Biomedical subjects

A V Ivlev

Publications and source records attributed to A V Ivlev.

At least 19 recordsLinked to original sources

PubMed2006

Critical point in complex plasmas.

The occurrence of liquid-vapor phase transition and the possible existence of a critical point in complex plasmas--systems that consist of charged micrograins in a neutralizing plasma background--is investigated theoretically. An analysis based on the consideration of the intergrain interaction potential suggests that under certain conditions systems near and at the critical point should be observable. Measurements under microgravity conditions would appear to be required. The analysis aims at determining the plasma parameter regime most suitable for planned experimental investigations.

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PubMed2005

Coupled dust-lattice modes in complex plasmas.

The coupling between transverse and longitudinal dust-lattice modes due to the particle-wake interactions and vertical dust charge gradient is considered. It is shown that the dust-lattice waves can be subjected to a specific instability, the criterion for which has been derived. This instability can explain experimentally observed spontaneous excitation of vibrational modes in a plasma crystal when the pressure is decreased below a critical value.

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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

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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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

Melting of monolayer plasma crystals.

Melting of a monolayer plasma crystal in a radio-frequency discharge with no particles suspended above or below is studied. The experimental data are compared with results of molecular dynamics simulations and theory. It is shown that the melting is caused by the resonance coupling between the longitudinal and the transverse dust-lattice wave modes, due to the interaction of particles with the plasma wakes.

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PubMed2003

Rodlike particles in gas discharge plasmas: theoretical model.

Recently, complex plasmas with strongly asymmetric (rodlike) particles were investigated experimentally in rf and dc discharges [V. I. Molotkov et al., JETP Lett. 71, 102 (2000); B. M. Annaratone et al., Phys. Rev. E 63, 036406 (2001)]. In this paper, a theoretical model is proposed which describes the behavior of such systems. Major results of the proposed model are the following: Equilibrium charge is calculated for particles orientated perpendicular and parallel to the ion flux (electric field); equilibrium states of particles (orientation angle and levitation height) are obtained; energy of electrostatic interaction between rods is derived, depending on the mutual orientation. Comparison of experimental and theoretical results shows quite good agreement. In conclusion, some important theoretical issues as well as possible new experiments are discussed.

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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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PubMed2003

Weakly dissipative dust-ion-acoustic solitons.

We investigate the possibility for dust ion-acoustic solitons to exist. Compressive solitonlike perturbations are damped and slowed down, mainly due to the plasma absorption and ion scattering on microparticles. The perturbations are shown to possess the main properties of solitons. There is a principal possibility to study experimentally the role of trapped electrons in the soliton formation.

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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

Ion drag force in complex plasmas.

The problem of calculating the ion drag force in complex plasmas is considered. It is shown that the standard theory of Coulomb scattering usually fails for the ion-dust elastic collisions. A simple approach to extend this theory is proposed. This leads to a considerable enhancement in the ion-dust elastic scattering cross section and, hence, increases the ion drag force in comparison with the previous analytical results. Analysis shows that the ion drag usually exceeds the electrostatic force in the limit of weak electric field. We suggest that this is the cause of the central "void" observed in microgravity complex plasma experiments.

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PubMed2002

Coagulation of charged microparticles in neutral gas and charge-induced gel transitions.

Coagulation of charged particles was studied using the mean-field Smoluchowski equation. The coagulation equation was generalized for the case of a conserved system of charged particles. It was shown that runaway cluster growth (gelation) solutions exist if the charge-dipole (induced) interaction of clusters is included. When clusters are in thermal equilibrium with the ambient gas, the charge-dipole interaction dramatically enhances the aggregation process and considerably increases the likelihood of a gelation transition.

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PubMed2002

Dissipative longitudinal solitons in a two-dimensional strongly coupled complex (dusty) plasma.

Solitary waves are experimentally studied in a monolayer hexagonal dust lattice which is formed from monodisperse plastic microspheres and levitated in the sheath of an rf discharge. It is found that the product of the soliton amplitude and the square of the soliton width is constant as the soliton propagates. The analytical theory describing the experiment is based on the equations of motion written for a linear chain. It takes into account damping, dispersion, and nonlinearity. The numerical simulation of a linear chain produces double solitons like those observed in the experiment.

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PubMed2001

Interaction potential of microparticles in a plasma: role of collisions with plasma particles.

The interaction potential of two charged microparticles in a plasma is studied. Violation of the plasma equilibrium around the dust particles due to plasma-particle inelastic collisions results in three effects: long-range (non-Yukawa) electrostatic repulsion, attraction due to ion shadowing, and attraction or repulsion due to neutral shadowing (depending on the sign of the temperature difference between the particle surface and neutral gas). An analytical expression for the total potential is obtained and compared with previous theoretical results. The relative contribution of these effects is studied in two limiting cases-an isotropic bulk plasma and the plasma sheath region. The results obtained are compared with existing experimental results on pair particle interaction. The possibility of the so-called dust molecule formation is discussed.

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PubMed2001

Vertical pairing of identical particles suspended in the plasma sheath.

It is shown experimentally that vertical pairing of two identical microspheres suspended in the sheath of a radio-frequency (rf) discharge at low gas pressures (a few Pa) appears at a well-defined instability threshold of the rf power. The transition is reversible, but with significant hysteresis on the second stage. A simple model which uses measured microsphere resonance frequencies and takes into account, in addition to the Coulomb interaction between negatively charged microspheres, their interaction with positive-ion-wake charges, seems to explain the instability threshold quite well.

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PubMed2001

Levitation of cylindrical particles in the sheath of an rf plasma.

Microrods were levitated in the collisional sheath of a rf plasma. Rods below a critical length settle vertically, parallel to the electric field, while longer rods float horizontally. Usually rods with other inclinations spin about a vertical axis. These experimental features fit well with a model that includes a theoretical profile for the sheath, a plasma model for the screening length, which increases going deeper in the sheath, and a plasma theory for the charging of the rod's elements. Despite the agreement this paper highlights the need for a better understanding of the charging mechanism of bodies in sheaths and of the transition region in collisional sheaths.

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PubMed2001

Dust acoustic solitons with variable particle charge: role of the ion distribution.

Dust-acoustic solitons of large amplitude with variable particle charge are studied using the Sagdeev quasipotential analysis. Two limiting cases of ion distribution are considered separately: Boltzmann and highly energetic cold ions. It is shown that in both cases only compressive (density) solitons are possible. The charge variation is not important in rarefied particle clouds, but becomes crucial if the particle number density is sufficiently high. Analytical expressions for the range of Mach numbers where solitons might exist are obtained. It is found that solitons are allowed in the supersonic regime, and that in dense clouds the width of the Mach number range remains finite for the Boltzmann ions, but tends to zero for highly energetic ions.

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