1,720,974 research outputs found
A theory of electric polarisation in liquids. I. Nonpolar liquids
No full textThe static dielectric constant of nonpolar liquids is described by analyzing the pair distribution function and the dipole-dipole interaction into a finite set of Fourier components. In a mean field approximation the theory leads to a final formula that does not contain any adjustable parameter, and proves to work better than the Clausius-Mossotti equation. The theory explains in a satisfactory way the temperature and pressure dependence of the dielectric constant of nonpolar liquids, as well as the temperature variation of the refractive index of many organic polar liquids. © 1976
Role of grain boundaries as phonon diffraction gratings in the theory of thermal conductivity
Full text linkThe picture of a grain boundary as a periodic array of dislocations implies the occurrence of phonon scattering processes that the Klemens theory of thermal conductivity does not account for. A grain boundary works similar to a diffraction grating, producing diffraction spectra of various orders: each order number n is associated with a class of scattering processes contributing to thermal resistance. The Klemens theory corresponds to n=0 : it is shown that processes with
n ≠ 0 are essential to explain the heat transport properties of a specimen containing grain boundaries. The theory is used to explain the behavior of thermal conductivity, both in the range below 5 K and in the region of the conductivity peak, as observed in crystals of lithium fluoride, alumina, and quartz. It is also applied to the conductivity curve of fused silica, in the frame of a model where a glass is pictured as a solid with a high-density distribution of grain boundaries
An iterative approach to the phonon Boltzmann equation in the theory of thermal conductivity
No full text
Effect of phonon scattering by isotope impurities on the thermal conductivity of dielectric solids
No full textThermal diffusivity of solids with low expansion coefficient: a dilatometric technique
Full text linkBeyond the isotropic model approximation in the theory of thermal conductivity
No full textBy the use of an iterative method the linearized phonon-Boltzmann equation for a dielectric solid subjected to a thermal gradient is solved in the frame of three-phonon interactions. In this way it is possible to calculate the thermal conductivity of rare-gas solids starting from the pair potential and accounting for the real Brillouin zone of the lattice. The numerical results are in full agreement with experiment and represent a considerable improvement with respect to those previously deduced for an isotropic solid
Thermal diffusivity and Biot number: a new experimental method
Full text linkA new simple method is presented for measuring thermal diffusivity and Biot number in cylindrical samples made of relatively highly conducting materials, subjected to laminar air flow. The basic idea is a heat source in the middle section of the sample, acting also as a thermocouple; only one additional temperature sensor at the cylinder basis is required to give all information, without requiring any hypothesis about the effective time dependence of the heat source
A new kind of oscillating crucible viscometer
No full textA new oscillating crucible viscometer, having a torus shaped crucible, is presented. The geometry of the torus allows a rigorous treatment of the fluidodynamical problem for an oscillating viscous liquid. The damping coefficient δ is shown to characterize two possible distinct zones of oscillation: In the first zone, δ rises when the viscosity η of the liquid rises; in the second one, δ is lowered by an increase of η. The second zone proves to be much more convenient for fixing the working point of the instrument because here the sensitivity is expected to be twice that of the first zone. Some preliminary experiments have confirmed the results of the theory. © 1971 The American Institute of Physics
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