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181.
Identification of stable remanence carriers through a magneto-impedance scanning magnetic microscope
To identify the stable remanence carrier in rock samples, we conducted magnetic microscopic observations combined with conventional
stepwise demagnetization experiments. The instrument, which employs an amorphous wire-based magneto-impedance sensor (30 μm
diameter, 5 mm length), can document magnetic anomalies (vertical component) of the millimeter to sub-millimeter-thick rock
samples with a resolution of 500 μm. Our new technique allows identification of the sources of both stable and unstable remanence
components in meteorite and shocked granite samples. However, stray magnetic fields from the sensor magnetize the magnetic
minerals in the sample and makes serious artifacts on the magnetic images. Although the artifacts of the induced magnetization
should be solved, this new corroborative technique leads to a microscopic discrimination of stable paleomagnetic records from
terrestrial and extraterrestrial materials. 相似文献
182.
Naohiro Nakamura 《地震工程与结构动力学》2008,37(4):495-515
The author has studied the transform method of complex stiffness, which is strongly dependent on frequency, to the time domain. In this paper, new transform methods that use only the real part or the imaginary part data are proposed. By applying them to example problems, it is confirmed that the accuracy of the proposed methods is almost high in both causal and noncausal cases. These methods can also be thought as a standby for the Hilbert transform, because the undefined part is easily calculated by the recovering complex function from the obtained impulse response. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
183.
Ryoji Tanaka Akio Makishima Eizo Nakamura 《Earth and Planetary Science Letters》2008,265(3-4):450-465
The two parallel loci of recent Hawaiian volcanoes, Kea and Loa, have been regarded as the best targets to interpret the chemical structure of an upwelling mantle plume derived from the lower mantle. Here we show that the Sr–Nd–Hf–Pb isotopic data of the shield-building lavas along the Loa locus form a systematic trend from the main shield stage of Koolau (> 2.9 Ma) to the active Loihi volcanoes. During the growth of the Koolau volcano, the dominant material in the melting region successively changed from the proposed KEA, DMK (depleted Makapuu), to EMK (enriched Makapuu) components. The proportion of EMK, dominated by a recycled mafic component, is typified by some Koolau Makapuu-stage and some Lanai lavas. Subsequently, the EMK component decreased and LOIHI component increased toward the Loihi lavas. The temporal coincidence between the episodically elevated magma production rate and the abrupt appearance of the typical Loa-type lavas that is restricted to the last 3 Myr should be linked to magma genesis. We suggest that the abrupt appearance of Loa-type magmatism should be attributed to the transient incorporation of the relatively dense recycled material and surrounding less degassed lower mantle material that accumulated near the core–mantle boundary into the upwelling plume. This episodic involvement could have been trigged by episodic thermal pulses and buoyancy increases in the plume. The continuous appearance of Kea-type lavas during the long history of Hawaiian-chain magmatism and the larger magma volume of Kea-type lavas relative to that of the Loa-type lavas in the last 3 Myr indicate that the Kea locus is closer to the thermal centre of the Hawaiian plume relative to that of the Loa locus. 相似文献
184.
A new method of stiffness‐damping simultaneous identification of building structures is proposed using limited earthquake records. It is shown that when horizontal accelerations are recorded at the floors just above and below a specific storey in a shear building model, the storey stiffness and the damping ratio can be identified uniquely. The viscous damping coefficient and the linear hysteretic damping ratio can also be identified simultaneously in a numerical model structure. The accuracy of the present identification method is investigated through the actual limited earthquake records in a base‐isolated building. It is further shown that an advanced identification technique for mechanical properties of a Maxwell‐type model can be developed by combining the present method with a perturbation technique. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
185.
K. Kawata T. K. Sako M. Ohnishi M. Takita Y. Nakamura K. Munakata 《Experimental Astronomy》2017,43(1):1-17
ASTRI SST-2M is one of the prototypes of the small size class of telescopes proposed for the Cherenkov Telescope Array. Its optical design is based on a dual-mirror Schwarzschild-Couder configuration, and the camera is composed by a matrix of monolithic multipixel silicon photomultipliers managed by ad-hoc tailored front-end electronics. This paper describes the procedures for the gain calibration on the ASTRI SST-2M. Since the SiPM gain depends on the operative voltage and the temperature, we adjust the operative voltages for all sensors to have equal gains at a reference temperature. We then correct gain variations caused by temperature changes by adjusting the operating voltage of each sensor. For that purpose the SiPM gain dependence on operating voltage and on temperature have been measured. In addition, we present the calibration procedures and the results of the experimental measurements to evaluate, for each pixel, the parameters necessary to make the trigger uniform over the whole focal plane. 相似文献
186.
Multiple‐indicator study of groundwater flow and chemistry and the impacts of river and paddy water on groundwater in the alluvial fan of the Tedori River,Japan 下载免费PDF全文
Yumi Iwasaki Yoshioka Kimihito Nakamura Takanori Nakano Haruhiko Horino Ki‐Cheol Shin Satoko Hashimoto Shigeto Kawashima 《水文研究》2016,30(16):2804-2816
To investigate the source, flow paths, and chemistry of rich resources of high‐quality, shallow groundwater in the alluvial fan between the Tedori and Sai rivers in central Japan, we analysed stable isotope ratios of H, O, and Sr and concentrations of major dissolved ions and trace elements in groundwater, river water, and paddy water. The 87Sr/86Sr ratios of the groundwater are related to near‐surface geology: groundwater in sediment from the Tedori River has high 87Sr/86Sr ratios (>0.711), whereas that from the Sai River in the north of the fan has low 87Sr/86Sr ratios (<0.711). δ2H and δ18O values and 87Sr/86Sr ratios indicate that groundwater in the central and southern fans is recharged by the Tedori River, whereas recharge in the north is from the Sai River. Mg2+, Ca2+, Sr2+, HCO3?, and SO42? concentrations and δ2H and δ18O values in the groundwater are high in the central fan and, except for the northern area, tend to increase with distance from the Tedori River. There are linear relationships between 87Sr/86Sr ratio and the reciprocal concentrations of Sr2+, Mg2+, and Ca2+. These geochemical characteristics suggest that as groundwater recharged from the Tedori River flows towards the central fan, it mixes with waters derived from precipitation and paddy water that have become enriched in these components during downward infiltration. These results are consistent with our hydrological analysis and numerical simulation of groundwater flow, thus verifying the validity of the model we used in our simulation of groundwater flow. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
187.
M. E. Zolensky K. Nakamura M. Gounelle T. Mikouchi T. Kasama O. Tachikawa E. Tonui 《Meteoritics & planetary science》2002,37(5):737-761
Abstract— In this paper we describe the recovery, handling and preliminary mineralogical investigation of the Tagish Lake meteorite. Tagish Lake is a type 2 carbonaceous chondrite which bears similarities to CI1 and CM chondrite groups, but is distinct from both. Abundant phyllosilicates as well as chondrules (however sparse) and common olivine grains in the matrix preclude any other classification. The bulk density of Tagish Lake (1.67 g/cc) is far lower than CI or CM chondrites (2.2‐2.3 and 2.6‐2.9 g/cc, respectively), or any other meteorite for that matter. We have identified two lithologies: a dominant carbonate‐poor lithology and a less‐abundant carbonate‐rich lithology. The meteorite is a breccia at all scales. We have noted similarities between Tagish Lake and some clasts within the enigmatic meteorite Kaidun; possibly there are genetic relationships here worth exploring. In the paper we describe a clast of CM1 material within Tagish Lake which is very similar to a major lithology in Kaidun. 相似文献
188.
We investigated by numerical integrations the long-term orbital evolution of four giant comets or comet-like objects. They are Chiron, P/Schwassmann-Wachmann 1 (SW1), Hidalgo, and 1992AD (5145), and their orbits were traced for 100–200 thousand years (kyr) toward both the past and the future. For each object, 13 orbits were calculated, one for the nominal orbital elements and other 12 with slightly modified elements based on the rms residual of the orbit determination and on the number of observations. As past studies indicate, their orbital evolution is found to be very chaotic, and thus can be described only in terms of probability. Plots of the semi-major axis (a) and perihelion distance (q) of the objects treated here seem to cross each other frequently, suggesting a possibility of their common evolutionary paths. About a half of all the calculated orbits showedq- ora-decreasing evolution. This indicates that, at least on the time scale in question, the giant comet-like objects are possibly on a dynamical track that can lead to capture from the outer solar system. We could hardly find the orbits with perihelia far outside the orbit of Saturn (q>15 AU). This is perhaps because the evolution of the orbits beyond Saturn is so slow that substantial orbital changes do not take place within 100–200 kyr. 相似文献
189.
Kazushige Tomeoka Ichiro Ohnishi Noboru Nakamura 《Meteoritics & planetary science》2001,36(11):1535-1545
Abstract— The Kobe CK4 chondrite, like most metamorphosed CK chondrites, exhibits pronounced silicate darkening of matrix and chondrule mesostases. Our petrographic and scanning electron microscopic study reveals that the matrix of Kobe consists mostly of intermixtures of two types of fine‐grained olivine. One forms subhedral to anhedral normal crystals. The other fills interstices of the subhedral to anhedral olivine crystals, exhibiting a complex network of veinlets. The latter type of olivine contains high densities of small spherical vesicles (<0.05‐3 μm in diameter) and grains (<0.05‐5 μm) of magnetite and pentlandite as well as round to anhedral grains (1–10 μm) of plagioclase, low‐Ca pyroxene, diopside and chlorapatite. The vesicular olivine is particularly abundant in regions of matrix that exhibit a relatively high degree of darkening and commonly fills chondrule mesostases. The vesicular olivine is clearly the principal cause of the silicate darkening in Kobe. The internal texture of the vesicular olivine closely resembles those of local melts produced from the matrices of experimentally and naturally shocked carbonaceous chondrites. The occurrence and texture of the vesicular olivine suggest that it resulted from recrystallization of partially melted matrix olivine by shock. Kobe exhibits light shock effects in olivine that are consistent with shock stage S2 that is too low to explain the occurrence of olivine melting. We suggest that the vesicular olivine in Kobe was produced by shock metamorphism at a relatively mild shock pressure (<25 GPa) and a high temperature (>600 °C). Thus, it is probable that the shock effects in olivine, manifest as fracturing and deformation, were relatively minor, but heating was strong enough to cause partial melting of matrix olivine. 相似文献
190.
Nitrate and phosphate uptake kinetics ofChattonella antiqua were examined under light and dark conditions. The uptake kinetics ofC. antiqua followed the Michaelis-Menten equation. The maximal uptake rates (V max) of nitrate and phosphate in the dark were 86 and 93% of those in the light, respectively. The half-saturation constants (K 8 ) were not significantly affected by illumination and were comparable to those of other phytoplankton. However, specific maximal uptake rates ofC. antiqua for these substrates were much smaller than those of other phytoplankton. 相似文献