Titan's diverse landscapes as evidenced by Cassini RADAR's third and fourth looks at Titan     

J.I. Lunine  C. Elachi  S.D. Wall  M.D. Allison  R. Boehmer  P. Encrenaz  G. Franceschetti  G. Hamilton  W.T.K. Johnson  R.L. Kirk  R. Lorenz  D.O. Muhleman  S.J. Ostro  P. Paillou  F. Posa  L.E. Roth  S. Shaffer  B. Stiles  S. Vetrella  C.A. Wood  H. Zebker  E. Karkoschka  E. McFarlane  B. Kazeminejad 《Icarus》2008,195(1):415-433

Cassini's third and fourth radar flybys, T7 and T8, covered diverse terrains in the high southern and equatorial latitudes, respectively. The T7 synthetic aperture radar (SAR) swath is somewhat more straightforward to understand in terms of a progressive poleward descent from a high, dissected, and partly hilly terrain down to a low flat plain with embayments and deposits suggestive of the past or even current presence of hydrocarbon liquids. The T8 swath is dominated by dunes likely made of organic solids, but also contain somewhat enigmatic, probably tectonic, features that may be partly buried or degraded by erosion or relaxation in a thin crust. The dark areas in T7 show no dune morphology, unlike the dark areas in T8, but are radiometrically warm like the dunes. The Huygens landing site lies on the edge of the T8 swath; correlation of the radar and Huygens DISR images allows accurate determination of its coordinates, and indicates that to the north of the landing site sit two large longitudinal dunes. Indeed, had the Huygens probe trajectory been just 10 km north of where it actually was, images of large sand dunes would have been returned in place of the fluvially dissected terrain actually seen—illustrating the strong diversity of Titan's landscapes even at local scales.  相似文献   

Europium sorption to sediments in the presence of natural organic matter: A laboratory and modeling study     

Daniel I. Kaplan  Steven M. Serkiz  Jerry D. Allison 《Applied Geochemistry》2010

Cellulosic materials, such as wood, paper products and cardboard that have been co-disposed with low-level nuclear waste have been shown to produce leachate with natural organic matter (NOM) concentrations of hundreds of mg/L C and, as such, have the potential to influence the fate and transport of radionuclides in the subsurface environment. The objective of this study was to examine the influence of NOM on the sorption of Eu (an analogue for trivalent radionuclides) to two coastal plain sediments from the US Department of Energy’s Savannah River Site. Particular attention was directed at quantifying Eu interactions with NOM sorbed to sediments (NOM_sed) in laboratory experiments and developing conditional stability constants for that interaction using the thermodynamic equilibrium speciation model MINTEQA2. Europium sorption to the two sediments systematically increased as pH increased from 3.9 to 6.7. With increasing additions of NOM to the aqueous phase from 0 to 222 mg/L C, Eu sorption initially increased to a maximum at 10 mg/L C NOM_aq and then decreased with increasing NOM_aq concentrations. Increases in Eu sorption at low NOM additions was attributed to the sorption of NOM to the sediment surface increasing the number of sorption sites on the low cation-exchange capacity sediments and/or increasing the association constant (log K) for the Eu-sediment surface reaction. Decreases in Eu sorption at higher NOM levels was attributed to Eu_aq complexation to NOM_aq being more favored than Eu sorption to the solid phase. A component additivity model was developed to describe the Eu–NOM-sediment system by the additive effects of the three binary system models: Eu–NOM, Eu-sediment and NOM-sediment. The model generally captured the data trends in the ternary system. Conditional stability constants developed from the experimental data for the complexation of Eu to NOM_sed were as much as four orders of magnitude greater than Eu complexation with NOM_aq, presumably due to the NOM_sed deriving additional negative (attractive) charge from the sediment surface. At high initial NOM_aq levels, >99 mg/L C, the model captured the trend of reduced Eu sorption but tended to over-estimate Eu sorption. The additivity approach of combining binary models to form a ternary model was only successful when the unique complexation properties of the NOM_sed were properly calculated.  相似文献   

The Effect of Contaminated Prey on Feeding,Activity, and Growth of Young-of-the-Year Bluefish, <Emphasis Type="Italic">Pomatomus saltatrix</Emphasis>, in the Laboratory     

Allison C. Candelmo  Ashok Deshpande  Bruce Dockum  Peddrick Weis  Judith S. Weis 《Estuaries and Coasts》2010,33(4):1025-1038

Young-of-the-year (YOY) bluefish, Pomatomus saltatrix, reside in some contaminated estuaries of the mid-Atlantic bight during their early life history, and as a result of this exposure, they may bioaccumulate high levels of contaminants, including polychlorinated biphenyls (PCBs), pesticides, and methyl mercury. Young-of-the-year bluefish from the Tuckerton, NJ, area of Great Bay (TK) were fed daily in a laboratory with common prey fish, menhaden, and mummichog from two sites: TK (reference) or Hackensack River (HR) (contaminated). Bluefish fed HR prey and the HR prey themselves had significantly elevated concentrations of PCBs, pesticides, and total mercury compared to TK counterparts. The bluefish fed contaminated prey for 4 months displayed significantly reduced feeding, spontaneous activity, and growth compared to the bluefish fed TK prey. Alterations of bluefish behavior and growth from exposure to contaminants may have detrimental effects on migration, overwinter survival, and recruitment success.  相似文献   

Strontium in coral aragonite: 3. Sr coordination and geochemistry in relation to skeletal architecture     

Nicola Allison  Adrian A. Finch  Matthew Newville 《Geochimica et cosmochimica acta》2005,69(15):3801-3811

Use of the coral Sr palaeothermometer assumes that the Sr in coral skeletons is substituted randomly for Ca in the aragonite structure. The presence of Sr in additional phases e.g., strontianite, or the non random distribution of Sr across metal sites in aragonite, would complicate the Sr/Ca-sea surface temperature relationship. We have used Sr K-edge microEXAFS (extended X-ray absorption fine structure) to determine the structural state of Sr across selected microvolumes of four coral skeletons (Porites lobata, Acropora palmata, Pavona clavus, and Montastrea annularis). We used a 5 × 3 μm beam to analyse specific areas of the coral skeletal architecture, i.e., centres of calcification, fasciculi, and dissepiments. All EXAFS analyses refine, within error, to an ideally substituted Sr in aragonite, and we found no evidence of strontianite or partly ordered structural states. Anisotropy in the first shell responses results from the fact that the analysed microvolumes are not necessarily averaged for the responses of all crystal orientations in the aragonite. Although secondary ion mass spectrometry confirmed that Sr/Ca composition can vary substantially between skeletal components, we find no evidence for any contrast in Sr structural state. Sr heterogeneity may result from kinetic effects, reflecting complex disequilibrium processes during crystal precipitation, or biological effects, resulting from variations in the composition of the calcifying fluid which are biologically mediated.  相似文献   

A Technology Fusion Approach for Augmented Reality Applications     

Allison Kealy  Stephen Scott-Young 《Transactions in GIS》2006,10(2):279-300

Technology fusion through the integration of multiple sensors and data sources is a common feature of current spatial information applications. Augmented reality is one such example. Augmented reality is a technology that overlays views of the real world with digital information. It provides an innovative application of spatial databases and can be applied in both real‐time and non‐real‐time applications. In order to correctly align digital (augmented) data with views of the real world, position and attitude determination is required. This paper describes the development of an augmented reality prototype, which includes the design and implementation of a position and attitude determination component. The prototype relies on spatial information to improve the accuracy of position and attitude determination. Successful field tests of the prototype are carried out in Melbourne, Australia. The field tests are focused around a case study that uses the prototype to enable drivers to ‘see’ the road and surrounding vehicles despite heavy fog, rain, snow or other low visibility situations.  相似文献   

Structural control considering soil–structure interaction effects     

H. Allison Smith  Wen-Hwa Wu  Ronaldo I. Borja 《地震工程与结构动力学》1994,23(6):609-626

A discussion of the effects of Soil-Structure Interaction (SSI) on the formulation of active structural control algorithms is presented. Two approaches for incorporating SSI effects in linear optimal control theory are developed: one which performs the control analysis on a structure with a fixed base and then considers the effects of SSI on the controlled structural response; and another which performs the control analysis using a structural equation of motion reformulated to include SSI effects. The two control formulations are studied and compared using a single-degree-of-freedom structure supported through a rigid foundation resting on a linear, elastic half-space. Results show that control effectiveness is affected by the approach used in formulating the equations of motion of the interacting system.  相似文献   

Beaches and dunes of developed coasts by Karl F. Nordstrom,Cambridge University Press,Cambridge, 2000. No. of pages: xiii + 338. Price: £47·50. ISBN 0 521 47013 7     

Robert J. Allison 《地球表面变化过程与地形》2001,26(5):577-578

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The 1933 M_s= 7.3 Baffin Bay earthquake: strike-slip faulting along the northeastern Canadian passive margin     

Allison L. Bent 《Geophysical Journal International》2002,150(3):724-736

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Developments in a non-destructive method of determining rock strength: A reply     

Robert J. Allison 《地球表面变化过程与地形》1991,16(5):473-476

In a previous publication (Allison, 1989), a non-destructive method for indirectly determining rock strength by measuring Dynamic Young's Modulus was described. Data were presented to assess the Grindosonic apparatus in relation to standard laboratory techniques. A further Short Communication (Allison, 1990) evaluated the non-destructive test as a field technique, in part achieved by comparing the Grindosonic results with data collected using the Schmidt hammer. The Schmidt hammer is a widely used field technique in geomorphology for determining rock strength (see for example Day and Goudie, 1977; Day, 1981). Allison (1989, 1990) also suggested that the elastic properties of materials are becoming increasingly important in geomorphological studies. The opportunity to provide additional information and comments here is appreciated.  相似文献   

The East Antarctic sea ice zone: Ice characteristics and drift   总被引：2，自引：0，他引：2  

Dr. Ian Allison 《GeoJournal》1989,18(1):103-115

Results from studies of the surface energy balance and the ocean structure in the presence of fast ice near Mawson on the Antarctic coast are used to illustrate the important ways in which sea ice interacts with the ocean and atmosphere. Away from the coast, ship and drifting buoy observations are used to characterize the E Antarctic sea ice zone in a study area between 60° E and 120° E and S of 61° S. Divergent drift over most of the region plays a dominant role in expanding the ice extent in autumn and in determining the characteristics of the pack. Much of the sea ice in the region is young thin ice which forms in leads and polynyas, and in late spring in the study area, the ice thickness averaged over the total ocean surface within the ice edge less than 0.4 m. Even in winter the majority of ice floes off E Antarctica are probably less than 1 m thick.  相似文献