An information retrieval system uses phrases to index, retrieve, organize and describe documents. 1 wt % unstable sulfur compounds is treated in a reaction zone at low temperature to convert at least 50 wt % of the unstable sulfur compounds contained therein. The cover includes a rim coupled with the bearing outer ring, a radially-extending end wall spaced axially from the shaft end, and an annular side wall extending axially between the end wall and the rim. The well has a varying depth in the substrate. A skew factor may further be derived to represent the excess capacity required on the first system due to the imbalance of the workload across multiple computers.