Energy content of biofuel (J/kg) or equivalent units. Energy density is the amount of energy stored in a fuel per unit volume, expressed in SI units as joule per litre (J/L) or equivalent units. The table below includes entries for popular substances already used for their energy, or being discussed for such use. The second column shows specific energy, the energy content in megajoules per unit of mass in kilograms, useful in understanding the energy that can be extracted from the fuel. The third column in the table lists energy density, the energy content per liter of volume, which is useful for understanding the
UNIT to be some kind of covert counter-terrorist unit. Although the Brigadier originally states that UNIT do not arrest people, as of the 21st century, UNIT has the authority to detain persons indefinitely without trial, appeal, outside contact or legal representation, as experienced by Toshiko Sato before she was recruited to work for the British government by the Torchwood Institute in a flashback in the "Torchwood" episode "Fragments" (2008). The organisation was rearranged by Kate Stewart, the daughter of Brigadier Lethbridge-Stewart. In "The Power of Three" (2012), Kate heads UNIT's scientific research department, which now has authority over the military branch.