Assembling/Worlding Cities     

Eugene McCann  Ananya Roy 《Urban geography》2013,34(5):581-589

This article explores the assembling and worlding of cities as both aspirational and evaluative processes in which cities are assembled, compared, and “positioned.” These practices involve the global circulation of expertise, best practices, models, and technologies related to how best to develop and govern cities. From specific examples from the authors' research, it is argued that the two distinct but overlapping notions of assembling and worlding help us conceptualize the contemporary urban–global condition. Building on the article's insights, we end this Urban Pulse with some questions for future global urban studies.  相似文献   

A new laboratory technique for determining the compressional wave properties of marine sediments at sonic frequencies and in situ pressures     

Clive McCann  Jeremy Sothcott  Angus I. Best 《Geophysical Prospecting》2014,62(1):97-116

We describe a new laboratory technique for measuring the compressional wave velocity and attenuation of jacketed samples of unconsolidated marine sediments within the acoustic (sonic) frequency range 1–10 kHz and at elevated differential (confining – pore) pressures up to 2.413 MPa (350 psi). The method is particularly well suited to attenuation studies because the large sample length (up to 0.6 m long, diameter 0.069 m) is equivalent to about one wavelength, thus giving representative bulk values for heterogeneous samples. Placing a sediment sample in a water‐filled, thick‐walled, stainless steel Pulse Tube causes the spectrum of a broadband acoustic pulse to be modified into a decaying series of maxima and minima, from which the Stoneley and compressional wave, velocity and attenuation of the sample can be determined. Experiments show that PVC and copper jackets have a negligible effect on the measured values of sediment velocity and attenuation, which are accurate to better than ± 1.5% for velocity and up to ± 5% for attenuation. Pulse Tube velocity and attenuation values for sand and silty‐clay samples agree well with published data for similar sediments, adjusted for pressure, temperature, salinity and frequency using standard equations. Attenuation in sand decreases with pressure to small values below Q^?1 = 0.01 (Q greater than 100) for differential pressures over 1.5 MPa, equivalent to sub‐seafloor depths of about 150 m. By contrast, attenuation in silty clay shows little pressure dependence and intermediate Q^?1 values between 0.0206–0.0235 (Q = 49–43). The attenuation results fill a notable gap in the grain size range of published data sets. Overall, we show that the Pulse Tube method gives reliable acoustic velocity and attenuation results for typical marine sediments.  相似文献   

Attenuation of P- and S-waves in limestones   总被引：2，自引：1，他引：1  

Solomon Assefa  Clive McCann  & Jeremy Sothcott 《Geophysical Prospecting》1999,47(3):359-392

Ultrasonic compressional- and shear-wave attenuation measurements have been made on 40, centimetre-sized samples of water- and oil-saturated oolitic limestones at 50 MPa effective hydrostatic pressure (confining pressure minus pore-fluid pressure) at frequencies of about 0.85 MHz and 0.7 MHz respectively, using the pulse-echo method. The mineralogy, porosity, permeability and the distribution of the pore types of each sample were determined using a combination of optical and scanning electron microscopy, a helium porosimeter and a nitrogen permeameter. The limestones contain a complex porosity system consisting of interparticle macropores (dimensions up to 300 microns) and micropores (dimensions 5–10 microns) within the ooids, the calcite cement and the mud matrix. Ultrasonic attenuation reaches a maximum value in those limestones in which the dual porosity system is most fully developed, indicating that the squirt-flow mechanism, which has previously been shown to occur in shaley sandstones, also operates in the limestones. It is argued that the larger-scale dual porosity systems present in limestones in situ could similarly cause seismic attenuation at the frequencies of field seismic surveys through the operation of the squirt-flow mechanism.  相似文献   

Compressional- and shear-wave velocities as a function of confining stress in dry sandstones   总被引：3，自引：0，他引：3  

Khaksar  Griffiths  & McCann 《Geophysical Prospecting》1999,47(4):487-508

A laboratory study was carried out to investigate the influence of confining stress on compressional- and shear-wave velocities for a set of rock samples from gas-producing sandstone reservoirs in the Cooper Basin, South Australia. The suite of samples consists of 22 consolidated sublitharenites with helium porosity ranging from 2.6% to 16.6%. We used a pulse-echo technique to measure compressional- and shear-wave velocities on dry samples (cylindrical 4.6 × 2 cm) at room temperature and at elevated confining stress (≤ 60 MPa). Compressional- and shear-wave velocities in samples increase non-linearly with confining stress. A regression equation of the form V = A ? Be^?DP gives a good fit to the measured velocities with improved prediction of velocities at high confining stresses compared with equations suggested by other studies. The predicted microcrack-closure stresses of the samples show values ranging from 70 MPa to 95 MPa and insignificant correlation with porosity, permeability or clay content. There is a positive correlation between change in velocity with core porosity and permeability, but this association is weak and diminishes with increasing confining stress. Experimental results show that pore geometry, grain-contact type, and distribution and location of clay particles may be more significant than total porosity and clay content in describing the stress sensitivity of sandstones at in situ reservoir effective stress. The stress dependence of Cooper Basin sandstones is very large compared with data from other studies. The implication of our study for hydrocarbon exploration is that where the in situ reservoir effective stress is much less than the microcrack-closure stress of the reservoir rocks, the variation of reservoir effective stress could cause significant changes in velocity of the reservoir rocks. The velocity changes induced by effective stress in highly stress-sensitive rocks can be detected at sonic-log and probably surface-seismic frequencies.  相似文献   

Resilience in the post-welfare inner city: voluntary sector geographies in London,Los Angeles and Sydney by Geoffery DeVerteuil,Bristol, Policy Press, 2016, 300 pp.,  US$45.95 (paperback), ISBN 1447316649     

Eugene McCann 《Urban geography》2017,38(4):626-628

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Facies and provenance analysis of Paleogene‐age alluvial conglomerates from the northern part of the Mesta Basin,SW Bulgaria     

A. Ebinghaus  T. McCann  C. Augustsson 《Geological Journal》2012,47(4):409-425

The Mesta Basin in southwest Bulgaria is a graben that contains a Paleogene‐age siliciclastic and volcaniclastic succession deposited in alluvial and fluvial settings. A sedimentological analysis has shed light on conglomerate provenance, and the links between deposition and tectonic setting. Petrographical and chemical analysis of conglomerate clasts and matrix from the Dobrinishka, Gradinishka, Osikovo (or Osenovo) and Zlataritsa formations reveal both local, and more distal source provenance ages. The basal conglomerates are subdivided into three types, a lower and upper polymictic and a middle granitic conglomerate type. Petrographical and chemical analysis reveals granite, gneiss and amphibolite clasts that were sourced from the Sidironero–Mesta Unit of the Middle Allochthon of the Rhodope Metamorphic Complex, and the Rila–Rhodope Batholith to the east of the basin. Cathodoluminescence analysis of quartz sand grains reveals an increased input of red‐ and violet‐luminescent volcanic grains. Volcanic quartz in the oldest conglomerates indicates a hitherto unknown early (pre‐Oligocene) phase of volcanic activity in the vicinity of the Mesta Basin. The conglomerates were deposited in association with movement on the Ribnovo low‐angle normal fault during the Late Eocene, creating subsidence and the development of considerable accommodation space. The establishment of a fluvial environment followed subsequent Oligocene‐age volcanic activity. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Relationality/territoriality: Toward a conceptualization of cities in the world   总被引：3，自引：0，他引：3  

Eugene McCann  Kevin Ward 《Geoforum》2010,41(2):175-184

The paper contributes to the conceptualization of cities in the world by first outlining the conceptual and empirical challenges of theorizing the urban/global nexus in both relational and territorial terms. It argues that the most useful and appropriate approach to understanding contemporary urban governance in global context is to develop a conceptualization that is equally sensitive to the role of relational and territorial geographies, of fixity and flow, of global contexts and place-specificities (and vice versa), of structural imperatives and embodied practices, in the production of cities. In order to illustrate the benefits of this conceptualization, the paper will apply it to the case of how downtown development is governed in many contemporary cities. The role of the Business Improvement District (BID) program and New Urbanist planning models in shaping downtowns will be examined in terms of: (1) how and by whom these models are developed in a global-relational context and are set in motion through scaled circuits of policy knowledge and (2) how the mobilization of these models are conditioned by their territorialization in specific spatial and political economic contexts. The paper emphasizes that the ‘local globalness’ of policy models like BIDs and New Urbanism and their consequences for cities can best be understood through a combined focus on relationality and territoriality.  相似文献   

Observations of fluid‐dependent shear‐wave splitting in synthetic porous rocks with aligned penny‐shaped fractures‡     

Philip Tillotson  Angus Ian Best  Jeremy Sothcott  Clive McCann  Wang Shangxu  Xiang‐Yang Li 《Geophysical Prospecting》2011,59(1):111-119

P‐ and S‐wave velocity and attenuation coefficients (accurate to ±0.3% and ±0.2 dB/cm, respectively) were measured in synthetic porous rocks with aligned, penny‐shaped fractures using the laboratory ultrasonic pulse‐echo method. Shear‐wave splitting was observed by rotating the S‐wave transducer and noting the maximum and minimum velocities relative to the fracture direction. A block of synthetic porous rock of fracture density 0.0201 ± 0.0068 and fracture size 3.6 ± 0.38 mm (measured from image analysis of X‐ray CT scans) was sub‐sampled into three 20–30 mm long, 50 mm diameter core plugs oriented at 0°, 45° and 90° to the fracture normal (transversely isotropic symmetry axis). Full waveform data were collected over the frequency range 500–1000 kHz for both water and glycerin saturated cores to observe the effect of pore fluid viscosity at 1 cP and 100 cP, respectively. The shear‐wave splitting observed in the 90° core was 2.15 ± 0.02% for water saturated and 2.39 ± 0.02% for glycerin saturated, in agreement with the theory that suggests that the percentage splitting should be 100 times the fracture density and independent of the saturating fluid. In the 45° core, by contrast, splitting was 0.00 ± 0.02% for water saturation and ?0.77 ± 0.02% for glycerin saturation. This dependence on fracture orientation and pore fluid viscosity is consistent with the poro‐visco‐elastic theory for aligned, meso‐scale fractures in porous rocks. The results suggest the possible use of shear‐ or converted‐wave data to discriminate between fluids on the basis of viscosity variations.  相似文献   

Compositional variations and morphological evolution in platinum beach placers, southern New Zealand     

D. Craw  M. Mitchell  R. McCann  A. Reay 《Mineralium Deposita》2013,48(1):81-97

Morphologies of placer platinum group minerals (PGM) are more variable and resistant to modification during transport than placer gold grains. This study documents morphological evolution of PGM placer grains during up to 120 km of transport in beach placers after river transport from inferred sources up to 200 km inland. PGM morphological changes are calibrated with changes in morphology of associated placer gold. Most of the PGM are Pt-Fe alloy and have been fed into the beach placer system from a large river at the western end of the beaches on the south coast of New Zealand. The incoming fluvial PGM suite includes Os, Ir and Ru alloys which may have been derived from distal ophiolitic sources. More proximal sources have Ural-Alaskan affinities and these contributed cooperite and braggite, or sperrylite, locally, as well as Pt-Fe alloy grains. Some PGM may have been recycled through Cretaceous-Quaternary fluvial sediments before entering the modern placer system. Recycled placer PGM grains have also been derived from elevated Quaternary beaches near the coastline. PGM grains entering beach placers have rough surfaces, with remnants of crystal faces, and these evolve to smooth flakes with progressive long-shore transport. PGM flakes have slightly thickened rims caused by impacts by saltating sand on windy beaches, and the most distal beach placers contain flakes with incipient toroidal shapes. These PGM incipient toroids are poorly developed compared to accompanying well-formed toroidal gold that has developed in nearly all beach placers, including those on elevated Quaternary beaches. Typical PGM and gold placer grain size decreases with increasing distance of transport, from fluvial grain size of 400–1,000 to ～200 microns on the most distal beaches, accompanied by eastward loss of equant PGM grains and associated increase in proportion of flakes. Although net transport distance is ～120 km in the beach placer complex, frequent aeolian transport of grains from beach to dunes and subsequent recycling by storm surges substantially increased total transport distance in a dynamic windy tectonic environment.  相似文献   

Policy Boosterism,Policy Mobilities,and the Extrospective City   总被引：1，自引：1，他引：0  

Eugene McCann 《Urban geography》2013,34(1):5-29

Abstract

This study develops the notion of “policy boosterism,” a subset of traditional branding and marketing activities that involves the active promotion of locally developed and/or locally successful policies, programs, or practices across wider geographical fields as well as to broader communities of interested peers. It is argued that policy boosterism is (1) an important element of how urban policy actors engage with global communities of professional peers and with local residents, and (2) a useful concept with which to interrogate and understand how policies and policy knowledge are mobilized among cities. A conceptualization of policy boosterism and its role in global-urban policymaking is developed by combining insights from the burgeoning “policy mobilities” literature with those of the longstanding literature on entrepreneurial city marketing. It is supported by illustrative examples of policy boosterism in Vancouver: the city's Greenest City and Green Capital initiatives, the use of the term “Vancouverism” among the city's urban design community, and demonstrations of new urban technologies during the 2010 Winter Olympics that were used to market a particular vision of the city's governance to people from elsewhere, but also—crucially—to local audiences. The article concludes by highlighting four foci that might frame future work at the intersections of policy boosterism and policy mobilities.  相似文献