用地面核磁共振方法评估含水层涌水量的实例

地面核磁共振(NMR)方法是地球物理上采用的探测地下水的最新方法,能够探测地下含水层中的自由水.但是有时会出现对地下含水层的出水量判断失误的现象,这种失误发生的主要原因是由于IRIS仪器设计时假设利用NMR信号的弛豫时问就能够区分地下含水层中的自由水和束缚水,实际上弛豫时间取决于以下几个参数即:孔隙度、渗透率和导水率.地层孔隙水中氢质子弛豫时间不仅与其本身的弛豫特点有关,还与岩石孔隙结构、成份密切相关.为了更好的理解以上这些参数对地下含水层涌水量的影响,本文讨论了含水多孔介质的弛豫特性,研究有效孔隙度与含水量之间的关系,给出计算渗透率和导水率的方法,利用几个实测地点数据资料分析地下含水层岩性对涌水量的影响,结果表明地层中平均含水量大而且含水地层弛豫时间较长的地点才能获得较大的涌水量.     

垃圾填埋场渗滤液污染地下含水层及修复过程的三维动态监测实验

为实现垃圾填埋场渗滤液在地下含水层中动态扩散及污染层修复过程的实时监测,利用自行设计的三维电学观测系统开展了室内相关监测实验.实验表明渗滤液在含水层中的扩散过程会引起不同时期实测电剖面上低阻异常区的动态变化.对比分析这种变化特征可确定渗滤液扩散区的污染程度、扩散速度及扩散方向.在注水修复过程中,扩散区污染物含量的降低会引起对应区域实测视电阻率值的升高和异常区范围的变化.实验结果对于实现垃圾渗滤液污染地下含水层现状调查及动态监测具有重要意义.     

基于ε-SVR算法的大地电磁测深资料去噪

消除噪声干扰对大地电磁测深资料的影响是大地电磁(MT)工作中的首要问题.基于结构风险最小化原则的支持向量机能够解决小样本情况下非线性函数拟合的通用性和推广性问题,是求复杂的非线性拟合函数的一种有效技术.本文首先介绍了ε-SVR(ε不敏感损失函数—支持向量机回归)的原理及SVR相关参数的选择,在此基础上,利用该算法对大地电磁测深实测资料进行回归处理,并与当前常用的去噪方法(Robust变换结合人工筛选)进行对比,结果表明ε-SVR算法可以较好地消除MT测深曲线所受噪声影响,提高工作效率.同时给原始数据加入10%噪声,并利用该算法对加噪后的数据进行回归处理,加噪前后拟合结果的绝对误差的均方差为9.454,相对误差的均方差为1.61%,证明该模型具有良好的泛化能力和稳健性.     

一种测求水井含水层导水系数的新方法

本文给出了一种测求水井含水层导水系数的新方法。利用Cooper理论和振动理论,通过简单的试验,可以测求出水井含水层的导水系数。用这种方法计算出珍珠泉井含水层的导水系数为2439m~2/d,用抽水试验法测得该系数为2618m~2/d,两者符合得较好。     

基于支持向量机回归多属性在地震应急决策中的应用探讨

地震应急是为了减轻地震灾害而采取的异于正常工作程序的紧急防灾和抢险行动。传统的震后应急决策主要依据应急条例标准以及决策者的经验,导致出队决策可能并非最优方案。随着数据挖掘和人工智能技术的发展,目前多种推荐算法在决策推荐领域正在被广泛的应用,对应急成员的基本情况按工龄、集合时间、应急次数3个属性进行分析,利用遗传算法全局最优收敛的特性,通过对支持向量机的3个属性参数进行寻优推荐,得到最优地震应急出队成员。     

一种新的实时电磁逆散射方法

为解决介质圆柱体逆散射问题,提出一种新的在线逆散射方法,通过支持向量机将逆散射问题转化成一个回归估计问题. 该方法可应用于各种逆散射方面, 尤其是目标的几何与电磁参数重构和埋地目标探测. 文中首次将支持向量机方法应用到该领域,设置多个散射场的观测点,通过提取散射场的不同信息作为样本信息训练支持向量机, 建立了介质圆柱体的逆散射模型, 利用该模型重构了介质圆柱体的电磁参数,同时探测了埋地位置. 数值结果显示了该方法的有效性和准确性,为目标的实时逆散射研究提供了一种有效方法.     

基于支持向量机的多维地震时间序列建模

文中首先介绍了支持向量机回归方法,然后对其进行了数值仿真实验,最后利用该方法对首都圈地区的地震活动进行回归建模与内符检验。分析认为,利用该方法可以获得较强的多维地震样本学习、建模与外推泛化能力,具有较高的中长期地震危险性估计能力。     

基于PCA-PSO-SVM的地震死亡人数预测模型研究

为准确预测地震死亡人数,提出了基于主成分分析法(PCA)和粒子群算法(PSO)优化的支持向量机(SVM)模型。首先利用主成分分析法对地震死亡人数7个影响因子中的6个进行数据降维,同时对第7个发震时刻因子单独进行区间分类,然后对提取出的主成分进行归一化处理,将归一化的主成分数据作为支持向量机的输入向量,通过粒子群算法寻优获得最优支持向量机模型参数,最终建立基于PCA-PSO-SVM的地震死亡人数预测模型,并对5组样本进行死亡人数预测,同时对比分析包含和不包含发震时刻因子的2种情况下的模型预测效果。结果表明:在不考虑发震时刻因子的情况下,使用PCA-PSO-SVM模型的最小误差、最大误差和平均误差分别为0.85%、20%、10%,其平均误差相比PSO-SVM、SVM模型分别降低2.08%、2.28%;输入向量加入发震时刻因子分类数据后,PCA-PSO-SVM模型的最小误差、最大误差和平均误差分别为0.25%、20%、7.18%,其平均误差相比PSO-SVM、SVM模型分别降低3.34%、3.50%。因此,加入发震时刻因子后3种模型的平均误差明显降低,同时由于PCA-PSO-SVM模型进行主成分降维处理,能够明显提高运行效率和预测精度,故降低了模型复杂度。     

宝石能谱CT及机器学习算法在判断胃癌浆膜浸润中的初步应用

目的:探讨宝石能谱CT及机器学习算法在判断胃癌浆膜浸润中的价值。方法:回顾性分析在我院行宝石能谱CT双期GSI增强检查的胃癌患者24例,其中p T2 8例,p T3 4例,p T4 12例。12例患者(p T4)归为浆膜阳性组(组A);12例(T2和T3)归为浆膜阴性组(组B)。采用独立样本t检验或卡方检验比较两组患者的临床信息(如性别、年龄等)。此外,所有图像利用GE AW4.4工作站进行后处理,分别得出两组病灶双期能谱信息,随后采用SVM-RFE算法对两组能谱信息进行分析。结果:两组患者的临床信息中,肿瘤长径和短径在两组间有统计学差异(P均<0.05)。SVM-RFE算法的准确率为87.5%-94.4%。SVM-RFE的输出结果为门脉期脂肪(钙)、门脉期尿酸(钙)、动脉期钙(碘)、门脉期水(钙)、门脉期碘(水)。结论:肿瘤大小和门脉期脂肪(钙)、门脉期尿酸(钙)、动脉期钙(碘)、门脉期水(钙)及门脉期碘(水)特征值可用于辅助判定胃癌是否浸润浆膜层。     

基于粗糙集-支持向量机的震害预测模型及应用

结合粗糙集理论的属性约简与支持向量机的分类功能,建立了基于粗糙集与支持向量机的建筑物震害预测模型.该模型首先运用粗糙集理论,建立决策表,进行属性离散、属性重要性排序、属性约简和分类规则的提取,然后用所提取的关键成分训练支持向量机.该模型不但能有效降低建筑物震害影响因子数据维数及支持向量机的复杂程度,提高训练速度和分类精度,而且还能对各因子的影响程度进行排序.最后,通过实例验证了该模型的性能.     

A model to predict stream water temperature across the conterminous USA

Stream water temperature (t_s) is a critical water quality parameter for aquatic ecosystems. However, t_s records are sparse or nonexistent in many river systems. In this work, we present an empirical model to predict t_s at the site scale across the USA. The model, derived using data from 171 reference sites selected from the Geospatial Attributes of Gages for Evaluating Streamflow database, describes the linear relationship between monthly mean air temperature (t_a) and t_s. Multiple linear regression models are used to predict the slope (m) and intercept (b) of the t_a–t_s linear relation as a function of climatic, hydrologic and land cover characteristics. Model performance to predict t_s resulted in a mean Nash–Sutcliffe efficiency coefficient of 0.78 across all sites. Application of the model to predict t_s at additional 89 nonreference sites with a higher human alteration yielded a mean Nash–Sutcliffe value of 0.45. We also analysed seasonal thermal sensitivity (m) and found strong hysteresis in the t_a–t_s relation. Drainage area exerts a strong control on m in all seasons, whereas the cooling effect of groundwater was only evident for the spring and fall seasons. However, groundwater contributions are negatively related to mean t_s in all seasons. Finally, we found that elevation and mean basin slope are negatively related to mean t_s in all seasons, indicating that steep basins tend to stay cooler because of shorter residence times to gain heat from their surroundings. This model can potentially be used to predict climate change impacts on t_s across the USA. Copyright © 2014 John Wiley & Sons, Ltd.     

Conceptualizing a multi-layered shingle aquifer model based on volcanic stratigraphy and water inflow to lava caves in Jeju Island,Korea

Volcanic aquifers supply a substantial portion of water resources in many parts of the world, including islands, and their productivity depends strongly on volcanic stratigraphy, which exhibits considerable heterogeneity. We investigated water inflow to lava tube caves formed from numerous basaltic lava flows in the northeastern coastal area of Jeju Island after storm events and monitored relative inflow rates monthly over 1 year to characterize groundwater flow processes in the upper parts of volcanic aquifers, and to evaluate the applicability of the previous hydrogeological models proposed for the island. Considerable water inflow arose shortly after storms from exposed palaeosol layers on the walls of the caves. The monthly monitoring results showed that wall inflow associated with these palaeosol layers is substantial. In both cases, discharge from ceiling drips was much less and more temporally variable compared to wall inflow discharge. Water flowing into the caves was rapidly drained through the floor at all monitoring sites. The lateral extent of the palaeosol layers was identified using drill core logs near the cave and outcrops in the coastal area. Based on these results, we inferred that multiple perched aquifers are formed by low-permeability palaeosol layers between lava flows, which are connected by vertical flows at discontinuities in the palaeosol layer, eventually reaching the basal aquifer. This study revealed the water inflow processes observed in lava tube caves constrained by palaeosol layers, and established a hydrogeological conceptual model incorporating multiple perched aquifers in both coastal and mountainous areas associated with extensive palaeosol layers formed during volcanic hiatuses. This finding would help elucidate recharge, groundwater flow, and contaminant transport processes in many volcanic aquifers that are not adequately represented by the previous models, and contribute to better management of groundwater in those areas.     

A neural network model for predicting aquifer water level elevations

Artificial neural networks (ANNs) were developed for accurately predicting potentiometric surface elevations (monitoring well water level elevations) in a semiconfined glacial sand and gravel aquifer under variable state, pumping extraction, and climate conditions. ANNs "learn" the system behavior of interest by processing representative data patterns through a mathematical structure analogous to the human brain. In this study, the ANNs used the initial water level measurements, production well extractions, and climate conditions to predict the final water level elevations 30 d into the future at two monitoring wells. A sensitivity analysis was conducted with the ANNs that quantified the importance of the various input predictor variables on final water level elevations. Unlike traditional physical-based models, ANNs do not require explicit characterization of the physical system and related physical data. Accordingly, ANN predictions were made on the basis of more easily quantifiable, measured variables, rather than physical model input parameters and conditions. This study demonstrates that ANNs can provide both excellent prediction capability and valuable sensitivity analyses, which can result in more appropriate ground water management strategies.     

A new analytical solution of tidal water table fluctuations in a coastal unconfined aquifer

This paper presents a new perturbation solution of the non-linear Boussinesq equation for one-dimensional tidal groundwater flow in a coastal unconfined aquifer. Built upon the work of Parlange et al. [Parlange, J.-Y., Stagnitti, F., Starr, J.L., Braddock, R.D., 1984. Free-surface flow in porous media and periodic solution of the shallow-flow approximation, J. Hydrol., 70, 251–263], the solution adopts a new perturbation parameter that is by definition less than unit, and thus is applicable to a wider range of physical conditions within the constraint of the Boussinesq approximation. This approach avoids a secular term in the third-order perturbation equation of Parlange et al. (1984), enabling the derivation of the third- and higher-order solutions. In comparison with a numerical (“exact”) solution, the new perturbation solution is shown to be slightly more accurate than that of Parlange et al. (1984) with the second-order approximation. The obtained third-order solution exhibits considerable improvement in accuracy. In relatively simple analytical forms, the present perturbation solution will help to understand better the non-linear characteristics of tidal water table fluctuations in as modeled by the non-linear Boussinesq equation coastal unconfined aquifers.     

Stack unit mapping of coastal aquifer to predict and control sea water intrusion using remote sensing and a geographical information system

Aquifers are inherently susceptible to contamination and coastal aquifers in specific are highly vulnerable to sea water intrusion. For efficient planning and management of coastal aquifers in Kayalpattu and Tiruchopuram villages, which extend over 4·05 km², it is essential to delineate and predict the extent of intrusion into the shallow aquifer. Management of ground water in coastal aquifers is composed of major elements that should be properly evaluated, and special attention is given to the sea water intrusion problem. Different data, like hydro‐geomorphological and depth‐wise iso‐apparent resistivity, are integrated spatially using a geographical information system. The stack‐unit mapping approach is used to delineate the zones with iso‐apparent resistivity of less than 10 Ω m have been found to be increasing in areal extent with reference to depth. Copyright © 2003 John Wiley & Sons, Ltd.     

Estimating aquifer properties from the water level response to Earth tides

Water level fluctuations induced by tidal strains can be analyzed to estimate the elastic properties, porosity, and transmissivity of the surrounding aquifer material. We review underutilized methods for estimating aquifer properties from the confined response to earth tides. The earth tide analyses are applied to an open well penetrating a confined carbonate aquifer. The resulting range of elastic and hydraulic aquifer properties are in general agreement with that determined by other investigators for the area of the well. The analyses indicate that passive monitoring data from wells completed in sufficiently stiff, low porosity formations can provide useful information on the properties of the surrounding formation.     

A mathematical model to predict the inelastic response of a steel frame: Formulation of the model

The purpose of this research is to use data from experiments to formulate a mathematical model that will predict the non-linear response of a single-storey steel frame to an earthquake input. The process used in this formulation is system identification. The form of the model is a second-order non-linear differential equation with linear viscous damping and Ramberg—Osgood type hysteresis. The damping coefficient and the three parameters in the hysteretic model are to be established. An integral weighted mean squared error function is used to evaluate the [goodness of fit] between the model's response and the structure's response when both are subjected to the same excitation. The function includes errors in displacement and acceleration and is integrated from zero to a time T, which may be the full duration of the recorded response or only a portion of it. The parameters are adjusted using a modified Gauss-Newton method until the error function is minimized. The computer program incorporating these steps in the system identification process is verified with simulated data. Results given in the paper show that in every case the program converges in few iterations to the assigned set of parameters.     

An analysis of the salt water inflow into the Baltic in 1975 to 1976

Time series measurements from light vessel and coastal stations in the transition area of the Kattegat and the Baltic Sea are analyzed for the period August 1975 to March 1976. The data consist of daily sampled salinities from different depth levels and daily means of sea levels, surface current, and wind, respectively. The purpose of this paper is to examine the dynamics of the mass- and salt-transport during a major salt water inflow.The principal conclusions of this paper are that

Effects of water use on arsenic release to well water in a confined aquifer

Field-based experiments were designed to investigate the release of naturally occurring, low to moderate (< 50 microg/L) arsenic concentrations to well water in a confined sandstone aquifer in northeastern Wisconsin. Geologic, geochemical, and hydrogeologic data collected from a 115 m2 site demonstrate that arsenic concentrations in ground water are heterogeneous at the scale of the field site, and that the distribution of arsenic in ground water correlates to solid-phase arsenic in aquifer materials. Arsenic concentrations in a test well varied from 1.8 to 22 microg/L during experiments conducted under no, low, and high pumping rates. The quality of ground water consumed from wells under typical domestic water use patterns differs from that of ground water in the aquifer because of reactions that occur within the well. Redox conditions in the well can change rapidly in response to ground water withdrawals. The well borehole is an environment conducive to microbiological growth, and biogeochemical reactions also affect borehole chemistry. While oxidation of sulfide minerals appears to release arsenic to ground water in zones within the aquifer, reduction of arsenic-bearing iron (hydr)oxides is a likely mechanism of arsenic release to water having a long residence time in the well borehole.