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Pagurus hermit crabs have a well‐developed right cheliped (major cheliped) and in some species the major cheliped of males is longer than that of females. This paper describes sex‐related differences in major cheliped length and regeneration pattern of the major cheliped in the hermit crab Pagurus filholi. We also examined the function of the major cheliped in male–male competition. Major cheliped length of males was longer than that of females in P. filholi. Males regenerated larger chelipeds than females at the first molt after experimentally induced autotomy. Body size growth in males of the regeneration group was less than that in intact males of the control group while there was no significant difference in body size growth of females between regeneration and control groups. Major cheliped length was included in the best model to explain the outcome of male–male competition and thus sexual selection appears to be a causative factor in the sex‐related difference of the major cheliped length. Sex‐related differences in the regeneration pattern may reflect differences in evolutionary pressures on males for large major chelipeds and females for large body size.  相似文献   
3.
An estimated 3.5 ± 0.7 × 1015 Bq of 137Cs is thought to have been discharged into the ocean following the melt down at Fukushima Dai-ichi Nuclear Power Plant (F1NPP). While efforts have been made to monitor seafloor radiation levels, the sampling techniques used cannot capture the continuous distribution of radionuclides. In this work, we apply in situ measurement techniques using a towed gamma ray spectrometer to map the continuous distribution of 137Cs on the seafloor within 20 km of the F1NPP. The results reveal the existence of local 137Cs anomalies, with levels of 137Cs an order of magnitude higher than the surrounding seafloors. The sizes of the anomalies mapped in this work range from a few meters to a few hundreds of meters in length, and it is demonstrated that the distribution of these anomalies is strongly influenced by meter scale features of the terrain.  相似文献   
4.
The outflow from the Sea of Okhotsk to the North Pacific is important in characterising the surface-to-intermediate-depth water masses in the Pacific Ocean. The two basins are separated by the Kuril Islands with numerous straits, among which the Bussol and the Kruzenshterna Straits are deeper than 1000 m. The physics governing the transport between the two basins is complicated, but when the semidiurnal and diurnal tides are subtracted, the observed density and velocity structures across the Bussol Strait suggest a significant contribution from geostrophic balance. Using a two-layer model with the interface at 27.5σ θ , part of the upper layer transport that is not driven by tides is estimated using two previously unexplored data sets: outputs from the Ocean General Circulation Model for Earth Simulator (OFES), and historical hydrographic data. The Pacific water flows into the Sea of Okhotsk through the northeastern straits. The greatest inflow is through the Kruzenshtern Strait, but the OFES results show that the contributions from other shallower straits are almost half of the Kruzenshtern inflow. Similarly, the outflow from the Sea of Okhotsk is through the southwestern straits of the Kuril Islands with the largest Bussol Strait contributing 60% of the total outflow. The OFES and hydrographic estimates agree that the exchange is strongest in February to March, with an inflow of about −6 to −12 Sv (negative indicates the flow from the North Pacific, 1 Sv = 106 m3s−1), and an outflow from the Sea of Okhotsk of about +8 to +9 Sv (positive indicates the flow from the Sea of Okhotsk), which is weakest in summer (−3 to +1 Sv through the northeastern straits and +0 to +3 Sv through the southwestern straits). The estimated seasonal variation is consistent with a simple analytic model driven by the difference in sea surface height between the two basins.  相似文献   
5.
Coastal vegetation is widely recognized to reduce tsunami damage to people and buildings, and it has been studied recently because it requires relatively little capital investment compared with artificial measures, provides human-friendly beach fronts, and enhances inter-relationships with other ecological systems. However, the tsunami caused by the Great East Japan Earthquake at 14:46 JST on March 11, 2011, with a magnitude of 9.0 and epicenter 129?km east of Sendai, broke most of the sea wall (tsunami gates, large embankments) and caused catastrophic damage to coastal forests in the Tohoku and Kanto districts of Japan. A field survey was conducted to elucidate the critical breaking condition of Japanese coastal pine trees. Tree-trunk breakage was observed when the sea embankment was washed out or when there was no sea embankment and the tree was under strong inertia force or impact force by debris. Even though the trunk bending and breaking phenomena are different, statistical analysis showed that the critical diameters for trunk bending and trunk breaking were not very different. The overturning phenomenon is a little more complex than trunk breaking because the resistive force is a function of the substrate and root anchorage. An equation to determine the critical diameters for trunk bending, trunk breaking, and overturning was derived as a function of tsunami water depth, soil-root strength, and the hydrodynamic parameter (H D ) formulated by Froude number, drag coefficient, and the ratio of impact force to drag force considering the physical mechanisms to resist the tsunami. Trunk bending and breaking were closely related to tsunami water depth and the hydrodynamic parameter (H D ), but tree overturning was found to be more site specific, and the root-soil strength greatly affected the critical value. The proposed critical diameter equation and its coefficient are useful for the design of an inland forest of pine trees that can trap large trees, cars, debris, etc., to its breaking limit. The trapping function should be utilized more in the future designs of inland forests, if possible, on embankments.  相似文献   
6.
Formation and deformation processes of the late Paleogene sedimentary basins related to a strike–slip fault system in southern central Hokkaido are described by a combination of paleomagnetic study and numerical analysis. After correction of the Miocene counter‐clockwise rotation associated with back‐arc opening of the Japan Sea, paleomagnetic declination data obtained from surface outcrops in the Umaoi and Yubari areas show significant easterly deflections. Although complicated differential rotation is anticipated as a result of recent thrust movements, clockwise rotation in the study areas is closely linked with development of the Paleogene Minami‐naganuma Basin as a pull‐apart depression along the north–south fault system. Numerical modeling suggests that 30 km of strike–slip is required to restore the distribution and volume of the Minami‐naganuma Basin. The relative slip rate on the long‐standing fault system is about 10 mm/yr, which corresponds to global‐scale plate motion. It has inevitably caused regional rearrangement of the eastern Eurasian margin. A rotation field simulated by simplified dextral motion using dislocation modeling basically accords with the paleomagnetic data around the pull‐apart basin.  相似文献   
7.
A buried, old volcanic body (pre‐Komitake Volcano) was discovered during drilling into the northeastern flank of Mount Fuji. The pre‐Komitake Volcano is characterized by hornblende‐bearing andesite and dacite, in contrast to the porphyritic basaltic rocks of Komitake Volcano and to the olivine‐bearing basaltic rocks of Fuji Volcano. K‐Ar age determinations and geological analysis of drilling cores suggest that the pre‐Komitake Volcano began with effusion of basaltic lava flows around 260 ka and ended with explosive eruptions of basaltic andesite and dacite magma around 160 ka. After deposition of a thin soil layer on the pre‐Komitake volcanic rocks, successive effusions of lava flows occurred at Komitake Volcano until 100 ka. Explosive eruptions of Fuji Volcano followed shortly after the activity of Komitake. The long‐term eruption rate of about 3 km3/ka or more for Fuji Volcano is much higher than that estimated for pre‐Komitake and Komitake. The chemical variation within Fuji Volcano, represented by an increase in incompatible elements at nearly constant SiO2, differs from that within pre‐Komitake and other volcanoes in the northern Izu‐Bonin arc, where incompatible elements increase with increasing SiO2. These changes in the volcanism in Mount Fuji may have occurred due to a change in regional tectonics around 150 ka, although this remains unproven.  相似文献   
8.
On October 15, 2010, the Japanese Geotechnical Society (JGS) announced the public release of ‘Nation-wide Electronic Geotechnical Database Systems,’ which provides geotechnical information to the public on the internet. The information the system provides is a collection of ground models at 250 m by 250 m in plan built by using data from various geotechnical information databases. The paper first describes historical development of the geotechnical information databases in Japan, and introduces a 5-year project, ‘Integrated Geophysical and Geological Information Database in Japan,’ led by the National Research Institute for Earth Science and Disaster Prevention (NIED), and participated by the JGS. The paper then presents the JGS’ ‘Nation-wide Electronic Geotechnical Database Systems,’ and describes why such system was proposed and built, followed by the presentation of the examples for possible application of the system.  相似文献   
9.
An analytical method for describing horizontal matter dispersion in shear currents is presented using a tensor expression from the point of view that matter dispersion due to the shear effect should be one of the principal mixing dilution processes. Although the behavior of horizontal dispersion is considerably more complicated than common longitudinal dispersion, the present study elucidates the vertical structure of dispersion and the dispersing process from the initial to the stationary stage, besides the usual depth-averaged dispersion coefficient at the stationary stage. As one of the typical applications of horizontal dispersion, dispersion due to the pure drift current with an Ekman layer is examined theoretically using the present method. This examination reveals that the displacement of the centroid and the major axis of dispersion are twisted in the vertical direction more than the direction of the current vector forming the Ekman spiral; that the variance increases in proportion to the third power of the elapsed time; and that the dispersion coefficient at the stationary stage remains constant, independent of the depth normalized by an Ekman layer thickness. Such dependence of the dispersion coefficient in the steady current is shown to be different from that in the oscillatory current, which is inversely proportional to the depth normalized by a Stokes layer thickness. This is considered to be induced by the difference of the vertical profiles of the first order moment in both currents, that is, the shear region of the first order moment is restricted around the floor by the alternation of the current shear in the oscillatory current while it is diffused in the whole depth in the steady current.  相似文献   
10.
Residual currents induced by the tidal current flowing over a rotating ridge, which is infinitely elongated in they-direction and the width of which is so large that the nonlinear effect is weak enough, have been analysed theoretically. The currents are restrained by Stokes and Ekman layers which are given through a constant viscosity. This study shows that the direction of the cross-isobath residual current just above the sea floor varies with the value off *(=Coriolis parameter/tide frequency), that the along-isobath residual current forms a clockwise circulation around the rotating ridge and that it is stronger asf * grows larger.  相似文献   
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