Deconvolution of overcritical P-wave reflections from the top of D″     

Tim Pointer  Jürgen Neuberg 《Physics of the Earth and Planetary Interiors》1995,90(3-4)

We have developed a method to retrieve overcritical PdP reflections from the top of D″ from the data. The differential travel-time, amplitude ratio and phase advance of the reflected PdP waveform relative to the direct P waveform are accurately obtained. Kirchhoff synthetics have been used to model the reflected waveforms for a set of different incidence angles i and velocity contrasts δα at the reflector which were then used as reference wavelets for the deconvolution.The results from a Gräfenberg data set differ markedly from the values predicted by the one-dimensional PWDK model derived from the same data. However, there are large uncertainties in i and δα. This could be caused by the presence of significant lateral heterogeneity in D″ or the need to model other phases which may exist such as the diving waves PDP and PDDP. The method is also applied to two other data examples. The trade-offs between different model parameters are examined.  相似文献   

Oil pollution on Israeli coasts     

Trevor Dixon  Tim Dixon 《Marine pollution bulletin》1975,6(5):70-72

Israel has long experienced the effects of oil discharged offshore into the Eastern Mediterranean. A 7-week survey discovered that the country now faces an additional inshore problem resulting from the changing regional pattern of oil transportation.  相似文献   

Re-viewing the Entrapment controversy: Megaprojection, (mis)representation and postcolonial performance     

Tim Bunnell 《GeoJournal》2004,59(4):297-305

Becoming the tallest building in the world in the mid-1990s, the Petronas Towers was the centre piece of an image of national progress and development that Malaysian authorities sought to project internationally. The release of Fox Movies' Entrapment in Malaysia in May 1999 provoked political outrage and popular disappointment at the way in which the Petronas Towers in Kuala Lumpur had been spliced alongside riverside ‘slums’ filmed in the town of Malacca some 150 km away. This paper provides a critical reading of the spliced scene in the movie. At one level, the angry response of the Malaysian Prime Minister, Dr Mahathir Mohamad, to the scene diagnoses a geopolitics of asymmetrical representational power. However, I show how Mahathir's criticism of Entrapment in Malaysia was as much a defence of domestic political legitimacy (and national economic investibility) as it was ‘opposition’ or ‘resistance’ to hegemonic ‘Western’ (mis)representation. In addition, while the material and symbolic work of reimaging Kuala Lumpur had sought to negate (neo)orientalist imaginings of ‘Asian’ cities, the controversial scene rendered visible environmental ‘underdevelopment’ that has no place in a modern (vision of) Malaysia. Entrapment thus performed something in inducing Malaysian cities and citizens to ‘clean up’ their act, to practice ‘fully developed’ ways of seeing, being and being seen. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Assessment of downstream trends in channel gradient, total and specific stream power: a GIS approach     

Ivars Reinfelds  Tim Cohen  Paul Batten  Gary Brierley 《Geomorphology》2004,60(3-4):403-416

Geographic Information Systems (GIS) analyses of Digital Elevation Models (DEMs) coupled with catchment area based discharge estimation techniques provide a relatively simple means of modelling contiguous downstream trends in channel gradient, total stream power, and in riverscapes conducive to regime analysis, also specific stream power. For a small, high relief, coastal catchment in SE Australia, good agreement was obtained between channel gradients derived from a 25 m cell-size DEM and field survey equivalents over distances of several kilometres, indicating that channel gradients derived from DEMs can have a reasonable degree of absolute as well as relative accuracy over multi-kilometre reach scales. Assessment of downstream rates of change in channel gradient and specific stream power across four river systems suggests that some of the river reaches most responsive to high magnitude floods occur in zones where these variables rapidly decrease downstream. Modelling of downstream trends in channel gradient, total and specific stream power from catchment-wide DEMs has potential to provide a framework with which to investigate conceptual and empirical models between channel gradient, stream power and the form and dynamics of river systems.  相似文献   

DFT study of the cation arrangements in the octahedral and tetrahedral sheets of dioctahedral 2:1 phyllosilicates     

Alfonso Hernández-Laguna  Elizabeth Escamilla-Roa  Vicente Timón  Martin T. Dove  C. Ignacio Sainz-Díaz 《Physics and Chemistry of Minerals》2006,33(10):655-666

Quantum mechanical calculations based on the density functional theory (DFT) are used to study the crystal structures of dioctahedral 2:1 phyllosilicates. The isomorphous cation substitution is investigated by exploring different substitutions of octahedral Al³⁺ by Mg²⁺ or Fe³⁺, tetrahedral substitution of Si⁴⁺ by Al³⁺, and different interlayer cations (IC) (Na⁺, K⁺, Ca²⁺, and Mg²⁺). Samples with different kinds of layer charges are studied: only tetrahedrally charged, only octahedrally charged, or mixed octahedral/tetrahedral charged. The effect of the relative arrangements of these substitutions on the lattice parameters and total energy is studied. The experimental observation of segregation tendency of Fe³⁺ and dispersion tendency of Mg²⁺ in the octahedral sheet is reproduced and explained with reference to the relative energies of the octahedral cation arrangements. These energies are higher than those due to the IC/tetrahedral and IC/octahedral relative arrangements. The tetrahedral and octahedral substitutions that generate charged layers also tend to be dispersed. The octahedral cation exchange potentials change with the IC-charge/ionic radius value.  相似文献   

用ANUDEM建立水文地貌关系正确DEM的方法研究   总被引：4，自引：0，他引：4  

杨勤科  Tim R. McVicar  Mike Hutchinson  李领涛 《测绘科学》2006,31(6):155-157,148

针对区域尺度的径流、水土流失定量评价和植被适宜性评价等研究工作需要,利用1∶25万数字地形图和ANUDEM软件,对黄土丘陵区中等分辨率水文地貌关系正确DEM建立方法进行了研究。结果表明该方法所建立的DEM,可以正确反映地貌梁、沟结构及其与流水线网络的关系,对地形描述的能力优于TIN方法建立的DEM;利用ANUDEM和1∶25万地形图插值建立黄土丘陵区DEM的三个主要参数分别为分辨率50或100,计算迭代次数40,第二糙率系数0.8。  相似文献   

Satellite-Based Guidance for Precision Approach and Landing of Commercial Aircraft     

Lingan Satkunanathan  Tim Murphy 《GPS Solutions》1998,2(1):21-26

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Dissolved loads of rivers and surface water quantity/quality relationships,B. W. Webb (Ed.), International Association of Hydrological Sciences Publication 141, 1983. No. of pages: 439 + xi     

Tim Burt 《地球表面变化过程与地形》1985,10(1):88-88

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Seabirds and oil pollution     

Tim Stowe  Lesley Underwood 《Marine pollution bulletin》1985,16(6):256-257

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Garnet zoning and metamorphism of the Barrovian type area,Scotland   总被引：6，自引：0，他引：6  

T. J. Dempster 《Contributions to Mineralogy and Petrology》1985,89(1):30-38

A microprobe investigation of the high grade metamorphic zones from the Barrovian type area in Angus, Scotland, shows the importance of local zones of retrograde cation exchange between garnet, staurolite and biotite. The interpretation of this zoning, established during a slow cooling history, is critical to any study of metamorphic reactions or conditions. The extent and intensity of these diffusion effects are dependent on a number of parameters including grainsize, fabric orientation, heating and cooling history, and the modal abundance of the phases. Increasing diffusion within garnets with metamorphic grade, and the subsequent retrograde effects are modelled using Temperature-Time-Transformation diagrams and provide information on the activation energy for Fe-Mg diffusion in garnet.  相似文献