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871.
Paolo Farinella Andrea Milani Anna M. Nobili Giovanni B. Valsecchi 《Earth, Moon, and Planets》1979,20(4):415-421
We analyze the system formed by Pluto and its satellite Charon from the point of view of the theory of tidal evolution. The singular feature of the system, i.e. the configuration of complete synchronism which has been suggested by the available data, is found to represent the stable end-product of the evolution. The time needed for the synchronization is shown to be less than the age of the solar system, provided that Pluto's tidal dissipation function is smaller than 104–105. Moreover, the initial orbital radius of the system could not be largerthan two or three times the present radius, so that Charon has been always a close satellite.Finally, we discuss Lyttleton's hypothesis that Pluto is an escaped satellite of Neptune, suggesting that a possible mechanism of Pluto's ejection could be connected with a retrograde capture of Triton by Neptune or with the subsequent tidal evolution of Triton's orbit. 相似文献
872.
Magdalena Falco Andrea F. Carril Laurent Z. X. Li Carlos Cabrelli Claudio G. Menndez 《Climate Dynamics》2020,54(3):1553-1569
This paper aims to identify those regions within the South American continent where the Regional Climate Models (RCMs) have the potential to add value (PAV) compared to their coarser-resolution global forcing. For this, we used a spatial-scale filtering method based on the wavelet theory to distinguish the regional climatic signal present in atmospheric surface fields from observed data (CPC and TRMM) and 6 RCM simulations belonging to the CORDEX Project. The wavelet used for filtering was Haar wavelet, but a comparative analysis with Daubechies 4 wavelet indicated that meteorological fields or regional indices were not very sensitive to the wavelet selected. Once the longer wavelengths were filtered, we focused on analyzing the spatial variability of extreme rainfall and the spatiotemporal variability of maximum and minimum surface air temperature on a daily basis. The results obtained suggest essential differences in the spatial distribution of the small-scale signal of extreme precipitation between TRMM and regional models, together with a large dispersion between models. While TRMM and CPC register a large signal throughout the continent, the RCMs place it over the Andes Cordillera and some over tropical South America. PAV signal for surface air temperature was found over the Andes Cordillera and the Brazilian Highlands, which are regions characterized by complex topography, and also on the coasts of the continent. The signal came specially from the small-scale stationary component. The transient part is much smaller than the stationary one, except over la Plata Basin where they are of the same order of magnitude. Also, the RCMs and CPC showed a large spread between them in representing this transient variability. The results confirm that RCMs have the potential to add value in the representation of extreme precipitation and the mean surface temperature in South America. However, this condition is not applicable throughout the whole continent but is particularly relevant in those terrestrial regions where the surface forcing is strong, such as the Andes Cordillera or the coasts of the continent. 相似文献
873.
Andrea Koschinsky Marc Van Gerven Peter Halbach 《Marine Georesources & Geotechnology》2013,31(4):375-391
Ferromanganese crusts comparable with central Pacific occurrences with respect to thickness and extension have been discovered at the Tropic Seamount in the subtropical NE Atlantic. A comparison with typical hydrogenetic crusts from a central Pacific seamount revealed lower concentration of the Mn phase with Mn, Co, Ni, Zn, and Cu but a strongly increased terrigenous input of Fe, Pb, Al, and Si in the Atlantic crusts. Growth rates are increased compared with the Pacific crusts, and crust ages average at 10 My. The old phosphatized crust generation that started to grow about 20 My ago on the Pacific seamounts is not pronounced at the Tropic Seamount. The typical hydrographic and morphological parameters for hyrogenetic crust growth have also been found at the Tropic Seamount, which implies that the Tropic Seamount crusts have developed according to the hydrogenetic growth model. There are no indications of hydrothermal influence. 相似文献
874.
Remote sensing techniques using Landsat ETM+ applied to the detection of iron ore deposits in Western Africa 总被引:1,自引:0,他引:1
Andrea Ciampalini Francesca Garfagnoli Benedetta Antonielli Sandro Moretti Gaia Righini 《Arabian Journal of Geosciences》2013,6(11):4529-4546
Remote sensing methods enable the rapid and inexpensive mapping of surface geological and mineralogical features. This capability proves highly useful when working on isolated or inaccessible areas. In this study, several enhancements of Landsat Enhanced Thematic Mapper plus (i.e. band ratios, false colour composites and principal component analysis) were used and evaluated to obtain the best possible visualisation of iron deposits hosted in the Devonian sedimentary rocks of northwestern Africa. In particular, two test sites were chosen: southern Algeria (Djebilet area), where the literature mineralogical and geological data on iron mine fields were already available, and the Western Sahara (the southern flank of Tindouf Basin), which was investigated during a field campaign and was where the occurrence of an analogous sedimentary succession led us to hypothesise the possible presence of exploitable iron deposits. This work demonstrates the usefulness of multispectral imagery in the detection of iron-rich areas and establishes a full remote sensing procedure, which can be profitably applied to a wider region of Western Sahara and can provide interesting perspectives on the possibility of detecting new exploitable iron ore deposits in arid environments. 相似文献
875.
Jesse L. Morris Andrea Brunelle R. Justin DeRose Heikki Seppä Mitchell J. Power Vachel Carter Ryan Bares 《Quaternary Research》2013,79(1):24-36
Paleoenvironmental reconstructions are important for understanding the influence of long-term climate variability on ecosystems and landscape disturbance dynamics. In this paper we explore the linkages among past climate, vegetation, and fire regimes using a high-resolution pollen and charcoal reconstruction from Morris Pond located on the Markagunt Plateau in southwestern Utah, USA. A regime shift detection algorithm was applied to background charcoal accumulation to define where statistically significant shifts in fire regimes occurred. The early Holocene was characterized by greater amounts of summer precipitation and less winter precipitation than modern. Ample forest fuel and warm summer temperatures allowed for large fires to occur. The middle Holocene was a transitional period between vegetation conditions and fire disturbance. The late Holocene climate is characterized as cool and wet reflecting an increase in snow cover, which reduced opportunities for fire despite increased availability of fuels. Similarities between modern forest fuel availability and those of the early Holocene suggest that warmer summers projected for the 21st century may yield substantial increases in the recurrence and ecological impacts of fire when compared to the fire regime of the last millennium. 相似文献
876.
Marion A. Stevens-Kalceff 《Mineralogy and Petrology》2013,107(3):455-469
Cathodoluminescence (CL) techniques are used to investigate the defect structures of pure synthetic silicon dioxide (SiO2) polymorphs. Pure, synthetic Types I, II, III and IV amorphous SiO2 polymorphs, pure, synthetic crystal α-SiO2 and pure, synthetic amorphized crystal α-SiO2 have been investigated and their characteristic defects have been determined and compared. The CL emission from pure SiO2 polymorphs is generally related to local point defects in the tetrahedrally coordinated SiO2 host lattice. A range of CL emissions associated with non bridging oxygen defects, oxygen deficient defects and the radiative recombination of self trapped excitons are observed from both the pure synthetic crystal and amorphous SiO2 polymorphs. In addition CL emissions associated with residual concentrations of Aluminium impurities are also observed from α-SiO2 (quartz) and Type I and II a-SiO2 (fused quartz). Localised amorphous micro-volumes may exist within natural α-SiO2 due to the presence of a high concentration of pre-existing or induced defects. Amorphization of α-SiO2 diminishes the difference between the defect structures and associated CL from α-SiO2 and a-SiO2. Thus CL investigation of the defect structure of a-SiO2 polymorphs provides useful insight into the microstructure of amorphized α-SiO2. 相似文献
877.
Andrea Zanchi 《Geodinamica Acta》2013,26(3):187-201
AbstractComplex fault assemblages associated to liquefaction structures have been analyzed in a Pliocene basin located along the Gulf of California. The studied outcrop shows a fossil fault plane formed ill soft flat lying sediments. The liquefaction and fluidification structures have been recognized in voleaniclastic layers deposited ill a lagoonal environment and are potentially related to seismic wave shaking and to successive dewatering along fractures. This strati-graphic record is explained by the progressive development of a seismic fault zone, related to the transtensional regime still active in the Gulf. The present analysis can he considered as an useful case study for the reconnaissance of the different types of structures formed during synsedimentary deformation in hydroplastic conditions. 相似文献
878.
Marco Belan Sergio de Ponte Daniela Tordella Silvano Massaglia Andrea Mignone Eberhard Bodenschatz Attilio Ferrari 《Astrophysics and Space Science》2011,336(1):9-14
Stars form in regions of the galaxy that are denser and cooler than the mean interstellar medium. These regions are called
Giant Molecular Clouds. At the beginning of their life, up to 105–106 years, stars accrete matter from their rich surrounding environment and are origin of a peculiar phenomenon that is the jet
emission. Jets from Young Stellar Objects (YSOs) are intensively studied by the astrophysical community by observations at
different wavelengths, analytical and numerical modeling and laboratory experiments. Indications about the jet propagation
and its resulting morphologies are here obtained by means of a combined study of hypersonic jets carried out both in the laboratory
and by numerical simulations. 相似文献
879.
Many recent studies have implicated hydrothermal systems as the origin of martian minerals across a wide range of martian sites. Particular support for hydrothermal systems include silica (SiO2) deposits, in some cases >90% silica, in the Gusev Crater region, especially in the Columbia Hills and at Home Plate. We have developed a model called CHEMCHAU that can be used up to 100 °C to simulate hot springs associated with hydrothermal systems. The model was partially derived from FREZCHEM, which is a colder temperature model parameterized for broad ranges of temperature (<−70 to 25 °C), pressure (1-1000 bars), and chemical composition. We demonstrate the validity of Pitzer parameters, volumetric parameters, and equilibrium constants in the CHEMCHAU model for the Na-K-Mg-Ca-H-Cl-ClO4-SO4-OH-HCO3-CO3-CO2-O2-CH4-Si-H2O system up to 100 °C and apply the model to hot springs and silica deposits.A theoretical simulation of silica and calcite equilibrium shows how calcite is least soluble with high pH and high temperatures, while silica behaves oppositely. Such influences imply that differences in temperature and pH on Mars could lead to very distinct mineral assemblages. Using measured solution chemistries of Yellowstone hot springs and Icelandic hot springs, we simulate salts formed during the evaporation of two low pH cases (high and low temperatures) and a high temperature, alkaline (high pH) sodic water. Simulation of an acid-sulfate case leads to precipitation of Fe and Al minerals along with silica. Consistency with martian mineral assemblages suggests that hot, acidic sulfate solutions are plausibility progenitors of minerals in the past on Mars. In the alkaline pH (8.45) simulation, formation of silica at high temperatures (355 K) led to precipitation of anhydrous minerals (CaSO4, Na2SO4) that was also the case for the high temperature (353 K) low pH case where anhydrous minerals (NaCl, CaSO4) also precipitated. Thus we predict that secondary minerals associated with massive silica deposits are plausible indicators on Mars of precipitation environments and aqueous chemistry. Theoretical model calculations are in reasonable agreement with independent experimental silica concentrations, which strengthens the validity of the new CHEMCHAU model. 相似文献
880.
Giulia Schettino Ernesto Oliva Massimo Inguscio Carlo Baffa Elisabetta Giani Andrea Tozzi Pablo Cancio Pastor 《Experimental Astronomy》2011,31(1):69-81
A spectrally filtered Optical Frequency Comb (OFC) laser is proposed as a versatile calibration source for astronomical spectrometers in the 1?C2 ??m spectral range. Such a source overcomes the limitations of current calibration lamps providing a uniform spectrum of equally spaced lines with similar intensity and extremely high long-term frequency stability. We present preliminary studies and results of a system which filters the OFC from a 100 MHz comb spacing to 16 GHz one, an adequate spacing for spectrometers with resolving power ????/???>30000. The first approach employs two Fabry-Perot cavities in series, made of dielectric coated mirrors, followed by a non-linear optical broadening system. The limitations of such a filtering process are discussed. These can be overcome by the second approach, based on filtering cavities with metallic coated mirrors. 相似文献