Electrochemical study of hydrothermal and sedimentary pyrite dissolution     

Ran Liu  Amy L. Wolfe  David A. Dzombak  Colin P. Horwitz  Brian W. Stewart  Rosemary C. Capo 《Applied Geochemistry》2008

The dissolution of pyrite is of interest in the formation of acid mine drainage and is a complex electrochemical process. Being able to measure the rate of dissolution of particular pyrite samples under particular conditions is important for describing and predicting rates of AMD generation. Electrochemical techniques offer the promise of performing such measurements rapidly and with small samples. The oxidation of pyrite and the reduction of Fe³⁺ ions and/or O₂ half reactions involved in the pyrite dissolution process were investigated by cyclic voltammetry and steady-state voltammetry using three pyrite materials formed in both sedimentary and hydrothermal environments. For each sample, two kinds of pyrite working electrodes (conventional constructed compact solid electrode, and carbon paste electrode constructed from fine-grained pyrite particles) were employed. Results indicated that for both the hydrothermal and sedimentary pyrite samples the oxidation and reduction half reactions involved in dissolution were governed by charge transfer processes, suggesting that hydrothermal and sedimentary pyrites obey the same dissolution mechanism despite their different formation mechanisms. In addition, the results showed that it is feasible to use a C paste electrode constructed from fine-grained or powdered pyrite to study the pyrite dissolution process electrochemically and to derive approximate rate expressions from the electrochemical data.  相似文献   

Comparison of dissolution under oxic acid drainage conditions for eight sedimentary and hydrothermal pyrite samples   总被引：1，自引：0，他引：1  

Ran Liu  Amy L. Wolfe  David A. Dzombak  Brian W. Stewart  Rosemary C. Capo 《Environmental Geology》2008,56(1):171-182

The abiotic oxidative dissolution behaviors of eight natural pyrite samples, five sedimentary and three hydrothermal, from various geological environments were compared under oxic conditions at pH 3 and 6 in a highly controlled batch reactor dissolution system. The three sedimentary pyrite samples associated with coal had greater specific surface areas and also exhibited greater apparent dissolution rates and extent than the other two sedimentary and three hydrothermal samples under both pH conditions. However, after normalizing for surface area, the dissolution rate constants for the different pyrite samples were similar; the greatest difference was between the two non-coal sedimentary pyrite samples. Pyrite morphology and the presence of trace metals could contribute to the differences in dissolution behavior as reflected in the normalized dissolution rates. The sulfur:iron ratio observed in the aqueous solution at pH 3 increased with time, but was always less than 2.0 (predicted from the stoichiometry of dissolution) for all the pyrite samples during the 24-h experimental duration. This can be explained by the disproportionation dissociation of thiosulfate, an initial product of pyrite dissolution, to elemental sulfur and sulfate which does not occur in a 1:1 ratio. The results of this work indicate the importance of extracting and using the specific pyrite(s) relevant to particular mining areas in order to understand pyrite dissolution rates and the influence of environmental conditions on those rates.  相似文献   

Comment on “The International Association of Hydrogeologists (IAH): reflecting on 60 years of contributions to groundwater science and water management”: article published in <Emphasis Type="Italic">Hydrogeology Journal</Emphasis> (2016) 24: 1069–1086, by Willi Struckmeier,Ken Howard and John Chilton     

Michael J. Knight 《Hydrogeology Journal》2016,24(8):2189-2190

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Could working less reduce pressures on the environment? A cross-national panel analysis of OECD countries, 1970–2007     

Kyle W. Knight  Eugene A. Rosa  Juliet B. Schor 《Global Environmental Change》2013,23(4):691-700

Many scholars and activists are now advocating a program of economic degrowth for developed countries in order to mitigate demands on the global environment. An increasingly prominent idea is that developed countries could achieve slower or zero economic growth in a socially sustainable way by reducing working hours. Research suggests that reduced working hours could contribute to sustainability by decreasing the scale of economic output and the environmental intensity of consumption patterns. Here, we investigate the effect of working hours on three environmental indicators: ecological footprint, carbon footprint, and carbon dioxide emissions. Using data for 1970–2007, our panel analysis of 29 high-income OECD countries indicates that working hours are significantly associated with greater environmental pressures and thus may be an attractive target for policies promoting environmental sustainability.  相似文献   

Sensitivity of Solute Advective Travel Time to Porosities of Hydrogeologic Units     

Jianting Zhu  Karl F. Pohlmann  Jenny B. Chapman  Charles E. Russell  Rosemary W. H. Carroll  David S. Shafer 《Ground water》2010,48(3):442-447

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Palaeoglaciology of the last Irish ice sheet reconstructed from striae evidence     

M.J. Smith  J. Knight 《Quaternary Science Reviews》2011,30(1-2):147-160

A database comprising some ～5200 individual striation measurements on bedrock surfaces across the island of Ireland was used to produce maps of flowsets corresponding to individual ice flow events during the last (late Devensian) glacial cycle. These flowsets were identified on the basis of regional-scale correspondence between striae orientations which, when linked together spatially, are able to identify consistent ice flow vectors. Four main chronological stages are identified on the basis of this evidence: (i) incursion of Scottish ice into Ireland; (ii) glacial maximum conditions; (iii) ice retreat and dissolution; and (iv) development of localised ice domes. Striae-based reconstructions of the glaciology of the last Irish ice sheet are qualitatively different from those based on bedform (mainly drumlin and ribbed moraine) evidence. Significant differences are apparent in upland areas which have fewer preserved bedforms and a higher concentration of striae. Combining bedform and striae datasets will enable a better understanding of the temporal evolution of the ice sheet. It is likely that both datasets record a snapshot of ice flow direction and subglacial conditions and environments immediately prior to preservation of this directional evidence.  相似文献   

Assessing the ‘usability’ of climate change research for decision-making: A case study of the Canadian International Polar Year     

James D. Ford  Maggie Knight  Tristan Pearce 《Global Environmental Change》2013,23(5):1317-1326

The creation of ‘usable science’ is widely promoted by many environmental change focused research programs. Few studies however, have examined the relationship between research conducted as part of such programs and the decision-making outcomes that the work is supposed to advance, and is constrained by limited methodological development on how to empirically assess the ‘usability’ of science. Herein, this paper develops a conceptual model and assessment rubric to quantitatively and systematically evaluate the usability of climate change research for informing decision-making. We focus on the process through which data is collected, analyzed and reported and examine the extent to which key principles of usable science are integrated into project design, using grant proposals as our data source. The approach is applied to analyze climate change research conducted as part of the International Polar Year in Canada, with 23 projects identified as having explicit goals to inform decision-making.While the creation of usable science was promoted by funded projects in the International Polar Year, this was not generally reflected in research design: fewer than half determined objectives with input of decision makers, decision context was not widely considered, and knowledge users were not widely reported to be engaged in assessing the quality of data or in resolving conflict in evidence. The importance of science communication was widely emphasized, although only 8/23 projects discussed tailoring specific results for end user needs. Thus while International Polar Year research has made significant advances in understanding the human dimensions of Arctic climate change, key attributes necessary for determining success in linking science to decision-making (pertinence, quality, timeliness) were not captured by many projects. Integrating these attributes into research design from the outset is essential for creating usable science, and needs to be at the forefront of future research programs which aim to advance societal outcomes. The framework for assessing usability here, while developed and tested in an Arctic climate change context, has broader applicability in the general environmental change field.  相似文献   

A locally-constrained YOLO framework for detecting small and densely-distributed building footprints     

Yiqun Xie  Jiannan Cai  Rahul Bhojwani  Shashi Shekhar  Joseph Knight 《International journal of geographical information science》2020,34(4):777-801

ABSTRACT

Building footprints are among the most predominant features in urban areas, and provide valuable information for urban planning, solar energy suitability analysis, etc. We aim to automatically and rapidly identify building footprints by leveraging deep learning techniques and the increased availability of remote sensing datasets at high spatial resolution. The task is computationally challenging due to the use of large training datasets and large number of parameters. In related work, You-Only-Look-Once (YOLO) is a state-of-the-art deep learning framework for object detection. However, YOLO is limited in its capacity to identify small objects that appear in groups, which is the case for building footprints. We propose a LOcally-COnstrained (LOCO) You-Only-Look-Once framework to detect small and densely-distributed building footprints. LOCO is a variant of YOLO. Its layer architecture is determined by the spatial characteristics of building footprints and it uses a constrained regression modeling to improve the robustness of building size predictions. We also present an invariant augmentation based voting scheme to further improve the precision in the prediction phase. Experiments show that LOCO can greatly improve the solution quality of building detection compared to related work.  相似文献   

A bimillennial-length tree-ring reconstruction of precipitation for the Tavaputs Plateau, Northeastern Utah     

Troy A. Knight  David M. Meko 《Quaternary Research》2010,73(1):107-159

Despite the extensive network of moisture-sensitive tree-ring chronologies in western North America, relatively few are long enough to document climatic variability before and during the Medieval Climate Anomaly (MCA) ca. AD 800-1300. We developed a 2300-yr tree-ring chronology extending to 323 BC utilizing live and remnant Douglas-fir (Pseudotsuga menziesii) from the Tavaputs Plateau in northeastern Utah. A resulting regression model accounts for 70% of the variance of precipitation for the AD 1918-2005 calibration period. Extreme wet and dry periods without modern analogues were identified in the reconstruction. The MCA is marked by several prolonged droughts, especially prominent in the mid AD 1100s and late 1200s, and a lack of wet or dry single-year extremes. The frequency of extended droughts is not markedly different, however, than before or after the MCA. A drought in the early AD 500s surpasses in magnitude any other drought during the last 1800 yr. A set of four long high-resolution records suggests this drought decreased in severity toward the south in the western United States. The spatial pattern is consistent with the western dipole of moisture anomaly driven by El Niño and is also similar to the spatial footprint of the AD 1930s “Dust Bowl” drought.  相似文献   

Ground-based visible and near-IR observations of Comet 9P/Tempel 1 during the Deep Impact encounter     

Matthew M. Knight  Kevin J. Walsh  Robert A. Swaters  B. Ashley Zauderer  Roberto Vázquez 《Icarus》2007,187(1):199-207

We present the results of our visible and near-IR observations of Comet 9P/Tempel 1 during the Deep Impact encounter. The comet was observed before, during, and after impact from Kitt Peak National Observatory (J, H, K) and Observatorio Astronómico Nacional-San Pedro Mártir, Mexico (B, V, R, I). High time-resolution images in R, J, H, and K the night of impact with a 3^.″5 radius aperture revealed a rapid brightening which had multiple slopes and lasted for approximately 25 min before leveling off. The brightness decreased on subsequent nights and returned to near pre-impact levels by July 8 UT. The R-J, R-H, R-K, J-H, J-K, and H-K colors became bluer the night of impact. The R-J, R-H, and R-K colors remained blue on the night after impact while the J-H, J-K, and H-K colors returned to baseline levels. The observed color changes suggest the bluening was due to an increase in small grains relative to the ambient coma, an increase in ice relative to refractory dust in the coma, or a combination of the two. The ejecta were initially directed towards the southwest but had been driven southeast by solar radiation pressure by the second night after impact. The mean projected ejecta velocity was estimated at 0.20-0.23 km s⁻¹ over the first 24 h after impact.  相似文献