DiPerna was known for his work on nonlinear partial differential equations, especially those that are important in fluid dynamics and the kinetic theory of gases. Probably his best known work is his development and application of the method of compensated compactness. This is a very powerful method for controlling oscillation and thereby proving existence theorems. DiPerna proved existence of weak solutions in the large for the equations of compressible gas dynamics and obtained important results concerning the uniqueness of solutions, their large time behavior, and their local regularity as elements of the appropriate abstract spaces.[3]
In the last part of his career he worked with Pierre-Louis Lions on integro-differential equations in the kinetic theory of gases (Cauchy problem for Boltzmann equations) and the plasma physics generalization (Vlasov equation). He also worked on singularities in compressible flow. DiPerna with Andrew Majda began in 1986 research on the question of the existence of solutions to the Euler equations in two dimensions with initial conditions that are found in the evolution of vortex sheets. DiPerna and Majda introduced the Concentration-Cancellation Method.[4][5]
Diperna, Ronald J. (1973). "Global solutions to a class of nonlinear hyperbolic systems of equations". Comm. Pure Appl. Math. 26: 1–28. doi:10.1002/cpa.3160260102.
with Pierre-Louis Lions: Diperna, R. J.; Lions, P. L. (1989). "Global weak solutions of Vlasov-Maxwell systems". Comm. Pure Appl. Math. 42 (6): 729–757. doi:10.1002/cpa.3160420603.
with Pierre-Louis Lions: Diperna, R. J.; Lions, P. L. (1989). "On the Cauchy problem for Boltzmann equations: global existence and weak stability". Annals of Mathematics. 130 (2): 321–366. doi:10.2307/1971423. JSTOR1971423.
with Lions: "Ordinary differential equations, Sobolev spaces and transport theory". Inventiones Mathematicae. 98: 511–547. 1989. doi:10.1007/BF01393835. S2CID123097609.
^DiPerna, R.; Majda, A. (1987). "Concentrations in regularizations for 2-D incompressible flow". Communications on Pure and Applied Mathematics. 40 (3): 301–345. doi:10.1002/cpa.3160400304.
^DiPerna, R.; Majda, A. (1988). "Reduced Hausdorff dimension and concentration-cancellation for two-dimensional incompressible flow". J. Amer. Math. Soc. 1 (1): 59–95. doi:10.2307/1990967. JSTOR1990967.