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排序方式: 共有117条查询结果,搜索用时 765 毫秒
21.
Charlotte Prud'homme Riccardo Vassallo Christian Crouzet Julien Carcaillet Jean-Louis Mugnier Joaquin Cortés-Aranda 《地球表面变化过程与地形》2020,45(5):1168-1180
Cosmogenic nuclide dating of glacial landforms may lead to ambiguous results for ice retreat histories. The persistence of significant cosmogenic concentrations inherited from previous exposure may increase the apparent exposure ages for polished bedrocks affected by limited erosion under ice and for erratic boulders transported by glaciers and previously exposed in high-altitude rock walls. In contrast, transient burying by moraines, sediments and snow decreases the apparent exposure age. We propose a new sampling strategy, applied to four sites distributed in the Arc and Arve valleys in the Western Alps, to better constrain the factors that can bias exposure ages associated with glacial processes. We used the terrestrial cosmogenic nuclide 10Be (TCN) to estimate the exposure time from paired sampling of depth profiles in polished bedrock and on overlying erratic boulders. For a given sampling site, the exposure ages for both the polished bedrock and boulder are expected to be the same. However, in six cases out of seven, boulders had significantly higher 10Be surface concentrations than those of the associated polished surfaces. In present and past glacial processes, the 10Be distribution with depth for boulders and bedrocks implies the presence of an inheritance concentration of 10Be. Our study suggests that 10Be concentrations in erratic boulders and in polished bedrocks provide maximum and minimum exposure ages of the glacial retreat, respectively. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd 相似文献
22.
Statistical analyses regarding climate studies have often used the average temperature as one of the main variables. However, the tails of the respective distributions are also crucial and have become increasingly considered in recent years. As the Intergovernmental Panel on Climate Change in its fourth assessment report (IPCC 2007) states, ??the type, frequency and intensity of extreme events are expected to change as Earth??s climate changes??. In this paper, the focus is on the statistical behaviour of extreme (maximum and minimum) values of temperature, both in winter and summer. Under the framework of the Extreme Value Theory, the methodology of block maxima is employed. The generalised extreme value distribution, allowing for a linear trend in the location parameter, is fitted to data in order to capture the time tendency in the non-stationary processes. We are able to approximate expected values with a determined probability and to identify time trends of such events. Particularly, an increasing time trend in maximum and minimum temperature is generally detected which could be of great concern to public and private sectors. 相似文献
23.
Gómez-Herrero Raúl RodrÍguez-FrÍas M. Dolores del Peral Luis Sequeiros Juan Müller-Mellin Reinhold Kunow Horst Sierks Holger 《Solar physics》2000,194(2):405-413
An analysis of the hydrogen and helium isotopic composition from EPHIN data, during the quiet-time period from January 1 to June 1, 1996, is presented. An isotopic discrimination and background rejection have been applied and relationships between the abundances of 2H/1H, 3He/4He, and 4He/1H have been calculated. The energy spectra in the 4–50 MeV nucl–1 range have been obtained and the contribution of the different spectral components have been analysed in this energy range. We conclude that the main contribution to the 4He spectrum is of anomalous origin, while the proton and 3He spectra have contributions mainly from particles of solar origin at low energies and from the galactic cosmic radiation modulated by the heliosphere at high energies. The deuterium spectrum is mainly of galactic origin. 相似文献
24.
A large artisanal fleet made up of small-sized vessels fishes along the Galician coastline using passive gear and traps. The aim of this study is to analyse the economic profitability of this fleet in the last 5 years by looking at the average rate of return on the vessel and the investment payback period. The results show a slight drop in the return per vessel half-way through the period studied caused by the effects of the Prestige oil spill, to quickly recover over the following 2 years. Considerably high profitability rates from fishing activity were observed, especially in the second half of the period, and slightly lower payback periods, in general, than the average life of a standard fleet vessel. 相似文献
25.
Gurri Francisco D. Ruiz-García Wilma Molina-Rosales Dolores O. Vallejo-Nieto Mirna I. 《Natural Hazards》2019,96(1):149-171
Natural Hazards - We built an easy-to-interpret individual vulnerability index to floods that is amenable for empirical testing and may be adapted to any perceived hazard or ecological setting. An... 相似文献
26.
L. Guerrero S. Montalvo C. Huiliñir A. Barahona R. Borja A. Cortés 《International Journal of Environmental Science and Technology》2016,13(10):2325-2338
One of the technologies used for wastewater nitrogen removal consists in simultaneous nitrification–denitrification. The low microbial growth rate and the low availability of organic material for the denitrification stage make it necessary to study new operational conditions and the use of microbial supports. The aim of this study was to evaluate the operational behavior of a simultaneous nitrification–denitrification process in a sequential batch reactor utilizing zeolite as a biomass support and step-feed strategy. Two reactors of 2 L were used, one with zeolite and another without zeolite, both operated at constant temperature (31 °C), varying nitrogen loading rate (NLR) from 0.041 to 0.113 kg total Kjeldahl nitrogen (TKN/m3/day). After 209 days, removals higher than 86 and 96 % in nitrogen compounds and organic matter were obtained, respectively. There was not accumulation of nitrate and nitrite in any case; this means that there was a simultaneous nitrification–denitrification in the reactors. The incorporation of zeolite in the system held higher concentration of biomass in the reactor; this led to reduce start-up to 21 days and to improve 11.31 % removal kinetic. The use of a step-feed strategy prevents events of inhibition by substrate, even duplicating tolerance to higher NLR for the same operation time. 相似文献
27.
Tomàs Artés Andrés Cencerrado Ana Cortés Tomàs Margalef 《International journal of geographical information science》2016,30(3):594-611
AbstractForest fires are a kind of natural hazard with a high number of occurrences in southern European countries. To avoid major damages and to improve forest fire management, one can use forest fire spread simulators to predict fire behavior. When providing forest fire predictions, there are two main considerations: accuracy and computation time. In the context of natural hazards simulation, it is well known that part of the final forecast error comes from uncertainty in the input data. These data typically consist of a set of GIS files, which should be appropriately conflated. For this reason, several input data calibration methods have been developed by the scientific community. In this work, the Two-Stage calibration methodology, which has been shown to provide good results, is used. This calibration strategy is computationally intensive and time-consuming because it uses a Genetic Algorithm as a solution. Taking into account the aspect of urgency in forest fire spread prediction, it is necessary to maintain a balance between accuracy and the time needed to calibrate the input parameters. In order to take advantage of this technique, one must deal with the problem that some of the obtained solutions are impractical, since they involve simulation times that are too long, preventing the prediction system from being deployed at an operational level. A new method which finds the minimum resolution reduction for such long simulations, keeping accuracy loss to a known interval, is proposed. The proposed improvement is based on a time-aware core allocation policy that enables real-time forest fire spread forecasting. The final prediction system is a cyberinfrastructure, which enables forest fire spread prediction at real time. 相似文献
28.
Sedimentation processes in Golfo Dulce, a periodically anoxic fjord-like embayment on the Pacific coast of Costa Rica, have been investigated by analyses of surface sediments and 3.5-m-long sediment cores. The large proportion of non-biogenic material (>90%) reflects the dominance of terrigenous sediment input to Golfo Dulce. Biogenic components such as organic carbon and carbonate are also supplied from terrigenous sources. The two components, however, originate from different parts of the coast surrounding the gulf. The sediment cores did not show any laminated sections. The sediments can be divided into turbiditic basin deposits and almost undisturbed, hemipelagic slope deposits. 相似文献
29.
An evaluation of approaches for modelling hydrological processes in high‐elevation,glacierized Andean watersheds 下载免费PDF全文
We use two hydrological models of varying complexity to study the Juncal River Basin in the Central Andes of Chile with the aim to understand the degree of conceptualization and the spatial structure that are needed to model present and future streamflows. We use a conceptual semi‐distributed model based on elevation bands [Water Evaluation and Planning (WEAP)], frequently used for water management, and a physically oriented, fully distributed model [Topographic Kinematic Wave Approximation and Integration ETH Zurich (TOPKAPI‐ETH)] developed for research purposes mainly. We evaluate the ability of the two models to reproduce the key hydrological processes in the basin with emphasis on snow accumulation and melt, streamflow and the relationships between internal processes. Both models are capable of reproducing observed runoff and the evolution of Moderate‐resolution Imaging Spectroradiometer snow cover adequately. In spite of WEAP's simple and conceptual approach for modelling snowmelt and its lack of glacier representation and snow gravitational redistribution as well as a proper routing algorithm, this model can reproduce historical data with a similar goodness of fit as the more complex TOPKAPI‐ETH. We show that the performance of both models can be improved by using measured precipitation gradients of higher temporal resolution. In contrast to the good performance of the conceptual model for the present climate, however, we demonstrate that the simplifications in WEAP lead to error compensation, which results in different predictions in simulated melt and runoff for a potentially warmer future climate. TOPKAPI‐ETH, using a more physical representation of processes, depends less on calibration and thus is less subject to a compensation of errors through different model components. Our results show that data obtained locally in ad hoc short‐term field campaigns are needed to complement data extrapolated from long‐term records for simulating changes in the water cycle of high‐elevation catchments but that these data can only be efficiently used by a model applying a spatially distributed physical representation of hydrological processes. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
30.
Haris Ahmed KHAN Ali Asghar SHAHID Muhammad Jahangir KHAN Taher ZOUAGHI Maria Dolores ALVAREZ Syed Danial Mehdi NAQVI 《《地质学报》英文版》2023,97(1):256-268
This research is focused on the analysis of the sequence stratigraphic units of F3 Block, within a wave-dominated delta of Plio–Pleistocene age. Three wells of F3 block and a 3D seismic data, are utilized in this research. The conventional techniques of 3D seismic interpretation were utilized to mark the 11 surfaces on the seismic section. Integration of seismic sequence stratigraphic interpretation, using well logs, and subsequent 3D geostatistical modeling, using seismic data, aided to evaluat... 相似文献