Impact of root architecture on the erosion‐reducing potential of roots during concentrated flow

Many studies focus on the effects of vegetation cover on water erosion rates, whereas little attention has been paid to the effects of the below ground biomass. Recent research indicates that roots can reduce concentrated flow erosion rates significantly. In order to predict this root effect more accurately, this experimental study aims at gaining more insight into the importance of root architecture, soil and flow characteristics to the erosion‐reducing potential of roots during concentrated flow. Treatments were (1) bare, (2) grass (representing a fine‐branched root system), (3) carrots (representing a tap root system) and (4) carrots and fine‐branched weeds (representing both tap and fine‐branched roots). The soil types tested were a sandy loam and a silt loam. For each treatment, root density, root length density and mean root diameter (D) were assessed. Relative soil detachment rates and mean bottom flow shear stress were calculated. The results indicate that tap roots reduce the erosion rates to a lesser extent compared with fine‐branched roots. Different relationships linking relative soil detachment rate with root density could be established for different root diameter classes. Carrots with very fine roots (D < 5 mm) show a similar negative exponential relationship between root density and relative soil detachment rate to grass roots. With increasing root diameter (5 < D < 15 mm) the erosion‐reducing effect of carrot type roots becomes less pronounced. Additionally, an equation estimating the erosion‐reducing potential of root systems containing both tap roots and fine‐branched roots could be established. Moreover, the erosion‐reducing potential of grass roots is less pronounced for a sandy loam soil compared with a silt loam soil and a larger erosion‐reducing potential for both grass and carrot roots was found for initially wet soils. For carrots grown on a sandy loam soil, the erosion‐reducing effect of roots decreases with increasing flow shear stress. For grasses, grown on both soil types, no significant differences could be found according to flow shear stress. The erosion‐reducing effect of roots during concentrated flow is much more pronounced than suggested in previous studies dealing with interrill and rill erosion. Root density and root diameter explain the observed erosion rates during concentrated flow well for the different soil types tested. Copyright © 2007 John Wiley & Sons, Ltd.     

Pure aluminium shear panels as dissipative devices in moment‐resisting steel frames

The use of energy dissipation systems for the seismic control of steel structures represents a valid alternative to conventional seismic design methods. The seismic devices currently employed are mostly based on the metallic yielding technology due to the large feasibility and efficiency they can provide. Within this context, in the current paper an innovative solution based on the adoption of low‐yield‐strength pure aluminium shear panels (SPs) for seismic protection of steel moment‐resisting frames is proposed and investigated. In order to prove the effectiveness of the system, a wide numerical study based on both static and dynamic non‐linear analyses has been carried out, considering a number of different frame‐to‐shear panel combinations, aiming at assessing the effect of the main influential parameters on the seismic response of the structure. The obtained results show that the contribution provided by aluminium SPs is rather significant, allowing a remarkable improvement of the seismic performance of the structure in terms of stiffness, strength and ductility, with the possibility to strongly limit the damage occurring in the members of moment‐resisting frames. In particular, it is clearly emphasized that the stiffening effect provided by SPs allows a more rational design procedure to be adopted, since the serviceability limit state check does not lead to unavoidable and uneconomical increase of the size of main structural members. Copyright © 2007 John Wiley & Sons, Ltd.     

平坦地区转换GPS高程的混合转换方法

简要介绍了转换GPS高程的二次曲面拟合法和神经网络方法。然而 ,这 2种方法都有缺点 ,介绍的CF&NNM方法充分利用了 2者的优点 ,通过 2个平坦地区的工程实例 ,证实该方法的有效性 ,并得到一些有工程应用价值的结论。     

海量数据CDT快速建立及其实时更新

对海量地形数据快速整体CDT生成、实时更新等算法进行了研究，并在AutoCAd环境下研制了公路数字地面模型软件BID－Land,实现了与公路CAD的集成。190多公里国家重点公路工程勘察设计中的实际应用表明，程序算法具有很强的实用性、极高的效率和良好的地形模拟精度。     

p-范分布参数σ的估计

用极大似然法估计一元 p_范分布参数σ。在 μ、p已知的条件下 ,得出 ^σp 是σp 的无偏估计及 npλp·^σpσp服从 χp 分布 ,进而给出方差的假设检验方法。     

IP网络技术的现状及其多媒体应用研究

介绍了IP网络的现状、实现方式以及发展趋势，并分析了基于IP网络的多媒体通信若干技术和应用。     

基于核空间的多光谱遥感图像分类方法

提出了多光谱遥感图像分类方法中解决非线性问题的一种思路。通过引入核空间理论,将在输入空间中不能线性分类的问题映射到一个可以进行线性分类的高维空间,并利用核函数避免了在高维空间中运算的复杂度,较好地解决了非线性分类问题。利用这种思路,本文对一种比较简单的分类算法———自适应最小距离分类方法加以改进,并将其应用于多光谱遥感图像的分类中,提出了一种核函数的选择策略。     

支持ITU-T H.324协议的桌面式可视电话系统

介绍了支持ITU－TH．324协议的桌面式可视电话系统VP324的系统原理、总体构成及各个子系统的实现方法，论述了VP324系统中一系列难点的实现策略和主要性能指标。该系统视频清晰流畅，传输帧率最高可达25帧／s，单路时延不超过350ms，在有效带宽仅12k时仍然能够正常工作。     

水泥—丙烯酸盐复合浆液的实验性研究

水泥-丙烯酸盐复合浆液是在丙烯酸盐浆液的基础上研制出来的一种复合浆液，它既保留了丙烯酸盐浆液流动性好，固结体弹性好的优点，又大幅度地提高了浆液的抗压强度和粘结强度，因此在注浆时可以带来良好的综合灌注效果，还对复合浆液的粘度和强度进行了试验性研究。     

裂隙概化模型的非饱和渗流试验研究

借鉴多孔介质非饱和渗流试验的研究成果,研制出一套可同时测定单裂隙毛细压力-饱和度以及非饱和渗透系数-毛细压力关系的试验装置.为检验试验装置的可信度和试验原理的正确性,并初步探讨单裂隙非饱和渗流的机理,特制作了一阶梯开度的裂隙概化模型(本文称之为“S-H”裂隙模型),并在上述试验装置上进行了“S-H”裂隙模型的非饱和渗流试验,初步阐明了单裂隙非饱和渗流的一些基本水力特性,同时试验结果也表明本文试验装置和试验原理合理可靠.