Observations on the crystal structures of lueshite     

Roger H. Mitchell  Peter C. Burns  Kevin S. Knight  Christopher J. Howard  Anton R. Chakhmouradian 《Physics and Chemistry of Minerals》2014,41(6):393-401

Laboratory powder XRD patterns of the perovskite-group mineral lueshite from the type locality (Lueshe, Kivu, DRC) and pure NaNbO₃ demonstrate that lueshite does not adopt the same space group (Pbma; #57) as the synthetic compound. The crystal structures of lueshite (2 samples) from Lueshe, Mont Saint-Hilaire (Quebec, Canada) and Sallanlatvi (Kola, Russia) have been determined by single-crystal CCD X-ray diffraction. These room temperature X-ray data for all single-crystal samples can be satisfactorily refined in the orthorhombic space group Pbnm (#62). Cell dimensions, atomic coordinates of the atoms, bond lengths and octahedron tilt angles are given for four crystals. Conventional neutron diffraction patterns for Lueshe lueshite recorded over the temperature range 11–1,000 K confirm that lueshite does not adopt space group Pbma within these temperatures. Neutron diffraction indicates no phase changes on cooling from room temperature to 11 K. None of these neutron diffraction data give satisfactorily refinements but suggest that this is the space group Pbnm. Time-of-flight neutron diffraction patterns for Lueshe lueshite recorded from room temperature to 700 °C demonstrate phase transitions above 550 °C from Cmcm through P4/mbm to \(Pm\overline{3} m\) above 650 °C. Cell dimensions and atomic coordinates of the atoms are given for the three high-temperature phases. The room temperature to 400 °C structures cannot be satisfactorily resolved, and it is suggested that the lueshite at room temperature consists of domains of pinned metastable phases with orthorhombic and/or monoclinic structures. However, the sequence of high-temperature phase transitions observed is similar to those determined for synthetic NaTaO₃, suggesting that the equilibrated room temperature structure of lueshite is orthorhombic Pbnm.  相似文献   

Discrete element modelling of material non‐coaxiality in simple shear flows     

Jun Ai  Paul A. Langston  Hai‐Sui Yu 《国际地质力学数值与分析法杂志》2014,38(6):615-635

We investigate the quasi‐static simple shear flow of a two‐dimensional assembly of cohesionless particles using discrete element method (DEM) simulations. We focus on the unsteady flow regime where the solid would experience significant evolution of stresses, mobilised shear strength and dilation. We construct the DEM model using a discretised‐wall confined granular cell where the apparent boundary is allowed to dilate or contract synchronously with the confined solid. A rather uniform simple shear field is achieved across the whole assembly, which benefits rheological studies in generalising constitutive laws for continuum methods. We examine two aspects of the simple shear behaviour: macroscopic stress and strain rate evolution, particularly the non‐coaxiality between the principal directions of the two; and micromechanics such as evolution of fabric. For an initially anisotropic specimen sheared under constant normal pressure, the direction of principal stress rotates towards that of the principal strain rate, gradually reducing the degree of non‐coaxiality from about 45° to fluctuating around 0°. The rate in approaching coaxiality is slower in samples with larger initial porosity, stress ratio and mean stress. Generally, a faster rate in approaching coaxiality in simple shear is observed in a more dilatant sample, which often shows a larger degree of mobilised fabric anisotropy, suggesting the possible important role of instantaneous internal friction angle. The evolution of principal fabric direction resembles that of the principal stress direction. © 2013 The Authors. International Journal for Numerical and Analytical Methods in Geomechanics published by John Wiley & Sons, Ltd.  相似文献   

Crack Initiation and Crack Propagation in Heterogeneous Sulfate-Rich Clay Rocks   总被引：2，自引：1，他引：1  

Florian Amann  Ömer Ündül  Peter K. Kaiser 《Rock Mechanics and Rock Engineering》2014,47(5):1849-1865

Brittle fracture processes were hypothesized by several researches to cause a damage zone around an underground excavation in sulfate-rich clay rock when the stress exceeds the crack initiation threshold, and may promote swelling by crystal growth in newly formed fractures. In this study, laboratory experiments such as unconfined and confined compression tests with acoustic emission monitoring, and microstructural and mineralogical analyses are used to explain brittle fracture processes in sulfate-rich clay rock from the Gipskeuper formation in Switzerland. This rock type typically shows a heterogeneous rock fabric consisting of distinct clayey layers and stiff heterogeneities such as anhydrite layers, veins or nodules. The study showed that at low deviatoric stress, the failure behavior is dominated by the strength of the clayey matrix where microcracks are initiated. With increasing deviatoric stress or strain, growing microcracks eventually are arrested at anhydrite veins, and cracks develop either aligned with the interface between clayey layers and anhydrite veins, or penetrate anhydrite veins. These cracks often link micro-fractured regions in the specimen. This study also suggest that fracture localization in sulfate-rich clay rocks, which typically show a heterogeneous rock fabric, does not take place in the pre-peak range and renders unstable crack propagation less likely. Sulfate-rich clay rocks typically contain anhydrite veins at various scales. At the scale of a tunnel, anhydrite layers or veins may arrest growing fractures and prevent the disintegration of the rock mass. The rock mass may be damaged when the threshold stress for microcrack initiation is exceeded, thus promoting swelling by crystal growth in extension fractures, but the self-supporting capacity of the rock mass may be maintained rendering the possibility for rapidly propagating instability less likely.  相似文献   

Adaptation to climate change in the insurance sector: examples from the UK,Germany and the Netherlands     

E. Carina H. Keskitalo  Gregor Vulturius  Peter Scholten 《Natural Hazards》2014,71(1):315-334

Adaptation to climate change, particularly flood risks, may come to pose large challenges in the future and will require cooperation among a range of stakeholders. However, there presently exists little research especially on the integration of the private sector in adaptation. In particular, recently developed state programs for adaptation have so far been focused on the public sector. Insurance providers may have much to contribute as they offer other parts of society services to appropriately identify, assess and reduce the financial impacts of climate change-induced risks. This study aims to explore how the institutional distribution of responsibility for flood risk is being renegotiated within the UK, Germany and Netherlands. Examining how the insurance industry and the public sector can coordinate their actions to promote climate change adaptation, the study discusses how layered natural hazard insurance systems may result from attempts to deal with increasing risks due to increasing incidences of extreme events and climate change. It illustrates that concerns over the risks from extreme natural events have prompted re-assessments of the current systems, with insurance requiring long-term legislative frameworks that defines the objectives and responsibilities of insurers and the different political authorities.  相似文献   

“Washed away”—assessing community perceptions of flooding and prevention strategies: a North Queensland example     

Richard C. Franklin  Jemma C. King  Peter J. Aitken  Peter A. Leggat 《Natural Hazards》2014,73(3):1977-1998

This article explored the perceptions of residents of a regional city in North Queensland of how to remain safe during flood events. It also explored reasons for and how to prevent risk-taking behaviour in floodwater using the protection motivation theory (PMT). PMT is a psychological theory which has recently been applied to assess behaviour during floods and was used as a framework to analyse the themes of responses to the online survey. The online survey was conducted prior to the wet season of 2011/2012 with 130 Townsville residents participating. The results indicate that about half of respondents (55 %) had some experience with floods of which driving through floodwater (38 %) was the most common type of flood experience listed and was more common amongst male respondents. Respondents’ advice to keep friends and family safe during floods was consistent with “coping appraisal”, which would improve their ability to cope with the flood. Prior experiences with floodwater influenced the reasons given for why people drive through floodwater and were taken to be indicative of an actor/observer bias. Respondents who had experience driving through floodwater (the actors) indicate how the context of the situation can influence decision-making, whereas those respondents who had no personal experience of driving through floodwater (the observers) were more likely to cite low perceived vulnerability of harm as a motivator. Prevention strategies focused on structural mechanisms to block access, information provision and punishment of offenders. It is suggested that in communities which regularly experience flooding, timely and context-specific reminders of the dangers inherent in floodwater along with the type, effectiveness and cost of protective action could minimise the public’s contact with floodwater and prove useful regardless of past experiences.  相似文献   

Komsomolskaya diamondiferous eclogites: evidence for oceanic crustal protoliths     

John F. Pernet-Fisher  Geoffrey H. Howarth  Yang Liu  Peter H. Barry  Laura Carmody  John W. Valley  Robert J. Bodnar  Zdislav V. Spetsius  Lawrence A. Taylor 《Contributions to Mineralogy and Petrology》2014,167(3):1-17

The Komsomolskaya kimberlite is one of numerous (>1,000) kimberlite pipes that host eclogite xenoliths on the Siberian craton. Eclogite xenoliths from the adjacent Udachnaya kimberlite pipe have previously been geochemically well characterized; however, data from surrounding diamond-bearing kimberlite pipes from the center of the craton are relatively sparse. Here, we report major- and trace-element data, as well as oxygen isotope systematics, for mineral separates of diamondiferous eclogite xenoliths from the Komsomolskaya kimberlite, suggesting two distinct subgroups of a metamorphosed, subducted oceanic crustal protolith. Using almandine contents, this suite can be divided into two subgroups: group B1, with a high almandine component (>20 mol%) and group B2, with a low almandine component (<20 mol%). Reconstructed REE profiles for B1 eclogites overlap with typical oceanic basalts and lack distinct Eu anomalies. In addition, elevated oxygen isotope values, which are interpreted to reflect isotopic exchange with seawater at low temperatures (<350 °C), are consistent with an upper-oceanic crustal protolith. Reconstructed REE profiles for B2 eclogites are consistent with oceanic gabbros and display distinct Eu anomalies, suggesting a plagioclase-rich cumulate protolith. In contrast to B1, B2 eclogites do not display elevated oxygen isotope values, suggesting an origin deep within the crustal pile, where little-to-no interaction with hydrothermal fluids has occurred. Major-element systematics were reconstructed based on mineral modes; group B1 eclogites have higher MgO wt% and lower SiO₂ wt%, with respect to typical oceanic basalts, reflecting a partial melting event during slab subduction. Calculated residues from batch partial melt modeling of a range of Precambrian basalts overlap with group B1 trace-element chemistry. When taken together with the respective partial melt trajectories, these melting events are clearly linked to the formation of Tonalite–Trondhjemite–Granodiorite (TTG) complexes. As a result, we propose that many, if not all, diamondiferous eclogite xenoliths from Komsomolskaya represent mantle ‘restites’ that preserve chemical signatures of Precambrian oceanic crust.  相似文献   

Remarkable Species Diversity on Adjacent Salt Lakes in South Australia   总被引：1，自引：0，他引：1  

Peter HUDSON 《《地质学报》英文版》2014,88(Z1):73-73

正Lakes Acraman,Gairdner,Harris and Everard are a cluster of large episodic salt lakes on Eyre Peninsula,South Australia.These lakes have a characteristic terrestrial invertebrate fauna including various spiders,  相似文献   

Multi‐Scale Qualitative Location: A Topology‐Based Model     

Shihong Du  Chen‐Chieh Feng  Qiao Wang  Luo Guo 《Transactions in GIS》2014,18(4):604-631

Qualitative locations describe spatial objects by relating the spatial objects to a frame of reference (e.g. a regional partition in this study) with qualitative relations. Existing models only formalize spatial objects, frames of reference, and their relations at one scale, thus limiting their applicability in representing location changes of spatial objects across scales. A topology‐based, multi‐scale qualitative location model is proposed to represent the associations of multiple representations of the same objects with respect to the frames of reference at different levels. Multi‐scale regional partitions are first presented to be the frames of reference at multiple levels of scale. Multi‐scale locations are then formalized to relate multiple representations of the same objects to the multiple frames of reference by topological relations. Since spatial objects, frames of reference, and topological relations in qualitative locations are scale dependent, scale transformation approaches are presented to derive possible coarse locations from detailed locations by incorporating polygon merging, polygon‐to‐line and polygon‐to‐point operators.  相似文献   

Where Am I? Investigating Map Matching During Self‐Localization With Mobile Eye Tracking in an Urban Environment     

Peter Kiefer  Ioannis Giannopoulos  Martin Raubal 《Transactions in GIS》2014,18(5):660-686

Self‐localization is the process of identifying one's current position on a map, and it is a crucial part of any wayfinding process. During self‐localization the wayfinder matches visually perceptible features of the environment, such as landmarks, with map symbols to constrain potential locations on the map. The success of this visual matching process constitutes an important factor for the success of self‐localization. In this research we aim at observing the visual matching process between environment and map during self‐localization with real‐world mobile eye tracking. We report on one orientation and one self‐localization experiment, both in an outdoor urban environment. The gaze data collected during the experiments show that successful participants put significantly more visual attention to those symbols on the map that were helpful in the given situation than unsuccessful participants. A sequence analysis revealed that they also had significantly more switches of visual attention between map symbols and their corresponding landmarks in the environment, which suggests they were following a more effective self‐localization strategy.  相似文献   

How to compare movement? A review of physical movement similarity measures in geographic information science and beyond     

Peter Ranacher  Katerina Tzavella 《制图学和地理信息科学》2014,41(3):286-307

In geographic information science, a plethora of different approaches and methods is used to assess the similarity of movement. Some of these approaches term two moving objects similar if they share akin paths. Others require objects to move at similar speed and yet others consider movement similar if it occurs at the same time. We believe that a structured and comprehensive classification of movement comparison measures is missing. We argue that such a classification not only depicts the status quo of qualitative and quantitative movement analysis, but also allows for identifying those aspects of movement for which similarity measures are scarce or entirely missing.

In this review paper we, first, decompose movement into its spatial, temporal, and spatiotemporal movement parameters. A movement parameter is a physical quantity of movement, such as speed, spatial path, or temporal duration. For each of these parameters we then review qualitative and quantitative methods of how to compare movement. Thus, we provide a systematic and comprehensive classification of different movement similarity measures used in geographic information science. This classification is a valuable first step toward a GIS toolbox comprising all relevant movement comparison methods.  相似文献