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291.
We examined the diet of juvenile fish of four species – Eucinostomus melanopterus (Gerreidae), Ethmalosa fimbriata (Clupeidae), Monodactylus sebae (Monodactylidae), and Sarotherodon melanotheron (Cichlidae) – between their appearance on the nursery ground and the end of the recruitment season, when they began to shift to deeper parts of the estuary. Fish were collected from the Sine-Saloum, an inverse estuary in Senegal, West Africa. Sampling was conducted at six sites located along the salinity gradient. The study was conducted in the context of an inverse estuary where increasing salinity leads to the disappearance of mangroves. 相似文献
292.
Io: Thermal models and chemical evolution 总被引:1,自引:0,他引:1
Guy J. Consolmagno 《Icarus》1981,47(1):36-45
A combined thermal and chemical evolution model of Io is presented, outlining limits on the possible starting materials, heating history, chemical history, and present state of Io. Our best scenario starts with Io being accreted from material in a proto-Jovian nebula which condensed between 400–600°K. Radionuclides and tidal heating would lead to large-scale convection within Io and chemical reactions leading to the outgassing of water and methane. Reactions between Fe0FeS and water, at least near the surface, go to completion, resulting in all Fe being oxidized with elemental sulfur producing a low-conductivity crust. In the deep interior, these reactions may not completely exhaust Fe metal, and an FeS-rich core may be formed. 相似文献
293.
造山型金矿是全球重要的金矿类型。造山型金矿包含三种类型:产于绿岩带的含金石英碳酸盐脉、产于浊积岩中的含金石英脉和产于条带状铁矿(BIF)中的含金石英脉。造山型金矿的形成受板块构造控制,处于压缩或者转换挤压的造山构造环境。造山型金矿中的绿岩带金矿主要受剪切带、转换断层控制,浊积岩型金矿受褶皱和层间走滑断层控制,而赋存于BIF中的金矿则受剪切带和断层所控制。在这些金矿床中发现了4类流体包裹体:H_2O-CO_2型、富CO_2型、气液包裹体和含Na Cl子矿物的包裹体。所有年代的造山型金矿成矿流体的成分均为低盐度的水溶液和富CO_2的流体,温度在200~400℃范围内。稳定同位素研究表明造山型金矿的成矿流体源自变质流体和岩浆流体。金在成矿流体中的络合物应为Au HS~-或Au H_2S。虽然成矿流体中有丰富的CO_2,但Au在CO_2流体中的溶解度很低,有丰富的CO_2时Au在H_2S中的溶解度增大。流体包裹体研究表明,Au的成矿流体是Na Cl-H_2O-CO_2体系的流体,并在成矿过程中发生了相分离,即Na Cl-H_2O-CO_2流体分成两个流体:H_2O-Na Cl和CO_2-H_2O,Au的沉淀是在这种相分离过程中发生的。 相似文献
294.
Morad Lakhssassi Bernard Guy Eric Touboul Jean-Yves Cottin 《Comptes Rendus Geoscience》2010,342(9):701-709
Our aim is to explain the possible bimodality of the compositions of the magmatic rocks of the same province. In order to do so, we present a model for the crystallization of a magmatic chamber, coupling the three phenomena: solidification, sedimentation, chemical reactions between the solid and the liquid. These three phenomena make two independent dimensionless parameters appear: the ratios of the solidification rate to the transport velocity, and of the chemical kinetics to the transport velocity. The model is written for one independent chemical component. It is shown that, for certain values of the dimensionless parameters, the chemical composition of the chamber can present a bimodal distribution, starting from uniform initial conditions. This model shows that the coupling between three elementary phenomena is enough to explain the bimodality, or more generally the appearance of discontinuities of chemical compositions, without making any additional assumption. 相似文献
295.
Laurent?TestutEmail author Guy?W?ppelmann Bernard?Simon Philippe?Téchiné 《Ocean Dynamics》2006,56(5-6):464-472
Relative sea level rise at Kerguelen Island over the last 55 years has been investigated using a combination of historical and recent tide gauge data. The best estimate of relative sea level trend from data sets spanning 38 years is estimated to be 1.1±0.7 mm year?1. We have tried to quantify the error budget due to some of the possible sources of uncertainty. As expected, the main source of uncertainty comes from oceanic interannual variability, preventing an accurate estimate of sea level trend over short record lengths. However, our values are reasonably consistent with other reported southern hemisphere sea level trends for similar time periods. 相似文献
296.
James C. A. Miller-Jones Michael P. Rupen Marc Türler Elina J. Lindfors Katherine M. Blundell Guy G. Pooley 《Monthly notices of the Royal Astronomical Society》2009,394(1):309-322
We present simultaneous dual-frequency radio observations of Cygnus X-3 during a phase of low-level activity. We constrain the minimum variability time-scale to be 20 min at 43 GHz and 30 min at 15 GHz, implying source sizes of 2–4 au. We detect polarized emission at a level of a few per cent at 43 GHz which varies with the total intensity. The delay of ∼10 min between the peaks of the flares at the two frequencies is seen to decrease with time, and we find that synchrotron self-absorption and free–free absorption by entrained thermal material play a larger role in determining the opacity than absorption in the stellar wind of the companion. A shock-in-jet model gives a good fit to the light curves at all frequencies, demonstrating that this mechanism, which has previously been used to explain the brighter, longer lived giant outbursts in this source, is also applicable to these low-level flaring events. Assembling the data from outbursts spanning over two orders of magnitude in flux density shows evidence for a strong correlation between the peak brightness of an event, and the time-scale and frequency at which this is attained. Brighter flares evolve on longer time-scales and peak at lower frequencies. Analysis of the fitted model parameters suggests that brighter outbursts are due to shocks forming further downstream in the jet, with an increased electron normalization and magnetic field strength both playing a role in setting the strength of the outburst. 相似文献
297.
M. Ollivier O. Absil F. Allard J.-P. Berger P. Bordé F. Cassaing B. Chazelas A. Chelli O. Chesneau V. Coudé du Foresto D. Defrère P. Duchon P. Gabor J. Gay E. Herwats S. Jacquinod P. Kern P. Kervella J.-M. Le Duigou A. Léger B. Lopez F. Malbet D. Mourard D. Pelat G. Perrin Y. Rabbia D. Rouan J.-M. Reiss G. Rousset F. Selsis P. Stee J. Surdej 《Experimental Astronomy》2009,23(1):403-434
PEGASE is a mission dedicated to the exploration of the environment (including habitable zone) of young and solar-type stars
(particularly those in the DARWIN catalogue) and the observation of low mass companions around nearby stars. It is a space
interferometer project composed of three free flying spacecraft, respectively featuring two 40 cm siderostats and a beam combiner
working in the visible and near infrared. It has been proposed to ESA as an answer to the first “Cosmic Vision” call for proposals,
as an M mission. The concept also enables full-scale demonstration of space nulling interferometry operation for DARWIN.
相似文献
M. OllivierEmail: |
298.
Guy R. Holdgate Brian McGowran Tom Fromhold Barbara E. Wagstaff Stephen J. Gallagher Malcolm W. Wallace Ian R.K. Sluiter Michael Whitelaw 《Global and Planetary Change》2009,65(1-2):89-103
The carbon-isotope and palynological record through 580 m thick almost continuous brown coal in southeast Australia's Gippsland Basin is a relatively comprehensive southern hemisphere Middle Eocene to Middle Miocene record for terrestrial change. The carbon isotope δ13Ccoal values of these coals range from ? 27.7‰ to ? 23.2. This isotopic variability follows gymnosperm/angiosperm fluctuations, where higher ratios coincide with heavier δ13C values. There is also long-term variability in carbon isotopes through time. From the Eocene greenhouse world of high gymnosperm-heavier δ13Ccoal values, there is a progressive shift to lighter δ13Ccoal values that follows the earliest (Oi1?) glacial events around 33 Ma (Early Oligocene). The overlying Oligocene–Early Miocene brown coals have lower gymnosperm abundance, associated with increased %Nothofagus (angiosperm), and lightening of isotopes during Oligocene cooler conditions.The Miocene palynological and carbon-isotope record supports a continuation to the Oligocene trends until around the late Early Miocene (circa 19 Ma) when a warming commenced, followed by an even stronger isotope shift around 16 Ma that peaked in the Middle Miocene when higher gymnosperm abundance and heavier isotopes prevailed. The cycle between the two major warm peaks of Middle Eocene and Middle Miocene was circa 30 Ma long. This change corresponds to a fall in inferred pCO2 levels for the same period. The Gippsland data suggest a link between gymnosperm abundance, long-term plant δ13C composition, climatic change, and atmospheric pCO2. Climatic deterioration in the Late Miocene terminated peat accumulation in the Gippsland Basin and no further significant coals formed in southeast Australia.The poor correspondence between this terrestrial isotope data and the marine isotope record is explained by the dominant control on δ13C by the gymnosperm/angiosperm abundance, although in turn this poor correspondence may reflect palaeoclimate control. From the brown coal seam dating, the coal appears to have accumulated during a considerable part of the allocated 30 Ma Cenozoic time period. These brown coal carbon isotope and palynological data appear to record a more gradual atmospheric carbon isotope change compared to the marine record. 相似文献
299.
Guy J. Monnet 《Experimental Astronomy》2009,25(1-3):91-106
Spectroscopic astronomical instrumentation has much evolved in the last 40 years. Long-slit grating spectrographs with a photographic plate as the detector working in the 0.3–1 μm range were prevalent up to the early 1970s. The replacement of photographic plates by two-dimensional digital detectors provided gains in sensitivity of two orders of magnitude and much better photometric and radial velocity precision, and opened the 1 to 25 μm infrared domain. Another gain in speed by up to two orders of magnitude was then obtained through the development of various spectroscopic systems, each optimized for a subset of astronomical objects. This development was underpinned by a number of technological advances, in particular the development of automatic data reduction pipelines using sophisticated algorithms. With ever larger and more complex instrument systems for the present 8–10 m diameter telescopes—and soon even more for the next generation of Extremely Large Telescopes, the development of an instrument is now a big enterprise, ranging all the way from long-term enabling technology efforts to management of large teams for construction and deployment over typically 7–8 years. 相似文献
300.
Michael E. Barber Akram Hossain John J. Covert Guy J. Gregory 《Hydrogeology Journal》2009,17(6):1459-1470
Conjunctive management of surface water and groundwater requires sophisticated spatial and temporal analysis. In situations involving multiple jurisdictions such as state boundaries, management problems are magnified due to often conflicting regulations and policies. A transient MODFLOW model of the Spokane Valley-Rathdrum Prairie (SVRP) aquifer/river system mutually accepted by both the states of Idaho and Washington, USA, was used to evaluate regional solutions to potential water shortages through the use of strategically placed infiltration basins or injection wells. Artificial recharge of the SVRP aquifer was simulated using diversions from Lake Pend Oreille during winter periods when flows are high and excess water is available. Alternative locations for potential wells and detention basins were examined. Lag times for the water to impact stream/groundwater interaction areas along the Spokane River were evaluated to assess the potential for augmenting stream flows from July through September. Results indicated that the aquifer could be used to improve low-flow season streamflow values utilizing both infiltration basins and injection wells with winter surface water diversions. Depending on the location, as much as 30% of the winter diversion rate could be lagged to improve summer flows at the Spokane gage. Thus, a regional mitigation strategy is scientifically feasible. 相似文献