914 research outputs found
Rare and unique meteorites from Antarctica
The detection of Antarctic meteorites of Lunar and perhaps Martian origin, belongs to the most important discoveries in planetology during the last years. There is such a wealth of new information on differentiated and undifferentiated planetary bodies deduced from Antarctic meteorites that it is at present not possible to even qualitatively foresee the impact that these meteorites will have on the understanding of the formation and differentiation of large and small planets in the solar system. Martian meteorites, Lunar meteorites, meteorites from the parent body of basaltic achondrites, and chrondritic meteorites are discussed
Strong Sequestration of Hydrogen Into the Earth's Core During Planetary Differentiation
We explore the partitioning behavior of hydrogen between coexisting metal and silicate melts at conditions of the magma ocean and the current core–mantle boundary with the help of density functional theory molecular dynamics. We perform simulations with the two-phase and thermodynamic integration methods. We find that hydrogen is weakly siderophile at low pressure (20 GPa and 2,500 K), and becomes much more strongly so with pressure, suggesting that hydrogen is transported to the core in a significant amount during core segregation and is stable there. Based on our results, the core likely contains ~1 wt% H, assuming single-stage formation and equilibration at 40 GPa. Our two-phase simulations further suggest that silicon is entrained in the core-forming metal, while magnesium remains in the silicate phase. This preferred incorporation of silicon hints at an explanation for the elevated Mg/Si ratio of the bulk silicate Earth relative to chondritic compositions
Siderophile elements in the upper mantle of the Earth: New clues from metal-silicate partition coefficients
New, precise data on the solubilities of Ni, Co, and Mo in silicate melts at 1400 C and fO2 from IW to IW-2 are presented. The results suggest NiO, CoO as stable species in the melt. No evidence for metallic Ni or Co was found. Equilibrium was ensured by reversals with initially high Ni and Co in the glass. Mo appears to change oxidation state at IW-1, from MoO3 to MoO2. Metal-silicate partition coefficients calculated from these data and recent data on Pd indicate similar partition coefficients for Pd and Mo at the conditions of core formation. This unexpected result constrains models of core formation in the Earth
Genetic relationships between chondrules, rims and matrix.
Published versio
Magnetic Resonance in the Spin-Peierls compound
We present results from magnetic resonance measurements for 75-350 GHz in
'-NaVO. The temperature dependence of the integrated
intensity indicates that we observe transitions in the excited state. A
quantitative description gives resonances in the triplet state at high symmetry
points of the excitation spectrum of this Spin-Peierls compound. This energy
has the same temperature dependence as the Spin-Peierls gap. Similarities and
differences with the other inorganic compound CuGeO are discussed.Comment: 2 pages, REVTEX, 3 figures. to be published in Phys.Rev.
Field-induced structural evolution in the spin-Peierls compound CuGeO: high-field ESR study
The dimerized-incommensurate phase transition in the spin-Peierls compound
CuGeO is probed using multifrequency high-resolution electron spin
resonance (ESR) technique, in magnetic fields up to 17 T. A field-induced
development of the soliton-like incommensurate superstructure is clearly
indicated as a pronounced increase of the ESR linewidth (magnon
excitations), with a at 13.8 T. The anomaly is
explained in terms of the magnon-soliton scattering, and suggests that the
soliton-like phase exists close to the boundary of the dimerized-incommensurate
phase transition. In addition, magnetic excitation spectra in 0.8% Si-doped
CuGeO are studied. Suppression of the anomaly observed in the
doped samples suggests a collapse of the long-range-ordered soliton states upon
doping, that is consistent with high-field neutron scattering experiments.Comment: Accepted to Phys. Rev.
Submillimeter Wave ESR Study of Spin Gap Excitations in CuGeO3
Transitions between the ground singlet state to the excited triplet state has
been observed in CuGeO3 by means of submillimeter wave electron spin resonance.
The strong absorption intensity shows the break down of the selection rule. The
energy gap at zero field is evaluated to be 570 GHz(2.36 meV) and this value is
nearly identical to the gap at the zone center observed by inelastic neutron
scattering. The absorption intensity shows strong field orientation dependence
but shows no significant dependence on magnetic field intensity. These features
have been explained by considering the existence of Dzyaloshinsky-Moriya (DM)
antisymmetric exchange interaction. The doping effect on this singlet-triplet
excitation has been also studied. A drastic broadening of the absorption line
is observed by the doping of only 0.5 % of Si.Comment: 6 pages, 8figures submitted to J. Phys. Soc. Jp
Abundances of the elements in the solar system
A review of the abundances and condensation temperatures of the elements and
their nuclides in the solar nebula and in chondritic meteorites. Abundances of
the elements in some neighboring stars are also discussed.Comment: 42 pages, 11 tables, 8 figures, chapter, In Landolt- B\"ornstein, New
Series, Vol. VI/4B, Chap. 4.4, J.E. Tr\"umper (ed.), Berlin, Heidelberg, New
York: Springer-Verlag, p. 560-63
Excitations of the field-induced soliton lattice in CuGeO3
Here we report the first inelastic neutron scattering study of the magnetic
excitations in the incommensurate phase of a spin-Peierls material. The results
on CuGeO3 provide direct evidence of a finite excitation gap, two sharp
magnetic excitation branches and a very low-lying excitation which is
identified as a phason mode, the Goldstone mode of the incommensurate soliton
lattice.Comment: 5 pages, revtex, 4 figures (*.eps), win-zippe
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