Physics
A NOT gate can be implemented by:

A single diode
Two diodes
A single transistor
A single resistor

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Physics
Radiocarbon is produced in the atmosphere as a result of

Action of solar radiations particularly cosmic rays on carbon dioxide present in the atmosphere.
Collision between fast neutrons and nitrogen nuclei present in the atmosphere.
Lightning discharge in atmosphere.
Action of ultraviolet light from the sun on atmospheric oxygen.

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