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Numerical Study of Water Transport and Operating Strategy for Fuel Cells with Segmented Water Management Flow Fields

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Journal of Thermal Science 2024年第4期33卷 1577-1589页

作者： CHEN Chengdai WANG changhong ZHENG Zijun School of Materials and Energy Guangdong University of TechnologyGuangzhou510006China

The effective cathode flow field design can realize the internal water balance and higher current density output of proton exchange membrane fuel cells(PEMFC).Therefore,a segmented water management flow field is proposed in this study,i.e.a half separated-half coupled cathode(HSHC)flow field which has two inlets but just one outlet.A 3D numerical PEMFC model is applied to study the effect of the HSHC flow field on PEMFC performance and its operating strategy in terms of operating *** study results are shown as follows:Compared with the two conventional cathode flow fields,the HSHC flow field improves the water balance along the channel and increases the current density by 1..1.at a cathode stoichiometry of *** is because the HSHC flow field can overcome the water loss at channels upstream and the water accumulation at channels *** draw water phenomenon(DWP)in the HSHC flow field is observed,which is mainly affected by the water vapor pressure of *** on the DWP,cooling channel inlet flow rates can be used to adjust water balance,but severe water loss should be *** addition,the inlet temperature control in HSHC flow field should be that cell temperature>cathode channel inlet temperature>cooling channel inlet temperature>ambient temperatures for better water balance.

关键词： proton exchange membrane fuel cells channel design segmented water management water balance operating strategy

Domain wall network:A dual solution for gravitational waves and Hubble tension?

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Science China(Physics,Mechanics & Astronomy) 2024年第11期67卷 39-46页

作者： Ligong Bian Shuailiang Ge changhong Li Jing Shu Junchao Zong Department of Physics and Chongqing Key Laboratory for Strongly Coupled Physics Chongqing UniversityChongqing 401331China Center for High Energy Physics Peking UniversityBeijing 100871China School of Physics and State Key Laboratory of Nuclear Physics and Technology Peking UniversityBeijing 100871China Department of Astronomy Key Laboratory of Astroparticle Physics of Yunnan ProvinceSchool of Physics and AstronomyYunnan UniversityKunming 650091China Beijing Laser Acceleration Innovation Center Beijing 101400China Department of Physics Nanjing UniversityNanjing 210093China CAS Key Laboratory of Theoretical Physics Institute of Theoretical PhysicsChinese Academy of SciencesBeijing 100190China

We explore the possibility that domain wall networks generate the stochastic gravitational wave background(SGWB) observed as a strong common power-law process in the Data Release-2 of Parkes Pulsar Timing Array. We find that a broad range of parameters, specifically wall tension around σ_(DW)^(29-41. TeV)^(3) and wall-decay temperature within T_(d) ~ 20-257 MeV, can explain this phenomenon at a 68% credible level. Meanwhile, the same parameters could ease the Hubble tension if particles from these domain wall networks decay into dark radiation. We establish a direct analytical relationship, ΩGW(f_(p), T_(0))h^(2)~ Ω_(rad)h^(2)(Ω_νΩN_(eff))^(2),to illustrate this coincidence, underlining its importance in the underlying physics and potential applicability to a wider range of models and data. Conversely, if the common power-law process is not attributed to domain wall networks, our findings impose tight limits on the wall tension and decay temperature.

关键词： domain wall gravitational waves Hubble tension

Data-driven Static Equivalence with Physics-informed Koopman Operators

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CSEE Journal of Power and Energy Systems 2024年第1期10卷 432-438页

作者： Wei Lin changhong Zhao Maosheng Gao C.Y.Chung Department of Electrical Engineering The Hong Kong Polytechnic UniversityHong Kong SARChina Department of Information Engineering The Chinese University of Hong KongHong Kong SARChina School of Electrical Engineering Chongqing UniversityChongqing 400044China

With deployment of measurement units,fitting static equivalent models of distribution networks(DNs)by linear regression has been recognized as an effective method in power flow analysis of a transmission *** volatility of measurements caused by variable distributed renewable energy sources makes it more difficult to accurately fit such equivalent *** tackle this challenge,this letter proposes a novel data-driven method to improve equivalency accuracy of DNs with distributed energy *** letter provides a new perspective that an equivalent model can be regarded as a mapping from internal conditions and border voltages to border power *** mapping can be established through 1.Koopman operator theory,and 2)physical features of power flow equations at the root node of a *** of the proposed method is demonstrated on the IEEE 33-bus and IEEE 1.6-bus test systems connected to a 661.bus utility system.

关键词： Data-driven distribution network Koopman operator theory static equivalent model

Ensemble successor representations for task generalization in offline-to-online reinforcement learning

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Science China(Information Sciences) 2024年第7期67卷 240-255页

作者： changhong WANG Xudong YU Chenjia BAI Qiaosheng ZHANG Zhen WANG Space Control and Inertial Technology Research Center Harbin Institute of Technology Shanghai Artificial Intelligence Laboratory Shenzhen Research Institute of Northwestern Polytechnical University School of Cybersecurity Northwestern Polytechnical University

In reinforcement learning(RL), training a policy from scratch with online experiences can be inefficient because of the difficulties in exploration. Recently, offline RL provides a promising solution by giving an initialized offline policy, which can be refined through online interactions. However, existing approaches primarily perform offline and online learning in the same task, without considering the task generalization problem in offline-to-online adaptation. In real-world applications, it is common that we only have an offline dataset from a specific task while aiming for fast online-adaptation for several tasks. To address this problem, our work builds upon the investigation of successor representations for task generalization in online RL and extends the framework to incorporate offline-to-online learning. We demonstrate that the conventional paradigm using successor features cannot effectively utilize offline data and improve the performance for the new task by online fine-tuning. To mitigate this, we introduce a novel methodology that leverages offline data to acquire an ensemble of successor representations and subsequently constructs ensemble Q functions. This approach enables robust representation learning from datasets with different coverage and facilitates fast adaption of Q functions towards new tasks during the online fine-tuning *** empirical evaluations provide compelling evidence showcasing the superior performance of our method in generalizing to diverse or even unseen tasks.

关键词： offline reinforcement learning online fine-tuning task generalization successor representations ensembles

Surface Coating Enabling Sulfide Solid Electrolytes with Excellent Air Stability and Lithium Compatibility

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Energy & Environmental Materials 2024年第6期7卷 41-49页

作者： Min Luo changhong Wang Yi Duan Xuyang Zhao Jiantao Wang Xueliang Sun National Power Battery Innovation Center GRINM Group Corporation LimitedBeijing 100088China China Automotive Battery Research Institute Co. Ltd.Beijing 100088China General Research Institute for Nonferrous MetalsBeijing 100088China Eastern Institute for Advanced Study Eastern Institute of TechnologyNingbo 315200China

All-solid-state lithium metal batteries(ASSLMBs)featuring sulfide solid electrolytes(SEs)are recognized as the most promising next-generation energy storage technology because of their exceptional safety and much-improved energy ***,lithium dendrite growth in sulfide SEs and their poor air stability have posed significant obstacles to the advancement of sulfide-based ***,a thin layer(approximately 5 nm)of g-C_(3)N_(4)is coated on the surface of a sulfide SE(Li_(6)PS_(5)Cl),which not only lowers the electronic conductivity of Li_(6)PS_(5)Cl but also achieves remarkable interface stability by facilitating the in situ formation of ion-conductive Li3N at the Li/Li_(6)PS_(5)Cl ***,the g-C_(3)N_(4)coating on the surface can substantially reduce the formation of H_(2)S when Li_(6)PS_(5)Cl is exposed to humid *** a result,Li-Li symmetrical cells using g-C_(3)N_(4)-coated Li_(6)PS_(5)Cl stably cycle for 1.00 h with a current density of 0.2 mA cm^(-2).ASSLMBs paired with LiNbO_(3)-coated LiNi_(0.6)Mn_(0.2)Co_(0.2)O_(2)exhibit a capacity of 1.2.8 mAh g^(-1.at 0.1.C and a high-capacity retention of 99.1.after 200 ***,g-C_(3)N_(4)-coated Li_(6)PS_(5)Cl effectively mitigates the self-discharge behavior observed in *** surface-coating approach for sulfide solid electrolytes opens the door to the practical implementation of sulfide-based ASSLMBs.

关键词： anode interface g-C_(3)N_(4)coating Li_(6)PS_(5)Cl lithium dendrite inhibition solidstate lithium metal batteries

Reliability evaluation of IGBT power module on electric vehicle using big data

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Journal of Semiconductors 2024年第5期45卷 50-60页

作者： Li Liu Lei Tang Huaping Jiang Fanyi Wei Zonghua Li changhong Du Qianlei Peng Guocheng Lu The School of Electrical Engineering Chongqing UniversityChongqing 400044China The Deepal Automobile Technology Co. Ltd.Chongqing 400023China

There are challenges to the reliability evaluation for insulated gate bipolar transistors(IGBT)on electric vehicles,such as junction temperature measurement,computational and storage *** this paper,a junction temperature estimation approach based on neural network without additional cost is proposed and the lifetime calculation for IGBT using electric vehicle big data is *** direct current(DC)voltage,operation current,switching frequency,negative thermal coefficient thermistor(NTC)temperature and IGBT lifetime are *** the junction temperature(T_(j))is *** the rain flow counting method,the classified irregular temperatures are brought into the life model for the failure *** fatigue accumulation method is then used to calculate the IGBT *** solve the limited computational and storage resources of electric vehicle controllers,the operation of IGBT lifetime calculation is running on a big data *** lifetime is then transmitted wirelessly to electric vehicles as input for neural *** the junction temperature of IGBT under long-term operating conditions can be accurately estimated.A test platform of the motor controller combined with the vehicle big data server is built for the IGBT accelerated aging ***,the IGBT lifetime predictions are derived from the junction temperature estimation by the neural network method and the thermal network *** experiment shows that the lifetime prediction based on a neural network with big data demonstrates a higher accuracy than that of the thermal network,which improves the reliability evaluation of system.

关键词： IGBT junction temperature neural network electric vehicles big data

Ocean wave directional spectrum estimation using spatio-temporal array of acoustic ranging and current measurement

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Chinese Journal of Acoustics 2024年第3期43卷 311-331页

作者： RAO Liang DENG Kai ZHANG Zhaowei WANG changhong Institute of Acoustics Chinese Academy of SciencesBeijing100190 University of Chinese Academy of Sciences Beijing100049 Beijing Engineering Technology Research Center of Ocean Acoustic Equipment Beijing100190

An approach to estimate ocean wave directional spectrum using spatio-temporal array of acoustic ranging and current measurement is proposed,and the 5-beam acoustic Doppler current profiler(ADCP)constructs a spatio-temporal array of acoustic ocean surface elevation tracking and acoustic Doppler current velocity measuring for directional wave *** on the linear wave theory and the space-time equivalence principle,the time-space transfer function applicable to the spatio-temporal array is proposed,and then the time delay term is compensated in the calculation of the covariance *** method can reduce the error of the directional spectrum *** results show that for the low signal-to-noise ratio from 0 dB to 5 dB,compared with the 4-beam synchronous array method,this method has a smaller root-mean-square error of the peak estimation of the directional *** field test shows that,compared with the 4-beam synchronous array method,the 5-beam spatio-temporal array method improves the kurtosis index of the directional spectrum from 2.31.to 2.80,and the correlation coefficient between the peak wave direction results of the ADCP and the buoy is increased from 0.80 to 0.83 in mild wave ***,the spatio-temporal array method can increase the degree of freedom of wave measurement,reduce the minimum aperture of the array,and increase the upper cut-off frequency of the estimable directional spectrum.

关键词： spectrum ocean directional

The Tenth Anniversary of Free Trade Pilot Zones in China:Fundamental Experiences and Enhancement Strategies

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China Economist 2024年第3期19卷 2-20页

作者： Pei changhong Chinese Academy of Social Sciences Shanghai Research Institute BeijingChina University of International Business and Economics Beijing

Since the 1.th National Congress of the Communist Party of China,the country has established 21.Free Trade Pilot Zones(FTZs),achieving significant pioneering results in reform and opening up and creating a strong demonstrative effect *** basic experience from a decade of FTZs includes:adhering to the centralized and unified leadership of the CPC Central Committee;combining top-level design with encouragement of grassroots innovation;leveraging the distinct characteristics and strengths of FTZs to form a differentiated development pattern;maintaining the integration of opening up with domestic reforms;using openness to drive reforms;and organically combining openness with national security *** the current and future new circumstances,China’s FTZs face new challenges and *** accordance with the directives of the 20th National Congress of the Communist Party of China,an enhancement strategy for the FTZs needs to be *** involves the following:First,accurately understanding and responding to the changing situation to create strategic ***,shifting paradigms to implement innovation-driven strategies,using the new development pattern concept to guide the reform experiments and construction of the ***,granting more autonomy to FTZs for reforms,pursuing progress while maintaining stability,and solidly advancing the reform experiments in the ***,orderly expanding the opening up of the service sector and cautiously advancing the internationalization of the ***,promoting innovative development in trade to build a strong trade ***,establishing synergy with bilateral FTZs,Belt and Road cooperation,and national diplomatic strategies to enhance the linkage effect.

关键词： Tenth anniversary of Free Trade Pilot Zones experience summary enhancement strategy conception

Direct Ischemic Postconditioning Following Stroke Thrombectomy:A Promising Therapy for Reperfusion Injury

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Neuroscience Bulletin 2024年第7期40卷 1017-1020页

作者： Jing Wang Lu Yang Longfei Wu Sijie Li changhong Ren Yuchuan Ding Ming Wei Xunming Ji Wenbo Zhao Department of Neurology Xuanwu HospitalCapital Medical UniversityBeijing 100053China Department of Emergency Xuanwu HospitalCapital Medical UniversityBeijing 100053China Beijing Key Laboratory of Hypoxic Conditioning Translational Medicine Xuanwu HospitalCapital Medical UniversityBeijing 100053China Department of Neurosurgery Wayne State University School of MedicineDetroitMI48201USA Beijing Institute for Brain Disorders Capital Medical UniversityBeijing 100069China Department of Neurosurgery Tianjin Huanhu HospitalTianjin 300222China Department of Neurosurgery Xuanwu HospitalCapital Medical UniversityBeijing 100053China

Recanalization of occluded vessels and timely reperfusion are the primary therapies for acute ischemic stroke(AIS),with endovascular thrombectomy proven as the most effective therapy for large-vessel recanalization and improved outcomes of AIS ***,despite a high recanalization rate of 90% or even higher,the rate of 3-month functional independence is approximately 50%,while mortality remains around 1.%[1..

关键词： mortality acute Therapy