Place and Health: Towards a Reformed Medical Geography*   总被引：1，自引：0，他引：1  

Robin A. Kearns 《The Professional geographer》1993,45(2):139-147

An engagement with public health concerns and aspects of social theory such as the structure/agency debate is crucial to medical geography. The imperatives underlying this engagement center on place, a geographical concept which is prominent in both social theory and recent health philosophy. Without detracting from its distinguished heritage, this reformed medical geography will analyze issues such as the consequences of illness and health service provision for both personal well-being and the collective experience of place by communities.  相似文献   

Computer simulation of nearshore bar formation     

Robin G. D. Davidson-Arnott 《地球表面变化过程与地形》1981,6(1):23-34

A computer simulation model, developed from a conceptual model of sediment transport patterns associated with nearshore bars, is presented. The model simulates wave shoaling, breaking and reformation along a profile normal to the shore from deep water to the beach and determines rates and directions of sediment transport under wave orbital currents and rip cell circulation. The model successfully generates a barred profile from an initial planar profile and under most conditions achieves a state of dynamic equilibrium with sediment circulating across the bars. Input values for wave height, wave period, offshore slope and tidal range were varied in turn in order to determine their individual effect on the shape of the equilibrium profile formed. Breaker type—spilling or plunging—is incorporated in the model and also appears to be a significant factor in determining the shape of the equilibrium profile.  相似文献   

Clarke and Law comment as follows     

Andrew Clarke  Robin Law 《Marine pollution bulletin》1981,12(12):409-410

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Theory of metamorphic segregation and related processes     

Pierre-Yves F. Robin 《Geochimica et cosmochimica acta》1979,43(10):1587-1600

Metamorphic segregation is defined here as the formation and growth of bands or domains of different bulk compositions within an originally unbanded rock. It can result from an instability arising in some deforming rocks when diffusion transfer is significant. The nature of this instability is demonstrated separately for a differentiation associated with a crenulation (Type C) and for one without crenulation (Type L). However, the continuous gradation between the two types observed in nature is also expected from the models.A requirement for both types is that one chemical component of the rock, typically silica, diffuse more rapidly than others, e.g. phyllosilicate components, in response to stress-induced pressure gradients. In addition, Type L requires that, at least at an early stage, portions of the rock rich in this mobile component, e.g. rich in quartz, be more competent than those portions which are poor in quartz. By a process akin to the development of pressure shadows, silica diffuses toward domains which are already the richest in quartz. Alternatively, if the rock is chemically open to loss of silica, this silica preferentially originates from dissolution of quartz in the more mica-rich domains. In either case the compositional contrast between domains is increased and metamorphic segregation results. Type C differentiation is best explained if we accept the suggestion made by many petrographers that layer silicates catalyse the pressure-induced transfer of silica. This suggestion can in fact account for other features of metamorphic segregation bands.Metamorphic segregation should also proceed during the development of quartz segregations, quartz rods, slaty cleavage and mylonite banding. The stress distribution argued for Type L bands may also occur in many banded migmatites. In migmatites. however, the assemblage crystallizing in the leucosome may be derived from a circulating hydrothermal fluid as well as from diffusion transfer.  相似文献   

Unconformities as mineralogical breaks in the burial metamorphism of the Andes     

Luis Aguirre  Beatriz Levi  Robin Offler 《Contributions to Mineralogy and Petrology》1978,66(4):361-366

Stratigraphical-structural units separated by regional unconformities in the Andes of Peru and Chile, display a pattern of low grade burial metamorphism. Each stratigraphical-structural unit shows a particular facies series covering part or all the range between the zeolite and the greenschist facies. These facies series were episodically generated as part of the geological evolution of each unit prior to its own folding. Mineralogical breaks are found to coincide with the regional unconformities and often cases of higher grade assemblages on top of lower grade ones occur. This pattern may be explained by a process of sealing of each unit after its particular metamorphic episode took place. Porosity and permeability conditioning P _f, as demonstrated for individual lava flows, are the significant controlling factors in the production of the metamorphic assemblages.  相似文献   

Thicknesses of some lunar mare basalt flows and ejecta blankets based on chemical kinetic data     

Robin Brett 《Geochimica et cosmochimica acta》1975,39(8):1135-1141

Data on the kinetics of some chemical reactions occurring in lunar samples are used to estimate cooling rates over limited temperature ranges. These results, together with data on thermal conductivity and specific heats of lunar samples, have been applied to estimate the thicknesses of the cooling units.Estimates for mare basalts indicate that they were derived from cooling units no thicker than 10 m. Breccias are derived from cooling units up to a few meters in thickness. This suggests that most lunar breccias are the product of a series of relatively local events rather than large basin-forming events. If this conclusion is correct, the significance of the radiometric ages of lunar breccias needs to be re-evaluated, as does the assignment of breccias to individual basin-forming events on the basis of their trace element contents. If the breccias are a product of the major basin-forming events, it is unlikely that so many would show an age of about 4.0 b.y. It is likely that a large proportion of materials sampled would have escaped resetting by these major events, and a wider spread of ages would be observed. Attempts to link a given breccia to a specific basin-forming event on the basis of its crystallization age therefore appear to be unfounded.  相似文献   

A lunar rock of deep crustal origin: sample 76535     

R Gooley  Robin Brett  Jeff Warner  J.R Smyth 《Geochimica et cosmochimica acta》1974,38(9):1329-1339

Lunar sample 76535 is a coarse-grained troctolitic granulite exhibiting a texture indicative of long annealing times. It is composed of homogeneous crystals of plagioclase (58 per cent, An₉₆), olivine (37 per cent, Fo₈₈) and bronzite (4 per cent, En₈₆).Chromian spinel-bronzite-diopside (Wo₄₆En₅₀Fs₄) symplectic intergrowths commonly occur along olivine-plagioclase boundaries and as tiny inclusions within olivine grains. These symplectites apparently formed by a reaction of the type: . The reaction is related to the experimentally determined reaction of Kushiro and Yoder (1966). The enstatite content of the diopside coexisting with the bronzite indicates equilibration at about 1000°C. Thermodynamic calculations for 1000°C indicate that the symplectites formed at a minimum pressure of about 0.6 kb. Low alumina contents of the pyroxenes indicate equilibration near this minimum pressure.Clusters of the same assemblage found in the symplectic intergrowths, but containing accessory metal, troilite, Ca-phosphates, baddeleyite, plagioclase and/or K-feldspar occur sporadically throughout the rock. These apparent late stage products crystallized in the low temperature-high pressure region discussed above.Phase relations of co-existing metal phases indicate that the rock cooled at a few tens of degrees/my, corresponding to depths of 10–20 km below the lunar surface, in agreement with the above pressure estimate.We infer that 76535 represents an original cumulate deposited at a depth between about 10 and 30 km. The last liquid crystallized in the relatively high pressure-low temperature field opx + cpx + Al-Mg-chromite. Cooling was extremely slow and accompanied by extensive chemical and textural re-equilibration. Reaction to form the symplectites occurred during the late stages of re-equilibration.  相似文献   

Komatiites and nickel sulfide ores of the Black Swan area,Yilgarn Craton,Western Australia. 3: Komatiite geochemistry,and implications for ore forming processes     

Stephen?J.?BarnesEmail author  Robin?E.?T.?Hill  Noreen?J.?Evans 《Mineralium Deposita》2004,39(7):729-751

The Black Swan komatiite sequence is a package of dominantly olivine-rich cumulates with lesser volumes of spinifex textured rocks, interpreted as a section through an extensive komatiite lava flow field. The sequence hosts a number of nickel sulfide orebodies, including the Silver Swan massive shoot and the Cygnet and Black Swan disseminated orebodies. A large body of whole rock analyses on komatiitic rocks from the Black Swan area has been filtered for metasomatic effects. With the exception of mobile elements such as Ca and alkalis, most samples retain residual igneous geochemistry, and can be modelled predominantly by fractionation and accumulation of olivine. Whole rock MgO–FeO relationships imply a relatively restricted range of olivine compositions, more primitive than the olivine which would have been in equilibrium with the transporting komatiite lavas, and together with textural data indicate that much of the cumulus olivine in the sequence was transported. Flow top compositions show evidence for chromite saturation, but the cumulates are deficient in accumulated chromite. Chromite compositions are typical of those found in compound flow-facies komatiites, and are distinct from those in komatiitic dunite bodies. Incompatible trace element abundances show three superimposed influences: control by the relative proportion of olivine to liquid; a signature of crustal contamination and an overprint of metasomatic introduction of LREE, Zr and Th. This overprint is most evident in cumulates, and relatively insignificant in the spinifex rocks. Platinum and palladium behaved as incompatible elements and are negatively correlated with MgO. They show no evidence for wholesale depletion due to sulfide extraction, which was evidently restricted to specific lava tubes or pathways. The lack of correspondence between PGE depletion and contamination by siliceous material implies that contamination alone is insufficient to generate S-saturation and ore formation in the absence of sulfide in the assimilant. Contamination signatures in spinifex-textured rocks may be a guide to Ni-sulfide mineralisation, but are not entirely reliable in the absence of other evidence. The widespread vesicularity of the sequence may be attributable to assimilated water rather than to primary mantle-derived volatiles, and cannot be taken as evidence for primary volatile-rich magmas. The characteristic signature of the Black Swan Succession is the presence of highly localised disseminated sulfide within a sequence showing more widespread evidence for crustal contamination and interaction with its immediate substrate. This has important implications for the applicability of trace element geochemistry in exploration for komatiite-hosted nickel deposits.Electronic Supplementary Material Supplementary material is available in the online version of this article at Editorial handling: Peter Lightfoot  相似文献   

Evaluation of bioremediation strategies of a controlled oil release in a wetland   总被引：1，自引：0，他引：1  

Mills MA  Bonner JS  Page CA  Autenrieth RL 《Marine pollution bulletin》2004,49(5-6):425-435

A controlled petroleum release was conducted to evaluate bioremediation in a wetland near Houston, Texas. The 140-day study was conducted using a randomized, complete block design to test three treatments with six replicates per treatment. The three treatment strategies were inorganic nutrients, inorganic nutrients with an alternative electron acceptor, and a no-action oiled control. Samples were analyzed for petroleum chemistry and inorganic nutrients. These results are discussed in the context of our related research involving toxicology and microbiology at the site during the experiment. To evaluate biodegradation, the targeted compounds were normalized to the conservative compound C3017alpha, 21beta-[H]hopane, thus reducing the effects of spatial heterogeneity and physical transport. The two biostimulation treatments demonstrated statistically-higher rates of biodegradation than the oiled no-action control. For the majority of the experiment, target nutrient levels were maintained. Further research may be warranted to optimize these bioremediation strategies as well as evaluating additional treatment strategies for wetlands and other shoreline systems.  相似文献   

The loss of the chemical tanker Ievoli Sun in the English Channel,October 2000     

Law RJ  Kelly C  Matthiessen P  Aldridge J 《Marine pollution bulletin》2003,46(2):254-257

A chemical product tanker, The Ievoli Sun, was abandoned and later sank approximately 11 miles NW of Alderney in the English Channel in October 2000. The vessel carried a mixed cargo comprising 4000 tonnes of styrene, and 1000 tonnes each of methyl ethyl ketone and isopropyl alcohol. These chemicals are of low to moderate toxicity to aquatic life, are not persistent and have a low potential for bio-accumulation. Both of the solvents are miscible in water, whilst styrene is practically insoluble and, following release, it will rise to the sea surface and rapidly evaporate. More than 1000 tonnes of styrene are believed to have been lost to sea during the incident, resulting in an aerial plume of vapour which crossed Alderney and episodic contamination of air and water in the immediate vicinity of the wreck site. Analysis of edible tissues using coupled gas chromatography/mass spectrometry demonstrated low-level styrene contamination of crabs recovered from pots laid very close to the wreck site prior to the incident. These concentrations posed no risks to human consumers, and no fishery controls were implemented. The remainder of the styrene and the ship's main bunker fuel were recovered from the wreck on the seabed, whilst the two chemical solvents were released to the water column in a slow, controlled manner.  相似文献