Mode coupling analysis and differential rotation in a flow driven by a precessing cylindrical container     

Thierry Lehner  Waleed Mouhali  Jacques Leorat  Alex Mahalov 《地球物理与天体物理流体动力学》2013,107(4):369-401

We present a theoretical weakly nonlinear analysis of the dynamics of an inviscid flow submitted to both rotation and precession of an unbounded cylindrical container, by considering the coupling of two Kelvin (inertial) waves. The parametric centrifugal instability known for this system is shown to saturate when one expands the Navier–Stokes equation to higher order in the assumed small precession parameter (ratio of precession to rotation frequencies) with the derivation of two coupled Landau equations suitable to describe the dynamics of the modes. It is shown that an azimuthal mean flow with differential rotation is generated by this modes coupling. The time evolution of the associated dynamical system is studied. These theoretical results can be compared with water experiments and also to some numerical simulations where viscosity and finite length effects cannot be neglected.  相似文献   

Evaluating legacy contaminants and emerging chemicals in marine environments using adverse outcome pathways and biological effects-directed analysis     

Thomas H. Hutchinson  Brett P. Lyons  John E. Thain  Robin J. Law 《Marine pollution bulletin》2013

Natural and synthetic chemicals are essential to our daily lives, food supplies, health care, industries and safe sanitation. At the same time protecting marine ecosystems and seafood resources from the adverse effects of chemical contaminants remains an important issue. Since the 1970s, monitoring of persistent, bioaccumulative and toxic (PBT) chemicals using analytical chemistry has provided important spatial and temporal trend data in three important contexts; relating to human health protection from seafood contamination, addressing threats to marine top predators and finally providing essential evidence to better protect the biodiversity of commercial and non-commercial marine species. A number of regional conventions have led to controls on certain PBT chemicals over several years (termed ‘legacy contaminants’; e.g. cadmium, lindane, polycyclic aromatic hydrocarbons [PAHs] and polychlorinated biphenyls [PCBs]). Analytical chemistry plays a key role in evaluating to what extent such regulatory steps have been effective in leading to reduced emissions of these legacy contaminants into marine environments. In parallel, the application of biomarkers (e.g. DNA adducts, CYP1A-EROD, vitellogenin) and bioassays integrated with analytical chemistry has strengthened the evidence base to support an ecosystem approach to manage marine pollution problems. In recent years, however, the increased sensitivity of analytical chemistry, toxicity alerts and wider environmental awareness has led to a focus on emerging chemical contaminants (defined as chemicals that have been detected in the environment, but which are currently not included in regulatory monitoring programmes and whose fate and biological impacts are poorly understood). It is also known that natural chemicals (e.g. algal biotoxins) may also pose a threat to marine species and seafood quality. Hence complex mixtures of legacy contaminants, emerging chemicals and natural biotoxins in marine ecosystems represent important scientific, economic and health challenges. In order to meet these challenges and pursue cost-effective scientific approaches that can provide evidence necessary to support policy needs (e.g. the European Marine Strategy Framework Directive), it is widely recognised that there is a need to (i) provide marine exposure assessments for priority contaminants using a range of validated models, passive samplers and biomarkers; (ii) integrate chemical monitoring data with biological effects data across spatial and temporal scales (including quality controls); and (iii) strengthen the evidence base to understand the relationship between exposure to complex chemical mixtures, biological and ecological impacts through integrated approaches and molecular data (e.g. genomics, proteomics and metabolomics). Additionally, we support the widely held view that (iv) that rather than increasing the analytical chemistry monitoring of large number of emerging contaminants, it will be important to target analytical chemistry towards key groups of chemicals of concern using effects-directed analysis. It is also important to evaluate to what extent existing biomarkers and bioassays can address various classes of emerging chemicals using the adverse outcome pathway (AOP) approach now being developed by the Organization for Economic Cooperation and Development (OECD) with respect to human toxicology and ecotoxicology.  相似文献   

经验模态分解与神经网络的GPS可降水量预测     

刘严萍  杨晶  王勇 《测绘科学》2013,38(5):91-93

本文将经验模态分解与神经网络相结合的方法应用于GPS可降水量预测。对GPS可降水量进行经验模态分解,在分解过程中采用径向基神经网络处理端点问题,针对经验模态分解得到的每个分量分别运用径向基神经网络进行预测,并重构出最后的预测结果。重构结果与直接运用神经网络进行预测的GPS可降水量、实测GPS可降水量进行比较,结果表明,相对于直接预测,经验模态分解与神经网络结合的方法具有更高的预测精度。  相似文献   

1971—2018年陕西省人体舒适度日数时空变化特征     

雷杨娜  毛明策  李明  张侠 《气象与环境学报》2022,38(2):89-96

根据1971—2018年陕西省94个气象观测站逐日气象资料,采用线性倾向率、累积距平、小波分析和EOF分析等方法,对陕西省人体舒适度日数时空变化特征进行了统计分析。结果表明: 陕西全省大部分时间体感状态为从冷到舒适,日数占85.2%;体感状态为暖和以上日数较少,无炎热和酷热天气。1981—2018年陕西省平均人体舒适日数为132 d,呈显著增多趋势,线性倾向率为0.524 d·a^-1,四季中春、夏两季人体舒适日数增加最为显著。人体舒适日数存在准4 a和准8 a的振荡周期,滑动T检验表明陕西省及三个地区的人体舒适日数均在1997年左右发生了明显的突变。陕西全省3—11月均存在舒适日,舒适日数主要分布在5—9月,陕北7—8月舒适日数较多,陕西中部6—8月舒适日数较多,陕西南部6—9月舒适日数较多。年人体舒适日数呈现南多北少的空间分布特征,陕南汉中和安康地区最多。EOF分析结果显示,年均人体舒适日数异常分布在全省存在一致性。倾向率空间分布表明陕西全省80%的地区人体舒适日数均呈增长趋势,仅榆林北部、延安北部和安康东部11个区县人体舒适日数呈减少趋势。陕西全省不舒适日数变化呈显著减少趋势,倾向率为-0.548 d·a^-1,其中冷不舒适日数减少显著。陕西省人体不舒适主要表现为冷不舒适,主要集中在陕北西北部、南部山区和中部的太白和华山两个高山区; 人体热不舒适主要分布在在陕南的汉中和安康地区及关中的西安地区,且日数很少。  相似文献   

Application of Proper Orthogonal Decomposition (POD) to inverse problems in saturated groundwater flow     

Corey Winton  Jackie Pettway 《Advances in water resources》2011,34(12):1519-1526

We develop a new Proper Orthogonal Decomposition (POD) reduced order model for saturated groundwater flow, and apply that model to an inverse problem for the hydraulic conductivity field. We use sensitivities as the POD basis. We compare the output when the optimizer uses the reduced order model against results obtained with a full PDE based model. The solutions generated using the POD reduced model are comparable in residual norm to the solutions formed using only the full-scale model. The material parameters are similarly comparable. The time to solution when using the reduced model is reduced by at least an order of magnitude, as are the number of calls to the full model.  相似文献   

与西澳州西南部冬季降水相联系的大气环流特征分析     

李建平  李艳杰  冯娟 《大气科学》2011,35(5):801-817

西澳大利亚州西南部(SWWA)是西澳大利亚州首府Perth的所在地,也是西澳州政治、经济、文化、教育和旅游的中心.自20世纪中期以来,SWWA地区雨季降水持续减少.本文利用近60年的观测及再分析数据,分析了已知的影响澳大利亚降水的热带海洋模态:厄尔尼诺—南方涛动(ENSO)、印度洋偶极子(IOD)和ENSOModoki...  相似文献   

1979-2008年华北地区对流层顶高度变化特征   总被引：2，自引：0，他引：2       下载免费PDF全文

张红雨  周顺武  张国勇  李毓富  李新生 《气象与环境学报》2011,27(2):8-13

利用1979-2008年华北地区12个测站逐日对流层顶探空资料,运用统计学方法对该地区不同类别对流层顶发生及其高度的季节特征进行探讨,并采用线性趋势、小波分析和EOF分解等方法对其高度变化等气候特征进行分析,揭示了该地区对流层顶的季节特征及其高度变化的基本事实和规律.结果表明:华北地区第一对流层顶冬季出现多,夏季少,近...  相似文献   

1964-2008年辽宁省旱涝时空分布特征及演变趋势     

唐亚平  张凯  李忠娴  李岚  戴新童  严晓瑜 《辽宁气象》2011,(2):50-55

利用1964—2008年辽宁51站降水量资料,采用Z指数和区域旱涝HL指数分析了全区近45a旱涝变化。结果表明：近45a辽西、辽北以及辽东南地区单站旱涝发生频率均明显高于辽中、辽东地区;区域性洪涝指数逐渐减小,区域性干旱指数逐步增大。对辽宁51站Z指数进行了EOF和REOF分析,可知辽宁旱涝的空间分布特征除受大尺度天气系统所带来的降水量变化影响外,同时还受地理位置、海陆分布等多种因子影响。通过REOF方法可将全区分为4个区域,即Ⅰ辽西地区,Ⅱ辽北、辽西北地区,Ⅲ辽中、辽东地区和Ⅳ辽东南地区。  相似文献   

长江口水下三角洲泥质区近期沉积物粒度变化特征及其影响因素   总被引：4，自引：0，他引：4  

张瑞  汪亚平  高建华  潘少明 《海洋地质与第四纪地质》2011,(5):9-16

河口水下三角洲是河流和海洋环境共同作用的产物,沉积地层中蕴藏了许多环境变化信息.在长江口水下三角洲泥质区采集了柱样SC09,首先利用放射性同位素210Pb确定了沉积柱样的平均沉积速率,其次对沉积柱样以0.2 cm间隔进行高分辨率取样,获得了沉积物粒度参数,然后提取了沉积物粒度敏感组分,并对其进行了经验模态分解(EMD)...  相似文献   

An empirical formula for friction coefficient of a perforated wall with vertical slits     

Kyung-Duck Suh  Yeul Woo KimChang-Hwan Ji 《Coastal Engineering》2011

The friction coefficient in the permeability parameter of a perforated wall has been estimated on the basis of a best fit between measured and predicted values of such hydrodynamic coefficients as reflection and transmission coefficients. In the present study, an empirical formula for the friction coefficient is proposed in terms of known variables, i.e., the porosity and thickness of the perforated wall and the water depth. This enables direct estimation of the friction coefficient without invoking a best fit procedure. To obtain the empirical formula, hydraulic experiments are carried out, the results of which are used along with other researchers' results. The proposed formula is used to predict the reflection and transmission coefficients of various types of structures including a perforated wall. The concurrence between the experimental data and calculated results is good, verifying the appropriateness of the proposed formula. It is also shown that the proposed formula can be used for irregular waves as well.  相似文献