Search Results (193)

Massachusetts Bay in the northeastern United States is highly vulnerable to ocean acidification (OA) due to reduced buffering capacity from significant freshwater inputs. We hypothesize that acidification varies across temporal and spatial scales, with short-term variability driven by seasonal biological respiration, precipitation–evaporation balance, and river discharge, and long-term changes linked to global warming and river flux shifts. These patterns arise from complex nonlinear interactions between physical and biogeochemical processes. To investigate OA variability, we applied the Northeast Biogeochemistry and Ecosystem Model (NeBEM), a fully coupled three-dimensional physical–biogeochemical system, to Massachusetts Bay and Boston Harbor. Numerical simulation was performed for 2016. Assimilating satellite-derived sea surface temperature and sea surface height improved NeBEM’s ability to reproduce observed seasonal and spatial variability in stratification, mixing, and circulation. The model accurately simulated seasonal changes in nutrients, chlorophyll-a, dissolved oxygen, and pH. The model results suggest that nearshore areas were consistently more susceptible to OA, especially during winter and spring. Mechanistic analysis revealed contrasting processes between shallow inner and deeper outer bay waters. In the inner bay, partial pressure of pCO₂ (pCO₂) and aragonite saturation (Ω_a) were influenced by sea temperature, dissolved inorganic carbon (DIC), and total alkalinity (TA). TA variability was driven by nitrification and denitrification, while DIC was shaped by advection and net community production (NCP). In the outer bay, pCO₂ was controlled by temperature and DIC, and Ω_a was primarily determined by DIC variability. TA changes were linked to NCP and nitrification–denitrification, with DIC also influenced by air–sea gas exchange. Full article

Lightning strikes pose a significant risk during outdoor activities. The connection between conventionally used rescue blankets in alpine emergencies and the risk of lightning injury is unclear. This experimental study investigated whether rescue blankets made of aluminum-coated polyethylene terephthalate increase the likelihood of lightning injuries. High-voltage experiments of up to 2.5 MV were conducted in a controlled laboratory setting, exposing manikins to realistic lightning discharges. In a balanced test environment, two conventionally used brands were investigated. Upward leaders frequently formed on the edges along the fold lines of the foils and were significantly longer in crumpled rescue blankets (p = 0.004). When a lightning strike occurred, the thin metallic layer evaporated at the contact point without igniting the blanket or damaging the underlying plastic film. The blankets diverted surface currents and prevented current flow to the manikins, indicating potentially protective effects. The findings of this experimental study suggest that upward leaders rise from the edge areas of rescue blankets, although there is no increased risk for a direct strike. Rescue blankets may even provide partial protection against exposure to electrical charges. Full article

Background: The Da Silva Cone procedure for Ebstein anomaly has dramatically improved tricuspid valve competence and clinical outcomes. However, preoperative left ventricular (LV) dysfunction and immediate postoperative right ventricular (RV) systolic dysfunction are frequently observed. While excellent valve outcomes are well established, recovery of biventricular function following the Cone remains less defined. This study aimed to evaluate longitudinal changes in RV and LV function postoperatively and over a minimum of six months post-Cone operation. Methods: A single center retrospective review of 134 patients who underwent Cone repair for Ebstein’s anomaly from 2016 to 2024 was performed. Echocardiograms were analyzed at three time points: preoperative (Time 1), hospital discharge (Time 2), and ≥6 months postoperative (Time 3). RV parameters included fractional area change (FAC), tricuspid annular plane systolic excursion (TAPSE), and tricuspid S′. LV parameters included left ventricular ejection fraction (LVEF), end-diastolic volume indexed to body surface area (LVEDVi), left ventricular stroke volume (LVSVi), and mitral E/E′. Subgroup analyses examined outcomes by prior Glenn, Starnes procedure, and degree of RV dilation. Paired two sample t-tests were used to compare serial measures. Results: Median age at surgery was 7.8 years (IQR: 2.3–17.7). All patients had discharge echocardiograms; 70 had follow-up studies at ≥6 months. RV function declined postoperatively with reductions in FAC (35% to 21%), TAPSE (2.0 to 0.8 cm), and S′ (13 to 5 cm/s), all p < 0.001. By Time 3, these measures improved (FAC to 29%, TAPSE to 1.3 cm, S′ to 7 cm/s) but did not fully return to baseline. LVEDVi and LVSVi increased significantly by Time 3 (LVEDVi: 47 to 54 mL/m²; LVSVi: 30 to 34 mL/m²; p < 0.001), while LVEF remained unchanged. Patients with prior Glenn or Starnes had greater Time 1 LV volumes and lower RV function, but by Time 3, most differences resolved. Moderate–severe preoperative RV dilation was associated with worse RV function at Time 2 and normalized by Time 3. Conclusions: The Da Silva Cone procedure leads to early postoperative RV dysfunction with partial recovery over the mid-term follow-up. Concurrently, LV filling and stroke volume improve, reflecting favorable interventricular interaction. These findings support echocardiographic surveillance to guide functional recovery post-Cone and inform patient counseling. Full article

The event scale method, employed for assessing changes in nitrogen (N) dynamics pre- and post-rain, provides insights into its transport to surface water systems. However, the relationships between N discharge in catchments dominated by different land uses and water quality remain unclear. This study quantified variations in key N components in ponds across forest, paddy field, and orchard catchments before and after six rainfall events. The results showed that nitrate (NO₃⁻-N) was the main N component in the ponds. Post-rainfall, N concentrations increased, with ammonium (NH₄⁺-N) and particulate nitrogen (PN) exhibiting significant elevations in agricultural ponds. Orchard catchments contributed the highest N load to the ponds, while forest catchments contributed the lowest. Following a heavy rainstorm event, total nitrogen (TN) loads in the ponds within forest, paddy field, and orchard catchments reached 6.68, 20.93, and 34.62 kg/ha, respectively. These loads were approximately three times higher than those observed after heavy rain events. The partial least squares structural equation model (PLS-SEM) identified that rainfall amount and changes in water volume were the dominant factors influencing N dynamics. Furthermore, the greater slopes of forest and orchard catchments promoted more N loss to the ponds post-rain. In paddy field catchments, larger catchment areas were associated with decreased N flux into the ponds, while larger pond surface areas minimized the variability in N concentration after rainfall events. In orchard catchment ponds, pond area was positively correlated with N concentrations and loads. This study elucidates the effects of rainfall characteristics and catchment heterogeneity on N dynamics in surface waters, offering valuable insights for developing pollution management strategies to mitigate rainfall-induced alterations. Full article

Welding and cutting behaviour may affect the mechanical properties of titanium alloy welded structures, which may have some impact on the safety assessment of the structure. This study analyses changes in residual stress in Ti80 butt-welded thick plates before and after wire-cut electric discharge machining, using numerical simulations based on thermo-elastoplastic theory and the element birth and death method, validated by X-ray non-destructive testing. The transverse residual tensile stress near the weld exhibits an asymmetric bimodal distribution, while the longitudinal stress is significantly higher than the transverse stress. Wire-cut electric discharge machining had minimal influence on the transverse residual stress distribution but led to partial relief of the longitudinal residual tensile stress. The maximum reductions in transverse and longitudinal welding residual tensile stresses are approximately 60% and 36%, respectively. The findings indicate that wire-cut electric discharge machining can alter surface residual stresses in Ti alloy butt-welded thick plates. This study also establishes a numerical simulation methodology for analysing welding residual stresses and their evolution due to wire-cut electric discharge machining. The results provide a theoretical basis for analysing the structural strength and safety of Ti-alloy-based deep-sea submersibles. Full article

This study fabricated a C/C-CuNi composite using the hydrothermal co-deposition method and investigated its friction and wear behavior as well as the underlying mechanisms after being subjected to arc discharge ablation. The results indicate that the graphitization degree of the material matrix was significantly enhanced after arc discharge ablation, accompanied by a transformation in the carbon microstructure. Carbon nanotubes and graphene structures were generated in the arc ablation zone. Under low arc discharge density, limited pits and open pores are formed on the material surface, with the generated graphene structures effectively reducing friction. Specifically, CN-5 exhibited a stable friction coefficient, a wear rate of 5.2 mg/km, and partial self-repair capability. In contrast, CN-10, under high arc discharge density, suffered from structural collapse, matrix-fiber debonding, and extensive open pores, leading to increased surface roughness. The combined effects of frictional heat and Joule heating elevated the wear surface temperature, triggering matrix oxidation and a sharp rise in wear rate to 14.7 mg/km. The wear mechanisms of C/C-CuNi composites under continuous arc conditions involve arc erosion wear, oxidative wear, abrasive wear, and adhesive wear. Full article

This study investigates the degradation mechanisms of fiber-reinforced polymer (FRP) matrices in composite insulators under partial discharge (PD) conditions. The degradation products may further cause deterioration of the electrical and chemical resistance (ECR) glass fibers. Using pyrolysis–gas chromatography-mass spectrometry (PY-GC-MS) and high-performance liquid chromatography–tandem mass spectrometry (HPLC-MS-MS), the thermal degradation gas and liquid products of the degraded FRP matrix were analyzed, revealing the presence of organic acids. These acids form when the epoxy resin’s cross-linked bonds break at high temperatures, generating anhydrides that hydrolyze into carboxylic acids in the presence of moisture. The hydrolyzation process is accelerated by hydroxyl radicals produced during PD. The resulting carboxylic acids deteriorate the glass fibers within the FRP matrix by degrading surface coupling agents and reacting with the alkali metal–silica network, leading to the substitution and precipitation of metal ions. Organic acids, particularly carboxylic acids, were found to have a more severe deteriorating effect on glass fibers compared to inorganic acids, with high temperatures exacerbating this process. These findings provide critical insights into the deterioration mechanisms of FRP under operational conditions, offering valuable guidance for optimizing manufacturing processes and enhancing the longevity of composite insulators. Full article

High-voltage electrical pulses (HVEPs), a new technology designed to enhance the permeability of coal seams, have received significant attention for their application in gas extraction from low-permeability coal seams. This study designed a high-pressure adjustable electrical pulse experimental system to investigate the effects of HVEPs on the pore structure and gas adsorption–desorption characteristics of bituminous coal samples. The results revealed that HVEPs effectively restructured pore morphology in coal samples through the opening of previously sealed and partially enclosed pores. This led to a significant increase in the average pore diameter, total pore volume, and porosity. However, the increase in total specific surface area was minimal. Moreover, the connectivity of pores was continuously enhanced. As the discharge voltage increased, the pore structure significantly improved. However, HVEP treatment slightly increased the adsorption pores (micropores and transition pores) and significantly increased the seepage pores (mesopores and macropores), which facilitated the free flow of gas within the coal samples. Additionally, HVEP treatment significantly reduced both the adsorption rate and the maximum gas adsorption capacity of the coal samples, indicating a strong inhibitory effect of HVEPs on gas adsorption. Conversely, HVEPs significantly increased the gas desorption capacity and desorption rate, suggesting that HVEPs facilitated the rapid desorption and release of gas from the coal samples. Furthermore, HVEP treatment increased the gas diffusion coefficient of the coal samples, which reduced their resistance to free diffusion after desorption and promoted gas extraction from the coal seam. Full article

Detecting partial discharges in cable joints is critical for timely defect identification and reliable transmission system operation. To improve the long-term reliability and sensitivity of the sensing system, a novel method for cable joint monitoring based on implanting optical fibers within the joint structure is proposed. The electric field distribution of the optical fiber-implanted cable joint was simulated, followed by electrical performance tests, demonstrating that optical fiber implantation had a negligible effect on the electrical properties of the cable joint. A platform utilizing Mach–Zehnder–Sagnac (MZ–Sagnac) interferometry was developed to evaluate the frequency response of the implanted optical fiber sensor, with calibration performed on a non-standard curved surface. The results show that the average sensitivity of the sensor in the 10 kHz–80 kHz range is 71.6 dB, 2.0 dB higher than that of the piezoelectric transducer, with a maximum signal-to-noise ratio of 65.2 dB. To simulate common fault conditions in the actual operation of cable joints, four types of discharge defects were introduced. Partial discharge tests conducted on an optical fiber-implanted cable joint, supplemented by measurements using a partial discharge detector, demonstrate that the optical fiber sensors can detect a minimum discharge of 16.0 pC. Full article

Methylene blue (MB), a widely used industrial dye, is a persistent pollutant with documented toxicity to aquatic organisms and potential health risks to humans, even at ultra-trace levels. Conventional monitoring techniques such as UV–Vis spectroscopy and fluorescence emission suffer from limited sensitivity, typically failing to detect MB below ~10⁻⁷ M. In this study, we introduce a surface-enhanced Raman spectroscopy (SERS) platform based on silver nanowire (AgNW) substrates that enables MB detection over an unprecedented dynamic range—from 1.5 × 10⁻⁴ M down to 1.5 × 10⁻¹⁶ M. Raman mapping confirmed the presence of individual signal hot spots at the lowest concentration, consistent with the theoretical number of analyte molecules in the probed area, thereby demonstrating near-single-molecule detection capability. The calculated enhancement factors reached up to 1.90 × 10¹², among the highest reported for SERS-based detection platforms. A semi-quantitative calibration curve was established spanning twelve orders of magnitude, and this platform was successfully applied to monitor MB degradation during two advanced oxidation processes (AOPs): TiO₂ nanotube-mediated photocatalysis under UV irradiation and atmospheric-pressure dielectric barrier discharge (DBD) plasma treatment. While UV–Vis and fluorescence techniques rapidly lost sensitivity during the degradation process, the SERS platform continued to detect the characteristic MB Raman peak at ~1626 cm⁻¹ throughout the entire treatment duration. These persistent SERS signals revealed the presence of residual MB or partially degraded aromatic intermediates that remained undetectable by conventional optical methods. The results underscore the ability of AgNW-based SERS to provide ultra-sensitive, molecular-level insights into pollutant transformation pathways, enabling time-resolved tracking of degradation kinetics and validating treatment efficiency. This work highlights the importance of integrating SERS with AOPs as a powerful complementary strategy for advanced environmental monitoring and water purification technologies. By delivering an ultra-sensitive, low-cost sensor (<USD 0.16 per test) and promoting reagent-free treatment methods, this study directly advances SDG 6 (Clean Water and Sanitation) and SDG 12 (Responsible Consumption and Production). Full article

In three-phase three-post insulators, air gaps and crack defects are important sources of partial discharge and surface flashover. Using finite element analysis software, this study created a three-dimensional simulation model to investigate the effect of these defects on electric field distribution. The effects of crack defects and air gaps of different sizes and locations on the electric field distribution were then methodically investigated. According to the results, the most significant electric field distortion is caused by air gap defects close to the phase A conductor, and the distortion is exacerbated by shorter air gap lengths. Air gap length has much less effect on the electric field in the phase B conductor. There is no obvious change in electric field strength with the radius of air gap defects (0.1–2 mm). The electric field strength is negatively correlated with crack height; greater height reduces distortion, while crack width and depth are positively correlated with the surrounding field strength; greater dimensions increase distortion. Full article

Water pollution is a major environmental issue caused by the discharge of untreated or partially treated wastewater into rivers and oceans. Self-healing materials, which can repair localized damage, have become a promising approach to counter membrane performance decline from mechanical wear. However, ensuring stability and effectiveness in self-healing membranes remains a challenge. Polyvinyl alcohol (PVA) has been widely studied for its self-healing properties, while polyacrylic acid (PAA) is often used as a crosslinking agent due to its compatibility with PVA, especially in biomedical and filtration applications. In this study, a self-healing PVA-PAA coating was applied to a PES membrane. The PVA solution (5 wt%) was prepared by dissolving beads in distilled water and stirring at 80 °C for 6 h, while the PAA solution was diluted to match this concentration. The two solutions were mixed in a 3:1 molar ratio and heated to form a homogenous mixture, then coated onto PES membranes and crosslinked at 140 °C. Scanning electron microscopy (SEM) revealed a uniform, crack-free coating on the membrane surface. The mechanical properties of the membrane show a tensile strength of 4.85 MPa and elongation of 71.9%. Filtration tests showed that the PVA-PAA-coated PES membrane achieved a water flux of 36.16 L/m²h. The performance of the PVA-PAA coated PES membrane remained stable in terms of water flux and dye rejection after it healed, and the water flux was recorded at the range of 34.24 to 36.02 L/m²h after the seal healing. This self-healing PVA-PAA coated PES membrane demonstrates the practical potential for sustainable water treatment, offering reduced maintenance and extended lifespan for filtration systems. Full article

Online monitoring of partial discharge (PD) is a complex task traditionally requiring specialized expertise. However, recent advancements in signal processing and machine learning have facilitated the development of automated tools to identify and categorize PD patterns, aiding those without extensive experience. This paper aims to identify PD types and estimate the density distribution of frequency characteristics for three PD types, internal PD, surface PD, and corona PD, using verified PD data. The proposed method employs a findpeaks algorithm based on Fast Fourier Transform (FFT) to extract frequency key features, denoted as f₁ and f₂, from the frequency spectrum. These features are used to estimate model parameters for each PD type, enabling the representation of their frequency density distributions in a 2D map (f₁, f₂) via Gaussian Mixture Models (GMMs). The optimal number of Gaussian components, determined as five using the Bayesian Information Criterion (BIC), ensures accurate modeling. For PD identification, log-likelihood and softmax functions are applied, achieving an evaluation accuracy of 96.68%. The model also demonstrates robust performance in identifying unknown PD data, with accuracy ranging from 78.10% to 95.11%. This approach enhances the distinction between PD types based on their frequency characteristics, providing a reliable tool for PD signal analysis and identification. Full article

Gas Insulated Switchgear (GIS) is a type of critical substation equipment in the power system, and its safe and stable operation is of great significance for ensuring the reliability of power system operation. To accurately identify partial discharge in GIS, this paper proposes an acoustic identification method based on improved mel frequency cepstral coefficients (MFCC) and dung beetle algorithm optimized random forest (DBO-RF) based on the ultrasonic detection method. Firstly, three types of typical GIS partial discharge defects, namely free metal particles, suspended potential, and surface discharge, were designed and constructed. Secondly, wavelet denoising was used to weaken the influence of noise on ultrasonic signals, and conventional, first-order, and second-order differential MFCC feature parameters were extracted, followed by principal component analysis for dimensionality reduction optimization. Finally, the feature parameters after dimensionality reduction optimization were input into the DBO-RF model for fault identification. The results show that this method can accurately identify partial discharge of typical GIS defects, with a recognition accuracy reaching 92.2%. The research results can provide a basis for GIS insulation fault detection and diagnosis. Full article

This paper investigates partial discharge (PD) characteristics and breakdown behavior in five electrode configurations fabricated from fiberglass circuit boards, including parallel electrode (PE), triangular electrode (TE), right-angled electrode (RE), and two floating electrode (FE) designs with 0.3 and 0.5 mm insulation gaps. The electrodes are tested according to IEC 60270:2000 using a commercial device with eight samples per configuration. Key parameters such as the PD inception voltage (PDIV) and breakdown voltage are measured. The TE configuration exhibited the highest breakdown voltage of 14.9 kV, with a PDIV of 6.13 kV and RPDIV of 8.04 kV, indicating strong dielectric properties. The RE configuration showed a PDIV of 7 kV, RPDIV of 8.5 kV, and a breakdown voltage of 13.3 kV. The FE_0.5 mm sample exhibited surface discharges, whereas the FE_0.3 mm sample experienced breakdown at 18 kV with an average breakdown voltage of 15.3 kV. The results indicate that the electrode geometry and insulation spacing strongly influence PD behavior and breakdown resilience. The phase-resolved partial discharge (PRPD) patterns at PDIV and breakdown provide further understanding of the dielectric stability. These findings offer critical insights into designing insulation systems under electrical stress. Full article