Engineering topics
Shimizu, N.
Publications and source records attributed to Shimizu, N..
Ab initio multishell valence-space Hamiltonians and the island of inversion
In the shell-model framework, valence-space Hamiltonians connecting multiple major-oscillator shells are of key interest for investigating the physics of neutron-rich nuclei, which have been the subject of intense experimental activity for decades. Here we present an extension of the ab initio valence-space in-medium similarity renormalization group, which allows the derivation of such Hamiltonians nonperturbatively. Starting from initial two- and three-nucleon forces from chiral effective field theory, we then calculate properties of nuclei in the important island-of-inversion region above oxygen, so far unexplored with ab initio methods. In this work, our results in the neon and magnesium isotopes indicate the importance of neutron excitation from the $\textit{sd}$ to $\textit{pf}$ shells and ground states dominated by intruder configurations around $\textit{N}$ = 20, consistent with the conclusions from phenomenological studies. We also benchmark the excitation spectrum of 16 O with coupled-cluster theory, finding generally good agreement, and discuss implications for ground-state energies and charge radii in oxygen and calcium isotopes. Finally we outline the proper procedure for treating the longstanding issue of center-of-mass contamination, and show that with a particular choice of valence space, these spurious states can be removed successfully.
The formation of FeO-rich pyroxene and enstatite in unequilibrated enstatite chondrites: A petrologic-trace element (SIMS) study
Enstatite (En) chondrites record the most reducing conditions known in the early solar system. Their oxidation state may be the result of condensation in a nebular region having an enhanced C/O ratio, reduction of more oxidized materials in a reducing nebula, reduction during metamorphic reheating in a parent body, or a combination of these events. The presence of more oxidized Fe-rich silicates, two types of En (distinguished by red and blue CL), and the juxtaposition of FeO-rich pyroxenes (Fe-pyx) surrounded by blue En (enstatite) in the UEC's (unequilibrated enstatite chondrites) is intriguing and led to the examination of the question of enstatite chondrite formation. Previously, data was presented on the petrologic-geochemical characteristics of the Fe-pyx and coexisting red and blue En. Here minor and trace element abundances (determined by ion probe-SIMS) on these three types of pyroxenes are reported on in the following meteorites: Kota Kota and LEW87223 (EH3), MAC88136 (EL3), St. Marks (EH4), and Hvittis (EL6). More data are currently being collected.
Exploring the lunar mantle with secondary ion mass spectrometry - A comparison of lunar picritic glass beads from the Apollo 14 and Apollo 17 sites
Results are presented from SIMS analyses of major, minor, and trace elements in lunar picritic glass beads obtained from the Apollo 14 (A-14) and Apollo 17 (A-17) landing sites. The results obtained indicate that the glasses from each site differed significantly in their Ba/Sr and light-REE/heavy-REE ratios. The differences between the A-14 and the A-17 glasses appear to be the result of a higher KREEP component in all the A-14 glasses, indicating that the mantle source of the A-14 site is intrinsically different from the A-17 mantle source.
Inter- and intra-group compositional variations in Apollo 15 pyroclastic green glass - An electron- and ion-microprobe study
Results are presented on major- and trace-element abundance analyses of Apollo 15 pyroclastic green glasses from groups A, B, C, D, and E, carried out using electron- and ion-microprobe techniques. The diagrams depicting Sr, Zr, Ba, and Nd vs Co variations indicate the presence of a high-Co trend in groups A and D and a low-Co trend in groups B and C. Group-E glasses were found to be significantly enriched in Sr, relative to the other four glass groups. Chemical data of this study were integrated with previous data to evaluate various magmatic processes that have been proposed in the past to explain chemical variations in the lunar green glass. Results of calculations using a source mixing model suggest that the Apollo 15 green glasses represent multiple eruptive events from three chemically distinct but compositionally variable source regions.
A SIMS study of lunar 'komatiitic glasses' - Trace element characteristics and possible origin
In Apollo 16 regolith breccias, Wentworth and McKay (1988) identified a suite of minute (less than 120 microns) 'komatiitic glass beads'. The wide major element compositional range, and ultra-Mg-prime character of the glasses suggest a variety of possible origins from complex impact processes to complex volcanic processes involving rather unusual and primitive magmatism. The extent of trace element depletion or enrichment in these glasses appears to be correlated to the siderophile character of the element (ionization potential or experimentally determined silicate melt/Fe metal partition coefficients. The ultra-Mg-prime glasses are depleted in Co relative to a bulk Moon Mg/Co exhibited by many lunar samples (volcanic glasses, basalts, regolith breccia, estimated upper mantle). The low Co and high incompatible element concentrations diminish the possibility that these glasses are a product of lunar komatiitic volcanism or impact, excavation, and melting of a very high Mg-prime plutonic unit.
Ion microprobe studies of trace elements in Apollo 14 volcanic glass beads - Comparisons to Apollo 14 mare basalts and petrogenesis of picritic magmas
Results are presented from trace element analysis, by ion microprobe techniques, of individual glass beads representing seven compositionally distinct types of picritic glass beads from the Apollo 14 landing site. The picritic glass beads at the A-14 exhibited a wide range of primary magma compositions and a lack of petrogenetic linkage (via crystal fractionation) to crystalline basalts. The wide range of major and trace element characteristics of the picritic glass beads is consistent with derivation from mineralogically distinct sources which consist of varying proportions of olivine + orthopyroxene +/- clonopyroxene +/- ilmenite +/- plagioclase +/- KREEP component.
An ion microprobe study of the intra-crystalline behavior of REE and selected trace elements in pyroxene from mare basalts with different cooling and crystallization histories
The effects of crystallization interaction on the trace element zoning characteristics of pyroxenes are analyzed using electron and ion microprobe techniques. Four pigeonite basalts with similar isochemical composition, but different cooling rates and crystallization histories are studied. Pyroxene quadrilaterals displaying crystallization trends are presented. The crystal chemical rationalization of REE zoning, pattern shapes, and abundances are examined. The data reveal that the trace element zoning characteristics in pyroxene and the partitioning of trace elements between pyroxene and the melt are related to the interaction between the efficiency of the crystallization process, the kinetics at the crystal-melt interface, the kinetics of plagioclase nucleation and the characteristics of the crystal chemical substitutions in the pyroxene and the associated crystallizing phase.