Wave boundary layers in rough turbulent flow     

Tai-Wen Hsu  Shan-Hwei Ou 《Ocean Engineering》1997,24(1):25-43

A one-layer time-invariant eddy viscosity model is specified to develop a mathematical model for describing the essential features of the turbulent wave boundary layer over a rough bed. The functional form of the eddy viscosity is evaluated based on a modified one-equation turbulence model in which the eddy viscosity varies in time and space. The present eddy viscosity model simplifies much of the mathematical complexity in many existing models. Predictions from the present model have been compared favorably with a wide range of experimental data. It is found that the eddy viscosity model adopted in the present study is physically reasonable.  相似文献   

福建省5级地震的气候前兆     

顾延芬 《台湾海峡》1991,10(4):399-402

本文通过相关统计事实,初步探讨了福建5级地震前期的气象异常,提出了“气压、气温和雨量”模式,发现一次中强震前的1～3a间,先出现大面积降压和最高气温的异常增温,后出现大面积的干旱。这一时序演变,似可作为一次完整的孕震过程的气象前兆而用于中长期地震预报。  相似文献   

Genetical study on the parthenogenesis in Laminaria japonica   总被引：3，自引：0，他引：3  

Dai Jixun  Cui Jingjin  Ou Yulin  Fang Zongxi 《海洋学报(英文版)》1993,12(2):295-298

The parthenogenesis and natural doubling of chromosomes in wild type female gametophytes of Laminaria japonica were studied. The results indicate that not all the female gametophytes from the wild type hybrid parent can propagate through parthenogenesis. Most parthenosporophytes can mature, their spores germinate into gametophytes, the latter then developed into female sporophytes. To form these parthenosporophytes the natural doubling of chromosomes occurred mainly at the first and second cell divisions of the spores. It is thus considered that the parthenogenesis of L. japonica is inheritable and the relative genes link closely with the genes controlling the natural doubling of chromosomes and the female determination.  相似文献   

The effects of semi-lunar spring and neap tidal change on nitrification, denitrification and N₂O vertical distribution in the intertidal sediments of the Yangtze estuary, China   总被引：3，自引：0，他引：3  

L.J. Hou  M. Liu  S.Y. Xu  D.N. Ou  J. Yu  S.B. Cheng  X. Lin  Y. Yang 《Estuarine, Coastal and Shelf Science》2007,73(3-4):607-616

To explore the influences of semi-lunar spring and neap tidal changes on nitrogen cycling in intertidal sediments, a comparative study among waterlogged, desiccated and reflooded systems was carried out in August 2005 and February 2006 by analyzing nitrification, denitrification and N₂O depth profiles in the intertidal flats of the Yangtze estuary. Laboratory experiments showed that alternating emersion and inundation resulted in the significant changes in nitrification and denitrification rates in the intertidal sediment systems. Due to the desiccation-related effects, lowest nitrification and denitrification rates were observed in the desiccated sediment cores. Highest nitrification and denitrification rates were however detected in the waterlogged and reflooded systems, respectively. It is hypothesized that the highest nitrification rates in the waterlogged sediments were mainly attributed to higher nitrifier numbers and NH₄⁺ being more available, whereas the availability of NO₃⁻ might dominate denitrification in the reflooded sediments. In addition, the highest N₂O concentrations were detected in the reflooded sediment cores, and the lowest found in the dried sediment cores. It was also shown that N₂O in the intertidal sediments was mainly from nitrification under the desiccated condition. In contrast, N₂O in the intertidal sediments was produced mainly via denitrification under the waterlogged and reflooded conditions. It is therefore concluded that the semi-lunar tidal cycle has a significant influence on nitrification, denitrification and N₂O production in the intertidal sediment systems.  相似文献   

土工格栅加筋珊瑚砂的强度及变形特性试验研究     

骆赵刚  丁选明  欧强  蒋春勇  方华强 《岩土力学》2023,(4):1053-1064

珊瑚岛礁钙质砂作为海洋工程建设的主要原材料,具有碳酸钙含量高、多孔隙、颗粒易破碎等特征。为了进一步提高海洋工程建设中岩土构筑物的强度及稳定性,采用土工格栅加筋珊瑚砂是一种潜在的有效手段。通过一系列的室内三轴压缩试验,探究土工格栅加筋层数、初始含水率、围压等因素对加筋珊瑚砂强度及变形特性的影响。研究发现：格栅加筋能够明显地改善珊瑚砂的力学性能,随着格栅层数的增加,加筋珊瑚砂整体的强度逐渐上升,偏应力-应变关系总体呈现硬化趋势,侧向的鼓胀变形得到明显改善;似黏聚力随着格栅层数增加近似呈线性递增,内摩擦角轻微降低;随着初始含水率的增加,格栅加筋珊瑚砂的强度呈轻微衰减趋势,似黏聚力变化不大,但内摩擦角相比干砂最大下降了约4°;三轴应力状态下的格栅加筋珊瑚砂颗粒破碎受围压影响较大,低于400k Pa围压下的相对破碎率主要在3%以内。此外,基于格栅与珊瑚砂相互作用特征,考虑并计算得到格栅产生的侧向与轴向附加应力,研究结果进一步丰富了对格栅加筋珊瑚砂机制的认识。  相似文献   

A fuzzy neural network bagging ensemble forecasting model for 72-h forecast of low-temperature chilling injury     

Lu  Hong  Ou  Yi  Qin  Chuan  Jin  Long 《Natural Hazards》2021,105(2):2147-2160

Natural Hazards - On the basis of the daily temperature and precipitation data of Guangxi and the NCEP/NCAR reanalysis data and forecast field data, the paper aims to determine the significant...  相似文献   

冰川沉积释光测年： 采样策略与测试选择     

欧先交  曾兰华  陈仁容  姚盼 《冰川冻土》2021,43(3):756-766

释光测年是可对冰川地貌进行直接定年的一种测年技术,已被广泛应用于冰川沉积测年中,推动了第四纪冰川研究的深入发展。但冰川沉积释光测年还没有达到标准化的程度,实际应用中仍有不少问题需要探究,其中最受关注的是冰川沉积物释光信号晒退不完全的问题,即样品在埋藏前因曝光机会有限导致信号没有归零或仅部分归零。冰川沉积释光信号晒退程度与地貌部位和沉积环境密切相关。冰川沉积释光采样需注意几个方面：（1）详细的地貌学和沉积学调查及对采样点的选择;（2）较适合释光测年的冰水沉积和冰缘风成沉积采集及其与冰川作用期次的联系;（3）冰碛夹层中的冰水砂透镜体的选取;（4）冰碛垄采样时垂直与水平方向上的考量;（5）岩石释光测年的发展使砾石成为当前第四纪冰川释光测年采样的一种选择。室内进行释光等效剂量测试时,也有几个关键的选择：（1）粗颗粒石英光释光测年是末次冰期以来冰川作用的首选方法;（2）如果样品年代老于石英测年上限,或者石英不适合测试,则可考虑钾长石后红外高温释光测年方法;（3）单颗粒、小测片和岩石释光埋藏测年技术可以鉴别样品的晒退情况,是目前最适合冰川沉积释光测年的几种选择;（4）如有条件,尝试用不同矿物、不同粒径、不同方法进行测试对比和交叉检验。要获得第四纪冰川释光测年的最佳年代学结果,地貌学、沉积学和年代学的结合是非常必要的。  相似文献   

荔枝越冬期间冠层气温与大气温度关系的初步分析   总被引：2，自引：0，他引：2  

谭宗琨  何鹏  尤明双  杨鑫  欧钊荣  黄兴春 《气象》2009,35(12):102-108

基于野外实测数据,按晴天、阴天、雨天、多云到晴等天气类型,分析2007/2008年、2008/2009年冬季荔枝果园大气温度、冠层气温与观测站大气温度的变化关系,结果表明:晴天荔枝冠层温度昼夜变化最为剧烈,多云到晴天气次之,阴天和雨天冠层大气温度变化相对平缓;果园和观测站大气温度昼夜变化同样与天气类型有关.按天气类型分别建立的观测站与荔枝冠层之间的夜间、白天和全天大气温度线性、曲线回归关系模型表明:阴天和雨天模型效果好于多云到晴、晴天天气,夜间模型好于全天和白天.这一结果对应用观测站大气温度开展荔枝寒害冻害监测有参考作用.  相似文献   

动力延伸预报产品在广西月尺度降水滚动预测中的释用   总被引：1，自引：0，他引：1  

何慧  欧艺  覃志年 《气象研究与应用》2009,30(1):15-18

对广西88个站全年各旬月尺度降水距平百分率作自然正交展开(EOF分解),选取累积方差贡献接近75%的前几个主成分为预报量.利用1982年至今的国家气候中心月动力延伸集合预报资料或回算实验资料,从月尺度平均500hPa位势高度、700hPaU、V向水平风速延伸预报场中选取初选预报因子,并运用EOF分解构建成综合预报因子,分别选取其中与各个预报分量相关程度高的主成分建立预报方程,滚动制作广西月尺度降水量预报.91个独立样本试验和实际应用证明,预报效果较好.  相似文献   

近50年影响广西的热带气旋变化特征   总被引：4，自引：2，他引：2  

李艳兰  欧艺  唐炳莉  黄雪松 《气象研究与应用》2009,30(2):1-3,45

分析了1951～2007年影响广西的热带气旋频数、强度以及初旋、终旋影响日期的变化,结果表明:影响广西的热带气旋年频数、最大强度、强度超过32.7m·s-1的热带气旋频数均呈减少(减弱)趋势,且年际、年代际变化明显,20世纪50年代至70年代为热带气旋影响偏多、偏强期,80年代以后为偏少、偏弱期.初旋影响日期呈偏晚趋势,终旋影响日期变化趋势不显著.  相似文献