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51.
J. A. Sanchidrián P. Segarra F. Ouchterlony L. M. López 《Rock Mechanics and Rock Engineering》2009,42(1):95-116
Summary Size distributions of fragments of crushed rock in conveyor belts and of blasted rock in a muckpile obtained by sieving are
compared with the size distributions obtained by digital image analysis of photographs of the same materials taken on-site.
Several calculation methods are tested, based on the raw distribution of fragment areas and on the volume-transformed ones.
The influence of the calibration of the system on the results and the performance of the system in a non-calibrated mode are
evaluated. The capacity of some distributions (Rosin-Rammler, Swebrec and lognormal) to fit the data in the coarse region
(where particles can be delineated, i.e. discriminated individually) and to extrapolate to the non-delineated fines (where
particles cannot be outlined and their contour delineated) is assessed. The error between the sizes measured and the sizes
of the reference distributions (determined by sieving) increases from the coarse to the fines region. The maximum error at
a given size depends primarily on its value relative to the fines cut-off (FCO) of the image analysis. In general, at sizes
greater than the FCO, where the system is able to delineate fragments reliably, both volume and surface-based, calibrated,
calculations can determine the sizes with maximum error expectancy of about 30%. Below the FCO, only the calibrated, volume
calculation maintains a maximum error of 30%, down to sizes of about one fourth the FCO, rapidly increasing for smaller sizes.
Where the calibration is done based on data above the FCO, errors can be large below this point, in excess of 80% at sizes
half the FCO. In the fines range (sizes smaller than 0.2 times the FCO) the maximum errors can be close to or greater than
100% for most of the calculations and function fittings. Of the distributions tested, all of them are acceptable at sizes
above the FCO; below that, the Swebrec function seems to adapt better towards the fines than the Rosin-Rammler and lognormal.
Correspondence: José A. Sanchidrián, Universidad Politécnica de Madrid, E.T.S.I. Minas, Rios Rosas 21, 28003 Madrid, Spain 相似文献
52.
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54.
Herbert W. Schnopper Eric Silver Stephen Murray Suzanne Romaine Simon Bandler Christine Jones William Forman Norman Madden Jeffery Beeman Eugene Haller Finn Christensen Niels Westergaard Juan Fabregat Victor Reglero Alvaro Gimenez Noah Brosch Elia Liebowitz Hagai Netzer Marco Barbera Alfonso Collura Salvatore Sciortino 《Astrophysics and Space Science》2001,276(1):49-65
The X-Ray Spectroscopic Explorer (XRASE) has a unique combination of features that will make it possible to address many of NASA's scientific goals. These include how galaxy clusters form, the physics and chemistry of the ISM, the heating of stellar coronae, the amount and content of intergalactic baryonic matter, the mass of black holes and the formation of disks and jets in AGN and galactic binaries. XRASE has a thin foil, multilayered telescope with a large collecting area up to 10 keV, especially in the Fe K region (1100 cm2). Its microcalorimeter array combines high energy resolution (7 eV at 6 keV) and efficiency with a field-of-view of 26 arcmin2 . A deep orbit allows for long, continuous observations. Monitoring instruments in the optical (WOM-X), UV (TAUVEX) and hard X-RAY (GRAM) bands will offer exceptional opportunities to make simultaneous multi-wavelength observations. 相似文献
55.
Comparison of the relative abundance of fish species from different life-history groups and their temporal patterns of estuarine habitat use from two estuaries north and south of Cape Cod indicates that the Cape acts as a zoogeographic boundary. Between April 1988 and December 1989, monthly seine and trawl samples were collected from nearshore, shallow-water marsh, and beach and deeper open-water habitats in Wells Harbor, Maine, and Waquoit Bay, Massachusetts. Forty-eight species and 80,341 individuals were collected from Waquoit Bay compared to 24 species and 22,561 individuals from Wells Harbor. Waquoit Bay had proportionally fewer resident species and more marine, nursery, and occasional species than Wells Harbor. Annual density and biomass values were greater across all habitats in Waquoit Bay, with the summer values from the marsh habitat an order of magnitude higher than comparable summer data from the Wells habitats. We suggest that marsh and beach habitats provide a nursery area for young-of-the-year fishes, while deeper, open-water habitats serve as a corridor for fishes moving to nearshore habitats or serve as a refuge during low tide. 相似文献
56.
W. D. Liam Finn 《Pure and Applied Geophysics》2003,160(10-11):1879-1894
— Landslide-induced tsunamis are particularly dangerous because the warning time is very short in the coastal area. Therefore it is critical to identify the potential for coastal landslides involving large masses of material. Almost invariably such large landslides will occur in material susceptible to liquefaction, particularly during earthquakes. This paper discusses characteristics of such materials, how they may be identified, and offers suggestions for estimating the potential for large deformations. 相似文献
57.
The Maastrichtian chalk of the southern Central Graben, Danish North Sea, is a homogeneous pure white coccolithic chalk mudstone deposited in a deep epeiric shelf sea, which covered large parts of northern Europe. The sediment displays a pronounced cyclicity marked by decimetre‐thick bioturbated beds alternating with slightly thinner non‐bioturbated, mainly laminated beds. The laminated half‐cycles consist of alternating millimetre‐thick, graded, high‐porosity laminae and non‐graded, low‐porosity laminae. The cyclicity has been interpreted previously as caused by periods of slow background sedimentation and bioturbation interrupted by periods of rapid deposition of laminated beds, with the latter reflecting random and local resedimentation processes. Based on textural and structural analysis, the millimetre‐scale, non‐graded laminae are interpreted as having been deposited directly from pelagic rain of pelleted coccoliths representing the primary production. The graded laminae were deposited from small‐volume, low‐density turbidity currents and suspension clouds. The sedimentation rates of the cyclical chalk are similar to those known elsewhere, and the lamination is interpreted as having been preserved from destruction through bioturbation by anoxic conditions at the seafloor. Bioturbated–laminated cycles are thus formed by slow sedimentation during alternating seafloor redox conditions probably on a Milankovitch scale. A direct implication of this interpretation is that the cycles are areally widespread, probably extending throughout the southern Central Graben area and may be useful for correlation and high‐resolution cyclostratigraphy in the chalk fields of the Danish North sea. If the laminated half‐cycles represent a few rapid resedimentation events, with a high sedimentation rate as suggested by most workers, then the sediment would not be truly cyclic, but would represent event sedimentation within a pelagic background represented by the bioturbated beds. In this case, the cycles would have very limited potential for correlation. 相似文献
58.
Paul H. Warren Finn Ulff-Møller Heinz Huber Gregory W. Kallemeyn 《Geochimica et cosmochimica acta》2006,70(8):2104-2126
New bulk-compositional data, including trace siderophile elements such as Ir, Os, Au, and Ni, are presented for 25 ureilites. Without exception, ureilites have siderophile abundances too high to plausibly have formed as cumulates. Ureilites undoubtedly underwent a variety of “smelting,” by which C was oxidized to CO gas while olivine FeO was reduced to Fe-metal. However, pressure-buffered equilibrium smelting is not a plausible model for engendering the wide range (75-96 mol%) of mafic-silicate core mg among ureilites. The smelting reaction produces too much CO gas. Even supposing a disequilibrium process with the smelt-gas leaking out of the mantle, none of the ureilites, least of all the ureilite with the most “reduced” (highest) olivine-core mg (ALH84136), has the high Fe-metal abundance predicted by the smelted-cores model. In principle, the Fe-metal generated by smelting could have been subsequently lost, but siderophile data show that ureilites never underwent efficient depletion of Fe-metal. Ureilites display strong correlations among siderophile ratios such as Au/Ir, Ni/Ir, Co/Ir, As/Ir, Se/Ir, and Sb/Ir. Ureilite siderophile depletion patterns loosely resemble siderophile fractionations, presumably nebular in origin, among carbonaceous chondrites. However, Zn, for an element of moderate volatility, is anomalously high in ureilites. A tight correlation between Au and Ni extrapolates to the low-Ni/Au side of the compositional range of carbonaceous chondrites. From this mismatch, mild but nonetheless significant depletions of refractory siderophile elements such as Ir and Os, and moderate depletions of strongly siderophile, weakly chalcophile elements such as Ni and Au, we infer that the ureilite siderophile fractionations are largely the result of a non-nebular process, i.e., removal of S-rich metallic melt, possibly with minor entrainment of Fe-metal. Several lines of trace-element evidence indicate that melt porosity during ureilite anatexis was at least moderate. The ureilite pattern of very mild depletions of extremely siderophile elements, but much deeper depletions of moderately siderophile, chalcophile elements, suggests that asteroidal core formation probably occurs in two discrete stages. In general, separation of a considerable proportion (several wt%) of S-rich metallic melt probably occurs long before, and at a far lower temperature than, separation of the remaining S-poor Fe-metal. Apart from the Fe-metal itself, only extremely siderophile elements wait until the second stage to sequester mainly into the core. 相似文献
59.
We present a cylindrically symmetric model for a sunspot atmosphere using the similarity principle of Schlüter and Temesvary for the magnetic field configuration. The equations of magnetostatic equilibrium are used, augmented by a radial Evershed flow. The LTE radiative transfer equations for the Stokes vector were solved under a variety of conditions for a ray emerging from a typical penumbral point. The contribution from isolated lines to the broadband circular polarization in sunspot penumbrae is evaluated using a more realistic model sunspot atmosphere than has hitherto been considered. Results indicate that the inclusion of a velocity field along B is unable to give a net circular polarization of sufficient magnitude, although the variation with the angle between the line-of-sight and B is in qualitative agreement with observations. The corresponding results for the net linear polarization are satisfactory. 相似文献
60.
Christian Zeeden Ulrich Hambach Nicole Klasen Peter Fischer Philipp Schulte Janina J. Nett Daniel Veres Igor Obreht Wei Chu Maria Papadopoulou Finn Viehberg Frank SchÄBitz Milivoj B. Gavrilov Slobodan B. MarkoviĆ Andreas VÖTT Frank Lehmkuhl 《第四纪科学杂志》2021,36(8):1414-1425
The Upper Pleistocene geoarchives in the south-eastern Carpathian Basin are represented predominantly by loess–palaeosol records. In 2015, a 10 m sediment core composed of clay-rich lacustrine sediments was recovered by vibracoring a dry lake basin located between the Vršac Mountains (Serbia) and the Banat Sands in the south-eastern Carpathian Basin; a location relevant for placing regional archaeological results in a palaeoenvironmental context. Here, we present results from geoelectrical prospection and a lithostratigraphic interpretation of this sequence supported by a detailed granulometric study supplemented by ostracod analysis. An age model based on luminescence dating is discussed against sedimentological proxy data and its implication for palaeoenvironmental change. The cores show a stratigraphy of lighter ochre-coloured and darker greyish sediment, related to the deposition of clay and silt trapped in an aquatic environment. Geophysical measurements show ~20 m thick lacustrine sediments. The grain-size distributions including the variability in fine clay are indicative of a lacustrine environment. Fine particles were brought into the depositional environments by aquatic input and settled from suspension; also, direct dust input is constrained by grain-size results. Riverine input and aeolian dust input interplayed at the locality. 相似文献