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111.
Sergio Caetano-Filho Pierre Sansjofre Magali Ader Gustavo M.Paula-Santos Cristian Guacaneme Marly Babinski Carolina Bedoya-Rueda Matheus Kuchenbecker Humberto L.S.Reis Ricardo I.F.Trindade 《地学前缘(英文版)》2021,12(1):203-218
Carbon isotope compositions of both sedimentary carbonate and organic matter can be used as key proxies of the global carbon cycle and of its evolution through time,as long as they are acquired from waters where the dissolved inorganic carbon(DIC)is in isotope equilibrium with the atmospheric CO2.However,in shallow water platforms and epeiric settings,the influence of local to regional parameters on carbon cycling may lead to DIG isotope variations unrelated to the global carbon cycle.This may be especially true for the terminal Neoproterozoic,when Gondwana assembly isolated waters masses from the global ocean,and extreme positive and negative carbon isotope excursions are recorded,potentially decoupled from global signals.To improve our understanding on the type of information recorded by these excursions,we investigate the pairedδ^13Ccarb andδ^13Corg evolution for an increasingly restricted late Ediacaran-Cambrian foreland system in the West Gondwana interior:the basal Bambui Group.This succession represents a 1~(st)-order sedimentary sequence and records two majorδ^13Ccarb excursions in its two lowermost lower-rank sequences.The basal cap carbonate interval at the base of the first sequence,deposited when the basin was connected to the ocean,hosts antithetical negative and positive excursions forδ^13Ccarb andδ^13Corg,respectively,resulting inΔ^13C values lower than 25‰.From the top of the basal sequence upwards,an extremely positiveδ^13Ccarb excursion is coupled toδ^13Corg,reaching values of+14‰and-14‰,respectively.This positive excursion represents a remarkable basin-wide carbon isotope feature of the Bambui Group that occurs with only minor changes inΔ^13C values,suggesting change in the DIC isotope composition.We argue that this regional isotopic excursion is related to a disconnection between the intrabasinal and the global carbon cycles.This extreme carbon isotope excursion may have been a product of a disequilibria between the basin DIC and atmospheric CO2 induced by an active methanogenesis,favored by the basin restriction.The drawdown of sulfate reservoir by microbial sulfate reduction in a poorly ventilated and dominantly anoxic basin would have triggered methanogenesis and ultimately methane escape to the atmosphere,resulting in a^13C-enriched DIC influenced by methanogenic CO2.Isolated basins in the interior of the Gondwana supercontinent may have represented a significant source of methane inputs to the atmosphere,potentially affecting both the global carbon cycle and the climate. 相似文献
112.
This study investigates how physical urban environments affect academic performance of urban public elementary schools in the Philippines by analysing the physical environment of school facilities and slum areas. Global, local, and semi-parametric regression analyses indicate that there is disproportionate provision of resources among the government schools and that lower academic performance is associated with the provision of fewer clinics rather than the proximity to poverty hotspots. Semiparametric, geographically weighted regression modelling outperformed global and local modelling, and estimated up to 30 % of the variation in math scores where the semi-parametric regression model is based on each school’s number of teachers and rooms, building conditions, availability of health clinics, and the location of slum areas near the school. On the basis of the research findings, it is concluded that the current state of school buildings is adequate and is a lower priority than the provision of health care support and smaller pupil–teacher ratios. Hence, government programs that aim to enhance the academic performance of children from the deprived physical urban environments should prioritize the provision of health clinics as well as maintaining few large schools with small pupil–teacher ratios. 相似文献
113.
de Azevedo Reis Gabriela de Souza Filho Francisco Assis Nelson Donald Robert Rocha Renan Vieira da Silva Samiria Maria Oliveira 《Natural Hazards》2020,104(2):1781-1799
Natural Hazards - Although climate change vulnerability research in general has increased over the last decade, Latin American countries have more directed more limited efforts toward vulnerability... 相似文献
114.
Sergio Caetano-Filho Pierre Sansjofre Magali Ader Gustavo M.Paula-Santos Cristian Guacaneme Marly Babinski Carolina Bedoya-Rueda Matheus Kuchenbecker Humberto L.S.Reis Ricardo I.F.Trindade 《地学前缘(英文版)》2021,12(1):203-218
Carbon isotope compositions of both sedimentary carbonate and organic matter can be used as key proxies of the global carbon cycle and of its evolution through ... 相似文献
115.
Periodic Orbits Around a Massive Straight Segment 总被引:1,自引:0,他引:1
Andrés Riaguas Antonio Elipe Martín Lara 《Celestial Mechanics and Dynamical Astronomy》1999,73(1-4):169-178
In this paper, we consider the motion of a particle under the gravitational field of a massive straight segment. This model
is used as an approximation to the gravitational field of irregular shaped bodies, such as asteroids, comet nuclei and planets's
moons. For this potential, we find several families of periodic orbits and bifurcations.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
116.
Martin Lara 《Celestial Mechanics and Dynamical Astronomy》2017,127(3):285-300
This study analyzes a recently discovered class of exterior transfers to the Moon. These transfers terminate in retrograde ballistic capture orbits, i.e., orbits with negative Keplerian energy and angular momentum with respect to the Moon. Yet, their Jacobi constant is relatively low, for which no forbidden regions exist, and the trajectories do not appear to mimic the dynamics of the invariant manifolds of the Lagrange points. This paper shows that these orbits shadow instead lunar collision orbits. We investigate the dynamics of singular, lunar collision orbits in the Earth–Moon planar circular restricted three-body problem, and reveal their rich phase space structure in the medium-energy regime, where invariant manifolds of the Lagrange point orbits break up. We show that lunar retrograde ballistic capture trajectories lie inside the tube structure of collision orbits. We also develop a method to compute medium-energy transfers by patching together orbits inside the collision tube and those whose apogees are located in the appropriate quadrant in the Sun–Earth system. The method yields the novel family of transfers as well as those ending in direct capture orbits, under particular energetic and geometrical conditions. 相似文献
117.
Lara Loughrey Dan Marshall Peter Jones Paul Millsteed Arthur Main 《Central European Journal of Geosciences》2012,4(2):287-299
The Emmaville-Torrington emeralds were first discovered in 1890 in quartz veins hosted within a Permian metasedimentary sequence, consisting of meta-siltstones, slates and quartzites intruded by pegmatite and aplite veins from the Moule Granite. The emerald deposit genesis is consistent with a typical granite-related emerald vein system. Emeralds from these veins display colour zonation alternating between emerald and clear beryl. Two fluid inclusion types are identified: three-phase (brine+vapour+halite) and two-phase (vapour+liquid) fluid inclusions. Fluid inclusion studies indicate the emeralds were precipitated from saline fluids ranging from approximately 33 mass percent NaCl equivalent. Formational pressures and temperatures of 350 to 400 °C and approximately 150 to 250 bars were derived from fluid inclusion and petrographic studies that also indicate emerald and beryl precipitation respectively from the liquid and vapour portions of a two-phase (boiling) system. The distinct colour zonations observed in the emerald from these deposits is the first recorded emerald locality which shows evidence of colour variation as a function of boiling. The primary three-phase and primary two-phase FITs are consistent with alternating chromium-rich ??striped?? colour banding. Alternating emerald zones with colourless beryl are due to chromium and vanadium partitioning in the liquid portion of the boiling system. The chemical variations observed at Emmaville-Torrington are similar to other colour zoned emeralds from other localities worldwide likely precipitated from a boiling system as well. 相似文献
118.
M. Povi A.M. Prez García M. Snchez‐Portal A. Bongiovanni J. Cepa M. Fernndez Lorenzo M.A. Lara‐Lpez J. Gallego A. Ederoclite I. Mrquez J. Masegosa E. Alfaro H. Castaeda J.I. Gonzlez‐Serrano J.J. Gonzlez 《Astronomische Nachrichten》2013,334(3):288-299
Luminosity functions are one of the most important observational clues when studying galaxy evolution over cosmic time. In this paper we present the X‐ray luminosity functions for X‐ray detected AGN in the SXDS and GWS fields. The limiting fluxes of our samples are 9.0 ×10–15 and 4.8 ×10–16 erg cm–2 s–1 in the 0.5–7.0 keV band in the two fields, respectively. We carried out analysis in three X‐ray bands and in two redshift intervals up to z ≤ 1.4. Moreover, we derive the luminosity functions for different optical morphologies and X‐ray types. We confirm strong luminosity evolution in all three bands, finding the most luminous objects at higher redshift. However, no signs of density evolution are found in any tested X‐ray band. We obtain similar results for compact and early‐type objects. Finally, we observe the “Steffen effect”, where X‐ray type‐1 sources are more numerous at higher luminosities in comparison with type‐2 sources. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
119.
Cleiton Da Silva Silveira Francisco Das Chagas Vasconcelos Junior Francisco De Assis De Souza Filho Sullyandro Oliveira Guimarães Antonio Duarte Marcos Junior Giullian Nicola Lima Dos Reis 《水文科学杂志》2013,58(11):1279-1296
ABSTRACTRepresentations of precipitation from CMIP5 models over the 1950–1999 period in hydrographic basins that are relevant to the Brazilian electricity sector are evaluated in this study. The majority of ensemble members adequately represented seasonal variability, although they differed about the patterns of high-frequency interannual variation. The models did not adequately represent seasonal-scale precipitation in the southern region of Brazil. Relative to other models, the CNRM_CM5 and HadGEM2-ES models demonstrated good seasonal and interannual representation over most basins, while the global CanESM2, GFDL-ESM2M and IPSL_CM5A-LR models demonstrated relatively poor performance. The models concur on the impact of the RCP8.5 scenario in the Southeast/Midwest and South sectors over the period 2015–2044, suggesting that precipitation will decrease up to 15% in the basin supplying the Furnas hydropower plant and by 12% in the basin supplying the Itaipú plant, which represents 25% of the hydroelectric production in Brazil. 相似文献
120.
ABSTRACTIn this paper, we explore for the first time the interactions of the net downward, time-dependent, γ-pumping overlying an imposed layer of magnetic fluid, in a polytropic atmosphere. Our calculations show that an equipartition of energy, between the magnetic and kinetic components, must be reached for buoyancy-driven magnetic structures to rise into the pumping region. However, structures do not rise unhindered, as in a previous investigation. We show that the evolution and other features of the emerging magnetic flux structures are significantly affected by the temporal variation of the γ-pumping. The rate of emerging structures, the strength of magnetic concentrations and the extent to how far magnetic field can travel were all found to depend on the timescale of the γ-pumping. 相似文献