The relationship between gravity and bathymetry in the Pacific Ocean   总被引：2，自引：0，他引：2  

A. B. Watts  D. P. McKenzie  B. E. Parsons  M. Roufosse 《Geophysical Journal International》1985,83(1):263-298

Summary. Surface-ship and satellite derived data have been compiled in new free-air gravity anomaly, bathymetry and geoid anomaly maps of the Pacific Ocean basin and its margin. The maps are based on smoothed values of the gravity anomaly, bathymetry and geoid interpolated on to a 90 × 90 km grid. Each smoothed value was obtained by Gaussian filtering measurements along individual ship and subsatellite tracks. The resulting maps resolve features in the gravity, bathymetry and geoid with wavelengths that range from a few hundred to a few thousand kilometres. The smoothed values of bathymetry and geoid anomaly have been corrected for age. The resulting maps show the Pacific ocean basin is associated with a number of ENE–WSW-trending geoid anomaly highs with amplitudes of about ± 5 m and wavelengths of about 3000 km. The most prominent of these highs correlate with the Magellan seamounts–Marshall Gilbert Islands–Magellan rise and the Hess rise–Hawaiian ridge regions. The correlation between geoid anomaly and bathymetry cannot be explained by models of static compensation, but is consistent with a model in which the geoid anomaly and bathymetry are supported by some form of dynamic compensation. We suggest that the dynamic compensation, which characterizes oceanic lithosphere older than 80 Myr, is the result of mantle convection on scales that are smaller than the lithospheric plates themselves.  相似文献   

A tilted Bianchi type-V perfect fluid solution for stiff matter     

Grant Baillie  Mark S. Madsen 《Astrophysics and Space Science》1985,115(2):413-415

We present a solution to the Einstein field equations for a massless scalar field in a Bianchi type-V spacetime, which can be interpreted as a solution for a perfect fluid with the equation of state of stiff matter. This solution complements a solution previously given by us for an anisotropic fluid.  相似文献   

Conference review: Wallace E. Pratt memorial conference on future petroleum provinces of the world 2–5 December, 1984, Phoenix,Arizona, USA     

A.C. Grant 《Marine and Petroleum Geology》1985,2(2):189-190

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Recolonization of Intertidal Infauna in Relation to Organic Deposition at an Oyster Farm in Atlantic Canada—A Field Experiment     

Lin Lu  Jon Grant 《Estuaries and Coasts》2008,31(4):767-775

A field experiment was carried out to investigate the patterns of macrobenthic recolonization and to determine the effects of biodeposition on benthic communities at an intertidal oyster culture site in New Brunswick, Canada. Total organic deposition in azoic organic-free sediment trays was generally higher within the farm compared to reference sites. Two weeks after deployment of trays, total organic content had reached 1.1%. The abundance, species number, and diversity of the macrobenthic community were positively correlated with the total organic content in the experimental trays, but the correlations between community parameters and organic content were negative in the ambient sediment. The results suggest that organic matter in sediment may have positive effects on macrobenthic infauna at low levels as an additional food source but may be harmful to benthic animals at high levels. This study also indicates that location in the intertidal zone is a major parameter affecting the community structure of macrobenthic colonization.  相似文献   

Reactive flow models of the Anarraaq Zn–Pb–Ag deposit,Red Dog district,Alaska     

Christian Schardt  Grant Garven  Karen D. Kelley  David L. Leach 《Mineralium Deposita》2008,43(7):735-757

The Red Dog ore deposit district in the Brooks Range of northern Alaska is host to several high-grade, shale-hosted Zn + Pb deposits. Due to the complex history and deformation of these ore deposits, the geological and hydrological conditions at the time of formation are poorly understood. Using geological observations and fluid inclusion data as constraints, numerical heat and fluid flow simulations of the Anarraaq ore deposit environment and coupled reactive flow simulations of a section of the ore body were conducted to gain more insight into the conditions of ore body formation. Results suggest that the ore body and associated base metal zonation may have formed by the mixing of oxidized, saline, metal-bearing hydrothermal fluids (<200°C) with reducing, HS-rich pore fluids within radiolarite-rich host rocks. Sphalerite and galena concentrations and base metal sulfide distribution are primarily controlled by the nature of the pore fluids, i.e., the extent and duration of the HS⁻ source. Forward modeling results also predict the distribution of pyrite and quartz in agreement with field observations and indicate a reaction front moving from the initial mixing interface into the radiolarite rocks. Heuristic mass calculations suggest that ore grades and base metal accumulation comparable to those found in the field (18% Zn, 5% Pb) are predicted to be reached after about 0.3 My for initial conditions (30 ppm Zn, 3 ppm Pb; 20% deposition efficiency).  相似文献   

Habitat use by small mammals in coastal marshes of Southwestern Louisiana     

Richard P. Martin  Robert B. Hamilton  Paul M. McKenzie  Robert H. Chabreck  David A. Dell 《Estuaries and Coasts》1991,14(1):107-110

A short-term study based on snap-trap capture rates of small mammals in the marsh and levee system in southwestern Louisiana was conducted in the winter-spring period. Marsh rice rats (Oryzomys palustris) dominated marsh habitats and rice rats and fulvous harvest mice (Reithrodontomys fulvescens) were co-dominants on levees. Least shrews (Cryptotis parva) and house mice (Mus musculus) were also taken. Although rice rat capture rate in marshes was twice that from levees, the difference was not significant (p=0.1428). When found on levees, rice rats preferred portions of levees adjacent to marshes and canals (p<0.0001). We found few differences in rice rat capture rates from marsh and levee habitats, although capture rates from fresh marsh and adjacent levees were select levee ridges over the marsh and canal edges (0.1≥p≥0.05). The abundance of harvest mice on levees adjacent to intermediate marshes exceeded all other levee habitats. For reasons as yet unexplained, intermediate marshes and adjacent levees had the highest small mammal abundance and species richness. Conversely, fresh marshes and their adjacent levees had the lowest abundance and variety of small mammals.  相似文献   

Sulfur isotope evidence for penetration of MVT fluids into igneous basement rocks,southeast Missouri,USA     

K. L. Shelton  I. B. Burstein  R. D. Hagni  C. B. Vierrether  S. K. Grant  Q. T. Hennigh  M. F. Bradley  R. T. Brandom 《Mineralium Deposita》1995,30(5):339-350

Previous studies of galena and sphalerite from Paleozoic MVT deposits in the Viburnum Trend, southeast Missouri documented large variations in ³⁴S values throughout the ore-forming event. The present study of Cu-Fe-sulfides reveals a similar ³⁴S variation that reflects two end-member sulfur reservoirs whose relative importance varied both temporally and spatially. More ³⁴S-enriched sulfides (³⁴S approaching 25) indicate introduction of sulfur from basinal sedimentary sources, whereas more ³²S-enriched sulfides (³⁴S < 5) may reflect fluids moving through underlying granitic basement. Two areas containing Precambrian, igneous-hosted FeCu mineralization in southeast Missouri (West and Central Domes of Boss-Bixby) were investigated to elucidate their relationship to Cu-rich MVT orebodies hosted nearby within the overlying Cambrian Bonneterre Dolomite. Mineralization at Boss-Bixby is composed of an early phase of iron oxide deposition followed by Cu-Fe-sulfides. The Central Dome is faulted and its mineralization is more fracture-controlled than the typically podiform ores of the West Dome. The ³⁴S values of West Dome sulfides are 0.9 to 6.5 and pyrite-chalcopyrite indicate a temperature of 525° ± 50 °C. These data indicate an igneous source of sulfur during Precambrian ore deposition. In contrast, ³⁴S values of Central Dome sulfides are 9.4 to 20.0 and pyrite-chalcopyrite indicate temperatures of 275° ± 50 °C. Similar ³⁴S values are obtained for chalcopyrite from the overlying MVT deposits. We speculate that deeply circulating, basin-derived MVT fluids mobilized sulfur and copper from the underlying igneous basement and redeposited them in overlying Curich MVT orebodies, as well as overprinting earlier Precambrian sulfides of the Central Dome with a later, Paleozoic MVT sulfur isotope signature. Many models for MVT fluid circulation in the Midcontinent region of North America assume that igneous basement rocks are an impermeable boundary, but in southeast Missouri, evidence exists for structurally controlled MVT fluid movement > 600 m vertically through underlying Precambrian igneous rocks. Such basement involvement has been suggested for other carbonate-hosted base-metal districts (e.g. Irish base metal deposits) and should be considered an integral part of the ore-forming process in southeast Missouri.  相似文献   

Spatial signatures for geographic feature types: examining gazetteer ontologies using spatial statistics   总被引：1，自引：0，他引：1       下载免费PDF全文

Rui Zhu  Yingjie Hu  Krzysztof Janowicz  Grant McKenzie 《Transactions in GIS》2016,20(3):333-355

Digital gazetteers play a key role in modern information systems and infrastructures. They facilitate (spatial) search, deliver contextual information to recommended systems, enrich textual information with geographical references, and provide stable identifiers to interlink actors, events, and objects by the places they interact with. Hence, it is unsurprising that gazetteers, such as GeoNames, are among the most densely interlinked hubs on the Web of Linked Data. A wide variety of digital gazetteers have been developed over the years to serve different communities and needs. These gazetteers differ in their overall coverage, underlying data sources, provided functionality, and geographic feature type ontologies. Consequently, place types that share a common name may differ substantially between gazetteers, whereas types labeled differently may, in fact, specify the same or similar places. This makes data integration and federated queries challenging, if not impossible. To further complicate the situation, most popular and widely adopted geo‐ontologies are lightweight and thus under‐specific to a degree where their alignment and matching become nothing more than educated guesses. The most promising approach to addressing this problem, and thereby enabling the meaningful integration of gazetteer data across feature types, seems to be a combination of top‐down knowledge representation with bottom‐up data‐driven techniques such as feature engineering and machine learning. In this work, we propose to derive indicative spatial signatures for geographic feature types by using spatial statistics. We discuss how to create such signatures by feature engineering and demonstrate how the signatures can be applied to better understand the differences and commonalities of three major gazetteers, namely DBpedia Places, GeoNames, and TGN.  相似文献   

An archetype hydrogen atmosphere problem     

R. Grant Athay  Dimitri Mihalas  R. A. Shine 《Solar physics》1975,45(1):15-23

Populations for the first three bound states and the continuum of hydrogen are determined for an isothermal, hydrostatic atmosphere at 20 000 K. The atmosphere is treated as being optically thin in the Balmer and Paschen continua and illuminated by continuum radiation at these wavelengths with prescribed radiation temperatures. The atmosphere is optically thick in the 2-1, 3-1, 3-2 and c-1 transitions. Three stages of approximation are treated:

1. radiative detailed balance in the 2-1, 3-1 and 3-2 transitions,
2. radiative detailed balance in the 3-1 and 3-2 transitions, and
3. all transitions out of detailed balance.

The solution of this problem is non-trivial, and presents sufficient difficulty to have caused failure of at least one rather standard technique. The problem is thus a good archetype against which new methods, or new implementations of old methods may be tested.  相似文献   

Physical conditions in eruptive prominences at several solar radii     

Rainer M. E. Illing  R. Grant Athay 《Solar physics》1986,105(1):173-190

SMM data from the Corograph/Polarimeter experiment giving intensities of H and continuum emission in eight erupting prominences are analyzed to obtain the physical conditions in the regions of H emission. Since the H intensity depends upon three unknowns whereas only two independent observations are available, it is necessary to assume one additional condition in order to obtain unique solutions. Solutions are chosen that give the maximum expansion of the prominence volume as reflected by minimum values of the electron density. These solutions correspond closely with those giving the best agreement between the gas pressure in the prominence and the ambient coronal pressure. Electron densities are found to be of the order of 10⁸ cm^-3 at temperatures near 2 × 10⁴ K.The National Center for Atmospheric Research is operated by the University Corporation for Atmospheric Research under sponsorship of the National Science Foundation.  相似文献