Geological and geochemical data from the proposed Sirente crater field: New age dating and evidence for heating of target     

Jens Orm  Christian Koeberl  Angelo Pio Rossi  Goro Komatsu 《Meteoritics & planetary science》2006,41(9):1331-1345

Abstract— The proposed Sirente crater field consists of a slightly oblong main structure (main crater) 120 m in width and about 30 smaller structures (satellite craters), all in unconsolidated but stiff carbonate mud. Here we focus on the subsurface structure of the satellite craters and compare the Sirente field with known meteorite crater fields. We present a more complete outline of the crater field than previously reported, information on the subsurface morphology of a satellite crater (C8) 8 m in width, radiocarbon and thermoluminescence (TL) ages of material from this crater, and evidence for heated material in both crater C8 and the rim of the main crater. Crater C8 has a funnel shape terminating downwards, and evidence for soil injection from the surface to a depth of 9 m. The infill contained dispersed charcoal and small, irregular, porous fragments of heated clay with a calibrated age of b.p. 1712 (¹³C‐corrected radiocarbon age: b.p. 1800 ± 100) and a TL age of b.p. 1825 (calculated error ± 274). Together with previous radiocarbon age (b.p. 1538) of the formation of the main crater (i.e., target surface below rim), a formation is suggested at the beginning of the first millennium a.d. Although projectile vaporization is not expected in Sirente‐sized craters in this type of target material, we used geochemistry in an attempt to detect a meteoritic component. The results gave no unequivocal evidence of meteoritic material. Nevertheless, the outline of the crater field, evidence of heated material within the craters, and subsurface structure are comparable with known meteorite crater fields.  相似文献   

Microwave geodesy by interferometric radiometry     

Angelo James Skalafuris 《Astrophysics and Space Science》1987,137(2):317-345

The aim of this paper is to establish a new method-first introduced by Soviet scientists in 1972 —for mapping the Earth in the microwave region passively using the interference pattern which results by correlating the signals from two radiometers which presumably can be mounted in two or more moving satellites. In such a procedure, the image is enhanced progressively by synthetic composition similar to that achieved by air-borne synthetic aperture radar. The only question left open by the Soviet originators is if the signal-to-backround ratio was sufficiently strong to think about implementing the system in more practical terms. By practical terms, I mean the construction of electronics to surmount instrumental noise and possible atmospheric interference. These two latter questions are not addressed at this stage of the analysis, but only the basic question of signal-to-backround. It appears that the signal-to-backround ratio can be reduced to a minimum level determined by the fringe spacing created which in turn is a function of satellite separation. It is shown that the signal-to-backround ratio becomes proportional to target area over resolution cell size and is enhanced by a mechanism of defocusing the interferometric radiometer. This reduction in the field of view suppresses background noise which surrounds the target within the foot-print size, to the enhancement of signal-to-background ratio. In addition, near field viewing in the Fresnel region permits the determination of cross range as well as range by measurement of the difference in the radii of curvature of the impinging wave front at the different vantage points of the two detectors. Thus near-field interferometric viewing permits two-dimensional range determination contrary to the usual astronomical applications which are far field and only one dimensional.  相似文献   

Head-wave parametric rolling of a surface combatant   总被引：1，自引：0，他引：1  

Hamid Sadat-Hosseini  Angelo Olivieri  Hirotada Hashimoto  Gabriele Bulian 《Ocean Engineering》2010,37(10):859-878

Complementary CFD, towing tank EFD, and nonlinear dynamics approach study of parametric roll for the ONR Tumblehome surface combatant both with and without bilge keels is presented. The investigations without bilge keels include a wide range of conditions. CFD closely agrees with EFD for resistance, sinkage, and trim except for Fr>0.5 which may be due to free surface and/or turbulence modeling. CFD shows fairly close agreement with EFD for forward-speed roll decay in calm water, although damping is over/under predicted for largest/smaller GM. Most importantly CFD shows remarkably close agreement with EFD for forward-speed parametric roll in head waves for GM=0.038 and 0.033 m, although CFD predicts larger instability zones at high and low Fr, respectively. The CFD and EFD results are analyzed with consideration ship motion theory and compared with Mathieu equation and nonlinear dynamics approaches. Nonlinear dynamics approaches are in qualitative agreement with CFD and EFD. The CFD and nonlinear dynamics approach results were blind in that the actual EFD radius of gyration k_xx was not known a priori.  相似文献   

Estimation of biogenic silica contents in marine sediments using seismic and well log data: Sediment Drift 7, Antarctica     

R. C. Neagu  U. Tinivella  V. Volpi  M. Rebesco  A. Camerlenghi 《International Journal of Earth Sciences》2009,98(4):839-848

Petrophysical properties (wet bulk density, porosity, P-wave velocity) are used to predict biogenic silica contents along a seismic reflection profile that ties two well sites, 1095 and 1096, drilled by Ocean Drilling Program (ODP) Leg 178 on sediment drifts on the Pacific continental margin of the Antarctic Peninsula. The biogenic silica contents along the seismic reflection profile were estimated on the basis of three hypotheses about petrophysical properties distributions in the two boreholes and statistical relationships between biogenic silica and other petrophysical properties, which were established on various sediment layers within the boreholes. Our study demonstrates the possibility to reliably predict the distribution of biogenic silica in the sub-seabed sediments if seismic data processed with amplitude preservation are used and statistical relations are considered. We conclude that the statistical extrapolation of biogenic silica content along seismic reflection profiles tied to borehole data is an efficient tool to quantify the amounts of silica undergoing crystalline transformation, which may have strong implications for submarine slope destabilisation.  相似文献   

European Mars Science and Exploration Conference (EMSEC)     

Angelo Pio Rossi  Olivier Witasse 《Planetary and Space Science》2009,57(8-9):893-894

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Evidence for Mg-rich carbonates on Mars from a 3.9 μm absorption feature     

Ernesto Palomba  Angelo Zinzi  Edward A. Cloutis  Davide Grassi 《Icarus》2009,203(1):58-6003

The origin and nature of the early atmosphere of Mars is still debated. The discovery of sulfate deposits on the surface, coupled with the evidence that there are not large abundances of carbonates detectable on Mars in the optically accessible part of the regolith, leaves open different paleoclimatic evolutionary pathways. Even if carbonates are responsible for the feature observed by TES and Mini-TES at 6.76 μm, alternative hypotheses suggest that it could be due to the presence of Hydrated Iron Sulfates (HIS). Carbonates can be discerned from HIS by investigating the spectral region in which a strong overtone carbonate band is present. The Planetary Fourier Spectrometer on board the Mars Express spacecraft has acquired several thousand martian spectra in the range 1.2-45 μm since January 2004, most of which show a weak absorption feature between 3.8 and 4 μm. A similar feature was observed previously from the Earth, but its origin could not be straightforwardly ascribed to surface materials, and specifically to carbonates. Here we show the surficial nature of this band that can be ascribed to carbonate mixed with the martian soil materials. The materials that best reproduce the detected feature are Mg-rich carbonates (huntite [CaMg₃(CO₃)₄] and/or magnesite [MgCO₃]). The presence of carbonates is demonstrated in both bright and dark martian regions. An evaluation of the likeliest abundance gives an upper limit of ∼10 wt%. The widespread distribution of carbonates supports scenarios that suggest carbonate formation occurred not by precipitation in a water-rich environment but by weathering processes.  相似文献   

Parametric study on seismic ground response by finite element modelling     

Angelo Amorosi  Daniela Boldini  Gaetano Elia 《Computers and Geotechnics》2010

In this paper the results of 2D FE analyses of the seismic ground response of a clayey deposit, performed adopting linear visco-elastic and visco-elasto-plastic constitutive models, are presented. The viscous and linear elastic parameters are selected according to a novel calibration strategy, leading to FE results comparable to those obtained by 1D equivalent-linear visco-elastic frequency-domain analyses. The influence of plasticity on the numerical results is also investigated, with particular reference to the relation between the hysteretic and viscous damping effects. Finally, different boundary conditions, spatial discretisation and time integration parameters are considered and their role on the FE results discussed.  相似文献   

The Western Mediterranean lamproitic magmatism: origin and geodynamic significance   总被引：1，自引：0，他引：1  

Angelo Peccerillo  Giorgio Martinotti 《地学学报》2006,18(2):109-117

Ultrapotassic lamproitic rocks in the Western Alps, Tuscany‐Corsica and SE Spain (c. 30 to 1 Ma) show high MgO, Ni and Cr denoting a mantle origin, but also have incompatible element and radiogenic isotope abundances that resemble upper crustal rocks, such as local metapelites and global subducting sediments. The coexistence of mantle and crustal signatures in lamproites indicates a genesis in a lithospheric mantle, which had been contaminated by crustal rocks. The occurrence of lamproitic magmatism along the Alpine collision front suggests that mantle contamination occurred during east‐verging Cretaceous‐Oligocene subduction of the European plate beneath the African margin. We suggest that crustal material originated from the overriding continental margin, which was eroded by the low‐angle subducting European slab. Mantle melting and generation of lamproites took place later, during diachronous opening of Western Mediterranean basins, contemporaneously with a new cycle of magmatism, which was genetically related to the west‐north‐dipping Apennine‐Maghrebian subduction.  相似文献   

Improved assessment of biodegradation extent and prediction of petroleum quality     

Rouven Elias  Andrea Vieth  Angelo Riva  Brian Horsfield  Heinz Wilkes 《Organic Geochemistry》2007,38(12):2111-2130

Biodegradation of crude oil causes volumetrically important compositional changes, which lead to significant deterioration in quality, in particular during the early stages of alteration. To better understand these effects we focussed on a detailed assessment of light to moderate levels of alteration. We investigated a suite of 40 crude oil samples from five different petroleum systems to evaluate the extent of alteration occurring in reservoirs. Based on a comprehensive geochemical characterization, five individual crude oil sequences were defined, where compositional variability is mainly due to microbial activity in the reservoir. In particular, samples from the Gullfaks field (offshore Norway) and from a petroleum system offshore Angola illustrate that conventional molecular biodegradation parameters, such as the Pr/n-C₁₇ and Ph/n-C₁₈ alkane ratios are not suitable for defining the extent of biodegradation in petroleum reservoirs. Here, we suggest a new molecular biodegradation parameter, the degradative loss, that can be used to quantify depletion in individual crude oil constituents. The approach allows improved assessment of the extent of biodegradation in crude oil samples by means of the mean degradative loss. It is demonstrated that crude oil quality, as assessed from API gravity, can be predicted directly from the molecular composition of crude oils. Our data clearly indicate that the degradation patterns of light hydrocarbons and n-alkanes differ in different petroleum systems. This suggests that microbial communities are different and therefore generate different molecular degradation patterns which have to be evaluated individually for each system.  相似文献   

The structure of a shock front in atomic hydrogen     

Angelo J. Skalafuris 《Astrophysics and Space Science》1968,2(2):258-278

A shock wave passing through a stellar atmosphere disturbs the gas, and the consequent adjustment of the fluid is a redistribution of the shock's kinetic energy among the various degrees of freedom. This paper deals with the effects of the Lyman continuum on the shock front. The shock heated gas is cooled principally by ionizing collisions of ground state atoms. This process is followed by a large quasi-isothermal region in which radiative recombinations occur. A final cycle of processes consisting of ionization, photo-recombinations to upper-level and collisional de-excitation, gives way to a sequence of statistical balances as each degree of freedom in the fluid attains equilibrium. Our calculations show that to a great extent, the shock structure is separated into successive regions of internal and radiative relaxation by an intermediate layer of ionized gas appearing at high shock speeds. Numerical results are presented for a range of shock speeds typifying a cepheid atmosphere.Radiation field and gas motions in shock waves are coupled, but the gas reacts little to the radiation it produces. Only the Lyman continuum has an appreciable effect on the shock structure. The principal escape of energy from the shock wave is through continuum radiation produced in recombinations to upper levels; thus the continuum emission in the red is stronger than an equivalent black body. Lyman photons are trapped in the shock while 20–30% of the shock's kinetic energy escapes to the Balmer and Paschen continua after the Lyman continuum is in equilibrium. The post- and pre-shock lines, as well as the post-shock continuum above the Lyman constitute the only observable spectra which emanate from the shock wave. The shock structure is perturbed only by the radiation which is not observed, and its absence tends to distort the emission profile from a Planck distribution.This work was originally started at Smithsonian Observatory and was completed at City College New York under contract with NASA Institute for Space Studies, New York.  相似文献