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81.
Qualitative modelling of spatial relationships has often been considered as a contextindependent task that aims at a reasoning model in generic form. Despite the primary interest in these models, there is still a sufficiently large scope for context-dependent reasoning in space and time. This paper proposes a qualitative spatial reasoning model, oriented to the modelling and simulation of several cars acting in a multi-lane circuit, which can be considered as an illustrative example of a constrained frame of reference. The modelling objects of interest are individual cars whose cardinal relationships to external cars and actions are modelled. This dynamic system is analysed, and a set of interrelationships is identified at different levels of abstraction, together with inference rules that model the displacement of several cars in a circuit. The potential of this model is illustrated and calibrated using an agent-based prototype. 相似文献
82.
83.
Nicholas P. Wallerstein Carlos V. Alonso Sean J. Bennett Colin R. Thorne 《地球表面变化过程与地形》2001,26(12):1265-1283
This paper presents the results of a movable‐boundary, distorted, Froude‐scaled hydraulic model based on Abiaca Creek, a sand‐bedded channel in northern Mississippi. The model was used to examine the geomorphic and hydraulic impact of simplified large woody debris (LWD) elements. The theory of physical scale models is discussed and the method used to construct the LWD test channel is developed. The channel model had bed and banks moulded from 0·8 mm sand, and flow conditions were just below the threshold of motion so that any sediment transport and channel adjustment were the result of the debris element. Dimensions and positions of LWD elements were determined using a debris jam classification model. Elements were attached to a dynamometer to measure element drag forces, and channel adjustment was determined through detailed topographic surveys. The fluid drag force on the elements decreased asymptotically over time as the channel boundary eroded around the elements due to locally increased boundary shear stress. Total time for geomorphic adjustment computed for the prototype channel at the Q2 discharge (discharge occurring once every two years on average) was as short as 45 hours. The size, depth and position of scour holes, bank erosion and bars created by flow acceleration past the elements were found to be related to element length and position within the channel cross‐section. Morphologies created by each debris element in the model channel were comparable with similar jams observed in the prototype channel. Published in 2001 John Wiley & Sons, Ltd. 相似文献
84.
The retrieval of cloud microphysical properties using satellite measurements and an in situ database
Christophe Poix Guy Febvre Anne Fouilloux Howard Larsen Jean-Francois Gayet 《Annales Geophysicae》1996,14(1):98-106
By combining AVHRR data from the NOAA satellites with information from a database of in situ measurements, large-scale maps can be generated of the microphysical parameters most immediately significant for the modelling of global circulation and climate. From the satellite data, the clouds can be classified into cumuliform, stratiform and cirrus classes and then into further sub-classes by cloud top temperature. At the same time a database of in situ measurements made by research aircraft is classified into the same sub-classes and a statistical analysis is used to derive relationships between the sub-classes and the cloud microphysical properties. These two analyses are then linked to give estimates of the microphysical properties of the satellite observed clouds. Examples are given of the application of this technique to derive maps of the probability of occurrence of precipitating clouds and of precipitating water content derived from a case study within the International Cirrus Experiment (ICE) held in 1989 over the North Sea. 相似文献
85.
A deterministic near-surface correction procedure is developed for multicomponent VSP data, shot using directional sources and recorded using three-component receivers. The method is capable of removing unwanted effects of acquisition such as unequal source strengths or misorientations, but may also remove near-surface multiples and anisotropy. This is of considerable benefit for obtaining accurate and consistent estimates of subsurface anisotropy from different source combinations. Application of the technique is illustrated using a dataset from the Romashkino reservoir in Russia, where three or four different directional sources are used at the same source locations. The technique corrects for the large discrepancies which exist between the estimates obtained using different source combinations. Application of the technique to three wells in the survey region reveals a nearly isotropic subsurface, except for a few isolated zones of moderate to high (2 to 8%) anisotropy which lie close to the expected depth for the reservoir. Although there is no significant correlation with the production figures for each well, the qS1 polarization azimuth within the reservoir does vary at each well location, suggesting that this may be a more sensitive indicator of reservoir Drocess. 相似文献
86.
87.
The results of an extensive study of streamwater chemistry during stormflow events, for a montane Mediterranean area, are presented. Four groups of variables are identified as having contrasting behaviour: alkalinity and pH; nitrate and potassium; sulphate and chloride; sodium, calcium and magnesium. The results show a complex pattern of response to flow that can be broadly linked to: (1) antecedent hydrological conditions; (2) rainfall intensity; (3) supplies of water from chemically distinct areas within the catchment. However, comparisons between this study and a parallel one which examined the composition of waters within the catchment, show that it is presently impossible to quantify the relative supplies from each part of the catchment. The findings are reviewed in relation to analogous studies within a European setting and in relation to modelling initiatives. 相似文献
88.
Instruments and institutions for environmental management in Antarctica have evolved from beginnings in the Antarctic Treaty, with subsequent introduction of the Convention for the Conservation of Antarctic Seals, the Convention on the Conservation of Antarctic Marine Living Resources, and recommendations made at Treaty meetings. The Protocol on Environmental Protection to the Antarctic Treaty will improve existing provisions for environmental management in Antarctica. When it enters into force the Protocol will apply to all activities in the Treaty area: it provides rules for environmental impact assessment, conservation of fauna and flora, disposal of wastes, prevention of marine pollution and specially protected and managed areas. The Protocol's Committee for Environmental Protection will facilitate discussion and advice on environmental management. Management of information is a vital part of ensuring measures are effective. The Protocol should be ratified quickly to improve the basis for environmental protection, but the test will be whether and how it is implemented in practice. 相似文献
89.
Colin J. Lonsdale 《Astrophysics and Space Science》1999,266(1-2):119-124
High resolution radio observations provide a unique tool for investigation ofultraluminous infrared galaxies, due to the combination of high angularresolution and source transparency available at centimeter wavelengths. Thetypical angular size of the IR emitting region in the most luminous systems isof order 0.1 arcsec, while dust absorption appears to obscure this region fromdirect view at wavelengths shorter than 100 microns. Radio observationswith VLBI and MERLIN are revealing compact radio structures indicative of bothstarburst and AGN activity in these systems. Additional observations arerequired to clarify relationships between radio structures and the energygeneration mechanisms, and to realize the full potential of radio interferometryfor ULIRG studies. 相似文献
90.
Acid mine drainage (AMD) from an abandoned copper mine at Britannia Beach, British Columbia, Canada, enters the marine environment through Britannia Creek. The surrounding intertidal zone is devoid of rockweed, Fucus gardneri Silva, a seaweed that dominates nearby shores. Rockweed plants were transplanted to the intertidal zone near Britannia Creek and monitored for changes in percent cover, survivorship, growth rate and Cu content. Autumn and winter transplants to within 100 m of Britannia Creek resulted in negative growth rates and high mortality within 57 days of exposure to AMD, with Cu levels in rockweed surpassing 2,300 ppm in dry tissue. Summer transplants to sites 300-700 m from Britannia Creek showed no consistent differences between AMD-exposed rockweed and control plants, possibly because the plants were stressed by desiccation. The results are consistent with ecological effects observed in other studies, and provide strong evidence for the role of AMD in excluding rockweed from the shores near Britannia Creek. 相似文献