The impact of permanganate on the ability of granular iron to degrade trichloroethene     

Geoffrey J. Okwi  Neil R. Thomson  Robert W. Gillham 《Ground Water Monitoring & Remediation》2005,25(1):123-128

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Surface elevation dynamics in vegetatedSpartina marshes versus unvegetated tidal ponds along the Mid-Atlantic coast, USA, with implications to waterbirds   总被引：1，自引：0，他引：1  

R. Michael Erwin  Donald R. Cahoon  Diann J. Prosser  Geoffrey M. Sanders  Phillippe Hensel 《Estuaries and Coasts》2006,29(1):96-106

Mid Atlantic coastal salt marshes contain a matrix of vegetation diversified by tidal pools, pannes, and creeks, providing habitats of varying importance to many species of breeding, migrating, and wintering waterbirds. We hypothesized that changes in marsh elevation were not sufficient to keep pace with those of sea level in both vegetated and unvegetatedSpartina alterniflora sites at a number of mid lagoon marsh areas along the Atlantic Coast. We also predicted that northern areas would suffer less of a deficit than would southern sites. Beginning in August 1998, we installed surface elevation tables at study sites on Cape Cod, Massachusetts, southern New Jersey, and two locations along Virginia's eastern shore. We compared these elevation changes over the 4–4.5 yr record with the long-term (>50 yr) tidal records for each locale. We also collected data on waterbird use of these sites during all seasons of the year, based on ground surveys and replicated surveys from observation platforms. Three patterns of marsh elevation change were found. At Nauset Marsh, Cape Cod, theSpartina marsh surface tracked the pond surface, both keeping pace with regional sea-level rise rates. In New Jersey, the ponds are becoming deeper while marsh surface elevation remains unchanged from the initial reading. This may result in a submergence of the marsh in the future, assuming sea-level rise continues at current rates. Ponds at both Virginia sites are filling in, while marsh surface elevation rates do not seem to be keeping pace with local sea-level rise. An additional finding at all sites was that subsidence in the vegetated marsh surfaces was less than in unvegetated areas, reflecting the importance of the root mat in stabilizing sediments. The implications to migratory waterbirds are significant. Submergence of much of the lagoonal marsh area in Virginia and New Jersey over the next century could have major negative (i.e., flooding) effects on nesting populations of marsh-dependent seaside sparrowsAmmodramus maritimus, saltmarsh sharp-tailed sparrowsAmmodramus caudacutus, black railsLaterallus jamaicensis, clapper railsRallus longirostris. Forster's ternsSterna forsteri, common ternsSterna hirundo, and gull-billed ternsSterna nilotica. Although short-term inundation of many lagoonal marshes may benefit some open-water feeding ducks, geese, and swans during winter, the long-term ecosystem effects may be detrimental, as wildlife resources will be lost or displaced. With the reduction in area of emergent marsh, estuarine secondary productivity and biotic diversity will also be reduced.  相似文献   

Abiogenic Origin of Hydrocarbons: An Historical Overview   总被引：1，自引：0，他引：1  

Geoffrey P. Glasby 《Resource Geology》2006,56(1):83-96

Abstract. The two theories of abiogenic formation of hydrocarbons, the Russian-Ukrainian theory of deep, abiotic petroleum origins and Thomas Gold's deep gas theory, have been considered in some detail. Whilst the Russian-Ukrainian theory was portrayed as being scientifically rigorous in contrast to the biogenic theory which was thought to be littered with invalid assumptions, this applies only to the formation of the higher hydrocarbons from methane in the upper mantle. In most other aspects, in particular the influence of the oxidation state of the mantle on the abundance of methane, this rigour is lacking especially when judged against modern criteria as opposed to the level of understanding in the 1950s to 1980s when this theory was at its peak. Thomas Gold's theory involves degassing of methane from the mantle and the formation of higher hydrocarbons from methane in the upper layers of the Earth's crust. However, formation of higher hydrocarbons in the upper layers of the Earth's crust occurs only as a result of Fischer-Tropsch-type reactions in the presence of hydrogen gas but is otherwise not possible on thermodynamic grounds. This theory is therefore invalid. Both theories have been overtaken by the increasingly sophisticated understanding of the modes of formation of hydrocarbon deposits in nature.  相似文献   

Glaciology of the British Isles Ice Sheet during the last glacial cycle: form, flow, streams and lobes     

Geoffrey Boulton  Magnus Hagdorn 《Quaternary Science Reviews》2006,25(23-24):3359

The last ice sheet over the British Isles, together with other mid-latitude Pleistocene ice sheets, and in contrast to the modern ice sheets of Greenland and Antarctica, had a relatively low profile, low summit elevation and extensive, elongated lobes at its margin. A thermo-mechanically coupled numerical ice sheet model, driven by a proxy climate, has been used to explore the properties that would have permitted these characteristics to develop. The approach, the key to quantitative palaeoglaciology, is to determine the boundary conditions that permit the simulated ice sheet to mimic the evolution of the real ice sheet through the last glacial cycle. Simulations show how a British ice sheet may have been confluent with a Scandinavian ice sheet during some parts of its history and how unforced periodic and asynchronous oscillations could occur in different parts of its margins. Marginal lobes are a reflection of streaming within the ice sheet. Such streams can be ephemeral, dynamic streams located because of ice sheet properties, or fixed streams whose location is determined by bed properties. The simulations that best satisfy constraints of extent, elevation and relative sea levels are those with major fixed streams that strongly draw down the ice sheet surface. In these, the core upland areas of the ice sheet were cold based at the Last Glacial Maximum, basal streaming velocities were between 500 and 1000 ma⁻¹ compared with surface velocities of 10–50 ma⁻¹ in inter-stream zones, shear stresses were as low as 15–25 kPa in streams compared with 70–110 kPa in upland areas and 60–84% of the ice flux was delivered to the margin via streams.  相似文献   

Morphology and sedimentology of a tributary confluence bar in a regulated river: North Tyne,U.K.     

Geoffrey E. Petts  Martin C. Thoms 《地球表面变化过程与地形》1987,12(4):433-440

The form and structure of a tributary confluence bar in a regulated channel are analysed and related to channel adjustment to the imposed flow regime. The bar is characterized by a tripartite structure with two facies, and by marked lateral coarsening, characteristics which relate to the changing hydraulic conditions within the narrowing channel form.  相似文献   

The kinematics of gouge deformation   总被引：13，自引：0，他引：13  

Charles Sammis  Geoffrey King  Ronald Biegel 《Pure and Applied Geophysics》1987,125(5):777-812

The methods and first results of a new approach to examining fault gouge are described. Samples of undisturbed fault gouge from the exhumed Lopez fault zone in the San Gabriel Mountains, California were impregnated with low viscosity epoxy resin and sectioned to produce microscope slides. The slides were photographed using optical and electron microscopy with magnifications ranging in factors of 2 from 12.5 to 1600. At all scales, the particles appeared angular with planar faces, suggesting tensile failure. No shear zones were discernable. The particle size distribution was studied. At each magnification the particles were sorted by diameter into four classes, differing in mean diameter by factors of 2. The numbers in each class were then scaled by the characteristic class dimension. The process revealed a remarkable degree of self-similarity. Over the range examined, the fractal dimension was within 5% of 2.60.On the basis of the observations, a new model for the mechanical processes that generate gouge is offered. It is argued that self-similarity results from repeated tensile splitting of grains. Unlike earlier models that consider splitting probability to be either independent of particle size or due to the preexisting distribution of defects, we propose that failure probability depends largely on the relative size of nearest neighbors. If nearest neighbors of the same size are preferentially broken, any initial distribution of particles will tend toward a self-similar distribution having a fractal dimension of 2.58.The model allows us to outline a procedure whereby the observed comminution in a fault zone can be related to the shear strain that the zone has accommodated and propose a theoretical frequency magnitude relation for the seismic energy emitted by the fracture process.  相似文献   

The theory of motion of the horizontal pendulum with a Zöllner suspension and some indications for the instrumental design     

Petr Vaníček  Geoffrey W. Lennon  Reviewer M. Schneider  Reviewer L. Skalský 《Studia Geophysica et Geodaetica》1972,16(1):30-50

Summary The aim of this paper is to examine the physical laws which govern the motion of a horizontal pendulum, mounted with the familiar Zöllner suspension geometry and to establish the equations of its motion. It is possible in this process to determine calibration parameters with greater precision and confidence and to demonstrate that procedures based upon period measurement can inherently claim a precision superior to some modern alternatives. Moreover in approaching the problem from a theoretical viewpoint it is possible to pinpoint those features of design which give rise to the troublesome aberrations. This facility makes it possible to comment upon design improvements so that a closer approach may be made to an ideal instrument.  相似文献   

An evaluation of three-body interatomic forces and formulation of a general model     

Geoffrey F. Davies 《Physics and Chemistry of Minerals》1981,7(6):246-252

Several deficiencies are demonstrated in previous formulations of three-body interatomic forces, and revised and extended formulations are presented for the case of the NaCl lattice. A commonly used formulation of non-central forces and a formulation of the effect of ellipsoidal atom deformation are incorrect. Atom deformation should in general introduce two degrees of freedom in the NaCl lattice, but the only previous correct formulation of deformation effects, the commonly used “breathing shell model,” includes only one degree of freedom. The “shell model” of polarizable atoms has been correctly formulated, but applications seem to have been arbitrarily restricted to the case where short-range forces act only on shells, and not on cores. Because of these errors and incompletenesses, it is concluded that no three-body forces have been convincingly established or characterized, although the necessity of their inclusion in models is clear.  相似文献   

Trade-offs between mitigation costs and temperature change     

Geoffrey Blanford  James Merrick  Richard Richels  Steven Rose 《Climatic change》2014,123(3-4):527-541

This paper uses the MERGE integrated assessment model to identify the least-cost mitigation strategy for achieving a range of climate policies. Mitigation is measured in terms of GDP foregone. This is not a benefit-cost analysis. No attempt is made to calculate the reduction in damages brought about by a particular policy. Assumptions are varied regarding the availability of energy-producing and energy-using technologies. We find pathways with substantial reductions in temperature change, with the cost of reductions varying significantly, depending on policy and technology assumptions. The set of scenarios elucidates the potential energy system transformation demands that could be placed on society. We find that policy that allows for “overshoot” of a radiative forcing target during the century results in lower costs, but also a higher temperature at the end of the century. We explore the implications of the costs and availability of key mitigation technologies, including carbon capture and storage (CCS), bioenergy, and their combination, known as BECS, as well as nuclear and energy efficiency. The role of “negative emissions” via BECS in particular is examined. Finally, we demonstrate the implications of nationally adopted emissions timetables based on articulated goals as a counterpoint to a global stabilization approach.  相似文献   

Harmonization vs. fragmentation: overview of climate policy scenarios in EMF27     

Geoffrey J. Blanford  Elmar Kriegler  Massimo Tavoni 《Climatic change》2014,123(3-4):383-396

This paper synthesizes results of the multi-model Energy Modeling Forum 27 (EMF27) with a focus on climate policy scenarios. The study included two harmonized long-term climate targets of 450 ppm CO₂-e (enforced in 2100) and 550 pm CO₂-e (not-to-exceed) as well as two more fragmented policies based on national and regional emissions targets. Stabilizing atmospheric GHG concentrations at 450 and 550 ppm CO₂-e requires a dramatic reduction of carbon emissions compared to baseline levels. Mitigation pathways for the 450 CO₂-e target are largely overlapping with the 550 CO₂-e pathways in the first half of the century, and the lower level is achieved through rapid reductions in atmospheric concentrations in the second half of the century aided by negative anthropogenic carbon flows. A fragmented scenario designed to extrapolate current levels of ambition into the future falls short of the emissions reductions required under the harmonized targets. In a more aggressive scenario intended to capture a break from observed levels of stringency, emissions are still somewhat higher in the second half due to unabated emissions from non-participating countries, emphasizing that a phase-out of global emissions in the long term can only be reached with full global participation. A key finding is that a large range of energy-related CO₂ emissions can be compatible with a given long-term target, depending on assumptions about carbon cycle response, non-CO₂ and land use CO₂ emissions abatement, partly explaining the spread in mitigation costs.  相似文献