蜂巢约束系统边坡防雨水侵蚀特性研究

路基边坡的稳定性是路基安全的重要指标。本文通过试验模拟边坡滑动以及边坡冲蚀,对比附加蜂巢约束前后边坡稳定性的变化来研究蜂巢约束系统边坡防雨水侵蚀特性。试验发现,附加蜂巢后边坡冲蚀量大幅下降,最大可达40%。相同冲蚀时间下,附加蜂巢约束的边坡冲蚀量随流量增加速度较慢,冲蚀速率下降5%~15%;釆用绕流雷诺数分析判断水流的流态,发现雷诺数均大于取定的下临界雷诺数,判断坡面薄层水流为紊流。且有蜂巢约束时,弗汝德数小于1,属于缓流;而在无蜂巢约束系统时,其值大于1,属于急流。结果表明,蜂巢约束可以有效缓解降雨对边坡的侵蚀作用。

粗集料对沥青混合料空隙结构影响分析

沥青混合料的空隙率与性能密切相关,空隙细观结构直接影响着沥青混合料的各种性能。针对粗集料,设计不同级配和针片状含量的混合料,通过CT扫描、数字图像获取技术方法的研究,获得三维重构图,采用VG Studio MAX2.2设定不同灰度范围,进而提取空隙,构建沥青混合料的空隙空间变化特征图,分析空隙结构评价指标,进而对空隙结构进行研究。通过空隙定性对比发现,该方法获得的空隙变化同表干法实测规律一致;空隙粒径分布受粗集料级配和针片状含量影响显著;通过设定灰度阈值的方法计算沥青混合料空隙率,其结果大于实测空隙率;构建的面积比值参数,能准确地表征沥青混合料中粗集料和空隙的比例关系。

Multidisciplinary and multiscale nanoscience research roadmap based on large scientific facilities

With the advancement of modern science and technology, large scientific facilities are increasingly oriented toward demand and application, and can be used for basic research as well as serving multiple disciplines. Developing large scientific facilities and related analytical technologies enhances understanding of large scientific facilities and popularizes their application in research across multiple disciplines. The combination of light or neutron sources from large scientific facilities and advanced analytical technologies can be achieved for materials structure information, dynamics study of chemical reactions, high dissociation of biomolecules, 3D visualization of energy materials or biological samples, etc. We first introduce the progress of domestic large scientific facilities of synchrotron radiation(SR) and free electron lasers(FELs) with different wavelengths and neutron sources.We further discuss the comparison between Chinese and typical foreign facilities in X-ray radiation from X-ray tubes, synchrotrons, X-ray FELs, and neutron sources based on physical parameters of light and neutron sources. In addition, we focus on the technological progress and perspectives combined with advanced X-ray radiation and neutron sources of large scientific facilities in China, especially in the nanoscience fields of energy catalysis and biological science. We hope that this roadmap will provide references on technology and methods to experimental users, as well as prospects for future development of technologies based on large research infrastructure facilities. Comprehensive studies and guidelines for basic research to practical application in various disciplines can be made with the assistance of large scientific facilities.

X光和中子散射方法在团簇及其聚合物复合材料表征中的应用

复杂材料体系多组分且跨多空间尺度的层级结构、同组分的多聚集态共存以及难以定量描述的组分界面相互作用和非晶态结构,致使目前对于其形成机制和构效关系缺乏清晰认识.作为一种非破坏性的、跨多个时空尺度的材料表征方法,散射技术广泛应用于复杂材料体系多级结构和动力学研究.团簇具备明确和单分散结构,其与聚合物可通过多能级相互作用形成复合物,为研究材料共性科学问题提供了模型体系.基于大科学装置弹性和准弹性X光和中子散射多模式联用,可提供衬度互补、多时空维度原位实验表征方案,实现结构演变动力学、溶液动力学和结构松弛动力学在单链(单粒子)精度上的解析,结合材料中物质、动量和能量传输规律,实现定量化材料构效关系解析.本文首先介绍X射线和中子散射技术原理和基本数据分析方法,包括以小角散射和超小角散射为主的弹性散射以及准/非弹性散射,之后结合具体团簇复合材料体系总结散射技术联用在研究形成机制和构效关系中的应用,进而评述X光和中子散射方法在材料表征中的研究特点,为解决共性材料科学问题提供可借鉴的实验方案.

Impact of distance between two hubs on the network coherence of tree networks

We study the impact of the distance between two hubs on network coherence defined by Laplacian eigenvalues.Network coherence is a measure of the extent of consensus in a linear system with additive noise.To obtain an exact determination of coherence based on the distance,we choose a family of tree networks with two hubs controlled by two parameters.Using the tree’s regular structure,we obtain analytical expressions of the coherences with regard to network parameters and the network size.We then demonstrate that a shorter distance and a larger difference in the degrees of the two hubs lead to a higher coherence.With the same network size and distance,the best coherence occurs in the tree with the largest difference in the hub’s degrees.Finally,we establish a correlation between network coherence and average path length and find that they behave linearly.

Newly discovered Palaeolithic artefacts from loess deposits and their ages in Lantian,central China

Eight new Palaeolithic open-air sites were identified and 770 stone artefacts were collected from 2009 to 2011 in the Lantian area of the Bahe River valley, central China. Because the famous Homo erectus fossils were unearthed at the Gongwangling and Chenjiawo localities, and more than 30 Palaeolithic open-air sites were investigated in the 1960s in this region, the catchment of Bahe River is regarded as one of the most important hominin sites from the late early Pleistocene to the middle Pleistocene. These eight newly discovered open-air sites are located at the second(n = 6), third(n = 1) or higher terraces(n = 1) of the Bahe River. The Diaozhai section on the second terrace was sampled in detail. Two samples were collected for optically stimulated luminescence dating(OSL). The OSL results suggest that a buried lithic artefact layer at the Diaozhai site spans approximately 70–30 ka. The lithic assemblage analysis suggests that the stone artefacts were made of local pebbles/cobbles such as greywacke, quartz, sandstone and igneous rocks. The main percussion techniques that were used were direct hard hammer percussion and bi-polar techniques. The lithic artefacts comprise hammer stones, cores, flakes, retouched tools and flaking debris. Acheulian-type large cutting tools(LCTs) such as hand-axes, picks and cleavers were indentified in the Lantian region as well. This is the first time Acheulian-type LCTs from the late Pleistocene have been identified in this region. This study distinguishes age gaps between Western world and East Asian Acheulian-type tools.