الفهرس 
Introduction
Macroscopic neutralityOnly 14 pages are availabe for public view
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Abstract
The effect of variable dust charge, dust temperature and trapped electrons on small amplitude dust acoustic waves (DAWs) is investigated. It is found that both compressive and rarefactive solitons as well as double layers (DLs) exist, depending on the nonisothermality parameter. At critical densities,Korteweg de Vries (KdV) and further. MKdV (FMKdV) equations are obtained. Employing quasipotential analysis, the Sagdeev potential equation for different cases has been deduced. The Sagdeev potential equation shows that the ordering of nonisothermality in the dusty plasma plays a unique role. The solution reveals the coexistence of both compressive and rarefactive solitary waves. In addition, for certain plasma parameters, the solitary wave disappears and a DL is expected. With twotemperature ions in dusty plasma, the effects of variable dust charge on smallamplitude DA solitons and largeamplitude DAWs are investigated. It is found that both compressive and rarefactive solitons as well as DLs exist. The inclusion of small, but finite, number density of the lower temperature ions provides the possibility of the coexistence of rarefactive with compressive dust density solitary waves. The amplitudes of those dust solitary waves become smaller. The effects of variable dust charge, dust temperature and an arbitrary streaming ion beam on small amplitude DAWs are also investigated. It is found that both compressive and rarefactive solitons as well as DLs exist. There exists a critical ion beam velocity below which the ion beam is unable to generate solitons. KdV equations with thirdand fourthorder nonlinearity at the critical values are derived and the properties of DA solitary waves are discussed. The quite dense positive ion, the dust temperature, the ion beam density, mass ratio and temperature govern the existence of DAWs. These findings of this investigation may be useful in understanding laboratory plasma phenomena and astrophysical situtions.