Search

A comprehensive experimental investigation of XLPE and its nanocomposite with fumed silica (SiO2) has been performed by CIGRE Working Group D1.24, in cooperative tests conducted by a number of members; covering materials characterization, real and imaginary permittivity, dc conductivity, space charge formation, dielectric breakdown strength, and partial discharge resistance. The research is unique, since all test samples were prepared by one source, and then evaluated by several expert members and their research organizations. The XLPE used for preparation of the nanocomposites was a standard commercial material used for extruded power cables. The improved XLPE samples, based on nanocomposite formulations with fumed silica, were prepared specifically for this study. Results of the different investigations are summarized in each section; conclusions are given. Overall, several important improvements over unfilled XLPE are confirmed, which augur well for future potential application in the field of extruded HV and EHV cables. Some differences/discrepancies in the data of participants are thought to be the result of instrumental and individual experimental technique differences. [ABSTRACT FROM AUTHOR]

Submerged tropical karst features were discovered in Nagura Bay on Ishigaki Island in the southern Ryukyu Islands, Japan. The coastal seafloor at depths shallower than ~ 130 m has been subjected to repeated and alternating subaerial erosion and sedimentation during periods of Quaternary sea-level lowstands. We conducted a broadband multibeam survey in the central area of Nagura Bay (1.85 × 2.7 km) and visualized the high-resolution bathymetric results over a depth range of 1.6–58.5 m. Various types of humid tropical karst landforms were found to coexist within the bay, including fluviokarst, doline karst, cockpit karst, polygonal karst, uvalas, and mega-dolines. Although these submerged karst landforms are covered by thick postglacial reef and reef sediments, their shapes and sizes are distinct from those associated with coral reef geomorphology. The submerged landscape of Nagura Bay likely formed during multiple glacial and interglacial periods. According to our bathymetric results and the aerial photographs of the coastal area, this submerged karst landscape appears to have developed throughout Nagura Bay (i.e., over an area of approximately 6 × 5 km) and represents the largest submerged karst in Japan. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract We present stratigraphic, geochemical (CNS elemental analysis), and micropaleontological (ostracode assemblages) evidence for the 2011 Tohoku-oki tsunami impact in Matsushima Bay, northeastern Japan, and examine the recovery process after the impact to the bay environment using short sediment cores from two different topographic settings at a water depth of approximately 4 m. At both sites, tsunami deposits are composed of two sedimentary layers that recorded the first tsunami run-up and backwash. At the western site near the channel that connects the bay with the Pacific Ocean, the first tsunami wave eroded the bay floor sediments and left the tsunami deposits composed of medium sand rich in shell fragments, but with sparse numbers of meiobenthic ostracodes. By contrast, at the eastern site, which is surrounded by many small islands, the first wave eroded very little of the bay floor sediments and left tsunami deposits consisting of sandy mud, rich in exotic ostracodes, such as phytal species, shallow marine sand dwelling species, and brackish water species. Overlying post-tsunami deposits are composed mainly of organic-rich mud in which organic matter was derived primarily from marine plankton. Ostracode assemblages in the tsunami deposits lack the offshore species that live in water depths >50 m and are dominated by the species from Matsushima Bay and its adjacent nearshore, upper sublittoral areas, and brackish water environments. The distance from deep-water offshore areas to the core sites is too far to transport ostracode valves by tsunami waves. Highlights • The larger first tsunami wave was the main source of the tsunami deposit. • Ostracode assemblages in the tsunami deposits lack the offshore species. • Ostracode assemblages had not yet recovered from the 2011 tsunami impact. • The post-tsunami deposit contained organic-rich muds attributed to marine planktons. [ABSTRACT FROM AUTHOR]

Abstract: The USS Emmons, a 106m US Navy Gleaves‐class destroyer minesweeper that sank in 40m of water off Okinawa Island, Japan after kamikaze attack in 1945, is used as a case study for examining the history, multivocal significance, and heritage management of a World War II naval battle site. A baseline record of the site was made using an innovative method incorporating precise control points obtained from high‐resolution multibeam echosounding bathymetry to generate 3D models using structure‐from‐motion photogrammetry. The 3D models produced can be used for sharing information about this underwater cultural heritage and for future in situ monitoring of the archaeological remains. [ABSTRACT FROM AUTHOR]

AC dissipation current waveform shows nonlinear distortion at AC high field, and this nonlinear distortion is supposed to be related to the behavior of space charge under AC field (AC space charge). We investigated the relationship between the nonlinear distortion of AC dissipation current waveform and AC space charge formation in ethylene–vinyl acetate copolymer film (EVA film). At low field, the capacitive current component was subtracted from the output signal of AC current, and then, the AC dissipation current waveform was obtained with the increase of applied AC field. As the result, the AC dissipation current waveform of EVA film showed nonlinear distortion at high field. In addition, the AC dissipation current waveform has a phase advanced from the phase of the applied AC field. The phase advance is considered to be caused by the increase of the capacitive current component due to space charge injection. We suggested that the nonlinear distortion and the phase advance of AC dissipation current waveform of EVA film were affected by the space charge injection. In addition, we developed a new evaluation method of the AC space charge injection layer based on the phase advance and the nonlinear deformation of the AC dissipation current waveform. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

SUMMARY To understand the properties of composite insulating materials, dc breakdown testing and the thermal conductivity measurement of polymethylmethacrylate (PMMA)/aluminum oxide (alumina) composite material created using the electrostatic adsorption method were performed. In the PMMA/alumina sample, which has an alumina as a main particle and a PMMA as an adsorption particle, the dc breakdown strength decreased as the alumina content was increased. It is thought that the increase of the interface between an alumina particle and a PMMA particle leads to a lower dc breakdown strength. The thermal conductivity in PMMA/alumina composite material increased with an increase in the alumina content. From these results, it is suggested that the electrostatic adsorption method can produce the various structures in the material and the insulating materials with various properties such as a higher thermal conductivity and greater tolerable breakdown strength by using a combination of the particle size of the main particle and the adsorption particles. [ABSTRACT FROM AUTHOR]

The Yarabuoki underwater site contains seven iron grapnel anchors and Early Modern Okinawan ceramic jars and is dated to the 16th-19th centuries. The site lies at a depth of 12-32 m off the western coast of Ishigaki Island in Okinawa, Japan. Based on underwater archaeological and broadband multibeam surveys, as well as historical research of the artefacts and Early Modern Ryukyuan shipping, we discuss the possible anchor and vessel types in Ryukyu and Eastern Asia in Early Modern times. We also discuss the efficacy of low-cost ROV for assisting surveys in shallow-water environments and the value of educational programmes for promoting the management and conservation of underwater cultural heritage. [ABSTRACT FROM AUTHOR]

We evaluated mixed materials made from dephosphorization slag, a byproduct of the steelmaking process, as a basal material and dredged material (DM) as a silt-clay source in constructing beds to grow eelgrass ( Zostera marina L.). Silica sand was used as a reference basal material. The slag increased in pH to about 9.0 in interstitial water, but adding DM to slag mitigated the increase. The addition of DM to slag and sand enhanced the growth of eelgrass, primarily because of the increased NH 4 -N and PO 4 -P supply. No difference was found in growth between slag- and sand-based sediments having the same proportion of DM even though slag-based sediments exhibited substantially higher pH and lower PO 4 -P concentrations than sand-based sediments. No significant differences were found between the macrobenthic community structures in the two sediment types. Dephosphorization slag mixed with DM was considered useful as a construction material for eelgrass beds. [ABSTRACT FROM AUTHOR]

Abstract: In order to understand settling process of particles in high sedimentation area, one mooring of sediment trap was deployed right above the IMAGES coring site in the northwestern North Pacific. In spite of two large maxima of settling particle fluxes in June–July 2002 and October–early January 2003, organic matter (OM) and carbonate showed higher peaks in June–July while lithogenics showed a large peak in October–early January with degraded OM (low aspartic acid/beta-alanine (Asp/Bala) and glutamic acid/gamma-aminobutyric (Glu/Gaba) ratios). Fresh OM production peaked in June–July 2002 and April–May 2003. Thus a large export production occurred in spring–early summer (April–June). Alkenone production was enhanced mainly in June–July. The mean alkenone SST of the settling particles was rather consistent with the observed annual mean SST and alkenone SST determined from the surface sediments. On the other hand, the maximum lithogenic flux along with the degradation of OM indicated that a significant amount of resuspended matter contaminated the bottom sediments. Based upon idealized model, the current and settling speeds make fractionation by size and density of resuspended particles during the settling process. Accumulation rates of lithogenics were ~5 times those in the sediment traps, which indicate large contribution of resuspended particles to settling particles especially during October–early January, when the Tsugaru current showed high current speed. These observations call our attention to carefully reconstruct paleo-environments based upon lithogenics and several other proxies such as biogenic silica, which would be biased for example in the record of IMAGES core at Site Shimokita located on the gentle continental slope. [Copyright &y& Elsevier]

This report deals with the scanning acoustic microscope for imaging cross sectional acoustic impedance of biological soft tissues. A focused acoustic beam was transmitted to the tissue object mounted on the "rear surface" of plastic substrate. A cerebellum tissue of rat and a reference material were observed at the same time under the same condition. As the incidence is not vertical, not only longitudinal wave but also transversal wave is generated in the substrate. The error in acoustic impedance assuming vertical incidence was estimated. It was proved that the error can precisely be compensated, if the beam pattern and acoustic parameters of coupling medium and substrate had been known. [ABSTRACT FROM AUTHOR]

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 nano- sized 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. [ABSTRACT FROM AUTHOR]

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 °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. [ABSTRACT FROM AUTHOR]

Polymer materials have excellent dielectric and insulation properties; however, those properties in AC high field region have not been known well. Recently we established an evaluation method of high-field AC dissipation current waveform of polymer materials 1. AC dissipation current waveforms of polyethylene and polypropylene films show nonlinear distortion in AC high-field region. This nonlinearity was thought to be related to the behavior of AC space charge formation in the sample near electrodes. The properties of space charge formed under AC high field at power frequency seem to differ from those formed under DC high field. The measurement of AC space charge distribution is not so easy due to the resolution limit of the space charge measurement. We studied the dielectric properties of biaxially oriented polypropylene (BOPP) film under AC high field up to 120 °C. It was found that tan δ, AC dissipation current (Ixr), and unbalanced component of capacitive current (ΔIxc) increased when the temperature became higher. In particular, ΔIxc increased above some threshold field and was considered to be due to the AC space charge formation. This AC space charge layer near electrode is thought to be formed due to carrier injection under AC high-field application. Usually, the carrier mobility becomes smaller on lowering the temperature. Most of the carriers injected from the electrode are trapped near the electrode in the sample film. But in the high-temperature region, the carrier mobility becomes larger and the carrier injection starts to increase from lower field. Many more carriers are injected from the electrode. It is thought that some of the injected carriers are trapped inside the sample film; the others go through the sample to the opposite side. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(2): 8–16, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10018 [ABSTRACT FROM AUTHOR]

This paper deals with the influence of interface between polyethylene and semiconducting electrode on the space charge formation and electrical breakdown. Low-density polyethylene (LDPE) films attached with different semiconducting electrodes were subjected to the DC breakdown test, and corresponding space charge distribution was measured. A heat treatment to LDPE itself did not bring about a significant change in space charge profile; however, when a semiconducting electrode was hot-pressed, the impurities would migrate into LDPE at high temperature, leading to the change in space charge profile. Furthermore, it was suggested from the comparison between the results with degassed and as-received semiconducting electrodes that some carriers relating to impurities in the electrode would move into LDPE under the voltage. In addition, it was shown that the breakdown is not determined by the field at the cathode which can supply sufficient electrons, but by the maximum field across the specimen, suggesting that an increase in conduction current due to the generation and/or injection, rather than the electronic avalanche process, leads to the breakdown. © 2001 Scripta Technica, Electr Eng Jpn, 138(3): 19–25, 2002 [ABSTRACT FROM AUTHOR]

Heavy metal pollution of marine sediments has attracted a great deal of attention because of its persistence, bioaccumulation, and toxicity. To evaluate the effects of mega-tsunami, anthropogenic activities, and redox conditions on heavy metal accumulation in coastal areas, sediments from Matsushima Bay, Miyagi Prefecture, Japan, were sampled to test variations in heavy metal spatial distribution on the bay floor during 4 years following the 2011 Tohoku Earthquake tsunami. Cluster analysis and principal component analysis were performed to assess the influencing factors and potential sources of heavy metal enrichment in the sediments of the bay. Additionally, the sediment enrichment levels of heavy metals were assessed on the basis of the enrichment factor (EF). The results of multivariate statistical analyses showed that the Ti, Fe, V, Pb, and Zn contents in Matsushima Bay sediments, which were transported mainly from Sendai Bay, depended on the mud content. The value of EF < 2 for Fe, V, Pb, and Zn indicated that these elements were not enriched. The value of EF > 7 for Cu suggested that the contamination levels in western Matsushima Bay were moderate to severe in every sampling year from 2012 to 2016 by anthropogenic activities. From the values of EF > 5 for U and Mo during 2012 and 2014, the severe enrichment of both elements in these periods may be explained by contamination with 2011 tsunami deposits; the improvement in 2015–2016 suggests that there was recovery of the tsunami-affected sediment composition to its original state. The values of EF > 3 for Mn and As indicated moderate to severe contamination with these heavy metals in the bay mouth area during 2015. This was likely explained by more oxic bottom conditions in the mouth of Matsushima Bay during that year. Unlabelled Image • Potential risks of metals in Matsushima Bay were assessed by the enrichment factor. • Ti, Fe, V, Zn and Pb contents in Matsushima Bay were not enriched. • Sporadic enrichments of Mo may be effected by the 2011 tsunami sediments. • Severe enrichment of Cu may be induced by anthropogenic activities such as shipping. • Mn and As in the sediments showed slight increases in the offshore area in 2015. [ABSTRACT FROM AUTHOR]

Abstract: We have been developing a scanning acoustic microscope (SAM) system for medicine and biology featuring quantitative measurement of ultrasonic speed and attenuation of soft tissues. In the present study, we will propose a new concept ultrasonic speed microscopy that can measure the thickness and ultrasonic speed using fast Fourier transform of a single pulsed wave instead of continuous waves used in conventional SAM systems. Six coronary arteries were frozen and sectioned approximately 10μm in thickness. They were mounted on glass slides without cover slips. The scanning time of a frame with 300×300 pixels was 121s and two-dimensional distribution of ultrasonic speed was obtained. The ultrasonic speed was 1720m/s in the thickened intima with collagen fiber, 1520m/s in lipid deposition underlying fibrous cap and 1830m/s in calcified lesion in the intima. These basic measurements will help understanding echogenecity in intravascular ultrasound (IVUS) images. Imaging of coronary artery with the ultrasonic speed microscopy provides important information for study of IVUS coronary imaging. [Copyright &y& Elsevier]