Temperature and density measurements in a recombining argon plasma with diluent

Spectroscopic and callorimetric measurements of temperature arid number density have been made using a 50-kW radio-frequency inductively coupled plasma (RFICP) torch operated at atmospheric pressure with maximum temperatures and electron densities near 8,1000 K and 2 x 10²¹ m³, respectively These measurements enabled the determination o/ the stale o/ equilibrium and of the corresponding applicability of rarious diagnostic techniques in hoth a recombining argon plasma and a recombining plasma with hydrogen or nitrogen. Results indicate that the Pure argon plasma is well described by u partial equilibrium model in which the free and bound-excited electrons are in mutual equilibrium irespective of possible departures from equilibrium with the ground state. The addition of just tenths of a percent of either atomic Hydrogen or nitrogen, however, disturbs this partial equilibrium hr argon plasmas with electron densities roughly less than 10²¹ m³ such that only diagnostic techniques which are independent o/ partial equilibrium assumptions can be reliably implemented.     

Depinning of a domain wall in the 2d random-field Ising model

We report studies of the behaviour of a single driven domain wall in the 2-dimensional non-equilibrium zero temperature random-field Ising model, closely above the depinning threshold. It is found that even for very weak disorder, the domain wall moves through the system in percolative fashion. At depinning, the fraction of spins that are flipped by the proceeding avalanche vanishes with the same exponent as the infinite percolation cluster in percolation theory. With decreasing disorder strength, however, the size of the critical region decreases. Our numerical simulation data appear to reflect a crossover behaviour to an exponent at zero disorder strength. The conclusions of this paper strongly rely on analytical arguments. A scaling theory in terms of the disorder strength and the magnetic field is presented that gives the values of all critical exponent except for one, the value of which is estimated from scaling arguments. Received: 13 February 1998 / Accepted: 30 March 1998     

Generalization of the Gibbsian relation for dilute systems

The Gibbsian relation is of fundamental importance to the thermodynamics of nonequilibrium systems. In this paper, we shall present an analytical derivation and several generalizations of this relation for dilute, nonequilibrium and certain highly nonequilibrium, systems. Our analysis will beindependent of the collision dynamics, because it will be based on the general kinetic equation witharbitrary collision integrals. Consequently, our analysis can provide athermodynamic derivation and several generalizations of the Gibbsian relation. Our distribution functions can also admit some arbitrary, nonequilibrium and highly nonequilibrium, forms. With the help of the generalized Gibbsian relation and a fundamental axiom to be postulated, the entropy production rates and the generalized forces and fluxes will be studied for our highly nonequilibrium systems. The second law of thermodynamics will be postulated and verified in specific cases. Onsager's reciprocity relations will be discussed.     

Generalized Fokker–Planck equations derived from generalized linear nonequilibrium thermodynamics

Recently, Compte and Jou derived nonlinear diffusion equations by applying the principles of linear nonequilibrium thermodynamics to the generalized nonextensive entropy proposed by Tsallis. In line with this study, stochastic processes in isolated and closed systems characterized by arbitrary generalized entropies are considered and evolution equations for the process probability densities are derived. It is shown that linear nonequilibrium thermodynamics based on generalized entropies naturally leads to generalized Fokker–Planck equations.     

Flow properties of the optically isotropic tetrahedratic phase

We discuss the coupling between flow and other hydrodynamic variables that can occur in the optically isotropic tetrahedratic phase (T_d) characterized by a third rank tensor order parameter T_ijk. We point out that an applied electric field or an applied temperature gradient will lead to flow. Reciprocally we predict that, for example, a shear flow applied to a tetrahedratic phase leads to an induced electric field and a temperature gradient. Similarities to recent experimental observations in the vicinity of the isotropic-B7 phase transitions in materials formed by banana-shaped molecules are discussed. Received 31 July 2001     

Theory on Morphological Instability in Driven Systems

Motivated by recent findings from simulation of a driven lattice gas under shifted periodic boundary conditions, we study within the context of a continuum model the interfacial stability of driven diffusive systems. In this model, an external driving field maintains the system away from equilibrium. Well below criticality, steady-state solutions of the associated bulk kinetic equation are obtained. Our results successfully account for the novel features found in simulation. In particular, the solution describing a pair of interfaces tilted with respect to the driving field under periodic boundary conditions shows a tilt-dependent bulk density (and internal energy), and boundary layers near one of the interfaces. Focusing on the interface dynamics, one finds that such an interface exhibits a characteristic Mullins-Sekerka instability. This is argued to be responsible for the onset of the single- to multistrip transformation observed in simulation.     

Two-Dimensional Numerical Modeling of Direct-Current Electric Arcs in Nonequilibrium

A numerical model has been developed to analyze arc-anode attachment in direct-current electric arcs. The developed model fully couples a plasma flow with electromagnetic fields in a self-consistent manner. Electrons and heavy species are assumed to have different temperatures. Species continuities are taken into account to address the chemical nonequilibrium with the Self-Consistent Effective Binary Diffusion (SCEBD) formulation. Electric and magnetic field equations are determined with a newly developed Ohm’s law, an improvement over the conventional generalized Ohm’s law. The governing equations are discretized and solved using the Finite Volume Method (FVM) and Gauss–Seidel Line Relaxation (GSLR) method in a two-dimensional domain. The model is applied to a two-dimensional axisymmetric high-intensity argon arc. The results are compared favorably with experimental and other numerical data. A significant electric potential drop has been observed in the vicinity of the anode due to the thermal and chemical nonequilibrium effects.     

Self-motion of a phenanthroline disk on divalent metal ion aqueous solutions coupled with complex formation

The self-motion of a 1,10-phenanthroline disk on divalent metal ion aqueous solutions was investigated as a simple autonomous motor coupled with complex formation. The characteristic features of motion (continuous and oscillatory motion) and their concentration regions differed among metal ions, and the frequency of oscillatory motion depended on the temperature of the aqueous solution. The nature of the characteristic motion is discussed in relation to the stability constant of complex formation between phenanthroline and a metal ion, and the difference in surface tension between phenanthroline and its metal complex as the driving force.