Benchmarking analogue models of brittle thrust wedges

We performed a quantitative comparison of brittle thrust wedge experiments to evaluate the variability among analogue models and to appraise the reproducibility and limits of model interpretation. Fifteen analogue modeling laboratories participated in this benchmark initiative. Each laboratory received a shipment of the same type of quartz and corundum sand and all laboratories adhered to a stringent model building protocol and used the same type of foil to cover base and sidewalls of the sandbox. Sieve structure, sifting height, filling rate, and details on off-scraping of excess sand followed prescribed procedures.Our analogue benchmark shows that even for simple plane-strain experiments with prescribed stringent model construction techniques, quantitative model results show variability, most notably for surface slope, thrust spacing and number of forward and backthrusts. One of the sources of the variability in model results is related to slight variations in how sand is deposited in the sandbox. Small changes in sifting height, sifting rate, and scraping will result in slightly heterogeneous material bulk densities, which will affect the mechanical properties of the sand, and will result in lateral and vertical differences in peak and boundary friction angles, as well as cohesion values once the model is constructed. Initial variations in basal friction are inferred to play the most important role in causing model variability.Our comparison shows that the human factor plays a decisive role, and even when one modeler repeats the same experiment, quantitative model results still show variability. Our observations highlight the limits of up-scaling quantitative analogue model results to nature or for making comparisons with numerical models. The frictional behavior of sand is highly sensitive to small variations in material state or experimental set-up, and hence, it will remain difficult to scale quantitative results such as number of thrusts, thrust spacing, and pop-up width from model to nature.     

On feminism and feminist allies in knowledge production in urban geography

In this response to Ananya Roy’s paper, I ask: who are the allies of feminist knowledge production about the urban? To explore this question, I specifically ask what feminist scholars may find of use in two books, namely Arrival Cities by Doug Saunders and Implosions/Explosions edited by Neil Brenner, that are representative of two major discourses on the urban, respectively, the “Urban Age” and planetary urbanization, currently favored by policy bodies and (some) academics. Their limited engagement with politics leads me to conclude with a call for a feminist mode of situated knowledge production to engage with (the limits of) urban theory and the urban as a site of praxis.     

Heretical geopolitics of Central Europe. Dissidents intellectuals and an alternative European order

This paper analyses the emergence, spread and demise of a coherent program of radical geopolitical revision developed in East European dissident circles in the 1980s. Its foundation was the insistence on the need to completely overthrow the post-Yalta, bipolar division of Europe, combined with an emphasis on the priority of human rights in political and peace issues, as well as the belief in the value of the CSCE process. It was also marked by explicit consent for the reunification of Germany as well as the insistence on the need for a democratic Russia to be part of a wider European setup. Through seminal documents, such as the Prague Appeal of 1985 intellectuals, like Jaroslav Šabata, as well as his Czechoslovak, Polish and Hungarian counterparts, were able to convince large parts of the western peace movement and some political circles to adopt the “heretic” perspective. The paper also shows how a seemingly “cultural” discourse of Central Europe, put forth by intellectuals and artists can, together with the “Yalta debate” of the mid-1980s, be read as a specific (critical) geopolitical project. Finally, the post-communist foreign policies of the dissident-led governments are investigated in an attempt to explain the partial demise of “heretical geopolitics”.     

Compensating victims of a European Deepwater Horizon accident: OPOL revisited

The introduction sketches the importance of the Deepwater Horizon incident that occurred five years ago on 20 April 2010 in the Gulf of Mexico. The question central to this contribution is how compensation would be provided if such an incident were to occur in European waters. A mechanism that plays an important role in Europe, more particularly for the North Sea is the Offshore Pollution Liability Association Limited, referred to as OPOL. Section 2 introduces OPOL by elaborating the origins, main features, membership rules, financial responsibility and claims handling. Section 3 discusses OPOL in the UK regulatory environment which is particularly interesting since OPOL membership in the UK is mandatory. Section 4 provides a critical analysis by first describing the practice of OPOL and next discussing the advantages and limits of this particular scheme. Section 5 discusses which insurance and financial instruments are used in Europe in areas where OPOL does not apply. In turn self-insurance, (re)insurance as well as risk-pooling schemes are discussed. Finally Section 6 examines to what extent it would be possible to expand OPOL either in amount or in geographical scope (more particularly beyond the North Sea). Section 7 concludes.     

Indicators of critical point behavior prior to rock failure inferred from pre-failure damage

To investigate possible indicators of critical point behavior prior to rock failure, the statistical properties of pre-failure damage were analyzed based on acoustic emission events (AE) recorded during the catastrophic fracture of typical rock samples under differential compression. AEs were monitored using a high-speed 32-channel waveform recording system. Time-dependent statistics, including the energy release rate, b-value of the magnitude–frequency distribution, fractal dimension and spatial correlation length (SCL) of the AE hypocenters were calculated for each data set. Each parameter is a function of the time-to-failure and thus can be treated as an indicator of the critical point. It is clear that the pre-failure damage evolution prior to catastrophic failures in several common rock-types is generally characterized by: 1) accelerated energy release, 2) a decrease in fractal dimension and SCL with a subsequent precursory increase, and 3) a decrease in b-value from  1.5 to  0.5 for hard rocks, and from  1.1 to  0.8 for soft rocks such S–C cataclasite. However, each parameter also reveals more complicated temporal evolution due to either the heterogeneity of the rock mass or the micro-mechanics of shear fracturing. This confirms the potential importance of integrated analysis of two or more parameters for successfully predicting the critical point. The decreasing b-value and increasing energy release may prove meaningful for intermediate-term prediction, while the precursory increase in fractal dimension and SCL may facilitate short-term prediction.     

An improved formula for incipient sediment motion in vegetated open channel flows

Quantifying incipient sediment motion in vegetated open channel flow is pivotal for estimating bed load transport and the aquatic ecological environment in rivers.A new formula is developed to predict the critical flow velocity for incipient sediment motion in the presence of emergent vegetation,by incorporating the influence of vegetation drag that characterizes the effects of mean flow and turbulence on sediment movement.The proposed formula is shown to agree with existing experimental data.Mo...     

锂辉石:巨型花岗伟晶岩锂-铯-钽矿床中关键含锂矿物SCIEI北大核心CSCD

寻找传统化石燃料的替代能源已成为全球性议题。受动力电池消费的拉动,锂资源需求急剧上升,伟晶岩型锂矿勘查热度持续攀升。虽然众多伟晶岩型锂矿地质特征尚不清晰,已有证据表明锂辉石是大多数大型-巨型伟晶岩型锂矿床的主要含锂矿物。与许多近直立的伟晶岩脉群不同,世界范围内大多数太古代伟晶岩矿脉往往呈近水平或缓倾斜在角闪岩相围岩中产出,它们往往具有复杂的三维形态并发育明显的矿物和地球化学分带。这些太古代伟晶岩脉通常形成于挤压或压剪构造体制下同变质环境中,成岩期最小主应力(σ;)近竖直。因此,伟晶岩常常侵位于近水平的构造局部引张区而形成复杂的几何学形态。压性的构造环境为富锂熔体多次脉动式注入和富含挥发分熔体垂向结晶分异提供了充足的时间;锂辉石在中高温压条件下结晶成为缓倾富锂带中最为常见的含锂矿物。     

Making Sense of Claims across Institutional Divides: critical PGIS and mapping customary land in Timor-Leste

This article explores land-tenure issues faced by Timor-Leste, specifically with reference to customary land, and the significance of mapping in resolving those difficulties. A critical review is undertaken of the pitfalls of Indigenous mapping and applications of Participatory Geographic Information Systems (PGIS) to achieve sensitive and empowering outcomes for customary groups seeking land claims. A methodology for mapping customary land in Timor-Leste is described and an analysis of the author's on-the-ground research is presented. Although the importance of customary institutions for rural land management across Timor-Leste is ascertained, this article does not advance a definitive land rights framework for the country or prescribe national mapping of customary areas. Instead, it argues for a mapping methodology to support land-use decision-making that can make sense of Indigenous knowledge and appropriate cultural practices in rural land-use claims. Identified as crucial in the process is the equal value attributed to evidence presented in myriad forms that may act as key information bridges across epistemological divides and knowledges. PGIS is a potentially important tool for resolving land-use conflicts in rural Timor-Leste when resolution occurs within a formalised institutional framework.     

Characterizing incipient motion of low fines content soils with varying compositions,water contents,and relative densities

Laboratory flume experiments were conducted to quantify the effects of the soil characteristics on the critical shear stress of low fines content soil samples collected from the Montauk shores in New York. The collected soils were reconstituted at five different fines contents, ranging between 0 and 20%. These soil mixtures were composed of two initial water contents, dry of optimum and optimum moistures, and two relative densities, one moderate dense and the other dense. The strength indices of...     

考虑水压效应的基坑边坡稳定性计算分析

地下水的存在给工程带来了巨大的隐患。如何研究分析地下水对工程的作用是地质工程界的一个重点和难点。本文基于地下水的破坏效应,分析研究了地下水引起的接触面积的变化,并推导了饱水情况下平面滑动的临界角变化公式。A* 越小,即越小,发生失稳破坏的临界角就越小。而地下水p的增加有助于A* 的减小,造成了在水压作用下土体更容易发生失稳破坏。