Rationalization of building micro-dams equipped with fish passages in West African savannas   总被引：1，自引：1，他引：0  

Koichi Unami  Macarius Yangyuoru  Abul Hasan Md. Badiul Alam 《Stochastic Environmental Research and Risk Assessment (SERRA)》2012,26(1):115-126

Micro-dams in West African savannas are investigated in conjunction with aquatic fauna and human activities at a community level. A study area is chosen in the Northern Region of Ghana. The micro-dams in the study area serve as habitats for fish, providing food and job opportunities for inhabitants, but their construction has sacrificed rice fields and fragmented migration routes of fish. A stochastic population dynamics model is developed to rigorously assess the effect of establishing fish passages between the fragmented habitats containing the micro-dams on the ichthyological fauna. Values of the model parameters are estimated from the literature and results of field surveys, in which ten fish species including cichlidae, clariidae, bagridae, schilbeidae, cyprinidae, and alistidae are reported to be present. A sustainability criterion is proposed to judge whether a set of model parameters realizes stationarity of the stochastic process representing the population dynamics. It is suggested that ichthyological fauna can be sustainable provided that the fishing activity is restricted to upstream migrating and fast growing species. More generally, building micro-dams in West African savannas will be much better justified when the dams are equipped with appropriately designed fish passages.  相似文献   

Verifying optimality of rainfed agriculture using a stochastic model for drought occurrence   总被引：1，自引：1，他引：0  

Erfaneh Sharifi  Koichi Unami  Macarius Yangyuoru  Masayuki Fujihara 《Stochastic Environmental Research and Risk Assessment (SERRA)》2016,30(5):1503-1514

It may be paradoxical but subsistence rainfed agriculture is the predominant source of food in Sub-Saharan Africa where the production uncertainty is associated with the stochastic nature of rainfall. This paper attempts to comprehend the rationale of this situation by a mathematical approach. Considering the level of drought severity as the zero-reverting Ornstein–Uhlenbeck process, optimality of rainfed agriculture is investigated in the context of stochastic control theory. Occurrence of drought terminating growth of crops is modelled with the concept of first exit time. A stochastic control problem allowing for virtual cost of irrigation, water stress to crops, and benefits of farming is formulated with irrigation effort as the control variable. The Hamilton–Jacobi–Bellman equation governing the optimal control is studied to identify the set of cost functions optimizing rainfed agriculture in an inverse problem approach. Data and information were collected in the coastal savanna agro-ecological zone of Ghana, to identify model parameters, formulate the stochastic control problem, solve the inverse problem, and then verify optimality of rainfed agriculture. The results indicated that rainfed agriculture is not optimal when the crop is more tolerant to water stress.  相似文献   

Earthquake response of submerged gravity foundation on soft rock     

Mamoru Kanatani  Koichi Nishi  Toyoaki Nogami 《Soil Dynamics and Earthquake Engineering》1997,16(2):125-139

A gravity foundation submerged in the water is subject to the buoyancy force and is hence vulnerable to sliding at the base when it is subjected to a large lateral load. The effects of sliding on the earthquake response were investigated for this type of foundation on soft rock, considering the friction characteristics at the contact between concrete and soft rock. Shake table tests were conducted to observe the behavior of a submerged foundation on soft rock which slid during the excitation. Large-scale cyclic direct shear tests were conducted to examine in detail the friction characteristics at the contact between the concrete and soft rocks. Based on the results obtained in shake table and cyclic shear tests, a numerical model was established for simulating the earthquake response behavior of a submerged gravity foundation on soft rock. Numerical parametric studies were conducted by using this model and selected earthquake ground motion records. Various important features were observed in the earthquake response of this foundation.  相似文献   

Diagenesis of Neogene diatoms and their importance as a source of petroleum in Japan     

Koichi  Aoyagi Mamoru  Omokawa 《Island Arc》1993,2(4):273-279

Abstract Various siliceous rocks are found in the Ohdoji, Akaishi and Maido Formations from the western Aomori basin, and the Yotsuzawa and Wadagawa Formations from the eastern Aomori basin of northern Honshu, Japan. These rocks are classified into diatomite, siliceous shale and chert.
Diatomite is composed of abundant amorphous silica and has porosity between 50 and 65%. Siliceous shale is composed of a large amount of quartz, and has porosity ranging from 25 to 35%. Chert is chiefly composed of cristobalite or quartz, and has porosity between 20 to 30%.
Average contents of total organic carbon, S₁ and S₂ generally increase from argillaceous rocks → diatomites → siliceous shales → cherts. Maturation of organic matter in these rocks is generally lower than that in average source rocks. Diatoms, which appeared in the late Cretaceous and became increasingly important in the Miocene, are the principal primary producers of organic matter in the marine environment during the Cenozoic. Excellent organic components and higher biological productivity show that diatoms might be the most important source of petroleum during the Neogene in Japan.
Proteins, carbohydrates and lipids in diatoms have been transformed into fulvic acids, humic acids and humin by polycondensation and polymerization. Later, these humin materials could be changed into insoluble kerogen under the effect of mild temperature and pressure. A part of the lipids would transform to geochemical fossils (biomarkers). Amorphous silica in cells of diatoms would change to low-cristobalite and low-quartz by the increase of geothermal temperature.  相似文献   

Counter-clockwise rotation of the eastern part of the Mongolia block: Early Cretaceous palaeomagnetic results from Bikin, Far Eastern Russia     

Yo-ichiro Otofuji  Daisuke Miura  Koichi Takaba  Kazuhiro Takemoto  Kazutoshi Narumoto  Haider Zaman  Hiroo Inokuchi  Ruslan G. Kulinich  Petr S. Zimin  Vladimir G. Sakhno 《Geophysical Journal International》2006,164(1):15-24

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RC pile–soil interaction analysis using a 3D‐finite element method with fibre theory‐based beam elements     

Takeshi Maki  Koichi Maekawa  Hiroshi Mutsuyoshi 《地震工程与结构动力学》2006,35(13):1587-1607

To evaluate the overall response of a structural system including its foundation and surrounding soil, an equivalent finite element model with reduced degrees of freedom using fibre theory‐based beam element was proposed. The proposed model was based on investigations of the subgrade soil reaction of a single‐layer model, and was verified for the cyclic behaviour of a laterally loaded single RC pile in terms of the load–displacement relationship, pile deformation, and soil pressures on the pile surface. Also investigated was the effect of the interfacial element between pile and soil on the behaviour of the laterally loaded pile. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Geochemical mapping in Aichi prefecture,Japan: Its significance as a useful dataset for geological mapping     

Koshi Yamamoto  Tsuyoshi Tanaka  Masayo Minami  Koichi Mimura  Yoshihiro Asahara  Hidekazu Yoshida  Setsuo Yogo  Makoto Takeuchi  Masami Inayoshi 《Applied Geochemistry》2007

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Essential cellular modules for the proliferation of the primitive cell     

Koichi Higashi  Yoshikazu Kawai  Tomoya Baba  Ken Kurokawa  Taku Oshima 《地学前缘(英文版)》2018,9(4):1155-1161

Bacteria appeared early in the evolution of cellular life on planet Earth, and therefore the universally essential genes or biological pathways found across bacterial domains may represent fundamental genetic or cellular systems used in early life. The essential genes and the minimal gene set required to support bacterial life have recently been experimentally and computationally identified. It is, however,still hard to estimate the ancient genes present in primitive cells compared to the essential genes in contemporary bacteria, because we do not know how ancestral primitive cells lived and proliferated, and therefore cannot directly evaluate the essentiality of the genes in ancestral primitive cells. The cell wall is normally essential for bacterial proliferation and cellular division of walled bacterial cells is normally highly controlled by the essential FtsZ cell division machinery. But, bacteria are capable of reverting to their cell wall deficient ancestral form, called the "L-form". Unlike "normal" cells, L-forms divide by a simple physical mechanism based on the effects of membrane dynamics, suggesting a mode of primitive proliferation before the appearance of the cell wall. In this review, we summarize the experimental and computational investigations of minimal gene sets and discuss the minimal cellular modules required to support the proliferation of primitive cells, based on L-form proliferation.  相似文献   

Correction to: A web-based real-time and full-resolution data visualization for Himawari-8 satellite sensed images     

Ken T. Murata  Praphan Pavarangkoon  Atsushi Higuchi  Koichi Toyoshima  Kazunori Yamamoto  Kazuya Muranaga  Yoshiaki Nagaya  Yasushi Izumikawa  Eizen Kimura  Takamichi Mizuhara 《Earth Science Informatics》2018,11(2):239-240

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Factors Controlling the Fractionation and Seasonal Mobility Variations of Ga and In in Systems Impacted by Acidic Thermal Waters: Effects of Thermodynamics and Bacterial Activity     

Yasumasa Ogawa  Daizo Ishiyama  Naotatsu Shikazono  Koichi Suto  Chihiro Inoue  Noriyoshi Tsuchiya  Bernhardt Saini-Eidukat  Scott A. Wood 《Aquatic Geochemistry》2018,24(1):5-25

This work assessed both the fractionation and the seasonal mobility variations of Ga and In in systems impacted by acidic thermal waters. This was accomplished by performing thermodynamic calculations using the PHREEQC algorithm and by assessing the activity of acidophilic iron-oxidizing bacteria. The pH of the Kusatsu thermal waters in Gunma Prefecture, central Japan, is rapidly increased following the addition of a lime suspension. After an abrupt pH increase, under which conditions free ions of Ga and In and their complexes with Cl^? and SO₄^2? exist only in negligible quantities, the majority of dissolved Ga and In is removed by sorption onto suspended hydrous ferric oxides (HFOs). These HFOs are then transported to an artificial lake without significant sedimentation along the river. Subsequently, the suspended HFOs settle out and are added to sediments without significant fractionation between Ga and In. The Tamagawa thermal waters in Akita Prefecture, northeast Japan, are also treated with lime. However, complete neutralization requires mixing with some tributary streams, leading to a gradual downstream increase in pH. Dissolved Ga is, in general, sorbed by HFOs in upstream areas, leading to wide dispersal of Ga across the entire watershed. In comparison, In is transported to the lake inlet predominantly as a Cl^? complex species without significant removal along the river, with the majority being precipitated in an artificial lake, where Cl^? concentrations are too low to form stable complex species with In, and thus, dissolved In is sorbed by HFOs. As a result, In is effectively concentrated within downstream lakebed sediments, whereas Ga is dispersed along the river. Seasonal variations in Ga mobility within the Tamagawa field between snowmelt and low-flow seasons are primarily controlled by pH, because hydrolysis reactions of these metals, which are related to sorption reactions, tend to occur in the upstream regions in the snowmelt season. However, under warmer conditions, HFO formation preferably occurs due to the activity of acidophilic iron-oxidizing bacteria. Thus, under similar pH variations, dissolved Ga is more effectively removed by HFOs during warmer seasons. On the contrary, because HFOs are abundantly formed in low-flow season, even under colder conditions, before In hydrolysis reaction starts to occur, In mobility is less affected by water temperature and then bacterial activity.  相似文献