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This dissertation, "Solitons and Wave Propagation in Hydrodynamical and Optical Media" by Chun-chung, Mak, 麥振忠, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstractofthesisentitled SolitonsandWavePropagation inHydrodynamicalandOpticalMedia submittedby Chun-ChungMAK forthedegreeofMasterofPhilosophy attheUniversityofHongKong inAugust2004 Solitons, which have been extensively studied over the past five decades, rep- resent one of the most important concepts in nonlinear science. These particle-like nonlinearwaveshavebeendemonstratedboththeoreticallyandexperimentally, and arebelievedtohavehighengineeringpotentialinsomeapplications. Theaimofthis studywastostudythesolitonswhichexistinsomeconfigurationsofhydrodynam- ical and optical media. In particular, soliton solutions of a number of completely integrablenonlinearevolutionequationsarenewlyobtainedorre-derived. The Hirota's bilinear method is adopted to obtain the exact soliton solutions in this study. This differentiation-based method, which requires no sophisticated mathematics, isabletoderiveexact, analyticsolutionsefficiently. An optical fiber system with decaying/amplifying and broadening/compressing effects is modelled by a variable coefficient nonlinear Schro]dinger (NLS) equa- tion. This equation is also able to describe the propagation of optical pulses in a dispersion-managed fiber system, averaged over one dispersion map. Bright anddark, one- and two-soliton solutions are obtained. These solitons are shown to havevaryingwavenumberandfrequencyintheirsolitonexpansions. Inadditionto the decaying and broadening effects, the bright solitons also demonstrate a special property, namely that the trajectory of their center of mass can have three possible modesinthex-t domain. A coupled NLS system with a group velocity mismatch is considered to be the relevant equation for a three-layer stratified shear flow. While the coupled NLS systemhasbeenstudiedindetail, theeffectofaddingagroupvelocitymismatchis still unknown. Dark one- and two-soliton solutions are obtained for an integrable system. TheSasa-Satsumaequationisoneintegrablesettingofthemoregeneralhigher- orderNLSequation, whichtakesintoaccounthigher-ordernonlineareffects. Adark one-solitonsolutionisobtained, butitisfoundtohaveonelessarbitraryparameter than its NLS counterpart. Because of this additional constraint, a dark two-soliton solutionisnotfound. Somespecialexpansionseriesmaybeneededforthebilinear formtoobtainmulti-solitonsolutions, andtheseareleftforfuturestudies. Inmicrochannelflows, interfacialeffectssuchastheelectricdoublelayercannot be neglected. This layer will interact with the ions and hence the liquid flow in the microchannel. The associated electric potential is shown to be modelled by the sinh-Poisson equation, a different version of which also has applications in vortex dynamics. Techniques from nonlinear waves are applied to solve for one- to three- solitonsolutions, buttheyarefoundtobethesameasthoseobtainedforthecontexts of vortex dynamics. A comparison is also made between an exact doubly periodic solutionandanapproximatesolutionfromtheDebye-Hu]ckelapproximation, anda considerableamountofdifferenceisfoundinsomeregions. DOI: 10.5353/th_b3051366 Subjects: Solitons Fiber optics Hydrodynamics