Article
Mechanics
Di Liu
Summary: In this study, the two-dimensional Navier-Stokes flows with time-periodic external forces are investigated. Invariant solutions are extracted using recurrent flow analysis, and the cost of searching for nearly-recurrent flows is reduced using low-dimensional projections based on the dynamic mode decomposition algorithm. The flows undergo a transition from a stable time-periodic state to oscillating and even turbulent flows as the period of forces increases. The existence of periodic orbits and their influence on the flow dynamics in different regimes are discussed.
Article
Optics
Bingxin Yan, Dongwei Li, Lanzhi Zhang, Tingting Xi, Yangjian Cai, Zuoqiang Hao
Summary: In this article, we experimentally investigate the performance of filamentation of femtosecond vortex laser pulses in turbulent air. We evaluate the pointing stability, longitudinal wandering, intensity, and spectral broadening by comparing them with femtosecond Gaussian laser pulses. The results show that femtosecond vortex pulses are less affected by air turbulence compared to Gaussian pulses, making them more stable for long-distance applications in the atmosphere.
OPTICS AND LASER TECHNOLOGY
(2023)
Article
Optics
Kilian Baudin, Josselin Garnier, Adrien Fusaro, Nicolas Berti, Guy Millot, Antonio Picozzi
Summary: This study investigates the propagation of temporally incoherent waves in multimode optical fibers and establishes a dynamic equation to describe the behavior of these waves. The results reveal the presence of different collective behaviors in multimode fibers, where the modes of light form collective synchronized oscillations in the frequency spectrum.
Article
Optics
Wei Liang, Dongwei Li, Junwei Chang, Tingting Xi, Longfei Ji, Deming Li, Lanzhi Zhang, Zuoqiang Hao
Summary: In this work, the self-focusing critical power of femtosecond vortex beams in air is experimentally determined by measuring fluorescence using a photomultiplier tube. The relation between the self-focusing critical power and the topological charge is obtained. This work provides a simple method to determine the self-focusing critical power for various structured laser beams.
Article
Optics
Larry B. Stotts, Antonio Oliver, Gregory DiComo, Michael Helle, Jeremy Young, Joshua Isaacs, Joseph R. Penano, Jason A. Tellez, Jason D. Schmidt, Joseph Coffaro, Vincent J. Urick
Summary: This paper introduces a new analytical model for predicting the onset distance of filamentation/light channels in real atmospheres during the propagation of high peak-power laser beams. The model is compared with computer simulations and field experiments, and is used to quantify the expected radius of light channels resulting from self-focusing. Additionally, a set of field experiments is described for further validation of the theoretical calculations.
Article
Multidisciplinary Sciences
Zahra Eslami, Lauri Salmela, Adam Filipkowski, Dariusz Pysz, Mariusz Klimczak, Ryszard Buczynski, John M. Dudley, Goery Genty
Summary: This study reports the generation of a two-octave supercontinuum from visible to mid-infrared in a non-silica graded-index multimode fiber. The fiber design utilizes a nanostructured core composed of two types of drawn lead-bismuth-gallate glass rods with different refractive indices, resulting in an effective parabolic index profile and increased nonlinearity compared to silica fibers. By studying the supercontinuum generation mechanisms and instabilities, the researchers found that appropriate injection conditions resulted in beam self-cleaning from nonlinear mode mixing. Experimental observations were supported by numerical simulations and demonstrated that the enhanced nonlinear refractive index of the lead-bismuth-gallate fiber yielded a significantly larger bandwidth compared to silica fibers.
NATURE COMMUNICATIONS
(2022)
Article
Astronomy & Astrophysics
Simon Opie, Daniel Verscharen, Christopher H. K. Chen, Christopher J. Owen, Philip A. Isenberg
Summary: In this study, high-resolution data from Solar Orbiter is used to investigate the plasma conditions necessary for the occurrence of mirror-mode and oblique firehose instabilities in the solar wind. The analysis reveals the dependencies on the angle between magnetic field direction and solar wind velocity, suggesting a possible role of perpendicular heating in Alfvenic wind. The study also quantifies the occurrence rate of the two instabilities and highlights the requirement of a certain spatial interval for the plasma to reach a marginally stable state.
ASTROPHYSICAL JOURNAL
(2022)
Article
Physics, Fluids & Plasmas
D. S. Agafontsev, S. Randoux, P. Suret
Summary: In the framework of the focusing one-dimensional nonlinear Schrödinger equation, integrable turbulence developing from partially coherent waves are studied numerically. It is found that narrower initial spectra lead to higher frequencies of rogue waves in the turbulence. In the extreme case of very narrow initial spectrum, a quasi-steady state is entered with slow statistical evolution before reaching asymptotic stationary state.
Article
Computer Science, Artificial Intelligence
Andreas Look, Melih Kandemir, Barbara Rakitsch, Jan Peters
Summary: Neural Stochastic Differential Equations (NSDEs) model stochastic processes using neural networks. While NSDEs are accurate in prediction, their uncertainty estimation has not been explored. We find that obtaining well-calibrated uncertainty estimations from NSDEs is computationally prohibitive. To address this, we propose a computationally affordable deterministic scheme for approximating the transition kernel of NSDEs, which improves uncertainty calibration and prediction accuracy.
IEEE TRANSACTIONS ON PATTERN ANALYSIS AND MACHINE INTELLIGENCE
(2023)
Article
Optics
Yu E. Geints, D. Mokrousova, D. Pushkarev, G. E. Rizaev, L. Seleznev, I. Yu Geints, A. A. Ionin, A. A. Zemlyanov
Summary: The study identified a specific range of laser pulse numerical apertures where distortions in both frequency-angular spectrum and pulse spatial shape are minimal. Threshold pulse energy and peak power were also found for the transition between linear and strongly nonlinear laser pulse focusing in air. These findings provide insights into obtaining maximum laser intensity with good beam quality suitable for various laser micropatterning and micromachining technologies.
OPTICS AND LASER TECHNOLOGY
(2021)
Article
Optics
Yury E. Geints, Alexander A. Zemlyanov
Summary: The study investigates multiple filamentation in air of high-power ultrashort laser radiation with a transverse intensity profile resembling a corona composed of several annularly distributed independent top-hat sub-beams. By manipulating the number and power of beamlets, significant advances in the manipulation of multiple filamentation regions and achieving long-range filamentation are theoretically revealed. The use of annular combined beams (CB) can delay the onset of filamentation and increase filamentation length, while also reducing angular divergence post-filamentation, enhancing laser power delivery efficiency.
Article
Optics
Yury E. Geints, Olga V. Minina, Daria V. Mokrousova, Dmitrii V. Pushkarev, Georgy E. Rizaev, Leonid V. Seleznev
Summary: The results of numerical simulations show that using metal mesh masks for amplitude modulation of high-power femtosecond laser pulses reduces beam filamentation and improves the continuity of the laser plasma distribution. The parameters of the filamentation region, including starting coordinate, length, and longitudinal continuity, are strongly dependent on the position and size of the mesh mask. Increasing the size of the mesh cells can shift the spatial position of the filaments, while sparser mesh cells result in a monotonic decrease in the filamentation start coordinate. The thickness of the mesh wire also has a significant influence on the parameters of the filamentation region, sometimes dominating the effects of mesh position and cell size.
OPTICS COMMUNICATIONS
(2023)
Article
Physics, Mathematical
George Vahala, Linda Vahala, Abhay K. Ram, Min Soe
Summary: The effect of the thickness of the dielectric boundary layer on the propagation of an electromagnetic pulse connecting materials with different refractive indices is studied. A qubit lattice algorithm (QLA) is theoretically determined to recover the Maxwell equations, with slight deviations in a small parameter epsilon. As the boundary layer becomes thicker, deviations from the Fresnel conditions are observed, approaching the expected WKB limit. However, a small and unusual dip in part of the transmitted pulse persists. The QLA simulations still recover the solutions to Maxwell equations, even when the parameter epsilon approaches 1.
COMMUNICATIONS IN COMPUTATIONAL PHYSICS
(2023)
Article
Physics, Multidisciplinary
M. A. Eftekhar, H. Lopez-Aviles, F. W. Wise, R. Amezcua-Correa, D. N. Christodoulides
Summary: Advancements in computational capabilities and accessing high power levels have led to a reevaluation of multimode fibers, which are now being pursued to address information bandwidth issues and implement new high-power laser sources. The complexity of interacting modes in multimode fibers has provided fertile ground for observing novel physical effects, but also presents challenges in understanding emerging physical phenomena. A comprehensive theory has been developed to explain the distinct Cherenkov radiation produced during multimode soliton fission events, enhancing understanding of the complex nonlinear processes. The multifaceted nature of nonlinear multimode fibers allows for the observation of unique physical effects, not possible in single-mode settings.
COMMUNICATIONS PHYSICS
(2021)
Article
Multidisciplinary Sciences
Pierre Walch, Benoit Mahieu, Victor Moreno, Thomas Produit, Ugo Andral, Yves-Bernard Andre, Laurent Bizet, Magali Lozano, Clemens Herkommer, Michel Moret, Robert Jung, Robert Bessing, Sandro Klingebiel, Yann Bertho, Thomas Metzger, Andre Mysyrowicz, Jean-Pierre Wolf, Jerome Kasparian, Aurelien Houard
Summary: In the framework of the Laser Lightning Rod project, the spatial evolution of laser-induced filaments is investigated over a distance of 140 m using different laser parameters.
SCIENTIFIC REPORTS
(2023)
Article
Mathematics, Applied
Melanie Kobras, Valerio Lucarini, Maarten H. P. Ambaum
Summary: In this study, a minimal dynamical system derived from the classical Phillips two-level model is introduced to investigate the interaction between eddies and mean flow. The study finds that the horizontal shape of the eddies can lead to three distinct dynamical regimes, and these regimes undergo transitions depending on the intensity of external baroclinic forcing. Additionally, the study provides insights into the continuous or discontinuous transitions of atmospheric properties between different regimes.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Shu-hong Xue, Yun-yun Yang, Biao Feng, Hai-long Yu, Li Wang
Summary: This research focuses on the robustness of multiplex networks and proposes a new index to measure their stability under malicious attacks. The effectiveness of this method is verified in real multiplex networks.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Julien Nespoulous, Guillaume Perrin, Christine Funfschilling, Christian Soize
Summary: This paper focuses on optimizing driver commands to limit energy consumption of trains under punctuality and security constraints. A four-step approach is proposed, involving simplified modeling, parameter identification, reformulation of the optimization problem, and using evolutionary algorithms. The challenge lies in integrating uncertainties into the optimization problem.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Ling An, Liming Ling, Xiaoen Zhang
Summary: In this paper, an integrable fractional derivative nonlinear Schrodinger equation is proposed and a reconstruction formula of the solution is obtained by constructing an appropriate Riemann-Hilbert problem. The explicit fractional N-soliton solution and the rigorous verification of the fractional one-soliton solution are presented.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Marzia Bisi, Nadia Loy
Summary: This paper proposes and investigates general kinetic models with transition probabilities that can describe the simultaneous change of multiple microscopic states of the interacting agents. The mathematical properties of the kinetic model are proved, and the quasi-invariant asymptotic regime is studied and compared with other models. Numerical tests are performed to demonstrate the time evolution of distribution functions and macroscopic fields.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Carlos A. Pires, David Docquier, Stephane Vannitsem
Summary: This study presents a general theory for computing information transfers in nonlinear stochastic systems driven by deterministic forcings and additive and/or multiplicative noises. It extends the Liang-Kleeman framework of causality inference to nonlinear cases based on information transfer across system variables. The study introduces an effective method called the 'Causal Sensitivity Method' (CSM) for computing the rates of Shannon entropy transfer between selected causal and consequential variables. The CSM method is robust, cheaper, and less data-demanding than traditional methods, and it opens new perspectives on real-world applications.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Feiting Fan, Minzhi Wei
Summary: This paper focuses on the existence of periodic and solitary waves for a quintic Benjamin-Bona-Mahony (BBM) equation with distributed delay and diffused perturbation. By transforming the corresponding traveling wave equation into a three-dimensional dynamical system and applying geometric singular perturbation theory, the existence of periodic and solitary waves are established. The uniqueness of periodic waves and the monotonicity of wave speed are also analyzed.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Wangbo Luo, Yanxiang Zhao
Summary: We propose a generalized Ohta-Kawasaki model to study the nonlocal effect on pattern formation in binary systems with long-range interactions. In the 1D case, the model displays similar bubble patterns as the standard model, but Fourier analysis reveals that the optimal number of bubbles for the generalized model may have an upper bound.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Corentin Correia, Ana Cristina Moreira Freitas, Jorge Milhazes Freitas
Summary: The emergence of clustering of rare events is due to periodicity, where fast returns to target sets lead to a bulk of high observations. In this research, we explore the potential of a new mechanism to create clustering of rare events by linking observable functions to a finite number of points belonging to the same orbit. We show that with the right choice of system and observable, any given cluster size distribution can be obtained.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Enyu Fan, Changpin Li
Summary: This paper numerically studies the Allen-Cahn equations with different kinds of time fractional derivatives and investigates the influences of time derivatives on the solutions of the considered models.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Yuhang Zhu, Yinghao Zhao, Chaolin Song, Zeyu Wang
Summary: In this study, a novel approach called Time-Variant Reliability Updating (TVRU) is proposed, which integrates Kriging-based time-dependent reliability with parallel learning. This method enhances risk assessment in complex systems, showcasing exceptional efficiency and accuracy.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Chiara Cecilia Maiocchi, Valerio Lucarini, Andrey Gritsun, Yuzuru Sato
Summary: The predictability of weather and climate is influenced by the state-dependent nature of atmospheric systems. The presence of special atmospheric states, such as blockings, is associated with anomalous instability. Chaotic systems, like the attractor of the Lorenz '96 model, exhibit heterogeneity in their dynamical properties, including the number of unstable dimensions. The variability of unstable dimensions is linked to the presence of finite-time Lyapunov exponents that fluctuate around zero. These findings have implications for understanding the structural stability and behavior modeling of high-dimensional chaotic systems.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Christian Klein, Goksu Oruc
Summary: A numerical study on the fractional Camassa-Holm equations is conducted to construct smooth solitary waves and investigate their stability. The long-time behavior of solutions for general localized initial data from the Schwartz class of rapidly decreasing functions is also studied. Additionally, the appearance of dispersive shock waves is explored.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Vasily E. Tarasov
Summary: This paper extends the standard action principle and the first Noether theorem to consider the general form of nonlocality in time and describes dissipative and non-Lagrangian nonlinear systems. The general fractional calculus is used to handle a wide class of nonlocalities in time compared to the usual fractional calculus. The nonlocality is described by a pair of operator kernels belonging to the Luchko set. The non-holonomic variation equations of the Sedov type are used to describe the motion equations of a wide class of dissipative and non-Lagrangian systems. Additionally, the equations of motion are considered not only with general fractional derivatives but also with general fractional integrals. An application example is presented.
PHYSICA D-NONLINEAR PHENOMENA
(2024)