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排序方式: 共有267条查询结果,搜索用时 15 毫秒
91.
Sin Chan Chou Andr de Arruda Lyra Jorge Lus Gomes Daniel Andrs Rodriguez Minella Alves Martins Nicole Costa Resende Priscila da Silva Tavares Claudine Pereira Dereczynski Isabel Lopes Pilotto Alessandro Marques Martins Lus Felipe Alves de Carvalho Jos Luiz Lima Onofre Idalcio Major Manuel Penhor Adrito Santana 《Climate Dynamics》2020,54(9):4021-4042
Sao Tome and Principe is a small insular African country extremely vulnerable to rising sea levels and impacts such as inundation, shore line change, and salt water intrusion into underground aquifers. Projections of climate change have considered coarse model resolutions. The objective of this work is to dynamically downscale the global model projections to 4-km resolution and to assess the climate change in the Sao Tome and Principe islands. The global climate projections are provided by the Canadian Earth System Model under two Representative Concentration Pathways greenhouse gas scenarios, RCP4.5 and RCP8.5. The downscaling is produced by the Eta regional climate model. The baseline period is taken between 1971 and 2000, and the future climate period is taken between 2041 and 2070. The 2-m temperature simulations show good agreement with station data. The model simulates temperature more accurately than precipitation. The precipitation simulations systematically show underestimation and delay of the rainy and the dry seasons by about 1 month, a feature inherited from the global climate model. In the middle of the 21st century, projections show the strongest warming in the elevated parts of the Sao Tome Island, especially in February under RCP8.5. Warmer nights and warmer days become more frequent in the islands when compared with those in the present. While under RCP4.5, precipitation increases in the islands; under RCP8.5, it decreases everywhere in both islands. Heavy precipitation rates should increase, especially in the south-southwestern parts of the Sao Tome islands. Detailed spatial variability of the temperature and precipitation changes in the islands can only be revealed at very high spatial model resolution. Implications for the potential energy production from two major river basins are assessed in this work. 相似文献
92.
Weak ion-acoustic (IA) solitary wave propagation is investigated in the presence of electron trapping and background nonextensivity. A physically meaningful distribution is outlined and a Schamel-like equation is derived. The role a background electron nonextensivity may play on the energy carried by the IA soliton is then examined. It is found that nonextensivity may cause a soliton energy depletion. An increase of the amount of electron trapping leads to a net shift towards higher values of the soliton energy. 相似文献
93.
Carla Carvalho 《Astrophysics and Space Science》2003,283(4):531-536
We present a calculation of the probability distribution of the invariant separation between the nucleation centers of colliding
bubbles resulting from the decay of a false de Sitter space vacuum. We also discuss the probability of a collision with a
`third' bubble. This study is motivated by the proposed `colliding bubble braneworld' scenario in which the value of Ω0 today is a function of this invariant.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
94.
M. S. M. B. Salomo M. M. Molisani A. R. C. Ovalle C. E. Rezende L. D. Lacerda C. E. V. Carvalho 《水文研究》2001,15(4):587-593
In the present study an attempt has been made to calculate the mass transfers of suspended particulate matter and associated heavy metal within the lower portion of the Paraíba do Sul River drainage basin and the contribution of its tributaries. The highest metal loads were related with the highest water flows and, consequently, with the highest suspended particulate matter loads, which increased both by surface runoff and sediment resuspension. The highest flow month for the total transported load contributed between 34 and 66% of the total metal transported per year. The total load transported during the entire rainy season ranges from 82 to 93% of the total transported load. The importance of the tributary input for the total transported load of the Paraíba do Sul River was generally lower than 10%, although in some months, when the Paraíba do Sul River had low water discharge and strong local rain occurred, this increased upto 40%. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
95.
Nowadays, the difficulties of the mining sector in accessing the territory are mostly related to inadequate land use plans. Mineral potential maps have become quite relevant for the land use planning authorities as a decision support tool. This work’s goal is to present a methodology based on geological criteria, for the delimitation of potential areas for ornamental stones production in a limestone area of Portugal known as Maciço Calcário Estremenho. This is one of the world’s most important regions producing limestone blocks for ornamental purposes. The methodology, applied at a scale similar to the commonly used in land use planning, considers two main geological-based criteria for the definition of potential areas, namely the homogeneity criterion, related to the textural and chromatic homogeneity of the potentially productive lithologic units, and the dimension criterion, which refers to the thickness of the productive unit, to the volume of the deposit and to its spatial layout. Based on the criteria, two main types of potential areas for ornamental stones’ production were delimited: specific areas, where the lithostratigraphic units demonstrate ornamental suitability at a very local scale due to highly appreciated particular features, and areas corresponding to the entire outcrop area of some of the lithostratigraphic units, which due to the resource volume are the most relevant potential areas. 相似文献
96.
Neoproterozoic peritidal phosphorite from the Sete Lagoas Formation (Brazil) and the Precambrian phosphorus cycle 总被引:1,自引:0,他引:1 下载免费PDF全文
Justin B. R. Drummond Peir K. Pufahl Claudio G. Porto Mariana Carvalho 《Sedimentology》2015,62(7):1978-2008
The Neoproterozoic Sete Lagoas Formation (ca 610 Ma) of the São Francisco Basin, Brazil, is a succession of siltstone, limestone and phosphorite. Phosphorite forms part of a previously unrecognized 150 to 200 m thick, unconformity bounded depositional sequence. Lithofacies stacking patterns indicate that deposition was punctuated by higher order fluctuations in base level that produced aggradational parasequences. These shallowing‐upward cycles record the progradation of phosphate‐rich intertidal flats over shallow subtidal deposits as accommodation filled. The presence of mudcracks, authigenic chert nodules, lack of coarse terrigenous clastics and the abundance of silt with fine, abraded quartz grains suggests accumulation along an arid coastline with significant aeolian input. Delivery of phosphorus adsorbed on aeolian Fe‐(oxyhydr)oxide and clay is interpreted as having stimulated phosphogenesis in peritidal environments. Lithofacies associations indicate that windblown phosphorus promoted the establishment of cyanobacterial communities along the coast, which produced photosynthetic oxygen and the suboxic conditions necessary for the precipitation of authigenic carbonate fluorapatite. As in other Precambrian phosphatic systems, nearshore oxygen oases were a prerequisite for phosphorite accumulation because redox sensitive phosphogenic processes were pushed into the sediment to concentrate phosphorus. In more distal, anoxic environments phosphorite could not form because these biotic and abiotic processes were suspended in the water column, which cycled phosphorus in sea water rather than at the sediment–water interface. Such shallow‐water phosphorite is unlike larger, younger Neoproterozoic–Phanerozoic phosphatic deposits inferred to have formed in deeper‐upwelling related environments. The increasing size of phosphatic deposits through the latest Precambrian is interpreted as reflecting the progressive ventilation of the oceans during the Neoproterozoic Oxygenation Event, and resultant expansion of phosphogenic environments into distal settings. The widespread cycling of bioavailable phosphorus at the sea floor not only produced the first true phosphorite giants, but may have also been an important precondition for the evolution of multicellular animals. 相似文献
97.
Weak ion-acoustic double-layers (IA-DLs) in a two-component plasma are investigated in the context of the nonextensive statistics
proposed by Tsallis. Due to the entropic index q, our plasma model can admit compressive as well as rarefactive IA-DLs. It is shown that the values
\frac53 < q < 3\frac{5}{3}
q-parameters for the existence of small-DLs. As long as the Mach number M is less than ∼1.42, the only admissible q-values which may lead to IA-DLs are all positive. For −1<q<1 (1<q<5/3), the effect of increasing q is to lower (to shift towards higher values) the critical Mach number M cr above which only compressive IA-DL are admitted. Beyond q=3, only compressive small-amplitude ion-acoustic double layers are observed. Furthermore, due to the flexibility of the q-parameter, the obtained results bring a possibility to deal with small-DLs with relatively high Mach numbers. Our investigation may be of wide relevance to astronomers and space scientists working on interstellar plasmas. 相似文献
98.
J. F. Borges H. G. Silva R. J. G. Torres B. Caldeira M. Bezzeghoud J. A. Furtado J. Carvalho 《Journal of Seismology》2016,20(3):875-887
During its history, several significant earthquakes have shaken the Lower Tagus Valley (Portugal). These earthquakes were destructive; some strong earthquakes were produced by large ruptures in offshore structures located southwest of the Portuguese coastline, and other moderate earthquakes were produced by local faults. In recent years, several studies have successfully obtained strong-ground motion syntheses for the Lower Tagus Valley using the finite difference method. To confirm the velocity model of this sedimentary basin obtained from geophysical and geological data, we analysed the ambient seismic noise measurements by applying the horizontal to vertical spectral ratio (HVSR) method. This study reveals the dependence of the frequency and amplitude of the low-frequency (HVSR) peaks (0.2–2 Hz) on the sediment thickness. We have obtained the depth of the Cenozoic basement along a profile transversal to the basin by the inversion of these ratios, imposing constraints from seismic reflection, boreholes, seismic sounding and gravimetric and magnetic potentials. This technique enables us to improve the existing three-dimensional model of the Lower Tagus Valley structure. The improved model will be decisive for the improvement of strong motion predictions in the earthquake hazard analysis of this highly populated basin. The methodology discussed can be applied to any other sedimentary basin. 相似文献
99.
Scott T. Kay Leila C. Powell rew R. Liddle Peter A. Thomas 《Monthly notices of the Royal Astronomical Society》2008,386(4):2110-2114
The relativistic Sunyaev–Zel'dovich (SZ) effect offers a method, independent of X-ray, for measuring the temperature of the intracluster medium (ICM) in the hottest systems. Here, using N -body/hydrodynamic simulations of three galaxy clusters, we compare the two quantities for a non-radiative ICM, and for one that is subject both to radiative cooling and to strong energy feedback from galaxies. Our study has yielded two interesting results. First, in all cases, the SZ temperature is hotter than the X-ray temperature and is within 10 per cent of the virial temperature of the cluster. Secondly, the mean SZ temperature is less affected by cooling and feedback than the X-ray temperature. Both these results can be explained by the SZ temperature being less sensitive to the distribution of cool gas associated with cluster substructure. A comparison of the SZ and X-ray temperatures (measured for a sample of hot clusters) would therefore yield interesting constraints on the thermodynamic structure of the intracluster gas. 相似文献
100.
Mônica L. Botter-Carvalho Paulo V.V.C. Carvalho Ana Paula M.C. Valença Paulo J.P. Santos 《Marine pollution bulletin》2014
A field experiment to assess the effects of continuous nutrient addition on the macrobenthic community was carried out on an estuarine mudflat on the northeast coast of Brazil. The experiment began on 5 October 2005 and ended on 8 February 2006. Macrofauna was compared at approximately four-week intervals in triplicate plots with three levels (Control – C, Low Dose – LD and High Dose – HD) of weekly fertilizer additions for 17 weeks. Inorganic fertilizer (N–P–K) was applied on nine randomly defined quadrangular plots (4 m2 each). All measurements were calculated from species abundances. Multivariate analyses as well as the univariate indices (richness, abundance and Shannon–Wiener index) showed statistically significant differences between the enriched and control areas during the period of the experiment. The expected gradual response based on the succession model of Pearson and Rosenberg was not observed. The nutrient doses used were high enough to cause severe decreases in abundance, richness and evenness, and an increase in dominance. 相似文献