Anheier, Norman C.; Bernacki, Bruce E. & Krishnaswami, Kannan. FY 2006 Miniature Spherical Retroreflectors Final Report, report, December 28, 2006; (https://digital.library.unt.edu/ark:/67531/metadc886707/m1/1/: accessed October 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .