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Constraints on holographic QCD phase transitions from PTA observations

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science China(Physics,Mechanics & Astronomy) 2025年第1期Mechanics & Astronomy) .卷 71-78页

作者： Song He Li Li Sai Wang Shao-Jiang Wang Center for Theoretical Physics and College of Physics Jilin University School of Physical science and Technology Ningbo University Max Planck Institute for Gravitational Physics (Albert Einstein Institute) CAS Key Laboratory of Theoretical Physics Institute of Theoretical Physics Chinese Academy of Sciences School of Fundamental Physics and Mathematical sciences Hangzhou Institute for Advanced StudyUniversity of Chinese Academy of Sciences (UCAS) School of Physical sciences University of Chinese Academy of Sciences (UCAS) Theoretical Physics division Institute of High Energy Physics Chinese Academy of Sciences

The underlying physics of QCD phase transition in the early Universe remains largely unknown due to its strong-coupling nature during the quark-gluon plasma/hadron gas transition, yet a holographic model has been proposed to quantitatively fit the lattice QCD data while with its duration of the first-order phase transition(FoPT) left undetermined. At specific baryon chemical potential, the first-order QCD phase transition agrees with the observational constraint of baryon asymmetry. It, therefore, provides a scenario for phase transition gravitational waves(GWs) within the standard model of particle physics. If these background GWs could contribute dominantly to the recently claimed common-spectrum red noise from pulsar timing array(PTA) observations, the duration of this FoPT can be well constrained, and the associated primordial black holes are still allowed by current observations.

关键词： pulsar timing array QCD phase transition gravitational waves primordial black holes

High–Speed electron beam curing of thick electrode for high energy density Li-ion batteries

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Green energy & Environment 2019年第4期4卷 375-381页

作者： Zhijia Du Christopher J.Janke Jianlin Li David L.Wood III energy and transportation science division Oak Ridge National LaboratoryOak RidgeTN 37831USA Chemical sciences division Oak Ridge National LaboratoryOak RidgeTN 37831USA

Electron beam curing is demonstrated as a promising method for high speed,low cost and environmentally friendly battery electrode *** work reports transfer of this process to pilot scale equipment and evaluation of electrochemical performance in prototype 1.5 Ah pouch *** LiNi0.5Mn0.3Co0.2O2(NMC532)composite electrodes with an areal loading of 25 mg cm^-2(~4 mAh cm^-2)are successfully cured at a line speed of 500 feet per minute at 275 *** to the NMC532 cathode processed via a conventional coating method,the electron beam cured electrodes show higher capacity fade in the first 100 cycles,but similar fade rate *** improvement strategies are proposed and *** work demonstrates that electron beam curing is a promising method for manufacturing thick battery electrodes at high speeds and low capital/operation cost.

关键词： Electron beam curing Li-ion batteries Thick electrode

Temperature-dependent constitutive modeling of a magnesium alloy ZEK100 sheet using crystal plasticity models combined with in situ high-energy X-ray diffraction experiment

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Journal of Magnesium and Alloys 2022年第10期10卷 2801-2816页

作者： Hyuk Jong Bong Xiaohua Hu Xin Sun Yang Ren Materials Deformation Department Korea Institute of Materials ScienceChangwonGyeongnam 51508South Korea energy and transportation science division Oak Ridge National LaboratoryOak RidgeTN 37831USA X-ray science division Argonne National LaboratoryIL 60439USA

A multiscale crystal plasticity model accounting for temperature-dependent mechanical behaviors without introducing a larger number of unknown parameters was *** model was implemented in elastic-plastic self-consistent(EPSC)and crystal plasticity finite element(CPFE)frameworks for grain-scale simulations.A computationally efficient EPSC model was first employed to estimate the critical resolved shear stress and hardening parameters of the slip and twin systems available in a hexagonal close-packed magnesium alloy,*** constitutive parameters were thereafter refined using the *** crystal plasticity frameworks incorporated with the temperature-dependent constitutive model were used to predict stress–strain curves in macroscale and lattice strains in microscale at different testing temperatures up to 200℃.In particular,the predictions by the crystal plasticity models were compared with the measured lattice strain data at the elevated temperatures by in situ high-energy X-ray diffraction,for the first *** comparison in the multiscale improved the fidelity of the developed temperature-dependent constitutive model and validated the assumption with regard to the temperature dependency of available slip and twin systems in the magnesium ***,this work provides a time-efficient and precise modeling scheme for magnesium alloys at elevated temperatures.

关键词： High-energy X-ray diffraction Crystal plasticity finite element Elastic-plastic self-consistent model Twin Temperature

Mechanisms of Accelerated Degradation in the Front Cells of PEMFC Stacks and Some Mitigation Strategies

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Chinese Journal of Mechanical Engineering 2013年第6期26卷 1250-1258页

作者： LI Pengcheng PEI Pucheng HE Yongling YUAN Xing CHAO Pengxiang WANG Xizhong School of transportation science and Engineering Beihang University State Key Laboratory of Automotive Safety and energy Tsinghua University

The accelerated degradation in the front ceils of a polymer electrolyte membrane fuel cell（PEMFC） stack seriously reduces the reliability and durability of the whole stack. Most researches only focus on the size and configuration of the gas intake manifold, which may lead to the maldistribution of flow and pressure. In order to find out the mechanisms of the accelerated degradation in the front cells, an extensive program of experimental and simulation work is initiated and the results are reported. It is found that after long-term lifetime tests the accelerated degradation in the front cells occurs in all three fuel cell stacks with different flow-fields under the U-type feed configuration. Compared with the rear cells of the stack, the voltage of the front cells is much lower at the same current densities and the membrane electrode assembly（MEA） has smaller active area, more catalyst particle agglomeration and higher ohmic impedance. For further investigation, a series of three dimensional isothermal numerical models are built to investigate the degradation mechanisms based on the experimental data. The simulation results reveal that the dry working condition of the membrane and the effect of high-speed gas scouting the MEA are the main causes of the accelerated degradation in the front cells of a PEM fuel cell stack under the U-type feed configuration. Several mitigation strategies that would mitigate these phenomena are presented： removing cells that have failed and replacing them with those of the same aging condition as the average of the stack; choosing a Z-type feed pattern instead of a U-type one; putting several air flow-field plates without MEA in the front of the stack; or exchanging the gas inlet and outlet alternately at a certain interval. This paper specifies the causes of the accelerated degradation in the front cells and provides the mitigation strategies.

关键词： Proton exchange membrane fuel cell Degradation mechanism Mitigation strategy

Adsorption of rare earth ions using carbonized polydopamine nano carbon shells

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Journal of Rare Earths 2016年第1期34卷 77-82页

作者：孙晓琦 LUO Huimin Shannon M.Mahurin LIU Rui HOU Xisen DAI Sheng Chemical sciences division Oak Ridge National Laboratory Xiamen Institute of Rare Earth Materials Haixi Institute Chinese Academy of sciences energy and transportation science division Oak Ridge National Laboratory Department of Chemistry University of Tennessee

Herein we reported the structure effects of carbon nano-shells prepared by the carbonization of polydopamine for the ad- sorption of rare earth elements （REEs） for the first time. Solid carbon spheres, 60 nm carbon shells and 500 nm carbon shells were prepared and evaluated for adsorption and desorption of REEs. The adsorption performance of carbon nano-shells for REEs was far superior to the solid carbon spheres. In addition, the effect of acidity on the adsorption and desorption properties was discussed. The good adsorption performance of the carbon nano-shells could be attributed to their pore structure, specific surface area, and the pres- ence of both amine and carbonyl groups from the grafted dopamine.

关键词： carbon shells rare earths adsorption separation

A hydrometallurgical method of energy saving type for separation of rare earth elements from rare earth polishing powder wastes with middle fraction of ceria

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Journal of Rare Earths 2016年第5期34卷 536-542页

作者： UM Namil HIRATO Tetsuji Resource Recirculation Research division National Institute of Environmental Research Department of energy science and Technology Graduate School of Energy ScienceKyoto University

This study described a hydrometallurgical method to investigate the separation of rare earth elements（REEs）from rare earth polishing powder wastes（REPPWs）containing large amounts of rare earth oxides with a major phase of CeO2 and minor phases of La2O3,Pr2O3,and Nd2O3 using a process devised by the *** suggested approach consisted of five processes：the synthesis of NaR E（SO4）2·xH2O from rare earth oxides in Na2SO4-H2SO4-H2 O solutions（Process 1）,the conversion of NaR E（SO4）2·xH2O into RE（OH）3 using NaO H（Process 2）,and the oxidation of Ce（OH）3 into Ce（OH）4 using air with O2 injection（Process 3）,followed by Processes 4 and 5 for separation of REEs by acid leaching using HCl and H2SO4,*** confirm the high yield of NaR E（SO4）2·xH2O in Process 1,experiments were carried out under various Na2SO4 concentrations（0.4–2.5 mol/L）,sulfuric acid concentrations（6–14 mol/L）,and reaction temperatures（95–125 oC）.In addition,the effect of the pH value on the separation of Ce（OH）4 in HCl-H2 O solutions with Ce（OH）4,La-,Pr-,and Nd（OH）3 in Process 4 was also *** the basis of above results,the possibility of effective separation of REEs from REPPWs could be confirmed.

关键词： rare earth elements(REEs) rare earth polishing powder wastes(REPPWs) separation sodium cerium sulfate hydrometallurgical process

Anti-flooding of polymer electrolyte membrane fuel cell with in-plate adverse-flow flow-field

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Journal of Central South University 2013年第4期20卷 1001-1009页

作者：李鹏程裴普成何勇灵张红飞 School of transportation science and Engineering Beihang University State Key Laboratory of Automotive Safety and energy (Tsinghua University)

The stoichiometric ratios and related regimes, which can promote anti-flooding of polymer electrolyte membrane fuel cell （PEMFC） with in-plate adverse-flow flow-field （IPAF）, were investigated. Two flow combinations, which are the simple and complex adverse-flow between plates （ABP） that can be realized by IPAF, were employed. Constant stoichiometric ratios examination indicates that the complex ABP could improve anti-flooding of PEMFC better in the medium （greater than 200 mA/cm2 and less than 1 000 mA/cm2） and high （greater than 1 000 mA/cm2） current densities than the simple ABP. More stoichiometric ratios were introduced to find the cathode critical stoichiometry. Under the condition of cathode critical stoichiometry, the maximal local relative humidity of both electrodes of complex ABP is equal to 100% and below while the anti-flooding of the cathode of simple ABP is not satisfactory in the medium and high current densities. Further study shows that the mechanism of fuel cell, which is the imerdependence between the electrodes effect, can make significant contribution to anti-flooding.

关键词： proton exchange membrane fuel cell in-plate adverse-flow flow-field stoichiometry anti-flooding

Design for aircraft engine multi-objective controllers with switching characteristics

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Chinese Journal of Aeronautics 2014年第5期27卷 1097-1110页

作者： Liu Xiaofeng Shi Jing Qi Yiwen Yuan Ye School of transportation science and Engineering Beihang University School of Automation Shenyang Aerospace University School of energy and Power Engineering Beihang University

The aircraft engine multi-loop control system is described and the switching control theory is introduced to solve the regulating and protecting control problems in this paper. The aircraft engine multi-loop control system is firstly described and the control problems are formulated. Secondly, the theory of the smooth switching control is devoted and a new extended scheme for the smooth switching of a switched control system is introduced. Then, for the key technologies of aero-engines switching control, a design algorithm is presented which can determine which candidate controller should be put in feedback with the plant to achieve a desired performance and the procedure to design the aircraft engine multi-loop control system is detailed. The switching performance objectives and the switching scheme are given and a family of PID controllers and compensators is designed. The simulation shows that using the switching control design method can not only improve the dynamic performance of the aircraft engine control system and reduce the switching times, but also guarantee the stability in some peculiar occasions.

关键词： Aircraft engine Compensatory controller Min/Max switching Multi-objectives control Smooth switching Switching scheme

Effects of charging rates on LiNi_(0.6)Mn_(0.2)Co_(0.2)O_(2)(NMC622)/graphite Li-ion cells

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Journal of energy Chemistry 2021年第5期30卷 121-126页

作者： Xianyang Wu Yaocai Bai Zhenglong Li Jue Liu Kejie Zhao Zhijia Du energy and transportation science division Oak Ridge National LaboratoryOak RidgeTN 37830USA School of Mechanical Engineering Purdue UniversityWest LafayetteIN 47907USA Neutron Scattering division Oak Ridge National LaboratoryOak RidgeTN 37830USA

Enabling fast charging capability of lithium-ion battery is of great importance to widespread adoption of electric *** the charging rates from state-of-the-art 2 C(30 min)to 6 C(10 min)requires deep understanding on the cell aging *** this study,400 mAh pouch cells are cycled at 1 C,4 C and 6 C charging rates with 1 C discharging *** fading,cathode structural changes,Li inventory loss,electrolyte composition changes and Li plating on graphite electrodes are thoroughly studied by various characterization *** rapid capacity fading in cells at 6 C charging rate is mainly due to Li inventory loss from cathode structure and metallic Li plating on graphite electrode at higher charging ***-mortem analysis also revealed changes in electrolyte such as increased salt molarity and transesterification during fast charging.

关键词： Li-ion cells Fast charging Post-test analysis Neutron powder diffraction