4,82,538; 4,901,387; 4,914,760; 4,942,635; 4,967,431; 4,995,124; 5,007,124; 5,025,519; 5,029,352; 5,036,559; 5,070,560; 5,142,717; 5,252,278; 5,446,933

5,070,560; 5,412,821; 5,487,196; 5,649,331; 5,652,985; 5,699,570; 6,036,271