In an apparatus and method for performing secure messaging in a digital communications network, a module sends a registration message including an initial challenge and an identification of itself to the server. The heat-resistant porous layer is provided on one of surfaces of the porous sheet. Oxygen enhances the ability of coal to function as a source of carbon and to be gasified within the blast furnace thereby generating an improved fuel-containing top gas. A pair of the output rotors 72 are disposed to the inside in the radial direction of the pair of input rotors 71, and are fixed to the turbine hub 43. The buoyant viewing platform may include a body portion dimensioned and adapted to accommodate a human user on a top surface, wherein the body portion forms a viewing port for scanning bottom of the aquatic environment, and wherein a canopy may be disposed along the top surface so as to protect the user from the elements. The method constantly compares the unobstructed flow vacuum level with the current vacuum level and sounds an alert or automatically proceeds to the next step in the surgical procedure when the vacuum level approaches the unobstructed vacuum level and remains at that level for a certain duration.