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Abstract Epoxy‐impregnated paper transformer bushings are prone to water absorption due to the presence of water‐attracting moieties in the cellulose chemical structure and epoxy resin, leading to moisture‐induced insulation defects. To understand the mechanism of moisture's impact on epoxy‐impregnated paper, this study developed a testing platform that integrated moisture diffusion, adsorption, and dielectric properties of insulating materials. Insulation specimens made of epoxy resin and epoxy‐impregnated paper were prepared and their water diffusion characteristics were investigated using the Fick diffusion model and the Langmuir model, respectively. The Guggenheim–Anderson–de Boer equation was used to examine the vacuum vapour adsorption characteristics of the materials, providing a theoretical foundation for examining the form of water present within them. The dielectric response of materials with varying moisture levels was then tested to study the effect of water on the dielectric spectrum curve. Using the Extended Derivative Method, the characteristic frequency reflecting the water content of the epoxy‐impregnated paper was extracted. The results demonstrate that 0.01‐Hz characteristic frequency provides superior accuracy for moisture assessment in epoxy resins compared to 50 Hz, and extracting and fitting the relaxation peak characteristic frequency in epoxy‐impregnated paper moisture evaluation yields higher accuracy than using tan δ at the power frequency.

Background and aimThe number of elderly patients with biliary stones is increasing. Endoscopic retrograde cholangiography (ERCP) is considered to be an effective treatment for biliary stones. Having a sound knowledge of the risk factors can help reduce the incidence and severity of complications for ERCP. Furthermore, limited research has been published on patients aged over 85 years undergoing endoscopic biliary stone removal. This study aims to determine the risk factors that lead to complications of ERCP in patients over 85 years of age.MethodsThis was a single-center retrospective study. We analyzed 156 patients aged ≥ 85 years with biliary stones who underwent their first ERCP at Chinese PLA General Hospital from February 2002 to March 2021. Logistic regression models were employed to identify the independent risk factors for complications.ResultsA total of 13 patients (8.3%) had complications. Thereinto, pancreatitis, cholangitis, bleeding, and other complications occurred in 4 cases (2.6%), 1 cases (0.6%), 4 cases (2.6%), and 4 cases (2.6%), respectively. There was no perforation or death related to ERCP. Independent risk factors for complications were acute biliary pancreatitis (ABP) (P = 0.017) and Charlson Comorbidity Index (CCI) (P = 0.019). Significantly, reasons for incomplete stone removal at once were large stone (>10 mm) (P

A one-dimensional Vlasov–Poisson simulation code is employed to investigate the plasma sheath considering electron-induced secondary electron emission (SEE) and backscattering. The SEE coefficient is commonly treated as constant in a range of plasma simulations; here, an improved SEE model of a charged dielectric wall is constructed, which includes the wall charging effect on the SEE coefficient and the energy dependency of the SEE coefficient. Pertinent algorithms to implement the previously mentioned SEE model in plasma simulation are studied in detail. It is found that the SEE coefficient increases with the amount of negative wall charges, which in turn reduces the emissive sheath potential. With an energy-dependent SEE coefficient, the sheath potential is a nonlinear function of the plasma electron temperature, as opposed to the linear relation predicted by the classic emissive sheath theory. Simulation combining both wall-charging effect and SEE coefficient’ energy dependency suggests that the space-charged limited sheath is formed at high plasma electron temperature levels, where both sheath potential and surface charging saturate. Additionally, different algorithms to implement the backscattering in the kinetic simulation are tested and compared. Converting backscattered electrons to secondary electrons via an effective SEE coefficient barely affects the sheath properties. The simulation results are shown to be commensurate with the upgraded sheath theory predictions.

Abstract A 3D particle‐in‐cell/Monte Carlo collision model is used to investigate the streamer discharge inception in CO2 at elevated pressures including gaseous, liquid and supercritical phases. Generation of free electrons is a prerequisite for initiation and development of positive streamers. Field ionization from impurity molecules of low density and low ionization energy is assumed as the source of primary ionization in the model. The field dependent generation rate of electrons is calculated by Zener's model. Tree‐like streamer with filamentary shape presents at the needle tip and propagates towards the plane electrode in all three phases of CO2, with differing in length and propagation speed. Furthermore, the influence of different parameters such as applied voltage, electrode tip size, and ionizable density and ionization potential of impurity molecules on the evolution of streamer discharge in supercritical CO2 are investigated. Simulation results obtained from the 3D model agree well with experimental observations in the literature, which show that field ionization might be one of possible ionization sources in pressurized CO2 in the presence of high electric field.

Objectives: Most patients with gallbladder cancer (GBC) present with advanced-stage disease and have a poor prognosis. Radical resection remains the only therapeutic option to improve survival in patients with GBC. This study aimed to analyze the prognostic factors in patients with stage Ⅳ GBC and to identify a subgroup of patients who might benefit from R0 resection. Methods: A total of 285 patients with stage Ⅳ GBC were retrospectively analyzed at our institution from January 2008 to December 2012. Factors potentially influencing the prognosis of GBC after surgery were analyzed by univariate and multivariate analyses. Results: The 1-, 3-, and 5-year overall survival rates were 6.6% (15/229), 0.9% (2/229), and 0 (0/229), respectively. Ascites (relative risk [RR] = 1.631, 95% confidence interval [CI]: 1.221–2.180, P = 0.001), pathological grade (RR = 1.337, 95% CI: 1.050–1.702, P = 0.018), T stage (RR = 1.421, 95% CI: 1.099–1.837, P = 0.000), M stage (RR = 1.896, 95% CI: 1.409–2.552, P = 0.000), and surgery (RR = 1.542, 95% CI: 1.022–2.327, P = 0.039) were identified as independent risk factors influencing prognosis. The median survival time (MST) was significantly higher in patients undergoing R0 resection than in those undergoing R1/R2 resection (6.0 vs. 2.7 months; P

Stereolithography (SL) is a promising 3D printing method for the fabrication of high dielectric constant polymer matrix composites (high-k PMCs) because of its high geometric accuracy and few manufacturing defects. However, the presence of ceramic filler destroys the fluidity and transparency of high-k PMCs, reducing their 3D printability. In this study, we fabricated barium titanate microspheres (BT-S) to facilitate the SL-based 3D printing of high-k PMCs using radio-frequency thermal plasma spheroidization (RF-TPS) technology. Experimental results showed that the prepared BT-S particles have spherical shape, smooth surface, large particle size, improved mechanical strength and higher purity, which lead to the enhancement in the 3D printability of UV curable high-k composites: i) the employment of BT-S significantly reduces the apparent viscosity and yield stress; and ii) the UV curing depth increased by 542% maximum. As a result, high-k composites were successfully printed using digital light processing (DLP) technique under low UV light energy. Moreover, the increase of dielectric constant was experimentally verified, which is explained by electrostatic energy increment according to finite element method (FEM) simulations. This study provided an effective approach (i.e. RF-TPS technology) to enhance the 3D printability of high-k PMCs, and also promoted the usage of SL-based 3D printing in advanced electrical and electronic components

The vacuum discharge along the dielectric surface, also called surface flashover, brings significant damages to the vacuum-solid insulation system. Here the authors implement shape-flexible, complex surface groove microstructures on the dielectric to mitigate the initiation of vacuum flashover. A particle-in-cell simulation is employed to reveal the real-time discharge development considering the blockage of the multipactor propagation as well as the space field distortion in the presence of specific surface microstructures. Electron trajectories within barriers are theoretically analysed to present how the barrier shape affects the discharge process, showing consistent results with the simulation. By analysing three parameters, namely the anode current, the surface average charge density and the flashover threshold, it is found that the effect of suppressing surface flashover remarkably augments when the groove number and depth rise up, while such effect gradually saturates when the groove depth reaches a critical value. Theoretical analyses are also provided for the decay factor as well as the optimal shape and trapezoid grooves are proved as the optimal shape distribution of microstructures. Furthermore, different secondary emission yield (SEY) distributions are considered with two kinds of structures, including the material with low-SEY inside and on the top surface of grooves.

Underwater discharges are considered to be promising solutions to water disinfection problems. In this paper, the sterilization effects of different discharge modes and gas bubbling conditions on E. coli are investigated. The experimental results show that spark discharge owns a much higher sterilization efficiency than the streamer discharge. The larger discharge volume and stronger UV emission during spark discharge may play a more important role than the electric field and active species in the sterilization efficiency of discharge modes. To further increase the sterilization efficiency, two kinds of feeding gases, O2 and Ar, are introduced in underwater discharges, and experimental results show that O2 bubbling presents a greater promotion than Ar. Higher sterilization efficiency of O2 bubbling than that of Ar can be explained by the combination of physical and chemical reactions, while in the case of Ar, only physical interactions play a major role.

Objective: To analyze the clinical epidemiological characteristics of patients with gallbladder carcinoma recruited from 17 hospitals in five northwestern provinces of China (Shaanxi Province, Gansu Province, Qinghai Province, Ningxia Hui Autonomous Region, and Xinjiang Uygur Autonomous Region) from 2009 to 2013, and to summarize the clinical diagnosis and treatment data of gallbladder carcinoma. Methods: Clinical information of 2379 patients with gallbladder carcinoma from 17 hospitals in five northwestern provinces of China was retrospectively collected and analyzed using the âQuestionnaire for Gallbladder Carcinoma Patients in Northwestern Area of China.â All information was verified with EpiData software and analyzed with SPSS 13.0 software. Results: (1) Gallbladder carcinoma accounted for 2.7% (2379/86,609) of all biliary tract diseases during the study period, which was significantly higher than that from 1986 to 1998 (PÂ

Low temperature plasma (LTP) has emerged as a new research hotspot of promising therapy to fight against cancer. Autophagy is a multifunctional process that digests and recycles cellular contents within lysosomes to maintain homeostasis, which is the underlying mechanism of cancer cell death and anti-cancer treatment. This study aimed at investigating whether autophagy of HepG2 cells could be induced by LTP and revealing the related molecular mechanism. For this purpose, the atmospheric pressure plasma jet (APPJ) in helium was utilized to generate plasma-actived medium (PAM) to treat HepG2 cells in vitro. Catalase (CAT), superoxide dismutase (SOD) and 3-methyladenine (3-MA) were respectively added into the PAM as the intervention group. The cell viability, formation of autophagosomes, intracellular reactive oxygen species (ROS) level, expression levels of autophagy-associated proteins and key proteins involved in PI3K/AKT/mTOR pathways were detected. The results showed that LTP inhibited cell viability in a dose- and time-dependent manner. Autophagy was induced through the formation of autophagosomes, conversion of LC3-II/LC3-I, increased expression of beclin 1 and degradation of p62. The mechanism was deduced that LTP enhanced the intracellular ROS level and decreased the phosphorylation level of key proteins in PI3K/AKT/mTOR/p70S6K pathway. However, these effects were blocked by the autophagy inhibitor 3-MA and ROS scavengers (CAT and SOD). The therapeutic efficacy of LTP against HepG2 cells may involve autophagy via suppressing PI3K/AKT/mTOR signaling pathway by LTP-mediated ROS.

Primary equipment failure in substation has a significant impact on the reliability of the power supply, and even threatens the thermal stability of power grid. This study presents a method identification of electrical connectivity and thermal stability assessment of power grid after primary equipment failure. The identification method of electrical connectivity based on incidence matrix provides a way to determine load curtailment after equipment failure. Subsequently, the inject power of substation bus in power grid is modified by load curtailment. Moreover, based on the DC power flow model, the active power flow distribution of power grid is calculated, which is used to evaluate whether the active power of lines exceeds limit. Compared to the traditional N − 1 assessment method, this method not only has the advantages of fast calculation and strong pertinence but also of convenience for the field application.

Near Infrared Spectroscopy (NIRS), as one of analysis technologies, has shown promisingly industrial applications for significant properties for recent decades such as fast response, preciseness, non-intrusion etc. Here, the authors employed NIRS coupled with a series of physical and chemical tests to assess the ageing condition of oil-paper insulation, which is responsible for the main insulation type of high-voltage power transformer. Among these procedures, the data analytic algorithms are of utmost importance to determine the evaluation precision. After plenty of trial-and-error, Savitzky-Golay (S-G) convolution was finally utilised to de-noise samples and improve the spectral data quality. The competitive adaptive reweighted sampling (CARS) was used to select the optimal wavelength combination of NIRS, which is found able to fully extract the effectively spectral information and reduce dimensions of spectral data. Based on the above-mentioned techniques, the quantitative analysis model of NIRS was established by partial least squares (PLS), which could synthetically process the spectral data and the degree of polymerisation (DP) of paper samples. The results indicated that compared with the traditional detection methods, the NIRS analysis is a powerful and informative tool to characterise the condition of oil-paper insulation without intrusion or damage to transformers.

Cross-linked polyethylene (XLPE) is often manufactured as pipe, film and foam products and used as electric insulation material. To improve the dielectric properties of XLPE film, CF4 dielectric barrier discharge (DBD) is applied as a surface modification method. The surface of XLPE film was modified at the low pressure of 1 kPa with different treatment time (15s, 30s, 60s, 120s, 240s and 480s). Electrical and optical characteristics are observed during DBD process, including applied voltage, measured current, photograph and emission spectra. Then, the surface properties, which are hydrophobicity, chemical composition, surface morphology, trap depth, dielectric loss and AC breakdown voltage, have been measured or observed by water contact angle test, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), isothermal relaxation current (IRC), frequency domain spectroscopy (FDS) and withstand voltage test. After the surface modification, the water contact angle, trap depth and breakdown voltage increase first and then decrease with treatment time extending. Meanwhile, the dielectric loss has an opposite trend, which represents better dielectric properties. The reason is that fluorine can reduce the surface energy, which can significantly influence the water contact angle. Better hydrophobicity can restrain the accumulation of outside pollution on the surface. Moreover, fluorine has strong electronegativity, so amorphous crystalline and impurities interface trap depth become deeper and the dielectric loss becomes lower. Therefore, appropriate DBD treatment conditions can apparently improve XLPE dielectric properties.

Dielectric response is closely related to the aging status of XLPE cables, and the isothermal relaxation current (IRC) has been applied to find out the change trend of cable insulation as a non-destructive method. In this paper, 4 groups of XLPE cable samples (16 cables in total) are artificially acceleratedly aged with different time interval at 120, 140 and 160°C, respectively, and their IRC curves are measured by a micro-current device. The results show that with the increasing aging time, IRC curves decrease slower and the absolute values of steady current become larger. In order to quantify the aging characteristics of XLPE cables, the trap parameters calculation theory is employed to work out the peak trap level of different polarization types. The experiment results show that the peak trap level of bulk polarization (type 1) remains stable and is around 0.76eV which is considered to be independent of aging degree. As the aging time increases, the peak trap level of amorphous crystalline relaxation (type 2), which is from 0.785eV to 0.82eV, increases at low temperature (120°C) due to the breaking of molecular chain and decreases at high temperature (more than 140°C) due to the over cross-linking. The peak trap level of impurities interface relaxation (type 3) is highly influenced by aging temperature, which is most sensitive to the aging degree of power cable. It is considered that IRC can be used as a practical way to judge cable insulation in the future.

The luminescence evolution phenomena from alumina ceramic surface in vacuum under high voltage of direct and alternating current are reported, with the voltage covering a large range from far below to close to the flashover voltage. Its time resolved and spatial distributed behaviors are examined by a photon counting system and an electron-multiplying charge-coupled device (EMCCD) together with a digital camera, respectively. The luminescence before flashover exhibits two stages as voltage increasing, i.e., under a relative low voltage (Stage A), the luminescence is ascribed to radiative recombination of hetero-charges injected into the sample surface layer by Schottky effect; under a higher voltage (Stage B), a stable secondary electron emission process, resulting from the Fowler-Nordheim emission at the cathode triple junction (CTJ), is responsible for the luminescence. Spectrum analysis implies that inner secondary electrons within the surface layer of alumina generated during the SSEE process also participate in the luminescence of Stage B. A comprehensive interpretation of the flashover process is formulated, which might promote a better understanding of flashover issue in vacuum.