He is an expert in theoretical physics.

He is an expert in biophysics.

He is an expert in nuclear physics.

He is an expert in nuclear physics and has won many awards in the field.

He is an expert in astrophysics, and his research is highly valued around the world.

He is an expert in applied physics.

This particle is very small.

He is known as a person with learning.

He received the letter challenging him to a duel and began preparing for the duel.

Gender roles are an important element in defining individual behavior in society.