He is an expert in ornithology, studying types of birds all over the world.

He has a deep interest in etymology.

He is an expert in theoretical physics.

He is an expert in electrodynamics.

Demography is a branch of social science that studies the structure, distribution, and changes in human population.

He has a deep interest in etymology.

My mother has been suffering from temporomandibular joint dysfunction for many years.

He is an expert in dynamics.

He is an expert in dynamics, helping to solve complex problems in physics.

He is passionate about his research in futurology.