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31.
Alessandro Pavese 《Physics and Chemistry of Minerals》1998,26(1):44-54
A theoretical study of some thermoelastic and structural properties of forsterite, at non-ambient conditions, is presented
in this work. A site-dependent potential (NP) has been developed, and successfully used to carry out theoretical investigations
on the lattice parameters, specific heat and tensorial elastic properties of forsterite, at P and T conditions representative of the actual thermobaric environment of the upper mantle of the Earth. Calculations have been
performed in the framework of lattice dynamics and of quasi-harmonic approximation. The results, from high temperature or
high pressure simulations, have been compared with experimental data. Calculations at high pressure and high temperature have
provided unprecedented data, which are not easy to achieve experimentally.
Received: October 10 1997 / Revised, accepted: January 26 1998 相似文献
32.
33.
The availability of reliable constitutive models linking the bulk electric properties of porous media to their inner structure is a key requirement for useful quantitative applications of noninvasive methods. This study focuses on the use of dielectric measurements to monitor fluid saturation changes in porous materials. A number of empirical, semi-empirical and theoretical relationships currently exists that link the bulk dielectric constant with volumetric water content. One such relationship, named complex refractive index model or Lichteneker-Rother model has been extensively applied in recent years. Here we first analyse the characteristics of this Lichteneker-Rother model by means of theoretical considerations. This theoretical analysis indicates that the Lichteneker-Rother exponent is dependent upon the geometrical properties of the porous structure, as well as the permittivity contrast between the different phases. Pore-scale modelling and experimental data further support this result. The parameter estimation robustness in presence of synthetic data error is also assessed. This demonstrates that Lichteneker-Rother parameters cannot, in general, be independently identified on the basis of bulk dielectric constant versus moisture content data. 相似文献
34.
We have performed new simulations of two different scenarios for the excitation and depletion of the primordial asteroid belt, assuming Jupiter and Saturn on initially circular orbits as predicted by the Nice Model of the evolution of the outer Solar System [Gomes, R., Levison, H.F., Tsiganis, K., Morbidelli, A., 2005. Nature 435, 466-469; Tsiganis, K., Gomes, R., Morbidelli, A., Levison, H.F., 2005. Nature 435, 459-461; Morbidelli, A., Levison, H.F., Tsiganis, K., Gomes, R., 2005. Nature 435, 462-465]. First, we study the effects of sweeping secular resonances driven by the depletion of the solar nebula. We find that these sweeping secular resonances are incapable of giving sufficient dynamical excitation to the asteroids for nebula depletion timescales consistent with estimates for solar-type stars, and in addition cannot cause significant mass depletion in the asteroid belt or produce the observed radial mixing of different asteroid taxonomic types. Second, we study the effects of planetary embryos embedded in the primordial asteroid belt. These embedded planetary embryos, combined with the action of jovian and saturnian resonances, can lead to dynamical excitation and radial mixing comparable to the current asteroid belt. The mass depletion driven by embedded planetary embryos alone, even in the case of an eccentric Jupiter and Saturn, is roughly 10-20× less than necessary to explain the current mass of the main belt, and thus a secondary depletion event, such as that which occurs naturally in the Nice Model, is required. We discuss the implications of our new simulations for the dynamical and collisional evolution of the main belt. 相似文献
35.
Alessandro Fortunati Stephen Wiggins 《Celestial Mechanics and Dynamical Astronomy》2016,125(2):247-262
The paper deals with the problem of the existence of a normal form for a nearly-integrable real-analytic Hamiltonian with aperiodically time-dependent perturbation decaying (slowly) in time. In particular, in the case of an isochronous integrable part, the system can be cast in an exact normal form, regardless of the properties of the frequency vector. The general case is treated by a suitable adaptation of the finite order normalization techniques usually used for Nekhoroshev arguments. The key point is that the so called “geometric part” is not necessary in this case. As a consequence, no hypotheses on the integrable part are required, apart from analyticity. The work, based on two different perturbative approaches developed by Giorgilli et al., is a generalisation of the techniques used by the same authors to treat more specific aperiodically time-dependent problems. 相似文献
36.
Konstantin Batygin Alessandro Morbidelli 《Celestial Mechanics and Dynamical Astronomy》2011,111(1-2):219-233
As a result of resonance overlap, planetary systems can exhibit chaotic motion. Planetary chaos has been studied extensively in the Hamiltonian framework, however, the presence of chaotic motion in systems where dissipative effects are important, has not been thoroughly investigated. Here, we study the onset of stochastic motion in presence of dissipation, in the context of classical perturbation theory, and show that planetary systems approach chaos via a period-doubling route as dissipation is gradually reduced. Furthermore, we demonstrate that chaotic strange attractors can exist in mildly damped systems. The results presented here are of interest for understanding the early dynamical evolution of chaotic planetary systems, as they may have transitioned to chaos from a quasi-periodic state, dominated by dissipative interactions with the birth nebula. 相似文献
37.
Landslides constitute one of the most important natural hazards in Italy as they are widespread and result in considerable damage and fatalities every year. The Italian Landslide Inventory (IFFI) Project was launched in 1999 with the aim of identifying and mapping landslides over the entire Italian territory. The inventory currently holds over 480,000 landslides and has been available by means of Web services since 2005. The aim of this study is to define quality indices for evaluation of the homogeneity and completeness of the IFFI database. In order to estimate the completeness of the landslide attribute information, a heuristic approach has been used to assign weighting values to significant parameters selected from the landslide data sheet. The completeness and homogeneity of the landslide mapping has been evaluated by means of three different methods: an area-frequency distribution analysis; the proximity of the landslides surveyed to urban areas; variation of the landslide index within the same lithology. The quality indices have allowed identification of areas with a high level of completeness and critical areas in which the data collected have been underestimated or are not very accurate. The quality assessment of collected and stored data is essential in order to use the IFFI database for definition and implementation of landslide susceptibility models and for land use planning and management. 相似文献
38.
Umberto Triacca Antonello Pasini Alessandro Attanasio 《Theoretical and Applied Climatology》2014,118(3):491-495
Studies on persistence are important for the clarification of statistical properties of the analyzed time series and for understanding the dynamics of the systems which create these series. In climatology, the analysis of the autocorrelation function has been the main tool to investigate the persistence of a time series. In this paper, we propose to use a more sophisticated econometric instrument. Using this tool, we obtain an estimate of the persistence in global land and ocean and hemispheric temperature time series. 相似文献
39.
40.
Samaneh Masoumi Lars Reuning Stefan Back Alessandro Sandrin Peter A. Kukla 《International Journal of Earth Sciences》2014,103(2):563-578
Three-dimensional (3D) seismic data from the southern Danish North Sea were used to analyse the morphology and spatial distribution of depressions in the Danian Chalk deposit. Previously, these depressions were either interpreted as karst structures or pockmarks. The observed depressions occur in an interval from 25 ms below to 12 ms above the Top Chalk surface. Three types of depressions were differentiated based on their plan-view geometry and their degree of symmetry: Type 1, comprising sub-circular and symmetrical depressions, is the dominant group (ca. 70 %). Type 2, elongated and symmetrical depressions, represents only a small fraction (ca. 5 %). The elongated and asymmetrical depressions of Type 3 compose ca. 25 %. In cross section, each depression type can be either characterised by a V- or a U-shape. The maximum size of the depressions ranges from 50 to 580 m, with an average internal depth of 10 m. We interpret the depressions as pockmarks formed by the expulsion of biogenic or thermogenic fluids at the Danian seafloor. Likely, the initial form of the pockmarks has been circular (Type 1) and was subsequently modified for Types 2 and 3 to an elongated form by currents. The long axis of the pockmarks is interpreted to represent the effective current direction. The inferred direction is sub-parallel to the palaeobathymetric contours. The 3D seismic interpretation of pockmarks presented in this paper contributes to the understanding of fluid migration and palaeocirculation patterns during the sedimentation of the terminal Chalk Group in the southern Danish North Sea. 相似文献