Concentrating dilute aerosols by electrostatic methods / J.F. van der Wal ; uitg. R.V.O./T.N.O. Chemisch Laboratorium use of semi-micro techniques in infrared spectroscopy / F.H. Meppelder ; uitg. R.V.O./T.N.O. Chemisch Laboratorium efficiency of electrostatic air filters in a SPF rat breeding unit / J.L.F. Gerbrandy, D. van der Waay and H.C. Bartlema