The Large Magellanic Cloud and the distance scale     

Alistair R. Walker 《Astrophysics and Space Science》2012,341(1):43-49

The Magellanic Clouds, especially the Large Magellanic Cloud, are places where multiple distance indicators can be compared with each other in a straight-forward manner at considerable precision. We here review the distances derived from Cepheids, Red Variables, RR Lyraes, Red Clump Stars and Eclipsing Binaries, and show that the results from these distance indicators generally agree to within their errors, and the distance modulus to the Large Magellanic Cloud appears to be defined to ±3% with a mean value (m−M)₀=18.48 mag, corresponding to 49.7 kpc. The utility of the Magellanic Clouds in constructing and testing the distance scale will remain as we move into the era of Gaia.  相似文献   

Coded spatialities of fieldwork     

Alistair Fraser 《Area》2007,39(2):242-245

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In situ U-series dating by laser-ablation multi-collector ICPMS: new prospects for Quaternary geochronology   总被引：2，自引：0，他引：2  

Stephen M. Eggins  Rainer Grün  Malcolm T. McCulloch  Alistair W.G. Pike  John Chappell  Les Kinsley  Graham Mortimer  Michael Shelley  Colin V. Murray-Wallace  Christoph Sptl  Lois Taylor 《Quaternary Science Reviews》2005,24(23-24):2523-2538

The capabilities and potential applications of in situ dating of Quaternary materials using laser ablation-MC-ICPMS are explored. ²³⁴U/²³⁸U and ²³⁰Th/²³⁴U can be measured with precision sufficient for dating at a spatial resolution of 100 μm or better in samples that contain as a little as 1 ppm uranium. Moreover, U and Th concentrations and U-series isotope ratios can be continuously profiled to determine changes in age that occur with sample growth (e.g. in speleothems). These capabilities additionally permit the dating of bones, teeth and possibly molluscs, which are subject to post-mortem open-system behaviour of U-series isotopes, and can be employed to elucidate processes of U-series migration during weathering and diagenesis. A drawback of laser ablation-MC-ICPMS is that it cannot in general provide U-series age estimates with the high precision and accuracy of conventional TIMS or solution MC-ICPMS methods. However, sample preparation is straightforward, the amount of sample consumed negligible, and it can be used to rapidly characterise or screen and select samples from which more precise and accurate dates can be obtained using conventional methods. Given further instrumental developments and the establishment of suitable matrix-matched standards for carbonates and other materials, we foresee that laser ablation-MC-ICPMS will play an increasingly important role in Quaternary dating research.  相似文献   

The LOWNET Radio-Linked Seismometer Network in Scotland     

Stuart Crampin  A. W. Brian Jacob  Alistair Miller  Graham Neilson 《Geophysical Journal International》1970,21(2):207-216

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Transaction costs of the Kyoto Mechanisms   总被引：2，自引：0，他引：2  

Axel Michaelowa  Marcus Stronzik  Frauke Eckermann  Alistair Hunt 《Climate Policy》2003,3(3):261-278

Transaction costs will reduce the attractiveness of the Kyoto Mechanisms compared to domestic abatement options. Especially the project-based mechanisms Clean Development Mechanism (CDM) and Joint Implementation (JI) are likely to entail considerable costs of baseline development, verification and certification. The Activities Implemented Jointly (AIJ) pilot phase and the Prototype Carbon Fund (PCF) programme give indications about the level of these costs. Under current estimates of world market prices for greenhouse gas emission permits, projects with annual emission reductions of less than 50,000 t CO₂ equivalent are unlikely to be viable; for micro projects transaction costs can reach several hundred € per t CO₂ equivalent. Thus, the Marrakech Accord rule to have special rules for small scale CDM projects makes sense, even if the thresholds chosen advantage certain project types; projects below 1000 t CO₂ equivalent per year should get further exemptions. An alternative solution with no risk for the environmental credibility of the projects would be to subsidise baseline setting and charge lower, subsidised fees for small projects for the different steps of the CDM/second track JI project cycle.  相似文献   

Spatial patterns of water surface topography at a river confluence     

Pascale M. Biron  Antoine Richer  Alistair D. Kirkbride  Andr G. Roy  Sangsoo Han 《地球表面变化过程与地形》2002,27(9):913-928

Understanding flow structures in river confluences has largely been the product of interpretations made from measured flow velocity data. Here, we turn the attention to the investigation of the patterns of both the average and standard deviations of the micro‐topography of the water surface at an asymmetrical natural discordant confluence for different flow conditions. Water surface topography is measured using a total station to survey the position of a reflector mounted on a custom‐built raft. To limit error problems related to changes in the water level, measurements are taken and analysed by cross‐stream transects where five water surface profiles are taken before moving to the next transect. Three‐dimensional numerical simulations of the flow dynamics at the field site are used to examine predicted water surface topography for a steady‐state situation. The patterns are interpreted with respect to flow structure dynamics, visual observations of boils, and bed topography. Results indicate that coherent patterns emerge at the water surface of a discordant bed confluence for different flow conditions. The zone of stagnation and the mixing layer are characterized by super‐elevation, a lateral tilt is present at the edge of the mixing layer, and a zone of super‐elevation is present on the tributary side at the downstream junction corner. The latter seems associated with periodical upwelling and is not present in the numerical simulations that do not take into account instantaneous velocity fluctuations. Planform curvature, topographic steering related to the tributary mouth bar, and turbulent structures associated with the mixing layer all play a key role in the pattern of both the average and standard deviation of the water surface topography at confluences. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Fragile empowerment: The dynamic cultural economy of British drum and bass music     

Alistair Fraser  Nancy Ettlinger   《Geoforum》2008,39(5):1647-1656

This paper discusses the dynamic cultural economy of British drum and bass (D&B) music, which emerged out of Britain’s rave culture in the early 1990s. We suggest that D&B offers insight into more general issues regarding the relation between alternative cultural economies and capitalism. We examine relations between D&B and the mainstream capitalist economy and argue that D&B calls attention to the possibility for alternatives to conventional capitalist relations to survive and possibly thrive without pursuing separation from capitalism. We also theorize D&B as a vehicle towards empowerment regarding the industry segment vis-à-vis the mainstream music industry and also regarding D&B’s practitioners, many of whom can be understood as marginalized discursively and/or materially. However, D&B empowerment is fragile, due in part to technological changes that threaten practices that have helped cultivate innovativeness as well as communal relations. The empowerment of alternative practices is fragile not only for D&B as an industry segment, but also from the vantage point of internal power relations – notably with respect to differences along axes of gender and generation/age. Our conclusions indicate the broader significance of the paper for critical social theory and propose how new research might build on our dynamic view of D&B’s cultural economy.  相似文献   

The structure of galaxy clusters in various cosmologies     

Peter A. Thomas  Jörg M. Colberg  Hugh M. P. Couchman  George P. Efstathiou  Carlos S. Frenk  Adrian R. Jenkins  Alistair H. Nelson  Roger M. Hutchings  John A. Peacock  Frazer R. Pearce  & Simon D. M. White 《Monthly notices of the Royal Astronomical Society》1998,296(4):1061-1071

We investigate the internal structure of clusters of galaxies in high-resolution N -body simulations of four different cosmologies. There is a higher proportion of disordered clusters in critical-density than in low-density universes, although the structure of relaxed clusters is very similar in each case. Crude measures of substructure, such as the shift in the position of the centre-of-mass as the density threshold is varied, can distinguish the two in a sample of just 20 or so clusters; it is harder to differentiate between clusters in open and flat models with the same density parameter. Most clusters are in a quasi-steady state within the virial radius and are well-described by the density profile of Navarro, Frenk & White.  相似文献   

Flow kinematics of focused wave groups on a plane beach in the U.K. Coastal Research Facility   总被引：1，自引：0，他引：1  

Alistair G.L. Borthwick  Alison C. Hunt  Tong Feng  Paul H. Taylor  Peter K. Stansby   《Coastal Engineering》2006,53(12):1033-1044

Measurements are presented of the water particle kinematics of focused wave groups generated in the U.K. Coastal Research Facility. Single and repeated wave groups are considered at normal and 20° incidence to a 1:20 plane beach. The single focused wave groups model extreme transient events without the complication of reflections during the data acquisition process. A symmetry-based separation of harmonics method is used to interpret the water particle kinematics at the point of focus. Although the largest component is linear, there are also considerable second order kinematics terms (both low frequency and high frequency). Away from the free surface, the 2nd order difference contribution to the kinematics is a return current opposed to the direction of wave advance. For repeated wave groups, the measured kinematics confirms the presence of a low frequency free wave, followed by higher frequency waves of the main group and trailing higher order harmonic waves. In the breaker and surf zones, there is also evidence of the saw-tooth behaviour of broken waves, followed by scatter due to breaker-induced turbulence. Pulsatile wave breaking of repeated wave groups at oblique incidence is found to drive a longshore current.  相似文献   

The photo-oxidations of propyl acetates in synthetic air-HONO-NO x mixtures: Product formation studies and proposed kinetic mechanisms     

J. Alistair Kerr  David W. Stocker 《Journal of Atmospheric Chemistry》1986,4(2):263-276

The formation of products following the hydroxyl radical initiated photo-oxidations of n-and isopropyl acetates has been studied. Mixtures of synthetic air containing a few ppm of nitrous acid, nitric oxide, nitrogen dioxide and one of the propyl acetates were irradiated with sunlamps in a Teflon bag smog chamber. The decay of reactants and the formation of products was monitored by chemiluminescent analysis or by gas chromatography. The major primary products from the photo-oxidation of n-propyl acetate are acetaldehyde and propionaldehyde while from isopropyl acetate they are acetone and methyl nitrate. It was not possible to analyse for formaldehyde, an expected primary product in these systems. The nature and distribution of products indicate that a significant fraction of primary products arise from decomposition reactions of the alkoxy-type radicals generated following the initial attack of hydroxyl radicals on the esters. The derived reaction stoichiometries (molecules of NO oxidised per molecule of ester reacted) are also consistent with the proposed mechanisms.  相似文献