This thesis is an investigation into biogenic sulfide oxidation and sulfate reduction associated with hydrothermal systems at oceanic spreading centers. First, the production of sulfur floc and 'snowblower' events due to sulfide oxidizing bacteria is investigated. The effects of sulfur floc on the pososity is shown to be negligible. 'Snowblower' events are shown to be sulfur floc that is stored over long periods of time mixed with a component of sulfur floc being created in a bloom event. Secondly, biogenic sulfate reduction in hydrothermal recharge zones is investigated and the effects on the concentration profiles is considered.

ABSTRACT PREPARATION OF CROSS-LINKED TYROSINASE AGGREGATES Aytar, Burcu Selin M.S., Department of Chemical Engineering Supervisor: Prof. Dr. Ufuk Bakir June 2006, 82 pages The aim of this study was to prepare cross-linked enzyme aggregate (CLEA) from crude mushroom (Agaricus bisporus) extract. However, the optimization of CLEA production was performed by using pure tyrosinase. Important parameters were determined as protein, ammonium sulfate and glutaraldehyde concentrations, CLEA particle size, and cross-linking temperature and period. On the other hand, the order of ammonium sulfate and glutaraldehyde addition did not affect the yield of CLEA. Optimum CLEA preparation conditions were 60 % ammonium sulfate saturation, 2 % (v/v) glutaraldehyde, and 3 hour cross-linking reaction at room temperature. Particle size of the CLEAs should be reduced by mechanical stirring to eliminate mass transfer limitations. Under these circumstances, 100 % recovery was obtained from both pure and crude tyrosinases. Optimum temperature and the activation energy for catechol oxidation were determined as 34 oC and 16.9 kcal/mol for CLEAs, whereas, 32 oC and 12.5 kcal/mol for the free enzyme. Furthermore, the thermostability of CLEAs was significantly higher than the free enzyme. CLEAs, prepared from crude mushroom extract, retained 72 % of its maximum activity in eight months storage at 4 oC. Moreover, changing the storage temperature from 4 oC to room temperature did not decrease CLEAs stabilities.

Numerous agents and mechanisms are known to affect the durability of a concrete structure during its service life. Examples include freezing and thawing, corrosion of reinforcing steel, alkali-aggregate reactions, sulfate attack, carbonation, and leaching by neutral or acidic ground waters. Among these, external sulfate attack was first identified in 1908, and led to the discovery of sulfate resistant Portland cement (SRPC). Besides SRPC, another way of coping with the problem of sulfate attack is the use of pozzolans either as an admixture to concrete or in the form of blended cements This study presents an investigation on the sulfate resistance of blended cements containing different amounts of natural pozzolan and/or low-lime fly ash compared to ordinary Portland cement and sulfate resistant Portland cement. Within the scope of this study, an ordinary Portland cement (OPC) and five different blended cements were produced with different proportions of clinker, natural pozzolan, low-lime fly ash and limestone. For comparison, a sulfate resistant Portland cement (SRPC) with a different clinker was also obtained. For each cement, two different mixtures with the water/cement (w/c) ratios of 0.485 and 0.560 were prepared in order to observe the effect of permeability controlled by water/cement ratio. The performance of cements was observed by exposing the prepared 25x25x285 mm prismatic mortar specimens to 5% Na2SO4 solution for 78 weeks and 50mm cubic specimens for 52 weeks. Relative deterioration of the specimens was determined by length, density and ultrasonic pulse velocity change, and strength examination at different ages. It was concluded that depending on the amount and effectiveness of the mineral additives, blended cements were considered to be effective for moderate or high sulfate environments. Moreover, the cement chemistry and w/c ratio of mortars were the two parameters affecting the performance of mortars against an attack. As a result of this experimental study it was found out that time to failure is decreasing with the increasing w/c ratio and the effect of w/c ratio was more important for low sulfate resistant cements with higher C3A amounts when compared to high sulfate resistant cements with lower C3A amounts.

Researches on bone defects are focused on the use of composites due to the composite and well-organized hierarchical structure of the bone. In this study, it is aimed to develop Polycaprolactone based implants with different organic &amp / #8211 / DBM, HYA- and/or inorganic &amp / #8211 / bioglass, calcium sulfate- compositions for augmenting bone healing. Bioactivity of the discs was evaluated by scanning electron microscopy and EDS analysis after incubation in SBF for 1, 7 and 14 days. All bioglass containing groups showed apatite molecules at different incubation times. Degradation studies demonstrated that only PCL/BG/HYA discs had fast degradation upon incubations in PBS (4 and 6 weeks). Initial mechanical properties of composites were found to be directly related to the composition. However, decreases in disc mechanical properties were also obtained in the same order with the amount of water uptake at composite groups. According to biocompatibility studies investigated with cytotoxicity tests on Saos-2 cells, all groups, except the HYA involving one were found as biocompatible. After in vivo application of discs to critical size defects on rabbit humeri (for 7 weeks), their efficacy on healing was studied with computerized tomography, SEM and biomechanical tests. The results revealed that bone-implant interface formation has started for all groups with high bone densities at the interface of implant groups compared to empty defect sites of negative controls. Also the healing was suggested to be gradual from bone to implant site as microhardness values increased at regions closer to bone. However, regeneration was found to not reach to healthy bone levels.

Osteoarthritis (OA) is a degenerative joint disease which has yet no complete treatment with medication. Doxycycline, a well-known antibiotic, has been shown to prevent matrixmetallopreoteinases-MMPs, indicating potency on OA treatment. However, long term systemic use can cause side effects on other tissues. This study aimed to develop controlled drug delivery systems of doxycycline/doxycycline-chondroitin sulfate (D/D-CS) in the form of PCL microspheres for providing a better and new treatment approach via local application. After optimization studies for size, loading efficiency, surface/structure and release properties, microspheres of low Mw PCL (14 kDa) was decided to be more suitable than those of high Mw (65 kDa). The release profile of former was also more compatible with diffusion model than that of latter. The bio-effectiveness of the microspheres was evaluated with three-dimensional in vitro model / osteoarthritic-rabbit chondrocytes embedded in agarose and subjected to interleukin-1&beta / throughout incubations. In vitro treatments with D/D-CS microspheres showed significant reduction in MMP-13 activity compared with untreated OA controls for 15 and 24-day incubations. Although collagen and GAG analysis results showed no enhancement of synthesis with MS treatments, significant decrease in GAG and collagen release from D/D-CS MS treated groups and from D MS treated ones respectively. Overall evaluations of the efficacy using in vivo rabbit OA model showed better radiographic scores and histological outcomes for D/D-CS MS groups compared to only hyaluronan injected and/or untreated controls in 8 weeks. The ex-vivo biomechanical properties of cartilages demonstrated improved hardness with values comparable to healthy group upon application of D-CS MS.

No description available.

Expansive soils are treated with anhydrous or hydrated lime. The use of calcium-based stabilizers such as calcium oxide (lime) in sulfate-bearing clay soils has historically led to distress due to the formation of an expansive mineral called ettringite and possibly another such mineral, thaumasite. Predicting the precipitation of these minerals is a complex problem related not only to soil composition but also construction methods, availability of water, ion migration, and whether the expansive mineral growth can be accommodated by the void structure in the surrounding soil. In trying to control the damage associated with such occurrences, engineers have attempted to determine a threshold value of soluble sulfates, a quantity that is relatively easy and quick to measure, at which significant ettringite growth and, therefore, structural distress occurs. Unfortunately, experience alone and “rules-of-thumb” based on experience are not sufficient to deal with this complex issue. This thesis describes how thermodynamic geochemical models of lime-treated soil can be used as a first step toward establishing problematic threshold levels of soluble sulfates for a specific soil. A foundation for the model development is presented, and two different soils are compared to illustrate their very different sensitivities to ettringite growth upon the addition of hydrated lime. Various soil series along the route of SH 130 between Austin and San Antonio have been identified to contain soluble sulfate that may pose a problem for soil stabilization using lime and cement. Since the model predicts ettringite growth based upon site-specific properties, this thesis also shows how the model can be used to assess the potential amelioration effects of soluble silica. Research was conducted at the Texas Transportation Institute to develop a methodology for identifying areas which are susceptible for ettringite formation. The proposed methodology uses a magnetometer to quickly screen large areas for high sulfate. Application of GIS to identify ettringite formation using soils, topographical, and geological maps is also illustrated in this thesis.

This work focuses on the chemical substitution of cations and anions in the frameworks of materials that have been known to exhibit negative thermal expansion (NTE). Zr2(PO4)2(SO4) is a member of the A(2)M(3)O(12) family which has been known to exhibit NTE. We have shown that Zr2(PO4)2(SO4) exhibits anisotropic positive thermal expansion. We have also shown that this material has been characterized in the wrong space group. Hf2(PO4)2(SO4) behaves similarly to Zr2(PO4)2(SO4) and follows this trend. Under pressure, Hf2(PO4)2(SO4) appears to undergo a phase transition. We have still yet to determine what space group the materials transitions to. While many members of the AX(2)O(7) family of frameworks have been fully characterized, the thermal expansion of PbP2O7 has yet to be reported. We were unable to obtain a reproducible procedure for synthesis of PbP2O7 from its precursor. Finally, variable temperature and variable pressure studies were performed on ZrMo2O8 in an attempt to learn more about the local structure. We found that space groups P213 and Pa-3 gave poor fits of the local structure at low r. Behavior of the nearest neighbor Zr-Mo distance was very similar to the bulk CTE. On compression, pressure induced amorphization is observed in ZrMo2O8. All interatomic correlations above 4 angstroms are washed out. Zr-O-Mo linkages remain well defined and do not massively deform as the pressure is increased. Finally, we we observed that Zr-O-Mo linkages change geometry reversibly as the pressure is increased.

Naturally occurring bacterial populations are capable of detoxifying chlorinated compounds and immobilizing the radionuclide uranium via reductive processes. This study addressed the following three knowledge gaps in the fields of chlorinated solvent and uranium bioremediation, 1) the risks and benefits of coupling bioremediation with thermal treatment for clean-up of chlorinated ethene-contaminated sites, 2) the accuracy of available techniques for the monitoring of chlorinated solvent bioremediation, and 3) the role of gram positive Desulfitobacterium spp. in uranium immobilization. Experiments demonstrated that thermal treatment increases electron donor availability, but the increased electron donor was not used to fuel reductive dechlorination and was actually consumed for methanogenesis. Two approaches for monitoring chlorinated solvent bioremediation were investigated, molecular techniques and compound-specific isotope analysis (CSIA). Results demonstrated that while Dehalococcoides (Dhc) gene expression was up-regulated under conditions inhibitory to dechlorination, the isotope effects associated with dechlorination reactions catalayzed by Dhc populations in consortia and in pure cultures were similar. U(VI) reduction by multiple Desulfitobacterium isolates was demonstrated. Interestingly, while almost all U(VI)-reducing populations have been reported to produce uraninite (UO2), the product of U(VI) reduction by Desulfitobacterium isolates was a unique form of insoluble mononuclear U(IV).

Le volcanisme plinien modifie le climat pendant plusieurs années en injectant de grandes quantités de dioxyde de soufre directement dans la stratosphère, oxydé ensuite en gouttelettes d'acide sulfurique qui réfléchissent les rayonnements solaires et changent les propriétés radiatives de l'atmosphère. L'étude de signaux volcaniques préservés dans les archives glaciaires, consistait jusqu'à présent à simplement mesurer les concentrations de sulfate. Nous proposons l'utilisation de nouveaux traceurs que sont les anomalies isotopiques de l'oxygène et du soufre de sulfate volcanique enregistré à Dôme C et Pôle Sud pour apporter de nouvelles informations sur le volcanisme passé.<br />Une étude de l'évolution temporelle des anomalies isotopiques de l'oxygène et du soufre dans les sulfates volcaniques de l'Agung (mars 1963) et du Pinatubo (juin 1991) a été menée. L'anomalie isotopique du soufre change de signe au cours du temps et passe d'une phase positive, au début du dépôt de sulfate à une phase négative à la fin. Ce changement de signe s'accompagne d'un appauvrissement en isotopes lourds avec le temps. L'anomalie isotopique du soufre est créée à partir d'une réaction d'oxydation photochimique de SO2 en acide sulfurique, suggérant un processus rapide qui dure un mois environ. L'anomalie isotopique de l'oxygène, quant à elle, a permis d'établir un lien avec l'oscillation quasi-biennale de la stratosphère.<br />Douze signaux volcaniques ont été étudiés dans leur globalité au cours du dernier millénaire. L'anomalie isotopique du soufre a permis d'identifier 6 éruptions volcaniques stratosphériques révélant l'utilité d'un tel traceur lorsque la nature des éruptions est méconnue.