Can my fallout 3 mods be used in fallout new Vegas

Nope. Fallout 3 and Fallout: New Vegas are completely different games, sure they are in the same title and the same game engine, but the configurations and in-outs are different for both games, so you cannot simply apply a mod you used for Fallout 3 and try to run it on Fallout: New Vegas. You may be able to find mods that match your Fallout 3 mods for New Vegas on an assortment of different websites all over the net.