Kei Hirose

Earth's solid inner core is mainly composed of iron (Fe). Because the relevant ultrahigh pressure and temperature conditions are difficult to produce experimentally, the preferred crystal structure of Fe at the inner core remains uncertain. Static compression experiments showed that the hexagonal close-packed (hcp) structure of Fe is stable up to 377 gigapascals and 5700 kelvin, corresponding to inner core conditions. The observed weak temperature dependence of the c/a axial ratio suggests that

Research Article| January 01, 1997 Melting experiments on lherzolite KLB-1 under hydrous conditions and generation of high-magnesian andesitic melts Kei Hirose Kei Hirose 1Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Ookayama, Tokyo 152, Japan Search for other works by this author on: GSW Google Scholar Author and Article Information Kei Hirose 1Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Ookayama, Tokyo 152, Japan Publisher: Geologica

Phase relations in the natural pyrolitic mantle composition (KLB‐1) around 670‐km depth have been determined at 1600–2200°C by high‐pressure experiments using multianvil apparatus. A phase transition between majorite garnet and Al‐bearing Mg‐rich perovskite occurs at depths similar to the postspinel phase transition. The seismic discontinuity observed at this depth could be caused by a combination of both transitions. The majorite‐perovskite transition boundary has a positive Clausius‐Clapeyron

The composition and state of Earth's core, located deeper than 2,900 km from the surface, remain largely uncertain. Recent static experiments on iron and alloys performed up to inner core pressure and temperature conditions have revealed phase relations and properties of core materials. These mineral physics constraints, combined with theoretical calculations, continue to improve our understanding of the core, in particular the crystal structure of the inner core and the chemical composition, th

Partial melt compositions of natural carbonated peridotite (KLB‐1 + 2.5 wt% CO 2 ) have been determined at 3 GPa using the diamond aggregate method. Melt obtained at 1350 °C is carbonatitic, and with increasing temperature melt composition becomes silicate‐rich. These melts are lower in SiO 2 and Al 2 O 3 and higher in MgO and CaO compared to dry partial melts of KLB‐1 generated at the same pressure. The 1400 and 1450 °C liquids have melilititic compositions, which are in good agreement with tho

Constraining the core’s composition is essential for understanding Earth accretion, core formation and the sustainment of Earth’s magnetic field. Earth’s outer and inner core exhibit a density deficit relative to pure iron, attributed to the presence of substantial amounts of low atomic number ‘light’ elements, such as sulfur, silicon, oxygen, carbon and hydrogen. However, owing to its inaccessibility, estimates of core composition can only be indirectly obtained by matching results from high-pr

We present a method for the first-principles calculation of the electronic states under strong field and current, which is effective for the bielectrode system with atomic structures around the surface regions. A microscopic electron distribution is calculated self-consistently together with the field and current distributions. In our method the scattering waves are calculated by the step-by-step recursion-matrix method and two different Fermi levels are assigned to each jellium electrode in acc

The stability of (Mg,Fe)SiO 3 perovskite in the deep lower mantle has long been uncertain. Recently, a phase transition from perovskite to postperovskite was discovered through a significant change in the X‐ray diffraction pattern at high‐pressure and high‐temperature conditions corresponding to the core‐mantle boundary region. This phase transition was also confirmed by first‐principles calculations. These suggest that (Mg,Fe)SiO 3 postperovskite is the predominant mineral in the lowermost mant

Using spin-density-functional theory, we study the electronic states of a two-dimensional parabolic quantum dot with up to $N=58$ electrons. We observe a shell structure for the filling of the dot with electrons. Hund's rule determines the spin configuration of the ground state, but only up to 22 electrons. At specific N, the ground state is degenerate, and a small elliptical deformation of the external potential induces a rotational charge-density-wave state. Previously identified spin-density-