Search results for "Classical Mechanics"

Kinematic analysis — the sense of shear-sense. Discussion of: ‘Essay Review: Kinematic analysis — pure nonsense or simple nonsense’ by D. Flinn

1995

Statistical mechanics of fullerene coalescence growth

2006

Among the different carbon allotropes fullerenes are exceptionally intriguing for their spheroidal topology out of pentagons and hexagons. However, the dominant formation mode is still ambiguous. Here, we analyze the fullerene formation process by the statistical analysis of fullerene sizes produced in a laser-induced microplasma finding that a simple two-parameter lognormal distribution describes impressively well the cluster frequencies under various conditions. Our findings clearly reveal coalescent growth following a classical collision dynamics and disagree with several earlier assumptions.

A numerical study of attraction/repulsion collective behavior models: 3D particle analyses and 1D kinetic simulations

2013

39p; International audience; We study at particle and kinetic level a collective behavior model based on three phenomena: self-propulsion, friction (Rayleigh effect) and an attractive/repulsive (Morse) potential rescaled so that the total mass of the system remains constant independently of the number of particles N . In the first part of the paper, we introduce the particle model: the agents are numbered and described by their position and velocity. We iden- tify five parameters that govern the possible asymptotic states for this system (clumps, spheres, dispersion, mills, rigid-body rotation, flocks) and perform a numerical analysis on the 3D setting. Then, in the second part of the paper…

Flow properties and hydrodynamic interactions of rigid spherical microswimmers.

2017

We analyze a minimal model for a rigid spherical microswimmer and explore the consequences of its extended surface on the interplay between its self-propulsion and flow properties. The model is the first order representation of microswimmers, such as bacteria and algae, with rigid bodies and flexible propelling appendages. The flow field of such a microswimmer at finite distances significantly differs from that of a point-force (Stokeslet) dipole. For a suspension of microswimmers, we derive the grand mobility matrix that connects the motion of an individual swimmer to the active and passive forces and torques acting on all the swimmers. Our investigation of the mobility tensors reveals tha…

Collision Theory for Two- and Three-Particle Systems Interacting via Short-Range and Coulomb Forces

1996

In two- and three-particle reactions with light nuclei, a rich body of precise experimental data exists in which both projectile and target and/or the fragments occurring in the final state are charged. In order to make optimal use of these data for extracting physically interesting information about the nuclear interactions, the effects of the Coulomb force must be separated out in a reliable manner. For this purpose the mastering of the intricacies of charged-particle scattering theory is of vital importance.

Types of Motion in the Oblate Planet Problem

1985

We consider a mass point in the gravitational field of an oblate planet and in a meridianal plane. The Hamiltonian of the problem is: $$ \frac{1}{2}\left( {p_r^2 + \frac{{p_{\theta }^2}}{{{r^2}}}} \right) - \frac{1}{r} - \frac{\varepsilon }{{{r^3}}}\left( {1 - 3{{\sin }^2}\theta } \right) $$ .

About Compactness of Faddeev Integral Equations for Three Charged Particles

1999

Momentum space three-body integral equations of the Faddeev type can not be used for Coulomb-like potentials, for energies above the breakup threshold. The reason is the occurrence of singularities in their kernels which destroy the compactness properties known to exist for purely short-range interactions. Using the rigorously equivalent formulation in terms of an effective-two- body theory, we prove that the nondiagonal kernels occurring therein possess on and off the energy shell only integrable singularities, provided all three particles have charges of the same sign (ie., only repulsive Coulomb interactions). In contrast, if some of the charges have opposite signs the nondiagonal kernel…

Fermion sign problem in imaginary-time projection continuum quantum Monte Carlo with local interaction

2016

We use the Shadow Wave Function formalism as a convenient model to study the fermion sign problem affecting all projector Quantum Monte Carlo methods in continuum space. We demonstrate that the efficiency of imaginary time projection algorithms decays exponentially with increasing number of particles and/or imaginary-time propagation. Moreover, we derive an analytical expression that connects the localization of the system with the magnitude of the sign problem, illustrating this prediction through some numerical results. Finally, we discuss the fermion sign problem computational complexity and methods for alleviating its severity.

Efficient parallel computations of flows of arbitrary fluids for all regimes of Reynolds, Mach and Grashof numbers

2002

This paper presents a unified numerical method able to address a wide class of fluid flow problems of engineering interest. Arbitrary fluids are treated specifying totally arbitrary equations of state, either in analytical form or through look‐up tables. The most general system of the unsteady Navier–Stokes equations is integrated with a coupled implicit preconditioned method. The method can stand infinite CFL number and shows the efficiency of a quasi‐Newton method independent of the multi‐block partitioning on parallel machines. Computed test cases ranging from inviscid hydrodynamics, to natural convection loops of liquid metals, and to supersonic gasdynamics, show a solution efficiency i…

A Meshfree Solver for the MEG Forward Problem

2015

Noninvasive estimation of brain activity via magnetoencephalography (MEG) involves an inverse problem whose solution requires an accurate and fast forward solver. To this end, we propose the Method of Fundamental Solutions (MFS) as a meshfree alternative to the Boundary Element Method (BEM). The solution of the MEG forward problem is obtained, via the Method of Particular Solutions (MPS), by numerically solving a boundary value problem for the electric scalar potential, derived from the quasi-stationary approximation of Maxwell’s equations. The magnetic field is then computed by the Biot-Savart law. Numerical experiments have been carried out in a realistic single-shell head geometry. The p…