aumento de hormônio folículo estimulante (FSH) em mulheres na menopausa estão sendo associados à perda óssea. A terapia de reposição hormonal (TRH) é o tratamento mais comum para atenuar os distúrbios menopáusicos e, as concentrações sanguíneas de estrôncio (Sr) e ferro (Fe) têm mostrado influenciar no metabolismo ósseo. Os objetivos deste estudo foram avaliar a influência da TRH na atividade de enzimas antioxidantes (SOD, CAT e GPx) e lipoperoxidação (TBARS); e determinar os níveis de Sr e Fe e sua relação com a densidade mineral óssea (DMO) e parâmetros bioquímicos em mulheres na pré e pós menopausa com e sem TRH. As atividades das enzimas antioxidantes foram determinadas no sangue total de mulheres na pré-menopausa (n= 18) e na pós-menopausa sem (n= 21) e com TRH (n= 19); a idade média dos grupos foi de 47, 59 e 57 anos, respectivamente. As concentrações de Sr e Fe foram avaliadas por espectrofotometria (espectrometria de massas com plasma acoplado indutivamente - ICP-MS e espectrometria de emissão óptica com plasma acoplado indutivamente - ICP-OES, respectivamente), no sangue de mulheres na pré-menopausa (n= 17) e na pós-menopausa sem (n= 20) e com TRH (n= 19), com idade média de 47, 60 e 57 anos, respectivamente. A DMO foi determinada na lombar (L1-L4) e no colo do fêmur por absorciometria de duplo feixe de raios-X (DEXA). Em nosso estudo TBARS, CAT e GPx não foram significativamente diferentes entre os grupos. No entanto, a atividade da SOD foi significativamente menor em mulheres na pós-menopausa sem TRH (0,68±0,04 U/mg Hb) quando comparado com os grupos pós-menopausa com TRH (0,89±0,07 U/mg Hb) e na pré-menopausa (0,91±0,04 U/mg Hb). A atividade da SOD também apresentou correlação positiva com o tempo de TRH (r=0,33; p<0,05) nas mulheres menopausadas. As concentrações de Sr e Fe não diferiram entre as mulheres não menopausadas (33,66±3,57 µg L-1 e 502,09±19,90 mg L-1, respectivamente) e aquelas na pós-menopausa sem (31,47±2,58 µg L-1 e 523,65±9,91 mg L-1, respectivamente) ou com TRH (29,74±3,02 µg L-1 e 540,30±20,24 mg L-1, respectivamente). A DMO da L1-L4 e fêmur foi maior nas mulheres que não estavam na menopausa (1,05±0,23 e 0,84±0,02 g/cm2, respectivamente) quando comparado com os grupos de mulheres na pós-menopausa sem (0,90±0,37 e 0,75±0,02 g/cm2, respectivamente) e com TRH (0,94±0,04 e 0,74±0,02 g/cm2, respectivamente). No entanto, a DMO não apresentou correlação com as concentrações de metais encontradas. A DMO foi negativamente influenciada pelos níveis de FSH (β=-0,47, p<0,01 para DMO L1-L4 e β=-0,42, p<0,01 para DMO fêmur), e pela idade (r=-0,48, p<0,01 para DMO L1-L4 e r=-0,38, p<0,01 para DMO fêmur). Concluiu-se que a TRH antagoniza a diminuição da atividade antioxidante da SOD que ocorre após a menopausa, sugerindo o papel protetor da terapia contra o estresse oxidativo. Também demonstramos que as concentrações sanguíneas de Sr e Fe encontradas não exerceram efeito significativo na DMO e outros parâmetros bioquímicos e não foram influenciadas pela menopausa ou pela TRH em mulheres na pré e pós-menopausa. A diminuição na DMO observada foi em decorrência do aumento nos níveis circulantes de FSH e do processo de envelhecimento.

La valutazione della qualità dell’osso è un passo importante nel campo clinico, sia in condizioni patologiche che non patologiche. In particolare, in pazienti sottoposti ad intervento di sostituzione totale d’anca, la presenza della protesi altera le condizioni di stress fisiologiche del femore, causando un processo di adattamento dell’osso che può avere conseguenze sulla stabilità dell’impianto e sulle condizioni dell’osso. Perciò, è evidente l’importanza di monitorare la qualità dell’osso che circonda lo stelo, sia nel breve che nel lungo termine. A partire da rilevazioni densitometriche effettuate su immagini TC, questa tesi affronta due argomenti principali: 1) miglioramento del protocollo corrente per la valutazione della variazione di densità minerale ossea (tridimensionalmente attorno alla protesi) dopo un anno dall’operazione e applicazione ad un ampio dataset (11 pazienti) per esaminare le differenze tra soggetti; 2) studio di fattibilità su 8 pazienti di nuovi approcci 2D basati su sezioni standard del femore, con lo scopo di ottenere uno strumento per la valutazione della qualità dell’osso che possa essere affidabile per i clinici, ma anche minimamente invasivo per i pazienti, riducendo la dose di radiazione. I risultati dell’approccio 3D suggeriscono che può essere usato come strumento di monitoraggio post-operatorio del paziente. Inoltre la tesi mostra la fattibilità di nuovi approcci 2D, sebbene alcuni limiti devono essere superati prima di poterli utilizzare in ambito clinico.

The hypothesis that interface coupled dissolution-reprecipitation reactions (ICDR) can play a key role in scavenging minor elements has been investigated via exploring the fate of U during the experimental sulfidation of hematite to chalcopyrite and the exsolution of chalcopyrite from bornite digenite solid solution (bdss) under hydrothermal conditions. The results of experiments with two kinds of Uranium (U) sources; either as solid UO₂₊ₓ(s) or as a soluble uranyl complex, differed from the U-free experiments. In the reactions from hematite to chalcopyrite under 220-300°C hydrothermal conditions, pyrite precipitated initially, before the onset of chalcopyrite precipitation. In addition, when UO₂₊ₓ(s) was included in the experiments, enhanced hematite dissolution led to increased porosity and precipitation of pyrite+magnetite within the hematite core. However, in uranyl nitrate bearing experiments, abundant pyrite formed initially, before being replaced by chalcopyrite. Uranium scavenging was mainly associated with the pyrite precipitation, as a result that a thin U-rich layer along the original hematite grain surface precipitated out. In the reactions of chalcopyrite exsolution from bdss during annealing under hydrothermal conditions in a solutions nominally containing Cu(I) and hydrosulfide in a pH₂₅°C [°C subscript] ~6 acetate buffer, a similar U-rich rim was observed along the original grain when uranyl nitrate as U-source was included in the reactions. The precipitation of uranium was related to the presences of HS- in buffer. Chemical mapping and X-ray absorption near edge structure (XANES) spectroscopy showed the UO₂₊ₓ(s) was the mainly restricted to the U-rich layer. The two sets of experiments demonstrate that the presence of minor components can affect the pathway of ICDR reactions. Reactions between U- and Cu-bearing fluids and hematite or chalcopyrite can explain the Cu-U association prominent in some iron oxide-copper-gold (IOCG) deposits. In this study, synchrotron-based X-ray fluorescence (SXRF) mapping was used to trace the distribution of uranium in natural samples from different geological contexts (sandstone-hosted U-deposit; IOCG) for investigating the deportment of uranium and its paragenesis in the context of thin-section scale textural complexity. It has been confirmed that the enrichment of U occurs via late dissolution-reprecipitation reactions in the bornite ores of the Moonta and Wallaroo IOCG deposits (South Australia), and that the U distribution in the ores of sandstone-hosted U-deposit is complex. Image analysis also revealed a number of new results for other minor elements, e.g. (i) the distribution of μm-sized Pt-rich grains and evidence for Ti-mobility during the formation of schistosity at the Fifield Pt prospect (New South Wales, Australia); (ii) the presence of Ge contained in organic matter and of Hg minerals associated within quartzite clasts in the Lake Frome U ores (South Australia); and (iii) confirmation of the two-stage Ge-enrichment in the Barrigão deposit, with demonstration of the presence of Ge in solid solution in the early chalcopyrite (Portuguese Iberian Pyrite Belt).
Thesis (Ph.D.) (Research by Publication) -- University of Adelaide,School of Chemical Engineering, 2016.

The objective of this study was to examine the link between radiographic measures of bone quality and total knee implant migration as measured by radiostereometric analysis (RSA). Two uncemented total knee arthroplasty studies (n=65) with RSA and bone mineral density (BMD) exams up to two years post surgery, and one study with cemented total knees with one year RSA data (n=18) were examined. Radiograph image texture analysis was used to characterize the bone microarchitecture, and a feasibility study was conducted to determine if a given x-ray machine could be used to obtain bone mineral density at the same time as the RSA exams. Random ForestTM ensemble classification tree statistical models classified patients into groups based on implant migration with a range of cut-points. Models based on bone texture parameters measured from the two year radiographs had a sensitivity of 87.5% and specificity of 80% when classifying patients who had more than 0.3mm maximum total point motion (MTPM) at two years using the one year exam as reference. Other cut-points were examined, with models generally having a lower specificity if the acceptable migration was smaller, and lower sensitivity if higher migrations were tolerable. In a predictive model, post-operative bone texture could be used to create a model with a sensitivity of 75% and a specificity of 80% when predicting those subjects with cemented implants who went on to more than 0.4mm total migration by one year. Bone mineral density of the proximal tibia, as determined by clinical scanners, was not found to increase the accuracy of implant migration group classification. An empirical fit to central regions of a purposed-built cross-wedge calibration phantom returned residuals of less than ±1.5% for the bone-equivalent thicknesses. The coefficient of variation of the region greyscale values in three images spread over three days is under 4%, showing the stability of the system to hold a calibration between phantom exams and patient scans. Scatter and dynamic range issues will need to be considered for an accurate calibration across the full range of areal bone mineral densities in the distal femur and proximal tibia.

Recombinant human bone morphogenic proteins (rhBMPs) are extensively studied and employed clinically for treatment of various bone defects. Current clinical delivery vehicles suffer wasteful burst releases that mandate supra-physiological dosing driving concerns over safety and cost. It was therefore investigated whether a unique drug delivery vehicle sequestered within a composite scaffold could lower the burst release of rhBMP-2. PLGA-calcium phosphate tri-phasic composite scaffolds delivered model protein BSA with burst release of ~13% and sustained kinetics of 0.5-1.5% BSA/day up to 45 days. rhBMP-2 was delivered with zero burst release however at much lower levels, totaling 0.09% to 0.9 % release over 10 days, but had up to 6.3-fold greater bioactivity than fresh rhBMP-2 (p<0.05). In conclusion, the three-phase composite scaffold can deliver bioactive proteins with a reduced burst release and sustained secondary kinetics.