Mean free path

About: Mean free path is a research topic. Over the lifetime, 4412 publications have been published within this topic receiving 114418 citations.

The ion flux from a thermal plasma to a surface

Abstract: On the basis of a continuum multi-fluid description of a plasma, a theory is developed of an ionization layer between a plasma in ionization (Saha) equilibrium and the space-charge sheath near a surface of a cathode or of an insulating wall. The crucial parameter determining the character of the solution is the ratio of the recombination length to the mean free path ion-neutral species; if this ratio is large, then the developed theory is consistent with a conventional diffusion approach. Numerical and asymptotic solutions of a stated problem are obtained. It is found that the problem is solvable only if the degree of ionization does not exceed a certain value, which varies between approximately 0.6 and 1. Beyond this value, the equation of the pressure balance cannot be satisfied and the plasma as a whole in the considered layer cannot stay in static equilibrium. A simple approximate formula for the ion flux is obtained.

Phonon mean free path spectrum and thermal conductivity for Si1−xGex nanowires

Abstract: We reformulate the linearized phonon Boltzmann transport equation by incorporating the direction-dependent phonon-boundary scattering, and based on this equation, we study the thermal conductivity of Si1−xGex nanowires and derive their phonon mean free path spectrum. Due to the severe suppression of high-frequency phonons by alloy scattering, the low frequency phonons in Si1−xGex nanowires have a much higher contribution to the thermal conductivity than pure silicon nanowires. We also find that Si1−xGex nanowires possess a stronger length-dependent, weaker diameter-dependent, and weaker surface roughness-dependent thermal conductivity than silicon nanowires. These findings are potentially useful for engineering Si1−xGex nanowires for thermoelectric applications.

Mean free path effects in superfluid 4 He

Abstract: The mean free path effects in superfluid He II was studied with a vibrating wire method in the temperature range from Tλ down to 20 mK under the saturated vapour pressure. The transition from the hydrodynamic regime to the ballistic regime was clearly observed at around 0.7 K with a 47 µm diameter wire. In the hydrodynamic regime the usual Stokes' approximation was found to be insufficient to interpret the results. In the ballistic regime the results can be explained quantitatively with the kinetic theory of phonons. However, below about 0.15 K there appear non-linear effects such as the distortion of the resonance line shape and a hysteresis behavior, which become stronger with decreasing temperature.

Structural scattering of phonons in quasicrystals

Abstract: The concept of phonon scattering involving what is known as Umklapp processes is generalized to quasicrystals. It is shown that such processes in quasicrystals lead to a power law temperature dependence of the mean free path of delocalized quasilattice excitations, contrary to the exponential temperature dependence of the phonon mean free path characteristic for periodically structured crystals at intermediate temperatures. This result provides a plausible explanation for the plateau-type feature in the quasilattice thermal conductivity λph(itT) of highly ordered icosahedral quasicrystals in the Al−Mn−Pd and Al−Re−Pd systems.