Time splitting and linear stability of the slow part of the barotropic component     

Yves Morel  Remy Baraille  Annick Pichon   《Ocean Modelling》2008,23(3-4):73-81

In this paper, the authors analyse the stability of particular numerical schemes used in oceanic general circulation models to deal with the barotropic momentum advection term. It is shown that, when this term is integrated using time splitting, its stability properties can be drastically reduced in configurations where there exists shallow areas, where velocities become comparable to the propagation speed of external gravity waves. A simple alternative scheme with improved stability is proposed and discussed.  相似文献   

Multivariate techniques as alternative statistical tools applied to magnetic proxies for pollution: a case study from Argentina and Antarctica     

Marcos A. E. Chaparro  Mauro A. E. Chaparro  Claudia Marinelli  Ana M. Sinito 《Environmental Geology》2008,54(2):365-371

Several statistical analyses—as alternative tools—were applied to magnetic monitoring studies. Magnetic and chemical data from two environments have been gathered from previous papers and studied separately. Univariate and multivariate analyses were first examined, revealing a link between magnetic and chemical variables. The latter analyses, in particular, canonical correlation analysis, showed very good canonical correlations: R = 0.950 (Antarctica) and R = 0.891 (Argentina). On the other hand, in order to classify the data according to the degree of contamination, principal coordinates and discriminant analyses, as well as the comparison of several multivariate means were performed. Three groups were distinguished in both case studies, which were well classified at a low margin of error and quite different from each other at a significant level: 0.01 (Antarctica) and 0.05 (Argentina). The joint use of these statistical analyses also showed, in agreement with previous studies, that the relevant variables in order to identify atmospheric pollution are: magnetic susceptibility, saturation of isothermal remanent magnetisation, anhysteric susceptibility/magnetic susceptibility, remanent coercivity, and copper, lead, zinc and chromium contents.  相似文献   

基于普通数码相机的近景摄影测量方法与精度的试验研究   总被引：3，自引：0，他引：3  

张慧鑫  李非栗  雷巨光 《北京测绘》2008,(4)

普通数码相机由于体积小、重量轻、价格低廉、像素几何位置精度高、影像可直接输入计算机进行处理等优点备受人们青睐。随着数字摄影测量技术的发展,数码相机分辨率的不断提高,人们开始考虑能否将普通数码相机应用于工程实践。本文以普通数码相机作为影像信息的获取手段,就控制点的数量、分布、精度、影像获取及其量测方法、数据处理解算方法、解算精度等问题进行了研究。  相似文献   

抗饱和研究历史与发展综述     

查苗  何汉林 《南京气象学院学报》2017,9(4):423-429

首先介绍了饱和问题的由来,分三个时期对抗饱和研究的发展进行了说明;然后细述了一般抗饱和框架,以及抗饱和补偿器设计需要解决的问题,并指出了两个抗饱和研究难点：吸引域估计和饱和环节处理;接着概述了直接法和抗饱和法的设计思路及所运用的理论,并比较了两种方法处理含有饱和非线性系统的优缺点;最后分线性与非线性介绍了近年来抗饱和的研究成果,并对部分拓展性饱和问题做了整理,丰富了抗饱和研究的内容.  相似文献   

Measuring and monitoring linear woody features in agricultural landscapes through earth observation data as an indicator of habitat availability     

《International Journal of Applied Earth Observation and Geoinformation》2016

The loss of natural habitats and the loss of biological diversity is a global problem affecting all ecosystems including agricultural landscapes. Indicators of biodiversity can provide standardized measures that make it easier to compare and communicate changes to an ecosystem. In agricultural landscapes the amount and variety of available habitat is directly correlated with biodiversity levels. Linear woody features (LWF), including hedgerows, windbreaks, shelterbelts as well as woody shrubs along fields, roads and watercourses, play a vital role in supporting biodiversity as well as serving a wide variety of other purposes in the ecosystem. Earth observation can be used to quantify and monitor LWF across the landscape. While individual features can be manually mapped, this research focused on the development of methods using line intersect sampling (LIS) for estimating LWF as an indicator of habitat availability in agricultural landscapes. The methods are accurate, efficient, repeatable and provide robust results. Methods were tested over 9.5 Mha of agricultural landscape in the Canadian Mixedwood Plains ecozone. Approximately 97,000 km of LWF were estimated across this landscape with results useable both at a regional reporting scale, as well as mapped across space for use in wildlife habitat modelling or other landscape management research. The LIS approach developed here could be employed at a variety of scales in particular for large regions and could be adapted for use as a national scale indicator of habitat availability in heavily disturbed agricultural landscape.  相似文献   

Characteristic friction coefficient and scale effects in oscillatory porous flow     

Dulce María Pérez-Romero  Miguel Ortega-Sánchez  Antonio Moñino  Miguel A. Losada 《Coastal Engineering》2009

This work presents a simple method to evaluate the performance of a porous breakwater when it is impinged with normal incidence by a non-breaking monochromatic wave train. It is based on: 1) a potential flow model for wave interaction with permeable structures and 2) a set of experimental tests on a rectangular porous structure with uniform granular distribution. A characteristic friction diagram is obtained considering wave energy balance in a control volume, minimising the error between the numerical model and the experimental results for the wave transmission coefficient. Results show that, for large breakwater widths, the reflection process reaches a saturation regime before the waves exit the structure at a distance from the seaside between the interval 0.2 < x/L < 0.45. For larger breakwater widths, the reflection coefficient is almost constant (except for “resonant” conditions) and wave transmission decreases exponentially. Under such conditions, the wave propagation through the porous medium depends on the relative diameter D/L and the porosity of the material; the dependence on the relative breakwater width B/L and the ratio diameter wave height D/H is weak. This diagram intends to be useful for preliminary engineering studies of breakwater's efficiency and performance and as an adequate selection criteria of the experimental stone diameter to minimize scale effects in laboratory studies.  相似文献   

Discussion on “Soft computing approach for real-time estimation of missing wave heights” by S.N. Londhe [Ocean Engineering 35 (2008) 1080-1089]     

A.H. Alavi  A.H. Gandomi 《Ocean Engineering》2010,37(13):1239-25

The paper studied by Londhe (2008) utilizes genetic programming (GP) for estimation of missing wave heights. The paper includes some problems about the fundamental aspects and use of the GP approach. In this discussion, some controversial points of the paper are given.  相似文献   

Trends in chronic marine oil pollution in Danish waters assessed using 22 years of beached bird surveys     

Larsen JL  Durinck J  Skov H 《Marine pollution bulletin》2007,54(9):1333-1340

Beached bird surveys provide an important tool for monitoring the level of oil pollution at sea, which is the most significant observable cause of death for a large number of waterbird species and pose a serious threat to wintering seabird populations. Linear regression analyses of oil rates from the Danish 22 year dataset show a decline in the oil pollution level in offshore areas of the eastern North Sea and Skagerrak and in near-shore parts of the Kattegat; but a worsening in the offshore areas of the Kattegat. These results raise concern for species such as common scoter, velvet scoter, eider and razorbill, for which the Kattegat serves as a globally important wintering area. It is recommended that surveillance for oil spills is intensified in inner Danish waters, and that action is taken to make responses towards offenders faster, and penalties for oil seepage higher.  相似文献   

ICP-AES光谱法测定铅锌矿石中Cu Pb Zn As Bi   总被引：1，自引：0，他引：1  

张微  张丽微  徐玉蓉  唐毅  朱松 《云南地质》2010,29(2):201-205

铅锌矿经王水分解处理,标准溶液中配入与样品组分相匹配的标准物质,用电感耦合等离子体发射光谱法可稳定、准确地测定矿石中铜、铅、锌、砷、铋。  相似文献   

夏季中国中东部不同历时降水时空分布特征   总被引：7，自引：2，他引：5  

金炜昕  李维京  孙丞虎  左金清 《气候与环境研究》2015,20(4):465-476

利用1961~2012年台站逐时降水资料,分析了夏季中国中东部不同历时降水的主要气候分布和长期变化特征,为深入认识其时空变化规律和形成机理奠定基础。分析结果表明,降水事件的平均历时由南向北呈"短—长—短"分布型,华南和北方地区以6 h以下的短历时降水为主;而中部地区(28°N~37°N)6 h以上长历时降水占总降水量60%以上。随着降水历时的增加,小雨事件(0.1~1.0 mm/h)的发生概率降低,中雨事件(1.1~10.0 mm/h)的发生概率升高;大雨、暴雨事件(10.0 mm/h)更易出现在35°N以南历时偏短的降水事件中。1961~2012年,中国中东部总降水量呈"南升北降"的趋势分布,夏季南方大部分地区降水强度、时数和事件数均呈上升趋势;而北方地区降水时数和事件数显著减少,不过降水强度呈增强趋势。中东部降水历时总体呈上升趋势,尤其以我国长江与黄河之间的中部地区变化最为显著。同时,该地区短历时(1~6 h)降水无显著的年代际转折,长历时(6 h)降水的年代际增加是20世纪70年代末至20世纪90年代初降水增多的主要原因。20世纪90年代初期以来,南方地区降水的年代际增多则是长、短降水共同作用的结果,但超过6 h降水的影响范围更广,且影响中心较短历时降水偏北。  相似文献