JD has a broad interest in computational cosmology. His research is focused on the development and application of numerical techniques for large-scale cosmological structure formation simulations. This includes both N-body as well as hydrodynamic methods in order to gain insight into various astrophysical phenomena including dark energy, neutrinos, substructure, and reionization. He is one of the main developers of HACC with an emphasis on integrating robust hydrodynamical modeling for use on next-generation Exascale platforms. JD has a keen interest in scientific data visualization; a collection of animations from his recent simulation endeavors can be found on his professional website.