Topic
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.
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TL;DR: In this paper, the authors studied the effect of carrier mobility and saturation velocity on charge transport in a single-walled carbon nanotube (CNT) channel, and showed that a higher mobility in an SWCNT does not necessarily lead to a higher saturation velocity.
Abstract: The carriers in a carbon nanotube (CNT), like in any quasi-1-dimensional (Q1D) nanostructure, have analog energy spectrum only in the quasifree direction; while the other two Cartesian directions are quantum-confined leading to a digital (quantized) energy spectrum. We report the salient features of the mobility and saturation velocity controlling the charge transport in a semiconducting single-walled CNT (SWCNT) channel. The ultimate drift velocity in SWCNT due to the high-electric-field streaming is based on the asymmetrical distribution function that converts randomness in zero-field to a stream-lined one in a very high electric field. Specifically, we show that a higher mobility in an SWCNT does not necessarily lead to a higher saturation velocity that is limited by the mean intrinsic velocity depending upon the band parameters. The intrinsic velocity is found to be appropriate thermal velocity in the nondegenerate regime, increasing with the temperature, but independent of carrier concentration. However, this intrinsic velocity is the Fermi velocity that is independent of temperature, but depends strongly on carrier concentration. The velocity that saturates in a high electric field can be lower than the intrinsic velocity due to onset of a quantum emission. In an SWCNT, the mobility may also become ballistic if the length of the channel is comparable or less than the mean free path.
65 citations
TL;DR: Divertors allow reduction of the electron-neutral collision frequency to values where the RMFo coupling indicates full penetration of theRMFo to the major axis.
Abstract: Odd-parity rotating magnetic fields (RMFo) applied to mirror-configuration plasmas have produced average electron energies exceeding 200 eV at line-averaged electron densities of approximately 10(12) cm-3. These plasmas, sustained for over 10(3)tauAlfven, have low Coulomb collisionality, vc* triple bond L/lambdaC approximately 10(-3), where lambdaC is the Coulomb scattering mean free path and L is the plasma's characteristic half length. Divertors allow reduction of the electron-neutral collision frequency to values where the RMFo coupling indicates full penetration of the RMFo to the major axis.
64 citations
TL;DR: In this article, a microscopic analysis of the viscous energy gain of energetic particles in (gradual) nonrelativistic shear flows is presented, and the Fokker-Planck coefficients for the average rate of momentum change and dispersion in the general case of a momentum-dependent scattering time τ(p) ∝ pα with α ≥ 0.
Abstract: A microscopic analysis of the viscous energy gain of energetic particles in (gradual) nonrelativistic shear flows is presented. We extend previous work and derive the Fokker-Planck coefficients for the average rate of momentum change and dispersion in the general case of a momentum-dependent scattering time τ(p) ∝ pα with α ≥ 0. We show that in contrast to diffusive shock acceleration, the characteristic shear acceleration timescale depends inversely on the particle mean free path, which makes the mechanism particularly attractive for high-energy seed particles. Based on an analysis of the associated Fokker-Planck equation we show that above the injection momentum p0, power-law differential particle number density spectra n(p) ∝ p-(1+α) are generated for α > 0 if radiative energy losses are negligible. We discuss the modifications introduced by synchrotron losses and determine the contribution of the accelerated particles to the viscosity of the background flow. Possible implications for the plasma composition in mildly relativistic extragalactic jet sources are addressed.
64 citations
TL;DR: In this paper, the theoretical expression for the thermoelectric power of polycrystalline metal films is derived from an effective Fuchs-Sondheimer conduction model, and a procedure is proposed to determine the variation in the electronic mean free path.
Abstract: Starting from an effective Fuchs-Sondheimer conduction model, the theoretical expression for the thermoelectric power of polycrystalline metal films is derived. From the approximate expression for thick films, a procedure is proposed to determine the variation in the electronic mean free path.
64 citations
TL;DR: In this article, the authors considered situations in which the thermodynamical equilibrium is described by a heavy-tail distribution function rather than a maxwellian distribution and proposed a different method to obtain similar results.
Abstract: This paper is devoted to hydrodynamic limits of linear kinetic equations. We consider situations in which the thermodynamical equilibrium is described by a heavy-tail distribution function rather than a maxwellian distribution. A similar problem was addressed in [14] using Fourier transform and it was shown that the long time/small mean free path behavior of the solution of the kinetic equation is described by a fractional diffusion equation. In this paper, we propose a different method to obtain similar results. This method is somewhat reminiscent of the so-called "moments method" which plays an important role in kinetic theory. This new method allows us to consider space dependent collision operators (which could not be treated in [14]). We believe that it also provides the relevant tool to address nonlinear problems.
64 citations