1. MATRILUB -Materials-Tribology-Lubrication, Limonenstr. 16, Berlin 12203, Germany (Corresponding author), e-mail: m.woydt@matrilub.de, http://orcid.org/0000-0002-0599-0109
2. Koehler Instrument Company, Inc., 1595 Sycamore Ave., Bohemia, NY 11716-1796, USA