Comment on "Quantum diffusion of 3-He impurities in solid 4- He"

In this comment I show that the experimental data on quantum diffusion of 3-He impurities in solid 4-He can be explained using the adopted quasiparticle theory. The contention by E.G. Kisvarsanyi and N.S. Sullivan (KS) in Phys.Rev.B v. 48, 16557 (1993) as well as in their Reply (ibid. v. 55, 3989 (1997)) to the Grigor'ev's Comment (Phys.Rev. B v. 55, 3987 (1997)) that "Pushkarov's theory of phonon scattering fails to fit the data by very large factors" is groundless and may result from their bad arithmetical error. This means that the phonon-impurity scattering mechanism of diffusion is consistent with experiment and its neglecting by KS makes their results questionable.Comment: RevTex, 5 pages, no figures, to be published in Phys.Rev.

Dark solitons in ferromagnetic chains with first- and second-neighbor interactions

We study the ferromagnetic spin chain with both first- and second-neighbor interactions. We obtained the condition for the appearance and stability of bright and dark solitons for arbitrary wave number inside the Brillouin zone. The influence of the second-neighbor interaction and the anisotropy on the soliton properties is considered. The scattering of dark solitons from point defects in the discrete spin chain is investigated numerically.Comment: 7 pages,5 figure

Solitary wave propagation and bistability in the normal dispersion region of highly nonlinear optical fibres and waveguides

Properties of bright solitary wave solutions of the cubic-quintic nonlinear Schrödinger equation are considered in the normal dispersion region of optical fibres and waveguides with third- and fifth-order nonlinearities. The case of an optical fibre is concretely considered but other possible waveguide geometries are also discussed. For comparison, the properties of the black solitary wave existing in the same parameter range are also considered. All soliton parameters are presented in a unified way as functions of the normalised pulse energy. The possibility for bistable behaviour of the solitary waves is examined and a new type of solitary wave bistability (bright-dark) is introduced. The role of the geometry of the waveguide and the appropriate materials for experimental observation of such waves are also discussed

General nonlinear theory of quasiparticle dynamics and kinetics in crystals

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Soliton excitations in deformable solids

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