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21.
《The Professional geographer》1987,39(1):85-94
Reviews of geographic software in this article: DEMO-GRAPHICS: WORLD POPULATIONS AND PROJECTIONS. ESP GAUSS. CEMODEL S. Damus LIMDEP. William H. Greene MICROSTAT 4.1 OTIS PCIPS. (Personal Computer Image Processing System) . H.J. Meyers and R. Bernstein. REGRESSION ANALYSIS OF TIME SERIES (RATS) SPSS/PC+ URBAN DATA MANAGEMENT SOFTWARE (UDMS) 相似文献
22.
Statistical analysis of sand grain/bed collision process recorded by high-speed digital camera 总被引:1,自引:0,他引:1
A high‐speed digital camera was employed to record the sand grain/bed collision process. With image processing and a statistical method, a series of parameters of the collision process were obtained. The results show that the collision process of a grain with rebounding can be represented by two parameters: the kinetic energy restitution coefficient and the collision angle. Both parameters satisfy a normal distribution, and they are dependent on one another. With an increase of the collision angle, the distribution of the kinetic energy restitution gradually reduces from a broad to a narrow range with low values. The percentage of vertical velocity restitution coefficients greater than 1 can reach 70% or more, which ensures that the settling time of the sand grains in the air increases and that they receive more energy from the air to progress the saltation movement. 相似文献
23.
Soil erosion susceptibility assessment and validation using a geostatistical multivariate approach: a test in Southern Sicily 总被引:2,自引:0,他引:2
A certain number of studies have been carried out in recent years that aim at developing and applying a model capable of assessing
water erosion of soil. Some of these have tried to quantitatively evaluate the volumes of soil loss, while others have focused
their efforts on the recognition of the areas most prone to water erosion processes. This article presents the results of
a research whose objective was that of evaluating water erosion susceptibility in a Sicilian watershed: the Naro river basin.
A geomorphological study was carried out to recognize the water erosion landforms and define a set of parameters expressing
both the intensity of hydraulic forces and the resistance of rocks/soils. The landforms were mapped and classified according
to the dominant process in landsurfaces affected by diffuse or linear water erosion. A GIS layer was obtained by combining
six determining factors (bedrock lithology, land use, soil texture, plan curvature, stream power index and slope-length factor)
in unique conditions units. A geostatistical multivariate approach was applied by analysing the relationships between the
spatial distributions of the erosion landforms and the unique condition units. Particularly, the density of eroded area for
each combination of determining factors has been calculated: such function corresponds, in fact, to the conditional probability
of erosion landforms to develop, under the same geoenvironmental conditions. In light of the obtained results, a general geomorphologic
model for water erosion in the Naro river basin can be depicted: cultivated areas in clayey slopes, having fine-medium soil
texture, are the most prone to be eroded; linear or diffuse water erosion processes dominate where the topography is favourable
to a convergent or divergent runoff, respectively. For each of the two erosion process types, a susceptibility map was produced
and submitted to a validation procedure based on a spatial random partition strategy. Both the success of the validation procedure
of the susceptibility models and the geomorphological coherence of the relationships between factors and process that such
models suggest, confirm the reliability of the method and the goodness of the predictions. 相似文献
24.
By using small scale model tests, the interference effect on the vertical load-deformation behavior of a number of equally
spaced strip footings, placed on the surface of dry sand, was investigated. At any stage, all the footings were assumed to
(i) carry exactly equal magnitude of load, and (ii) settle to the same extent. No tilt of the footing was permitted. The effect
of clear spacing (s) among footings on the results was explored. A new experimental setup was proposed in which only one footing
needs to be employed rather than a number of footings. The bearing capacity increases continuously with decrease in spacing
among the footings. The interference effect becomes further prominent with increase in soil friction angle. In contrast to
an increase in the bearing capacity, with decrease in spacing of footings, an increase in the footing settlement associated
with the ultimate state of shear failure was observed. The present experimental observations were similar to those predicted
by the available theory, based on the method of characteristics. As compared to the theory, the present experimental data,
however, indicates much greater effect of interference especially for larger spacing among footings. 相似文献
25.
饱和软黏土动力学特性循环扭剪试验研究 总被引:2,自引:0,他引:2
以饱和软黏土的循环扭剪试验研究为基础,阐明不固结不排水条件下饱和软黏土的动力学特性。在循环扭剪和循环三轴两种不同试验应力状态下,通过研究不同围压和不同静、动应力组合下饱和软黏土的应力等效破坏关系和应变等效破坏关系,提出在循环荷载作用下饱和软黏土的循环破坏同样遵循Mises屈服准则,且在Mises屈服准则下,饱和软黏土的循环强度趋于不变量。循环破坏的过程可以等效为一种拟静力弹塑性循环蠕变,建立了饱和软黏土循环累积变形随静荷载、循环荷载以及循环破坏振次之间的关系式。上述结论分别从应力和变形两个方面阐述饱和软黏土的动力学特性,与试验应力状态和围压无关,可以推广到一般应力状态下。 相似文献
26.
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28.
Low-frequency damping of a moored semisubmersible drilling platform was obtained from numerical extinction tests simulated in still water and in regular waves and from mean wave drift forces calculated at zero forward speed. The influence of drag forces was represented by the modified Morison equation. The platform as used for the 18th ITTC Comparative Mooring Study was analyzed in irregular beam waves. The computed time series of sway as well as the corresponding sway response spectrum compared favourably with model test measurements, demonstrating that this procedure to determine low-frequency damping can be effective. 相似文献
29.
During the period August 1985 to May 1986, phytoplankton in the southern Taiwan Strait was collected and studied for distributional variability in relation to hydrography. The results indicated that maximum standing crops of phytoplankton occurred in October and May due to the outgrowth of certain species of diatoms and blue-green algae. The majority of phytoplankton appeared in the water in the top 25 m and occurred in distinct clusters under the influence of water movement. Multivariate analysis indicated that hydrographic parameters, which accounted for the variability of phytoplankton distribution, varied seasonally. Vertical, spatial and temporal variabilities were also apparent. The close relationship between hydrography and algal distribution justifies the use of variations in the phytoplankton population as a useful tracer of water movement. 相似文献
30.