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31.
Vittorio Di Federico Marco Pinelli Rita Ugarelli 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(7):1067-1076
An understanding of the interplay between non-Newtonian effects in porous media flow and field-scale domain heterogeneity
is of great importance in several engineering and geological applications. Here we present a simplified approach to the derivation
of an effective permeability for flow of a purely viscous power–law fluid with flow behavior index n in a randomly heterogeneous porous domain subject to a uniform pressure gradient. A standard form of the flow law generalizing
the Darcy’s law to non-Newtonian fluids is adopted, with the permeability coefficient being the only source of randomness.
The natural logarithm of the permeability is considered a spatially homogeneous and correlated Gaussian random field. Under
the ergodic hypothesis, an effective permeability is first derived for two limit 1-D flow geometries: flow parallel to permeability
variation (serial-type layers), and flow transverse to permeability variation (parallel-type layers). The effective permeability
of a 2-D or 3-D isotropic domain is conjectured to be a power average of 1-D results, generalizing results valid for Newtonian
fluids under the validity of Darcy’s law; the conjecture is validated comparing our results with previous literature findings.
The conjecture is then extended, allowing the exponents of the power averaging to be functions of the flow behavior index.
For Newtonian flow, novel expressions for the effective permeability reduce to those derived in the past. The effective permeability
is shown to be a function of flow dimensionality, domain heterogeneity, and flow behavior index. The impact of heterogeneity
is significant, especially for shear-thinning fluids with a low flow behavior index, which tend to exhibit channeling behavior. 相似文献
32.
Dynamics of grains falling on a sloping granular medium: application to the evolution of a talus
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Numerous field surveys have provided quantitative information on the characteristics of talus deposits. Much less has been done to quantify the basic dynamics processes of blocks involved in talus evolution. In this work, we perform a set of experiments at the reduced scale of some metres using an inclined board covered with a loose granular medium. The complexity of the processes forming a talus is simplified by studying the interaction of only two kinds of grain sizes at a time. Grains of one class size are dropped from a fixed height onto the board covered by a layer of grains of a different class size, and their final distribution is recorded. We find that when small grains fall on large grains, the granular abundance decreases rapidly as a function of the distance from the fall point, which is explained by the effect of multiple bouncing on the irregular surface. In contrast, large grains falling on a bed of smaller grains lose much more energy at impact. They may stop at once, or roll down slope, often reaching the whole board length; as a consequence, their abundance peaks in the fall zone and at the change of slope. Experiments also show that grains travel longer with increasing fall height and sloping angle. The results clarify in a physical manner one mechanism that might explain why large blocks are typically found in the distal part of a talus slope, while smaller blocks remain near the fall zone. Based on these and previous experiments, a schematic view of talus evolution is discussed. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
33.
D. Marinucci D. Pietrobon A. Balbi P. Baldi P. Cabella G. Kerkyacharian P. Natoli D. Picard N. Vittorio 《Monthly notices of the Royal Astronomical Society》2008,383(2):539-545
We discuss spherical needlets and their properties. Needlets are a form of spherical wavelets which do not rely on any kind of tangent plane approximation and enjoy good localization properties in both pixel and harmonic space; moreover needlet coefficients are asymptotically uncorrelated at any fixed angular distance, which makes their use in statistical procedures very promising. In view of these properties, we believe needlets may turn out to be especially useful in the analysis of cosmic microwave background (CMB) data on the incomplete sky, as well as of other cosmological observations. As a final advantage, we stress that the implementation of needlets is computationally very convenient and may rely completely on standard data analysis packages such as healp ix. 相似文献
34.
B and V data of Population II Cepheids in M2, M5, M10, M13, M80 and ω Cen are combined in order to obtain period-luminosity and period-colour relations. The mean absolute magnitudes are determined adopting as distance modulus the quantily [V(RR)-M v(RR)], whereV(RR) is the apparent mean magnitude of RR Lyrae andM v(RR) is the absolute magnitude derived from the transistion periodP tr. It is shown that the scatter of the points around the (P-L) and (P-C) relations depends also from the width of the instability strip. In fact the position of the variables in the instability strip may be correlated with their amplitude in the sense that the short period variables (logP<1) which have largest amplitudes are brightest and bluest while the long period variables (logP>1) show a reversed relation. Finally, after correcting the observed colours for the amplitude effect, period-colour-amplitude relations are derived for the both short and long period variables. 相似文献
35.
Vittorio Banfi 《Earth, Moon, and Planets》1991,54(3):269-282
A theoretical model, based on particular type of the restricted three-body problem, is here presented in order to demonstrate the existence of a possible planetary motion near the center of mass in a binary star system. The superposition principle is used, with the introduction of two fictitious negative masses in order to simulate the real two primary bodies system. 相似文献
36.
Abstract. Density of barnacle larvae in plankton and settlement on atoxic plane surfaces have been compared at one station of Genoa harbour over sixteen months.
There were two periods of larval emission, during summer and autumn, with a slight one during winter. Barnacle settlement varied according to sea temperature, the amount of larvae and competition for the substratum. 相似文献
There were two periods of larval emission, during summer and autumn, with a slight one during winter. Barnacle settlement varied according to sea temperature, the amount of larvae and competition for the substratum. 相似文献
37.
Landslides in Valles Marineris (Mars): A possible role of basal lubrication by sub-surface ice 总被引:1,自引:0,他引:1
Fabio Vittorio De Blasio 《Planetary and Space Science》2011,59(13):1384-1392
There is much interest on the occurrence of water and ice in the past history of Mars. Because landslides on Mars are much better conserved than their terrestrial counterparts, a physical examination and morphological analysis can reveal significant details on the depositional environment at the instant of failure. A study of the landslides in Valles Marineris based on their physical aspect is presented and the velocity of the landslides is calculated with a stretching block model. The results show that the landslides were subject to strong basal lubrication that made them travel at high speed and to long distances. We use physical analysis to explore the four alternative possibilities that the natural lubricant of the landslides in Valles Marineris was either ice, deep water, a shallow carpet of water, or evaporites. Examination of the furrows present on the surface of the landslide deposits shows that either sub-surface ice or evaporites were likely present on the floor of Valles Marineris during the mass failures. 相似文献
38.
David Iacopini Stefano Tavani Sara Pentagallo Vittorio Maselli Marina Dottore Stagna Cynthia Ebinger David Reynolds Arjan van Vliet 《Basin Research》2023,35(1):387-412
The Southeastern portion of the East African Rift System reactivates Mesozoic transform faults marking the separation of Madagascar from Africa in the Western Indian Ocean. Earlier studies noted the reactivation of the Davie Fracture Zone in oceanic lithosphere as a seismically active extensional fault, and new 3D seismic reflection data and exploration wells provide unprecedented detail on the kinematics of the sub-parallel Seagap fault zone in continental/transitional crust landward of the ocean-continent transition. We reconstruct the evolution of the seismically active Seagap fault zone, a 400-km-long crustal structure affecting the Tanzania margin, from the late Eocene to the present day. The Seagap fault zone is represented by large-scale localized structures affecting the seafloor and displaying growth geometries across most of the Miocene sediments. The continuous tectonic activity evident by our seismic mapping, as well as 2D deep seismic data from literature, suggests that from the Middle-Late Jurassic until 125 Ma, the Seagap fault acted as a regional structure parallel to, and coeval with, the dextral Davie Fracture Zone. The Seagap fault then remained active after the cessation of both seafloor spreading in the Somali basin and strike-slip activity on the Davie Fracture Zone, till nowaday. Its architecture is structurally expressed through the sequence of releasing and restraining bends dating back at least to the early Neogene. Seismic sections and horizon maps indicate that those restraining bends are generated by strike-slip reactivation of Cretaceous structures till the Miocene. Finally based on the interpretation of edge-enhanced reflection seismic surfaces and seafloor data, we shows that, by the late Neogene, the Seagap fault zone switched to normal fault behaviour. We discuss the Seagap fault's geological and kinematic significance through time and its current role within the microplate system in the framework of the East African rift, as well as implications for the evolution and re-activation of structures along sheared margins. The newly integrated datasets reveal the polyphase deformation of this margin, highlighting its complex evolution and the implications for depositional fairways and structural trap and seal changes through time, as well as potential hazards. 相似文献
39.
Gianfranco Brambilla Stefania Paola De Filippis Vittorio Esposito Gaetano Settimo 《洁净——土壤、空气、水》2013,41(2):113-118
Dioxin‐like compounds from regular, occasional or fugitive airborne sources of emission may fall out on fodders close to be harvested for silage and hay production. In this way, a prolonged long‐term intake of contaminated forages in dairy animals may be envisaged, able to determine a rise of the background contamination in milk. We simulated different risk scenarios taking into account the inventoried bulk dry depositions in rural areas of the aforesaid contaminants, silage and hay biomass production per hectare, forages regimen in dairy animals, and the congeners carry‐over rate (COR) from forages to milk. Considering atmospheric depositions >10 pg I‐TE m?2 day?1 and accounting for a 30% COR, dairy milk could rise up to the PCDD/F level of 3 pg WHO1998‐TE g?1 fat. The modelling indicates that in rural areas bulk emissions should be selectively minimised, accounting for the calendar of the different agricultural practices, because of their potential impact on the fodders. Since environmental factors play a non‐negligible role in food production, a stronger harmonisation between I‐TE and WHO1998–2005‐TE scales with respect to dioxin‐like polychlorobiphenyl congeners inclusion is envisaged. This will allow the prevention of the human indirect exposure to such contaminants when released in the air. 相似文献
40.
Gennaro Magliulo Vittorio Capozzi Roberto Ramasco 《Bulletin of Earthquake Engineering》2012,10(2):679-694
The paper presents the results of a research study concerning the seismic response and design of r/c frames with overstrength
discontinuities in elevation. The discontinuities are obtained assigning overstrengths either to the beams or to the columns
of a “regular frame” (assumed as reference). Two “regular frames” are designed: one according to the Eurocode 8 (EC8) medium
ductility class (DCM) rules and the other one according to the EC8 high ductility class (DCH) rules. For all frames the criteria
of vertical strength irregularity of many international seismic codes are applied. Non linear static and dynamic analyses
are performed; mechanical non linearity is concentrated at the element ends. These analyses are carried out according to EC8
provisions: for non linear static analysis the N2 method is applied; in the case of non linear time-history analyses, seven
real earthquakes, selected in order to fit on average the elastic design spectrum, are used as input. The seismic response
of frames characterised by the assigned overstrength is not very different with respect to the “regular frame” one; furthermore
all the frames satisfy the Ultimate Limit State, verified by the application of non linear static and dynamic analyses. This
demonstrates that the sensitivity of frames, designed according to EC8 medium and high ductility classes, to overstrength
vertical variations is low. Consequently, international code provisions on vertical strength regularity should be reviewed. 相似文献