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Search Publications by

Keith A Gillis (Fed)

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Displaying 26 - 44 of 44

Amplification of the optical absorption cross section for aerosols of soot with a nonabsorbing coating from photoacoustic measurements

May 13, 2011
Pedro Bueno, Daniel K. Havey, George W. Mulholland, Joseph T. Hodges, Keith A. Gillis, Russell R. Dickerson, Michael R. Zachariah
A quantitative understanding of the absorption and scattering properties of mixed soot and aerosol particles is necessary for evaluating the Earth's energy balance. Uncertainty in the net radiative forcing of atmospheric aerosols is relatively large and

Standard Photoacoustic Spectrometer: Model and Validation using O2 A-Band Spectra

June 30, 2010
Keith A. Gillis, Daniel K. Havey, Joseph T. Hodges
We model and measure the absolute response of an intensity-modulated photoacoustic spectrometer comprising a 10 cm long resonator and having a Q-factor of approximately 30. We present a detailed theoretical analysis of the system and predict its response

Cylindrical Acoustic Resonator for the Re-determination of the Boltzmann Constant

June 1, 2010
J.T. Zhang, H. Lin, X.J. Feng, Keith A. Gillis, Michael R. Moldover
We describe progress towards re-determining the Boltzmann constant kB using two fixed-path, gas-filled, cylindrical, acoustic cavity resonators. The longitudinal acoustic resonance modes of a cylindrical cavity have lower quality factors Q than the radial

Perturbations from Ducts on the Modes of Acoustic Thermometers

September 1, 2009
Keith A. Gillis, Michael R. Moldover, Hong Lin
We examine the perturbations of the modes of an acoustic thermometer caused by circular ducts used either for gas flow or as acoustic waveguides coupled to remote transducers. We calculate the acoustic admittance of circular ducts using a model based on

Bulk Viscosity of Stirred Xenon Near the Critical Point

November 1, 2005
Keith A. Gillis, Iosif I. Shinder, Michael R. Moldover
Following Gillis, Shinder, and Moldover [Phys. Rev. E 70, 021201 (2004)], we deduce the thermophysical properties of near-critical xenon from measurements of the frequencies and half-widths of the acoustic resonances of xenon maintained at its critical

Thermoacoustic Boundary Layers Near the Liquid-Vapor Critical Point

August 1, 2004
Keith A. Gillis, Iosif I. Shinder, Michael R. Moldover
We measure and calculate the sound attenuation within thermoacoustic boundary layers between solid surfaces and xenon at its critical density rc as the reduced temperature t=(T -Tc)/Tc approaches zero. (Tc is the critical temperature.) Using the singular

The Viscosity of Seven Gases Measured with a Greenspan Viscometer

November 1, 2003
John J. Hurly, Keith A. Gillis, J B. Mehl, Michael R. Moldover
We determined the viscosity of seven gases (Ar, CH4, C3H8, N2, SF6, CF4, C2F6) by interpreting frequency-response data from a Greenspan acoustic viscometer with a detailed model developed by Gillis, Mehl, and Moldover. The model contains a parameter er

Theory of the Greenspan Viscometer

July 1, 2003
Keith A. Gillis, J B. Mehl, Michael R. Moldover
We present a detailed acoustic model of the Greenspan acoustic viscometer, a practical instrument for accurately measuring the viscosity eta of gases. As conceived by Greenspan, the viscometer is a Helmholtz resonator composed of two chambers coupled by a

Acoustic Measurements in Gases, Chapter 10

September 15, 2001
Michael R. Moldover, Keith A. Gillis, John J. Hurly, J B. Mehl, J Wilhelm
Cylindrical acoustic resonators developed at the National Institute of Standards and Technology (NIST) are routinely used to measure the speed of sound in gases with uncertainties of 0.01% or less. The pressure dependence of the data is fitted with model

An Improved Greenspan Acoustic Viscometer

September 1, 2000
J Wilhelm, Keith A. Gillis, J B. Mehl, Michael R. Moldover
We improved the Greenspan acoustic viscometer (double Helmholtz resonator) to measure the viscosity of gases at temperatures from 250 K to 400 K and at pressures up to 3.4 MPa. In anticipation of handling corrosive gases, all wetted parts of the apparatus

Primary Acoustic Thermometer for Use Up to 800 K

April 1, 1999
Dean C. Ripple, Dana R. Defibaugh, Keith A. Gillis, Michael R. Moldover
Primary acoustic thermometers determine the thermodynamic temperature of a monatomic gas from measurements of the speed of sound in the gas. Here, we describe the design and construction of an acoustic thermometer designed to operate at temperatures up to

Acoustic Methods for Transport Properties Measurements in Gases

June 1, 1998
Keith A. Gillis, J B. Mehl, Michael R. Moldover
Two novel acoustic resonators have been developed, one for measuring the viscosity and a second for measuring the Prandtl number of gases. For viscosity measurements, we use a double Helmholtz resonator called the Greenspan viscometer. The Greenspan