Sulfur isotope composition of putative primary troilite in chondrules from Bishunpur and Semarkona

The sulfur isotopic compositions of putative primary troilite grains within 15 ferromagnesian chondrules (10 FeO-poor and 5 FeO-rich chondrules) in the least metamorphosed ordinary chondrites, Bishunpur and Semarkona, have been measured by ion microprobe. Some troilite grains are located inside metal spherules within chondrules. Since such an occurrence is unlikely to be formed by secondary sulfidization processes in the solar nebula or on parent bodies, those troilites are most likely primary, having survived chondrule-forming high-temperature events. If they are primary, they may be the residues of evaporation at high temperatures during chondrule formation and may have recorded mass-dependent isotopic fractionations. However, the supposed primary troilites measured in this study do not show any significant sulfur isotopic fractionations (<1 ‰/amu) relative to large troilite grains in matrix. Among other chondrule troilites that we measured, only one (BI-CH22) apparently has a small excess of heavy isotopes (2.7 ± 1.4 ‰/amu) consistent with isotopic fractionation during evaporation. All other grains have isotopic fractionations of <1 ‰/amu. Because sulfur is so volatile that evaporation during chondrule formation is probably inevitable, non-Rayleigh evaporation most likely explains the lack of isotopic fractionation in putative primary troilite inside chondrules. Evaporation through the surrounding silicate melt would have suppressed the isotopic fractionation after silicate dust grains melted. At lower temperatures below extensive melting of silicates, a heating rate of >10⁴-10⁶ K/h would be required to avoid a large degree of sulfur isotopic fractionation in the chondrule precursors. This heating rate may provide a new constraint on the chondrule formation processes.     

Low-temperature single crystal reflection spectra of forsterite

The infrared reflectivities of crystalline forsterite (Mg₂SiO₄) were measured for the temperature range 295–50 K for each crystal axis, between wavenumber 5000 and 100 cm⁻¹. The reflection spectra show clear dependence of temperature; most of the bands become more intense, sharper and their peak positions shift to higher wavenumber with decreasing temperature. Reflection spectra were fitted with dispersion formula of damped oscillator model of the dielectric constants and the oscillator parameters in the model were derived. The absorption spectra of forsterite particle are calculated with the derived dielectric constants to show that the forsterite features are good thermal indicator for cold temperature range below 295 K.     

Curation protocol of Phobos sample returned by Martian Moons eXploration

Japan Aerospace Exploration Agency's Martian Moons eXploration (MMX) mission will launch a spacecraft in 2024 to return samples from Phobos in 2029. Curatorial work for the returned Phobos samples is critical for the sample allocation without degrading the sample integrity and subsequent sample analysis that will provide new constraints on the origin of Phobos and the evolution of the circum-Mars environment. The Sample Analysis Working Team of the MMX is designing the sample curation protocol. The curation protocol consists of three phases: (1) quick analysis (extraction and mass spectrometry for gases), (2) pre-basic characterization (bulk-scale observation), and (3) basic characterization (grain-by-grain observation and allocation of the sample aliquots). Nondestructive analyses within the clean chamber (e.g., visible and near-infrared spectral imaging) and outside the chamber (e.g., gas mass spectrometry) are incorporated into the curation flow in coordination with the MMX mission instrument teams for ground-truthing the remote-sensing data sets. The MMX curation/sample analysis flow enables the seamless integration between the sample and remote-sensing data sets to maximize the scientific value of the collected Phobos samples.     

Elemental distribution of coastal sea and stream sediments in the island-arc region of Japan and mass transfer processes from terrestrial to marine environments

A total of 49 elements have been identified in 338 coastal sea sediment samples collected from an area situated off the Ise-Tokai region of Japan for a nationwide marine geochemical mapping project. The spatial distribution patterns of the elemental concentrations in coastal seas along with the existing geochemical maps in terrestrial areas were used to define the natural geochemical background variation, mass transport, and contamination processes. The elemental concentrations of coastal sea sediments are determined primarily by particle size and regional differences. Most elemental concentrations increase with a decrease in particle size. Some elements such as Ca, Mn, and Yb are found to exist in large quantities in coarse particles containing calcareous shells, Fe–Mn oxides, and felsic volcanic sediments. Regional differences reflect the mass transfer process from terrestrial areas to coastal seas and the influence of the local marine geology. An analysis of variance (ANOVA) reveals that for many elements, the particle size effect is predominant over regional difference. The mean chemical compositions of coastal sea sediments are similar to those of stream sediments in adjacent terrestrial areas and in the upper crust of Japan. This observation supports the fact that coastal sea sediments have certainly originated from terrestrial materials. However, the spatial distributions of elemental concentrations are not always continuous between the land and coastal seas. The scale of mass movement observed in marine geochemical maps occurs at a distance of 20 km from the river mouth. A detailed examination of the spatial distribution patterns of K (K₂O) and Cr concentrations suggests that terrestrial materials supplied through rivers are deposited near the shore initially, and then gravity-driven processes shift the sediments deeper into the basin. Contamination with heavy metals such as Zn, Cd and Pb was observed in coastal bays surrounded by urban and industrial areas. It is noteworthy that the areas with the highest concentration of these elements usually do not occur near the shore (not near the contamination source) but at the center of the bay. Unexpected low concentrations of Zn, Cd and Pb near shore may either be due to a decreased anthropogenic load in the most recent sediments or to dilution by unpolluted flood sediments.     

End bearing capacity comparison of screw pile with straight pipe pile under similar ground conditions

In the present study, the end bearing capacity of screw and straight pipe pile under similar pile tip area and ground conditions were investigated. The effect of increasing overburden pressure was also considered in this research. Pile load tests on close-ended screw and straight pipe piles were conducted in the small scale. Dry Toyoura sand was used to develop the model ground. The sand was compacted at relative density of 70, 80 and 92 %. It was observed that in case of straight pipe pile, load settlement curve plunges downward without increase in load around settlement equals to 10 % of pile tip diameter, whereas in case of screw pile, the load settlement curve plunges around settlement equals to 15 % of pile tip diameter. Moreover, the screw piles having helix-to-shaft diameter ratio 2–4.1 showed 2–12 times higher end bearing capacity than straight pipe piles with similar pile shaft diameter. It was also observed from the test results that the end bearing capacity of single-helix screw pile was in average 16.25 % less than straight pipe pile with similar pile tip area and ground conditions irrespective of the effect of increasing overburden pressure.     

Survivability of presolar oxygen isotopic signature of amorphous silicate dust in the protosolar disk

Oxygen isotope exchange experiments between tens of nanometer‐sized amorphous enstatite grains and water vapor were carried out under a condition of protoplanetary disk‐like low water vapor pressure in order to investigate the survivability of distinct oxygen isotope signatures of presolar silicate grains in the protosolar disk. Oxygen isotope exchange between amorphous enstatite and water vapor proceeded at 923–1003 K and 0.3 Pa of water vapor through diffusive isotope exchange in the amorphous structure. The rate of diffusive isotope exchange is given by D (m² s^–1) = (5.0 ± 0.2) × 10^–21 exp[–161.3 ± 1.7 (kJ mol^–1) R^–1 (1/T–1/1200)]. The activation energy for the diffusive isotope exchange for amorphous enstatite is the same as that for amorphous forsterite within the analytical uncertainties, but the isotope exchange rate is ~30 times slower in amorphous enstatite because of the difference in frequency factor of the reaction. The reaction kinetics indicates that 0.1–1 μm‐sized presolar amorphous silicate dust with enstatite and forsterite compositions would avoid oxygen isotope exchange with protosolar disk water vapor only if they were kept at temperatures below ~500–650 K within the lifetime of the disk gas.     

The relative formation ages of ferromagnesian chondrules inferred from their initial aluminum‐26/aluminum‐27 ratios

Abstract— We performed a systematic high‐precision secondary ion mass spectrometry ²⁶Al‐²⁶Mg isotopic study for 11 ferromagnesian chondrules from the highly unequilibrated ordinary chondrite Bishunpur (LL3.1). The chondrules are porphyritic and contain various amounts of olivine and pyroxene and interstitial plagioclase and/or glass. The chemical compositions of the chondrules vary from FeO‐poor to FeO‐rich. Eight chondrules show resolvable ²⁶Mg excesses with a maximum δ²⁶Mg of ?1% in two chondrules. The initial ²⁶Al/²⁷Al ratios inferred for these chondrules range between (2.28 ± 0.73) × 10^?5 to (0.45 ± 0.21) × 10^?5. Assuming a homogeneous distribution of Al isotopes in the early solar system, this range corresponds to ages relative to CAIs between 0.7 ± 0.2 Ma and 2.4_+0.7^?0.4 Ma. The inferred total span of the chondrule formation ages is at least 1 Ma, which is too long to form chondrules by the X‐wind. The initial ²⁶Al/27Al ratios of the chondrules are found to correlate with the proportion of olivine to pyroxene suggesting that olivine‐rich chondrules formed earlier than pyroxene‐rich chondrules. Though we do not have a completely satisfactory explanation of this correlation we tentatively interpret it as a result of evaporative loss of Si from earlier generations of chondrules followed by addition of Si to the precursors of later generation chondrules.     

QN control method for building vibration caused by periodic excitation acting on intermediate story

It has been proved in the authors' latest paper that the effective location of active control devices for building vibration caused by periodic excitation acting on intermediate story is the adjacent three floors to the vibration source. However, in terms of the Discrete‐Optimizing control method, the control forces are on‐line calculated step‐by‐step and time‐delay must exist. The degradation of control effect caused by time‐delay can not be avoided. In this paper, QN control method is proposed in order to resolve this practical problem. Since the external excitations which the building structure would experience are supposed to be periodic to some degree, Quasi‐Newton method is applied into the close‐loop Linear–Quadratic optimal control method and the new control method is called the ‘QN control method’. In this new control method, instead of solving the Riccati equation, the feedback gain matrix is determined by optimizing the quadratic performance index of the structure with the Quasi‐Newton method, one of the most commonly used minimization of functions. The new control law can easily be implemented for time‐delay problems, the degradation can be greatly improved with compensated feedback gain matrix. As a result, the QN control method is proved to be an efficient method to determine the feedback gain matrix. Copyright © 2000 John Wiley & Sons, Ltd.     

Geochemical mapping in Shikoku, southwest Japan

Geochemical mapping of Shikoku in the SW Japan Arc was conducted using stream sediments (<0.18 mm fraction) with sample densities of 1 site per 106 km². Concentrations of 51 elements in 173 stream sediments were determined. Areas with especially high Cr, Ni, Mg and Co concentrations run intermittently and linearly through Shikoku, and coincide with exposures of the Mikabu greenstone complex composed of oceanic basaltic and gabbroic rocks with minor ultramafic bodies. Areas with higher concentrations of Fe, V, Sc, Ti, Mn, Cr, Ni, Mg, Co and Eu are distributed widely along the Shikoku Island axis; they mainly overlap with the zones of the high-pressure type metamorphic rocks (Sanbagawa Belt) and of the Jurassic accretionary complexes with sedimentary rocks (Chichibu Belt): in contrast, areas with lower concentrations spread over the northern coastal zone of Cretaceous granitoids (Ryoke Belt) and in the southern coastal zone of Cretaceous-Paleogene accretionary complexes (Shimanto Belt). Distribution patterns of these elements reflect that various amounts of mafic and ultramafic materials, possibly of oceanic origin, are associated with the rocks in the Sanbagawa and Chichibu Belts, although such components occur sparsely in the Shimanto and Ryoke Belts. Calcium, Sr, Na, Nb, Sm and Gd contents are lower along the southern coastal zone. High values of Th, U, La, Ce and Ba are associated with granitic rocks. The positive anomalies of Cu and Cd coincide with the distribution of stratabound Cu deposits in the Sanbagawa Belt. Positive anomalies of Sb in the northern area are associated with Sb deposits near the large Median Tectonic Line fault zone. A high-Hg zone is present in the southern fore-arc area. The median concentrations for stream sediments in Shikoku are higher in Hg, Cu, Ni, Cr, Rb, Li, Cs, K, slightly higher in Nb, Ta, La, Ce, Sn and lower in Ca than those for average Japanese stream sediments. The median concentrations for the four geologic zones show systematic wide variations of mafic associated elements, and narrow variations of lithophile elements generally more abundant in felsic rocks. The chemical compositions of the stream sediments in Shikoku largely reflect the concentrations in the pre-Neogene accretionary complexes and in the high-P metamorphic rocks mainly formed from clastic materials derived from continental margins, and ratios of mafic and ultramafic materials within surface rocks; they are partly influenced by sulfide mineralization and fluid migration.