Acoustic damping relaxation

The observed behavior is remarkable Why an electronic transition should affect so much the acoustic damping and more in detail the microscopic relaxation Generally speaking, we could have expected changes in the shape of the acoustic dispersion, due to changes in the electronic screening contribution to the interparticle potential. However, this is not the case, as we showed in Ref. [13] and as it appears from the data here reported. Only the acoustic damping is affected. 

Here, 6 is the scattering angle and n the refractive index of the medium. The Brillouin doublet at CO 0)b is broadened due to acoustic damping of the propagating phonons, and in a non-relaxing medium the broadening is given approximately by ... 

In NMR-SIM the simulation of an NMR experiment is based on the density matrix approach with relaxation phenomena implemented using a simple model based on the Bloch equations. Spectrometer related difficulties such as magnetic field inhomogenity, acoustic ringing, radiation damping or statistical noise cannot be calculated using the present approach. Similarly neither can some spin system effects such as cross-relaxation and spin diffusion can be simulated. 

As shown in Fig. 19 for solid samples, monochromatic light, chopped at a frequency in the order of magnitude of 10-1000 cps which is low compared with the velocity of deactivation, strikes the solid sample contained in a sample holder. After excitation and relaxation the released heat diffuses to the surface, passes into the gas phase and acts as an acoustic piston which generates a pressure wave detected by the microphone and amplified by a phase-sensitive amplifier locked to the chopping frequency co. Solution of the heat diffusion equation proves that after a distance x from their starting point the heat waves are damped by ... 

Description of the mechanics of elastin requires the understanding of two interlinked but distinct physical processes the development of entropic elastic force and the occurrence of hydrophobic association. Elementary statistical-mechanical analysis of AFM single-chain force-extension data of elastin model molecules identifies damping of internal chain dynamics on extension as a fundamental source of entropic elastic force and eliminates the requirement of random chain networks. For elastin and its models, this simple analysis is substantiated experimentally by the observation of mechanical resonances in the dielectric relaxation and acoustic absorption spectra, and theoretically by the dependence of entropy on frequency of torsion-angle oscillations, and by classical molecular-mechanics and dynamics calculations of relaxed and extended states of the P-spiral description of the elastin repeat, (GVGVP) . The role of hydrophobic hydration in the mechanics of elastin becomes apparent under conditions of isometric contraction. 

Based on the acoustic equations, Millikan s formula for the drag of droplets and the transport matrix for heat and mass transfer between droplets and their surrounding vapour, a numerical solution for the sound attenuation is given and the influences of droplet size and the evaporation coefficient are discussed. A simplified relationship for the sound damping is suggested which reveals 3 typical relaxation times characterizing the dependence of sound attenuation on the sound frequency. 

The consequence is then that the microscopic relaxation, which accounts for the low-frequency intensity in the spectra and thus possibly for the pseudo-transverse modes, discontinuously changes at the LLT, as well as the damping of the acoustic modes derived using a single-excitation fitting model. 

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