不同直径对非开挖近孔壁位移响应数值分析

非开挖水平定向钻进敷设管道的质量直接受到水平孔壁的位移特征影响,而水平孔直径则是影响孔壁位移的重要因素之一。采用快速拉格朗日的计算方法,利用Mohr—Coulomb准则对粘土地层中不同直径条件下的近水平孔壁位移响应特征进行了数值计算分析。获得了在不同钻孔直径（0．6-1．6m）条件下近水平孔壁X、Y和Z三个方向的位移矢量、应力分布数据。分析结果表明,随着水平钻孔直径的不断增加,近孔壁各点的Z位移也不断增加,其中水平孔下部各点Z方向变化更为明显。同时,位移变化区域随着环形区域的不断向外扩展,增加幅度不断降低。因此,合理控制施工的终孔直径对于减少孔壁位移扰动具有重要意义。     

新疆东天山地区"大草滩运动"的建立与其地质意义

通过对东天山中泥盆统头苏泉组与下泥盆统大南湖组之间不整合的研究,确认下泥盆统大南湖组为海相岛弧沉积,中泥盆统头苏 且为陆相沉积,二者之间的不整合代表一次造陆运动,因而建立了“大草滩运动”。“大草滩运动”造成地壳抬升,使北天山洋闭合,结束了北天山洋的演化历史。     

The future of Geography: when the whole is less than the sum of its parts

In a recent article, Thrift has presented an optimistic account of the future of Geography. While this reply is broadly supportive of his claims that Geography is more diverse, and has more to offer than ever before, it is less optimistic with respect to the prospects for the survival of Geography as a unitary academic discipline. Experiences over the last 20 years in the UK higher education, in particular, the 2001 RAE exercise, point to an unfavourable institutional climate for the discipline. Within Geography, the ever-increasing diversity of its subject matter and research philosophy poses problems for disciplinary identity. This is reflected in the more restricted perspective of the subject outside the universities, and is compounded by a weakening of the link between Geography in the universities and the schools. In these circumstances, serious attention must be given to the changing nature of the discipline, to its positioning with respect to other subjects, and to its relations with the wider world. At a time of academic, cultural, technological and social dynamism, there are, nevertheless, opportunities as well as dangers for the subject. Although this reply is an explicitly bleak one regarding the future, the implicit message is that Geography can (and should) still prosper. The more positive outcome, however, rests on an appreciation and nurturing of a more traditional geographical heritage than Thrift identifies, as well as a more creative view of the relationship between fundamental and applied research.     

What if negative emission technologies fail at scale? Implications of the Paris Agreement for big emitting nations

A cumulative emissions approach is increasingly used to inform mitigation policy. However, there are different interpretations of what ‘2°C’ implies. Here it is argued that cost-optimization models, commonly used to inform policy, typically underplay the urgency of 2°C mitigation. The alignment within many scenarios of optimistic assumptions on negative emissions technologies (NETs), with implausibly early peak emission dates and incremental short-term mitigation, delivers outcomes commensurate with 2°C commitments. In contrast, considering equity and socio-technical barriers to change, suggests a more challenging short-term agenda. To understand these different interpretations, short-term CO₂ trends of the largest CO₂ emitters, are assessed in relation to a constrained CO₂ budget, coupled with a ‘what if’ assumption that negative emissions technologies fail at scale. The outcomes raise profound questions around high-level framings of mitigation policy. The article concludes that applying even weak equity criteria, challenges the feasibility of maintaining a 50% chance of avoiding 2°C without urgent mitigation efforts in the short-term. This highlights a need for greater engagement with: (1) the equity dimension of the Paris Agreement, (2) the sensitivity of constrained carbon budgets to short-term trends and (3) the climate risks for society posed by an almost ubiquitous inclusion of NETs within 2°C scenarios.

POLICY RELEVANCE

Since the Paris meeting, there is increased awareness that most policy ‘solutions’ commensurate with 2°C include widespread deployment of negative emissions technologies (NETs). Yet much less is understood about that option’s feasibility, compared with near-term efforts to curb energy demand. Moreover, the many different ways in which key information is synthesized for policy makers, clouds the ability of policy makers to make informed decisions. This article presents an alternative approach to consider what the Paris Agreement implies, if NETs are unable to deliver more carbon sinks than sources. It illustrates the scale of the climate challenge for policy makers, particularly if the Agreement’s aim to address ‘equity’ is accounted for. Here it is argued that much more attention needs to be paid to what CO₂ reductions can be achieved in the short-term, rather than taking a risk that could render the Paris Agreement’s policy goals unachievable.     

Street as a big geo-data assembly and analysis unit in urban studies: A case study using Beijing taxi data

Quantitative research of urban geography has benefited greatly from the rapid development of big geo-data. Spatial assembly is an essential analytical step to summarize and perceive geographical environment from individual behaviours. Most research focuses on the methodology of how to utilize the big data, while the adopted spatial units for data aggregation remain areal in nature. This article conceptually proposes an idea of sensing cities from a street perspective, emphasizes the significance of street units in quantitative urban studies. Using a three-month taxi trajectory dataset and the major streets in Beijing, we explore the spatio-temporal patterns of urban mobility on streets, cluster streets into nine types based on their dynamic functions and capacities. Additionally, we discuss the differences and connections between the linear street unit and traditional areal units, investigate the possibility of uncovering urban communities using streets, and point out the complexity of streets. We conclude that street unit as a supplement to areal units, is able to effectively minify the modifiable areal unit problem (MAUP), sense urban dynamics, depict urban functions, and understand urban structures.     

Scaling of foreign attractiveness for countries and states

People’s behavior on online social networks, which store geo-tagged information showing where people were or are at the moment, can provide information about their offline life as well. In this paper we present one possible research direction that can be taken using Flickr dataset of publicly available geo-tagged media objects (e.g., photographs, videos). Namely, our focus is on investigating attractiveness of countries or smaller large-scale composite regions (e.g., US states) for foreign visitors where attractiveness is defined as the absolute number of media objects taken in a certain state or country by its foreign visitors compared to its population size. We also consider it together with attractiveness of the destination for the international migration, measured through publicly available dataset provided by United Nations. By having those two datasets, we are able to look at attractiveness from two different perspectives: short-term and long-term one. As our previous study showed that city attractiveness for Spanish cities follows a superlinear trend, here we want to see if the same law is also applicable to country/state (i.e., composite regions) attractiveness. Finally, we provide one possible explanation for the obtained results.     

Analyzing the distribution of human activity space from mobile phone usage: an individual and urban-oriented study

Travel activities are embodied as people’s needs to be physically present at certain locations. The development of Information and Communication Technologies (ICTs, such as mobile phones) has introduced new data sources for modeling human activities. Based on the scattered spatiotemporal points provided in mobile phone datasets, it is feasible to study the patterns (e.g., the scale, shape, and regularity) of human activities. In this paper, we propose methods for analyzing the distribution of human activity space from both individual and urban perspectives based on mobile phone data. The Weibull distribution is utilized to model three predefined measurements of activity space (radius, shape index, and entropy). The correlation between demographic factors (age and gender) and the usage of urban space is also tested to reveal underlying patterns. The results of this research will enhance the understanding of human activities in different urban systems and demographic groups, as well as providing novel methods to expand the important and widely applicable area of geographic knowledge discovery in the age of instant access.     

变径凹凸形钻孔灌注桩的成孔工艺及其承载力估算

本文着重介绍,为提高软土地基钻孔灌注桩的单桩承载力,采用变径方法施工的新型钻孔桩的成孔工艺,使得钻孔桩桩身形态、规格从无控制变为有控制;从无规则变为有规则,进而为承载力的估算,提供了可靠的依据。     

大科学思维与现代地理学的发展问题

本文结合钱学森先生关于“建立地理科学体系”的倡议,主张从当代大科学思维出发,研究现代地理学的发展问题,并以大科学为参照框架,提出了发展“大地理学”的思想。并探讨了围绕“大地理学”的若干理论问题和现代地理学向“大地理学”转变的途径。     

The “von Karman vortex street” to the west of Big Island

Satellite-tracked drifting buoy data and altimetry data are used to study the active vortex field to the west of Big Island. A pair of vortexes were observed at the trajectory of buoy in 1995. The westward propagation of the vortex pair is studied in detail by reproducing the loops of each vortex. The orbital period and radius of the pair of vortex are determined to be 10-11 d and 58-68 km. Two arrays of contra-rotating vortices are displayed in the average sea surface height anomaly (SSHA) field to the west of Big Island. Based on the calculation of the fluid dynamical parameter, the “von Karman vortex street” is proved to be generated to the west of Big Island as the North Equatorial Current impinges upon Big Island from the east. Finally, the analysis of the buoy trajectories in a decade contributes to the conclusion of the pattern of VKVS in a statistical view.