An airlock is a room or compartment which permits passage between environments of differing atmospheric pressure or composition, while minimizing the changing of pressure or composition between the differing environments.
An airlock consists of a chamber with two airtight doors or openings, usually arranged in series, which do not open simultaneously. Airlocks can be small-scale mechanisms, such as those used in fermenting, or larger mechanisms, which often take the form of an antechamber.
A kleroterion (Ancient Greek: κληρωτήριον, romanized: klērōtērion) was a randomization device used by the Athenian polis during the period of democracy to select citizens to the boule, to most state offices, to the nomothetai, and to court juries.
The kleroterion was a slab of stone incised with rows of slots and with an attached tube. Citizens' tokens—pinakia—were placed randomly in the slots so that every member of each of the tribes of Athens had their tokens placed in the same column. There was a pipe attached to the stone which could then be fed dice that were coloured differently (assumed to be black and white) and could be released individually by a mechanism that has not survived to posterity (but is speculated to be by two nails; one used to block the open end and another to separate the next die to fall from the rest of the dice above it, like an airlock.) When a die was released, a complete row of tokens (so, one citizen from each of the tribes of Athens) was either selected if the die was coloured one colour, or discarded if it was the alternate colour. This process continued until the requisite number of citizens was selected.
Space Shuttle Columbia (OV-102) was a Space Shuttle orbiter manufactured by Rockwell International and operated by NASA. Named after the first American ship to circumnavigate the globe, and the female personification of the United States, Columbia was the first of five Space Shuttle orbiters to fly in space, debuting the Space Shuttle launch vehicle on its maiden flight on April 12, 1981 and becoming the first spacecraft to be re-used after its first flight when it launched on STS-2 on November 12, 1981. As only the second full-scale orbiter to be manufactured after the Approach and Landing Test vehicle Enterprise, Columbia retained unique external and internal features compared with later orbiters, such as test instrumentation and distinctive black chines. In addition to a heavier aft fuselage and the retention of an internal airlock throughout its lifetime, these made Columbia the heaviest of the five spacefaring orbiters: around 1,000 kilograms (2,200 pounds) heavier than Challenger and 3,600 kilograms (7,900 pounds) heavier than Endeavour when originally constructed. Columbia also carried ejection seats based on those from the SR-71 during its first six flights until 1983, and from 1986 onwards carried an imaging pod on its vertical stabilizer.
During its 22 years of operation, Columbia was flown on 28 missions in the Space Shuttle program, spending over 300 days in space and completing over 4,000 orbits around Earth. NASA's flagship orbiter, Columbia often flew flights dedicated to scientific research in orbit following the loss of Challenger in 1986. Columbia was used for eleven of the fifteen flights of Spacelab laboratories, all four United States Microgravity Payload missions, and the only flight of Spacehab's Research Double Module. Columbia flew many of the longest duration space shuttle missions, all dedicated to scientific research. The only space shuttle that could rival Columbia's long missions was Endeavour, which flew the STS-67 mission that lasted for nearly 17 days. In 1992, NASA modified Columbia to be able to fly some of the longest missions in the Shuttle Program history using the Extended Duration Orbiter pallet. The orbiter used the pallet in thirteen of the pallet's fourteen flights, which aided lengthy stays in orbit for scientific and technological research missions. The longest duration flight of the Shuttle Program, STS-80, was flown with Columbia in 1996, at over 17 days in orbit. Columbia was also used to deploy the first ever satellites into orbit by the Shuttle on STS-5, retrieve the Long Duration Exposure Facility and deploy the Chandra observatory, which was the heaviest payload ever carried by the Space Shuttle. Columbia also carried into space the first female commander of an American spaceflight mission, the first ESA astronaut, the first female astronaut of Indian origin, and the first Israeli astronaut.
Air-free techniques refer to a range of manipulations in the chemistry laboratory for the handling of compounds that are air-sensitive. These techniques prevent the compounds from reacting with components of air, usually water and oxygen; less commonly carbon dioxide and nitrogen. A common theme among these techniques is the use of a fine (10–10 Torr) or high (10–10 Torr) vacuum to remove air, and the use of an inert gas: preferably argon, but often nitrogen.
The two most common types of air-free technique involve the use of a glovebox and a Schlenk line, although some rigorous applications use a high-vacuum line. In both methods, glassware (often Schlenk tubes) are pre-dried in ovens prior to use. They may be flame-dried to remove adsorbed water. Prior to coming into an inert atmosphere, vessels are further dried by purge-and-refill — the vessel is subjected to a vacuum to remove gases and water, and then refilled with inert gas. This cycle is usually repeated three times or the vacuum is applied for an extended period of time. One of the differences between the use of a glovebox and a Schlenk line is where the purge-and-refill cycle is applied. When using a glovebox the purge-and-refill is applied to an airlock attached to the glovebox, commonly called the "port" or "ante-chamber". In contrast when using a Schlenk line the purge-and-refill is applied directly to the reaction vessel through a hose or ground glass joint that is connected to the manifold.