A lithographic apparatus includes an illumination system for providing beam of radiation, and a support structure for supporting a patterning device. The gravity gradiometer comprises a pair of first and second transversely arranged sensor masses that are arranged for movement about an axis and relative to each other in response to a gravity gradient. An estimated current position is generated based on the output position outputted at the latest update time. The sole is integrally attached to the outer casing and includes a foam inner sole, an outer sole having a non-skid grip material, a contoured wedge therebetween having an adjustable rubber build-up and a rounded bottom. Accordingly, an access cycle time of a semiconductor memory can be reduced. The present invention further relates to a superabsorbent polymer comprising an internal crosslinker agent comprising a silane compound comprising at least one vinyl group or one allyl group attached to a silicon atom, and at least one Si\u2014O bond.