The Data Quality Objectives (DQO) process provides a logical planning structure for specifying th... more The Data Quality Objectives (DQO) process provides a logical planning structure for specifying the optimal sample allocation for defensible decision making, depending on acceptable levels of decision uncertainty and anticipated sampling and measurement errors. These planning inputs must be established prior to designing the data collection activity. Application of the DQO process has traditionally been performed under the framework of Classical statistical theory; elicited decision errors have been interpreted as Classical Type I and Type II errors; mean and variance constraints have been incorporated based on historical information; and, Classical statistical testing methods have been used to determine optimal sample sizes. However, decision errors are usually stated, for dichotomous hypotheses, in terms of the probability of making a false positive or false negative decision; these probabilities, at best, relate loosely to probabilities of Classical Type I and Type II errors. Stat...
ABSTRACT Carbonates are one of the most abundant groups of minerals in earth systems and are impo... more ABSTRACT Carbonates are one of the most abundant groups of minerals in earth systems and are important in many geological settings and industrial processes. Calcite (CaCO3) thin films produced by atomic layer deposition offer a method to evaluate the surficial properties of carbonates as well as interactions at the carbonate–fluid interface. Using synchrotron X-ray reflectivity and X-ray diffraction, these films are observed to be porous, polycrystalline, and have crystallites oriented with the major (104) calcite cleavage plane parallel to the surface of the z-cut single crystal quartz substrate. An Al2O3 buffer layer, present between quartz and the calcite film, does not affect the as-deposited film, but does influence how the films reorganize in contact with fluid. Without a buffer layer, calcite reorients its crystallites to have populations of (006) and (030) parallel to the substrate, while those with an Al2O3 buffer layer become more amorphous. Amorphous films may represent an analog to amorphous calcium carbonate and provide insights into that material's thermophysical behavior. Due to a higher percentage of pore spaces available for fluid infiltration, films deposited at higher temperature make the calcite thin films more susceptible to amorphization. These films are chemically similar, but structurally dissimilar to bulk natural calcite. Nevertheless, they can be a complementary system to traditional single crystal X-ray surface scattering studies on carbonates, particularly for important but less common minerals, to evaluate mineral–fluid interfacial interactions.
Time series of hillslope or catchment water content, subsurface flow, and solute chemistry typica... more Time series of hillslope or catchment water content, subsurface flow, and solute chemistry typically show complex and highly variable behavior. Event-based approaches are often used to characterize input-output responses (e.g., tracking an isotopically unique precipitation event, or by fitting a seasonality curve to the data). However, such approaches typically quantify just one characteristic response when we know that hillslopes and catchments have a distribution of characteristic time scales. Thus, we seek an alternative approach, one where we can identify distributions of characteristic responses and quantify individual variance contributions. Besides improving our conceptual understanding of how hillslopes and catchments work, the goal is to develop low-dimensional "empirical" and/or physically based models that more fully represent the distribution of characteristic responses. To this end, singular spectrum time series analysis is used to identify characteristic times of hydrologic and geochemical variables at hillslope and catchment scales. For our semiarid study sites we find that soil water content, spring flow (representing catchment scale behavior), and geochemical responses can be characterized by a small suite of periodic or quasi-periodic characteristic "modes' that account for a major fraction of the total system variance. The remaining modes (i.e., those that only account for a small fraction of the variance) typically display "red-noise" type behavior suggesting a simple stochastic model. Our results show that singular spectrum analysis offers new insights on hydrologic and geochemical response and should be a fruitful way of developing improved hillslope- and catchment-scale models.
We have studied phase stability of three quartz-related phases, Mg0.5AlSiO4, Mg0.25Li0.5AlSiO4 an... more We have studied phase stability of three quartz-related phases, Mg0.5AlSiO4, Mg0.25Li0.5AlSiO4 and LiAlSiO4 (beta-eucryptite), at high pressures and/or temperatures using the multi-anvil press technique in conjunction with synchrotron X-ray diffraction. These phases can be considered as structural derivatives of quartz in which half the Si^{4+} cations are replaced by Al3+, and the charge is balanced by incorporation of Mg2+ and/or Li+ into the structural channels. With increasing pressure, the stuffed quartz phases gradually lost their crystallinity and became completely X-ray amorphous at 12-17 GPa. The amorphization processes were similar to that of quartz, but they reached completion at much lower pressures (quartz becomes amorphous at ~30 GPa). Moreover, these phases exhibited the so-called "structural memory" behavior, i.e., when they were partially amorphized, they reverted back to their original crystalline states after pressure release. Upon heating at high pressures, the partially or completely amorphous phases transformed into their corresponding stable polymorphs or phase assemblages. Thus the occurrence of pressure-induced amorphization in these quartz- derivatives is related to the kinetic hindrance to their transformations to the thermodynamically stable phases. Further, as observed in pure silica, the densities of these amorphous states may be higher than those allowed in the stuffed-quartz structures, thereby driving the amorphization processes at high pressures.
Jarosite, KFe3(SO4)2(OH)6, and its related sulfates commonly occur in acid drainage environments ... more Jarosite, KFe3(SO4)2(OH)6, and its related sulfates commonly occur in acid drainage environments as the weathering products of sulfide ore deposits. They can also precipitate from aqueous sulfates due to oxidation of H2S in epithermal environments and hot springs associated with volcanic activities. In 2004, jarosite was detected by the Mars Exploration Rover Mössbauer spectrometer, which has been interpreted as a strong evidence for the existence of water (and thus life) on Mars. In this work, we have investigated the crystal structure and thermodynamic stability of jarosite at temperatures up to 650 K and/or pressures up to 8 GPa using in situ neutron and synchrotron X-ray diffraction. To avoid the large incoherent scattering of neutrons by hydrogen, a deuterated sample was synthesized and characterized. Rietveld analysis of the obtained diffraction data allowed determination of unit-cell parameters, atomic positions and atomic displacement parameters as a function of temperature and pressure. In addition, the coefficients of thermal expansion, bulk moduli and pressure-temperature stability regions of jarosite were determined.
Processes at mineral-fluid interfaces control a wide-range of phenomena of crucial importance in ... more Processes at mineral-fluid interfaces control a wide-range of phenomena of crucial importance in energy and environmental applications, including fluid flow, mineral precipitation and dissolution, and corrosion and scaling. In geological systems, geothermal energy production, CO2 sequestration, oil and gas production, and nuclear reactors and waste repositories, these critical mineral-fluid interactions occur at high pressures (P) and temperatures (T). Unfortunately the details of these phenomena are poorly understood because of the technical difficulties with conducting in-situ investigations of mineral/fluid interfaces at relevant geological conditions. Neutron reflectometry offers the possibility of studying fluid/solid processes in-situ at elevated Ps and Ts. In neutron reflectometry an unpolarized neutron beam (wavelength 1.5 to 16 Å) is directed at a solid/fluid (or other) interface at a glancing angle and a range of momentum transfer vectors (Q) are measured elucidating chang...
The Data Quality Objectives (DQO) process provides a logical planning structure for specifying th... more The Data Quality Objectives (DQO) process provides a logical planning structure for specifying the optimal sample allocation for defensible decision making, depending on acceptable levels of decision uncertainty and anticipated sampling and measurement errors. These planning inputs must be established prior to designing the data collection activity. Application of the DQO process has traditionally been performed under the framework of Classical statistical theory; elicited decision errors have been interpreted as Classical Type I and Type II errors; mean and variance constraints have been incorporated based on historical information; and, Classical statistical testing methods have been used to determine optimal sample sizes. However, decision errors are usually stated, for dichotomous hypotheses, in terms of the probability of making a false positive or false negative decision; these probabilities, at best, relate loosely to probabilities of Classical Type I and Type II errors. Stat...
ABSTRACT Carbonates are one of the most abundant groups of minerals in earth systems and are impo... more ABSTRACT Carbonates are one of the most abundant groups of minerals in earth systems and are important in many geological settings and industrial processes. Calcite (CaCO3) thin films produced by atomic layer deposition offer a method to evaluate the surficial properties of carbonates as well as interactions at the carbonate–fluid interface. Using synchrotron X-ray reflectivity and X-ray diffraction, these films are observed to be porous, polycrystalline, and have crystallites oriented with the major (104) calcite cleavage plane parallel to the surface of the z-cut single crystal quartz substrate. An Al2O3 buffer layer, present between quartz and the calcite film, does not affect the as-deposited film, but does influence how the films reorganize in contact with fluid. Without a buffer layer, calcite reorients its crystallites to have populations of (006) and (030) parallel to the substrate, while those with an Al2O3 buffer layer become more amorphous. Amorphous films may represent an analog to amorphous calcium carbonate and provide insights into that material's thermophysical behavior. Due to a higher percentage of pore spaces available for fluid infiltration, films deposited at higher temperature make the calcite thin films more susceptible to amorphization. These films are chemically similar, but structurally dissimilar to bulk natural calcite. Nevertheless, they can be a complementary system to traditional single crystal X-ray surface scattering studies on carbonates, particularly for important but less common minerals, to evaluate mineral–fluid interfacial interactions.
Time series of hillslope or catchment water content, subsurface flow, and solute chemistry typica... more Time series of hillslope or catchment water content, subsurface flow, and solute chemistry typically show complex and highly variable behavior. Event-based approaches are often used to characterize input-output responses (e.g., tracking an isotopically unique precipitation event, or by fitting a seasonality curve to the data). However, such approaches typically quantify just one characteristic response when we know that hillslopes and catchments have a distribution of characteristic time scales. Thus, we seek an alternative approach, one where we can identify distributions of characteristic responses and quantify individual variance contributions. Besides improving our conceptual understanding of how hillslopes and catchments work, the goal is to develop low-dimensional "empirical" and/or physically based models that more fully represent the distribution of characteristic responses. To this end, singular spectrum time series analysis is used to identify characteristic times of hydrologic and geochemical variables at hillslope and catchment scales. For our semiarid study sites we find that soil water content, spring flow (representing catchment scale behavior), and geochemical responses can be characterized by a small suite of periodic or quasi-periodic characteristic "modes' that account for a major fraction of the total system variance. The remaining modes (i.e., those that only account for a small fraction of the variance) typically display "red-noise" type behavior suggesting a simple stochastic model. Our results show that singular spectrum analysis offers new insights on hydrologic and geochemical response and should be a fruitful way of developing improved hillslope- and catchment-scale models.
We have studied phase stability of three quartz-related phases, Mg0.5AlSiO4, Mg0.25Li0.5AlSiO4 an... more We have studied phase stability of three quartz-related phases, Mg0.5AlSiO4, Mg0.25Li0.5AlSiO4 and LiAlSiO4 (beta-eucryptite), at high pressures and/or temperatures using the multi-anvil press technique in conjunction with synchrotron X-ray diffraction. These phases can be considered as structural derivatives of quartz in which half the Si^{4+} cations are replaced by Al3+, and the charge is balanced by incorporation of Mg2+ and/or Li+ into the structural channels. With increasing pressure, the stuffed quartz phases gradually lost their crystallinity and became completely X-ray amorphous at 12-17 GPa. The amorphization processes were similar to that of quartz, but they reached completion at much lower pressures (quartz becomes amorphous at ~30 GPa). Moreover, these phases exhibited the so-called "structural memory" behavior, i.e., when they were partially amorphized, they reverted back to their original crystalline states after pressure release. Upon heating at high pressures, the partially or completely amorphous phases transformed into their corresponding stable polymorphs or phase assemblages. Thus the occurrence of pressure-induced amorphization in these quartz- derivatives is related to the kinetic hindrance to their transformations to the thermodynamically stable phases. Further, as observed in pure silica, the densities of these amorphous states may be higher than those allowed in the stuffed-quartz structures, thereby driving the amorphization processes at high pressures.
Jarosite, KFe3(SO4)2(OH)6, and its related sulfates commonly occur in acid drainage environments ... more Jarosite, KFe3(SO4)2(OH)6, and its related sulfates commonly occur in acid drainage environments as the weathering products of sulfide ore deposits. They can also precipitate from aqueous sulfates due to oxidation of H2S in epithermal environments and hot springs associated with volcanic activities. In 2004, jarosite was detected by the Mars Exploration Rover Mössbauer spectrometer, which has been interpreted as a strong evidence for the existence of water (and thus life) on Mars. In this work, we have investigated the crystal structure and thermodynamic stability of jarosite at temperatures up to 650 K and/or pressures up to 8 GPa using in situ neutron and synchrotron X-ray diffraction. To avoid the large incoherent scattering of neutrons by hydrogen, a deuterated sample was synthesized and characterized. Rietveld analysis of the obtained diffraction data allowed determination of unit-cell parameters, atomic positions and atomic displacement parameters as a function of temperature and pressure. In addition, the coefficients of thermal expansion, bulk moduli and pressure-temperature stability regions of jarosite were determined.
Processes at mineral-fluid interfaces control a wide-range of phenomena of crucial importance in ... more Processes at mineral-fluid interfaces control a wide-range of phenomena of crucial importance in energy and environmental applications, including fluid flow, mineral precipitation and dissolution, and corrosion and scaling. In geological systems, geothermal energy production, CO2 sequestration, oil and gas production, and nuclear reactors and waste repositories, these critical mineral-fluid interactions occur at high pressures (P) and temperatures (T). Unfortunately the details of these phenomena are poorly understood because of the technical difficulties with conducting in-situ investigations of mineral/fluid interfaces at relevant geological conditions. Neutron reflectometry offers the possibility of studying fluid/solid processes in-situ at elevated Ps and Ts. In neutron reflectometry an unpolarized neutron beam (wavelength 1.5 to 16 Å) is directed at a solid/fluid (or other) interface at a glancing angle and a range of momentum transfer vectors (Q) are measured elucidating chang...
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