 Complete the following phrase:  In May 1941, Zeldovich worked with Khariton in constructing a theory, on the kinetics of nuclear reactions in the presence of the critical conditions. The work of Khariton and Zeldovich was extended into theories of ignition, combustion and detonation; these accounted for features which had not previously been correctly predicted, observed, nor explained. The modern theory of detonation accordingly is called the Zeldovich-von Neumann-Dohring, or ZND, theory, and its development involved tedious fast neutron calculations; this work had been delayed, due to the 