# David Harker

david harker (October 19, 1906 – February 27, 1991) was an American medical researcher who according to The New York Times was "a pioneer in the use of X-rays to decipher the structure of critical substances in the life process of cells".He is also well known for Harker–Kasper inequalities (statistical relationships between the phases of structure factors), which he devised in collaboration with John S. Kasper. Harker made seminal discoveries in the field of chemical crystallography.His lab solved the structure of the pancreatic enzyme ribonuclease A, the third protein structure ever solved by protein crystallography. Harker was a member of the National Academy of Sciences, director of the protein structure program at the Polytechnic Institute of Brooklyn, director of the Center for Crystallographic Research at Roswell Park Comprehensive Cancer Center, and the head of the crystallography division of General Electric.