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Toshiaki Masuda Shotaro Nakayama Nozomi Kimura Atsushi Okamoto 《Tectonophysics》2008,460(1-4):230-236
We revised an equation for estimating palaeostress magnitude using the microboudin technique by incorporating the influence of time on the fracture strength of minerals. The equation was used to estimate triaxial palaeostresses from a rare sample of metachert from Turkey that contains microboudinaged, columnar tourmaline grains in a wide range of orientations within the foliation plane. The estimated principal palaeostresses are σ1 = 605 MPa, σ2 = 598 MPa, and σ3 = 597 MPa. As the microboudinage is considered to have occurred immediately before the rock encountered the brittle-plastic transition during exhumation, these stress values correspond to conditions at approximately 18 km depth and 300 °C within a Cretaceous orogenic belt. 相似文献
2.
State Estimation of the North Pacific Ocean by a Four-Dimensional Variational Data Assimilation Experiment 总被引：1，自引：0，他引：1
Toshiyuki Awaji Shuhei Masuda Yoichi Ishikawa Nozomi Sugiura Takahiro Toyoda Tomohiro Nakamura 《Journal of Oceanography》2003,59(6):931-943
A four-dimensional variational data assimilation system has been applied to an experiment to describe the dynamic state of
the North Pacific Ocean. A synthesis of available observational records and a sophisticated ocean general circulation model
produces a dynamically consistent dataset, which, in contrast to the nudging approach, provides realistic features of the
seasonally-varying ocean circulation with no artificial sources/sinks for temperature and salinity fields. This new dataset
enables us to estimate heat and water mass transports in addition to the qualification of water mass formation and movement
processes. A sensitivity experiment on our assimilation system reveals that the origin of the North Pacific Intermediate Water
can be traced back to the Sea of Okhotsk and the Bering Sea in the subarctic region and to the subtropical Kuroshio region
further south. These results demonstrate that our data assimilation system is a very powerful tool for the identification
and characterization of ocean variabilities and for our understanding of the dynamic state of ocean circulation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
Mumbfu Ernestine Mimba Takeshi Ohba Salomon César Nguemhe Fils Melvin Tamnta Nforba Nozomi Numanami Tasin Godlove Bafon Festus Tongwa Aka Cheo Emmanuel Suh 《Geochemical transactions》2018,19(1):11
The distribution of trace metals in active stream sediments from the mineralized Lom Basin has been evaluated. Fifty-five bottom sediments were collected and the mineralogical composition of six pulverized samples determined by XRD. The fine fraction (<?150 µm) was subjected to total digestion (HClO4?+?HF?+?HCl) and analyzed for trace metals using a combination of ICP-MS and AAS analytical methods. Results show that the mineralogy of stream sediments is dominated by quartz (39–86%), phyllosilicates (0–45%) and feldspars (0–27%). Mean concentrations of the analyzed metals are low (e.g. As?=?99.40 µg/kg, Zn?=?573.24 µg/kg, V?=?963.14 µg/kg and Cr?=?763.93 µg/kg). Iron and Mn have significant average concentrations of 28.325 and 442 mg/kg, respectively. Background and threshold values of the trace metals were computed statistically to determine geochemical anomalies of geologic or anthropogenic origin, particularly mining activity. Factor analysis, applied on normalized data, identified three associations: Ni–Cr–V–Co–As–Se–pH, Cu–Zn–Hg–Pb–Cd–Sc and Fe–Mn. The first association is controlled by source geology and the neutral pH, the second by sulphide mineralization and the last by chemical weathering of ferromagnesian minerals. Spatial analysis reveals similar distribution trends for Co–Cr–V–Ni and Cu–Zn–Pb–Sc reflecting the lithology and sulphide mineralization in the basin. Relatively high levels of As were concordant with reported gold occurrences in the area while Fe and Mn distribution are consistent with their source from the Fe-bearing metamorphic rocks. These findings provide baseline geochemical values for common and parallel geological domains in the eastern region of Cameroon. Although this study shows that the stream sediments are not polluted, the evaluation of metal composition in environmental samples from abandoned and active mine sites for comparison and environmental health risk assessment is highly recommended. 相似文献
4.
Impact of mesoscale eddies on particulate organic carbon flux in the western subarctic North Pacific
Dobashi Ryo Ueno Hiromichi Matsudera Nozomi Fujita Isao Fujiki Tetsuichi Honda Makio C. Harada Naomi 《Journal of Oceanography》2022,78(1):1-14
The mechanism that controls particulate organic carbon (POC) flux in the deep sea differs depending on the season and sea. The POC produced in the western subarctic North Pacific are known to be transported to the deep sea efficiently, but the direct relationship between the POC flux and physical processes is still unclear. In this study, we evaluated the effect of mesoscale eddies on POC flux in the western subarctic North Pacific. The seasonal and interannual variabilities of POC flux were investigated using data from a time-series sediment trap deployed at 4810 m at station K2 (47°N, 160°E) from 2005 to 2018. POC flux was high during May–November, appearing to reflect spring and fall blooms at the ocean surface. POC flux also showed interannual variability, with twelve peaks that were mostly affected by enhanced bloom just before the peak. Nine peaks of the twelve peaks were affected by mesoscale eddies, which enhanced bloom around K2 by extending the area with a high chlorophyll-a concentration along the coastal region into the offshore region, suggesting that mesoscale eddies strongly impact the interannual variability of POC flux at K2.
相似文献5.
Development of Taprang landslide,West Nepal 总被引：1，自引：1，他引：0
This paper is about a large landslide located at Taprang, on the right bank of the Madi River in the west Nepal Himalaya. It attempts to reconstruct the evolution of the landslide from its initial state to the present conditions. Many large landslides involve multiple failure incidents in different times to attain their present size and shape. The Taprang landslide has also been active for more than 75 years and experienced many failure episodes. The slide lies in a very complex geological setting characterized by the presence of Main Central Thrust and some other folds as well as several joint sets and shear zones. It is developed on weathered graphitic schists, highly fractured and jointed quartzites, marbles, gneisses, and a few amphibolites. Landslide mapping revealed that the rocks are deformed and fractured. They have also undergone intense weathering. Laboratory analysis of rock and soil samples collected from the landslide and surrounding area shows that the weathered rocks, joint infillings, and shear zones are rich in clay minerals, especially smectite and montmorillonite having swelling properties. Besides, hydrologic, climatic, and anthropogenic factors operating simultaneously since a long time have also contributed significantly to the enlargement of the slide. The study indicates that the landslide has a high potential of future enlargement towards upper slopes. 相似文献
6.
Nozomi Ytow Motoo Utsumi Humitake Seki 《Aquatic Sciences - Research Across Boundaries》1996,58(2):91-102
Ultraviolet (UV) spectra were measured to characterize the dissolved and particulate organic matter in a bog and to investigate the seasonal fluctuation of this organic matter. The optical density spectra in the UV region of dissolved organic matter (DOM) were proportional to
–4, where is the wavelength of incident light. There was also small absorption on the
–4 spectra. The optical density at a wavelength of 280 nm was proportional to the concentration of dissolved organic carbon (DOC). The spectra and the dependency of optical density on DOC did not vary throughout the investigation period. The UV spectra of acid extractions of particulate organic matter (POM) showed two absorption peaks at the wavelengths of 220 nm and 335 nm. These peaks are well represented by the sum of two Lorentz functions. The ratio of the absorbances,A
280/A
335, was dependent on the nitrogen/carbon ratio of POM and the chlorophyll fraction in particulate organic carbon (POC), and not dependent on POC itself. The dependency of POC absorption at 280 nm varied with this ratio which fluctuated seasonally. 相似文献
7.
A mathematical model of attached bacterial dynamics based on microcolonization was devised using data obtained from a bog. Bacterial samples obtained from any natural water body can be examined by this model with the method of non-linear least squares. The model comprises three bacterial processes; i.e., (1) the attachment rate which was dependent on time after submergence by adsorption onto the substratum surface, and both (2) growth and (3) detachment rate which were dependent on the number of bacterial cells in the microcolony. The population dynamics are expressed as $$\frac{{dC_i }}{{dt}} = - g_i C_i + g_{i - 1} C_{i - 1} - b_i C_i + b_{i + 1} C_{i + 1} + a_i F_i ,$$ where suffixi denotes cell number in each microcolony,C i is microcolony number on the substratum,F i is bacterial clump drifting in the water column,a i , g i andb i are the rate coefficients of attachment, growth and detachment. The growth rate was reciprocally proportional to the cell number in the microcolony. The detachment was shown to increase up to a maximum, and then to decrease as the number of bacterial cells increased in each microcolony. 相似文献
8.
The population dynamics of attached bacteria at the water-sediment interface were studied in a mesotrophic swampy bog, Matsumi-ike,
near Tsukuba, Japan. The density of attached bacteria was higher at the sediment boundary layer than in the water column,
and low inside the sediment (deeper, than 10 mm below the sediment surface) throughout the year. The density of bacteria attached
on the glass slide was highest during spring when the source of organic matter in the water column was mainly withered cattail,
and gradually decreased toward summer, while the phytoplankton became the dominant source of organic matter in the water column.
The epibacterial populations in the water column and at the boundary showed almost the same seasonal fluctuation in attachment
and detachment rates. However, bacterial growth rates did not show the same seasonal fluctuation, and annual average growth
rates on the glass slides were all lower than that of bacterioplankton (free-living bacteria in water) in the water column. 相似文献
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