Three-dimensional mapping of red stingray (Dasyatis akajei) movement with reference to bottom topography     

Otaki  Takayoshi  Hamana  Masahiro  Tanoe  Hideaki  Miyazaki  Nobuyuki  Shibuno  Takuro  Komatsu  Teruhisa 《Ocean Science Journal》2015,50(2):327-334

Most demersal fishes maintain strong relations with bottom substrates and bottom depths and/or topography during their lives. It is important to know these relations to for understand their lives. In Tokyo Bay, red stingray, Dasyatis akajei, classified as near-threatened species by IUCN, has increased since the 1980s. It is a top predator and engages in ecosystem engineer by mixing the sand bed surface through burring behavior, and greatly influences a coastal ecosystem. It is reported that this species invades in plage and tidal flats and has sometimes injured beachgoers and people gathering clams in Tokyo bay. Thus, it is necessary to know its behavior and habitat use to avoid accidents and to better conserve the biodiversity of ecosystems. However, previous studies have not examined its relationship with the bottom environment. This study aims to describe its behavior in relation to the bottom environment. We sounded three dimensional bottom topography of their habitat off Kaneda Cove in Tokyo Bay with interferometric sidescan sonar system and traced the movement of red stingrays by attaching a data logger system to survey their migration. The results revealed that red stingray repeated vertical movement between the surface and bottom, and used not only sand beds but also rocky beds.

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An overview of decadal climate predictability in a multi-model ensemble by climate model MIROC   总被引：1，自引：1，他引：0  

Yoshimitsu Chikamoto  Masahide Kimoto  Masayoshi Ishii  Takashi Mochizuki  Takashi T. Sakamoto  Hiroaki Tatebe  Yoshiki Komuro  Masahiro Watanabe  Toru Nozawa  Hideo Shiogama  Masato Mori  Sayaka Yasunaka  Yukiko Imada 《Climate Dynamics》2013,40(5-6):1201-1222

Decadal climate predictability is examined in hindcast experiments by a multi-model ensemble using three versions of the coupled atmosphere-ocean model MIROC. In these hindcast experiments, initial conditions are obtained from an anomaly assimilation procedure using the observed oceanic temperature and salinity with prescribed natural and anthropogenic forcings on the basis of the historical data and future emission scenarios in the Intergovernmental Panel of Climate Change. Results of the multi-model ensemble in our hindcast experiments show that predictability of surface air temperature (SAT) anomalies on decadal timescales mostly originates from externally forced variability. Although the predictable component of internally generated variability has considerably smaller SAT variance than that of externally forced variability, ocean subsurface temperature variability has predictive skills over almost a decade, particularly in the North Pacific and the North Atlantic where dominant signals associated with Pacific decadal oscillation (PDO) and the Atlantic multidecadal oscillation (AMO) are observed. Initialization enhances the predictive skills of AMO and PDO indices and slightly improves those of global mean temperature anomalies. Improvement of these predictive skills in the multi-model ensemble is higher than that in a single-model ensemble.  相似文献   

Mechanisms of enhanced ocean surface warming in the Kuroshio region for 1951–2010     

Toda  Masaki  Watanabe  Masahiro 《Climate Dynamics》2020,54(9):4129-4145

Climate Dynamics - Since the early twentieth century, observations have shown that the ocean surface has warmed almost globally, but the rate of sea surface temperature (SST) rise in the Kuroshio...  相似文献   

Zonation of Sulfate and Sulfide Minerals and Isotopic Composition in the Far Southeast Porphyry and Lepanto Epithermal Cu–Au Deposits,Philippines          下载免费PDF全文

Jeffrey W. Hedenquist  Antonio Arribas R.  Masahiro Aoki 《Resource Geology》2017,67(2):174-196

The world‐class Far Southeast (FSE) porphyry system, Philippines, includes the FSE Cu–Au porphyry deposit, the Lepanto Cu–Au high‐sulfidation deposit and the Victoria–Teresa Au–Ag intermediate‐sulfidation veins, centered on the intrusive complex of dioritic composition. The Lepanto and FSE deposits are genetically related and both share an evolution characterized by early stage 1 alteration (deep FSE potassic, shallow Lepanto advanced argillic‐silicic, both at ~1.4 Ma), followed by stage 2 phyllic alteration (at ~1.3 Ma); the dominant ore mineral deposition within the FSE porphyry and the Lepanto epithermal deposits occurred during stage 2. We determined the chemical and S isotopic composition of sulfate and sulfide minerals from Lepanto, including stage 1 alunite (12 to 28 permil), aluminum–phosphate–sulfate (APS) minerals (14 to 21 permil) and pyrite (?4 to 2 permil), stage 2 sulfides (mainly enargite–luzonite and some pyrite, ?10 to ?1 permil), and late stage 2 sulfates (barite and anhydrite, 21 to 27 permil). The minerals from FSE include stage 2 chalcopyrite (1.6 to 2.6 permil), pyrite (1.1 to 3.4 permil) and anhydrite (13 to 25 permil). The whole‐rock S isotopic composition of weakly altered syn‐mineral intrusions is 2.0 permil. Stage 1 quartz–alunite–pyrite of the Lepanto lithocap, above about 650 m elevation, formed from acidic condensates of magmatic vapor at the same time as hypersaline liquid formed potassic alteration (biotite) near sea level. The S isotopic composition of stage 1 alunite–pyrite record temperatures of approximately 300–400°C for the vapor condensate directly over the porphyry deposit; this cooled to <250°C as the acidic condensate flowed to the NW along the Lepanto fault where it cut the unconformity at the top of the basement. Stage 1 alunite at the base of the advanced argillic lithocap over FSE contains cores of APS minerals with Sr, Ba and Ca; based on back‐scattered electron images and ion microprobe data, these APS minerals show a large degree of chemical and S‐isotopic heterogeneity within and between samples. The variation in S isotopic values in these finely banded stage 1 alunite and APS minerals (16 permil range), as well as that of pyrite (6 permil range) was due largely to changes in temperature, and perhaps variation in redox conditions (average ~ 2:1 H₂S:SO₄). Such fluctuations could have been related to fluid pulses caused by injection of mafic melt into the diorite magma chamber, supported by mafic xenoliths hosted in diorite of an earlier intrusion. The S isotopic values of stage 2 minerals indicate temperatures as high as 400°C near sea level in the porphyry deposit, associated with a relatively reduced fluid (~10:1 H₂S:SO₄) responsible for deposition of chalcopyrite. Stage 2 fluids were relatively oxidized in the Lepanto lithocap, with an H₂S:SO₄ ratio of about 4. The oxidation resulted from cooling, which was caused by boiling during ascent and then dilution with steam‐heated meteoric water in the lithocap. This cooling also resulted in the sulfidation state of minerals increasing from chalcopyrite stability in the porphyry deposit to that of enargite in the lithocap‐hosted high‐sulfidation deposit. The temperature at the base of the lithocap during stage 2 was ≥300°C, cooling to <250°C within the main lithocap, and about 200°C towards the limit of the Lepanto orebody, approximately 2 km NW of the porphyry deposit. Approximate 300°C and 200°C isotherms, estimated from S isotopic and fluid inclusion temperatures during stage 1 and stage 2, shifted towards the core of the FSE porphyry deposit with time. This general retreat in isotherms was more than 500 m laterally within Lepanto and 500 m vertically within FSE as the magmatic–hydrothermal system evolved and collapsed over the magmatic center. During this evolution, there is also evidence recorded by large S isotopic variations in individual crystals for sharp pulses of higher temperature, relatively reduced fluid injected into the porphyry deposit.  相似文献   

Fractal structure of the time distribution of microfracturing in rocks   总被引：6，自引：0，他引：6  

Xia-Ting Feng  & Masahiro Seto 《Geophysical Journal International》1999,136(1):275-285

Using acoustic emission data obtained from laboratory double torsion tests, we have analysed the fractal nature of a series of 29 granite microfracturing processes in time. The data represent a wide variety of timescales, stress environments (increasing load with a constant displacement rate, relaxation, creep), soaking conditions [air, water, dodecyl trimethyl ammonium bromide (DTAB), polyethelene oxide (PEO) ], and material anisotropy. We find that the time distribution of rock microfracturing displays fractal and multifractal properties. In some cases, it has a single fractal or a multifractal structure. In other cases, it changes from a single fractal structure into a multifractal structure as the system evolves dynamically. We suggest that the heterogeneity of the rock, the distribution of joints or weak planes, the stress level, and the nature of the microfracturing mechanism lead to these multifractal properties. Whatever the fractal structure of the system, a lower fractal dimension is generally produced at near-failure of the rock due to an increased clustering. This result concerning the fractal-dimension decrease is consistent with the conclusion drawn from the spatial distribution of rock microfracturing. Therefore, from the vantage point of observation of the time distribution of rock microfracturing, the decrease of the fractal dimension has a potential use as a rock failure predictor.  相似文献   

Plio–Pleistocene Hydrothermal Activity Related to Gold Mineralization in the Seta Area, Northeastern Hokkaido, Japan     

Masahiro YAHATA  Hiroharu MATSUEDA 《Resource Geology》1999,49(3):131-145

Abstract: Plio–Pleistocene hydrothermal activity resulted in high grade low sulfidation epithermal gold mineralization in the Seta area, the southern end of the Monbetsu-Kamishihoro Graben of northeastern Hokkaido, Japan. Hydrothermal activity and accompanying hydrothermal eruptions began at approximately 2 Ma along NNW-SSE trending faults, the Tohbu-ko fault I and II. This activity resulted in two main zones of gold mineralization, the west quartz-adularia veins(QAV) and east stock-work zone(STZ), formed between 1. 8 and 1. 2 Ma. A smectite-chlorite alteration zone is observed at deeper levels, while kaolinite and kaolinite-smectite zones occur at shallower levels with an acid-leached zone present near the surface. The kaoli-nite and kaolinite-smectite zones are also distributed along faults and the STZ, to depths of several hundred meters. δ³⁴S values of pyrite and alunite from the kaolinite and silicified zones indicate alunite formed by the oxidation of sulfide, either H₂S(vapor) or mineral.
Formation of the STZ and the southern part of the QAV took place during lacustrine sedimentation, while formation of the northern part of the QAV took place after eruption of andesitic lava; the latter being associated with widespread alteration formed under neutral-pH conditions. δ¹⁸O values of quartz veins and silicified rocks indicate that the paleo-hydrothermal waters have a large meteoric component, increasing with decreasing depth in the STZ. Acid hydrothermal waters, resulting from near surface oxidation of H₂S were responsible for acid-leaching and kaolinization of surrounding rocks. Between 1. 4 and 0. 3 Ma, the acid hot waters drained back along the STZ to depths of at least 500m, as a result of a fall in the paleo-water table level.  相似文献   

Decoupling algorithm for evaluating multiple beam damages in steel moment‐resisting frames          下载免费PDF全文

Xiaohua Li  Masahiro Kurata  Akiko Suzuki 《地震工程与结构动力学》2017,46(7):1045-1064

Post‐earthquake safety evaluation of steel moment‐resisting frames mainly relies on the inspection of seismic damage to beam–column connections. Recently, in order to evaluate seismic damage of steel connections in a prompt and precise manner, a local damage evaluation method based on dynamic strain responses has been proposed and receives attention. In the evaluation method where strain responses are measured by piezoelectric strain sensors, a strain‐based damage index has been developed for evaluating individual seismic beam damage in a steel frame. However, for a steel frame suffering multiple beam damages, the damage index deteriorates its performance in identifying small damages with the presence of neighboring severe damages because of the moment redistributions induced by larger damages. This paper presents a decoupling algorithm that removes the issue of damage interaction and improves the performance of the damage index. The decoupling algorithm was derived on the basis of damage‐induced moment release and redistribution mechanism. The effectiveness of the decoupling algorithm was numerically and experimentally investigated using a nine‐story steel frame model and a large scale five‐story steel frame testbed that can simulate multiple fractures at beam ends. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Formal education and disaster response of children: evidence from coastal villages in Indonesia     

Shoji  Masahiro  Takafuji  Yoko  Harada  Tetsuya 《Natural Hazards》2020,103(2):2183-2205

Natural Hazards - Although children are exposed to a high mortality risk during disasters, what determines their disaster response, especially during earthquakes, remains largely unexplored. The...  相似文献   

A zone of columnar joints beneath the roof of a granitic pluton: The Okueyama granite,southwestern Japan     

Masahiro Chigira  Hironori Kato 《Island Arc》2024,33(1):e12524

Igneous rocks are fractured during cooling from magma to form cooling joints, which are typically columnar joints in volcanic rocks, while orthogonal joints are considered typical for plutonic rocks. We performed a 3D study of joint systems in a granitic batholith of the Okueyama granite in western Japan, which has its roof and its internal structures from the roof to 1000 m downward exposed. We used an unmanned aerial vehicle (UAV) to observe the joints in outcrops from various angles. Based on our study, we propose a schematic model for joint systems in a granitic pluton. A granitic pluton has zones of rock columns below the roof and next to the wall. The rock column zone below the roof is as thick as 300 m, and its higher portions form steep cliffs, probably because of increased resistance to weathering. The axes of the rock columns are nearly vertical below the roof and gently plunge next to the walls, with high intersection angles with the wall. The distribution of columnar joints near only the roof and walls suggests that the granite cooled more rapidly near the roof and walls than in the core of the pluton. When the granite was jointed by parallel joints during cooling, the rock slabs between the parallel joints near the roof and the walls are subdivided into columns with polygonal cross-sections. This suggests that the granite was fractured by parallel joints at a temperature immediately below the solidus, after which the rock slabs were subdivided into rock columns during further cooling.  相似文献   

A simple and robust procedure for coring unconsolidated sediment in shallow water     

Hiroshi Adachi  Hiroya Yamano  Toshihiro Miyajima  Masahiro Nakaoka 《Journal of Oceanography》2010,66(6):865-872

This article describes a simple, quick, and inexpensive procedure for coring unconsolidated sediment in shallow water (<30 m from water surface). A ∼1 m core is retrieved by a PVC pipe that penetrates sediment in response to the percussive force of a hand-operated hammering tool or air hammer. After retrieving the first core segment, a casing is inserted to allow access to deeper sediment layers. Pulverized sediment produced during coring is removed by a water-lubrication system that is powered by an electric pump attached to a generator. Using this system and procedure, five 2-m-long cores with excellent quality were retrieved.  相似文献