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Onset of inverse magnetic energy transfer in collisionless turbulent plasmas

Physical Review E 2021年第2期104卷 025204-025204页

作者： Z. H. Zhao Y. Xie Z. Lei J. L. Jiao W. M. Zhou C. T. Zhou S. P. Zhu X. T. He B. Qiao Center for Applied Physics and Technology HEDPS and SKLNPT School of Physics Peking University Beijing 100871 China Science and Technology on Plasma Physics Laboratory Research Center of Laser Fusion China Academy of Engineering Physics Mianyang 621900 China Center for Advanced Material Diagnostic Technology Shenzhen Technology University Shenzhen 518118 China Institute of Applied Physics and Computational Mathematics Beijing 100094 China

Inverse magnetic energy transfer from small to large scales is a key physical process for the origin of large-scale strong magnetic fields in the universe. However, so far, from the magnetohydrodynamic perspective, the onset of inverse transfer is still not fully understood, especially the underlying dynamics. Here, we use both two-dimensional and three-dimensional particle-in-cell simulations to show the self-consistent dynamics of inverse transfer in collisionless decaying turbulent plasmas. Using the space filtering technique in theory and numerical analyses, we identify magnetic reconnection as the onset and fundamental drive for inverse transfer, where, specifically, the subscale electromotive force driven by magnetic reconnection do work on the large-scale magnetic field, resulting in energy transfer from small to large scales. The mechanism is also verified by the strong correlations in locations and characteristic scales between inverse transfer and magnetic reconnection.

关键词： High-energy-density plasmas Magnetic field generation & plasma dynamo Magnetohydrodynamic turbulence Plasma turbulence Space & astrophysical plasma Particle-in-cell methods Plasma kinetic theory

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Equivalence of f(Q) cosmology with quintom-like scenario: the phantom field as effective realization of the non-trivial connection

arXiv

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arXiv 2025年

作者： Basilakos, Spyros Paliathanasis, Andronikos Saridakis, Emmanuel N. National Observatory of Athens Lofos Nymfon Athens11852 Greece Academy of Athens Research Center for Astronomy and Applied Mathematics Soranou Efesiou 4 Athens11527 Greece School of Sciences European University Cyprus Diogenes Street Engomi Nicosia1516 Cyprus Institute of Systems Science Department of Mathematics Faculty of Applied Sciences Durban University of Technology Durban4000 South Africa School for Data Science and Computational Thinking Stellenbosch University 44 Banghoek Rd Stellenbosch7600 South Africa Departamento de Matemáticas Universidad Católica del Norte Avda. Angamos 0610 Casilla Antofagasta1280 Chile CAS Key Laboratory for Researches in Galaxies and Cosmology Department of Astronomy University of Science and Technology of China Anhui Hefei230026 China

We show that f(Q) cosmology with a non-trivial connection, namely the Connection II of the literature, is dynamically equivalent with a quintom-like model. In particular, we show that the scalar field arising from the non-linear f(Q) form, and the scalar field associated to the non-trivial connection, are combined to provide one canonical and one phantom field in the minisuperspace Lagrangian. Hence, the combination of two well-behaved fields appears effectively as a phantom field. This is fundamentally different from the usual approach in phantom and quintom cosmology, in which the phantom field is introduced ad hoc, and thus it may open a new way to handle the phantom fields, namely as effective realizations of the connection-related canonical fields. Copyright © 2025, The Authors. All rights reserved.

关键词： Phantoms

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Lower Bounds on Quantum Annealing Times

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Physical Review Letters 2023年第14期130卷 140601-140601页

作者： Luis Pedro García-Pintos Lucas T. Brady Jacob Bringewatt Yi-Kai Liu Joint Center for Quantum Information and Computer Science University of Maryland College Park Maryland 20742 USA Joint Quantum Institute University of Maryland College Park Maryland 20742 USA Theoretical Division (T4) Los Alamos National Laboratory Los Alamos New Mexico 87545 USA Quantum Artificial Intelligence Laboratory NASA Ames Research Center Moffett Field California 94035 USA KBR 601 Jefferson Street Houston Texas 77002 USA Applied and Computational Mathematics Division National Institute of Standards and Technology Gaithersburg Maryland 20899 USA

The adiabatic theorem provides sufficient conditions for the time needed to prepare a target ground state. While it is possible to prepare a target state much faster with more general quantum annealing protocols, rigorous results beyond the adiabatic regime are rare. Here, we provide such a result, deriving lower bounds on the time needed to successfully perform quantum annealing. The bounds are asymptotically saturated by three toy models where fast annealing schedules are known: the Roland and Cerf unstructured search model, the Hamming spike problem, and the ferromagnetic p-spin model. Our bounds demonstrate that these schedules have optimal scaling. Our results also show that rapid annealing requires coherent superpositions of energy eigenstates, singling out quantum coherence as a computational resource.

关键词： Adiabatic quantum optimization Quantum algorithms Quantum computation

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Cumulant gan

arXiv

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arXiv 2020年

作者： Pantazis, Yannis Fasoulakis, Michail Paul, Dipjyoti Stylianou, Yannis Katsoulakis, Markos Institute of Applied and Computational Mathematics Foundation for Research & Technology Hellas Greece Institute of Computer Science Foundation for Research & Technology Hellas Greece Computer Science Department University of Crete Greece Department of Mathematics and Statistics University of Massachusetts at Amherst United States

In this paper, we propose a novel loss function for training Generative Adversarial Networks (GANs) aiming towards deeper theoretical understanding as well as improved stability and performance for the underlying optimization problem. The new loss function is based on cumulant generating functions giving rise to Cumulant GAN. Relying on a recently-derived variational formula, we show that the corresponding optimization problem is equivalent to Rényi divergence minimization, thus offering a (partially) unified perspective of GAN losses: the Rényi family encompasses Kullback-Leibler divergence (KLD), reverse KLD, Hellinger distance and χ2-divergence. Wasserstein GAN is also a member of cumulant GAN. In terms of stability, we rigorously prove the linear convergence of cumulant GAN to the Nash equilibrium for a linear discriminator, Gaussian distributions and the standard gradient descent ascent algorithm. Finally, we experimentally demonstrate that image generation is more robust relative to Wasserstein GAN and it is substantially improved in terms of both inception score and Fréchet inception distance when both weaker and stronger discriminators are considered. Copyright © 2020, The Authors. All rights reserved.

关键词： Generative adversarial networks

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Atomic Rydberg-state excitation in strong spatially inhomogeneous fields

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Physical Review A 2023年第3期107卷 033104-033104页

作者： Shilin Hu Xiaopeng Yi Li Guo Chengrui Bi Jing Chen Guangdong Provincial Key Laboratory of Quantum Metrology and Sensing & School of Physics and Astronomy Sun Yat-Sen University (Zhuhai Campus) Zhuhai 519082 China Institute of Applied Physics and Computational Mathematics P. O. Box 8090 Beijing 100088 China Department of Physics Shanghai Normal University Shanghai 200234 China Department of Modern Physics and Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences University of Science and Technology of China Hefei 230026 China Shenzhen Key Laboratory of Ultraintense Laser and Advanced Material Technology Center for Advanced Material Diagnostic Technology and College of Engineering Physics Shenzhen Technology University Shenzhen 518118 China

We investigated the Rydberg-state excitation process of a hydrogen atom subjected to spatially homogeneous and inhomogeneous laser fields by means of ab initio calculations. It is found that, comparing with atoms exposed to spatially homogeneous laser fields, the excitation probability decreases and the electron tends to occupy the states with lower principal quantum numbers and angular quantum numbers for atoms in spatially inhomogeneous laser pulses. Furthermore, calculations of a quantum model without taking into account ionization of the electron after it is coherently captured by the Rydberg state are inconsistent with the above-stated findings by ab initio calculations. Analysis indicates that the aforementioned intriguing features can be attributed to the enhanced ionization of the Rydberg states by inhomogeneous laser fields since the distributions of Rydberg states of high principal quantum numbers and angular quantum numbers locate far away from the core where the inhomogeneous electric fields become significant.

关键词： Atomic & molecular processes in external fields Electronic excitation & ionization Ultrafast phenomena Atoms Rydberg atoms & molecules Schroedinger equation

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A posteriori error estimate for the IPDGFEM of a Kirchhoff-Love bending plate

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AIP Conference Proceedings 2022年第1期2611卷

作者： Konstantinos G. Eptaimeros Institute of Applied and Computational Mathematics Foundation for Research and Technology 100 N. Plastira Str. Vassilika Vouton Heraklion Crete GR 70013

This research objective revolves around a posteriori error analysis for the symmetric interior penalty discontinu- ous Galerkin finite element method (IPDGFEM) of a Kirchhoff-Love bending plate. To be more specific, a reliable a posteriori error estimate of residual type in the energy seminorm for the IPDG method of a Kirchhoff-Love bending plate model is established.

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Hybrid fluid–particle modeling of shock-driven hydrodynamic instabilities in a plasma

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Matter and Radiation at Extremes 2021年第3期6卷 24-32页

作者： Hong-bo Cai Xin-xin Yan Pei-lin Yao Shao-ping Zhu Institute of Applied Physics and Computational Mathematics Beijing 100094China Center for Applied Physics and Technology HEDPSand College of EngineeringPeking UniversityBeijing 100871China Center for Applied Physics and Technology HEDPSSchool of Physicsand College of EngineeringPeking UniversityBeijing 100871China Department of Engineering Physics Tsinghua UniversityBeijing 100084China Graduate School China Academy of Engineering PhysicsP.O.Box 2101Beijing 100088China Science and Technology on Plasma Physics Laboratory Laser Fusion Research CenterCAEP621900 MianyangChina

Shock-driven hydrodynamic instabilities in a plasma usually lead to interfacial mixing and the generation of electromagnetic fields,which are nonequilibrium processes coupling kinetics with meso-and macroscopic *** understanding and modeling of these physical processes are very challenging tasks for single-fluid hydrodynamic *** work presents a new framework that incorporates both kinetics and hydrodynamics to simulate shock waves and hydrodynamic instabilities in high-density *** this hybrid code,ions are modeled using the standard particle-in-cell method together with a Monte Carlo description of collisions while electrons are modeled as a massless fluid,with the electron heat flux and fluid–particle energy exchange being considered in the electron pressure *** high-density plasmas,Maxwell’s equations are solved using Ohm’s law instead of Ampere’s *** hybrid algorithm retains ion kinetic effects and their consequences for plasma interpenetration,shock wave propagation,and hydrodynamic ***,we investigate the shock-induced(or gravity-induced)turbulent mixing between a light and a heavy plasma,where hydrodynamic instabilities are initiated by a shock wave(or gravity).This study reveals that self-generated electromagnetic fields play a role in the formation of baroclinic vorticity along the interface and in late-time mixing of the *** results confirm the ability of the proposed method to describe shock-driven hydrodynamic instabilities in a plasma,in particular,nonequilibrium processes that involve mixing and electromagnetic fields at the interface.

关键词： hydrodynamic shock mixing

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Commissioning experiment of the high-contrast SILEX-Ⅱ multi-petawatt laser facility

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Matter and Radiation at Extremes 2021年第6期6卷 1-11页

作者： Wei Hong Shukai He Jian Teng Zhigang Deng Zhimeng Zhang Feng Lu Bo Zhang Bin Zhu Zenghai Dai Bo Cui Yuchi Wu Dongxiao Liu Wei Qi Jinlong Jiao Faqiang Zhang Zuhua Yang Feng Zhang Bi Bi Xiaoming Zeng Kainan Zhou Yanlei Zuo Xiaojun Huang Na Xie Yi Guo Jingqin Su Dan Han Ying Mao Leifeng Cao Weimin Zhou Yuqiu Gu Feng Jing Baohan Zhang Hongbo Cai Minqing He Wudi Zheng Shaoping Zhu Wenjun Ma Dahui Wang Yinren Shou Xueqing Yan Bin Qiao Yi Zhang Congling Zhong Xiaohui Yuan and Wenqing Wei Science and Technology on Plasma Physics Laboratory Laser Fusion Research CenterCAEPMianyangSichuan Province 621900China Institute of Applied Physics and Computational Mathematics Beijing 100871China Institute of Heavy Ion Physics Peking UniversityBeijing 100871China School of Physics Peking UniversityBeijing 100871China School of Physics and Astronomy Shanghai Jiao Tong UniversityShanghai 200240China

The results of a commissioning experiment on the SILEX-Ⅱlaser facility(formerly known as CAEP-PW)are ***-Ⅱis a complete optical parametric chirped-pulse amplification laser *** peak power reached about 1 PWin a 30 fs pulse duration during the *** laser contrast was better than 1010 at 20 ps ahead of the main *** the basic laser foil target interaction,a set of experimental data were collected,including spatially resolved x-ray emission,the image of the coherent transition radiation,the harmonic spectra in the direction of reflection,the energy spectra and beam profile of accelerated protons,hot-electron spectra,and transmitted laser energy fraction and spatial *** experimental results show that the laser intensity reached 531020 W/cm^(2) within a 5.8μm focus(FWHM).Significant laser transmission did not occur when the thickness of theCHfoil was equal to or greater than 50 *** maximum energy of the accelerated protons in the target normal direction was roughly unchanged when the target thickness varied between 50 nm and 15μ*** maximum proton energy via the target normal sheath field acceleration mechanism was about 21 *** expect the on-target laser intensity to reach 10^(22) W/cm^(2) in the near future,after optimization of the laser focus and upgrade of the laser power to 3 PW.

关键词： experiment unchanged facility

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Data-driven Uncertainty Quantification for Systematic Coarse-grained Models

arXiv

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arXiv 2020年

作者： Jin, Tangxin Chazirakis, Anthony Kalligiannaki, Evangelia Harmandaris, Vagelis Katsoulakis, Markos A. Department of Mathematics and Statistics University of Massachusetts Amherst United States Institute of Applied and Computational Mathematics Foundation for Research and Technology - Hellas Heraklion Crete Greece Department of Mathematics and Applied Mathematics University of Crete Heraklion Crete Greece

In this work, we present methodologies for the quantification of confidence in bottom-up coarse-grained models for molecular and macromolecular systems. Coarse-graining methods have been extensively used in the past decades in order to extend the length and time scales accessible by simulation methodologies. The quantification, though, of induced errors due to the limited availability of fine-grained data is not yet established. Here, we employ rigorous statistical methods to deduce guarantees for the optimal coarse models obtained via approximations of the multi-body potential of mean force, with the relative entropy, the relative entropy rate minimization, and the force matching methods. Specifically, we present and apply statistical approaches, such as bootstrap and jackknife, to infer confidence sets for a limited number of samples, i.e., molecular configurations. Moreover, we estimate asymptotic confidence intervals assuming adequate sampling of the phase space. We demonstrate the need for non-asymptotic methods and quantify confidence sets through two applications. The first is a two-scale fast/slow diffusion process projected on the slow process. With this benchmark example, we establish the methodology for both independent and time-series data. Second, we apply these uncertainty quantification approaches on a polymeric bulk system. We consider an atomistic polyethylene melt as the prototype system for developing coarse-graining tools for macromolecular systems. For this system, we estimate the coarse-grained force field and present confidence levels with respect to the number of available microscopic data. Copyright © 2020, The Authors. All rights reserved.

关键词： Uncertainty analysis

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Deep operator network models for predicting post-burn contraction

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Clinical Biomechanics 2025年

作者： Selma Husanovic Ginger Egberts Alexander Heinlein Fred Vermolen Delft Institute of Applied Mathematics (DIAM) Faculty of Electrical Engineering Mathematics & Computer Science Delft University of Technology Mekelweg 4 2628 CD Delft the Netherlands Research Group Computational Mathematics (CMAT) Department of Mathematics and Statistics University of Hasselt Hasselt Belgium Department of Plastic Reconstructive & Hand Surgery Amsterdam UMC Amsterdam the Netherlands Dutch Burns Foundation Beverwijk the Netherlands

Background Burn injuries present a significant global health challenge. Among the most severe long-term consequences are contractures , which can lead to functional impairments and disfigurement. Understanding and predicting the evolution of post-burn wounds is essential for developing effective treatment strategies. Traditional mathematical models, while accurate, are often computationally expensive and time-consuming, limiting their practical application. Recent advancements in machine learning, particularly in deep learning, offer promising alternatives for accelerating these predictions. Methods This study explores the use of a deep operator network , a type of neural operator, as a surrogate model for finite element simulations aimed at predicting post-burn contraction across multiple wound shapes. A deep operator network was trained on three distinct initial wound shapes, with enhancements made to the architecture by incorporating initial wound shape information and applying sine augmentation to enforce boundary conditions. Findings The performance of the trained deep operator network was evaluated on a test set including finite element simulations based on convex combinations of the three basic wound shapes. The model achieved an R 2 score of 0.99 , indicating strong predictive accuracy and generalization. Moreover, the model provided reliable predictions over an extended period of up to one year, with speedups of up to 128-fold on the Central Processing Unit and 235-fold on the Graphical Processing Unit, compared to the numerical model. Interpretation These findings suggest that deep operator networks can effectively serve as a surrogate for traditional finite element methods in simulating post-burn wound evolution, with potential applications in medical treatment planning.

关键词： Operator learning Neural networks Surrogate model Wound modeling

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