Typology and working mechanism of a hybrid power router based on power-frequency transformer electromagnetic coupling with converters

The power router(PR)is a promising piece of equipment for realizing multi-voltage level interconnection and flex-ible power control in the future distribution power grid.In this paper,a hybrid PR(HPR)topology based on power-frequency transformer electromagnetic coupling with converters is proposed for the medium distribution power grid.The power-frequency transformer is used to undertake power transmission,voltage conversion,and other main tasks,while the power electronic converters are combined to achieve active control.Equivalent magnetic and electrical circuit models are established to help discuss the operating principle of the proposed HPR.Additionally,the power flow and control principle of the HPR in different operating conditions are analyzed,with the control system design scheme presented.The theoretical analysis results are verified by MATLAB/Simulink+Plecs simulation and a controller hardware-in-the-loop study,as well as a down-scale experimental test,indicating that the proposed HPR is flexible in active voltage support and current control.

Hybrid working mechanism enables highly reversible Zn electrodes

Zn dendrite growth and water-related side reactions have been criticized to hinder actual applications of aqueous Zn-ion batteries.To address these issues,a series of Zn interfacial modifications of building solid/electrolyte interphase(SEI)and nucleation layers have been widely proposed,however,their effectiveness remains debatable.Here,we report a boron nitride(BN)/Nafion layer on the Zn surface to efficiently solve Zn problems through combining the hybrid working mechanisms of SEI and nucleation layers.In our protective layer,Nafion exhibits the SEI mechanism by blocking water from the Zn surface and providing abundant channels for rapid Zn^(2+)þtransmission,whilst BN nanosheets induce Zn deposition underneath with a preferred(002)orientation.Accordingly,dendrite-free and side-reaction-free Zn electrode with(002)deposition under the protective layer is realized for the first time,as reflected by its high reversibility with average Coulombic efficiency of 99.2%for>3000 h.The protected Zn electrode also shows excellent performance in full cells when coupling with polyaniline cathode under the strict condition of lean electrolyte addition.This work highlights insights for designing highly reversible metal electrodes towards practical applications.

Recent Advances on Early-Stage Fire-Warning Systems: Mechanism, Performance, and Perspective

Early-stage fire-warning systems(EFWSs)have attracted significant attention owing to their superiority in detecting fire situations occurring in the pre-combustion process.Substantial progress on EFWSs has been achieved recently,and they have presented a considerable possibility for more evacuation time to control constant unintentional fire hazards in our daily life.This review mainly makes a comprehensive summary of the current EFWSs,including the working mechanisms and their performance.According to the different working mechanisms,fire alarms can be classified into graphene oxide-based fire alarms,semiconductor-based fire alarms,thermoelectric-based fire alarms,and fire alarms on other working mechanisms.Finally,the challenge and prospect for EFWSs are briefly provided by comparing the art of state of fire alarms.This work can propose a more comprehensive understanding of EFWSs and a guideline for the cutting-edge development direction of EFWSs for readers.

Superficial Inquiry on the Mechanism of Psychological Health Education of College Students under the Background of Anti Epidemic

Psychological health education has been highly valued by the party and the state.During the fight against the COVID-19,colleges and universities have made a beneficial exploration in carrying out psychological health education.In older to further understand the impact of the epidemic on the psychological health of college students,a survey was carried out based on questionnaire survey,depth interview and expert consultation.The survey found that the epidemic increased the psychological pressure and posed new challenges to the psychological health education in colleges and universities.Based on the analysis of the causes from the four aspects of society,family,college and individual,this thesis put forwards some suggestions on how to effectively carry out the psychological health education of college students in the context of fighting against the epidemic.

Harvesting Environment Mechanical Energy by Direct Current Triboelectric Nanogenerators

As hundreds of millions of distributed devices appear in every corner of our lives for information collection and transmission in big data era,the biggest challenge is the energy supply for these devices and the signal transmission of sensors.Triboelectric nanogenerator(TENG)as a new energy technology meets the increasing demand of today’s distributed energy supply due to its ability to convert the ambient mechanical energy into electric energy.Meanwhile,TENG can also be used as a sensing system.Direct current triboelectric nanogenerator(DC-TENG)can directly supply power to electronic devices without additional rectification.It has been one of the most important developments of TENG in recent years.Herein,we review recent progress in the novel structure designs,working mechanism and corresponding method to improve the output performance for DC-TENGs from the aspect of mechanical rectifier,tribovoltaic effect,phase control,mechanical delay switch and air-discharge.The basic theory of each mode,key merits and potential development are discussed in detail.At last,we provide a guideline for future challenges of DC-TENGs,and a strategy for improving the output performance for commercial applications.

Multifunctional Perovskite Photodetectors: From Molecular-Scale Crystal Structure Design to Micro/Nano-scale Morphology Manipulation

Multifunctional photodetectors boost the development of traditional optical communication technology and emerging artificial intelligence fields, such as robotics and autonomous driving. However, the current implementation of multifunctional detectors is based on the physical combination of optical lenses, gratings, and multiple photodetectors, the large size and its complex structure hinder the miniaturization, lightweight, and integration of devices. In contrast, perovskite materials have achieved remarkable progress in the field of multifunctional photodetectors due to their diverse crystal structures, simple morphology manipulation, and excellent optoelectronic properties. In this review, we first overview the crystal structures and morphology manipulation techniques of perovskite materials and then summarize the working mechanism and performance parameters of multifunctional photodetectors. Furthermore, the fabrication strategies of multifunctional perovskite photodetectors and their advancements are highlighted, including polarized light detection, spectral detection, angle-sensing detection, and selfpowered detection. Finally, the existing problems of multifunctional detectors and the perspectives of their future development are presented.

Latest progresses and the application of various electrolytes in high-performance solid-state lithium-sulfur batteries

With the emergence of some solid electrolytes(SSEs)with high ionic conductivity being comparable to liquid electrolytes,solid-state lithium-sulfur batteries(SSLSBs)have been widely regarded as one of the most promising candidates for the next generation of power generation energy storage batteries,and have been extensively researched.Though many fundamental and technological issues still need to be resolved to develop commercially viable technologies,SSLSBs using SSEs are expected to address the present limitations and achieve high energy and power density while improving safety,which is very attractive to large-scale energy storage systems.SSLSBs have been developed for many years.However,there are few systematic discussions related to the working mechanism of action of various electrolytes in SSLSBs and the defects and the corresponding solutions of various electrolytes.To fill this gap,it is very meaningful to review the recent progress of SSEs in SSLSBs.In this review,we comprehensively investigate and summarize the application of SSEs in LSBs to determine the differences which still exist between current progresses and real-world requirements,and comprehensively describe the mechanism of action of SSLSBs,including lithium-ion transport,interfacial contact,and catalytic conversion mechanisms.More importantly,the selection of solid electrolyte materials and the novel design of structures are reviewed and the properties of various SSEs are elucidated.Finally,the prospects and possible future research directions of SSLSBs including designing high electronic/ionic conductivity for cathodes,optimizing electrolytes and developing novel electrolytes with excellent properties,improving electrode/-electrolyte interface stability and enhancing interfacial dynamics between electrolyte and anode,using more advanced test equipment and characterization techniques to analyze conduction mechanism of Li^(+)in SSEs are presented.It is hoped that this review can arouse people’s attention and enlighten the development of functional materials and novel structures of SSEs in the next step.

Recent progress on electrolyte functional additives for protection of nickel-rich layered oxide cathode materials

In advantages of their high capacity and high operating voltage,the nickel(Ni)-rich layered transition metal oxide cathode materials(LiNi_(x)Co_(y)Mn_(z)O_(2)(NCMxyz,x+y+z=1,x≥0.5)and LiNi_(0.8)Co_(0.15)Al_(0.05)O_(2)(NCA))have been arousing great interests to improve the energy density of LIBs.However,these Nirich cathodes always suffer from rapid capacity degradation induced by unstable cathode-electrolyte interphase(CEI)layer and destruction of bulk crystal structure.Therefore,varied electrode/electrolyte interface engineering strategies(such as electrolyte formulation,material coating or doping)have been developed for Ni-rich cathodes protection.Among them,developing electrolyte functional additives has been proven to be a simple,effective,and economic method to improve the cycling stability of Nirich cathodes.This is achieved by removing unfavorable species(such as HF,H_(2)O)or constructing a stable and protective CEI layer against unfavorable reactive species(such as HF,H_(2)O).Herein,this review mainly introduces the varied classes of electrolyte functional additives and their working mechanism for interfacial engineering of Ni-rich cathodes.Especially,key favorable species for stabilizing CEI layer are summarized.More importantly,we put forward perspectives for screening and customizing ideal functional additives for high performance Ni-rich cathodes based LIBs.

Research progress and development direction of low-temperature drilling fluid for Antarctic region

By combing the characteristics of drilling in Antarctic region, performance requirements on drilling fluid for Antarctic low temperature conditions, and research progress of low temperature drilling fluid, current problems of the drilling fluid have been sorted out, and the development direction of the drilling fluid has been pointed out. Drilling in the Antarctic region mainly includes drilling in snow, ice and subglacial rock formations, and drilling in Antarctic low temperature conditions will face problems in four aspects:(1) low temperature and large temperature changes in the drilling area;(2) likely well leakage and drillstring-sticking in the snow layer, creep in the ice layer, ice chip gathering jamming in the warm ice layer, well wall collapse in the subglacial rock formations;(3) lack of infrastructure and difficulty in logistical support;(4) fragile environment and low carrying capacity. After years of development, progresses have been made on low-temperature drilling fluids for the Antarctic region. Low-temperature petroleum-based drilling fluid, ethanol/ethylene glycol-based drilling fluid, ester-based drilling fluid and silicone oil-based drilling fluid have been developed. However, these drilling fluids have problems such as insufficient low-temperature tolerance, low environmental performance and weak wellbore stability, etc. In order to meet the performance requirements of drilling fluid under low-temperature conditions in Antarctic region, the working mechanisms of low-temperature drilling fluid must be examined in depth;environment-friendly low-temperature base fluid of drilling fluid and related additives must be developed to prepare environmentally friendly low temperature drilling fluid systems;multi-functional integrated adjustment method for drilling fluid must be worked out to ensure well wall stability and improve cutting-carry capacity when drilling ice formations and ice-rock interlayers;and on-site support operation codes must be established to provide technical support for Antarctic drilling.

MY WORK IN THE FIELD OF FLUID MECHANICS

I graduated from the National Peiyang University (now called Tianjin University) in 1950, majoring in hydraulic engineering. Starting from 1952, my teaching work was basically in mechanics.My first academic probe was in cybernetics, resulting in the publication of the first Chinese paper concerning optimal control. After 1963, I worked on the theory of hydrodynamic stability. My explorative thrust is at the eigenvalues of the Orr Sommerfeld Equation,a non-self adjoint problem in

Recent advances in electrochemical decontamination of perfluorinated compounds from water: a review

Per- and polyfluoroalkyl substances (PFAS) pose serious human health and environmental risks due to their persistence and toxicity. Among the available PFAS remediation options, the electrochemical approach is promising with better control. In this review, recent advances in the decontamination of PFAS from water using several state-of-the-art electrochemical strategies, including electro-oxidation, electro-adsorption, and electro-coagulation, were systematically reviewed. We aimed to elucidate their design principles, underlying working mechanisms, and the effects of operation factors (e.g., solution pH, applied voltage, and reactor configuration). The recent developments of innovative electrochemical systems and novel electrode materials were highlighted. In addition, the development of coupled processes that could overcome the shortcomings of low efficiency and high energy consumption of conventional electrochemical systems was also emphasized. This review identified several major knowledge gaps and challenges in the scalability and adaptability of efficient electrochemical systems for PFAS remediation. Materials science and system design developments are forging a path toward sustainable treatment of PFAS-contaminated water through electrochemical technologies.

An in-depth mechanistic insight into the redox reaction and degradation of aqueous Zn-MnO_(2) batteries

Rechargeable aqueous Zn/MnO_(2)batteries raise massive research activities in recent years. However, both the working principle and the degradation mechanism of this battery chemistry are still under debate. Herein, we provide an in-depth electrochemical and structural investigation on this controversial issue based on α-MnO_(2)crystalline nanowires. Mechanistic analysis substantiates a two-electron reaction pathway of Mn2+/Mn4+redox couple from part of MnO_(2)accompanying with a reversible precipitation/dissolution of flaky zinc sulfate hydroxide(ZSH) during the discharge/charge processes. The formation of the ZSH layer is double-edged, which passivates the deep dissolution of MnO_(2)upon discharging,but promotes the electrochemical deposition kinetics of active MnO_(2)upon charging. The cell degradation originates primarily from the corrosion failure of metallic zinc anode and the accumulation of irreversible ZnMn2O_(4)phases on the cathode. The addition of MnSO_(4)to the electrolyte could afford supplementary capacity contribution via electro-oxidation of Mn2+. However, a high MnSO_(4)concentration will expedite the cell failure by corroding the metallic zinc anodes. The present study will shed a fundamental insight on developing new strategies toward practically viable Zn/MnO_(2)batteries.