Irregular Satellites of Jupiter: a study of the capture direction     

Douglas Soldan de Oliveira  Othon Cabo Winter  Ernesto Vieira Neto  Gislaine de Felipe 《Earth, Moon, and Planets》2007,100(3-4):233-239

The irregular satellites of Jupiter are believed to be captured asteroids or planetesimals. In the present work is studied the direction of capture of these objects as a function of their orbital inclination. We performed numerical simulations of the restricted three-body problem, Sun-Jupiter-particle, taking into account the growth of Jupiter. The integration was made backward in time. Initially, the particles have orbits as satellites of Jupiter, which has its present mass. Then, the system evolved with Jupiter losing mass and the satellites escaping from the planet. The reverse of the escape direction corresponds to the capture direction. The results show that the Lagrangian points L1 and L2 mainly guide the direction of capture. Prograde satellites are captured through these two gates with very narrow amplitude angles. In the case of retrograde satellites, these two gates are wider. The capture region increases as the orbital inclination increases. In the case of planar retrograde satellites the directions of capture cover the whole 360° around Jupiter. We also verified that prograde satellites are captured earlier in actual time than retrograde ones. This paper was presented at the Asteriods, Comets and Meteors meeting held at Búzios, Rio de Janeiro, Brazil in August 2005 and could not be included in the special issue related to that conference.  相似文献   

Direct dating of the Sete Lagoas cap carbonate (Bambuí Group,Brazil) and implications for the Neoproterozoic glacial events     

Marly Babinski  Lucieth Cruz Vieira  Ricardo I. F. Trindade 《地学学报》2007,19(6):401-406

The end of the Neoproterozoic is punctuated by glacial deposition, but the chronology of these deposits is hindered presently by the paucity of geochronological data. Here, we present new radiometric dating for the basal Sete Lagoas cap carbonate deposits that overlie glacial units in the São Francisco craton. Six samples from aragonite‐pseudomorph crystal‐rich facies, showing pristine textures and constant ⁸⁷Sr/⁸⁶Sr ratios around 0.7075, yielded a Pb–Pb isochron age of 740 ± 22 Ma, which is interpreted as the depositional age for these remarkably preserved rocks. This age can be used to infer a low‐to‐moderate palaeolatitude of 20–30° for carbonate (and glacial) deposition. In addition, as it overlaps the ages obtained for the oldest Neoproterozoic glacial successions, our result reinforces the idea of a long‐standing ‘Sturtian’ interval, suggesting that this event represents either different discrete glaciations or a protracted event encompassing almost 80 Ma.  相似文献   

Tidal transport and dispersal of marine toxic microalgae in a shallow, temperate coastal lagoon     

Cerejo M  Dias JM 《Marine environmental research》2007,63(4):313-340

A numerical model was used to predict toxic microalgal transport and dispersion in Ria de Aveiro in Portugal. A previously developed Lagrangean particle tracking model coupled to a calibrated two-dimensional hydrodynamic model of Ria de Aveiro was used. Microalgae were regarded as passive particles and the methodology used allowed the determination of their trajectories, as induced by the tidal currents predicted by the hydrodynamic model. The model assumes Ria de Aveiro as vertically homogeneous and does not take into account the vertical distribution patterns of microalgae. Simulations were carried out during extreme spring and neap tides, with microalgal released at the mouth of the lagoon at the local flood. The maximum and minimum areas affected during the occurrence of toxic microalgal blooms were estimated to evaluate the suitability of the distribution of the sampling stations included in the local monitoring program. It was found that the tidal currents greatly determine the microalgal horizontal distribution and dispersal in the lagoon. The results confirmed that the locations of water and bivalve shellfish sampling stations, postulated by INIAP/IPIMAR, in the context of the local harmful algal bloom (HAB) program, were appropriate, although some possible refinements were identified.  相似文献   

Mobility of potentially harmful metals in latosols impacted by the municipal solid waste deposit of Londrina,Brazil     

Raquel Souza Teixeira  Philippe Cambier  Regina Davison Dias  José Paulo Peccinini Pinese  Anne Jaulin-Soubelet 《Applied Geochemistry》2010

The contamination of soils by metals issuing from municipal solid waste (MSW) disposal in tropical environments has hardly been studied with regard to the particular problems associated with them, i.e., generally a high permeability of soils despite the abundance of clay, and the role of reactive Fe compounds. From a previous geotechnical and chemical survey, three latosol profiles differently affected by MSW leachates in the region of Londrina (Paraná, Brazil) were selected. The aims were to evaluate the extent of their contamination, to better understand the fate of potentially harmful metals in tropical soils and rank the determining factors. Samples between 0.5 and 7 m depth were analyzed for their physical, mineralogical and chemical properties, and their micro-morphology was described by optical and transmission electron microscopy. Two steps of a sequential extraction procedure helped to assess the mobility of elements and to better discriminate between metals originating from pedogenesis and issued from MSW. These combined approaches showed that exposed soil profiles have been impacted at various depths, down to 7 m, through increased metal content, especially enhanced mobility of Zn, Co, Mn, Cu and Fe, and through increased salinity and organic matter. The mobility of potentially harmful metals should decrease with pH, which significantly increased in some impacted horizons, but other factors can reverse this trend.  相似文献   

2D Tunnel Numerical Investigation: The Influence of the Simplified Excavation Method on Tunnel Behaviour     

Ngoc-Anh Do  Daniel Dias  Pierpaolo Oreste  Irini Djeran-Maigre 《Geotechnical and Geological Engineering》2014,32(1):43-58

Tunnel excavation is a three-dimensional (3D) problem. However, despite recent advances in computing resources, 3D models are still computationally inefficient and two-dimensional (2D) simulations are therefore often used. Modelling the tunnelling process in a 2D plane strain analysis requires a specific approach that allows a 3D tunnelling effect to be taken into consideration. As far as the urban tunnels are concerned, most cases reported in the literature have focused on estimating the applicability of these equivalent approaches that are based on the evaluation of the settlement that develops on the ground surface, without considering the influence of segment joints. The main objective of this study was to provide a 2D numerical investigation to highlight the influence of two equivalent approaches, that is, the convergence-confinement method (CCM) and the volume loss method (VLM), on the behaviour of a tunnel built in an urban area, in terms of not only the surface settlement but also the structural lining forces, taking into account the effect of segment joints. A technique that can be used to simulate the tunnel wall displacement process, based on the principles of the VLM, has been developed using the FLAC^3D finite difference program (Itasca in FLAC fast Lagrangian analysis of continua, version 4.0; User’s manual, http.itascacg.com, 2009). A comparison with 3D numerical results has been introduced to estimate the precision of these 2D equivalent approaches. The results have shown a significant influence of the tunnel boundary deconfinement technique and segment joints on the tunnel lining behaviour and surface settlements. The structural forces obtained by means of the CCM are often smaller than those determined with the VLM for the same surface settlement. Generally, the structural lining forces determined by the CCM are in better agreement with the 3D numerical results than the ones obtained with the VLM. However, in order to obtain an accurate estimation of the structural forces, the impact of the construction loads during tunnelling should be taken into account.  相似文献   

Coastal vulnerability in barrier islands: The high risk areas of the Ria Formosa (Portugal) system     

Filipe Rafael Ceia  Joana Patrício  João Carlos Marques  João Alveirinho Dias 《Ocean & Coastal Management》2010,53(8):478-486

Coastal vulnerability in barrier island systems is extremely high. The barrier island shoreline is exposed to many threats, such as storm erosion, reductions in sediment longshore drift and sea level rise. Many of these threats to coastal areas, such as Ria Formosa, are likely to increase in the near future. The main objectives of the present study are to identify the areas in the system that are at most risk by assessing the evolution of the Ria Formosa barrier island system since the 1940s, and determine which interventions would be necessary to protect these areas.The coastal vulnerability of the system was assessed based on current literature, data available from official institutions, and aerial and terrestrial in situ examination. The results obtained for the evolution of the Ria Formosa coastal system reveal that there are several vulnerable areas that have very dynamic processes, such as extremely high evolution rates of islands and inlets. Human actions that affect the whole system, namely the construction of many physical structures, are the main cause of the instability. Moreover, as several stakeholders are involved, efficient management of the coastal system is imperative. Extensive and careful interventions are urgently needed to avoid irreversible negative impacts on the barrier island system. Three types of techniques could be adopted to deal with the threats to barrier islands: hard stabilization, soft techniques, and non-structural alternatives. However, using hard techniques has many negative effects compared to soft techniques, and as a result it is necessary to remove existing structures from the areas at most risk.  相似文献   

Feminism and Social Theory in Geography: An Introduction*   总被引：1，自引：0，他引：1  

Karen Dias  Jennifer Blecha 《The Professional geographer》2007,59(1):1-9

This essay introduces a collection of articles based on papers developed for a Fall 2004 speaker series at the University of Minnesota. The articles address the continued relevance of feminist geography and the unique contributions of feminist perspectives in various areas of geographic research. They also point out directions for needed future research. This introduction briefly reviews the successes of and remaining challenges to feminist geography, including material inequities yet unresolved in two other (nonresearch) “places” of academic life: teaching and the workplace. We discuss the ongoing underrepresentation of women and people of color on our faculties and in the front of classrooms.  相似文献   

A study of the sea level and current effects on the sea state in Galway Bay,using the numerical model COAWST     

Calvino  Cl&#;ment  Dabrowski  Tomasz  Dias  Fr&#;d&#;ric 《Ocean Dynamics》2022,72(11):761-774

A coupled wave and ocean model is applied to the region of Galway Bay in the west of Ireland, using the numerical modelling suite COAWST. The coupled model was validated in a previous study. Here we focus on the impact of the currents and sea level on the sea state during Storm Hector (2018/06/14). The purpose of the research is to improve the wave dynamics knowledge specifically in Galway Bay by highlighting and quantifying the dominant current-induced mechanisms on the sea state observed numerically. We want to know where wave-current interaction is modifying the sea state in the bay, and if the change is significant to justify the use of a coupled model for an operational application. We show that the impacts of the tidal sea surface height on bottom friction and of the current-induced refraction on the spatial distribution of the waves are the dominant mechanisms. Those two effects are well-documented and observed in the literature already. A strong feedback impact of the coupling is also put into evidence. The wave-induced response in terms of currents leads to a noticeable variation in terms of wave height. Less documented in the literature, we discuss the link between current-induced refraction and the reduction of wave generation by wind.

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Study of a neutral hydrogen feature previously observed by Cugnon     

I. F. Mirabel  W. G. L. Pöppel  E. R. Vieira 《Astrophysics and Space Science》1975,35(1):23-41

An anomalous velocity cloud nearl=349°,b=+3°, was investigated by Cugnon (1968). The authors made a new set of observations in order to obtain a more complete picture of the feature, including the region originally out of Cugnon's limit of observation. A comparison with optical and radio observations was made and several possibilities of interpretation as to the nature of the object were analyzed.  相似文献   

Mantle-like Sr–Nd isotope composition of Fe–K subalkaline granites: the Peneda–Gerês Variscan massif (NW Iberian Peninsula)     

A. C. Mendes  G. Dias 《地学学报》2004,16(3):109-115

The Peneda–Gerês massif is one of the most representative NW Iberian late‐ to post‐orogenic Variscan granitic plutons. It resulted essentially from the subsynchronous emplacement, at 290–296 Ma, of two granitic magmas of Fe–K subalkaline affinity, with primitive isotopic composition: Sr_i = 0.703–0.707 and εNd_i=?1.5 to ?2.4. An origin by mantle input followed by mantle–crust interactions is proposed, implying the contribution of a less enriched mantle component than that involved in the genesis of synorogenic hybrid granitoids of Mg–K subalkaline affinity. A less voluminous aluminopotassic and isotopically more evolved magma (Sr_i=0.708–0.709 and εNd_i=?3.5 to ?3.9) with little or no mantle input was also generated, suggesting the involvement of lower crust materials. Therefore, this study suggests an input of juvenile magmas in late Variscan times, the mantle‐like isotope signature of Fe–K granitic magmatism being clearly related to a geodynamic setting of extensional processes, large‐scale uplift and thinning.  相似文献