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371.
372.
地质人员经常依照V字型法则连接地层出露界线,但因其随意性和局限性容易出现误差和错误.基于GIS的机助地质填图系统中,基于等高线求取界线由于等高线的不连续性有着明显的局限性.为此,在DEM形成的三维空间中通过求解DEM与空间平面交线的方法来获取地质界线,可以有效地提高精度.文章分析探讨了基于不规则三角形网的地层界线求取思路,并通过实际例子对V字型法则给以实现,结果证明该方法执行速度较快、精度高. 相似文献
373.
YU Jie YANG Haiquan TAN Ming ZHANG Guoning 《地球空间信息科学学报》2006,9(4):281-284
IntroductionThanks to a large number of applications ,suchas map updating, urban planning or land useanalysis ,extraction of artificial objects ,such asbuildings ,roads fromthei mages has been an ac-tive research field for many years . Since build-ings ar… 相似文献
374.
The presented results of cyclic triaxial tests on sand demonstrate that the cumulative effects due to small cycles obey a kind of flow rule. It mainly depends on the average stress ratio about which the cycles are performed. This so-called “cyclic flow rule” is unique and can be well approximated by flow rules for monotonic loading. Amongst others it is shown that the cyclic flow rule is only moderately influenced by the average mean pressure, by the strain loop (span, shape, polarization), the void ratio, the loading frequency, the static preloading and the grain size distribution curve. A slight increase of the compactive portion of the flow rule with increasing residual strain (due to the previous cycles) was observed. These experimental findings prove that the cyclic flow rule is an essential and indispensable concept in explicit (N-type) accumulation models. 相似文献
375.
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377.
粗集在知识发现中的应用 总被引:1,自引:1,他引:0
介绍了粗集的基本概念,包括粗集的定义、“属性-值”系统、属性依赖与归约及粗集概念的若干推广,最后指出粗集理论在知识发现(KDD)中的一个可能应用途径。 相似文献
378.
1 IntroductionMapgeneralizationisoneoftheclassicalcartographicprob lems.Allmaps,aregeneralizedrepresentationsofthereality.Generalizationisnecessarytoimprovethedisplayqualityofsmallscalemaps,allowanalysiswithdifferentgradesofdetail;andreducedatastoragere… 相似文献
379.
The main driving force behind Al/Si ordering in tetrahedral framework aluminosilicates is nearest-neighbour Al/Al avoidance.
Computer simulation is used to explore the direct consequences of such Al/Al avoidance. The main result is that the order-disorder
transition temperature T
c
falls dramatically as the concentration x of Al in the structure is reduced, and if the only interactions are those associated with nearest-neighbour Al/Al avoidance,
T
c
becomes zero for x less than some critical value x
c
, where x
c
=0.31 for the feldspar framework and x
c
=0.34 for cordierite. Also a large degree of short range order is found above T
c
. Both results differ radically from the standard Bragg-Williams model. Plots of entropy and enthalpy of ordering are given
as functions of x and T, which may be used to interpret experimental data or for extrapolation into ranges of x and T inaccessible to experiment.
Received: 14 May 1997 / Revised, accepted: 2 June 1997 相似文献
380.
Cleophas Lado 《GeoJournal》1998,45(3):165-176
In many developing countries, research institutions or centres have been established to develop and/or adapt technologies that would help agricultural development. This is particularly true in Africa where national efforts have been supplemented with international research institutes. Although some modest progress has been achieved in improving agricultural technology, on the whole, the improvement record is not quite encouraging among the small-scale farmers. In many areas, either there are no improved technologies, or where they exist, are unacceptable by farmers. However, where useful technologies exist, their spread has been very limited and where they have been adapted, the benefits only accrue to a small segment of the community. The logical question posed is: why and how do we find ourselves in the current situation? This paper considers the view that to understand fully why the available technologies have remained largely at the research centres, there is need to examine the whole process of research, development, dissemination and utilization of agricultural technology. It is significant to investigate the structural constraints and prospects under which those involved in the process work, their motivations and the interactions between different groups. The traditional ‘top-down’ of development strategy should be supplemented with farmers' indigenous knowledge, and programmes encouraging transfer of agricultural technology should include institutional support. Only by the identification of farmers' environmental and resource utilisation, preferences, socio-economic circumstances and constraints can a development programme of optimum meaning to farmers be devised and implemented with success. 相似文献