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31.
Angelo Sajeva Davide Scarpellini Pamela Tempone Simone Capaccioli 《Geophysical Prospecting》2019,67(4):872-887
The effective medium theory based on the Hertz–Mindlin contact law is the most popular theory to relate dynamic elastic moduli (or elastic velocities) and confining pressure in dry granular media. However, many experimental results proved that the effective medium theory predicts pressure trends lower than experimental ones and over-predicts the shear modulus. To mitigate these mispredictions, several evolutions of the effective medium theory have been presented in the literature. Among these, the model named modified grain contact theory is an empirical approach in which three parametric curves are included in the effective medium theory model. Fitting the parameters of these curves permits to adjust the pressure trends of the Poisson ratio and the bulk modulus. In this paper, we present two variations of the modified grain contact theory model. First, we propose a minor modification in the fitting function for the porosity dependence of the calibration parameters that accounts for non-linearity in the vicinity of the critical porosity. Second, we propose a major modification that reduces the three-step modified grain contact theory model to a two-step model, by skipping the calibration parameter–porosity fit in the model and directly modelling the calibration parameter–pressure relation. In addition to an increased simplicity (the fitting parameters are reduced from 10 to 6), avoiding the porosity fit permits us to apply the model to laboratory data that are not provided with accurate porosity measurements. For this second model, we also estimate the uncertainty of the fitting parameters and the elastic velocities. We tested this model on dry core measurements from literature and we verified that it returns elastic velocity trends as good as the original modified grain contact theory model with a reduced number of fitting parameters. Possible developments of the new model to add predictive power are also discussed. 相似文献
32.
33.
Giampaolo Di Silvio Chiara Dall’Angelo Davide Bonaldo Giacomo Fasolato 《Continental Shelf Research》2010
This model is based on the concept of transport concentration, defined as the time-averaged concentration in a given location of a lagoon, which determines the long-term net transport of sediments as the sum of a dispersive and an advective flux. Dispersive net flux of sediments is due to the alternate components of the tidal flow, while the advective net flux of sediments is due to the residual (Eulerian) component of the tidal, fluvial and littoral flow and possibly to the asymmetry between flow and ebb tide. 相似文献
34.
Chiara Turino Paola Morasca Gabriele Ferretti Davide Scafidi Daniele Spallarossa 《Journal of Seismology》2010,14(2):393-411
Reliable automatic procedure for locating earthquake in quasi-real time is strongly needed for seismic warning system, earthquake
preparedness, and producing shaking maps. The reliability of an automatic location algorithm is influenced by several factors
such as errors in picking seismic phases, network geometry, and velocity model uncertainties. The main purpose of this work
is to investigate the performances of different automatic procedures to choose the most suitable one to be applied for the
quasi-real-time earthquake locations in northwestern Italy. The reliability of two automatic-picking algorithms (one based
on the Characteristic Function (CF) analysis, CF picker, and the other one based on the Akaike’s information criterion (AIC),
AIC picker) and two location methods (“Hypoellipse” and “NonLinLoc” codes) is analysed by comparing the automatically determined
hypocentral coordinates with reference ones. Reference locations are computed by the “Hypoellipse” code considering manually
revised data and tested using quarry blasts. The comparison is made on a dataset composed by 575 seismic events for the period
2000–2007 as recorded by the Regional Seismic network of Northwestern Italy. For P phases, similar results, in terms of both
amount of detected picks and magnitude of travel time differences with respect to manual picks, are obtained applying the
AIC and the CF picker; on the contrary, for S phases, the AIC picker seems to provide a significant greater number of readings
than the CF picker. Furthermore, the “NonLinLoc” software (applied to a 3D velocity model) is proved to be more reliable than
the “Hypoellipse” code (applied to layered 1D velocity models), leading to more reliable automatic locations also when outliers
(wrong picks) are present. 相似文献
35.
Rockfall Hazard Analysis From Discrete Fracture Network Modelling with Finite Persistence Discontinuities 总被引:2,自引:1,他引:1
Cédric Lambert Klaus Thoeni Anna Giacomini Davide Casagrande Scott Sloan 《Rock Mechanics and Rock Engineering》2012,45(5):871-884
Developing an accurate representation of the rock mass fabric is a key element in rock fall hazard analysis. The orientation, persistence and density of fractures control the volume and shape of unstable blocks or compartments. In this study, the discrete fracture modelling technique and digital photogrammetry were used to accurately depict the fabric. A volume distribution of unstable blocks was derived combining polyhedral modelling and kinematic analyses. For each block size, probabilities of failure and probabilities of propagation were calculated. A complete energy distribution was obtained by considering, for each block size, its occurrence in the rock mass, its probability of falling, its probability to reach a given location, and the resulting distribution of energies at each location. This distribution was then used with an energy–frequency diagram to assess the hazard. 相似文献
36.
Modeling water resources of a highly irrigated alluvial plain (Italy): calibrating soil and groundwater models 总被引:1,自引:0,他引:1
Chiara Vassena Michele Rienzner Giansilvio Ponzini Mauro Giudici Claudio Gandolfi Cinzia Durante Davide Agostani 《Hydrogeology Journal》2012,20(3):449-467
Modern and effective water management in large alluvial plains that have intensive agricultural activity requires the integrated modeling of soil and groundwater. The models should be complex enough to properly simulate several, often non-linear, processes, but simple enough to be effectively calibrated with the available data. An operative, practical approach to calibration is proposed, based on three main aspects. First, the coupling of two models built on well-validated algorithms, to simulate (1) the irrigation system and the soil water balance in the unsaturated zone and (2) the groundwater flow. Second, the solution of the inverse problem of groundwater hydrology with the comparison model method to calibrate the model. Third, the use of appropriate criteria and cross-checks (comparison of the calibration results and of the model outputs with hydraulic and hydrogeological data) to choose the final parameter sets that warrant the physical coherence of the model. The approach has been tested by application to a large and intensively irrigated alluvial basin in northern Italy. 相似文献
37.
Benthic diatoms represent an important element of global nutritional productivity; to raise attention on their role, which is often neglected due to analytical difficulties, surface (1 cm top layer) coastal sediments from Gerlache inlet to Penguin Bay at Terra Nova Bay were collected and stored at -20 °C. DNA amplification by real-time PCR, based on diatom-specific oligonucleotide primers designed on small-subunit rRNA (SSU rRNA), was performed in addition to diatom conventional cell counting and spectrophotometric determination of photo-pigments. Moreover, cations and anions were determined in sediments with the aim to identify factors involved in the control of diatom abundance. Diatom distribution was found quite heterogeneous displaying significant differences from site to site. The salinity in sediments ranged from 45.1 at Gerlache inlet to 76.2 at Penguin Bay and it was correlated with cell abundance, biodiversity, amount of pigments and amplified DNA. The dominant species, Fragilariopsis curta, was associated to sediment salinity brines. 相似文献
38.
Marco Cuffaro Federica Riguzzi Davide Scrocca Carlo Doglioni 《International Journal of Earth Sciences》2011,100(8):1915-1924
We performed geodetic strain rate analyses in southern Italy, using new GPS velocities. Two-dimensional strain and rotation
rate fields were estimated and results show that most of the shortening is distributed in the northern Sicily offshore. Extension
becomes more evident and comparable with shortening on the eastern side of the same margin, and greater in the eastern Sicily
offshore. Principal shortening and extension rate axes are consistent with long-term geological features: seismic reflection
profiles show both active compressive and extensional faults affecting Pleistocene strata. We show evidence for contemporaneous
extension and transtension in the Cefalù Basin. Combining geodetic data and geological features point to the coexistence of
independent geodynamic processes, i.e., the active E–W backarc spreading in the hangingwall of the Apennines subduction zone
and shortening along the southern margin of the Tyrrhenian backarc basin operated by the NNW-motion of Africa relative to
Eurasia. 相似文献
39.
Davide Lenaz Henrik Skogby Alla M. Logvinova Nikolai V. Sobolev Francesco Princivalle 《Physics and Chemistry of Minerals》2013,40(9):671-679
Oxygen fugacity ( $ f_{{{\text{O}}_{ 2} }} $ f O 2 ) is a fundamental but little known intensive variable in mantle processes. It influences the P/T position of a mantle solidus and the composition of mantle-derived melts and fluids and constrains mantle-core equilibria and a number of geophysical properties of the mantle. An important source of information on oxidation states is the ferric–ferrous iron ratio in mantle spinels. Since the magnetite component is low in mantle spinels, normal analytical errors translate into considerable $ f_{{{\text{O}}_{ 2} }} $ f O 2 uncertainties. In this study, we analyzed the Fe3+–Fetot ratio of chromites present as inclusions in diamond and other mantle-related occurrences by point-source Mössbauer spectroscopy using single-crystal absorbers as well as conventional Mössbauer spectroscopy using powder absorbers. The studied spinels have been previously analyzed by single-crystal X-ray diffraction and electron microprobe. The ferric–ferrous ratios found are normally similar to the different techniques apart from some samples where a large number of grains have been used for the analyses (powder absorbers). The general agreement between the different techniques allows us to conclude that the studied chromites are stoichiometric. However, conventional Mössbauer spectroscopy on powder absorbers should be conducted with great care, since the method requires a relatively large amount of sample material. Spinel frequently occurs as small grains, and the large number of crystals required may possess different degrees of oxidation/alteration and, consequently, different ferric–ferrous ratio leading to possible errors in the interpretation of the results. 相似文献
40.
Davide D’Alimonte Dan Cornford 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(5):613-620
This paper, addresses the problem of novelty detection in the case that the observed data is a mixture of a known ‘background’ process contaminated with an unknown other process, which generates the outliers, or novel observations. The framework we
describe here is quite general, employing univariate classification with incomplete information, based on knowledge of the
distribution (the probability density function, pdf) of the data generated by the ‘background’ process. The relative proportion of this ‘background’ component (the prior ‘background’ probability), the pdf and the prior probabilities of all other components are all assumed unknown. The main contribution is a new classification scheme that
identifies the maximum proportion of observed data following the known ‘background’ distribution. The method exploits the Kolmogorov–Smirnov test to estimate the proportions, and afterwards data are Bayes
optimally separated. Results, demonstrated with synthetic data, show that this approach can produce more reliable results
than a standard novelty detection scheme. The classification algorithm is then applied to the problem of identifying outliers in the SIC2004 data set, in order
to detect the radioactive release simulated in the ‘joker’ data set. We propose this method as a reliable means of novelty
detection in the emergency situation which can also be used to identify outliers prior to the application of a more general
automatic mapping algorithm.
相似文献
Davide D’AlimonteEmail: |
Dan Cornford (Corresponding author)Email: |