Sentence:  This project was carried out under sponsorship of the Ballistic Missile Division of the Air Research and Development Command , U. S. Air Force , and had as its goal the investigation of the transport by <WSD>diffusion</WSD> of the heat energy of chemical binding . 
Meaning of the word marked with <WSD> tags:  (physics) the process in which there is movement of a substance from an area of high concentration of that substance to an area of lower concentration