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tally and theoretically [27—29]. Sound wave is a pressure wave propagates

by collisions between air molecules. Furthermore, in no neutrals plasma

with a very few collisions, an identical phenomena is produced and called
ion acoustic wave. Ion acoustic waves are  low frequency vibration and

electrons must be moved. More specifically, ions are presented in most

models of plasma. They lead to existence of various low frequency os-

cillations which otherwise not propagate on the electron—positron plasma
models. Ion acoustic solitons arise due to the balance of nonlinearity

and medium dispersion. The structures of IAWs have been inspected in

electron - positron (e-p) plasma [30-34], electron - positrion - ion (e-p-
i) plasmas [35-37] and relativistic behaviors [38-41]. Ion acoustic waves

have been observed in nonthermal plasma using Viking spacecraft [42]

and Freja satellite [43]. Accordingly, Cairns et al. [44, 45] confirmed that,
the nonthermal electrons distribution changed the nature of ion solitary

wave structures observed by Viking and Freja satellites [42, 43]. These

waves are found in ionosphere and laser-plasma [46].

1.7 Dust Acoustic Waves (DAWs)

It is well known that, dusty plasma is defined as "a normal electron-ion

plasma with an additional charged component of micron- or submicron-

sized particulates". Dusty plasmas are found in many astrophysical envi-
ronments such as cometary tails and planetary rings. Also, they were used

in laboratory devices and industrial processes [47-49]. For typical labora-

tory and space plasmas, the condition  ¿   ¿  is satisfied, where  

are the grain radius and the average inter-grain distance, respectively. For
  ¿ , the dusty plasma is considered as a dust in a plasma as shown in

Fig.(1.1) whereas for  ¿  , a true dusty plasma shown in Fig.(1.1).

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