A wheel track closing assembly is described for use with a drive unit of a mechanized irrigation system. The memory device comprises a bit formed using a perovskite material interposed at a cross point of an upper electrode and lower electrode. Alternatively, there may be a plurality of different reference sensors having different filters, or there may be a plurality of different measurement sensors. The grip reduces impact shock and provides a feeling of tackiness while providing increased variation in the physical characteristics of the gripping surface. A method of making an X-ray source is also disclosed.