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1.
The motion of fragments following a catastrophic destruction by either a normal or an oblique impact at 2.5–2.9 km sec?1 into cubic and spherical basalt targets was studied with a high-speed framing camera. Velocities at the antipodes of the targets vary as (E/M)0.75 (E = impact energy; M = target mass) and are lower than 200 m sec?1 at E/M ? 109 ergs g?1. Excluding fine-grained particles from the impact site, 70 to 80% by mass fraction of the fragments have velocities lower than twice the antipodal velocity. Comminution and ejection energies wasted in this mass fraction were a few percent of the impact energy at E/M ? 5 × 107 ergs g?1. During a catastrophic impact into asteroids some of the fragmented bodies can be reconcentrated by mutual gravitation. 相似文献
2.
Hiroshi Shimizu Hideyuki Sawatari Yousuke Kawata Peter N. Dunkley Akimasa Masuda 《Contributions to Mineralogy and Petrology》1992,110(2-3):242-252
138Ce/142Ce isotope ratios in Cenozoic island arc volcanic rocks are reported for the first time, together with isotope ratios of Nd and Sr and abundances of REE, Ba and Sr. The island arc volcanics studies here are boninites from Chichijima, the Bonin Islands, and basalts and andesites from the Solomon Islands. REE patterns of the island arc volcanic rocks from the Solmon Islands and the Bonin Islands are confirmed to have negative Ce anomalies. It is also disclosed that the majority of these island arc volcanic rocks show mainly positive values for both Ce and Nd. It is shown that these Ce and Ce values can hardly be interpreted by simple mixing between MORB and oceanic or continental crustal rocks; the former have positive Nd and negative Ce and the latter have negative Ce and positive or negative Nd. Existence of sources having positive Ce and Nd values is strongly suggested. If the sources are assumed to have been fractionated from CHUR (chondritic uniform reservoir) at the early or middle Precambrian era, the sources from which the volcanics were derived are concluded to have kept concave REE patterns with larger (La/Ce)N and smaller (Nd/Sm)N ratios than chondritic values over a substantial period of time, until the time of Cenozoic magmatism forming island arc volcanic rocks in question. During the periods of the Cenozoic magmatic activities and their related events, Ce anomalies are considered to have been created. From Ce and Nd isotope ratios, however, it is difficult to determine which of the following processes was responsible for the Ce anomaly; the incorporation process of subducted oceanic crust into magma at the mantle or the slab dehydration and metasomatism process. Nevertheless, so far as Ce and Nd isotopic ratios are concerned, incorporation of oceanic sediments did not take place to any clearly detectable degree. 相似文献
3.
Yasutaka Terakado Hiroshi Shimizu Akimasa Masuda 《Contributions to Mineralogy and Petrology》1988,99(1):1-10
Initial Nd and Sr isotopic ratios were obtained for middle Miocene igneous rocks as well as for related rocks from the Outer Zone of Southwest Japan to investigate the petrogenesis of acidic magmas and their relation to a peculiar tectonic environment bearing on the back-arc spreading of the Japan Sea. On the
Nd-
Sr diagram, data points for the acidic rocks fall in the –
Nd, +
Sr quadrant occupying different positions from those for sedimentary and old crustal rocks, and seem to define several subparallel lines which extend towards the lower-righthand sedimentary field. The S-type acidic rocks occupy an intermediate position between I-type rocks and sedimentary ones, a fact suggesting mixing of an igneous component and a sedimentary one. The linear mixing trend observed on the
Nd-
Sr diagram can be attained in the restricted case that the igneous component has similar Sr/Nd concentration ratios to that of the sedimentary one, which implies an intermediate to acidic composition for the igneous component. Inconsistency between the elemental and isotopic variations observed may be reconciled by considering that mixing, probably in the relatively deep part of the crust, might have occured prior to chemical differentiation processes. The episodic igneous activity and the high heat energy required to melt such materials involving sedimentary rocks may be explained by a model in which a hot mantle region probably corresponding to the rising part of the mantle convection supplied the heating energy to the Outer Zone of Southwest Japan when passing beneath Southwest Japan in the course of movement of the hot rising part from the Shikoku basin areas to the Japan Sea area. 相似文献
4.
Isotopic ratios and abundances of all REE in two Oklo ore samples have been measured. We have succeeded in developing a new method to estimate the neutron fluence, the conversion factor of uranium and the average neutron energy (or temperature) based on Gd and U isotopic ratios. This new calculation is found to be useful in evaluating those parameters for the natural nuclear reactors at Oklo. Comparison is made between the neutron fluence values evaluated by our new method employing Gd isotopes and a previous one [11] employing Sm and Nd isotopes. The relative agreement becomes better with the increase of fluence. A relationship between the abundances of fissiongenic nuclides of La, Ce, Nd, Sm, and Gd and their mass numbers is also presented. 相似文献
5.
6.
From the mathematical analysis of the rare-earth data on some of the Apollo 12 samples studied by Hubbard et al. (1971), the possible europium-normal primitive rare-earth pattern, in which europium is normal with respect to the adjacent rare-earth elements, has been estimated. A fact that the igneous rocks (Japanese geosynclinal basalts) appearing to reflect the analogous effect occur locally on the earth enhances our interests in the pattern resulting from the above estimation. 相似文献
7.
Akimasa Masuda Noboru Nakamura Tsuyoshi Tanaka 《Contributions to Mineralogy and Petrology》1971,32(4):295-306
Two foliated metagabbros from the Mid-Atlantic Ridge near 30° N were analyzed for rare earth elements. The chondrite-normalized rare earth pattern for one of them is quite similar to those for abyssal tholeiites. The pattern for another sample, however, is somewhat different from the above one. A new set of bulk partition coefficients for rare earth elements has been estimated correspondingly. This set throws a new light on the interpretation that many alkali olivine basalts were produced by a zone melting or partial melting of primary-liquid-type material. Also the same partition coefficients lead us to an inference that the high-temperature peridotite intrusion in the Lizard area, Cornwall, England, is a secondary-solid-type material which was once in equilibrium with a primary-solid-type material, whereas the pyroxenite, Canyon Mountain, Oregon, is a primary-solid-type material.Both of the metagabbros studied show positive europium anomaly. 相似文献
8.
Miguel B. Brito Mitsuyoshi Akiyama Yoshitaka Ichikawa Hiroki Yamaguchi Riki Honda Naomitsu Ishigaki 《地震工程与结构动力学》2020,49(8):817-837
A novel low-cost friction sliding system for bidirectional excitation is developed to improve the seismic performance of reinforced concrete (RC) bridge piers. The sliding system is a spherical prototype developed by combining a central flat surface with an inclined spherical segment, characterized by stable oscillation and a large reduction in response accelerations on the flat surface. The inclined part provides a restoring force that limits the residual displacements of the system. Conventional steel and concrete are employed to construct a flat-inclined spherical surface atop an RC pier. The seismic forces are dissipated through the frictions generated during the sliding movements; hence, the seismic resilience of bridges can be ensured with a low-cost design solution. The proposed system is fabricated utilizing a mold created by a three-dimensional printer, which facilitates the use of conventional concrete to construct spherical shapes. The concrete surface is lubricated with a resin material to prevent abrasion from multiple input ground motions. To demonstrate the effectiveness of the system, bidirectional shaking table tests are conducted in the longitudinal and transverse directions of a scaled bridge model. The effect of the inclination angle and the flat surface size is investigated. The results demonstrate a large decrease in response acceleration when the system exhibits circular sliding displacement. Furthermore, the inclination angle that generates the smallest residual displacement is identified experimentally. 相似文献
9.
Sudarmanto Budi Nugroho Akimasa Fujiwara Junyi Zhang 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(5):655-669
A bus rapid transit (BRT) system began operation in Jakarta City, Indonesia, in January 2004 and led to a modal shift from
private to public modes of transport. This modal shift from car and motorcycle to BRT reduced the emission intensity of primary
pollutants, such as NOx and CO. We applied a combined structural equation model and an artificial neural network to evaluate the impact of the BRT
system on the concentration of secondary pollutants in the roadside areas in the BRT corridors. An empirical analysis was
carried out using data collected at five continuous ambient air quality monitoring stations located near to the BRT TransJakarta
corridors in 2005. The establishment of our structural equation model gives a better understanding of the cause–effect relationship
among the factors influencing roadside ambient air pollution, and was useful in simplifying the complexity of our artificial
neural network model for predicting the modal shift’s impact on the PM10 values and concentration of O3. The introduction of the BRT system, and the modal shift it produced, had a greater influence on rapidly decaying pollutants,
such as PM10, than on O3 because of the exposure to near-source microenvironments, such as the roadside of the TransJakarta corridors. 相似文献
10.
Rare-earth elements in a whole-rock sample and in major components of the Allende meteorite were investigated; for a few samples, abundances of Ba, Sr, Ca, and Al were also determined. Of the materials investigated in the present work, CaAl-rich inclusions G and O seem to be of the greatest significance. In spite of the minor difference in mineralogy between them, the apparent chondrite-normalized RE pattern is much different between these two inclusions. (Yb and Eu in inclusion G appear exceptionally irregular). This observation is inferred to reflect a rather subtle difference in condition of condensation. It is also worthwhile to note that, while two portions (pink and white) of the inclusion G show similar aspects in the abundances of lithophile trace elements investigated, they show a remarkable difference at the same time. The white portion (Gw) of inclusion G can be considered to be a mixture of chondritic material and highly fractionated material like the faintly pink portion (Gp) picked from the same inclusion. This would suggest the possibility that the Gp-like material was produced from chondritic dust.The “matrix” separated from Allende was found to be fractionated with respect to the RE abundances relative to representative chondrite. It has also a very high value for the Ba abundance. 相似文献