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At Sekisei Reef in southwestern Japan (24° N), coral cover dramatically decreased in the mid-1980s, probably due to a population outbreak of the coral predator Acanthaster planci. Coral communities subsequently recovered well outside the semiclosed lagoon, but recovery has been poor inside it. Hence, water-quality degradation including eutrophication has been a concern inside the lagoon. In addition, temporal variation in eutrophication parameters is common among high-latitude coral reefs, resulting in difficulties in evaluating them. Therefore, to address these issues, we monitored temperature, salinity, turbidity, chlorophyll-a, N[O.sub.x]-N (N[O.sub.3]-N + N[O.sub.2]-N), and N[H.sub.4]-N concentrations year-round across the lagoon at Sekisei Reef. Turbidity and N[O.sub.x]-N concentration increased with increasing wind velocity, suggesting that variation in turbidity and N[O.sub.x]-N concentrations was attributed to resuspension of bottom sediments, and N[O.sub.x]-N release through regeneration processes of microorganisms from the sediments and reef frameworks, respectively. In contrast, variation in chlorophyll-a and N[H.sub.4]-N concentrations appears to be mainly controlled by the seasonality of temperature and irradiance. Long retention time of seawater inside the lagoon seems to have enhanced N[H.sub.4]-N assimilation and increase of phytoplankton during summer. Inside the lagoon, turbidity, N[O.sub.x]-N, and summer chlorophyll-a concentrations were higher, and variation in temperature was larger than outside it. Although water quality appears not to be seriously degraded, multiple effects of these water-quality variables might have negatively affected recovery of coral communities inside the lagoon. Recent expansion of land use on nearby islands might have contributed to water-quality degradation inside the lagoon. doi: 1032984/64.1.113, Many coral reefs are threatened by degradation both globally and locally (e.g., Wilkinson 2004, Knowlton and Jackson 2008). At Sekisei Reef in East Asia (Figure 1), the coral cover has [...]

Epoxy resin is widely used as an insulation material in many electrical apparatuses because of its excellent electrical and manufacture characteristics. It is usually mixed with filler to improve mechanical and thermal characteristics. In order to qualitatively clarify the effect of fillers on treeing phenomena, treeing tests were performed with epoxy specimens mixed with different kinds of fillers. The property of the interface is also clarified by the treatment of silica filler using silane coupling. Although tree initiation voltage decreased with introducing silica fillers, the fillers prevented the growth of the tree. The effect of filler shape was more significant on round-shape filler than on square-shape filler. Silane coupling treatment to the fillers did not bring a significant change in tree initiation voltage, however, brought a reduction in tree propagation. The change in tree propagation rate was explained by considering the field relaxation and energy dispersion due to branching at the filler-resin interface. Tree propagation along the interface between resin and a quartz plate was observed and analyzed in order to ensure the above explanation. Index Terms--Epoxy resin, filler, treeing, silane coupling treatment, release agent, adhesion property, moisture.

To understand basic electric properties of nano-sized magnesium oxide (MgO) / low-density polyethylene (LDPE) nanocomposite under DC voltage application, the volume resistivity, the space charge distribution and the breakdown strength were investigated. By the addition of nanosized MgO filler, both the DC breakdown strength and the volume resistivity of LDPE increased. At the average DC electric field of about 85 kV/mm and more, a positive packet space charge was observed in LDPE without MgO nano-filler, whereas a little homogeneous space charge was observed in MgO/LDPE nanocomposite material at the front of electrode. From these results, it is confirmed that the addition of MgO nano-filler leads to the improvement of DC electrical insulating properties of LDPE. Index Terms--Nano-composite, polyethylene, magnesium oxide, electric breakdown, conduction current.

The effect of silica filler and moisture absorption on the structural characteristics of tree growth in epoxy resin has been investigated. The physical properties of the resin were varied by changing its filler concentration and immersed in distilled water at 50 [degrees]C. The fractal dimension of the electrical tree and its relationship with filler and moisture contents were determined. The damaged area of tree in various concentrations of filler was also estimated. Furthermore, the lacunarity of tree with identical fractal dimension was calculated as a complement of fractal dimension characterization. In addition, moisture absorption and diffusion properties of the specimens used were also examined. It is considered that the filler would create such an obstruction to the tree growth both in moisture and non-moisture conditions. Under non-moisturized condition, the more filler concentration, the more obstruction would be generated, leading to the significant suppression of tree growth. Likewise, the introduction of filler brought a rise in fractal dimension due to the increase of branches. It is concluded that the existence of filler makes the tree structure more complicated by introducing obstacles to tree propagation, leading to the high fractal dimension of the tree. In addition, it was found that the fractal dimension of the tree was related to the fractal dimension of the composite material including filler particles. On the other hand, the lacunarity of 'without-filler' specimen would be lower than that of in filled specimens. It is considered that the tree growth in filled specimen would have 'localized-branching' at the interface between filler and resin leading to the heterogeneous inherent structures of the trees. As a complement of the complexity characterization by fractal dimension, the lacunarity can be a useful tool to quantify the heterogeneous structures of trees growth in composite materials. The moisture could hardly be absorbed into the filler compared to the resin. It is shown by the higher value of diffusion coefficient of without-filler specimens than with-filler. 20 h of immersing is appropriate to achieve 40% in moisture content at the needle tip. Index Terms--Epoxy resin, filler, moisture, diffusion coefficient, electrical tree, fractal dimension, damaged area, lacunarity.

Mechanical and electrical properties of ethylene propylene rubber (EPR) pieces were studied in comparison with polyethylene (PE) in the cryogenic temperature region to examine the possibility of its use as solid electrical insulating material in superconducting cables. Mechanical properties of EPR are preferable to those of PE mainly because of its low shrinkage. The electric strength and dielectric loss tangent of EPR are comparable with those of PE at liquid helium temperature. Based on these encouraging results, an extruded EPR-insulated cable was fabricated and its 15 m length was cooled down to liquid helium temperature successfully. Partial discharge experiments at that temperature showed good electrical characteristics. This is a breakthrough in terms of the electrical insulation design of cryogenic cables.

We have developed a new method for the detection of ac dissipation in dielectric materials under high ac field. Using this technique, high-field dielectric loss properties and their relation to ac dissipation current of low-density polyethylene (LDPE) films are measured. Near room temperature, tan[delta] of a LDPE film has small electric field dependence. In this temperature region, the dissipation current shows saturation around the voltage peaks in phase even with high-field application. At higher temperatures, however, the high-field tan[delta] tends to have a strong field dependence, and the ac dissipation current deforms and is nonlinear near the voltage peaks. The nonlinearity of the ac dissipation current decreases under the decrease of tan[delta] with the voltage application period. Above results show that the large increase of tan[delta] in the high-field and high-temperature region is related to the loss due to dc-like carrier motion.