He is an expert in theoretical physics.

He is an expert in phytopathology, making a significant contribution to agriculture.

Kunminjōon is a book for teaching the correct pronunciation of Hangul.

Infrasound is a type of sound that is inaudible to the human ear.

Debuccalization refers to the phenomenon in phonetics where a specific sound is pronounced outside the oral cavity.

Understanding the concept of 'Ha-line conversion sounds' is important in learning Japanese.

He explained the importance of studying while young, saying 'If you do not study when you are young, it will be difficult to learn when you are old.'