Residual ultimate strength of steel plates with longitudinal cracks under axial compression–experiments

The main objective of the present study is to examine the residual ultimate strength characteristics of steel plates with cracking damages under axial compressive actions through experimental investigations. The present study is a sequel of the author's previous paper (Paik, J.K., Satish Kumar, Y.V., Lee, J.M., 2005. Ultimate strength of cracked plate elements under axial compression or tension. Thin-Walled Structures, 43, 237–272). In contrast to the previous paper which dealt with transverse cracks located in the direction normal to the axial loading direction, the present paper is concerned with longitudinal cracks which are located in parallel to the axial loading direction. Similar to the previous paper, the orientation/location and size of cracks inside the plates are varied for the present experimental investigations. The details of experimental results are documented. The database and insights developed from the present work will be useful for cracking damage-tolerant design of steel-plated structures and also for condition assessment or health monitoring of aging steel-plated structures.     

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.     

Experimentally-based investigation of effects of wave interference on the wave resistance of asymmetric di-hulls

Significant reduction of steady-state resistance of a di-hull system with certain hull configurations (relative stagger and separation between the hulls) occurs because of interference effects between the two sets of ship-generated waves. The far-field wave interference and the resulting wave-resistance reduction of an asymmetric di-hull system, consisting of two distinct Series 60 hull models with various hull configurations are studied. The initial search for optimal configurations of the maximum prospective resistance reduction is conducted by an existing di-hull thin-ship computation. These theoretical results are then compared to the ones acquired by towing-tank measurements and those given by a semi-experimental approach. The latter approach obtains the wave resistance by combining experimental “wave-cut” data and analytical expressions developed for such a di-hull system. Experimental uncertainties are briefly discussed. Results of this study show that a considerable amount of wave-resistance reduction is indeed possible for the investigated hull configurations. However, beyond the far-field interference of the waves, near-field interactions of the two hulls are found to have non-negligible influence on the total resistance performance of the di-hull system.     

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。     

Kinematical and Structural Patterns of the Yingjing-Mabian- Yanjin Thrust Fault Zone, Southeast of the Qinghai-Xizang （Tibet） Plateau and Its Segmentation from Earthquakes

INTRODUCTIONThe Yingjing-Mabian-Yanjinthrust fault zone lies on the southeastern margin of Tibet .It startsfromthe south of Tianquaninthe north,and it extends southwards through Yingjing, Emei , Ebian,Mabian,Lidian to the north of Yanjin of Yunnan, with a total length of 275 km. The fault zoneintersects withthe southernsegment of the Longmengshanthrust fault zone onits northernsegment andborders the Huayingshan-Lianfengfault zone onits southernsegment .It is a 30 km-wide NW-trendin…     

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.     

岷江上游茂县退化生态系统及人工恢复植被地上生物量及净初级生产力

测定了岷江上游四川茂县退化灌丛和退化草丛及5种人工恢复植被(连香树林、油松林、华山松林、日本落叶林和云南松林)的地上生物量和生产力。灌、草丛生物量生产力采用样方收获法测定,人工林采用生物量回归模型和生产力方程。地上生物量与胸径关系模型的相关性都达到极显著。退化灌丛和草丛的生物量分别为51 06t/hm2和5 76t/hm2,5种人工林的地上生物量在75 8～150 55t/hm2,地上生产力在10 36～18 17t/hm2·a-1。人工恢复植被比退化植被的生物量增加,生产力显著提高。5种恢复模式中云南松、华山松和日本落叶松在当地显示了良好的生长特性,适合在当地退化生态系统恢复中推广。     

岩体变形参数渐变取值模型及工程应用

分析了当前岩体现场试验、变形参数取值和常规计算模式存在的问题。针对河谷、斜坡岩体从表部到深部 ,岩体风化、岩体波速和岩体地应力等彼此均呈现渐变性特征 ,提出了岩体变形参数渐变取值模型 ,并以黄河上游李家峡水电站初期蓄水监测资料 ,论证了岩体变形参数空间上连续性渐变取值的合理性和科学性 ,对今后其它岩体工程的力学参数取值和计算模型的概化提供了指导意义.     

Two types of longitudinal dune fields and possible mechanisms for their development

Longitudinal dune fields characterized by nearly uniform interdune spacing are distinguished from longitudinal dune fields characterized by fairly variable interdune spacing and high frequencies of dune coalescence. The empirical and theoretical evidence indicating that the former may be due to helical air currents aligned with the dunes is reviewed. Hypotheses arguing that the latter may arise indirectly from horizontal pressure gradients or bidirectional wind regimes are discussed. Evenly spaced linear sand banks aligned with tidal currents may be shown mathematically to result from energy optimalization within two-dimensional, sand-transporting flow regimes, and a similar simple or non-rotational flow model is considered for the problem of desert longitudinal dunes. An initial complex or rotational flow analysis is undertaken to discern the likely significance of roll vortices in desert sediment transport. An ‘evolutionary timescale’ is estimated for the formation of desert longitudinal dune fields. A simple analysis is performed for the effect of regional sand mass change on longitudinal dune field ordering. Recommendations are made for future empirical and theoretical research.     

LONGITUDINAL DISPERSION IN OPEN-CHANNEL FLOW

Laboratory experiments on longitudinal dispersion in clear-water and sedimentladen flows are reported. These experiments indicate that the presence of suspended sediment does not have a significant effect on the dispersion process other than its possible effect on the friction factor. Analysis of the writers' and other's data collected in laboratory flumes and natural streams Shows that Taylor's model of longitudinal dispersion based on one-dimensional Fickian diffusion equation with a constant dispersion coefficient, DL, is not suitable for describing the dispersion process in natural streams as DL tends to increase in the downstream direction. Therefore, a similarity analysis of the concentration distributions, on the lines of Day and Wood, has been carried out. Based on dimensional analysis an improved empirical method has been obtained for predicting the concentration-time relation without the use of DL