THE TEMPERATURE DISTRIBUTION PRODUCED BY ACOUSTIC ABSORPTION: II. BOLTZMANN EQUATION APPROACH

1966 ◽  
Vol 44 (12) ◽  
pp. 3013-3023 ◽  
Author(s):  
S. Simons
Keyword(s):  
Boltzmann Equation ◽  
Temperature Distribution ◽  
Free Path ◽  
Low Temperatures ◽  
Mean Free Path ◽  
Collision Term ◽  
Acoustic Absorption ◽  
Time Approximation ◽  
Relaxation Time Approximation ◽  
The Mean

A calculation is given of the time-independent temperature distribution produced by the absorption of an acoustic wave under conditions in which the mean free path of the thermal particles is of the order of the specimen dimensions. Results are obtained for plane geometry by solving the relevant Boltzmann equation with a relaxation time approximation for the collision term. The results suggest an experimental method for obtaining the mean free path of electrons in metals at low temperatures, similar in some respects to the method of conduction in thin films.

scholarly journals The mean free path of electrons in polar crystals

1939 ◽  
Vol 171 (947) ◽  
pp. 496-504 ◽  
Keyword(s):  
Free Path ◽  
Conduction Band ◽  
Thermal Energy ◽  
Low Temperatures ◽  
Energy Levels ◽  
Stoichiometric Composition ◽  
Mean Free Path ◽  
Polar Crystals ◽  
Absorption Of Light ◽  
The Mean

Polar crystals of stoichiometric composition at low temperatures are insulators of electricity. If, however, electrons are raised into the normally empty conduction band of energy levels, either through the absorption of light or the thermal energy of surrounding atoms, the crystal can conduct. The purpose of this note is to calculate the mean free path of such electrons, and hence their mobility (velocity of drift in unit field). The results obtained will be compared with experimental material obtained from semi-conductors and from substances which show photoconductivity.

scholarly journals Ballistic Heat Transport in Nanocomposite: The Role of the Shape and Interconnection of Nanoinclusions

Nanomaterials ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1982
Author(s):  
Paul Desmarchelier ◽  
Alice Carré ◽  
Konstantinos Termentzidis ◽  
Anne Tanguy
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Free Path ◽  
Mean Free Path ◽  
Strong Increase ◽  
Moderate Increase ◽  
Energy Propagation ◽  
The Mean ◽  
Dynamics Simulations

In this article, the effect on the vibrational and thermal properties of gradually interconnected nanoinclusions embedded in an amorphous silicon matrix is studied using molecular dynamics simulations. The nanoinclusion arrangement ranges from an aligned sphere array to an interconnected mesh of nanowires. Wave-packet simulations scanning different polarizations and frequencies reveal that the interconnection of the nanoinclusions at constant volume fraction induces a strong increase of the mean free path of high frequency phonons, but does not affect the energy diffusivity. The mean free path and energy diffusivity are then used to estimate the thermal conductivity, showing an enhancement of the effective thermal conductivity due to the existence of crystalline structural interconnections. This enhancement is dominated by the ballistic transport of phonons. Equilibrium molecular dynamics simulations confirm the tendency, although less markedly. This leads to the observation that coherent energy propagation with a moderate increase of the thermal conductivity is possible. These findings could be useful for energy harvesting applications, thermal management or for mechanical information processing.

Experiments on the flow of heat in liquid helium below 0.7 °K

1958 ◽  
Vol 246 (1246) ◽  
pp. 390-405 ◽  
Keyword(s):  
Thermal Conductivity ◽  
Liquid Helium ◽  
Free Path ◽  
Empirical Relation ◽  
Mean Free Path ◽  
Series Of Experiments ◽  
The Mean ◽  
Set Up ◽  
Low Pressures ◽  
Measured Thermal Conductivity

A series of experiments has been performed to study the steady flow of heat in liquid helium in tubes of diameter 0.05 to 1.0 cm at temperatures between 0.25 and 0.7 °K. The results are interpreted in terms of the flow of a gas of phonons, in which the mean free path λ varies with temperature, and may be either greater or less than the diameter of the tube d . When λ ≫ d the flow is limited by the scattering of the phonons at the walls, and the effect of the surface has been studied, but when λ ≪ d viscous flow is set up in which the measured thermal conductivity is increased above that for wall scattering. This behaviour is very similar to that observed in the flow of gases at low pressures, and by applying kinetic theory to the problem it can be shown that the mean free path of the phonons characterizing viscosity can be expressed by the empirical relation λ = 3.8 x 10 -3 T -4.3 cm. This result is inconsistent with the temperature dependence of λ as T -9 predicted theoretically by Landau & Khalatnikov (1949).

Light scattering by phonons in the presence of a heat flow

1968 ◽  
Vol 46 (24) ◽  
pp. 2843-2845 ◽  
Author(s):  
Allan Griffin
Keyword(s):  
Light Scattering ◽  
Heat Flow ◽  
Temperature Gradient ◽  
Free Path ◽  
Mean Free Path ◽  
Photon Scattering ◽  
The Mean ◽  
Anti Stokes

If the temperature in an insulating crystal decreases in the z-direction, there are more phonons with momentum qz > 0 than with qz < 0. The resulting difference between the Stokes and anti-Stokes Brillouin intensities is proportional to the mean free path of the phonon involved and to the temperature gradient. The effect should be observable by either neutron or photon scattering.

Role of neutral-particle bombardment in dust–dust interactions in plasmas

2001 ◽  
Vol 65 (4) ◽  
pp. 257-272 ◽  
Author(s):  
Ya. K. KHODATAEV ◽  
G. E. MORFILL ◽  
V. N. TSYTOVICH
Keyword(s):  
Free Path ◽  
Particle Bombardment ◽  
Neutral Particle ◽  
Mean Free Path ◽  
Dust Particles ◽  
Neutral Particles ◽  
Additional Force ◽  
Numerical Coefficient ◽  
The Mean

It is shown that the interaction of dust with neutral plasma particles can lead to attractive forces between dust particles, both in the case where the distance between dust particles is less than the mean free path of neutral particles and in the case where it is greater. The expressions for attractive forces differs in the two limits only by a numerical coefficient. The additional force of dust interaction is found to be due to the neutrals created by recombination of charged plasma particles on the surface of dust particles. The influence of radiative dust cooling on dust–dust interaction is considered.

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