The interactions between lignin oligomers and solvents determine the behaviors of lignin oligomers self-assembling into uniform lignin nanoparticles(LNPs).Herein,several alcohol solvents,which readily interact with th...The interactions between lignin oligomers and solvents determine the behaviors of lignin oligomers self-assembling into uniform lignin nanoparticles(LNPs).Herein,several alcohol solvents,which readily interact with the lignin oligomers,were adopted to study their effects during solvent shifting process for LNPs’production.The lignin oligomers with widely distributed molecular weight and abundant guaiacyl units were extracted from wood waste(mainly consists of pine wood),exerting outstanding self-assembly capability.Uniform and spherical LNPs were generated in H_(2)O-n-propanol cosolvent,whereas irregular LNPs were obtained in H_(2)O-methanol cosolvent.The unsatisfactory self-assembly performance of the lignin oligomers in H_(2)O-methanol cosolvent could be attributed to two aspects.On one hand,for the initial dissolution state,the distinguishing Hansen solubility parameter and polarity between methanol solvent and lignin oligomers resulted in the poor dispersion of the lignin oligomers.On the other hand,strong hydrogen bonds between methanol solvent and lignin oligomers during solvent shifting process,hindered the interactions among the lignin oligomers for self-assembly.展开更多
According to the structural characteristics of the automobile engine bracket, the finite element model of the bracket is established. As the connecting part between the engine and the body, the performance requirement...According to the structural characteristics of the automobile engine bracket, the finite element model of the bracket is established. As the connecting part between the engine and the body, the performance requirements of the automobile engine bracket affect the comfort and the safety of the vehicle directly. Using the RADIOSS solver, the dangerous point of the bracket is analyzed. Under the premise of ensuring its reliability, with the help of OptiStruct software to carry out the topology optimization design, to get the optimal material distribution of the bracket and the final design will meet the performance requirements.展开更多
This article dissects the challenges faced and the integration strategies for embracing the educational metaverse from existing research,preparing for the new educational trend-the educational metaverse-by controlling...This article dissects the challenges faced and the integration strategies for embracing the educational metaverse from existing research,preparing for the new educational trend-the educational metaverse-by controlling the target direction,technical direction,teacher training direction,and ethical direction.Starting from the origin,it analyzes the reasons for the entry of the metaverse into the educational field and summarizes the three characteristics of the educational metaverse supported by current technical means.Combining the current situation of classroom teaching and the advantages of the educational metaverse,it analyzes the inevitability of the metaverse entering the classroom.Subsequently,it analyzes the four major challenges of the current stage:the pressure of college entrance examinations,the challenge of technical implementation,the limited ability of teachers,and the digital ethical risks brought by the metaverse.It prescribes the right remedy,giving strategies for integrating the educational metaverse into the classroom from the four directions of reducing the burden of college entrance examinations,technology research,teacher ability development,and rule formulation.It is hoped that in the future,while the metaverse lands in the educational field,it can overcome challenges at various levels and achieve breakthroughs at the target level,technical level,teacher training level,and ethical level to truly realize the entry of the educational metaverse into the classroom.展开更多
Detection of high impedance faults(HIFs)has been traditionally a main challenge in the protection of distribution systems,since they do not generate enough current to be reliably detected by conventional over-current ...Detection of high impedance faults(HIFs)has been traditionally a main challenge in the protection of distribution systems,since they do not generate enough current to be reliably detected by conventional over-current relays.Data-based methods are alternative HIF detection methods which avoid threshold settings by training a classification or regression model.However,most of them lack interpretability and are not compatible with various distribution networks.This paper proposes an object detection-based HIF detection method,which has higher visualization and can be easily applied to different scenarios.First,based on the analysis of HIFs,a Butterworth band-pass filter is designed for HIF harmonic feature extraction.Subsequently,based on the synchronized data provided by distribution-level phasor measurement units,global HIF feature gray-scale images are formed through combining the topology information of the distribution network.To further enhance the feature information,a locally excitatory globally inhibitory oscillator region attention mechanism(LEGIO-RAM)is proposed to highlight the critical feature regions and inhibit useless and fake information.Finally,an object detection network based You Only Look Once(YOLO)v2 is established to achieve fast HIF detection and section location.The obtained results from the simulation of the proposed approach on three different distribution networks and one realistic distribution network verify that the proposed method is highly effective in terms of reliability and generalization.展开更多
With the development of power electronics technology,the flexible DC grid will play a significant role in promoting the transformation and reformation of the power grid.It is immune to commutation failure and has high...With the development of power electronics technology,the flexible DC grid will play a significant role in promoting the transformation and reformation of the power grid.It is immune to commutation failure and has high flexibility in power control and renewable energy grid integration.However,the protection and fault handling technology for a flexible DC grid is a big challenge because of the limited overcurrent capability of the converters.This paper summarizes the development of the flexible DC grid,and analyzes the fault characteristics in detail.Next,the applicability,advantages and disadvantages of the existing protection principle,fault isolation and recovery schemes are reviewed.Finally,the key problems and development trend of the future flexible DC grid are pointed out and forecasted respectively.展开更多
In order to ensure the safety of railway transportation,it is necessary to regularly check for faults and defects in the railway system.Visual inspection technology is conducive to improving the low efficiency,poor ec...In order to ensure the safety of railway transportation,it is necessary to regularly check for faults and defects in the railway system.Visual inspection technology is conducive to improving the low efficiency,poor economy and inaccurate detection results of traditional detection methods.This paper introduces the research and contribution of various scholars in the field of visual inspection,summarizes the application and development of visual inspection technology in the railway industry,and finally forecasts the future research direction of visual inspection technology.展开更多
Summary of main observation and conclusion In this work,the promotion effect of NaCl on the conversion of xylose to furfural in H2O was studied.it was found that xylose conversion and furfural yield increased with NaC...Summary of main observation and conclusion In this work,the promotion effect of NaCl on the conversion of xylose to furfural in H2O was studied.it was found that xylose conversion and furfural yield increased with NaCl concentration.NaCl decreased the pH of the solution providing H+ for the acid catalytic dehydration of xylose.The formation of oligomers was determined by GPC and ESI-MS in the initial stage of reaction,especially at low temperature.Excess NaCl promoted the formation of humins in the late stage of the reaction.NaCl could also change the decomposition route of formic acid.Meanwhile,NaCl had the ability of phase separation.Combining these effects with organic solvent during the reaction could inhibit the formation of humins and increase the yield of furfural.In NaCl-H2O-THF biphasic system without other catalyst,the optimal furfural yield of 76.7% and selectivity of 77.6% were achieved at 463 K in 2 h.展开更多
基金supported by the National Natural Science Foundation of China(22078211)the China Postdoctoral Science Foundation(2022M721115).
文摘The interactions between lignin oligomers and solvents determine the behaviors of lignin oligomers self-assembling into uniform lignin nanoparticles(LNPs).Herein,several alcohol solvents,which readily interact with the lignin oligomers,were adopted to study their effects during solvent shifting process for LNPs’production.The lignin oligomers with widely distributed molecular weight and abundant guaiacyl units were extracted from wood waste(mainly consists of pine wood),exerting outstanding self-assembly capability.Uniform and spherical LNPs were generated in H_(2)O-n-propanol cosolvent,whereas irregular LNPs were obtained in H_(2)O-methanol cosolvent.The unsatisfactory self-assembly performance of the lignin oligomers in H_(2)O-methanol cosolvent could be attributed to two aspects.On one hand,for the initial dissolution state,the distinguishing Hansen solubility parameter and polarity between methanol solvent and lignin oligomers resulted in the poor dispersion of the lignin oligomers.On the other hand,strong hydrogen bonds between methanol solvent and lignin oligomers during solvent shifting process,hindered the interactions among the lignin oligomers for self-assembly.
文摘According to the structural characteristics of the automobile engine bracket, the finite element model of the bracket is established. As the connecting part between the engine and the body, the performance requirements of the automobile engine bracket affect the comfort and the safety of the vehicle directly. Using the RADIOSS solver, the dangerous point of the bracket is analyzed. Under the premise of ensuring its reliability, with the help of OptiStruct software to carry out the topology optimization design, to get the optimal material distribution of the bracket and the final design will meet the performance requirements.
文摘This article dissects the challenges faced and the integration strategies for embracing the educational metaverse from existing research,preparing for the new educational trend-the educational metaverse-by controlling the target direction,technical direction,teacher training direction,and ethical direction.Starting from the origin,it analyzes the reasons for the entry of the metaverse into the educational field and summarizes the three characteristics of the educational metaverse supported by current technical means.Combining the current situation of classroom teaching and the advantages of the educational metaverse,it analyzes the inevitability of the metaverse entering the classroom.Subsequently,it analyzes the four major challenges of the current stage:the pressure of college entrance examinations,the challenge of technical implementation,the limited ability of teachers,and the digital ethical risks brought by the metaverse.It prescribes the right remedy,giving strategies for integrating the educational metaverse into the classroom from the four directions of reducing the burden of college entrance examinations,technology research,teacher ability development,and rule formulation.It is hoped that in the future,while the metaverse lands in the educational field,it can overcome challenges at various levels and achieve breakthroughs at the target level,technical level,teacher training level,and ethical level to truly realize the entry of the educational metaverse into the classroom.
基金supported by the National Key Research and Development Program of China(2017YFB0902800)Science and Technology Project of the State Grid Corporation of China(52094017003D).
文摘Detection of high impedance faults(HIFs)has been traditionally a main challenge in the protection of distribution systems,since they do not generate enough current to be reliably detected by conventional over-current relays.Data-based methods are alternative HIF detection methods which avoid threshold settings by training a classification or regression model.However,most of them lack interpretability and are not compatible with various distribution networks.This paper proposes an object detection-based HIF detection method,which has higher visualization and can be easily applied to different scenarios.First,based on the analysis of HIFs,a Butterworth band-pass filter is designed for HIF harmonic feature extraction.Subsequently,based on the synchronized data provided by distribution-level phasor measurement units,global HIF feature gray-scale images are formed through combining the topology information of the distribution network.To further enhance the feature information,a locally excitatory globally inhibitory oscillator region attention mechanism(LEGIO-RAM)is proposed to highlight the critical feature regions and inhibit useless and fake information.Finally,an object detection network based You Only Look Once(YOLO)v2 is established to achieve fast HIF detection and section location.The obtained results from the simulation of the proposed approach on three different distribution networks and one realistic distribution network verify that the proposed method is highly effective in terms of reliability and generalization.
基金funded by the Fundamental Research Funds for the Central Universities(No.2019YJS179).
文摘With the development of power electronics technology,the flexible DC grid will play a significant role in promoting the transformation and reformation of the power grid.It is immune to commutation failure and has high flexibility in power control and renewable energy grid integration.However,the protection and fault handling technology for a flexible DC grid is a big challenge because of the limited overcurrent capability of the converters.This paper summarizes the development of the flexible DC grid,and analyzes the fault characteristics in detail.Next,the applicability,advantages and disadvantages of the existing protection principle,fault isolation and recovery schemes are reviewed.Finally,the key problems and development trend of the future flexible DC grid are pointed out and forecasted respectively.
文摘In order to ensure the safety of railway transportation,it is necessary to regularly check for faults and defects in the railway system.Visual inspection technology is conducive to improving the low efficiency,poor economy and inaccurate detection results of traditional detection methods.This paper introduces the research and contribution of various scholars in the field of visual inspection,summarizes the application and development of visual inspection technology in the railway industry,and finally forecasts the future research direction of visual inspection technology.
基金the National Natural Science Foundation of China(No.21536007)the 111 Project(B17030)the Fundamental Research Funds for the Central Un iversities.
文摘Summary of main observation and conclusion In this work,the promotion effect of NaCl on the conversion of xylose to furfural in H2O was studied.it was found that xylose conversion and furfural yield increased with NaCl concentration.NaCl decreased the pH of the solution providing H+ for the acid catalytic dehydration of xylose.The formation of oligomers was determined by GPC and ESI-MS in the initial stage of reaction,especially at low temperature.Excess NaCl promoted the formation of humins in the late stage of the reaction.NaCl could also change the decomposition route of formic acid.Meanwhile,NaCl had the ability of phase separation.Combining these effects with organic solvent during the reaction could inhibit the formation of humins and increase the yield of furfural.In NaCl-H2O-THF biphasic system without other catalyst,the optimal furfural yield of 76.7% and selectivity of 77.6% were achieved at 463 K in 2 h.
