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Abstract This study focuses on the degradation behaviour of metallised film capacitors, which are the essential components for the stability of converter valves in flexible ultra‐high voltage direct current (HVDC) transmission systems. Through systematic experimentation, we investigated the failure mechanisms of MFCs under HVDC fields with superimposed harmonics, considering both equipment and material perspectives. The experiments subjected capacitors to 500 h of ageing under two conditions: a DC/AC‐superimposed field with a constant DC component of 290 kV/mm and an AC ripple rate varying from 12% to 28%, and a control group aged solely under a DC field. Our findings indicate that capacitors aged under the DC/AC‐superimposed field exhibited shorter lifespans and more significant capacitance loss than those aged under only the DC field. This difference in performance is primarily attributed to the distinct electrode loss behaviours observed under each ageing condition, which are key factors in the capacitors' capacitance decay. Moreover, the biaxially oriented polypropylene films in the DC‐aged samples showed more severe deterioration, characterised by more noticeable molecular chain scission and reduced breakdown strength, compared to those aged under the DC/AC superimposed field. This difference is partly due to the moderate temperature increase caused by harmonics, which benefits the aggregation structure, and partly to the reduced molecular structure damage from the AC field.

High-performance dielectric tunable materials with both high dielectric tunability and low dielectric loss are urgently needed for new-generation electronic tunable devices. In the present study, a new system, (Ba0.675Sr0.325)1−xLaxTi1−xMnxO3 (x = 0.25%, 0.5%, 0.75%, and 1.0%), was designed. The acceptor dopant Mn was added to lower dielectric loss, while the donor dopant La was introduced to enhance dielectric tunability. The samples were prepared using the conventional solid-state (CS) reaction method and the semi-solution (SS) method. The experimental results showed that the morphology of the ceramics was optimized by further improving the processing procedure. Dense microstructures, homogeneous grains, and uniform dopant distributions could be achieved successfully by the semi-solution method. Moreover, a significant enhancement in the tunable properties was realized owing to the improved microstructure mentioned above. The optimum tunable properties occurred in the samples prepared by the semi-solution method at x = 0.75%, with a high dielectric tunability of 85.0%, a low dielectric loss of 0.0011, and an excellent figure of merit (FOM) of 773. The tunable properties of (Ba,Sr)TiO3 (BST) ceramics were even superior to those of lead-based materials, with an FOM of approximately 700. All the results suggested that the semi-solution method rendered BST ceramics more promising for applications in tunable devices.

Abstract The unsatisfactory insulating properties of solid–gas interfaces seriously restrict the development of high‐voltage electrical equipment and threaten their power supply stability. Electron‐beam irradiation (EBI) can effectively improve the surface flashover voltage of dielectrics. However, the underlying mechanism of EBI in tailoring the surface trap and improving the flashover voltage remains unclear. In this study, the surface morphologies and chemical compositions of epoxy composites treated with EBI were investigated. In addition, the surface wetting properties, surface charge migration parameters, and surface flashover voltages were experimentally characterised. It was found that EBI aggravated the surface morphology, changed the surface chemical components, and repressed surface charge transportation. As a result, the contact angle was reduced from 103.7° to 78.43°, and the flashover voltage in SF6 was increased from 35.26 to 38.90 kV. DFT calculations showed that the newly generated C–O–H and C=O bonds on the surface molecules after EBI formed charge centres at the molecular electrostatic potential, which enhanced the trapping effect of the surface deep trap. As a result, surface charge migration was repressed, and the surface flashover voltage was improved. This study could promote the further development of EBI on materials modification.

High voltage direct-current (HVDC) cable is key equipment for utilizing offshore wind power. The high-temperature mechanical and DC electrical properties are two key figures for crosslinked polyethylene cable insulation, which are always contradictory and difficult to satisfy synchronously. To address the problem, we proposed crosslinked polyolefin (XLPO) insulation with 20.3% enhanced high-temperature mechanical stability and improved DC breakdown strength and volume resistivity. The thermally stimulated current results of XLPO showed depolarization current peaks at higher temperatures, responding to better inhibition of space charge and improved DC insulation. In addition, the XLPO exhibited thermodynamic compatibility with only one endothermic peak in differential scanning calorimetry thermograms and decreased small-angle X-ray scattering long-period. The strategy proposed in this work to enhance the comprehensive performance of cable insulation provides a promising route to next-generation HVDC cables.

Abstract Owing to advanced power electronic and electrical applications developing towards miniaturisation and integration, the thickness‐dependent DC breakdown mechanism of epoxy/multiwall‐carbon‐nanotube nanocomposites is under investigation. The results indicate that the breakdown strength of nanocomposites containing 0.05 wt% multiwall‐carbon‐nanotubes rises by ∼18%, and the breakdown strength falls exponentially with increasing thickness. To clarify the microscopic mechanism, a simulation model of DC breakdown, including carriers transport and segmental dynamics, is developed, and the accordant simulation results with experimental results indicate that the thickness‐dependent DC breakdown of epoxy/multiwall‐carbon‐nanotube nanocomposites is determined both by segment chain dynamics and charge transport. According to the breakdown model analysis, the effects of multiwall‐carbon‐nanotube on enhanced breakdown strength are caused by the increased amount of deep traps in the interfacial region, while the influence of thickness is attributed to the enlarged segment chain displacement and electric field distortion as the voltage raising time increases.

Abstract The semi‐conductive shielding layer is an important part of the high‐voltage cable, playing a role in uniform electric field and reducing the air gap at the interface. The overall performance of the cable is affected by the semi‐conductive shielding layer with different base resin composition. The matrix resins of ethylene‐vinyl acetate (EVA), ethylene‐ethyl acrylate (EEA) and ethylene‐butyl acrylate (EBA) were used to prepare the semi‐conductive shielding materials of CB/EVA, CB/EEA and CB/EBA. The influences of different matrix resins on the chemical, electrical, thermal and mechanical properties of the shielding materials were investigated. The results show that CB has the best dispersion in EBA resin and the worst dispersion in EEA resin. The temperature inflection points of CB/EVA, CB/EEA and CB/EBA shielding materials are 90°C, 100°C and 110°C, respectively, and the CB/EBA shielding material has the lowest resistivity and the weakest positive temperature coefficient effect at room temperature. The thermal conductivity of all three matrix resins is smaller than that of the shielding material, the thermal conductivity of CB/EVA and CB/EBA shielding materials show a slow increase with temperature, and the CB/EEA shielding material is the least affected by the temperature. The mechanical properties of the three matrix resins and the three shielding materials are EBA > EVA > EEA, among them the stress of CB/EBA shielding material is 31.0 MPa and the strain is 570%. This work has important reference significance for the selection of shielding layer matrix resin and material formulation in engineering applications.

Faults in three-core armored cable lines in distribution networks are frequent, and using only zero-sequence current time-frequency data to identify fault lines has its limitations. To increase the accuracy of cable fault identification, this paper utilizes the cable ground wire current and proposes a new fault line identification method that integrates a Bidirectional Gated Recurrent Unit (BiGRU), a Residual Network (ResNet), and a Multi-head Attention Mechanism (MA). Firstly, the Northern Goshawk Algorithm optimizes Variational Mode Decomposition (NGO-VMD) for denoising the ground wire current signal, reducing interference from the complex external environment. Secondly, the processed current signal is used to generate two-dimensional images using the Markov Transition Field (MTF), expanding signal features. Finally, BiGRU-ResNet-MA is utilized to deeply extract, enhance, and identify the multi-dimensional features of the ground wire current signal. The BiGRU-ResNet-MA model combines the two-dimensional image spatial characteristic extraction capability of ResNet with the temporal characteristic extraction capability of BiGRU, and further enhances feature weighting through MA, improving the fault line identification capability. The simulation findings show that this identification method can effectively address the issue of traditional methods relying too heavily on subjective selection. It accurately identifies fault lines even in the presence of strong noise, unstable faults, and asynchronous sampling, showcasing its strong robustness.

Reinjection is thought to be the most effective way to maintain reservoir pressure and production capacity for hydrothermal resources. The use of external water injection to replenish deep geothermal reservoirs is a new approach in China to addressing the problems of declining groundwater levels and energy depletion caused by the excessive and uneven exploitation of geothermal resources. However, the key challenge and focus of the feasibility assessment of this method lies in the chemical compatibility of the external water with the native geothermal reservoir water and surrounding rocks. In this paper, we discuss the geochemical response of a dolomite reservoir to lake water injection based on experiments on water–rock interaction in the Wumishan formation in the Dongli Lake area of Tianjin. The results show that after reactions with dolomite, the TDS of the reacted water decreases, indicating the occurrence of precipitation. According to the calculation results obtained using the PHQREEC program, the precipitation amount is found to be quite limited. Geochemical analysis indicates that at the initial stage of the reactions, plagioclase dissolves and releases alkaline metals like Ca-, Na-, SiO2- and Al-bearing compositions, leading to the oversaturation and precipitation of dolomite and calcite. As the reaction progresses, a portion of the dolomite dissolves, while the calcite continues to precipitate at a later stage. Illite precipitates and its effects on reservoir structure depend on its shape. Based on the experimental data, it can be concluded that the dolomite reservoir will be slightly affected by the reinjection of lake water; however, it is still a good method for the sustainable development of geothermal resources.

Abstract Objective To investigate the efficacy of treating patients with HIV-positive osteonecrosis of the femoral head using drilled decompression autologous bone marrow and allogeneic bone grafting. Methods 40 patients (44 hips) with early osteonecrosis of the femoral head treated by drilling decompression autologous bone marrow and allogeneic bone grafting since October 2015 were retrospectively analyzed, among which 20 patients (24 hips) were HIV-positive patients with early osteonecrosis of the femoral head, 16 males and 4 females, age 22–43 years, average 39.6 ± 10.18 years, and 20 patients (20 hips) in the same period HIV-negative early osteonecrosis of the femoral head patients, 13 males and 7 females, aged 48–78 years, mean 63.50 ± 7.94 years were negative controls. General information including ARCO stage, Harris score, VAS score, hematological indexes including CD4+ T lymphocyte count, and HIV viral load was recorded for all patients before surgery. All patients were operated on by drilling and decompression of the necrotic area, harvesting autologous iliac bone marrow with allogeneic bone, and bone grafting through the decompression channel. The patients were followed up regularly at 6, 12, and 24 months after surgery and annually thereafter, and the repair of the necrotic femoral head was observed by reviewing the frontal and lateral X-ray, CT or MRI of the hip joint, and the complications and functional recovery of the hip joint was counted and compared between the two groups. Results All patients were followed up, and the ARCO stages in the HIV-positive group were stage I 2 hips, stage IIA 6 hips, stage IIB 8 hips, stage IIC 6 hips, and stage III 2 hips, with a follow-up time of 12 to 60 months and a mean of 24.6 months. In the negative control group, there were 3 hips in ARCO stage I, 7 hips in stage IIA, 5 hips in stage IIB, 3 hips in stage IIC, and 2 hips in stage III, and the follow-up time ranged from 13 to 62 months, with an average of 24.8 months. The Harris score and VAS score of the hip in both groups improved significantly at 6 months postoperatively compared with those before surgery (P

Abstract Surface flashover is a devastating electronic avalanche along the gas–solid interface when a high electric field is applied, which is a potential issue that threatens the safe operations of advanced power electronic, electrical, and spacecraft applications. However, the underlying physical mechanisms for surface flashover development are still under investigation owing to the complex charge transport processes through the gas phase, solid phase, and gas–solid interface. In this study, the history of surface flashover theory in the last 50 years is introduced, and several key questions are reviewed from the perspective of the competing mechanisms of charge transport: the role of each phase in a surface flashover, the origin of surface charging, and effects of traps in solid on surface flashover. Then, some suggestions involve charge transport processes in each phase, and their correlations are put forward, and a predictable ‘charge transport competitive flashover model’ is proposed by clarifying the competing mechanisms of charge transport processes through multiple phases. This study summarises the history and hot topics of physical mechanisms of surface flashover proposed based on classic and recent progress and offers promising routes for developing a more precise surface flashover theory and improving surface flashover performances.

Hindered phenolic antioxidants are the most prevalent antioxidants used in crosslinked polyethylene (XLPE) insulating materials of high-voltage (HV) cables. Doping antioxidants is conducive to delaying the low-temperature pre-crosslinking, but decreases final crosslinking degree. In order to comprehensively reveal the effect of hindered phenolic antioxidants on the crosslinking characteristics of XLPE insulating materials, four kinds of insulating materials doped with different hindered phenolic antioxidants are studied by experiment and simulation methods. The results demonstrate that antioxidant 300 is better for delaying low-temperature pre-crosslinking of insulating materials, but negative for maintaining high crosslinking efficiency and degree. Although insulating materials with antioxidant 1010 have higher crosslinking degree, it is poor to delay the low-temperature pre-crosslinking. Notably, antioxidant 245 with phenolic hydroxyl of lower bond dissociation energies can delay the low-temperature pre-crosslinking to some extent, meanwhile, crosslinking efficiency and degree of XLPE are still higher. Notably, the crosslinking characteristics of XLPE insulating materials are closely related to molecular structure of antioxidants, including functional group and ortho-substituents. Comprehensively considering the demands of delaying low-temperature pre-crosslinking and maintaining high crosslinking degree of insulating materials, antioxidant 245 is the better choice. This study provides a theoretical guidance for the choice of hindered phenolic antioxidants used for HV cable insulating materials.

Drying involves the evaporation of moisture, accompanied by simultaneous heat transfer, mass transfer, and momentum transfer. While the diffusion law is considered an applicable model for explaining the drying phenomenon, the actual drying process cannot be accurately predicted using an analytical solution with a constant diffusion coefficient. Energy efficiency in the drying process is low due to an insufficient understanding of the mechanisms governing moisture migration from solids to air. The development of drying theory has stalled due to an unsolvable discrepancy between experimental results and analytical results. This study analyzes the effect of the binding energy of moisture in paddy rice on the diffusion coefficient. The theoretical relationship between water activity and drying rate in paddy rice was investigated, and the drying process was successfully explained by analyzing free energy transfer and transition theory. The mechanism of rice grain drying was described using a new theoretical solution for the drying process. These results provide new insights into the development of a scientific evaluation standard for assessing the efficiency of actual drying processes.

The Northern Jiangsu Basin (NJB), located at the northeast edge of the Yangtze block, is not only rich in oil and gas resources but also contains abundant geothermal resources. Nevertheless, the distribution of geothermal resources at medium depth in the NJB is still unclear due to its complex geological structure and tectonic–thermal evolution process, which restricts its exploitation and utilization. The characteristics of the geothermal field and distribution of geothermal reservoirs within the NJB are preliminarily analyzed based on available temperature measurements and geothermal exploration data. The prospective areas for the exploration of deep geothermal resources are discussed. The analysis results show that (1) Mesozoic–Paleozoic marine carbonate rocks are appropriate for use as principal geothermal reservoirs for the deep geothermal exploration and development within the NJB; (2) the geothermal field is evidently affected by the base fluctuation, and the high-temperature area is mainly concentrated at the junction of the Jianhu uplift and Dongtai depression; (3) the southeast margin of Jinhu sag, Lianbei sag, the east and west slope zone of Gaoyou sag, the low subuplifts within the depression such as Lingtangqiao–Liubao–Zheduo subuplifts, Xiaohai–Yuhua subuplifts and the west of Wubao low subuplift, have good prospects for deep geothermal exploration.

Water scarcity poses a significant challenge for people living in arid areas. Despite the effectiveness of many bioinspired surfaces in promoting vapor condensation, their water-harvesting efficiency is insufficient. This is often exacerbated by overheating, which decreases the performance in terms of the micro-droplet concentration and movement on surfaces. In this study, we used a spotted amphiphilic surface to enhance the surfaces’ water-harvesting efficiency while maintaining their heat emissivity. Through hydrophilic particle screening and hydrophobic groove modifying, the coalescence and sliding characteristics of droplets on the amphiphilic surfaces were improved. The incorporation of boron nitride (BN) nanoparticles further enhanced the surfaces’ ability to harvest energy from condensation. To evaluate the water-harvesting performance of these amphiphilic surfaces, we utilized a real-time recording water-harvesting platform to identify microscopic weight changes on the surfaces. Our findings indicated that the inclusion of glass particles in hydrophobic grooves, combined with 1.0 wt.% BN nanoparticles, enhanced the water-harvesting efficiency of the amphiphilic surfaces by more than 20%.

Deep heterogeneous carbonate reservoirs have become more and more important in the deep exploration of geothermal resources in China. The essential seismic exploration technology has many difficulties, such as serious attenuation of deep energy, low signal-to-noise ratio, difficult imaging of inner basement in tectonic uplift areas. In order to acquire high-quality deep seismic exploration data, a large number of vibroseis excitation parameters and geophone receiving parameters experiments have been received in a typical areas of the Central Hebei Plain in North China. On the basis of a large number of field experimental data, a qualitative analysis of the original single-shot records is carried out, and quantitative analysis is also carried out from the aspects of frequency band energy, inter-channel frequency, signal-to-noise ratio, etc., to study the parameter selection such as the number of vibroseis, sweep frequency, sweep length, vibration times, driving amplitude and geophone combination mode, which can affect the quality of the seismic data. In this paper, the field construction parameters for 2D seismic exploration of deep carbonate reservoirs in the North China Plain are optimized as follows: 4 sets of 28 tons vibrate 4–6 times, 75% driving amplitude, non-linear sweep (slope –3), 6–84 Hz sweep frequency, and 12 s sweep length. The quality of the single-shot records and data processing profiles are greatly improved after parameter optimization, which can be more clearly divided into the bottom interface of the Gaoyuzhuang Formation of the Jixian System and the top interface of the Archean Erathern in the Niutuozhen uplift tectonic area. The optimized seismic acquisition parameters are of certain reference and guiding significance for deep seismic exploration in sedimentary basins.

The exploitation and utilization of clean energy is a resource and environmental issue of common concern for global sustainable development. As a vital strategic and sustainable future energy, hot dry rock (HDR) has attracted more and more attention. In this paper some thoughts on the future research direction of HDR resources in China are provided based on a worldwide experience summary, hoping to provide a useful reference for the future exploration and engineering development of HDR. Since the concept of HDR was put forward in the 1970s, the number of worldwide HDR construction has been increasingly growing. Although a lot of theoretical and technical breakthroughs have been made, only a small fraction of projects still in operation due to the lack of sustained financial support, induced microearthquakes and other issues. At present, the global development of HDR is gradually entering a new stage of exploration, and the basic theories of HDR to tackle the key problems are strengthening around the world. Since 2012, the China Geological Survey has organized and implemented the nationwide terrestrial HDR resources survey, evaluation, exploration and development, and significant stage progress has been achieved. A series of fundamental maps have been compiled, such as terrestrial heat flow value, curie surface depth, distribution of acidic rock, and heat-controlling structure in China. The resource potential of terrestrial HDR in China has been preliminarily estimated and a sounding basis for the target site selection is provided. HDR exploration and evaluation have been carried out in typical areas of Qinghai, Shandong, Hebei, Shanxi and Jiangsu provinces, and a breakthrough has been achieved in the Gonghe Basin of Qinghai. The first HDR resources exploration and production demonstration project in China was carried out in 2019, which made a series of meaningful outcomes in deep HDR exploration, high-temperature hard rock drilling, large-scale reservoir stimulation, reservoir connectivity and flow circulation, organic Rankine cycle (ORC) power generation, etc. The large-scale reservoir stimulation was carried out in 2020, and the first power generation test was completed in 2021. In general, the global exploration and development of HDR has made great progress. Practice has proved that HDR resources are a promising green energy and are expected to become an inexhaustible energy support for the world in the future. However, there is still a large gap between the existing path of HDR development and utilization and the economics of its supporting technologies compared with commercial development expectations at present. Although the development of HDR resources in China has achieved a breakthrough from “0” to “1”, there is still a long way to go from the international level. In order to solve the problems of large-scale and economic development, it is still needed to promote disruptive technological innovation in high temperature hard rock drilling and completion, fine characterization of deep reservoirs, safe large-scale reservoir construction, efficient heat transfer and heat recovery and other aspects.

The determination of the low-temperature plasma propagation of SF6/N2 in gas discharge will accelerate the application of SF6/N2 in advanced electrical equipment. This study investigates the positive streamer propagation characteristics of SF6/N2 by establishing a plasma discharge model and discusses the effects of SF6 ratio on the electron density, electric field, chemical reaction rates, ion concentrations, and streamer thickness and velocity. As the streamer propagates, the shapes of the electron density and electric field become “narrower and taller.” Moreover, the ionization and attachment reaction rates increase, and the streamer thickness and velocity decrease with increasing SF6 mixing ratio and propagation time. As the SF6 ratio increases, the electric field distortion degree and particle mobility near the high-voltage electrode decrease due to the increase in the ionization and attachment rates. Consequently, the streamer velocity remains nearly unchanged, but the streamer thickness obviously decreases in the corona discharge process. In the streamer propagation process, the decrease in the streamer thickness and velocity with increasing SF6 ratio is attributed to the reduction in the electric field distortion and particle mobility, which stems from the increase in the DC breakdown voltage with the SF6 mixing ratio. The study results clarify the influence mechanisms of the SF6 mixing ratio on the particles’ spatiotemporal evolution during streamer propagation.

The ultra-fine dredged sand (DS) from the lower reaches of the Yangtze River is a large amount of solid waste with the potential to be recycled and applied as a replacement for fine aggregate. This article discussed the utilization of dredged sand by producing alkali activated materials (AAMs). The chemical and physical characteristics of the DS were analyzed. The effect of the DS on durability and mechanical characteristics of the alkali activated slag/fly materials were studied with different precursor systems. From the results, it was found that the addition of DS improved the 28 d strength and even 56 d strength. The 25% DS content increased the compressive strength of both slag rich and fly ash (FA) rich AAMs by about 5%, and the microstructure showed a denser matrix at this content. However, excessive DS can cause a decrease in flowability, early compressive strength and a decline in the compactness of the matrix. Adding an appropriate amount of DS can control the drying shrinkage. The 25% DS content has an inhibitory effect on the shrinkage development of slag rich mortar, while the similar effect on FA rich mortar appears at a content of over 50%. The adoption of DS addition to produce AAMs improves the ecological benefits of concrete engineering projects on the Yangtze River coast.

Highly stable ZnO varistor ceramics with steadily decreasing power loss have been put into applications in electrical and electronic systems for overvoltage protections, even with the absence of general understandings on their aging behaviors. In this paper, we investigated their aging nature via conducting comparative direct current (DC) aging experiments both in air and in nitrogen, during which variations of electrical properties and interface properties were measured and analyzed. Notably, continuously increasing power loss with severe electrical degradation was observed for the sample aged in nitrogen. The power loss transition was discovered to be closely related to the consumption of oxygen adsorption at the grain boundary (GB), which could, however, remain constant for the sample aged in air. The interface density of states (DOS) Ni, which is crucial for pinning the potential barrier, was proved to decrease in nitrogen, but keep stable in air. Therefore, it is concluded that the oxygen adsorption at the GB is significant for the stability of interface states, which further correlates to the long-term stability of modern stable ZnO varistor ceramics.

The past decade witnessed remarkable success in synthetic molecular nanographenes. Encouraged by the widespread application of chiral nanomaterials, the design, and construction of chiral nanographenes is a hot topic recently. As a classic nanographene unit, hexa-peri-hexabenzocoronene generally serves as the building block for nanographene synthesis. This review summarizes the representative examples of hexa-peri-hexabenzocoronene-based chiral nanographenes.

Abstract The electric field distortion due to space charge accumulations plays a significant role in the ageing, degradation and breakdown in failure of HVDC power cables. Currently, limited experimental results of the electric field dominated by space charges are insufficient to diagnose the power cables. This paper proposes an improved long short‐term memory network (LSTM) model for predicting the fluctuating maximum electric field (Emax) in cross‐linked polyethylene (XLPE) cable insulation. The various Emax data derived from the complex space charge behaviours were measured using the pulsed electroacoustic method. The model uses regularisation and dropout feedback in the LSTM unit, reducing the phenomenon of over‐fitting due to the limited data. It enhances the prediction accuracy and ability of long time prediction by improving the prediction of Emax with the non‐linear fluctuation. The predicted Emax approaches 190 kV/mm under 150 kV/mm and 60°C after 2 h. The predicted large variation in Emax under 120 kV/mm and 20°C after 4 h ranges from 130 to 160 kV/mm. It indicates high electric stress in the cable insulation during continuous operation. The proposed LSTM model is of great importance to guide the diagnosis of cable degradation in HVDC power cables.

PurposeIt is well known that the CD4/CD8 ratio is a special immune-inflammation marker. We aimed to explore the relationship between the CD4/CD8 ratio and the risk of surgical site infections (SSI) among human immunodeficiency virus (HIV)-positive adults undergoing orthopedic surgery.MethodsWe collected and analyzed data from 216 HIV-positive patients diagnosed with fractures at the department of orthopedics, Beijing Ditan Hospital between 2011 and 2019. The demographic, surgical, and hematological data for all patients were collected in this retrospective cohort study. We explored the risk factors for SSI using univariate and multivariate logistic regression analysis. Then, the clinical correlation between the CD4 count, CD4/CD8 ratio, and SSI was studied using multivariate logistic regression models after adjusting for potential confounders. Furthermore, the association between the CD4/CD8 ratio and SSI was evaluated on a continuous scale with restricted cubic spline (RCS) curves based on logistic regression models.ResultsA total of 23 (10.65%) patients developed SSI during the perioperative period. Patients with hepatopathy (OR=6.10, 95%CI=1.46-28.9), HIV viral load (OR=8.68, 95%CI=1.42-70.2; OR=19.4, 95%CI=3.09-179), operation time (OR=7.84, 95%CI=1.35-77.9), and CD4 count (OR=0.05, 95%CI=0.01-0.23) were risk factors for SSI (P-value < 0.05). Our study demonstrated that a linear relationship between CD4 count and surgical site infection risk. In other words, patients with lower CD4 counts had a higher risk of developing SSI. Furthermore, the relationship between CD4/CD8 ratio and SSI risk was non-linear, inverse ‘S’ shaped. The risk of SSI increased substantially when the ratio was below 0.913; above 0.913, the risk of SSI was almost unchanged. And there is a ‘threshold-saturation’ effect between them.ConclusionOur research shows the CD4/CD8 ratio could be a useful predictor and immune-inflammation marker of the risk of SSI in HIV-positive fracture patients. These results, from a Chinese hospital, support the beneficial role of immune reconstitution in HIV-positive patients prior to orthopedic surgery.

Crosslinking reaction behaviors can determine the network morphology and further influence macroscopic properties of polymers, while the current comprehension about crosslinking reaction behaviors of peroxide-induced low-density polyethylene (PLDPE) is quite lacking, which seriously limits its development and application. Here, for the first time, the crosslinking reaction behaviors of PLDPE are fully characterized and analyzed by combining kinetic and thermodynamic analysis. The kinetic behaviors are investigated by non-isothermal DSC and isothermal rheology methods, and thermodynamic characteristics of crosslinking reaction are analyzed by Arrhenius law and transition state theory. The results demonstrate that the crosslinking reaction of PLDPE involves complex order and autocatalysis reactions. Notably, the autocatalysis reaction is considered as the driving force of the whole crosslinking reaction. Furthermore, the autocatalysis reaction is proved to be strongly dependent on the diffusion of macromolecular chains under isothermal conditions, whereas the effect of diffusion on order reaction can be ignored. Given that, a new kinetic model incorporates the single diffusion factor to significantly describe the diffusion effect on the autocatalysis reaction during crosslinking, which grasps the complexity of crosslinking reaction mechanism. This model is able to characterize and predict the kinetic results of PLDPE crosslinking reaction very well. It provides an effective analysis methodology and an accurate kinetic model for characterizing and predicting the diffusion-limited crosslinking reaction behaviors of polymers.

Abstract Interfaces are essential components in polymer contact systems, which widely exist in electronic devices and power equipment. Interface charge originating from the mismatch of the electronic structure in interfaces is one of the key issues to modify the device performance due to its multifunctional migration and accumulation behaviors. Hence, the detection and analysis of the interface charge characteristics are of great importance to deeply understand the polymer contact system in various devices. This paper presents an overview of recent research progress in the interface charge properties at dielectric interfaces. Based on the theoretical analysis of the MWS polarization and electronic localized states, two typical approaches of discussing the interface charges from micrometer to millimeter are mainly studied. Acoustic method is prevalent in detecting the space charge in various dielectrics. However, owing to its limited resolution (several µm), it is difficult to clarify the charge distributions at the interface with a micro‐scale. Probe microscopy presents a promising technique due to its flexible surface potential detection at a submicron scale. The challenges and prospects of acoustic and probe microscopy methods are discussed in this paper. The advanced techniques of interface charges can promote the development of new energy electronic devices.

This article presents a command-filtered finite-time consensus tracking control strategy for the considered single-link flexible-joint robotic multi-agent systems. First, each agent system considered in this article is a nonlinear nonstrict-feedback system with unknown nonlinearities, so the traditional backstepping method cannot be directly applied to the design controller. However, by applying the unique structure of the Gaussian function in radial basis function neural networks, the challenges in controller design caused by the aforementioned nonstrict-feedback system have been overcome. Second, the problem of unknown nonlinearities in the system is solved by the approximation property of radial basis function neural network technology. In addition, the traditional backstepping approach often leads to an “explosion of complexity” resulting from repeated derivation of virtual control signals. Our design addresses this issue by employing command filtering technology, which simplifies the controller design process. Meanwhile, new compensation signals are designed, which successfully eliminate the error influence posed by the filters. It is seen that the control strategy presented in this article can guarantee the tracking errors converge to a small neighborhood of origin in a finite time, and all signals in the closed-loop systems remain bounded. Eventually, the simulation results show the validity of the acquired control scheme.

The weld quality of copper and aluminum thin electrode sheets in molecular diffusion bonding was non-destructively evaluated using ultrasonic resonance techniques. During the welding process, the intermediate layer material nickel diffuses into the molecules of both the copper sheet and aluminum sheet, resulting in the formation of a solid solution phase layer. This leads to a 5-layer structure in the welded body. If there are defects in this solid solution phase layer, it can cause mutations in the ultrasonic resonance signals within the weld body. In order to characterize the weld quality between copper and aluminum sheets, an acoustic attenuation coefficient was introduced. The ultrasonic resonance signals within the weld body of copper and aluminum thin electrode sheets were analyzed under four different welding states. Experimental testing revealed significant differences in acoustic attenuation coefficients among these different welding states. A smaller acoustic attenuation coefficient indicates better welding quality. Therefore, by setting a reasonable threshold for this coefficient, it is possible to effectively evaluate the welding quality of molecular diffusion bonding between copper and aluminum thin electrode sheets.

Abstract Space charge accumulation in the insulation layer of high‐voltage direct current (HVDC) cable is one of the key factors restricting the development of HVDC cable. The inner semi‐conductive layer as an important structure of cable will affect the charge accumulation characteristics in the insulation layer. This work intends to explore the method of modifying the semi‐conductive layer with graphene, to suppress charge accumulation in the insulation layer. First, the semi‐conductive layer with different contents of Graphene (G) and carbon black (CB) are prepared. Second, the morphology and surface roughness of the cross section are analysed. Further, the effects of the semi‐conductive layer on space charge accumulation of the insulation layer are studied by pulsed electro‐acoustic method and thermal stimulation depolarisation current method. The experimental results show that a moderate amount of graphene replacing CB can effectively reduce charge accumulation in the insulation layer and inhibit positive temperature coefficient (PTC) effect at the same time. The surface roughness of specimens decreases with the increase of G content from 0 to 3 phr (parts per hundreds of resin), when the CB content decreases from 25 to 10 phr, the surface roughness of specimen increases. The resistivity test shows that doping G can significantly inhibit the PTC effect of the semi‐conductive layer. The volume resistivity of the semi‐conductive layer decreases with the increase of G content and CB content. In addition, charge accumulation of the insulation layer rises and then drops under the action of the semi‐conductive layer.

Electrical breakdown is an important physical phenomenon in power equipment and electronic devices. Recently, the mechanism of AC and DC breakdown has been preliminarily revealed as electrode–dielectric interface breakdown and bulk breakdown, respectively, based on space charge dynamics through numerical calculations. However, the AC breakdown mechanism still lacks enough direct experimental support, which restricts further understanding and the design and development of electrical structures. Here, in this study, LDPE films with various thicknesses ranging from 33 μm to 230 μm were surface modified with ozone for different durations to experimentally investigate DC and AC breakdown mechanism. The results indicate that carbonyl groups (C=O) were introduced onto the film surface, forming shallow surface traps and leading to a decreased average trap depth and an increased trap density. Such a surface oxidation modulated trap distribution led to enhanced space charge injection and bulk electrical field distortion, which decreased DC breakdown strength as the oxidation duration went longer, in all film thicknesses. However, such decreases in breakdown strength occurred only in films below 55 μm under AC stresses, as the enhanced electrical field distortion at the electrode–dielectric interface was more obvious and dominating in thin films. These experimental results further confirm the proposed electrode–dielectric interface breakdown of dielectric films and provide new understandings of space charge modulated electrical breakdown, which fulfills dielectric breakdown theory and benefits the miniaturization of power equipment and electronic devices.

Abstract This study reviews the failure of high‐voltage submarine cables used in offshore power transmission and provides highlights of their failure characteristic, mechanisms, key issues and prospects. High‐voltage submarine cables are designed and applied according to the high‐voltage alternating current and high‐voltage direct current requirements. Inevitably, the fault occurs in HV submarine cables that is different from that of an underground cable. External aggression remains the primary cause of faults, such as fishing and anchors. Most faults continue to occur at a shallow depth (300 m). The optical fiber inside the submarine cables plays a substantial role in the temperature and stress‐strain monitoring and diagnosis. However, it is regarded as a weak point for electrical fault. Insulation breakdown is the leading reason for the short fault. The failure mechanism is complicated when associated with marine conditions. Some defects of insulation and extensive voids, water treeing, mechanical stress, partial discharges, overheating, and electrochemical erosion contribute to the insulation breakdown. Several key issues, including anchoring damage, treeing, defects, and thermal‐electric ageing, are proposed. Prospects and new methods related to the cable failure, especially for insulation ageing by treeing and electrothermal effects, are also discussed.

The rheological behaviors of low-density polyethylene doped with additives (PEDA) determine the dynamic extrusion molding and structure of high-voltage cable insulation. However, the coupling effect of additives and molecular chain structure of LDPE on the rheological behaviors of PEDA is still unclear. Here, for the first time, the rheological behaviors of PEDA under uncross-linked conditions are revealed by experiment and simulation analysis, as well as rheology models. The rheology experiment and molecular simulation results indicate that additives can reduce the shear viscosity of PEDA, but the effect degree of different additives on rheological behaviors is determined by both chemical composition and topological structure. Combined with experiment analysis and the Doi–Edwards model, it demonstrates that the zero-shear viscosity is only determined by LDPE molecular chain structure. Nevertheless, different molecular chain structures of LDPE have different coupling effects with additives on the shear viscosity and non-Newtonian feature. Given this, the rheological behaviors of PEDA are predominant by the molecular chain structure of LDPE and are also affected by additives. This work can provide an important theoretical basis for the optimization and regulation of rheological behaviors of PEDA materials used for high-voltage cable insulation.

Distributed fiber optic sensors (DFOS) can detect structural cracks and structural deformation with high accuracy and wide measurement range. This study monitors the segmental prestressed bent cap, assembled with a large key dry joint, based on optical fiber technology, and it allows the comparison of its damaging process with that of a monolithic cast in place counterpart. The obtained results, comprising cross-section strain distributions, longitudinal strain profiles, neutral axis location, crack pattern, and the damage process, show that the DFOS technology can be successfully used to analyze the complex working stress state of the segmental beam with shear key joints, both in the elastic range and at the ultimate load, and to successfully identify the changing characteristics of the stress state of the segmental capping beam model when elastic beam theory no longer applies. The DFOS data confirm that the shear key joint, as the weak point of the segmental cap beam, results in the high stress concentration area, and the damage rate is higher than that of the cast-in-place beam. The accurate monitoring by the DFOS allows for the realization that the damage occurs at the premature formation of a concentrated compression zone on the upper part of the shear key.

The insulation of high-frequency transformers (HFTs) has a significant impact on the safety and reliability of high voltage power electronic transformers (PETs). The transient voltages from the rapid turn-off and turn-on of the high voltage power semiconducting device increase the insulation stress and loss, resulting in thermal stress distortion. However, few studies have presented an accurate evaluation of the dielectric loss, especially under high dV/dt square waves. This paper focuses on the dielectric loss calculation in HFT insulation by analyzing the loss from a high-frequency square wave with spike voltages. A step function that is equivalent to spike voltage superposition is proposed for the quantitative calculation of the dielectric loss of epoxy resin. A cutoff frequency ( $f_{\mathrm {c}}$ ) is defined to indicate high dV/dt characteristics. A similar narrow step function is used for simulating spike voltage at the rising/falling edge. The additional dielectric loss increases with the spike voltage and the duration. The electric field and temperature distributions are simulated in a 10 kW, 10 kHz HFT by considering the calculation of dielectric loss. The spike voltages enhance the electric field and temperature in the insulation. The increase in the external temperature (close to the glass transition temperature ( $T_{\mathrm {g}}$ ) of epoxy resin) causes a significant increase in the insulation temperature. This paper is of great importance to the design and application of HFT insulation.

The end-to-end network traffic information is the basis of network management for a large-scale intelligent transportation systems-oriented backbone network. To obtain exact network traffic data, a prevalent idea is to deploy NetFlow or sFlow on all routers of the network. However, this method not only increases operational expenditures, but also affects the network load. Motivated by this issue, we propose an optimized traffic measurement method based on reinforcement learning in this paper, which can collect most of the network traffic data by activating NetFlow on a subset of interfaces of routers in a network. We use the Q-learning-based approach to deal with the problem of the interface-selection. We propose an approach to compute the reward, furthermore a modified Q-learning approach is proposed to handle the problem of interface-selection. The method is evaluated by the real data from the Abilene and GÉANT backbone networks. Simulation results show that the proposed method can improve the efficiency of traffic measurement distinctly.

Surface charge density has been demonstrated to be significantly impacted by the dielectric properties of tribomaterials. However, the ambiguous physical mechanism of dielectric manipulated charge behavior still restricts the construction of high-performance tribomaterials. Here, using the atomic force microscopy and Kelvin probe force microscopy, an in situ method was conducted to investigate the contact electrification and charge dynamics on a typical tribomaterial (i.e., BaTiO3/PVDF-TrFE nanocomposite) at nanoscale. Combined with the characterization of triboelectric device at macroscale, it is found that the number of transferred electrons increases with contact force/area and tends to reach saturation under increased friction cycles. The incorporated high permittivity BaTiO3 nanoparticles enhance the capacitance and electron trapping capability of the nanocomposites, efficiently inhibiting the lateral diffusion of electrons and improving the output performance of the triboelectric devices. Exponential decay of the surface potential is observed over monitoring time for all dielectric samples. At high BaTiO3 loadings, more electrons can drift into the bulk and combine with the induced charges on the back electrode, forming a large leakage current and accordingly accelerating the electron dissipation. Hence, the charge trapping/storing and dissipating, as well as the charge attracting properties, should be comprehensively considered in the design of high-performance tribomaterials.

AbstractThe development of sandstone-type geothermal energy is an important part of the development of geothermal resources and has great significance in promoting environmental protection and energy structural transformation. In sandstone geothermal energy development, recharging is the main method to ensure bottom hole pressure. However, the pressure and temperature changes of sandstone reservoirs under recharge conditions have not been extensively studied. It is easy to ignore the hydraulic relationship between the production and the injection wells, which leads to an increased risk of thermal breakthrough. Therefore, a three-dimensional hydrothermal coupling model is established, and simulation studies of different flow rates, well lengths, and well spacings are completed in this paper. Here, we show the numerical simulation results. The low temperature expansion zone and hydrostatic pressure near the injection well increase with increasing flow rate, and the maximum expansion of the low temperature zone is about 350 m. The low temperature expansion area near the injection well has a small relationship with the well spacing, and the increase in hydrostatic pressure is proportional to the well spacing. As the length of the well increases, the increase in hydrostatic pressure near the injection well decreases, indicating that the injected water under the long well section easily enters the reservoir. When no thermal breakthrough occurs and the hydrostatic pressure drops significantly near the production well, it is recommended that the flow rate be controlled at approximately 20–25 L/s, the well spacing should be 600–800 m, and the well length should be greater than 100 m.

During the operation of an enhanced geothermal system (EGS), the non-equilibrium temperature, pressure, and hydrochemistry caused by fluid injection intensify water–rock interactions, induce the mineral dissolution and precipitation in the reservoir near an injection well (also referred to as the near-well reservoir), and change reservoir permeability, thus affecting continuous and efficient geothermal exploitation. Based on the investigation of the M-1 injection well of the EGS in the Matouying uplift of Hebei Province, China, a THC reactive solute transport model using the TOUGHREACT program was established in this study to explore the mineral dissolution and precipitation laws of the near-well reservoir and their influencing mechanisms on the reservoir porosity and permeability in the long-term fluid injection of this well. As indicated by the results, the dissolution of primary feldspar and chlorite and the precipitation of secondary minerals (mainly dolomite and illite) occurred and water–rock interaction significantly reduced the porosity and permeability of the near-well reservoir in the long-term continuous injection process. Appropriate reduction in the injection flow rate, injection temperature, and the Mg2+ and K+ contents in the injected water can help inhibit the formation of secondary minerals and delay the plugging process of the near-well reservoir.

Nowadays, remote sensing datasets with long temporal coverage generally have a limited spatial resolution, most of the existing research uses the single image super-resolution (SISR) method to reconstruct high-resolution (HR) images. However, due to the lack of information in low-resolution (LR) images and the ill-posed nature of SISR, it is difficult to reconstruct the fine texture of HR images under large-scale magnification factors (e.g., four times). To address this problem, we propose a new reference-based super-resolution method called a Residual-Dense Hybrid Attention Network (R-DHAN), which uses the rich texture information in the reference image to make up for the deficiency of the original LR image. The proposed SR model employs Super-Resolution by Neural Texture Transfer (SRNTT) as a backbone. Based on this structure, we propose a dense hybrid attention block (DHAB) as a building block of R-DHAN. The DHAB fuses the input and its internal features of current block. While making full use of the feature information, it uses the interdependence between different channels and different spatial dimensions to model and obtains a strong representation ability. In addition, a hybrid channel-spatial attention mechanism is introduced to focus on important and useful regions to better reconstruct the final image. Experiments show that compared with SRNTT and some classical SR techniques, the proposed R-DHAN method performs well in quantitative evaluation and visual quality.

Gradually increasing power transmission voltage requires an improved high-voltage capability of polymeric insulating materials. Surface modification emerges as an easily accessible approach in enhancing breakdown and flashover performances due to the widely acknowledged modification of space-charge behaviors. However, as oxidation and fluorination essentially react within a limited depth of 2 μm underneath polymer surfaces, the nature of such bulk space-charge modulation remains a controversial issue, and further investigation is needed to realize enhancement of insulating performance. In this work, the surface oxidation-dependent space-charge accumulation in LDPE film was found to be dominated by an electrode/polymer interfacial barrier, but not by the generation of bulk charge traps. Through quantitative investigation of space-charge distributions along with induced electric field distortion, the functions of surface oxidation on the interfacial barrier of a typical dielectric polymer, LDPE, is discussed and linked to space-charge behaviors. As the mechanism of surface modification on space-charge behaviors is herein proposed, space-charge accumulation can be effectively modified by selecting an appropriate surface modification method, which consequentially benefits breakdown and flashover performances of polymeric insulating films for high-voltage applications.

Field-effect mobility (μFET) of organic semiconductor films plays a key role in the performance of field-effect transistors (FETs). Numerical extraction of μFET from organic FET characteristics is not only time-consuming due to patterning of source/drain electrodes, but also frequently unreliable because of the contact resistances (RC) between source/drain electrodes and semiconductors. Here, we propose an approach to rapidly evaluate μ by a point-contact four-probes method (μPFP) for organic semiconductor films. Four tip-like probes quickly contact the semiconductor film surface directly, without deposition of the conventional source/drain electrodes, to simultaneously inject current and measure the electric potential. The charge density and thus conductance of the film is manipulated upon scanning gate voltage, from which the extraction of μPFP, in good agreement with μFET, could be realized in a few seconds. This method, with easily accessible setup and numerical model, substantially accelerates the evaluation of μPFP, and thus could help screen materials and optimize film morphology for organic FETs applications.

Transformer insulation paper is a key indicator for transformer remaining operational life. Paper decomposition is evaluated using the degree of polymerization (DP) which calls for samples of insulation paper from operating transformers. Since collecting such paper samples is extremely difficult, other indicators have been used to indirectly reveal the DP value of insulation paper. This includes dissolved gases in transformer oil such as carbon oxides and hydrocarbon gases, furan compounds, methanol, ethanol, and moisture along with some oil characteristics such as interfacial tension. However, for the same oil sample, these individual parameters lead to different DP values. This is attributed to the lack of accuracy of the established mathematical and artificial intelligence models correlating DP with each of the above mentioned individual parameters. This paper presents a self-learning method to estimate the DP value of transformer insulation paper based on multiple transformer oil aging parameters. The proposed method comprises data processing, fuzzy c-means and linear regression. Results reveal that estimating the DP value based on multiple aging parameters is more accurate than estimating it using one single parameter as per the current practice. The proposed method not only helps to understand the correlation between multiple oil aging parameters and the DP value of paper insulation, but also promotes the establishment of more accurate life assessment models for power transformers based on these oil aging parameters.

Dissolved gas in oil analysis (DGA) is one of the most reliable condition monitoring techniques, which is currently used by the industry to detect incipient faults within the power transformers. While the technique is well matured since the development of various offline and online measurement techniques along with various interpretation methods, no much attention was given so far to the oil sampling time and its correlation with the transformer loading. A power transformer loading is subject to continuous daily and seasonal variations, which is expected to increase with the increased penetration level of renewable energy sources of intermittent characteristics, such as photovoltaic (PV) and wind energy into the current electricity grids. Generating unit transformers also undergoes similar loading variations to follow the demand, particularly in the new electricity market. As such, the insulation system within the power transformers is expected to exhibit operating temperature variations due to the continuous ramping up and down of the generation and load. If the oil is sampled for the DGA measurement during such ramping cycles, results will not be accurate, and a fault may be reported due to a gas evolution resulting from such temporarily loading variation. This paper is aimed at correlating the generation and load ramping with the DGA measurements through extensive experimental analyses. The results reveal a strong correlation between the sampling time and the generation/load ramping. The experimental results show the effect of load variations on the gas generation and demonstrate the vulnerabilities of misinterpretation of transformer faults resulting from temporary gas evolution. To achieve accurate DGA, transformer loading profile during oil sampling for the DGA measurement should be available. Based on the initial investigation in this paper, the more accurate DGA results can be achieved after a ramping down cycle of the load. This sampling time could be defined as an optimum oil sampling time for transformer DGA.

The effects of surface traps on surface flashover remain controversial. To clarify the relation between surface flashover and surface trap level, in this work, the surface trap level of epoxy composites was modified by nanoparticles incorporation, electron beam irradiation, and ozone treatment. Surface trap characteristics were analyzed by surface potential decay. Surface flashover voltages were measured in a vacuum for dc voltage and in SF6 for ac voltage. The “U-shaped” curve is founded to describe the relation between surface flashover voltage and surface deep trap level, surface flashover voltage first decreases and then increases with surface deep trap level. Enhancement of surface flashover voltage is attributed to reduced surface charge density, which was calculated by a double-trap flashover model. The simulation results indicate that the surface charge density on left side of “U-shaped” curve is controlled by surface shallow traps, whereas that on the right side is determined by surface deep traps. The effects of surface shallow and deep traps on surface charge accumulation and dissipation are used to demonstrate the reduced surface charges and improved surface flashover voltage for the “U-shaped” curve. The proposed “U-shaped” curve offers a promising way to improve surface flashover performance for high-voltage applications by tailoring surface trap characteristics with surface modifications.

Abstract As a solid pollutant, the recycled aggregate can be reused to replace the natural aggregate to cast pervious concrete, promoting resource recycling and reducing environmental pollution. Pervious concrete is usually applied to transportation engineering as pavements and decks, which are often subjected to fatigue loads in service. Therefore, it is essential to investigate the fatigue mechanical properties of pervious concrete. In this study, four-point cyclic bending loading test of natural aggregate pervious concrete and recycled aggregate pervious concrete were conducted under four different stress levels. By analyzing the experimental results, the mechanical performances, including hysteresis curve characteristics, damping ratio, dynamic elastic modulus and cyclic strain, of two kinds of pervious concrete under cyclic loading were revealed. Based on the improved EPF model, the relationship between fracture parameters, plastic strain and unloading strain were obtained. Besides, the relationship between the loading cycles and the ratio of plastic strain to unloading strain was received according to fatigue testing data under different stress levels. Further, the simplified fatigue model of pervious concrete was proposed and the experimental data was fitted with the model results. The fitting result reached a good agreement.

Summary: N-glycosylation is a fundamental post-translational protein modification in the endoplasmic reticulum of eukaryotic cells. The biosynthetic and catabolic flux of N-glycans in eukaryotic cells has long been analyzed by metabolic labeling using radiolabeled sugars. Here, we introduce a non-radiolabeling protocol for the isolation, structural determination, and quantification of N-glycan precursors, dolichol-linked oligosaccharides, and the related metabolites, including phosphorylated oligosaccharides and nucleotide sugars. Our protocol allows for capturing of the biosynthesis and degradation of N-glycan precursors at steady state.For complete details on the use and execution of this protocol, please refer to Harada et al. (2013), Harada et al. (2020), and Nakajima et al. (2013).

The energy density of polymers for high temperature applications is still relatively low. Among them, polyimide (PI) is one of the most attractive matrixes because of its high thermal stability. Instead of the mono thermal imidization method to fabricate multilayer PI nanocomposites in the literature, a novel method was proposed herein to better control the multilayer morphology, which could help to further enhance the energy storage properties. The method's effect on the morphology especially on the interfaces between adjacent layers was studied, and then the mechanism of breakdown strength change was discussed by a proposed model based on bipolar charge transport. The sandwich-structured PI nanocomposites, composed of the middle polarization layer with high BaTiO3 (BT) content and the two outer insulation layers with low BT content, were fabricated. Enhanced breakdown field and discharged energy density of 550 kV/mm and 5.1 J/cm3 with the efficiency of about 70% were achieved, while keeping a high thermal stability (500 kV/mm and 3.9 J/cm3 at 100 °C). This work presents a promising polymer nanocomposite for energy storage capacitors especially in extreme temperature environments, and a new concept to fabricate multilayer dielectric composites.

Ram Adapa (Fellow, IEEE) received the B.S. degree from Jawaharlal Nehru Technological University, India, the M.S. degree from IIT Kanpur, India, and the Ph.D. degree from the University of Waterloo, ON, Canada, all in electrical engineering.

Due to the complex operation conditions in a power transformer, an oil-impregnated pressboard (OIP) simultaneously suffers from thermal, electrical, and mechanical stress. Since most research studies have paid much attention to thermal or electrical aging of OIPs, this paper analyzes the effects of long-term mechanical vibrations on cellulose degradation in OIPs under simultaneous multi-stress. The aging experiments were firstly conducted at 130 °C, with a DC electric voltage of +6 kV, vibration amplitude of 10–50 μm, and vibration frequency of 100–300 Hz. The finite element analysis (FEA) of the pressboard vibration model was then performed on Abaqus to investigate the time–frequency domain characteristic parameters of compressive stress on the pressboard under varied vibration frequencies and amplitudes. The FEA results reveal that compressive stress on the pressboard in a multi-stress aging experiment coincided with the axial compressive stress on the insulation spacers in an SZ-50000/110 transformer. Moreover, combined with the degree of polymerization (DP) of cellulose, the effects of long-term vibration on cellulose degradation are reflected in two ways: the increase in compressive stress on the pressboard generates more links available for degradation, while more high frequency harmonic components in compressive stress accelerate the reaction rate in cellulose degradation.

Breakdown failure in insulation material is one of the key problems that threaten the safe operation of high-voltage direct current cable. In this work, the effect of boron nitride nanosheets (BNNSs) concentration, space charge and temperature on DC breakdown strength have been explored. Cross-linked polyethylene (XLPE)/BNNS nanocomposites were prepared by the melt blending method, and the basic characteristics of nanoparticles and composite were characterised. The experimental results indicate that DC breakdown strength of nanocomposite can be effectively improved when a small amount of BN nanosheet is doped into the matrix. The breakdown strength of the sample reaches the maximum value of 407.52 kV/mm when BNNS content is 0.5 wt%, which is about 33% higher than that of pure XLPE. Further, the effect of space charge on the breakdown of nanocomposites has been studied by pre-injecting charges. For the samples with different BNNS contents, all the breakdown strength present ascending trend when the polarity of the applied voltage is the same as that of the pre-injected charges. Besides, it can be found that the breakdown strength of the XLPE/BNNSs composite decreases significantly at 50°C, which is due to more charge accumulation at 50°C. It reaches 2.06 × 10^−8 C which increases by about 2.2 times than the room temperature.

Surface flashover of insulation systems is a basic issue in the field of high voltage and electrical insulation. To improve the surface flashover performance is of great significance for the development of advanced power transmission equipment and insulation materials. This study reviews the research progress of surface flashover in vacuum regarding to effective methods to improve the surface flashover performance in vacuum, including insulation system optimisation and material modification. The former one is beneficial to reduce the electric field distortion, and the later one is able to adjust the surface trap parameters of the material through physical and chemical methods. In addition, the ‘U-shaped’ curve is proposed to reveal the relationship between surface flashover voltage and surface trap level, discovering the synthetic effects of surface traps on surface flashover. It is expected that the ‘U-shaped’ curve will become a guidance to improve surface flashover performance through adjusting trap parameters. Moreover, several suggestions are made to build unified surface flashover model which is suitable to the range from high vacuum to high pressure.