Effects of cyclonic mesoscale eddies on the marine ecosystem in the Kuroshio Extension region using an eddy-resolving coupled physical-biological model

Effects of mesoscale eddies on the marine ecosystem in the Kuroshio Extension (KE) region are investigated using an eddy-resolving coupled physical-biological model. The model captures the seasonal and intra-seasonal variability of chlorophyll distribution associated with the mesoscale eddies, front variability, Kuroshio meanders, and upwelling. The model also reproduces the observed interannual variability of sea surface height anomaly (SSHA) in the KE region along a zonal band of 32–34°N from 2002 to 2006. The distribution of high surface chlorophyll corresponds to low SSHA. Cyclonic eddies are found to detach from the KE jet near 150°E and 158°E and propagate westward. The westward propagating cyclonic eddies lift the nutrient-rich thermocline into the euphotic zone and maintain high levels of chlorophyll in summer. In the subsurface layer, the pattern in chlorophyll is influenced by both lateral and vertical advection. In winter, convection inside the eddy entrains high levels of nutrients into the mixed layer, increasing production, and resulting in high chlorophyll concentration throughout the surface mixed layer. There is significant interannual variability in both the cyclonic eddy activity and the surface phytoplankton bloom south of the KE jet, although whether or not there is a causal link is unclear.     

Distribution of petroleum hydrocarbons in soils and the underlying unsaturated subsurface at an abandoned petrochemical site,North China

Contamination characteristics of petroleum hydrocarbons in soils and the underlying unsaturated subsurface were analysed by investigating and sampling at different depth of five boreholes named SH1 through SH5 at a typical petrochemical site, North China. Topsoil volatile organic gas measurement revealed that SH‐3 was the center of one pollution plume. Soil samples analysis showed that aromatic hydrocarbons and chlorinated hydrocarbons were major pollutants. Their maximum concentration was found at 6.5 and 14.6 m of SH‐2, 13 m of SH‐5, and 18.5 m of SH‐3. These pollutants are mostly accumulated on the interface between two different lithological layers, especially between the sand and silt clay layers. Denitrifying and iron reducing were main biogeochemical processes in this site. Under the influence of groundwater level fluctuation, free NAPLs passed through the boundary and dissolved into the lower groundwater. Knowledge of these associations between contaminant distributions and affecting factors could have implications for soil and groundwater pollution prevention and control. Copyright © 2013 John Wiley & Sons, Ltd.     

Timescale of material circulation in subduction zone: U–Pb zircon and K–Ar phengite double‐dating of the Sanbagawa metamorphic complex in the Ikeda district,central Shikoku,southwest Japan

We have estimated the timescale of material circulation in the Sanbagawa subduction zone based on U–Pb zircon and K–Ar phengite dating in the Ikeda district, central Shikoku. The Minawa and Koboke units are major constituents of the high‐P Sanbagawa metamorphic complex in Shikoku, southwest Japan. For the Minawa unit, ages of 92–81 Ma for the trench‐fill sediments, are indicated, whereas the age of ductile deformation and metamorphism of garnet and chlorite zones are 74–72 Ma and 65 Ma, respectively. Our results and occurrence of c. 150 Ma Besshi‐type deposits formed at mid‐ocean ridge suggest that the 60‐Myr‐old Izanagi Plate was subducted beneath the Eurasian Plate at c. 90 Ma, and this observation is consistent with recent plate reconstructions. For the Koboke unit, the depositional ages of the trench‐fill sediments and the dates for the termination of ductile deformation and metamorphism are estimated at c. 76–74 and 64–62 Ma, respectively. In the Ikeda district, the depositional ages generally become younger towards lower structural levels in the Sanbagawa metamorphic complex. Our results of U–Pb and K–Ar dating show that the circulation of material from the deposition of the Minawa and Koboke units at the trench through an active high‐P metamorphic domain to the final exhumation from the domain occurred continuously throughout c. 30 Myr (from c. 90 to 60 Ma).     

A New Solar Imaging System for Observing High-Speed Eruptions: <Emphasis Type="Italic">Solar Dynamics Doppler Imager</Emphasis> (SDDI)

A new solar imaging system was installed at Hida Observatory to observe the dynamics of flares and filament eruptions. The system (Solar Dynamics Doppler Imager; SDDI) takes full-disk solar images with a field of view of \(2520~\mbox{arcsec} \times 2520~\mbox{arcsec}\) at multiple wavelengths around the \(\mathrm{H}\alpha\) line at 6562 Å. Regular operation was started in May 2016, in which images at 73 wavelength positions spanning from \(\mathrm{H}\alpha -9~\mathring{\mathrm{A}}\) to \(\mathrm{H}\alpha +9~\mathring{\mathrm{A}}\) are obtained every 15 seconds. The large dynamic range of the line-of-sight velocity measurements (\({\pm}\,400~\mbox{km}\,\mbox{s}^{-1}\)) allows us to determine the real motions of erupting filaments in 3D space. It is expected that SDDI provides unprecedented datasets to study the relation between the kinematics of filament eruptions and coronal mass ejections (CME), and to contribute to the real-time prediction of the occurrence of CMEs that cause a significant impact on the space environment of the Earth.     

Ventilation of the North Pacific subtropical pycnocline and mode water formation

The annual subduction rate of the North Pacific was calculated based on isopycnally averaged hydrographic climatology (HydroBase), high-resolution winter mixed-layer climatology (NWMLC), and various wind stress climatologies from ship reports, numerical weather prediction products, and satellite products. The calculation was performed using Lagrangian coordinates in the same manner as in previous works, except a less smoothed oceanic climatology (HydroBase and NWMLC) was used instead of a World Ocean Atlas. Differences in the wind stress climatologies have very little effect on subduction rate estimates. The subduction rate census for density classes showed peaks corresponding to subtropical mode water (STMW), central mode water (CMW), and eastern subtropical mode water (ESTMW). The deeper mixed layer and the associated sharper mixed-layer fronts in the present climatology resulted in a larger lateral induction, which boosted the subduction rate, especially for the potential density anomaly (σ_θ) range of the lighter STMW (25.0 < σ_θ < 25.2 kg m⁻³) and lighter CMW (26.0 < σ_θ < 26.2 kg m⁻³), compared to previous estimates. The renewal time of permanent pycnocline water was estimated as the volume of water divided by the subduction rate for each σ_θ class: 2–4 years for ESTMW (24.5 < σ_θ < 25.2 kg m⁻³), 2 years for the lighter STMW (25.0 < σ_θ < 25.3 kg m⁻³), 5–9 years for the denser STMW (25.3 < σ_θ < 25.6 kg m⁻³), 10–20 years for the lighter CMW (26.0 < σ_θ < 26.2 kg m⁻³), 20–30 years for the middle CMW (26.2 < σ_θ < 26.3 kg m⁻³), and 60 years or longer for the denser CMW (26.3 < σ_θ < 26.6 kg m⁻³). A comparison of the water volume and subduction rate in potential temperature–salinity (θ–S) space indicated that the upper permanent pycnocline water (25.0 < σ_θ < 26.2 kg m⁻³) was directly maintained by nondiffusive subduction of winter surface water, including STMW and lighter CMW. The lower permanent pycnocline water (26.2 < σ_θ < 26.6 kg m⁻³) may be maintained through the subduction of fresher and colder water from the subarctic–subtropical transition region and subsequent mixing with saltier and warmer water. Diagnosis of the potential vorticity (PV) of the subducted water demonstrated that the low PV of STMW was mainly due to the large subduction rate, whereas that of both ESTMW and CMW was due mainly to the small density advection rate (cross-isopycnal flow). Additionally, a relatively large subduction rate probably contributes to the low PV of part of the lighter CMW (ESTMW) formed in the region around 38°N and 170°W (28°N and 145°W), which is characterized by a relatively thick winter mixed layer and an associated mixed-layer front, causing a large lateral induction rate.     

Consistent DOF reduction of tall steel frames

This paper presents an energy‐consistent approach for reducing the number of degrees‐of‐freedom (DOFs) in tall steel frames. In the present approach, the moment resistance of beams and columns in each story is represented by the moment resistance of a rotational spring and a beam‐column element, respectively. The shear resistance provided by braces in each story is represented by the shear resistance of a shear spring. Furthermore, the resistance to the overturning moment provided by axial resistance of columns in each story is represented by the moment resistance of a rotational spring. These representations are carried out by achieving the equivalence between the strain energy stored and dissipated in the elements in the full (unreduced) DOF models and the strain energy stored and dissipated in the corresponding elements in the reduced DOF models. The accuracy of the present approach is demonstrated through numerical examples, which compare the results of nonlinear time history analyses obtained using the full and reduced DOF models. In the numerical examples, the response is estimated for 20‐story and 40‐story steel frames with and without buckling‐restraint braces subjected to a suite of near‐fault and far‐fault ground motions. The present approach is useful in estimating the response of tall steel frames having non‐regular member arrangements to a suite of intense ground motions including near‐fault ones, where it is crucial to capture the influence of higher mode effects on collapse mechanisms. Copyright © 2017 John Wiley & Sons, Ltd.     

Adjustable vertical vibration isolator with a variable ellipse curve mechanism

This paper presents a passive vertical quasi‐zero‐stiffness vibration isolator intended for relatively small objects. The present isolator has features of compactness, long stroke, and adjustability to various load capabilities. To realize these features, we use constant‐force springs, which sustain constant load regardless of their elongation, and propose a variable ellipse curve mechanism that is inspired by the principle of ellipsographs. The variable ellipse curve mechanism can convert the restoring force of the horizontally placed constant‐force springs to the vertical restoring force of the vibration isolator. At the same time as converting the direction, the vertical restoring force can be adjusted by changing the ratio of the semi‐minor axis to the semi‐major one of the ellipse. In this study, a prototype of a class of quasi‐zero‐stiffness vibration isolator with the proposed variable ellipse curve mechanism is created. Shaking table tests are performed to demonstrate the efficacy of the present mechanism, where the prototype is subjected to various sinusoidal and earthquake ground motions. It is demonstrated through the shaking table tests that the prototype can reduce the response acceleration within the same specified tolerance even when the mass of the vibration isolated object is changed. Copyright © 2017 John Wiley & Sons, Ltd.     

Dynamics of attached bacteria at the water-sediment interface in a mesotrophic swampy bog of Japan

The population dynamics of attached bacteria at the water-sediment interface were studied in a mesotrophic swampy bog, Matsumi-ike, near Tsukuba, Japan. The density of attached bacteria was higher at the sediment boundary layer than in the water column, and low inside the sediment (deeper, than 10 mm below the sediment surface) throughout the year. The density of bacteria attached on the glass slide was highest during spring when the source of organic matter in the water column was mainly withered cattail, and gradually decreased toward summer, while the phytoplankton became the dominant source of organic matter in the water column. The epibacterial populations in the water column and at the boundary showed almost the same seasonal fluctuation in attachment and detachment rates. However, bacterial growth rates did not show the same seasonal fluctuation, and annual average growth rates on the glass slides were all lower than that of bacterioplankton (free-living bacteria in water) in the water column.     

Effectiveness of superelastic bars for seismic rehabilitation of clay‐unit masonry walls

This paper presents the results on shaking table tests of half‐scale brick walls performed to investigate the effectiveness of newly developed Cu–Al–Mn superelastic alloy (SEA) bars in retrofitting of historical masonry constructions. Problems associated with conventional steel reinforcing bars lie in degradation of stiffness and strength, or pinching phenomena, under cyclic loading, and presence of large residual cracks in structures during and after intense earthquakes. This paper attempts to resolve the problems by applying newly developed Cu–Al–Mn SEA bars, characterized by large recovery strain, low material cost, and high machinability, as partial replacements for steel bars. Sets of unreinforced, steel reinforced, and SEA‐reinforced specimens are subjected to scaled earthquake excitations in out‐of‐plane direction. Whereas steel‐reinforced specimens showed large residual inclinations, SEA‐reinforced specimens resulted in stable rocking response with slight residual inclinations. Corresponding nonlinear finite element (FE) models are developed to simulate the experimental observations. The FE models are further used to examine the sensitivity of the response with respect to the variations in experimental conditions. Both the experimental and numerical results demonstrate the superiority of Cu–Al–Mn SEA bars to conventional steel reinforcing bars in avoiding pinching phenomena. Copyright © 2012 John Wiley & Sons, Ltd.     

The period–luminosity relation for type II Cepheids in globular clusters

We report the result of our near-infrared observations ( JHK _s) for type II Cepheids (including possible RV Tau stars) in galactic globular clusters. We detected variations of 46 variables in 26 clusters (10 new discoveries in seven clusters) and present their light curves. Their periods range from 1.2 d to over 80 d. They show a well-defined period–luminosity relation at each wavelength. Two type II Cepheids in NGC 6441 also obey the relation if we assume the horizontal branch stars in NGC 6441 are as bright as those in metal-poor globular clusters in spite of the high metallicity of the cluster. This result supports the high luminosity which has been suggested for the RR Lyr variables in this cluster. The period–luminosity relation can be reproduced using the pulsation equation     assuming that all the stars have the same mass. Cluster RR Lyr variables were found to lie on an extrapolation of the period–luminosity relation. These results provide important constraints on the parameters of the variable stars.
Using Two Micron All-Sky Survey (2MASS) data, we show that the type II Cepheids in the Large Magellanic Cloud (LMC) fit our period–luminosity relation within the expected scatter at the shorter periods. However, at long periods (   P > 40  d, i.e. in the RV Tau star range) the LMC field variables are brighter by about one magnitude than those of similar periods in galactic globular clusters. The long-period cluster stars also differ from both these LMC stars and galactic field RV Tau stars in a colour–colour diagram. The reasons for these differences are discussed.