Mosquitoes in the mix: How transferable is creative city thinking?     

Susan Luckman  Chris Gibson  Tess Lea 《Singapore journal of tropical geography》2009,30(1):70-85

This paper contributes to recent debates about whether urban policy discourses are transferable and what is at stake in their translation. It draws on discussion of Darwin (Northwest Territory, Australia), a tropical savanna location that the local government wants to promote as a 'creative city', without quite knowing what this might require. We discuss relevant debates on research knowledge construction, the creative city and the path-dependent character of neoliberal governmental objectives. We then turn to the geographical, demographic and cultural characteristics that make Darwin a challenging and distinct context for translation of global theories of creative city rejuvenation. As well as arguing a case for more nuanced, locationally specific, analysis of the capacity of places to embrace travelling policy discourses, we suggest ways in which creative city research can be refreshed through engaging with literatures on (post)colonial urban politics and intersections with policy initiatives other than those targeted at 'creative industries' per se . We systematically outline the particular challenges that tropical cities in remote locations provide to accepted wisdom about creativity-led urban planning.  相似文献   

El Niño in history: Storming through the ages     

David W. Lea 《Geoarchaeology》2002,17(8):877-879

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Effects of shock pressure and temperature on titanomagnetite from ICDP cores and target rocks of the El’gygytgyn impact structure,Russia     

Agnes?KontnyEmail author  Lea?Grothaus 《Studia Geophysica et Geodaetica》2017,61(1):162-183

The aim of this study was to investigate the effect of meteorite impacts on magnetic properties including magnetic susceptibility and the Verwey transition of Ti-poor titanomagnetite of volcanic rocks from the 3.6 Ma old El’gygytgyn impact structure located in the Okhotsk-Chukotka volcanic belt in north-eastern Russia. The target rocks consist mainly of rhyolite with some andesites, and is a rare example of impact structures within volcanic target rocks on Earth. 27 samples from outside the crater, the crater rim and from the depth interval 316 to 517 m below lake bottom (mblb) of the El’gygytgyn ICDP drilling were studied. A significant decrease of the average specific magnetic susceptibility by around 90% was observed between felsic volcanic rocks from the surface (18.1 × 10^-6 m³/kg) and the drill cores from near the crater central uplift (1.9 × 10^-6 m³/kg). Ferrimagnetic Fe-Ti oxide assemblages (Verwey transition temperature, T_V: -161 to -150°C, Curie temperature, T_C: 451 to 581°C), occurring in all studied samples, differ significantly. At the surface titanomaghemite is ubiquitously associated with titanomagnetite. The drill cores lack titanomaghemite, but either show a transformation into titanomagnetite and ilmenite or a strong fragmentation associated with a second T_V between -172 and -188°C. Reversible curves of temperature dependence of magnetic susceptibility in the suevite indicate high depositional temperatures of at least 500°C. In the polymict and monomict impact breccia mechanical deformation of titanomagnetite and temperatures of at least 200-350°C related to the shock are suggested from temperature dependent magnetic susceptibility cycling. Lowtemperature oxidation along strongly brecciated grain surfaces in titanomagnetite is suggested to cause the lower TV and we suggest that this phenomenon is related to postimpact hydrothermal activity. The strong magnetic susceptibility decrease at El’gygytgyn is mainly influenced by shock, and post-impact hydrothermalism causes a significant additional depletion. These observations explain why magnetic lows are a ubiquitous phenomenon over impact structures.  相似文献   

Radio flares and plasmon size in Cygnus X-3     

R.N. Ogley †  S.J. Bell Burnell  R.E. Spencer  S.J. Newell  A.M. Stirling  R.P. Fender 《Monthly notices of the Royal Astronomical Society》2001,326(1):349-357

We have observed a number of minor radio flares in Cyg X-3 using the MERLIN array. Photometric observations show the system to be highly active with multiple flares on hourly time-scales over the one month observing programme. Analysis of the power spectrum of the source show no persistent periodicities in these data, and no evidence of the 4.8-h orbital period. An upper limit of 15 mJy can be placed on the amplitude of any sinusoidal variation of source flux at the orbital period. The brightness temperature of a flare is typically T _b≥10⁹–10¹⁰ K , with a number of small flares of 5-min duration having brightness temperatures of T _b≥ few×10¹¹ K . For such a change in flux to occur within a typical 10-min time-scale, the radiation must originate from plasmons with a size ≤1.22 au. This emission is unlikely to originate close to the centre of the system as both the jets and compact object are buried deep within an optically thick stellar wind. Assuming a spherically symmetric wind, plasmons would become visible at distances ∼13 au from the core.  相似文献   

Timing of the first drainage of the Baltic Ice Lake synchronous with the onset of Greenland Stadial 1          下载免费PDF全文

Francesco Muschitiello  James M. Lea  Sarah L. Greenwood  Faezeh M. Nick  Lars Brunnberg  Alison MacLeod  Barbara Wohlfarth 《Boreas: An International Journal of Quaternary Research》2016,45(2):322-334

Glacial varves can give significant insights into recession and melting rates of decaying ice sheets. Moreover, varve chronologies can provide an independent means of comparison to other annually resolved climatic archives, which ultimately help to assess the timing and response of an ice sheet to changes across rapid climate transitions. Here we report a composite 1257‐year‐long varve chronology from southeastern Sweden spanning the regional late Allerød–late Younger Dryas pollen zone. The chronology was correlated to the Greenland Ice‐Core Chronology 2005 using the time‐synchronous Vedde Ash volcanic marker, which can be found in both successions. For the first time, this enables secure placement of the Lateglacial Swedish varve chronology in absolute time. Geochemical analysis from new varve successions indicate a marked change in sedimentation regime accompanied by an interruption of ice‐rafted debris deposition synchronous with the onset of Greenland Stadial 1 (GS‐1; 12 846 years before AD 1950). With the support of a simple ice‐flow/calving model, we suggest that slowdown of sediment transfer can be explained by ice‐sheet margin stabilization/advance in response to a significant drop of the Baltic Ice Lake level. A reassessment of chronological evidence from central‐western and southern Sweden further supports the hypothesis of synchronicity between the first (penultimate) catastrophic drainage of the Baltic Ice Lake and the start of GS‐1 in Greenland ice‐cores. Our results may therefore provide the first chronologically robust evidence linking continental meltwater forcing to rapid atmosphere–ocean circulation changes in the North Atlantic.  相似文献   

European summer temperature response to annually dated volcanic eruptions over the past nine centuries   总被引：1，自引：0，他引：1  

Jan Esper  Lea Schneider  Paul J. Krusic  Jürg Luterbacher  Ulf Büntgen  Mauri Timonen  Frank Sirocko  Eduardo Zorita 《Bulletin of Volcanology》2013,75(7):1-14

The drop in temperature following large volcanic eruptions has been identified as an important component of natural climate variability. However, due to the limited number of large eruptions that occurred during the period of instrumental observations, the precise amplitude of post-volcanic cooling is not well constrained. Here we present new evidence on summer temperature cooling over Europe in years following volcanic eruptions. We compile and analyze an updated network of tree-ring maximum latewood density chronologies, spanning the past nine centuries, and compare cooling signatures in this network with exceptionally long instrumental station records and state-of-the-art general circulation models. Results indicate post-volcanic June–August cooling is strongest in Northern Europe 2 years after an eruption (?0.52?±?0.05 °C), whereas in Central Europe the temperature response is smaller and occurs 1 year after an eruption (?0.18?±?0.07 °C). We validate these estimates by comparison with the shorter instrumental network and evaluate the statistical significance of post-volcanic summer temperature cooling in the context of natural climate variability over the past nine centuries. Finding no significant post-volcanic temperature cooling lasting longer than 2 years, our results question the ability of large eruptions to initiate long-term temperature changes through feedback mechanisms in the climate system. We discuss the implications of these findings with respect to the response seen in general circulation models and emphasize the importance of considering well-documented, annually dated eruptions when assessing the significance of volcanic forcing on continental-scale temperature variations.  相似文献   

Quantification of turbate microstructures through a subglacial till: dimensions and characteristics     

James M. Lea  Adrian Palmer 《Boreas: An International Journal of Quaternary Research》2014,43(4):869-881

Despite extensive study and debate regarding the significance of turbate (also known as ‘rotational’) microstructures in glacially deformed sediments, characteristics regarding the dimensions of these features remain unresolved. This study presents the first explicitly quantitative measurement and analysis of turbate microstructure dimensions, and their relation to till texture through thin section analysis. Samples were taken from coarse‐resolution horizontal and vertical transects of a macroscopically homogenous subglacial till, with subset areas of each thin section (30 mm²) analysed. The frequency and apparent a‐axes and b‐axes of both coreless and cored turbate structures (and their corestones) were measured, and simple univariate statistical methods used to establish the (in‐)variability of these dimensions through the till profile. Summarizing findings, (i) the dimensions of both cored and coreless turbate populations display log‐normal distributions when all measurements are analysed together, although not all individual sample populations possess these same distributions; (ii) turbate dimension populations are inconsistent within a sample block, precluding evaluation of turbate variability through a profile from single thin sections; (iii) analysis of turbate morphology and variability provisionally indicate that the three‐dimensional structure of turbates are likely to be cylindrical or flared, while weak relationships are also observed amongst till texture, turbate dimensions and frequency.  相似文献   

The timing of sea-level high-stands during Marine Isotope Stages 7.5 and 9: Constraints from the uranium-series dating of fossil corals from Henderson Island     

Morten B. Andersen  Claudine H. Stirling  Emma-Kate Potter  Steve G. Blake  Bridget F. Ayling 《Geochimica et cosmochimica acta》2010,74(12):3598-7020

Direct dating of fossil coral reefs using the U-series chronometer provides an important independent test of the Milankovitch orbital forcing theory of climate change. However, well-dated fossil corals pre-dating the last interglacial period (>130 thousand years ago; ka) are scarce due to, (1) a lack of sampling localities, (2) insufficient analytical precision in U-series dating methods, and (3) diagenesis which acts to violate the assumption of closed-system U-series isotopic decay in fossil corals. Here we present 50 new high-precision U-series age determinations for fossil corals from Henderson Island, an emergent coral atoll in the central South Pacific. U-series age determinations associated with the Marine Isotope Stage (MIS) 9 interglacial and MIS 7.5 interstadial periods are reported. The fossil corals show relatively little open-system U-series behaviour in comparison to other localities with fossil coral reefs formed prior to the last glacial cycle, however, open-system U-series behaviour is still evident in most of the dated corals. In particular, percent-level shifts in the [²³⁰Th/²³⁸U]_act composition are observed, leading to conventional U-series ages that are significantly younger or older than the true sample age. This open-system U-series behaviour is not accounted for by any of the open-system U-series models, indicating that new models should be derived. The new U-series ages reported here support and extend earlier findings reported in Stirling et al. (2001), providing evidence of prolific coral reef development on Henderson Island at ∼320 ka, most likely correlated with MIS 9.3, and subsequent reef development at ∼307 ka during MIS 9.1, while relative sea-level was potentially ∼20 m lower than during MIS 9.3. The U-series ages for additional well-preserved fossil corals are suggestive of minor reef development on Henderson Island during MIS 7.5 (245-230 ka) at 240.3 ± 0.8 and 234.7 ± 1.3 ka. All U-series observations are consistent with the Milankovitch theory of climate change, in terms of the timing of onset and termination of the dated interglacial and interstadial periods. The best preserved samples also suggest that the oceanic ²³⁴U/²³⁸U during MIS 9 and MIS 7.5 was within five permil of the modern open ocean composition.  相似文献   

Introduction: Geographical Education for Sustainable Living   总被引：1，自引：0，他引：1  

Lea Houtsonen 《GeoJournal》2004,60(2):147-148

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Post fire induced soil water repellency—Modeling short and long-term processes     

Dan Malkinson  Lea Wittenberg 《Geomorphology》2011,125(1):186-192

Soil water repellency has direct implications to hydrological as well as geomorphological processes, especially in fire-prone ecosystems. Five predominant mechanisms have been described as generating water repellency in soils: fungal and microbial activity, growth of particular vegetation species, organic matter, heating of the soils by wildfires and soil characteristics. Herein we synthesize among these mechanisms and propose a general model describing the long-term properties of water repellency in soils. Using non-linear regression analysis methods we compare among different variants of the model in order to assess the relative role of vegetation on water-repellency dynamics. We suggest that following a wildfire event hydrophobic peak soil properties are dictated by vegetation properties, but that the rapid decrease is not associated with the vegetation. Following wildfires, the recovery of the ecosystem commences and water-repellency is characterized by increased predominance of the biotic activity. Thus, the general pattern of a rapid decrease and a long-term increase in water repellency can be described by a mathematical model presented herein.  相似文献