“一带一路”若干区域社会发展态势大数据分析   总被引：1，自引：0，他引：1  

马明清  袁武  葛全胜  袁文  杨林生  李汉青  李萌 《地理科学进展》2019,38(7):1009-1020

“一带一路”倡议已成为中国的基本国际政策,及时掌握沿线国家的社会发展态势,对确保该倡议的稳步推进与顺利实施至关重要。为此,论文将GDELT数据库作为数据来源,获取了“一带一路”沿线25个国家近5 a的英文新闻全文数据,引入主题模型,结合无监督方法(LDA)与监督方法(Labeled LDA)挖掘新闻数据中蕴含的主题,构建社会稳定度模型,分析各国社会发展态势。研究发现：① 沿线国家社会发展态势不均衡,可划分为4类,即稳定型,如阿曼、越南等;较稳定型,如乌兹别克斯坦、伊朗等;较高风险型,如科威特、约旦、巴基斯坦、缅甸;高风险型,如叙利亚、阿富汗等。② 通过新闻主题时空挖掘,可有效发现热点区域,例如论文发现安集延对中亚地区社会发展与稳定具有重要影响。③ 利用监督主题模型,能够发现乌兹别克斯坦经济产业结构,识别出重大社会事件,发现其社会安全风险及变化趋势。采用论文方法可有效挖掘新闻事件时空变化规律,发现各国潜在风险,支撑对沿线国家社会发展态势的实时动态监控,为“一带一路”倡议的实施提供辅助决策支持,具有重要的应用价值。  相似文献   

潜在生态风险指数法应用中的一些问题     

马建华  韩昌序  姜玉玲 《地理研究》2020,39(6):1233-1241

收集2001—2018年有关Håkanson潜在生态风险指数法应用论文2323篇,重点分析2008年以来发表在国内外著名期刊上的论文203篇,发现存在以下问题：① Håkanson潜在生态风险指数是基于水环境沉积学理论建立的一种生态风险评价方法,不适合土壤潜在生态风险或污染评价,更不能被应用于水相溶质、大气颗粒物、地表灰尘、植物或作物等介质的生态风险或污染评价,但现实研究中评价对象错位的论文占2323篇论文的49.29%。② 不能生搬硬套Håkanson潜在生态风险系数（Er）和潜在生态风险指数（RI）分级标准,必须根据具体参评污染物的种类和数量进行调整。Er第一级界限值应为所有参评污染物毒性系数（St）的最大值,RI第一级界限值可用∑St ⁱ×1.13并取十位整数得到。但是多数研究罔顾其参评污染物的种类和数量,照搬Håkanson的Er和RI分级标准而出现错误的论文分别占203篇论文的45.32%和61.08%;虽然有些学者对RI分级标准进行了调整,但调整正确的论文只占23.81%。③ 只评价Hg单项生态风险或包括Hg在内的多个重金属综合生态风险时,不能用St ^Hg代替其毒性响应系数（Tr ^Hg）。  相似文献   

基于应变的变形副反射面位姿形貌快速重构方法          下载免费PDF全文

许谦  王从思  易乐天 《天文学报》2020,61(5):51

随着双反射面天线口径的增大、工作频段的升高,天线对副反射面的精度要求也越来越高.当天线受到自重以及风荷、温度等外界因素的影响时,为了更好地保证满足天线的高指向精度等电性能要求,基于应变传感器和模态叠加原理,分别利用天线变形后副反射面支撑腿与副反射面自身结构的应变值来快速重构副反射面的位姿、形貌,便于副反射面调整机构对其进行实时修正,以实现更加精准的主副反射面位置匹配,降低因天线结构变形造成的波束指向误差和增益损失.  相似文献   

利用后向预报方法分析印度洋黄鳍金枪鱼资源评估模型     

官文江  吴佳文  曹友华 《中国海洋大学学报(自然科学版)》2020,(2):52-59

当前,对渔业资源评估模型的诊断与选择,主要依赖于模型对观察数据的拟合度,很少评价模型的预测能力、并将其作为评价渔业资源评估与管理质量的依据。为此,本文利用后向预报方法评价了印度洋黄鳍金枪鱼(Thunnus albacores)资源评估模型的预测能力,并在此基础上分析了印度洋黄鳍金枪鱼的资源评估与管理质量。研究表明,在利用贝叶斯剩余产量模型对印度洋黄鳍金枪鱼进行资源评估时,存在如下问题:(1)拟合较好的模型其预测能力较差;(2)利用不同时段数据拟合模型时,采用DIC(Deviance Information Criterion)选择的最佳模型缺少稳定性;(3)不同模型估计的TAC (Total Allowable Catch)存在较大差异。据此可以判断,利用贝叶斯剩余产量模型对印度洋黄鳍金枪鱼进行资源评估与管理效果较差。本研究结果表明:(1)利用后向预报方法可评价模型的预测能力、DIC选择模型的稳定性,从而能在一定程度上判断模型模拟的种群演化动态是否正确、资源评估结果是否存在问题;(2)利用后向预报方法可揭示评估结果的不确定性及其可能引起的渔业管理风险,从而有利于避免渔业管理风险、实现渔业管理目标。  相似文献   

Long-wave instability of an isolated front     

Peter D. Killworth 《地球物理与天体物理流体动力学》2013,107(4):235-258

Abstract

The stability of an isolated one-layer reduced gravity front is examined. It is shown that the system is unstable to long-wave disturbances provided merely that a simple condition on the depth profile is satisfied far from the front. The instability does not require the extremum of potential vorticity needed by quasi-geostrophic theory. The instability releases mean kinetic and mean potential energy from the system, but lacking a second layer cannot truly be termed baroclinic instability.  相似文献   

Probabilistic analysis of three-dimensional tunnel face stability in soft rock masses using Hoek–Brown failure criterion     

Jiahua Zhang  Lianyang Zhang  Weijun Wang  Daobing Zhang  Biao Zhang 《国际地质力学数值与分析法杂志》2020,44(11):1601-1616

This paper investigates tunnel face stability in soft rock masses via coupled limit and reliability analyses. Specifically, a 3D face collapse mechanism was first constructed. Then the Hoek–Brown failure criterion was introduced into the limit analysis via the tangential technique. Taking the variability of rock mass parameters and loads into consideration, a reliability model was established. The collapse pressure and failure range of tunnel faces were determined. In addition, the required factor of safety (FS) and supporting pressure under three safety levels were obtained, and the corresponding safety level graphs for support design were presented. Comparison of the obtained results with previous work demonstrates the rationality of the 3D collapse mechanism and the validity of the results. A decrease in the geological strength index, Hoek–Brown parameter m_i, and uniaxial compressive strength or an increase in the disturbance factor results in a nonlinear increase of the collapse pressure and an enlargement of the failure zone. Such changes also lead to a nonlinear increase of the required support pressure under a certain safety level. By contrast, the FS does not exhibit any obvious change when these parameters vary. Therefore, when a rock mass is of poor quality or heavily disturbed, the advance support should be enlarged from upper front to right above the tunnel face. Moreover, as the safety level increases, both the required FS and supporting pressure of the tunnel face increase nonlinearly at a higher rate.  相似文献   

A single numerically efficient equation for approximating the Mohr–Coulomb and the Matsuoka–Nakai failure criteria with rounded edges and apex     

Andrea Panteghini  Rocco Lagioia 《国际地质力学数值与分析法杂志》2014,38(4):349-369

This paper presents a novel formulation for defining soil failure. It plots in the principal stress space as a surface with the shape ranging between an approximation of the Matsuoka–Nakai and of the Mohr–Coulomb criteria depending on the value of a single parameter. The new function can be used as a replacement of the original equations of these well‐established criteria for implementing in a program for numerical analyses, and it is particularly effective for approximating the Matsuoka–Nakai criterion. Both the Mohr–Coulomb and the Matsuoka–Nakai failure criteria present numerical difficulties during implementation and also at run‐time. In the case of the Matsuoka–Nakai, the new formulation plots in the first octant only, whereas the original criterion plots in all octants, which causes severe convergence problems particularly for those Gauss points with low stress state, such as those on the side of a shallow footing. When the shape parameter is set to reproduce the Mohr–Coulomb failure criterion, on the other hand, the new formulation plots as a pyramid with rounded edges. Moreover, as the new function is at least of class C², the second derivatives are continuous, thus ensuring quadratic convergence of the Newton's method used within the integration scheme of the constitutive law. The proposed formulation can also provide both sharp and rounded apex of the surface at the origin of the stress space by setting accordingly one additional parameter. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Long-term strength attenuation characteristics and yield criterion of frozen soil北大核心CSCD     

申明德  周志伟  马巍 《冰川冻土》2022,44(2):437-447

Frozen soil is generally regarded as a strongly rheological geomaterial. The strength attenuation of frozen soil is an important inducement for disease and instability in subgrade engineering, pile engineering and artificial freezing construction. Few efforts have been made to investigate the attenuation characteristics of strength envelope surface for frozen soil under complex stress states experimentally and theoretically. Considering this, at a temperature of -6 ℃, a series of triaxial stress relaxation tests under various confining pressures were carried out on the frozen subgrade soil specimens at strength points. The degeneration of strength parameters and stress attenuation process of frozen soil under complex stress states were systematically studied. The degradation law and mechanism of cohesion and internal friction angle are synchronously revealed in the stress relaxation process. Testing results indicate that the stress relaxation process of compacted frozen soil is significantly influenced by confining pressure. The stress relaxation ratio is increasing linearly with the rise of confining pressure if the confining pressure is beyond 1. 5 MPa. The anti-relaxation ability of frozen soil is greatly reduced during high confining pressure conditions:the stress relaxation ratio of frozen soil is only 41. 94% under 1. 5 MPa, but exceeds 90. 30% under 16 MPa. The strength of frozen soil attenuates linearly with time in the semi-logarithmic coordinate system. When the confining pressure is higher than 1. 5 MPa, the strength attenuation rate of frozen soil increases with the rise of confining pressure. As the development of stress relaxation of frozen soil, cohesion decreases linearly but internal friction angle increases linearly with time in the semi-logarithmic coordinate system. It manifested that the cementation in frozen soil shows evident rheological features and it is a key inducement for strength attenuation. Moreover, the attenuation law and value of cohesion in frozen soil which is measured by triaxial stress relaxation test are similar to the spherical template indenter test results. This may provide a new test method for obtaining the long-term strength and cohesion of frozen soil. On the basis of test results, the stress states of frozen soil in all stress relaxation curves at 12 relaxation durations were captured, and the rate-dependent variation characteristics of strength envelope in p-q stress space were analyzed in detail. Under high confining pressures, the strength envelope of frozen soil shows different geometric features as time goes on. In addition to the decline of level, the strength surface exhibits clockwise rotation with time, and the third stage sharply decreases at first and then becomes flat. Based on the analysis of characteristics of experimental strength surface and evolution law of strength parameters during the stress relaxation process, a rate-dependent strength theory for frozen soil considering the stress relaxation effect is established in this paper. © 2022 Science Press (China). All rights reserved.  相似文献   

颗粒形状对粒状材料破碎演化规律及强度准则影响     

郅彬  王小婵  刘恩龙 《岩土力学》2023,(3):649-662

为探讨颗粒形状对粒状材料的颗粒破碎演化规律及强度特征的影响,提出了一个新的粒状材料颗粒形状量化参数,设计了一种考虑三维颗粒形状的人工试样制备方法,随即进行了常规三轴压缩试验,并分析了颗粒破碎和强度特征,最终建立了一个二元介质强度准则,具体的研究成果为：建立颗粒形状量化参数——球形模量GM,在此基础上制备了5种不同形状的可破碎粒状材料三轴试样,并发现球形模量影响着粒状材料的三轴压缩强度特征;通过筛分确定试样的颗粒破碎情况,对试样的颗粒破碎演化规律和临界状态进行探讨,发现颗粒形状通过影响颗粒破碎规律而控制着宏观强度的非线性演化特征;以二元介质理论为基础,建立了考虑颗粒形状的可破碎粒状材料强度准则,并通过试验对其适用性进行了验证。  相似文献   

降相关对模糊度解算中搜索效率的影响分析   总被引：1，自引：1，他引：0  

卢立果  刘万科  李江卫 《测绘学报》2015,44(5):481-487

首先理论分析了条件数、正交缺陷度、S(A)等降相关评价指标所表示的几何意义,然后采用LAMBDA算法、LLL规约算法和Seysen规约算法通过模拟和实际数据对模糊度的搜索效果和不同评价指标之间的关系进行了深入计算分析。进一步验证得出"降低模糊度方差分量间的相关性实现最大程度地压缩椭球可以提高搜索效率"的观点是片面的,并通过结果分析表明提高搜索效率的本质在于尽可能地促使基向量按照一定方向排序。  相似文献