DEVELOPMENT OF LONGITUDINAL PROFILE OF THE LOWER YELLOW RIVER

１ＩＮＴＲＯＤＵＣＴＩＯＮＦｒｏｍ１４ｔｏｅａｒｌｙ２０ｃｅｎｔｕｒｙ,ｔｈａｔｉｓｉｎｔｈｅＭｉｎｇａｎｄＱｉｎｇＤｙｎａｓｔｉｅｓｉｎＣｈｉｎａ,ｔｈｅｒｅｅｘｉｓｔｅｄａｐｏｉｎｔｏｆｖｉｅｗｔｈａｔｔｈｅｃｏｎｔｉｎｕｏｕｓｓｉｌｔａｔｉｏｎ...     

长江第一弯成因及形成时代探讨

长江第一弯成因及形成时代关系到金沙江—长江水系的形成演化、西南纵向岭谷地理环 境演化、青藏高原隆升对周边环境的影响等重大科学问题, 故近百年来一直为学术界所关注。本 文通过综合考察、地貌和沉积物等的综合分析认为: 长江第一弯是在金沙江水系未曾溯源连通至 三江口段之前的古金沙江与古冲江河、水洛河的汇流口。长江在三江口袭夺了水洛河, 导致水洛 河倒流, 古金沙江与三江口下的长江贯通, 才形成真正的金沙江—长江水系。根据玉龙山强烈隆 起时间、周边层状地貌发育年代、中国水系大局形成等进行推断, 长江第一弯形成时代为中更新 世以来, 说明昆黄运动为本区构造地貌—水系发育的重大转型事件。     

IMF Bz周期震荡期间日间热层扰动风的经度差异分析

基于磁层-电离层-热层耦合模型(Coupled Magnetosphere-Ionosphere-Thermosphere Model,CMIT),本文探究了当行星际磁场Bz分量(Interplanetary magnetic field,IMF) 60 min周期震荡时,白天热层扰动风的经度差异特征.由于地磁构型、热...     

Estimation of stream water quality parameter using regime channel theory

For predicting and forecasting fate of non-conservative pollutants downstream from source using advection–dispersion–decay equation (ADDE), estimation of three parameters; mean flow velocity (U), longitudinal dispersion co-efficient (D _L) and decay rate co-efficient (λ), is required a priori. In this three parameters model, estimation of D _L holds difficulties and draws interest towards it. The empirical formulae use the field and experimental data of channel and flow characteristics to estimate D _L. In this paper, an innovative approach has been proposed towards the estimation of D _L using regime channel concept. Having known discharge of flow and silt factor of the riverbed material, hydraulic parameters of the channel can be determined theoretically, which in turn can be used to estimate D _L appropriately making use of a suitable empirical formula.     

西南纵向岭谷地形对季风的“通道-阻隔”作用

地形格局对大气环流与区域气候具有重要影响。已有研究认为纵向岭谷区主要受到印度洋季风与太平洋季风的共同影响,二者在哀牢山山脉附近交汇,哀牢山山脉是一条重要的地理分界线。本文从大气环流、水汽输送、区域气候、河川径流以及植物稳定氧同位素等多个方面研究发现:纵向岭谷地区主要受印度洋季风的影响,太平洋季风的影响在8月份有一定的作用,但不够明显;在地形格局作用下,地表水汽、降水以及河川径流在纵向岭谷区表现出明显的纬向差异、经向延伸的特征;大流环流、水汽输送、区域气候以及河川径流等的空间差异,是特殊环境对水热再分配的结果,即"通道-阻隔"作用的效应;这些差异不是地理地带性的表现,而是非地带性作用的结果;这种"通道—阻隔"作用导致地表水热条件的再分配,是该区生态地理格局形成与演化的主驱动力之一。纵向岭谷地形对季风的"通道—阻隔"作用导致了一系列地理要素的空间分异和相关联的生态效应。     

Longitudinal vibration of a pile embedded in layered soil considering the transverse inertia effect of pile

The dynamic response of a viscoelastic bearing pile embedded in multilayered soil is theoretically investigated considering the transverse inertia effect of the pile. The soil layers surrounding the pile are modeled as a set of viscoelastic continuous media in three-dimensional axisymmetric space, and a simplified model, i.e., the distributed Voigt model, is proposed to simulate the dynamic interactions of the adjacent soil layers. Meanwhile, the pile is assumed to be a Rayleigh–Love rod with material damping and can be divided into several pile segments allowing for soil layers and pile defects. Both the vertical and radial displacement continuity conditions at the soil–pile interface are taken into account. The potential function decomposition method and the variable separation method are introduced to solve the governing equations of soil vibration in which the vertical and radial displacement components are coupled. On this basis, the impedance function at the top of the pile segment is derived by invoking the force and displacement continuity conditions at the soil–pile interface as well as the bottom of pile segment. The impedance function at the pile head is then obtained by means of the impedance function transfer method. By means of the inverse Fourier transform and convolution theorem, the velocity response in the time domain can also be obtained. The reasonableness of the assumptions of the soil-layer interactions have been verified by comparing the present solutions with two published solutions and a set of well-documented measured pile test data. A parametric analysis is then conducted using the present solutions to investigate the influence of the transverse inertia effect on the dynamic response of an intact pile and a defective pile for different design parameters of the soil–pile system.     

Longitudinal variation in E- and F-region ionospheric trends

A novel technique is used to examine northern hemisphere midlatitude longitudinal variations in ionospheric long-term trends. Differences in hour-by-hour monthly median ionospheric parameters between equilatitudinal observatory pairs are analysed for long-term trends, thus eliminating at source the large solar cycle and geomagnetic variability that normally hinders ionospheric trend calculations. The results confirm the finding of Bremer [1998. Trends in the ionsopheric E- and F-regions over Europe. Annales Geophysicae 16, 698–996] that there are longitudinal variations in the F-region altitude trend across Europe, but suggest the influence of a stationary wave-like feature between 3°W and 104°E. Possible causes such as scaling errors, insufficient account of changes in ionisation underlying the F-region, varying gravity wave fluxes, and secular change in the geomagnetic field are ruled out. The data suggest that the longitudinal variation may reflect long-term changes in a large-scale stationary feature induced via non-migrating tides induced by latent heat release in the troposphere.Significant differences in the long-term trend of E-region peak plasma frequency between observatories were also found. These E-region differential trends varied with solar zenith angle reaching over 0.3 MHz per decade between Juliusruh and Moscow at midday in summer.     

Lithologic and structural controls on fluvial knickzones in basalts of the Paraná Basin,Brazil

Knickzones are common features along rivers on the basaltic plateaus of the Paraná Basin. According to current conceptual models, knickpoints are formed in massive basalts that have a high density of vertical joints. Vesicular–amygdaloidal basalts and those with horizontal joints tend to form reaches of low slope due to their lower resistance to erosion. However, field surveys revealed complexities in this general relationship. The research presented here sought to verify the controls on the genesis of knickzones in this type of geological environment. We studied a 61 km-long mixed bedrock–alluvial river. The longitudinal profile of the river was surveyed on a topographic map with 5 m contour intervals. Tectonic lineaments oriented transverse to the channel and longitudinal lineaments in which the river lies were identified from maps. A detailed field survey of the lithologic characteristics of the riverbed was also performed. The results show that knickzones may form in any litho-structural zone in the flood basalts. On the other hand, low slope zones are predominantly sculpted into vesicular–amygdaloidal basalts, which are less resistant to erosion. The fracture densities of vesicular–amygdaloidal basalts are similar in low slope zones and in knickzones (4.86 and 4.93 m/m², respectively). This indicates that knickzones in this type of basalt are not caused by higher resistance to erosion. Approximately 60% of the 18 knickzones identified are associated with tectonic lineaments, irrespective of the structural characteristics of the basalts. Vesicular–amygdaloidal basalt and/or basalt with horizontal joints allow the fastest knickzone migration and aid in the formation of convexities. Knickpoints in these basalts do not migrate, but erosion in the pools advances downstream and breaks the bedrock steps, thus increasing the slope. Massive basalt with vertical joints causes slower migration, and its presence at convexities indicates local uplift. Convex segments are only formed upstream of faults.     

Wood anatomical variation of Neobuxbaumia tetetzo: A columnar Cactaceae

Anatomical variation in radial and longitudinal wood in Neobuxbaumia tetetzo was studied in four monopodic individuals. Vascular bundles in the radial direction from the pith to the vascular cambium and in the longitudinal direction from the base to the stem apex were analysed. Except for vessel density in the radial direction, the anatomical characters studied showed a pattern of cambial maturation similar to those reported for other angiosperms. The patterns of fiber anatomical variation show higher mechanical strength in the lower part of the stem, while the increase in vessel diameter towards the vascular cambium produces a positive relationship between plant water demands and larger size.