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Dynamical properties of neuromorphic Josephson junctions

Physical Review E 2022年第4期106卷 044206-044206页

作者： D. Chalkiadakis J. Hizanidis Department of Physics University of Crete 71003 Herakleio Greece and Institute of Applied and Computational Mathematics Foundation for Research and Technology-Hellas 70013 Herakleio Greece

Neuromorphic computing exploits the dynamical analogy between many physical systems and neuron biophysics. Superconductor systems, in particular, are excellent candidates for neuromorphic devices due to their capacity to operate at great speeds and with low energy dissipation compared to their silicon counterparts. In this paper, we revisit a prior work on Josephson Junction-based neurons to identify the exact dynamical mechanisms underlying the system's neuronlike properties and reveal complex behaviors which are relevant for neurocomputation and the design of superconducting neuromorphic devices. Our paper lies at the intersection of superconducting physics and theoretical neuroscience, both viewed under a common framework—that of nonlinear dynamics theory.

关键词： Bifurcations Chaos Neuronal dynamics Spiking neurons Josephson junctions Chaos & nonlinear dynamics

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Robust analytic continuation of Green's functions via projection, pole estimation, and semidefinite relaxation

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Physical Review B 2023年第7期107卷 075151-075151页

作者： Zhen Huang Emanuel Gull Lin Lin Department of Mathematics University of California Berkeley California 94720 USA Department of Physics University of Michigan Ann Arbor Michigan 48109 USA Applied Mathematics and Computational Research Division Lawrence Berkeley National Laboratory Berkeley California 94720 USA

Green's functions of fermions are described by matrix-valued Herglotz-Nevanlinna functions. Since analytic continuation is fundamentally an ill-posed problem, the causal space described by the matrix-valued Herglotz-Nevanlinna structure can be instrumental in improving the accuracy and in enhancing the robustness with respect to noise. We demonstrate a three-pronged procedure for robust analytic continuation called PES: (1) projection of data to the causal space; (2) estimation of pole locations; and (3) semidefinite relaxation within the causal space. We compare the performance of PES with the recently developed Nevanlinna and Carathéodory continuation methods and find that PES is more robust in the presence of noise and does not require the usage of extended precision arithmetics. We also demonstrate that a causal projection improves the performance of the Nevanlinna and Carathéodory methods. The PES method is generalized to bosonic response functions, for which the Nevanlinna and Carathéodory continuation methods have not yet been developed. It is particularly useful for studying spectra with sharp features, as they occur in the study of molecules and band structures in solids.

关键词： Green's function methods Many-body techniques Quantum field theory

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Manipulation and optimization of electron transport by nanopore array targets

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Plasma Science and Technology 2021年第1期23卷 8-14页

作者： Yue YANG Boyuan LI Yuchi WU Bin ZHU Bo ZHANG Zhimeng ZHANG Minghai YU Feng LU Kainan ZHOU Lianqiang SHAN Lihua CAO Zongqing ZHAO Weimin ZHOU Yuqiu GU Laser Fusion Research Center China Academy of Engineering PhysicsMianyang 621900People’s Republic of China Key Laboratory for Laser Plasmas(Ministry of Education) School of Physics and AstronomyShanghai Jiao Tong UniversityShanghai 200240People’s Republic of China Institute of Applied Physics and Computational Mathematics Beijing 100088People’s Republic of China Key Laboratory of HEDP of the Ministry of Education&CAPT Peking UniversityBeijing 100871People’s Republic of China

The transport of sub-picosecond laser-driven fast electrons in nanopore array targets is *** to the generation of micro-structured magnetic fields,most fast electron beams are proven to be effectively guided and restricted during the *** transport patterns of fast electrons in the targets are observed in experiments and reproduced by particle-in-cell simulations,representing two components:initially collimated low-energy electrons in the center and high-energy scattering electrons turning into surrounding annular *** critical energy for confined electrons is deduced *** electron guidance and confinement by the nano-structured targets offer a technological approach to manipulate and optimize the fast electron transport by properly modulating pulse parameters and target design,showing great potential in many applications including ion acceleration,microfocus x-ray sources and inertial confinement fusion.

关键词： nanopore array laser-driven electrons fast electron transport electron collimation

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Benchmarking phonon anharmonicity in machine learning interatomic potentials

arXiv

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arXiv 2024年

作者： Bandi, Sasaank Jiang, Chao Marianetti, Chris A. Department of Applied Physics and Applied Mathematics Columbia University New YorkNY10027 United States Computational Mechanics and Materials Department Idaho National Laboratory Idaho FallsID83415 United States

Machine learning approaches have recently emerged as powerful tools to probe structure-property relationships in crystals and molecules. Specifically, Machine learning interatomic potentials (MLIP) can accurately reproduce first-principles data at a cost similar to that of conventional interatomic potential approaches. While MLIP have been extensively tested across various classes of materials and molecules, a clear characterization of the anharmonic terms encoded in the MLIP is lacking. Here, we benchmark popular MLIP using the anharmonic vibrational Hamiltonian of ThO2 in the fluorite crystal structure. This anharmonic Hamiltonian was constructed from density functional theory (DFT) using our highly accurate and efficient irreducible derivative methods, and then used to generate molecular dynamics trajectories. This data set was used to train three classes of MLIP: Gaussian Approximation Potentials, Artificial Neural Networks (ANN), and Graph Neural Networks (GNN). The results were assessed by directly comparing phonons and their interactions, as well as phonon linewidths, phonon lineshifts, and thermal conductivity. The models were also trained on a DFT molecular dynamics dataset, demonstrating good agreement up to fifth-order for the ANN and GNN. Our analysis demonstrates that MLIP have great potential for accurately characterizing anharmonicity in materials systems at a fraction of the cost of conventional first principles-based approaches. © 2024, CC BY.

关键词： Crystal structure

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A Class of Fast and Accurate Multi-layer Block Summation and Dot Product Algorithms 18th

A Class of Fast and Accurate Multi-layer Block Summation a...

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18th IFIP WG 10.3 International Conference on Network and Parallel Computing, NPC 2021

作者： He, Kang Barrio, Roberto Chen, Lin Jiang, Hao Liu, Jie Gu, Tongxiang Qi, Jin Science and Technology on Parallel and Distributed Processing Laboratory National University of Defense Technology Changsha410073 China Department of Applied Mathematics University of Zaragoza ZaragozaE50009 Spain College of Computer National University of Defense Technology Changsha410073 China Institute of Applied Physics and Computational Mathematics Beijing100000 China

ISBN: (纸本)9783030935702

Basic recursive summation and common dot product algorithm have a backward error bound that grows linearly with the vector dimension. Blanchard [1] proposed a class of fast and accurate summation and dot product algorithms respectively called FABsum and FABdot, which trades off the calculation accuracy and speed by the block size. Castaldo [2] proposed a multi-layer block summation and dot product algorithm called SuperBlocksum and SuperBlockdot that can increase the accuracy while adding almost no additional calculations. We combine the idea of [1] with the multi-layer block structure to propose SuperFABsum (for "super fast and accurate block summation") and SuperFABdot (for "super fast and accurate block dot product"). Our algorithms have two variants, one is SuperFAB(within), the other is SuperFAB(outside). Our algorithms further improve accuracy and speed compared with FAB and SuperBlock. We conducted accuracy and speed tests on the high-performance FT2000+ processor. Experimental results show that SuperFABdot(within) algorithm is more accurate than FABdot and SuperBlockdot. Compared with FABdot, SuperFABdot(outside) algorithm can achieve up to 1.2 × performance speedup while ensuring similar accuracy. © 2022, IFIP International Federation for Information Processing.

关键词： Artificial intelligence

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Enhancing Strong-Field Dissociation of H2+ in Helium Nanodroplets

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Physical Review Letters 2023年第3期130卷 033201-033201页

作者： Lianrong Zhou Xiaoqing Hu Yigeng Peng Junjie Qiang Peifen Lu Kang Lin Shengzhe Pan Xiaochun Gong Wenyu Jiang Zhejun Jiang Chenxu Lu Hongcheng Ni Cheng Jin Ruifeng Lu Yong Wu Jianguo Wang Jian Wu State Key Laboratory of Precision Spectroscopy East China Normal University Shanghai 200241 China Key Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Beijing 100088 China Department of Applied Physics Nanjing University of Science and Technology Nanjing 210094 China Institut für Kernphysik Goethe-Universität Frankfurt am Main Frankfurt am Main 60438 Germany HEDPS Center of Applied Physics and Technology Peking University Beijing 10084 China Collaborative Innovation Center of Extreme Optics Shanxi University Shanxi 030006 China Chongqing Key Laboratory of Precision Optics Chongqing Institute of East China Normal University Chongqing 401121 China

We investigate the above-threshold multiphoton ionization of H2 embedded in superfluid He nanodroplets driven by ultraviolet femtosecond laser pulses. We find that the surrounding He atoms enhance the dissociation of in-droplet H2+ from lower vibrational states as compared to that of isolated gas-phase molecules. As a result, the discrete peaks in the photoelectron energy spectrum correlated with the HHe+ from the dissociative in-droplet molecule shift to higher energies. Based on the electron-nuclear correlation, the photoelectrons with higher energies are correlated to the nuclei of the low-vibrationally excited molecular ion as the nuclei share less photon energy. Our time-dependent nuclear wave packet quantum simulation using a simplified He−H2+ system confirms the joint contribution of the driving laser field and the neighboring He atoms to the dissociation dynamics of the solute molecular ion. The results strengthen our understanding of the role of the environment on light-induced ultrafast dynamics of molecules.

关键词： Atomic & molecular clusters Atomic & molecular processes in external fields Electronic excitation & ionization Photodissociation

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Intermolecular Charge Transfer Induced Fragmentation of Formic Acid Dimers

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Physical Review Letters 2023年第23期130卷 233001-233001页

作者： Jiaqi Zhou Shaokui Jia Xiaoqing Hu Enliang Wang Xiaorui Xue Yong Wu Jianguo Wang Alexander Dorn Xueguang Ren School of Physics Xi’an Jiaotong University Xi’an 710049 China Institute of Applied Physics and Computational Mathematics Beijing 100088 China Hefei National Laboratory for Physical Sciences at the Microscale and Department of Modern Physics University of Science and Technology of China Hefei 230026 China Max-Planck-Institut für Kernphysik Saupfercheckweg 1 69117 Heidelberg Germany

We investigate the intermolecular nonradiative charge transfer process in a double hydrogen-bonded formic acid (FA) dimer, initiated by electron-collision induced double ionization of one FA molecule. Through fragment ions and electron coincident momentum measurements and ab initio calculations, we obtain direct evidence that electron transfer from the neighboring FA molecule to fill one of the two vacancies occurs by a potential energy curve crossing of FA+++FA with FA++FA+* curves, forming an electronic excited state of dicationic dimers. This process causes the breaking of two hydrogen bonds and subsequently the cleavage of C─H and C─O covalent bonds in the dimers, which is expected to be a general phenomenon occurring in molecular complexes and can have important implications for radiation damage to biological matter.

关键词： Atomic & molecular structure Electronic excitation & ionization Interatomic & molecular potentials Molecular dynamics

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A POLYNOMIAL ROTH THEOREM FOR CORNERS IN R2 AND A RELATED BILINEAR SINGULAR INTEGRAL OPERATOR

arXiv

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arXiv 2023年

作者： Chen, Xuezhi Guo, Jingwei Institute of Applied Physics & Computational Mathematics Beijing100088 China School of Mathematical Sciences University of Science and Technology of China Hefei230026 China

We prove a quantitative Roth-type theorem for polynomial corners in R2. Let P1 and P2 be two linearly independent polynomials with zero constant term. We show that any measurable subset of [0, 1]2 with positive measure contains three points (x, y), (x + P1(t), y), (x, y + P2(t)) with a gap estimate on t. We also prove boundedness results for a variant of the triangular Hilbert transform involving two polynomials and its associated maximal function. These results extend some earlier work of Christ, Durcik and Roos. The key of the proof is to establish certain smoothing inequalities involving two polynomials. To accomplish that we give sublevel set estimates with general polynomials, explicit exponents and simplified *** Codes 42B20 Copyright © 2023, The Authors. All rights reserved.

关键词： Polynomials

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Prediction of ambient-pressure superconductivity in the perovskite hydrides MScH3(M=K,Rb,Cs)

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Physical Review B 2025年第13期111卷 134509-134509页

作者： Hao Quan Xian-Biao Shi Yu-Lin Han Ping Zhang Bao-Tian Wang Institute of High Energy Physics Chinese Academy of Sciences Beijing 100049 China Institute of Theoretical Physics State Key Laboratory of Quantum Optics and Quantum Optics Devices Collaborative Innovation Center of Extreme Optics Shanxi University Taiyuan 030006 China Spallation Neutron Source Science Center Dongguan 523803 China School of Physics and Physical Engineering Qufu Normal University Qufu 273165 China Institute of Applied Physics and Computational Mathematics Beijing 100088 China

Cubic perovskite hydrides with the general formula of MXH3 have recently been predicted to have the potential to achieve superconductivity at ambient pressure. Here, based on first-principles calculations as well as the BCS theory, we propose that replacing the Mg in KMgH3, which is an experimentally synthesized cubic perovskite hydride exhibiting insulating behavior, with Sc can give rise to a mechanically, dynamically, and kinetically stable superconductor, KScH3. Its superconducting transition temperature (Tc) is up to 40.37 K at ambient pressure. Further substitution of the K in KScH3 with Rb and Cs leads to structurally stable RbScH3 and CsScH3, with Tc's of 32.91 and 18.64 K, respectively. Electron-phonon coupling calculations reveal that the soft modes in the intermediate-frequency region associated with the vibrations of H atoms in the phonon spectra play a non-negligible role in determining the high Tc's of MScH3 (M = K, Rb, Cs). All these three perovskite hydrides are intermediate or strong BCS superconductors. Our results provide guidance for the design and study of ambient-pressure hydride superconductors and supply fundamental understanding of the superconductivity physical mechanism.

关键词： Perovskite

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Normalized solutions for a class of Sobolev critical Schrodinger systems

arXiv

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arXiv 2024年

作者： Li, Houwang Liu, Tianhao Zou, Wenming Beijing Institute of Mathematical Sciences and Applications Beijing100084 China Institute of Applied Physics and Computational Mathematics Beijing100088 China Department of Mathematical Sciences Tsinghua University Beijing100084 China

This paper focuses on the existence and multiplicity of normalized solutions for the following coupled Schrödinger system with Sobolev critical coupling term: (Formula presented) where N ≥ 3, a, b > 0, ω1, ω2, ν ∈ \ {0}, and the exponents p, α, β satisfy (Formula presented) The parameters λ1, λ2 ∈ will arise as Lagrange multipliers that are not prior given. This paper mainly presents several existence and multiplicity results under explicit conditions on a, b for the focusing case ω1, ω2 > 0 and attractive case ν > 0: (1) When 2 *, we prove that there exists a mountain-pass type solution, which serves as a normalized ground state. (3) When p = 2*, the existence and classification of normalized ground states are provided for and N ≥ 5, alongside a non-existence result for N = 3, 4. These results reflect the properties of the Aubin-Talenti bubble, which attains the best Sobolev embedding constant. Furthermore, we present a non-existence result for the defocusing case ω1, ω2 © 2024, CC BY.

关键词： Lagrange multipliers

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