共查询到20条相似文献，搜索用时 31 毫秒
1.
2.
3.
On the rate of aeolian sand transport 总被引：3，自引：0，他引：3
Michael Srensen 《Geomorphology》2004,59(1-4):53
A simple explicit formula for the transport rate of windblown sand is derived based on physical reasoning. The curve relating the dimensionless transport rate to the dimensionless friction speed exhibits the empirically well-established peak. In fact, the theory developed in the paper can explain the peaked shape of this curve. Three empirically determined coefficients in the formula can be given a physical interpretation. The formula is shown to fit transport rates measured in wind-tunnel experiments well, except for very coarse sand. Formulae for the wind profile in the saltation layer and for the grain dislodgement rate in dependence on the friction speed are obtained as part of the theory. 相似文献
4.
5.
Wibjörn Karlén & Jessica L. Black 《Geografiska Annaler: Series A, Physical Geography》2002,84(3&4):225-232
Two lichenometric techniques were compared in a study of lichen growth–rate in northern Sweden. The first technique, based on the maximum lichen diameter on glacier moraines, was identical to the technique used in the 1970s, whereas the other utilized the lichen diameter measured on 100 randomly selected boulders. The results indicate that it does not matter which technique is chosen, as long as the technique is used consistently on both the calibration surfaces and the surfaces to be dated. The use of data from both the 1970s and the 2000s increased the number of calibration surfaces available. The new calibration curve indicates that the age of Little Ice Age moraines was underestimated by up to about 30 years in the study conducted in the 1970s. 相似文献
6.
白洋淀流域地下水更新速率 总被引：4，自引：0，他引：4
受到水库拦蓄、抽水灌溉等人类活动的影响,白洋淀流域平原区河流断流,非承压含水层逐渐被疏干。下游的白洋淀无法得到河流和地下水的补给,时刻面临干涸。鉴于白洋淀对区域生态环境和气候有重要的影响,多次实施调水补淀工程。然而,白洋淀渗漏严重,调水补淀的效果不理想。为了保护白洋淀,亟需恢复地下水的可持续性,这首先需要查明地下水的更新能力。2009年,对白洋淀流域平原区地下水进行实地调查,并采集采集地表水和地下水水样共36个,分析其氚含量。利用线性插值法、吴秉钧法和连炎清法恢复了该地区降水氚含量的历史数据,结合数学物理模型估算了非承压地下水的更新能力。结果表明,氚含量较高的白洋淀水渗漏使得周边地下水氚含量增高。总体上,沿山区到淀区的方向非承压地下水更新速率逐渐由15.0%/a降低至4.0%/a。山前平原冲洪积扇区域是非承压地下水的主要补给区,平均更新速率达9.8%/a。冲积平原区域非承压地下水的平均更新速率仅为4.4%/a。为此,需要限制在冲积平原区域开采非承压地下水,以逐步恢复其更新速率,使其重新补给白洋淀。地下水的恢复过程可能较慢,但可从根本上解决调水补淀无法解决的干淀问题。 相似文献
7.
J. &#;ílený 《Geophysical Journal International》1997,131(3):767-769
When discussing error estimates of the point-source mechanism and the source time function obtained by the two-step procedure by Šílený, Panza & Campus (1992), the authors insist that in the first step—inversion of seismograms (after Sipkin 1982) to get the moment tensor rate functions (MTRFs)—a homogeneous variance for all the data is needed to keep the advantageous symmetry of the normal equations. We show that this is too strong a requirement and can be dropped. 相似文献
8.
Wibjörn Karlén & Jessica L. Black 《Geografiska Annaler: Series A, Physical Geography》2002,84(3-4):225-232
Two lichenometric techniques were compared in a study of lichen growth–rate in northern Sweden. The first technique, based on the maximum lichen diameter on glacier moraines, was identical to the technique used in the 1970s, whereas the other utilized the lichen diameter measured on 100 randomly selected boulders. The results indicate that it does not matter which technique is chosen, as long as the technique is used consistently on both the calibration surfaces and the surfaces to be dated. The use of data from both the 1970s and the 2000s increased the number of calibration surfaces available. The new calibration curve indicates that the age of Little Ice Age moraines was underestimated by up to about 30 years in the study conducted in the 1970s. 相似文献
9.
基于风洞试验对青藏铁路沿线不同类型防沙措施防沙效果进行模拟研究，探讨了不同类型挡沙墙的防沙效果。结果表明：挂板式、轨枕式和箱式挡沙墙输沙率随高度基本呈递增缓变型趋势，最大输沙率低于20%；铃铛式和高立式聚乙烯（PE）网挡沙墙随高度呈递减陡降型趋势，距地表6~8 cm处为转折点，转折点以上输沙率随高度增大急剧减小，转折点以下输沙率随高度变化较为平缓，最大输沙率低于50%。随着风速的增大，各挡沙墙的阻沙率呈递减趋势：挂板式和轨枕式挡沙墙对风速的敏感性最弱，整体阻沙效果较优，可大范围推广；箱式挡沙墙对风速的敏感性较弱，建议在风速18 m·s-1以下的地区使用；PE网挡沙墙防沙效果对风速的敏感性最强，建议在风速10 m·s-1以下的地区使用。 相似文献
10.
The migration speed of a typical barchan on the border of Minqin oasis,Gansu Province,northwestern China,was estimated by means of two methods.One is on the basis of a simple physical model and short-term field measurements.The other comes from the combination of the barchan internal structure detected by ground-penetrating radar and optical/radiocarbon dating techniques.The upper limit of migration speed given by conventional C-14 dating is 3.42 m/yr.The optically stimulated luminescence dating indicates that the time-average migration speed of the studied barchan was 1.78 m/yr in 28 years prior to 2007.The physical estimation further suggests that the annual migration speed has increased in recent years. 相似文献
11.
Pore‐ice sublimation is a prerequisite for aeolian activity in cold environments where surface sediments hold significant amounts of frozen water. Few quantitative studies have defined the rate of grain release from cemented surfaces by pore‐ice sublimation. In 1996–1997, controlled field experiments at Presqu'ile Beach, Ontario, were implemented to measure sediment release from frozen surfaces. The release rates were compared to the local wind regime, ambient temperature and humidity. In additional field experiments, the effect of sediment water content on grain release by sublimation was examined. From the experimental results, an equation which predicts grain release based on local wind speed, ground temperature, humidity, and surface water content is proposed. Predicted release rates show reasonable agreement with natural deflation measured on the beach at Presqu'ile Provincial Park. 相似文献
12.
The paper presents some methods of numerical modeling and a study of moisture changing in frozen clay soils considering rates of freezing in the base of construction.An impact assessment of moisture changes in clay soils affecting strength characteristics during thawing was carried out in stability tests. 相似文献
13.
促进女性就业,不仅能够提高女性社会经济地位,还有助于提高社会生产力和经济活力。论文以东北三省“五普”“六普”和2015年1%人口抽样调查数据为基础,借助空间自回归模型方法,探讨东北地区城市女性就业水平的时空特征及其驱动机制。结果表明：① 东北地区城市女性就业水平整体较低,其中南部城市的女性就业水平高于北部。② 从影响因素来看,高学历、便捷的交通、较高的工业水平、完整的家庭以及更多的家庭支持对城市女性就业水平具有积极效应;而养育负担对女性就业水平具有负向效应。其中,三代及以上家庭户比例是2000—2015年老工业基地城市女性就业水平空间分异的主导因素,可见,一个完整的家庭对女性就业具有极其重要的作用。 相似文献
14.
15.
16.
婚姻是人口再生产必要的社会关系,维系着社会的安定和谐,而离婚的空间特征是社会地理学关注的重要问题,本文以2005-2014年间中国大陆31个省(市、区)离婚率变化为数据源,结合传统数理分析和空间计量分析方法探究其空间依赖性与空间异质性特征。结果表明：①2005-2014年间地区间离婚差异不断缩小,离婚水平空间分布呈现出北高南低的分异态势;②地区间离婚显著的空间溢出效应是由地理邻近和网络社会空间共同作用的结果,而地区间离婚现象的高低分异与特定地理的社会经济及文化等因素有关;③城市化水平、经济发展水平、受教育程度、互联网普及率的提高及家庭规模的增加对离婚起到显著的影响;失业率的增加及城乡收入的加大对离婚起到正向影响,但不显著;全球化、性别比的增加、家庭负担对离婚的影响为负,但未通过显著性检验。 相似文献
17.
The Fuzzy Kappa statistic expresses the agreement between two categorical raster maps. The statistic goes beyond cell‐by‐cell comparison and gives partial credit to cells based on the categories found in the neighborhood. When matching categories are found at shorter distances the agreement is higher. Like the well‐established Kappa statistic the Fuzzy Kappa statistic expresses the mean agreement relative to the expected agreement. The model underlying the expected agreement assumes absence of spatial autocorrelation in both compared maps. In reality however, spatial autocorrelation does lower the expected agreement as matching categories become less likely to be found close‐by. Since most maps have some degree of spatial autocorrelation, the calculated expected agreement is generally higher than the true expected agreement. This leads to counterintuitive results when maps that appear to have considerable agreement obtain negative Fuzzy Kappa values. Furthermore, the Fuzzy Kappa may be biased, as it systematically attributes lower agreement to maps with stronger spatial autocorrelation. This paper proposes an improved Fuzzy Kappa statistic that is based on the same local agreement and has the same attractive properties as the original Fuzzy Kappa. The novelty is that the new statistic accounts for spatial autocorrelation, such that the expected Fuzzy Kappa for maps that are not cross‐correlated is equal to zero. The improved statistic is applied on two cases to demonstrate its properties. 相似文献
18.
中国省域犯罪率影响因素的空间非平稳性分析 总被引：4，自引：2，他引：2
收入差距和流动人口是影响犯罪率的两个重要因素, 以往研究基于OLS模型, 在假设地域空间为均质的前提下分析其对犯罪率的影响, 但现实世界的空间单元往往难以满足“均质”的假设, 多数表现为“空间异质”。以OLS计量空间异质会造成计量结果出现偏差, 同时无法了解不同空间单元的不同影响。而地理加权回归模型通过将空间结构嵌入线性回归模型中, 很好的解决了空间异质的计量问题。利用地理加权回归模型研究2008 年中国大陆省域单元犯罪率的影响因素, 结果表明:① 犯罪率的影响因素表现出空间非平稳性, 流动人口与犯罪率显著相关, 但各个省份相关程度并不相同, 影响关系随空间位置变化而变化;② 地理加权回归模型的计量精度和拟合度比OLS模型有大幅提高 相似文献
19.
20.
Relative importance of strain rate and rheology for the mode of continental extension 总被引：3，自引：0，他引：3
G. Bassi 《Geophysical Journal International》1995,122(1):195-210