Dispersion relations of Yukawa fluids at weak and moderate coupling.

In this paper we compare different theoretical approaches to describe the dispersion of collective modes in Yukawa fluids when the interparticle coupling is relatively weak, so that the kinetic and potential contributions to the dispersion relation compete with each other. A thorough comparison with the results from molecular dynamics simulation allows us to conclude that, in the investigated regime, the best description is provided by the sum of the generalized excess bulk modulus and the Bohm-Gross kinetic term.

Tracking and Linking of Microparticle Trajectories During Mode-Coupling Induced Melting in a Two-Dimensional Complex Plasma Crystal.

In this article, a strategy to track microparticles and link their trajectories adapted to the study of the melting of a quasi two-dimensional complex plasma crystal induced by the mode-coupling instability is presented. Because of the three-dimensional nature of the microparticle motions and the inhomogeneities of the illuminating laser light sheet, the scattered light intensity can change significantly between two frames, making the detection of the microparticles and the linking of their trajectories quite challenging. Thanks to a two-pass noise removal process based on Gaussian blurring of the original frames using two different kernel widths, the signal-to-noise ratio was increased to a level that allowed a better intensity thresholding of different regions of the images and, therefore, the tracking of the poorly illuminated microparticles. Then, by predicting the positions of the microparticles based on their previous positions, long particle trajectories could be reconstructed, allowing accurate measurement of the evolution of the microparticle energies and the evolution of the monolayer properties.

Thermoacoustic Instability in Two-Dimensional Fluid Complex Plasmas.

Thermoacoustic instability in a fluid monolayer complex plasma is studied for the first time. Experiments, theory, and simulations demonstrate that nonreciprocal effective interactions between particles (mediated by plasma flows) provide positive thermal feedback leading to acoustic sound amplification. The form of the generated sound spectra obtained both in experiments and simulations excellently agrees with theory, justifying thermoacoustic instability in the fluid complex plasma. The results indicate a physical analogy between collective fluctuation dynamics in reactive media and in systems with nonreciprocal effective interactions exposing an activation behavior.

Computational Prediction of Rate Constants for Reactions Involved in Al Clustering.

Aluminum (Al) clustering processes via three types of association reactions are herein studied using classical molecular dynamics trajectory calculations. The simulations were carried out under realistic experimental conditions. The dependence of rate constants on temperature and cluster size was obtained. The association reactions have a very small activation barrier, and the activation energy increases with increasing temperature. Our prediction of reaction rate constants can be of interest for the study of Al nanoparticle growth using kinetic models.

Collective modes in simple melts: Transition from soft spheres to the hard sphere limit.

We study collective modes in a classical system of particles with repulsive inverse-power-law (IPL) interactions in the fluid phase, near the fluid-solid coexistence (IPL melts). The IPL exponent is varied from n = 10 to n = 100 to mimic the transition from moderately soft to hard-sphere-like interactions. We compare the longitudinal dispersion relations obtained using molecular dynamic (MD) simulations with those calculated using the quasi-crystalline approximation (QCA) and find that this simple theoretical approach becomes grossly inaccurate for [Formula: see text]. Similarly, conventional expressions for high-frequency (instantaneous) elastic moduli, predicting their divergence as n increases, are meaningless in this regime. Relations of the longitudinal and transverse elastic velocities of the QCA model to the adiabatic sound velocity, measured in MD simulations, are discussed for the regime where QCA is applicable. Two potentially useful freezing indicators for classical particle systems with steep repulsive interactions are discussed.

Threshold phenomena in a throbbing complex plasma.

In complex plasmas, the trapped dust particle cloud is often characterized by a central dust-free region ("void"). The void induces a spatial inhomogeneity of the dust particle distribution and is at the origin of many intricate unstable phenomena. One type of this kind of behavior is the so-called heartbeat instability consisting of successive contractions and expansions of the void. This instability is characterized by a strong nonlinear dynamics which can reveal the occurrence of incomplete sequences corresponding to failed contractions. Experimental results based on high-speed imaging are presented for the first time and underline this threshold effect in both the dust cloud motion and the evolution of the plasma light emission.

Mixed-mode oscillations in complex-plasma instabilities.

Instabilities in dusty plasmas are frequent phenomena. We show that some instabilities can be described by mixed-mode oscillations often encountered in chemical systems or neuronal dynamics and studied through dynamical system theories. The time evolution of these instabilities is studied through the change in the associated waveform. Frequency and interspike interval are analyzed and compared to results obtained in other scientific fields concerned by mixed-mode oscillations.