J. Freitas et al.,  "Automatic speech recognition based on ultrasonic doppler sensing for European Portuguese", in Advances in speech and language technologies for iberian languages: IberSPEECH 2012, Conf. Proc., Doroteo Torre Toledano, Alfonso Ortega Giménez , António Teixeira, Joaquín González Rodríguez, Luis Hernández Gómez, Rubén San Segundo Hernández, Daniel Ramos Castro, Ed., Heidelberg, Springer, 2012, vol. 328, pp. 227-236