A polyurethane coating made by: applying to a surface a polyol composition and an isocyanate composition, such that a mixture of the polyol composition and the isocyanate composition is formed during the application; and allowing the mixture to cure to the polyurethane coating. The spanning tree producing portion produces a spanning tree of the network whenever it receives connection information sent from slave nodes of the network. The data storage system includes a control processor configured to establish a timer synchronization signal and distribute the timer synchronization signal to the processing systems. The laser scalpel includes a housing having first and second fiber optic cables extending therethrough. The surface light source unit provides uniform illumination and high brightness for a liquid crystal display panel. Excess wastewater passing through the zone is collected and reintroduced.