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排序方式: 共有115条查询结果,搜索用时 125 毫秒
1.
Boyuan Zhu Yao Yue Alistair G.L. Borthwick Wenjun Yu Enhang Liang Jinwu Tang Yuanfang Chai Yitian Li 《地球表面变化过程与地形》2020,45(11):2689-2705
In estuaries, the morphology of inland and offshore areas usually evolves synergistically. This study examines the decadal link between longitudinal changes in morphology of branching channels and movement of the offshore depo-center (where sediment deposition rate is maximum) of the Yangtze River estuary, under intense human interference. Integrated data analysis is provided on morphology, runoff discharge, and ebb partition ratio from 1950 to 2017. Channel-volume reductions and change rates between isobaths in branching channels reflect the impact of estuarine engineering projects. Ebb partition ratio and duration of discharge ≥ 60 000 m3 s-1 act as proxies for the water excavating force in branching channels and runoff intensity. It is found that deposition occurs in the lower/upper sub-reaches (or further downstream/upstream channels) of the inland north/south branching channels, and the offshore depo-center moves southward or southeastward, as runoff intensity grows; the reverse occurs as runoff intensity declines. This is because the horizontal circumfluence in the Yangtze estuary rotates clockwise as ebb partition ratios of the north/south branching channels increase/decrease for increasing runoff, and conversely rotates anticlockwise for decreasing runoff. Land reclamation activities, the Deepwater Channel Project, and the Qingcaosha Reservoir have impacted greatly on longitudinal changes of morphology in the North Branch and the South Passage and on ebb partition ratio variations in the North/South Channel and the North/South Passage. Dam-induced runoff flattening has enhanced deposition in the upper/lower sub-reaches of the north/south branching channels and caused northward movement of the offshore depo-center, except in areas affected by estuarine engineering projects. Dam-induced longitudinal evolution of branching channel morphology and offshore depo-center movement will likely persist in the future, given the ongoing construction of large cascade dams in the upper Yangtze and the completion of major projects in the Yangtze estuary. © 2020 John Wiley & Sons, Ltd. 相似文献
2.
Tephra shards for electron probe microanalysis are most efficiently extracted from peat using acid digestion, which removes organic material that hinders density separation methods. However, strong acids are known to alter glass chemical compositions, and several studies have examined how acid digestion affects rhyolitic volcanic glass. The focus on rhyolitic tephra in these studies leaves considerable uncertainty, as the dissolution rates of natural glasses (including tephra) are determined by the chemical composition and surface area/volume ratio, both of which vary in tephra deposits. Here, we use duplicate samples of basaltic, trachydacitic and rhyolitic tephra to examine physical and geochemical alteration following acid digestion. Scanning electron microscope imagery reveals no discernible degradation of glass surfaces, and electron probe microanalysis results from duplicate samples are statistically indistinguishable. These findings suggest the acid digestion protocol for organic peats does not significantly alter glass geochemistry regardless of shard morphologies or geochemical compositions. 相似文献
3.
Paula Lindgren Lydia Hallis Fredrik S. Hage Martin R. Lee John Parnell Anders Plan Alistair Doye Ian MacLaren 《Meteoritics & planetary science》2019,54(11):2698-2709
A carbon‐rich melt fragment from the Gardnos impact structure has been studied for a better understanding of the preservation and structural form(s) of carbon that have been processed by impact melting. The carbon was analyzed in situ in its original petrographic context within the melt fragment, using high‐resolution techniques including focused ion beam‐transmission electron microscopy and electron energy loss spectroscopy. Results show that the carbon is largely uniform and has a nanocrystalline grain size. The Gardnos carbon has a graphitic structure but with a large c/a ratio indicating disorder. The disorder could be a result of rapid heating to high temperatures during impact, followed by rapid cooling, with not enough time to crystallize into highly ordered graphite. However, temperature distribution during impact is extremely heterogenous, and the disordered Gardnos carbon could also represent material that avoided extreme temperatures, and thus, it was preserved. Understanding the structure of carbon during terrestrial impacts is important to help determine if the history of carbon within extraterrestrial samples is impact related. Furthermore, the degree of preservation of carbon during impact is key for locating and detecting organic compounds in extraterrestrial samples. This example from Gardnos, together with previous studies, shows that not all carbon is lost to oxidation during impact but that impact melting can encapsulate and preserve carbon where it is available. 相似文献
4.
Climate change is one of the greatest threats to humanity and requires immediate action. Schuldt, Konrath, and Schwarz (2011) suggested that beliefs in environmental phenomena can be influenced by the terminology used to describe it: changing question wording from global warming to climate change resulted in a 6.3 percentage point increase in belief in environmental phenomena. This association was moderated by political self-identification, with Republicans being 16.2 percentage points more likely to believe in climate change than in global warming, with Democrats showing no difference. The potential for connotative meanings to shift over time and the sociopolitical changes since the original study, potential policy and environmental campaign implications, and an expansion of these findings to other countries, motivated an attempt to replicate this important finding. This pre-registered study repeated the original procedures in the United States of America and two other countries (United Kingdom and Australia; total N = 5,717). Although question wording no longer had a significant effect on beliefs in climate change/global warming, the association of political self-identification with beliefs in environmental phenomena replicated in all three countries, with Conservatives consistently believing less in climate change/global warming than Liberals. The potential impacts of temporal and methodological differences on the discrepancies between this study's and the original's findings are discussed. 相似文献
5.
6.
Many of the decisions relating to future urban development require information on climate change risks to cities This review
of the academic and “grey” literature provides an overview assessment of the state of the art in the quantification and valuation
of climate risks at the city-scale. We find that whilst a small number of cities, mostly in OECD countries, have derived quantitative
estimates of the costs of climate change risks under alternative scenarios, this form of analysis is in its infancy. The climate
risks most frequently addressed in existing studies are associated with sea-level rise, health and water resources. Other
sectors such as energy, transport, and built infrastructure remain less studied. The review has also undertaken a case study
to examine the progress in two cities—London and New York—which are relatively advanced in the assessment of climate risks
and adaptation. The case studies show that these cities have benefited from stakeholder engagement at an early stage in their
risk assessments. They have also benefited from the development of specific institutional responsibilities for co-ordinating
such research from the outset. This involvement has been critical in creating momentum and obtaining resources for subsequent
in-depth analysis of sectoral impacts and adaptation needs..While low cost climate down-scaling applications would be useful
in future research, the greatest priority is to develop responses that can work within the high future uncertainty of future
climate change, to build resilience and maintain flexibility. This can best be used within the context of established risk
management practices. 相似文献
7.
Kevin Tansey Ian Chambers Andrew Anstee Anthony Denniss Alistair Lamb 《Applied geography (Sevenoaks, England)》2009,29(2):145-157
The recent advancement in technology for the airborne collection and subsequent processing and analysis of digital remotely sensed data has been significant. An investigation into the contributions that recent developments have made to the assessment and extraction of hedgerow and field margins is presented. Research into the active legislation by which hedgerows and agricultural biodiversity in England are bound is brought together in the concept of an ideal classification. Using Leica Geosystems ADS40 data, collected for Berkshire (UK), the degree to which the ideal classification can be reached is investigated, focusing on the extraction of hedgerows and unploughed field margin protective boundary strips as image objects. Elevation data were derived from the ADS40 imagery data to accompany true-colour and colour-infrared spectral information. By buffering the detected hedgerow objects in a GIS, we facilitated an investigation of the presence of measures that satisfy the minimum hedgerow protection requirements stipulated by the UK Department for Environment, Food and Rural Affairs (DEFRA). In our study area, it was estimated that 68% of areas that need to be classified as ‘grassy hedgerow boundary strip’ to satisfy the minimum requirements of the legislation were established with low-lying grassy cover before the introduction of the legislation in July 2005. The implications of this research for the development of automated classification methods for field scale agricultural mapping are discussed. 相似文献
8.
This paper scopes a number of the health impacts of climate change in Europe (EU-27) quantitatively, using physical and monetary
metrics. Temperature-related mortality effects, salmonellosis and coastal flooding-induced mental health impacts resulting
from climate change are isolated from the effects of socio-economic change for the 2011–2040 and 2071–2100 time periods. The
temperature-induced mortality effects of climate change include both positive and negative effects, for winter (cold) and
summer (heat) effects, respectively, and have welfare costs (and benefits) of up to 100 billion Euro annually by the later
time-period, though these are unevenly distributed across countries. The role of uncertainty in quantifying these effects
is explored through sensitivity analysis on key parameters. This investigates climate model output, climate scenario, impact
function, the existence and extent of acclimatisation, and the choice of physical and monetary metrics. While all of these
lead to major differences in reported results, acclimatisation is particularly important in determining the size of the health
impacts, and could influence the scale and form of public adaptation at the EU and national level. The welfare costs for salmonellosis
from climate change are estimated at potentially several hundred million Euro annually by the period 2071–2100. Finally, a
scoping assessment of the health costs of climate change from coastal flooding, focusing on mental health problems such as
depression, are estimated at up to 1.5 billion Euro annually by the period 2071–2100. 相似文献
9.
10.
Inga Golbeck Xin Li Frank Janssen Thorger Brüning Jacob W. Nielsen Vibeke Huess Johan Söderkvist Bjarne Büchmann Simo-Matti Siiriä Olga Vähä-Piikkiö Bruce Hackett Nils M. Kristensen Harald Engedahl Ed Blockley Alistair Sellar Priidik Lagemaa Jose Ozer Sebastien Legrand Patrik Ljungemyr Lars Axell 《Ocean Dynamics》2015,65(12):1603-1631