The role of massive AGB stars in the early solar system composition     

Josep M. TRIGO‐RODRÍGUEZ  Domingo Aníbal GARCÍA‐HERNÁNDEZ  Maria LUGARO  Amanda I. KARAKAS  M. van RAAI  Pedro García LARIO  Arturo MANCHADO 《Meteoritics & planetary science》2009,44(5):627-639

Abstract— We demonstrate that a massive asymptotic giant branch (AGB) star is a good candidate as the main source of short‐lived radionuclides in the early solar system. Recent identification of massive (4–8 M⊙) AGB stars in the galaxy, which are both lithium‐ and rubidium‐rich, demonstrates that these stars experience proton captures at the base of the convective envelope (hot bottom burning), together with high‐neutron density nucleosynthesis with ²²Ne as a neutron source in the He shell and efficient dredge‐up of the processed material. A model of a 6.5 M⊙ star of solar metallicity can simultaneously match the abundances of ²⁶Al, ⁴¹Ca, ⁶⁰Fe, and ¹⁰⁷Pd inferred to have been present in the solar nebula by using a dilution factor of 1 part of AGB material per 300 parts of original solar nebula material, and taking into account a time interval between injection of the short‐lived nuclides and consolidation of the first meteorites equal to 0.53 Myr. Such a polluting source does not overproduce ⁵³Mn, as supernova models do, and only marginally affects isotopic ratios of stable elements. It is usually argued that it is unlikely that the short‐lived radionuclides in the early solar system came from an AGB star because these stars are rarely found in star forming regions, however, we think that further interdisciplinary studies are needed to address the fundamental problem of the birth of our solar system.  相似文献   

Tsunamis on Mars: Earth analogues of projected Martian sediment     

William C. Mahaney  James M. Dohm  Pedro Costa  David H. Krinsley 《Planetary and Space Science》2010,58(14-15):1823-1831

Bolide impacts on Mars, within the proposed ocean boundaries (“contacts 1 and 2”) in the northern lowlands, would certainly have generated ultra high energy waves similar to tsunamis on Earth. Impacts into putative Noachian and Hesperian seas of variable areal extents and depths would have experienced high-energy inundations (transgressions), which would have left an imprint in the stack of deposits adjacent to the proposed shorelines. On Earth, the principal influencing factors for tsunami-wave energy are the character of shoreline topography and coastal water depth, which control wave compression and shoreline friction. Shorelines with narrow embayments and steep offshore gradients produce wave compression and increased collision of grains within the carried load contrasted with linear shorelines and shallow offshore gradients that dissipate energy. Steep offshore gradients produce concentrated major wave friction with the bed engendering high kinetic energy in the wave during emplacement of tsunami-generated sediment, which differs from shallow offshore beds that produce lower frictional effects over a wider area and drawdown of wave energy. Thus, overprinting of transported quartz grains on Earth is greatest where wave energy is highest, attenuated down to minor or nil overprinting where wave energy is less. Such grain overprinting in the form of energy-induced microtextures would also be observed in other grain types such as olivine and plagioclase, as such mineralogies are expected to dominate the Martian landscape based on orbital and local field (lander and rover) perspectives. Kinetic energy variation in tsunamis is controlled more by the square of velocity than mass, the resulting collisional effects of which produce swarms of v-shaped percussion microfeatures on quartz and other silicate mineral surfaces when velocity and compression are highest. This work indicates that a valid test for the ocean hypothesis is targeting “coastal” areas adjacent to narrow embayments where offshore depths are known to be highest, as possible tsunami-emplaced sediments, especially those that have been protected from atmospheric conditions through relatively rapid burial, may reveal a high frequency of percussion cracks, features of which appear to be unique to such terrestrial environments.  相似文献   

Daily scale modelling of aquifer–river connectivity in the urban alluvial aquifer in Langreo, Spain     

Pedro Martínez-Santos  Pedro E. Martínez-Alfaro  Eugenio Sanz  Angel Galindo 《Hydrogeology Journal》2010,18(6):1525-1537

Evaluating aquifer–river interactions is naturally complex, particularly within urban settings. This is largely due to the difficulties involved in quantifying most elements of the water balance. The ability of numerical models to deal with several dynamic variables simultaneously makes them valuable tools to address this kind of problem. An applied, modeling-based approach to investigate the spatial and temporal variations of aquifer–river connectivity within a shallow urban aquifer is presented. Model development is based on comprehensive field campaigns in Langreo, Spain. Two calibration runs (for summer and winter conditions) were carried out in order to evaluate the spatial distribution of recharge rates. The model suggests that baseflows are largely negligible in comparison with total streamflows. This is mostly attributed to the abrupt nature of the catchment, which prevents the existence of sufficiently large alluvial systems to a great extent. Modelling results also show that aquifer–river connectivity at the study site is constrained by urban pumping as well as by seasonal fluctuations.  相似文献   

The Sierra Ballena Shear Zone in the southernmost Dom Feliciano Belt (Uruguay): evolution, kinematics, and deformation conditions     

Pedro Oyhantçabal  Siegfried Siegesmund  Klaus Wemmer  Paul Layer 《International Journal of Earth Sciences》2010,99(6):1227-1246

The Sierra Ballena Shear Zone (SBSZ) is part of a high-strain transcurrent system that divides the Neoproterozoic Dom Feliciano Belt of South America into two different domains. The basement on both sides of the SBSZ shows a deformation stage preceding that of the transcurrent deformation recognized as a high temperature mylonitic foliation associated with migmatization. Grain boundary migration and fluid-assisted grain boundary diffusion enhanced by partial melting were the main deformation mechanisms associated with this foliation. Age estimate of this episode is >658 Ma. The second stage corresponds to the start of transpressional deformation and the nucleation and development of the SBSZ. During this stage, pure shear dominates the deformation, and is characterized by the development of conjugate dextral and sinistral shear zones and the emplacement of syntectonic granites. This event dates to 658–600 Ma based on the age of these intrusions. The third stage was a second transpressional event at about 586 to <560 Ma that was associated with the emplacement of porphyry dikes and granites that show evidence of flattening. Deformation in the SBSZ took place, during the late stages, under regional low-grade conditions, as indicated by the metamorphic paragenesis in the supracrustals of the country rocks. Granitic mylonites show plastic deformation of quartz and brittle behavior of feldspar. A transition from magmatic to solid-state microstructures is also frequently observed in syntectonic granites. Mylonitic porphyries and quartz mylonites resulted from the deformation of alkaline porphyries and quartz veins emplaced in the shear zone. Quartz veins reflect the release of silica associated with the breakdown of feldspar to white mica during the evolution of the granitic mylonites to phyllonites, which resulted in shear zone weakening. Quartz microstructures characteristic of the transition between regime 2 and regime 3, grain boundary migration and incipient recrystallization in feldspar indicate deformation under lower amphibolite to upper greenschist conditions (550–400°C). On the other hand, the mylonitic porphyries display evidence of feldspar recrystallization suggesting magmatic or high-T solid-state deformation during cooling of the dikes.  相似文献   

A special perturbation method in orbital dynamics     

Jesús Peláez  José Manuel Hedo  Pedro Rodríguez de Andrés 《Celestial Mechanics and Dynamical Astronomy》2007,97(2):131-150

The special perturbation method considered in this paper combines simplicity of computer implementation, speed and precision, and can propagate the orbit of any material particle. The paper describes the evolution of some orbital elements based in Euler parameters, which are constants in the unperturbed problem, but which evolve in the time scale imposed by the perturbation. The variation of parameters technique is used to develop expressions for the derivatives of seven elements for the general case, which includes any type of perturbation. These basic differential equations are slightly modified by introducing one additional equation for the time, reaching a total order of eight. The method was developed in the Grupo de Dinámica de Tethers (GDT) of the UPM, as a tool for dynamic simulations of tethers. However, it can be used in any other field and with any kind of orbit and perturbation. It is free of singularities related to small inclination and/or eccentricity. The use of Euler parameters makes it robust. The perturbation forces are handled in a very simple way: the method requires their components in the orbital frame or in an inertial frame. A comparison with other schemes is performed in the paper to show the good performance of the method.  相似文献   

B‐bar based algorithm applied to meshfree numerical schemes to solve unconfined seepage problems through porous media          下载免费PDF全文

Pedro Navas  Susana Lpez‐Querol  Rena C. Yu  Bo Li 《国际地质力学数值与分析法杂志》2016,40(6):962-984

The object of this work is to establish a meshfree framework for solving coupled, steady and transient problems for unconfined seepage through porous media. The Biot's equations are formulated in displacements (or u − w) assuming an elastic solid skeleton. The free surface location and its evolution in time are obtained by interpolation of pore water pressures throughout the domain. Shape functions based on the principle of local maximum entropy are chosen for the meshfree approximation schemes. In order to avoid the locking involved in the fluid phase of the porous media, a B‐bar based algorithm is devised to compute the average volumetric strain in a patch composed of various integration points. The efficiency of such an implementation for one phase problems is shown through the Benchmark problem, Cook's membrane loaded by a distributive shear load. The proposed methodology is firstly applied to various classical examples in unconfined steady seepage problems through earth dams, then to the dynamic consolidation of a soil column. The results obtained for both problems are quite satisfactory and demonstrate the feasibility of the proposed method in solving coupled problems in porous media. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Using Argo data to investigate the Meridional Overturning Circulation in the North Atlantic     

Alonso Hernández-Guerra  Terrence M. Joyce  Eugenio Fraile-Nuez  Pedro Vélez-Belchí 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(1):29-36

Using a variety of oceanographic data, including direct volume transports in the Florida Strait, and Argo float profiles and drift velocities at 24°N and 36°N in the North Atlantic, inverse calculations are presented in which the net meridional transport, down to a depth of approximately 1600 m, is estimated at both latitudes for a 5-year period 2003–2007. The upper ocean is divided into seven layers using neutral density, and mass conservation constraints have been applied to a closed box bounded by these latitudes, including the Florida Strait. Ekman layer transports have been included in the top-most layer, and the inverse calculation has solved for changes from the initial reference velocities, Ekman and Florida Strait transports, given a priori estimates on the accuracy of each of these quantities. Solutions with and without transformations due to Mediterranean Water (MW) formation are made. Our results indicate that (1) time-averaged transport estimates derived from Argo have significant less eddy noise than individual hydrographic sections, (2) Argo drift velocities provide information to the inverse solution for the ocean interior, and (3) comparison of the total integrated interior mass transports in the thermocline waters for the period 2003–2007 with the previous estimates based on trans-ocean hydrographic sections shows that, within the errors of our estimation, the upper limb of the Atlantic Meridional Overturning Circulation has not significantly changed since 1957.  相似文献   

Hydrological and geomorphological criteria to evaluate the dispersion risk of waste sludge generated by the Aznalcollar mine spill (SW Spain)   总被引：2，自引：0，他引：2  

G. Benito  Alfonso Benito-Calvo  Francesc Gallart  Juan Pedro Martín-Vide  David Regües  Ernest Bladé 《Environmental Geology》2001,40(4-5):417-428

Following the Aznalcóllar pyrite mine disaster (Seville, Spain) which caused the spilling of some 4.5?hm³ of acid water, the floodplains of the rivers Agrio and Guadiamar were rapidly cleaned of waste sludge. However, despite the efficiency of cleaning activities, there is still evidence of a fine superficial layer of sludge and some soil contamination, with the consequent risk of remobilisation of the pollutants by water erosion. There is much concern that these contaminated sediments may affect the precious ecosystems of the Doñana National Park and the Guadalquivir marshlands. This report describes the evaluation of the risk of mobilisation of the waste sludge through (1) detailed geomorphological analysis, indicating potential areas of erosion-sedimentation on the floodplains of the rivers Agrio and Guadiamar, and predicted dynamics of the waste sludge, and (2) evaluation of the potential dispersion of the waste sludge provoked by future flood events, including hydraulic calculations to model channel flow and the analysis of the texture of the sludge to obtain critical transport and sedimentation values. Findings suggest that the waste sludge is likely to be transported and deposited within the Doñana National Park during future flood events.  相似文献   

用陆地卫星TM6数据演算地表温度的单窗算法   总被引：263，自引：3，他引：263  

覃志豪 《地理学报》2001,56(4):456-466

陆地卫星 TM数据 (TM6)热波段表示地表热辐射和地表温度变化。长期以来 ,从 TM6数据中演算地表温度通常是通过所谓大气校正法。这一方法需要估计大气热辐射和大气对地表热辐射传导的影响 ,计算过程很复杂 ,误差也较大 ,在实际中应用不多。根据地表热辐射传导方程 ,推导出一个简单易行并且精度较高的演算方法 ,把大气和地表的影响直接包括在演算公式中。该算法需要用地表辐射率、大气透射率和大气平均温度 3个参数进行地表温度的演算。验证表明 ,该方法的地表温度演算较高。当参数估计没有误差时 ,该方法的地表温度演算精度达到 <0 .4℃ ,在参数估计有适度误差时 ,演算精度仍达 <1 .1℃。因该方法适用于仅有一个热波段的遥感数据 ,故称为单窗算法。  相似文献   

Development of a Data Visualization and Analysis Tool to Study the Particle Dynamics in the Coastal Zone   总被引：1，自引：0，他引：1  

Dimitra Kitsiou  Xavier Durrieu de Madron  Pedro Antonio Arnau 《Marine pollution bulletin》2001,43(7-12):262-269

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