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161.
Franco Cataldo Giovanni Strazzulla Susana Iglesias-Groth 《Monthly notices of the Royal Astronomical Society》2009,394(2):615-623
The stability of C60 and C70 fullerenes in the interstellar medium deposited on dust surface or embedded in meteorites and comets has been simulated with γ irradiation and with He+ ion bombardment. It is shown by vibrational spectroscopy that a γ radiation dose of 2.6 MGy (1 Gy = 1 joule absorbed energy per kilogram) causes partial oligomerization of both C60 and C70 fullerenes. Oligomers are made by fullerene cages chemically connected each other which can yield back free fullerenes by a thermal treatment. The amount of irreversibly polymerized fullerenes caused by 2.6 MGy as deduced as the toluene insoluble fraction has been determined as 1.7 and 15 per cent by weight, respectively, for C60 and C70 fullerene. The radiation dose generated by radionuclides decay and expected to be delivered to fullerenes buried at a depth of more than 20 m in comets and meteorites is about 3 MGy per 109 yr. Since fullerenes are by far resistant to such radiation dose they can survive for at least some billion years inside comets and meteorites and in fact have been detected inside certain carbonaceous chondrites. On the other hand, the direct exposure of fullerenes to cosmic rays for instance when they are adsorbed or deposited on the surface of carbon dust corresponds to the delivery of a radiation dose comprised between 30 and 65 MGy per 109 yr. Experimental bombardment of both C60 and C70 fullerenes for instance with He+ ions has shown that the complete amorphization occurs at about 250 MGy. Thus in ∼4 Gyr exposure to cosmic rays it is expected a complete amorphization. 相似文献
162.
163.
Boutheina Farhat Abdallah Ben Mammou Lamia Kouzana Ismail Chenini Francesca Podda Giovanni De Giudici 《Resource Geology》2010,60(4):377-388
The present paper investigates hydrochemical processes and water quality in the Mornag aquifer in NE Tunisia. Groundwater samples were collected during a field campaign, and were analysed for major and trace elements. The collected waters have a chemical facies rich in Ca2+, Na+ and Cl-. Piper diagram shows a progressive increase in chloride ions along with increasing salinity. Saturation indexes calculated by using PHREEQC (USGS) show that the Mornag waters are slightly saturated with respect to carbonates (calcite and dolomite), while undersaturated with respect to gypsum, halite and other evaporitic minerals. The current composition of waters takes place via dissolution of halite and Ca-sulfates, where the increase in calcium is partially balanced by possible calcite precipitation. The relevant recorded pollutant is nitrate, which was likely dispersed from agricultural soils, while heavy metals were generally far below values of pollution thresholds, indicating no influence by mining activity. 相似文献
164.
Transpressional tectonics and nappe stacking along the Southern Variscan Front of Morocco 总被引:1,自引:0,他引:1
Andrea Cerrina Feroni Alessandro Ellero Marco G. Malusà Giovanni Musumeci Giuseppe Ottria Riccardo Polino Leonardo Leoni 《International Journal of Earth Sciences》2010,99(5):1111-1122
The Southern Variscan Front in the Tinerhir area involves Palaeozoic allochthonous units (Ouaklim and Tilouine units) thrust
onto the northern edge of the West African Craton during late Carboniferous time. Illite crystallinity data highlight an anchizonal
grade for the Ouaklim Unit, and a diagenesis-anchizone transition for the Tilouine Unit during deformation phase D1. The tectonic
stack is crosscut by major dextral reverse faults bounding E–W trending domains of dominant shortening deformation (central
domain) and strike-slip deformation (northern and southern domains), later segmented by a network of post-Variscan faults.
This complex deformation pattern is the result of kinematic partitioning of dextral transpression along the Southern Variscan
Front, coeval with the Neovariscan (300–290 Ma) oblique convergence observed at the scale of the whole Moroccan Variscides.
Partitioning of dextral transpression described in the Tinerhir area is consistent with dextral wrench faulting along the
Tizi n’ Test Fault, and with Appalachian-style south-directed thrusting in the Tinerhir and Bechar-Bou Arfa areas. 相似文献
165.
A geostatistical approach for mapping and uncertainty assessment of geogenic radon gas in soil in an area of southern Italy 总被引:2,自引:2,他引:0
Gabriele Buttafuoco Adalisa Tallarico Giovanni Falcone Ilaria Guagliardi 《Environmental Earth Sciences》2010,61(3):491-505
Spatial distribution of concentrations of radon gas in the soil is important for defining high risk areas because geogenic
radon is the major potential source of indoor radon concentrations regardless of the construction features of buildings. An
area of southern Italy (Catanzaro-Lamezia plain) was surveyed to study the relationship between radon gas concentrations in
the soil, geology and structural patterns. Moreover, the uncertainty associated with the mapping of geogenic radon in soil
gas was assessed. Multi-Gaussian kriging was used to map the geogenic soil gas radon concentration, while conditional sequential
Gaussian simulation was used to yield a series of stochastic images representing equally probable spatial distributions of
soil radon across the study area. The stochastic images generated by the sequential Gaussian simulation were used to assess
the uncertainty associated with the mapping of geogenic radon in the soil and they were combined to calculate the probability
of exceeding a specified critical threshold that might cause concern for human health. The study showed that emanation of
radon gas radon was also dependent on geological structure and lithology. The results have provided insight into the influence
of basement geochemistry on the spatial distribution of radon levels at the soil/atmosphere interface and suggested that knowledge
of the geology of the area may be helpful in understanding the distribution pattern of radon near the earth’s surface. 相似文献
166.
This study proposes a new geostatistical methodology that accounts for roughness characteristics when downscaling fracture
surface topography. In the proposed approach, the small-scale fracture surface roughness is described using a “local roughness
pattern” that indicates the relative height of a location compared to its surrounding locations, while the large-scale roughness
is considered using the surface semivariogram. By accounting for both components–the minimization of the local error variance
and the reproduction of the local roughness characteristics–into the objective function of simulated annealing, the fracture
surface topography downscaling process was improved compared to standard geostatistical methodologies such as ordinary kriging
and sequential Gaussian simulation. Downscaled topography data were then assessed in terms of prediction errors and roughness
distribution. 相似文献
167.
Earthquakes are widely recognized as triggers for turbidites, submarine debris flows and slumps. In tectonically active areas, surprisingly small changes in stress can trigger seismic events, implying that past sea level changes may be important in controlling the timing of seismicity and the occurrence of turbidites. We apply this idea in an analysis of turbidites from the upper Cretaceous–Paleocene Scaglia Rossa Formation of the Umbria‐Marches region of Italy. These turbidites are composed of resedimented foraminiferal tests derived from fluidizing deep‐water (∼1500 m), pelagic sediments; seismic triggering is the most likely triggering mechanism given this setting and composition. The timing of these turbidites (and associated synsedimentary slumps), constrained by biostratigraphy and magnetostratigraphy, reveals an unusual, non‐random temporal pattern that appears to correlate well with proposed eustatic fluctuations. This correlation between turbidites and eustatic fluctuations leads us to suggest that stress and pore fluid pressure changes associated with changing sea level may trigger periods of increased seismicity in the geological past. 相似文献
168.
Probabilistic thresholds for triggering shallow landslides by rainfall are developed using two approaches: a logistic regression model and Iverson's physically based model. Both approaches are applied to a 180 km2 area in northern Italy. For the physically based model a Monte Carlo approach is used to obtain probabilities of slope failure associated with differing combinations of rainfall intensity and duration as well as differing topographic settings. For the logistic regression model hourly and daily rainfall data and split‐sample testing are used to explore the effect of antecedent rainfall on triggering thresholds. It is demonstrated that both the statistical and physically based models provide stochastic thresholds that express the probability of landslide triggering. The resulting thresholds are comparable, even though the two approaches are conceptually different. The physically based model also provides an estimate of the percentage of potentially unstable areas in which failure can be triggered with a certain probability. The return period of rainfall responsible for landslide triggering is studied by using a Gumbel scaling model of rainfall intensity–duration–frequency curves. It is demonstrated that antecedent rainfall must be taken into account in landslide forecasting, and a method is proposed to correct the rainfall return period by filtering the rainfall maxima with a fixed threshold of antecedent rainfall. This correction produces an increase of the return periods, especially for rainstorms of short duration. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
169.
170.
Summary The magnetosphere depends on the astronomical orientation of the geomagnetic field with respect to the solar wind. The statistical distribution of polar auroras must therefore depend on the orientation of the geomagnetic field with respect to the ecliptic plane. We have investigated this peculiar feature of auroras that we call auroral astronomical geometry. We give here some preliminary results concerning a limited set of pre-IGY auroras. The criteria that we have chosen to prepare the auroral collection are also briefly summarized. The results conform to the hypothesis of the auroral origin from the magnetospheric neutral sheet. Auroral particles are found to impinge over the earth with low angles with respect to the ecliptic plane (40°). Only in a 4-hours interval around midnight they are found to impinge with angles up to 70°. Definite evidence of these facts requires further investigation with a larger amount of data. — We have also prepared a complex code for recording the morphological features of each aurora, namely: standard information, movement. intensity, color, sunlight illumination, period of pulsation, location in the sky among stars and planets, time evolution, duration and general features of the auroral display. It is well known in fact that the auroral morphology affects auroral heights and latitudes, etc.; presumably it should also affect its astronomical geometry, which we will investigate later.Presented at the Inter-Union Symposium on Solar-Terrestrial Physics — Belgrade 1966. 相似文献