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111.
Pavlos S. Kanaroglou 《The Professional geographer》1994,46(3):359-368
Samples used to estimate discrete choice models in geography and regional science are typically assumed to be simple random samples. This assumption is not always met with existing samples. Furthermore, data collection is usually less costly if a stratified sampling strategy is adopted. Existing sampling theory suggests that stratified sampling can affect the consistency of parameter estimates. This paper reviews the salient points of this theory and relates theory to practice by means of a simple example on housing choice by elderly. 相似文献
112.
本文讨论20-200MHz频率范围内平行板电容法测量岩石介电常数和电导率的方法,指出常用的静电场公式的局限性,给出较精确的似稳场动态公式,并讨论20-50MHz频率范围内的岩石介电特性。 相似文献
113.
中国西北C-3植物的碳同位素组成与年降雨量关系初探 总被引:2,自引:0,他引:2
本文对不同年降雨量环境下生长的藜、独行菜、魁蓟和平车前这4种常见C-3植物的δ13C进行了分析,发现这4种C-3植物的δ13C组成都表现出随年降雨量减少而变重的趋势,其中藜和独行菜的碳同位素组成对降水变化的响应相对要较其它2种植物强烈得多。藜、独行菜和魁蓟的δ13C组成与年降雨量有显著的线性关系,平车前碳同位素组成与年降雨量没有显著的相关性,表明藜、独行菜和魁蓟的δ13C组成可作为年降雨量的替代性指标,平车前的δ13C组成不能作为年降水的替代性指标。 相似文献
114.
The Mapuche people have a deeply rooted tradition of wild plant use for their subsistence. In this study we evaluated whether plant selection by the Mapuche is influenced by environmental constraints. Selection patterns of wild plant richness were compared in two Mapuche communities sharing the same traditions and beliefs but inhabiting different environments. Similarities and differences in the use patterns of wild medicinal and edible plants were quantitatively analyzed by using concepts derived from ecological theory. The Cayulef community is settled in the NW Patagonian (herbaceous) steppe while the Curruhuinca community is established near the Andean temperate forest, 100 km away from each other. Free-listing and semi-structured interviews were conducted with 32 families in Cayulef and 39 in Curruhuinca corresponding to 80% and 40% of each population, respectively. Data were analyzed by means of the Jaccard similarity index and statistical tests. The main results of this study showed that the home environment is a determinant factor that influences which plant species are utilized, as is the anthropic environment (with its high exotic species richness) in each community. However, similar patterns were found with respect to plant families, ways of utilization, plant parts and life forms utilized irrespective of where the communities are settled. In addition, in both populations, wild plant richness was significantly higher for medicinal than for edible species. Our results showed that the use of wild plants is primarily based on the utilization of species belonging to the nearest ecological environments that have both therapeutic and dietary functions. 相似文献
115.
Characteristics of soil erosion change along a long slope in the gentle hilly areas in black soil region in Northeast China are discussed. A simplified slope model based on seg-ments was used to analyze the runoff data and soil erosion data observed between 2003 and 2004 over 10 field plots with different slope length in Heshan Farm, Heilongjiang Province. We found that soil erosion rate over long slopes in the black soil region changed alternatively along the slope and creates alternative zones of intensive erosion and week erosion.The exact place of each zone is different for different rainfall conditions. In a year with less and mild precipitation, rill cannot happen within the top 50 m, while in a year with large and inten-sive precipitation, rill can be formed starting even at 15 m from the top of the slope. 相似文献
116.
Technical difficulties associated with excavation works in tectonized geological settings are frequent. They comprise instantaneous
and/or delayed convergence, sudden collapse of gallery roof and/or walls, outpouring of fault-filling materials and water
inflows. These phenomena have a negative impact on construction sites and their safety. In order to optimize project success,
preliminary studies on the reliability of rock material found on site are needed. This implies in situ investigations (surface
mapping, prospective drilling, waterflow survey, etc.) as well as laboratory investigations on rock samples (permeability
determination, moisture and water content, mineralogy, petrography, geochemistry, mechanical deformation tests, etc.). A set
of multiple parameters are then recorded which permit better insight on site conditions and probable behavior during excavation.
Because rock formations are by nature heterogeneous, many uncertainties remain when extrapolating large-scale behavior of
the rock mass from analyses of samples order of magnitudes smaller. Indirect large-scale field investigations (e.g. geophysical
prospecting) could help to better constrain the relationships between lithologies at depth. At a much smaller scale, indirect
analytical methods are becoming more widely used for material investigations. We discuss in this paper X-ray computed tomography
(XRCT) and neutron tomography (NT), showing promising results for 3D petrographical investigations of the internal structure
of opaque materials. Both techniques record contrasts inside a sample, which can be interpreted and quantified in terms of
heterogeneity. This approach has the advantage of combining genetic parameters (physico-chemical rock composition) with geometric
parameters resulting from alteration or deformation processes (texture and structure). A critical analysis of such 3D analyses
together with the results of mechanical tests could improve predictions of short- and long-term behavior of a rock unit. Indirect
methods have the advantage of being non-destructive. However, as it is the case with large-scale geophysical surveying, XRCT
and NT are affected by several error factors inherent to the interaction of a radiation modality (X-ray or neutron beam) with
the atomic structure of the investigated materials. Recorded signals are therefore in particular cases not artifact-free and
need to be corrected in a subsequent stage of data processing. 相似文献
117.
原子荧光光谱分析环境样品中砷锑铋汞易出现的问题及解决方法 总被引:2,自引:0,他引:2
针对原子荧光光谱法测试砷锑铋汞中易出现的仪器空白不稳定、样品制备及仪器污染等问题,总结出相应的解决方法。 相似文献
118.
利用卫星ETM与样方统计数据研究西鄂尔多斯珍稀濒危植物种群分布规律 总被引:9,自引:0,他引:9
使用1999年8月30m分辨率的ETM遥感数据、DEM数据和25个典型的4^4m^2的地面实测样方统计数据、数字化了1994年的珍稀淑危植物分布图,用遥感技术西鄂尔多斯珍稀濒危植物群落进行了水平和垂直带分布规律的研究。图像处理采用遥感弱信息提取技术,识别了建群植物及其种群组合特征;并结合三维景观影像对珍稀植物种群生存生境的地貌、土壤等条件的相关性进行了分析,揭示了垂直、水平地带分异规律,建立了相关分析模型。研究结果为珍稀濒危植物动态监测和物种多样性保护提供了新的技术方法和分析决策依据。 相似文献
119.
120.
改进了游离二氧化硅(fSiO2)测定中试样的分解方法,采用硫-磷混酸替代单独使用磷酸分解试样,防止了焦磷酸盐的形成,同时,氟硼酸对fSiO2的溶解率符合测定要求。改进的方法用于标准物质中fSiO2的测定,结果与标准值或磷酸溶矿重量法相符。对于ω(fSiO2)=3.26%的标样10次测定的RSD为2.4%。 相似文献