Kawahara Nagaaki, Yamamoto Shigeki, Osamoto Yoshio, Igarashi Hiroshi, Nakagawa Hidenori. Relevance of the results of a study achievement test carried out by Institute of National College of Technology Japan and the mathematical grades in Ibaraki National College of Technology. 2012. 47. 19-22
Kawahara Nagaaki, Igarashi Hiroshi, Nakagawa Hidenori, Yamamoto Shigeki. Construction of finite element used to search for minute cracks in composite materials. Research reports of Ibaraki National College of Technology. 2011. 46. 23-30
Kawahara Nagaaki, Yamamoto Shigeki, Osamoto Yoshio, Igarashi Hiroshi, Nakagawa Hidenori. An Analysis of Achievement Test of Mathematics for The First and Second Year Students of Ibaraki National College of Technology. Research reports of Ibaraki National College of Technology. 2011. 46. 31-35