Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

<p>Prior studies of groundwater systems have associated increasing salinity and anoxic conditions with increasing radium (Ra) activities in water due to the decreasing effectiveness of Ra removal processes. However, the components of salinity (e.g. Ca vs. Na and SO₄^2- vs. Cl^--dominated waters), and the relative importance of salinity-sensitive vs. redox-sensitive processes for Ra mobilization, are less well understood. In this research, the response of Ra to hydrochemical change was examined using a multiple tracer approach to obtain detailed information on divalent cation and Ra mobility. A range of salinity and redox conditions was examined in five field-based studies in the United States and Morocco: (1) fresh waters in fractured crystalline rocks in the Piedmont region of North Carolina; (2) the Willcox Basin, an oxic alluvial basin-fill aquifer in southeastern Arizona; (3) the Jordan sandstone aquifer, a carbonate-cemented quartz sandstone in southeastern Minnesota; (4) an unconfined coastal aquifer undergoing salinization in the city of Agadir, Morocco; and (5) the confined, fresh to saline Cretaceous and Pliocene aquifers of the Atlantic Coastal Plain in North Carolina.</p><p> </p><p>In addition to analysis of major element concentrations, trace metal concentrations, and ²²⁴Ra, ²²⁶Ra, and ²²⁸Ra activities, complementary isotope systems were applied to gain insights on the relative stability of chemical processes that remove radium and other alkaline earth metals: (1) strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) trace divalent cation release from sources such as clay and carbonate minerals in the aquifer solids and also indicate conditions in which divalent cation release (rather than uptake) is dominant; (2) boron concentrations and isotopes (&delta;¹¹B) coincide with the opposite condition in freshening conditions of the Atlantic Coastal Plain, in which divalent cations are removed in exchange for Na; and (3) sulfur and oxygen isotopes (&delta;³⁴S, &delta;¹⁸O) of sulfate trace sulfate sources and provide information on sulfate-reducing conditions, which can inhibit barite (BaSO₄) from removing Ra by coprecipitation. In addition, other isotopic and ion measurements trace salinity sources and groundwater residence time, including &delta;²H, &delta;¹⁸O, ³H, Br^-/Cl^-, Na/Cl^-, and Ca/Na.</p><p>This dissertation documents correlations between salinity and radium in the brackish to saline North Carolina coastal plain aquifer with total dissolved solids (TDS) up to ~18,000 mg L^-1 and to some degree in the Moroccan coastal aquifer, but even the lower-salinity waters (TDS <3000 mg L^-1) exhibit a range of Ra activities spanning approximately 3 orders of magnitude. Among these low-TDS waters, the highest Ra activities were observed in the anoxic Jordan sandstone aquifer and the lowest were observed in the oxic Willcox Basin aquifer. Although the main control on radium activities in fresh groundwater is the U- and Th-series radionuclide content of the aquifer solids, important secondary controls include the stability of redox-sensitive radium adsorption sites (Mn and Fe oxides), the relative dominance of divalent vs. monovalent cations (e.g. the Ca/Na ratio), formation of the uncharged RaSO₄⁰ complex, and/or the saturation state with respect to barite. These processes interact in varied ways in the field-based studies. Increasing radium activities and decreasing ²²²Rn/²²⁶Ra ratios in the North Carolina fractured crystalline rock groundwater system are correlated with increasing Ba, Mn, and Fe concentrations and decreasing dissolved oxygen concentrations, related to weathering and/or organic carbon oxidation. Radium activities in the oxic, neutral to slightly basic Willcox Basin are very low (median ²²⁶Ra activity 2 mBq L^-1), probably due to a combination of effective Ra removal processes including adsorption to Mn and/or Fe oxides and the overall removal of divalent cations during groundwater evolution in this system. These are the same surface charge conditions that release arsenic, of regional water concern, in this pH range. Radium in Jordan aquifer groundwater is dependent on local variations in solid-phase radionuclide levels, probably hosted in the carbonate cement phase. Also, Ra is inefficiently adsorbed to the aquifer solids in the aquifer's anoxic conditions, resulting in the highest radium levels reported in this dissertation (²²⁶Ra up to 420 mBq L^-1) despite apparent barite precipitation that partially removes Ra. Radium-224 activity in the Moroccan coastal aquifer is associated with salinity, but Ra overall is apparently controlled by barite, indicated by conditions near BaSO₄ saturation. Radium activity in the saline waters of the Atlantic Coastal Plain aquifers is associated with TDS concentrations, but the cation exchange properties of the aquifer may provide a major mechanism of Ra removal in the Na-HCO₃^- and Na-Cl^- waters. Overall, the complex interaction between groundwater chemistry and Ra-removing processes implies that in waters with TDS below approximately 3,000 mg L^-1, dissolved solids concentration alone does not fully describe radium's response to hydrochemical conditions, but rather that aquifer-specific examination of Ra removal mechanisms is needed.</p> / Dissertation

Hydroxyapatite (HA) based bioceramics have been developed to treat bone defects for the last 30 years. Doping HA with elements is a common approach to increase mechanical strength, biocompatibility and osteointegrity. Bone morphogenetic protein (BMP)-containing bioceramic composites enhance osteointegrity and induce bone formation. Strontium (Sr) is currently used to treat osteoporosis clinically as this element inhibits bone resorption and stimulates bone formation. In this study, HA was doped with silicon (Si), Sr, BMP-2 and evaluated in cortical bone defect healing. Ceramics were produced and tested mechanically after characterization. Sr release from ceramics was assessed. Ceramics were further evaluated in in vitro and in vivo conditions. X-ray diffraction analysis results of HA were in line with the literature and Sr-Si-HA ceramics showed similar intensities with HA. Ceramics had 36.9 to 41.6% porosity. Compression strength of Sr1000-Si-HA ceramics was 117.5 MPa which was more than that of the other groups. Consistent Sr release was observed in the Sr1000-Si-HA and the Sr250-Si-HA groups. Sr1000-Si-HA and Sr250-Si-HA ceramics showed higher cellular proliferation rates than the other groups in vitro. BMP addition increased alkaline phosphatase activities and DNA amounts. BMP-Sr-Si-HA group presented higher (0.304&plusmn / 0.02 g/cm2) bone mineral density values than the other groups 4 weeks after implantation however differences between groups were not significant in vivo. Sr-Si-HA and BMP-Sr-Si-HA composites stimulated new bone formation at cortical bone defects of tibia according to micro computerized-tomography and histological results. Findings of this study promote future research on Sr containing bioceramics in treatment of orthopedic problems.

Growth and dissolution of the mineral calcite is important for prediction and control of surface and subsurface water quality, calculation of past sea-surface temperatures using paleoenvironmental proxies, and sequestration of contaminants through engineered calcite precipitation. At high concentrations of strontium, calcite growth is known to be inhibited, but the mechanism by which strontium inhibits growth is not well understood. Seeking to better understand this mechanism, atomic force microscopy is used with a flow-through fluid cell to measure real time growth rates of the obtuse and acute monomolecular step orientations on the calcite surface. Growth was measured at two saturation indices as a function of the ratio of the concentrations of aqueous calcium-to-carbonate and varying aqueous strontium concentration. It was found that the amount of strontium required to inhibit growth correlated with the aqueous calcium concentration, but did not correlate with carbonate concentration. This suggests that strontium inhibits attachment of calcium, but not carbonate, during growth. Analytical models of nucleation and propagation of steps are expanded from previous studies to capture multiple saturation indices.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

Anterior cruciate ligament (ACL) rupture is a major clinical problem in sports medicine. The current mainstay of treatment is arthroscopic-assisted ACL reconstruction with a soft tissue tendon graft. However, the affected patients are required to abstain from any pivoting activity for at least six to nine months after the operation to protect the graft-host bone interface in order to allow the graft to heal. In this study, a method to accelerate the graft healing within the bone tunnel is proposed by using a local application of an osteoconductive bone cement (Strontium enriched calcium phosphate cement, Sr-CPC) at the graft-host bone interface. It is postulated that Sr-CPC can induce earlier new bone formation in the gap between the graft and host bone tunnel and hence can result in an accelerated healing of the graft within the bone tunnel in ACL reconstruction. Preparation of Sr-CPCs using the conventional setting method (a dissolution/precipitation process) leads to a delay in setting. This study adopted a new setting reaction, a chelate reaction, to manufacture a Sr-CPC system. The Sr-CPC system was fast-setting, injectable and cohesive, and it was suitable for use in minimally invasive orthopaedics surgeries (e.g. arthroscopic-assisted ACL reconstruction). In order to investigate the biocompatibility and osteoconductivity of the Sr-CPC, in vitro cell experiments and an in vivo animal study were carried out. The in vitro experiments showed that the Sr-CPC was biocompatible with no local toxicity. In addition, a higher proliferation rate of osteoblastic-like MG-63 cells, accompanying higher alkaline phosphatase activity, was found in the Sr-CPC group. The in vivo study using a rat femur metaphyseal bone defect model showed evidence of earlier endochondral ossification which was noted at 2 weeks post operation. Moreover, a higher peri-cement bone formation rate, accompanied by a higher cement resorption rate, was found in the Sr-CPC group at 32 weeks after the operation compared with the convention calcium phosphate cement group. To study the effect of the Sr-CPC on the graft healing within the bone tunnel, a one-stage bilateral ACL reconstruction using an Achilles tendon allograft was performed in 30 rabbits. One study (15 rabbits) was to investigate the effect of the Sr-CPC on the healing of a soft tissue tendon graft within the bone tunnel, and the other study (15 rabbits) was to study the difference between the Sr-CPC and the conventional CPC in the healing of a soft tissue tendon graft within the bone tunnel. The Sr-CPC treated graft showed an accelerated healing at all of the time points when compared with the non-treated graft; and at time points of 3 to 12 weeks when compared with the CPC treated graft. In conclusion, a strontium enriched calcium phosphate cement, which is suitable for the arthroscopic use, was manufactured. It is biocompatible, osteoconductive and degradable. It accelerates the graft healing within the bone tunnels in a rabbit ACL reconstruction model using an Achilles tendon allograft when compared with both of the non-treated group and the conventional CPC-treated group. / published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

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During the Medieval period of Denmark, economic and trade relations grew inter-regionally, with culture, ideas, and products being transferred on a more regular basis through the 11th to 13th centuries. Beginning around 1050 AD and lasting until AD 1536, the country faced drastic climatic changes, shifting economic and agricultural practices, and disease outbreaks (most notably the bubonic plague). The current study seeks to investigate mobility during this period from two medieval cemeteries around Horsens, Denmark: the rural site of Sejet and the urban site of Ole Wormsgade, both used throughout the 12th to 16th centuries. A previous isotopic analysis using oxygen indicated that some movement was seen at these sites, with three individuals identified as potential migrants from other Scandinavian regions. This study compares the existing oxygen isotopic data with variations in 87Sr/86Sr ratios from these samples. Such ratios represent local bedrock baselines of strontium, which are slightly different between eastern and western Denmark. ICP-MS was used to measure 87Sr/86Sr ratios, and results are interpreted in the context of climatic changes and shifting socioeconomic practices. The results suggest that longer-distance movements into Denmark were seen during the Early Medieval Period. The potential migrant identified in this research points to movement towards the rural population at Sejet, and could possibly connect this migration with marriage rules influencing immigration at the time. This research demonstrates that movement during the medieval period of Denmark was a complex, dynamic, and multilinear process during a time of increasing urbanization. / October 2015

No description available.