A few shots from the studio shoot I did with Elise recently. The technique involved using the camera on a tripod, opening the shutter for approximately 2 seconds and varying the balance of ambient/strobe lighting.
I used a Elinchrom RX500 fired through a gridded beauty dish camera right, with a gelled & gridded reflector providing the rim light from behind left. Camera settings ISO 125 @f16. I fired the flash manually a second time with the remote trigger to get the double exposure. The amount of ambient determined the movement flow between the two.