|Supercritical fluids have the low viscosity of a gas and the high density of a liquid, making it impossible to liquefy the matter using any amount of pressure. However, it is possible to go from a gas to a liquid without crossing the boundary between the vapor and liquid phase using a supercritical fluid just by lowering the temperature of the liquid.
The densities and viscosity of a supercritical fluid are subject to change when pressure or temperature is tampered with, and the supercritical fluid of a substance can have very different properties than the regular fluids. For instance, water that is supercritical differs from regular water in the fact that it is non-polar and acidic.
Open access to the scientific literature means the removal of barriers (including price barriers) from accessing scholarly work. There are two parallel roads towards open access: Open Access articles and self-archiving. Open Access articles are immediately, freely available on their Web site, a model mostly funded by charges paid by the author (usually through a research grant). The alternative for a researcher is self-archiving (i.e., to publish in a traditional journal, where only subscribers have immediate access, but to make the article available on their personal and/or institutional Web sites (including so-called repositories or archives)), which is a practice allowed by many scholarly journals.
Open Access raises practical and policy questions for scholars, publishers, funders, and policymakers alike, including what the return on investment is when paying an article processing fee to publish in an Open Access articles, or whether investments into institutional repositories should be made and whether self-archiving should be made mandatory, as contemplated by some funders.