Biomedical subjects

S K Zhdanov

Publications and source records attributed to S K Zhdanov.

9 recordsLinked to original sources

PubMed2005

Force field inside the void in complex plasmas under microgravity conditions.

Observations of complex plasmas under microgravity conditions onboard the International Space Station performed with the Plasma-Kristall experiment-Nefedov facility are reported. A weak instability of the boundary between the central void (region free of microparticles) and the microparticle cloud is observed at low gas pressures. The instability leads to periodic injections of a relatively small number of particles into the void region (by analogy this effect is called the "trampoline effect"). The trajectories of injected particles are analyzed providing information on the force field inside the void. The experimental results are compared with theory which assumes that the most important forces inside the void are the electric and the ion drag forces. Good agreement is found clearly indicating that under conditions investigated the void formation is caused by the ion drag force.

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PubMed2005

Kinetic approach for the ion drag force in a collisional plasma.

The linear kinetic approach to calculate the ion drag force in a collisional plasma is generalized. The model collision integral (for ion-neutral collisions) is discussed and employed to calculate the plasma response for arbitrary velocity of the plasma flow and arbitrary frequency of the collisions. The derived plasma response is used to calculate the self-consistent force on the test charged particle. The obtained results are compared to those of the traditional pair collision approach, and the importance of the self-consistent kinetic consideration is highlighted. In conclusion, the applicability of the proposed approach is discussed.

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PubMed2004

Kinetics of ensembles with variable charges.

Kinetics of particle ensembles with variable charges is investigated. It is shown that the energy of such ensembles is not conserved in the interparticle collisions. The case when the equilibrium charge depends on the particle coordinate is studied, and the collision integral describing the momentum and energy transfer in collisions is derived. Solution of the resulting kinetic equation shows that the system is unstable--the mean thermal energy exhibits explosion-like growth, diverging at a finite time.

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PubMed2004

Shock melting of a two-dimensional complex (dusty) plasma.

Shock waves with a linear front were experimentally studied in a monolayer hexagonal Yukawa lattice which was formed from charged monodisperse plastic microspheres and levitated in the sheath of a radio-frequency discharge. It was found that the shock can cause phase transitions from a crystalline to gaslike and liquidlike states. Melting occurred in two stages. First, the lattice was compressed in the direction of shock propagation and second, the particle velocities were randomized a few lattice lines downstream. The Mach number of the shock reached 2.7.

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PubMed2004

Force on a charged test particle in a collisional flowing plasma.

The force on a charged test particle embedded in a flowing (electron-ion) plasma is calculated using the linear dielectric response formalism. This approach allows us to take into account ion-neutral collisions self-consistently. The effect of collisions on the ion drag force is analyzed. It is shown that collisions can play a major role and can enhance the force substantially.

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PubMed2004

Origin of the curved nature of Mach cone wings in complex plasmas.

While the propagation and refraction of waves and shocks which constitute Mach cones have been well studied in continuous slowly varying stratified media such as gases, liquids, and solids, here we investigate these processes at the kinetic, discrete (or "molecular") level in a complex plasma where the stratification scale is of the order of the damping length. The shape of Mach cones formed by nondispersive linear sound waves in a nonuniform complex plasma was calculated analytically using the method of wave rays. The cases of transversely and longitudinally inhomogeneous media as well as a medium with a sound speed maximum were considered. The theory was compared with experimental observations of Mach cones with curved wings (dynamic Mach cones) in a two-dimensional complex plasma. A good quantitative agreement was obtained.

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PubMed2003

Coupled dust-lattice solitons in monolayer plasma crystals.

Nonlinearly coupled dust-lattice (DL) waves in monolayer plasma crystals are studied theoretically. It is shown that the high-frequency transverse (vertical) oscillations can form localized wave envelopes--solitons coupled with "slow" longitudinal DL perturbations. Using the molecular dynamics simulations, the derived soliton solution is shown to be stable.

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PubMed2003

Scattering in the attractive Yukawa potential in the limit of strong interaction.

Scattering in the attractive screened Coulomb (Yukawa) potential in the limit of strong interaction is investigated. It is shown that the scattering occurs mostly with large angles. The corresponding momentum-transfer cross section is calculated. The results are applied to estimate the ion drag force acting on an isolated micron-sized grain in low-pressure bulk plasmas.

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PubMed2002

Anisotropic plasma crystal solitons.

An analytical two-dimensional model for weakly dispersive and weakly nonlinear longitudinal and transverse shear waves propagating in an ideal two-dimensional hexagonal Yukawa crystal is presented. The model takes into account the nonlinear terms up to the third order. Both compressional and shear soliton solutions are found in the long-wavelength approximation. It is shown that the compressional solitons are always supersonic and weakly anisotropic. The shear solitons, on the other hand, exhibit strong anisotropy and can be both subsonic and supersonic, depending on the direction of propagation. In the model, shear solitons cannot propagate along the main axes. The role of weak damping as well as formation of multiple solitons is analyzed. The results are discussed in connection with wave and Mach cone experiments in a monolayer hexagonal plasma crystal, and a diagnostic method is proposed to measure both the charge of the microparticles and the lattice parameter.

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