U.S. Patent number 6,404,341 http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=6404341.PN.&OS=PN/6404341&RS=PN/6404341 http://patimg1.uspto.gov/.piw?Docid=06404341&homeurl=http%3A%2F%2Fpatft.uspto.gov%2Fnetacgi%2Fnph-Parser%3FSect1%3DPTO1%2526Sect2%3DHITOFF%2526d%3DPALL%2526p%3D1%2526u%3D%25252Fnetahtml%25252FPTO%25252Fsrchnum.htm%2526r%3D1%2526f%3DG%2526l%3D50%2526s1%3D6404341.PN.%2526OS%3DPN%2F6404341%2526RS%3DPN%2F6404341&PageNum=&Rtype=&SectionNum=&idkey=NONE&Input=View+first+page