Multi-body Collisions Research Articles

A molecular dynamics simulation of charged particle transfer through metals: The role of multi-body collisions

Exploring the transport of high-energy charged particles through solid matter is crucial in various domains, such as radiation shielding and radiation protection. The primary focus lies in accurately quantifying energy deposition and understanding induced reactions. However, addressing this through the solution of the transfer equation poses challenges, largely stemming from the long-range Coulomb interactions that involve multiple particles concurrently. When charged particles traverse dense matter, overlooking multi-body collisions results in notably inaccurate approximations.In a prior study Molinari and Teodori (2015), we delved into a numerical simulation of the Fokker–Planck equation, incorporating contributions from multi-body collisions. This model facilitated the precise calculation of point-wise energy and momentum transferred to the target, specifically from high-energy protons. Over the years, the scope of the model has expanded to encompass the description of electron transfer as well. This extension allows for a more comprehensive understanding of the intricate dynamics involved in the interaction of high-energy charged particles with solid materials.

Plasma-Assisted Dinitrogen Activation via Dual Platinum Cluster Catalysis: A Strategy for Ammonia Synthesis under Mild Conditions

Plasma-Assisted Dinitrogen Activation via Dual Platinum Cluster Catalysis: A Strategy for Ammonia Synthesis under Mild Conditions

Dynamics of polydisperse multiple emulsions in microfluidic channels.

Multiple emulsions are a class of soft fluid in which small drops are immersed within a larger one and stabilized over long periods of time by a surfactant. We recently showed that, if a monodisperse multiple emulsion is subject to a pressure-driven flow, a wide variety of nonequilibrium steady states emerges at late times, whose dynamics relies on a complex interplay between hydrodynamic interactions and multibody collisions among internal drops. In this work, we use lattice Boltzmann simulations to study the dynamics of polydisperse double emulsions driven by a Poiseuille flow within a microfluidic channel. Our results show that their behavior is critically affected by multiple factors, such as initial position, polydispersity index, and area fraction occupied within the emulsion. While at low area fraction inner drops may exhibit either a periodic rotational motion (at low polydispersity) or arrange into nonmotile configurations (at high polydispersity) located far from each other, at larger values of area fraction they remain in tight contact and move unidirectionally. This decisively conditions their close-range dynamics, quantitatively assessed through a time-efficiency-like factor. Simulations also unveil the key role played by the capsule, whose shape changes can favor the formation of a selected number of nonequilibrium states in which both motile and nonmotile configurations are found.

Soft gravitational radiation from multi-body collisions

We derive a universal expression for the gravitational radiation energy spectrum dEGW/dω at sub-leading order emitted from a generic gravitational hard scattering of multi-particles or multi-bodies. Our result includes all mathcal{O} (ω) corrections to the gravitational radiation flux from a generic 2 → N collision, in both the cases of massless and massive particles/bodies. We also show the dependence of the radiation energy flux by the quantum spin in case of particle collisions. Then, we consider the specific case of a gravitational elastic scattering of two massive bodies, i.e. m + M → m + M with m, M the masses of the two bodies respectively. We demonstrate that in this case all mathcal{O} (ω) contributions to the energy flux exactly cancel each others. Nevertheless, we also show that, for a 2 → 2 inelastic scattering, the inclusion of sub-leading soft gravitons leads to a not zero radiation flux, having a simple expression in certain asymptotic regimes. Our results can be applied to the case of Black Hole collisions with possible testable implications in gravitational waves physics.

Simulation of interaction between shocks and particle cloud using a second-order conservative sharp interface method

In this paper we present a second-order accurate conservative sharp interface method capable of simulating displacements and collisions of many particles in compressible inviscid flows. We implement a cut cell algorithm to resolve moving particles of arbitrary shape on a Cartesian mesh, thereby generating unstructured body-fitted meshes near the particle surfaces and structured meshes away from the particles. A second-order finite volume method in the arbitrary Lagrange-Eulerian framework is used for the discretization of the Euler equations, so that exact conservation of mass, momentum and energy is enforced for the flow computations, even in the presence of moving particles. The boundary condition at the particle surfaces is enforced by solving a local Riemann problem, which is constructed in the direction normal to the solid surface. The movement of a particle is affected by the forces exerted by the surrounding fluid and its collisions with other particles. A hard sphere model is proposed to deal with the particle collisions; in particular, it is capable of handling multi-body collisions occurring in no-dilute particle clouds, regardless of the number of particles involved. Furthermore, the model ensures the conservation of momentum and energy during the collision process. The method is validated by comparing against benchmark solutions or experimental data available in the literature, for test cases such as supersonic flows past a stationary cylinder and lift-off of rigid cylinders after shock impact. Good agreement has been achieved qualitatively and quantitatively. The method is also used to investigate the complicated flow phenomena, e.g. transport of particle clouds in supersonic flows through a confined channel and the interaction between shocks and three-dimensional particles.

The vortex-driven dynamics of droplets within droplets

Understanding the fluid-structure interaction is crucial for an optimal design and manufacturing of soft mesoscale materials. Multi-core emulsions are a class of soft fluids assembled from cluster configurations of deformable oil-water double droplets (cores), often employed as building-blocks for the realisation of devices of interest in bio-technology, such as drug-delivery, tissue engineering and regenerative medicine. Here, we study the physics of multi-core emulsions flowing in microfluidic channels and report numerical evidence of a surprisingly rich variety of driven non-equilibrium states (NES), whose formation is caused by a dipolar fluid vortex triggered by the sheared structure of the flow carrier within the microchannel. The observed dynamic regimes range from long-lived NES at low core-area fraction, characterised by a planetary-like motion of the internal drops, to short-lived ones at high core-area fraction, in which a pre-chaotic motion results from multi-body collisions of inner drops, as combined with self-consistent hydrodynamic interactions. The onset of pre-chaotic behavior is marked by transitions of the cores from one vortex to another, a process that we interpret as manifestations of the system to maximize its entropy by filling voids, as they arise dynamically within the capsule.

Video analysis of one-dimensional multi-body collisions: linear momentum, impulse and energy

Collisions are a key topic in physics and engineering education. An experiment with multiple body one-dimensional collisions is presented, aiming to measure relevant physical quantities by tracking the motion of the system of particles during the collision. Relations between different physical quantities can be explored in the experiment, such as linear momentum, impulse, and energy. Equations are presented for modeling velocity changes during the collisions under the elastic and inelastic conditions and extensions to many body colliders can be easily implemented. Predictions for the velocities and other collision quantities were verified for a set of mass parameters by photogrammetry and digital video analysis.

Higher-Order Photon Correlation as a Tool To Study Exciton Dynamics in Quasi-2D Nanoplatelets.

Colloidal semiconductor nanoplatelets, in which carriers are strongly confined only along one dimension, present fundamentally different excitonic properties than quantum dots, which support strong confinement in all three dimensions. In particular, multiple excitons strongly confined in just one dimension are free to rearrange in the lateral plane, reducing the probability for multibody collisions. Thus, while simultaneous multiple photon emission is typically quenched in quantum dots, in nanoplatelets its probability can be tuned according to size and shape. Here, we focus on analyzing multiexciton dynamics in individual CdSe/CdS nanoplatelets of various sizes through the measurement of second-, third-, and fourth-order photon correlations. For the first time, we can directly probe the dynamics of the two, three, and four exciton states at the single nanocrystal level. Remarkably, although higher orders of correlation vary substantially among the synthesis’ products, they strongly correlate with the value of second order antibunching. The scaling of the higher-order moments with the degree of antibunching presents a small yet clear deviation from the accepted model of Auger recombination through binary collisions. Such a deviation suggests that many-body contributions are present already at the level of triexcitons. These findings highlight the benefit of high-order photon correlation spectroscopy as a technique to study multiexciton dynamics in colloidal semiconductor nanocrystals.

A numerical framework for the direct simulation of dense particulate flow under explosive dispersal

In this paper, we present a Cartesian grid-based numerical framework for the direct simulation of dense particulate flow under explosive dispersal. This numerical framework is established through the integration of the following numerical techniques: (1) operator splitting for partitioned fluid–solid interaction in the time domain, (2) the second-order SSP Runge–Kutta method and third-order WENO scheme for temporal and spatial discretization of governing equations, (3) the front-tracking method for evolving phase interfaces, (4) a field function proposed for low-memory-cost multimaterial mesh generation and fast collision detection, (5) an immersed boundary method developed for treating arbitrarily irregular and changing boundaries, and (6) a deterministic multibody contact and collision model. Employing the developed framework, this paper further studies particle jet formation under explosive dispersal by considering the effects of particle properties, particulate payload morphologies, and burster pressures. By the simulation of the dispersal processes of dense particle systems driven by pressurized gas, in which the driver pressure reaches $$1.01325\times 10^{10}\,\,\mathrm {Pa}$$ ( $$10^5$$ times the ambient pressure) and particles are impulsively accelerated from stationary to a speed that is more than $$12000\,\,\mathrm {m/s}$$ within $$15\,\,\mathrm {\upmu s}$$ , it is demonstrated that the presented framework is able to effectively resolve coupled shock–shock, shock–particle, and particle–particle interactions in complex fluid–solid systems with shocked flow conditions, arbitrarily irregular particle shapes, and realistic multibody collisions.

Multibody collision contribution to the slowing down of charged particles through metals

Investigating charged particle transport through solid matter is important in those fields, such as particle induced x‐ray emission analysis, where quantifying and identifying the reactions produced in the medium are of fundamental interest. A rigorous approach by solving the transfer equation means to face many difficulties most of which arise from the long range nature of the Coulomb interactions, involving more than one particle simultaneously. The common practice of neglecting the multibody collisions, though correct for rarefied neutral gases, often leads to very poor approximations, when charged particles move through dense matter. Here, we discuss a numerical simulation of the Fokker–Planck equation where the multibody collisions are taken into account. The model allows to calculate point‐wise the distribution of energy and momentum transferred to the target. Copyright © 2015 John Wiley & Sons, Ltd.

Discontinuous variational time integrators for complex multibody collisions

SUMMARYThe objective of the present work is to formulate a new class of discontinuous variational time integrators that allow the system to adopt two possibly different configurations at each sampling time tk, representing predictor and corrector configurations of the system. The resulting sequence of configuration pairs then represents a discontinuous—or non‐classical—trajectory. Continuous or classical trajectories are recovered simply by enforcing a continuity constraint at all times. In particular, in systems subject to one‐sided contact constraints simulated via discontinuous variational time integrators, the predictor configuration is not required to satisfy the one‐sided constraints, whereas the corrector configuration is obtained by a closest‐point projection (CPP) onto the admissible set. The resulting trajectories are generally discontinuous, or non‐classical, but are expected to converge to classical or continuous solutions for decreasing time steps. We account for dissipation, including friction, by means of a discrete Lagrange–d'Alembert principle, and make extensive use of the spacetime formalism in order to ensure exact energy conservation in conservative systems, and the right rate of energy decay in dissipative systems. The structure, range and scope of the discontinuous variational time integrators, and their accuracy characteristics are illustrated by means of examples of application concerned with rigid multibody dynamics. Copyright © 2014 John Wiley & Sons, Ltd.

GPU-accelerated Classical Trajectory Calculation Direct Simulation Monte Carlo applied to shock waves

In this work we outline a Classical Trajectory Calculation Direct Simulation Monte Carlo (CTC-DSMC) implementation that uses the no-time-counter scheme with a cross-section determined by the interatomic potential energy surface (PES). CTC-DSMC solutions for translational and rotational relaxation in one-dimensional shock waves are compared directly to pure Molecular Dynamics simulations employing an identical PES, where exact agreement is demonstrated for all cases. For the flows considered, long-lived collisions occur within the simulations and their implications for multi-body collisions as well as algorithm implications for the CTC-DSMC method are discussed. A parallelization technique for CTC-DSMC simulations using a heterogeneous multicore CPU/GPU system is demonstrated. Our approach shows good scaling as long as a sufficiently large number of collisions are calculated simultaneously per GPU (∼100,000) at each DSMC iteration. We achieve a maximum speedup of 140× on a 4 GPU/CPU system vs. the performance on one CPU core in serial for a diatomic nitrogen shock. The parallelization approach presented here significantly reduces the cost of CTC-DSMC simulations and has the potential to scale to large CPU/GPU clusters, which could enable future application to 3D flows in strong thermochemical nonequilibrium.

Three-dimensional numerical simulation method for gas–solid injector

A three-dimensional turbulent gas–solid two-phase flow model for a gas–solid injector is developed in the present study. Time-averaged conservation equation for mass and momentum and a two-equation k– ɛ closure are used to model the carried fluid phase. The solid phase is simulated by using a Lagrangian approach. In this model, the drag and lift forces on particles, the multi-body collisions among particles and the mutual interaction between gas and particles were taken into account. Interparticle interactions and particle–wall collisions are emulated by using the three-dimensional distinct element method (DEM). A new correlation, β ( δ ⁡ v p ⁢ δ ⁡ v p ― − δ ⁡ u ⁢ δ ⁡ v p ― ) = − 2 ⁢ β ⁢ K ( 1 − τ L τ L + τ d ) τ L τ L + τ d , which represents the transfer of kinetic energy of the particle motion to kinetic energy of the carrier fluid, is introduced in the additional source term S d ɛ of the transport equation of turbulence kinetic energy, K. The calculated pressure distributions along the axis in the different parts of gas–solid injectors using pressured pneumatic conveying system under different driving jet velocities, pressures and values of angle of convergent section ( α) are found to be in agreement with the experimental results. The axial mean velocity of particles and the behavior of gas and particles in the gas–solid injector are calculated, their results reasonably explaining actual phenomenon observed in experiment.

Study of the slowing down of high energy proton shots through metals via a Monte Carlo simulation of the Fokker-Planck equation

The aim of this work is to analyze the diffusion and the slowing down of high energy proton shots through a target. Analyzing the phenomenon rigorously with the full transport equations, means tack ling many difficulties, most of which arise from the long range nature of the Coulomb interactions involving more than one particle simultaneously. The commonly used approach of neglecting the multi-body collisions, though correct for rarefied neutral gases, of ten leads to very poor approximations when charged particles moving through dense matter are considered. Here we present a Monte Carlo simulation of the Fokker-Planck equation where the multi-body collisions are taken into account. The model al lows the calculation of a point-wise distribution of energy and momentum transferred to the tar get.

Numerical simulation of air and particle motions in bubbling fluidized bed of small particles

Air and particle motions in a bubbling fluidized bed of about 100,000 particles of 310 μm in diameter, which are classified as the B particles in the Geldart map, are numerically simulated. Particle–particle interactions were calculated, using the three-dimensional distinct element method (DEM). The Navier–Stokes equation and the Lagrangian type particle equation were simultaneously solved, where the drag and lift forces on particles, the multi-body collisions among particles and the mutual interaction between air and particles were taken into account. The corresponding experiments were also performed. It was found that the calculated results describe well the experimental instantaneous particle positions, and enable us to know the mechanisms of bubble formation, bubble coalescence and bubble disruption in a bubbling fluidized bed.

Dense, strongly interacting matter: strangeness in heavy-ion reactions 1-10 A GeV

This talk reviews the physics of dense, strongly interacting matter. The newly acquired experimental data on strangeness production in heavy-ion reactions from 1-10 A GeV is used to probe the physics of in-medium properties of matter, multi-body collisions, and the search for the baryon-rich quark-gluon plasma.

Kaon production and multi-body collisions in dense nuclear matter

The spectra and yields of K + and K − production in Au+Au reactions at 11.6 A GeV are compared to the predictions of a hadronic transport model, RQMD. This not only provides a quantitative test for the model but also explores the possibility of multi-body hadronic collisions within dense matter. At nuclear densities three to four times normal matter density the estimated mean-free path is smaller than the size of a typical hadron. Each hadron is likely to suffer multiple collisions within the duration of any one collision. The effects of these multi-body collisions in heavy-ion reactions are discussed, in particular the possibility that multi-body collisions may increase the absorption of particles, e.g. K −.