Vertical distribution of trace elements in the surface waters offshore Nova Scotia     

Marc Stoffyn 《Estuarine, Coastal and Shelf Science》1984,18(4):433-445

Concentrations of the trace elements Fe, Al, Mn, Cu, Cd, Zn and Ni were measured in shallow vertical profiles (maximum depth 500 m) off the Scotian Shelf in the western North Atlantic. The distributions of the trace elements show variations with depth, the most consistent of which are for Fe and Zn. A minimum concentration near the surface followed by an increase with depth is attributed to in situ mechanisms.  相似文献   

Interstellar extinction toward the ultradeep Galactic field of the Chandra observatory from 2MASS data     

M. G. Revnivtsev  R. A. Burenin  S. Yu. Sazonov 《Astronomy Letters》2009,35(5):305-310

We have measured the interstellar extinction in the region of ultradeep Galactic-field observations by the Chandra telescope (l ^II, b ^II) ≈ 0.1–1.42 using photometric data from the 2MASS infrared allsky survey. The angular resolution of our interstellar extinction map is 1′.8. We show that the interstellar extinction has a minimum, A _V ～ 3.4, near the center of the Chandra field of view and increases to A _V ～ 5.8–6 at the edge of the field of view. In addition, we show that the bulk of the extinction is gained in the Galactic disk and is approximately the same for all bulge stars. Our results will be subsequently used to process the Chandra data and to estimate the properties of the stellar population in this region.  相似文献   

A computer method to calculate the convolution of statistical distributions     

Thomas A. Jones 《Mathematical Geology》1977,9(6):635-647

It is becoming increasingly important to determine probability distributions of combinations of random variables. Convolution is a technique by which the distribution of a sum of random variables can be determined. This paper presents some simplifications in order to reduce the numerical integrations and computer time. In addition, the method may be used with empirical nonanalytic distributions. While Monte Carlo methods are also appropriate for calculating the distribution, convolution can give at least as much accuracy as Monte Carlo methods with a reduction in computation. Two applications are presented: one approximates the distribution of percent sand in an area, and the other indicates a method of determining sample size when using the distribution of means to approximate normality.  相似文献   

基于栅格叠合的沉积物底质图生成方法   总被引：2，自引：0，他引：2  

杨康  张永战 《第四纪研究》2007,27(5):889-895

文章提出了一种基于GIS空间插值和栅格图叠合技术,分析生成沉积物底质图的方法,并以曹妃甸海区为例,以170个海底表层沉积物样的粒度分析结果为依据,应用本文设计的方法生成这一海区的底质分布图,并用预留的20个采样点进行了精度分析和检验,在此基础上比较了不同的空间插值方法对生成的底质图结果的影响.结果显示出这一方法成图速度快、自动化程度高,但也存在对原始数据精度要求高、插值方法带来误差等问题.在借鉴传统底质图生成方法的基础上,运用三维TIN模型对成图结果进行改进,最终形成一种结合地貌要素的栅格叠合的沉积物底质图生成方法.  相似文献   

闪电产生氮氧化物(LNOX)及其输送过程的模式计算   总被引：2，自引：2，他引：2  

郭凤霞  言穆弘  张义军 《高原气象》2006,25(2):229-235

利用三维强风暴动力电耦合模式,模拟分析了一次雷暴过程中放电活动特征及平流和湍流对LNOX的输送特征。结果表明,在中部负电荷区域的上边缘,对应上升气流区外围、水平流场中心部位的区域,因为放电传输距离较长,所以强放电区主要落在这些部位,且向上传输。在负电荷中心区也有少数放电点,但传输距离较短。闪电产生的氮氧化物逸出闪道后,被云中平流和湍流输送,最后在弱流场区域内形成LNOX浓度中心,峰值达9×10-9。LNOX的输送主要以平流为主,但在云底层及雷暴消散阶段,湍流输送也起重要作用。在雷暴云消亡期,LNOX的峰值为2.7×10-9,比晴天值大1个量级。  相似文献   

The fate of inorganic colloidal particles in Lake Brienz     

Vincent Chanudet  Montserrat Filella 《Aquatic Sciences - Research Across Boundaries》2007,69(2):199-211

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Application of bivariate extreme value distribution to flood frequency analysis: a case study of Northwestern Mexico   总被引：1，自引：0，他引：1  

Carlos Escalante-Sandoval 《Natural Hazards》2007,42(1):37-46

In Mexico, poverty has forced people to live almost on the water of rivers. This situation along with the occurrence of floods is a serious problem for the local governments. In order to protect their lives and goods, it is very important to account with a mathematical tool that may reduce the uncertainties in computing the design events for different return periods. In this paper, the Logistic model for bivariate extreme value distribution with Weibull-2 and Mixed Weibull marginals is proposed for the case of flood frequency analysis. A procedure to estimate their parameters based on the maximum likelihood method is developed. A region in Northwestern Mexico with 16 gauging stations has been selected to apply the model and regional at-site quantiles were estimated. A significant improvement occurs, measured through the use of a goodness-of-fit test, when parameters are estimated using the bivariate distribution instead of its univariate counterpart. Results suggest that it is very important to consider the Mixed Weibull distribution and its bivariate option when analyzing floods generated by a␣mixture of two populations.  相似文献   

地理学的特点     

李容全  邱维理 《地理与地理信息科学》2006,22(6):79-82

现代地理学强调过程与演变的研究,在定量研究方面取得了显著的进步。但在热衷于建立各种模型时,地理学的特点或性质却被忽视,这在国内尤其明显。认识地理学的本质特点,对于学习地理学、发展地理学科和从事地理学研究非常重要。地理学的特点可概括为4方面:即地理学是“研究行星地球表面的科学”、“研究关系的科学”、“强调位置的科学”和“考察分布的科学”。这4个方面缺少任何一方,都不能反映有别于其他任何学科的地理学自身的特点。  相似文献   

海南省澄迈县雷暴气候特征及其灾害防御   总被引：2，自引：0，他引：2  

黄明旺许向春  赵学华陈长丘 《广西气象》2007,28(3):50-52,46

通过统计分析海南省澄迈县1959-2004年逐日雷暴资料,找出雷暴发生时空分布特征,统计1995-2004年10a雷暴发生的影响天气系统,计算出各天气系统影响下雷暴发生的概率。分析结果表明：澄迈县雷暴日46a平均雷暴频次437次,年际变化呈波动减少趋势,5-8月是雷暴发生的高发期,占全年雷暴的53%,16-17时是一天中发生雷暴的最高期,西南方向发生的雷暴略多于其他方向,澄迈县受西南低压槽、南海低压槽和副热带高压等天气系统影响时发生雷暴的概率较大。  相似文献   

基于DEM的黄河流域天文辐射空间分布   总被引：23，自引：3，他引：23  

曾燕  邱新法  刘昌明  吴险峰 《地理学报》2003,58(6):810-816

基于1 km×1 km分辨率的数字高程模型(DEM) 数据,利用建立的起伏地形下天文辐射分布式计算模型,计算了黄河流域1 km×1 km分辨率各月天文辐射的空间分布。结果表明:局部地形对黄河流域年和四季天文辐射的空间分布影响明显;在太阳高度角较低的冬季,地理和地形因子对天文辐射的影响相当强烈,山区天文辐射的空间差异大,1月份向阳山坡(偏南坡) 天文辐射可为背阴山坡(偏北坡) 的2~3倍,极端天文辐射的差异可达10倍以上;而在太阳高度角较高的夏季,天文辐射空间差异较小,7月份不同地形极端天文辐射的差异仅在16%左右;四季中,地形对天文辐射影响的程度为冬季>秋季>春季>夏季。  相似文献