Variation on PAR to global solar radiation ratio along altitude gradient in Naeba Mountain

Summary We investigated the ratio of photosynthetically active photon flux (Q _p ) to global solar radiation (R _s ) at three sites along different altitudes in Naeba Mountain, Japan at various temporal scales based on 3 years measurement data (1999–2001). The lowest values of the ratio ever reported were found for all sites on both an hourly and a daily scale. A similar slight diurnal pattern was found for all sites based on the monthly mean hourly values of the ratio. However, different sites exhibited different seasonal courses. Statistically significant altitude dependencies were found for the hourly Q _p /R _s under both clear and cloudy weather conditions (t-test, P < 0.001). For clear weather conditions, the hourly Q _p /R _s exhibited an increasing trend with altitude at an average rate of 3.6% per km. The increasing rate was more noticeable below 900 m (8.8% per km) than above (0.7% per km). The inverse trend was found for hourly Q _p /R _s with the altitude under cloudy weather conditions. The hourly Q _p /R _s decreased from 550 m to 1500 m at a rate of 1.8% per km. Again, a major decrease occurred below 900 m, which had the rate of 4.2% per km, compared with 0.2% per km over 900 m. Although the same tendencies were noted for daily Q _p /R _s , under clear sky conditions, they were not as statistically significant as the hourly counterpart (t-test, P < 0.021). The increasing rate of Q _p /R _s at this scale under clear weather conditions was near that of the hourly rate, but below the 900 m rate was reduced to near half of the hourly rate (4.7% per km). And the rate over 900 m increased to 2.7% per km. On the other hand, statistically significant altitude effect was noted for the daily under cloudy weather conditions (t-test, P < 0.002). A rapidly decreasing rate was found for it along the altitude gradient. The reason was due to the large decreasing rate below 900 m (12.4% per km). But again similar to the hourly Q _p /R _s , a very small decreasing rate of daily Q _p /R _s was found over 900 m under cloudy weather conditions. These results suggest the necessity of considering the altitude dependency of Q _p /R _s in future studies.     

Petrography of Late Cambrian to Middle Ordovician radiolarian chert in Kazakhstan with special reference to the emergence of benthic animals in the pelagic realm

Upper Cambrian to Middle Ordovician radiolarian chert successions from Kazakhstan were studied to clarify the history of the emergence of benthic animals in ocean floor sediments. Radiolarian tests and clay were deposited for a period of 30 Myr without experiencing an influx of continent-derived coarse clastic materials. Red, grey and black cherts of the Upper Cambrian to the upper mid-Darriwilian are thinly laminated, and no trace of benthic animal activity is recognized in that time interval. Bioturbation structures and burrow traces in mid-Darriwilian stage red chert in Kazakhstan suggest that benthic animals colonized the location where radiolarian chert formed, but that there was a significant delay in colonization when compared with similar reported occurrences in Australia and Canada.     

Raman spectra of methane hydrate up to 86 GPa

High-pressure Raman studies of methane hydrate were performed using a diamond anvil cell in the pressure range of 0.1–86 GPa at room temperature. Raman spectra of the methane molecules revealed that new softened intramolecular vibration mode of ν ₁ appeared at 17 GPa and that the splitting of vibration mode of ν ₃ occurred at 15 GPa. The appearance of these two modes indicates that an intermolecular attractive interaction increases between the methane molecules and the host water molecules and between the neighboring methane molecules. These interactions might result in the exceptional stability of a high-pressure structure, a filled ice Ih structure (FIIhS) for methane hydrate, up to 40 GPa. At 40 GPa, a clear change in the slope of the Raman shift versus pressure occurred, and above 40 GPa the Raman shift of the vibration modes increased monotonously up to 86 GPa. A previous XRD study showed that the FIIhS transformed into another new high-pressure structure at 40 GPa. The change in the Raman spectra at 40 GPa may be induced by the transition of the structure.     

Internal differentiation of Kutsugata lava flow from Rishiri Volcano,Japan: Processes and timescales of segregation structures' formation

Internal differentiation processes in a solidifying lava flow were investigated for the Kutsugata lava flow from Rishiri Volcano in northern Japan. In a representative 6-m thick lava flow that was investigated in detail in this study, segregation products darker than the host lavas manifested mainly in the form of pipes (vesicle cylinders) and layers (vesicle sheets), occurring around 0.5–2.3 m and 2.0–4.0 m above the base, respectively. Both the cylinders and sheets are significantly richer in incompatible elements such as TiO₂ and K₂O than the host lavas, which suggest that these products essentially represent residual melt produced during solidification of the lava flow. Field observation and the geochemical features of the lavas suggest that the vesicle cylinders grew upward from near the base of the flow by continuous feeding of residual melt from the neighboring host lavas to the heads of the cylinders. On the other hand, the vesicle sheets were produced in situ in the solidifying lava flow as fracture veins caused by horizontal compression. The vesicle cylinders have a remarkably higher MgO content (up to 8 wt.%) than the host lava (< 6 wt.%), whereas the vesicle sheets display MgO depletion (as low as 3.5 wt.%). The relatively high MgO content of the vesicle cylinders cannot be explained solely by the mechanical mixing of olivine phenocrysts with the residual melt. It is suggested that the vesicle cylinders were produced by the extraction of olivine-bearing interstitial melt from an augite-plagioclase network in the host lava, whereas the vesicle sheets were formed by the migration of the residual melt from a crystal network consisting of plagioclase, augite, and olivine in the host lava into platy fractures. We infer that this selective crystal fractionation for forming the vesicle cylinders resulted from processes in which abundant vesicles rejected from the upward-migrating floor solidification front prevented olivine crystals from being incorporated into the crystal network in the host lava. The vesicle cylinders are considered to have formed in ∼ 1 day after the lava flow came to rest, while relatively large vesicle sheets (> 1 cm thick) appeared much later (after ∼ 9 days). The formation of these segregation products was essentially complete within 20 days after the lava emplacement.     

Bidirectional shaking table tests of a low-cost friction sliding system with flat-inclined surfaces

A novel low-cost friction sliding system for bidirectional excitation is developed to improve the seismic performance of reinforced concrete (RC) bridge piers. The sliding system is a spherical prototype developed by combining a central flat surface with an inclined spherical segment, characterized by stable oscillation and a large reduction in response accelerations on the flat surface. The inclined part provides a restoring force that limits the residual displacements of the system. Conventional steel and concrete are employed to construct a flat-inclined spherical surface atop an RC pier. The seismic forces are dissipated through the frictions generated during the sliding movements; hence, the seismic resilience of bridges can be ensured with a low-cost design solution. The proposed system is fabricated utilizing a mold created by a three-dimensional printer, which facilitates the use of conventional concrete to construct spherical shapes. The concrete surface is lubricated with a resin material to prevent abrasion from multiple input ground motions. To demonstrate the effectiveness of the system, bidirectional shaking table tests are conducted in the longitudinal and transverse directions of a scaled bridge model. The effect of the inclination angle and the flat surface size is investigated. The results demonstrate a large decrease in response acceleration when the system exhibits circular sliding displacement. Furthermore, the inclination angle that generates the smallest residual displacement is identified experimentally.     

Current Nature of the Kuroshio in the Vicinity of the Kii Peninsula

The Kuroshio flows very close to Cape Shionomisaki when it takes a straight path. The detailed observations of the Kuroshio were made both on board the R/V Seisui-maru of Mie University and on board the R/V Wakayama of the Wakayama Prefectural Fisheries Experimental Station on June 11–14, 1996. It was confirmed that the current zone of the Kuroshio touches the coast and bottom slope just off Cape Shionomiaki, and that the coastal water to the east of the cape was completely separated from that to the west. The relatively high sea level difference between Kushimoto and Uragami could be caused by this separation of the coastal waters when the Kuroshio takes a straight path. This flow is rather curious, as the geostrophic flow, which has a barotropic nature and touches the bottom, would be constrained to follow bottom contours due to the vorticity conservation law. The reason why the Kuroshio leaves the bottom slope to the east of Cape Shionomisaki is attributed to the high curvature of the bottom contours there: if the current were to follow the contours, the centrifugal term in the equation of motion would become large and comparablee to the Coriolis (or pressure gradient) term, and the geostrophic balance would be destroyed. This creates a current-shadow zone just to the east of the cape. As the reason why the current zone of the Kuroshio intrudes into the coastal region to the west of the cape, it is suggested that the Kii Bifurcation Current off the southwest coast of the Kii Peninsula, which is usually found when the Kuroshio takes the straight path, has the effect of drawing the Kuroshio water into the coastal region. The sea level difference between Kushimoto and Uragami is often used to monitor the flow pattern of the Kuroshio near the Kii Peninsula. It should be noted that Uragami is located in the current shadow zone, while Kushimoto lies in the region where the offshore Kuroshio water intrudes into the coastal region. The resulting large sea level difference indicates that the Kuroshio is flowing along the straight path.     

Millennium‐scale recurrent uplift inferred from beach deposits bordering the eastern Nankai Trough,Omaezaki area,central Japan

A flight of Holocene marine terraces on the southwestern coast of Cape Omaezaki of central Japan provides evidence of recurrent millennium‐scale uplift events. We reconstructed the uplift history of these terraces by using facies analysis of drill core and geoslicer samples, environmental analysis of trace fossils, and ¹⁴C age determinations. Coastal uplift can be identified by the displacement of beach deposits such as foreshore deposits, which represent the intertidal swash zone of a wave‐dominated sandy coast. Three levels of former beach deposits facing the Nankai Trough were identified near the coast in the Omaezaki area. The highest of these, dated at about 3020–2880 BC, records a maximum of 2.2–2.7 m of emergence. The middle beach surface, of minimum age 370–190 BC, shows 1.6–2.8 m of emergence. The lowest beach surface, which is older than 1300–1370 AD, records 0.4–1.6 m of emergence. Our analysis of vertical crustal deformation data during the Holocene in this region suggests that rapid and strong uplift was restricted to the southwestern coast of the Omaezaki area and was probably caused by high‐angle thrusting on subsidiary faults branching from the underlying plate boundary megathrust.     

Seismic response of a cut‐and‐cover tunnel isolated by polymer material

An effective method for the seismic retrofitting of the sidewalls of cut‐and‐cover tunnels has not yet been established. Thus, a new method of seismic retrofitting for cut‐and‐cover tunnels, called the ‘polymer isolation method’, is developed here. In this method, thin walls made of polymer materials, called ‘isolation walls’, are inserted between the ground and the sidewalls of a tunnel. We demonstrate the effectiveness of the proposed method in reducing the seismic response of tunnels by using some numerical simulations. It is found that the proposed method depends on the thickness of the soil cover over the tunnel and the ratio of the stiffness between the soil and the structure. Furthermore, a simple chart is proposed for convenience to represent the applicability of the polymer isolation method to the design of seismic retrofits for cut‐and‐cover tunnels. Although this particular chart has been obtained through a limited case, some other typical cases in which the chart can also be implemented for special conditions are addressed, and the applicability and the limitations of this chart are suggested for possible conditions of the ground and of tunnel structures. Copyright © 2012 John Wiley & Sons, Ltd.