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Biomedical subjects

J Vranjes

Publications and source records attributed to J Vranjes.

9 recordsLinked to original sources
PubMed2004

Ion temperature gradient instability in a dusty plasma.

An analysis of the temperature-gradient-driven ( eta(i) ) instability of drift waves in dusty plasma is presented. Various limits that allow for the coupling of the drift wave with the dynamics of dust grains are discussed. In particular, the cases of tiny (magnetized) and relatively heavy (unmagnetized) grains are studied. It is shown that in both limits the behavior of the eta(i) mode is considerably affected by the dust dynamics. The growth rate turns out to be higher in the presence of dust, and the instability threshold is lower, resulting in a more unstable plasma.

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PubMed2003

Nonlinear drift waves in electron-positron-ion plasmas.

It is suggested that low-frequency drift waves can play an important role in the dynamics of electron-positron plasmas comprising some concentration of ions. In the electromagnetic case the drift wave couples with the shear Alfvén wave in an electron-positron-ion plasma. The drift wave frequency can be very low in such plasmas depending on the concentration and density scale lengths of the plasma components. In the nonlinear regime these waves can give rise to dipolar vortices in both electrostatic and electromagnetic limits. The velocity of the nonlinear structure turns out to be different compared to the case of an electron-ion plasma.

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PubMed2003

Interchange mode in the presence of dust.

The linear and nonlinear development of an electrostatic interchange mode which involves a magnetized nonuniform electron-ion fluid in the presence of nonuniform static charged dust grains is investigated. The charge on grains is taken as spatially dependent, and the consequences of that condition are investigated. It is shown that standardly accepted stabilization of the interchange mode in the presence of negatively charged grains can be violated due to the spatial dependence of the charge on grains. Also, the ion drift, which is caused by the action of a gravity term perpendicular to the magnetic field lines, is taken as nonuniform as a result of the magnetic field nonuniformity, and it is shown that due to such a nonuniformity the instability condition can be significantly modified. In the nonlinear regime several types of coherent stationary vortex structures are found: namely, dipolar and tripolar vortices and vortex chains. The dipolar vortex is found to propagate in the direction of the ion drift, while the tripole and vortex chains are carried by the drift flow. The spatial dependence of these structures is determined by parameters describing the nonuniformity of the equilibrium plasma.

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PubMed2002

Analytical description of a neutral-induced tripole vortex in a plasma.

An analytical description of a stationary triple vortex, observed in a cylindrical plasma, is presented. The concentration of neutrals, which is rather high in the experiment, turns out to be of crucial importance due to a spatially dependent distribution. In the radial direction the neutral concentration is paraboliclike, yielding an effective radial force directed towards the axis of the system. This neutral force causes the rotation of the plasma in the direction which is opposite to the E-->xB--> drift. The stationary triple vortex develops for a starting Gaussian-density distribution and a rigid-body rotation of the plasma column.

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PubMed2002

Electrostatic interaction in dusty plasma.

Two modifications of the standard description of electrostatic interaction in a dusty plasma are emphasized. First, the Coulomb-type potential profile is not applicable at very short distances around a dust grain, due to the polarization of the charge on the grain, i.e., the image charge effect, and, second, at larger distances, the standard Debye-Hückel potential screening is modified due to nonlinear corrections in the expanded Boltzmann distribution for plasma particles.

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PubMed2002

Three-wave interaction in a self-gravitating fluid.

Nonlinear three-wave interaction is investigated in rotating self-gravitating astrophysical fluids. Both direct and inverse cascades are found. The latter should be of importance for the formation of structures in rotating astrophysical objects like protogalaxies and galaxies. Linear gravitational instability is shown to be a process that develops on much longer time scales, compared to the nonlinear wave interaction, and the nonlinear precipitation of energy from the linearly unstable, slowly contracting mode towards smaller spatial and time scales is shown to be possible.

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PubMed2001

Effects of dust charge fluctuations on current-driven dust-ion-acoustic waves.

The effects of fluctuating grain charge on current-driven dust-ion-acoustic modes are investigated in the presence of various physical parameters which are varied in order to describe the behavior of the mode in detail. Variation of the charge clearly influences the ion-acoustic mode by changing of its frequency and growth rate. We report here the existence of a dust charge fluctuation mode in the system, and it is shown that the mode is unstable for a negative charge on the dust per unit volume not exceeding some critical value.

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PubMed2000

Nonlinear magnetic electron tripolar vortices in streaming plasmas.

Magnetic electron modes in nonuniform magnetized and unmagnetized streaming plasmas, with characteristic frequencies between the ion and electron plasma frequencies and at spatial scales of the order of the collisionless skin depth, are studied. Two coupled equations, for the perturbed (in the case of magnetized plasma) or self-generated (for the unmagnetized plasma case) magnetic field, and the temperature, are solved in the strongly nonlinear regime and stationary traveling solutions in the form of tripolar vortices are found.

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