Article
Astronomy & Astrophysics
Yossef Zenati, Ethan T. Vishniac
Summary: Magnetic helicity is robustly conserved in systems with very large magnetic Reynolds numbers, playing a major role in dynamo processes. However, numerical simulations of astrophysical systems often lack sufficient resolution to preserve global magnetic helicity. We propose an algorithm to enforce strict local conservation of magnetic helicity in numerical simulations, improving their approximation of real systems.
ASTROPHYSICAL JOURNAL
(2023)
Article
Physics, Multidisciplinary
Akash Biswas, Bidya Binay Karak, Robert Cameron
Summary: A striking feature of the solar cycle is the migration of sunspots from midlatitudes to the equator over time. The level of activity and width of sunspot belts increase rapidly and then decline, while in the late stages of the cycle, the statistical properties remain the same regardless of the cycle's strength during its rise and maximum phases.
PHYSICAL REVIEW LETTERS
(2022)
Article
Multidisciplinary Sciences
Archie F. A. Bott, Petros Tzeferacos, Laura Chen, Charlotte A. J. Palmer, Alexandra Rigby, Anthony R. Bell, Robert Bingham, Andrew Birkel, Carlo Graziani, Dustin H. Froula, Joseph Katz, Michel Koenig, Matthew W. Kunz, Chikang Li, Jena Meinecke, Francesco Miniati, Richard Petrasso, Hye-Sook Park, Bruce A. Remington, Brian Reville, J. Steven Ross, Dongsu Ryu, Dmitri Ryutov, Fredrick H. Seguin, Thomas G. White, Alexander A. Schekochihin, Donald Q. Lamb, Gianluca Gregori
Summary: Understanding magnetic field generation and amplification in turbulent plasma is crucial for explaining observations of magnetic fields in the universe. This study validates a theoretical framework for the origin and sustainment of these fields, and reports an experiment on laboratory plasma dynamo with Pm & 1. By characterizing plasma evolution and measuring various properties, it is shown that plasma turbulence from strong shear can generate fields more efficiently than previously thought, potentially explaining large-scale fields in astrophysical systems.
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
(2021)
Article
Physics, Multidisciplinary
Radhika Achikanath Chirakkara, Christoph Federrath, Pranjal Trivedi, Robi Banerjee
Summary: The study shows that in the highly subsonic regime, the saturation efficiency of magnetic field amplification by the turbulent dynamo increases as the Mach number decreases. Even with purely longitudinal forcing modes, a high saturation efficiency can be achieved.
PHYSICAL REVIEW LETTERS
(2021)
Article
Astronomy & Astrophysics
Naveen Jingade, Nishant K. Singh
Summary: In this study, we investigate the impact of temporal fluctuations in kinetic helicity on the generation of large-scale magnetic fields in the presence of a background linear shear flow. Our findings show that growing solutions can be obtained when the correlation time of helicity is greater than the correlation time of velocity. Interestingly, under certain conditions, the axisymmetric modes exhibit non-monotonic behavior in relation to shear rate.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Hongzhe Zhou, Eric G. Blackman
Summary: The study combines analytical approaches with simulations to investigate the shear-current effect in mean-field dynamo theory. The results show that the kinetic contribution can transition from positive to negative values with the kinetic energy spectral index, while the magnetic contribution remains negative regardless of the spectral index.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Neco Kriel, James R. Beattie, Amit Seta, Christoph Federrath
Summary: The turbulent dynamo mechanism involves converting turbulent kinetic energy into magnetic energy and determining the scales at which magnetic fields concentrate, with a focus on the roles of viscous and resistive scales. Through numerical simulations, the dependence of characteristic scales on kinematic phases is explored, showing a principal dependence on the resistive scale k(eta). The study reveals dichotomies in the dynamo properties based on different hydrodynamic Reynolds numbers, with a minimum critical value of Re-crit = 100 for turbulent dynamo action.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Physics, Applied
Tomas Scepka, Juraj Feilhauer, Jaroslav Tobik, Sergei Krylov, Tetiana Kalmykova, Vladimir Cambel, Michal Mruczkiewicz
Summary: We experimentally and numerically demonstrate the control of magnetization circulation in the closure domain state of thin permalloy squares. By applying an appropriate external magnetic field and interacting with a magnetic force microscopy (MFM) tip, we achieve control over the magnetization circulation. Numerical simulations confirm the validity of the proposed switching protocol for a wide range of MFM tips. Experimental results show that this method is robust against slight imperfections in the fabrication process and exhibits proper symmetry response under different experimental conditions.
JOURNAL OF APPLIED PHYSICS
(2023)
Article
Astronomy & Astrophysics
Amit Seta, Christoph Federrath
Summary: Magnetic fields in the turbulent interstellar medium play an important role in star-forming galaxies. This study investigates the properties of the turbulent dynamo in different phases, showing that the growth rate of magnetic fields is similar in both warm and cold phases. Additionally, it is found that the final ratio of magnetic to turbulent kinetic energy is lower in the cold phase.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Sivan Ginzburg, Jim Fuller, Adela Kawka, Ilaria Caiazzo
Summary: Recent studies suggest that white dwarfs generate magnetic fields through convection driven by core crystallization and rotation. These crystallization-driven dynamos are mostly in a fast-rotating regime, where the magnetic field is enhanced by convective motion and can explain some observed magnetic field phenomena.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Axel Brandenburg, Igor Rogachevskii, Jennifer Schober
Summary: Small-scale dynamos are important in astrophysics and understanding their behavior is crucial for various observations and theoretical aspects. In this study, the authors show that during the kinematic phase of the dynamo, the cutoff wavenumber of the magnetic energy spectra scales differently than expected for small magnetic Prandtl numbers. However, in the non-linear saturated regime, the behavior changes and the cutoff scale has a different scaling with magnetic Prandtl number.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Alexander Mordvinov, Bidya Binay Karak, Dipankar Banerjee, Elena M. Golubeva, Anna Khlystova, Anastasiya Zhukova, Pawan Kumar
Summary: Detailed study of solar activity cycles reveals important conclusions about polar field reversals and the causal relationship between polar field formation and magnetic flux transport. The characteristics of different solar activity cycles are influenced by the spatiotemporal organization and properties of emergent magnetic flux, leading to complex restructuring of high-latitude magnetic fields.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
A. Zhukova, A. Khlystova, V Abramenko, D. Sokoloff
Summary: Long observational series for bipolar active regions (ARs) provide valuable information about the transformation of the global solar magnetic field. Most bipolar ARs follow the Hale's polarity law, but a small percentage of ARs have the opposite polarity. However, the lack of statistics hinders the study of these anti-Hale ARs.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Mathematics
Olga Sheremetyeva
Summary: The article investigates a large-scale model of an a?-dynamo in the low-mode approximation. The intensity of the a-effect is regulated by a process with hereditarity properties. The stability of the MHD-system solution is studied based on the control parameters and the parameters of the alternating kernel. The results are represented on the phase plane, and the change in pattern depending on the damping coefficient, damping frequency, and waiting time is compared with previous studies.
Article
Chemistry, Multidisciplinary
Shi Feng, Cunliang Pan, Hongfei Ye, Wendong Liu, Wenbo Yang, Yingdi Lv, Shengyang Tao
Summary: Enhanced mixing in microchannels is achieved by using magnetic nonspherical particles (MNSPs), which generate secondary vortices with cyclical characteristics due to their shape. Increasing the rotation rate of MNSPs enlarges the secondary vortices, expanding the mixing zone and enhancing the mixing efficiency. Complementary micro-particle image velocimetry (mu PIV) analysis clarifies the mixing mechanism and demonstrates the potential of employing MNSPs as efficient mixers in lab-on-chip devices.
