正12面体框架构型（RDFC）—立方格子与五次旋转对称轴共存的几何构型     

肖序刚 《矿物学报》1998,18(4):496-508

本文提出一个既具有五次旋转的20面体点群（Ih,5m3）也显示由5个共轭立方格子表征的三维平移周期性的几何构型──正12面体框架构型（RDFC）所对20面体相原子结构进行了诠释,同时也诠释了1981年发现的20面体相（Ⅰ相）的电子衍射图（EDPs）和高分辨电子显微象。  相似文献   

Are our ideas about Dst correct?     

A. Grafe 《Annales Geophysicae》1998,17(1):1-10

The idea of two separate storm time ring currents, a symmetric and an asymmetric one has accepted since the 1960s. The existence of a symmetric equatorial ring current was concluded from Dst. However, the asymmetric development of the low-latitude geomagnetic disturbance field during storms lead to the assumption of the real existence of an asymmetric ring current. I think it is time to inquire whether this conception is correct. Thus, I have investigated the development of the low-latitude geomagnetic field during all the magnetic local times under disturbed and quiet conditions. The storm on February 6–9, 1986 and a statistical analysis of many storms has shown that the asymmetry does not vanish during the storm recovery phase. The ratio between the recovery phase asymmetry and the main phase asymmetry is low only for powerful storms. Storms of moderate intensity show the opposite. The global picture of the field evolution of the February storm shows clear differences at different local times. For instance the main phase and recovery phase start time does not coincide with Dst. Also the ring current decay is not the same at different local times. Therefore, Dst gives an incorrect picture of the field development. Moreover, asymmetry does not disappear during international quiet days as the investigation of the low-latitude geomagnetic field shows. Considering all these observations, I think we must revise our ideas about the ring current. In my opinion only one ring current exists and this is an asymmetric one. This asymmetry increases during storms and develops rather fast to more or less symmetric conditions. However, in no case is itjustified to conclude from Dst that a symmetric ring current exists.  相似文献   

Velocity profiles and bed shear stress over various bed configurations in a river bend     

John S. Bridge  Jack Jarvis 《地球表面变化过程与地形》1977,2(4):281-294

Vertical velocity profiles measured over various bed configurations (plane beds, ripples, and dunes) in. the meandering River South Esk, Glen Clova, Scotland are presented on semilogarithmic paper. Local bed shear stress and roughness height are calculated from the lowermost parts of the profiles using the Karman-Prandtl law of the wall; these parameters, and the geometrical properties of the profiles, are related to the various bed configurations. A graphical model is used to identify profiles developed on specific regions of dune geometry, in order to discriminate those profiles that define bed shear effective in transporting sediment over dunes. An assessment is made of the errors involved in estimating local mean velocity from extrapolating the law of the wall to the water surface. A Darcy-Weisbach friction coefficient is related to bed configuration and local stream power.  相似文献   

南京北郊大气垂直扩散参数特征的测量及其应用     

曹琪敏  邹嘉南  马欣  等. 《气象与环境科学》2018,41(4):56-61

利用平面照相法,以江苏南热发电有限责任公司#Q2号烟囱为研究对象,进行了500次拍摄,通过风向风速、云量、太阳高度角等气象数据,确定了不同稳定度下南京北郊大气扩散参数的特征。与P-G扩散曲线对比发现,在强不稳定A、弱不稳定C、中性D层结中,南京北郊的大气垂直扩散参数在距离排放源200 m范围内更不稳定,而在200—1000 m范围内更稳定。其中,不稳定B层结的扩散曲线与P-G扩散曲线一致,较稳定E、稳定F层结出现于白天的频率很低。对比垂直扩散参数幂函数表达式σ_z=γx~α的系数值γ和α,本研究中α值分别比国家标准增加了28. 6%(A层结)、56. 4%(C层结)、30. 4%(D层结),而B层结的α值却比国家标准减少了22. 9%。此外,通过高斯扩散公式计算得到SO_2和NO_X扩散到观测点的浓度,发现该计算值仅占气象楼污染气体监测平台实测SO_2和NO_X浓度的0. 82%和0. 69%。结合风场发现,SO_2和NO_X实测值受观测点东部工业污染物排放的叠加效应影响较大。其中,NO_X的实测值在受到偏东风和偏南风的影响时具有较大值,且在0. 5～1. 5 m·s~(-1)的较弱风速影响时,NO_X的实测值将达到60μg·m~(-3)以上。  相似文献   

水下物体磁探测线间距的影响因素     

柯泽贤  赵俊生  任来平  刘雁春 《物探与化探》2010,34(1):71-73

建立合理水下小目标磁探测线间距需以定量分析各种因素对其影响为基础。将水下小目标的磁场模型视为磁偶极子,建立水下小目标的磁场空间衰减规律。根据水下目标磁探测的原理及其工作背景,对目标磁距大小、仪器信噪比、地磁变化、日变影响、测船的定位误差等因素进行综合分析,得出磁力仪在探测某一已知物时的测线间距计算公式。  相似文献   

绿色海堤的沉积地貌与生态系统动力学原理: 研究综述*     

高抒  贾建军  于谦 《热带海洋学报》2022,41(4):1-19

绿色海堤是传统结构工程与海岸生态系统共同组合而成的新型海堤, 用以应对未来海面上升、风暴加剧给低地海岸防护带来的挑战。需解决的问题主要有海岸生态系统消浪过程及生态系统在海堤体系中的配置方式。理论分析、现场观测、物模数模所获结果表明, 海岸生态系统确有显著的消浪功能: 1) 陆架泥区消浪, 其机制以再悬浮和浮泥运动为主, 底部摩擦为次; 2) 潮滩下部的粉砂细砂滩底部摩擦和推移质运动共同造成波能耗散, 而上部的泥滩则以再悬浮和悬沙输运为主; 3) 在盐沼、红树林、海草床等由植被构成的生态系统, 植物通过形态阻力、茎秆运动来阻滞水流、耗散波能, 其效能高于沉积物床面对波能的耗散; 4) 生物礁主要有珊瑚礁和牡蛎礁, 其消能作用主要通过床面摩擦和波浪破碎, 效能较高, 尤其是在风暴期间。生态系统如何成为海堤的有机组成部分, 尤其是侵蚀型海岸的生态位修复和绿色海堤整体设计, 还需进一步研究相关的科学问题: 与硬质工程结合的盐沼-牡蛎礁的适应性生物学; 未来环境变化条件下生态系统的稳定性; 绿色海堤生态系统空间配置及其与风暴事件的时间尺度匹配; 基于均衡剖面理论的海堤形态优化。  相似文献   

海上油气田工程压裂作业船及装备配置技术探讨     

薄玉宝 《海洋地质译丛》2014,(1):98-102

用于海上油气田的压裂作业船具备高效性和安全性,具有优越的操控性能和良好的稳定性,配备了先进的船舶航行系统、动力定位系统和强大的动力系统.全船配备的压裂作业设备包括支撑剂存储装置,酸液和胶液存储装置,搅拌混合系统,各类液体和化学药剂添加系统,压裂作业泵系统,中央控制室以及数据采集系统,完备的质量控制体系,安全的作业管线和快速脱离装置.压裂作业船能连续施工作业,效率高,安全可靠.  相似文献   

不同天线组合对GPS姿态测量精度的影响分析          下载免费PDF全文

鲁洋为  王振杰  聂志喜  王毅 《海洋测绘》2014,34(6):43-45,48

GPS姿态确定的精度不仅与单历元基线解算精度有关,还受基线长度和天线布设结构的影响。探讨了GPS姿态测量系统中基线长度和天线布设结构与姿态测量精度的关系。仿真结果表明:增加航向基线长度,能够提高航向角和俯仰角的精度,增加横向基线长度,能提高横滚角的精度;当基线长度一定时,将两基线正交布设,横滚角的精度最高。  相似文献   

A Dipole Pattern of Summer Precipitation over Mid-high Latitude Asia and Related Snow Cover Anomalies in the Preceding Spring          下载免费PDF全文

HAN Jin-Ping  LIU Ge  XIN Yu-Fei 《大气和海洋科学快报》2014,(4):364-368

A dipole pattern of summer precipitation over the mid-high latitudes of Asia, which is characterized by opposing summer precipitation variations between the Mongolian and Northeast China （MNC） region and the West Siberian Plain （WSP）, is found to be clear and stable on both interdecadal and interannual scales during 1981- 2011. Spring snow cover anomalies over a small region within the WSP and the Heilongjiang River （HR） region are closely related to the variation of this dipole mode during the subsequent summer, and they can therefore be considered as forecasting factors. Our statistical results imply a potential process explaining the relationship between the spring snow anomalies and the summer rainfall dipole. Corresponding to the snow anomalies, Rossby waves propagate along a path from the WSP region, via the Mongolian Plateau, to the Stanovoy Range during summer. At the same time, Rossby-wave energy divergences and convergences along this path maintain and reinforce an anomalous cyclone and anticyclone pairing over the Asian continent, which is significantly linked to opposite summer precipitation anomalies between the MNC and WSP regions. Numerical experiments are need- ed to further confirm the above conjecture and demonstrate the detailed physical mechanisms linking the spring snow cover anomalies and summer precipitation dipole.  相似文献   

水中电偶极子空中磁场响应的一维频率域分析     

张双狮  王绪本  王堃鹏  祝忠明  王卫华 《物探化探计算技术》2014,(2):134-141

海洋电磁中浅海作业由于受到空气波的干扰而难于进行,而如果于空中接收电偶极子的磁场响应则可避免空气波的干扰,是一种新的海洋电磁勘探思路。用一维频率域程序,对水中电偶极子在空中的磁场响应进行了计算分析,比较了海底有高阻异常层和低阻异常层时空中磁场响应的变化规律。分别计算测线布置、发射信号频、海水深度、异常储层埋深、异常储层厚度、储层电阻率、空中测量高度等多种因素对空中磁场响应的影响,结果表明,海底有低阻层时空中磁场有更强的响应,归一化幅度异常变化约为10%~60%,而海底有高阻异常储层时响应较弱,归一化异幅度常变化约为2%~8%。因此海洋电磁勘探中于空中接收磁场的模式,更适合浅海区低阻矿产资源的大面积调查。  相似文献