黄河下游泥沙输移数值模拟   总被引：2，自引：0，他引：2  

励强  徐小惠 《地理研究》1989,8(2):55-63

本文从数学模型入手,探讨黄河下游在多年平均来水来沙条件下,泥沙输移与泥沙淤积的特性,得出黄河下游泥沙沿程淤积分布不均匀主要是由于粗沙、中沙沿程淤积不均匀造成的,如果使来沙减少42.6%,黄河下游可望达到冲淤平衡.  相似文献   

21cm波段太阳爆发中的精细结构     

龚元芳  吕松泉  尚琼珍  胡汉明  施硕彪  李琼英 《中国天文和天体物理学报》1989,(1)

本文简要介绍了云南天文台新建立的21cm波段快速(不中断采样)记录系统,及使用该系统观测到的快速尖峰事件。系统得到的太阳分米波段爆发中不同时间尺度的精细结构与Stu-rroch等提出的太阳耀斑中能量释放的模式相一致。  相似文献   

论十九世纪德国地理学的统一性观点   总被引：1，自引：1，他引：0  

李旭旦  陆诚 《地理研究》1983,2(3):1-7

“地理学要免被瓜分,就要坚持它的中心原则,这个原则就是各种自然现象和形态同人类的相关。”欧洲古希腊、罗马时代的光辉地理思想经历中世纪黑暗时代的长期窒息,其生命力日见衰竭。十六世纪的地理大发现与文艺复兴使人们的眼光既回顾到古希腊时代的地理观念,又萌生出对于地理学探讨的浓厚兴趣。但十九世纪之前的地理研究大多是抽象的哲理性的探讨和单纯的地理资料的堆砌。十九世纪以德国地理学为代表的欧洲地理学,由于洪堡和李特尔等人的富有创造性的工作,赋予了地理学以新的生机和新的个性,井促使其迅猛发展。本文旨在通过对当时哲学和自然科学发展情况的分析,论述这一时期德国地理学统一性观点的确立。  相似文献   

WILD PPO-8制作正射影象图的实时控制     

吕绍裘  吴正春 《地球科学与环境学报》1988,(2)

本文从倾斜象片与水平象片的透视关系出发,考虑A_8精密立体测图仪的转角系关,导出了模拟计算机比例尺缩放和影象旋转改正公式和实际运算公式,进而阐述了PPO-8正射投影装置是如何实现对ZOOM系统和DOVE系统两个基本公式的控制。  相似文献   

    

Lu Keli  Zhu Yongchun 《大气科学进展》1994,11(4):427-435

The wave rays and their seasonal variation of stationary and low-frequency Rossby waves are studied by using the Runge—Kutta scheme. The results show that for stationary waves the rays can reach lower latitudes in winter, and are limited in higher latitudes in summer. The main differences between the stationary and low-frequency wave rays are that low—frequency waves can propagate across the equator and the easterlies will not be an obstacle on their propagation. It explained to some extent the interaction of disturbances between the Northern and Southern Hemispheres. The lower wave frequencies and the stronger easterly flow are, the more difficult low—frequency waves will be to propagate across the equator. The waves with 20-day period are easier to propagate across the equator than that with 50—day period. The winter is the most favorable season for low—frequency waves to propagate into another hemisphere.  相似文献   

A study on the flux,speciation, and budget of mercury in controlled experimental ecosystems     

Lu Xiankun  K. W. Johnson  F. A. Whitney  C. S. Wong  Wu Jinping 《中国海洋湖沼学报》1987,5(2):146-160

The lowest addition of mercury (0.1 ug Hg 1⁻¹) was used in CEEs for research on mercury flux, speciation and budget. The removal behavior of mercury by phytoplankton in water columns of CEEs can be described by first order kinetic equations for total and particulate mercury in the CEE spiked by mercury. The removal rate of mercury in water columns depends on the size and productivity of phytoplanton in a water column to which mercuric ions were added. A 4.4 day half-life time and a 2.8 day half-life time for total and particulate mercury respectively was obtained in diatom bloom. During microflagellate bloom a 30 day total mercury half-life time was estimated with increase of particulate mercury in the water column. The 0.010 ug Hg cm⁻²y⁻¹ mercury flux rate that was attained in the control bag agreed with the values from field measurements in Saanich Inlet where the bags were launched. The proportion of total mercury to dissolved and particulate mercury depended also on the size, productivity, and concentration of mercury in a water column. A more or less constant distribution of mercury species in the control bag was observed as follows: dissolved Hg 0.73, particulate Hg 0.27, inorganic Hg 0.42, dissolved organic Hg 0.31. After spiking with mercury, the particulate mercury rose rapidly and reached to over 70% of the total mercury. The concentration factor of mercury by phytoplankton in the CEEs in the order of 10⁵ was consistent with the results from field measurements in Saanich Inlet. The mercury recovery from the water column, sediment, water with sediment, and the CEE bag walls was only 52.3% of total mercury spiked in the CEE. The losses of mercury by vaporization into the ambient air and diffusion through the wall of the enclosure should be considered. This paper was published in Chinese inOcean. Limn. Sinica,17(4):307–317, 1986.  相似文献   

宇宙常数Λ≠0的平面引力波     

陆惠卿 《中国天文和天体物理学报》1988,(2)

本文讨论了宇宙常数Λ≠0时的平面引力波问题。在弱场近似下,得到了平面引力波传播方程及色散方程。通过对Kretschmann曲率标量的讨论发现,不同于Λ=0时h_(μv)仅有横场这一众所周知的结果,Λ<0时不存在一个坐标系,使h_(μv)的标量场、纵场、混合场分量全为零。最后讨论引力波辐射,结论是与Λ=0时无偶极辐射这一结果不同,Λ<0时,混合场的辐射有偶极辐射。  相似文献   

地形对南北低空气流重力惯性波稳定度的影响     

陈刚毅  卢敬华 《成都信息工程学院学报》1987,(2)

在南北向低空急流下,通过简单二层模式讨论地形起伏对重力惯性波的影响,研究指出:(1)存在一个对重力惯性波稳定度无影响的函数和不产生不稳定重力惯性波地形函数;(2)地形起伏越大,不稳定重力惯性波越强;(3)无论南风或北风基流,都是南坡比北坡更有利于产生不稳定重力惯性波。最后,通过实例计算表明,动力分析结果与实况有较好的一致性。  相似文献   

新的γ射线脉冲星PSR1055－52的COS－B证认     

宋黎明  陆埮 《天文学报》1994,(1)

本文利用ＣＯＳ－Ｂ卫星观测资料对ＣＧＲＯ卫星新近发现的一颗γ射线脉冲星进行了守时性分析，得到了显著的周期结构。这个结果对ＰＳＲ１０５５－５２是一颗γ射线脉冲星提供了新的、独立的证认，本文对普遍公认的六颗γ射线脉冲星也作了比较和讨论。  相似文献   

Towfish orientation and position estimation     

Kirlin  R.L. Lu  W.S. Hedstrom  B. Leung  C.M. 《Oceanic Engineering, IEEE Journal of》1993,18(3):319-326

The towfish location and orientation problems that arise in using side-scan sonar to detect objects on the sea bottom are treated separately. Data which locate the towfish relative to the ship are usually deteriorated by multipath receptions and other effects. In order to overcome this serious degradation in the location measurements, a modified Kalman filter is proposed. An estimate of the state transition matrix for this filter is derived, and a means of switching between two Kalman gains is suggested. The feasibility of the proposed filter is justified by a case study. Improved estimates of towfish pitch and heading measurements are obtained by a separate system employing model identification and subsequent Kalman filtering. Application of these methods to data from similar towed side-scan sonar systems should yield significant gains in object location accuracy  相似文献