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Franco JL Posser T Mattos JJ Sánchez-Chardi A Trevisan R Oliveira CS Carvalho PS Leal RB Marques MR Bainy AC Dafre AL 《Marine environmental research》2008,66(1):88-89
The aim of this study was to investigate biochemical changes in juvenile carp (Cyprinus carpio) exposed to zinc chloride (10, 30 and 100 microM) for a period of 48 h. Zinc exposure caused a concentration-dependent reduction in glutathione reductase (GR) activity in gills, liver and brain. Gill glutathione S-transferase (GST) was reduced when animals were exposed to the highest concentration of 100 microM zinc. The phosphorylation of p38(MAPK) increased in the brain of fish exposed to zinc 100 microM, while phosphorylation of the extracellular signal-regulated protein kinase 1/2 (ERK1/2) and c-Jun N-terminal protein kinase 1/2 (JNK1/2) remained unchanged. Expression of proteins HSP60 and HSP70 were not affected by zinc exposure. Considering the significant concentration-dependent inhibition of GR in all tissues analyzed, this enzyme could be a potential biomarker of exposure to zinc, which has to be confirmed. 相似文献
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A simple technique for studying near-bed hydrodynamics and sediment dynamics is presented. The method combines the use of (1) a benthic tripod hosting a series of electromagnetic current meters, and (2) a newly developed near-bed multi-level water-sediment mixture sampler. The instrument package was deployed successfully at a shallow water station in the eastern English Channel. The currents at elevation 0.9 m above the bottom were asymmetrical, the flood current peak being slightly stronger than the ebb current peak. At elevation 0.3 m above the bottom, the ebb/flood current peak asymmetry vanished. The observed SSCs (suspended sediment concentrations) were tidally modulated, with a contrasting vertical distribution over the ebb and flood phases of the tidal current: the profile was uniform in the ebb phase whereas a stratification appeared in the flood phase. The depth dependence and time evolution of the SSCs are attributable to a combination of local resuspension and advection-dispersion of remotely suspended fine sediment by ebb currents. Suspended sediment fluxes were uniform during the ebb phase and increased with elevation above the bottom during the flood phase. 相似文献
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S. Turck-Chi??ze G. Loisel D. Gilles L. Piau C. Blancard T. Blenski M. Busquet T. Caillaud P. Coss?? F. Delahaye G. Faussurier J. Fariaut F. Gilleron J. A. Guzik J. Harris D. P. Kilcrease N. H. Magee J. C. Pain Q. Porcherot M. Poirier G. Soullier C. J. Zeippen S. Bastiani-Ceccotti C. Reverdin V. Silvert F. Thais B. Villette 《Astrophysics and Space Science》2011,336(1):103-109
The lifetime of solar-like stars, the envelope structure of more massive stars, and stellar acoustic frequencies largely depend on the radiative properties of the stellar plasma. Up to now, these complex quantities have been estimated only theoretically. The development of the powerful tools of helio- and astero- seismology has made it possible to gain insights on the interiors of stars. Consequently, increased emphasis is now placed on knowledge of the monochromatic opacity coefficients. Here we review how these radiative properties play a role, and where they are most important. We then concentrate specifically on the envelopes of ?? Cephei variable stars. We discuss the dispersion of eight different theoretical estimates of the monochromatic opacity spectrum and the challenges we need to face to check these calculations experimentally. 相似文献
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Spectroscopic observations of Asteroid (4) Vesta and numerous members of the Vesta family located in the inner asteroid belt have determined that these objects have reflectance properties of basaltic material. A plausible hypothesis is that the surface of Vesta was punctured by large impacts in the past which dispersed fragments of its basaltic crust into space and produced one of the most prominent asteroid families ever created in the belt. Until recently, Vesta was the only known object in the asteroid belt which underwent differentiation and survived to the present epoch. Since 2000, many new small basaltic asteroids have been discovered in the inner and outer parts of the asteroid belt, possibly representing fragments from distinct differentiated bodies. These discoveries may help us to better understand the number and nature of objects in the inner Solar System that underwent geological differentiation. To investigate these issues we performed extensive numerical simulations whose aim was to reproduce, as precisely as possible, the dynamical evolution of Vesta's ejected fragments over timescales comparable to the family's age. Specifically, we numerically integrated the orbital evolution of 6600 test bodies with orbits that started within the Vesta family and dynamically evolved over 2 Gy. Our model included gravitational perturbation of all planets (except Mercury) and the Yarkovsky effect. The results show that a relatively large fraction of the original Vesta family members may have evolved out of the family borders defined by clustering algorithms and are now dispersed over the inner asteroid belt. We compared the orbital distribution of our model fragments with the orbital locations of known basaltic asteroids in various parts of the inner main belt to find that: (i) Most basaltic asteroids with semimajor axis located outside the Vesta family's borders in the inner main belt, including (809) Lundia and (956) Elisa, are most likely fugitives from the Vesta family that have evolved to their current orbits via various identified dynamical pathways. Our results also suggest that the Vesta family is at least ∼1 Gy old. (ii) Interestingly, orbits of many basaltic asteroids with , like those of (4796) Lewis and (5379) Abehiroshi, are displaced from the Vesta family to low inclinations and are not obtained in our simulations with sufficient efficiency. We propose that: (i) these small basaltic asteroids may be fragments of differentiated bodies other than (4) Vesta; or (ii) they were liberated from the Vesta's surface before (or during) the Late Heavy Bombardment epoch ∼3.8 Gy ago and their orbital inclinations separated from that of Vesta when secular resonances swept through the region. 相似文献
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Niquito Thais Waideman Pozzobon Fernando Halmenschlager Vinícius Ribeiro Felipe Garcia 《Natural Hazards》2021,109(3):2313-2341
Natural Hazards - This article analyzes the short-term economic impacts of the collapse of the ‘Fundão’ mining tailings dam, located in the Brazilian state of Minas Gerais. This... 相似文献
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Victor Hugo Dominato Dimila Mothé Rafael Costa da Silva Leonardo dos Santos Avilla 《Journal of South American Earth Sciences》2011,31(2-3):171-177
This study reports implications of different tooth marks left by carnivorous mammals on long bones of Haplomastodon waringi from the Quaternary of Águas de Araxá, Minas Gerais, Brazil. Analyses of gnawing damage by ursids, felids, and canids have shown that these groups produce pits on bone surfaces when the gnawing is superficial, and punctures more often when the prey is intensely consumed. Scratches or scoring marks are most often associated with gnawing by canids, which may spend a long time gnawing the bones, leading to differential tooth marking. The gomphothere bones at Águas de Araxá did not result from predation, but are a consequence of a local mass mortality in a period of low environmental humidity, with little water and a scarcity of food. Canids frequently act as opportunistic scavengers during periods when herbivores face food shortages. Previous studies of necrophagous dermestid larvae indicate that the gomphothere carcasses of Águas de Araxá were exposed for a long period of time after death. These insects are the last consumers of a carcass because they act only when the body fat is completely lost. Thus, the gomphothere carcasses at Águas de Araxá suffered canid necrophagy in the early stages of decomposition, possibly during a drought period. Thereafter, the gomphothere carcasses would have been exposed for a period about 230 days until the final burial event. 相似文献
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Paul S. HARDERSEN Edward A. CLOUTIS Vishnu REDDY Thais MOTHÉ‐DINIZ Joshua P. EMERY 《Meteoritics & planetary science》2011,46(12):1910-1938
Abstract– Diagnostic mineral absorption features for pyroxene(s), olivine, phyllosilicates, and hydroxides have been detected in the near‐infrared (NIR: approximately 0.75–2.50 μm) spectra for 60% of the Tholen‐classified ( Tholen 1984, 1989 ) M‐/X‐asteroids observed in this study. Nineteen asteroids (42%) exhibit weak Band I (approximately 0.9 μm) ± Band II (approximately 1.9 μm) absorptions, three asteroids (7%) exhibit a weak Band I (approximately 1.05–1.08 μm) olivine absorption, four asteroids (9%) display multiple absorptions suggesting phyllosilicate ± oxide/hydroxide minerals, one (1) asteroid exhibits an S‐asteroid type NIR spectrum, and 18 asteroids (40%) are spectrally featureless in the NIR, but have widely varying slopes. Tholen M‐asteroids are defined as asteroids exhibiting featureless visible‐wavelength (λ) spectra with moderate albedos ( Tholen 1989 ). Tholen X‐asteroids are also defined using the same spectral criterion, but without albedo information. Previous work has suggested spectral and mineralogical diversity in the M‐asteroid population ( Rivkin et al. 1995, 2000 ; Busarev 2002 ; Clark et al. 2004 ; Hardersen et al. 2005 ; Birlan et al. 2007 ; Ockert‐Bell et al. 2008, 2010 ; Shepard et al. 2008, 2010 ; Fornasier et al. 2010 ). The pyroxene‐bearing asteroids are dominated by orthopyroxene with several likely to include higher‐Ca clinopyroxene components. Potential meteorite analogs include mesosiderites, CB/CH chondrites, and silicate‐bearing NiFe meteorites. The Eos family, olivine‐bearing asteroids are most consistent with a CO chondrite analog. The aqueously altered asteroids display multiple, weak absorptions (0.85, 0.92, 0.97, 1.10, 1.40, and 2.30–2.50 μm) indicative of phyllosilicate ± hydroxide minerals. The spectrally featureless asteroids range from metal‐rich to metal‐poor with meteorite analogs including NiFe meteorites, enstatite chondrites, and stony‐iron meteorites. 相似文献
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Vishnu Reddy Jorge M. Carvano Daniela Lazzaro Tatiana A. Michtchenko Michael J. Gaffey Michael S. Kelley Thais Mothé-Diniz Alvaro Alvarez-Candal Nicholas A. Moskovitz Edward A. Cloutis Erin L. Ryan 《Icarus》2011,216(1):184-197
Bottke et al. [Bottke, W.F., Vokrouhlicky, D., Nesvorný, D., 2007. Nature 449, 48–53] linked the catastrophic formation of Baptistina Asteroid Family (BAF) to the K/T impact event. This linkage was based on dynamical and compositional evidence, which suggested the impactor had a composition similar to CM2 carbonaceous chondrites. However, our recent study [Reddy, V., Emery, J.P., Gaffey, M.J., Bottke, W.F., Cramer, A., Kelley, M.S., 2009. Meteorit. Planet. Sci. 44, 1917–1927] suggests that the composition of (298) Baptistina is similar to LL-type ordinary chondrites rather than CM2 carbonaceous chondrites. This rules out any possibility of it being related to the source of the K/T impactor, if the impactor was of CM-type composition. Mineralogical study of asteroids in the vicinity of BAF has revealed a plethora of compositional types suggesting a complex formation and evolution environment. A detailed compositional analysis of 16 asteroids suggests several distinct surface assemblages including ordinary chondrites (Gaffey SIV subtype), primitive achondrites (Gaffey SIII subtype), basaltic achondrites (Gaffey SVII subtype and V-type), and a carbonaceous chondrite. Based on our mineralogical analysis we conclude that (298) Baptistina is similar to ordinary chondrites (LL-type) based on olivine and pyroxene mineralogy and moderate albedo. S-type and V-type in and around the vicinity of BAF we characterized show mineralogical affinity to (8) Flora and (4) Vesta and could be part of their families. Smaller BAF asteroids with lower SNR spectra showing only a ‘single’ band are compositionally similar to (298) Baptistina and L/LL chondrites. It is unclear at this point why the silicate absorption bands in spectra of asteroids with formal family definition seem suppressed relative to background population, despite having similar mineralogy. 相似文献
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