排序方式： 共有39条查询结果，搜索用时 15 毫秒
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Parsons ML Walsh WJ Settlemier CJ White DJ Ballauer JM Ayotte PM Osada KM Carman B 《Marine pollution bulletin》2008,56(6):1138-1149
Four coral-dominated coastal sites within two embayments (Kealakekua Bay and Honokōhau Bay) on the lee of the island of Hawai'i were studied to assess evidence of anthropogenic impacts in these relatively pristine locales. Nutrient-loading parameters were analyzed in relation to benthic composition data. Statistically, there were significant positive relationships between nitrate+nitrite, silicate, and ammonium with the abundance of macroalgae, coralline algae, and dead coral, and between delta(15)N and dead coral abundance. The north outside site of Kealakekua Bay and the south outside site of Honokōhau Bay appear to be most impacted by nutrient-loading factors in each bay, respectively. Comparisons with past nutrient data indicate that nutrient inputs have increased to the two bays, and that early impacts of these increased loadings are evident. It is predicted that at current nutrient-loading rates, the north sites of Kealakekua Bay and the south sites of Honokōhau Bay will exhibit evidence of further degradation in future years. 相似文献
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The recent loss of mountain glaciers in response to climate warming has been reported across a range of latitudes globally, but the processes involved are not always straightforward. In southern Pacific mid‐latitudes, twentieth‐century glacier fluctuations are thought to reflect the strength of westerly atmospheric circulation, which brings increased precipitation, leading to mass gains. We present a study of the response of Mangaehuehu Glacier, a cirque glacier on Mt Ruapehu, to climate over the last two decades. Glacier surface area fluctuated in size over this period, corresponding closely with mean end‐of‐summer snowlines in the Southern Alps. The key control on glacier extent appears to be ablation season temperature, itself controlled by regional atmospheric circulation, including El Niño‐Southern Oscillation, Interdecadal Pacific Oscillation (IPO), and to a lesser extent, Southern Annular Mode (SAM). Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Mark E. Stelten Kari M. Cooper Jorge A. Vazquez Mary R. Reid Gry H. Barfod Josh Wimpenny Qing-zhu Yin 《Contributions to Mineralogy and Petrology》2013,166(2):587-613
The nature of compositional heterogeneity within large silicic magma bodies has important implications for how silicic reservoirs are assembled and evolve through time. We examine compositional heterogeneity in the youngest (~170 to 70 ka) post-caldera volcanism at Yellowstone caldera, the Central Plateau Member (CPM) rhyolites, as a case study. We compare 238U–230Th age, trace-element, and Hf isotopic data from zircons, and major-element, Ba, and Pb isotopic data from sanidines hosted in two CPM rhyolites (Hayden Valley and Solfatara Plateau flows) and one extracaldera rhyolite (Gibbon River flow), all of which erupted near the caldera margin ca. 100 ka. The Hayden Valley flow hosts two zircon populations and one sanidine population that are consistent with residence in the CPM reservoir. The Gibbon River flow hosts one zircon population that is compositionally distinct from Hayden Valley flow zircons. The Solfatara Plateau flow contains multiple sanidine populations and all three zircon populations found in the Hayden Valley and Gibbon River flows, demonstrating that the Solfatara Plateau flow formed by mixing extracaldera magma with the margin of the CPM reservoir. This process highlights the dynamic nature of magmatic interactions at the margins of large silicic reservoirs. More generally, Hf isotopic data from the CPM zircons provide the first direct evidence for isotopically juvenile magmas contributing mass to the youngest post-caldera magmatic system and demonstrate that the sources contributing magma to the CPM reservoir were heterogeneous in 176Hf/177Hf at ca. 100 ka. Thus, the limited compositional variability of CPM glasses reflects homogenization occurring within the CPM reservoir, not a homogeneous source. 相似文献
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Beth Ellen Clark Richard P. Binzel Ellen S. Howell Edward A. Cloutis Maureen Ockert-Bell Phil Christensen Maria Antonietta Barucci Francesca DeMeo Dante S. Lauretta Harold Connolly Jr. Alicia Soderberg Carl Hergenrother Lucy Lim Josh Emery Michael Mueller 《Icarus》2011,216(2):462-475
We present reflectance spectra from 0.4 to 2.4 μm of Asteroid (101955) 1999 RQ36, the target of the OSIRIS-REx spacecraft mission. The visible spectral data were obtained at the McDonald Observatory 2.1-m telescope with the ES2 spectrograph. The infrared spectral data were obtained at the NASA Infrared Telescope Facility using the SpeX instrument. The average visible spectrum is combined with the average near-infrared wavelength spectrum to form a composite spectrum. We use three methods to constrain the compositional information in the composite spectrum of Asteroid (101955) 1999 RQ36 (hereafter RQ36). First, we perform a least-squares search for meteorite spectral analogs using 15,000 spectra from the RELAB database. Three most likely meteorite analogs are proposed based on the least-squares search. Next, six spectral parameters are measured for RQ36 and their values are compared with the ranges in parameter values of the carbonaceous chondrite meteorite classes. A most likely meteorite analog group is proposed based on the depth of overlap in parameter values. The results of the least-squares search and the parametric comparisons point to CIs and/or CMs as the most likely meteorite analogs for RQ36, and COs and CHs as the least likely. RQ36 has a spectrally “blue” continuum slope that is also observed in carbonaceous chondrites containing magnetite. We speculate that RQ36 is composed of a “CM1”-like material. Finally, we compare RQ36 to other B-type asteroids measured by Clark et al. (Clark, B.E. et al. [2010]. J. Geophys. Res. 115, E06005). The results of this comparison are inconclusive. RQ36 is comparable to Themis spectral properties in terms of its albedo, visible spectrum, and near-infrared spectrum from 1.1 to 1.45 μm. However, RQ36 is more similar to Pallas in terms of its near-infrared spectrum from 1.6 to 2.3 μm. Thus it is possible that B-type asteroids form a spectral continuum and that RQ36 is a transitional object, spectrally intermediate between the two end-members. This is particularly interesting because Asteroid 24 Themis was recently discovered to have H2O ice on the surface (Rivkin, A., Emery, J. [2010]. Nature 464, 1322–1323; Campins, H. et al. [2010a]. Nature 464, 1320–1321). 相似文献
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Roger Brewer Josh Nagashima Mark Rigby Martin Schmidt Harry O'Neill 《Ground Water Monitoring & Remediation》2014,34(4):79-92
Generic indoor air:subslab soil gas attenuation factors (SSAFs) are important for rapid screening of potential vapor intrusion risks in buildings that overlie soil and groundwater contaminated with volatile chemicals. Insufficiently conservative SSAFs can allow high‐risk sites to be prematurely excluded from further investigation. Excessively conservative SSAFs can lead to costly, time‐consuming, and often inconclusive actions at an inordinate number of low‐risk sites. This paper reviews two of the most commonly used approaches to develop SSAFs: (1) comparison of paired, indoor air and subslab soil gas data in empirical databases and (2) comparison of estimated subslab vapor entry rates and indoor air exchange rates (IAERs). Potential error associated with databases includes interference from indoor and outdoor sources, reliance on data from basements, and seasonal variability. Heterogeneity in subsurface vapor plumes combined with uncertainty regarding vapor entry points calls into question the representativeness of limited subslab data and diminishes the technical defensibility of SSAFs extracted from databases. The use of reasonably conservative vapor entry rates and IAERs offers a more technically defensible approach for the development of generic SSAF values for screening. Consideration of seasonal variability in building leakage rates, air exchange rates, and interpolated vapor entry rates allows for the development of generic SSAFs at both local and regional scales. Limitations include applicability of the default IAERs and vapor entry rates to site‐specific vapor intrusion investigations and uncertainty regarding applicability of generic SSAFs to assess potential short‐term (e.g., intraday) variability of impacts to indoor air. 相似文献
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Mainstream and alternative media play an important role in circulating powerful narratives within and often beyond a country's borders. This article specifically examines how Malaysia's media have framed the relationship between information and communication technologies (ICTs) and the country's electoral process. To this end, the authors conducted a content analysis of selected domestic mainstream and alternative media sources for two weeks before and two weeks after Malaysia's last three federal elections – 1999, 2004 and 2008 – to gauge how coverage has changed over time with shifts in the local political landscape and growing ICT access and usage. 相似文献
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Josh Lepawsky 《Geoforum》2005,36(6):370-719
The Malaysian government has embarked on an ambitious refashioning of the nation called Vision 2020 in pursuit of its goal of becoming a ‘developed country’. A pivotal component of this ‘vision’ is the planning and provision of information technology (IT) infrastructure in a multi-billion dollar urban mega-project called the Multimedia Super Corridor (MSC). The purpose of my paper is twofold. First, I situate an official planning document for the MSC entitled Physical Design Guidelines for the Multimedia Super Corridor in the activity of transnational planning practice. Second, I argue that a thematic series of organizing planning concepts and practices can be identified in this document. These concepts and practices work in two ways: first, by representing highly positioned notions of sub-urban, middle-class urban design conventional in specific North American cities as universally applicable to, and desirable for, the broader national development goals the MSC is intended to lead; second, by creating a ‘total image’ for the MSC that suggests an apparently seamless relationship between the MSC and the proper citizens for it at every imaginable scale. One important effect of these plans is the material transformation of a rural landscape of and for production into an urban landscape of and for consumption. This transformation raises the question of who can belong to the ‘nation’ being (re)imagined via the MSC. 相似文献