Article
Materials Science, Multidisciplinary
E. Alfinelli, F. Caporaletti, F. Dallari, A. Martinelli, G. Monaco, B. Ruta, M. Sprung, M. Zanatta, G. Baldi
Summary: The atomic displacements induced by a low energy x-ray beam in pure boron oxide and sodium silicate glasses were studied using x-ray photon correlation spectroscopy. The initial glass was completely transformed into a new amorphous state under the beam, which remained stable. The restructuring of the new phase showed exponential relaxation similar to macroscopic measurements in the high-temperature supercooled liquid, suggesting a higher energy minimum. The observed dynamics had a temperature dependence, indicating thermal activation of defect creation.
Article
Physics, Multidisciplinary
Alain Ghizzo, Daniele Del Sarto, Homam Betar
Summary: In this study, we conducted high-resolution kinetic simulations of interpenetrating plasma beams. We found that this configuration is unstable to Weibel-type and two-stream instabilities, which linearly induce a growth of magnetic and electrostatic energy, respectively, at the expense of kinetic energy. We also discovered the possibility of a reversal of energy flow associated with these beam-plasma instabilities with the excitation of secondary propagating oblique modes.
PHYSICAL REVIEW LETTERS
(2023)
Article
Physics, Multidisciplinary
Alain Ghizzo, Daniele Del Sarto, Homan Betar
Summary: We perform simulations to study the interpenetrating plasma beams, which are susceptible to Weibel-type and two-stream instabilities. We find that the energy flow associated with beam-plasma instabilities can be reversed when secondary propagating oblique modes are excited. This reversal is caused by the reinforcement of the filamentation process in the phase space.
PHYSICAL REVIEW LETTERS
(2023)
Article
Physics, Fluids & Plasmas
O. B. Ericok, J. K. Mason
Summary: This paper proposes that topological and geometric changes are associated with phase transitions, rather than statistical thermodynamics. Numerical evidence from simulations of hard-disk and hard-sphere systems suggests that a discontinuity in the mixing time coincides with the solid-fluid phase transition in the thermodynamic limit.
Article
Physics, Multidisciplinary
Pierre-Henri Chavanis
Summary: This study develops the kinetic theory of collisionless relaxation for systems with long-range interactions, specifically in relation to Lynden-Bell's statistical theory. The authors discuss the multi-level case and establish the connection between the kinetic equation derived from the quasilinear theory of the Vlasov equation and the relaxation equation obtained from a maximum entropy production principle. They propose a method to close the infinite hierarchy of kinetic equations and obtain a generalized Landau, Lenard-Balescu, or Kramers equation for the coarse-grained distribution function. The authors also explore the analogies with two-dimensional turbulence and potential applications to fermionic and bosonic dark matter halos.
PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS
(2022)
Article
Mechanics
Kyeong-Soo Yun, Sung-Kie Youn
Summary: This paper presents a topology optimization method for microstructures of viscoelastic composites, utilizing numerical methods and adjoint sensitivity analysis to find the optimal microstructures and minimize the difference between prescribed and effective relaxation moduli. Several numerical examples demonstrate the effectiveness of the proposed approach in optimizing viscoelastic composites based on volume fraction, relaxation time, and stiffness.
INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES
(2022)
Article
Polymer Science
Davide Michieletto, Takahiro Sakaue
Summary: The study introduces a novel dynamical entanglement analysis (DEA) method to extract spatiotemporal entanglement structures from pairwise displacement correlation of entangled chains. Applying DEA to molecular dynamics simulations reveals a strong and unexpected cooperative dynamics between entangled chains, providing previously unnoticed insights into the dynamics of generic entangled polymers. The method is proposed to be useful in analyzing the dynamical evolution of entanglements in generic polymeric systems like blends and composites.
Article
Astronomy & Astrophysics
Liliya L. R. Williams, Jens Hjorth
Summary: This article introduces the concept of maximum entropy state and energy distribution to describe self-gravitating Newtonian systems, particularly the structures of dark matter halos. By defining a nonequilibrium functional, the evolution towards equilibrium of the systems can be better understood.
ASTROPHYSICAL JOURNAL
(2022)
Article
Multidisciplinary Sciences
Muni Zhou, Vladimir Zhdankin, Matthew W. Kunz, Nuno F. Loureiro, Dmitri A. Uzdensky
Summary: In this study, we investigate the generation of seed magnetic fields through the Weibel instability in an initially unmagnetized plasma driven by a large-scale shear force. We develop an analytical model and confirm its predictions through particle simulations. This work has important implications for magnetogenesis in dilute astrophysical systems.
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
(2022)
Article
Mechanics
Yu Lu, Guo-Hui Hu
Summary: In this study, the diffusion of linear polymers in the semi-flexible polymer network inside the cell is investigated using dissipative particle dynamics (DPD). The analysis of Rouse modes reveals that the geometric constraint length N-a plays a crucial role in describing the network effect on polymer diffusion. Based on the analysis of Rouse modes and mean square displacements, a non-dimensional conformational dynamics function dependent on time is proposed, along with a scaling law to predict the long time diffusivity of linear polymers in a semi-flexible polymer network with different mesh sizes.
Article
Polymer Science
Lingyi Zou, Wenlin Zhang
Summary: This study investigates the effects of entanglement on polymer crystallization using atomistic molecular dynamics simulations. The results show that decreasing entanglement density increases the nucleation rate of the polymer, but has mild effects on crystal nucleation. The absence of conventional entanglements in unlinked rings only enhances the nucleation rate by a factor of two. Additionally, the nucleation process of the polymer is localized and does not require large-scale relaxation of polymer chains.
Article
Physics, Multidisciplinary
Lev Arzamasskiy, Matthew W. Kunz, Jonathan Squire, Eliot Quataert, Alexander A. Schekochihin
Summary: We present results from 3D hybrid-kinetic simulations of Alfvenic turbulence in a high-fl, collisionless plasma, revealing its key features and implications for various astrophysical phenomena. The interplay between local wave-wave interactions and nonlocal wave-particle interactions plays a crucial role in this turbulence. Our theoretical estimates and simulations demonstrate the effective collisionality and plasma viscosity in pressure-anisotropic high-fl turbulence, with significant contributions from anisotropic viscous stress. The dissipation of cascade energy is mainly through ion heating caused by Landau damping and anisotropic viscous heating.
Article
Physics, Mathematical
Stephen Pankavich
Summary: In this study, a multispecies, collisionless plasma is modeled using the Vlasov-Poisson system. It is shown that the velocity characteristics and spatial averages of particle distributions converge as time goes to infinity, leading to the establishment of precise asymptotic profiles of the electric field, charge, and current densities. Modified spatial characteristics are proven to converge using the limiting electric field, with a modified L-infinity scattering result established for each particle distribution function showing convergence as time approaches infinity. The estimates of quantities in non-neutral plasma are sharp, while in the neutral case they may imply faster decay rates.
COMMUNICATIONS IN MATHEMATICAL PHYSICS
(2022)
Article
Astronomy & Astrophysics
S. Selvi, O. Porth, B. Ripperda, F. Bacchini, L. Sironi, R. Keppens
Summary: Magnetic reconnection can generate nonthermal energy distributions and power high-energy astrophysical phenomena. This study investigates relativistic collisionless plasmoid-mediated reconnection in magnetically dominated pair plasmas using kinetic particle-in-cell simulations. The mechanisms driving the nonideal electric field in fully developed plasmoid chains are identified based on a statistical analysis using the full Ohm law. A kinetic physics motivated nonuniform effective resistivity model is proposed, capturing the essentials of collisionless reconnection in nonideal magnetohydrodynamic descriptions.
ASTROPHYSICAL JOURNAL
(2023)
Article
Multidisciplinary Sciences
D. Michieletto, P. Neill, S. Weir, D. Evans, N. Crist, V. A. Martinez, R. M. Robertson-Anderson
Summary: The study demonstrates time-dependent rheology of DNA solutions via enzymatically-driven architectural alterations by restriction endonucleases. The rheological properties of the systems depend on the concentrations and properties of DNA and REs, showcasing tunable behaviors with potential applications in both industry and biology.
NATURE COMMUNICATIONS
(2022)
Article
Physics, Multidisciplinary
Renato Pakter, Yan Levin
Summary: This paper introduces a new method to predict the stability limits of a shear layer through mapping Euler's equations onto a system of interacting vortices. The authors successfully predict the wavelength of the most unstable mode and compare it with molecular dynamics simulations.
PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS
(2021)
Article
Chemistry, Physical
Daniel Alejandro Gomez, Derek Frydel, Yan Levin
Summary: The work discusses a lattice-gas model of charge regulation with electrostatic interactions, including both long-range electrostatic interactions and nearest-neighbor interactions for non-electrostatic forces between adsorbed ions. The Frumkin-Fowler-Guggenheim isotherm obtained accurately reproduces simulation data points.
JOURNAL OF CHEMICAL PHYSICS
(2021)
Article
Chemistry, Physical
Igor M. Telles, Rogerio K. Bombardelli, Alexandre P. dos Santos, Yan Levin
Summary: The method presents two different approaches to study electroosmotic flows inside cylindrical nanopores with uniform surface charge. One approach uses surface point sites to represent the charge, while the other treats the surface charge implicitly. The latter method is about 40% more efficient and produces identical results compared to the former method.
JOURNAL OF MOLECULAR LIQUIDS
(2021)
Article
Chemistry, Physical
Amin Bakhshandeh, Derek Frydel, Yan Levin
Summary: In this study, a reactive Monte Carlo simulation method and the primitive model of electrolyte were used to investigate the acid-base equilibrium that controls charge regulation in colloidal systems. The simulations were performed in a semi-grand canonical ensemble, where the colloidal suspension was in contact with a reservoir of salt and strong acid. The interior of colloidal particles was modeled as a low dielectric medium. The effective colloidal charge was calculated for different numbers of surface acidic groups, pH, salt concentrations, and types of electrolyte. Good agreement was found between the titration curves obtained from simulations and experimental measurements in the case of potassium chloride. For lithium chloride, the specific ionic adsorption was taken into account through the partial dehydration of the lithium ions.
JOURNAL OF CHEMICAL PHYSICS
(2022)
Article
Chemistry, Physical
Rogerio K. Bombardelli, Igor M. Telles, Alexandre P. dos Santos, Yan Levin
Summary: A simulation method for studying electroosmotic flow in charged nanopores with dielectric contrast is presented. It is found that polarization is particularly important for systems with multivalent counterions and narrow nanopores, increasing volumetric flow rate significantly. In systems with 3:1 electrolyte, a saturation of the volumetric flow rate is observed, with polarizable pores having flow rate 100% higher than nonpolarizable ones.
JOURNAL OF PHYSICAL CHEMISTRY B
(2021)
Article
Physics, Fluids & Plasmas
Antonio H. Carlan Jr, Renato Pakter
Summary: This paper investigates halo formation in a sheet beam model, focusing on the core-halo boundary. A theory to determine the final stationary state of initially mismatched beams is developed, with self-consistent numerical simulations used to obtain particle distributions for the sheet beam stationary state. The core-halo boundary is evaluated using maximum Laplacian criteria, comparing results to predicted values.
PHYSICS OF PLASMAS
(2021)
Article
Chemistry, Physical
Amin Bakhshandeh, Yan Levin
Summary: We discuss the application of the Widom insertion method for calculating the chemical potential of individual ions in computer simulations. Two approaches are considered, and the second approach shows a better agreement with the results of grand canonical Monte Carlo simulation.
JOURNAL OF CHEMICAL PHYSICS
(2022)
Article
Chemistry, Multidisciplinary
Igor M. Telles, Yan Levin, Alexandre P. dos Santos
Summary: It has been found that condensation of multivalent counterions can lead to the reversal of surface charge in nanopores, resulting in the reversal of electroosmotic flow. By shifting the shear plane from the position of the Stern contact surface, the Smoluchowski equation can quantitatively account for the electroosmotic flow.
Article
Chemistry, Multidisciplinary
Amin Bakhshandeh, Derek Frydel, Yan Levin
Summary: This study presents a new theory that can calculate the effective surface charge of colloidal particles and obtain titration curves for different salt concentrations efficiently. The theory takes into account the shift of pH in solution caused by the presence of 1:1 electrolyte and the electrostatic potential generated by deprotonated surface groups. Extensive reactive Monte Carlo simulations confirm the accuracy of the theory, showing excellent agreement with simulations without any adjustable parameters.
Article
Physics, Fluids & Plasmas
Samuel Marini, Felipe B. Rizzato, Renato Pakter
Summary: This paper investigates the relativistic Brillouin flow in a crossed-field gap, specifically in the case of a planar magnetron. Unlike previous studies, it assumes that the electron discharge occurs in a time scale longer than the magnetic diffusion time in the metal. The study reveals that the properties of Brillouin flow and the loss of magnetic insulation differ from the short pulse case. Two branches of equilibrium Brillouin flow solutions can coexist inside the gap, with one being stable and the other being unstable. Varying the parameters leads to the coalescence and disappearance of these branches, resulting in a complete loss of magnetic insulation. The existence of the unstable solution inside the gap affects electron dynamics and induces cathode-anode currents.
PHYSICS OF PLASMAS
(2023)
Article
Physics, Multidisciplinary
Tarcisio N. Teles, Calvin A. F. Farias, Renato Pakter, Yan Levin
Summary: We propose a Monte Carlo approach for implementing Lynden-Bell entropy maximization for arbitrary initial particle distributions. Our results show that for most initial distributions, the relaxation process is incomplete.
Article
Chemistry, Physical
Thiago Colla, Igor M. Telles, Muhammad Arfan, Alexandre P. dos Santos, Yan Levin
Summary: In this paper, the authors review recent research that uses dissipative particle dynamics simulations to study the motion of ions through narrow pores. They also introduce a classical density functional theory (DFT) based on the hypernetted-chain approximation (HNC) to calculate the velocity of electroosmotic flows. The simulations and theoretical calculations show that the fluid velocity profiles deviate from the predictions of the Smoluchowski equation in the case of charged pores with 2:1 electrolyte.
FARADAY DISCUSSIONS
(2023)
Article
Physics, Fluids & Plasmas
Calvin A. F. Farias, Renato Pakter, Yan Levin
Summary: In this paper, we explore the equilibrium state of a 2D incompressible fluid using Kirchhoff's vortex formulation of 2D Euler fluid equations. By expressing the fluid state in terms of infinitesimal vortices, we aim to find the maximum entropy state of the fluid through a Monte Carlo method. However, we find that the final state predicted by the maximum entropy assumption differs significantly from the actual final state observed in molecular dynamics simulation. Therefore, we propose a different approach based on core-halo distribution, which accurately predicts the final relaxation state of the fluid from an arbitrary initial condition.
