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Recent studies in satellite observations of three-dimensional magnetic reconnection

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Science China(Technological Sciences) 2007年第3期50卷 380-384页

作者： XIAO ChiJie WANG XiaoGang PU ZuYin MA ZhiWei ZHAO Hui ZHOU GuiPing WANG JingXiu LIU ZhenXing National Astronomical Observatories Chinese Academy of SciencesBeijing 100012China School of physics Peking UniversityBeijing 100871China School of Earth and Space Sciences Peking UniversityBeijing 100871China institute for fusion theory and simulation Zhejiang UniversityHangzhou 310027China Center for Space Science and Applied Research Chinese Academy of SciencesBeijing 100080China

Magnetic reconnection is a main process converting the magnetic energy into thermal and kinetic energy in plasmas. It is one of the fundamental problems of crucial importance not only to space plasmas physics and space weather studies,such as the solar flare,coronal mass ejections and magnetospheric substorms,but also to the stability analysis in magnetically confined fusion. In general,except for cases with periodical boundary conditions,three-dimensional(3D) magnetic re-connection occurs on magnetic separatrices generated by magnetic nulls. Here we briefly introduce/review the theories and some recent satellite observations of 3D magnetic reconnection. Topics to be further studied are also discussed.

关键词： magnetic reconnection null separatrix separator X-point X-line

Proton beams from intense laser-solid interaction:Effects of the target materials

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Matter and Radiation at Extremes 2020年第6期5卷 42-47页

作者： Y.X.Geng D.Wu W.Yu Z.M.Sheng S.Fritzsche Q.Liao M.J.Wu X.H.Xu D.Y.Li W.J.Ma H.Y.Lu Y.Y.Zhao X.T.He J.E.Chen C.Lin X.Q.Yan Key Laboratory of HEDP of the Ministry of Education CAPTand State Key Laboratory of Nuclear Physics and TechnologyPeking UniversityBeijing 100871China institute for fusion theory and simulation Department of PhysicsZhejiang University310058 HangzhouChina State Key Laboratory of High Field Laser physics Shanghai Institute of Optics and Fine Mechanics201800 ShanghaiChina SUPA department of physics University of StrathclydeGlasgow G40NGUnited Kingdom Key Laboratory for Laser Plasmas(Ministry of Education) School of Physics and AstronomyShanghai Jiao Tong UniversityShanghai 200240China Helmholtz Institut-Jena and Friedrich-Schiller-University D-07743 JenaGermany

We report systematic studies of laser-driven proton beams produced with micrometer-thick solid targets made of aluminum and plastic,respectively.Distinct effects of the target materials are found on the total charge,cutoff energy,and beam spot of protons in the experiments,and these are described well by two-dimensional particle-in-cell simulations incorporating intrinsic material properties.It is found that with a laser intensity of 8×10^(19) W/cm^(2),target normal sheath acceleration is the dominant mechanism for both types of target.For a plastic target,the higher charge and cutoff energy of the protons are due to the greater energy coupling efficiencies from the intense laser beams,and the larger divergence angle of the protons is due to the deflection of hot electrons during transport in the targets.We also find that the energy loss of hot electrons in targets of different thickness has a significant effect on the proton cutoff energy.The consistent results obtained here further narrow the gap between simulations and experiments.

关键词： properties. intense solid

Ultra-fast interpretable machine-learning potentials

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npj Computational Materials 2023年第1期9卷 649-657页

作者： Stephen R.Xie Matthias Rupp Richard G.Hennig department of Materials Science and Engineering University of FloridaGainesvilleFLUSA Quantum theory Project University of FloridaGainesvilleFLUSA department of Computer and Information Science University of KonstanzKonstanzGermany Materials Research and Technology department Luxembourg Institute of Science and Technology(LIST)Esch-sur-AlzetteLuxembourg

All-atom dynamics simulations are an indispensable quantitative tool in physics,chemistry,and materials science,but large systems and long simulation times remain challenging due to the trade-off between computational efficiency and predictive accuracy.To address this challenge,we combine effective two-and three-body potentials in a cubic B-spline basis with regularized linear regression to obtain machine-learning potentials that are physically interpretable,sufficiently accurate for applications,as fast as the fastest traditional empirical potentials,and two to four orders of magnitude faster than state-of-the-art machine-learning potentials.For data from empirical potentials,we demonstrate the exact retrieval of the potential.For data from density functional theory,the predicted energies,forces,and derived properties,including phonon spectra,elastic constants,and melting points,closely match those of the reference method.The introduced potentials might contribute towards accurate all-atom dynamics simulations of large atomistic systems over long-time scales.

关键词： method spline faster

Development of Multi-hierarchy simulation Model for Studies of Magnetic Reconnection

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Communications in Computational physics 2008年第8期4卷 537-544页

作者： S.Usami H.Ohtani R.Horiuchi M.Den department of simulation Science National Institute for Fusion ScienceToki509-5292Japan The Graduate University for Advanced Studies(Soken-dai) Toki509-5292Japan

The multi-hierarchy simulation model for magnetic reconnection is developed,where both micro andmacro hierarchies are expressed consistently and simultaneously.Two hierarchies are connected smoothly by shake-hand scheme.As a numerical test,propagation of one-dimensional Alfv´en wave is examined using the multihierarchy simulation model.It is found that waves smoothly pass through frommacro to micro hierarchies and vice versa.

关键词： Multi-hierarchy magnetic reconnection MHD particle-in-cell

Ab-initio investigation of AGeO_3(A=Ca, Sr) compounds via Tran Blaha-modified Becke Johnson exchange potential

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Chinese physics B 2017年第11期26卷 375-382页

作者： Rasul Bakhsh Behram M A Iqbal Muhammad Rashid M Atif Sattar Asif Mahmood Shahid M Ramay physics department University of the Punjab Quaid-e-Azam Campus Allama Iqbal Open University Regional Campus department of physics School of Science University of Management and Technology department of physics COMSATS Institute of Information Technology department of physics simulation Lab The Islamia University of Bahawalpur Chemical Engineering department College of Engineering King Saud University physics and Astronomy department College of Science King Saud University

We employ ab-initio calculations to analyze the mechanical, electronic, optical and also thermoelectric properties associated with AGeO3（A = Ca, Sr） compounds. The full-potential linearized augmented plane wave（FP-LAPW） technique in the generalized gradient approximation（GGA-PBEsol） and the lately designed Tran-Blaha-modified Becke-Johnson exchange potential are utilized to examine the mechanical and optoelectronic properties respectively. To explore the thermoelectric quality, we use the semi-classical Boltzmann transport theory. The particular structural stabilities regarding AGeO3（A = Ca, Sr） materials are validated simply by computations from the elastic constants. The energy band structural framework and the density of states are displayed to indicate indirect bandgap under ambient conditions. The particular computed optical attributes that reveal prospective optoelectronic applications are usually elucidated simply by studying ε1（0） and also Eg, which can be connected by means of Penn＇s design. The optical details uncover the actual suitability to power ranging products. Finally, the Boltz Tra P code is executed to analyze the actual thermoelectric properties, which usually presents that the increase of internal temperatures can enhance the electric conductivity, thermal conductivity and also the power factor, whilst Seebeck coefficient decreases. Therefore, the studied materials will also be ideal for thermoelectric products to understand helpful option for alternative energy resources.

关键词： semiconductors elastic properties optical properties thermal properties

Efficient ORR catalysts for zinc-air battery: Biomass-derived ultra-stable Co nanoparticles wrapped with graphitic layers via optimizing electron transfer

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Journal of Energy Chemistry 2022年第7期31卷 211-218,I0006页

作者： Yu Feng Kexin Song Wei Zhang Xinyan Zhou Seung Jo Yoo Jin-Gyu Kim Sifan Qiao Yugang Qi Xu Zou Zhongjun Chen Tingting Qin Nailin Yue Zizhun Wang Dabing Li Weitao Zheng State Key Laboratory of Automotive simulation and Control School of Materials Science&EngineeringKey Laboratory of Automobile Materials MOEElectron Microscopy Centerand International Center of Future ScienceJilin UniversityJilin UniversityChangchun 130012JilinChina Division of Scientific Instrumentation&Management Korea Basic Science InstituteDaejeon 34133Republic of Korea institute of High Energy physics Chinese Academy of SciencesBeijing 100049China State Key Laboratory of Luminescence and Applications Changchun Institute of OpticsFine Mechanics and PhysicsChinese Academy of SciencesChangchun 130033JilinChina

The poor stability of non-noble metal catalysts in oxygen reduction reaction(ORR) is a main bottleneck that limits their big-scale application in metal-air batteries. Herein, we construct a chainmail catalyst(Co-NC-AD) with outstanding stability, via the competitive complexation and post absorption strategy,consisting of highly graphitic layers wrapped uniform-size Co nanoparticles(Co-NPs). Experiments combined with density functional theory(DFT) calculations jointly confirmed that the electron transfer occurred from the inner Co-NPs to the external graphitic layers. It facilitated the adsorption process of oxygen molecules and the hybridization of the O-2 p and C-1 p orbitals, which accelerated the ORR reaction kinetics. Consequently, our prepared Co-NC-AD shows excellent ORR activity, offered with a more positive initial potential(E_(onset)= 0.95 V) and half-wave potential(E_(1/2)= 0.86 V). The remarkable stability and resistance of methanol poisoning are merited from the protection effect of stable graphitic layers. In addition, the high electrochemical performance of Co-NC-AD-based zinc-air battery demonstrates their potential for practical applications. Therefore, our work provides new ideas for the design of nanoconfined catalysts with high stability and activity.

关键词： Chainmail catalyst Graphitic layers Co nanoparticles Oxygen reduction reaction

Nanoparticle meta-grid for enhanced light extraction from light-emitting devices

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Light(Science & Applications) 2020年第1期9卷 842-852页

作者： Debabrata Sikdar John B.Pendry Alexei A.Kornyshev department of Chemistry Molecular Sciences Research HubImperial College LondonWhite CityLondon W120BZUK department of Electronics and Electrical Engineering Indian Institute of Technology GuwahatiGuwahati 781039India The Blackett Laboratory Department of PhysicsImperial College LondonLondon SW72AZUK Thomas Young Centre for theory and simulation of Materials Imperial College LondonLondon SW72AZUK

Based on a developed theory,we show that introducing a meta-grid of sub-wavelength-sized plasmonic nanoparticles(NPs)into existing semiconductor light-emitting-devices(LEDs)can lead to enhanced transmission of light across the LED-chip/encapsulant interface.This results from destructive interference between light reflected from the chip/encapsulant interface and light reflected by the NP meta-grid,which conspicuously increase the efficiency of light extraction from LEDs.The“meta-grid”,should be inserted on top of a conventional LED chip within its usual encapsulating packaging.As described by the theory,the nanoparticle composition,size,interparticle spacing,and distance from the LED-chip surface can be tailored to facilitate maximal transmission of light emitted from the chip into its encapsulating layer by reducing the Fresnel loss.The analysis shows that transmission across a typical LEDchip/encapsulant interface at the peak emission wavelength can be boosted up to ~99%,which is otherwise mere~84% at normal incidence.The scheme could provide improved transmission within the photon escape cone over the entire emission spectrum of an LED.This would benefit energy saving,in addition to increasing the lifetime of LEDs by reducing heating.Potentially,the scheme will be easy to implement and adopt into existing semiconductor-device technologies,and it can be used separately or in conjunction with other methods for mitigating the critical angle loss in LEDs.

关键词： light particle reflected

Nonlinear saturation amplitude of cylindrical Rayleigh Taylor instability

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Chinese physics B 2014年第9期23卷 278-282页

作者：刘万海于长平叶文华王立峰 Research Center of Computational physics Mianyang Normal University Key Laboratory of High Energy Density physics simulation (HEDPS) and Center for Applied Physics and TechnologyPeking University Key Laboratory of High Temperature Gas Dynamics (LHD) Institute of MechanicsChinese Academy of Sciences institute of Applied physics and Computational Mathematics department of physics Zhejiang University

The nonlinear saturation amplitude （NSA） of the fundamental mode in the classical Rayleigh-Taylor instability with a cylindrical geometry for an arbitrary Atwood number is analytically investigated by considering the nonlinear corrections up to the third order. The analytic results indicate that the effects of the initial radius of the interface （r0） and the Atwood number （A） play an important role in the NSA of the fundamental mode. The NSA of the fundamental mode first increases gently and then decreases quickly with increasing A. For a given A, the smaller the ro/λ（λ is the perturbation wavelength）, the larger the NSA of the fundamental mode. When ro/λ is large enough （r0 〉〉 λ）, the NSA of the fundamental mode is reduced to the prediction in the previous literatures within the framework of the third-order perturbation theory.

关键词： nonlinear saturation amplitude Rayleigh-Taylor instability cylindrical interface

The semileptonic decays of B/B_s meson in the perturbative QCD approach:a short review

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Chinese Science Bulletin 2014年第29期59卷 3787-3800页

作者： Zhen-Jun Xiao Ying-Ying Fan Wen-Fei Wang Shan Cheng department of physics and institute of Theoretical physics Nanjing Normal University Jiangsu Key Laboratory for Numerical simulation of Large Scale Complex Systems Nanjing Normal University institute of High Energy physics and Theoretical physics Center for Science Facilities Chinese Academy of Sciences

In this short review,we present the current status about the theoretical and experimental studies for some important semileptonic decays of B=Bsmesons.We firstly gave a brief introduction for the experimental measurements for B=Bs!Peltl;l ml;m mT decays,the BaBar’s ReDT and ReD T anomaly,the P05deviation for B0!K 0ltl decay.We then made a careful discussion about the evaluations for the relevant form factors in the light-cone QCD sum rule,the heavy quark effective theory,and the perturbative QCD factorization approach.By using the form factors calculated in the perturbative(pQCD)approach,we then calculate and show the pQCD predictions for the decay rates of many semileptonic decays of B=Bsmesons.We also made careful phenomenological analysis for these pQCD predictions and found,in general,the following points:(a)For all the considered B=Bssemileptonic decays,the next-to-leading order pQCD predictions for their decay rates agree well with the data and those from other different theoretical methods;(b)For ReDT and ReD T,the pQCD predictions agree very well with the data,the BaBar’s anomaly of ReDe TT are therefore explained successfully in the standard model by employing the pQCD approach;and(c)We defined several new ratios Rl;s Dand Rl;s Ds,they may be more sensitive to the QCD dynamics which controls the B=Bs!eDe T;De T sT transitions than the old ratios,we therefore strongly suggest LHCb and the forthcoming Super-B experiments to measure these new ratios.

关键词：微扰QCD 衰变率 BS 介子光锥QCD求和规则实验测量评论 QCD因子化