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991.
Anna Maria Nobili 《Earth, Moon, and Planets》1978,18(2):203-216
We separate the tidal evolution of a planet-satellite system with zero eccentricity in two phases:phase 1—from the formation of the system to satellite's corotation (satellite's corotation means that its spin angular velocity equals the orbital angular velocity);phase 2—after satellite's corotation.We study the planet-satellite system during phase 1 with Darwin's graphical method and obtain an upper limit to satellite'sQ which discloses whether or not it is corotating. Moreover we obtain some qualitative information about the future evolution of the corotating satellites.The present work does not give any new result for the Earth-Moon case and for the Neptune-Triton case. 相似文献
992.
993.
Arsenic incorporation into FeS2 pyrite and its influence on dissolution: A DFT study 总被引:3,自引:0,他引:3
FeS2 pyrite can incorporate large amounts of arsenic (up to ca. 10 wt%) and hence has a strong impact on the mobility of this toxic metalloid. Focussing on the lowest arsenic concentrations for which the incorporation occurs in solid solution, the substitution mechanisms involved have been investigated by assuming simple incorporation reactions in both oxidising and reducing conditions. The solution energies were calculated by Density Functional Theory (DFT) calculations and we predict that the formation of AsS dianion groups is the most energetically favourable mechanism. The results also suggest that the presence of arsenic will accelerate the dissolution and thus the generation of acid drainage, when the crystal dissolves in oxidising conditions. 相似文献
994.
Leonel da S.L. Sternberg Maria C. Pinzon William T. Anderson Kristina Beuning 《Geochimica et cosmochimica acta》2007,71(10):2463-2473
Oxygen atoms within fossil wood provide high-resolution records of climate change, particularly for the Quaternary. However, current analysis methods of fossil cellulose do not differentiate between different positions of the oxygen atoms. Here, we propose a refinement to tree-cellulose paleoclimatology modeling, using the cellulose-derived compound phenylglucosazone as the isotopic substrate. Stem samples from trees were collected at northern latitudes as low as 24°37′N and as high as 69°00′N. We extracted stem water and cellulose from each stem sample and analyzed them for their 18O content. In addition, we derived the cellulose to phenylglucosazone, a compound which lacks the oxygen attached to the second carbon of the cellulose-glucose moieties. Oxygen isotope analysis of phenylglucosazone allowed us to calculate the 18O content of the oxygen attached to the second carbon of the cellulose-glucose moieties. By way of these analyses, we tested two hypotheses: first, that the 18O content of the oxygen attached to second carbon will more closely reflect the 18O content of the stem water, and will not resemble the 18O content of either cellulose or its derivative phenylglucosazone. Second, tree-ring models that incorporate the variable oxygen isotope fractionation shown here and elsewhere are more accurate than those that do not. Our first hypothesis was rejected on the basis that the oxygen isotope ratios of the oxygen attached to the second carbon of the glucose moieties had a noisy isotopic signal with a large standard deviation and gave the poorest correlation with the oxygen isotope ratios of stem water. Related to this isotopic noise, we observed that the correlation between oxygen isotope ratios of phenylglucosazone with both stem water and relative humidity were higher than those observed for cellulose. Our hypothesis about tree-ring models which account for changes in the oxygen isotopic fractionation during cellulose synthesis was consistent only for the 18O content of phenylglucosazone. We showed that the tree-ring model based on the 18O content of phenylglucosazone was an improvement over existing models that are based on whole cellulose. Additionally, this approach may be used in other cellulose based archives such as peat deposits and lacustrine sediments. 相似文献
995.
Martin Piringer Sylvain Joffre Alexander Baklanov Andreas Christen Marco Deserti Koen De Ridder Stefan Emeis Patrice Mestayer Maria Tombrou Douglas Middleton Kathrin Baumann-Stanzer Aggeliki Dandou Ari Karppinen Jerzy Burzynski 《Boundary-Layer Meteorology》2007,124(1):3-24
The specific problems of determining and simulating the surface energy balance (SEB) and the mixing height (MH) over urban
areas are examined. The SEB and MH are critical components of algorithms and numerical models for the urban boundary layer,
though the constituent parts of the SEB and the MH are not routinely measured by national weather services. Parameterisations
are thus needed in applications. In this investigation, several recently developed algorithms and models for estimating the
SEB and MH were applied to new datasets and assessed. Results are discussed in terms of the need for spatial resolution and
the parameters needed to describe the urban atmosphere. Limitations of models are identified and recommendations for further
development and observations are given. Having identified gaps in knowledge, key findings from new urban experiments and numerical
modelling for the SEB and MH are given. The diurnal cycle for the SEB is significantly different from rural conditions—urban
heat storage is needed in urban parameterisations. The urban MH is increased over the rural MH, as shown by several numerical
schemes and careful sodar analyses. This work has been carried out within the COST-715 Action “Meteorology applied to urban
air pollution problems (1998–2004). COST 715 reached a consensus proposing representatively sited measurements of meteorological
parameters and turbulent fluxes above roof-tops, and recognised that such data are needed to improve numerical models of the
urban surface processes. 相似文献
996.
André Sabino Pedro Poseiro Armanda Rodrigues Maria Teresa Reis Conceição J. Fortes Rui Reis João Araújo 《Journal of Geographical Systems》2018,20(2):159-184
The run-up and overtopping by sea waves are two of the main processes that threaten coastal structures, leading to flooding, destruction of both property and the environment, and harm to people. To build early warning systems, the consequences and associated risks in the affected areas must be evaluated. It is also important to understand how these two types of spatial information integrate with sensor data sources and the risk assessment methodology. This paper describes the relationship between consequences and risk maps, their role in risk management and how the HIDRALERTA system integrates both aspects in its risk methodology. It describes a case study for Praia da Vitória Port, Terceira Island, Azores, Portugal, showing that the main innovations in this system are twofold: it represents the overtopping flow and consequent flooding, which are critical for coastal and port areas protected by maritime structures, and it works also as a risk assessment tool, extremely important for long-term planning and decision-making. Moreover, the implementation of the system considers possible known variability issues, enabling changes in its behaviour as needs arise. This system has the potential to become a useful tool for the management of coastal and port areas, due to its capacity to effectively issue warnings and assess risks. 相似文献
997.
Integrated modelling for water quality management in a eutrophic reservoir in south-eastern Portugal
David Brito Tiago B. Ramos Maria C. Gonçalves Manuela Morais Ramiro Neves 《Environmental Earth Sciences》2018,77(2):40
The Enxoé Reservoir was built in 1998. Since 2000, it has exhibited frequent high chlorophyll-a concentrations, reaching a geometric mean three times higher than the national limit for eutrophication, presenting the reservoir with the highest eutrophic state in Portugal. Toxic algal blooms have also often been observed, which pose serious challenges to water managers, as the reservoir is used for potable water production (25,000 inhabitants). The objective of this study was to implement a reservoir model (CE-QUAL-W2), with inputs from a watershed model (SWAT), in order to represent the actual reservoir state and to test management measures to reduce its trophic level and algal bloom concentration peaks. The integrated model was used to depict the origin of its trophic status. Simulations were also compared to measured data at the reservoir surface (water level, nitrate, orthophosphate, suspended solids, and oxygen) and in water profiles (temperature, oxygen). The model was able to represent stratification and thermocline depths, as well as the actual chlorophyll-a and dissolved oxygen concentrations. The model results showed that internal phosphorus load from deposited sediments was an important factor in fuelling the algal blooms. This process occurs predominantly in summer, when stratification takes place and aeration is reduced, promoting anoxic conditions in the bottom waters. Since the reservoir is relatively shallow (average 5 m), released phosphorus is then easily able to reach the photic zone in most parts of the reservoir, where it is consumed. Different management scenarios were tested, suggesting that a mesotrophic level could barely be reached and maintained simply by reducing the nutrient loads (both external and internal). It is suggested that only an increase in the reservoir dam height could produce a mesotrophic level, averting anoxia by blocking the release of phosphorus from sediments to the photic zone. Future work should focus on a cost–benefit analysis to test the feasibility of each of the proposed scenarios, taking advantage of the integration strategy to assess where in the watershed load reductions would be most effective. 相似文献
998.
Adriana Sturion Lorenzi Micheline Kézia Cordeiro-Araújo Mathias Ahii Chia Maria do Carmo Bittencourt-Oliveira 《Environmental Earth Sciences》2018,77(16):595
Changing global climatic conditions and the continuous eutrophication of aquatic ecosystems have led to increased frequency, duration and toxicity of cyanobacterial blooms worldwide. This makes the provision of time series information on cyanotoxins extremely crucial for effective monitoring and management of water resources. The objective of the present study was to investigate seasonal and annual changes in microcystins (MCs), cylindrospermopsins (CYNs), saxitoxins (STXs), neo-saxitoxin (neo-STX) and anatoxin-a (ATX-a) concentrations in 11 public water supply reservoirs in the semiarid region of Brazil, from 2004 to 2011. Per time, at least one cyanotoxin was present in all the investigated reservoirs. High levels of MCs, CYNs, STXs and Neo-STX were detected simultaneously in Carpina, Duas Unas, Ipojuca, and Jucazinho reservoirs. All the investigated reservoirs had significant concentrations of MCs. The highest levels of MCs were found in Carpina (303,300.0 ng g?1) and Duas Unas (122,053.9 ng g?1) reservoirs, while the lowest concentration of the hepatotoxins was recorded in Ipojuca (10.3 ng g?1) reservoir. On the other hand, CYN was detected in four reservoirs, STXs and Neo-STX in ten reservoirs and ATX-a in two reservoirs. The first record of CYN in Carpina reservoir was obtained in 2006. In addition, Carpina reservoir had the highest concentration of STXs and Neo-STX in the dry and rainy seasons, respectively. The high concentration of cyanotoxins observed in most samples obtained from semiarid reservoirs in Brazil demonstrates the need for regular monitoring and updated management programs. 相似文献
999.
Thalita Costa de Moraes Vitor Juste dos Santos Maria Lúcia Calijuri Fillipe Tamiozzo Pereira Torres 《Environmental Earth Sciences》2018,77(6):250
The Southeast Region of Brazil has undergone major changes in land cover, especially after the eighteenth century. It is currently the most populous region of the country, highly urbanized, with a high degree of industrial and agricultural development. Extensive areas of native vegetation have been replaced by pastures, crops and urban areas, which have increased runoff, causing environmental, economic and social problems related to flooding. The objective of this study was to analyze effects of land cover changes in a basin with rural and urban characteristics on the flow of its main river. Hydrological data, orbital images, soils and topographical maps were used for this purpose. Based on the land cover maps for the years of 1989, 2001 and 2015, and on the hydrological modeling performed using the Hec-HMS 4.1 software, scenarios were simulated and showed that the land cover changes in this basin significantly affect the flow behavior of the main river. The simulated runoff was calibrated using the data observed in the field during 2001, and validation was performed using data from 1989. After the calibration and validation processes, a scenario was simulated where the rainiest month of the whole series measured by the rainfall station (during December 1989) acted on the land cover of 2015. There was an increase in pasture areas and impermeable spaces in the basin, which caused a decrease in infiltration and an increase in surface runoff, and also an increase in the flow peaks and a reduction in the time of concentration. The hydrological modeling was satisfactory, since the uncertainties related to the simulation were low. 相似文献
1000.
Maria Navarro Olivier P. Le Maître Ibrahim Hoteit David L. George Kyle T. Mandli Omar M. Knio 《Computational Geosciences》2018,22(6):1447-1463
This work tackles the problem of calibrating the unknown parameters of a debris flow model with the drawback that the information regarding the experimental data treatment and processing is not available. In particular, we focus on the evolution over time of the flow thickness of the debris with dam-break initial conditions. The proposed methodology consists of establishing an approximation of the numerical model using a polynomial chaos expansion that is used in place of the original model, saving computational burden. The values of the parameters are then inferred through a Bayesian approach with a particular focus on inference discrepancies that some of the important features predicted by the model exhibit. We build the model approximation using a preconditioned non-intrusive method and show that a suitable prior parameter distribution is critical to the construction of an accurate surrogate model. The results of the Bayesian inference suggest that utilizing directly the available experimental data could lead to incorrect conclusions, including the over-determination of parameters. To avoid such drawbacks, we propose to base the inference on few significant features extracted from the original data. Our experiments confirm the validity of this approach, and show that it does not lead to significant loss of information. It is further computationally more efficient than the direct approach, and can avoid the construction of an elaborate error model. 相似文献