基于随机变异—Kennard—Stone和偏最小二乘法的土壤重金属镉含量反演——以雄安新区西南部为例

土壤重金属污染对人类身体健康造成了严重威胁,作为快捷、高效、无损监测分析土壤重金属含量的方法之一,高光谱遥感反演土壤重金属含量的方法正逐步得到发展。本文以雄安新区西南部作为研究区,针对潜在生态风险最大且活性最强并易被植物吸收的重金属镉,开展高光谱反演研究。将采集来的426件土壤样品除杂、风干、过筛在实验室测得重金属含量,并用SVC便携式地面光谱仪测量样品350~2500 nm范围光谱。采用Savitzky—Golay卷积平滑方法进行光谱降噪平滑处理。由于粒径大小而不是化学成分差异可能会导致基线效应和漂移现象,为了增强光谱差异和光谱曲线形状,将数据进行标准正态变量变换(SNV)、一阶微分(FD)、二阶微分(SD)、多元散射校正(MSC)等数学变换,并分析变换后光谱与Cd含量的相关性。本文提出一种集成随机变异法—Kennard—Stone法—偏最小二乘回归的方法。针对变换后的光谱集和Cd含量集,第一步采用随机变异法—Kennard—Stone法将样本集分为70%训练集和30%验证集,使样本数随性质分布均匀并覆盖整个样本空间;第二步用偏最小二乘回归法结合交叉验证建立回归模型,用确定系数R2、均方根误差RMSE、偏差比值RPD、误差范围比值RER等参数开展模型评价,如果没有达到预期效果,则回到第一步,迭代反复选择,直至达到最优效果。结果表明,适用的最优反演重金属镉含量的技术方法是采用FD变换后,不断迭代集成RM—KS样本选择和PLS偏最小二乘法回归建立的模型,其验证综合效果最好,建模主成分数为11个,确定系数R2达到0.909,RMSE为0.604,RPD为2.696,RER达为15.516。成果可为类似区域快速、无损的土壤重金属Cd含量反演提供技术支撑。     

Multivariate statistical analysis of heavy metals in foliage dust near pedestrian bridges in Guangzhou, South China in 2009

The heavy metal content of particulate matter was investigated in the city of Guangzhou in southern China. Samples of urban foliage near 36 pedestrian bridges were analyzed to determine their Zn, Pb, Cu, Cr, V, Ni, and Co contents after digestion in a mixture of strong acids composed of HNO₃, HCl, HF, and HClO₄. The results revealed a severe heavy metal pollution compared with the background levels in Chinese soils, except for Co and V. The mean concentrations of Zn (1,024 mg kg^?1), Pb (233 mg kg^?1), Cu (203 mg kg^?1), Cr (118 mg kg^?1), V (41.9 mg kg^?1), Ni (41.4 mg kg^?1), and Co (11.3 mg kg^?1) in urban dust were higher than the reference levels, and were highest in samples located near high-traffic areas. Multivariate statistical methods (correlation analysis, principal-components analysis, and clustering analysis) were used to identify the possible sources of the metals. Three main pollutant sources are assigned: Zn, Cu and Ni levels were strongly correlated and were possibly related to combustion processes and vehicles; Pb, Cr and Co were mainly derived from traffic sources, combined with soil sources; and V mainly originated from natural sources.     

Experimental study of unidirectional irregular wave slamming on the three-dimensional structure in the splash zone

The experimental investigation of unidirectional random wave slamming on the three-dimensional structure in the splash zone is presented. The experiment is conducted in the marine environment channel in the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology. The test wave is unidirectional irregular wave. The experiments are carried out with perpendicular random waves (β=0°) and oblique random waves (β=15°, 30°, 45°), the significant wave heights H_1/3 ranging from 7.5 to 20 cm with 2.5 cm increment, the peak wave periods T_p ranging from 0.75 to 2.0 s with 0.25 s increment, and the clearance of the model with respect to the significant wave height s/H_1/3 ranging from 0.0 to 0.5 with 0.1 increment. The statistical analysis results of different test cases are presented. The statistical distribution characteristics of the perpendicular irregular wave impact pressures are compared with that of the oblique irregular wave on the underside of the structure. The effect of the wave direction β on the wave impact forces on the underside of the structure is determined. The relation between the impact forces and the parameters such as the significant wave height, the relative structure width and the relative clearance of the structure is also discussed.     

单台多震和达法研究山西地区的波速比变化特征

基于山西数字地震台网2001年1月～2014年10月ML≥2.0地震震相到时数据,利用单台多震和达法计算山西地区波速比,并结合2010年3次MS≥4.5地震探讨地震前后波速比的变化特征。结果表明,在3次地震前远台波速比异常出现时间较早,为震前6个月至1年;而近台波速比异常出现时间相对较晚,为震前10天至2个月不等,因此可通过远台、近台所围限的范围来缩小地震预测地点。东山台计算结果表明,发震时刻残差大小会影响波速比变化细节,因此在实际应用中,应首先确定每个台站发震时刻的残差阈值,以确保波速比计算结果的科学性和稳定性。     

基于磁感应的跨介质通信技术研究

随着海洋军事与战略的发展,传统声学难以完成空水跨介质通信需求。磁感应通信技术由于在空水介质中磁导率一致,且具有信道稳定、速度快、体积灵活、成本低的优势,可以作为空水跨介质的技术补充。以磁偶极子为基础,对空水跨介质感应磁场传播模型进行了研究,证明磁场在空水界面的传播连续性,之后基于USRP设计通信收发电路并实现一套磁感应通信系统。该系统在收发线圈半径10 cm,发射功率1 mW情况下,实现空水（湖水）跨介质20m,通信速率10kbps的无误码文本传输,证实了磁感应通信在空水跨介质场景下的可行性,对后续的相关研究具有一定的指导意义。     

Spatiotemporal characteristics of droughts and floods in northeastern China and their impacts on agriculture

Heilongjiang Province is a major grain production base in China, and its agricultural development plays an important role in China’s social economy. Drought and flood events are the primary disasters in Heilongjiang Province and have considerable impacts on agriculture. In this study, relatively complete monthly precipitation data from 26 meteorological stations in Heilongjiang Province during the period of 1958–2013 were analyzed using the standardized precipitation index (SPI) combined with principal component analysis, Mann–Kendall trend analysis and Morlet wavelet analysis to determine the spatial and temporal distributions of drought and flood events in this province. The results were as follows: (1) the whole of Heilongjiang exhibited an aridity trend. In northern Heilongjiang, spring and summer experienced a wetting trend, and autumn and winter experienced an aridity trend. (2) The SPI3 exhibited 8- and 16-year periodic variation characteristics in spring, 10- and 22-year periodic variation characteristics in summer, and 10- and 32-year periodic variation characteristics in autumn. In addition to the 10-year periodic variation characteristics in winter, other periodic variation characteristics were observed. (3) The increasing trend in the percentage of stations affected by flood was more obvious than that affected by drought. Therefore, Heilongjiang Province is more vulnerable to flooding. (4) The influence of drought and flood disasters in Heilongjiang Province showed a growth trend, but the flood effect was more remarkable. (5) The agricultural area affected by drought and flood disasters in Heilongjiang Province showed an increasing trend. Although there was a greater increase in flood disaster area, the main types of disasters were drought-dominated.     

莺歌海盆地LD10区高含CO2天然气充注期次精细厘定与成藏模式

莺歌海盆地LD10区中深层黄流组?梅山组重力流水道、海底扇储层已被证实具有重大的天然气资源潜力.但是前期测试结果显示气藏中混有高含量CO₂气体.因此,精细厘定天然气充注期次,明确CH₄、CO₂等时空分布规律对规避高CO₂风险至关重要.本研究在对不同产状流体包裹体岩相学特征精细观察的基础上,综合激光拉曼光谱分析和包裹体显微测温技术识别出3幕不同成分天然气充注,时间分别为:4.0~2.9 Ma、2.0~1.2 Ma和0.8~0.3 Ma.其中,第一幕充注以烃类气为主,伴有少量有机CO₂和N₂;第二幕和第三幕充注以大量无机CO₂、烃类气为主,伴有少量N₂.结合天然气及烃源岩地化特征、天然气组分分析及输导体系识别,总结了LD10区的成藏模式,以期为研究区下一步天然气勘探开发和规避高含量CO₂风险提供依据.      

黏性土中结合水测定及影响因素分析

土中结合水是形成黏性土的物理、化学、力学等性质的重要因素。通过对一系列人工混合黏性土和2种天然红黏土进行比表面积测试和等温吸附试验,确定各类黏性土的比表面积和土中不同结合水类型及含量,在此基础上探讨黏性土中结合水与矿物成分、比表面积等影响因素之间的定量关系。研究结果表明：(1)黏性土的比表面积与黏土矿物含量线性正相关;(2)等温吸附法中,相对湿度RH=0.90和0.98分别为黏性土中强结合水、弱结合水、自由水的界限划分点;(3)相同矿物成分的混合黏性土吸附结合水含量随蒙脱土含量、比表面积的增加而递增,大致呈线性关系;(4)天然红黏土的吸附结合水含量与其矿物成分总量、比表面积具有正相关关系,黏土矿物含量是最根本的影响因素。     

单台多震和达法研究山西地区的波速比变化特征

基于山西数字地震台网2001年1月~2014年10月ML≥2.0地震震相到时数据,利用单台多震和达法计算山西地区波速比,并结合2010年3次MS≥4.5地震探讨地震前后波速比的变化特征。结果表明,在3次地震前远台波速比异常出现时间较早,为震前6个月至1年;而近台波速比异常出现时间相对较晚,为震前10天至2个月不等,因此可通过远台、近台所围限的范围来缩小地震预测地点。东山台计算结果表明,发震时刻残差大小会影响波速比变化细节,因此在实际应用中,应首先确定每个台站发震时刻的残差阈值,以确保波速比计算结果的科学性和稳定性。