Showing papers on "Equations of motion published in 2003"
Book•
29 Oct 2003TL;DR: In this paper, the authors present a general framework for nonlinear Equations of Mathematical Physics using a general form of the form wxy=F(x,y,w, w, wx, wy) wxy.
Abstract: SOME NOTATIONS AND REMARKS PARABOLIC EQUATIONS WITH ONE SPACE VARIABLE Equations with Power-Law Nonlinearities Equations with Exponential Nonlinearities Equations with Hyperbolic Nonlinearities Equations with Logarithmic Nonlinearities Equations with Trigonometric Nonlinearities Equations Involving Arbitrary Functions Nonlinear Schrodinger Equations and Related Equations PARABOLIC EQUATIONS WITH TWO OR MORE SPACE VARIABLES Equations with Two Space Variables Involving Power-Law Nonlinearities Equations with Two Space Variables Involving Exponential Nonlinearities Other Equations with Two Space Variables Involving Arbitrary Parameters Equations Involving Arbitrary Functions Equations with Three or More Space Variables Nonlinear Schrodinger Equations HYPERBOLIC EQUATIONS WITH ONE SPACE VARIABLE Equations with Power-Law Nonlinearities Equations with Exponential Nonlinearities Other Equations Involving Arbitrary Parameters Equations Involving Arbitrary Functions Equations of the Form wxy=F(x,y,w, wx, wy ) HYPERBOLIC EQUATIONS WITH TWO OR THREE SPACE VARIABLES Equations with Two Space Variables Involving Power-Law Nonlinearities Equations with Two Space Variables Involving Exponential Nonlinearities Nonlinear Telegraph Equations with Two Space Variables Equations with Two Space Variables Involving Arbitrary Functions Equations with Three Space Variables Involving Arbitrary Parameters Equations with Three Space Variables Involving Arbitrary Functions ELLIPTIC EQUATIONS WITH TWO SPACE VARIABLES Equations with Power-Law Nonlinearities Equations with Exponential Nonlinearities Equations Involving Other Nonlinearities Equations Involving Arbitrary Functions ELLIPTIC EQUATIONS WITH THREE OR MORE SPACE VARIABLES Equations with Three Space Variables Involving Power-Law Nonlinearities Equations with Three Space Variables Involving Exponential Nonlinearities Three-Dimensional Equations Involving Arbitrary Functions Equations with n Independent Variables EQUATIONS INVOLVING MIXED DERIVATIVES AND SOME OTHER EQUATIONS Equations Linear in the Mixed Derivative Equations Quadratic in the Highest Derivatives Bellman Type Equations and Related Equations SECOND-ORDER EQUATIONS OF GENERAL FORM Equations Involving the First Derivative in t Equations Involving Two or More Second Derivatives THIRD-ORDER EQUATIONS Equations Involving the First Derivative in t Equations Involving the Second Derivative in t Hydrodynamic Boundary Layer Equations Equations of Motion of Ideal Fluid (Euler Equations) Other Third-Order Nonlinear Equations FOURTH-ORDER EQUATIONS Equations Involving the First Derivative in t Equations Involving the Second Derivative in t Equations Involving Mixed Derivatives EQUATIONS OF HIGHER ORDERS Equations Involving the First Derivative in t and Linear in the Highest Derivative General Form Equations Involving the First Derivative in t Equations Involving the Second Derivative in t Other Equations SUPPLEMENTS: EXACT METHODS FOR SOLVING NONLINEAR PARTIAL DIFFERENTIAL EQUATIONS Classification of Second-Order Semilinear Partial Differential Equations in Two Independent Variables Transformations of Equations of Mathematical Physics Traveling-Wave Solutions and Self-Similar Solutions. Similarity Methods Method of Generalized Separation of Variables Method of Functional Separation of Variables Generalized Similarity Reductions of Nonlinear Equations Group Analysis Methods Differential Constraints Method Painleve Test for Nonlinear Equations of Mathematical Physics Inverse Scattering Method Conservation Laws Hyperbolic Systems of Quasilinear Equations REFERENCES INDEX
809 citations
TL;DR: D dissipative particle dynamics is discussed as a thermostat to molecular dynamics, and some of its virtues are highlighted, including universal applicability irrespective of the interatomic potential.
Abstract: We discuss dissipative particle dynamics as a thermostat to molecular dynamics, and highlight some of its virtues: (i) universal applicability irrespective of the interatomic potential; (ii) correct and unscreened reproduction of hydrodynamic correlations; (iii) stabilization of the numerical integration of the equations of motion; and (iv) the avoidance of a profile bias in boundary-driven nonequilibrium simulations of shear flow. Numerical results on a repulsive Lennard-Jones fluid illustrate our arguments.
406 citations
TL;DR: In this article, the propagation of finite-amplitude waves in a homogeneous, isotropic, stress-free elastic plate is investigated theoretically, and perturbation is used to obtain solutions of the non-linear equations of motion for harmonic generation in the waveguide.
330 citations
TL;DR: In this article, the authors developed a theory for fast flows of entangled polymer melts which includes the processes of reptation, convective and reptation-driven constraint release, chain stretch and contour length fluctuations.
Abstract: Recently we developed a theory for fast flows of entangled polymer melts which includes the processes of reptation, convective and reptation-driven constraint release, chain stretch and contour length fluctuations The theory is derived from a stochastic microscopic equation of motion of the chain inside the tube and of the tube itself As a result we obtain a partial differential equation for the tube tangent correlation function, the solution of which requires quite intensive calculations At the same time the application of this theory to realistic flows (which is anything other than the laboratory rheometer) requires a simple and less computationally intensive set of equations for the stress tensor similar to the Giesekus, PTT, Larson or Pom–Pom equations In particular, the last was derived from molecular theory for a generic type of branched polymer In this paper we demonstrate that molecular tube theory can also provide a route to constructing a family of very simple differential constitutive equations for linear polymers They capture the full model quite well and therefore can be used in flow solving software to model spatially inhomogeneous flows We present a comparison of the proposed equations with our full model and with experimental data
314 citations
TL;DR: In this paper, a method for determining the nonlinear modal stiffness coefficients for an arbitrary finite element model is presented, which is suitable for use with commercial finite element codes having a geometrically nonlinear static capability.
279 citations
TL;DR: In this article, the basic theory of internal solitary waves is developed, with the main emphasis on environmental situations, such as the many occurrences of such waves in shallow coastal seas and in the atmospheric boundary layer.
Abstract: The basic theory of internal solitary waves is developed, with the main emphasis on environmental situations, such as the many occurrences of such waves in shallow coastal seas and in the atmospheric boundary layer. Commencing with the equations of motion for an inviscid, incompressible density-stratified fluid, we describe asymptotic reductions to model long-wave equations, such as the well-known Korteweg-de Vries equation. We then describe various solitary wave solutions, and propose a variable-coefficient extended Korteweg-de Vries equations as an appropriate evolution equation to describe internal solitary waves in environmental situations, when the effects of a variable background and dissipation need to be taken into account.
210 citations
TL;DR: In this paper, a four-stroke heat engine model with a coupled two-level system as a working fluid is used to explore the fundamental relations between the quantum framework and thermodynamical observables.
Abstract: The fundamentals of a quantum heat engine are derived from first principles. The study is based on the equation of motion of a minimum set of operators, which is then used to define the state of the system. The relation between the quantum framework and the thermodynamical observables is examined. A four-stroke heat engine model with a coupled two-level system as a working fluid is used to explore the fundamental relations. In the model used, the internal Hamiltonian does not commute with the external control field, which defines the two adiabatic branches. Heat is transferred to the working fluid by coupling to hot and cold reservoirs under constant field values. Explicit quantum equations of motion for the relevant observables are derived on all branches. The dynamics on the heat transfer constant field branches is solved in closed form. On the adiabats, a general numerical solution is used and compared with a particular analytic solution. These solutions are combined to construct the cycle of operation. The engine is then analyzed in terms of the frequency-entropy and entropy-temperature graphs. The irreversible nature of the engine is the result of finite heat transfer rates and frictionlike behavior due to noncommutability of the internal and external Hamiltonians.
188 citations
TL;DR: In this article, the elastic strain energy of simply supported circular cylindrical shells was derived by an energy approach, retaining damping through Rayleigh's dissipation function, using four different non-linear thin shell theories, namely, Donnell's, Sanders-Koiter, Flugge-Lur-e-Byrne and Novozhilov's theories.
173 citations
TL;DR: In this paper, the authors derived equations of motion for the tachyon field living on an unstable non-BPS D-brane in the level truncated open cubic superstring field theory.
Abstract: We derive equations of motion for the tachyon field living on an unstable non-BPS D-brane in the level truncated open cubic superstring field theory in the first non-trivial approximation. We construct a special time dependent solution to this equation which describes a rolling tachyon. It starts from the perturbative vacuum and approaches one of stable vacua in infinite time. We investigate conserved energy functional and show that its different parts dominate in different stages of the evolution. We show that the pressure for this solution has its minimum at zero time and goes to minus energy at infinite time.
169 citations
TL;DR: For the initial value problem for vortex sheets with surface tension with sufficiently smooth data, it is proved that solutions exist locally in time, are unique, and depend continuously on the initial data.
Abstract: We study the initial value problem for two-dimensional, periodic vortex sheets with surface tension. We allow the upper and lower fluids to have different densities. Without surface tension, the vortex sheet is ill-posed: it exhibits the well-known Kelvin--Helmholtz instability. In the linearized equations of motion, surface tension removes the instability. It has been conjectured that surface tension also makes the full problem well-posed. We prove that this conjecture is correct using energy methods. In particular, for the initial value problem for vortex sheets with surface tension with sufficiently smooth data, it is proved that solutions exist locally in time, are unique, and depend continuously on the initial data. The analysis uses two important ideas from the numerical work of Hou, Lowengrub, and Shelley. First, the tangent angle and arclength of the vortex sheet are used rather than Cartesian variables. Second, instead of a purely Lagrangian formulation, a special tangential velocity is used in o...
152 citations
TL;DR: In this article, the authors show explicitly how the Newton?Hooke groups N?10 act as symmetries of the equations of motion of non-relativistic cosmological models with a Cosmological constant.
Abstract: We show explicitly how the Newton?Hooke groups N?10 act as symmetries of the equations of motion of non-relativistic cosmological models with a cosmological constant. We give the action on the associated non-relativistic spacetimes M?4 and show how these may be obtained from a null reduction of five-dimensional homogeneous pp-wave Lorentzian spacetimes M?5. This allows us to realize the Newton?Hooke groups and their Bargmann-type central extensions as subgroups of the isometry groups of M?5. The extended Schr?dinger-type conformal group is identified and its action on the equations of motion given. The non-relativistic conformal symmetries also have applications to time-dependent harmonic oscillators. Finally we comment on a possible application to Gao's generalization of the matrix model.
TL;DR: In this paper, the covariant nonlocal action for long-distance modifications of gravity theory motivated by the cosmological constant and cosmologically acceleration problems is constructed. But it is not shown that the nonlocal nature of the Euclidean action does not contradict the causality of effective equations of motion, and it is emphasized that for certain class of quantum initial value problems nonlocal form factors in the action of both quantum and brane-induced nature are briefly discussed.
TL;DR: In this paper, the authors derived equations of motion for the tachyon field living on an unstable non-BPS D-brane in the level truncated open cubic superstring field theory.
Abstract: We derive equations of motion for the tachyon field living on an unstable non-BPS D-brane in the level truncated open cubic superstring field theory in the first non-trivial approximation. We construct a special time dependent solution to this equation which describes the rolling tachyon. It starts from the perturbative vacuum and approaches one of stable vacua in infinite time. We investigate conserved energy functional and show that its different parts dominate in different stages of the evolution. We show that the pressure for this solution has its minimum at zero time and goes to minus energy at infinite time.
TL;DR: It is shown how to find first-order differential equations that solve the equations of motion, and how to solve models in D dimensions via soluble problems in D=1.
Abstract: We investigate the presence of defects in systems described by real scalar field in (D,1) spacetime dimensions. We show that when the potential assumes specific form, there are models which support stable global defects for D arbitrary. We also show how to find first-order differential equations that solve the equations of motion, and how to solve models in D dimensions via soluble problems in D=1. We illustrate the procedure examining specific models and finding explicit solutions.
TL;DR: In this paper, the large-amplitude response of perfect and imperfect, simply supported circular cylindrical shells to harmonic excitation in the spectral neighbourhood of some of the lowest natural frequencies is investigated.
TL;DR: In this article, the mass-on-moving-belt model for describing friction-induced vibrations is considered, with a friction law describing friction forces that first decreases and then increases smoothly with relative interface speed.
Abstract: The classical “mass-on-moving-belt” model for describing friction-induced vibrations is considered, with a friction law describing friction forces that first decreases and then increases smoothly with relative interface speed. Approximate analytical expressions are derived for the conditions, the amplitudes, and the base frequencies of friction-induced stick–slip and pure-slip oscillations. For stick–slip oscillations, this is accomplished by using perturbation analysis for the finite time interval of the stick phase, which is linked to the subsequent slip phase through conditions of continuity and periodicity. The results are illustrated and tested by time-series, phase plots and amplitude response diagrams, which compare very favorably with results obtained by numerical simulation of the equation of motion, as long as the difference in static and kinetic friction is not too large.
TL;DR: The dynamics of Bose-Einstein condensates trapped in a deep optical lattice is governed by a discrete nonlinear equation (DNL) and its degree of nonlinearity and the intersite hopping rates are retrieved from a nonlinear tight-binding approximation taking into account the effective dimensionality of each condensate.
Abstract: The dynamics of Bose-Einstein condensates trapped in a deep optical lattice is governed by a discrete nonlinear equation (DNL). Its degree of nonlinearity and the intersite hopping rates are retrieved from a nonlinear tight-binding approximation taking into account the effective dimensionality of each condensate. We derive analytically the Bloch and the Bogoliubov excitation spectra and the velocity of sound waves emitted by a traveling condensate. Within a Lagrangian formalism, we obtain Newtonian-like equations of motion of localized wave packets. We calculate the ground-state atomic distribution in the presence of a harmonic confining potential, the frequencies of small amplitude dipole, and quadrupole oscillations. We finally quantize the DNL, recovering an extended Bose-Hubbard model.
TL;DR: In this article, an explicit solution for the linearized motion of a chaser in a close neighborhood of a target in an elliptic orbit is given, which is a direct generalization of the Clohessy-Wiltshire equations that are widely used for circular orbits.
Abstract: An explicit solution is given for the linearized motion of a chaser in a close neighborhood of a target in an elliptic orbit. The solution is a direct generalization of the Clohessy-Wiltshire equations that are widely used for circular orbits. In other words, when the eccentricity is set equal to zero in the new formulas, the well-known Clohessy-Wiltshire formulas are obtained. The solution is completely explicit in the time. As a starting point, a closed-form solution is found of the de Vries equations of 1963. These are the linearized equations of elliptic motion in a rotating coordinate system, rotating with a variable angular velocity. This solution is shown to be obtained simply by taking the partial derivatives, with respect to the orbit elements, of the two-body solution in polar coordinates. When four classical elements are used, four linearly independent solutions of the de Vries equations are obtained. However, the classical orbit elements turn out to be singular for circular orbits. The singularity is removed by taking appropriate linear combinations of the four solutions. This gives a 4 by 4 fundamental solution matrix R that is nonsingular and reduces to the Clohessy-Wiltshire solution matrix when the eccentricity is set equal to zero.
TL;DR: In this paper, the dynamic Lagrangian mixed frequency-time method (DLFT) is proposed to calculate the non-linear steady state response to periodic excitation of structural systems subject to dry friction damping.
TL;DR: In this paper, the authors used the Rayleigh-Ritz procedure to formulate a discrete model with quadratic and cubic non-linear terms to describe the modal interactions between lateral oscillations of the catenary cable and longitudinal oscillation of the vertical rope.
TL;DR: In this paper, a non-viscous damping model is proposed for linear non-linear systems with instantaneous generalized velocities, which is the most common model for vibration damping in linear systems.
Abstract: Multiple-degree-of-freedom linear nonviscously damped systems are considered. It is assumed that the nonviscousdampingforcesdependonthepasthistoryofvelocitiesviaconvolutionintegralsoverexponentiallydecaying kernel functions. The traditional state-space approach, well known for viscously damped systems, is extended to such nonviscously damped systems using a set of internal variables. Suitable numerical examples are provided to illustrate the proposed approach. I. Introduction V ISCOUSdampingisthemostcommonmodelforthemodeling of vibration damping in linear systems. This model, e rst introduced by Rayleigh, 1 assumes that the instantaneous generalized velocities are the only relevant variables that determine damping. Viscous damping models are used widely for their simplicity and mathematical convenience, even though the behavior of real structural materials is, at best, poorly mimicked by simple viscous models.Forthisreason,itiswellrecognizedthat,ingeneral,aphysically realistic model of damping will not be viscous. Damping models in whichthedissipativeforcesdependonanyquantityotherthantheinstantaneous generalized velocities are nonviscous damping models. Mathematically, any causal model that makes the energy dissipation functional nonnegative is a possible candidate for a nonviscous damping model. Clearly, a wide range of choice is possible, either based on the physics of the problem or by selecting a model a priori and e tting its parameters from experiments. Here, we will use a particular type of damping model that is not viscous, and throughout the paper the terminology nonviscous damping will refer to this specie c model only. Possiblythemostgeneralwaytomodeldampingwithinthelinear range is to use nonviscous damping models that depend on the past history of motion via convolution integrals over kernel functions. 2 The equations of motion of an N-degree-of-freedom linear system with such damping can be expressed by
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TL;DR: In this article, sound propagation on M5 and M2-branes in the hydrodynamic limit was studied. But the authors focused on the low energy description of a stack of N M-brane at finite temperature.
Abstract: We consider sound propagation on M5- and M2-branes in the hydrodynamic limit. In particular, we look at the low energy description of a stack of N M-branes at finite temperature. At low energy, the M-branes are well described, via the AdS/CFT correspondence, in terms of classical solutions to the eleven dimensional supergravity equations of motion. From this gravitational description, we calculate Lorentzian signature two-point functions of the stress-energy tensor on these M-branes in the long-distance, low-frequency limit, i.e. the hydrodynamic limit. The poles in these Green's functions show evidence for sound propagation in the field theory living on the M-branes.
TL;DR: In this article, a post-Newtonian 3PN! equation of motion for an inspiraling binary consisting of two spherical compact stars with strong internal gravity is derived under the harmonic coordinate condition using the strong field point particle limit.
Abstract: A third post-Newtonian ~3PN! equation of motion for an inspiraling binary consisting of two spherical compact stars with strong internal gravity is derived under the harmonic coordinate condition using the strong field point particle limit. The equation of motion is complete in the sense that it is Lorentz invariant in the post-Newtonian perturbative sense, admits the conserved energy of the orbital motion, and is unambiguous, that is, with no undetermined coefficient. In this paper, we show explicit expressions of the 3PN equation of motion and an energy of the binary orbital motion in the case of a circular orbit ~neglecting the 2.5PN radiation reaction effect! and in the center of mass frame. It is argued that the 3PN equation of motion we obtained is physically unambiguous. Full details will be reported elsewhere.
TL;DR: In this paper, the authors present two new numerical algorithms for updating the equations of motion for a viscoelastic fluid that can be described by the finite extensible nonlinear elastic polymer model with the closure proposed by Peterlin (so called FENE-P model) in a transient calculation.
TL;DR: In this article, the 3PN-accurate expressions of the centre-of-mass positions and equations of the relative binary motion are derived from a Lagrangian, from which the conserved centre-ofthe-mass energy and angular momentum at 3PN order can be deduced.
Abstract: The equations of motion of compact binary systems and their associated Lagrangian formulation have been derived in previous works at the third post-Newtonian (3PN) approximation of general relativity in harmonic coordinates. In the present work, we investigate the binary's relative dynamics in the centre-of-mass frame (centre of mass located at the origin of the coordinates). We obtain the 3PN-accurate expressions of the centre-of-mass positions and equations of the relative binary motion. We show that the equations derive from a Lagrangian (neglecting the radiation reaction), from which we deduce the conserved centre-of-mass energy and angular momentum at the 3PN order. The harmonic-coordinates centre-of-mass Lagrangian is equivalent, via a contact transformation of the particles' variables, to the centre-of-mass Hamiltonian in ADM coordinates that is known from the post-Newtonian ADM-Hamiltonian formalism. As an application we investigate the dynamical stability of circular binary orbits at the 3PN order.
TL;DR: A nonlinear modal analysis approach based on the invariant manifold method proposed earlier by Boivin et al. as discussed by the authors is applied in this paperto perform the dynamic analysis of a micro switch, which is modeled as a clamped-clamped microbeam subjected to a transverseelectrostatic force.
Abstract: A nonlinear modal analysis approach based on the invariant manifoldmethod proposed earlier by Boivin et al. [10] is applied in this paperto perform the dynamic analysis of a micro switch. The micro switch ismodeled as a clamped-clamped microbeam subjected to a transverseelectrostatic force. Two kinds of nonlinearities are encountered in thenonlinear system: geometric nonlinearity of the microbeam associatedwith large deflection, and nonlinear coupling between two energydomains. Using Galerkin method, the nonlinear partial differentialgoverning equation is decoupled into a set of nonlinear ordinarydifferential equations. Based on the invariant manifold method, theassociated nonlinear modal shapes, and modal motion governing equationsare obtained. The equation of motion restricted to these manifolds,which provide the dynamics of the associated normal modes, are solved bythe approach of nonlinear normal forms. Nonlinearities and the pull-inphenomena are examined. The numerical results are compared with thoseobtained from the finite difference method. The estimate for the pull-involtage of the micro device is also presented.
TL;DR: The Constructive Methods of Invariant Manifolds for model reduction in physical and chemical kinetics, developed during last two decades, were studied as a problem of constructing the slow invariant manifold as mentioned in this paper.
Abstract: We present the Constructive Methods of Invariant Manifolds for model reduction in physical and chemical kinetics, developed during last two decades. The problem of reduced description is studied as a problem of constructing the slow invariant manifold. The invariance conditions are formulated as the differential equation for a manifold immersed in the phase space (the invariance equation). The equation of motion for immersed manifolds is obtained (the film extension of the dynamics). Invariant manifolds are fixed points for this equation, and slow invariant manifolds are Lyapunov stable fixed points, thus slowness is presented as stability. A collection of methods for construction of slow invariant manifolds is presented, in particular the analogue of KAM methods for dissipative systems. We systematically consider a discrete analogue of the slow (stable) positively invariant manifolds for dissipative systems, invariant grids. The following examples of applications are presented: Nonperturbative deviation of physically consistent hydrodynamics from the Boltzmann equation and from the reversible dynamics, for Knudsen numbers ~ 1; construction of the moment equations for nonequilibrium media and their dynamical correction (instead of extension of list of variables) to gain more accuracy in description of highly nonequilibrium flows; invariant grids for chemical reactions; universal continuous media description of dilute polymeric solution, etc.
Book•
01 Dec 2003
TL;DR: In this paper, the authors present a theoretical treatment of the forces and moments that act on marine craft in calm water and in waves. And they provide the tools necessary for the prediction or simulation of craft motions.
Abstract: This book presents a theoretical treatment, as well as a summary of practical methods of computation, of the forces and moments that act on marine craft. Its aim is to provide the tools necessary for the prediction or simulation of craft motions in calm water and in waves. In addition to developing the required equations, the author gives relations that permit at least approximate evaluation of the coefficients so that useful results can be obtained. The approach begins with the equations of motion for rigid bodies, relative to fixed- and moving-coordinate systems: then, the hydrodynamic forces are examined, starting with hydrostatics and progressing to the forces on a moving vehicle in calm water and (after a review of water-wave theory) in waves. Several detailed examples are presented, including calculations of hydrostatics, horizontal- and vertical-plane directional stability, and wave-induced motions. Also included are unique discussions on various effects, such as fin-hull interactions, numerical stability of integrators, heavy torpedoes, and the dynamics of high-speed craft. The book is intended to be an introductory level graduate text and a reference for the practicing professional.
TL;DR: In this article, the dissipative dynamics of a Morse oscillator coupled nonlinearly to a heat bath is investigated, and the propagations are done with a general purpose implementation of the multiconfiguration time-dependent Hartree method.
Abstract: We investigate the dissipative dynamics of a Morse oscillator coupled nonlinearly to a heat bath. To this end, we compare several reduced equations of motion with the dynamics of a full-dimensional wave packet with up to 61 spatial degrees of freedom. The discretized bath is converged for the relevant times considered in this paper. The propagations are done with a general purpose implementation of the multiconfiguration time-dependent Hartree method.
TL;DR: The dynamics of a relativistic, hot charged fluid is expressed in terms of a hybrid magnetofluid field which unifies the electromagnetic field with an appropriately defined but analogous flow field, and the changes brought about by the plasma temperature are highlighted.
Abstract: The dynamics of a relativistic, hot charged fluid is expressed in terms of a hybrid magnetofluid field which unifies the electromagnetic field with an appropriately defined but analogous flow field. The unification is affected by a well-defined prescription that allows the derivation of the equations of motion of a plasma embedded in an electromagnetic field from the field-free equations. The relationship of this prescription with the minimal coupling prescription of particle dynamics is discussed; the changes brought about by the plasma temperature are highlighted. A few consequences of the unification are worked out.