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The acoustic sound dispersion of nitrogen in its liquid and supercritical phases has been studied by Inelastic X-Ray Scattering. Approaching supercritical conditions, the gradual disappearance of the positive sound dispersion, characteristic of the low temperature liquid, is observed. In the supercritical state, evidence for a crossover between adiabatic and isothermal sound propagation regimes is inferred by an analysis of the dynamic structure factor based on generalized hydrodynamics.
We comment on three incorrect claims in the paper by Fomin et al (arXiv:1507.06094) concerning the generalized hydrodynamic methodology and positive sound dispersion in fluids.
We report a molecular dynamics simulation study of the sound waves in vitreous silica in the mesoscopic exchanged momentum range. The calculated dynamical structure factors are in quantitative agreement with recent experimental inelastic neutron and
The adiabatic elastic modulus is often useful in the high frequency response of materials. Unfortunately, it can be much more difficult to directly measure the adiabatic elastic modulus of material than the isothermal elastic modulus. We derive the r
The high frequency dynamics of fluid oxygen have been investigated by Inelastic X-ray Scattering. In spite of the markedly supercritical conditions ($Tapprox 2 T_c$, $P>10^2 P_c$), the sound velocity exceeds the hydrodynamic value of about 20%, a fea
Three classes of harmonic disorder systems (Lennard-Jones like glasses, percolators above threshold, and spring disordered lattices) have been numerically investigated in order to clarify the effect of different types of disorder on the mechanism of