Prior to writing the research proposal required by the formal application, prospective applicants should contact the Group Leader, Michael Moldover or another research advisor. More information is available from the NIST website and from the National Research Council . Thus, theoretical values can now be used to calibrate the experimental apparatus used for measuring these quantities. We are investigating the feasibility of combining ab initio calculations with measurements of the dielectric constant of helium to establish a standard of pressure in the vicinity of 1 Mpa and to measure the difference between the International Temperature Scale of 1990 and the thermodynamic scale. Gases 50.83.61.B1678 K.A. Gillis and M.R. Moldover Conventional instruments for measuring the transport properties of gases are fragile and expensive to use.
Acoustic instruments can be robust and accurate under a wide range of conditions.
NIST is optimizing the design of these instruments and developing sophisticated algorithms for interpreting the data obtained with them. To measure the viscosity, we have refined the Greenspan acoustic viscometer. This compact device is comprised of two cavities connected by a long narrow duct. The gas oscillates between the cavities passing through the duct where most of the viscous dissipation occurs. One challenge is to develop comparable acoustic instruments optimized to measure the thermal conductivity of gases and the mutual diffusion coefficient and thermodiffusion ratio in gas mixtures.