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排序方式： 共有140条查询结果，搜索用时 15 毫秒
1.
Lisa E. Mayhew Graham E. Lau Tom M. McCollom Sam Webb Alexis S. Templeton 《Applied Geochemistry》2011
Hydrogen gas produced in the subsurface from the hydration of mafic rocks is known to be a major energy source for chemolithotrophic life in extreme environments such as hydrothermal vents. The possibility that in situ anaerobic microorganisms present in the deep subsurface are sustained by low temperature H2-generating water–rock reactions taking place around them is being investigated. Whether the growth and activity of H2-utilizing microbes directly influences aqueous geochemistry, rates of mineral dissolution, and the chemical composition of the alteration products is also being quantitatively evaluated.To explore how microorganisms are affected by water–rock reactions, and how their activity may in turn affect reaction progress, laboratory experiments have been conducted to monitor the growth of a methanogenic Archaea in the presence of H2(g) produced from low temperature water–Fe0–basalt reactions. In these systems, the conversion of Fe(II) to Fe(III) and subsequent hydrolysis of water is responsible for the production of H2(g). To characterize key components of the geochemical system, time series measurements of H2 and CH4 gas concentrations, Fe and Si aqueous concentrations, and spatially resolved synchrotron-based analyses of microscale Fe distribution and speciation were conducted. Culture experiments were compared with an abiotic control to document changes in the geochemistry both in the presence and absence of the methanogen.In the control abiotic batch experiment, H2 was continuously produced, until the headspace became saturated, while in the biotic experiments, microbial consumption of H2 for methanogenesis draws H2 down and produces CH4. Purging the headspace gas reinitiates H2 and CH4 production in abiotic and culture experiments, respectively. Mass balance analysis of the amount of CH4 produced suggests that the total H2 production in microbial experiments does not exceed the abiotic experiment. Soluble Si concentrations, while buffered to relatively constant values, were higher in culture experiments than the abiotic control.Iron(aq) concentrations appear to respond to perturbations of H2 and CH4 gas concentrations in both culture experiments and the abiotic control. A pulse of Fe preceded the rise in either H2 or CH4 production, and as the gas concentrations increased the Fe(aq) decreased. Iron-bearing mineral assemblages change with increasing reaction time and mineral assemblages vary between culture experiments and the abiotic control. These geochemical trends suggest that there are different reaction paths between the culture experiments and the abiotic control.The hydration of mafic rocks is a common geologic reaction and one that has taken place on Earth for the majority of its history and is postulated to occur on Mars. These reactions are important because of their effect on the rheology and geochemistry of the ocean crust. While most often studied at temperatures of ～250 °C, this work suggests that at lower temperatures microorganisms may have a profound effect on what has long been thought to be solely an abiotic reaction, and may produce diagnostic mineral assemblages that will be preserved in the geological record. 相似文献
2.
Joel Sanchez-Bermudez Florentin Millour Fabien Baron Roy van Boekel Laurent Bourgès Gilles Duvert Paulo J. V. Garcia Nuno Gomes Karl-Heinz Hofmann Thomas Henning Jacob W. Isbell Bruno Lopez Alexis Matter J-Uwe Pott Dieter Schertl Eric Thiébaut Gerd Weigelt John Young 《Experimental Astronomy》2018,46(3):457-473
During the last two decades, the first generation of beam combiners at the Very Large Telescope Interferometer has proved the importance of optical interferometry for high-angular resolution astrophysical studies in the near- and mid-infrared. With the advent of 4-beam combiners at the VLTI, the u ? v coverage per pointing increases significantly, providing an opportunity to use reconstructed images as powerful scientific tools. Therefore, interferometric imaging is already a key feature of the new generation of VLTI instruments, as well as for other interferometric facilities like CHARA and JWST. It is thus imperative to account for the current image reconstruction capabilities and their expected evolutions in the coming years. Here, we present a general overview of the current situation of optical interferometric image reconstruction with a focus on new wavelength-dependent information, highlighting its main advantages and limitations. As an Appendix we include several cookbooks describing the usage and installation of several state-of-the art image reconstruction packages. To illustrate the current capabilities of the software available to the community, we recovered chromatic images, from simulated MATISSE data, using the MCMC software SQUEEZE. With these images, we aim at showing the importance of selecting good regularization functions and their impact on the reconstruction. 相似文献
3.
4.
Diana Tingley Jóhann Ásmundsson Edward Borodzicz Alexis Conides Ben Drakeford Ingi Rúnar Eðvarðsson Dennis Holm Kostas Kapiris Sakari Kuikka Bogi Mortensen 《Marine Policy》2010
This paper presents the findings of risk identification and risk perception research conducted in relation to the fisheries systems of four distinct and diverse European countries: Faroes, Iceland, Greece and the UK. Risk research traditionally attempts to quantify the potential threat or consequences from a range of risk events or hazards. This research, however, adopted a social sciences perspective and so assumed that a risk event or hazard can mean different things to different people and that these perceptions are also context and culturally dependent. Risk perceptions were examined and risk registers developed in each country for a range of stakeholder groups. A ‘mental modelling’ approach was adopted in a series of qualitative interviews. Findings were examined in terms of a wide range of psychological, social and cultural risk theories. Differences in risk perceptions were noted between stakeholder groups and countries and contextual influences were examined such as the widely differing fisheries management systems used in each country. This research provides one of the first attempts to systematically evaluate risks and perceptions across a range of fisheries-systems. The findings support social science theories which argue that risk is a subjective, as opposed to objective, concept and that this subjectivity will therefore affect our attempts to assess and manage those hazards we think we can potentially influence or control. 相似文献
5.
Gas hydrate disturbance fabrics of southern Hydrate Ridge sediments (ODP Leg 204): Relationship with texture and physical properties 总被引：1，自引：0，他引：1
Elena Piñero Eulàlia Gràcia Francisca Martínez-Ruiz Juan Cruz Larrasoaña Alexis Vizcaino Gemma Ercilla 《Geo-Marine Letters》2007,27(2-4):279-288
Soupy and mousse-like fabrics are disturbance sedimentary features that result from the dissociation of gas hydrate, a process
that releases water. During the core retrieval process, soupy and mousse-like fabrics are produced in the gas hydrate-bearing
sediments due to changes in pressure and temperature conditions. Therefore, the identification of soupy and mousse-like fabrics
can be used as a proxy for the presence of gas hydrate in addition to other evidence, such as pore water freshening or anomalously
cool temperature. We present here grain-size results, mineralogical composition and magnetic susceptibility data of soupy
and mousse-like samples from the southern Hydrate Ridge (Cascadia accretionary complex) acquired during Leg 204 of the Ocean
Drilling Program. In order to study the relationship between sedimentary texture and the presence of gas hydrates, we have
compared these results with the main textural and compositional data available from the same area. Most of the disturbed analyzed
samples from the summit and the western flank of southern Hydrate Ridge show a mean grain size coarser than the average mean
grain size of the hemipelagic samples from the same area. The depositional features of the sediments are not recognised due
to disturbance. However, their granulometric statistical parameters and distribution curves, and magnetic susceptibility logs
indicate that they correspond to a turbidite facies. These results suggest that gas hydrates in the southern Hydrate Ridge
could form preferentially in coarser grain-size layers that could act as conduits feeding gas from below the BSR. Two samples
from the uppermost metres near the seafloor at the summit of the southern Hydrate Ridge show a finer mean grain-size value
than the average of hemipelagic samples. They were located where the highest amount of gas hydrates was detected, suggesting
that in this area the availability of methane gas was high enough to generate gas hydrates, even within low-permeability layers.
The mineralogical composition of the soupy and mousse-like sediments does not show any specific characteristic with respect
to the other samples from the southern Hydrate Ridge. 相似文献
6.
ZHAO Xiaoxia Michael G FOX David C. LASENBY Alexis C. ARMIT Dolly N. KOTHAWALA 《中国海洋湖沼学报》2007,25(2):215-220
The abundance and size composition of stream isopods Lirceus fontinalis were investigated from April 2001 to August 2002 in 3 streams in southern Ontario, Canada. Effects of current speed was released from the analysis by choosing slow flowing water. The effects of substrate, season and water depth on the abundance, distribution and size composition of the isopods were analyzed. It was found that substrate and season influence isopods the most. The rocky substrate with attached filamentous macro-algae contains an isopod abundance 7.05 times that of bare rock substrate and 14.6 times that of fine-sand and mud substrate. There was a large variation with respect to seasonality in both abundance and size composition of the isopods, with the highest abundance occurring in summer and the lowest in winter and spring; individual isopods also tend to be larger in the winter and spring. In all substrates, shallow areas tend to support higher densities of isopods than deeper areas. 相似文献
7.
John F. Hoffecker Vance T. Holliday Vadim N. Stepanchuk Alexis Brugre Steven L. Forman Paul Goldberg Oleg Tubolzev Igor Pisarev 《Geoarchaeology》2014,29(1):61-77
New geoarchaeological and bioarcheological research was undertaken at the open‐air site of Mira, which is buried in deposits of the Second Terrace of the Dnepr River, roughly 15 km downstream from the city of Zaporozhye in Ukraine. Previous excavation of the site revealed two occupation layers dating to ∼32,000 cal BP. The lower layer (II/2) yielded bladelets similar to those of the early Gravettian, while the upper layer (I) contained traces of an artificial shelter and hundreds of bones and teeth of horse (Equus latipes). Mira represents the only firmly dated early Upper Paleolithic (EUP) site in the Dnepr Basin, and occupies a unique topographic setting for the EUP near the center of the broad floodplain of the Dnepr River. The site was visited during a period of floodplain stability, characterized by overbank deposition and weak soil formation under cool climate conditions. Mira was used as a long‐term camp, but also was the locus of large‐mammal carcass processing associated with a nearby kill of a group of horses (Layer I). 相似文献
8.
Jonathan Gewirtzman Sujay Natson Julie-Anne Richards Victoria Hoffmeister Alexis Durand Romain Weikmans 《Climate Policy》2018,18(8):1076-1086
After decades of pressure from vulnerable developing countries, the Warsaw International Mechanism on Loss and Damage (the WIM) was established at the nineteenth Conference of the Parties (COP 19) in 2013 to address costly damages from climate change. However, little progress has been made towards establishing a mechanism to fund loss and damage. The WIM's Executive Committee issued its first two-year workplan the following year at COP 20 which offered, among other things, a range of approaches to financing loss and damage programmes, which we review here. We provide brief overviews of each mechanism proposed by the WIM ExCom, describe their current applications, their statuses under the United Nations Framework Convention on Climate Change (UNFCCC), some of their advantages and disadvantages, and their current or potential application to loss and damage. We find that several of these mechanisms may be useful in supporting loss and damage programmes, but identify some key gaps. First, most of the mechanisms identified by the WIM ExCom are insurance schemes subsidized with voluntary contributions, which may not be adequate or reliable over time. Second, none were devised to apply to slow-onset events, or to non-economic losses and damages. That is, if harms are inflicted on parts of a society or its ecosystems that have no price, or if they occur gradually, they would probably not be covered by these mechanisms. Finally, the lack of a dedicated and adequate flow of finance to address the real loss and damage being experienced by vulnerable nations will require the use of innovative financial tools beyond those mentioned in the WIM ExCom workplan.
Key policy insights
Despite a full article of the 2015 Paris Agreement devoted to loss and damage, there is little international agreement on the scope of loss and damage programmes, and especially how they would be funded and by whom.
Most of the loss and damage funding mechanisms identified by the WIM ExCom are insurance schemes subsidized with voluntary contributions, which may burden the most vulnerable countries and may not be reliable over time.
None of the mechanisms were devised to apply to slow-onset events, or to non-economic losses and damages.
9.
Agricultural Census data is summarised over spatially coarse reporting units for reasons of farm confidentiality. This is problematic for research at a local level. This article describes an approach combining dasymetric and volume preserving techniques to create a national land use dataset at 1 km2 resolution. The results for an English county are compared with contemporaneous aggregated habitat data. The results show that the accurate estimates of local agricultural land use (Arable and Grass) patterns can be estimated when individual 1 km squares are combined into blocks of > 9 squares, thereby providing local estimates of agricultural land use. This in turn allows more detailed modelling of land uses related to specific livestock and cropping activities. The dataset created by this work has been subject to extensive external validation through its incorporation into a number of other national models: nitrate leaching (e.g. MAGPIE, NEAP‐N), waste, and pathogen modelling related to agricultural activity. 相似文献
10.
