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Now showing items 1 - 16 of 169

  • Argon-neon binary diagram and ArNe2 Laves phase

    Dewaele, Agnes   Rosa, Angelika D.   Guignot, Nicolas  

    Mixtures of argon and neon have been experimentally studied under high pressure. One stoichiometric compound, with ArNe2 composition, is observed in this system. It is a Laves phase with a hexagonal MgZn2 structure, stable up to at least 65 GPa, the highest pressure reached in the experiments. Its equation of state follows closely the one of an ideal Ar+2Ne mixture. The binary phase diagram of the Ar-Ne system resembles the diagram predicted for hard sphere mixtures with a similar atomic radius ratio, suggesting that no electronic interactions appear in this system in this pressure range. ArNe2 can be a convenient quasihydrostatic pressure transmitting medium under moderate pressure.
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  • Solving Controversies on the Iron Phase Diagram Under High Pressure

    Morard, Guillaume   Boccato, Silvia   Rosa, Angelika D.   Anzellini, Simone   Miozzi, Francesca   Henry, Laura   Garbarino, Gaston   Mezouar, Mohamed   Harmand, Marion   Guyot, Francois   Boulard, Eglantine   Kantor, Innokenty   Irifune, Tetsuo   Torchio, Raffaella  

    As the main constituent of planetary cores, pure iron phase diagram under high pressure and temperature is of fundamental importance in geophysics and planetary science. However, previously reported iron-melting curves show large discrepancies (up to 1000 K at the Earth's core-mantle boundary, 136 GPa), resulting in persisting high uncertainties on the solid-liquid phase boundary. Here we unambiguously show that the observed differences commonly attributed to the nature of the used melting diagnostic are due to a carbon contamination of the sample as well as pressure overestimation at high temperature. The high melting temperature of pure iron under core-mantle boundary (4250 +/- 250 K), here determined by X-ray absorption experiments at the Fe K-edge, indicates that volatile light elements such as sulfur, carbon, or hydrogen are required to lower the crystallization temperature of the Earth's liquid outer core in order to prevent extended melting of the surrounding silicate mantle. Plain Language Summary Iron is the main constituent of planetary cores; however, there are still large controversies regarding its melting temperature and phase diagram under planetary interior conditions. The present study reconciles different experimental approaches using laser-heated diamond anvil cell with different in situ X-ray diagnostics (absorption, diffraction, and Mossbauer spectroscopy). The main reason of discrepancies (over 1000 K at core-mantle boundary conditions) is attributed to carbon contamination from the diamond anvils and metrology issues related to thermal pressure overestimation. A high-melting temperature for iron at core-mantle boundary pressure would imply the presence of volatile elements in the liquid outer core, such as sulfur, carbon, or hydrogen, in order to lower its crystallization temperature and avoid extended melting of the surrounding silicate mantle.
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  • Elasticity of phase D and implication for the degree of hydration of deep subducted slabs

    Rosa, Angelika D.   Sanchez-Valle, Carmen   Ghosh, Sujoy  

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  • Elasticity of phase D and implication for the degree of hydration of deep subducted slabs

    Rosa, Angelika D.   Sanchez-Valle, Carmen   Ghosh, Sujoy  

    Seismic anomalies in subducted slabs, including low velocity zones and shear wave splitting, have often been related to hydrous regions. Phase D (MgSi2H2O6, 10-18 wt.% H2O) may be the ultimate water carrier in hydrous subducted peridotite and its seismic properties are thus essential for interpreting observed anomalies in terms of hydration. Here, we report the sound velocities and elasticity of Mg- and Al-Fe-bearing phase D single-crystals measured by Brillouin spectroscopy. The room conditions adiabatic bulk and shear modulus are: K-S0 = 154.8 (3.2) GPa and mu = 104.3(2.1) GPa for Mg-phase D and K-S0 = 158.4(3.9) GPa and mu = 104.7(2.7) GPa for AlFe-phase D, suggesting minor effect of cation substitution on the elasticity of phase D. Based on the seismic velocity data, we found that 16 vol.% of AlFe-phase D in hydrous subducted peridotite with 1.2 wt.% H2O could provide a plausible explanation for the negative velocity anomalies of 3% observed in fragments of the Tonga slab below the transition zone. Citation: Rosa, A. D., C. Sanchez-Valle, and S. Ghosh (2012), Elasticity of phase D and implication for the degree of hydration of deep subducted slabs, Geophys. Res. Lett., 39, L06304, doi:10.1029/2012GL050927.
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  • Kr environment in feldspathic glass and melt:A high pressure,high temperature X-ray absorption study

    Crepisson, Celine   Sanloup, Chrystele   Cormier, Laurent   Blanchard, Marc   Hudspeth, Jessica   Rosa, Angelika D.   Mathon, Olivier   Irifune, Tetsuo  

    Noble gases are used to trace the evolution of the Earth's atmosphere and magmatic processes. However little is known about their solubility mechanisms in silicate melts or glasses, whereas it could be fundamental to interpret these data. We report here the first in situ X-ray absorption spectroscopy data at the Kr K-edge on a feldspathic Kr-bearing glass and melt (0.5 wt% Kr) up to 2.7 GPa and 1086 degrees C. Kr fitting of the EXAFS signal shows that Kr is surrounded by oxygen atoms. Two Kr-O distances are identified: 2.49 +/- 0.1 A and 3.32 +/- 0.1 A. Results can be interpreted as two Kr populations. Kr surrounded by O atoms at 3.32 +/- 0.1 A suggests a filling of the large cavities available in the silicate network, in agreement with previous studies. On the contrary, Kr surrounded by O atoms at 2.49 +/- 0.1 A, and the observed +0.6 eV shift of the edge position at high pressure, suggest Kr bonding to O atoms and Kr oxidation inside cages formed by the largest aluminosilicate rings (i.e. similar to 12-membered-rings). Present results show that heavy noble gases incorporation in silicate melts can no longer be considered as a passive filling of the voids.
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  • Shear wave anisotropy in textured phase D and constraints on deep water recycling in subduction zones

    Rosa, Angelika D.   Sanchez-Valle, Carmen   Nisr, Carole   Evans, Shaun R.   Debord, Regis   Merkel, Sébastien  

    Highlights • Phase D forms strong textures already at low stresses. • Textured phase D is a potential source of seismic shear anisotropy in Tonga slab. • Hydration at depth may be detectable seismically if water is stored in phase D. • Implications for deep water recycling into the lower mantle via subduction. Abstract Regions of low seismic velocity and high shear anisotropies in cold subducted slabs have often been related to anisotropic fabrics in hydrous phases mainly induced by slab deformation. The interpretation of these seismic anomalies in terms of hydration thus relies on a better knowledge of the elasticity and plastic deformation mechanisms of candidate hydrous phases. Here we investigate the development of lattice preferred orientations (LPO) in phase D [MgSi2H2O6, 10–18 wt% H2O], the ultimate water carrier in hydrous subducted peridotite. The samples were deformed non-hydrostatically up to 48 GPa in a diamond anvil cell and the texture and strength were obtained from analysis of the X-ray diffraction patterns collected in radial diffraction geometry. We find that at low strains the layered structure of phase D displays strong 0001 texture, where the stacking fault axis (c-axis) preferentially align parallel to the compression axis. A subsidiary 1 0 1 ¯ 0 texture develops at higher strains. Plasticity simulations in polycrystalline aggregates using a viscoplastic self-consistent model suggest that these LPO patterns are consistent with shape preferred orientation mechanism during the first compaction steps and, with dominant easy glide on basal planes and harder first order pyramidal slip, respectively, upon further compression. We find that phase D displays the lowest strength and the highest anisotropy among phases in hydrous peridotite in the uppermost lower mantle and might thus control the shear wave anisotropy generated in subducted slabs below the transition zone. We further evaluate the effect of textured phase D on the seismic velocity structure and shear wave anisotropy of deformed hydrous peridotite and compare the results to seismic observations in Tonga subduction. We show that 16 vol% of phase D in hydrous subducted peridotite is required to explain the negative velocity anomalies of 3%, the extent of shear wave splitting (0.9±0.3% 0.9 ± 0.3 % ) and the shear wave ray polarization geometry (VSH>VSV V SH > V SV ) observed in a detached fragment of the Tonga slab laying sub-horizontally below the transition zone. Seismic observations may thus place constraints on the degree of hydration of the Tonga slab beyond the transition zone, leading to the requirement that a minimum of 1.2 wt% H2O is retained in the slab by hydrous peridotite below 670 km depth.
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  • Elasticity of superhydrous phase B, seismic anomalies in cold slabs and implications for deep water transport

    Rosa, Angelika D.   Sanchez-Valle, Carmen   Wang, Jingyun   Saikia, Ashima  

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  • Sound velocities of ferromagnesian carbonates and the seismic detection of carbonates in eclogites and the mantle

    Sanchez-Valle, Carmen   Ghosh, Sujoy   Rosa, Angelika D.  

    Ferromagnesian carbonates are the stable high pressure carbonates in eclogite and peridotite and their physical properties are thus important for understanding the dynamics of reintroduction of carbon into the Earth's mantle. Using Brillouin scattering spectroscopy, we have determined the sound velocities and elasticity of carbonates along the (Mg1-xFex) CO3 join (with x =3D 0, 0.65, 0.95 and 0.99) at room conditions to evaluate the effect of carbonates on the seismic velocity structure of the subducting lithosphere. Within experimental uncertainties, Fe substitution has a negligible effect on the adiabatic bulk modulus K-s of Mg-Fe carbonates whereas the shear modulus m decreases by 34% from MgCO3 to FeCO3. We find that the seismic velocity contrast between carbonate-bearing eclogite and peridotite with 5 wt% CO2 and their carbon-free counterparts is less than 1%, indicating that moderately carbonated regions in the subducting mafic crust and mantle may be difficult to detect seismically. The threshold of seismic detection with present methods (similar to 2%) would require significantly high carbonate contents of 24.5 vol% (Mg0.79Fe0.21) CO3 (15 wt% CO2) in eclogite and more than 30 vol% (Mg0.93Fe0.07) CO3 (> 20 wt% CO2) in peridotite. Citation: Sanchez-Valle, C., S. Ghosh, and A. D. Rosa (2011), Sound velocities of ferromagnesian carbonates and the seismic detection of carbonates in eclogites and the mantle, Geophys. Res. Lett., 38, L24315, doi: 10.1029/2011GL049981.
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  • Measurement of temperature in the laser heated diamond anvil cell:comparison between reflective and refractive optics

    Giampaoli, Ruggero   Kantor, Innokenty   Mezouar, Mohamed   Boccato, Silvia   Rosa, Angelika D.   Torchio, Raffaella   Garbarino, Gaston   Mathon, Olivier   Pascarelli, Sakura  

    In this article we present a direct comparison between reflective (Schwarzschild mirrors) and refractive (achromatic doublets) optics commonly used in spectroradiometric temperature measurements in laser heated diamond anvil cells. Emission spectra are fitted with the Planck's law and are further analysed with the two-colour technique; theoretical simulations are used to compare the temperature measurement accuracy of the two optical systems. The first result obtained is that achromatic doublets with large numerical aperture (NA approximate to 0.2) produce extensive accuracy errors in the full T range (1500-3000K). When reduced apertures (NA =3D 0.8) are used a good agreement is found with measurements from reflective optics up to 2600K while systematic differences (around 200K) appear at higher temperatures. However, these temperature differences cannot explain the discrepancies between the iron melting curves obtained in the past years using laser heated diamond anvil cells.
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  • A new catechin derivative from the fruits of Rosa sterilis S. D. Shi

    Luo, Xu-Lu   Dan, Han-Long   Li, Na   Li, Yong-He   Zhang, Ying-Jun   Zhao, Ping  

    A new catechin derivative named as sterilin A (1), and three known compounds, (+)-catechin (2), kaji-ichigoside F1 (3) and 2 alpha, 3 alpha, 19 alpha-trihydroxyurs- 12-en-28-oic acid-28-O-beta-D-xylopyranosyl-(1 -> 2)-beta-D-glucopyranoside (4), was isolated from the fresh fruits of Rosa sterilis. Their structures were elucidated by means of extensive spectroscopic analysis and by comparison with data reported in the literatures.
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  • Postharvest 1-methylcyclopropene treatments maintain the quality of Rosa sterilis D. shi during storage

    Guofang, XIE   Lirong, WANG   Kuanxiu, FAN   Na, LIU   Yongling, LIU   Zhibing, ZHAO  

    Abstract Effects of different concentrations of aqueous 1-methylcyclopropene (1-MCP) on Rosa sterilis D. shi fruits were investigated. The fruits were harvested at commercial maturity stage and treated with 1-MCP treatment at 0.5, 1.0, and 1.5 =CE=BCL L-1 for 20 h at 25 =C2=B0C in an air tight chamber along with control sample to evaluate the effect of 1-MCP concentration on its quality during storage. The result showed that postharvest treatment with 1.0 =CE=BCL L-1 1-MCP suppressed the respiration rate, ethylene production rate and POD activity in Rosa sterilis D. shi fruits, inhibited the transport of reducing sugar and the increase of cellulose, delayed the increase in PPO activity, and retarded the decrease in ascorbic acid. The regulation of fibrosis process with postharvest 1.0 =CE=BCL L-11-MCP treatment could be used to maintain the quality of Rosa sterilis D. shi fruits.=09
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  • Carmen de figuris vel schematibus. (Bibliotheca Weidmanniana, 5)by Rosa Maria D\"angelo

    Review by: Pierre-Jacques Dehon  

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  • Rosa Luxemburg and the Noble Dreamby D. E. Shepardson

    Review by: Ben Fowkes  

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  • Rosa Luxemburg and the Noble Dreamby D. E. Shepardson

    Review by: Ben Fowkes  

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  • Giorni d\"acqua corrente: Quando la vita delle donne diventa raccontoby Maria Rosa Cutrufelli

    Review by: Angela M. Jeannet  

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  • The Maravillas Districtby Rosa Chacel; D. A. Démers

    Review by: Eunice D. Myers  

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