Characterisation of particle concentration at the respiration zone in an office environment using four different types of ventilation systems - Pereira, Marcelo Luiz; Graudenz, Gustavo Silveira; Felix, Victor Barbosa; Tribess, Arlindo (Feira e Congresso de Ar Condicionado, Refrigeração, Aquecimento e Ventilação do Mercosul, 2006)