Sand sheets and ventifacts: the legacy of aeolian action in west Norfolk, UK   总被引：2，自引：1，他引：1  

Peter G. HoareC. Robin Stevenson  Steven P. Godby 《Proceedings of the Geologists' Association. Geologists' Association》2002,113(4):301-317

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Nutrients in coastal waters: A chronology and synopsis of research     

S. B. Bricker  J. C. Stevenson 《Estuaries and Coasts》1996,19(2):337-341

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Predation has no competition: factors influencing space and resource use by echinoids in deep‐sea coral habitats,as evidenced by continuous video transects          下载免费PDF全文

Angela Stevenson  Fraser J. G. Mitchell  Jaime S. Davies 《Marine Ecology》2015,36(4):1454-1467

Predation and competition are highly influential factors determining space use in foraging animals, and ultimately contribute to the spatial heterogeneity observed within habitats. Here we investigated the influence of competition and predation on space and resource use via continuous video transect observations – a tool that has not previously been employed for this purpose. This study therefore also evaluates video data as a pragmatic tool to study community interactions in the deep sea. Observations were compiled from 15 video transects spanning five submarine canyons in the Bay of Biscay, France. Substrate choice, positioning on the coral, echinoid aggregate size, and the presence/absence of predators (e.g. fish and decapods) as well as competitors (both inter‐ and intra‐specific) were recorded. Two dominant co‐existing echinoid taxa, echinothurids and Cidaris cidaris (3188 total observations), were observed in the study. For the echinothurids, no significant trends were detected in the inter‐ and intra‐specific competition data. For Cidaris cidaris, significant shifts in substrate use were correlated to the presence of inter‐specific competitors (echinothurids), whereby an increase in dead coral substrate usage was observed. Highly significant patterns were detected amongst echinoids near fish and decapod predators. A shift to the base of the coral infra‐structure was correlated to the presence of fish, and fewer individuals were observed in the open areas of the reef and a greater number were found in the mid and top sections of the coral when in the presence of decapods. Aggregates formed irrespective of the presence of predators. Aggregations are likely to form for feeding and reproduction rather than for defensive purposes; and migration along the coral infra‐structure may be a predator‐driven behaviour as echinoids seek refuge from predators. Predation risk might play a stronger – or more detectable – role in structuring echinoid space and resource use in deep‐sea coral habitats. In addition, the study successfully detected patterns in the video data thereby demonstrating its potential usefulness for similar ecological studies on other deep‐dwelling megabenthos.  相似文献   

Decadal predictability of soil water,vegetation, and wildfire frequency over North America     

Yoshimitsu Chikamoto  Axel Timmermann  Samantha Stevenson  Pedro DiNezio  Sally Langford 《Climate Dynamics》2015,45(7-8):2213-2235

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Observation of stable auroral red arcs from Southern Africa     

E.H. Carman  M.P. Heeran  R.W.H. Stevenson 《Planetary and Space Science》1973,21(4):683-686

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Effect of humidity on dynamic foam stability     

Xueliang Li  Ryan Shaw  Paul Stevenson 《International Journal of Mineral Processing》2010,94(1-2):14-19

It is experimentally shown that the stability of non-overflowing pneumatic foams, such as those used in the Bikerman foam stability test, is strongly dependent upon the gradient of humidity within the freeboard of the column. Growing foams can be prevented from exhibiting collapse, even at surfactant concentrations significantly lower than the critical micelle concentration, by saturating the air above the foam surface thereby preventing liquid evaporation. These observations have important implications for the performance of flotation devices, as well as instruments designed to measure the stability of aqueous foams. Meteorological data for two mining sites in Australia throughout a single year shows the variability of humidity, and therefore stability, of flotation froths.  相似文献   

Direct observation of adakite melts generated in the lower continental crust, Fiordland, New Zealand   总被引：3，自引：0，他引：3  

James A. Stevenson  Nathan R. Daczko  Geoffrey L. Clarke  Norman Pearson  Keith A. Klepeis 《地学学报》2005,17(1):73-79

Adakites have a distinct chemistry that links them to melting of a mafic source at high pressure. They have been attributed to melting of subducted oceanic crust or melting of the mafic crustal roots of thick continental arcs, and are an important contrast to mantle wedge melting as a means of generating continental crust. We report the first direct evidence for the generation of adakitic melts in mafic lower continental crust, in an exhumed Cretaceous arc in the South Island of New Zealand. The lower crustal Pembroke Granulite has the bulk chemistry and partial melting textures involving peritectic garnet appropriate for a source region for an adakitic melt. The melt migrated from the area through a fracture network now filled with trondhjemitic veins. Emplacement of the melt was in the upper crust of the Cretaceous section, illustrated by the presence of coeval adakites in the upper crustal Nelson-Westland region.  相似文献   

Cosmochemistry and structure of the giant planets and their satellites     

David J. Stevenson 《Icarus》1985,62(1):4-15

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Internal structures of the Galilean satellites     

G. Schubert  D.J. Stevenson  K. Ellsworth 《Icarus》1981,47(1):46-59

New models for the interiors of Io, Ganymede, and Callisto are proposed. The model of Io consists of a thin, high-rigidity outer layer separated from a solid interior by a thin, molten or partially molten shell. The modulus of rigidity of the outer layer must be at least 100 times larger than that of the underlying partially molten shell. These layers have thicknesses of order 100 km or less. The near-surface partially molten layer was most likely produced early in Io's history as a consequence of accretional heating; enhanced tidal heating in the outer rigid layer has kept the underlying region partially molten to the present day. The model of Ganymede consists of an ice outer layer, a shell of undifferentiated, primordial ice-silicate mixture, and a rock core. Accretional heating is responsible for melting the ice in the outer layers of Ganymede's initially homogeneous ice-silicate interior. Most of the rock in this outer layer accumulates in a shell on top of Ganymede's early cold and rigid central region; the water in the outer layer quickly refreezes. Heating of the undifferentiated region by the decay of radioactive elements in the silicate fraction would gradually warm it and reduce its viscosity. The rock layer would become gravitationally unstable and sink through the undifferentiated materials to form a rock core. Callisto's heavily cratered surface strongly suggests that relatively little, if any, ice-rock differentiation has occured in its interior.  相似文献   

Formation of the galilean satellites in a gaseous nebula     

Jonathan I. Lunine  David J. Stevenson 《Icarus》1982,52(1):14-39

A model for Galilean satellite formation was analyzed in which the satellites accrete in the presence of a dense, gaseous disk-shaped nebula and rapidly form optically thick, gravitationally bound primordial atmospheres. Upper-bound temperatures expected during accretion lead to partially differentiated structures for both Ganymede and Callisto, although with Ganymede much more differentiated than Callisto. When allowance is made for the aerodynamic breaking of infalling planetesimal fragments, lower surface temperatures result, and the amount of partial differentiation of Callisto is small, possibly approaching zero for a narrow size distribution of infalling planetesimals. The model is chosen to be consistent with the observed densities of the Galilean satellites and our current understanding of Jupiter formation. The retention of ices more volatile than H₂O is considered but not modeled in detail. A nominal nebula of ～0.1 Jupiter masses is constructed by consideration of likely surface density profiles and existing Jupiter collapse calculations. This nebula is optically thick (even if grain opacity is ignored) in both radial and vertical directions and has a temperature profile T ～ 3600 (R_J/R), where R_J is Jupiter's radius and R is the radial distance in the disk midplane. Satellites accrete very rapidly (dynamical time scales being 10²–10⁴ years) and their optically thick gaseous envelopes are unable to eliminate the heat of accretion by radiation. Water-saturated, convective, adiabatic envelopes form, through which planetesimals fall, break up, and partially disseminate their mass. The resulting satellite surface temperatures during accretion are calculated. Possible implications of these models for the subsequent evolution of Ganymede and Callisto are explored and it is suggested that the extensive differentiation undergone by Ganymede may provide the right environment for subsequent resurfacing, whereas the relative lack of extensive differentiation for Callisto may explain the inferred absence of endogenic tectonism.  相似文献