Pentlandite sulfur core electron binding energies     

Siew Wei Goh  Alan N. Buckley  Robert N. Lamb  Liang-Jen Fan  Ling-Yun Jang  Yaw-wen Yang 《Physics and Chemistry of Minerals》2006,33(7):445-456

A number of freshly abraded surfaces of pentlandite have been characterised by X-ray photoelectron spectroscopy to establish whether the initial intensity of the S 2p component near 161.4 eV, previously assigned to the 25% of S atoms in fourfold coordination by metal atoms in pentlandite, was always at least 25% of the total S 2p intensity. It was found that the intensity of this S 2p component could be lower than 20% for surfaces that were not significantly oxidised. To assess whether the proposed 0.75–0.8 eV 2p binding energy difference for the two sulfur environments in pentlandite was justified, ab initio calculations of the difference in core electron binding energies and of the densities of unfilled states have been carried out. The corresponding simulated S K near-edge X-ray absorption fine structure (NEXAFS) spectra have been compared with experimental spectra. The calculated S 2p and S 1s binding energy differences were 0.45 and 0.5 eV at most, in agreement with the experimental NEXAFS spectra. It was concluded that the S 2p component near 161.4 eV arises entirely from violarite present at the pentlandite surface rather than from 4-coordinate S in pentlandite itself. Ab initio calculations of the difference in S 2p binding energies for the 2- and 3-coordinate S in stibnite have also been carried out and found to be quite small, in agreement with previously reported experimental values. Nevertheless, for both pentlandite and stibnite, calculations have confirmed that an increase in coordination number is associated with an increase in sulfur core electron binding energies, even although that increase is barely measurable for the latter sulfide.  相似文献   

Spatial scale and measuring segregation: illustrated by the formation of Chicago’s ghetto     

Ron Johnston  David Manley  Kelvyn Jones 《GeoJournal》2018,83(1):73-85

Few studies of residential segregation in cities have directly addressed the issue of spatial scale, apart from noting that the traditional indices of segregation tend to be larger when calculated for small rather than large spatial units. That observation however ignores Duncan et al.’s (Statistical geography: problems in analyzing areal data. Free Press, Glencoe, 1961) explication that any measure of segregation at a fine-grained scale necessarily incorporates, to an unknown extent, segregation at a larger scale within which the finer-grained units are nested. To avoid that problem, a multi-level modelling perspective is introduced that identifies the intensity of segregation at each scale net of its intensity at any larger scale included in the analysis. It is applied to an analysis of the emergence of Chicago’s Black ghetto over the twentieth century’s first three decades, using data at the ward and ED scales. It shows that across Chicago as a whole segregation was equally as intense at the two scales, with statistically significant increases in that intensity at both scales across the three decades. At the finer scale, however, segregation was much more intense across the EDs within those wards that formed the core of the emerging ghetto than it was in the remainder of the city.  相似文献   

Inverse modeling of velocities and inferred cause of overwash that emplaced inland fields of boulders at Anegada, British Virgin Islands     

Mark L. Buckley  Yong Wei  Bruce E. Jaffe  Steve G. Watt 《Natural Hazards》2012,63(1):133-149

A combination of numeric hydrodynamic models, a large-clast inverse sediment-transport model, and extensive field measurements were used to discriminate between a tsunami and a storm striking Anegada, BVI a few centuries ago. In total, 161 cobbles and boulders were measured ranging from 1.5 to 830?kg at distances of up to 1?km from the shoreline and 2?km from the crest of a fringing coral reef. Transported clasts are composed of low porosity limestone and were derived from outcrops in the low lying interior of Anegada. Estimates of the near-bed flow velocities required to transport the observed boulders were calculated using a simple sediment-transport model, which accounts for fluid drag, inertia, buoyancy, and lift forces on boulders and includes both sliding and overturning transport mechanisms. Estimated near-bed flow velocities are converted to depth-averaged velocities using a linear eddy viscosity model and compared with water level and depth-averaged velocity time series from high-resolution coastal inundation models. Coastal inundation models simulate overwash by the storm surge and waves of a category 5 hurricane and tsunamis from a Lisbon earthquake of M 9.0 and two hypothetical earthquakes along the North America Caribbean Plate boundary. A modeled category 5 hurricane and three simulated tsunamis were all capable of inundating the boulder fields and transporting a portion of the observed clasts, but only an earthquake of M 8.0 on a normal fault of the outer rise along the Puerto Rico Trench was found to be capable of transporting the largest clasts at their current locations. Model results show that while both storm waves and tsunamis are capable of generating velocities and temporal acceleration necessary to transport large boulders near the reef crest, attenuation of wave energy due to wave breaking and bottom friction limits the capacity of storm waves to transport large clast at great inland distances. Through sensitivity analysis, we show that even when using coefficients in the sediment-transport model which yield the lowest estimated minimum velocities for boulder transport, storm waves from a category 5 hurricane are not capable of transporting the largest boulders in the interior of Anegada. Because of the uncertainties in the modeling approach, extensive sensitivity analyses are included and limitations are discussed.  相似文献   

Preface     

Ron Li 《Marine Geodesy》2013,36(1)

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Dietary niche separation of three Late Pleistocene bear species from Vancouver Island,on the Pacific Northwest Coast of North America     

Cara Kubiak  Vaughan Grimes  Geert Van Biesen  Grant Keddie  Mike Buckley  Reba Macdonald  M. P. Richards 《第四纪科学杂志》2023,38(1):8-20

Competition between taxa related to climate changes has been proposed as a possible factor in Pleistocene megafaunal extinctions, and here we present isotope evidence of the diets of three co-existing bear species [black bear (Ursus americanus), brown bear (Ursus arctos), and the now extinct short-faced bear (Arctodus simus)] from a locale in western North America dating to the Late (Terminal) Pleistocene (~14.5–11.7 ka). The three bear species were found at several sites on Vancouver Island, on the western coast of Canada. To examine the chronological overlap and niche partitioning between these species of bear, we used direct radiocarbon dating, stable isotope analysis and ZooMS proteomic identification methods. Here we present new radiocarbon evidence from Terminal Pleistocene U. americanus, U. arctos and A. simus from several sites on the island, along with both bulk collagen and compound-specific isotope data for these species. Radiocarbon dates confirm the chronological overlap of Arctodus and both Ursus species in the montane regions of the island at the end of the Pleistocene. Stable isotope data reveal niche differentiation between these species, with U. americanus occupying a distinctly lower trophic position than the other two taxa.  相似文献