He then saves the wounded soldier by unzipping his navel and retrieving the shell inside. Topoisomerase is the enzyme that aids in the unzipping and recombination of the double-helix. When the accused was unzipping the bag, the officer went to touch the bag. In situ unzipping of boron nitride nanotubes to nanoribbons was achieved by Li et al. Boron nitride nanosheets may also be synthesized by the unzipping of boron nitride nanotubes (BNNT). Built-in unzipping is used when running DOS virus scanners. GNRs can also be produced by "unzipping" or axially cutting nanotubes. Prior to performing the downstream applications several unzipping and rezipping cycles are performed.