A practical implementation of wave front construction for 3-D isotropic media     

K. Chambers  J.-M. Kendall 《Geophysical Journal International》2008,173(3):1030-1038

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The highly spotted photosphere of the young rapid rotator Speedy Mic     

J. R. Barnes 《Monthly notices of the Royal Astronomical Society》2005,364(1):137-145

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A Note on Reversals of Magnetic Fields due to Induction in Shelving Oceans by External Agencies     

R. C. Hewson-Browne  V. C. L. Hutson  P. C. Kendall 《Geophysical Journal International》1973,32(4):483-487

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Impact of GPS satellite and pseudolite geometry on structural deformation monitoring: analytical and empirical studies   总被引：4，自引：1，他引：3  

X.?MengEmail author  G. W.?Roberts  A. H.?Dodson  E.?Cosser  J.?Barnes  C.?Rizos 《Journal of Geodesy》2004,77(12):809-822

Global positioning systems (GPS) have in recent years been increasingly used to monitor the deformations of large structures, particularly the deflections of long suspension bridges. When appropriately employed, and with the presence of a strong satellite geometry, GPS can supply timely and accurate structural deformation information. However, the three-dimensional (3-D) positioning accuracies in a local coordinate system are uneven. For instance, the vertical component of 3-D coordinates is less accurate than the horizontal component. In addition, GPS satellite availability tends to be a function of the latitude of the observation site and its surrounding obstructions. As a consequence, the accuracy of the north–south component is typically worse than that of the east–west component in mid-latitude areas (>45), and in some of the worst situations the horizontal positioning accuracy could even degrade to the same level as that of the vertical component. With such measurements it might not be possible to correctly interpret the real structural deformations. Furthermore, an insufficient number of satellites, caused by signal obstruction, could make it impossible to use GPS alone for kinematic positioning, even when integrated with other sensors such as triaxial accelerometers. With the aim of improving 3-D positioning accuracies for the monitoring of structural deflections, especially in vertical and northern directions, the optimal location selection of an array of ground-based pseudolites to augment GPS satellite geometry using an analytical simulation technique proposed by the authors is considered. Achievable 3-D positioning accuracies are estimated by simulating a real bridge deformation scenario using augmented transmitter geometry and compared with actual positioning accuracies calculated from the measurements gathered from a bridge trial. The results show that with an augmented satellite geometry and multipath mitigation it is possible to achieve uniform 3-D positioning accuracies of a few millimetres.  相似文献   

A comment on the form of the geometrical spreading equations, with some numerical examples of seismic ray tracing in inhomogeneous, anisotropic media     

J-M. Kendall  C. J. Thomson 《Geophysical Journal International》1989,99(2):401-413

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Mobile ions on carbonate surfaces     

Treavor A. Kendall 《Geochimica et cosmochimica acta》2005,69(13):3257-3263

Surface ions move during the dissolution and growth of minerals. The present study investigates the density and the mobility of surface ions and the structure of the adsorbed water layer with changes in relative humidity (RH). The time evolution of the polarization force, which is induced by an electrically biased tip of an atomic force microscope, shows that the density and the mobility of surface ions increase with rising humidity, a finding which is consistent with increasing surface hydration. A marked change in the observations above 55% RH indicates a transition from a water layer formed by heteroepitaxial two-dimensional growth at low RH to one formed by multilayer three-dimensional growth at high RH. A comparison of the results of several rhombohedral carbonates (viz. CaCO₃, FeCO₃, ZnCO₃, MgCO₃, and MnCO₃) shows that a long relaxation time of the polarization force at high RH is predictive of a rapid dissolution rate. This finding is rationalized by long lifetimes in terrace positions and hence greater opportunities for detachment of the ion to aqueous solution (i.e., dissolution). Our findings on the density and the mobility of surface ions therefore help to better constrain mechanistic models of hydration, ion exchange, and dissolution/growth.  相似文献   

'This is like my comfort zone': Senses of place and belonging within Oruāmo/Beachhaven, New Zealand     

Tim McCreanor  Liane Penney  Victoria Jensen  Karen Witten  Robin Kearns  Helen Moewaka Barnes 《New Zealand geographer》2006,62(3):196-207

Abstract:  This paper examines the culturally specific experiences of belonging within Oruāmo/Beachhaven, a suburb in North Shore City. In-depth interviews with 32 caregivers of young children expose the fact that the ethnic groups represented – Māori, Samoan and Pākehā– vary in their uses and understandings of, as well as feelings for, residential neighbourhood. Examination of the themes of natural environment, social relations, continuity of residence, facilities, organisations and place transformation reveal that, while representatives of all groups had views on these matters, there was a variable degree of engagement with and priority afforded to these concerns.  相似文献   

Geomorphological significance of Ontario Lacus on Titan: Integrated interpretation of Cassini VIMS,ISS and RADAR data and comparison with the Etosha Pan (Namibia)     

T. Cornet  O. Bourgeois  S. Le Mouélic  S. Rodriguez  T. Lopez Gonzalez  C. Sotin  G. Tobie  C. Fleurant  J.W. Barnes  R.H. Brown  K.H. Baines  B.J. Buratti  R.N. Clark  P.D. Nicholson 《Icarus》2012,218(2):788-806

Ontario Lacus is the largest lake of the whole southern hemisphere of Titan, Saturn’s major moon. It has been imaged twice by each of the Cassini imaging systems (Imaging Science Subsystem (ISS) in 2004 and 2005, Visual and Infrared Mapping Spectrometer (VIMS) in 2007 and 2009 and RADAR in 2009 and 2010). We compile a geomorphological map and derive a “hydrogeological” interpretation of Ontario Lacus, based on a joint analysis of ISS, VIMS and RADAR SAR datasets, along with the T49 altimetric profile acquired in December 2008. The morphologies observed on Ontario Lacus are compared to landforms of a semi-arid terrestrial analog, which resembles Titan’s lakes: the Etosha Pan, located in the Owambo Basin (Namibia). The Etosha Pan is a flat-floored depression formed by dissolution, under semi-arid conditions, of a surface evaporitic layer (calcretes) controlled by groundwater vertical motions. We infer that Ontario Lacus is an extremely flat and shallow depression lying in an alluvial plain surrounded by small mountain ranges under climatic conditions similar to those of terrestrial semi-arid regions. Channels are seen in the southern part of Ontario Lacus in VIMS and RADAR data, acquired at a 2-years time interval. Their constancy in location with time implies that the southern portion of the depression is probably not fully covered by a liquid layer at the time of the observations, and that they most probably run on the floor of the depression. A shallow layer of surface liquids, corresponding to the darkest portions of the RADAR images, would thus cover about 53% of the surface area of the depression, of which almost 70% is located in its northern part. These liquid-covered parts of the depression, where liquid ethane was previously identified, are interpreted as topographic lows where the “alkanofer” raises above the depression floor. The rest of the depression, and mostly its southern part, is interpreted as a flat and smooth exposed floor, likely composed of a thick and liquid-saturated coating of photon-absorbing materials in the infrared. This hypothesis could explain its dark appearance both in the infrared and radar data and the persistence of channels seen on the depression floor over the time. Shorelines are observed on the border of Ontario Lacus suggesting past high-stand levels of the alkanofer table. The analogy with the Etosha Pan suggests that Ontario Lacus’ depression developed at the expense of a soluble layer covering the region. Dissolution of this layer would be controlled by vertical motions of the alkanofer table over the time. During flooding events, liquid hydrocarbons covering the depression floor would dissolve the surface layer, increasing progressively the diameter of the depression on geological timescales. During drought episodes, liquid hydrocarbons of the underground alkanofer would evaporate, leading to crystallization of “evaporites” in the pores and at the surface of the substratum, and to the formation of the regional soluble layer. The presence of specific landforms (lunette dunes or evaporites) is compatible with such evaporitic regional settings. Alternatively, but not exclusively, the surface soluble layer might have formed by accumulation on the ground of soluble compounds formed in the atmosphere.  相似文献   

Dissipation of Titan's north polar cloud at northern spring equinox     

Stéphane Le Mouélic  Pascal Rannou  Sébastien Rodriguez  Christophe Sotin  Caitlin A. Griffith  Lucille Le Corre  Jason W. Barnes  Robert H. Brown  Kevin H. Baines  Bonnie J. Buratti  Roger N. Clark  Philip D. Nicholson  Gabriel Tobie 《Planetary and Space Science》2012,60(1):86-92

Saturn's Moon Titan has a thick atmosphere with a meteorological cycle. We report on the evolution of the giant cloud system covering its north pole using observations acquired by the Visual and Infrared Mapping Spectrometer onboard the Cassini spacecraft. A radiative transfer model in spherical geometry shows that the clouds are found at an altitude between 30 and 65 km. We also show that the polar cloud system vanished progressively as Titan approached equinox in August 2009, revealing at optical wavelengths the underlying sea known as Kraken Mare. This decrease of activity suggests that the north-polar downwelling has begun to shut off. Such a scenario is compared with the Titan global circulation model of Rannou et al. (2006), which predicts a decrease of cloud coverage in northern latitudes at the same period of time.  相似文献   

A newly discovered impact crater in Titan's Senkyo: Cassini VIMS observations and comparison with other impact features     

B.J. Buratti  C. Sotin  K. Lawrence  R.H. Brown  S. Le Mouélic  J.M. Soderblom  J. Barnes  R.N. Clark  K.H. Baines  P.D. Nicholson 《Planetary and Space Science》2012,60(1):18-25

Senkyo is an equatorial plain on Titan filled with dunes and surrounded by hummocky plateaus. During the Titan targeted flyby T61 on August 25, 2009, the Cassini Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft observed a circular feature, centered at 5.4° N and 341°W, that superimposes the dune fields and a bright plateau. This circular feature, which has been named Paxsi by the International Astronomical Union, is 120±10 km in diameter (measured from the outer edge of the crater rim) and exhibits a central bright area that can be interpreted as the central peak or pit of an impact crater. Although there are only a handful of certain impact craters on Titan, there are two other craters that are of similar size to this newly discovered feature and that have been studied by VIMS: Sinlap (Le Mouélic et al., 2008) and Selk (Soderblom et al., 2010). Sinlap is associated with a large downwind, fan-like feature that may have been formed from an impact plume that rapidly expanded and deposited icy particles onto the surface. Although much of the surrounding region is covered with dunes, the plume region is devoid of dunes. The formation process of Selk also appears to have removed (or covered up) dunes from parts of the adjacent dune-filled terrain. The circular feature on Senkyo is quite different: there is no evidence of an ejecta blanket and the crater itself appears to be infilled with dune material. The rim of the crater appears to be eroded by fluvial processes; at one point the rim is breached. The rim is unusually narrow, which may be due to mass wasting on its inside and subsequent infill by dunes. Based on these observations, we interpret this newly discovered feature to be a more eroded crater than both Sinlap and Selk. Paxsi may have formed during a period when Titan was warmer and more ductile than it is currently.  相似文献