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Alkali-activated materials (AAMs) offer an eco-friendly alternative to traditional Portland cement, yet their rheological properties, particularly in concrete mixtures, remain largely underexplored. This study conducted rheological tests to investigate the flow properties and thixotropic behavior of alkali-activated slag (AAS) concrete with varying water-to-binder (w/b) ratios and silicate modulus (Ms). The thixotropy of AAS concrete was assessed using the thixotropic index, breakdown area, and variations in apparent viscosity under different shear rates, revealing correlations between thixotropic behaviors and rheological parameters. Mixtures with lower Ms and w/b ratios showed limited slump values and rapid structural build-up due to increased interparticle connections. As Ms increased, enhanced thixotropic behaviors were observed, attributed to the rapid formation of early hydration products. This led to a significant increase in peak torque values and a slight decrease in equilibrium torque values at various rotational speeds. In turn, AAS concrete with higher Ms demonstrated improved fluidity and workability retention after thixotropic build-up was erased. The results of this study provide valuable insights into the flow and thixotropic behaviors of fresh AAS concretes for practical applications. [ABSTRACT FROM AUTHOR]

The reliability of inverse-mode silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) under dc stress and its potential impact on the performance of basic analog amplifiers are investigated. In order to properly reflect the stress effects in various circuit applications, the degradations under three different configurations (active bias, diode connection, and off state) were experimentally characterized with the stress voltages applied up to 3000 s for each case. Based on the changes in the Gummel response, the degradations in device parameters such as current gain (β), transconductance (gm), and base-to-emitter resistance (rπ) were extracted and compared with the forward-mode counterpart. In addition, with the use of a small-signal equivalent model of a SiGe HBT, simple single-stage analog amplifiers were simulated as representative examples and their circuit-level performance metrics including gain and bandwidth were studied to estimate degradation characteristics with accumulated stress. It was found that transimpedance gain decreases and operation bandwidth increases to different levels due to device degradation, whereas a voltage amplifier exhibited much less changes. [ABSTRACT FROM AUTHOR]

The GaN photoconductive semiconductor switches (PCSSs) with low leakage current and large on-state current are suitable for several applications, including fast switching and high-power electromagnetic pulse equipment. This paper demonstrates a high-power GaN lateral PCSS device. An output peak current of 142.2 A is reached with an input voltage of 10.28 kV when the GaN lateral PCSS is intrinsically triggered. In addition, the method of retaining the AlGaN/GaN heterostructure between electrodes on PCSSs is proposed, which results in increasing the output peak current of the PCSS. The damage mechanism of the PCSS caused by a high electric field and high excitation laser energy is analyzed. The obtained results show that the high heat generated by the large current leads to the decomposition of GaN, and thus, the Ga forms a metal conductive path, resulting in the failure of the device. [ABSTRACT FROM AUTHOR]

The integration of self-assembled monolayers (SAM) into cobalt (Co)/porous low-dielectric-constant (low-k) dielectric interconnects is studied in terms of electrical characteristics and reliability in this work. Experimental results indicated that SAM derived from 3-aminopropyltrimethoxysilane (APTMS) improved breakdown field, time-dependent dielectric breakdown, and adhesion for Co/porous low-k integrated interconnects. However, the improvement magnitude was not large as compared to SAM in the Cu/porous low-k integration. Therefore, the integration of SAM into Co/porous low-k interconnects has a positive effect; however, in order to further promote the efficiency of SAM for Co/porous low-k interconnects, the option of precursors for the growth of SAM is required. [ABSTRACT FROM AUTHOR]

As unmanned ground vehicles (UGV) continue to be adapted to new applications, an emerging area lacks proper guidance for global route optimization methodology. This area is surveillance. In autonomous surveillance applications, a UGV is equipped with a sensor that receives data within a specific range from the vehicle while it traverses the environment. In this paper, the ant colony optimization (ACO) algorithm was adapted to the UGV surveillance problem to solve for optimal paths within sub-areas. To do so, the problem was modeled as the covering salesman problem (CSP). This is one of the first applications using ACO to solve the CSP. Then, a genetic algorithm (GA) was used to schedule a fleet of UGVs to scan several sub-areas such that the total distance is minimized. Initially, these paths are infeasible because of the sharp turning angles. Thus, they are improved using two methods of path refinement (namely, the corner-cutting and Reeds–Shepp methods) such that the kinematic constraints of the vehicles are met. Several test case scenarios were developed for Goheung, South Korea, to validate the proposed methodology. The promising results presented in this article highlight the effectiveness of the proposed methodology for UGV surveillance applications. [ABSTRACT FROM AUTHOR]

We investigated a flat-type p*-p LED composed of a p*-electrode with a local breakdown conductive channel (LBCC) formed in the p-type electrode region by applying reverse bias. By locally connecting the p*-electrode to the n-type layer via an LBCC, a flat-type LED structure is applied that can replace the n-type electrode without a mesa-etching process. Flat-type p*-p LEDs, devoid of the mesa process, demonstrate outstanding characteristics, boasting comparable light output power to conventional mesa-type n-p LEDs at the same injection current. However, they incur higher operating voltages, attributed to the smaller size of the p* region used as the n-type electrode compared to conventional n-p LEDs. Therefore, despite having comparable external quantum efficiency stemming from similar light output, flat-type p*-p LEDs exhibit diminished wall-plug efficiency (WPE) and voltage efficiency (VE) owing to elevated operating voltages. To address this, our study aimed to mitigate the series resistance of flat-type p*-p LEDs by augmenting the number of LBCCs to enhance the contact area, thereby reducing overall resistance. This structure holds promise for elevating WPE and VE by aligning the operating voltage more closely with that of mesa-type n-p LEDs. Consequently, rectifying the issue of high operating voltages in planar p*-p LEDs enables the creation of efficient LEDs devoid of crystal defects resulting from mesa-etching processes. [ABSTRACT FROM AUTHOR]

This study presents findings on the influence of gap length distance on the lightning impulse breakdown voltage of three dielectric liquids of different chemical origins. The liquids were tested in a model electrode system with a quasi-uniform electric field distribution and a pressboard plate placed on the grounded electrode. The experimental studies were supported using calculations and simulations to show the individual relationships between the lightning impulse breakdown voltage and gap distance, which represent the so-called volume effect of the most stressed liquid. The results of the experiment, which involved four considered gap distances of 2, 4, 6, and 8 mm, show that a dynamic increase in lightning impulse breakdown voltage with an increase in gap distance is associated with mineral oil and bio-based hydrocarbons. However, similar trends were not observed for synthetic ester. Calculations that allowed us to assess the impact of gap length distance on lightning impulse breakdown voltage support the observations from the experimental studies. The curves obtained in this field can be considered in the process of designing insulating systems for transformers. [ABSTRACT FROM AUTHOR]

This paper extends the k-out-of-n:G reliability system to a multi-server queue. We study a multi-server reliability-queuing model with the N-policy of repair. The queuing system considered here has n servers, each of which has identically and exponentially distributed service times with parameter μ. Servers are subject to breakdown at an exponential rate γ. The repair process follows the N-policy of repair. Although these servers work independently of each other, service can be provided only when k functional servers are available in the system. We study the model in the steady state, using the matrix analytic method. We evaluate some associated performance measures and provide graphical/numerical illustrations. We consider an optimization problem, and the results of the study are presented. [ABSTRACT FROM AUTHOR]

In this paper, a bulk arrival and two-phase bulk service with active Bernoulli feedback, vacation, and breakdown is considered. The server provides service in two phases as mandatory according to the general bulk service rule, with minimum bulk size ′ a ′ and maximum bulk size ′ b ′ . In the first essential service (FES) completion epoch, if the server fails, with probability ′ δ ′ , then the renewal of the service station is considered. On the other hand, if there is no server failure, with a probability ′ 1 − δ ′ , then the server switches to a second essential service (SES) in succession. A customer who requires further service as feedback is given priority, and they join the head of the queue with probability β . On the contrary, a customer who does not require feedback leaves the system with a probability ′ 1 − β ′ . If the queue length is less than ′ a ′ after SES, the server may leave for a single vacation with probability ′ 1 − β ′ . When the server finds an inadequate number of customers in the queue after vacation completion, the server becomes dormant. After vacation completion, the server requires some time to start service, which is attained by including setup time. The setup time is initiated only when the queue length is at least ′ a ′ . Even after setup time completion, the service process begins only with a queue length 'N' (N > b). The novelty of this paper is that it introduces an essential two-phase bulk service, immediate Bernoulli feedback for customers, and renewal service time of the first essential service for the bulk arrival and bulk service queueing model. We aim to develop a model that investigates the probability-generating function of the queue size at any time. Additionally, we analyzed various performance characteristics using numerical examples to demonstrate the model's effectiveness. An optimum cost analysis was also carried out to minimize the total average cost with appropriate practical applications in existing data transmission and data processing in LTE-A networks using the DRX mechanism. [ABSTRACT FROM AUTHOR]

Improvement techniques aimed at enhancing the dielectric strength and minimizing the dielectric loss of insulation materials have piqued the interest of many researchers. It is worth noting that the electrical breakdown traits of insulation material are determined by their electrochemical and mechanical performance. Possible good mechanical, electrical, and chemical properties of new materials are considered during the generation process. Thermoplastic polyurethane (TPU) is often used as a high-voltage insulator due to its favorable mechanical properties, high insulation resistance, lightweight qualities, recovery, large actuation strain, and cost-effectiveness. The elastomer structure of thermoplastic polyurethane (TPU) enables its application in a broad range of high-voltage (HV) insulation systems. This study aims to evaluate the feasibility of using TPU on transformer windings as a solid insulator instead of pressboards. The investigation conducted through experiments sheds light on the potential of TPU in expanding the range of insulating materials for HV transformers. Transformers play a crucial role in HV systems, hence the selection of suitable materials like cellulose and polyurethane is of utmost importance. This study involved the preparation of an experimental setup in the laboratory. Breakdown tests were conducted by generating a non-uniform electric field using a needle–plane electrode configuration in a test chamber filled with mineral oil. Various voltages ranging from 14.4 kV to 25.2 kV were applied to induce electric field stress with a step rise of 3.6 kV. The partial discharges and peak numbers were measured based on the predetermined threshold values. The study investigated and compared the behaviors of two solid insulating materials under differing non-electric field stress conditions. Harmonic component analysis was utilized to observe the differences between the two materials. Notably, at 21.6 kV and 25.2 kV, polyurethane demonstrated superior performance compared to pressboard with regards to the threshold value of leakage current. [ABSTRACT FROM AUTHOR]

This paper investigates the intriguing impact of surface V-shaped defects on the electrical and optical characteristics of GaN-based LEDs, particularly under reverse bias conditions. These defects introduce unique luminescence phenomena, notably giant dot-like luminescence (GDL), and exert significant influence on device performance. The size of these V-shaped defects plays a critical role: larger defects generate more indium-rich regions at their base, resulting in elevated tensile stress. This heightened stress promotes carrier tunneling, increasing reverse leakage current and leads to GDL formation. However, even with multiple V-shaped defects present, localized failure predominantly occurs at the defect experiencing the highest tensile stress, substantially reducing the breakdown voltage. Micro-Raman analysis further reveals distinct Raman shifts and increased tensile stress in these regions. These findings underscore the complexity of V-shaped defects' effects, highlighting their importance in GaN-based LED design and optimization. Recognizing their influence on electrical and optical properties can significantly impact device reliability and performance, particularly in reverse bias conditions. [ABSTRACT FROM AUTHOR]

Hydraulic systems are used in all kinds of industries. Mills, manufacturing, robotics, and Ports require the use of Hydraulic Equipment. Many industries prefer to use hydraulic systems due to their numerous advantages over electrical and mechanical systems. Hence, the growth in demand for hydraulic systems has been increasing over time. Due to its vast variety of applications, the faults in hydraulic systems can cause a breakdown. Using Artificial-Intelligence (AI)-based approaches, faults can be classified and predicted to avoid downtime and ensure sustainable operations. This research work proposes a novel approach for the classification of the cooling behavior of a hydraulic test rig. Three fault conditions for the cooling system of the hydraulic test rig were used. The spectrograms were generated using the time series data for three fault conditions. The CNN variant, the Residual Network, was used for the classification of the fault conditions. Various features were extracted from the data including the F-score, precision, accuracy, and recall using a Confusion Matrix. The data contained 43,680 attributes and 2205 instances. After testing, validating, and training, the model accuracy of the ResNet-18 architecture was found to be close to 95%. [ABSTRACT FROM AUTHOR]

This paper investigates the concept of a Markovian queueing model with heterogeneous, intermittently available servers with feedback under a hybrid vacation policy. Both the asymmetric transition representation and the hybrid vacation policy are addressed in this article. The necessary and sufficient conditions for system stability are presented. In addition, the steady-state probability distribution of the queueing model was derived by employing the matrix geometric method. Furthermore, a few formulae were constructed to determine the model's performance indicators. Finally, the influence of system parameters was also investigated using some numerical examples. [ABSTRACT FROM AUTHOR]

This article contains the analytical model of the drift of a separate ice field under the action of wind and current, in which velocities and directions can vary over time. The model takes into account the mass of ice, added mass of seawater, and the effects of the wind and current on the ice field in forming the friction on its upper and underwater surfaces and the frontal resistance on its end (forward and backward) surfaces. Simulation of the wind drift of the ice field showed the drift velocity exceeds the considerable known velocity of a compact ice cover drift. A drifting ice field has a certain kinetic energy that should be released when a collision occurs with an unmovable obstacle, and spent on brittle breakdown of a quantity of the ice field. The volume of formed small ice pieces (fragments of ice field) was estimated by comparison of the specific energy of the sea ice brittle destruction and the kinetic energy of the drifting ice field. The article presents the results of the estimation of the possible volume of the ice pieces and the scales of formed piles as a result of a collision with an obstacle, depending on the initial dimensions of the ice field and wind speed. Developed models and the results of computer modeling can be used to estimate the ice pile sizes near the stationary platforms and terminals on the Arctic seas. [ABSTRACT FROM AUTHOR]

Epoxy resin is extensively used in gas insulated switches as a renewable energy coating due to its exceptional insulation, mechanical characteristics, and environmental friendliness. The higher resistivity of the epoxy resin causes numerous surface charges to accumulate on the surface of the epoxy resin as a result of carrier injection due to the high DC electric field, which may cause insulation failure of the power transmission system. In this study, various concentrations of epoxy resins blended with nano-alumina (nano-Al2O3) at 0 wt%, 1 wt%, 3 wt%, and 5 wt% were created. Afterwards, the epoxy resin and Al2O3 nanocomposites were fluorinated by utilizing a combination of F2 and N2 with a ratio of 20% F2 at 0.05 MPa while maintaining the temperature at 40 °C. In order to improve dispersion, nano-Al2O3 was treated with a silane coupling agent called γ-aminopropyltriethoxysilane (KH550). Additionally, infrared spectroscopy based on the Fourier transform was used to investigate the structure of chemical bonds. Furthermore, the changes in the molecular chains were verified by the FTIR spectra. The DC breakdown strength of epoxy resin\Al2O3 nano-composites showed that breakdown strength significantly improved after gas-phase fluorination. Moreover, 1 wt% nano-Al2O3 showed a higher breakdown strength. The fluorinated layer had a charge-suppressing effect, reducing the charge injected into the polymer matrix of the epoxy-resin matrix and increasing its DC breakdown capability. Thermally stimulated current (TSC) measurements indicate that epoxy resin's trap energy and trap density are altered by nano-Al2O3 incorporation and fluorination treatment (gas-phase). It was also observed that introducing nano-Al2O3 at a lower concentration (e.g., 1 wt%) can hinder the growth of space charge in the polymer matrix of the epoxy resin, thus enhancing the deep traps' energy. Furthermore, a fluorination layer containing a strong polarization of C-F bonding would seize the charge injection from electrodes, thus decreasing the conductivity and suppressing the charge injection. [ABSTRACT FROM AUTHOR]

Self-assembled monolayers (SAMs) are the emerging materials to act as barriers in the back-end-of-line interconnects for advanced technological nodes. In this study, SAMs were formed on the porous SiOCH (p-SiOCH) films by using different precursors: 3-Aminopropyltrimethoxysilane (APTMS) or decyltrimethoxysilane (DTMOS), in the vapor phase. Effects of SAMs precursors on the electrical characteristics and reliability of p-SiOCH films were characterized and compared. Experimental results indicated that both SAMs derived from APTMS and DTMOS enhanced the breakdown field and time-dependent dielectric breakdown, provided Cu barrier capacity, and promoted adhesion with Cu. In particular, APTMS-SAMs had a larger improvement, but a larger increase in the dielectric constant was observed as compared to DTMOS-SAMs. Therefore, SAMs derived from APTMS are a promising candidate for sub-nanometer barrier application for advanced interconnects. [ABSTRACT FROM AUTHOR]

In this study, the reliability characteristics of metal-insulator-semiconductor (MIS) capacitor structures with low-dielectric-constant (low-k) materials have been investigated in terms of metal gate area and geometry and thickness of dielectric film effects. Two low-k materials, dense and porous low-k films, were used. Experimental results indicated that the porous low-k films had shorter breakdown times, lower Weibull slope parameters and electric field acceleration factors, and weaker thickness-dependence breakdowns compared to the dense low-k films. Additionally, a larger derivation in dielectric breakdown projection model and a single Weilbull plot of the breakdown time distributions from various areas merging was observed. This study also pointed out that the porous low-k film in the irregular-shaped metal gate MIS capacitor had a larger dielectric breakdown time than that in the square- and circle-shaped samples, which violates the trend of the sustained electric field. As a result, another breakdown mechanism exists in the irregular-shaped sample, which is required to explore in the future work. [ABSTRACT FROM AUTHOR]

In this paper, N, N'-m-phenylene dimaleimide (HVA-2) grafted crosslinked polyethylene (XLPE) insulation materials with different HVA-2 contents were prepared. The grafting, crosslinking, and crystalline structure were characterized by Fourier-transform infrared spectroscopy (FTIR), Soxhlet extraction, and differential scanning calorimetry (DSC), respectively. The space charge distribution, direct current (DC) breakdown strength, and DC conduction current density were tested and the electronic structure was calculated from first-principles. HVA-2 grafting modification can significantly reduce the accumulation of space charges and the conduction current density of XLPE, but have a negative effect on DC breakdown strength. The polar groups of the grafted HVA-2 anchored on XLPE by the grafting reaction can introduce deep traps densely and evenly in XLPE, which would capture and scatter charge carriers, thus reducing the carrier concentration and mobility and further improving the space charge distribution and reducing conduction current density. However, the grafting of HVA-2 can increase the crosslinking extent of XLPE to make the crystallinity decrease and the crystallization inhomogeous, leading to a certain decrease in the breakdown strength of the grafted XLPE. [ABSTRACT FROM AUTHOR]

Self-assembled monolayers (SAMs) are emerging as materials that are candidates of barriers used in back-end-of–line interconnects of integrated circuits for future generations. In this study, SAMs were formed on the SiO2 and porous SiOCH (p-SiOCH) films by using decyltrimethoxysilane (DTMOS) precursor in vapor phase at a temperature of 100 °C. The effects of the formation of SAMs at the surfaces of SiO2 and p-SiOCH films on the electrical characteristics were characterized and compared. With O2 plasma irradiation, SAMs could successfully form on both SiO2 and p-SiOCH films, thereby enhancing the adhesion and dielectric breakdown field. In the p-SiOCH films, SAMs sealed the surface pores and had higher coverage, promoting the effectiveness of the Cu barrier. In the Cu/porous low-k integrated interconnects for advanced technological nodes, therefore, SAMs are promising emerging materials acting as a barrier and adhesive. On the other hand, for SiO2 films, SAMs weakened the barrier; however, they can act as an interfacial adhesion enhancer. [ABSTRACT FROM AUTHOR]

Isopropyl alcohol (IPA) has been conventionally used for pre-cleaning processes. As the device size decreased, the gate oxide layer became thinner. As a result, the quality of the gate oxide was degraded by a pre-cleaning process, and oxide reliabilities and product yield were affected. In this study, we investigate whether the carbon generated on the silicon interface after the IPA drying process might have induced gate oxide breakdown. Time-dependent dielectric breakdown (TDDB) failure increased in frequency since carbon contaminations were increased in the oxide according to the amount of IPA. Organic contaminations resulted in a lower energy level, and electron tunneling occurred through the gate oxide. When an external electric field was applied, organic materials in the gate oxide layer were aligned, and a percolation path formed to cause breakdown. Finally, we suggest a new cleaning method using carbon-free O3 deionized (DI) water as a dry-cleaning method to improve oxide dielectric breakdown. An O3 DI dry cleaning process could reduce carbon particles in the oxide layer and decrease gate oxide failure by 7%. [ABSTRACT FROM AUTHOR]

The purpose of this present study is to prepare a stable mineral-oil (MO)-based nanofluid (NF) for usage as a coolant in a transformer. Nanoparticles (NPs) such as hexagonal boron nitride (h-BN) and titanium oxide (TiO2) have superior thermal and electrical characteristics. Their dispersion into MO is likely to elevate the electrothermal properties of NFs. Therefore, different batches of NFs are prepared by uniformly dispersing the insulating h-BN and semiconducting TiO2 NP of different concentrations in MO. Bulk h-BN NP of size 1μm is exfoliated into 2D nanosheets of size 150–200 nm, subsequently enhancing the surface area of exfoliated h-BN (Eh-BN). However, from the zeta-potential analysis, NP concentration of 0.01 and 0.1 wt.% are chosen for further study. The thermal conductivity and ACBDV studies of the prepared NF are performed to investigate the cooling and insulation characteristics. The charging-dynamics study verifies the enhancement in ACBDV of the Eh-BN NF. Weibull statistical analysis is carried out to obtain the maximum probability of ACBDV failure, and it is observed that 0.01 wt.% based NF has superior cooling and insulation properties than MO and remaining batches of NFs. [ABSTRACT FROM AUTHOR]

GaN vertical PiN diodes with different anode thicknesses were fabricated on three native GaN wafers with the same p-layer doping concentrations, and planar hybrid edge termination. The breakdown behavior in terms of the breakdown voltage and the electroluminescence were studied as functions of the anode thickness. A repeatable avalanche breakdown and highest breakdown voltage were measured with the thinnest anode of 300 nm and with the thinnest edge termination region. This indicates the efficacy of the nitrogen-implanted hybrid edge termination design that comprises of junction termination and guard rings hybrid design. As the anode thickness increases, the edge termination thickness increases, and the devices exhibit lower breakdown voltages and less robust breakdown characteristics, often destructive. From this study, we also conclude that a very high p-layer doping of 2 × 1019 cm−3 is not s practical doping level, because it is too sensitive to the edge termination thickness. [ABSTRACT FROM AUTHOR]

Nanocellulose-modified presspaper is a promising solution to achieve cellulose insulation with better performance, reducing the risk of electrical insulation failures of a converter transformer. Predicting the dielectric properties will help to further design and improvement of presspaper. In this paper, a multivariable method was adopted to determine the effect of softwood fiber on the macroscopic performance of presspaper. Based on the parameters selected using the optimum subset method, a multiple linear regression was built to model the relationship between the fiber properties and insulating performance of presspaper. The results show that the fiber width and crystallinity had an obvious influence on the mechanical properties of presspaper, and fiber length, fines, lignin, and nanocellulose had a significant impact on the breakdown properties. The proposed models exhibit a prediction accuracy of higher than 90% when verified with the experimental results. Finally, the effect of nanocellulose on the breakdown strength of presspaper was taken into account and new models were derived. [ABSTRACT FROM AUTHOR]

The breakdown property of oil-impregnated paper is a key factor for converter transformer design and operation, but it is not well understood. In this paper, breakdown voltages of oil-impregnated paper were measured at different temperatures. The results showed that with the increase of temperature, electrical, electro-thermal and thermal breakdown occurred successively. An electro-thermal breakdown model was proposed based on the heat equilibrium and space charge transport, and negative differential mobility was introduced to the model. It was shown that carrier mobility determined whether it was electrical or thermal breakdown, and the model can effectively explain the temperature-dependent breakdown. [ABSTRACT FROM AUTHOR]

In our studies, it was confirmed that the cause of image sticking on liquid crystal (LC) cells is based on attacks of electrostatic discharge (ESD), which can be greatly relieved by doping with a small amount of tin-doped indium oxide (ITO) nanoparticles. Our proposed remedy allows the residual time of image sticking to be significantly reduced by more than an order and may protect the LC displays against any adverse ESD conditions, thus enhancing the overall display quality and reliability. In this study, conventional voltage-transmittance (V-T) characterization, voltage holding ratio (VHR) measurement, and ESD testing were employed to investigate the properties of the ITO-doped LCs. Based on our low voltage measurement results, it is interesting to find that ITO nanoparticles do not evidently alter the intrinsic properties of the LC. Namely, ITO additive initiates an early breakdown of the doped LC samples exposed to high electric fields. A model is proposed in this paper to depict the possible role of ITO particles applied in LCs. [ABSTRACT FROM AUTHOR]

The formation of a nanosecond discharge with the use of a Hamamatsu streak-camera and with simultaneously wideband (10 GHz) measurement of voltage and displacement current caused by a streamer in one pulse has been studied. Nanosecond voltage pulses of various amplitudes (16, 20, and 27 kV) were applied across a point-to-plane gap (8.5 mm) filled with air at various pressures (13, 25, 50, 100, and 200 kPa). It was found that the voltage across the gap drops as soon as a streamer appears in the vicinity of the pointed electrode. At the same time, a pre-breakdown current begins to flow. The magnitude of the pre-breakdown current, as well as the voltage drop, is determined by the rate of formation of dense plasma and, accordingly, by the rate of redistribution of the electric field in the gap. The streamer velocity determines the rise time and amplitude of the current. The higher the streamer velocity, the shorter the rise time and the higher the amplitude of the pre-breakdown current. The propagation of a backward and third ionization waves was observed both with the streak camera and by measuring the displacement current. As they propagate, the discharge current increases to its amplitude value. [ABSTRACT FROM AUTHOR]

This paper centers on a discrete-time retrial queue where the server experiences breakdowns and repairs when arriving customers may opt to follow a discipline of a last-come, first-served (LCFS)-type or to join the orbit. We focused on the extensive analysis of the system, and we obtained the stationary distributions of the number of customers in the orbit and in the system by applying the generation function (GF). We provide the stochastic decomposition law and the application bounds for the proximity between the steady-state distributions for the queueing system under consideration and its corresponding standard system. We developed recursive formulae aimed at the calculation of the steady-state of the orbit and the system. We proved that our discrete-time system approximates M/G/1 with breakdowns and repairs. We analyzed the busy period of an auxiliary system, the objective of which was to study the customer's delay. The stationary distribution of a customer's sojourn in the orbit and in the system was the object of a thorough and complete study. Finally, we provide numerical examples that outline the effect of the parameters on several performance characteristics and a conclusions section resuming the main research contributions of the paper. [ABSTRACT FROM AUTHOR]

The substantial improvements in transmission voltage, which have been adopted to meet fast-growing energy demands, require more reliable power equipment and higher-quality insulating materials. The polytetrafluoroethylene (PTFE) nozzle, as the key part of a high-voltage circuit breaker, is often subjected to arc ablation and breakdown phenomena. Thus, it is very urgent to develop nozzles with better performance. In this study, PTFE/boron nitride (BN) composites were prepared. The relationships among the BN filler loading, thermal transition properties, spectral reflectance properties, arc ablation resistance, and AC dielectric breakdown performances, as well as their corresponding mechanisms, were studied. Experimental results show that the thermal conductivity and thermal diffusivity of PTFE/BN composites increased monotonously with BN loading, and that both parameters were improved by 41% and 44%, respectively, for 11 wt % composites compared with pure PTFE. Moreover, PTFE/BN composites had higher light reflectance in the wavelength range from 320 to 2500 nm. The PTFE/BN composites presented better arc ablation resistance performance with increased BN loading, which was improved by 88.5%. It is thought that the increased thermal conductivity, thermal diffusivity, the strong light reflectance, and surface sediment after arc ablation contribute to the improvement in arc ablation resistance performance. The AC breakdown strength of PTFE/BN composites was enhanced by 30.93%, attributed to the good heat dissipation properties introduced by the BN fillers. Thus, filling BN into the PTFE matrix would be helpful to solve the equipment issue that comes from the improvement in transmission voltage. [ABSTRACT FROM AUTHOR]

A polypropylene (PP) film is usually used as a dielectric material in capacitors as well as cables. However, PP films may degrade because of the combined effect of temperature and electric field. In an earlier study, plain PP films and PP films loaded with nano-metric natural clay were studied under sinusoidal (AC) electric fields at power frequency and temperatures above the ambient. To better understand the electrical characteristics of PP film under various conditions, the objective of this study is to determine the time-to-breakdown of the plain PP and PP filled with 2% (wt) natural nano-clay when subjected to time-invariant (DC) electric fields at elevated temperatures. In order to achieve this objective, the effects of uniform as well as non-uniform electric fields were compared at the same temperature for the PP film. In this study, experimental results indicated that the time-to-breakdown of all PP films, plain or filled with nano-clay, decreases with the increase in electric field intensity, non-uniformity of the electric field, and temperature. It was also found that the time-to-breakdown of PP film filled with 2% (wt) natural nano-clay under DC electric field is longer and less sensitive to temperature. Furthermore, when compared with the results under the uniform electric field, PP film filled with 2% (wt) nano-metric natural clay indicates shorter time-to-failure under non-uniform DC electric fields. Finally, the morphology of the samples was observed by digital camera, optical micrography, and SEM, to better understand the mechanism of the breakdown. [ABSTRACT FROM AUTHOR]

In an HVDC environment, space charge accumulated in polymeric insulators causes severe electric field distortion and degradation of breakdown strength. To analyze the breakdown characteristics, here, the space charge distribution was numerically evaluated using the bipolar charge transport (BCT) model, considering the temperature gradient inside the polymeric insulator. In particular, we proposed an electro-mechanical threshold energy condition, resulting in the modified molecular chain displacement model. The temperature gradient accelerates to reduce the breakdown strength with the polarity-reversal voltage, except during the harshest condition, when the temperature of the entire polymeric insulator was 70 °C. The energy imbalance inside the insulator caused by polarity-reversal voltage reduced the breakdown strength by 82%. Finally, this numerical analysis model can be used universally to predict the breakdown strength of polymeric insulators in various environments, and help in evaluating the electrical performance of polymeric insulators. [ABSTRACT FROM AUTHOR]

Micro/nano- BN co-doped epoxy composites were prepared and their thermal conductivity, breakdown strength at power frequency and voltage endurance time under high frequency bipolar square wave voltage were investigated. The thermal conductivity and breakdown performance were enhanced simultaneously in the composite with a loading concentration of 20 wt% BN at a micro/nano proportion of 95/5. The breakdown strength of 132 kV/mm at power frequency, the thermal conductivity of 0.81 W·m−1·K−1 and voltage endurance time of 166 s were obtained in the composites, which were approximately 28%, 286% and 349% higher than that of pristine epoxy resin. It is proposed that thermal conductive pathways are mainly constructed by micro-BN, leading to improved thermal conductivity and voltage endurance time. A model was introduced to illustrate the enhancement of the breakdown strength. The epoxy composites with high thermal conductivity and excellent breakdown performance could be feasible for insulating materials in high-frequency devices. [ABSTRACT FROM AUTHOR]

Ester liquids are environmentally friendly insulating oils, and they can be used as an alternative to mineral oil in transformers, even though in most countries spills of ester oils must be treated like spills of mineral oil. Furthermore, the breakdown characteristics of ester liquids are worse than those of mineral oils in heterogeneous electric fields. In this paper, we present a comprehensive experimental research on both positive and negative lightning impulse breakdown properties in point-plane geometries with gaps varying from 1 mm to 50 mm. The breakdown voltages and streamer velocities of five kinds of ester liquids, including natural ester, synthetic ester, and three kinds of single component esters have been measured. The results show that the double bonds have no effect on the breakdown voltage of ester liquids. The average streamer velocities of mono-esters are faster than that of other esters under positive polarity, and the breakdown voltages of all esters are close. [ABSTRACT FROM AUTHOR]

We propose to use a bilayer insulator (2.5 nm Al2O3 + 35 nm SiO2) as an alternative to a conventional uni-layer Al2O3 (35 nm), for improving the performance and the reliability of GaN-on-Si semi vertical trench MOSFETs. This analysis has been performed on a test vehicle structure for module development, which has a limited OFF-state performance. We demonstrate that devices with the bilayer dielectric present superior reliability characteristics than those with the uni-layer, including: (i) gate leakage two-orders of magnitude lower; (ii) 11 V higher off-state drain breakdown voltage; and (iii) 18 V higher gate-source breakdown voltage. From Weibull slope extractions, the uni-layer shows an extrinsic failure, while the bilayer presents a wear-out mechanism. Extended reliability tests investigate the degradation process, and hot-spots are identified through electroluminescence microscopy. TCAD simulations, in good agreement with measurements, reflect electric field distribution near breakdown for gate and drain stresses, demonstrating a higher electric field during positive gate stress. Furthermore, DC capability of the bilayer and unilayer insulators are found to be comparable for same bias points. Finally, comparison of trapping processes through double pulsed and Vth transient methods confirms that the Vth shifts are similar, despite the additional interface present in the bilayer devices. [ABSTRACT FROM AUTHOR]

Nanodoping is an effective way to improve the dielectric properties and the aging resistance of polyethylene. Nano-zeolite has a nano-level porous structure and larger specific surface area than ordinary nano-inorganic oxide, which can be used to improve dielectric properties of low-density polyethylene (LDPE) nanocomposite. The zeolite/LDPE nanocomposites were prepared and subjected to thermal aging treatment to obtain samples with different aging time. Using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and the differential scanning calorimetry (DSC) test to study the microscopic and structure characteristics, it was found that nano-zeolite doping can effectively reduce the thermal aging damage to the internal structure of the nanocomposite; carbonyl and hydroxyl decreased significantly during the thermal aging time, and the crystallinity effectively improved. Nano-zeolite doping significantly improved the morphology and strengthened the aging resistance of the nanocomposite. In the dielectric strength test, it was found that nanodoping can effectively improve the direct current (DC) and alternating current (AC) breakdown field strength and the stability after the thermal aging. The dielectric constant of nanocomposite can be reduced, and the dielectric loss had no obvious change during the aging process. Moreover, the zeolite/LDPE nanocomposite with the doping concentration of 1 wt % had the best performance, for the nano-zeolite was better dispersed. [ABSTRACT FROM AUTHOR]

A reconfigurable CMOS inverter-based stacked power amplifier (PA) is proposed to extend impedance coverage, while maintaining an output power exceeding the specific power level under the worst antenna impedance mismatch conditions. The adopted process technology supports multi-threshold metal-oxide-semiconductor field-effect transistor (MOSFET) devices, and therefore, the proposed PA employs high threshold voltage (Vth) MOSFETs to increase the output voltage swing, and the output power under a given load condition. The unit cell of the last PA stage relies on a cascode inverter that is implemented by adding cascode transistors to the traditional inverter amplifier. By stacking two identical cascode inverters, and enabling one or both of them through digital switch control, the proposed PA can control the maximum output voltage swing and change the optimum load Ropt, resulting in maximum output power with peak power added efficiency (PAE). The cascode transistors mitigate breakdown issues when the upper cascode inverter stage is driven by a supply voltage of 2 × VDD, and decrease the output impedance of the PA by changing its operation mode from the saturation region to the linear region. This variable output impedance characteristic is useful in extending the impedance coverage of the proposed PA. The reconfigurable PA supports three operation modes: cascode inverter configuration (CIC), double-stacked cascode inverter configuration (DSCIC) and double-stacked inverter configuration (DSIC). These show Ropt of around 100, 50 and 25 Ω, respectively. In the simulation results, the proposed PA operating under the three configurations showed a saturated output power (Psat) of +6.1 dBm and a peak PAE of 41.1% under a 100 Ω load impedance condition, a Psat of +4.5 dBm and a peak PAE of 44.3% under a 50 Ω load impedance condition, and a Psat of +5.2 dBm and a peak PAE of 37.1% under a 25 Ω load impedance condition, respectively. Compared to conventional inverter-based PAs, the proposed design significantly extends impedance coverage, while maintaining an output power exceeding the specific power level, without sacrificing power efficiency using only hardware reconfiguration. [ABSTRACT FROM AUTHOR]

The AlGaN/GaN materials with a wide band gap, high electron mobility, and high breakdown voltage are suitable for manufacturing high-power and high-frequency electronic devices. In this study, metal Schottky contact electrodes of different dimensions are prepared on AlGaN/GaN wafers to fabricate metal–semiconductor–metal (MSM) varactors. Voltage-dependent capacitance and breakdown voltages of the varactors are measured and studied. The corresponding breakdown mechanisms of varactors with different electrode gaps are proposed. Furthermore, an anti-surge application using GaN-based MSM varactors in a signal transmission module is demonstrated, and its surge suppression capability is shown. We believe that our study will be beneficial in developing surge protection circuits for RF applications. [ABSTRACT FROM AUTHOR]

Predicting the electrical breakdown of polymers is critical for certifying the endurance and lifetime of high voltage power equipment. Since various factors contribute nonlinearly to the breakdown phenomena of polymer insulators, it is difficult to assess the impact of each factor independently. In this study, we numerically analyzed the breakdown phenomenon because of the ramp rate of the DC voltage applied to a polymer insulator, low-density polyethylene (LDPE), using the finite element method (FEM). To predict the breakdown initiation, we analyzed the relaxation time of the conduction current through the insulator as a significant indicator. The bipolar charge transport (BCT) model was used to analyze the charge behavior within the LDPE, and the breakdown voltage was predicted by incorporating the molecular displacement model. This analysis was conducted for a wide range of ramp rates from 10 to 1500 V/s. The current density was calculated using two different methods, namely the energy and average methods, and the results were compared with each other. The results of the numerical model were further verified by comparing with those from experiments reported in the literature. [ABSTRACT FROM AUTHOR]

Dielectric breakdown is a significant property for the insulation system in high voltage power equipment. This paper is dedicated to the improvement of dielectric breakdown by surface-functionalized nanoparticles in low-density polyethylene (LDPE). Prior to the preparation of LDPE/TiO2 nanocomposites, the nanoparticles were surface modified by the silane coupling followed by the chemical reaction process. Results of Fourier transform infrared spectroscopy (FTIR) indicated that some polar groups and chemical bonding were introduced on the surface of TiO2 nanoparticles. A reduction of dielectric permittivity was observed at low nanoparticle loading (<2 wt%) samples, which responded to the restriction of the molecular chain in the interface region. High nanoparticle loadings (2 wt%, 5 wt%, 10 wt%) introduced an obvious relaxation polarization. The trap parameters detected by the thermally stimulated current (TSC) method indicated that the deep traps were introduced by small amounts of nanoparticles (≤2 wt%), while more shallow traps occurred in high loading (5 wt%, 10 wt%) samples. Meanwhile, the increase of breakdown strength at low loading samples were closely related to the deep traps, which was ascribed to the interface region by surface chemical modification. [ABSTRACT FROM AUTHOR]

To suppress space charge accumulation and improve direct current (DC) electrical properties of insulation materials, crosslinked polyethylene modified with 2-(4-benzoyl-3-hydroxyphenoxy) ethyl acrylate (XLPE/BHEA) containing polar functional groups was prepared by melt blending. The gel content, thermal elongation, tensile strength, elongation at break, elasticity modulus, differential scanning calorimetry (DSC) and X-ray photoelectron spectra (XPS) measurement results demonstrated that the BHEA could slightly enhance the crosslinking of polyethylene (PE) and affect the mechanical properties and crystallization of XLPE, and the BHEA molecule was not easy to precipitate from XLPE after the crosslinking process. XLPE modified with 3.0 phr (parts per hundreds by weight) BHEA could effectively suppress space charge accumulation, reduce DC conduction and improve DC breakdown strength of XLPE at a higher temperature. Deeper traps were introduced in XLPE/BHEA composites due to the polar functional groups in BHEA, which could raise the potential charge injection barrier and reduce the charge carrier number and mobility to suppress space charge accumulation and reduce the conduction current density. [ABSTRACT FROM AUTHOR]

This paper reports experimental and analytical results of partial discharge degradation of silicone rubber sheets in accordance with proposed procedures. Considering the actual usage condition of silicone rubber as an insulating material of polymer insulators, an experimental procedure is established to evaluate long-term surface erosion caused only by partial discharge. Silicone rubber is subjected to partial discharge for 8 h using an electrode system with air gap. Voltage application is stopped for subsequent 16 h for recovery of hydrophobicity. The 24 h cycle is repeated 50 or 100 times. Deterioration of sample surface is evaluated in terms of contact angle and surface roughness. It is confirmed the proposed experimental procedure has advantage of no arc discharge occurrence, good repeatability of results, and possible acceleration of erosion. Surface erosion of silicone rubber progresses gradually and finally breakdown of silicone rubber occurs. Alumina trihydrate (ATH), an additive to avoid tracking and erosion by discharge, is not necessarily effective to prevent breakdown caused by partial discharge when localized electric field in air is enhanced by adding ATH. In such a situation, lower permittivity and higher resistance of silicone rubber seem dominant factors to prevent partial discharge breakdown and a careful insulation design should be required. [ABSTRACT FROM AUTHOR]

The insulation of mineral oil-based nanofluids was found to vary with different concentration level of nanoparticles. However, the mechanisms behind this research finding are not well studied. In this paper, mineral oil-based nanofluids were prepared by suspending TiO2 nanoparticles with weight percentages ranging from 0.0057% to 0.0681%. The breakdown voltage and chop time of nanofluids were observed under standard lightning impulse waveform. The experimental results show that the presence of TiO2 nanoparticles increases the breakdown voltage of mineral oil under positive polarity. The enhancement of breakdown strength tends to saturate when the concentration of nanoparticle exceeds 0.0227 wt%. Electronic traps formed at the interfacial region of nanoparticles, which could capture fast electrons in bulk oil and reduce the net density of space charge in front of prebreakdown streamers, are responsible for the breakdown strength enhancement. When the particle concentration level is higher, the overlap of Gouy–Chapman diffusion layers results in the saturation of trap density in nanofluids. Consequently, the breakdown strength of nanofluids is saturated. Under negative polarity, the electrons are likely to be scattered by the nanoparticles on the way towards the anode, resulting in enhanced electric fields near the streamer tip and the decrement of breakdown voltage. [ABSTRACT FROM AUTHOR]

With the wide application of pulse width modulation (PWM) technology in motor driving, the bearing current problem has become more and more severe. The most complicated problem in analyzing bearing currents is modeling the equivalent circuit of the bearing and determination of the equivalent parameters of the model. During the process of bearing current breakdown, the bearing undergoes a transition from the capacitor state to the resistor state. The previously used equivalent model, which only consists of a capacitor parallel with a constant resistor, cannot reveal the real breakdown process. In this paper, an improved equivalent bearing model is derived from the waveform analysis of the experiment. The variable breakdown resistance model of the bearing is put forward and the calculation method of the breakdown resistance is given. The circuit simulation results from the variable resistance bearing model were much closer to the results of the experiment than those from the constant resistance model. [ABSTRACT FROM AUTHOR]

Researches of the theories and application of polymer composites with nonlinear conductivity are useful for dealing with the nonuniform electrical fields widely existing in the cable accessory insulation. In the present work, we fabricated CCTO (CaCu3Ti4O12)/EPDM (Ethylene Propylene Diene Monomer) composites and investigated their breakdown strength, dielectric and nonlinear conductivity properties in detail; the microstructures of fillers and composites were characterized by scanning electron microscopy (SEM) and X-ray diffraction. CCTO particles are uniformly dispersed in CCTO/EPDM composites, and the composites showed nonlinear conductivity with electric field changes. When the CCTO particle content is low, the conductivity of CCTO/EPDM composites does not present obvious nonlinearity. However, when CCTO content exceeds 2 vol %, the conductivity experiences a nonlinear change with increasing electric field strength and the threshold field (Eth) of nonlinear conductivity declines with the increase of CCTO contents. In addition, it can be found from experiment and simulation results that 8 vol % CCTO/EPDM exhibit significant nonlinear conductivity and dielectric properties as expected, and homogenizing the electrical field much more effectively. Therefore, this paper offers a preliminary discussion about the variation trend of nonlinear conductivity CCTO/EDPM composites, providing an effective reference to solve the application of nonlinear conductivity materials for cable accessories. [ABSTRACT FROM AUTHOR]

Polypropylene has been used in radio-frequency capacitors and has also started to be employed in cables as insulation. The objective of this study was to evaluate the electrical properties of polypropylene filled with natural clay as a nano-material. Polypropylene samples having 0%, 2% and 6% natural clay by weight were exposed to 60-Hz sinusoidal voltages at two different rates of rise. The breakdown voltage of each sample was recorded at these different ramp rates. Also, the Root-mean-squared (rms) current was measured as the voltage was increased across the test samples. The important findings of this study were (a) the breakdown strength of the natural nanoclay-filled polypropylene was higher than the unfilled polypropylene, and the optimum concentration of nanoclay appeared to be 2% by weight; (b) the current density as a function of the electric-field intensity indicated a non-linear behavior with saturation, and the saturation onset took place at a higher electric-field intensity in nanoclay-filled polypropylene, wherein 2% nanoclay seemed to be the optimum concentration as well for the onset electric field of saturation. [ABSTRACT FROM AUTHOR]

Endometrial cells perceive and respond to their microenvironment forming the basis of endometrial homeostasis. Errors in endometrial cell signaling are responsible for a wide spectrum of endometrial pathologies ranging from infertility to cancer. Intensive research over the years has been decoding the sophisticated molecular means by which endometrial cells communicate to each other and with the embryo. The objective of this review is to provide the scientific community with the first overview of key endometrial cell signaling pathways operating throughout the menstrual cycle. On this basis, a comprehensive and critical assessment of the literature was performed to provide the tools for the authorship of this narrative review summarizing the pivotal components and signaling cascades operating during seven endometrial cell fate "routes": proliferation, decidualization, implantation, migration, breakdown, regeneration, and angiogenesis. Albeit schematically presented as separate transit routes in a subway network and narrated in a distinct fashion, the majority of the time these routes overlap or occur simultaneously within endometrial cells. This review facilitates identification of novel trajectories of research in endometrial cellular communication and signaling. The meticulous study of endometrial signaling pathways potentiates both the discovery of novel therapeutic targets to tackle disease and vanguard fertility approaches. [ABSTRACT FROM AUTHOR]

Cellulose insulation polymer is an important component of oil-paper insulation, which is widely used in power transformer. The weight of the cellulose insulation polymer materials is as high as tens of tons in the larger converter transformer. Excellent performance of oil-paper insulation is very important for ensuring the safe operation of larger converter transformer. An effective way to improve the insulation and the physicochemical property of the oil impregnated insulation pressboard/paper is currently a popular research topic. In this paper, the polytetrafluoroethylene (PTFE) functional film was coated on the cellulose insulation pressboard by radio frequency (RF) magnetron sputtering to improve its breakdown voltage and the hydrophobicity properties. X-ray photoelectron spectroscopy (XPS) results show that the nano-structure PTFE functional film was successfully fabricated on the cellulose insulation pressboard surface. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) present that the nanoscale size PTFE particles were attached to the pressboard surface and it exists in the amorphous form. Atomic force microscopy (AFM) shows that the sputtered pressboard surface is still rough. The rough PTFE functional film and the reduction of the hydrophilic hydroxyl of the surface due to the shielding effect of PTFE improve the breakdown and the hydrophobicity properties of the cellulose insulation pressboard obviously. This paper provides an innovative way to improve the performance of the cellulose insulation polymer. [ABSTRACT FROM AUTHOR]

This article presents the results of the studies on negative streamer propagation in a point-to-sphere electrode system with a pressboard barrier placed between them. The proposed electrode system gave the opportunity to assess the influence of the insulating barrier on streamer development in the conditions close to the actual transformer insulating system where the liquid gap is typically divided in parts by using pressboard barriers. The studies were performed for five commercial dielectric liquids. Among them two were biodegradable synthetic esters and two were biodegradable natural esters. Mineral oil, as the fifth liquid, was used for comparison. The measurements were based on electrical and optical experimental techniques. From the results obtained it may be concluded that, independently of the liquids tested, the electrical strength of the insulating system considered was increased by about 50%. In the case of streamer development assessed using photomultiplier-based light registration it is not possible to indicate clearly which of the liquids tested is better under the conditions of the experiment. In all cases streamers always developed slowly (2nd mode) at all voltage levels applied during the studies. In turn, the intensity of the discharge processes, comparing the same voltage levels, was mostly higher when streamers developed in ester liquids, however, the differences noticed were minimal. [ABSTRACT FROM AUTHOR]