@articleSextro_Schmalhorst_1993, title=Static Behaviour of Drill Strings in Curved Boreholes, volume=73, journal=Zeitschrift für angewandte Mathematik und Mechanik (ZAMM), author=Sextro, Walter and Schmalhorst, B, year=1993, pages=255–257 

@inbookStelter_Sextro_1991, series=International Series of Numerical Mathematics / Internationale Schriftenreihe zur Numerischen Mathematik / S\rquote erie Internationale d’Analyse Num\rquote erique, title=Bifurcations in Dynamic Systems with Dry Friction, volume=97, DOI=10.1007/978-3-0348-7004-7_44, booktitle=Bifurcation and Chaos: Analysis, Algorithms, Applications, publisher=Birkhäuser Basel, author=Stelter, Peter and Sextro, Walter, editor=Seydel, R. and Schneider, F.W. and Küpper, T. and Troger, H.Editors, year=1991, pages=343–347, collection=International Series of Numerical Mathematics / Internationale Schriftenreihe zur Numerischen Mathematik / S\rquote erie Internationale d’Analyse Num\rquote erique