Widayat, Widayat, Haris Nu’man Aulia, H Hadiyanto, and Setia Budi Sasongko. 2015. “Kinetic Study on Ultrasound Assisted Biodiesel Production from Waste Cooking Oil”. Journal of Engineering and Technological Sciences 47 (4):374-88. https://doi.org/10.5614/j.eng.technol.sci.2015.47.4.3.