Results 1 - 10 of 629
Results 1 - 10 of 629. Search took: 0.026 seconds
|Sort by: date | relevance|
[en] We have studied the localization of normal modes in a model glass as a function of several parameters and found that the fraction of modes which are localized remains small even when the disorder is very large. We have also studied how anharmonic effects, such as the Grueneisen parameter, are influenced by whether or not a mode is localized or extended
[en] The strain derivatives of the Grueneisen parameter γ at room temperature are experimentally found to strongly depend on the plastic deformation epsilon sub(p) imposed to the solid. γ is very sensitive to the alterations of the microstructure, which in turn remarkably influences the lattice dynamics of the crystal. To test such a complex interaction, measurements were performed on α-titanium at values of epsilon sub(p) up to 10-1. The obtained exponential relations between the strain derivatives of γ at the origin and the epsilon sub (p) are discussed for the first- and the second-order derivatives, delta γ/delta epsilon0 and delta 2γ/delta epsilon20, respectively. The results allow not only for a deeper knowledge of the γ behaviour, but also for outlining the work-hardening evolution in metallic materials
[en] A critical review was made of the basic experimental data needed to determine the Grueneisen thermodynamic lattice gamma for α-plutonium. This value (3.37) is compared with the acoustic gamma and with similar data for α-uranium. 3 tables, 38 references
[en] An expression showing the dependence of the zero pressure Gruneisen gamma (GAMMA0) for solids on the water content (W) and total porosity (phi) of the material under consideration has been developed. It has been assumed in this treatment that the effects of the water can be treated separately from those of the solid material. Then GAMMA0 for the composite material is simply a linear combination of the individual Gruneisen gammas for the water (GAMMA/sub 0W/) and dry, porous material (GAMMA/sub 0S/), with the terms weighted according to the amount of water present, i.e., GAMMA0 = WGAMMA/sub 0W/ + (1 - W)GAMMA/sub 0S/. Values of GAMMA/sub 0S/ are found by using a technique where the Gruneisen gamma for dry, porous material is proportional to (1 - phi)5 times that for solid material. Using the derived expression for GAMMA0 the effects of varying W and phi were studied. For constant W, GAMMA0 decreases with increasing phi. However, for constant phi, the effect of varying W depends upon the value of phi
[en] We report a first-principles calculation of the phonon frequencies and mode-Grueneisen parameters of Al with the use of the atomic number and the atomic mass as the only inputs. The phonon frequencies are determined by calculating the total energy of the perfect crystal and that of the crystal distorted by a frozen phonon mode. Calculated results agree very well with experimental values. The contributions to the restoring force for various phonon modes are analyzed and discussed
[en] Reported Grueneisen parameters γ of alpha-plutonium range from 3.0 to 9.6, which is remarkable because typical Grueneisen parameter uncertainty seldom exceeds ± 0.5. Our six new estimates obtained by different methods range from 3.2 to 9.6. The new estimates arise from Grueneisen's rule, from Einstein model and Debye model fits to low-temperature ΔV/V, from the bulk modulus temperature dependence, from the zero-point-energy contribution to the bulk modulus, and from another Grueneisen relationship whereby γ is estimated from only the bulk modulus and volume changes with temperature (or pressure). We disregard several high estimates because of the itinerant-localized 5f-electron changes during temperature changes and pressure changes. Considering all these estimates, for alpha-plutonium, we recommend γ = 3.7 ± 0.4, slightly high compared with values for all elemental metals.
[en] A generalisation of the Lang-Ehrenreich-Heine model for the transition metals is applied to give specific formulae for their electronic Gruneisen parameters within normal band theory. Numerical values are calculated both with and without consideration of electron-photon interaction with the aid of data from band calculations. Agreement with the experimental values available is variable but a simple framework for discussing the factors affecting the parameter is developed from the results. (author)
[en] A method for developing invariant equations of state for which solutions of the Noh problem will exist is developed. The ideal gas equation of state is shown to be a special case of the general method. Explicit solutions of the Noh problem in planar, cylindrical and spherical geometry are determined for a Mie-Gruneisen and the stiff gas equation of state
[en] We study quantum criticality in the heavy-fermion metal YbRh2Si2 by means of the low-temperature magnetization and specific heat. The magnetic Grueneisen ratio Γmag=-(dM/dT)/C is derived, which is found to diverge in the approach of the field-induced quantum critical point. The data are compared with theoretical predictions for quantum criticality in heavy-fermion metals.