Energy dissipation behaviour of shear panels made of low yield steel

This paper presents the results of a pilot test conducted for evaluating the energy dissipation behaviour of shear panels made of low yield steel whose 0.2 per cent offset yield stress is 120 MPa. A total of six full-scale shear panels were tested with the loading condition, stiffener spacing, and magnitude of axial force as test variables. The shear panels tested yielded at a shear force that is approximately 1/3 of the yield shear force of equivalent shear panels made of common mild steel. Shear panels with proper stiffener arrangement exhibited stable hysteresis, thus ensuring large energy dissipation capacity. Sufficient strain hardening was observed in the shear panels tested, with their energy dissipation capacity about 1.5 times larger than that of an equivalent linear-elastic and perfect-plastic system. Plate buckling did not lead the shear panels to immediate degradation in their energy dissipation capacity. Post-buckling resistance was found to be a subject that requires further studies for quantifying the performance of shear panels made of low yield stress steel as hysteretic dampers.     

Landscape planning methodology based on geoecological land evaluation

This paper discusses new idea and technique of landscape-planning based on a concept of geoecological land evaluation to be measured by the degree of conservation of the natual environment and landscape. It will conclude by proposing a procedure for conservation-oriented landscape planning by way of: 1. the classification and mapping of biophysical land units and ecological landuse units, which are combined with one another through the intermediate factor of actual vegetation, and 2. the evaluation of land potential quality and landuse suitability shown by a matrix of both units. Results of land evaluation by this method will offer the best orientation for decisions on landuse for each land unit in the area or for the optimal location of each category of landuse unit, both of which would solidify as an important base for determining the landscape plan.     

Preventive disaster management of extreme natural events

Several recent extreme natural events resulted in great humanitarian tragedies because of weak preventive disaster management. Here we analyze several factors (natural, economical, political, awareness, and preparedness) that brought about the humanitarian tragedies of the early 21st century. We discuss then the role of science in the preventive disaster management of extreme natural events.     

Numerical study of the Subtropical Front and the Subtropical Countercurrent

Using a multi-level numerical model, it is shown that the Subtropical Front and the Subtropical Countercurrent can be reproduced realistically in a highly idealized model, as a consequence of the coupling effect of wind driven gyre circulation and differential heating. In the model, the North Pacific Ocean is idealized as a rectangular flat-bottomed model ocean, and is driven by wind stress, which features the Westerlies and the Trades, and by heat flux through the sea surface formulated after Haney (1971).In the model ocean, a shallow front and an eastward current associated with the front are formed around the central latitude of the Subtropical Gyre, which show close similarities to the Subtropical Front and the Subtropical Countercurrent in the real ocean.Although the detailed mechanism of formation of the Subtropical Front and the Subtropical Countercurrent is not clarified in the present study, two factors are found inessential for the formation of the Subtropical Front and the Subtropical Countercurrent. First, the results of the model indicate that a small trough of wind stress curl in the lower latitudes of the Subtropical Gyre, which Yoshida and Kidokoro (1967a, b) attributed to the Subtropical Countercurrent, is not necessary for the formation of the Subtropical Front and the Subtropical Countercurrent, since they are reproduced well in the model without the trough. Second, using a model driven by meridional wind stress, it is shown that the meridional Ekman convergence, which many authors related to the Subtropical Front, is not essential for the formation of the Subtropical Front and the Subtropical Countercurrent.     

Volume Transport Variability Southeast of Okinawa Island Estimated from Satellite Altimeter Data

A nine-year-long record of the northeastward volume transport (NVT) in the region southeast of Okinawa Island from 1992 to 2001 was estimated by an empirical relation between the volume transport obtained from the ocean mooring data and the sea surface height anomaly difference across the observation line during 270 days from November 2000. The NVT had large variations ranging from −10.5 Sv (1 Sv ≡ 10⁶ m³s⁻¹) to 30.0 Sv around its mean of 4.5 Sv with a standard deviation of 5.5 Sv. This large variation was accompanied by mesoscale eddies from the east, having a pronounced period from 106 to 160 days. After removal of the eddy, NVT was found to fluctuate from 2 Sv to 12 Sv with a quasi-biennial period.     

Pre-Japan-ARGO: Experimental Observation of Upper and Middle Layers South of the Kuroshio Extension Region Using Profiling Floats

We deployed two profiling floats in the region south of the Kuroshio Extension in March 2000. Temperature and salinity profiles from a depth of 1500 × 10⁴ Pa to the surface are reported every two and four weeks, respectively. The floats performed very well for first four months after deployment. Later they failed in surfacing for a few months when the sea surface temperature in the region was high. The salinity sensors seemed to suffer from some damage during their failure-in-surfacing period. Despite this trouble, the results clearly demonstrate that the profiling float is a very useful and cost-effective tool for physical oceanographic observation in the open sea. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interdecadal temperature variations in the North Pacific Central Mode Water simulated by an OGCM

The North Pacific Central Mode Water (CMW) is a water mass that forms in the Kuroshio-Oyashio Extension (KOE) region with characteristic low potential vorticity. Recent studies have suggested that the CMW, as low potential vorticity water, plays an important role in the adjustment of the subtropical gyre and subsurface variability on decadal to interdecadal timescales. We have forced a realistic ocean general circulation model (OGCM) with observed wind stress and sea surface temperature (SST) forcing to investigate the decadal variations of the CMW. Associated with the large atmospheric changes after the mid-1970s climate regime shift, the upper thermocline experiences a cooling as negative SST anomalies in the central North Pacific are subducted and advected southward. In addition to this thermodynamic response, the CMW’s path shifts anomalously eastward in response to anomalous Ekman pumping. This eastward shift of the core of the CMW produces a lowering of the isotherms, and a consequent warming, on the path of the CMW core. This warming partially counteracts the cooling associated with subducted surface anomalies, and it may be responsible for the reduced temperature variations at the climatological position of the CMW when both anomalous wind and heat fluxes are given. Lateral induction across the sloping bottom of the winter mixed layer in the KOE is critical to the formation of the low potential vorticity CMW. Coarse resolution models, which are widely used in climate modeling, underestimate the horizontal gradient of the mixed layer depth and form only a weak CMW or none at all. We have conducted a coarse resolution experiment with the same OGCM, showing that the subsurface response is much reduced. In particular, there is no dynamic warming in the CMW and the thermodynamic response to the SST cooling dominates. The resultant total response differs substantially from that in the finer resolution run where a strong CMW forms. This sensitivity to the model resolution corroborates the important dynamical role that the CMW may play with its distinctive low potential vorticity character and calls for its improved simulation.     

A neutron activation analysis of iridium concentration in Yamato carbonaceous chondrite

Iridium concentration in extra-terrestrial bodies is an important quantity in relation to Ir-rich geological layers. Ir concentration of a Yamato carbonaceous chondrite (Y-793321) has been measured by a neutron activation method. The measurement yields a value (0.57 ± 0.06) g per gramme for the chondrite.