A comparison of methods for evaluating soil redistribution in the severely eroded Stavropol region, southern European Russia   总被引：3，自引：1，他引：3  

V.R. Belyaev  P.J. Wallbrink  V.N. Golosov  A.S. Murray  A.Yu. Sidorchuk 《Geomorphology》2005,65(3-4):173-193

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Simulations of superhumps and superoutbursts     

Murray 《Monthly notices of the Royal Astronomical Society》1998,297(1):323-333

We numerically study the tidal instability of accretion discs in close binary systems using a two-dimensional SPH code. We find that the precession rate of tidally unstable, eccentric discs does not only depend upon the binary mass ratio q . Although the (prograde) disc precession rate increases with the strength of the tidal potential, we find that increasing the shear viscosity ν also has a significant prograde effect. Increasing the disc temperature has a retrograde impact upon the precession rate.   We find that motion relative to the binary potential results in superhump-like, periodic luminosity variations in the outer reaches of an eccentric disc. The nature and location of the luminosity modulation are functions of ν. Light curves most similar to observations are obtained for ν values appropriate for a dwarf nova in outburst.   We investigate the thermal–tidal instability model for superoutburst. A dwarf nova outburst is simulated by instantaneously increasing ν, which causes a rapid radial expansion of the disc. Should the disc encounter the 3: 1 eccentric inner Lindblad resonance and become tidally unstable, then tidal torques become much more efficient at removing angular momentum from the disc. The disc then shrinks and M _d increases. The resulting increase in disc luminosity is found to be consistent with the excess luminosity of a superoutburst.  相似文献   

Using an approximation of the three-point Gauss–Hermite quadrature formula for model prediction and quantification of uncertainty     

Jonathan Levy  Murray K. Clayton  Gordon Chesters 《Hydrogeology Journal》1998,6(4):457-468

 Computer models are commonly used by regulators and managers to make predictions regarding groundwater flow and contaminant concentrations at various locations and times. However, the uncertainty associated with those predictions is often overlooked, despite the fact that an assessment of such uncertainty is critical in the formulation of policy decisions. One method of quantifying the uncertainty of model predictions, based on the collective uncertainties of the model parameter input values, is to use an approximation of the three-point Gauss–Hermite quadrature formula. The Gauss–Hermite approximation is a convenient substitute for simple Monte Carlo sampling, because it requires fewer model runs and provides an immediate sensitivity analysis of parameter main effects and two-way interactions. For example, a model with four parameters, each with its own associated uncertainty, needs to be run only 33 times to complete the Gauss–Hermite analysis. For an application to a contaminant-transport model, the Gauss–Hermite approximation compares well to the full method, with considerable savings in computing effort. By comparison, Latin hypercube sampling can be more flexible, but it is more complex to use in some circumstances and cannot as easily generate the detailed sensitivity analysis that the Gauss–Hermite approach offers. Received, October 1997 Revised, August 1998 Accepted, August 1998  相似文献   

Multiple Sources for Sea-Rafted Loisels Pumice, New Zealand     

Phil Shane  Paul Froggatt  Ian Smith  Murray Gregory 《Quaternary Research》1998,49(3):271-279

Sea-rafted Loisels Pumice is one of the few stratigraphic markers used to correlate late Holocene coastal deposits in New Zealand. Along with underlying sea-rafted products of the local Taupo eruption of ca. 1800 yr B.P., these events have been used to bracket the first arrival of humans at New Zealand. Loisels Pumice is dacitic to rhyolitic (SiO₂63–78 wt%) in composition, but individual clasts are homogeneous (SiO₂range ± 1 wt%). Characteristics include very low K₂O (0.5–1.75 wt%) and Rb (<25 ppm) and a mineralogy dominated by calcic and mafic xenocrysts. Similar features are shared by pumices of the Tonga–Kermadec arc, suggesting a common tholeiitic oceanic source. Interclast diversity of Loisels Pumice suggests that it is the product of several eruptive events from different volcanoes. The differences in glass and mineral compositions found at various sites can be explained if the deposits are from different events. A multisource origin can also partially explain the discrepancy in reported¹⁴C ages (ca. 1500–600 yr B.P.) from different localities. Therefore, the value of Loisels Pumice as a stratigraphic marker is questionable, and it does not constrain the arrival of humans. The predominant westward drift of historic Tonga–Kermadec arc pumices and prevailing ocean currents suggest a long anticlockwise semicircular transport route into the Tasman Sea before sea-rafted pumice arrival in New Zealand. The diversity of the pumices indicates that silicic eruptions frequently occur from the predominantly basic oceanic volcanoes.  相似文献   

Reconstructing the development of a gully in the Upper Kalaus basin,Stavropol region (southern Russia)     

V.R. Belyaev  P.J. Wallbrink  V.N. Golosov  A.S. Murray  A.Yu. Sidorchuk 《地球表面变化过程与地形》2004,29(3):323-341

The Stavropol region of southern Russia is severely affected by human‐induced gully erosion. A lack of detailed information on the different stages of gully formation resulting from major agricultural expansion c. 100 years ago, is an obstacle for management and containment of these systems. In this study we combine measurements of particle‐bound radionuclides (¹³⁷Cs, ²¹⁰Pb_ex, ²²⁶Ra, ²³²Th and ⁴⁰K) and classical geomorphology to investigate and reconstruct the different phases of development of a gully during the last c. 100 years. We believe the ?rst phase (1) involved an initial incision into the bottom of a small valley (catchment area c. 1 km²) about 100 years ago. A short period of rapid growth was followed by a longer stage of gully stabilization. Subsequent phases were: (2) the period 1954–1960 – re‐incision in the lower gully reach was initiated by a high‐magnitude rainfall event, and a substantial amount of sediment was delivered to the gully fan; (3) c. 1960–1986 – the knickpoint retreated slowly, sediment was redeposited nearby, and the fan surface became stable; (4) 1986–1987 – a dam was built in the gully mouth and breached shortly after construction following 2 days of high rainfall, and substantial sediment accumulated in the gully above the dam and below the spillway channel on the fan surface; (5) 1987–1993 – the knickpoint retreat continued and the lower fan surface was stable until 1993 when the last signi?cant runoff event overlayed it with c. 10 cm of fresh sediment. These detailed reconstructions of gully development stages allow the contribution of high‐magnitude events to gully growth and regional sediment delivery to be assessed. They further guide management actions to prevent such dam failures in the future. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Tectonostratigraphic relationships and coalification trends in the Narragansett and Norfolk Basins, New England     

Daniel P. Murray  James W. Skehan  Jon Raben 《Journal of Geodynamics》2004,37(3-5):583

Carboniferous basins in southeastern New England provide insight into, and constraints on, models for Alleghanian orogenesis. In particular, the Narragansett and Norfolk basins represent Devonian- to Pennsylvanian-aged, non-marine basins in southeastern Massachusetts and Rhode Island that were variably deformed and metamorphosed during the Alleghanian orogeny, and intruded by Permian granites generated by crustal thickening. As such these basins provide an unusually complete documentation of the Alleghanian orogeny. We summarize their sedimentologic, structural and metamorphic features, with emphasis placed on the Narragansett basin, and provide a comprehensive bibliography of recent work. The Narragansett basin also contains complexly deformed and variably metamorphosed coals that are unlike coal describe from other orogenic terrains. Thus we describe these unusual, high rank coal deposits and their response to orogenesis.  相似文献   

Use of rhodamine WT with XAD-7 resin for determining groundwater flow paths     

Murray E. Close  Greg J. Stanton  Liping Pang 《Hydrogeology Journal》2002,10(3):368-376

A passive sampling system for use with rhodamine WT (RWT) in groundwater tracing experiments was developed to assist in the characterisation of groundwater flow paths. Amberlite XAD-7 resin was found to be suitable for adsorption of RWT, which can then be extracted using an ethanol/water mix and analysed fluorometrically. Batch and column experiments showed that XAD-7 resin has a high RWT capacity. The adsorption was slightly dependent on pH, but was always above 75% under batch conditions. The resin had a high percentage mass recovery at flow velocities around 1.5 m/day, but this decreased with increasing flow velocities. Desorption of RWT off the resin in water is dependent on the flow velocity of water and the time after the peak RWT has passed. The mass of RWT extracted from the resin bags correlated very well with both the RWT mass flux in the water and the peak concentrations observed in the monitoring wells in a field experiment. The results of resin bags were reproducible in the field with a mean coefficient of variation equal to 16%. This method has been successfully applied to two field situations with different flow velocities to indicate groundwater flow paths. Electronic Publication  相似文献   

The Thomson Orogen of the Tasman Orogenic Zone     

C.G. Murray  A.G. Kirkegaard   《Tectonophysics》1978,48(3-4)

The Thomson Orogen forms the northwestern segment of the Tasman Orogenic Zone. It was a tectonically active area with several episodes of deposition, deformation and plutonism from Cambrian to Carboniferous time.Only the northeastern part of the orogen is exposed; the remainder is covered by gently folded Permian and Mesozoic sediments of the Galilee, Cooper and Great Artesian Basins. Information on the concealed Thomson Orogen is available from geophysical surveys and petroleum exploration wells which have penetrated the Permian and Mesozoic cover.The boundaries of the Thomson Orogen with other tectonic units are concealed, but discordant trends suggest that they are abrupt. To the west, the orogen is bordered by Proterozoic structural blocks which form basement west of the northeast-trending Diamantina River Lineament. The most appropriate boundary with the Lachlan and Kanmantoo Orogens to the south is an arcuate line marking a distinct change in the direction of gravity trends. The north-northwest orientation of the northern part of the New England Orogen to the east cuts strongly across the dominant northeast trend of the Thomson Orogen.The Thomson Orogen developed as a tectonic entity in latest Proterozoic or Early Cambrian time when the former northern extension of the Adelaide Orogen * was truncated along the Muloorinna Ridge. Early Palaeozoic deposition was dominated by finegrained, quartz-rich clastic sediments. Cambrian carbonates accumulated in the southwest and a Cambro-Ordovician island arc was active in the north. Along the western margin of the orogen, sediments were probably laid down on downfaulted blocks of deformed Proterozoic rocks, with oceanic crust further to the east.A mid- to Late Ordovician orogeny which affected the whole of the Thomson Orogen marked the climax of its precratonic (orogenic) stage. The northeast structural trend of the orogen (parallel to its western boundary with the Precambrian craton) was imposed at this time and has controlled the orientation of later folding and faulting. Up to three generations of folding have been recognized and fine-grained metasediments exhibit a prominent slaty cleavage. Metamorphism was to the greenschist and amphibolite facies, the highest grade rocks being associated with synorogenic granodiorite batholiths in the north. Following deposition of Late Ordovician marine sediments at the eastern margin, emplacement of post-tectonic Late Silurian or Early Devonian batholiths ended the precratonic history of the Thomson Orogen.The subsequent transitional tectonic regime was characterized by deposition of Devonian to Early Carboniferous shallow marine and continental sediments including widespread red-beds and andesitic volcanics. The maximum marine transgression occurred in the early Middle Devonian. Localized folding affected the easternmost part of the Thomson Orogen at the end of Middle Devonian time and was followed by intrusion of Devono-Carboniferous granitic plutons. However, the terminal orogeny which deformed all Devonian to Early Carboniferous rocks of the orogen was of mid-Carboniferous age. It produced northeast-trending open folds and normal and high-angle reverse faults which are considered to reflect basement structures. The cratonization of the Thomson Orogen was completed with the emplacement of Late Carboniferous granites and the eruption of comagmatic volcanics in the northeast, permian and Mesozoic sediments accumulated in broad, relatively shallow down warps which covered most of the former orogen.  相似文献   

The adsorption of plutonium IV and V on goethite   总被引：1，自引：0，他引：1  

Arthur L. Sanchez  James W. Murray 《Geochimica et cosmochimica acta》1985,49(11):2297-2307

The adsorption of Pu(IV) and Pu(V) on goethite (αFeOOH) from NaNO₃ solution shows distinct differences related to the different hydrolytic character of these two oxidation states. Under similar solution conditions, the adsorption edge of the more strongly hydrolyzable Pu(IV) occurs in the pH range 3 to 5 while that for Pu(V) is at pH 5 to 7. The adsorption edge for Pu(V) shifts with time to lower pH values and this appears to be due to the reduction of Pu(V) to Pu(IV) in the presence of the goethite surface. These results suggest that redox transformations may be an important aspect of Pu adsorption chemistry and the resulting scavenging of Pu from natural waters.Increasing ionic strength (from 0.1 M to 3 M NaCl or NaNO₃ and 0.03 M to 0.3 M Na₂SO₄) did not influence Pu(IV) or Pu(V) adsorption. In the presence of dissolved organic carbon (DOC), Pu(V) reduction to Pu(IV) occurred in solution. Pu(IV) adsorption on goethite decreased by 30% in the presence of 240 ppm natural DOC found in Soap Lake, Washington waters. Increasing concentrations of carbonate ligands decreased Pu(IV) and Pu(V) adsorption on goethite, with an alkalinity of 1000 meq/l totally inhibiting adsorption.The Pu-goethite adsorption system provides the data base for developing a thermodynamic model of Pu interaction with an oxide surface and with dissolved ligands, using the MINEQL computer program. From the model calculations we determined equilibrium constants for the adsorption of Pu(IV) hydrolysis species. The model was then applied to Pu adsorption in carbonate media to see how the presence of CO₃^?2 could influence the mobility of Pu. The decrease in adsorption appears to be due to formation of a Pu-CO₃ complex. Model calculations were used to predict what the adsorption curves would look like if Pu-CO₃ complexes formed.  相似文献   

Sex offenders,housing and spatial restriction zones     

Tony H. Grubesic  Alan T. Murray  Elizabeth A. Mack 《GeoJournal》2008,73(4):255-269

Sex offenders are currently a major focus of crime control policies at the local, regional, state and federal levels throughout the United States. In part, the perceived threat of offender recidivism has motivated legislators to launch stringent community notification programs and to establish spatial restriction zones (SRZs) around schools, daycare facilities and public parks. The purpose of these restriction zones is to help protect children and minimize their exposure to convicted sex offenders living in the community. In addition to the concern that the implementation of SRZs dramatically reduces viable housing options for registered sex offenders, there are concerns that offenders will be forced to reside in socially disorganized areas that may encourage recidivism. The purpose of this paper is to explore the demographic and socioeconomic differences between areas inside and outside SRZs. Implications of these results for sex offender policies are discussed.

Tony H. GrubesicEmail:

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