A generalization of the Larkin-Pikin-Sak model in which an n-component order parameter is coupled to a general anisotropic elastic continuum is studied using the c expansion. It is found that the fixed-point structure is the same as the isotropic model but that all fixed points are unstable with respect to anisotropic perturbations, independent of external boundary conditions. The compressible smectic-A to smectic-C liquidcrystal transition is also studied. It is found to be unaffected by elastic degrees of freedom and is, therefore, expected to have helium exponents, as previously predicted by de Gennes.
We present an exact analytical solution by the use of an ansatz method for the modified nonlinear Schrödinger equation iU ϩ 1 2 U ϩN 2 ͉U͉ 2 UϩisN 2 (͉U͉ 2 U) ϭ0, describing the propagation of light pulses in optical fibers. The inclusion of the term isN 2 (͉U͉ 2 U) in the usual nonlinear Schrödinger equation arises from an intensity-dependent group velocity and produces a temporal pulse distortion leading to the development of an optical shock. Previous work ͓Xu Bingzhen and Wang Wenzheng, Phys. Rev. E 51, 1493 ͑1995͔͒ using the traveling-wave method does not exhibit this important physical picture. ͓S1063-651X͑98͒05004-1͔
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