Biomedical subjects
Publications and source records attributed to O F Petrov.
The results of numerical study of physical characteristics (the pair and triplet correlation functions, the isothermal compressibility, the heat capacities, and the diffusion constants) are presented for quasi-2D dissipative Yukawa systems. The specific features of these characteristics (reflecting the two-stage melting scenario) are investigated.
An experimental determination of particle charge in a bulk dc discharge plasma covering a wide range of neutral gas pressures, was recently reported [S. Ratynskaia, Phys. Rev. Lett. 93, 085001 (2004)]. The charges obtained were several times smaller than the predictions of collisionless orbital motion limited theory. This discrepancy was attributed to the effect of ion-neutral collisions. In the present paper a more detailed description of this experiment is provided and additional experimental results obtained with particles of different sizes are reported. The measurements are compared with molecular dynamics simulations of particle charging for conditions similar to those of the experiment, with other available experimental data on particle charge in the bulk of gas discharges, and with a simple analytical model accounting for ion-neutral collisions. All the considered evidence indicates that ion-neutral collisions represent a very important factor, which significantly affects (reduces) the particle charge under typical discharge conditions.
A jump of dust density propagating through the dusty plasma structure has been observed. To excite the disturbance an impulse of axial magnetic field to the dusty plasma in a dc glow discharge striation has been applied. This impulse resulted in the dynamical stretching of the dusty plasma structure. During the reconstruction of the structure a ramp-shaped perturbation of dust density appeared. The perturbation was steepening and formed into a dust-acoustic shock. The anomalously high shock compression is observed.
A method for measuring the interactions of charged dust particles within a three-dimensional dust cloud in a plasma is presented. The measurements have been performed with the help of gravity-driven heavy charged probe particles, which moved through a dust cloud levitating at the diffuse edge of an inductively coupled rf discharge plasma. Assuming a screened Coulomb potential surrounding each particle, both the particle charge and the effective screening length were calculated from an analysis of the elastic particle interactions for 20, 30, and 50 Pa of neon pressure. The basic parameters of the bulk discharge plasma have been diagnosed with a Langmuir probe to compare the experimental data with those deriving from different theoretical approaches. The observed discrepancies are discussed.
Results are given of experimental investigation of three-particle correlations for liquid plasma-dust structures formed in the electrode layer of a high-frequency capacitive discharge. The obtained three-particle correlation functions for experimental and numerical data are analyzed and compared with the superposition approximation. The forming of clusters of macroparticles in plasma-dust systems being analyzed is revealed.
A linear dispersion relation in a highly collisional complex plasma, including ion drift, was derived in the light of recent PKE-Nefedov wave experiment performed under microgravity conditions onboard the International Space Station. Two modifications of dust density waves with wave frequencies larger than the dust-neutral collision frequency were obtained. The relevance to the space observations was analyzed and a comparison of theory and observations was made for two different complex plasma domains formed by small and large microparticles. Good qualitative agreement is found between the measurements and the theoretical dispersion relations. This allows a determination of the basic complex plasma parameters.
A large-amplitude wave with two humps of dust density, separated by a dip was generated. To excite the wave in the dc glow discharge dusty plasma a gas-dynamic impact was used. The structure obtained had several interesting properties such as strong compression of dust in the humps, supersonic dust particles in the rarefaction zone, reconstruction of the initial dust configuration after the passing of the wave. The peculiarities of the phenomenon observed are discussed. The mechanism of generation and propagation for such kind of perturbation is proposed.
Measurements of effective structural (pair correlation function) and transport (diffusion constant) characteristics of the system of microparticles in dc and rf gas-discharge plasmas under microgravity conditions are reported. The comparison between these measurements and numerical simulations is used for complex plasma diagnostics.
The first experiment on the decharging of a complex plasma in microgravity conditions was conducted. After switching off the rf power, in the afterglow plasma, ions and electrons rapidly recombine and leave a cloud of charged microparticles. Because of microgravity, the particles remain suspended in the experimental chamber for a sufficiently long time, allowing precise measurements of the rest particle charge. A simple theoretical model for the decharging is proposed which agrees quite well with the experiment results and predicts the rest charge at lower gas pressures.
New empirical rules for different phase transitions (including the melting of cubic lattices and the transitions between body-centered-cubic and face-centered-cubic structures) are proposed. The arrangements of charged macroparticles in a complex "dusty" plasma are numerically investigated for the conditions of laboratory experiments on weakly ionized gas discharges.
Diffusion of macroparticles, charged by solar radiation in microgravity, is studied by analyzing experimental data obtained on the MIR space station. Temperature, velocity distributions, friction coefficient, and diffusion constants were obtained for bronze particles. A comparison of experimental and theoretical estimates shows that the dynamic behavior of the macroparticles for short observation times can be determined by observing the ambipolar diffusion.
The trapping of dust particles has been observed in a dc abnormal glow discharge dominated by electron attachment. A dust cloud of several tens of positively charged particles was found to form in the anode sheath region. An analysis of the experimental conditions revealed that these particles were positively charged due to emission process, in contrast to most other experiments on the levitation of dust particles in gas-discharge plasmas where negatively charged particles are found. An estimate of the particle charge, taking into account the processes of photoelectron and secondary electron emission from the particle surface, is in agreement with the experimental measured values.
A dust particle in a plasma acquires electric charge by collecting electrons and ions, and sometimes by emitting electrons. The charging currents consist of discrete charges, causing the charge to fluctuate around an equilibrium value. We developed a model yielding a general expression for the charge fluctuations' temporal autocorrelation function. Both the magnitude and characteristic time of fluctuations can be obtained, knowing the specific form of charging currents. Numerical results are presented for different charging mechanisms, including charging by thermionic and photoelectric emission. It is shown that for all charging mechanisms the amplitude of fluctuations varies as DeltaZ = alpha square root [ ], where is the equilibrium dust grain charge in units of electron charges.
Random charge fluctuations are always present in dusty plasmas due to the discrete nature of currents charging the dust particle. These fluctuations can be a reason for the heating of the dust particle system. Such unexpected heating leading to the melting of the dust crystals was observed recently in several experiments. In this paper we show by analytical evaluations and numerical simulation that charge fluctuations provide an effective source of energy and can heat the dust particles up to several eV, in conditions close to experimental ones.