The Allende multicompound chondrule (ACC)—Chondrule formation in a local super‐dense region of the early solar system          下载免费PDF全文

Addi Bischoff  Gerhard Wurm  Marc Chaussidon  Marian Horstmann  Knut Metzler  Mona Weyrauch  Julia Weinauer 《Meteoritics & planetary science》2017,52(5):906-924

In Allende, a very complex compound chondrule (Allende compound chondrule; ACC) was found consisting of at least 16 subchondrules (14 siblings and 2 independents). Its overall texture can roughly be described as a barred olivine object (BO). The BO texture is similar in all siblings, but does not exist in the two independents, which appear as relatively compact olivine‐rich units. Because of secondary alteration of pristine Allende components and the ACC in particular, only limited predictions can be made concerning the original compositions of the colliding melt droplets. Based on textural and mineralogical characteristics, the siblings must have been formed on a very short time scale in a dense, local environment. This is also supported by oxygen isotope systematics showing similar compositions for all 16 subchondrules. Furthermore, the ACC subchondrules are isotopically distinct from typical Allende chondrules, indicating formation in or reaction with a more ¹⁶O‐poor reservoir. We modeled constraints on the particle density required at the ACC formation location, using textural, mineral‐chemical, and isotopic observations on this multicompound chondrule to define melt droplet collision conditions. In this context, we discuss the possible relationship between the formation of complex chondrules and the formation of macrochondrules and cluster chondrites. While macrochondrules may have formed under similar or related conditions as complex chondrules, cluster chondrites certainly require different formation conditions. Cluster chondrites represent a mixture of viscously deformed, seemingly young chondrules of different chemical and textural types and a population of older chondrules. Concerning the formation of ACC calculations suggest the existence of very local, kilometer‐sized, and super‐dense chondrule‐forming regions with extremely high solid‐to‐gas mass ratios of 1000 or more.  相似文献   

Crossing new frontiers: extending tephrochronology as a global geoscientific research tool     

Peter M. Abbott  Britta J. L. Jensen  David J. Lowe  Takehiko Suzuki  Daniel Veres 《第四纪科学杂志》2020,35(1-2):1-8

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Power,coalitions and institutional change in South African climate policy     

Britta Rennkamp 《Climate Policy》2019,19(6):756-770

This paper examines power relations, coalitions and conflicts that drive and hinder institutional change in South African climate policy. The analysis finds that the most contested climate policies are those that create distributional conflicts where powerful, non-poor actors will potentially experience real losses to their fossil fuel-based operations. This finding opposes the assumption of competing objectives between emissions and poverty reduction. Yet, actors use discourse that relates to potentially competing objectives between emissions reductions, jobs, poverty reduction and economic welfare.

The analysis relates to the broader questions on how to address public policy problems that affect the two objectives of mitigating climate change and simultaneously boosting socio-economic development. South Africa is a middle-income country that represents the challenge of accommodating simultaneous efforts for emissions and poverty reduction.

Institutional change has been constrained especially in the process towards establishing climate budgets and a carbon tax. The opposing coalitions have succeeded in delaying the implementation of these processes, as a result of unequal power relations. Institutional change in South African climate policy can be predominantly characterized as layering with elements of policy innovation. New policies build on existing regulations in all three cases of climate policy examined: the climate change response white paper, the carbon tax and the renewable energy programme. Unbalanced power relations between coalitions of support in government and civil society and opposition mainly from the affected industry result in very fragile institutional change.

Key policy insights

• The South African government has managed to drive institutional change in climate policy significantly over the past 7 years.

• Powerful coalitions of coal-related industries and their lobbies have constrained institutional change and managed to delay the implementation of carbon pricing measures.

• A successfully managed renewable energy programme has started to transform a coal- and nuclear-powered electricity sector towards integrating sustainable energy technologies. The programme is vulnerable to intergovernmental opposition and requires management at the highest political levels.

• Potential conflict with poverty reduction measures is not a major concern that actively hinders institutional change towards climate objectives. Predominantly non-poor actors frequently use poverty-related discourse to elevate their interests to issues of public concern.

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New biocide-free anti-fouling paints are toxic   总被引：1，自引：0，他引：1  

Karlsson J  Eklund B 《Marine pollution bulletin》2004,49(5-6):456-464

A number of new anti-fouling paints claimed to be more friendly to the environment, have entered the market since prohibition of biocide containing paints have been enforced in many areas. Leakage waters from five new anti-fouling paints were tested for toxic effects to the macro algae Ceramium tenuicorne and Ceramium strictum and to the crustacean Nitocra spinipes. A banned copper and irgarol 1051 containing anti-fouling paint was used as reference. Five of the six paints tested were toxic to all or some of the organisms after two weeks of leakage with EC50 ranging from 0.08 to around 2% leakage water and LC50 ranging from 1.1% to 88%. The toxicity of leakage water from these paints was still high after 16 weeks. We conclude that these paints contain substances toxic to common organisms in the coastal Baltic ecosystem. A silicone based paint did not exhibit toxic effects to the two organisms. We recommend that biological tests should be used to identify the most harmful products before they are released on the market.  相似文献   

Review on toxicity testing with marine macroalgae and the need for method standardization--exemplified with copper and phenol     

Eklund BT  Kautsky L 《Marine pollution bulletin》2003,46(2):171-181

Toxic effects on macroalgae have been compiled. Eighty-two articles have been found in literature during 1959-2000. A total of 120 substances were investigated using 65 different macroalgae species. About one-third of the tested compounds were organic substances (33%), another third metal-organic substances (35%), and the last third were oils (14%), metals (8%), detergents (7.5%) and other inorganic chemicals (2.5%). Half of the substances were only tested once on a single species. Likewise, toxicity data has only been reported for one chemical tested on a single occasion for about half of the 65 species. Thus little is known about the toxic effects on marine macroalgae. The objectives of the previous studies undertaken varied and therefore the toxicity data was presented in numerous ways, e.g. using different exposure times, temperature, light intensity, light regime, salinity, and nutrients, which makes a direct comparison of the data difficult. This review also shows that many stages in the lifecycle of macroalgae are often more sensitive to toxic substances than other aquatic organisms. Consequently, tests using macroalgae may discover toxicity earlier, which would in turn also protect the fauna. If toxic compounds have a negative affect on the distribution and growth of structurally and functionally dominating macroalgae, there may indirectly be a large and harmful influence on the whole marine coastal ecosystem. For this reason tests on macroalgae should be included in control programs along the coasts.  相似文献   

Tidal exchange between a freshwater tidal marsh and an impacted estuary: the Scheldt estuary, Belgium   总被引：1，自引：0，他引：1  

Stefan Van Damme  Dehairs Frank  Tackx Micky  Beauchard Olivier  Struyf Eric  Gribsholt Britta  Van Cleemput Oswald  Meire Patrick 《Estuarine, Coastal and Shelf Science》2009,85(2):197-207

Tidal marsh exchange studies are relatively simple tools to investigate the interaction between tidal marshes and estuaries. They have mostly been confined to only a few elements and to saltwater or brackish systems. This study presents mass-balance results of an integrated one year campaign in a freshwater tidal marsh along the Scheldt estuary (Belgium), covering oxygen, nutrients (N, P and Si), carbon, chlorophyll, suspended matter, chloride and sulfate. The role of seepage from the marsh was also investigated. A ranking between the parameters revealed that oxygenation was the strongest effect of the marsh on the estuarine water. Particulate parameters showed overall import. Export of dissolved silica (DSi) was more important than exchange of any other nutrient form. Export of DSi and import of total dissolved nitrogen (DIN) nevertheless contributed about equally to the increase of the Si:N ratio in the seepage water. The marsh had a counteracting effect on the long term trend of nutrient ratios in the estuary.  相似文献   

Machine learning classifiers for attributing tephra to source volcanoes: an evaluation of methods for Alaska tephras     

Matthew S. M. Bolton  Britta J. L. Jensen  Kristi Wallace  Nore Praet  David Fortin  Darrell Kaufman  Marc De Batist 《第四纪科学杂志》2020,35(1-2):81-92

Glass composition-based correlations of volcanic ash (tephra) traditionally rely on extensive manual plotting. Many previous statistical methods for testing correlations are limited by using geochemical means, masking diagnostic variability. We suggest that machine learning classifiers can expedite correlation, quickly narrowing the list of likely candidates using well-trained models. Eruptives from Alaska's Aleutian Arc-Alaska Peninsula and Wrangell volcanic field were used as a test environment for 11 supervised classification algorithms, trained on nearly 2000 electron probe microanalysis measurements of glass major oxides, representing 10 volcanic sources. Artificial neural networks and random forests were consistently among the top-performing learners (accuracy and kappa > 0.96). Their combination as an average ensemble effectively improves their performance. Using this combined model on tephras from Eklutna Lake, south-central Alaska, showed that predictions match traditional methods and can speed correlation. Although classifiers are useful tools, they should aid expert analysis, not replace it. The Eklutna Lake tephras are mostly from Redoubt Volcano. Besides tephras from known Holocene-active sources, Holocene tephra geochemically consistent with Pleistocene Emmons Lake Volcanic Center (Dawson tephra), but from a yet unknown source, is evident. These tephras are mostly anchored by a highly resolved varved chronology and represent new important regional stratigraphic markers.  相似文献   

Recent contributions of geotechnical centrifuge modelling to the understanding of jack-up spudcan behaviour     

Christophe Gaudin  Britta Bienen 《Ocean Engineering》2011,38(7):900-48

The paper presents an overview of the recent contributions of centrifuge modelling to the understanding of soil-structure interaction and the development of design and predictive methods in the field of mobile jack-up drilling rig foundations. Both advantages and limitations of the centrifuge methods are detailed and key examples are presented. The benefits provided by centrifuge modelling to the development of analysis methods that are now being used within the jack-up industry are highlighted. To conclude, industry trends and research opportunities are discussed, as is the possible role of the geotechnical centrifuge in finding solutions to these new needs.  相似文献   

Book reviews     

M. M. Yoshino  G. H. Kakiuchi  Viggo Hansen  Wolf Tietze  Joan M. Kenworthy  Kurt Horstmann  Karl W. Butzer  F. Lentacker  Annie Reffay  J. C. Giacottino  A. Leveque 《GeoJournal》1980,4(3):290-292

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Uncertainty propagation in wildland fire behaviour modelling     

Andreas Bachmann  Britta Allgöwer 《International journal of geographical information science》2013,27(2):115-127

Rothermel's model is the most widely used fire behaviour model in wildland fire research and management. It is a complex model that considers 17 input variables describing fuel type, fuel moisture, terrain and wind. Uncertainties in the input variables can have a substantial impact on the resulting errors and have to be considered, especially when the results are used in spatial decision making. In this paper it is shown that the analysis of uncertainty propagation can be carried out with the Taylor series method. This method is computationally cheaper than Monte Carlo and offers easy-to-use, preliminary sensitivity estimations.  相似文献