Dispersion acoustic

Abnormal behaviours (e.g. unusual solubility, acoustic dispersion dielectric constant, thermal conductivity, chemical reactivity, etc.). 

Axe JD, Flarada J, Shirane G (1970) Anomalous acoustic dispersion in centrosymmetric crystals with soft optic phonons. Phys Rev B 1 1227... 

As follows from (15.14), the obtained quasiparticles have acoustic dispersion for k -C i/47ra/Vo and for k 3> y/4naNo become free particles with... 

Figure 4. Refractive index n(T) and opto-acoustic dispersion function E)(q °, T) of PVAC (O, ). n(T = 295 K) measured with an AbW refractometer at A, = 514.5 nm.

Figure 5. Refiactive index n ( , ) and opto-acoustic dispersion function D90AR 0 of EPON as a function of temperature T. Solid line refiactive index at A. = 514.5nm ( , measured with an AbW refiactometer) dashed line refiactive index for white light ( measured with an Abb6 refiactometer).

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. 

Figure 11 In the right part of the figure is shown the acoustic dispersion curve (frequency v versus wave vector q) for a linear monoatomic lattice. To the left is illustrated the densities of states, D(i>), for the dispersion curve.

For the 90A-scattering geometry, the sound wavelength does not depend on the refractive index, cf. eq. (2a). 3-l6 refractive index can be evaluated from sound frequency measurements in the 90A- and 90N-scattering geometries presuming that the acoustic dispersion is negligible.In order to take dispersion effects into account we have defined the... 

The results are shown in Fig. 2.26. Thus, for the three-dimensional motion of a diatomic chain there is one pair of dispersion curves (one acoustical and one optical branch) for each direction in space. In the three-dimensional motions of a diatomic chain, the transverse directions x and y are equivalent. Consequently, only one transverse optic and acoustic dispersion curve is displayed, as they are degenerate (i.e., have the energy or vibrational motion). 

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