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Search Publications by: Michael R Moldover (Assoc)

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Displaying 76 - 100 of 161

Capacitors and Electromagnetic Resonators for Gas Metrology

May 1, 2007
Author(s)
Michael R. Moldover, James W. Schmidt
Gas-filled capacitors are being used as primary thermometers and they show promise as primary pressure standards and for measuring the Boltzmann constant. With these metrological applications in mind, we discuss the advantages and disadvantages of audio

Transport Properties of Argon at Zero Density From Viscosity-Ratio Measurements

April 1, 2006
Author(s)
E May, Michael R. Moldover, Robert F. Berg, John J. Hurly
We determined the zero-density viscosity and thermal conductivity of argon with an uncertainty of only 0.039 % in the temperature range 200 K to 400 K. Our results will improve: (1) the argon-argon interatomic potential, (2) calculated boundary-layer

Acoustic Thermometry: New Results From 273 K to 77 K and Progress Towards 4 K

January 1, 2006
Author(s)
Laurent Pitre, Michael R. Moldover, Weston L. Tew
We used a quasi-spherical cavity as an acoustic and microwave resonator to measure the thermodynamic temperatures T of the triple points of mercury, argon, neon, and equilibrium hydrogen, and to measure the difference T - T90, in the range 7 K to 273 K.

Relaxation Effects in Small Critical Nozzles

January 1, 2006
Author(s)
Aaron N. Johnson, C L. Merkle, Michael R. Moldover, John D. Wright
We computed the flow of four gases (He, N 2, CO 2, and SF 6) through a critical nozzle by augmenting traditional computational fluid dynamics (CFD) with a rate equation that accounts for τ relax, a species-dependent relaxation time that characterizes the

Bulk Viscosity of Stirred Xenon Near the Critical Point

November 1, 2005
Author(s)
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
Author(s)
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

Gas Flowmeter Calibrations with the 34 L and 677 L PVTt Standards

June 23, 2004
Author(s)
John D. Wright, Aaron N. Johnson, Michael R. Moldover, Gina M. Kline
This document provides a description of the 34 L and 677 L pressure, volume, temperature, and time (PVTt) primary gas flow standards operated by the National Institute of Standards and Technology (NIST) Fluid Flow Group. These facilities are used to

Designing Quasi-Spherical Resonators for Acoustic Thermometry

June 1, 2004
Author(s)
J B. Mehl, Michael R. Moldover, J Pitre
We describe a quasi-spherical, noble-gas-filled cavity designed to determine the thermodynamic temperature of the gas from measurements of the frequencies and the half-widths of microwave and acoustic resonances in the cavity. The quasi-spherical shape

The Viscosity of Seven Gases Measured with a Greenspan Viscometer

November 1, 2003
Author(s)
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

Volumetric Gas Flow Standard with Uncertainty of 0.02% to 0.05%

November 1, 2003
Author(s)
John D. Wright, Michael R. Moldover, Aaron N. Johnson, A Mizuno
A new pressure, volume, temperature, and time (PVTt) primary gas flow standard for calibrating flowmeters has an expanded uncertainty (k = 2) of between 0.02% and 0.05%. The standard diverts a steady flow into a collection tank of known volume during a

Comment On 'General Principles for the Definition of the Base Units in the SI'

October 1, 2003
Author(s)
Michael R. Moldover, Dean C. Ripple
Recently, Kose et al. proposed general principles that should guide any future discussions regarding the redefinition of the SI base units and they illustrated their principles with an example of a revised SI. Part of their example (redefinition of the

Progress in Primary Acoustic Thermometry at NIST: 273 K to 505 K

September 1, 2003
Author(s)
Gregory F. Strouse, Dana R. Defibaugh, Michael R. Moldover, Dean C. Ripple
The NIST Acoustic Thermometer determines the thermodynamic temperature by measuring the speed of sound of argon in a spherical cavity. We obtained the thermodynamic temperature of three fixed points on the Interna-tionalTemperature Scale of 1990: the

Techniques for Primary Acoustic Thermometry to 800 K

September 1, 2003
Author(s)
Dean C. Ripple, Dana R. Defibaugh, Michael R. Moldover, Gregory F. Strouse
The NIST Primary Acoustic Thermometer will measure the difference between the International TemperatureScale of 1990 and the Kelvin Thermodynamic Scale throughout the range 273 K to 800 K with uncertainties of only afew millikelvins. The acoustic

Theory of the Greenspan Viscometer

July 1, 2003
Author(s)
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

Relative Permittivity and Refractive Index

March 28, 2003
Author(s)
Michael R. Moldover, K N. Marsh, J M. Barthel, R Buchner
Measurements of the relative electric permittivity (dielectric constant or relative permittivity) e(p,T) and refractive index of fluids n(p,T) as a function of the pressure and the temperature can be used to determine a wide range of thermodynamic

Dielectric Permittivity of Eight Gases Measured with Cross Capacitors

March 1, 2003
Author(s)
James W. Schmidt, Michael R. Moldover
A 4-ring, toroidal cross capacitor was used to measure accurately the relative dielectric permittivity ε(p,T) of He, Ar, N 2, O 2, CH 4, C 2H 6, C 3H 8, and CO 2. (ε is often called the dielectric constant. ) The data are in the range from 0 C to 50 C and

Design and Uncertainty Analysis for a PVTt Gas Flow Standard

February 1, 2003
Author(s)
John D. Wright, Aaron N. Johnson, Michael R. Moldover
A new pressure, volume, temperature, and time (PVTt) primary gas flow standard has been constructed at the National Institute of Standards and Technology with an expanded uncertainty of between 0.02 % and 0.05 % (k = 2). The standard covers a flow range of

Acoustic Measurements in Gases, Chapter 10

September 15, 2001
Author(s)
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