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The purpose of this paper is to develop a numerical simulation method based on the transient upstream finite element method (FEM) and Schottky emission theory to reveal the distribution characteristics of space charge in oil-paper insulation.

The main insulation medium of the converter transformer in high voltage direct current transmission is oil-paper insulation. However, the influence of space charge is difficult to be fully considered in the insulation design and simulation of converter transformers. To reveal the influence characteristics of the space charge, this paper proposes a numerical simulation method based on Schottky emission theory and the transient upstream FEM. This method considers the influence of factors, such as carrier mobility, carrier recombination coefficient, trap capture coefficient and diffusion coefficient on the basis of multi-physics field coupling calculation of the electric field and fluid field.

A numerical simulation method considering multiple charge states is proposed for the space charge problem in oil-paper insulation. Meanwhile, a space charge measurement platform based on the electrostatic capacitance probe method for oil-paper insulation structure is built, and the effectiveness and accuracy of the numerical simulation method is verified.

A variety of models are calculated and analyzed by the numerical simulation method in this paper, and the distribution characteristics of the space charge and total electric field in oil-paper insulation medium with single-layer, polarity reversal of plate voltage and double-layer are obtained. The research results of this paper have the guiding significance for the engineering application of oil-paper insulation and the optimal design of converter transformer insulation.

The paper aims to develop a cownose ray-inspired robotic fish which can be propelled by oscillating and chordwise twisting pectoral fins.

The bionic pectoral fin which can simultaneously realize the combination of oscillating motion and chordwise twisting motion is designed based on analyzing the movement of cownose ray’s pectoral fins. The structural design and control system construction of the robotic fish are presented. Finally, a series of swimming experiments are carried out to verify the effectiveness of the design for the bionic pectoral fin.

The experimental results show that the deformation of the bionic pectoral fin can be well close to that of the cownose ray’s. The bionic pectoral fin can produce effective angle of attack, and the thrust generated can propel robotic fish effectively. Furthermore, the tests of swimming performance in the water tank show that the robotic fish can achieve a maximum forward speed of 0.43 m/s (0.94 times of body length per second) and an excellent turning maneuverability with a small radius.

The oscillating and pitching motion can be obtained simultaneously by the active control of chordwise twisting motion of the bionic pectoral fin, which can better imitate the movement of cownose ray’s pectoral fin. The designed bionic pectoral fin can provide an experimental platform for further study of the effect of the spanwise and chordwise flexibility on propulsion performance.

This study examines the effects of the online brand community's (OBC) humor climate on the value cocreation (VCC) behavior of consumers using the affective events theory. It also evaluates the serial mediating roles of positive emotions and brand engagement and the moderating effect of membership duration.

The authors collected data from 601 Chinese consumers of OBCs using an online questionnaire survey and applied structural equation modeling to analyze the data.

The authors found a positive relationship between OBC humor climate and VCC behavior, which was mediated by positive emotions and brand engagement. Additionally, there was a serial mediation effect of these two variables. The influence of the OBC humor climate on positive emotions was stronger for short-term members than long-term ones.

This research contributes toward OBC management and VCC marketing strategy for constructing brand equity.

This study is among the first to focus on the significance of the OBC humor climate, thus enriching the OBC literature and providing a new perspective on how to facilitate VCC behavior. It also broadens the application of the affective events theory in marketing.

This study aims to explore the relationship between experience layoffs and employees’ work engagement. Drawing on the psychological contract theory, we examine the parallel mediating role of cognitive and affective job insecurity, along with the moderating role of perceived organisational support.

The hypotheses were tested based on data collected from 737 employees of companies in various industries in China in an online survey.

The results showed the significant effect of experiencing layoffs on employees’ work engagement through cognitive and affective job insecurity, and the effect was stronger when perceived organisational support was lower. The moderated mediation effect mainly occurred through affective job insecurity but not cognitive job insecurity.

This study deepens the understanding of the mechanism of the negative effect of experiencing layoffs and the boundaries of its impact from a psychological contract breach perspective. By analysing the mediating role of cognitive and affective job insecurity, we have enhanced our understanding of the exchange-based mechanism of employees after experiencing layoffs. By examining the moderating role of perceived organisational support, we reveal the important role of supportive behaviours of organisations in mitigating the negative effects of experiencing layoffs.

The paper aims to present a dynamic model of flexible oscillating pectoral fin for further study on its propulsion mechanism.

The chordwise and spanwise motions of cow-nosed ray’s pectoral fin are first analyzed based on the mechanism of active/passive flexible deformation. The kinematic model of oscillating pectoral fin is established by introducing the flexible deformation. Then, the dynamic model of the oscillating pectoral fin is developed based on the quasi-steady blade element theory. A series of hydrodynamic experiments on the oscillating pectoral fin are carried out to investigate the influences of motion parameters on the propulsion performance of the oscillating pectoral fin.

The experimental results are consistent with that obtained through analytical calculation within a certain range, which indicates that the developed dynamic model in this paper is applicable to describe the dynamic characteristics of the oscillating pectoral fin approximately. The experimental results show that the average thrust of an oscillating pectoral fin increases with the increasing oscillating amplitude and frequency. However, the relationship between the average thrust and the oscillating frequency is nonlinear. Moreover, the experimental results show that there is an optimal phase difference at which the oscillating pectoral fin achieves the maximum average thrust.

The developed dynamic model provides the theoretical basis for further research on propulsion mechanism of oscillating pectoral fins. It can also be used in the design of the bionic pectoral fins.

Automatic optical inspection (AOI) systems have been widely used in many fields to evaluate the qualities of products at the end of the production line. The purpose of this paper is to propose a local-to-global ensemble learning method for the AOI system based on to inspect integrated circuit (IC) solder joints defects.

In the proposed method, the locally statistically modeling stage and the globally ensemble learning stage are involved to tackle the inspection problem. At the former stage, the improved visual background extraction–based algorithm is used for locally statistically modeling to grasp tiny appearance differences between the IC solder joints to achieve potential defect images for the subsequent stage. At the latter stage, mean unqualified probability is introduced based on a novel ensemble learning, in which an adaptive weighted strategy is proposed for revealing different contributions of the base classifier to the inspection performance.

Experimental results demonstrate that the proposed method achieves better inspection performance with an acceptable inspection time compared with some state-of-the-art methods.

The approach is a promising method for IC solder joint inspection, which can simultaneously grasp the local characteristics of IC solder joints and reveal inherently global relationships between IC solder joints.

This paper aims to carry out the research on the influence of ground effect on the performance of robotic fish propelled by oscillating paired pectoral fins.

The two-dimensional ground effect model of the oscillating pectoral fin without considering flexible deformation is established by introducing a two-dimensional fluid ground effect model. The parameters of the influence of ground effect on the oscillating pectoral fin are analyzed. Finally, the ground effect test platform is built, and a series of hydrodynamic experiments are carried out to study the influence of ground effect on the propulsion performance of the robotic fish propelled by oscillating paired pectoral fins under different motion parameters.

The thickness of the trailing edge and effective clearance are two important parameters that can change the influence of ground effect on the rigid pectoral fin. The experimental results are consistent with that obtained through theoretical analysis within a certain extent, which indicates that the developed two-dimensional ground effect model in this paper can be used to analyze the influence of ground effect on the propulsion performance of the oscillating pectoral fin. The experiment results show that the average thrust increases with the decreasing distance between the robot fish and the bottom. Meanwhile, with the increase of oscillation frequency and amplitude, the average thrust increases gradually.

The developed two-dimensional ground effect model provides the theoretical basis for the further research on the influence of ground effect on the propulsion performance of the oscillating pectoral fin. It can also be used in the design of the bionic pectoral fins.

In the information commons (IC) space of library, it is very important to recognize the emotional state of users for better playing the role of IC. In view of this point, this paper aims to discuss the human expression of user emotion.

An emotional state recognition method based on body posture change under video monitoring is proposed. In this method, two parameters are proposed to represent the emotional state of users. Finally, the distribution of users’ overall emotional state is recognized.

It is found that the change of human posture reflects the emotional state of users to a certain extent. The spatial frequency of the user’s average body position change and per capita body position change can reflect the spatial distribution of individual and body position change, respectively.

The method in this paper can effectively overcome the inaccuracy of manual identification of video monitoring images, especially in the case of a large number of users and effectively help the construction of university library IC space and provide a basis for the setting of environmental parameters.

The purpose of this paper is to recognize and label the faults in wind turbines with a new density-based clustering algorithm, named contour density scanning clustering (CDSC) algorithm.

The algorithm includes four components: (1) computation of neighborhood density, (2) selection of core and noise data, (3) scanning core data and (4) updating clusters. The proposed algorithm considers the relationship between neighborhood data points according to a contour density scanning strategy.

The first experiment is conducted with artificial data to validate that the proposed CDSC algorithm is suitable for handling data points with arbitrary shapes. The second experiment with industrial gearbox vibration data is carried out to demonstrate that the time complexity and accuracy of the proposed CDSC algorithm in comparison with other conventional clustering algorithms, including k-means, density-based spatial clustering of applications with noise, density peaking clustering, neighborhood grid clustering, support vector clustering, random forest, core fusion-based density peak clustering, AdaBoost and extreme gradient boosting. The third experiment is conducted with an industrial bearing vibration data set to highlight that the CDSC algorithm can automatically track the emerging fault patterns of bearing in wind turbines over time.

Data points with different densities are clustered using three strategies: direct density reachability, density reachability and density connectivity. A contours density scanning strategy is proposed to determine whether the data points with the same density belong to one cluster. The proposed CDSC algorithm achieves automatically clustering, which means that the trends of the fault pattern could be tracked.