Magnetic twist and writhe of active regions - On the origin of deformed flux tubes M. C. López Fuentes, P. Démoulin, C. H. Mandrini, A. A. Pevtsov and L. van Driel-Gesztelyi A&A, 397 1 (2003) 305-318 Published online: 11 December 2002 DOI: 10.1051/0004-6361:20021487