边坡落石运动轨迹计算新方法

考虑落石形状对落石运动轨迹的影响,将落石近似成椭圆形。根据落石运动的5种常见形式,即自由落体运动、斜抛运动、碰撞、滑动和滚动,分别得到了各种运动形式的运动速度计算公式。在碰撞阶段考虑了地面的弹塑性变形,得到了与碰撞前速度、落石形状和地面材料有关的恢复系数计算公式,并根据接触力学的有关理论得到了碰撞冲击力的计算公式,给出了落石连续滚动的判别条件。将理论公式应用于重庆万州首立山落石运动轨迹预测,验证了理论公式的可行性和有效性。     

风沙运动的欧拉双流体模型参数研究

利用数值方法研究了双流体模型中动力黏度μ_s,kin、动量交换系数β和碰撞恢复系数e_ss对风沙运动的影响.结果显示:动力黏度μ_s,kin影响沙床面起沙率,动量交换系数β影响输沙率沿流程的变化,碰撞恢复系数e_ss影响输沙量的垂向分布.利用研究得到的参数,模拟风沙流运动,并与已有的诸多实验和数值模拟结果对比,结果吻合较好,说明该参数的选取可以有效地模拟风沙流运动.     

Simulations using terrestrial geological analogues to assess interpretability of potential geological features of the Hermean surface restituted by the STereo imaging Camera of the SIMBIOSYS package (BepiColombo mission)

The BepiColombo space mission is one of the European Space Agency's cornerstone projects; it is planned for launch in 2013 to study the planet Mercury. One of the imaging instruments of BepiColombo is a STereo Camera (STC), whose main scientific objective is the global stereo mapping of the entire surface of Mercury. STC will permit the generation of a Digital Terrain Model (DTM) of Mercury's surface, improving the interpretation of morphological features at different scales and clarifying the stratigraphic relationships between different geological units.To evaluate the effectiveness of the STC-derived DTM for geological purposes, a series of simulations has been performed to find out to what extent the errors expected in the DTM may prevent the correct classification and interpretation of geological features. To meet this objective, Earth analogues (a crater, a lava cone and an endogenous dome) of likely components of the Hermean surface, small enough to be near the detection limit of the STC, were selected and a photorealistic three-dimensional (3D) model of each feature was generated using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) stereo images. Stereoscopic pairs of synthetic images of each feature were then generated from the 3D model at different locations along the BepiColombo orbit. For each stereo pair, the corresponding Hermean DTM was computed using image correlation and compared to the reference data to assess the loss of detail and interpretability. Results show that interpretation and quantitative analysis of simple craters morphologies and small volcanic features should be possible all along the periherm orbit arc. At the apoherm only the larger features can be unequivocally distinguished, but they will be reconstructed to a poor approximation.     

The silent articulation of private land rights in Soviet Estonia: A geographical perspective

With an explicit focus on the spatial articulation of landownership, this paper explores various ways in which pre-Soviet land rights were expressed in rural Estonia during the Soviet period (1940-1941, 1944-1991). Drawing on cartographical analyses and interviews made in the rural district of Muhu, the paper demonstrates that people who owned land before the Soviet occupation kept track of the officially annulled pre-Soviet land rights, by relating to inertial landscape elements as memory-aids. To local inhabitants the landscape, in which past and present structures always merge, provided substantial evidence in support of the idea of legal continuity of pre-Soviet land rights. Hence, the post-Soviet land restitution reform often implied a re-discovery or re-expression of property rights that had been silenced, but not lost.     

隧道仰坡落石冲击模型试验研究与机制探讨

以在建的成都－兰州（成兰）铁路某隧道出口仰坡为研究对象,研发了大型落石冲击边坡模型试验系统,该系统由模型试验台架、落石三维空间释放装置、高速摄影系统等组成,结构强度高并能满足试验过程的可视化需求。根据现场岩样实测物理力学参数,采用凡士林、硅油、水泥、细沙、重晶石粉、石膏以及滑石粉等原料,研制出现场千枚岩和砂岩的相似材料,并用于模拟边坡和落石。通过开展物理模型试验研究了近长方体落石初始滑移角度、形状、质量等3种因素对碰撞恢复系数这一落石运动轨迹模拟中关键参数的影响,同时在落石下落冲击的过程中,利用高速摄影仪和坐标卡尺记录落石完整的运动轨迹,后期通过视频处理软件分析落石与边坡碰撞前后的速度变化,根据公式计算出落石法向和切向的碰撞恢复系数。试验结果表明：随着初始滑移角度的增加,板状试件的法向、切向恢复系数分别呈减小和增大的趋势,且切向恢复系数变化更加明显;落石法向恢复系数随质量的增加呈明显减小的趋势,而切向恢复系数值变化不大;对于近长方体落石,立方体试件的法向和切向恢复系数大于厚板状试件,条形试件的两向恢复系数值受碰撞接触形态的影响,呈现两极化的趋势。最后,结合试验现象以及前人的研究成果对落石运动冲击机制进行了初步探讨。     

滚石冲击碰撞恢复系数研究

在研究滚石的运动规律过程中,滚石的碰撞恢复系数是重要的控制参数,它不仅与滚石的冲击速度、质量有关,还与滚石、坡面覆盖层的物理力学性质密切相关,目前尚无合理的计算理论,这是滚石灾害研究的一个难点问题。根据Hertz接触理论、Cattaneo & Mindlin切向接触理论,在考虑材料弹塑性特性的基础上研究了滚石法向碰撞恢复系数和切向碰撞恢复系数的计算模式,给出了具体的计算公式,并阐明了影响滚石碰撞恢复系数的主要控制因素。通过一算例的计算分析并与已有结论的比较,表明该计算模式的合理性。     

Private property restitution: the geographical consequences of official government policies in Central and Eastern Europe

The restitution of private property has been a widespread and controversial part of the post-socialist transformation in Central and Eastern Europe, raising issues about social justice and the responsibilities of national governments for the actions of their predecessors. This paper reviews the implementation of the restitution process in the countries of the region and assesses the impact on the social and economic landscape. The policy has been most extensive in Germany and most controversial in Poland, and the impacts in these two countries are considered in detail. The results show that everywhere restitution has resulted in winners and losers, with some claimants having long-lost property returned, but too often at the cost of residents losing their homes. However, an important benefit, notably in Germany's New Bundesländer, has been the introduction of much-needed new investment into the urban fabric of towns and cities, although the landscape impacts elsewhere have been less significant. Nevertheless, throughout Central and Eastern Europe restitution policies have helped governments to come to terms with a difficult aspect of the past and move forward.     

Rural diversification in Eastern Europe: Introduction

The decline in agricultural production and the inevitability of reduced employment on the land makes rural diversification an important priority. The papers in this collection outline the problem and indicate the range of options available, noting the differences between the northern and southern parts of the region. Attention is given to the settlement system because opportunity will vary according to the accessibility of urban areas. The tourist industry offers considerable opportunity but has implications for environmental conservation which should therefore attract greater attention. This revised version was published online in July 2006 with corrections to the Cover Date.     

Equivalent viscous damping for modeling inelastic impacts in earthquake pounding problems

In studies of earthquake‐induced pounding between adjacent structures, spring–dashpot elements are often used to simulate the impacts. In this brief paper an equation is derived expressing the dashpot constant as a function of the coefficient of restitution, in terms of which inelastic impacts of colliding simple bodies have usually been described. Copyright © 2004 John Wiley & Sons, Ltd.     

Dynamic response and impact energy loss in controlled rocking members

Unbonded posttensioning anchors a rocking structural member to its foundation and produces its controlled rocking response when the member undergoes seismic action. Unlike rocking of free-standing bodies, little attention has been given to the dynamic behavior of these controlled rocking members. This paper utilizes experiments of concrete structural members with unbonded posttensioning, varying member geometries, and levels of initial posttensioning force to (a) characterize the associated impact energy loss and (b) improve modeling of controlled rocking motions. Experimental results show that impact energy loss in controlled rocking members can be captured accurately using the coefficient of restitution (r) approach of the modified simple rocking model (MSRM). Based on the MSRM, a controlled rocking model (CRM) is developed that additionally accounts for the variations in contact length at the member-to-foundation (rocking) interface. The CRM reproduces the experimental responses of controlled rocking members with good accuracy and is used to investigate controlled rocking motions under horizontal base excitations.