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Partial discharge (PD) is a critical indicator of insulation degradation in high-voltage DC systems, necessitating accurate diagnosis to ensure long-term reliability. Conventional AC-based diagnostic methods, such as phase-resolved partial discharge analysis (PRPDA), are ineffective under DC conditions, emphasizing the need for waveform-based analysis. This study presents a novel clustering framework for DC PD pulses, leveraging multi-level wavelet decomposition and statistical feature extraction. Each signal is decomposed into multiple frequency bands, and 70 distinctive waveform features are extracted from each pulse. To mitigate feature redundancy and enhance clustering performance, principal component analysis (PCA) is employed for dimensionality reduction. Experimental data were obtained from multiple defect types and measurement distances using a 22.9 kV cross-linked polyethylene (XLPE) cable system. The proposed method significantly outperformed conventional time-frequency (T-F) mapping techniques, particularly in scenarios involving signal attenuation and mixed noise. Propagation-induced distortion was effectively addressed through multi-resolution analysis. In addition, field noise sources such as HVDC converter switching transients and fluorescent lamp emissions were included to assess robustness. The results confirmed the framework’s capability to distinguish between multiple PD types and noise sources, even in challenging environments. Furthermore, optimal mother wavelet selection and correlation-based feature analysis contributed to improved clustering resolution. This framework supports robust PD classification in practical HVDC diagnostics. The framework can contribute to the development of real-time autonomous monitoring systems for HVDC infrastructure. Future research will explore incorporating temporal deep learning architectures for automated PD-type recognition based on clustered data.

Underground and submarine power cables are subjected to mechanical stress during installation and operation, which degrades the cable insulation and reduces the reliability of power transmission. Therefore, tests that can evaluate the mechanical properties of power cable insulation are very important. The purpose of this paper is to introduce an improved sampling method for the test sample, the peeling, for mechanical testing of power cable insulation and to evaluate the reliability of the method. The influence of the sampling method of the test sample on the mechanical property values was analyzed. The tensile strength and elongation of XLPE (cross-linked polyethylene) and PP (polypropylene) insulation prepared by the slice method and the peeling method were measured, and the surface of the test samples according to the sampling methods was photographed by SEM. The results show that the mechanical property of the cable insulation increased by more than 10% when the improved peeling method was used, and the precision of the peeling method was relatively better. The SEM analysis showed that the surface of the sliced test sample was rougher than the peeled test sample and was physically damaged. Therefore, the high reliability of the peeling method for mechanical testing of cable insulators was demonstrated.

The growing demand for direct current transmission emphasizes the need for advanced insulation suitable for high-capacity, long-distance applications. Thermoplastics, especially polypropylene, offer several advantages over conventional materials like XLPE (cross-linked polyethylene) and EPR (ethylene propylene rubber), including higher thermal stability, recyclability, and reduced space charge accumulation. However, due to the inherent rigidity and limited flexibility of PP, its mechanical aging becomes a critical factor in assessing its long-term reliability as a cable insulation. In this study, mechanical aging characteristics, specifically declines in tensile strength and elongation, were selected as key indicators of insulation aging. Accelerated aging tests were conducted at 90 °C, 110 °C, and 130 °C for up to 5000 h. The experimental data were fitted to exponential models to derive aging coefficients, which formed the basis for the proposed aging model and the ACI (aging condition index). The ACI enables quantitative assessment of the current insulation condition and estimation of the remaining lifetime until a predefined threshold (e.g., ACI = 0.5) is reached. These findings contribute to the development of condition-based maintenance strategies and long-term asset management for power cables, offering practical insights for improving the reliability of future power grid systems.

In this study, we investigated the effects of water-deficit stress on the leaf anatomical traits, physiological traits, and stem starch content in Quercus acutissima Carruth and Quercus serrata Murray by subjecting their seedlings to well-watered (WW) and water-deficit stress (WS) treatments. The water stress-induced changes in trichome density, trichome-to-stomata ratio, mesophyll thickness, vein density, vein distance, vein loopiness, vessel diameter, transpiration (E), stomatal conductance (gs), water use efficiency (WUE), and starch content were analyzed between two time points. While trichome density did not vary between treatments in Q. acutissima, it dramatically increased in Q. serrata (62.63–98.96 trichomes mm−2) at the final week. The WS-treated seedlings had a thicker palisade mesophyll (162.85–169.56 µm) than the WW-treated samples (118.56–132.25 µm) in both species. The vein density and loopiness increased significantly in the WS-treated Q. serrata seedlings. Small-sized vessels (10–50 µm) were more frequent in the WS than the WW in Q. serrata. The E, gs, WUE, and starch content declined significantly in the WS-treated seedlings compared with WW-treated samples in both species. Further, principal component analysis revealed significant relationships between anatomical and physiological traits, particularly in the WS-treated seedlings of Q. serrata. The coordinated changes in leaf anatomical traits, physiological traits, and stem starch content indicate an important role in the survival of Q. acutissima and Q. serrata seedlings in water-deficit stress environments, although Q. serrata may show higher survivability under prolonged water stress than Q. acutissima.

This paper compares the cases of Seoul, Taipei and Keelung to illustrate the dynamics of the local state in leading the process of cultural preservation. We argue that political ambitions of local leaders, driven by economic and political incentives to boost local development, create policy networks centered around local bureaucracies. Various actors, such as local political elites, local bureaucracies, civic groups and developers, are involved in the process of political and economic entangling. The cultural preservation projects are thus the reflection of the political interpretation of memory, as well as the realization of local state power to implement innovative goals of urban rebranding and regeneration. The Korean and Taiwanese cases demonstrate that political functions, such as regime legitimacy and the formation of new identities, have been instrumental in the process of urban regeneration. This paper brings the \"politics\" back into local developmentalism in the democratic societies of South Korea and Taiwan. This paper also argues that central-local relationship matters as well. The local developmental states are not totally isolated from political entanglements at the central level. Policy supports from the central level are mainly out of political concerns to legitimize ongoing efforts of historical reconstruction and re-interpretation.

Wood ash generated as a by-product of biomass combustion can be a sustainable and reasonable approach to counteract acidification and correct nutrient deficiency in forest soils. We investigated the influence of wood ash (WA) and combined WA + N (nitrogen) on soil chemical properties, growth and foliar nutrients of Zelkova serrata and their potential as a soil amender across different soil types. We applied four levels of WA (0, 5, 10, and 20 Mg ha −1 ) and two levels of N fertilizer (0 and 150 kg ha −1 ) across three different soil types: landfill saline (LS) soil, forest infertile (FI) soil, and forest acidic (FA) soil. The WA generally improved soil pH, organic matter, available P, exchangeable cations (K + , Na + , Ca 2+ , and Mg 2+ ), and EC of the three soils, but its ameliorating and neutralizing effects were predominant in FA soil. N fertilizer was more effective in improving plant growth, especially for biomass production in LS and FI soils. WA application significantly increased biomass production when it was applied over 5 Mg ha −1 in FA soil, but higher dose rate of WA (i.e. 20 Mg ha −1 ) seems to pose negative effects. Foliar P, K, and Ca concentrations also tended to increase with the increasing amount of WA. Therefore, lower dosage of WA without N can be applied as a soil amender to counteract forest soil acidity and improve plant growth and foliar nutrient concentration, whereas N fertilizer without WA can be added to correct nutrient soil deficiencies in landfill and infertile soils. This study should enhance our understanding of WA as a sustainable and reasonable approach to counteract acidification and correct nutrient deficiency in forest soils.

The effectiveness of restoration programs may differ in terms of environmental and socioeconomic metrics, depending on the strategies employed and ecological settings. Thus, we synthesized different restoration strategies and discussed the environmental and socioeconomic factors influencing restoration success. In the present systematic review, we examined peer-reviewed articles published between 1990 and 2024 that discussed strategies and factors impacting land-based restoration. Only 227 of 55,229 articles from ScienceDirect, PubMed, and Google Scholar databases met the inclusion criteria. China, Brazil, and India are more active in conducting studies about land restoration compared to other regions, particularly in megadiverse countries in Asia with high degradation rates. There is a strong emphasis on practical and adaptive restoration strategies, including soil and water management (e.g., agroforestry), the use of native plant species, and weed and invasive species management. The prevalence of Acacia, Leucaena, and Eucalyptus species in restoration programs can inform decisions about effective species selection. Here, a holistic understanding of the complex ecological processes is crucial for the development of effective restoration strategies. Although policy frameworks have received less attention in restoration research, their incorporation into restoration projects can help address policy implications for land-based restoration. Overall, successful restoration necessitates a thorough understanding of the optimal strategies and environmental and socioeconomic factors impacting restoration success. Future restoration initiatives can leverage such an understanding to ensure successful implementation.

Current understanding of litterfall and fine root dynamics in temperate forests is limited, even though these are the major contributors to carbon and nutrient cycling in the ecosystems. In this study, we investigated litterfall and fine root biomass and production in five deciduous and four coniferous forests at the Gwangneung Experimental Forest in Korea. We used ingrowth cores to measure fine root production and root turnover rate. The litterfall was separated into leaves, twigs, and others, and then leaves were further separated according to species. Annual litterfall mass was not significantly different between the years, 360 to 651 g m-2 in 2011 and 300 to 656 g m-2 in 2012. Annual fine root (<5 mm) production was significantly higher in 2012 (421 to 1342 g m-2) than in 2011 (99 to 872 g m-2). Annual litterfall mass was significantly different among the stands, while fine root production did not statistically differ among the stands. The average fine root turnover rate, calculated by dividing the annual fine root production by the maximum standing fine root biomass, was 1.65 for deciduous forests and 1.97 for coniferous forests. Fine root production constituted 18-44% of NPP, where NPP was the sum of woody biomass production, litterfall production, and fine root production. Belowground production was a greater fraction of NPP in more productive forests suggesting their greater carbon allocation belowground.

Apatite is ubiquitous in igneous, metamorphic, and sedimentary rocks, although usually in trace amounts. Apatite is the primary source of P and, due to its relatively rapid dissolution rate, can be an important Ca source in noncarbonate soils. We investigated the distribution of apatite using a 1 mol L-1 HNO3 extraction of glacial till soils at 31 sites across the northeastern United States. Parent materials formed from crystalline silicate and clastic sedimentary rocks contained 0.2 to 41 mmol Ca kg-1 soil and 1 to 27 mmol P kg-1 soil; at most of these sites, the P/Ca ratio was approximately 3:5, indicating the dominance of apatite. Parent materials underlain by carbonate rocks had 3 to 16 mmol P kg-1 soil, similar to the noncarbonate groups, but had large concentrations of easily weathered Ca (56-1890 mmol kg-1 soil) due to the extraction of carbonates. The same extraction procedure applied to samples from the upper 30 cm of mineral soil at the same sites showed lower concentrations of both Ca and P than in the C horizon, except for a few sites where the upper soil layers probably developed in different parent materials than the current C horizon. We also measured neutral-salt-exchangeable Ca concentrations in the 10- to 20-cm depth increment. Exchangeable Ca concentrations in soils underlain by carbonate bedrock were an order of magnitude higher than in soils underlain by crystalline silicate and clastic sedimentary rocks. For this reason, the exchangeable Ca concentration in the upper soil was correlated to the concentration of 1 mol L-1 HNO3 extractable Ca in the underlying soil parent material. To predict concentrations of apatite in parent materials and the concentrations of exchangeable Ca in overlying horizons in greater detail would require more specific characterization of bedrock sources.