Activator

Activator may refer to:

Enzyme activator

Enzyme activators are molecules that bind to enzymes and increase their activity. They are the opposite of enzyme inhibitors. These molecules are often involved in the allosteric regulation of enzymes in the control of metabolism. An example of an enzyme activator working in this way is fructose 2,6-bisphosphate, which activates phosphofructokinase 1 and increases the rate of glycolysis in response to the hormone insulin.

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Activator (phosphor)

In phosphors and scintillators, the activator is the element added as dopant to the crystal of the material to create desired type of nonhomogeneities.

In luminescence, only a small fraction of atoms, called emission centers or luminescence centers, emit light. In inorganic phosphors, these inhomogeneities in the crystal structure are created usually by addition of a trace amount of dopants, impurities called activators. (In rare cases dislocations or other crystal defects can play the role of the impurity.) The wavelength emitted by the emission center is dependent on the atom itself, its electronic configuration, and on the surrounding crystal structure.

The activators prolong the emission time (afterglow). In turn, other materials (such as nickel) can be used to quench the afterglow and shorten the decay part of the phosphor emission characteristics.

The electronic configuration of the activator depends on its oxidation state and is crucial for the light emission. Oxidation of the activator is one of the common mechanisms of phosphor degradation. The distribution of the activator in the crystal is also of high importance. Diffusion of the ions can cause depletion of the crystal from the activators with resulting loss of efficiency. This is another mechanism of phosphor degradation.

Laydown delivery

Laydown delivery is a mode of deploying a free-fall nuclear weapon in which the bomb's fall is slowed by parachute so that it actually lands on the ground before detonating. Laydown delivery requires that the weapon's case be reinforced so that it can survive the impact, and generally involves a time-delay fuse to trigger detonation. Laydown mode can be used to increase the effect of the weapon's blast on built-up targets such as submarine pens, or to transmit a shock wave through the ground to attack deeply buried targets. An attack of this type produces large amounts of radioactive fallout.

It has the additional advantage of allowing the carrier aircraft to fly very low and still get away without being destroyed in the detonation. This is particularly important where high-yield nuclear weapons such as the B41 and B53 nuclear bombs are concerned. The low altitude delivery also helps hide the aircraft from surface-to-air missiles. It was for this reason that laydown was selected for the Vickers Valiant bomber of the Royal Air Force, as this design became increasingly vulnerable to Soviet weapons, especially the SA-2 missile. Laydown was referred to as "Equipment 2 Foxtrot" in RAF parlance, with Echo referring to toss bombing and Hotel to a particular climbing delivery method used by the Avro Vulcan.