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陈鹏  陈家君 《大地测量与地球动力学》2014,34(2):105-110

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Extracting the subsonic anti-symmetric lamb wave from a submerged thin spherical shell backscattering through iterative time reversal     

Xiaotao Yu  Linhui Peng  Gaokun Yu 《中国海洋大学学报(英文版)》2014,13(4):589-596

The extraction of the weakly excited anti-symmetric Lamb wave from a submerged thin spherical shell backscattering is very difficult if the carrier frequency of the incident short tone burst is not at its frequency of greatest enhancement. Based on a single channel iterative time reversal technique, a method for isolating the subsonic anti-symmetric Lamb wave is proposed in this paper. The approach does not depend on the form function of a thin shell and any other priori knowledge, and it is also robust in the presence of some stochastic noise. Both theoretical and numerical results show that the subsonic anti-symmetric Lamb wave can be identified, even when the carrier frequency of the incident short tone burst is away from the frequency of greatest enhancement. The phenomenon may also be observed even in the case that the subsonic anti-symmetric Lamb wave is submerged in the noise, other than the case with the Signal to Noise Ratio being less than 10 dB, when the amplitude of the noise is comparable with the specular wave. In this paper, each iteration process contains a traditional transmission and time reversal transmission steps. The two steps can automatically compensate the time delay of the subsonic anti-symmetric Lamb wave relative to the specular wave and within-mode dispersion in the forward wave propagation.  相似文献   

镇江雷暴气候特征及天气学预报方法分析   总被引：2，自引：0，他引：2  

孙翠梅  沈兴建  钱鹏 《气象与环境科学》2014,37(3):8-13

雷暴是严重的气象灾害之一,给人民生命财产带来严重影响。雷暴的发生发展地域性强,因此加强镇江本地雷暴特征的研究和预警工作十分必要。利用镇江市1959--2010年的雷暴气候资料,通过气候倾向率、小波分析等统计方法,对其周期性、时空分布特征及年（代）际、季节变化特征等进行了分析,得出以下结论：1）镇江市雷暴呈现出市区少、周边地区多的特点,其中句容雷暴发生频率最多且持续时间长。2）镇江市平均雷暴日数存在4a、6a、10～12a左右、准20a的长周期振荡信号。从长周期分析,镇江市近几年的年平均雷暴日数处于偏多周期时段。3）年平均雷暴日数距平,20世纪60年代、70年代、21世纪的00年代是正距平,特别是2006--2010年连续5a的平均雷暴日数都大于气候值,是雷暴频发时期;80年代、90年代为负距平。1963年的雷暴日数最多,有53．3天;1979年的最少,为15天。通过对1999--2008年镇江市地面观测资料的194个雷暴天气过程个例进行统计分析,对影响镇江市的雷暴天气系统进行了分型,在此基础上提出了预报镇江市雷暴天气的思路,为开展雷暴预报预警业务提供理论依据。  相似文献   

基于潮沟定点观测的潮间带水、沙、盐交换研究     

李鹏  杨世伦 《海洋与湖沼》2014,45(1):126-133

为研究潮间带和潮下带的水、沙、盐交换,于2006年6月25~28日（夏季大潮）和2006年12月29日~2007年1月4日（冬季中-大潮和小潮）在长江口九段沙一典型潮沟的固定点利用OBS-3A和ADP-XR进行了水深、浊度、盐度、流速流向剖面和回声强度观测。结果和结论为：（1）夏季大潮、冬季中-大潮、冬季小潮的潮周期垂向平均流速分别为26.5、15.9和8.4 cm/s,夏、冬季观测到的最大流速分别为84 cm/s和35 cm/s。（2）夏季盐度变化范围为0.65~4.91,平均盐度2.14;冬季盐度变化范围为3.5~10.3,中-大潮和小潮平均盐度分别为6.26和7.98。（3）高悬沙浓度出现在涨潮初期和部分落潮末期的低水位阶段;涨潮阶段的平均悬沙浓度是落潮阶段的1.11~7.0倍。（4）涨、落潮阶段的水体和盐输运量大体上趋于平衡;（5）无论是冬夏季或大小潮,潮沟在潮周期内的净输沙方向均指向陆,即落潮输沙量小于涨潮输沙量（平均小40%）;平均每个潮周期的净输沙量为6102 kg,结合潮盆面积推算的潮周期沉积速率为0.0112 mm/tide,或8.2 mm/a。  相似文献   

The Combined Effect of Initial Error and Model Error on ENSO Prediction Uncertainty Generated by the Zebiak-Cane Model          下载免费PDF全文

ZHAO Peng  DUAN Wan-Suo 《大气和海洋科学快报》2014,(5):447-452

Initial errors and model errors are the source of prediction errors. In this study, the authors compute the conditional nonlinear optimal perturbation （CNOP）-type initial errors and nonlinear forcing singular vector （NFSV）- type tendency errors of the Zebiak-Cane model with respect to El Nifio events and analyze their combined effect on the prediction errors for E1 Nino events. The CNOP- type initial error （NFSV-type tendency error） represents the initial errors （model errors） that have the largest effect on prediction uncertainties for E1 Nifio events under the perfect model （perfect initial conditions） scenario. How- ever, when the CNOP-type initial errors and the NFSV- type tendency errors are simultaneously considered in the model, the prediction errors caused by them are not am- plified as the authors expected. Specifically, the predic- tion errors caused by the combined mode of CNOP-type initial errors and NFSV-type tendency errors are a little larger than those caused by the NFSV-type tendency er- rors. This fact emphasizes a need to investigate the opti- mal combined mode of initial errors and tendency errors that cause the largest prediction error for E1 Nifio events.  相似文献   

广西大气能见度气候特征分析     

曾鹏  郑凤琴  熊文兵 《气象研究与应用》2014,(1):60-62

对1980至2012年广西85个县市能见度资料进行统计分析得出：广西主要城市及其周边地区能见度较低,边远山区及边境地区较高,呈现东部低、西部高的特点;广西近32a能见度年均值在14.4至18.2km之间,总体呈下降趋势.一年之中,能见度夏季高、冬季低,汛期能见度明显好于非汛期;能见度与气象要素的相关分析表明,能见度与温度、风速成正比,与压强、降水、湿度成反比.  相似文献   

白令海颗粒有机物碳、氮同位素组成及其生物地球化学意义   总被引：1，自引：0，他引：1  

林峰  陈敏  童金炉  曹建平  邱雨生  郑敏芳 《海洋学报(英文版)》2014,33(12):40-47

Stable carbon and nitrogen isotopic composition of particulate organic matter(POM) were measured for samples collected from the Bering Sea in 2010 summer. Particulate organic carbon(POC) and particulate nitrogen(PN) showed high concentrations in the shelf and slope regions and decreased with depth in the slope and basin, indicating that biological processes play an important role on POM distribution. The low C/N ratio and heavy isotopic composition of POM, compared to those from the Alaska River, suggested a predominant contribution of marine biogenic organic matter in the Bering Sea. The fact that δ13C and δ15N generally increased with depth in the Bering Sea basin demonstrated that organic components with light carbon or nitrogen were decomposed preferentially during their transport to deep water. However, the high δ13C and δ15N observed in shelf bottom water were mostly resulted from sediment resuspension.  相似文献   

Physical and biological controls on the summer chlorophyll bloom to the east of Vietnam   总被引：1，自引：0，他引：1  

Gengxin Chen  Peng Xiu  Fei Chai 《Journal of Oceanography》2014,70(3):323-328

The contributions of physical and biological processes to the chlorophyll-a (Chl-a) bloom to the east of Vietnam in summer are examined. The offshore jet redistributes Chl-a concentration by transporting high Chl-waters from the continental margin to the east of Vietnam. The jet also contributes to high concentrations of nutrients and zooplankton biomass that lead to a dynamic balance between increased nutrients and grazing pressure for phytoplankton growth. As a consequence, the net biological processes reduce the Chl-a concentrations in the broader offshore region, but they also maintain the filaments with higher Chl-a stretching away from the coast due to the reduced grazing pressure.  相似文献   

鲜浒苔稀硫酸水解产糖工艺研究   总被引：1，自引：1，他引：0  

冯大伟  姜鹏  李富超  秦松  赵瑾  陈华新 《海洋科学》2014,38(12):29-33

分别用质量分数为0.6%、1.0%、1.4%、1.8%、2.2%的稀硫酸在121℃高温高压的条件下水解鲜浒苔30、60、90 min,浒苔水解残留物再用纤维素酶酶解,用DNS法测定上述各步骤中的还原糖产量。结果表明,浒苔总糖含量为67.2%。稀硫酸水解工艺中,硫酸质量分数为1.8%、水解90 min,浒苔还原糖转化率最高,达59.9%,每克干质量浒苔可产生447.0 mg还原糖。稀硫酸水解残留物纤维素酶酶解工艺中,浒苔还原糖转化率较低,在硫酸质量分数为0.6%、水解时间为60 min时还原糖转化率出现最大值,仅为6.5%。结果显示浒苔稀硫酸水解产还原糖效果显著,但并不能促进纤维素酶酶解。浒苔糖化可单独采用稀硫酸水解工艺,本实验条件下的最佳工艺条件为1.8%硫酸水解90 min。本研究探索了浒苔糖化工艺条件,对后续的浒苔燃料乙醇发酵研究具有一定的参考意义。  相似文献   

近红外CO₂高光谱探测仪通道选择          下载免费PDF全文

毕研盟  杨忠东  卢乃锰  张鹏  王倩 《应用气象学报》2014,25(2):143-149

近红外波段 (1.6 μm) 遥感可探测大气CO₂含量信息,应用于碳循环研究中。宽波段、高分辨率不但对仪器研制是一个挑战,而且巨大的数据量对观测的正演、反演也是一个挑战性课题。该文应用自由度及信息量分析法,对近红外高光谱波段中探测通道进行CO₂信息量分析,选择前20~100个高信息量的CO₂探测通道,并进行了反演模拟测试。结果表明:前20个高信息量通道占所有通道总信息量的76.4%,仅用所选的前20个通道进行反演,与所有通道参加反演的结果相比,误差增加0.3×10-6;通道数增至60时,信息量增加,通道数再增加,信息量则增加不显著;CO₂反演误差存在相似的关系。在高CO₂信息量分布上,弱吸收性质的1.6 μm波段和强吸收性质的2.06 μm波段表现出不同特点。  相似文献