double layers подвiйнi шари 05C10 05C25 05C40 Original contributions Sagdeev potential function Sagdeev potential method concentrations of positrons and negative ions connectivity cyclic group dicyclic group dihedral group double-layer solutions fast-mode phase plane trajectories fast-mode solitary waves heavier negative ions isothermal positrons iзотермiчнi позитрони phase velocity planarity power graph stream velocities temperatures of positive and negative ions two-temperature non-isothermal and isothermal electrons two-temperature non-isothermal electrons two-temperature nonisothermal electron plasmas бiльш важкi негативнi iони двотемпературнi неiзотермiчнi та iзотермiчнi електрони двотемпературна неiзотермiчна електронна плазма