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121.
The creation and accumulation of nanophase iron (npFe0) is a principal mechanism by which spectra of materials exposed to the space environment incur systematic changes referred to as “space weathering.” Since there is no reason to assume that cumulative space weathering products throughout the Solar System will be the same as those found in lunar soils, these products are likely to be very dependent on the specific environmental conditions under which they were produced. We have prepared a suite of analog soils to explore the optical effects of npFe0. By varying the size and concentration of npFe0 in the analogs we found significant systematic changes in the Vis/NIR spectral properties of the materials. Smaller npFe0 (<10 nm in diameter) dramatically reddens spectra in the visible wavelengths while leaving the infrared region largely unaffected. Larger npFe0 (>40 nm in diameter) lowers the albedo across the Vis/NIR range with little change in the overall shape of the continuum. Intermediate npFe0 sizes impact the spectra in a distinct pattern that changes with concentration. The products of these controlled experiments have implications for space-weathered material throughout the inner Solar System. Our results indicate that the lunar soil continuum is best modeled by npFe0 particles with bulk properties in the 15–25 nm size range. Larger npFe0 grains result in spectra that are similar in shape to the Mercury continuum. The continuum of S-type asteroid spectra appear to be best represented by low abundances of npFe0. The size of asteroidal npFe0 is similar to that of lunar soils, but slightly smaller on average (10–15 nm). 相似文献
122.
Anders Levermann Jonathan L. Bamber Sybren Drijfhout Andrey Ganopolski Winfried Haeberli Neil R. P. Harris Matthias Huss Kirstin Krüger Timothy M. Lenton Ronald W. Lindsay Dirk Notz Peter Wadhams Susanne Weber 《Climatic change》2012,110(3-4):845-878
We discuss potential transitions of six climatic subsystems with large-scale impact on Europe, sometimes denoted as tipping elements. These are the ice sheets on Greenland and West Antarctica, the Atlantic thermohaline circulation, Arctic sea ice, Alpine glaciers and northern hemisphere stratospheric ozone. Each system is represented by co-authors actively publishing in the corresponding field. For each subsystem we summarize the mechanism of a potential transition in a warmer climate along with its impact on Europe and assess the likelihood for such a transition based on published scientific literature. As a summary, the ‘tipping’ potential for each system is provided as a function of global mean temperature increase which required some subjective interpretation of scientific facts by the authors and should be considered as a snapshot of our current understanding. 相似文献
123.
124.
DEM smoothing is a common pre-processing technique used to remove undesirable roughness from a DEM. However, it is hypothesized that smoothing straightens and reduces the length of overland flow paths, which is an important factor controlling modelled time-to-peak flow. Currently, there is a lack of research comparing how different smoothing techniques alter the distribution of overland flow path length. Four low-pass filtering techniques were applied to three fine-resolution LiDAR DEMs of varying relief: the mean filter, the median filter, the Gaussian filter, and the feature-preserving DEM smoothing (FPDEMS) filter, each with different degrees of smoothing. Downslope-distance-to-stream distributions were then derived using D8 and D∞ flow directions and statistically compared to distributions derived from the unsmoothed DEM for each study site. The results indicate that the alteration of flow path length distributions as a result of smoothing is complex. Mean flow path lengths may decrease or increase in response to smoothing, depending on landscape relief and the derivation of flow directions, and generalized flow paths may become longer. The largest increase in mean flow path lengths was 19.2 m using the 21 × 21 median filter and D8 flow directions in the high-relief study site, relative to an unsmoothed mean length of 138.6 m in this site. The largest decrease in mean flow path length was 48.9 m using the 21 × 21 mean filter and D∞ flow directions in the low-relief study site, relative to an unsmoothed mean length of 290.9 m in this site. Furthermore, minimal flow path length alterations were achieved with the Gaussian filter when gentle smoothing is required, and with the FPDEMS filter when moderate to aggressive smoothing is required. These results suggest that an appropriate smoothing method should be chosen based on the relief of the landscape and the degree of smoothing required. 相似文献
125.
Characterizing ephemeral streams in a southern Ontario watershed using electrical resistance sensors 下载免费PDF全文
Ephemeral streams are small headwater streams that only experience streamflow in response to a precipitation event. Due to their highly complex and dynamic spatial and temporal nature, ephemeral streams have been difficult to monitor and are in general poorly understood. This research implemented an extensive network of electrical resistance sensors to monitor three ephemeral streams within the same small headwater catchment in Southern Ontario, Canada. The results suggest that the most common patterns of network expansion and contraction in the studied streams are incomplete coalescence and disintegration, respectively. Binary logistic regression analysis of the primary controls on ephemeral streamflow showed only weak Nagelkerke R2 values, suggesting that there are more complex processes at work in these ephemeral streams. A comparison of all three streams suggests that even ephemeral streams within the same subwatershed may experience differences in network expansion and contraction and may be dominated by different spatial and temporal controls. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
126.
Sean S. Lindsay Tasha L. Dunn Joshua P. Emery Neil E. Bowles 《Meteoritics & planetary science》2016,51(4):806-817
Near‐infrared reflectance spectra of S‐type asteroids contain two absorptions at 1 and 2 μm (band I and II) that are diagnostic of mineralogy. A parameterization of these two bands is frequently employed to determine the mineralogy of S(IV) asteroids through the use of ordinary chondrite calibration equations that link the mineralogy to band parameters. The most widely used calibration study uses a Band II terminal wavelength point (red edge) at 2.50 μm. However, due to the limitations of the NIR detectors on prominent telescopes used in asteroid research, spectral data for asteroids are typically only reliable out to 2.45 μm. We refer to this discrepancy as “The Red Edge Problem.” In this report, we evaluate the associated errors for measured band area ratios (BAR = Area BII/BI) and calculated relative abundance measurements. We find that the Red Edge Problem is often not the dominant source of error for the observationally limited red edge set at 2.45 μm, but it frequently is for a red edge set at 2.40 μm. The error, however, is one sided and therefore systematic. As such, we provide equations to adjust measured BARs to values with a different red edge definition. We also provide new ol/(ol+px) calibration equations for red edges set at 2.40 and 2.45 μm. 相似文献
127.
Heterogeneous histories of Ni‐bearing pyrrhotite and pentlandite grains in the CI chondrites Orgueil and Alais 下载免费PDF全文
Eve L. Berger Dante S. Lauretta Thomas J. Zega Lindsay P. Keller 《Meteoritics & planetary science》2016,51(10):1813-1829
Compositional and structural analyses of CI chondrite iron–nickel sulfide grains reveal heterogeneity both across and within the Orgueil and Alais meteorites. Orgueil grains with the 4C monoclinic pyrrhotite structure have variable metal‐to‐sulfur ratios and nickel contents. These range from the nominal ratio of 0.875 for Fe7S8 with <1 atom% nickel to a high metal‐to‐sulfur ratio of 0.97 with 15 atom% nickel. These data reveal a previously unrecognized low‐temperature solid solution between Fe7S8 and Fe5Ni3S8. We have also identified 6C monoclinic pyrrhotite among the Orgueil iron–nickel sulfides. The occurrence of pentlandite in Orgueil is confirmed for the first time crystallographically. In contrast, sulfide grains in Alais do not show the same spread in composition and structure; rather they represent the endmembers: low‐Ni 4C monoclinic pyrrhotite and pentlandite. We investigate possible formation/alteration scenarios: crystallization from a melt, solid‐state diffusion and/or exsolution, oxidation of pre‐existing sulfides, and precipitation from a fluid. Sulfide grains are sensitive to alteration conditions; these data suggest that the structures and compositions of the sulfide assemblages in Orgueil and Alais were established by late‐stage parent body aqueous alteration, followed in some cases by low‐temperature solid‐state processes. The samples record different alteration histories, with Orgueil experiencing lower equilibration temperatures (25 °C) than Alais (100–135 °C). We conclude that millimeter‐scale heterogeneity existed in alteration conditions (e.g., temperature, pH, oxygen fugacity, sulfur fugacity, duration of alteration) on the parent body. This variability is evidenced by the diversity among sulfide grains located within millimeters of one another. 相似文献
128.
Geotechnical Risk Assessment of Mine Development Intersections with Respect to Mining Sequence 总被引:2,自引:2,他引:0
Wael Abdellah Hani S. Mitri Denis Thibodeau Lindsay Moreau-Verlaan 《Geotechnical and Geological Engineering》2014,32(3):657-671
Mine developments such as haulage drifts and their intersections with cross-cuts are the only stope access in sub-level stoping mining system. Thus, they must remain stable during their service life. Haulage drift instability could lead to serious consequences such as: production delay, damage to equipment, loss of reserves and high operational cost. The goal of this paper is the stability of mine developments with respect to mining sequence with focus on the performance of haulage drift intersection during the production plan. A case study, the #1 Shear East orebody at Vale’s Garson Mine in Sudbury Ontario will be examined in this paper. A three-dimensional, elastoplastic, finite difference code (FLAC3D) is used for this study. The extent of strength-to-stress ratio corresponds to Mohr–Coulomb strength-to-stress ratio of 1.4 is used as failure evaluation criterion. The unsatisfactory performance is reached when the extent of strength-to-stress ratio exceeds the anchorage limit of the rockbolt. Stochastic analysis; adopting point-estimate method, is then employed with the numerical modelling to tackle the inherent uncertainty associated with rockmass properties. Then, the probability of instability at various mining steps is estimated for the roof and north wall of the studied intersection. The cost of consequence models is introduced to provide an economical solution if the intersection failed, blocked or damaged. Furthermore, the geotechnical risk associated with the instability of mine development intersection is estimated using risk-indexing tool. The results are presented and categorized in terms of probability, cost of consequence and risk-index at various mining stages. 相似文献
129.
In the southern Northwest Territories (NWT), long time series of historical observations of climate and hydrology are scarce. Gridded datasets have been used as an alternative to instrumental observations for climate analysis in this area, but not for driving models to understand hydrological processes in the southern NWT. The suitability of temperature and precipitation from three-gridded datasets (Australian National University Spline [ANUSPLIN], ERA-Interim, and Modern-Era Retrospective Analysis for Research and Application, Version 2 [MERRA-2]) as forcings for hydrological modelling in a small subcatchment in the southern NWT are assessed. Multiple statistical techniques are used to ensure that structural and temporal attributes of the observational datasets are adequately compared. Daily minimum and maximum air temperatures in gridded datasets are more similar to observations than precipitation. The ANUSPLIN temperature time series are more statistically similar to observations, based on population statistics and temporal structure, than either of ERA-Interim or MERRA-2. The gridded datasets capture the seasonal and annual seasonal variability of precipitation but with large biases. ANUSPLIN precipitation compares better with observations than either ERA-Interim or MERRA-2 precipitation. The biases in these gridded datasets affect run-off simulations. The biases in hydrological simulations are predictable from the statistical differences between gridded datasets and observations and can be used to make informed choices about their use. 相似文献
130.
Thomas R. Gregory Christopher W. Smart Malcolm B. Hart Guillaume Massé Lindsay L. Vare Simon T. Belt 《第四纪科学杂志》2010,25(7):1192-1192