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Search Results: 1 - 10 of 5806 matches for " Susan Carroll "
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Effect of solution saturation state and temperature on diopside dissolution
Suvasis Dixit, Susan A Carroll
Geochemical Transactions , 2007, DOI: 10.1186/1467-4866-8-3
Abstract: The ion exchange model assumes the formation of a Si-rich, Mg-deficient precursor complex. Lack of dependence of rates on steady-state aqueous calcium concentration supports the formation of such a complex, which is formed by exchange of protons for magnesium ions at the surface. Fit to the experimental data yields R a t e ( m o l d i o p s i d e c m ? 2 s ? 1 ) = k × 10 ? E a / 2.303 R T ( a H + 2 a M g 2 + ) n MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8akY=wiFfYdH8Gipec8Eeeu0xXdbba9frFj0=OqFfea0dXdd9vqai=hGuQ8kuc9pgc9s8qqaq=dirpe0xb9q8qiLsFr0=vr0=vr0dc8meaabaqaciaacaGaaeqabaqabeGadaaakeaaieaacqWFsbGucqWFHbqycqWF0baDcqWFLbqzcqqGGaaicqGGOaakcqWFTbqBcqWFVbWBcqWFSbaBcqWFGaaicqWFKbazcqWFPbqAcqWFVbWBcqWFWbaCcqWFZbWCcqWFPbqAcqWFKbazcqWFLbqzcqWFGaaicqWFJbWycqWFTbqBdaahaaWcbeqaaiabgkHiTiabikdaYaaakiab=bcaGiab=nhaZnaaCaaaleqabaGaeyOeI0IaeGymaedaaOGaeiykaKIaeyypa0Jaem4AaSMaey41aqRaeeymaeJaeeimaaZaaWbaaSqabeaacqGHsislcqWGfbqrdaWgaaadbaGaemyyaegabeaaliabc+caViabikdaYiabc6caUiabiodaZiabicdaWiabiodaZiabdkfasjabdsfaubaakmaabmaabaWaaSaaaeaacqWFHbqydaqhaaWcbaGaemisaG0aaWbaaWqabeaacqGHRaWkaaaaleaacqaIYaGmaaaakeaacqWFHbqydaWgaaWcbaGaemyta0Kaem4zaC2aaWbaaWqabeaacqaIYaGmcqGHRaWkaaaaleqaaaaaaOGaayjkaiaawMcaamaaCaaaleqabaGaemOBa4gaaaaa@6D9A@ where the Mg-H exchange coefficient, n = 1.39, the apparent activation energy, Ea = 332 kJ mol-1, and the apparent rate constant, k = 1041.2 mol diopside cm-2 s-1.Fits to the data with the pit nucleation model suggest that diopside dissolution proceeds through retreat of steps developed by nucleation of pits created homogeneously at the mineral surface or at defect sites, where homogeneous nucleation occurs at lower degrees of saturation than defect-assisted nucleation. Rate expressions for each mechanism (i) were fit to R i = c b i exp ? ( ? E b , i k T ) K T , e q exp ? ( π α T , i 2 ω h 3 ( k T ) 2
Geochemical detection of carbon dioxide in dilute aquifers
Susan Carroll, Yue Hao, Roger Aines
Geochemical Transactions , 2009, DOI: 10.1186/1467-4866-10-4
Abstract: For the scenarios we studied, our simulations show pH and carbonate chemistry are good indicators for leakage of stored CO2 into an overlying aquifer because elevated CO2 yields a more acid pH than the ambient groundwater. CO2 leakage into a dilute groundwater creates a slightly acid plume that can be detected at some distance from the leak source due to groundwater flow and CO2 buoyancy. pH breakthrough curves demonstrate that CO2 leaks can be easily detected for CO2 flux ≥ 104 t/yr within a 15-month time period at a monitoring well screened within a permeable layer 500 m downstream from the vertical gas trace. At lower flux rates, the CO2 dissolves in the aqueous phase in the lower most permeable unit and does not reach the monitoring well. Sustained pumping in a developed aquifer mixes the CO2-affected water with the ambient water and enhances pH signal for small leaks (103 t/yr) and reduces pH signal for larger leaks (≥ 104t/yr).The ability to detect CO2 leakage from a storage reservoir to overlying dilute groundwater is dependent on CO2 solubility, leak flux, CO2 buoyancy, and groundwater flow. Our simulations show that the most likely places to detect CO2 are at the base of the confining layer near the water table where CO2 gas accumulates and is transported laterally in all directions, and downstream of the vertical gas trace where groundwater flow is great enough to transport dissolved CO2 laterally. Our simulations show that CO2 may not rise high enough in the aquifer to be detected because aqueous solubility and lateral groundwater transport within the lower aquifer unit exceeds gas pressure build-up and buoyancy needed to drive the CO2 gas upwards.Carbon storage as a liquid, gas, dissolved carbon, or as carbonate minerals has the potential to significantly offset global warming caused by anthropogenic combustion of fossil fuels [1,2]. It is generally accepted that the most suitable systems for geologic storage are depleted oil and deep saline reservoirs,
Evaporative evolution of a Na–Cl–NO3–K–Ca–SO4–Mg–Si brine at 95°C: Experiments and modeling relevant to Yucca Mountain, Nevada
Maureen Alai, Mark Sutton, Susan Carroll
Geochemical Transactions , 2005, DOI: 10.1186/1467-4866-6-31
Abstract: Yucca Mountain, NV, is the designated site for a permanent geologic repository for high-level nuclear waste in the USA. The current waste package design consists of a double-walled container with an inner barrier of stainless steel, an outer barrier of highly corrosion resistant nickel–chromium–molybdenum alloy, and a titanium alloy drip-shield that covers the containers. Corrosion resistance and long-term integrity of the metal containers and shields are important for the safe disposal of the waste. Characterization of the compositional evolution of waters that affect waste package corrosion is necessary. If the site is licensed, the waste packages will be placed in tunnels several hundred meters below the ground surface and above the groundwater table in partially saturated volcanic tuff. Once the waste packages are in place, the repository will heat up due to the thermal energy of the nuclear waste. Although the waste packages will be above the groundwater table, pore water present in rock formations within (Topopah Spring Tuff) and above (Paintbrush Tuff) the repository may come into contact with the metal containers and shields. Additionally, brines may form from the deliquescence of salts found in dusts deposited on the containers.[1] In this study we focus on seepage brines formed by the evaporation of pore water at elevated temperature.One method of evaluating the evolution of a brine is the chemical divide theory, which has been used to describe saline lake geochemistry.[2-5] The chemical divide theory generally describes the chemical evolution of dilute waters upon evaporation in terms of their equivalent calcium, sulfate, and bicarbonate ratios and is shown in Fig. 1(a). The chemical evolution of evaporating water is controlled by the high solubility of salt minerals relative to the moderate solubility of calcium sulfate and low solubility of calcium carbonate minerals. A bicarbonate alkaline brine (Na–K–CO3–Cl–SO4–NO3) forms from dilute waters with disso
Deliquescence of NaCl–NaNO3, KNO3–NaNO3, and NaCl–KNO3 salt mixtures from 90 to 120°C
Susan Carroll, Laura Craig, Thomas J Wolery
Geochemical Transactions , 2005, DOI: 10.1186/1467-4866-6-19
Abstract: Yucca Mountain, NV is the designated geologic repository for permanent disposal of high-level nuclear waste. Current waste package design calls for double walled containers with an inner wall of stainless steel and an outer wall of highly corrosion resistant Ni–Cr–Mo alloy, which are protected with Ti shields to prevent rocks and seepage water from contacting the containers.[1] Of concern are the corrosion resistance and long-term integrity of these metal barriers. If the Yucca Mountain site license is approved, the waste packages will be placed in tunnels several hundred meters below the ground surface in partially saturated volcanic tuff, but still well above the groundwater table. A likely source of brines that may potentially corrode metal containers and drip shields are those formed by the absorption of water by hygroscopic salts found in local and regional dust deposited during repository construction and ventilation stages.Accurate prediction of brine formation is important for the safe disposal of radioactive waste, because brine composition is an indicator of the corrosiveness of the aqueous environment and the relationship between deliquescence relative humidity and temperature is an indicator of "repository dryness." Deliquescence refers to the formation of an aqueous solution by the absorption of water by hygroscopic salt minerals. This process allows brines to form above 100°C at standard atmospheric pressure of 1.01325 bar (or above 96°C and 0.9 bar at the repository elevation of 1039–1107 m; BSC, 2004a, Sec. The relative humidity at which salts deliquesce is dependent on temperature and is characteristic to each salt mineral or assemblage of salt minerals. For example at 90°C, MgCl2 deliquesces at 24% relative humidity and KC1 deliquesces at 78.5% relative humidity.[2] Generally, the deliquescence relative humidity for a salt mixture is lower than the deliquescence relative humidity for its pure salt components. Salt deliquescence data are l
Transformation of meta-stable calcium silicate hydrates to tobermorite: reaction kinetics and molecular structure from XRD and NMR spectroscopy
Jacqueline R Houston, Robert S Maxwell, Susan A Carroll
Geochemical Transactions , 2009, DOI: 10.1186/1467-4866-10-1
Abstract: Burning of fossil fuels is believed to be the largest contributor to anthropogenic CO2 emissions and global climate change [1,2]. To reduce emissions and subsequently offset global warming, one solution is to inject CO2 into well-bores of depleted oil and gas reservoirs. Well- bores, however, are lined and plugged with Portland-based cement, which can chemically degrade in the presence of CO2 and water over time [3,4]. This presents a problem for long-term CO2 storage if reservoirs have the potential to leak through abandoned well sites. Deleterious effects can occur from leakage, including contamination of groundwater and subsurface resources and drastic changes to ecosystems [5-8]. In order to predict these processes and subsequently assess the long-term fate and storage of CO2, we need experimental data coupled with accurate simulations to identify reaction rates and pathways for cement dissolution and growth. However, there are few rate data on precipitation reactions and even fewer studies that derive growth mechanisms for cement-based minerals.Calcium silicate hydrates are key components in cement minerals and have been suggested as precursor solids for the growth of stable minerals such as tobermorite and gyrolite [9,10]. Calcium silicate hydrates include many meta-stable and amorphous disordered structures, from which stable and highly crystalline materials such as tobermorite can form when heated. The mineral tobermorite is stable over a temperature range of ~80°C to ~150°C but can be produced at temperatures greater than 200°C as a meta-stable solid [9]. Orthorhombic tobermorite can be found as either a 9 ?, 11 ? or 14 ? polytype depending on the number of water molecules present in the structure. The structure of 11 ? tobermorite consists of layers of hydrated calcium ions bonded to repeating silicate chains that have bridging and non-bridging Si (Q2) and branching Si (Q3) sites [10-13]. The silicate chains repeat every third tetrahedron, giving rise to t
Experimental Study of Cement - Sandstone/Shale - Brine - CO2 Interactions
Susan A Carroll, Walt W McNab, Sharon C Torres
Geochemical Transactions , 2011, DOI: 10.1186/1467-4866-12-9
Abstract: We observe marked changes in solution composition when CO2 reacted with cement, sandstone, and shale components at reservoir conditions. The geochemical model for the reaction of sandstone and shale with CO2 and brine is a simple one in which albite, chlorite, illite and carbonate minerals partially dissolve and boehmite, smectite, and amorphous silica precipitate. The geochemical model for the wellbore environment is also fairly simple, in which alkaline cements and rock react with CO2-rich brines to form an Fe containing calcite, amorphous silica, smectite and boehmite or amorphous Al(OH)3.Our research shows that relatively simple geochemical models can describe the dominant reactions that are likely to occur when CO2 is stored in deep saline aquifers sealed with overlying shale cap rocks, as well as the dominant reactions for cement carbonation at the wellbore interface.Carbon dioxide is actively being stored at depth in a sandstone saline reservoir as part of the In Salah Gas Project in Krechba, Algeria [1]. It is one of few commercial scale CO2 storage projects and serves as an important platform to study the scientific and technical issues for safe and effective long-term CO2 storage in deep saline reservoirs [2-11].Wellbores are a potential risk pathway for leakage of CO2 from the storage reservoir to overlying drinking water aquifers and back into the atmosphere. Carbonation of cements, used in wellbores to seal off fluid flow from the reservoir, can bring about changes in permeability and alter the movement of fluids within the wellbore environment. Field, experimental and modeling studies suggest that carbonation of hydrated cements lowers porosity and has the potential to heal fractures within the cement [12-18].Risk of leakage from a CO2 storage reservoir would be significantly reduced if the CO2 could be stored as a solid carbonate mineral and if these reactions improved the seal within the cap rock above the reservoir. Field and laboratory experiments
Speciation and fate of trace metals in estuarine sediments under reduced and oxidized conditions, Seaplane Lagoon, Alameda Naval Air Station (USA)
Susan Carroll, Peggy A O'Day, Brad Esser, Simon Randall
Geochemical Transactions , 2002, DOI: 10.1186/1467-4866-3-81
Abstract: The fate of these metals during dredging was evaluated by comparing in situ geochemistry with that of sediments oxidized by seawater in laboratory experiments. Cadmium and zinc pose the greatest hazard from dredging because their sulfides were highly reactive in seawater. However, their dissolved concentrations under oxic conditions were limited eventually by sorption to or co-precipitation with an iron (oxy)hydroxide. About 50% of the reacted CdS and 80% of the reacted ZnS were bonded to an oxide-substrate at the end of the 90-day oxidation experiment. Lead and chromium pose a minimal hazard from dredging because they are bonded to relatively insoluble carbonate, phosphate, phyllosilicate, or oxide minerals that are stable in seawater. These results point out the specific chemical behavior of individual metals in estuarine sediments, and the need for direct confirmation of metal speciation in order to constrain predictive models that realistically assess the fate of metals in urban harbors and coastal sediments.A recent evaluation of sediment contamination of surface waters in the United States by the US Environmental Protection Agency identified 96 watersheds, mostly urban harbors, containing metal and/or organic chemical contents that are potentially hazardous to aquatic biota.[1] These harbors and coastal sediments are contaminated from past and present industrial and military waste disposal practices. One such example is the estuary sediments of the East Outfall Site of the Seaplane Lagoon, at the former Naval Air Station (NAS) Alameda located on an island in San Francisco Bay, USA (Fig. 1). The most abundant metals in the sediments are cadmium, lead, chromium, zinc, copper, and nickel. Concentrations of these metal contaminants above background levels in San Francisco Bay result from a 57 year history of military and industrial activity at this site. From 1940 to 1975, the Seaplane Lagoon received about 300 million gallons of waste-water from industrial and st
Handlungsforschung und partnerschaftliche Begleitung als Strategien zur Verbesserung der Praxis von Dissertationssupervision Enhancing the Practice of PhD Supervisory Relationships Through First- And Second-Person Action Research/Peer Partnership Inquiry Enriquecer la práctica de las relaciones de asesoría en el PhD por medio de la investigación acción primera-segunda persona / indagación del colaborar entre pares
Judith McMorland,Brigid Carroll,Susan Copas,Judith Pringle
Forum : Qualitative Social Research , 2003,
Abstract: Unsere Universit tserfahrung zeigt, dass individuelle und kollektive Reflektionen über die Praxis der Betreuung bzw. Supervision von Dissertationen in der akademischen Gemeinde der Doktorand(inn)en, Doktorv ter und Doktormütter wenig entwickelt sind. Obwohl ein wachsendes Interesse erkennbar ist, über Graduierungsvorhaben und deren Begleitung zu forschen, gibt es sehr wenige Studien, die sich mit dieser Praxis aus einer Binnensicht besch ftigen. In diesem zweisemestrigen Projekt benutzten Doktorand(inn)en und Doktorv ter (-mütter) eine partnerschaftliche Methode ("Peer Partnership"), um zu erforschen, wie das Verh ltnis zwischen Promovierenden und Doktorvater/-mutter verbessert werden kann. Der Gruppe geh rten Betreuende und Studierende zu, die miteinander in einem Netz sozialer Rollen verbunden waren, das die Komplexit t akademischer Verh ltnisse sehr gut widerspiegelte. Eigen- und fremdperspektivische Reflektionen sowie intentionale, engagierte und fokussierte Gespr che erbrachten Einsichten in die vielfachen Dimensionen, die auf die Beziehungen zwischen Doktorand(inn)en und zwischen kooperierenden Doktorv tern/-müttern Einfluss nehmen, sowie in unsere eigenen Praktiken. Wir alle waren von der Vielschichtigkeit dieser Beziehungen und der im Verlauf dieser Studie gewonnenen Einsichten überrascht. In diesem Artikel zeigen wir, in welcher Weise die Anwendung von "Peer Partnership"-Methoden zu diesen Einsichten beigetragen hat, wie die Integrit t des Materials erreicht wurde, welche individuellen Umgehensweisen auftraten, und wie wir uns bemüht haben, unseren Ansatz und unsere Befunde mittels typischer akademischer Medien – Tagungen, abteilungs-/universit tsweite Seminarvortr ge und Internet – zu verbreiten. Aus unseren Erfahrungen erwachsen Konsequenzen für institutionelle Praktiken: So sollte dem vielschichtigen und komplexen Beziehungsgeflecht zwischen Doktorand(inn)en, Doktorv tern/-müttern und Institutionen viel mehr Aufmerksamkeit als bisher geschenkt werden, damit die Promotionsjahre ein ertragreiches und kreatives Unternehmen für alle Beteiligten sein k nnen. Betreuende und Studierende müssen Fertigkeiten erwerben, die ihnen erlauben, a) ihre eigenen Kenntnisse zu reflektieren, die b) Lernprozesse mit Peers unterstützen, und die c) eine Lernkultur über die multiplen Rollen (-verflechtungen) hinweg vorantreiben und gew hrleisten. Im gegenw rtigen akademischen Kontext ist anhaltende Reflexivit t dieser Art radikal, da das etablierte Verh ltnis zwischen Doktorand(inn)en und Doktorv tern/-müttern auf vielen Ebenen in Frage gestellt wird. URN: urn:nbn:d
Will Carroll
Journal of Sports Science and Medicine , 2004,
Abstract: This hardcover book introduces and updates the average fan as well as coaches, trainers, pitchers, biomechanical experts and such people to the theory and practice of analyzing the mechanics of pitching and preventing the possible injuries as a result. The book addresses different aspects of pitcher conditioning, mechanics, workload, abuse and avoiding injury. It also brings some controversial ideas into the world of baseball.
Surface complexation model for strontium sorption to amorphous silica and goethite
Susan A Carroll, Sarah K Roberts, Louise J Criscenti, Peggy A O'Day
Geochemical Transactions , 2008, DOI: 10.1186/1467-4866-9-2
Abstract: Strontium surface complexation equilibrium constants determined in this study combined with other alkaline earth surface complexation constants are used to recalibrate a predictive model based on Born solvation and crystal-chemistry theory. The model is accurate to about 0.7 log K units. More studies are needed to determine the dependence of alkaline earth sorption on ionic strength and dissolved carbonate and sulfate concentrations for the development of a robust surface complexation database to estimate alkaline earth sorption in the environment.Ion sorption to mineral and amorphous solids has long been recognized as a process that controls the composition of trace elements in water. This process is particularly important for the transport of contaminants in the Earth's surface environment where sorption may retard transport by removing the contaminant from a mobile aqueous phase to a more stationary solid phase. Efforts to describe sorption in complex geological settings has evolved from a purely empirical approach in which distribution coefficients (Kd) are a measure of the total amount of specific ion between the solid and aqueous phases for a complex solution and solid matrix specific to a contaminated site. Although this approach provides a direct measure of the ability of the solid matrix to sequester the contaminant from a specific solution, its empirical nature does not allow it to be applied outside of the specific parameters of the contaminated site. Another approach measures thermodynamic surface complexation constants which describe sorption as a series of specific reactions between dissolved ions and surface sites. In principle, thermodynamic data from several single mineral and element experiments can be combined to build a model that represents the complex systems found in nature, especially when coupled with aqueous speciation, mineral solubility, and kinetic databases. However an internally consistent surface complexation database for a wide range
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