旋转扰动流体中壁面湍流不稳定及其拟序结构研究Ⅰ:实验     

Enrico Ferrero  张瑛  全利红  Luca Mortarini  Renato Forza 《气象与减灾研究》2009,32(3)

重点介绍和讨论了中性条件下旋转扰动流体中边界层强迫不稳定及其相关的一些问题,阐述了旋转体系中切变驱动边界层不稳定的动力学特征.这些不稳定状态的研究在大气物理学、流体动力学、海洋学等多个领域中引起科学家极大的兴趣,近年来在实验和理论研究中都得到了不断的发展.意大利都灵大学基础物理系地球科学实验组通过水槽旋转实验方法,不断改变水槽启动或结束时的旋转运动速度,以及底部壁面粗糙度等要素,所得到的实验结果与SDBL理论非常一致.  相似文献   

A numerical study of the hyperbolic manifolds in a priori unstable systems. A comparison with Melnikov approximations     

Elena Lega  Massimiliano Guzzo  Claude Froeschlé 《Celestial Mechanics and Dynamical Astronomy》2010,107(1-2):115-127

Using numerical methods we study the hyperbolic manifolds in a model of a priori unstable dynamical system. We compare the numerically computed manifolds with their analytic expression obtained with the Melnikov approximation. We find that, at small values of the perturbing parameter, the topology of the numerically computed stable and unstable manifolds is the same as in their Melnikov approximation. Increasing the value of the perturbing parameter, we find that the stable and unstable manifolds have a peculiar topological transition. We find that this transition occurs near those values of the perturbing parameter for which the error terms of Melnikov approximations have a sharp increment. The transition value is also correlated with a change in the behaviour of dynamical quantities, such as the largest Lyapunov exponent and the diffusion coefficient.  相似文献   

Low-T thermochronometric evidence for post-thrusting (< 11 Ma) exhumation in the Western Outer Carpathians,Poland     

Stefano Mazzoli  Leszek Jankowski  Rafal Szaniawski  Massimiliano Zattin 《Comptes Rendus Geoscience》2010,342(2):162-169

Thermal indicators record exhumation of sedimentary units from depths in excess of 6 km over most of the Outer Carpathian fold and thrust belt in Poland. Apatite fission track data, showing cooling ages ranging between 32.1 ± 4.8 and 7.0 ± 0.8 Ma, indicate that exhumation was partially coeval with shortening. However, new thermochronometric information obtained as part of this study allowed us to unravel a previously undetected, post-thrusting exhumation stage. The integration of new field data and structural analysis with low-T thermochronometry suggests that termination of thrusting – at ca. 11 Ma in the area of the present study – was followed by gravity disequilibria within the orogenic wedge. The related extension and denudation phenomena appear to have played a primary role in the recent (< 10 Ma) tectonic evolution of the Western Outer Carpathians, exerting a major control on exhumation processes in this key area of the Alpine–Carpathian mountain system.  相似文献   

The role of preconditioning in the solution to FE coupled consolidation equations by Krylov subspace methods     

Massimiliano Ferronato  Giorgio Pini  Giuseppe Gambolati 《国际地质力学数值与分析法杂志》2009,33(3):405-423

The repeated solution in time of the linear system arising from the finite element integration of coupled consolidation equations is a major computational effort. This system can be written in either a symmetric or an unsymmetric form, thus calling for the implementation of different preconditioners and Krylov subspace solvers. The present paper aims at investigating when either a symmetric or an unsymmetric approach should be better used. The results from a number of representative numerical experiments indicate that a major role in selecting either form is played by the preconditioner rather than by the Krylov subspace method itself. Two other important issues addressed are the size of the time integration step and the possible lumping of the flow capacity matrix. It appears that ad hoc block constrained preconditioners provide the most robust algorithm independently of the time step size, lumping, and symmetry. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Allozyme genotypes and tolerance to copper stress in Hediste diversicolor (Polychaeta: Nereididae)     

Virgilio M  Abbiati M 《Marine pollution bulletin》2004,49(11-12):978-985

This study analysed the occurrence of genotypic shifts in laboratory populations of Hediste diversicolor (Polychaeta: Nereididae) exposed to copper stress. Specimens of H. diversicolor were collected at three sites, up to 10 km apart, in the estuarine area of the Pialassa lagoons (North Adriatic Sea, Italy) and were used in acute toxicity tests. Specimens were assigned to copper exposure (0.34 mg/l Cu2+) or control conditions. Each combination of Treatment and Site was replicated in two tanks containing 35 specimens of H. diversicolor. The genotypic structure of both dead and survived specimens was analysed by allozyme electrophoresis at six loci (ALD, FH, HBDH LDH, PGI, SDH). Under copper exposure, specimens with the genotypes ALD100/100 and PGI102/102 had significantly lower mortalities than other genotypes Results were consistent across the three sites, suggesting that, under laboratory conditions, effects of copper stress on H. diversicolor is related to individual genotypes at ALD and PGI loci.  相似文献   

Volcanic geomorphology and tectonics of the Aeolian archipelago (Southern Italy) based on integrated DEM data   总被引：1，自引：0，他引：1  

Massimiliano FavalliM  Dávid Karátson  Roberto Mazzuoli  Maria Teresa Pareschi  Guido Ventura 《Bulletin of Volcanology》2005,68(2):157-170

The geomorphological and morphometric analysis of the sea floor topography surrounding the Aeolian Islands, South Tyrrhenian Sea, Italy, provides insights into the relationships between the volcanological evolution of the islands and their tectonic features. We constructed geomorphological maps of the submarine portions of the seven large edifices constituting the islands on the basis of a DEM with a 5 m resolution step. These maps include constructional and destructional landforms such as submarine volcanic vents located west of Lipari and north of Alicudi, and hummocky surfaces recognised north of Lipari and Salina. The latter landforms, together with the occurrence of large scars affecting the main edifices on land, suggest that sector collapses affected some islands. Geomorphological data indicate that the location of subaerial and submarine vents is strongly controlled by local tectonic structures striking WNW-ESE (Alicudi-Filicudi sector), NNW-SSE (Salina-Lipari-Vulcano sector) and NE-SW (Panarea-Stromboli sector). The islands can be divided into two groups on the basis of some morphometric parameters: a first group with a pancake-like shape, Dp/D (abrasion platform diameter/basal diameter) higher than 0.40 and H/D (total height/basal diameter) lower than 0.13, and a second group with a conical shape, characterised by Dp/D lower than 0.34 and H/D higher than 0.14. These ratios and other morphometric parameters reflect the different volcanological and structural evolution of the Aeolian Islands. The pancake-like shaped complexes have been created, in addition to their submarine stage, by extrusive and highly explosive activity, whereas the cone-shaped edifices have been characterised by effusive or moderate explosive activity.Editorial responsibility: C Kilburn  相似文献   

Thermodynamics of aluminosilicate garnet solid solution: new experimental data,an optimized model,and thermometric applications   总被引：10，自引：1，他引：10  

J. Ganguly  Weiji Cheng  Massimiliano Tirone 《Contributions to Mineralogy and Petrology》1996,126(1-2):137-151

 We have experimentally determined the displacement of the equilibrium Grossular + 2 Kyanite + Quartz ⇆ 3 Anorthite (GASP) as a function of garnet composition in the systems Mg-Ca-Mn, Fe-Mg-Ca and Fe-Mg-Ca-Mn at 1000°C. The results were treated along with selected experimental and observational data available in the literature as well as binary parameters from other workers to obtain a set of mutually compatible binary mixing parameters of the quaternary (Fe,Mg,Ca,Mn)- aluminosilicate garnet solid solution. Attempts to determine equilibrium garnet composition in the GASP equilibrium in the Ca-Mg binary were unsuccessful due to the formation of pyroxene. Calculations of binary and ternary miscibility gaps show that the P,T,X combination required for unmixing of garnet solid solution is not realized by natural samples. The solution model was applied to account for compositional effects on Fe-Mg exchange between garnet and ortho- or clino-pyroxene. Applications of the revised thermometric formulations to selected natural assemblages yield P-T conditions which are much less sensitive to compositional effects compared to the other available formulations, and are consistent with independent constraints. Received: 21 April 1995 / Accepted: 17 May 1996  相似文献   

Large roots dominate the contribution of trees to slope stability     

Filippo Giadrossich  Denis Cohen  Massimiliano Schwarz  Antonio Ganga  Roberto Marrosu  Mario Pirastru  Gian Franco Capra 《地球表面变化过程与地形》2019,44(8):1602-1609

Tree roots provide surface erosion protection and improve slope stability through highly complex interactions with the soil due to the nature of root systems. Root reinforcement estimation is usually performed by in situ pullout tests, in which roots are pulled out of the soil to reliably estimate the root strength of compact soils. However, this test is not suitable for the scenario where a soil progressively fails in a series of slump blocks – for example, in unsupported soils near streambanks and road cuts where the soil has no compressive resistance at the base of the hillslope. The scenario where a soil is unsupported on its downslope extent and progressively deforms at a slow strain rate has received little attention, and we are unaware of any study on root reinforcement that estimates the additional strength provided by roots in this situation. We therefore designed two complementary laboratory experiments to compare the force required to pull the root out. The results indicate that the force required to pull out roots is reduced by up to 50% when the soil fails as slump blocks compared to pullout tests. We also found that, for slump block failure, roots had a higher tendency to slip than to break, showing the importance of active earth pressure on root reinforcement behaviour, which contributes to reduced friction between soil and roots. These results were then scaled up to a full tree and tree stand using the root bundle and field-measured spatial distributions of root density. Although effects on the force mobilized in small roots can be relevant, small roots have virtually no effect on root reinforcement at the tree or stand scale on hillslopes. When root distribution has a wide range of diameters, the root reinforcement results are controlled by large roots, which hold much more force than small roots. © 2019 John Wiley & Sons, Ltd.  相似文献   

Long-Term Stability Analysis of Quasi Integrable Degenerate Systems Through the Spectral Formulation of the Nekhoroshev Theorem     

Massimiliano Guzzo 《Celestial Mechanics and Dynamical Astronomy》2002,83(1-4):303-323

We describe a numerical application of the Nekhoroshev theorem to investigate the long-term stability of quasi-integrable systems. We extend the results of a previous paper to a class of degenerate systems, which are typical in celestial mechanics.  相似文献   

Process‐based hydrological modelling: The potential of a bottom‐up approach for runoff predictions in ungauged catchments          下载免费PDF全文

Manuel Antonetti  Simon Scherrer  Peter Matthias Kienzler  Michael Margreth  Massimiliano Zappa 《水文研究》2017,31(16):2902-2920

Conceptual rainfall–runoff models are a valuable tool for predictions in ungauged catchments. However, most of them rely on calibration to determine parameter values. Improving the representation of runoff processes in models is an attractive alternative to calibration. Such an approach requires a straightforward, a priori parameter allocation procedure applicable on a wide range of spatial scales. However, such a procedure has not been developed yet. In this paper, we introduce a process‐based runoff generation module (RGM‐PRO) as a spin‐off of the traditional runoff generation module of the PREVAH hydrological modelling system. RGM‐PRO is able to exploit information from maps of runoff types, which are developed on the basis of field investigations and expert knowledge. It is grid based, and within each grid cell, the process heterogeneity is considered to avoid information loss due to grid resolution. The new module is event based, and initial conditions are assimilated and downscaled from continuous simulations of PREVAH, which are also available for real‐time applications. Four parameter allocation strategies were developed, on the basis of the results of sprinkling experiments on 60‐m² hillslope plots at several grassland locations in Switzerland, and were tested on five catchments on the Swiss Plateau and Prealps. For the same catchments, simulation results obtained with the best parameter allocation strategy were compared with those obtained with different configurations of the traditional runoff generation module of PREVAH, which was also applied as an event‐based module here. These configurations include a version that avoids calibration, one that transfers calibrated parameters, and one that uses regionalised parameter values. RGM‐PRO simulated heavy events in a more realistic way than the uncalibrated traditional runoff generation module of PREVAH, and, in some instances, it even exceeded the performance of the calibrated traditional one. The use of information on the spatial distribution of runoff types additionally proved to be valuable as a regionalisation technique and showed advantages over the other regionalisation approaches, also in terms of robustness and transferability.  相似文献