Potassic primary melts of Vulsini (Roman Province): evidence from mineralogy and melt inclusions     

Vadim Kamenetsky  Nicole Métrich  Raffaello Cioni 《Contributions to Mineralogy and Petrology》1995,121(3):336-336

The online version of the original article can be found at  相似文献   

Energy minimum criteria in modeling structures and properties of minerals     

V. S. Urusov  N. N. Eremin 《Physics and Chemistry of Minerals》1995,22(3):151-158

The leading principle in modeling procedures is the minimization of structural energy. It is assumed that the calculated minimal energy has to be compared with the experimental estimate of cohesion energy of a crystal. The reference state for structure energy depends on bonding type: the lattice energy for purely ionic crystals consisting of cations and anions, the atomization energy for covalent and metallic crystals consisting of atoms, the sublimation energy for molecular crystals consisting of molecules etc.As is well-known, a majority of minerals can not be correctly described as purely ionic crystals. Moreover, for these crystals lattice energy cannot be determined empirically because free anions, such as O^2-, S^2-, As^3-, etc., do not exist. In order to describe crystal structures and properties in a better approximation it is usually proposed that the bonding character of such crystals is intermediate between ionic and covalent, so that effective charges instead of formal ones, and an appropriate covalent contribution, are involved in energy calculations. However, the corresponding calculated structure energies are not comparable to any experimental values. Moreover, they decrease with increasing effective charges and a purely ionic structure seems, as before, to be most stable from energetic point of view.  相似文献   

Interaction of cations on octahedral and tetrahedral sites in simple spinels     

V. S. Urusov 《Physics and Chemistry of Minerals》1983,9(1):1-5

The cation distribution in the partly inversed binary spinel is usually treated in terms of octahedral site preference energies. Such a model is based on the assumption of ideal cation mixing in each position. The present version of theory includes explicitly the interaction between altervalent cations on octahedral and tetrahedral sites by using a simple regular model of mixing. The values of octahedral site preference energies as well as the site interaction energies are readily obtained from experimental data on the temperature dependence of the inversion parameter.  相似文献   

Crystal chemical and energy analysis of partition coefficients of impurities during melt crystallization: The case of olivine     

V. S. Urusov  V. B. Dudnikova  E. V. Zharikov 《Geochemistry International》2006,44(1):19-32

Partition coefficients (K) between forsterite crystal and melt are experimentally determined for many univalent, bivalent, trivalent, and tetravalent trace elements. Using numerical modeling, we calculated the energies of intrinsic and impurity defects in forsterite (E _df) and the energies of dissolution of univalent, bivalent, trivalent, and tetravalent impurities (E _ds). These results are compared with literature data. A linear dependence is established for the energy of defects on the charge of the impurity ion and the relative difference in the radii of the impurity and matrix ions Δr/d, where d is the average interatomic distance in the matrix. Partition coefficients are described by parabolic dependences on Δr/d and charge of the impurity ion using literature data on K of impurity elements in olivines and impurity ion dissolution energies. Linear dependences-RTlnK-(Δr/d)² and E _ds-(Δr/d)² pass through the origin for isovalent substitutions and are well apart from it for heterovalent substitutions. Linear dependence (Δr/d)² has a free term of about 200 kJ/mol, which is approximately equal to a half of the energy of formation of the Frenkel defect in forsterite; this defect maintains electroneutrality. If valency is compensated due to addition into the melt of an ion with another charge (than that of the impurity ion), E _ds-(Δr/d)² and-RTlnK-(Δr/d)² lines at low (Δr/d)² shift to the origin. This means that energy consumption for coupled isomorphism is lower than that for the formation of intrinsic structural defects. Correlation dependences are proposed for the distribution of impurities and the energy of their dissolution. They indicate the increasing contribution of the entropy components of impurity ion dissolution energy during heterovalent isomorphism.  相似文献   

Quaternary high-Mg ultrapotassic rocks from the Qal’eh Hasan Ali maars,southeastern Iran: petrogenesis and geodynamic implications     

Kwan-Nang Pang  Sun-Lin Chung  Mohammad Hossein Zarrinkoub  Fei Wang  Vadim S. Kamenetsky  Hao-Yang Lee 《Contributions to Mineralogy and Petrology》2015,169(3):1-19

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Potential and limits of double-difference tomographic methods     

Jean-Luc Got  Vadim Monteiller  Jean Virieux  Stéphane Operto 《Geophysical Prospecting》2008,56(4):477-491

Double-difference tomographic methods use directly accurate time delays computed between similar signals. Such methods are designed to image very heterogeneous media, such as volcanoes or fault zones. In seismological applications, similar signals are recorded at a given station from earthquakes sharing similar and close-by sources. In seismic exploration experiments, similar signals are often recorded at neighbouring receivers. After a brief presentation of the tomographic algorithm used, a seismological application is summarized. The potential and limits of double-difference tomographic methods are explored using various numerical experiments. They show that two effects are competing in double-difference tomography: (i) the degradation of the stability of the inversion due to the geometrical proximity of the rays used in the differentiation and (ii) the decrease in modelling error, which allows improving the stability of the inversion and using smaller quantities of a priori information when data are sufficiently accurate. The best resolution is obtained for an optimal value of the inter-source or inter-receiver distance. For optimal values of these distances and a priori information, tomography using traveltime differences provides significantly better resolved results than using traveltimes.  相似文献   

Attenuation mechanisms in fractured fluid-saturated porous rocks: a numerical modelling study     

Eva Caspari  Mikhail Novikov  Vadim Lisitsa  Nicolás D. Barbosa  Beatriz Quintal  J. Germán Rubino  Klaus Holliger 《Geophysical Prospecting》2019,67(4):935-955

Seismic attenuation mechanisms receive increasing attention for the characterization of fractured formations because of their inherent sensitivity to the hydraulic and elastic properties of the probed media. Attenuation has been successfully inferred from seismic data in the past, but linking these estimates to intrinsic rock physical properties remains challenging. A reason for these difficulties in fluid-saturated fractured porous media is that several mechanisms can cause attenuation and may interfere with each other. These mechanisms notably comprise pressure diffusion phenomena and dynamic effects, such as scattering, as well as Biot's so-called intrinsic attenuation mechanism. Understanding the interplay between these mechanisms is therefore an essential step for estimating fracture properties from seismic measurements. In order to do this, we perform a comparative study involving wave propagation modelling in a transmission set-up based on Biot's low-frequency dynamic equations and numerical upscaling based on Biot's consolidation equations. The former captures all aforementioned attenuation mechanisms and their interference, whereas the latter only accounts for pressure diffusion phenomena. A comparison of the results from both methods therefore allows to distinguish between dynamic and pressure diffusion phenomena and to shed light on their interference. To this end, we consider a range of canonical models with randomly distributed vertical and/or horizontal fractures. We observe that scattering attenuation strongly interferes with pressure diffusion phenomena, since the latter affect the elastic contrasts between fractures and their embedding background. Our results also demonstrate that it is essential to account for amplitude reductions due to transmission losses to allow for an adequate estimation of the intrinsic attenuation of fractured media. The effects of Biot's intrinsic mechanism are rather small for the models considered in this study.  相似文献   

Magnetorotational and Tayler Instabilities in the Pulsar Magnetosphere     

Vadim Urpin 《Journal of Astrophysics and Astronomy》2017,38(3):41

The magnetospheres around neutron stars should be very particular because of their strong magnetic field and rapid rotation. A study of the pulsar magnetospheres is of crucial importance since it is the key issue to understand how energy outflow to the exterior is produced. In this paper, we discuss magnetohydrodynamic processes in the pulsar magnetosphere. We consider in detail the properties of magnetohydrodynamic waves that can exist in the magnetosphere and their instabilities. These instabilities lead to formation of magnetic structures and can be responsible for short-term variability of the pulsar emission.  相似文献   

Numerical simulation of seismic waves in models with anisotropic formations: coupling Virieux and Lebedev finite-difference schemes   总被引：2，自引：0，他引：2  

Vadim Lisitsa  Vladimir Tcheverda  Dmitry Vishnevsky 《Computational Geosciences》2012,16(4):1135-1152

Anisotropy is widespread in the Earth’s interior. However, there is a number of models where anisotropic formations comprise as few as 10–20?% of the volume, and this includes fractured reservoirs, thin-layered packs, etc. while the major part of the medium is isotropic. In this situation, the use of computationally intense anisotropy-oriented approaches throughout the computational domain is prodigal. So this paper presents an original advanced finite-difference algorithm based on the domain decomposition technique with individual scheme used inside subdomains. It means that the standard staggered grid scheme or the Virieux scheme is used in the main part of the model which is isotropic, while the anisotropy-oriented Lebedev scheme is utilized inside domains with anisotropic formations. Finite-difference consistency conditions at the artificial interface where the schemes are coupled are designed to make the artificial reflections as low as possible, namely, for the second-order scheme, the third order of convergence of the reflection coefficients is proved.  相似文献   

Link between global cooling and mammalian transformation across the Eocene–Oligocene boundary in the continental interior of Asia     

Rui Zhang  Vadim A. Kravchinsky  Leping Yue 《International Journal of Earth Sciences》2012,101(8):2193-2200

Evidence in the world’s ocean current system indicates an abrupt cooling from 34.1 to 33.6?Ma across the Eocene–Oligocene boundary at 33.9?Ma. The remarkable cooling period in the ocean, called the Eocene–Oligocene transition (EOT), is correlated with pronounced mammalian faunal replacement as shown in terrestrial fossil records. For the first time within Asia, a section is magnetostratigraphically dated that also produces mammalian fossils that span the Late Eocene—Early Oligocene transition. Three fossil assemblages revealed through the EOT (34.8, 33.7, and 30.4?Ma) demonstrate that perissodactyl faunas were abruptly replaced by rodent/lagomorph-dominant faunas during climate cooling, and that changes in mammalian communities were accelerated by aridification in central Asia. Three fossil assemblages (34.8, 33.7, and 30.4?Ma) within the north Junggar Basin (Burqin section) tied to this magnetostratigraphically dated section, reveal that perissodactyl faunas were abruptly replaced by rodent/lagomorph-dominant faunas during climate cooling, and that changes in mammalian communities were accelerated by aridification in central Asia. The biotic reorganization events described in the Burqin section are comparable to the Grande Coupure in Europe and the Mongolian Remodeling of mammalian communities. That is, the faunal transition was nearly simultaneous all over the world and mirrored global climatic changes with regional factors playing only a secondary role.  相似文献