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101.
102.
Analysis of equivalent-dose distributions for single grains of quartz from modern deposits 总被引:1,自引:0,他引:1
Two modern coastal sands are studied through single-grain optical dating techniques. The first sample is estimated to be less than 10 y old by means of independent age control and is known to be well-bleached on the basis of preliminary single-aliquot studies. The second sample is less than 1 y old, but an age of 73±24 years had been determined through single-aliquot analysis. For both samples we compare equivalent doses obtained from single-grain analysis to those obtained by means of similar single-aliquot methods. We found that results are comparable although equivalent doses determined through single-aliquot methods are more precise. The reason for this may be ascribed to the limited number of grains on which single-grain measurements were carried out. The presence of poorly bleached grains within a sample could be identified by dose distribution analysis of individual grains. 相似文献
103.
104.
通过对风洞及室内模拟定向风条件下的风成沉积物磁化率各向异性与风向之间关系的研究,发现风成沉积物磁化率各向异性的长轴方向的偏角不仅与风向有关,而且与粉尘沉积量有关。风成沉积物磁化率各向异性的长轴方向的偏角在α95(α95≤20°)的区间范围内与粉尘沉积量大的风向一致.在干旱、半干旱区,现代风成沉积物(沙丘、黄土的表层土)的磁化率各向异性的长轴方向的偏角在此范围区间内与常年盛行风向一致,尤其与沉积物沉降时的盛行风向一致. 相似文献
105.
106.
By using 126 earthquake focal mechanism solutions (M S≥4.7) during the period of 1963~1998, modern tectonic stress field in North China is inverted by means of the step by step convergence. The inversion results indicate that the tectonic stress field in the research region is clearly variational in space and time: (1) The middling principal stress axis σ 2 is basically vertical. The maximum and minimum principal stress axes σ 1 and σ 2 are nearly horizontal, but the azimuths of σ 1 and σ 3 are inconsistent in different districts and periods. (2) Before the Tangshan earthquake in 1976, the three principal stress axes are uniform. The azimuth of maximum principal stress axis σ 1 is 68° (striking in a NEE-SWW direction). (3) After the Tangshan earthquake, the maximum principal stress axis σ 1 and minimum principal stress axis σ 3 have variations in different districts. In the northern area of North China and on the eastern side of the Tancheng-Lujiang fault zone, the maximum principal stress axis σ 1 is also striking in a NEE-SWW direction. Its azimuth is 68°. It is the same as that before the Tangshan earthquake. In the southern area of North China, the maximum principal stress axis σ 1 is striking in a E-W direction and its azimuth is 87°. 相似文献
107.
国外资源研究及其进展 总被引:2,自引:0,他引:2
资源研究是当代地理学与相关学科共同涉及的一个重要综合实践领域。近40年来,国外地理界在以土地为主的资源调查与评价、区域资源综合体分析和资源信息系统开发与建设等方面获得了举世瞩目的进展。本文围绕这些进展详细考察了国外资源研究的发展背景和现状,并就该领域面临的几个问题进行了初步探讨。 相似文献
108.
109.
西沙群岛现代滨岸的风暴沉积 总被引:1,自引:0,他引:1
李浩 《海洋地质与第四纪地质》1991,11(1):83-91
本文仅以1984年10号风暴为例,讨论了风暴前后的水动力条件及路径变化.重点阐述了该次风暴对西沙珊瑚礁区的潮间和潮上带现代砾堤和海滩的影响.描述了珊瑚礁区的砾堤沉积物的空间分布及垂向序列,并对沙质海滩的风暴搬运过程进行了适当的讨论.西沙砾质砾堤和沙质海滩无论从沉积序列上还是从沉积物的结构成份上,都存在着较大的差异,它们是在一种水动力条件下形成的两种不同的沉积体,在沉积过程中各有自身的沉积特点.本文尝试性地从上述角度提出一种沉积序列的空间格局,以便为古代沉积物的研究提供一些滨岸风暴沉积的信息. 相似文献
110.
This paper is concerned with the structure and dynamics of modern retail facilities in Israel. It presents the first comprehensive
quantitative study of the recent trends in Israeli retail. On the basis of an unique database that includes sizes and locations
of retailers for a number of years, we test and challenge some of the traditional theories, as well as the latest approaches
to the analysis of urban systems. Recent approaches view cities as self-organizing systems and utilize complexity theory and
concepts of order. In the case of Israeli retail application of alternate methods of analysis suggests that the conventional
regularities such as rank-size rule, as is implied by the central place theory or the more general power law do not hold.
The findings reveal that the sizes of modern retailers display an exponential distribution, consistent across time and scale.
This signifies a presence of stable regularity in the structure of retail sizes. Exponential distribution of the retail sizes
is shown to reflect a lack of interdependence between the existing and the planned retail facilities. The issue of order versus
randomness and self-organization in the size distribution of retailers remains debatable and requires further development
of tools and universal criteria for analyzing complex systems. 相似文献