TARDIS 2005–10, the roundels are built into hexagonal recesses in the walls. Ever since the TARDIS was redesigned at the beginning of the 2010 series, there have been a range of different roundel designs around the console room. These include circular holes that are recessed deep into the walls, hexagonal holes that are lit from behind each face, round indents with brass rings around the outside, and a glass centre that is illuminated blue. In "The Day of the Doctor", when the TARDIS' control room briefly appears as the War Doctor's room, the Eleventh Doctor points out to the Tenth Doctor
Two-fluid model Two-fluid model Two-fluid model is a macroscopic traffic flow model to represent traffic in a town/city or metropolitan area, put forward in the 1970s by Ilya Prigogine and Robert Herman. There is also a two-fluid model which helps explain the behavior of superfluid helium. This model states that there will be two components in liquid helium below its lambda point (the temperature where superfluid forms). These components are a normal fluid and a superfluid component. Each liquid has a different density and together their sum makes the total density, which remains constant. The ratio of superfluid density to the total