Experimental study of the K2ZrSi3O9 (wadeite)–K2TiSi3O9 and K2(Zr,Ti)Si3O9–phlogopite systems at 2–3 GPa     

Andrea Orlando  Yves Thibault  Alan D. Edgar 《Contributions to Mineralogy and Petrology》2000,139(2):136-145

Experiments ranging from 2 to 3 GPa and 800 to 1300 °C and at 0.15 GPa and 770 °C were performed to investigate the stability and mutual solubility of the K₂ZrSi₃O₉ (wadeite) and K₂TiSi₃O₉ cyclosilicates under upper mantle conditions. The K₂ZrSi₃O₉–K₂TiSi₃O₉ join exhibits complete miscibility in the P–T interval investigated. With increasing degree of melting the solid solution becomes progressively enriched in Zr, indicating that K₂ZrSi₃O₉ is the more refractory end member. At 2 GPa, in the more complex K₂ZrSi₃O₉–K₂TiSi₃O₉–K₂Mg₆Al₂Si₆O₂₀(OH)₄ system, the presence of phlogopite clearly limits the extent of solid solution of the cyclosilicate to more Zr-rich compositions [Zr/(Zr + Ti) > 0.85], comparable to wadeite found in nature, with TiO₂ partitioning strongly into the coexisting mica and/or liquid. However, at 1200 °C, with increasing pressure from 2 to 3 GPa, the partitioning behaviour of TiO₂ changes in favour of the cyclosilicate, with Zr/(Zr + Ti) of the K₂(Zr,Ti)Si₃O₉ phase decreasing from ∼0.9 to ∼0.6. The variation in the Ti content of the coexisting phlogopite is related to its degree of melting to forsterite and liquid, following the major substitution ^VITi+^VI□=2^VIMg. Received: 26 January 1999 / Accepted: 10 January 2000  相似文献   

Thermodynamics and phonon dispersion of pyrope and grossular silicate garnets from ab initio simulations     

Jacopo Baima  Matteo Ferrabone  Roberto Orlando  Alessandro Erba  Roberto Dovesi 《Physics and Chemistry of Minerals》2016,43(2):137-149

The phonon dispersion and thermodynamic properties of pyrope (\(\hbox {Mg}_3\hbox {Al}_2\hbox {Si}_3\hbox {O}_{12}\)) and grossular (\(\hbox {Ca}_3\hbox {Al}_2\hbox {Si}_3\hbox {O}_{12}\) ) have been computed by using an ab initio quantum mechanical approach, an all-electron variational Gaussian-type basis set and the B3LYP hybrid functional, as implemented in the Crystal program. Dispersion effects in the phonon bands have been simulated by using supercells of increasing size, containing 80, 160, 320, 640, 1280 and 2160 atoms, corresponding to 1, 2, 4, 8, 16 and 27 \(\mathbf {k}\) points in the first Brillouin zone. Phonon band structures, density of states and corresponding inelastic neutron scattering spectra are reported. Full convergence of the various thermodynamic properties, in particular entropy (S) and specific heat at constant volume (\(C_\mathrm{{V}}\)), with the number of \(\mathbf {k}\) points is achieved with 27 \(\mathbf {k}\) points. The very regular behavior of the S(T) and \(C_\mathrm{{V}}(T)\) curves as a function of the number of \(\mathbf {k}\) points, determined by high numerical stability of the code, permits extrapolation to an infinite number of \(\mathbf {k}\) points. The limiting value differs from the 27-\(\mathbf {k}\) case by only 0.40 % at 100 K for S (the difference decreasing to 0.11 % at 1000 K) and by 0.29 % (0.05 % at 1000 K) for \(C_\mathrm{{V}}\). The agreement with the experimental data is rather satisfactory. We also address the problem of the relative entropy of pyrope and grossular, a still debated question. Our lattice dynamical calculations correctly describe the larger entropy of pyrope than grossular by taking into account merely vibrational contributions and without invoking “static disorder” of the Mg ions in dodecahedral sites. However, as the computed entropy difference is found to be larger than the experimental one by a factor of 2–3, present calculations cannot exclude possible thermally induced structural changes, which could lead to further conformational contributions to the entropy.  相似文献   

Predicted γ-ray image of SN 1006 due to inverse Compton emission     

O. Petruk  F. Bocchino  M. Miceli  G. Dubner  G. Castelletti  S. Orlando  D. Iakubovskyi  I. Telezhinsky 《Monthly notices of the Royal Astronomical Society》2009,399(1):157-165

We propose a method to synthesize the inverse Compton (IC) γ-ray image of a supernova remnant starting from the radio (or hard X-ray) map and using results of the spatially resolved X-ray spectral analysis. The method is successfully applied to SN 1006. We found that synthesized IC γ-ray images of SN 1006 show morphology in nice agreement with that reported by the High Energy Stereoscopic System (HESS) collaboration. The good correlation found between the observed very high energy γ-ray and X-ray/radio appearance can be considered as evidence of the fact that the γ-ray emission of SN 1006 observed by HESS is leptonic in origin, although a hadronic origin may not be excluded.  相似文献   

Variability of zinc and manganese concentrations in relation to sex and season in the bivalve Donax trunculus     

Mauri Marina  Orlando Enzo 《Marine pollution bulletin》1983,14(9):342-346

Females of Donax trunculus L. show higher concentrations of Mn and Zn than males. Differences are very high for Mn which also shows very large monthly fluctuations. Both the metals present higher contents during the period of gonadic maturation. Some high values of manganese found in the period when gonads are resting suggest the influence of sharp environmental variations in the area where bivalves have been collected.  相似文献   

Optimum seismic zoning for multiple types of structures     

Jaime García‐Prez  Francisco Castellanos  Orlando Díaz 《地震工程与结构动力学》2003,32(5):711-730

We consider zoning for the design criterion that minimizes the expected present value of the total cost, including the initial cost as well as losses due to damage and failure. The problem consists of the following: given the number of zones, their boundaries and design coefficients must be such that they minimize the expected present value of all structures built in the region. We will refer to solutions in one or more dimensions, depending on the number of the types of structures built in the region to be zoned. Two methods are proposed to solve the problems. The first method is based on the different combinations performed in order to attain optimum zoning. The second method uses an analogy to the evolution of biological systems. The work ends by applying the methods developed to a region of known seismicity. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Ore mineralogy,fluid inclusion,and stable isotopic characteristics of stratiform copper deposits in the coastal Cordillera of northern Chile     

Shoji Kojima  José Astudillo  Juan Rojo  Dania Tristá  Ken-ichiro Hayashi 《Mineralium Deposita》2003,38(2):208-216

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Synthesis of pyrope–grossular garnets: an experimental study at P = 2.5 GPa     

A. Orlando  D. Borrini 《Mineralogy and Petrology》2003,78(1-2):37-51

Summary ?In order to evaluate the stability of Mg–Ca garnets at P = 2.5 GPa/T = 800–1500 °C, some experiments were performed using both natural and synthetic starting materials. Particular attention was paid to the investigation of the Ca rich side of the pyrope–grossular join and the maximum pyrope content in grossular was found to be about 10 mol.%. The addition of Cr to the system only slightly increases the observed pyrope solubility in grossular whereas Na stabilises melilite and merwinite. Clinopyroxene with a composition lying on the diopside – Ca Tschermak join appears to be the only stable crystalline phase in the middle part of the pyrope–grossular join. Received August 28, 2001; revised version accepted July 23, 2002 Published online February 24, 2003  相似文献   

Thermal springs,fumaroles and gas vents of continental Yemen: Their relation with active tectonics,regional hydrology and the country’s geothermal potential     

Angelo Minissale  Mohamed A. Mattash  Orlando Vaselli  Franco Tassi  Ismail N. Al-Ganad  Enrico Selmo  Nasr M. Shawki  Dario Tedesco  Robert Poreda  Abdassalam M. Ad-Dukhain  Mohammad K. Hazzae 《Applied Geochemistry》2007

Most thermal springs of continental Yemen (about 65 emergences at 48 sampling sites) and a couple of fumaroles and boiling water pools have been sampled and analyzed for chemical and isotopic composition in the liquid phase and the associated free-gas phase. Whatever the emergence, all the water discharges have an isotopic signature of meteoric origin. Springs seeping out from high altitudes in the central volcanic plateau show a prevalent Na–HCO₃-composition, clearly affected by an anomalous flux of deep CO₂ deriving from active hydrothermal systems located in the Jurassic Amran Group limestone sequence and/or the Cretaceous Tawilah Group, likely underlying the 2000–3000 m thick volcanic suite. At lower elevations, CO₂ also affects the composition of some springs emerging at the borders of the central volcanic plateau.  相似文献   

Atom‐probe analyses of nanodiamonds from Allende     

Philipp R. Heck  Frank J. Stadermann  Dieter Isheim  Orlando Auciello  Tyrone L. Daulton  Andrew M. Davis  Jeffrey W. Elam  Christine Floss  Jon Hiller  David J. Larson  Josiah B. Lewis  Anil Mane  Michael J. Pellin  Michael R. Savina  David N. Seidman  Thomas Stephan 《Meteoritics & planetary science》2014,49(3):453-467

Atom‐probe tomography (APT) is currently the only analytical technique that, due to its spatial resolution and detection efficiency, has the potential to measure the carbon isotope ratios of individual nanodiamonds. We describe three different sample preparation protocols that we developed for the APT analysis of meteoritic nanodiamonds at sub‐nm resolution and present carbon isotope peak ratios of meteoritic and synthetic nanodiamonds. The results demonstrate an instrumental bias associated with APT that needs to be quantified and corrected to obtain accurate isotope ratios. After this correction is applied, this technique should allow determination of the distribution of ¹²C/¹³C ratios in individual diamond grains, solving the decades‐old question of the origin of meteoritic nanodiamonds: what fraction, if any, formed in the solar system and in presolar environments? Furthermore, APT could help us identify the stellar sources of any presolar nanodiamonds that are detected.  相似文献   

Real-time radar detection of iceberg shadows     

Orlando  J.R. Haykin  S. 《Oceanic Engineering, IEEE Journal of》1990,15(2):112-118

The Hough transform is used to estimate the radial direction of shadows cast by icebergs in surface-based marine radar returns using a Warp systolic computer. Automatically locating these shadows leads directly to automatically locating the icebergs casting the shadows. This is useful for the unattended navigation of a vessel through sea ice, as well as for improving the accuracy of a classified sea-ice image. The results reported show that the Hough transform can successfully estimate the radial directions of the shadows cast by the icebergs, and that the implementation on the Warp computer is commensurate with a real-time requirement for shadow detection  相似文献