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  • 1
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    Multidisciplinary impact of the deep mantle phase transition in perovskite structure (2005)
    In:  Eos, Trans., Am. Geophys. Un., Tulsa, 450 pp.; 2nd modified and expanded ed., Society of Exploration Geophysics, vol. 86, no. 1, pp. 1 & 5, pp. B12408, (ISSN: 1340-4202)
    Details
    Publication Date: 2005
    Keywords: Mineralogy ; Seismology ; Earth model, also for more shallow analyses ! ; earth mantle
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    BIBLIOGRAPHY SEISMOLOGY
  • 2
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    Stability and structure of MgSiO3 perovskite to 2300-kilometer depth in Earth's mantle (2001)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2001-09-29
    Description: Unexplained features have been observed seismically near the middle (approximately 1700-kilometer depth) and bottom of the Earth's lower mantle, and these could have important implications for the dynamics and evolution of the planet. (Mg,Fe)SiO3 perovskite is expected to be the dominant mineral in the deep mantle, but experimental results are discrepant regarding its stability and structure. Here we report in situ x-ray diffraction observations of (Mg,Fe)SiO3 perovskite at conditions (50 to 106 gigapascals, 1600 to 2400 kelvin) close to a mantle geotherm from three different starting materials, (Mg0.9Fe0.1)SiO enstatite, MgSiO3 glass, and an MgO+SiO2 mixture. Our results confirm the stability of (Mg,Fe)SiO3 perovskite to at least 2300-kilometer depth in the mantle. However, diffraction patterns above 83 gigapascals and 1700 kelvin (1900-kilometer depth) cannot presently rule out a possible transformation from Pbnm perovskite to one of three other possible perovskite structures with space group P2(1)/m, Pmmn, or P4(2)/nmc.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Shim, S H -- Duffy, T S -- Shen, G -- New York, N.Y. -- Science. 2001 Sep 28;293(5539):2437-40.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Geosciences, Princeton University, Princeton, NJ 08544, USA., CARS, University of Chicago, Chicago, IL 60637, USA. sangshim@uclink.berkeley.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11577232" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
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    Thickness and Clapeyron slope of the post-perovskite boundary (2009)
    Nature Publishing Group (NPG)
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    Publication Date: 2009-12-17
    Description: The thicknesses and Clapeyron slopes of mantle phase boundaries strongly influence the seismic detectability of the boundaries and convection in the mantle. The unusually large positive Clapeyron slope found for the boundary between perovskite (Pv) and post-perovskite (pPv) (the 'pPv boundary') would destabilize high-temperature anomalies in the lowermost mantle, in disagreement with the seismic observations. Here we report the thickness of the pPv boundary in (Mg(0.91)Fe(2+)(0.09))SiO(3) and (Mg(0.9)Fe(3+)(0.1))(Al(0.1)Si(0.9))O(3) as determined in a laser-heated diamond-anvil cell under in situ high-pressure (up to 145 GPa), high-temperature (up to 3,000 K) conditions. The measured Clapeyron slope is consistent with the D'' discontinuity. In both systems, however, the pPv boundary thickness increases to 400-600 +/- 100 km, which is substantially greater than the thickness of the D'' discontinuity (〈30 km). Although the Fe(2+) buffering effect of ferropericlase could decrease the pPv boundary thickness, the boundary may remain thick in a pyrolitic composition because of the effects of Al and the rapid temperature increase in the D'' layer. The pPv boundary would be particularly thick in regions with an elevated Al content and/or a low Mg/Si ratio, reducing the effects of the large positive Clapeyron slope on the buoyancy of thermal anomalies and stabilizing compositional heterogeneities in the lowermost mantle. If the pPv transition is the source of the D'' discontinuity, regions with sharp discontinuities may require distinct compositions, such as a higher Mg/Si ratio or a lower Al content.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Catalli, Krystle -- Shim, Sang-Heon -- Prakapenka, Vitali -- England -- Nature. 2009 Dec 10;462(7274):782-5. doi: 10.1038/nature08598.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20010685" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 4
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    Seismic imaging of transition zone discontinuities suggests hot mantle west of Hawaii (2011)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2011-05-28
    Description: The Hawaiian hotspot is often attributed to hot material rising from depth in the mantle, but efforts to detect a thermal plume seismically have been inconclusive. To investigate pertinent thermal anomalies, we imaged with inverse scattering of SS waves the depths to seismic discontinuities below the Central Pacific, which we explain with olivine and garnet transitions in a pyrolitic mantle. The presence of an 800- to 2000-kilometer-wide thermal anomaly (DeltaT(max) ~300 to 400 kelvin) deep in the transition zone west of Hawaii suggests that hot material does not rise from the lower mantle through a narrow vertical plume but accumulates near the base of the transition zone before being entrained in flow toward Hawaii and, perhaps, other islands. This implies that geochemical trends in Hawaiian lavas cannot constrain lower mantle domains directly.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Cao, Q -- van der Hilst, R D -- de Hoop, M V -- Shim, S-H -- New York, N.Y. -- Science. 2011 May 27;332(6033):1068-71. doi: 10.1126/science.1202731.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. qinc@mit.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21617072" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 5
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    Seismostratigraphy and thermal structure of Earth's core-mantle boundary region (2007)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2007-03-31
    Description: We used three-dimensional inverse scattering of core-reflected shear waves for large-scale, high-resolution exploration of Earth's deep interior (D'') and detected multiple, piecewise continuous interfaces in the lowermost layer (D'') beneath Central and North America. With thermodynamic properties of phase transitions in mantle silicates, we interpret the images and estimate in situ temperatures. A widespread wave-speed increase at 150 to 300 kilometers above the coremantle boundary is consistent with a transition from perovskite to postperovskite. Internal D'' stratification may be due to multiple phase-boundary crossings, and a deep wave-speed reduction may mark the base of a postperovskite lens about 2300 kilometers wide and 250 kilometers thick. The core-mantle boundary temperature is estimated at 3950 +/- 200 kelvin. Beneath Central America, a site of deep subduction, the D'' is relatively cold (DeltaT = 700 +/- 100 kelvin). Accounting for a factor-of-two uncertainty in thermal conductivity, core heat flux is 80 to 160 milliwatts per square meter (mW m(-2)) into the coldest D'' region and 35 to 70 mW m(-2) away from it. Combined with estimates from the central Pacific, this suggests a global average of 50 to 100 mW m(-2) and a total heat loss of 7.5 to 15 terawatts.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉van der Hilst, R D -- de Hoop, M V -- Wang, P -- Shim, S-H -- Ma, P -- Tenorio, L -- New York, N.Y. -- Science. 2007 Mar 30;315(5820):1813-7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge MA, USA. hilst@mit.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17395822" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 6
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    ApAUF1 negatively regulates ApC/EBP and LTF [Neuroscience] (2012)
    National Academy of Sciences
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    Publication Date: 2012-09-19
    Description: The consolidation of long-term memory for sensitization and synaptic facilitation in Aplysia requires synthesis of new mRNA including the immediate early gene Aplysia CCAAT enhancer-binding protein (ApC/EBP). After the rapid induction of ApC/EBP expression in response to repeated treatments of 5-hydroxytryptamine (5-HT), ApC/EBP mRNA is temporarily expressed in sensory neurons...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 7
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    Inter-comparison of the Gold, Platinum, and MgO Pressure Scales up to 140 GPa and 2,500 K (2017)
    Wiley
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    Publication Date: 2017-05-03
    Description: In order to inter-calibrate the equations of state (EOS) of the three widely-used pressure standards, gold, platinum, and MgO, we have measured their unit-cell volumes together in the laser heated diamond-anvil cell up to 140GPa and 2,500K. At 300K, three scales agree with each other within ±2.5 GPa to 135GPa if the EOSs measured in quasi-hydrostatic media are used [ Zha et al. , 2000; Dewaele et al. , 2004]. We further refined the EOSs at 300K, making them consistent with each other within ±1GPa up to 135GPa. At high temperature ( T ), the three standards match the best within ±1GPa between 40 and 140GPa, when we use the scales by Dorogokupets and Dewaele [2007]. However, a 2–3GPa of discrepancy remains at 20–40GPa and 1500–2000K, with gold yielding the highest pressure ( P ). The pressure discrepancy is likely related to steep decreases in the Grüneisen parameter, the anharmonicity, and/or the electronic effects for the standards at the P – T conditions. Because gold melts near the temperatures expected for the mantle transition zone, severe anharmonic effects expected under pre-melting conditions make gold unsuitable for determining the phase boundaries in the region. The pressure scales by Dorogokupets and Dewaele [2007] provide tighter constrains on the Clapeyron slopes of the post-spinel boundary to −2.0 ∼− 2.7 MPa/K and the post-perovskite boundary to 7 ∼ 10 MPa/K. The data and refined EOSs presented here allow for reliable comparisons among experiments with different pressure standards for the entire P – T conditions expected for the Earth's lower mantle.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Stability, metastability, and elastic properties of a dense silica polymorph, seifertite (2013)
    Wiley
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    Publication Date: 2013-09-04
    Description: [1]  Dense silica polymorphs with six-fold coordinated Si have been found in SNC and lunar meteorites and may be important minerals for silica-rich components in the lower mantle. However, the stable crystal structure in the lower mantle and properties of dense silica remain controversial. Under stable heating and quasi-hydrostatic stress conditions, we found that the CaCl 2 type undergoes a phase transition to the α -PbO 2 type (seifertite) at 130–140 GPa and 2500 K. Our data suggests that this phase transition occurs at a greater depth than the perovskite → post-perovskite transition in basaltic materials in the lowermost mantle. The molar volume measured at 1 bar is the smallest among the reported silica polymorphs, therefore having the highest calculated density and in excellent agreement with recent first-principles calculations. The greater molar volume of seifertite found in the Shergottite meteorite and previous experiments supports a metastable synthesis of the phase outside its stability field. Our data combined with the Hugoniots of silica polymorphs also rule out the possibility of the formation of seifertite in the meteorite within its stability field. We found very little change in bulk sound speed across the CaCl 2 -type → seifertite transition. If shear wave velocity decreases at the transition to seifertite as suggested by some computational studies, this silica transition may provide an alternative explanation forthe discontinuities with a shear wave velocity decrease found at depths greater than the D″ discontinuity.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Inhibition of teratoma by small molecules [Cell Biology] (2013)
    National Academy of Sciences
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    Publication Date: 2013-08-28
    Description: The future of safe cell-based therapy rests on overcoming teratoma/tumor formation, in particular when using human pluripotent stem cells (hPSCs), such as human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs). Because the presence of a few remaining undifferentiated hPSCs can cause undesirable teratomas after transplantation, complete...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 10
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    Thermal Expansion of SiC at High Pressure–Temperature and Implications for Thermal Convection in the Deep Interiors of Carbide Exoplanets (2017)
    Wiley
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    Publication Date: 2017-01-10
    Description: Recent astrophysical observations have shown that some stars have sufficiently high carbon to oxygen ratios and may host planets composed mainly of carbides instead of silicates and oxides. From the low thermal expansion of SiC at 1 bar, it can be inferred that the buoyancy force of thermal anomalies is much lower in the carbide planets than in the silicate planets. However, numerous studies have shown that high pressure in planetary interiors can fundamentally change the physical properties of materials. We have measured the pressure–volume–temperature relations of two SiC polymorphs (3C and 6H) at pressures and temperatures up to 80 GPa and 1900 K and 65 GPa and 1920 K, respectively, in the laser-heated diamond anvil cell combined with synchrotron X-ray diffraction. We found no evidence of dissociations of these phases up to our maximum pressure condition, supporting the stability of SiC to 1900 km depth in Earth-size Si-rich carbide planets. Following the Mie-Grüneisen approach, we fit our data to the Birch-Murnaghan or the Vinet equations of state combined with the Debye approach. We found that the pressure induced change in the thermal expansion parameter of SiC is much smaller than that of Mg-silicate perovskite (bridgmanite). Our new measurements suggest that the thermal buoyancy force may be stronger in the deep interiors of Si-rich carbide exoplanets than in the “Earth-like” silicate planets.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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