Acidity in water leaching from a mass of sulphide tailings is prevented by de-oxygenating the water prior to entering the mass. The number of persistent connections between first and second data processing units of a system is adjusted according to monitored performance of communications between the nodes. Thus, a first-stage unfinished body is formed. The light beam is polarized in accordance with the aforementioned phase-shift amount of the variable optical unit and converged by an objective lens to radiate the information medium. The base portion is bonded to the elastomeric membrane so as to seal the proximal opening of the balloon.