Biomedical subjects

A P Nefedov

Publications and source records attributed to A P Nefedov.

7 recordsLinked to original sources

PubMed2003

Decharging of complex plasmas: first kinetic observations.

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.

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PubMed2002

Complex-plasma boundaries.

This study deals with the boundary between a normal plasma of ions and electrons, and an adjacent complex plasma of ions, electrons, and microparticles, as found in innumerable examples in nature. Here we show that the matching between the two plasmas involve electrostatic double layers. These double layers explain the sharp boundaries observed in the laboratory and in astrophysics. A modified theory is derived for the double layers that form at the discontinuity between two different complex plasmas and at the point of contact of three complex plasmas. The theory is applied to the first measurements from the Plasma Kristall Experiment (PKE) Nefedov Laboratory in the International Space Station.

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PubMed2002

Diffusion in microgravity of macroparticles in a dusty plasma under solar radiation.

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.

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PubMed2001

Positively charged particles in dusty plasmas.

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.

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PubMed2001

Dependence of the dust-particle charge on its size in a glow-discharge plasma.

Measurements of the charge of dust grains have been performed in a quasineutral plasma over a wide range of grain sizes. A new method was established for measuring the charge on grains levitating in the striations of a dc glow discharge. A single dust particle is moved out of a dust cloud with the help of a focused laser beam. When it leaves the beam it returns back to the cloud, and the charge on the grain is derived from the analysis of the returning trajectory. The obtained dependence of the dust-grain charge on its size was found to be strongly nonlinear in the experimental conditions.

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PubMed1999

Dynamical properties of random charge fluctuations in a dusty plasma with different charging mechanisms.

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.

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PubMed1999

Charge-fluctuation-induced heating of dust particles in a plasma.

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.

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