Characteristics of eigen-system for flexural gravity wave problems     

S. Mandal  A. Chakrabarti 《地球物理与天体物理流体动力学》2017,111(4):249-281

For a class of boundary value problems associated with flexural gravity waves, characteristics of the eigen-system are analysed which are used to study the convergence of the expansion formulae in both cases of single and two layer fluids in water of finite and infinite depths. Using Green’s function technique, the spectral representations of the vertical eigenfunctions are obtained which are used along with the orthogonal mode-coupling relations to prove the convergence of the expansion formulae. Using the expansion formulae flexural gravity wave scattering due to multiple articulations in the presence of compression are investigated. The problem is studied in both the cases of single-layer and two-layer fluids in finite water depth. Effects of compressive force, stiffness of the connectors, length of the elastic plates and water depth, position of interface on wave scattering by articulated plates are studied by analysing the reflection and transmission coefficients. This procedure of proving the convergence of expansion formulae is independent of water depth. The concept and methodology for dealing with wave-structure interaction problems discussed here can be generalised to deal with problems of similar nature arising in the broad area of mathematical physics and engineering.  相似文献   

从库仑破裂应力和余震分布角度探讨汶川地震和芦山地震的关系     

刘盼  李平恩  廖力 《震灾防御技术》2017,12(1):40-55

本文以龙门山及周边地区为研究对象，考虑区域地质构造差异、主要活动断裂带、地表附加重力影响，建立能反映地表起伏和岩石圈分层结构的龙门山地区三维粘弹性有限元模型。以地壳水平运动速率观测值为约束条件重建研究区现今构造背景应力场，在此基础上分别模拟了汶川地震和芦山地震的发生机理。通过分析同震库仑破裂应力变化与余震空间分布的关系，探讨了2次地震主震对余震的触发作用以及汶川地震对芦山地震的影响。研究表明，汶川地震和芦山地震的余震大部分由其主震触发，汶川地震对芦山地震的余震有约6.78%的触发作用。汶川地震的同震库仑破裂应力在芦山地震主震位置的增加值约为0.016MPa，如果龙门山断裂带南段库仑破裂应力年累积速率按照0.4×10-3-0.6×10-3MPa·a-1计算，汶川地震使芦山地震提前了约27-40年。计算还表明汶川地震和芦山地震的发生使鲜水河断裂带南段和虎牙断裂的库仑破裂应力增加，这些断裂带在未来发生地震的可能性增加。  相似文献   

衰减夹层GPR模拟的时频域全局反射误差   总被引：1，自引：1，他引：0       下载免费PDF全文

张彬  戴前伟  尹小波  冯德山 《地球物理学报》2017,60(3):1168-1178

全局反射误差分析是深入研究探地雷达(GPR)吸收边界条件吸收效率的有力工具.基于常规完全匹配层(PML)的标准交错网格有限差分算法必须满足严格的CFL条件限制,即在单位时间步长内,不容许电磁波传播的距离超过单元网格尺寸.为了提高主区域所有网格节点的计算效率,并有效地吸收传播后期出现的低频隐失波,提出基于非分裂递归卷积完全匹配层(UCPML)的旋转交错网格(RSG)GPR正演算法.该算法采用不同的网格交错策略,并在边界条件中引入了吸收低频隐失波的自由可变因子,使得该算法允许选取较大的时间步长,提高了计算效率,并且实现了对低频隐失波的高效吸收.本文首先给出了RSG差分格式,推导了基于UCPML的RSG差分更新方程,探讨了数值色散的稳定性条件,然后以绕射现象严重的衰减夹层数值模拟为例,分别从波场快照、单道波记录、时间域反射误差(TDRE)、频率域反射误差(FDRE)四个方面分析了UCPML与常规PML的全局反射误差,说明了基于UCPML和RSG的GPR正演算法能更有效地吸收低频隐失波.  相似文献   

The role of Quality of Place factors in expatriate international relocation decisions: A case study of Suzhou,a globally-focused Chinese city     

《Geoforum》2017

The role of ‘quality of place’ (QoP) in attracting and retaining workers has been a significant concern of urban related policy makers and research communities over the past decade. This paper aims to address the significance of QoP factors in attracting and/or retaining global talent by presenting the findings and implications of a study into the relocation decisions of expatriate workers in Suzhou, China. Findings from a survey questionnaire indicate that global talent moving to Suzhou have been driven primarily by career-related opportunities instead of QoP factors. However, binary logit analysis shows that QoP factors have contributed positively towards the retention of global talent in the city.  相似文献   

Using principal component analysis in the investigation of groundwater hydrochemistry of Upper Jezireh Basin,Syria     

Boulos Abou Zakhem  Abdulrahman Al-Charideh  Bassam Kattaa 《水文科学杂志》2017,62(14):2266-2279

Principal component analysis (PCA) was applied to hydrochemical and isotopic data of 34 groundwater samples. This allowed the reduction of 20 variables to four significant PCs that explain 81.9% of the total variance; F1 (47.1%) explains the groundwater mineralization, whereas F2 (17%) shows isotopic enrichment and nitrate pollution. Based on an iso-factor scores map of F1, three water zones were delineated: Zone A (F1 < ?1), with fresh groundwater from the unconfined aquifer; Zone B (1 > F1 > ?1), with moderate mineralization from the confined–unconfined aquifer boundary; and Zone C (F1 > 1), with the most mineralized hot water from the confined aquifer. The iso-factor scores map of F2 delineates positive values representing samples from the unconfined aquifer, with freshwater and nitrate contamination associated with stable isotope enrichment, whereas negative values represent samples from the confined aquifer. The results clearly demonstrate the usefulness of PCA in groundwater hydrochemistry investigations.  相似文献   

Frequency analysis of nonstationary annual maximum flood series using the time‐varying two‐component mixture distributions          下载免费PDF全文

Lei Yan  Lihua Xiong  Dedi Liu  Tiesong Hu  Chong‐Yu Xu 《水文研究》2017,31(1):69-89

The most popular practice for analysing nonstationarity of flood series is to use a fixed single‐type probability distribution incorporated with the time‐varying moments. However, the type of probability distribution could be both complex because of distinct flood populations and time‐varying under changing environments. To allow the investigation of this complex nature, the time‐varying two‐component mixture distributions (TTMD) method is proposed in this study by considering the time variations of not only the moments of its component distributions but also the weighting coefficients. Having identified the existence of mixed flood populations based on circular statistics, the proposed TTMD was applied to model the annual maximum flood series of two stations in the Weihe River basin, with the model parameters calibrated by the meta‐heuristic maximum likelihood method. The performance of TTMD was evaluated by different diagnostic plots and indexes and compared with stationary single‐type distributions, stationary mixture distributions and time‐varying single‐type distributions. The results highlighted the advantages of TTMD with physically‐based covariates for both stations. Besides, the optimal TTMD models were considered to be capable of settling the issue of nonstationarity and capturing the mixed flood populations satisfactorily. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Effect of riparian land use on environmental conditions and riparian vegetation in the east African highland streams     

《Limnologica》2017

Agricultural land use is expanding and at an accelerated rate. In Ethiopia, most of this expansion has occurred in highland areas and involve deforestation of natural riparian vegetation. However, the impacts on the water quality of streams are poorly understood, especially with regard to the influence of land use patterns on highland streams. In this study, we investigated the effects of land use modifications on the water quality and riparian condition of highland streams and examined whether the preservation of riparian vegetation would help mitigate the negative impacts of intensive agriculture practices. Our results show significant differences in the water quality of streams with different land use. Several parameters commonly used to indicate water quality, such as the concentrations of orthophosphate, turbidity, and suspended solids were significantly higher in the agricultural streams than in the forest stream. The preservation of riparian vegetation in the surrounding highland streams was associated with overall better riparian condition, floristic quality, and water quality such as lower turbidity, total suspended solids, orthophosphate, and higher dissolved oxygen. We conclude, that increases in vegetation cover improved riparian condition and water quality relative to other non-vegetated areas. Therefore, we strongly recommend the preservation of riparian vegetation in tropical highland streams surrounded by intensive agriculture. More studies on the effects of best management practices in areas dominated by agriculture can greatly improve our capacity to prevent the degradation of water quality in tropical highland streams of Africa.  相似文献   

中国地震台网监测能力评估和台站检测能力评分(2008—2015年)          下载免费PDF全文

王亚文  蒋长胜  刘芳  毕金孟 《地球物理学报》2017,60(7):2767-2778

针对中国地震台网"十五"项目建成后的地震监测能力科学评估的需求，为进一步优化台网布局、提升边疆海域等重点地区监测能力，本研究利用"基于概率的完整性震级"（PMC）方法，对中国地震台网1001个台站以及2008-10-01-2015-09-17期间实际产出的地震观测资料进行了研究，分析了指定震级档下的检测概率P_E和最小完整性震级M_P的分布.除台网整体监测能力分布外，为直观地用单分值表述逐个台站的地震检测能力，本文发展了基于等振幅曲线的"地震检测能力评分表"，给出了国家台和区域台每个台站的地震检测能力评分统计特征和空间分布特征.此外，研究中还采用设定"最佳"地震监测能力目标函数的方式，模拟了通过改进观测条件可获得的地震台网监测能力提升的理论结果.研究结果表明，我国华北和东南沿海等东部地区地震监测能力较高，西部尤其是青藏高原南部地区M_p仅约为4.5，近海海域M_p仅约为3.5；从单个地震台站的运行效益角度，台网运行水平和地震观测资料的分析程度对台站的实际的地震检测能力影响显著，新疆等部分台站稀疏地区地震检测能力较高，而中等台站密度的贵州等部分区域相对较低；国家台的地震检测能力评分D_score系统优于区域台，新疆等西部边疆地区，以及福建等东南沿海地区的D_score明显高于台站密集的东部地区；模拟结果显示，在现有台站布局条件下，通过台站优化改造和提升运维管理水平，可显著提升对内蒙古西部、四川西部、甘肃-青海的北部交界地区、鄂尔多斯地块内部、贵州大部分地区，以及我国近海海域、朝鲜半岛北部和中南半岛北部地区的地震监测能力.  相似文献   

Investigation of trace metals distribution in water,sediments and wetland plants of K(i)z(i)l(i)rmak Delta,Turkey     

Mehmet Soner Engin  Ahmet Uyanik  Seydahmet Cay 《国际泥沙研究》2017,32(1)

In this study,accumulation and distribution of Pb,Cu,Zn,Co,Ni,Mn and Fe in water,bottom sediments and four plant species (Myriophyllum verticillatum,Hydrocharis morsus-ranae,Nymphaea alba and Typha latifolia) were investigated in (C)ernek Lake of Kizihrmak Delta.The Kizdirmak Delta is one of the largest natural wetlands of Turkey and it is protected by the Ramsar convention since 1993.Selected physico-chemical parameters such as pH,conductivity and dissolved oxygen and also trace metal concentrations were monitored in water.All the parameters obtained were found higher than that of the national standards for the protected lakes and reserves.The accumulated amounts of various trace metals in bottom sediments and wetland plants were found in the following order of Fe ＞ Mn ＞ Zn ＞ Ni ＞ Co ＞ Cu ＞ Pb and Fe ＞ Mn ＞ Zn ＞ Ni ＞ Co respectively.The historical trace metal intake of Myriophyllum verticillatum,Hydrocharis morsus-ranae,Typha latifolia and Nymphaea alba were obtained higher than that of the toxic metal levels and these plants may be accepted as accumulators for the detected trace metals and also bioindicators in the historically polluted natural areas.  相似文献   

不同初始扰动对电离层扩展F影响的数值模拟          下载免费PDF全文

高泽  方涵先  汪四成  杨升高 《地球物理学报》2017,60(2):470-479

重力波、中性风场、电场是激发电离层扩展F的主要影响因子,本文基于中低纬电离层扩展F发展的物理模型,通过电场强度、背景风场对扩展F影响作用的分析和经验对比,首先验证了模型的有效性,后借助该模型数值模拟了给定背景环境下三种尺度初始电子密度扰动条件下扩展F的发展情况,同时研究了利用化学物质释放实现一定尺度扰动,进而激发扩展F的过程.结果表明,较强的背景电场、东向风场有利于扩展F的形成和抬升,与经验结论相吻合;电离层从被作用初始扰动到激发扩展F的过程中存在拐点效应,拐点之后扩展F被激发形成并且抬升迅速,同时短波长扰动相对于长波长扰动更有利于扩展F的激发和发展;化学物质H_2O释放通过耗散电子密度,形成了一定尺度扰动并诱发了扩展F的形成,该方法可作为一种人工激发扩展F的探索手段.  相似文献