J. Freitas et al.,  "Can ultrasonic doppler help detecting nasality for silent speech interfaces?:  An exploratory analysis based on alignement of the doppler signal with velum aperture information from real-time MRI", in Proc. of the Int. Conf. on Physiological Computing Systems (PhyCS 2014), Andreas Holzinger ; Stephen Fairclough; Dennis Majoe,; Hugo Plácido da Silva , Ed., Lisboa, SciTePress, 2014