They're accompanied at times by some of the youngest children, also residents of the shelter, serving as back-up dancers.
Another worry is that governments will end up extending the life of dirty coal plants to serve as back-up when renewable generation is low or when over-ambitious renewable roll-outs run out of steam.
Neither Roxbury nor Washington use drinking water from the Shepaug, but it is an important part of recreational life, and even serves as back-up water supply in case of fire emergencies.
The separate computers, which serve as back-up to each other, control the plane's rudder - preventing it from making turns that are too sharp - and prevent the aircraft from going too slowly.
The ground borehole heat exchanger serves as back-up air cooler during summer time.
The MCC team which toured Australia was extremely strong in batting, and Leyland served as back-up to the main batsmen.
They also serve as a safety net by establishing and managing captive populations, which essentially serve as back-up reserves for dwindling wild populations.
Evra was initially placed onto the squad to serve as back-up to Abidal, however, after failing to appear in the team's opening 0 0 draw with Romania, there were calls from the French media urging Domenech to insert Evra into the starting line-up at the behest of Abidal.
With that as the headliner and dozens of supporting facts to serve as back-up, the DigitalSportsDesk and its online site, DigitalSportsDesk.com have named the People of Great Britain, the Athletes of Great Britain, the Volunteers of the London Summer Olympic and Paralympic Games as Sports Person(s) of the Year 2012.
And even if the Punggye-ri site is permanently kaput, Bermudez and Lewis both noted that North Korea has a healthy mining industry and no shortage of mountains that could serve as back-up test sites should they feel the need to blow up another bomb.
Eight single colonies of each sample were picked and re-cultured on a new LB plate; three of these single colony clones were sequenced to determine the allelic forms of S1, S3, S5 and S24, and the other five served as back-ups.
