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As the unique power-discharging channel for high-speed trains, the ‘train-rail’ mobile coupling grounding system plays a vital role in sending the traction power back to the terrestrial substations, through the electrical contact between the rotating wheel and the steel rail. The whole system is composed of two kinds of grounding modes: working grounding is in charge of draining the traction power into the rail track; the protective grounding provides the reference grounding potential for the vehicle-mounted equipment. Different from the fixed terrestrial grounding technique normally implemented in power system, when the relative motion occurs between the train and the rail, both the ‘catenary-to-train’ and ‘train-to-ground’ impedances vary transiently, which may lead to the current flowing through each grounding wheel varying unpredictably. Herein, the ‘catenary-train-rail’ mobile coupling grounding model was built based on the equivalent circuit modeling technique for evaluating the transiently-varying tendency of the grounding impedances and currents flowing through each grounding wheel. To cope with different operational conditions, the adjustable grounding impedance methodology is firstly proposed for adapting the unpredictable variation of the grounding impedance, when the relative motion occurs between the train and the rail. Ultimately, the validity of the novel grounding system applying the adjustable grounding impedance technology is verified under different operational conditions, with the consideration of both TB current and voltage.

Background: This paper proposes a defect identification method for vehicle-mounted cable terminals in electric multiple units (EMUs) based on the improved Graham angle field and residual network to address the issue of low recognition accuracy caused by the lack of partial discharge (PD) and identification data for Ethylene Propylene Rubber (EPR) cable terminal defects. Methods: The improved Gramian angular field (IGAF) characteristic transformation method was used to transform the PD one-dimensional time-series signal into a two-dimensional one after cable terminals with four common insulation defects were constructed, and a PD detection platform was built. Finally, an anti-aliasing downsampling module and attention mechanism were added to the residual network ResNet101 model. The Center loss and Softmax loss functions were integrated to increase accuracy for training and recognition classification. Topological feature images improved the distinguishability of defect categories. Results: The test results showed that the diagnostic method has an accuracy rate of 97.3% for identifying PD at the cable terminal. Conclusion: The proposed diagnosis model has higher recognition accuracy and better balance than other conventional fault diagnosis methods, making it suitable for diagnosing high-voltage cable faults in EMU trains.

As a unique reflux path for trains, the ‘train-rail’ mobile grounding system has the double functions – the traction power feedback and the transmission of train's communication signal. With the constant increment of operational velocity and traction power for high-speed railway, the coupling relationship existing in the ‘train-rail’ mobile coupling grounding system becomes complicated, when the train's wheels roll over the insulated joint. It may result in the frequent occurrence of rolling arc and the ablation of rail ends and insulated joints, which might lead to the series connection of the rail circuit or even trigger the misjudgment of operational control system. As the impedances existing in the grounding system vary transiently when the relative distance between the train and the fixed terrestrial grounding installations changes, the dynamic coupling mechanism between the transiently-varying topology of reflux path and the distribution of reflux at each grounding wheel tends to be analyzed. Depending on the built ‘catenary-train-rail’ dynamic coupling grounding reflux model, the correlation between the ‘train-rail’ mobile grounding reflux and the evolutionary process of rolling arc is explored. In order to reduce the risk of ‘wheel-rail’ arcing phenomenon, a novel method of automatically controlling insulated joint is proposed herein, as its feasibility is verified via the comparison with the original type of the insulated joint.

So far, silicone rubber (SiR) insulators are widely used in the power industry all over the world, due to their outstanding insulation properties and high reliability. In practice, some of the insulators are applied in remote places with harsh environmental conditions such as high altitude, high temperature, high humidity, etc. Herein, the currently existing aging mechanisms are investigated, and some novel insights into these testing and evaluation methods are proposed. Via the investigation, it was found that thermal oxygen aging tends to occur when insulators are exposed to an environment surrounded by hot air. To analyze the different aging mechanisms of SiR insulator sheds, four types of aging testing and evaluation methods are systematically summarized based on the surface’s structural, chemical, optical, and electrical properties. The conclusion is that nondestructive and noncontact methods, such as hyperspectral imaging (HSI), along with the multisource information fusion methods, are becoming increasingly popular in the assessment of SiR insulator sheds aging. These research efforts provide assurance for reducing the incidence of pollution flashover accidents in power transmission lines and ensuring the safe and stable operation of power transmission and transformation equipment.

ABSTRACTDue to the constant pursuit for higher operating velocity, the traction power capacity for high-speed trains needs to be enlarged. When the train passes approach the insulating sections set between the two neighbouring contact lines carrying the traction current with different phases, the vehicle-mounted vacuumed circuit breaker (VCB) needs to be switched off. Generally, the arc may generate when connecting or separating the contacts, when switching on or off the VCB. In order to investigate the characteristics of the reignition overvoltage the ‘train-rail-catenary’ traction power supply model considering the reignition process between the VCB’s contacts is launched in this paper. The impact of the dielectric strength recovery rate between the contacts of the VCB on the number of reignition and the amplitude of the reignition overvoltage is analysed based on the experimental and simulation results. Ultimately, the corresponding restraining measures are proposed for suppressing the reignition overvoltage.

The mobile distributed grounding system plays an irreplaceable role in discharging power for intercity trains, including two types of grounding settings (GSs): the working GS provides the pathway for discharging the traction current; the protective GS provides the reference grounding potential for the vehicle-mounted equipment. As both working and protective GSs share the rail as the common current-releasing pathway, the traction current released by working GSs might return the carriage through the adjacent protective GSs, forming as the train body (TB) current which threatens the vehicle-mounted electrical equipment. Herein, an equivalent circuit of the mobile distributed grounding system is built to analyze the TB current. For evaluating the influence brought by TB current on the vehicle-mounted equipment, a 3D finite element (FEM) geometry is launched, meanwhile the comparison of the multi-physical distributions is undertaken when applying different grounding layouts, with the emphasis of the highlighted region containing critical devices.

As the research on deep learning methods gradually progresses, more and more classification models are applied in the classification of hyperspectral image (HSI). High-dimensional and low-resolution characteristics of HSI, however, make it difficult for conventional models to process its data effectively. In this article, a novel HSI classification model, namely, spatial–spectral pyramid network (SSPN), is designed by combining a 3-D convolutional neural network (3D CNN) with feature pyramid structure. SSPN taking advantage of 3-D convolution coupled with multiscale convolutional extraction is used to obtain a large set of diverse spatial–spectral features. Multiscale interfusion is also applied in SSPN to enrich the features contained in a single feature map and to improve the sensitivity on HSI spatial–spectral information, allowing it to better learn spatial–spectral features. Moreover, the losses of each combination based on multiscale interfusion are calculated via weighted average, which enables SSPN to avoid the excessive influence of single combination in the updating of model parameters. Four HSI public datasets and several comparison models are employed to validate the classification effect of SSPN. Experimental results show that SSPN achieves the highest overall accuracy (OA) in all datasets compared with other classification models, with 100%, 98.8%, 99.8%, and 98.7% on the datasets of Chikusei, Pavia University, Botswana, and Houston 2013, respectively. SSPN is demonstrated to possess higher classification accuracy and better generalization performance on HSI.

Pollution flashover of insulators has been viewed as a common issue existing in the area of power systems for a long term. However, traditional detection methods such as equivalent salt density and leakage current (LC) can hardly satisfy the requirements of the progressing smart grid. Herein, a novel highly-efficient method is proposed for classifying the pollution degree detection of insulators based on hyperspectral technology. The insulating sheets and actual insulators were set as the research object and their hyperspectral images are obtained. Moreover, the data for describing the characteristic wavelengths and the G color components of the samples were extracted from the images as the characterization of the equivalent salt deposit density (ESDD) and nonsoluble deposit density (NSDD) respectively. The ESDD and NSDD detection model is established based on the multiple linear regression (MLR) algorithm and the random forest (RF) algorithm. Ultimately, the proposed model reaches a detection accuracy of above 84% on the insulating sheets and 75% on the actual insulators, which can be viewed as acceptable. The hyperspectral imaging technique has considerable potential for the non-contact detection of ESDD and NSDD.

As the unique power entrance, the pantograph–catenary electrical contact system maintains the efficiency and reliability of power transmission for the high-speed train. Along with the fast development of high-speed railways all over the world, some commercialized lines are built for covering the remote places under harsh environment, especially in China; these environmental elements including wind, sand, rain, thunder, ice and snow need to be considered during the design of the pantograph–catenary system. The pantograph–catenary system includes the pantograph, the contact wire and the interface—pantograph slide. As the key component, this pantograph slide plays a critical role in reliable power transmission under dynamic condition. The fundamental material characteristics of the pantograph slide and contact wire such as electrical conductivity, impact resistance, wear resistance, etc., directly determine the sliding electrical contact performance of the pantograph–catenary system; meanwhile, different detection methods of the pantograph–catenary system are crucial for the reliability of service and maintenance. In addition, the challenges brought from extreme operational conditions are discussed, taking the Sichuan–Tibet Railway currently under construction as a special example with the high-altitude climate. The outlook for developing the ultra-high-speed train equipped with the novel pantograph–catenary system which can address the harsher operational environment is also involved. This paper has provided a comprehensive review of the high-speed railway pantograph–catenary systems, including its progress, challenges, outlooks in the history and future.

Along with the operating velocity and traction power increasing continuously, the issue related to the safety and reliability of the high-voltage traction power system for high-speed trains have gradually been exposed during the practical service process. When the train passes a neutral section settled roughly per 15 km between two neighboring substations, the on-board vacuum circuit breaker (VCB) must to be operated for changing the input powers with different phases. At the moment of switching on or off the VCB, the arc between the contacts in the arc-extinguishing chamber may be triggered, which tends to result in the operational overvoltage. Due to numerous inductances and capacitances existing in the traction power supply system, the overvoltage may lead to high-frequency electromagnetic oscillation spreading along the transmission routes. The on-board high-voltage equipments within the power supply system may suffer from the impulse brought from the VCB operational overvoltage frequently, which is possible to cause the insulation aging or breakdown issue. To investigate the characteristic of the operational overvoltage of VCBs, a ‘train-rail-catenary’ power supply model is built based on the measured impedance parameters, which has been verified by the experimental tests. The generating mechanism with the influence factors of the operational overvoltage when switching on or off the VCB has been explored, meanwhile the distribution of the train body overvoltage on each carriage has also been presented.

Previous research has suggested that individuals with different blood groups show varied incidences of noise-induced hearing loss. The reduced otoacoustic emissions amplitudes indicate the higher possibilities of outer hair cell damage for noise exposure.

Optical imaging of stained pathological slices has become the gold standard for disease diagnosis. However, the procedure of sample preparation is complex and time-consuming. Multiphoton microscopy (MPM) is promising for label-free imaging, but the imaging speed is limited, especially for whole slice imaging. Here we propose a high-speed, multi-modal, label-free MPM by Bessel scan-based strip mosaicking. With a Bessel beam for excitation, the extended depth-of-focus not only enables full axial information acquisition at once, but also alleviates the demanding requirement of sample alignment. With the strip mosaicking protocol, we can save the time of frequent sample transferring. Besides, we add a closely-attached reflection mirror under the sample for enhancing epi-detection signals, and employ circularly polarized beams for recording comprehensive information. We demonstrate its application in multi-modal, label-free imaging of human gastric cancer slices and liver cancer slices, and show its potential in rapid disease diagnosis.

To estimate the peening effects of different peening media by the same measuring parameters expediently, this paper focuses on the dynamic effects of different peening media with equal initial kinetic energy on the response of the target material. The expanding cavity model is developed to reveal the evolutions of effective strain rate, average contact pressure, peening media velocity, dimple size and plastic region size. Finite element simulations of impacting target by different peening media are performed. Shot peening and indenter impacting experiments are carried out to verify the calculated and simulated results. The comparison shows a good agreement among the calculated, simulated and experimentally measured data. It is found that the change of impacting velocity under the same kinetic energy has little influence on the residual stresses. The peening effects of different media that have the same indenting head size can be estimated by the kinetic energy.

ABSTRACTTo estimate the peening effects of different peening media by the same measuring parameters expediently, this paper focuses on the dynamic effects of different peening media with equal initial kinetic energy on the response of the target material. The expanding cavity model is developed to reveal the evolutions of effective strain rate, average contact pressure, peening media velocity, dimple size and plastic region size. Finite element simulations of impacting target by different peening media are performed. Shot peening and indenter impacting experiments are carried out to verify the calculated and simulated results. The comparison shows a good agreement among the calculated, simulated and experimentally measured data. It is found that the change of impacting velocity under the same kinetic energy has little influence on the residual stresses. The peening effects of different media that have the same indenting head size can be estimated by the kinetic energy.

To simulate the deformations of the strip peen formed plate more realistic, and using low computational resources, a strategy combining analytical and finite element methods is proposed in this article. First, the internal stresses in the target induced by single shot impact are calculated with expanding cavity model. Second, the stress field of single shot impact is used to derive the stress field of multiple shot impacts by considering the overlaps of adjacent shot impacts. Third, the calculated stress field is introduced to the finite element model to obtain the resultant shape of the plate. The shot dimple distribution in reality is detected and fitted with normal distribution function. The random distribution of the positions of shot impacts is involved in the simulation to make the simulation more realistic. In the finite element model, the plate is modeled with shell element to reduce the demand of the computational resources. The simulated shapes of the plate under different peen forming parameters are compared with the scanned three-dimensional experimental shapes with the same forming parameters. The comparison shows that the simulated shapes are in good agreement with the experiments.

Lithium-ion battery State of Health (SOH) estimation is an essential issue in battery management systems. In order to better estimate battery SOH, Extreme Learning Machine (ELM) is used to establish a model to estimate lithium-ion battery SOH. The Swarm Optimization algorithm (PSO) is used to automatically adjust and optimize the parameters of ELM to improve estimation accuracy. Firstly, collect cyclic aging data of the battery and extract five characteristic quantities related to battery capacity from the battery charging curve and increment capacity curve. Use Grey Relation Analysis (GRA) method to analyze the correlation between battery capacity and five characteristic quantities. Then, an ELM is used to build the capacity estimation model of the lithium-ion battery based on five characteristics, and a PSO is introduced to optimize the parameters of the capacity estimation model. The proposed method is validated by the degradation experiment of the lithium-ion battery under different conditions. The results show that the battery capacity estimation model based on ELM and PSO has better accuracy and stability in capacity estimation, and the average absolute percentage error is less than 1%.

•Whole stress field of single impact is obtained by developing the cavity model.•Strain hardening response of material is considered to determine impact effects.•Average stresses with general peening coverage are analytically obtained.•Analytical results are verified by finite element simulations and experiments.

In recent years, the speed and the current transmission density of high-speed railways are increased. As a result, the rate of the occurrence of pantograph–catenary arc also increases, which directly influences the service performance of the pantograph–catenary system. The detection and identification of the pantograph–catenary arc is of great significance for evaluating the off-line level to ensure the safe operation of the pantograph–catenary system. The currently used conventional optical arc detection method would be distorted by strong sunlight or other environmental lights in the actual operation, which would affect the accuracy of detection. On the contrary, the arc sound signal is not affected by the diurnal variation and can be easily obtained; it can also be distinguished well from other interfering sounds. In this paper, a new method that uses the arc sound is proposed to realize the effective detection of the pantograph–catenary arc. The frequency spectrum and the intensity characteristics of the pantograph–catenary arc sound are analyzed. The results show that the frequency band of the arc sound signal is wide and mainly gets distributed at 5–17 kHz. The curve of the sound waveform is drawn by calculating the short-time average energy, which is used to obtain the arc’s starting time, duration, and intensity, for calculating the off-line rate.

The mechanical behaviors of composite assembly structures of aircraft might change due to filling the fit-up gap between two components with liquid shim or laminated shim. In order to investigate the change qualitatively and quantitatively, a kind of implicit nonlinear finite element models are developed, and mixed failure criteria considering the nonlinear shear relationship between composite matrix and fiber, out-of-plane stresses, and buckling of fiber are incorporated into finite element models. And tensile experimental research is also performed to validate the finite element models. Good agreement between the numerical and experimental results builds confidence that the finite element models are effective in predicting the shimming effect. And it is also observed that the mechanical behaviors of composite assembly structures with different filling present obvious differences.

Lithium-ion battery (LIB) capacity degradation prediction plays an important role in the prediction of battery health degradation. Accurate prediction of its capacity can guide battery replacement and maintenance, and ensure the safety and stability of the energy storage system. In this paper, a hybrid method based on artificial bee colony (ABC) algorithm and multi-kernel support vector regression (MK-SVR) is proposed to predict the capacity degradation of LIB. Firstly, the capacity degradation prediction model of LIB is established by MK-SVR with few hyperparameters. Then, the hyperparameters of degradation prediction model are optimized by the ABC to improve the accuracy of prediction. Finally, the proposed method is verified by NASA's LIB degradation experiment. Compared with different optimization algorithms, ABC greatly improves the accuracy of capacity degradation prediction. Compared with traditional forecasting methods, the proposed method can predict the capacity degradation of LIB more accurately.

Pantograph arcing is an unavoidable phenomenon in electrified railways, which not only causes damage to the carbon strip and the catenary contact line but also results in voltage surge and electromagnetic interference. In recent years, there are more cases of pantograph arcing due to the increase in speed of trains. Therefore, it is essential to understand the basic electrical characteristics of pantograph arcing at different running speeds of trains. In this work, a pantograph arcing model was proposed, which considers the effects of the speed of a train on the arc-dissipated power. An overall electrical model, concerning the traction power system and the traction drive system, was further established. The results indicated that the running speed of trains significantly influenced the arcing voltage, duration of arcing, and the zero-crossing time. A qualitative relation between the average power of the arc and the speed of the train was also presented. Finally, field tests were carried out, and comparisons between the field testing data and the calculated results were made, which validate the accuracy of the developed model.

In order to access sensitive documents shared over government, army and enterprise intranets, users rely on an indexing facility where they can quickly locate relevant documents they are allowed to access: 1) without leaking information about the remaining documents; 2) with a balanced load on the index servers. To address this problem, we propose Mimir, a distributed cipher retrieval system for sensitive documents. Mimir constructs the distributed indexes based on load balanced term distribution for better search efficiency and load balanced query. Mimir utilises encryption with random key, partial key update to protect sensitive data and improve query efficiency. Our experiments show that Mimir can effectively protect secret data and answer queries nearly as fast as an ordinary inverted index.

A good contact between the pantograph and catenary is critically important for the working reliability of electric trains, while the basic understanding on the electrical contact evolution during the pantograph–catenary system working is still ambiguous so far. In this paper, the evolution of electric contact was studied in respects of the contact resistance, temperature rise, and microstructure variation, based on a home-made pantograph–catenary simulation system. Pure carbon strips and copper alloy contact wires were used, and the experimental electrical current, sliding speed, and normal force were set as 80 A, 30 km/h, and 80 N, respectively. The contact resistance presented a fluctuation without obvious regularity, concentrating in the region of 25 and 50 mΩ. Temperature rise of the contact point experienced a fast increase at the first several minutes and finally reached a steady state. The surface damage of carbon trips in microstructure analysis revealed a complicated interaction of the sliding friction, joule heating, and arc erosion.

The interfacial interaction between the carbonized matrix and binder directly correlates with the performance of the carbon-matrix composites. The involvement of the reduced graphene oxide (rGO) in composites is considered an effective strategy to enhance the performance of composites via improving the interface property. Herein, the rGO was converted in-situ from the graphene oxide (GO) on the interface between the matrix and the carbonized binder during the sintering process. Compared with the pristine composites, the compressive strength (203.90 MPa ±2.85 MPa) and flexural strength (40.53 ± 1.42 MPa) of carbon-matrix composites doping 0.2 wt% of GO can be increased by 112.1% and 71.2%, respectively. It is attributed to the fact that rGO forms an ideal interface bond with the carbonized matrix and binder, which effectively promotes the deflection of the crack propagation path. Meanwhile, molecular dynamics simulations unlocked an automatic protective reinforcement mechanism of the rGO-enhanced composites. A low-cost yet effective scheme for improving composites interfaces is proposed here, which lays a theoretical foundation for developing the high-strength carbon-matrix composites.

The poor interfacial interaction between carbon fiber (CF) and a matrix is the main factor restricting the enhancement in performance of carbon-matrix composites. Herein, CF was modified via a facile high-speed blending with matrix pitch-cokes particles. AFM force measurements and 3D particle tracking simulations unlocked the blending CF@pitch-cokes assembly mechanism. Inspired by the strong interaction between tree roots and soil, a tree-root-like reinforced structure was designed and developed in carbon-matrix composites by the subsequent carbonization coupling effect between the pitch-cokes adsorbed CF surface and the carbonized matrix. It was found that the tree-root-like structure significantly improved the interfacial interaction and enhanced the mechanical properties of the carbon-matrix composites. Compared with the pristine CF reinforced composites, the compressive strength (158.33 ± 1.95 MPa) and flexural strength (36.65 ± 1.32 MPa) of the carbon-matrix composites with tree-root-like structures increased by 101.4% and 65.8%, respectively. A mechanical interlock mechanism is suggested to explain the enhanced mechanical properties of the composites. This work provides a facile strategy for improving the interface of CF-reinforced carbon-matrix composites and paves the way for scalable, low-cost, and environment-friendly processing of high strength composites.

Photovoltaic responses were observed upon irradiating (>420 nm) an ITO electrode spin-coated with a mixture of TiO2 nanoparticles, polyvinylcarbazole, and carotenoid (canthaxanthin or β-carotene, Car) and immersed in an aqueous KCl solution also containing hydroquinone (QH2). The anodic photocurrent involves electron transfer from the excited state of the carotenoid (Car*) to the TiO2 conduction band; the resulting carotenoid radical cation (Car&z.rad;+) is reduced by QH2. The photocurrent was nearly constant during one hour of continuous irradiation, which indicates that these carotenoids are stable at the electrode/electrolyte interface, presumably because of rapid regeneration of Car from Car&z.rad;+ during the electron transfer cycle. In contrast, when the aqueous electrolyte solution was saturated with O2, a cathodic photocurrent was observed; this reversal of polarity is attributed to electron transfer from Car* to O2, and subsequent reduction of the resulting Car&z.rad;+ by electrons from the TiO2 conduction band.

Bulk electrolysis and chemical oxidation with FeCl₃ of all-trans canthaxanthin (I) and 8'-apo-β-caroten-8'-al (II) gave primarily the 9- and 13-cis-isomers, which were separated by HPLC and identified by 1H NMR spectroscopy. Optical absorption measurements showed that the 15-cis, 9,13-di-cis isomers of I are also formed by these methods. In the case of the unsymmetrical compound II, additional isomers were formed. The cis isomers account for about 40–60% of products formed. Formation of the isomers is believed to occur by rotation about certain bonds in the cation radicals or dications, which are formed in the oxidation processes. The neutral cis species are then formed by an electron exchange reaction of the cis-cation radicals with neutral all-trans carotenoids in solution. The electrochemical and iron(III) chloride oxidation induced isomerization are shown to be efficient and improved methods for forming selected carotenoid isomers.