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Z Donkó

Publications and source records attributed to Z Donkó.

13 recordsLinked to original sources
PubMed2006

Shear viscosity and shear thinning in two-dimensional Yukawa liquids.

A two-dimensional Yukawa liquid is studied using two different nonequilibrium molecular dynamics simulation methods. Shear viscosity values in the limit of small shear rates are reported for a wide range of Coulomb coupling parameter and screening lengths. At high shear rates it is demonstrated that this liquid exhibits shear thinning; i.e., the viscosity eta diminishes with increasing shear rate. It is expected that two-dimensional dusty plasmas will exhibit this effect.

Journal Article↗
PubMed2005

Equilibrium properties and phase diagram of two-dimensional Yukawa systems.

Properties of two-dimensional strongly coupled Yukawa systems are explored through molecular dynamics simulations. An effective coupling coefficient gamma* for the liquid phase is introduced on the basis of the constancy of the first peak amplitude of the pair-correlation functions. Thermodynamic quantities are calculated from the pair-correlation function. The solid-liquid transition of the system is investigated through the analysis of the bond-angular order parameter. The static structure function satisfies consistency relation, attesting to the reliability of the computational method. The response is shown to be governed by the correlational part of the inverse compressibility. An analysis of the velocity autocorrelation demonstrates that this latter also exhibits a universal behavior.

Journal Article↗
PubMed2004

Collective modes of quasi-two-dimensional Yukawa liquids.

Particles in dusty plasmas are often confined to a quasi-two-dimensional arrangement. In such layers--besides the formation of compressional and (in-plane) shear waves--an additional collective excitation may also show up, as small-amplitude oscillations of the particles perpendicular to the plane are also possible. We explore through molecular dynamics simulations the properties (fluctuation spectra, dispersion relation, Einstein frequency) of this out-of-plane transverse mode in the strongly coupled liquid phase of Yukawa systems.

Journal Article↗
PubMed2004

Two-dimensional Yukawa liquids: correlation and dynamics.

A combined theoretical and molecular dynamics (MD) simulation study of the collective modes and their dispersion in a two-dimensional Yukawa system in the strongly coupled liquid state is presented. The theoretical analysis relies upon the quasilocalized charge approximation; the MD simulation generates static pair correlation functions and dynamical current-current correlation spectra.

Journal Article↗
PubMed2004

Thermal conductivity of strongly coupled Yukawa liquids.

The thermal conductivity of strongly coupled Yukawa liquids, being relevant to dusty plasmas, is calculated from nonequilibrium molecular dynamics simulations. The calculations cover a wide range of plasma coupling (Gamma) and screening (kappa) parameters and yield data which are generally in good agreement with the results of recent independent calculations. An improved analytical formula, relating the thermal conductivity to the reduced temperature and to the screening length, is proposed.

Journal Article↗
PubMed2003

Dynamical structure functions, collective modes, and energy gap in charged-particle bilayers.

The dynamical properties of strongly coupled charged-particle bilayers are investigated by molecular dynamics (MD) simulation and theoretical analysis. The spectra of the current correlation functions show the existence of two (in-phase and out-of-phase) longitudinal and two (in-phase and out-of-phase) transverse collective modes. The out-of-phase modes possess finite frequencies at wave numbers k-->0, confirming the existence of the predicted long-wavelength energy gap in the bilayer system. A theoretical model based on an extended Feynman ansatz for the dynamical structure functions provides predictions on the strength of the collective modes that are verified by the MD experiment.

Journal Article↗
PubMed2002

Caging of particles in one-component plasmas.

Strongly coupled Coulomb systems are characterized by localization ("caging") of particles trapped and oscillating in slowly fluctuating local potential wells. This observation constitutes the basic assumption underlying the quasilocalized charge approximation. Using molecular dynamics simulation we study the changes in the particles' surroundings (cages) in a classical three-dimensional one-component plasma. The results of our analysis show that at high coupling values, substantial changes occur only after several plasma oscillation cycles. We also analyze the oscillation frequencies of the caged particles and relate the decorrelation of the cages to the process of self-diffusion.

Journal Article↗
PubMed2001

Apparent secondary-electron emission coefficient and the voltage-current characteristics of argon glow discharges.

The accuracy of secondary-electron emission coefficients, that are used as input data of discharge models, seriously influences the calculated discharge characteristics. As it is very difficult to consider all possible electron emission processes of a cold cathode separately, in most of the recent models an apparent secondary coefficient gamma is applied, which is often assumed to be constant, even for a wide range of discharge conditions. In contrast with this common assumption, the present calculations-based on a heavy-particle hybrid model-show that in abnormal glow discharges gamma varies considerably with changing discharge conditions: a factor of 3 change of gamma has been found in the range of reduced current densities (0.04 mA cm(-2) Torr(-2)< or =j/p(2)< or =4 mA cm(-2) Torr(-2)) covered in this study. The present simulations also confirm that ionization by heavy particles plays a significant role in the ion production at the abnormal cathode fall. Moreover, it is shown, that the fast heavy particles reflected from the cathode surface play the dominant role in the gas heating.

Journal Article↗
PubMed2001

Molecular dynamics studies of strongly coupled charged particle bilayers at finite temperatures.

The structure of strongly coupled charged particle bilayers was investigated using molecular dynamics simulation, in a wide range of the plasma coupling parameter Gamma=20-100. The simulations showed the existence of a series of structural transformations, controlled by the separation of the layers. At high values of Gamma a pronounced long-range order was found to develop at intermediate layer separations, with staggered square lattice configuration. The results show a fair agreement with those obtained by hypernetted chain calculations, in terms of intralayer and interlayer pair correlation functions and structure functions.

Journal Article↗
PubMed2000

Detection of CN radicals in DC nitrogen plasma used for deposition of CNx layers.

Emission spectra from a DC plasma discharge of nitrogen with a graphite cathode used for deposition of CNx layers were investigated in the visible range 350-900 nm. The spectra recorded at low and high resolution from both the negative glow and the positive column of the discharge were studied separately. All spectra are dominated by neutral and ionised N2 emission. In the positive column the violet band of the cyanogen (CN) radical was identified and analysed for vibrational structure. From a computer simulation of the rotationally resolved violet band, vibrational temperatures were derived and found to be in the intensity distribution for the nu = 0, 1 and 2 levels from thermal equilibrium. In the negative glow the strong N2+ features completely mask the spectral region of the violet band of CN. Conclusions were drawn concerning the CN formation by chemical sputtering, and the role of CN radicals in the formation of polymeric CNx layers of 1:1 = C:N stoichiometry.

Cyanides↗