Norio Nasu (Kobe City University of Foreign Studies), Takayuki Akimoto (Kogakuin University), Yusuke Yoda (Toyo Gakuen University) and I have published a paper in the proceedings of Glow in Asia XIII, whose title is “The Categorial Status of Embedded Questions in Japanese”.
http://ling.cuhk.edu.hk/glowxiii/Proceedings_of_GLOW-In_Asia_XIII_v2.pdf