The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
Jun-ichi Fukuda - One of the best experts on this subject based on the ideXlab platform.
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theoretical derivation of flow laws for quartz dislocation creep comparisons with experimental creep data and extrapolation to natural conditions using water Fugacity corrections
Journal of Geophysical Research, 2017Co-Authors: Jun-ichi Fukuda, Ichiko ShimizuAbstract:We theoretically derived flow laws for quartz dislocation creep using climb-controlled dislocation creep models and compared them with available laboratory data for quartz plastic deformation. We assumed volume diffusion of oxygen-bearing species along different crystallographic axes (//c, ⊥R, and ⊥c) of α-quartz and β-quartz, and pipe diffusion of H 2 O, to be the elementary processes of dislocation climb. The relationships between differential stress (σ) and strain rate (_ e) are written as _ e∝σ 3 D v and _ e∝σ 5 D p for cases controlled by volume and pipe diffusion, respectively, where D v and D p are coefficients of diffusion for volume and pipe diffusion. In previous experimental work, there were up to ~1.5 orders of magnitude difference in the water Fugacity values in experiments that used either gas-pressure-medium or solid-pressure-medium deformation apparatus. Therefore, in both the theories and flow laws, we included water Fugacity effects as modified preexponential factors and water Fugacity terms. Previous experimental data were obtained mainly in the β-quartz field and are highly consistent with the volume-diffusion-controlled dislocation creep models of β-quartz involving the water Fugacity term. The theory also predicts significant effects for the transition of α-β quartz under crustal conditions. Under experimental pressure and temperature conditions, the flow stress of pipe-diffusion-controlled dislocation creep is higher than that for volume-diffusion-controlled creep. Extrapolation of the flow laws to natural conditions indicates that the contributions of pipe diffusion may dominate over volume diffusion under low-temperature conditions of the middle crust around the brittle-plastic transition zone.
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Theoretical derivation of flow laws for quartz dislocation creep: Comparisons with experimental creep data and extrapolation to natural conditions using water Fugacity corrections
Journal of Geophysical Research : Solid Earth, 2017Co-Authors: Jun-ichi Fukuda, Ichiko ShimizuAbstract:We theoretically derived flow laws for quartz dislocation creep using climb-controlled dislocation creep models and compared them with available laboratory data for quartz plastic deformation. We assumed volume diffusion of oxygen-bearing species along different crystallographic axes (//c, ⊥R, and ⊥c) of α-quartz and β-quartz, and pipe diffusion of H 2 O, to be the elementary processes of dislocation climb. The relationships between differential stress (σ) and strain rate (_ ε) are written as _ ε∝σ 3 D v and _ ε∝σ 5 D p for cases controlled by volume and pipe diffusion, respectively, where D v and D p are coefficients of diffusion for volume and pipe diffusion. In previous experimental work, there were up to ~1.5 orders of magnitude difference in the water Fugacity values in experiments that used either gas-pressure-medium or solid-pressure-medium deformation apparatus. Therefore, in both the theories and flow laws, we included water Fugacity effects as modified preexponential factors and water Fugacity terms. Previous experimental data were obtained mainly in the β-quartz field and are highly consistent with the volume-diffusion-controlled dislocation creep models of β-quartz involving the water Fugacity term. The theory also predicts significant effects for the transition of α-β quartz under crustal conditions. Under experimental pressure and temperature conditions, the flow stress of pipe-diffusion-controlled dislocation creep is higher than that for volume-diffusion-controlled creep. Extrapolation of the flow laws to natural conditions indicates that the contributions of pipe diffusion may dominate over volume diffusion under low-temperature conditions of the middle crust around the brittle-plastic transition zone.
Ichiko Shimizu - One of the best experts on this subject based on the ideXlab platform.
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theoretical derivation of flow laws for quartz dislocation creep comparisons with experimental creep data and extrapolation to natural conditions using water Fugacity corrections
Journal of Geophysical Research, 2017Co-Authors: Jun-ichi Fukuda, Ichiko ShimizuAbstract:We theoretically derived flow laws for quartz dislocation creep using climb-controlled dislocation creep models and compared them with available laboratory data for quartz plastic deformation. We assumed volume diffusion of oxygen-bearing species along different crystallographic axes (//c, ⊥R, and ⊥c) of α-quartz and β-quartz, and pipe diffusion of H 2 O, to be the elementary processes of dislocation climb. The relationships between differential stress (σ) and strain rate (_ e) are written as _ e∝σ 3 D v and _ e∝σ 5 D p for cases controlled by volume and pipe diffusion, respectively, where D v and D p are coefficients of diffusion for volume and pipe diffusion. In previous experimental work, there were up to ~1.5 orders of magnitude difference in the water Fugacity values in experiments that used either gas-pressure-medium or solid-pressure-medium deformation apparatus. Therefore, in both the theories and flow laws, we included water Fugacity effects as modified preexponential factors and water Fugacity terms. Previous experimental data were obtained mainly in the β-quartz field and are highly consistent with the volume-diffusion-controlled dislocation creep models of β-quartz involving the water Fugacity term. The theory also predicts significant effects for the transition of α-β quartz under crustal conditions. Under experimental pressure and temperature conditions, the flow stress of pipe-diffusion-controlled dislocation creep is higher than that for volume-diffusion-controlled creep. Extrapolation of the flow laws to natural conditions indicates that the contributions of pipe diffusion may dominate over volume diffusion under low-temperature conditions of the middle crust around the brittle-plastic transition zone.
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Theoretical derivation of flow laws for quartz dislocation creep: Comparisons with experimental creep data and extrapolation to natural conditions using water Fugacity corrections
Journal of Geophysical Research : Solid Earth, 2017Co-Authors: Jun-ichi Fukuda, Ichiko ShimizuAbstract:We theoretically derived flow laws for quartz dislocation creep using climb-controlled dislocation creep models and compared them with available laboratory data for quartz plastic deformation. We assumed volume diffusion of oxygen-bearing species along different crystallographic axes (//c, ⊥R, and ⊥c) of α-quartz and β-quartz, and pipe diffusion of H 2 O, to be the elementary processes of dislocation climb. The relationships between differential stress (σ) and strain rate (_ ε) are written as _ ε∝σ 3 D v and _ ε∝σ 5 D p for cases controlled by volume and pipe diffusion, respectively, where D v and D p are coefficients of diffusion for volume and pipe diffusion. In previous experimental work, there were up to ~1.5 orders of magnitude difference in the water Fugacity values in experiments that used either gas-pressure-medium or solid-pressure-medium deformation apparatus. Therefore, in both the theories and flow laws, we included water Fugacity effects as modified preexponential factors and water Fugacity terms. Previous experimental data were obtained mainly in the β-quartz field and are highly consistent with the volume-diffusion-controlled dislocation creep models of β-quartz involving the water Fugacity term. The theory also predicts significant effects for the transition of α-β quartz under crustal conditions. Under experimental pressure and temperature conditions, the flow stress of pipe-diffusion-controlled dislocation creep is higher than that for volume-diffusion-controlled creep. Extrapolation of the flow laws to natural conditions indicates that the contributions of pipe diffusion may dominate over volume diffusion under low-temperature conditions of the middle crust around the brittle-plastic transition zone.
C D K Herd - One of the best experts on this subject based on the ideXlab platform.
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the oxygen Fugacity of olivine phyric martian basalts and the components within the mantle and crust of mars
Meteoritics & Planetary Science, 2003Co-Authors: C D K HerdAbstract:The oxygen Fugacity of olivine-phyric martian basalts is estimated using olivine-pyroxene- spinel equilibria, supported by detailed petrography. Results are plotted, along with previous oxygen Fugacity estimates, against La/Yb, which is used as a proxy for long-term incompatible-element depletion or enrichment in martian basalt reservoirs. In general, the correlation between oxygen Fugacity and La/Yb observed by Herd et al. (2002a) holds for the olivine-phyric basalts. The implications of the correlation are re-evaluated in light of work by Borg et al. (Forthcoming), which indicates that the variations in radiogenic isotopic composition can be modeled by mixing of mantle sources established by 4.5 Ga through crystallization of a magma ocean in lieu of assimilation of crustal material. The results demonstrate that the crust-like component, interpreted as trapped liquid in a magma ocean cumulate pile, must be oxidized to explain the oxygen Fugacity of the martian basalts. Consequently, the pre-eruptive water contents of the more oxidized basalts are expected to be higher, although water is not called upon as the cause of the oxidation. Unmixing of mantle components provides an important context for the interpretation of oxygen isotopes, demonstrated here, and of samples returned from the martian surface.
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oxygen Fugacity and geochemical variations in the martian basalts implications for martian basalt petrogenesis and the oxidation state of the upper mantle of mars
Geochimica et Cosmochimica Acta, 2002Co-Authors: C D K Herd, L E Borg, J H Jones, J J PapikeAbstract:Abstract The oxygen Fugacity of the Dar al Gani 476 martian basalt is determined to be quartz-fayalite-magnetite (QFM) −2.3 ± 0.4 through analysis of olivine, low-Ca pyroxene, and Cr-spinel and is in good agreement with revised results from Fe-Ti oxides that yield QFM −2.5 ± 0.7. This estimate falls within the range of oxygen Fugacity for the other martian basalts, QFM −3 to QFM −1. Oxygen Fugacity in martian basalts correlates with 87Sr/86Sr, 143Nd/144Nd, and La/Yb ratios, indicating that the mantle source of the basalts is reduced and that assimilation of crust-like material controls the oxygen Fugacity. This allows constraints to be placed on the oxidation state of the martian mantle and on the nature of assimilated crustal material. The assimilated material may be the product of early and extensive hydrothermal alteration of the martian crust, or it may be amphibole- or phlogopite-bearing basaltic rock within the crust. In either case, water may play a significant role in the oxidation of basaltic magmas on Mars, although it may be secondary to assimilation of ferric iron-rich material.
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oxygen Fugacity of martian basalts from electron microprobe oxygen and tem eels analyses of fe ti oxides
American Mineralogist, 2001Co-Authors: C D K Herd, J J Papike, Adrian J BrearleyAbstract:The stoichiometry of titanomagnetite spinel in the martian basaltic meteorites is assessed using quantitative analysis of oxygen measured by electron microprobe and electron energy loss spectroscopy in the transmission electron microscope. The spinels are stoichiometric within the errors of the techniques, enabling the calculation of oxygen Fugacity with confidence. The oxygen Fugacity is calculated using the Ghiorso-Sack and Ca-QUIlF models, which also yield estimates of temperature. The oxygen Fugacity of the martian basalts increases from 3 log units below the QFM buffer for QUE 94201 to QFM − 1.8 for EETA 79001 (both lithologies), to QFM − 1.0 for Shergotty, Zagami, and Los Angeles. Dar al Gani 476 spinels contain significant MgAl2O4 and FeCr2O4 components, complicating the use of Fe-Ti oxide models. The oxygen Fugacity of Dar al Gani 476 is estimated to be 1.5 log units below QFM, on the basis of the Ghiorso-Sack model. The absolute error on the oxygen Fugacity estimates is ± 0.5 log units; however, a consistent electron microprobe analytical routine was applied to all of the basalts, and the relative uncertainty is closer to 0.2 log units. Oxyexsolution has occurred in QUE 94201, but reconstruction of pre-exsolution titanomagnetite compositions permits the calculation of oxygen Fugacity. Subsolidus reactions involving oxides and adjacent Fe-rich silicates are documented and the use of the Ca-QUIlF model for calculation of oxygen Fugacity from these phases is discussed.
Donald Mackay - One of the best experts on this subject based on the ideXlab platform.
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a perspective on the role of Fugacity and activity for evaluating the pbt properties of organic chemicals and providing a multi media synoptic indicator of environmental contamination
Environmental Science: Processes & Impacts, 2020Co-Authors: Donald Mackay, Alena K D Celsie, Mark J Parnis, Jon A ArnotAbstract:The hazard and risk from organic chemicals present in the environment are routinely evaluated using P (persistence), B (bioaccumulation) and T (toxicity) criteria. We present a perspective on how models based on the equilibrium criteria of Fugacity and chemical activity can contribute to all three evaluations, thus providing a consistent and seamless assessment process. Persistence and its closely related, but fundamentally different property, chemical residence time can be determined from degradation half-lives (typically obtained from monitoring data) and multi-media mass balance models describing chemical fate and transport in real or evaluative environments. Bioaccumulation is driven by equilibrium partitioning processes that can be estimated from Fugacity models treating uptake by respiration and diet in single organisms and in food webs, most commonly for aquatic systems for which confirmatory monitoring data can be obtained. Biomagnification is readily evaluated both experimentally and as a Fugacity (or activity) increase from prey to predator. Toxicokinetic evaluations of chemical uptake and disposition in a variety of organisms, including humans, can be obtained using Fugacity- and physiologically-based pharmacokinetic models. Toxicodynamic processes of chemical interactions with organisms leading to adverse toxic outcomes are less obviously amenable to Fugacity assessment with the notable exception of baseline toxicity (narcosis), the most common mode of action of commercial chemicals. It is shown that a range of fugacities can be defined and correlated for specific species thus enabling direct comparison of fugacities estimated or monitored in the environment with fugacities resulting in baseline toxicity. Finally, it is shown that Fugacity and activity can serve as multi-media metrics of chemical contamination in ecosystems, thus enabling identification of specific regions and species at greatest risk in a pictorial format that is readily understandable to scientific and regulatory communities and to the general public.
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Fugacity and activity analysis of the bioaccumulation and environmental risks of decamethylcyclopentasiloxane d5
Environmental Toxicology and Chemistry, 2015Co-Authors: Frank A P C Gobas, Donald Mackay, Shihe Xu, Gary E Kozerski, David E Powell, Kent B Woodburn, Anne FairbrotherAbstract:As part of an initiative to evaluate commercial chemicals for their effects on human and environmental health, Canada recently evaluated decamethylcyclopentasiloxane (D5; CAS no. 541-02-06), a high–volume production chemical used in many personal care products. The evaluation illustrated the challenges encountered in environmental risk assessments and the need for the development of better tools to increase the weight of evidence in environmental risk assessments. The present study presents a new risk analysis method that applies thermodynamic principles of Fugacity and activity to express the results of field monitoring and laboratory bioaccumulation and toxicity studies in a comprehensive risk analysis that can support risk assessments. Fugacity and activity ratios of D5 derived from bioaccumulation measures indicate that D5 does not biomagnify in food webs, likely because of biotransformation. The Fugacity and activity analysis further demonstrates that reported no-observed-effect concentrations of D5 normally cannot occur in the environment. Observed fugacities and activities in the environment are, without exception, far below those corresponding with no observed effects, in many cases by several orders of magnitude. This analysis supports the conclusion of the Canadian Board of Review and the Minister of the Environment that D5 does not pose a danger to the environment. The present study further illustrates some of the limitations of a persistence-bioaccumulation-toxicity–type criteria-based risk assessment approach and discusses the merits of the Fugacity and activity approach to increase the weight of evidence and consistency in environmental risk assessments of commercial chemicals. Environ Toxicol Chem 2015;9999:1–9. © 2015 The Authors. Environmental Toxicology and Chemistry Published by Wiley Periodicals, Inc. on behalf of SETAC.
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the application of Fugacity and activity to simulating the environmental fate of organic contaminants
Journal of Chemical & Engineering Data, 2011Co-Authors: Donald Mackay, Jon A ArnotAbstract:The concept of Fugacity, which is widely used in chemical processing calculations, has also been successfully applied to a variety of environmental simulations of the fate and transport of organic contaminants. The challenges of estimating fugacities in environmental phases are discussed, especially for ill-defined phases such as soils, sediments, and biota for which activity coefficients and molar volumes cannot be measured. It is shown that by lumping these quantities and a reference Fugacity in a single parameter, empirical partition coefficient data can be used to deduce fugacities and thus the relative equilibrium status between phases and directions of diffusive transport. For assessments of substances that display narcosis, chemical activities, which can be readily deduced from fugacities, can provide valuable estimates of the proximity of calculated or measured environmental concentrations to potentially toxic levels. Five illustrations are presented to demonstrate the value of applying the fugaci...
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The Evolution and Future of Environmental Fugacity Models
Ecotoxicology Modeling, 2009Co-Authors: Donald Mackay, Jon A Arnot, Eva Webster, Lüsa ReidAbstract:In this chapter we first review the concept of Fugacity as a thermodynamic equilibrium criterion applied to chemical fate in environmental systems. We then discuss the evolution of Fugacity-based models applied to the multimedia environmental distribution of chemicals and more specifically to bioaccumulation and food web models. It is shown that the combination of multimedia and bioaccumulation models can provide a comprehensive assessment of chemical fate, transport, and exposure to both humans and wildlife. A logical next step is to incorporate toxicity information to assess the likelihood of risk in the expectation that most regulatory effort will be focused on those chemicals that pose the highest risk. This capability already exists for many well-studied chemicals but we argue that there is a compelling incentive to extend this capability to other more challenging chemicals and environmental situations and indeed to all chemicals of commerce. Finally, we argue that deriving the full benefits of these applications of the Fugacity concept to chemical fate and risk assessment requires continued effort to develop quantitative structure–activity relationships (QSARs) that can predict relevant chemical properties and programs to validate these models by reconciliation between modeled and monitoring data.
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Finding Fugacity feasible, fruitful, and fun.
Environmental Toxicology and Chemistry, 2004Co-Authors: Donald MackayAbstract:A review is presented concerning the evolution of the Fugacity concept as applied to environmental science. The series of serendipitous events that ultimately resulted in publication of the paper “Finding Fugacity Feasible” in 1979 is described. The use of Fugacity as a surrogate for concentration is shown to facilitate the compilation and solution of mass-balance equations. It has proved to be valuable in a number of contexts, notably the description of chemical fate in unit worlds at various levels of complexity. More complex systems can be simulated as sets of connected unit worlds. The Fugacity approach enables the multimedia character of organic chemicals to be deduced, thus contributing to the evaluation of chemical properties that impact persistence and long-range transport. It has proved to be especially insightful for describing bioconcentration, bioaccumulation, and pharmacokinetic phenomena. Applications to the sensing and monitoring of chemical presence in the environment are described. Suggestions are made for subject areas in which the Fugacity concept may prove to be particularly valuable in the future. Finally, the many colleagues who have contributed to the use of Fugacity when quantifying chemical behavior in the environment are acknowledged.
Sandrin T Feig - One of the best experts on this subject based on the ideXlab platform.
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effect of oxygen Fugacity and water on phase equilibria of a hydrous tholeiitic basalt
Contributions to Mineralogy and Petrology, 2010Co-Authors: Sandrin T Feig, Jurgen Koepke, J E SnowAbstract:The influence of oxygen Fugacity and water on phase equilibria and the link between redox conditions and water activity were investigated experimentally using a primitive tholeiitic basalt composition relevant to the ocean crust. The crystallization experiments were performed in internally heated pressure vessels at 200 MPa in the temperature range 940–1,220°C. The oxygen Fugacity was measured using the H2-membrane technique. To study the effect of oxygen Fugacity, three sets of experiments with different hydrogen fugacities were performed, showing systematic effects on the phase relations and compositions. In each experimental series, the water content of the system was varied from nominally dry to water-saturated conditions, causing a range of oxygen fugacities varying by ~3 log units per series. The range in oxygen Fugacity investigated spans ~7 log units. Systematic effects of oxygen Fugacity on the stability and composition of the mafic silicate phases, Cr–spinel and Fe–Ti oxides, under varying water contents were recorded. The Mg# of the melt, and therefore also the Mg# of olivine and clinopyroxene, changed systematically as a function of oxygen Fugacity. An example of the link between oxygen Fugacity and water activity under hydrogen-buffered conditions is the change in the crystallization sequence (olivine and Cr–spinel) due to a change in the oxygen Fugacity caused by an increase in the water activity. The stability of magnetite is restricted to highly oxidizing conditions. The absence of magnetite in most of the experiments allows the determination of differentiation trends as a function of oxygen Fugacity and water content, demonstrating that in an oxide-free crystallization sequence, water systematically affects the differentiation trend, while oxygen Fugacity seems to have a negligible effect.
