Measurement of water content as a control of particle entrainment by wind     

Cheryl McKenna Neuman  Greg Langston 《地球表面变化过程与地形》2006,31(3):303-317

Of all controls on particle transport by wind, which include texture, crusting, vegetation cover and roughness, the role of water content is one of the most difficult to parameterize because of its high degree of spatial and temporal variability and its operation at a particle‐scale level directly at the surface. This study demonstrates that measurement of the distribution of brightness for all pixels in an image, now routinely employed in digital photography, is strongly correlated with gravimetric water content. Wind tunnel experiments further suggest that measurement of the distribution of β, as normalized against the brightness of the dry sand surface, is very useful in determining the order of magnitude of the mass transport rate (q). Finer resolution will likely never be achieved because of the heterogeneity of the particle transport phenomenon. Analysis of the variability in surface brightness does suggest that q is governed by the partitioning of momentum to particle motion that terminates in adhesion to surrounding areas of the surface that remain relatively wet. The proportion of surface particles that becomes dry appears to be of less importance. Preliminary work suggests that field application of digital photography in tracking spatial and temporal changes in the water content of beach deposits looks promising. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Water and Radioactive Tracer Flow in a Heterogeneous Field-Scale System   总被引：1，自引：0，他引：1  

Frank M. Dunnivant  Meredith E. Newman  Carolyn W. Bishop  Dave Burgess  John R. Giles  Brian D. Higgs  Joel M. Hubbell  Erick Neher  Greg T. Norrell  M. Cathy Pfiefer  Indrek Porro  Robert C. Starr  Allan H. Wylie 《Ground water》1998,36(6):949-958

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Damage to structures by pyroclastic flows and surges, inferred from nuclear weapons effects     

Greg A. Valentine 《Journal of Volcanology and Geothermal Research》1998,87(1-4)

In order to define the risk from explosive eruptions, one must constrain both the probability of explosive events and the effects, or consequences, of those events. This paper focuses on the effects of pyroclastic flows and surges (here termed ‘pyroclastic density currents', or PDCs) on buildings, infrastructure elements, and to some extent on vehicles. PDCs impart a lateral force to such structures in the form of dynamic pressure, which depends on the bulk density of the PDC (which in turn depends mainly on particle concentration) and its velocity. For reasonable ranges of particle concentration (10⁻³ to 0.5) and velocities (10 to 300 m/s), dynamic pressure on the upstream face of a structure ranges from 0.1 kPa to 10⁴ kPa. Lateral loads ranging up to about 100 kPa were produced during nuclear weapons tests in the 1940s and 1950s that were designed to study the effects of such loading on a variety of structures for civil defense and emergency response purposes in the event of nuclear war. Although considerable simplifications are involved, the data from these weapon tests provide useful analog information for understanding the effects of PDCs. I reviewed data from the nuclear tests, describing the expected damage from different loadings. Tables are provided that define the response of different structural elements (e.g., windows, framing, walls) and whole structures to loading in probabilistic terms, which in principle account for variations in construction quality, orientation, and other factors. Finally, damage documented from historical eruptions at Mt. Lamington (1951), Herculaneum (AD 79 Vesuvius eruption), and St. Pierre (1902 Mt. Pelee eruption) is reviewed. Damage patterns, combined with estimates of velocity, provide an independent estimate of particle concentration in the PDCs. Details of structural damage should be recorded and mapped around future eruptions in order to help refine this aspect of consequence analysis. Another fruitful approach would be to combine numerical simulations of eruption scenarios, which can produce simulated maps of dynamic pressure, with GIS-based data on structures for a given region; the result would be predictions of consequences that could be used for planning and emergency response training.  相似文献   

U-Pb ages and tectonomagmatic relationships of early Ordovician low-Ti tholeiites, boninites and related plutonic rocks in central Newfoundland, Canada     

Kate MacLachlan  Greg Dunning 《Contributions to Mineralogy and Petrology》1998,133(3):235-258

The Wild Bight Group (WBG) and South Lake Igneous Complex (SLIC) together comprise one of the Ordovician accreted oceanic terranes of the central mobile belt of the Newfoundland Appalachians. Combined detailed mapping, geochemistry, Sm-Nd isotopic studies and U-Pb geochronology have shown that sheeted dykes and hornblende diorite and tonalite plutons of the SLIC are genetically related to a discrete package of volcanic rocks in the WBG. These igneous rocks are geochemically, isotopically and temporally distinct from volcanic rocks in the rest of the WBG. Plutonic rocks of the SLIC range in age from 486 ± 3 Ma to 489 ± 3 Ma, and a cross-cutting gabbro dyke gives a minimum age of 486 ± 4 Ma for the related volcanic sequence. Volcanic rocks in the rest of the WBG sequence are predominantly younger than 472 ± 3 Ma. The older volcanic sequence of the WBG and the SLIC occur as fault-bounded packages interleaved within the younger WBG sequence. A conformable stratigraphic relationship between the older and younger sequences of the WBG has not been demonstrated. The mafic rocks of the older package include boninites and low-Ti, high-Mg tholeiitic island arc basalts which are interpreted to be genetically related, and normal island arc tholeiites (IAT). The high-Mg mafic rocks are interpreted to have formed in an extensional setting during subduction zone initiation, and the normal IAT are thought to represent stabilisation of the volcanic front. The associated high-Si, low-K rhyolite and tonalite are interpreted to be the products of secondary melting at the base of thickened early arc crust. Sm-Nd isotopic compositions indicate that the characteristic trace element signature of the boninites developed at or near their time of generation and was not a long lived characteristic of the source region. The boninites and low-Ti tholeiites are interpreted to have originated from a similar source, which was metasomatized by different subduction-related components. Apparent decoupling of Sm-Nd geochemical and isotopic compositions suggests that these very depleted rocks may be recording the effect of subduction zone processes not yet fully understood. Received: 31 October 1997 / Accepted: 6 May 1998  相似文献   

X-ray and soft γ-ray spectra of broad-line radio galaxies     

Przemys&#;aw R. Wo&#;niak  rzej A. Zdziarski  David Smith  Greg M. Madejski  & W. Neil Johnson 《Monthly notices of the Royal Astronomical Society》1998,299(2):449-466

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Multiphase Numerical Simulation of Air Sparging Performance   总被引：2，自引：0，他引：2  

Paul D. Lundegard  Greg Andersen 《Ground water》1996,34(3):451-460

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Reply to CJN Wilson's comment on “Stratified flow in pyroclastic surges”     

Greg A. Valentine 《Bulletin of Volcanology》1988,50(5):352-355

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Discussion on: Guest Editorial, "Reliable Monitoring in Karst Terranes: It Can Be Done But Not by an EPA-Approved Method" by James F. Quinlan and Ralph Ewers in the Winter Issue of Ground Water Monitoring Review     

Greg Powell  John H. Mann  P.G. 《Ground Water Monitoring & Remediation》1986,6(3):35-35

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Grid transformation for incorporating the Arctic in a global ocean model   总被引：2，自引：0，他引：2  

Michael Eby  Greg Holloway 《Climate Dynamics》1994,10(4-5):241-247

A grid transformation is described which isolates the Arctic and North Atlantic, rotates the spherical grid to pass an equator up the Atlantic through the north pole and remaps the Coriolis parameter. Boundary condition information is exchanged along the equatorial Atlantic so that the Arctic-Atlantic model is dynamically coupled to a model of the rest of the global ocean (which remains on the geographic spherical grid). The transform produces a more regular grid over the Arctic and eliminates the need for filtering or special treatment at the pole. The transform has been implemented in the GFDL Modular Ocean Model. After testing with idealized geometry, a 300 y global integration is compared to an integration using the geographic spherical grid and Fourier filtering. Results are similar, with differences in the Arctic and western North Atlantic regions leading to smaller air-sea heat flux near the Gulf Stream separation latitude for the transform case. Use of the transform also leads to a reduction in computation time.  相似文献   

Diagenetic overprinting of the sphaerosiderite palaeoclimate proxy: are records of pedogenic groundwater δ18O values preserved?     

David F. Ufnar  Luis A. González†‡  Greg A. Ludvigson‡§¶  Robert L. Brenner¶  Brian J. Witzke§¶ 《Sedimentology》2004,51(1):127-144

Meteoric sphaerosiderite lines (MSLs), defined by invariant δ¹⁸O and variable δ¹³C values, are obtained from ancient wetland palaeosol sphaerosiderites (millimetre‐scale FeCO₃ nodules), and are a stable isotope proxy record of terrestrial meteoric isotopic compositions. The palaeoclimatic utility of sphaerosiderite has been well tested; however, diagenetically altered horizons that do not yield simple MSLs have been encountered. Well‐preserved sphaerosiderites typically exhibit smooth exteriors, spherulitic crystalline microstructures and relatively pure (> 95 mol% FeCO₃) compositions. Diagenetically altered sphaerosiderites typically exhibit corroded margins, replacement textures and increased crystal lattice substitution of Ca²⁺, Mg²⁺ and Mn²⁺ for Fe²⁺. Examples of diagenetically altered Cretaceous sphaerosiderite‐bearing palaeosols from the Dakota Formation (Kansas), the Swan River Formation (Saskatchewan) and the Success S2 Formation (Saskatchewan) were examined in this study to determine the extent to which original, early diagenetic δ¹⁸O and δ¹³C values are preserved. All three units contain poikilotopic calcite cements with significantly different δ¹⁸O and δ¹³C values from the co‐occurring sphaerosiderites. The complete isolation of all carbonate phases is necessary to ensure that inadvertent physical mixing does not affect the isotopic analyses. The Dakota and Swan River samples ultimately yield distinct MSLs for the sphaerosiderites, and MCLs (meteoric calcite lines) for the calcite cements. The Success S2 sample yields a covariant δ¹⁸O vs. δ¹³C trend resulting from precipitation in pore fluids that were mixtures between meteoric and modified marine phreatic waters. The calcite cements in the Success S2 Formation yield meteoric δ¹⁸O and δ¹³C values. A stable isotope mass balance model was used to produce hyperbolic fluid mixing trends between meteoric and modified marine end‐member compositions. Modelled hyperbolic fluid mixing curves for the Success S2 Formation suggest precipitation from fluids that were < 25% sea water.  相似文献