Search

Online job advertisements on various job portals or websites have become the most popular way for people to find potential career opportunities nowadays. However, the majority of these job sites are limited to offering fundamental filters such as job titles, keywords, and compensation ranges. This often poses a challenge for job seekers in efficiently identifying relevant job advertisements that align with their unique skill sets amidst a vast sea of listings. Thus, we propose well-coordinated visualizations to provide job seekers with three levels of details of job information: a skill-job overview visualizes skill sets, employment posts as well as relationships between them with a hierarchical visualization design; a post exploration view leverages an augmented radar-chart glyph to represent job posts and further facilitates users’ swift comprehension of the pertinent skills necessitated by respective positions; a post detail view lists the specifics of selected job posts for profound analysis and comparison. By using a real-world recruitment advertisement dataset collected from 51Job, one of the largest job websites in China, we conducted two case studies and user interviews to evaluate JobViz. The results demonstrated the usefulness and effectiveness of our approach.

Use of nonlinear conductive SiC/silicone rubber (SR) field grading material (FGM) can improve the local field concentration of composite insulators. Adding large volume fraction and large-size SiC particles (SiCp) into SR can obtain a good field grading effect, but it is accompanied by the deterioration of mechanical properties. Compounding SiC with different shapes can solve this contradiction. By incorporating one-dimensional SiC whiskers (SiCw) to synergize with granular SiCp, SiC/SR FGM with better field-dependent conductivity, mechanical properties and thermal conductivity than large-size SiCp and large volume fraction filling case can be obtained by using smaller size SiCp and lower filling contents. The simulations of 500 k V line insulators show that the modified SiC/SR FGM can reduce the maximum field strength along the insulator surface and at sheath-core rod interfaces by 55% and 71.4%, respectively. The combined application of FGM and grading ring can achieve a complementary effect. Using FGM to partially replace the role of the grading rings, the field strength indicators can still meet the operational requirements after the tube radius and shielding depth of the grading rings at both ends are reduced by 36.2% and 40% separately, which is a benefit to alleviating the problems of high weight and large volume faced by traditional field grading methods.

Abstract Electroluminescent composites have considerable potential for applications in photoelectric display, electric field measurement and other fields due to their advantages of simple preparation and uniform luminescence. However, high voltage required by the operation of electroluminescent composites hinders their applications in the electric domain, and research on the relationship between electroluminescence principle of composites and filler intrinsic attributes is insufficient. In this paper, the effects of electric field strength, filler mass fraction and voltage frequency on the electroluminescence intensity of ZnS:Cu/epoxy composites are studied, which are majorly used as the luminescent layer of electroluminescent devices. To enhance the electroluminescence intensity of composites, high‐temperature sintered BaTiO3 and zinc oxide whiskers (ZnOw) particles are introduced in the base matrix. The finite element method is applied to verify that the matrix of high dielectric constant is in favour of improving the electroluminescence intensity of composites. The band structure of the ZnS:Cu particle is calculated based on the density functional theory + U method to analyse the intrinsic relationship between electroluminescence and particle electronic structure. This paper provides a basis for the research of high electroluminescence intensity devices and will be conducive to better understanding on the relationship between electroluminescence principle and filler intrinsic attributes.

To enhance the energy and gas supply security and reduce the greenhouse gas emission simultaneously, this paper presents a new cryogen-based co-production concept of combined cooling, heating, power and oxygen (CCHPO) for hospital buildings. By integrating with local photovoltaic power generation, two cryogenic liquids of liquefied methane and liquefied oxygen are used to store and produce multiple energies and medical gas. Detailed system modeling and performance analysis are carried out regarding the actual energy and gas consumption data from hospital buildings. The results obtained show the proposed CCHPO solution can be expected to fulfill the simultaneous requirements of energy conservation during normal operation and sustainable energy and gas supply during emergency operations.

Over time, high-temperature superconductor (HTS)-coated conductors (CCs) have proven to be promising candidates for future high-efficiency and high-power density electrical machines. However, their commercialization is handicapped due to the AC dissipative loss that occurs upon exposure to external magnetic fields. In rotating electromagnetic devices, the external magnetic field is a combination of alternating and rotating magnetic fields. Most of the research is devoted to the effect of exposure of the superconductors to alternating magnetic fields only. This article presents an investigation to observe the behavior of HTSCCs under rotating magnetic fields, particularly the AC loss, using a finite-element-based homogeneous H-formulation technique. Our investigation shows that the AC loss could be considerably high when HTSCCs are exposed to rotating magnetic fields and, ultimately, could affect the cooling efficiency of future high-efficiency and high-power density electrical machines.

Abstract To break through the bottlenecks of the loss and size of conventional conductors and magnetic materials, replacing copper inductors by zero‐resistance superconducting inductors can be a promising solution. The experimental, theoretical and numerical investigations into the loss characteristics of an air‐core superconducting inductor have been carried out. All these results show that the loss from a superconducting inductor in the boost chopper circuit was reduced remarkably up to 373 times smaller than the loss from the magnetic‐core copper inductor having the same conditions. Moreover, the actual volume and weight of the superconducting inductor are only 5.61% and 10.97% of those of the copper inductor having the same inductance and current capacities. Advanced numerical models have been built to verify the experiments that their results of superconducting losses as well as the current and frequency dependencies are well matched. A compact, low‐loss and low‐cost cryostat has been designed to accommodate the superconducting inductor, which can further improve the practicability for superconducting inductor to be equipped into various power electronic applications. The superconducting inductor can lead power electronic devices towards ultra‐high‐efficiency power conversion.

Abstract Hybrid ships have recently garnered increasing attention as a promising solution for energy shortages and environmental pollution. However, changes in the navigation environment can greatly affect the energy efficiency of these vessels. Therefore, improving the energy efficiency of hybrid ships continues to be a key issue. Our study examined the energy efficiency of a diesel‐electric series hybrid ship operating on an inland river, and a method to optimise series hybrid ship energy efficiency was proposed. The energy consumption model, power demand model, and decision function with minimum fuel consumption as the evaluation criteria were established according to the ship's characteristics and hybrid system. By analysing the data collected from an actual ship, the operating conditions of the navigation environment were identified using the k‐means algorithm, and the total distance travelled by the ship was divided into several sub‐trajectories. Afterwards, the optimised speed of the ship and the optimised output power of each power source were determined using the grasshopper optimization algorithm. The ship's energy efficiency levels before and after using the energy efficiency enhancement method were compared and analysed, and the effects of this optimization method on the ship's energy efficiency in several typical voyages were analysed. Our findings demonstrated that this optimization method can distribute the output of the power source in a better way, thereby optimising the speed of the vessel and maintaining stable sailing. More importantly, the proposed method can reduce fuel consumption by 17.04%.

Abstract Persistent severe smog and dust weather exists in many regions of China. Particles accumulate on the surface of high‐voltage transmission lines, which affects the surface morphology of the transmission line and induces corona discharge. This work mainly studies the influence of electric field and photocatalysis on the corona characteristics of transmission lines. In this work, plasma spraying is used to prepare a dense, smooth and excellent photocatalytic TiO2 coating on the surface of transmission wires. An electron microscope and a white light interference profilometer is used to study the surface condition of the samples. The variation in the surface condition of the samples is observed under different fouling, light time and electric field intensity. The corona characteristics of power transmission lines under different surface conditions are studied. The results show that light and applied electric field promote the photocatalytic effect of TiO2, which helps to decompose the contamination on the surface of power transmission wires and thus reduce the corona discharge of transmission lines. The increase in corona inception voltage reduces the corona current pulse repetition rate and the ion current density during corona discharge.

This work investigates the corona inception voltage and the motion of space charge near a rod-plane electrode under combined DC-AC voltages. For a high AC component, the corona inception voltage of the equivalent negative corona exceeds that of the equivalent positive corona. For a small AC component, the corona inception voltage of the equivalent positive corona exceeds that of the equivalent negative corona. The corona inception voltage decreases with increasing AC component. The charge-motion model based on hydrodynamics is used to analyze the charge motion for different AC/DC voltage ratios. The charge remaining for equivalent negative coronas exceeds that for equivalent positive coronas with high AC components. In addition, the charge remaining for equivalent positive coronas exceeds that of equivalent negative coronas with small AC components. As the AC component decreases, the remaining space charge increases. The results show that space charge tends to “block” corona inception. The more space charge remains, the higher the corona inception voltage is. Therefore, the variation in space charge and the corona inception threshold conditions under combined DC-AC voltage differ from those under only DC or AC voltage.

High-temperature superconductor (HTS) bulks have demonstrated extremely intriguing potential for industrial and commercial applications due to their capability to trap significantly larger magnetic fields than conventional permanent magnets. The magnetic field in electrical rotating machines is a combination of alternating and rotational fields. In contrast, all previous research on the characterization of electromagnetic properties of HTS have solely engrossed on the alternating AC magnetic fields and the associated AC loss. This research paper gives a thorough examination of the AC loss measurement under various conditions. The obtained results are compared to the finite element-based H-formulation. The AC loss is measured at various amplitudes of circular flux density patterns and compared with the AC loss under one-dimensional alternating flux density. The loss variation has also been studied at other frequencies. The findings in this research paper provide more insights into material characterization, which will be useful in the design of future large-scale HTS applications.

Various measures have been taken to improve ship energy efficiency while decreasing CO2 emissions. In this work, the navigation environment between Wuhan and Shanghai in China has been classified based on an improved K-means algorithm in order to realize route division. A fuel consumption prediction model considering the navigation environment factors has been established. Consequently, speed optimization models with multiple different optimization objectives have been constructed and tested based on an actual case using an artificial fish swarm algorithm. Finally, sensitivity analysis has been carried out focusing on the navigation time, fuel price, charter rate, free carbon credits, and carbon tax rate. The results show that the total shipping cost and CO2 emissions could be reduced by 0.94% and 0.38%, respectively, after the optimization. Considering a carbon tax policy with a tax rate of roughly 1300 RMB/t, the optimization result (including the carbon tax cost) is close to the compromised solution of multi-objective optimization, and the corresponding carbon tax rate can provide a useful reference for policymakers.

This paper reviews the modeling of high-temperature superconductors (HTS) using the finiteelement method (FEM) based on the H-formulation of Maxwell's equations. This formulation has become the most popular numerical modeling method for simulating the electromagnetic behavior of HTS, especially thanks to the easiness of implementation in the commercial finite-element program COMSOL Multiphysics. Numerous studies prove that the H-formulation is able to simulate a wide scope of HTS topologies, from simple geometries such as HTS tapes and coils, to more complex HTS devices, up to large superconducting magnets. In this paper, we review the basics of the H-formulation, its evolution from 2D to 3D, its application for calculating critical currents and AC losses as well as magnetization of HTS bulks and tape stacks. We also review the use of the H-formulation for large-scale HTS applications, its use to solve multi-physics problems involving electromagnetic-thermal and electromagnetic-mechanical couplings, and its application to study the dynamic resistance of superconductors and flux pumps.

Kitchen waste is both a pollutant and an available resource. The anaerobic digestion (AD) technology can effectively treat waste and generate biogas. The concentration of volatile fatty acids (VFA) is one of the essential quality monitoring indicators in the anaerobic digestion process of kitchen waste and is difficult to measure online. In this paper, the hierarchical extreme learning machine (HELM) is applied to the soft sensor for the concentration of VFA considering the shortcomings of traditional soft sensor. The combined feature information is extracted by the multi-layer extreme learning machine-autoencoder (ELM-AE) structure in the HELM. Besides, the last layer is the combined manifold regularization extreme learning machine (ELM) and used to predict and mine the data structure of labeled data and unlabeled data. Considering that the characteristics of system operating conditions are prone to change in the actual production process of anaerobic digestion, the domain space transfer hierarchical extreme learning machine (DSTHELM) is used to solve the data drift problem caused by different initial conditions in the actual data; this is different from the traditional hierarchical extreme learning machine. This method increases the accuracy by 14.31% and 9.67% in training set and test set compared with HELM, indicating that the model possesses higher prediction accuracy and better generalization performance.

When the high-temperature superconducting (HTS) REBCO (rare-earth barium copper oxide) coil is applied in a power system, a large amount of heat may be generated due to the short-circuiting of the system, resulting in the thermal instability of the coil. Moreover, under complex working conditions, the oscillating external magnetic field will further aggravate the coil quench. In this paper, the electromagnetic–thermal coupling model is used to analyze the loss, current distribution and temperature distribution of the REBCO coil under short-circuit fault conditions and oscillating external magnetic fields. In order to get closer to the actual situation, the modeling of the superconducting tape adopts the real tape structure, and the resistivity of the superconductor is described by the modified E-J relationship. Four cases are considered for the oscillating external magnetic field, i.e., sine, triangle, sawtooth and square cases. This model has certain significance as a reference for understanding the thermal stability of coils in extreme cases.

High-temperature superconducting materials have shown great potential for the design of large-scale industry applications. However, they are complicated under AC conditions, resulting in penalties such as power loss or AC loss. This loss has to be considered in order to design reliable and efficient superconducting devices. Furthermore, when superconductors are used in rotating machines, they may be exposed to rotating magnetic fields, which is critical for the design of such machines. Existing AC loss measuring techniques are limited to measuring under one-dimensional AC magnetic fields or transport currents. Therefore, it is essential to develop and investigate robust experimental techniques to investigate the loss mechanism in HTS machines. In this paper, a new and novel experimental technique has been presented to measure AC loss in rotating magnetic field conditions. The loss under rotating magnetic fields is measured and compared by numerical modeling methods, and the results show a strong correlation with the numerical modeling and show the effectiveness of the experimental setup.

SiC/EP composites are promising insulating materials due to their high thermal conductivity, stable chemical properties, and nonlinear electrical conductivity. However, the compatibility of micron-sized SiC particles with the organic polymer matrix is poor, and defects such as air gaps may be introduced at the interface, which reduces the partial discharge resistance of the composite materials. In order to improve the partial discharge initial voltage (PDIV) of SiC/EP composites, in this paper, SiC/EP composites with different proportions were prepared by surface modification of filler and compound of micro/nano particles. Firstly, a method of secondary modification of SiC particles was proposed, which was first modified by alkali washing and then silane coupling agent KH560, and the effectiveness of the modification was verified. Therefore, the interface bonding ability between the filler and the matrix was improved, the air gap defects at the interface were reduced, and the PDIV of the composite material was improved. When the filling ratio is 10 wt%, the PDIV was enhanced by 13.75%, and when the filling ratio was further increased, the improvement was reduced. In contrast, the introduction of nanoparticles into the composites can effectively improve the PDIV of composite materials. In this study, nanoparticles were used to form a shell-core structure in epoxy resins to exert their huge specific surface area and active surface properties, thereby changing the overall crosslinking properties of the composites. Through experimental research, the optimal micro-nano particle compounding ratio was explored. Under the optimal mixing ratio, the PDIV of the composite material can be increased by more than 90%.

High-temperature superconductor (HTS) bulks have shown very promising potential for industrial applications due to the ability to trap much higher magnetic fields compared to traditional permanent magnets. In rotating electrical machines, the magnetic field is a combination of alternating and rotating fields. On the contrary, all studies on electromagnetic characterization of HTS presented in the literature so far have only focused on alternating AC magnetic fields and alternating AC loss due to the unavailability of robust experimental techniques and analytical models. This paper presents a numerical investigation on the characterization of HTS bulks subjected to rotating magnetic fields showing AC loss, current density distribution in three-dimensional axes, and trapped field analysis. A three-dimensional numerical model has been developed using H-formulation based on finite element analysis. An HTS cubic sample is magnetized and demagnetized with two-dimensional magnetic flux density vectors rotating in circular orientation around the XOY, XOZ, and YOZ planes.

The high-temperature superconductor (HTS) has been recognised as one of the most up-and-coming materials thanks to its superior electromagnetic performance (e.g., zero resistance). For a high-speed maglev, the HTS magnet can be the most crucial component because it is in charge of both the levitation and the propulsion of the maglev. Therefore, a fundamental study of HTS magnets for maglev is crucial. This article presents the fundamental design and modelling of the superconducting magnet for a high-speed maglev, including mechanics, electromagnetics, and loss analysis during instability. First, the measurements of the superconducting wire were performed. The HTS magnet was primarily designed and modelled to fulfil the basic electromagnetic requirements (e.g., magnetic field) in order to drive the maglev at a high speed. The modelling was verified by experimental tests on a scale-down HTS magnet. A more professional model using the H-formulation based on the finite element method (FEM) was built to further investigate some deeper physical phenomenon of the HTS magnet (e.g., current density and loss behaviours), particularly in situations where the high-speed maglev is in the normal steady state or encountering instability.

The dynamic voltage is a unique phenomenon of superconducting materials. It arises when the superconductor is carrying a DC transport current and spontaneously in subject to an AC magnetic field. This study excavates the aspects that previous studies have not comprehensively investigated: the dynamic voltage in a DC-carrying superconducting tape exposed to different oscillating AC magnetic fields. First, the fundamental physics of dynamic voltage/flux of superconductors is reviewed and further analysed in detail. We used the superconducting modelling method using the H-formulation merged into the finite-element method (FEM) software, to re-produce the typical dynamic voltage behaviour of a superconducting tape. The modelling was verified by both the analytical and experimental results, in order to precisely prove the reliability of the modelling. Afterwards, the modelling was performed for a DC-carrying superconducting tape under four different oscillating magnetic fields (sine, triangle, sawtooth and square), and their corresponding dynamic voltages and energy losses were analysed and compared. Results show the sinusoidal magnetic field can lead to the optimal combination of reasonable dynamic voltage but relatively lower loss, which is suitable for those superconducting applications requiring dynamic voltage as the energy source, e.g., flux pumps. This article presents novel investigation and analysis of the dynamic voltage in superconducting materials, and both the methodology and results can provide useful information for the future design/analysis of superconducting applications with DC transport currents and AC magnetic fields.

Orderly arranged Silicon carbide (SiC)/epoxy (EP) composites were fabricated. SiC was made magnetically responsive by decorating the surface with iron oxide (Fe3O4) nanoparticles. Three treatment methods, including without magnetization, pre-magnetization and curing magnetization, were used to prepare SiC/EP composites with different filler distributions. Compared with unmodified SiC, magnetic SiC with core-shell structure was conducive to improve the breakdown strength of SiC/EP composites and the maximum enhancement rate was 20.86%. Among the three treatment methods, SiC/EP composites prepared in the curing-magnetization case had better comprehensive properties. Under the action of magnetic field, magnetic SiC were orderly oriented along the direction of an external field, thereby forming SiC chains. The magnetic alignment of SiC restricted the movement of EP macromolecules or polar groups to some extent, resulting in the decrease in the dielectric constant and dielectric loss. The SiC chains are equivalent to heat flow channels, which can improve the heat transfer efficiency, and the maximum improvement rate was 23.6%. The results prove that the orderly arrangement of SiC had a favorable effect on dielectric properties and thermal conductivity of SiC/EP composites. For future applications, the orderly arranged SiC/EP composites have potential for fabricating insulation materials in the power electronic device packaging field.

In this paper, in order to improve the electrical and thermal properties of SiC/EP composites, the methods of compounding different crystalline SiC and micro-nano SiC particles are used to optimize them. Under different compound ratios, the thermal conductivity and breakdown voltage parameters of the composite material were investigated. It was found that for the SiC/EP composite materials of different crystal types of SiC, when the ratio of α and β silicon carbide is 1:1, the electrical performance of the composite material is the best, and the breakdown strength can be increased by more than 10% compared with the composite material filled with single crystal particles. For micro-nano compound SiC/EP composites, different total filling amounts of SiC correspond to different optimal ratios of micro/nano particles. At the optimal ratio, the introduction of nanoparticles can increase the breakdown strength of the composite material by more than 10%. Compared with the compound of different crystalline SiC, the advantage is that the introduction of a small amount of nanoparticles can play a strong role in enhancing the break-down field strength. For the filled composite materials, the thermal conductivity mainly depends on whether an effective heat conduction channel can be constructed. Through experiments and finite element simulation calculations, it is found that the filler shape and particle size have a greater impact on the thermal conductivity of the composite material, when the filler shape is rounder, the composite material can more effectively construct the heat conduction channel.

Due to the pressures caused by the energy crisis, environmental pollution, and international regulations, the largest ship-producing nations are exploring renewable resources, such as wind power, solar energy, and fuel cells to save energy and develop more environmentally-friendly ships. Solar energy has recently attracted a great deal of attention from both academics and practitioners; furthermore, the optimization of energy management has become a research topic of great interest. This paper takes a solar-diesel hybrid ship with 5000 car spaces as its research object. Then, following testing on this ship, experimental data were obtained, a multi-objective optimization model related to the ship’s fuel economy and diesel generator’s efficiency was established, and a partial swarm optimization algorithm was used to solve a multi-objective problem. The results show that the optimized energy management strategy for a hybrid energy system should be tested under different electrical loads. Moreover, the hybrid system’s economy should be taken into account when the ship’s power load is high, and the output power from the new energy generation system should be increased as much as possible. Finally, the diesel generators’ efficiency should be taken into consideration when the ship’s electrical load is low, and the injection power of the new energy system should be reduced appropriately.

The new round of electricity market reform in 2015 completely changed the profit pattern of power grid enterprises (PGEs) in China, and directly affected their investment plans. Under the new electricity market reform (NEMR), the government regulatory authority made higher requirements for the investment efficiency of PGEs, and the investment effectiveness hence became the core criterion for investment plans. Therefore, the PGEs are now attaching great importance to the investment efficiency. According to their geographical differences, this paper divides the Chinese provincial PGEs into three groups, namely eastern, central and western region enterprises. Based on the NEMR, we developed an evaluation system of investment efficiency for the above-mentioned enterprises. Moreover, this paper selects GDP per capita, electricity consumption in industry, and electrification rate as external environment variables, and conducts an empirical research on the investment efficiency of 31 provincial PGEs in China in 2017. The analysis reveals that three external environment variables have considerable impacts on the investment efficiency. Though the increase of GDP per capita and electricity consumption in industry are not conducive to improving investment efficiency, the advancement of electrification plays a positive role in its improvement. And from the real efficiency results, Tianjin, Liaoning, Jiangsu, and Fujian have relatively higher investment efficiency, while Henan, Shandong, and Shanghai exhibit lower investment efficiency. By comparing the investment efficiency of PGEs in the first and third stage, conclusions can be drawn that in the first stage the investment efficiency of PGEs was overestimated, and the inefficient investments prevailed some provincial PGEs, which caused by low scale efficiency.

Energy management strategy is a key technology of hybrid power ships. In recent years, renewable energy ship technologies have become a popular research field and one promising development direction to realize reasonable utilization of energy resource, as well as energy conservation and emission reduction. Among these technologies, the solar energy hybrid ship technology is currently attracting attention all over the word. In this paper, a 5000-car space solar energy hybrid ship is used as the research objective, and an energy management strategy that is based on fuzzy logic is proposed to distribute the ship power generation, solar energy, and battery output power according to the ship’s electrical load demand, and the fuzzification and stochasticity of solar energy. By comparing the simulation results with real ship testing results, it is identified that the proposed fuzzy logic energy management strategy can optimize the operation conditions of individual power generation sources, improve the overall performance of power system, and reduce the ship’s overall fuel consumption.