If my keyword search is not resulting in useful documents, how can I improve it?

In order to facilitate searching, keywords and search terms should be short and concise. Please try to avoid long, cumbersome phrases, acronyms, and vague concepts such as “analysis” or “modeling.” The search terms should be able to immediately convey the nature of your paper to a person using the PQDT database. We suggest you try to avoid using acronyms as keywords because the same acronym may apply to more than one concept. For example, “PCB” can mean both “printed circuit board” and “polychlorinated biphenyl.”