Non-classical types of loess     

M.H. Iriondo  D.M. Kröhling 《Sedimentary Geology》2007,202(3):352-368

The purpose of this contribution is to describe the sequence of physical and chemical processes resulting in the sediment-type named loess, a fine-grained sediment deposit of universal occurrence. Owing to historical causes, loess has been (and still is) implicitly linked to glacial/periglacial environments among most naturalists. However it is known today that most eolian dust is deflated from tropical deserts. Hence, that sequence of processes is more comprehensive than the former narrow cold scenario. Six examples of different “non-classical” cases (from South America and Europe) that fit well to the loess definition are developed: 1) volcanic loess in Ecuador: pyroclastic eruptions/valley wind/mountain praire/silica structuring; 2) tropical loess in northeastern Argentina, Brazil and Uruguay: deflation of river and fan splays/savanna/iron sesquioxide structuring; 3) gypsum loess in northern Spain: destruction of anhydrite/gypsiferous layers in a dry climate/valley wind/Saharian shrub peridesert/gypsum structuring; 4) trade-wind deposits in Venezuela and Brazil: deflation in tidal flats/trade wind into the continent/savanna/iron hydroxide structuring; 5) anticyclonic gray loess in Argentina: continental anticyclone on plains/anti-clockwise winds and whirls/steppe/carbonate structuring. All these non-classical types conform to the accepted loess definitions and they also share the most important field characteristics of loess such as grain size, friability, vertical or sub-vertical slopes in outcrops, subfusion and others. Other cases can probably be recognized when systematically scrutinized.  相似文献   

A numerical study on 2-D compressive wave propagation in rock masses with a set of joints along the radial direction normal to the joints   总被引：1，自引：0，他引：1  

W.D. Lei  A.M. Hefny  S. Yan  J. Teng 《Computers and Geotechnics》2007,34(6):508-523

An explosion in a borehole or an accidental explosion in a tunnel will generate a two-dimensional (2-D) compressive wave that travels through the surrounding rock mass. For the problem of 2-D compressive wave propagation in a rock mass with parallel joints in the radial direction normal to the joints, parametric studies on the transmission ratio and the maximum rebound ratio are performed in universal distinct element code. The variation of the transmission ratio with the ratio of joint spacing to wavelength is generalized into a characteristic curve, which can be used as a prediction model for estimating the transmission ratio. The relationship between the maximum rebound ratio and the influence factors is obtained in charts. The charts can be used as a prediction model for estimating the maximum rebound ratio. The proposed prediction models for estimating the transmission ratio and the maximum rebound ratio are applied to a field explosion test, Mandai test in Singapore. The minimum possible values of peak particle velocity (PPV) at the monitoring points are estimated by using the proposed prediction model for estimating the transmission ratio along the radial direction normal to the joints. On the other hand, the maximum possible values of PPV are estimated by using the proposed prediction model for estimating the maximum rebound ratio along the same radial direction. The comparison shows a good agreement between the field-recorded PPVs and the estimated range of PPVs given by the minimum possible PPVs and the maximum possible PPVs at the monitoring points in Mandai test. The good agreement between the estimated and field-recorded values validates the proposed prediction models for estimating peak particle velocity in a rock mass with a set of joints due to application of a compressive wave at the boundary of a tunnel or a borehole.  相似文献   

GRACE和SLR观测的地球动力学扁率最大熵谱及小波相关分析          下载免费PDF全文

张子占  陆洋  许厚泽 《地球物理学报》2007,50(5):1383-1389

卫星重力测量技术的实现为测定地球动力学扁率提供了新的方式和途径，GRACE卫星是目前最新的重力测量卫星，据其恢复的低阶重力场较以往精度得到大大提高，然而其观测地球动力学扁率（二阶项）却与卫星激光测距（SLR）结果相差较大.本文采用最大熵谱和小波分析方法对GRACE和SLR观测的地球动力学扁率时间序列信号进行定量比较分析，结果表明：GRACE观测的地球动力学扁率年际周期变化振幅仅为SLR观测结果的25%，并且目前GRACE观测的地球动力学扁率数据中含有系统输入信息和相位差，但前者较后者包含有较强的短周期（2～6月）信息.造成这种差异的主要原因可能来自于GRACE与SLR全球观测数据时空分布不同.  相似文献   

基于尺度因素的地下水随机分析          下载免费PDF全文

史良胜  杨金忠  林琳  李少龙 《水科学进展》2007,18(1):39-43

针对小尺度的各态历经假设的失效,研究了小尺度上多孔介质特性参数统计特征。利用基于K-L(Karhunen-Loeve)展开和混沌展开的谱模型,分析了尺度大小对地下水流动的影响。结果表明,尺度大小导致了特征值系列和特征函数系列的变化,尺度的变化对水头、含水量、流速影响程度不同;水头和流速方差与尺度相关,尺度越大,水头和流速方差越大;研究尺度的变化对水头、含水量、流速均值产生的影响较小。  相似文献   

导航卫星原子钟频率漂移特性分析   总被引：2，自引：0，他引：2  

郭海荣  杨生  何海波 《全球定位系统》2007,32(6):5-10

介绍了原子钟频漂定义，总结了频率漂移率测试评定方法，比较分析了不同噪声情况下的频率漂移率估计方法，并用实验室真空状态铷钟的频率偏差数据和GPS卫星钟的精密星历数据进行了计算分析，表明铷钟都有明显频漂，GPSIIR铷钟的日漂移率在10^-15。量级，而铯钟频漂不是很明显。研究了频漂对原子钟时域稳定性影响规律，还利用模拟数据进行了计算分析。验证了方法的有效性．  相似文献   

中国春季气温异常变率的非线性特征     

徐同  郭品文  居丽丽 《河南气象》2007,(2)

运用一种基于神经网络的非线性主成分分析法(NLPCA)对中国1951-2003年53 a春季气温距平场进行分析,结果表明,春季气温异常变率具有显著的非线性特征,当非线性主元u分别取最大值和最小值时,对应的空间气温异常分布型具有显著的非对称性。  相似文献   

Application of statistical method in pollution episode analyses     

Kuang-Jung Hsu  Ching-Chi Wu 《Journal of Atmospheric Chemistry》2007,57(1):19-40

Observed pollutants are of both primary and secondary origins, influenced by local topography and meteorology. Identifying sources and relative contribution often require vast detailed data collection and complicated models. This study applied a statistical time series analysis to two selected pollution events, spring and fall, at two sites in northern Taiwan. Vector moving average representations were used to quantitatively examine relationships among chemical pollutants and estimate their lifetimes. Results from impulse responses show that wind direction change alters the characteristic of pollution observed in opposite sites of Taipei City, from chemical dominant system to transport dominant one and vice versa. Chemicals are clearly separated into photochemical pollutants and primary pollutants. Results pointed out that Taipei City is the major source of photochemical smog, but not these primary pollutants. Derived chemical lifetimes at same location vary from 20% to four times under different meteorological condition. Estimated concentrations of hydroxyl radical range between 2 to 8 × 10⁷ cm⁻³. Photochemical pollutants are responsible for parts of PM10 collected in both station observed. Oxidation of SO₂ is only important in PM10 observed at one station. This study provides a simpler tool to derive information usually from complex models, therefore, is suitable as complement in decision-making process.  相似文献   

一种简化的Helmert方差分量估计算法   总被引：2，自引：0，他引：2  

田远平  孙敏 《测绘工程》1998,7(1):45-48,53

Ｈｅｌｍｅｒｔ方法是通过求出两类观测值的单位方差,来修正其先验权,用迭代法最终求得正确的权。本文提出,如果已知两类观测值的单位方差之比,即可定出正确的权,从而使计算简单化。  相似文献   

浦城地区火山岩型铀成矿远景预测   总被引：1，自引：0，他引：1  

肖斌  王勇 《华东地质学院学报》1998,21(1):14-19

本文根据浦城地区的成矿地质条件,利用信息量法、逻辑矢量长度法和逻辑矢量长度加权法,在已有成矿地质模型的基础上,筛选出有利的地质变量。根据地质变量对成矿的贡献大小,建立评价模型,圈出有利成矿区。经地质评价,认为各有利成矿区成矿条件有利,有较大的找矿前景。  相似文献   

地震时间序列的周期图分析方法和极大熵谱分析方法   总被引：1，自引：0，他引：1  

彭美煊  彭浩 《高原地震》1998,(1)

利用华北地震区的地震资料（1000～1977）,对地震时间序列进行了周期图分析和极大熵谱分析,提取了隐含在随机噪声中的隐含周期。结果表明,这两种方法所得结果很接近,地震应变能√Ei;释放的隐含周期利用周期图分析提取的主要周期是30年、245年和305年,极大熵谱分析方法提取的主要周期是30年、240年和300年。这三个主要周期存在“倍30”的关系,240年和300年周期是30年周期的整数倍。30年周期反映了各活跃幕中的幕式活动规律,300年周期同各活跃期高潮时段之间的时间差的平均值相符,华北自1000年以来的四个活跃期高潮时段之间的时间差平均值是300年。  相似文献