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排序方式: 共有113条查询结果,搜索用时 31 毫秒
21.
Giancarlo Benettin Massimiliano Guzzo Valerio Marini 《Celestial Mechanics and Dynamical Astronomy》2008,101(1-2):203-224
We provide evidences that the angular momentum of a symmetric rigid body in a spin–orbit resonance can perform large scale chaotic motions on time scales which increase polynomially with the inverse of the oblateness of the body. This kind of irregular precession appears as soon as the orbit of the center of mass is non-circular and the angular momentum of the body is far from the principal directions with minimum (maximum) moment of inertia. We also provide a quantitative explanation of these facts by using the theory of adiabatic invariants, and we provide numerical applications to the cases of the 1:1 and 1:2 spin–orbit resonances. 相似文献
22.
Dino Torri Jean Poesen Mauro Rossi Valerio Amici Daniele Spennacchi Cati Cremer 《地球表面变化过程与地形》2018,43(12):2547-2561
Predicting the location of gully heads in various environments is an important step towards predicting gully erosion rates. So far, field data collection and modelling of topographic thresholds for gully head development has mainly focused on gullies that formed in forested areas, rangelands, pastures and cropland. Such information for gullies in badlands however is very scarce. Therefore, this paper aims to extend the database on gully head topographical thresholds through data collection in a badland area and to improve the prediction of gully heads forming at sites with a very low erosion resistance value. For this, we chose a badland site located in central Italy that is characterized by biancana forms and both active and dormant gullies. The definition of the conditions under which present‐day gully heads developed allowed a better modelling of the gully head threshold equation, with modification of a previous model and the exemplification of how to use the updated model. The model shows that the resistance to gully head retreat depends on slope gradient and drainage area at gully heads, land use at the moment of gully development (as numerically expressed using parameters derived from the Runoff Curve Number method), surface rock fragment cover, presence of joints, pipes, and factors/processes affecting detachment rate. This study attempted to better understand environmental conditions that control the development of gully heads in badlands through a combination of field data collection of gully heads, an analysis of land use changes over 10 centuries, focusing on the period 1820–2005, and land use management through repeat photography and a critical examination of historical documents. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd. 相似文献
23.
Valerio Faraoni 《Mathematical Geosciences》2017,49(8):1057-1067
Very few exact solutions are known for the non-linear Vialov ordinary differential equation describing the longitudinal profiles of alpine glaciers and ice caps under the assumption that the ice deforms according to Glen’s constitutive relationship. Using a simple, yet wide, class of models for the accumulation rate of ice and Chebysev’s theorem on the integration of binomial differentials, many new exact solutions of the Vialov equations are obtained in terms of elementary functions. 相似文献
24.
Domenico Caracciolo Elisa Arnone Francesco Lo Conti Leonardo Valerio Noto 《Environmental Earth Sciences》2017,76(5):222
Critical rainfall thresholds for landslides are powerful tools for preventing landslide hazard. The thresholds are commonly estimated empirically starting from rainfall events that triggered landslides in the past. The creation of the appropriate rainfall–landslide database is one of the main efforts in this approach. In fact, an accurate agreement between the landslide and rainfall information, in terms of location and timing, is essential in order to correctly estimate the rainfall–landslide relationships. A further issue is taking into account the average moisture conditions prior the triggering event, which reasonably may be crucial in determining the sufficient amount of precipitation. In this context, the aim of this paper is exploiting historical landslide and rainfall data in a spatial database for the derivation of critical rainfall thresholds for landslide occurrence in Sicily, southern Italy. The hourly rainfall events that caused landslides occurred in the twentieth century were specifically identified and reconstructed. A procedure was proposed to automatically convert rain guages charts recorded on paper tape into digital format and then to provide the cumulative rainfall hyetograph in digital format. This procedure is based on a segmentation followed by signal recognition techniques which allow to digitalize and to recognize the hyetograph automatically. The role of rainfall prior to the landslide events was taken into account by including in the analysis the rainfall occurred 5, 15 and 30 days before each landslide. Finally, cumulated rainfall duration thresholds for different exceedance probability levels were determined. The obtained thresholds resulted in agreement with the regional curves proposed by other authors for the same area; antecedent rainfall turned out to be particularly important in triggering landslides. 相似文献
25.
Alexander Eleftheriou Carolina Filizzola Nicola Genzano Teodosio Lacava Mariano Lisi Rossana Paciello Nicola Pergola Filippos Vallianatos Valerio Tramutoli 《Pure and Applied Geophysics》2016,173(1):285-303
Real-time integration of multi-parametric observations is expected to accelerate the process toward improved, and operationally more effective, systems for time-Dependent Assessment of Seismic Hazard (t-DASH) and earthquake short-term (from days to weeks) forecast. However, a very preliminary step in this direction is the identification of those parameters (chemical, physical, biological, etc.) whose anomalous variations can be, to some extent, associated with the complex process of preparation for major earthquakes. In this paper one of these parameters (the Earth’s emitted radiation in the Thermal InfraRed spectral region) is considered for its possible correlation with M ≥ 4 earthquakes occurred in Greece in between 2004 and 2013. The Robust Satellite Technique (RST) data analysis approach and Robust Estimator of TIR Anomalies (RETIRA) index were used to preliminarily define, and then to identify, significant sequences of TIR anomalies (SSTAs) in 10 years (2004–2013) of daily TIR images acquired by the Spinning Enhanced Visible and Infrared Imager on board the Meteosat Second Generation satellite. Taking into account the physical models proposed for justifying the existence of a correlation among TIR anomalies and earthquake occurrences, specific validation rules (in line with the ones used by the Collaboratory for the Study of Earthquake Predictability—CSEP—Project) have been defined to drive a retrospective correlation analysis process. The analysis shows that more than 93 % of all identified SSTAs occur in the prefixed space–time window around (M ≥ 4) earthquake's time and location of occurrence with a false positive rate smaller than 7 %. Molchan error diagram analysis shows that such a correlation is far to be achievable by chance notwithstanding the huge amount of missed events due to frequent space/time data gaps produced by the presence of clouds over the scene. Achieved results, and particularly the very low rate of false positives registered on a so long testing period, seems already sufficient (at least) to qualify TIR anomalies (identified by RST approach and RETIRA index) among the parameters to be considered in the framework of a multi-parametric approach to t-DASH. 相似文献
26.
27.
Paola Sbarra Valerio De Rubeis Emiliano Di Luzio Marco Mancini Massimiliano Moscatelli Francesco Stigliano Patrizia Tosi Roberto Vallone 《Natural Hazards》2012,62(2):425-443
A detailed analysis of the earthquake effects on the urban area of Rome has been conducted for the L??Aquila sequence, which occurred in April 2009, by using an online macroseismic questionnaire. Intensity residuals calculated using the mainshock and four aftershocks are analyzed in light of a very accurate and original geological reconstruction of the subsoil of Rome based on a large amount of wells. The aim of this work is to highlight ground motion amplification areas and to find a correlation with the geological settings at a subregional scale, putting in evidence the extreme complexity of the phenomenon and the difficulty of making a simplified model. Correlations between amplification areas and both near-surface and deep geology were found. Moreover, the detailed scale of investigation has permitted us to find a correlation between seismic amplification in recent alluvial settings and subsiding zones, and between heard seismic sound and Tiber alluvial sediments. 相似文献
28.
The effects of nonylphenol (NP) on functional responses of haemocytes of the colonial ascidian Botryllus schlosseri were evaluated. Haemocytes were exposed to 0.1, 1 and 10 μM NP and the effects on haemocyte viability, adhesion, morphology, lysosomal membrane stability, phagocytic activity and early apoptosis were evaluated. Haemocyte viability and adhesion were not affected by NP. Phagocytic activity and the amoebocytic index decreased significantly at all the concentrations tested, while exposure of haemocytes to 1 and 10 μM NP caused a significant increase in the diffusion of Neutral Red into the cytosol. The percentage of cells positive to Annexin-V (indicative of early apoptosis) increased significantly at 1 and 10 μM NP. Results obtained suggested a relationship between NP and alterations in functional responses of haemocytes in B. schlosseri. Biomarkers measured resulted sensitive, rapid and reproducible, even if their responsiveness will be evaluated after in vivo exposure of animals to NP. 相似文献
29.
Alessandro Valiani Valerio Caleffi 《Advances in water resources》2011,34(2):227-242
This paper addresses the integral conservation of linear and angular momentum in the steady hydraulic jump in a linearly diverging channel.The flow is considered to be divided into a mainstream that conveys the total liquid discharge, and a roller where no average mass transport occurs. It is assumed that no macroscopic rheological relationship holds, so mass, momentum and angular momentum integral balances are independent relationships. Normal stresses are assumed to be hydrostatic on vertical, cylindrical surfaces. Viscous stresses are assumed to be negligible with respect to turbulent stresses. Assuming that the horizontal velocity distribution in the mainstream is uniform and that the horizontal momentum and angular momentum in the roller are negligible with respect to their mainstream counterparts, an analytical solution is obtained for the free surface profile of the flow. This solution is fundamental for finding the sequent depths and their positions. Consequently, it permits solving for the length of the jump, which is assumed to be equal to the length of the roller. Mainstream and roller thicknesses can also be derived from the present solution. This model may also be theoretically used to derive the average shear stresses exerted by the roller on the mainstream and the power losses per unit weight. This second relationship, which returns the well-known classical expression for total power loss in the jump, demonstrates that the strongly idealized mechanical model proposed here is internally consistent. 相似文献