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We study the thermodynamic and dynamic phase transitions in two-dimensional polydisperse hard disks using Monte Carlo methods. A conventional local Monte Carlo algorithm allows us to observe a dynamic liquid-glass transition at a density,…

Statistical Mechanics · Physics 2007-05-23 Ludger Santen , Werner Krauth

We use kinetic hybrid simulations (kinetic ions - fluid electrons) to characterize the fraction of ions that are accelerated to non-thermal energies at non-relativistic collisionless shocks. We investigate the properties of the shock…

High Energy Astrophysical Phenomena · Physics 2015-06-23 Damiano Caprioli , Ana-Roxana Pop , Anatoly Spitkovsky

The efficiency and uniqueness of the diffusive shock acceleration is studied on the basis of the novel kinetic solutions. These solutions obtained earlier (paper I, astro-ph/9707152) selfconsistently describe a strong coupling of cosmic…

Astrophysics · Physics 2009-10-30 M. A. Malkov

Global fits of physics models require efficient methods for exploring high-dimensional and/or multimodal posterior functions. We introduce a novel method for accelerating Markov Chain Monte Carlo (MCMC) sampling by pairing a…

High Energy Physics - Phenomenology · Physics 2023-09-06 N. T. Hunt-Smith , W. Melnitchouk , F. Ringer , N. Sato , A. W Thomas , M. J. White

Efficient mixing in high-speed compressible flows, crucial for scramjet operation, can be significantly enhanced by shock wave interactions. This study employs Direct Numerical Simulations (DNS) to comprehensively examine the interaction…

Fluid Dynamics · Physics 2025-05-13 Radouan Boukharfane

Media composed of colliding hard disks (2D) or hard spheres (3D) serve as good approximations for the collective hydrodynamic description of gases, liquids and granular media. In the present study, the compressible hydrodynamics and shock…

Fluid Dynamics · Physics 2015-05-30 Nick Sirmas , Marion Tudorache , Javier Barahona , Matei I. Radulescu

To simulate the dynamics of fluid with polydisperse particles on macroscale level, one has to solve hydrodynamic equations with several relaxation terms, representing momentum transfer from fluid to particles and vice versa. For small…

Understanding the conditions that enable particle acceleration at non-relativistic collisionless shocks is essential to unveil the origin of cosmic rays. We employ 2D and 3D hybrid simulations (with kinetic ions and fluid electrons) to…

High Energy Astrophysical Phenomena · Physics 2026-04-21 Luca Orusa , Damiano Caprioli , Lorenzo Sironi , Anatoly Spitkovsky

The first-order cosmic ray acceleration at ultrarelativistic shocks is investigated using the Monte Carlo method. We apply a method of discrete particle momentum scattering as a model of particle pitch angle diffusion to reproduce highly…

Astrophysics · Physics 2007-05-23 J. Bednarz

We develop numerical methods for reaction-diffusion systems based on the equations of fluctuating hydrodynamics (FHD). While the FHD formulation is formally described by stochastic partial differential equations (SPDEs), it becomes similar…

Fluid Dynamics · Physics 2018-01-17 Changho Kim , Andy Nonaka , John B. Bell , Alejandro L. Garcia , Aleksandar Donev

We present a new efficient method for Monte Carlo simulations of diffusion-reaction processes. First introduced by us in [Phys. Rev. Lett., 97:230602, 2006], the new algorithm skips the traditional small diffusion hops and propagates the…

Materials Science · Physics 2013-05-29 T. Oppelstrup , V. V. Bulatov , A. Donev , M. H. Kalos , G. H. Gilmer , B. Sadigh

The highly amplified magnetic fields suggested by observations of some supernova remnant (SNR) shells are most likely an intrinsic part of efficient particle acceleration by shocks. This strong turbulence, which may result from cosmic ray…

Astrophysics · Physics 2009-11-13 Andrey E. Vladimirov , Andrei M. Bykov , Donald C. Ellison

We present the results of large hybrid (kinetic ions - fluid electrons) simulations of particle acceleration at non-relativistic collisionless shocks. Ion acceleration efficiency and magnetic field amplification are investigated in detail…

High Energy Astrophysical Phenomena · Physics 2015-06-23 Damiano Caprioli

We report on a new Monte Carlo method for simulating diffusive shock acceleration (DSA) of solar energetic particles at upstream and downstream regions of quasi-parallel collisionless shock waves under the influence of self-generated…

Space Physics · Physics 2014-08-14 Arto Sandroos , Gang Li , Lulu Zhao

We are concerned with a model of ideal compressible isentropic two-fluid magnetohydrodynamics (MHD). Introducing an entropy-like function, we reduce the equations of two-fluid MHD to a symmetric form which looks like the classical MHD…

Analysis of PDEs · Mathematics 2018-12-26 Lizhi Ruan , Yuri Trakhinin

The Direct Simulation Monte Carlo (DSMC) method is widely employed for simulating rarefied nonequilibrium gas flows. With advances in aerospace engineering and micro/nano-scale technologies, gas flows exhibit the coexistence of rarefied and…

Computational Physics · Physics 2025-07-01 Hao Jin , Sha Liu , Sirui Yang , Junzhe Cao , Congshan Zhuo , Chengwen Zhong

The most stringent test of theoretical models of the first-order Fermi mechanism at collisionless astrophysical shocks is a comparison of the theoretical predictions with observational data on particle populations. Such comparisons have…

Astrophysics · Physics 2009-10-28 Matthew G. Baring , Keith Ogilvie , Donald Ellison , Robert Forsyth

The present research proposes a new memory-efficient method using diffusion models to inject turbulent inflow conditions into Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS) for various flow problems. A guided diffusion…

A magnetohydrodynamic (MHD) shock front can be unstable to the corrugation instability, which causes a perturbed shock front to become increasingly corrugated with time. An ideal MHD parallel shock (where the velocity and magnetic fields…

Solar and Stellar Astrophysics · Physics 2021-07-14 Ben Snow , Andrew Hillier

We present a nonlinear Monte Carlo model of efficient diffusive shock acceleration (DSA) where the magnetic turbulence responsible for particle diffusion is calculated self-consistently from the resonant cosmic-ray (CR) streaming…

High Energy Astrophysical Phenomena · Physics 2015-06-19 Andrei M. Bykov , Donald C. Ellison , Sergei M. Osipov , Andrey E. Vladimirov
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