Horizontal distribution and population dynamics of the dominant mysid Hyperacanthomysis longirostris along a temperate macrotidal estuary (Chikugo River estuary, Japan)     

Keita W. Suzuki  Kouji Nakayama  Masaru Tanaka 《Estuarine, Coastal and Shelf Science》2009,83(4):516-528

The estuarine turbidity maximum (ETM) that develops in the lower salinity areas of macrotidal estuaries has been considered as an important nursery for many fish species. Mysids are one of the dominant organisms in the ETM, serving as a key food source for juvenile fish. To investigate the horizontal distribution and population dynamics of dominant mysids in relation to the fluctuation of physical conditions (temperature, salinity, turbidity, and freshwater discharge), we conducted monthly sampling (hauls of a ring net in the surface water) along the macrotidal Chikugo River estuary in Japan from May 2005 to December 2006. Hyperacanthomysis longirostris was the dominant mysid in the estuary, usually showing peaks of density and biomass in or close to the ETM (salinity 1–10). In addition, intra-specific differences (life-cycle stage, sex, and size) in horizontal distribution were found along the estuary. Larger males and females, particularly gravid females, were distributed upstream from the center of distribution where juveniles were overwhelmingly dominant. Juveniles increased in size toward the sea in marked contrast with males and females. The findings suggest a possible system of population maintenance within the estuary; gravid females release juveniles in the upper estuary, juveniles grow during downstream transport, young males and females mature during the upstream migration. Density and biomass were primarily controlled by seasonal changes of temperature, being high at intermediate temperatures (ca. 15–25 °C in late spring and fall) and being low at the extreme temperatures (ca. 10 °C in midwinter and 30 °C in midsummer). High density (up to 666 ind. m⁻³) and biomass (up to 168 mg dry weight m⁻³) of H. longirostris were considered to be comparable with those of copepods in the estuary.  相似文献   

Experimental study on countermeasure against liquefaction-induced flotation of manhole using recycled materials packed in sandbags     

Masaho Yoshida Masaru Tonoo Masakatsu Miyajima Masaru Kitaura 《东北亚地学研究》2006,9(2):150-155

The 2004 Niigata-ken Chuetsu earthquake in Japan caused serious damage to sewage facilities such as uplift of manholes and settlement of pavement above backfill soil for pipes.This paper deals with shake table tests in a 1 g gravity field on application of recycled materials for ground improvement to mitigation of liquefaction-induced flotation of manhole during earthquakes.The recycled materials used in tests were tire chips made of waste tires and crushed gravels made of waste reinforced concrete,and they were packed in sandbags.From the test results,it was confirmed that the recycled materials packed in sandbags could be treated as one of the countermeasures to restrain the flotation of manholes and settlement of ground surrounded by sandbags.  相似文献   

Distinctive copepod community of the estuarine turbidity maximum: comparative observations in three macrotidal estuaries (Chikugo, Midori, and Kuma Rivers), southwestern Japan     

Keita W. Suzuki  Kouji Nakayama  Masaru Tanaka 《Journal of Oceanography》2013,69(1):15-33

Copepods are considered to be a vital component connecting the unique macrotidal environment to the high productivity and high biodiversity of the Ariake Sea. To examine the spatiotemporal succession of copepod communities, we conducted monthly sampling (vertical hauls of a 100-μm mesh plankton net) in three neighboring macrotidal estuaries between 2005 and 2006. Irrespective of the season, three copepod communities were recognized in relation to the relatively long gradients of salinity and turbidity along the Chikugo and Midori River estuaries. The oligohaline community (salinity 1–10) was observed at higher turbidities (>100 NTU), whereas the freshwater (salinity <1) and meso/polyhaline (salinity >10) communities were associated with lower turbidities (<100 NTU). The oligohaline calanoid Sinocalanus sinensis occurred only in the Chikugo River estuary, maintaining a large biomass (dry weight >10 mg m^?3) in or close to the well-developed estuarine turbidity maximum (ETM) throughout the year. In the Midori River estuary, the oligohaline community lacked S. sinensis and showed a minimum biomass during winter (<10 mg m^?3). In both estuaries, the freshwater community always remained at a small biomass (<1 mg m^?3), whereas the meso/polyhaline community showed marked seasonal changes in biomass (0.1–657 mg m^?3). The prevalence of higher salinities allowed only the meso/polyhaline community to occur in the Kuma River estuary. In summary, S. sinensis characterized the copepod community distinctive of the well-developed ETM, potentially serving as an important link to higher trophic levels during winter when copepods are scarce in other areas.  相似文献   

Microscale simulations of Venus’ convective adjustment and mixing near the surface: Thermal and material transport processes     

Masaru Yamamoto 《Icarus》2011,211(2):993-1006

Heat and material transport processes caused by convective adjustment and mixing are important in modeling of Venus’ atmosphere. In the present study, microscale atmospheric simulations near the venusian surface were conducted using a Weather Research and Forecasting model to elucidate the thermal and material transport processes of convective adjustment and mixing. When convective adjustment occurs, the heat and passive tracer are rapidly mixed into the upper stable layer with convective penetration. The convective adjustment produces large eddy diffusions of heat and passive tracer, which may explain the large eddy diffusions estimated in the radiative-convective equilibrium model.For values of surface heat flux Q greater than a threshold (=0.064 K m s⁻¹ in the present study), the convectively mixed layer with high eddy diffusion coefficients grows with time. In contrast, the mixed layer decays with time for Q values smaller than the threshold. The thermal structure near the surface is controlled not only by extremely long-term radiative processes, but also by microscale dynamics with time scales of several hours. A mixed layer with high eddy diffusion coefficients may be maintained or grow with time if the surface heat flux is high in the volcanic hotspot and adjacent areas.  相似文献   

Are geostrophic and quasi-geostrophic approximations valid in Venus’ differential super-rotation?     

Masaru Yamamoto§  Hiroshi Tanaka 《地球物理与天体物理流体动力学》2013,107(3):185-195

Geostrophic dynamics in the horizontally differential super-rotation of Venus are examined using f_A (the Coriolis parameter defined by the angular velocity of a basic flow in an inertial frame) and Γ (the differential rotation parameter defined by the latitudinal gradient of the angular velocity) under the conditions that vertical shear of the basic field is not considered and the intrinsic phase velocity has a magnitude comparable to that of an eddy horizontal flow. The geostrophic and quasi-geostrophic approximations are valid in the regions of weakly differential and rigid-body super-rotations; however, they are invalid in the regions of strongly differential super-rotation even when the Rossby number R _O is sufficiently smaller than unity for synoptic eddies. In a general circulation model of a Venus-like atmosphere, the horizontal divergence that results from the strong differential cannot be ignored over a wide range within latitudes ±60° and below 60?km elevation because of large Γ/f_A (≥1/2).  相似文献   

Waste loading in shrimp and fish processing effluents: potential source of hazards to the coastal and nearshore environments     

Islam MS  Khan S  Tanaka M 《Marine pollution bulletin》2004,49(1-2):103-110

On average, only 30-40% of the global fishery production is consumed fresh and the rest 60-70% is processed for human consumption and other purposes. Although the proportion of the total fishery production that are processed remained relatively stable over the last decade, the total bulk of processed fishery commodity increased due to the steady increase in the total fishery production. Processing of large bulk of fish, shrimp and other aquatic organisms produces a corresponding large bulk of by-products and wastes. Although recent trend shows that much of these wastes are made into various value added products, considerable quantities are discharged as the processing effluents with large volume of waters used in processing. Reports suggest that fish and shrimp processing effluents are very high in biological oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), fat-oil-grease (FOG), pathogenic and other microflora, organic matters and nutrients, etc. Fish and shrimp processing effluents are, therefore, highly likely to produce adverse effects on the receiving coastal and marine environments. Although substantial reduction of the waste loads is possible by applying available simple techniques, this is not in practice in most part of the world due to lack of proper managerial and regulatory approach. The present paper reviews the characteristics of fish and shrimp processing effluents as a potential source of coastal and marine pollution and, using the existing data, analyzes the global production and discharge of waste loads from the processing plants and discusses available options for waste treatment and management.  相似文献   

Intergalactic ionized hydrogen in nearby groups of galaxies     

Pierre Chamaraux  Thierry Montmerle  Masaru Tadokoro 《Astrophysics and Space Science》1972,15(3):383-394

Stability of the nearest 14 groups of galaxies is investigated by means of Jacobi's criterion. In this way these groups are found strongly unstable, except perhaps two. The result is unaltered when we discuss the validity of the assumptions needed for the computations and when we take into account the inaccuracy of the data. This apparent instability is tentatively explained by presence of intergalactic ionized hydrogen in each group. Physical parameters of the gas are derived by means of the general modified form of the virial theorem and through the assumption of the equiparatition among several modes of energy.The main results are the following: the ratios of the gas mass to the sum of the masses of the member galaxies are of the order of 10, densitiesg of the gas are about 10^–29 to 10^–28 g cm^–3, and temperatures are of the order of 10⁵K. Values of each physical parameter of the gas show little change from one group to the next. As significant correlation:G g ^0.9 is obtained betweeng and the densityG of the visible matter for the various groups; it may be compatible with the assumption that the intergalactic gas is a remnant of the condensation of the galaxies. Then it is shown that, at present, the observations are not opposed to our treatment. Finally, it is noticed that detection of intergalactic gas in the groups investigated will be very difficult, except if this gas is strongly cloudy.  相似文献   

Paleoseismological evidence for non-characteristic behavior of surface rupture associated with the 2004 Mid-Niigata Prefecture earthquake, central Japan     

Tadashi Maruyama  Katsutoshi Iemura  Takashi Azuma  Toshikazu Yoshioka  Masaru Sato  Riichiro Miyawaki   《Tectonophysics》2007,429(1-2):45-60

The 2004 Mid-Niigata Prefecture earthquake sequence (mainshock magnitude, M_JMA 6.8), which occurred in an active fold-and-thrust belt in northern central Japan, generated a small thrust surface rupture (< 20 cm of vertical displacement) along a previously unmapped northern extension of the active Muikamachi–Bonchi–Seien fault zone, on the eastern margin of the epicentral region. To better understand past seismic behavior of the rupture, we conducted a paleoseismic trenching study across the 10-cm-high west-side-up surface rupture at the foot of a pre-existing 1.8-m-high east-facing scarp, which probably resulted from past earthquake(s). A well-defined west-dipping thrust fault zone accompanied by drag folding and displacing the upper Pliocene to lower Pleistocene strata and the unconformably overlying upper Pleistocene (?) to Holocene strata was exposed. The principal fault zone is connected directly to the 2004 surface rupture. From the deformational characteristics of the strata and radiocarbon dating, we inferred that two large paleoseismic events occurred during the past 9000 years prior to the 2004 event. These two pre-2004 events have a nearly identical fault slip (at minimum, 1.5 m), which is ≥ 15 times that of the 2004 event (∼ 10 cm). These paleoseismic data, coupled with the geological and geomorphological features, suggest that the 2004 event represented non-characteristic behavior of the fault, which can potentially generate a more destructive earthquake accompanied by meter-scale surface displacement. This study provides insight into the interpretation of past faulting events and increases our understanding of rupture behavior.  相似文献   

International Seminar on Natural Disaster Mitigation and Issues on Technology Transfer in South and Southeast Asia — JICA Regional Seminar     

Masaru Yoshida  Bishal N. Upreti 《Gondwana Research》2005,8(4):629-631

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AVisit to the of Core of Yangtze Craton South China     

Masaru Yoshida 《Gondwana Research》1998,1(3-4):433-434

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