Radiation exposure and Mission Strategies for Interplanetary Manned Missions (REMSIM)

Cosmic radiation is an important problem for human interplanetary missions. The “Radiation Exposure and Mission Strategies for Interplanetary Manned Missions–REMSIM” study is summarised here. They are related to current strategies and countermeasures to ensure the protection of astronauts from radiation during interplanetary missions, with specific reference to: radiation environment and its variability; radiation effects on the crew; transfer trajectories and associated fluences; vehicle and surface habitat concepts; passive and active shielding concepts; space weather monitoring and warning systems.     

珠江口典型海岛周边水域浮游植物分布特征及其影响因素*

旅游业为海岛带来可观经济效益的同时, 人类活动也导致水体生态环境恶化, 如水体富营养化加剧、赤潮频发等。文章通过对珠江口东南部典型海岛——庙湾岛和外伶仃岛周边水域丰水期和枯水期现场环境数据与浮游植物分布特征的对比研究, 分析珠江径流等自然因素以及人类活动对河口天然海岛周边水体生态的潜在影响。枯水期外伶仃岛和庙湾岛周边水域海水分别镜检鉴定出76种和74种浮游植物, 两个海岛浮游植物平均细胞密度分别为2.62×10⁴个·L^-1和2.08×10⁴个·L^-1; 丰水期则分别鉴定出38种和47种浮游植物, 平均细胞密度分别为52.91×10⁴个·L^-1和170.57× 10⁴个·L^-1。在外伶仃岛和庙湾岛, 丰水期中肋骨条藻(Skeletonema coatatum)均为绝对优势种, 而枯水期两个岛的最主要优势种分别为窄隙角毛藻(Chaetoceros affinis)和新月筒柱藻(Cylindrotheca closterium), 物种多样性指数均明显高于丰水期。两个海岛微型浮游植物相对于其他两个粒级常占据优势地位, 但在丰水期, 小型浮游植物贡献明显上升, 其中外伶仃岛相对于枯水期由16.32%升至26.75%, 庙湾岛则由12.12%升高至24.78%。两个海岛在丰水期和枯水期均仅检出聚球藻(Synechococcus, Syn)和真核微微型藻类(eukaryotic, Euk)两大微微型浮游植物类群, 两者细胞密度分别为~10⁷个·L^-1及~10⁸个·L^-1量级。与环境因子的对比分析表明, 两个海岛浮游植物的区域分布与季节变化受多种因素影响, 其季节性差异主要受径流影响强度、影响范围以及相应的盐度、营养盐等环境因素的季节变化所调控。丰水期岛屿屏蔽效应对浮游植物丰度的区域分布特征有显著影响, 无论小型浮游植物还是微微型浮游植物均发现存在迎流面出现丰度高值分布的现象, 但对群落结构的分布影响不明显; 在枯水期, 水体环境很可能主要受人类活动与水体垂直混合扰动的综合影响, 总体上浮游植物分布的区域差异较小。     

铯原子喷泉钟均匀C场的实现

C场均匀度是影响铯原子喷泉钟性能的重要因素。为了消除漏磁等对磁场均匀度的影响,加入补偿线圈,通过用最小二乘法计算,逐次得出补偿线圈的个数、位置与电流。实验表明：计算数据与实验结果吻合,得到c场不均匀性小于2nT、长度达48cm的均匀区。     

Gravity Anomaly During the Mohe Total Solar Eclipse and New Constraint on Gravitational Shielding Parameter

By using a high-precision LaCoste-Romberg gravimeter, continuous and precise measurements were carried out during the March 9, 1997 total solar eclipse in Mohe region in Northeast China. The gravity variations were digitally recorded during the total solar eclipse so as to investigate the possible anomaly of the Sun and the Moon's gravitational fields on the Earth. After the careful processing and analysis of the observed data, no significant anomaly during the very solar eclipse was found. However, there are two ‘gravity anomaly valleys’ with near symmetrical decrease of about 6 ∼ 7 μg at the first contact and the last contact. This is the anomaly phenomenon observed and reported for the first time in the literature. This paper is intended to explain the observed anomaly by conducting the tilt experiment due to the thermal stress and temperature change in the solar eclipse. A new constraint limit on gravitational shielding is thus obtained. Some analysis and discussions are presented although further studies and research are highly needed. This revised version was published online in July 2006 with corrections to the Cover Date.     

利用线性旅行时插值射线追踪 计算近地表模型初至波走时

利用线性旅行时插值射线追踪对近地表模型进行正演计算,可以快捷、准确地获得初至波走时和射线路径。由于该算法计算的初至波不局限于折射波,因此很好地解决了浅层折射勘探中的低速"隐蔽层"问题;而且,由于该算法是基于网格划分和线性插值,因此它不仅可以追踪任意复杂介质的初至波,而且可以使得追踪的初至波射线路径逼于真实,避免了同类算法直接连接网络节点形成射线路径的缺陷(路径过于弯折,计算走时偏大)。将LTI算法同其他几种算法的追踪结果进行的对比和分析表明,LTI算法在计算初至波走时和射线路径方面较其他算法更为精准、稳定,是一种有效的射线追踪方法。     

影响广播中波转播站防雷系统作用的几个关键技术

电台中波转播站多建于城市近郊区,由于天线高耸落雷几率高,因而易受雷击干扰。针对建站时原已通过防雷验收的转播站设施在投入使用后依然频遭雷击受损的状况,分析了其防雷系统的内在布设技术问题,认为广播中波转播站原有防雷系统的一些关键技术缺漏是遭雷击受损的主要原因,并从转播站的实际情况出发,提出了转播站防雷设计的几个关键技术问题的解决方法：接地网逐级分流、屏蔽馈线再加设外屏蔽环群技术以及不同的线路、不同系统保护的配合方法等,从而形成广播转播站完整的防雷保护系统框架。     

�˼������ڵ�Ӱ������ǷDZ���������������㷨�о�

??????????????????????????????????????????????????????????????????????????????????????С????????????????????????????????????????????????????????????????,??????????????????????????????????????????????壬??????????????????????????????????Ч???б???????ж?????????????????????????????????????δ?????????????????ó??????????????????????GRACE?????????????????????????????????????Ч??????????????????     

Effects of terrain smoothing on topographic shielding correction factors for cosmogenic nuclide‐derived estimates of basin‐averaged denudation rates

Estimation of spatially averaged denudation rates from cosmogenic nuclide concentrations in sediments depends on the surface production rates, the scaling methods of cosmic ray intensities, and the correction algorithms for skyline, snow and vegetation shielding used to calculate terrestrial cosmogenic nuclide production. While the calculation of surface nuclide production and application of latitude, altitude and palaeointensity scaling algorithms are subjects of active research, the importance of additional correction for shielding by topographic obstructions, snow and vegetation is the subject of ongoing debate. The derivation of an additional correction factor for skyline shielding for large areas is still problematic. One important issue that has yet to be addressed is the effect of the accuracy and resolution of terrain representation by a digital elevation model (DEM) on topographic shielding correction factors. Topographic metrics scale with the resolution of the elevation data, and terrain smoothing has a potentially large effect on the correction of terrestrial cosmogenic nuclide production rates for skyline shielding. For rough, high‐relief landscapes, the effect of terrain smoothing can easily exceed analytical errors, and should be taken into account. Here we demonstrate the effect of terrain smoothing on topographic shielding correction factors for various topographic settings, and introduce an empirical model for the estimation of topographic shielding factors based on landscape metrics. Copyright © 2008 John Wiley and Sons, Ltd.     

河道砂体内部夹层岩性与遮挡性识别

河道砂体内部夹层作为储层构型界面,厚度较薄,岩性、遮挡性存在差异,对河道砂体内流体渗流及剩余油分布的影响不尽相同。本文以大庆油田萨北二区为例,利用密闭取芯井岩芯和纵向分辨率较高的微电极测井曲线等资料,以岩芯识别夹层岩性为基础,通过对测井曲线幅值、幅差、回返率交汇分析,优选出微电位回返最低值和微梯度回返率作为夹层岩性判别标准,夹层岩性识别符合率达82%;并以夹层含油性为依据,将夹层按遮挡性分为完全阻流型、强限流型、弱限流型等三种类型;分析密闭取芯井河道砂体内部夹层岩性与遮挡性对应关系,建立了非取芯井河道砂体内部夹层遮挡性的岩性解释法,夹层遮挡性识别符合率达72%。以此为深入研究地下河道砂体内部构型对注入剂驱替路径及剩余油分布的影响奠定基础。     

The Shielding Effect of Multi-Pile Structures on Ice Force

The shielding effect of the front pile-row on the ice force acting on the hack pile-row is studied by ice force model tests. In the tests, the front pile-row is designed to model jacket legs and the hack pile-row to model the water resisting pipe-phalanx within the jacket. The shielding factor for ice force corresponding to different conditions are given in this paper. The research indicates that there are many factors, including the longitudinal and lateral spacing between the front and hack pile-row, ice attacking angle and the ratio of pile diameter to ice thickness, that influence the shielding effect on ice force.