Raman spectra of methane hydrate up to 86 GPa     

Shin-Ichi Machida  Hisako Hirai  Taro Kawamura  Yoshitaka Yamamoto  Takehiko Yagi 《Physics and Chemistry of Minerals》2007,34(1):31-35

High-pressure Raman studies of methane hydrate were performed using a diamond anvil cell in the pressure range of 0.1–86 GPa at room temperature. Raman spectra of the methane molecules revealed that new softened intramolecular vibration mode of ν ₁ appeared at 17 GPa and that the splitting of vibration mode of ν ₃ occurred at 15 GPa. The appearance of these two modes indicates that an intermolecular attractive interaction increases between the methane molecules and the host water molecules and between the neighboring methane molecules. These interactions might result in the exceptional stability of a high-pressure structure, a filled ice Ih structure (FIIhS) for methane hydrate, up to 40 GPa. At 40 GPa, a clear change in the slope of the Raman shift versus pressure occurred, and above 40 GPa the Raman shift of the vibration modes increased monotonously up to 86 GPa. A previous XRD study showed that the FIIhS transformed into another new high-pressure structure at 40 GPa. The change in the Raman spectra at 40 GPa may be induced by the transition of the structure.  相似文献   

Carbonate deposits on submerged seamounts in the northwestern Pacific Ocean     

Hideko  Takayanagi  Yasufumi  Iryu  Tsutomu  Yamada  Motoyoshi  Oda  Kazuyuki  Yamamoto  Tokiyuki  Sato  Shun  Chiyonobu  Akira  Nishimura  Tsutomu  Nakazawa  Satoshi  Shiokawa 《Island Arc》2007,16(3):394-419

Abstract   The lithology of shallow-water carbonates collected from 19 sites on 16 seamounts in six areas of the northwestern Pacific Ocean using the Deep-sea Boring Machine System are described. The areas include the Amami Plateau, Daito Ridge, Oki-Daito Ridge, Urdaneta Plateau, Kyushu-Palau Ridge and Ogasawara Plateau. Chronological constraint is provided by calcareous nannofossil biostratigraphy, planktonic foraminiferal biostratigraphy, larger foraminiferal biostratigraphy and strontium (Sr) isotope stratigraphy. Large amounts of shallow-water carbonates accumulated on the seamounts during the Oligocene, a relatively cool period, whereas limited carbonate deposits formed during the Early Miocene, a relatively warm period. This might indicate that deposition of shallow-water carbonates on seamounts in the northwestern Pacific Ocean was not necessarily controlled by climatic conditions, but was related to volcanism and tectonics that served as foundations for reef/carbonate-platform formation. Remarkable differences in biotic composition exist between Cretaceous and Cenozoic shallow-water carbonates. Late Cretaceous shallow-water carbonates are distinguished by the occurrence of rudists, solenoporacean algae and microencrusters. Middle Eocene to Early Oligocene shallow-water carbonates are dominated by Halimeda or nummulitid and discocyclinid larger foraminifers. Scleractinian corals became common from the Oligocene onward. Nongeniculate coralline algae and larger foraminifers were common to abundant throughout the Eocene to the Pleistocene. The replacement of major carbonate producers in the shallow-water carbonate factory during post-Cretaceous time is in accordance with previous studies and is considered to reflect a shift in seawater chemistry.  相似文献   

Subaqueous eruption and emplacement of the Shinjima Pumice, Shinjima (Moeshima) Island, Kagoshima Bay, SW Japan     

Kazuhiko Kano  Takahiro Yamamoto  Koji Ono 《Journal of Volcanology and Geothermal Research》1996,71(2-4)

The Shinjima Pumice is a fines-depleted pumice lapilli tuff emplaced several thousands years ago at about 100–140 m below sea level. This 40-m-thick deposit comprises many poorly defined flow units, which are 1–10 m thick, diffusely stratified and showing upward-coarsening of pumice clasts with a sharp to transitional base. Parallel to wavy diffuse stratifications are commonly represented by alignment of pumice clasts, especially in the lower half of the flow units. Pumice clasts of block to coarse-lapilli size commonly have thermal-contraction cracks best developed on the surfaces, demonstrating that they were hot but cooled down to the ambient temperatures prior to their emplacement. These features are suggestive of the direct origin of the Shinjima Pumice from subaqueous eruptions. A theoretical consideration on the behavior of subaqueous eruption plumes and hot and cold pumice clasts suggests that subaqueous eruption plumes commonly collapse by turbulent mixing with the ambient water and are transformed into water-logged mass flows.  相似文献   

Prediction method of sand-movement direction in water by geochemical elements     

K. Mizumura  T. Nishimoto  H. Tsutsui  T. Yamamoto 《Environmental Geology》1995,25(2):100-108

The analysis of sand samples by x-ray fluorescent spectroscopy (XRF) gives the ratio of the geochemical elements to construct the sand samples. The x-ray analysis therefore shows the geochemical characteristics of sand in the sampled area. In this study, sand is sampled on coasts and rivers of the Noto Peninsula to determine the geochemical elements and to show the geological characteristics that occur, especially iron and calcium. The experiments show the effect of rivers and Kotogahama beach on iron and calcium, respectively. Applying the method of ratio matching to the measured data of the geochemical elements, the direction of movement of sand on the coast is determined by considering the correlation matrix and the ratio of geochemical elements between sand samples at two locations. The predominant longshore direction movement of sand offshore in the study area is from south to north. Sand in rivers is not directly transported to adjacent beaches; however, offshore sand is transported to beaches. The estimated direction of movement of sand longshore near coastal structures agrees with observations. The proposed method to predict the direction of movement of sand gives the correct one in comparison with the observed data in rivers.  相似文献   

Measurement of Impact Ejecta from Regolith Targets in Oblique Impacts     

S. Yamamoto 《Icarus》2002,158(1):87-97

This paper reports the results of experiments on projectile impact into regolith targets at various impact angles. Copper projectiles of 240 mg are accelerated to 197 to 272 m s⁻¹ using an electromagnetic gun. The ejecta are detected by thin Al foil targets as secondary targets, and the resulting holes on the foil are measured to derive the spatial distribution of the ejecta. The ejecta that penetrated the foil are concentrated toward the downrange azimuths of impacting projectiles in oblique impacts. In order to investigate the ejecta velocity distribution, the nondimensional volume of ejecta with velocities higher than a given value is calculated from the spatial distribution. In the case of the vertical impact of the projectile, most ejecta have velocities lower than 24% of the projectile speed (∼50 m s⁻¹), and there are only several ejecta with velocities higher than 72 m s⁻¹. This result confirms the existence of an upper limit to the ejection velocity in the ejecta velocity distribution (Hartmann cutoff velocity) (W. K. Hartmann, 1985, Icarus63, 69-98). On the other hand, it is found that, in the oblique impacts, there are a large number of ejecta with velocities higher than the Hartmann cutoff velocity. The relative quantity of ejecta above the Hartmann cutoff velocity increases as the projectile impact angle decreases. Taking these results with the results of S. Yamamoto and A. M. Nakamura (1997, Icarus128, 160-170) from impact experiments using an impact angle of 30°, it can be concluded that the ejecta from these regolith targets exhibit a bimodal velocity distribution. Below a few tens of m s⁻¹, we see the expected velocity distribution of ejecta, but above this velocity we see a separate group of high-velocity ejecta.  相似文献   

Multivariate correlation analysis of suspended-sediment characteristics     

Satoshi Yamamoto 《Mathematical Geology》1976,8(1):57-74

Principal component analysis (PCA) was employed to investigate interrelationships among various characteristics of seawater and suspended sediments obtained from surface waters of two Asian marginal seas. On the basis of multivariate correlation analysis for the two marginal seas combined, three important factors were extracted and interpreted: (1) current-energy conditions, (2) the influence of rivers, and (3) biochemical conditions of seawater. A relationship between anisotropic mineral grains and combustible organic matter is suggested by the fact that suspended sediment, containing coarser anisotropic mineral grains, also contains larger amounts of combustible organic matter.  相似文献   

Metaproteomic characterization of dissolved organic matter in coastal seawater     

Mitsuhiro Yoshida  Keitaro Yamamoto  Satoru Suzuki 《Journal of Oceanography》2014,70(1):105-113

We performed a comprehensive metaproteomic analysis of the dissolved organic matter (DOM) in Japanese coastal waters using liquid chromatography–tandem mass spectrometry and demonstrated that these proteomes were characterized by proteins with various functions, including metabolic enzymes, membranes, and photosynthetic proteins. The protein sources included cyanobacteria, heterotrophic bacteria, and eukaryotic phytoplankton. Most of the components were similar among samples and also similar to pelagic components. We also observed differences in the compositions of the microbial communities of origin among the different dissolved protein samples and differences in the relative abundance of specific dissolved protein types (e.g., cytoskeletal proteins), possibly indicating potential dynamics in the coastal DOM pool.  相似文献   

Nutricline shoaling in the eastern Pacific warm pool during the last two glacial maxima     

Hasrizal Bin Shaari  Masanobu Yamamoto  Tomohisa Irino  Tadamichi Oba 《Journal of Oceanography》2014,70(1):25-34

Isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) and alkenones were analyzed in sediment samples retrieved from Ocean Drilling Program Site 1241 covering the last 150000 years to understand the hydrological evolution of the eastern Pacific warm pool (EPWP). GDGT and alkenone concentrations showed higher values in marine isotope stage (MIS)-2 and MIS-6, which suggests the enhancement of primary production at glacial maxima. $ {\text{TEX}}_{86}^{\text{H}} $ - and $ U_{ 3 7^\prime }^{\text{K}} $ -derived temperature depicted different temperature evolutions. $ U_{ 3 7^\prime }^{\text{K}} $ -derived temperature was marked by small variation during the glacial–interglacial cycles, whereas $ {\text{TEX}}_{86}^{\text{H}} $ -derived temperature showed pronounced glacial–interglacial variation that was similar to Mg/Ca-derived temperature records from nearby cores in the EPWP. Given that enhanced primary production during glacial maxima suggests nutricline shoaling, unchanged $ U_{ 3 7^\prime }^{\text{K}} $ over glacial–interglacial cycles can be interpreted as the shift of alkenone production depth. $ {\text{TEX}}_{86}^{\text{H}} $ seems not to be influenced by glacial–interglacial changes in nutricline depths, recording an integrated temperature in surface and thermocline water. The shallow nutricline in the EPWP during glacial maxima most likely reflected the intense formation of Antarctic intermediate water.  相似文献   

Transient crater growth in granular targets: An experimental study of low velocity impacts into glass sphere targets     

Satoru Yamamoto  Koji Wada  Takafumi Matsui 《Icarus》2006,183(1):215-224

We experimentally studied the formation and collapse processes of transient craters. Polycarbonate projectiles with mass of 0.49 g were impacted into the soda-lime glass sphere target (mean diameters of glass spheres are ∼36, 72, and 220 μm, respectively) using a single-stage light-gas gun. Impact velocity ranged from 11 to 329 m s⁻¹. We found that the transient crater collapses even at laboratory scales. The shape (diameter and depth) of the transient crater differs from that of the final crater. The depth-rim diameter ratios of the final and transient craters are 0.11-0.14 and 0.26-0.27, respectively. The rim diameter of both the transient and final crater depends on target material properties; however, the ratio of final to transient crater diameter does not. This suggests that target material properties affect the formation process of transient craters even in the gravity regime, and must be taken into account when scaling experimental results to planetary scales. By observing impacts into glass sphere targets, we show that although the early stage of the excavation flow does not depend on the target material properties, the radial expansion of the cavity after the end of vertical expansion does. This suggests that the effect of target material properties is specifically important in the later part of the crater excavation and collapse.  相似文献   

VIDEO AND PHOTOGRAPHIC SPECTROSCOPY OF 1998 AND 2001 LEONID PERSISTENT TRAINS FROM 300 TO 930 nm     

Shinsuke Abe  Noboru Ebizuka  Hideyuki Murayama  Katsuhito Ohtsuka  Satoru Sugimoto  Masa-yuki Yamamoto  Hajime Yano  Jun-ichi Watanabe  Jiří Borovička 《Earth, Moon, and Planets》2004,95(1-4):265-277

Spectra of persistent meteor trains were observed at wavelength between 300 and 930 nm. Two obtained train spectra during the 1998 and 2001 Leonid meteor showers are reported here. During the 1998 Leonids, one train was detected by a photographic camera with a spectrograph covering 370–640 nm region. On the other hand, during the 2001 Leonids, video observations were carried out using image intensified cameras in ultraviolet (UV), visible and near infrared (near-IR) wavelengths. Temperatures in persistent trains have been measured by atmospheric O₂ A(0,1) band at the wavelength near 864.5 nm. From a video spectrum obtained just 7 s after parent fireball’s flare, a rotational temperature of 250 K at altitude of 88.0±0.5 km was estimated. We can say that the cooling time scale of train strongly depends on the initial mass of its fireball at least for Leonids. Based on cooling constant calculated from our results, we estimated a temperature of ∼ ∼130 K as a final exothermic temperature at early stage of persistent trains.  相似文献