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There are little researchers that combined satellite-based products and L-moments methods in frequency analysis. The objective of this study was to explore and evaluate the satellite precipitation data applied in univariate L-moments method. The Shaoguan City of South China was selected as the study area. Annual maximum precipitation (AMP) respectively from observational rainfall and Integrated Multi-satellitE Retrievals for Global Precipitation Mission (IMERG) gridded rainfall was used for the calculation of estimates using regional L-moments analysis (RLMA) method. Then, the quantiles at grids were corrected by mean bias correction (MBC) method with the estimates at sites. The results showed that the number of homogeneous regions as well as the spatial distribution of parameters ($${C}_{v}$$ C v , $${C}_{s}$$ C s , and $${C}_{k}$$ C k ) for two data sets are different. When the return periods are larger than 40 years, the estimates at sites are also larger than those at grids and the difference will increase as return period increases. After being modified, the quantiles from IMERG are more reasonable and combine the spatial distribution characteristic of estimates from two cases, which indicates that the estimation calculated by satellite products with L-moments approach is applicable and more reasonable. This study can also provide reference for solving the issues regarding the density and coverage of rain gauges that affect the accuracy of frequency analysis, especially in remote areas of China or most parts of the word.

Venture capital (VC) has played an important financial supplementary role in the development of high-tech enterprises. With the intensification of economic policy uncertainty, VC investment behavior has been affected to a certain extent. Under the framework of the impact of economic policy uncertainty (EPU) on general corporate investment behavior, this article examines the impact of EPU on the investment behavior of VC institutions from four aspects, namely, investment quantity, investment phase, investment industry, and investment region. The study finds that in China, EPU has a good news effect, and its intensification can boost the investment quantity of VC institutions and stimulate institutions to choose more specialized investment strategies in terms of investment phase, investment industry, and investment region. The impact of EPU on the investment behavior of VC institutions changes with the investment state of the institutions. The larger the investment quantity of the VC institutions, the greater the promotion effect. VC institutions with a higher degree of investment concentration will pay more attention to specialized investment strategies.

Visual working memory (WM) plays a pivotal role in integrating fragments into meaningful units, but no study has addressed how visual WM integration takes place in children. The current study examined whether WM integration emerges once preschoolers master Gestalt cue and can retain two representations in WM (automatic integration hypothesis), or still needs time to mature (maturation-of-integration hypothesis). Four experiments (N = 168, 81 females, 4- to 6-year-olds, Chinese, in Hangzhou, China, from 2016.10 to 2021.11) were conducted. Although 4-year-olds can retain two objects in WM and benefit from Gestalt cues in simultaneous display (Cohen's ds gt;1.00), they failed when memory arrays were presented sequentially. Meanwhile, 5- and 6-year-olds consistently demonstrated WM integration ability (all Cohen's ds gt;0.69), supporting the maturation-of-integration hypothesis.

Hollow porcelain insulators in substations are frequently confronted with rain flashovers under extreme rainfall. This study aims to investigate the spatial and temporal variation of electric fields between hollow porcelain insulator sheds affected by dynamic deformation of pendant water drops and effects of the dimensionless number of fluids, the Weber number (We) and the electric Bond number (BoE), on it for influencing factors' analysis. Flow‐electric field coupling simulations were carried out to compute the magnitude and the position of AC electric fields between the sheds. The results show that the maximum electric field at a point in time (Etmax) increases significantly after the breakup of the pendant water drop, and its position alters accordingly. For low We and BoE, the global maximum electric field (Egmax) increases with increasing We and BoE, respectively. It is much closer to the adjacent sheds and occurs later than Etmax at the breakup of the pendant water drop (Ebmax). By contrast, Egmax decreases in different degrees at high We and BoE, respectively. There is little difference between Egmax and Ebmax in the position and the occurring time. The influence mechanism on the maximum electric field and discharges and the relationship between discharges induced by the pendant water drop and rain flashover are discussed.

In order to solve the problem that defects of different scales have different terahertz imaging characteristics in fiber reinforced composites, the fusion processing method of two terahertz images with complementary defect information was studied. To reduce the Gibbs phenomenon, Non-subsampled Shearlet Transform (NSST) with the property of shift- invariance was used to decompose source images and get their low-frequency subband and high frequency subband coefficients. Regional variance was used as connection strength factor of the Pulse Coupled Neural Network (PCNN) in the low frequency coefficient fusion, which is more according with human visual characteristics. In the fusion of high frequency coefficients, the Regional Gradient Energy of Direction Information Measure (RGEDIM) was introduced to extract the edge, texture and other details of the image and integrated them into the final image, the impact of noise on image fusion was reduced better. Finally, the fusion image was obtained through NSST inverse transform. The experimental results show that this method is superior to wavelet, Non-subsampled Contourlet Transform (NSCT) and traditional PCNN method, the fusion image has more mutual information and contains more original image information, all the defects of the source image can be clearly seen on the fusion image.

Due to the worldwide pandemic and ‘Stay at Home’ order, many firms have experienced challenges for supply chain management. As the key parts of supply chain management, customer concentration may h...

The objective of this study was to obtain the 24-h precipitation frequency estimates for return periods of 1-1000 years in Shaoguan, South China, to provide scientific suggestions for flood disaster warning and urban flood control planning. Annual Maximum Precipitation (AMP) respectively from observational rainfall and Integrated Multi-satellitE Retrievals for GPM (IMERG) gridded rainfall which can supplement precipitation information in areas without rain gauges was used for the calculation of estimates using Regional L-Moments Analysis (RLMA) method. Then the quantiles at grids were corrected by Mean Bias Correction (MBC) method with the estimates at sites. The results showed that there has more and stronger extreme precipitation in the northwest of Shaoguan. The number of homogeneous regions as well as the spatial distribution of parameters (Cv , Cs and Ck) for two datasets is different. When the return periods are larger than 100 years, the estimates at sites are also larger than that at grids and the difference will increase as return period increases. After modified, the quantiles from IMERG are more reasonable and combine the spatial distribution characteristic of estimates from two cases, which indicates that the rainstorm high-risk area of Shaoguan is in the southwest to the central, as well as in the west-central.

Flashover accidents on high-voltage bushings frequently occur under extreme rainfall, which is generally attributed to the bridging of adjacent sheds by pendant drops, a result of the dynamic deformation of pendant drops. We numerically investigate the effects of the parameters of pendant drops and the electric field on the dynamic deformation of pendant drops on a 500 kV transformer bushing under extreme rainfall and verify the simulation results by artificial rain experiment. The dynamic deformation of pendant drops is described by solving the Navier-Stokes equations and using the level set method. The results show that the maximum length of the pendant drop increases with the increase in the initial diameter and the initial mass flow rate, respectively, but decreases under the electric field. The main influencing factor on the maximum length of the pendant drop alters with the variation of the initial diameter and the initial mass flow rate in the absence of the electric field, whereas the initial mass flow rate is the unique main influencing factor in the presence of the electric field. Furthermore, the variations of the maximum length and breakup time of the pendant drop are elucidated by the instability of the pendant drop.

The flashover performance of insulators can be improved by BS (booster sheds) in the rain, which is mainly attributed to the reasons that BS break up long cascades of water and block connections of arcs. However, surface rainwater characteristics and arc characteristics of bushing have not been quantitatively studied under heavy rainfall. In this article, the artificial rain tests were conducted on a 500 kV transformer high-voltage bushing equipped with and without BS under the rainfall intensity of 10 mm/min. X (the total length of water column) and Larc (the critical length of arc) on the bushing surface were taken as the feature parameters of surface rainwater characteristics and arc characteristics, respectively. The effects of BS on Eh (the rain flashover voltage gradient along the insulation height), X and Larc were investigated, respectively. Furtherly, the relationships were studied among Eh, X and Larc. Results indicate that Eh has a sharp rise as the number of BS (NBS) is from one to two, however the rise of Eh gradually decreases when NBS exceeds two. X decreases while Larc increases with the rise of NBS, however both the change ranges of them continually fall. Furthermore, Larc presents remarkable negative correlation to X because of the effect of the electric field. Eh rises nonlinearly with the decrease of X, which is due to the change of the wetting uniformity on the bushing surface and the potential redistribution along air gaps in the presence of the local arc.

The wide application of nanocomposites in the insulation system has greatly contributed to the performance improvement of power equipment. However, nano fillers are not omnipotent for improving the properties of composite dielectrics. In some situations, nano-modified materials are in fact a compromise of improving some performance features while sacrificing others. In this work, the breakdown characteristics and time-to-failure of polypropylene film with nano-clay fillers have been evaluated under combined thermal stress and AC electric fields. Experiments on plain polypropylene (PP) samples have also been carried out under the same test conditions as control. Test results indicated that the time-to-failure of the samples with nano-clay filler was shorter than those without nano filler, which is different from the previous experience. SEM and EDS analyses were conducted to study how the failure mechanism had taken place in both plain polypropylene and the nano-clay filled polypropylene. The failure phenomenon in these materials can be explained by molecular thermodynamics. The main reason for the premature thermal breakdown of PP nanocomposite is essentially due to the weak coupling between nano-clay filler and polymer matrix. Finally, suggestions are proposed for nano modification methods and lifespan prediction models of composite dielectrics.

Umbrella-type structure, the material of insulators and surface positions influence the wetting process of polluted insulator surfaces tremendously. Using a custom-made phase-angle-difference (PAD) detection device, the PAD of the different positions of different polluted insulators is measured, and the PAD curves and partial pollution surface electrical conductivity γ 20 varying with time are plotted. The results show that there is a certain difference in the wetting characteristics of different positions. The saturated wetting time of different positions of LXAY-70 insulators is 12.5-15 min; that for LXHY5-70 insulators is 12-25 min; that for XWP2-70 insulators is 8-14 min; and that for FXBW-10/70 insulators is 18-26.5 min. The umbrella-type structure is shown to have a direct effect on the wetting process of polluted insulators. The complicated umbrella-type structure, especially the existence of umbrella ribs, causes an uneven degree of wetting between the upper and lower surfaces, and leads to the increase of the difference in wetting state between the different positions. Furthermore, there is a certain difference in the wetting speed of insulators comprised of different materials. Hydrophilic porcelain and glass insulators are more easily wetted than composite insulators, even though the hydrophobicity class of composite insulators is 7.

Rain is one of the dominant meteorological factors threatening the outdoor insulation performance of ultra-high voltage (UHV) power stations. Discharge occurring on the polluted surface of post insulators in rain has always been a major concern of power stations. Previous studies have shown that suspended water droplets on the shed edge play an important role in the rain flashover process. In this work, artificial contamination rain flashover tests were carried out in a laboratory on a UHV DC (Ultra-High Voltage Direct Current) large-diameter composite post insulator, which had a rod diameter of 625 mm and alternating sheds (105 mm and 75 mm for larger and smaller shed overhang, respectively). The discharge mechanism was analyzed base on the observation of discharge phenomenon of suspended water-drops on the shed edge. Moreover, simulation models by COMSOL Multiphysics were established to investigate the electric field around sheds and suspended water-drops, as well as the shape change of water droplets on the insulation surface, especially at the edge of the shed. Results show that the shape parameters of water-droplets changed continuously under the combined action of gravity, surface tension, and capillary tension. Suspended water-droplets on the shed edge showed a great influence on the electric field distribution, and the resulting discharge lead to the bridging between sheds. This work paves a new way to revealing the contamination rain flashover mechanism on post insulators and provides critical knowledge for power stations on preventing flashover accidents.

Liquid metal (LM)–polymer composites that combine the thermal and electrical conductivity of LMs with the shape-morphing capability of polymers are attracting a great deal of attention in the fields of reconfigurable electronics and soft robotics. However, investigation of the synergetic effect between the shape-changing properties of LMs and polymer matrices is lacking. Herein, a self-healable and recyclable dual-shape memory composite, comprising an LM (gallium) and a Diels–Alder (DA) crosslinked crystalline polyurethane (PU) elastomer, is reported. The composite exhibits a bilayer structure and achieves excellent shape programming abilities, due to the phase transitions of the LM and the crystalline PU elastomers. To demonstrate these shape-morphing abilities, a heat-triggered soft gripper, which can grasp and release objects according to the environmental temperature, is designed and built. Similarly, combining the electrical conductivity and the dual-shape memory effect of the composite, a light-controlled reconfigurable switch for a circuit is produced. In addition, due to the reversible nature of DA bonds, the composite is self-healable and recyclable. Both the LM and PU elastomer are recyclable, demonstrating the extremely high recycling efficiency (up to 96.7%) of the LM, as well as similar mechanical properties between the reprocessed elastomers and the pristine ones.

Background Existing evidence has shown that mesenchymal stem cells (MSCs) can undergo malignant transformation, which is a serious limitation of MSC-based therapies. Therefore, it is necessary to monitor malignant transformation of MSCs via a noninvasive imaging method. Although reporter gene-based magnetic resonance imaging (MRI) has been successfully applied to longitudinally monitor MSCs, this technique cannot distinguish the cells before and after malignant transformation. Herein, we investigated the feasibility of using a tumor-specific promoter to drive reporter gene expression for MRI detection of the malignant transformation of MSCs. Methods The reporter gene ferritin heavy chain (FTH1) was modified by adding a promoter from the tumor-specific gene progression elevated gene-3 (PEG3) and transduced into MSCs to obtain MSCs-PEG3-FTH1. Cells were induced to undergo malignant transformation via indirect coculture with C6 glioma cells, and these transformed cells were named MTMSCs-PEG3-FTH1. Western blot analysis of FTH1 expression, Prussian blue staining and transmission electron microscopy (TEM) to detect intracellular iron, and MRI to detect signal changes were performed before and after malignant transformation. Then, the cells before and after malignant transformation were inoculated subcutaneously into nude mice, and MRI was performed to observe the signal changes in the xenografts. Results After induction of malignant transformation, MTMSCs demonstrated tumor-like features in morphology, proliferation, migration, and invasion. FTH1 expression was significantly increased in MTMSCs-PEG3-FTH1 compared with MSCs-PEG3-FTH1. Prussian blue staining and TEM showed a large amount of iron particles in MTMSCs-PEG3-FTH1 but a minimal amount in MSCs-PEG3-FTH1. MRI demonstrated that the T2 value was significantly decreased in MTMSCs-PEG3-FTH1 compared with MSCs-PEG3-FTH1. In vivo, mass formation was observed in the MTMSCs-PEG3-FTH1 group but not the MSCs-PEG3-FTH1 group. T2-weighted MRI showed a significant signal decrease, which was correlated with iron accumulation in the tissue mass. Conclusions We developed a novel MRI model based on FTH1 reporter gene expression driven by the tumor-specific PEG3 promoter. This approach could be applied to sensitively detect the occurrence of MSC malignant transformation.

Existing mobile robots cannot complete some functions. To solve these problems, which include autonomous learning in path planning, the slow convergence of path planning, and planned paths that are not smooth, it is possible to utilize neural networks to enable to the robot to perceive the environment and perform feature extraction, which enables them to have a fitness of environment to state action function. By mapping the current state of these actions through Hierarchical Reinforcement Learning (HRL), the needs of mobile robots are met. It is possible to construct a path planning model for mobile robots based on neural networks and HRL. In this article, the proposed algorithm is compared with different algorithms in path planning. It underwent a performance evaluation to obtain an optimal learning algorithm system. The optimal algorithm system was tested in different environments and scenarios to obtain optimal learning conditions, thereby verifying the effectiveness of the proposed algorithm. Deep Deterministic Policy Gradient (DDPG), a path planning algorithm for mobile robots based on neural networks and hierarchical reinforcement learning, performed better in all aspects than other algorithms. Specifically, when compared with Double Deep Q-Learning (DDQN), DDPG has a shorter path planning time and a reduced number of path steps. When introducing an influence value, this algorithm shortens the convergence time by 91% compared with the Q-learning algorithm and improves the smoothness of the planned path by 79%. The algorithm has a good generalization effect in different scenarios. These results have significance for research on guiding, the precise positioning, and path planning of mobile robots.

Aiming at the high requirements of marine diesel engine safety operation, based on depth analysis of the requirement of vibration monitoring and fault diagnosis for marine diesel engine, a design scheme of vibration monitoring and fault diagnosis system for marine diesel engine is proposed from three aspects, including system architecture, hardware design and software design. According to the design scheme, a principle prototype is developed and verified through experiments. The experimental result shows that fault diagnosis and early warning can be realized by the principle prototype and disassembling the diesel engine is not required. The principle prototype is simply operation and highly reliability, which means the design scheme of vibration monitoring and fault diagnosis system is feasibility.

The discharges of water columns and droplets between the sheds make the leakage distance not effectively used, which is one of the main reasons for flashover of composite post insulators under heavy rainfall. To study the influence of shed parameters on surface rainwater characteristics, artificial rain tests were carried out on the large-diameter composite post insulators under the rainfall intensity of 2–15 mm/min. Lwc (the length of water columns at the edge of large sheds), Nwc (the number of water columns at the edge of large sheds), Nwde (the number of water droplets at the edge of large sheds) and Nwds (the number of water droplets in the space between two adjacent large sheds) were proposed as the parameters of surface rainwater characteristics. The influences of large shed spacing, large shed overhang and rod diameter on the parameters of surface rainwater characteristics under different rainfall intensities were analyzed. The experimental results show that, under the same rainfall intensity, with the rise in large shed spacing, large shed overhang or rod diameter, Lwc, Nwc, Nwde and Nwds all increase. Under different rainfall intensities, the trends of the parameters with the change in shed parameters are basically invariant; however, the change ranges of the parameters are different. The increases in the parameters with the rises in shed parameters and rainfall intensity are mainly attributed to the change in the rainfall on the insulator surface. The experimental results can provide references for the quantitative description of surface rainwater characteristics and the design of large-diameter composite post insulators for DC transmission systems.

Composite insulators have been widely used in EHV and UHV transmission lines due to their excellent anti-pollution flashover performance, high strength and easy installation. As an important part of composite insulator, glass fiber reinforced polymer rod needs to bear the main mechanical load and is also the key to insulation performance. In recent years, although the brittle fracture of rod has been effectively solved, the abnormal temperature rise and decay-like fracture caused by rod defects still affect the safe operation of transmission lines seriously. In this paper, the microstructure of the rod is studied by improved dye penetration test and three-dimensional scanning, and the influence of microstructure difference is studied by water absorption and loss power experiments. The results show that moisture penetration caused by large porosity and penetration channel is the key factor to increase the loss power of rod. By improving the performance requirements of rod, the heating and decay-like fracture of composite insulator could be avoided to some extent.

Storm separation is a key step when carrying out storm transposition analysis for Probable Maximum Precipitation (PMP) estimation in mountainous areas. The World Meteorological Organization (WMO) has recommended the step-duration-orographic-intensification-factor (SDOIF) method since 2009 as an effective storm separation technique to identify the amounts of precipitation caused by topography from those caused by atmospheric dynamics. The orographic intensification factors (OIFs) are usually developed based on annual maximum rainfall series under such assumption that the mechanism of annual maximum rainfalls is close to that of the PMP-level rainfall. In this paper, an alternative storm separation technique using rainfall quantiles, instead of annual maximum rainfalls, with rare return periods estimated via Regional L-moments Analysis (RLMA) to calculate the OIFs is proposed. Based on Taiwan&rsquo, s historical 4- and 24-h precipitation data, comparisons of the OIFs obtained from annual maximum rainfalls with that from extreme rainfall quantiles at different return periods, as well as the PMP estimates of Hong Kong from transposing the different corresponding separated nonorographic rainfalls, were conducted. The results show that the OIFs obtained from rainfall quantiles with certain rare probabilities are more stable and reasonable in terms of stability and spatial distribution pattern.

This paper deals with the effects of rain conditions and shed parameters on flashover characteristics of hollow porcelain insulators through conducting artificial rain tests under extreme rainfall. And the effects of water droplet deformation on inter-shed discharge are examined especially. The results show that the rain flashover voltage gradient along the insulation height falls with the rise of rainfall intensity due to the increase in the maximum deformation length of water droplet, which can bring about two kinds of inter-shed discharge modes under different rainfall intensity. The fact that the maximum deformation length of water droplet is barely influenced by rainwater conductivity determines the consistency of inter-shed discharge modes under different rainwater conductivity. The rain flashover voltage gradient along the insulation height decreases with the rising rainwater conductivity since the insulator surface resistance falls with rainwater conductivity. Moreover, shed spacing can influence inter-shed discharge mode, which is reflected in the diverse direction of the discharge propagation at water droplet end under different shed spacing. The length of air gap on the breakdown path increasing improves rain flashover voltage gradient along the insulation height as shed spacing rises. However, the inter-shed discharge mode is independent of shed overhang. The rain flashover voltage gradient along the insulation height rising with shed overhang is attributed to the increase in the leakage distance along the shed surface. This work clarifies the inter-shed discharge mode of rain flashover and can provide valuable support for the shed design of insulators in extreme rainfall areas.

Research has found that preschoolers' imitation demonstrates in-group bias and is guided by behavior efficacy. However, little is known about whether children's sensitivity to behavior efficacy affects their in-group imitation. This study aimed to investigate preschoolers' imitation tendency when group preference and behavior efficacy are in conflict. Participants were 4-year-old (N = 72) and 6-year-old (N = 72) preschoolers in China. They observed two demonstrators (one in-group and one out-group) pressing two different buttons, respectively, to turn on a music box, and were then asked to try it themselves. In the experimental condition, the out-group demonstrator always succeeded, whereas the in-group demonstrator failed half the time. The results showed that more 6-year-old children imitated the less-effective behaviors of the in-group demonstrator, whereas 4-year-old children showed no such inclination. Two control conditions confirmed that children chose to imitate in-group rather than out-group members (Control 1: both in-group and out-group demonstrators succeeded all four times), and could imitate according to efficacy (Control 2: two in-group demonstrators succeeded two and four times, respectively). These results indicated that 6-year-olds faithfully followed the in-group modeled behavior, regardless of behavior efficacy. Results are discussed through the social function of in-group imitative learning.

Composite insulators are widely used in high voltage transmission lines in coast and polluted areas due to excellent pollution flashover resistance, high strength and convenient installation and maintenance. While there are still various kinds of defects such as abnormal temperature rise, aging of materials even fracture in the existing composite insulators which have drawn the close attention of the operation and maintenance department of power grid. In order to realize the basic performance of new composite insulator products in China, specimens from major manufacturers of composite insulators are sampled for mechanical, electrical and physical and chemical testing. The test results show that the composite insulator products meet the requirements overall, but a few of them have micro-interface and macro-interface defects which may cause local heating even fracture under high humidity conditions. At the same time, the raw materials of composite insulator housing from different manufacturers is quite different, which has certain influence on the service life of composite insulator.

The intelligent inspection of power lines and other difficult-to-access structures and facilities has been greatly enhanced by the use of Unmanned Aerial Vehicles (UAVs), which allow inspection in a safe, efficient, and high-quality fashion. This paper analyzes the characteristics of a scene containing power equipment and the operation mode of UAVs. A low-cost virtual scene is created, and a training sample for the power-line components is generated quickly. Taking a vibration-damper as the main object, an assembled detector based on geometrical constraint (ADGC) is proposed and is used to analyze the virtual dataset. The geometric positional relationship is used as the constraint, and the Faster Region with Convolutional Neural Network (R-CNN), Deformable Part Model (DPM), and Haar cascade classifiers are combined, which allows the features of different classifiers, such as contour, shape, and texture to be fully used. By combining the characteristics of virtual data and real data using UAV images, the power components are detected by the ADGC. The result produced by the detector with relatively good performance can help expand the training set and achieve a better detection model. Moreover, this method can be smoothly transferred to other power-line facilities and other power-line scenarios.

When it comes to safety accidents in power system, pollution flashover often causes more economic loss because of its large impact area and long impact time. To understand the contamination characteristics of insulators and predict the state of pollution, a typical insulator's contamination model in wind tunnel was established with Multiphysics simulation software, and a feature particle tracking method was proposed based on sample survey and feature particle analysis. The unitary pollution characteristics of insulator can be judged from the weighted average tracking results of sample particles with single particle size and charge amount. Based on this foundation, the effects of AC and DC electric fields were taken into consideration to analyze the influence of different kind of electric field on insulator contamination. The simulation results show that DC electric field has a significant effect on insulator fouling under the condition of weak wind and large particle size.

In this study, highly sensitive Ag 2 O-doped ZnO nanorods based sensor was presented and developed to detect CH 4 gas, an extremely significant fault characteristic gas extracted from power transformer oil. Ag 2 O-doped ZnO nanorods sensing materials were synthesized with facile hydrothermal method, and characterized via X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDS), respectively. Side heated chemical gas sensor was fabricated and its sensing performances towards CH 4 were systematically investigated. The optimal operating temperature of the Ag 2 O-doped ZnO sensor was 280 °C for CH 4 sensing, and its gas sensing response to 10 ppm CH 4 was measured to be as high as 12.28. In addition, good linearity for low concentration of CH 4 gas was also obtained. The corresponding response-recovery time of the Ag 2 O-doped ZnO sensor was measured to be about 17-10s. All results provide reference and guidance for developing high-performance ZnO based gas sensors for CH 4 detection. All these excellent sensors performances indicate the large potential of the fabricated Ag 2 O decorated ZnO nanorods sensor for practical application of CH 4 detection.

// Xiaoya He 1, 2, 3, 4 , Jinhua Cai 1, 2, 3, 4 , Hao Li 1, 2, 3, 4 , Bo Liu 1, 2, 3, 4 , Yong Qin 1, 2, 3, 4 , Yi Zhong 2, 3, 4 , Longlun Wang 1, 2, 3, 4 , Yifan Liao 2, 3, 4 1 Department of Radiology, Children's Hospital of Chongqing Medical University, Chongqing, China 2 Ministry of Education Key Laboratory of Child Development and Disorders, Chongqing, China 3 Key Laboratory of Pediatrics in Chongqing, Chongqing, China 4 Chongqing International Science and Technology Cooperation Center for Child Development and Disorders, Chongqing, China Correspondence to: Jinhua Cai, email: cai_jinhua@126.com Keywords: magnetic resonance imaging, ferritin heavy chain, tetracycline-inducible expression system, cell tracking, tumor xenograft Received: June 14, 2016 Accepted: October 03, 2016 Published: October 08, 2016 ABSTRACT As a promising magnetic resonance imaging (MRI) reporter, ferritin has been used to track cells in vivo ; however, its continuous overexpression can be cytotoxic, which restricts its application. In this study, we aimed to develop a switch to turn this genetic reporter “on” or “off” while monitoring cell grafts via MRI. To accomplish this, we genetically modified the ferritin heavy chain (FTH1) with a Tet-On switch and assessed the expression of FTH1 in transduced neuroblastoma cells (SK-N-SH) in vitro and in xenografted tumors in vivo . We found that FTH1 expression induced by doxycycline (Dox) in SK-N-SH-FTH1 cells depended on treatment dose and duration. We successfully detected T 2 -weighted MRI contrast in cell grafts after switching “on” the reporter gene using Dox, and this contrast disappeared when we switched it “off”. The genetic reporter FTH1 can thus be switched “on” or “off” throughout longitudinal monitoring of cell grafts, limiting expression to when MRI contrast is needed. The controllable imaging system we have developed minimizes risks from constitutive reporter gene overexpression and facilitates tumor cell monitoring in vitro and in vivo .

The flashover performance of insulators is significantly affected by the degrees and ways of wetting the pollution layer. However, there have only been a few reports on the wetting condition and its effects on the flashover characteristics of pollution on insulators to date. In this paper, a phase-angle difference-based method is proposed to test the wetting conditions of the pollution layer on insulators. A corresponding measuring device is also developed. The wetting process of the pollution layer on aerodynamic-type glass insulators is studied in an artificial climate chamber using the developed device. The related flashover performance is studied via the even-rising voltage method. Test results show that the phase-angle difference (PAD) curve accurately reflects the entire wetting process of the pollution layer from the initial stage, through the saturated stage to the oversaturated and washing away stages. Over the wetting process, the PAD curve initially drops sharply, and then remains stable for a few minutes before eventually rising slowly to the initial value. The PAD curve has its lowest value when the pollution layer is wetted to saturation, which occurs after approximately 5 min in our experiments. The flashover voltage characteristics of insulators are also significantly affected by the wetting conditions of the pollution layer. The flashover voltage in the saturated stage is shown to be lower than that in the other stages. Therefore, to improve the accuracy of the artificial pollution tests, quantitative methods (including PAD) should be used to obtain the exact time of wetting to saturation.

We investigated the combined effect of pressure and temperature on the elasticity of single-crystal superhydrous phase B (Shy-B) using Brillouin scattering and X-ray diffraction up to 12 GPa and 700 K. Using the obtained elasticity, we modeled the anisotropy of Shy-B along slab geotherms, showing that Shy-B has a low anisotropy and cannot be the major cause of the observed anisotropy in the region. Modeled velocities of Shy-B show that Shy-B will be shown as positive velocity anomalies at the bottom transition zone. Once Shy-B is transported to the topmost lower mantle, it will exhibit a seismic signature of lower velocities than topmost lower mantle. We speculate that an accumulation of hydrous phases, such as Shy-B, at the topmost lower mantle with a weight percentage of ~17–26% in the peridotite layer as subduction progresses could help explain the observed 2–3% low shear velocity anomalies in the region.

In order to solve the problem of complex function optimization, the ecological balance dynamics-based optimization (EBDO) algorithm is proposed based on the Lotka–Volterra ecological balance dynamics. The algorithm assumes that there are three populations of nurturers, consumers, and decomposers in an ecosystem. The self-plowing is mainly the plant; the consumer is mainly the animal who feeds on the nourish; the decomposer mainly breaks down the dead body of the consumer, and the nutrient is supplied to the self-raised person. According to the relationship among the populations in the above ecosystem, the consumer-autotrophic operator, the self-coter decomposer operator, the decomposer-consumer operator and the growth operator are constructed. The growth change of the population of the self-employed, the consumer and the decomposer is equivalent to the search space trying to move from one location to another. The algorithm has the characteristics of strong search ability and global convergence, it provides a solution for solving complex optimization problems.

With the rapid development of robots in the world, robots in various application scenarios have come into people's sight, especially various inspection robots appear in people's lives. At present, the application of fire patrol robots is more and more. Now, the fire patrol robots used in the warehouse are all land patrol robots. When they work on the designated route, they have high requirements for the environment. When there is a complex environment with uneven ground, it will have a great impact on the robot. This rail mounted fire inspection robot is running on the track, and the platform can be inspected without dead angle. It has low environmental requirements, high inspection efficiency, real-time alarm, and uses computer vision platform to track, which improves the accuracy of fire source identification. In this design, STM32F4 single chip microcomputer is used as the main control of the whole system, which is completed with a number of servo motors, alarms and other hardware, and computer vision and robot main control data interaction.

Recently, the COVID-19 has swept the whole world. Under this situation, the firm, as a member of the society, should also undertake social responsibilities to jointly respond to the COVID-19. The employee, as a principal part of firm, plays an important role in informatization management which may affects the level of corporate social responsibility. Their ability of informatization management will inevitably affect their access to the information of corporate social responsibility, thus affecting the level of corporate social responsibility. This paper takes A-share listed companies from 2011 to 2018 collected in CSMAR as samples to explore the relations between employees' ability of informatization and corporate social responsibility. This study, as an interdisciplinary research related to computer and management, adopts OLS, IV method and other mathematics methods to build models. Using the employee education level as a proxy for employees' ability of informatization management, this paper finds that firms with a high-quality workforce exhibit higher level of corporate social responsibility, especially in the areas with lower degree of marketization. According to the further analysis using the model of Sobel test, the internal control plays a mediating role between employees' ability of informatization management and corporate social responsibility. This study suggests that employee quality plays an important role in performing corporate social responsibility. This study should be of interest to top managers and regulators who wish to use information technology to improve corporate social responsibility. © The Authors, published by EDP Sciences, 2021.

The electric field distribution around the insulator is the main influencing factor of its flashover characteristics. And the electric field distribution of the insulator is affected by the external tower structure and connecting parts. Therefore, there are differences in electric field distribution of the insulators with different tower structures. And the insulator flashover characteristics vary depending on the tower structure and the suspension position of the insulators. In order to study the effect of tower structure on the electric field distribution around the insulator and its effect on flashover voltage, based on COMSOL Multiphysics, the finite element simulations on the electric field distributions around the composite three-phase insulators suspended on the umbrella-shape the drum-shape towers were conducted in this paper. The formation of the electric field distribution around the insulator suspended in the tower and the influence of the tower structure on its electric field distribution were analyzed. In addition, the flashover characteristics test of the composite insulator in the $110\mathrm {k}\mathrm {V}$ transmission line at high altitude area was carried out. The test was under a standard lightning impulse voltage of $1.2/50\mu \mathrm {s}$. Combined with the test results, the relationship between the 50% impulse discharge voltage of the three-phase insulators suspended in the tower and the uneven coefficient of electric field is further analyzed and verified.

The installation of grading rings for composite insulators on high voltage transmission lines was an effective measure to improve the distribution of electric field and prevent brittle fracture of the core bar. In this paper, the flashover characteristics of insulators with and without the installation of the grading ring on the 110 kV voltage grade cat head tower were tested and simulated. Firstly, The U 50 , volt-time characteristics and discharge images of the insulators are studied by experiments. The experimental results show that the unit length U 50 of the insulator with the grading ring will increase compared to the insulators without the grading, and the volt-time characteristic position is basically unchanged while the starting point of the discharge channel is transferred from the fitting of insulators to the grading ring and the number of leading channel branches increase. Secondly, the electric field distribution around the insulator before and after the installation of the grading ring is studied by simulation. The simulation results show that the maximum field strength around the insulator decreases when the grading ring is installed, while the unevenness coefficient decreases and the average electric field strength increases. The simulation results agrees well with the test data. The research results can be used as a reference for the optimization design of the voltage equalization loop and the lightning protection of high altitude transmission lines.

The rain flashover of insulators in rainy weather is an important factor which affects the external insulation of electric power system. In view of rain flashover problem of insulators, this paper carried out a lot of artificial rain test under different rainfall conditions for suspension composite insulators with different parameters. Selected the number of water column, the number of water droplets and the proportion of the water column to the large sheds spacing as the rain characteristic variables. And the rain characteristics of insulators were studied. Experimental results indicated that rainfall had a significant influence on the rain characteristic variables of insulator. When the rainfall increased, the number of water columns, the number of water droplets and the proportion of the water column to the large sheds spacing increased, and the possibility of bridging between the water column and the water droplets in the two large sheds increased, and the more easily the insulators were flashover. Shed configuration has effect on the rain characteristic variables of insulator. Under the same conditions of rainfall, the larger the rain area of the shed, the more water columns and water droplets between the shed units. The increase in the shed spacing can reduce the possibility of bridging and improve the utilization ratio of leakage distance.

Magnetic resonance imaging (MRI) based on the ferritin heavy chain 1 (FTH1) reporter gene has been used to trace stem cells. However, whether FTH1 expression is affected by stem cell differentiation or whether cell differentiation is affected by reporter gene expression remains unclear. Here, we explore the relationship between FTH1 expression and neural differentiation in the differentiation of mesenchymal stem cells (MSCs) carrying FTH1 into neuron-like cells and investigate the feasibility of using FTH1 as an MRI reporter gene to detect neurally differentiated cells. By inducing cell differentiation with all-trans retinoic acid and a modified neuronal medium, MSCs and MSCs-FTH1 were successfully differentiated into neuron-like cells (Neurons and Neurons-FTH1), and the neural differentiation rates were (91.56±7.89)% and (92.23±7.64)%, respectively. Neuron-specific markers, including nestin, neuron-specific enolase, and microtubule-associated protein-2, were significantly expressed in Neurons-FTH1 and Neurons without noticeable differences. On the other hand, FTH1 was significantly expressed in MSCs-FTH1 and Neurons-FTH1 cells, and the expression levels were not significantly different. The R2 value was significantly increased in MSCs-FTH1 and Neurons-FTH1 cells, which was consistent with the findings of Prussian blue staining, transmission electron microscopy, and intracellular iron measurements. These results suggest that FTH1 gene expression did not affect MSC differentiation into neurons and was not affected by neural differentiation. Thus, MRI reporter gene imaging based on FTH1 can be used for the detection of neurally differentiated cells from MSCs.

The hydrophobicity of composite insulators is a great significance to the safe and stable operation of transmission lines. In this paper, a recognition method of the hydrophobicity class (HC) of composite insulators based on features optimization was proposed. Through the spray method, many hydrophobic images of water droplets on the insulator surface at various hydrophobicity classes (HCs) were taken. After processing of the hydrophobic images, seven features were extracted: the number n, mean eccentricity Eav and coverage rate k1 of the water droplets, and the coverage rate k2, perimeter Lmax, shape factor fc, and eccentricity Emax of the maximum water droplet. Then, the maximum value Δxmax, the minimum value Δxmin, and the average value Δxav of the change rate of each feature value between adjacent HCs, and the volatility Δs of each feature value, were used as the evaluation indexes for features optimization. After this features optimization, the five features that are most closely related to the HC were obtained. Lastly, a recognition model of the HC with the five features as input and the seven HCs as output was established. When compared with the spray method and the contact angle method, the correct rate of the proposed recognition method was 98.1% and 95.2%, respectively. The influence of subjective factors on the spray method was effectively overcome.

In order to provide reference for the operation and maintenance of porcelain insulators on DC transmission lines, the test method for electrolytic corrosion of iron caps was studied in National Engineering Laboratory for Ultra High Voltage Engineering Technology (Kunming) of China, with XZP2-300 porcelain insulators that had no protection zinc collar. The results indicated that the spray water method could simulate the field corrosion condition when the conductivity and volume flow rate were 12 mS/cm and 6-12 L/h respectively, and the differences in the length, width and depth of corrosion area between the test results and the field condition were less than 8%. Besides, the differences in the test results with spray water method from two experimenters were less than 7%. Our study demonstrated that the spray water method proposed in this paper had good equivalence and repeatability, which could be used to research the electrolytic corrosion problem of iron caps of porcelain insulator on HVDC transmission line.

Power transformers have important roles as voltage converters in substations, which directly affect the safe operation of power grids. Online monitoring of winding deformation, which is one of the most common transformer faults, is crucial in protecting transformers from damage, particularly those induced by short-circuit current failures, and ensuring their safe operation. This study proposes an improved online monitoring method for winding deformations based on the Lissajous graphical analysis of voltage and current. A practical measurement system is also presented and discussed in this paper. A load normalization method is proposed to solve the problem of Lissajous diagrams changing as load varies. Finally, transformer and winding experiments are performed to verify the validity of the proposed load normalization method and the feasibility of the proposed monitoring method in distinguishing winding deformations with different degrees and locations.

In recent years, the phenomenon of electrolytic corrosion on porcelain insulators’ iron caps has occurred in many HVDC transmission lines in China such as the Yunguang, Xiangshang, Tianguang, Gaozhao and Xingan HVDC lines. The validity of using U-shaped zinc rings to restrain iron caps’ electrolytic corrosion is tested and verified in this paper. In order to research the influence of U-shaped zinc rings on the electric field intensity of insulators, Finite Element Method (FEM) simulation software was used to calculate the surface electric field of insulators with and without a zinc ring. The influence of zinc ring size on the inhibitory effect was studied by accelerated electrolytic corrosion tests, and the reason that zinc rings of the same size exert different inhibitory effects on insulators of different tonnage is explained in terms of iron caps’ curvature radii and water pocket characteristics. Test results indicate that the installation of U-shaped zinc rings is useful to suppress iron caps’ electrolytic corrosion, and that the inhibitory effect of zinc rings of the same size on insulators with larger cap curvature radii is better than that on smaller ones. Optimal designs of the structure and size of the U-shaped zinc ring and its service life are proposed in this paper, based on the test results and the actual engineering practice.

The auto-focusing method is described in this article based on image processing technology, and of an automatic iris image acquisition system is designed by the application of the principles. By using infrared lighting, the camera lens moving is control by computer, and in the human eye images are constantly collected in the process. First, the iris region is positioned in each image, and on the contrast of the area, we determines whether the iris image is a clear. By auto-focus, the captured image is used finally for identifying. Experiments proved that auto-focus is more accurate, iris images are captured with high contrast, and its texture features are rich significantly, and the requirements of subsequent processing and use are meet. Focusing mechanism is relatively simple, easy to implement the control system. It is applied to medical diagnostics to good effect.

In the concrete implementation of the fuzzy vault algorithm, the geometric hash method is a common technique for automatic calibration of biometric templates. For the fuzzy problem of parameter acquisition, the matching accuracy of fuzzy vault template is affected in the three parameters: the pixel size, hash table and hash table quantization parameters ([Formula: see text] and [Formula: see text]). The single factor experiment method obtains the optimal range of these three parameters, and the extraction range of the fuzzy point and the selection rule of the base point distance are improved for the fuzzy vault algorithm. Finally, based on the FVC fingerprint database, their matching precision is compared for the algorithm before and after optimization. The experimental results show that the false rejection rate (FRR) of the optimized algorithm is reduced by at least 9.84%, and the false acceptance rate (FAR) is reduced by at least 7.12%, indicating that the optimization scheme improves the matching accuracy of the algorithm. The algorithm has certain robustness and practicability.

Two experiments were carried out to determine if brief priming for cooperation or competition affects 4-year-old children’s visual perspective taking. In each experiment, children were tested for their flexibility to take different perspectives between themselves and an adult who cooperated with or competed against them earlier in a fishing game. The results of Experiment 1 (N = 48) showed that children who cooperated with, compared to those who competed against, an adult were more capable of comprehending perspectives that were different from their own. The results of Experiment 2 (N = 72) further clarified that children still had some difficulty in understanding others’ perspectives at the baseline. Further, compared to the baseline, cooperation, but not competition, significantly improved their flexibility in understanding others’ perspectives. The current findings extend knowledge about the development of high-level perspective taking and how it is correlated with different types of social interaction, especially cooperation.