Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:The gradient of VS with pressure becomes less steep above 40 GPa in contrast to its trend at lower pressures, which appears similar to the behavior of SiO2 glass (Murakami and Bass 2010) and MgSiO3 glass (Murakami and Bass 2011) (Fig.
Category: