Substructuring stability analysis in light of comprehensive transfer system dynamics     

Zhenyun Tang  Matt Dietz  Zhenbao Li 《Bulletin of Earthquake Engineering》2018,16(1):129-154

Real-time dynamic substructuring (RTDS) is an experimental technique that splits the structure under test into coupled parts that run in parallel. The structural component exhibiting unpredictable behaviour is tested in the laboratory while the remainder of the structure is modelled numerically. As the test proceeds, the dynamic force state at the physical–numerical interface is measured and a transfer system, usually a servo-hydraulic actuator or shaking table, is used to impose the commensurate response on the physical substructure. The integral dynamics of servo-hydraulic transfer systems can frustrate RTDS implementation by destabilising the system. Many have noted the deleterious stability implications of excessive phase lag in terms of a pure time-delay. However, because of the existence of magnitude variations and more complex phase characteristics, pure time-delay is too simple to represent the inherent nature of servo-hydraulic transfer systems. This paper considers RTDS stability in light of comprehensive transfer system dynamics. A transfer-function model of a servo-hydraulic transfer system is adopted and used to reflect the oversimplification of pure time-delay. The concept of gain margin is employed to reveal the drawbacks of the pure-delay based RTDS stability analyses. In order to overcome the drawbacks, a new method based on gain margin was developed. The comparative analyses demonstrate that the gain margin based method is tailored to predict the stability boundaries of a RTDS system incorporating comprehensive transfer system dynamics. The validity of the technique is verified experimentally through virtual and authentic RTDS system employing a shaking table. The performance of delay compensated shaking table RTDS is also assessed in perspective of stability.  相似文献   

Geographically distributed hybrid testing & collaboration between geotechnical centrifuge and structures laboratories     

Mobin Ojaghi  Ignacio Lamata Martínez  Matt S. Dietz  Martin S. Williams  Anthony Blakeborough  Adam J. Crewe  Colin A. Taylor  S. P. Gopal Madabhushi  Stuart K. Haigh 《地震工程与工程振动(英文版)》2018,17(1):53-71

Distributed Hybrid Testing (DHT) is an experimental technique designed to capitalise on advances in modern networking infrastructure to overcome traditional laboratory capacity limitations. By coupling the heterogeneous test apparatus and computational resources of geographically distributed laboratories, DHT provides the means to take on complex, multi-disciplinary challenges with new forms of communication and collaboration. To introduce the opportunity and practicability afforded by DHT, here an exemplar multi-site test is addressed in which a dedicated fibre network and suite of custom software is used to connect the geotechnical centrifuge at the University of Cambridge with a variety of structural dynamics loading apparatus at the University of Oxford and the University of Bristol. While centrifuge time-scaling prevents real-time rates of loading in this test, such experiments may be used to gain valuable insights into physical phenomena, test procedure and accuracy. These and other related experiments have led to the development of the real-time DHT technique and the creation of a flexible framework that aims to facilitate future distributed tests within the UK and beyond. As a further example, a real-time DHT experiment between structural labs using this framework for testing across the Internet is also presented.  相似文献   

Climate change projections for the surface ocean around New Zealand     

Cliff S. Law  Graham J. Rickard  Sara E. Mikaloff-Fletcher  Matt H. Pinkerton  Erik Behrens  Steve M. Chiswell 《新西兰海洋与淡水研究杂志》2018,52(3):309-335

The future status of the surface ocean around New Zealand was projected using two Earth System Models and four emission scenarios. By 2100 mean changes are largest under Representative Concentration Pathway 8.5 (RCP8.5), with a +2.5°C increase in sea surface temperature, and decreases in surface mixed layer depth (15%), macronutrients (7.5–20%), primary production (4.5%) and particle flux (12%). Largest macronutrient declines occur in the eastern Chatham Rise and subantarctic waters to the south, whereas dissolved iron increases in subtropical waters. Surface pH projections, validated against subantarctic time-series data, indicate a 0.335 decline to ～7.77 by 2100. However, projected pH is sensitive to future CO₂ emissions, remaining within the current range under RCP2.6, but decreasing below it by 2040 with all other scenarios. Sub-regions vulnerable to climate change include the Chatham Rise, polar waters south of 50°S, and subtropical waters north of New Zealand, whereas the central Tasman Sea is least affected.  相似文献   

First capture and description of larval torrentfish (Cheimarrichthys fosteri) during their seaward migration     

Matt G. Jarvis  Manna L. Warburton  Aurélien Vivancos  Gerard P. Closs 《新西兰海洋与淡水研究杂志》2018,52(1):138-144

While many of New Zealand’s freshwater fishes undertake larval migrations as part of their amphidromous life-history, little is known of the larval stages of these fish. Torrentfish (Cheimarrchthys fosteri), a New Zealand endemic, amphidromous, riffle specialist are particularly enigmatic; their spawning sites and behaviours are unknown, and larvae have never been collected either emigrating from freshwater or during their marine feeding phase. During summer drift sampling, we captured unidentified fish larvae emigrating downstream in the Waianakarua River, South Island, New Zealand. Based on multiple lines of evidence (meristic comparisons with adults, morphology, time of capture, and adult fish populations of the Waianakarua) we identify these larvae as torrentfish. This represents the first time torrentfish larvae have been captured or identified, laying the foundations for future studies into the early life-history and ecology of this unique and threatened fish.  相似文献   

New insights on measured and calculated vitrinite reflectance     

Tim Matava  Veit Matt  Jack Flannery 《Basin Research》2019,31(2):213-227

Measurement of dispersed vitrinite reflectance in organic sediments is one of the few regional data sets used for placing bounds on the thermal history of a sedimentary basin. Reflectance data are important when access to complementary information such as high‐quality seismic data is unavailable to place bounds on subsidence history and in locations where uplift is an important part of the basin history. Attributes which make vitrinite reflectance measurements a useful data set are the relative ease of making the measurement, and the availability of archived well cores and cuttings in state, provincial, and federal facilities. In order to fully utilize vitrinite data for estimating the temperature history in a basin, physically based methods are required to calibrate an equivalent reflectance from a modelled temperature history with measured data. The most common method for calculating a numerical vitrinite reflectance from temperature history is the EASY%R_o method which we show systematically underestimates measured data. We present a new calculated reflectance model and an adjustment to EASY%R_o which makes the correlation between measured vitrinite values and calculated vitrinite values a physical relationship and more useful for constraining thermal models. We then show that calibrating the thermal history to vitrinite on a constant age date surface (e.g., top Cretaceous) instead of calibrating the thermal history in depth removes the heating rate component from the reflectance calculation and makes thermal history calibration easier to understand and more directly related to heat flow. Finally, we use bounds on the vitrinite–temperature relationships on a constant age date surface to show that significant uncertainty exists in the vitrinite data reported in most data sets.  相似文献   

A New Method to Quantify Carbonate Rock Weathering     

Caroline Dubois  John Deceuster  Olivier Kaufmann  Matt D. Rowberry 《Mathematical Geosciences》2015,47(8):889-935

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Environmental learning and the social construction of an exurban landscape in Fremont County, Colorado   总被引：1，自引：0，他引：1  

Soren C. Larsen  Matt Foulkes  Amy Thompson 《Geoforum》2011,42(1):83-93

Across the rural American West, the restructuring of rural capitalism has transformed production landscapes into those increasingly structured by the development and consumption of natural and cultural amenities. This project used principles from symbolic interactionism, ethnographic methods, and the analytical framework of regional political ecology to understand the role of environmental learning in negotiating the new management regime associated with amenity-based capitalism in rural Fremont County, Colorado. The study found that most amenity residents participate regularly in social learning about the environment through a variety of interpersonal and organizational behaviors. In addition, they are responding collectively to environmental risks and opportunities associated with wildfire, noxious weeds and invasive grass species, prospective uranium mining, and restoration of cultural-landscape features. Ultimately, the practices of environmental learning concern how private properties and assets will be managed relative to the social construction of the environment as an amenity for personal consumption. Conservation and management prospects in this and other rural areas in the postindustrial world can be enhanced by understanding the microsociology of exurban geographies and by engaging the social forms and processes related to this distinctive landscape construction.  相似文献   

Earliest microbially mediated pyrite oxidation in ~ 3.4 billion-year-old sediments     

David Wacey  Martin Saunders  Martin D. Brasier  Matt R. Kilburn 《Earth and Planetary Science Letters》2011,301(1-2):393-402

Pyrite (FeS₂) oxidation in modern sedimentary environments is neither a purely chemical nor purely microbial process, but it is significantly enhanced by the activity of microorganisms that use reduced forms of iron and sulphur in their metabolisms. On the early Earth, where oxygen levels were thought to be < 10^?5 of the present atmospheric level and chemical oxidants scarce, such biological mediation may have been critical in the redox cycles of iron and sulphur. Here, we show that detrital sedimentary pyrite grains in a ~ 3.4 billion-year-old sandstone were colonised by microbial communities. The detrital pyrite comes from the basal quartz arenite member of the 3.43–3.35 Ga Strelley Pool Formation (SPF) in the East Strelley greenstone belt of the Pilbara Craton, Western Australia. Rock chips and petrographic thin sections of black sandstones occurring on two ridges close to the SPF type locality of Strelley Pool were investigated using optical microscopy, SEM, TEM, laser Raman and NanoSIMS. The detrital pyrite grains exhibit laminated carbonaceous coatings of early Archean age, with localised enrichments of nitrogen that are interpreted as the in situ remains of biofilms growing on these nutrient-rich minerals. Pyrite surfaces contain spherical pits, chains of pits and channels that are morphologically distinct from abiotic alteration features. The pits and channels are widespread, have a clustered distribution typical of microbial colonisation, and are closely comparable to biologically mediated microstructures in the younger rock record and those created by extant Fe- and S-oxidising microbes in the laboratory. They are thus interpreted as trace fossils formed by the attachment of bacteria to the pyrite surfaces. A nano-layer and discreet nano-grains of secondary mineral precipitates, namely Fe-oxides belonging to the magnetite-maghaemite group, attest to pyrite oxidation. These are intimately associated with the biofilms and trace fossils, and are interpreted to represent the fossilised mineral products of biologically mediated pyrite oxidation. These data extend the geological range of microbes capable of metabolising reduced Fe and/or S compounds back to the early Archean and indicate that pyrite-rich sedimentary rocks provide promising targets in the search for extraterrestrial life.  相似文献   

Stewardship of things: The radical potential of product stewardship for re-framing responsibilities and relationships to products and materials     

Ruth Lane  Matt Watson 《Geoforum》2012,43(6):1254-1265

In the context of broad-based concerns about the need to move towards a more sustainable materials economy, particularly as they are expressed in debates around Ecological Modernisation (EM), we argue that product stewardship has radical potential as a means to promote significant change in the relationship between society and the material world. We focus on two important dimensions that have been neglected in approaches to product stewardship to date. Firstly, we argue that immanent within the basic concept of stewardship is a problematisation of dominant understandings of property ownership in neoliberal market economies. In the space opened up by notions of stewardship, different ways of enacting both rights and responsibilities to products and materials emerge which have potential to advance the sustainability of material economies. Secondly, through exploration of existing expressions of product stewardship, we uncover a neglected scale of action. Both policy and dominant articulations of EM focus primarily on the efficiency of production processes; and secondarily, the attitudes and behaviours of individual consumers. Missing from this is the ‘meso-scale’ of social collectives including households, neighbourhoods, more distributed communities and small scale social enterprises. Based on a review of existing research from Australia and the UK, including our own, we argue that understanding of embedded practices of material responsibility at the household scale can both reinvigorate the concept of product stewardship as a potentially radical intervention, and reveal the potential of the meso-scale as a challenging but worthwhile realm of policy intervention.  相似文献   

Deferred decentralized movement pattern mining for geosensor networks     

Patrick Laube  Matt Duckham  Marimuthu Palaniswami 《International journal of geographical information science》2013,27(2):273-292

This article presents an algorithm for decentralized (in-network) data mining of the movement pattern flock among mobile geosensor nodes. The algorithm DDIG (Deferred Decentralized Information Grazing) allows roaming sensor nodes to ‘graze’ over time more information than they could access through their spatially limited perception range alone. The algorithm requires an intrinsic temporal deferral for pattern mining, as sensor nodes must be enabled to collect, memorize, exchange, and integrate their own and their neighbors' most current movement history before reasoning about patterns. A first set of experiments with trajectories of simulated agents showed that the algorithm accuracy increases with growing deferral. A second set of experiments with trajectories of actual tracked livestock reveals some of the shortcomings of the conceptual flocking model underlying DDIG in the context of a smart farming application. Finally, the experiments underline the general conclusion that decentralization in spatial computing can result in imperfect, yet useful knowledge.  相似文献