PubMed Health⌕ Search

Biomedical subjects

O Havnes

Publications and source records attributed to O Havnes.

5 recordsLinked to original sources
PubMed2006

Saturn's spokes: lost and found.

The spokes are intermittently appearing radial markings in Saturn's B ring that are believed to form when micrometer-sized dust particles are levitated above the ring by electrostatic forces. First observed by the Voyagers, the spokes disappeared from October 1998 until September 2005, when the Cassini spacecraft saw them reappear. The trajectories of the charged dust particles comprising the spokes depend critically on the background plasma density above the rings, which is a function of the solar elevation angle. Because the rings are more open to the Sun now than when Voyager flew by, the charging environment above the rings has prevented the formation of spokes until very recently. We show that this notable effect is capable of stopping spoke formation entirely and restricting the size of the particles in the spokes.

Journal Article↗
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.

Journal Article↗
PubMed2002

Dynamic Mach cone as a diagnostic method in reactive dusty plasma experiments.

We demonstrate how the observation of dynamic Mach cones in dusty plasma experiments allows one to follow the evolution of the dust acoustic wave velocity as charges on dust particles change, or as their mass changes. In experiments in which only the charge is changing due to, e.g., the application of a thin coating on UV-illuminated dust particles, the coating rate may be inferred through the analysis of the Mach cone pattern. In other experiments where the dust sizes are changing, also leading to some change in charge, the growth rate can be followed.

Journal Article↗
PubMed2001

Shock waves in a dusty plasma.

In the present paper, shocks in a dusty plasma are studied. A set of macroscopic shock equations are introduced in which the charge on the dust particles and the electrostatic potential in the dusty plasma have been taken into account. It is found that two shock modes may exist in a dusty plasma. One that is called the fast mode corresponds to an acoustic wave and the other, called the slow mode, corresponds to a dust-acoustic wave. The results show that the electrostatic energy of dust particles affects the shock speed and shock heating. The shock speed of the slow mode is found to be strongly dependent on the nondimensional dust density parameter p. In a tenuous dust plasma of p<<1 for the slow mode, the flow of energy as the shock heats is mainly converted into thermal energy of the dust particles; for the fast mode, the plasma heating may be reduced and partly transferred into an increase of the charge on the dust particles when they cross the shock.

Journal Article↗