U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Search Publications by: Michael R Moldover (Assoc)

Search Title, Abstract, Conference, Citation, Keyword or Author
Displaying 101 - 125 of 161

The Kelvin and Temperature Measurements

January 1, 2001
Author(s)
Billy W. Mangum, G T. Furukawa, Kenneth G. Kreider, Christopher W. Meyer, Dean C. Ripple, Gregory F. Strouse, Weston L. Tew, Robert D. Saunders, Bettye C. Johnson, Howard W. Yoon, Michael R. Moldover, Charles E. Gibson
The International Temperature Scale of 1990 (ITS90) is defined from 0.65 K upwards to the highest temperature measurable by spectral radiation thermometry, the radiation thermometry being based on the Planck radiation law. Part I of this paper describes

The Effect of Vibrational Relaxation of the Discharge Coefficient of Critical Flow Venturis

December 1, 2000
Author(s)
Aaron N. Johnson, John D. Wright, Shin-ichi Nakao, C L. Merkle, Michael R. Moldover
This paper identifies a new mechanism that can affect the discharge coefficient of critical nozzle flows. Specifically, vibrational relaxation effects are demonstrated to significantly influence the discharge coefficient of selected gases in critical

Ab Initio Values of the Thermophysical Properties of Helium as Standards

September 1, 2000
Author(s)
John J. Hurly, Michael R. Moldover
Recent quantum mechanical calculations of the interaction energy of pairs of helium atoms are accurate and some include reliable estimates of their uncertainty. We combined these recent ab initio results with earlier published results to obtain a helium

An Improved Greenspan Acoustic Viscometer

September 1, 2000
Author(s)
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

Toroidal Cross-Capacitor for Measuring the Dielectric Constant of Gases

July 1, 2000
Author(s)
T J. Buckley, J O. Hamelin, Michael R. Moldover
We describe toroidal cross capacitors built to accurately measure the dielectric constant of gases. We tested the capacitors by measuring the dielectric polarizability of helium and argon at 7 and 50 degrees C at pressures up to 3 MPa. For helium, the

Thermodynamic Properties of Sulfur Hexafluoride

May 1, 2000
Author(s)
John J. Hurly, Dana R. Defibaugh, Michael R. Moldover
We present new vapor phase speed-of-sound data u(P,T), new Burnett density-pressure-temperature data ρ(P,T), and a few vapor pressure measurements for sulfur hexafluoride (SF 6). The speed-of-sound data spanned the temperature range 230 K {less than or

Thermophysical Properties of Process Gases

November 1, 1999
Author(s)
John J. Hurly, Michael R. Moldover
We measured the speed of sound in the process gases Cl 2, HBr, BCl 3, and in the surrogate gases SF 6, CF 4, and C 2F 6. The data range up to 475 K (200 C) and from 25 kPa to 1500 kPa (or to 80% of the vapor pressure for condensable gases). The data were

Frequency-Dependent Viscosity of Xenon Near the Critical Point

October 1, 1999
Author(s)
Robert F. Berg, Michael R. Moldover, G A. Zimmerli
We used a novel, overdamped oscillator aboard the Space Shuttle to measure the viscosity Η of xenon near its critical density ρ c and temperature T c. In microgravity, useful data were obtained within 0.1 mK of T c, corresponding to a reduced temperature t

Electrostriction of Near-Critical SF 6 in Microgravity

June 1, 1999
Author(s)
G A. Zimmerli, R A. Wilkinson, R A. Ferrell, Michael R. Moldover
We used interferometry to measure the electric-field-induced (I.e., electrostrictive) increase of the density of sulfur hexafluoride near its critical point. The results at the temperatures T c + 5 mK, T c + 10 mK, and T c + 30 mK, with T c = 319 K, agree

Primary Acoustic Thermometer for Use Up to 800 K

April 1, 1999
Author(s)
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

Primary Acoustic Thermometry From 217 K to 303 K

April 1, 1999
Author(s)
Michael R. Moldover, S J. Boyes, A R. Goodwin, Christopher W. Meyer
We report new values for the difference (T T 90) between Kelvin thermodynamic temperatures T and ITS-90, the International Temperature Scale of 1990. The new data span the range 217 K {less then or equal to} T 303 K with standard uncertainties of 0.6 mK. A

Viscoelasticity of Xenon Near the Critical Point

February 1, 1999
Author(s)
Robert F. Berg, Michael R. Moldover, G A. Zimmerli
Using a novel, overdamped, oscillator flown aboard the Space Shuttle, we measured the viscosity of xenon near the liquid-vapor critical point in the frequency range 2 Hz [less than or equal to} f {less than or equal to} 12 Hz. The measured viscosity

Critical Viscosity of Xenon: Surprises and Scientific Results

October 1, 1998
Author(s)
Robert F. Berg, Michael R. Moldover, G A. Zimmerli
The Critical Viscosity of Xenon (CVX) experiment, which flew on board Space Shuttle flight STS-85 in August 1997, measured the viscosity of xenon near the liquid-vapor critical point. Very close to the critical temperature (T c = 290 K), the viscosity Η of

Proposed Pressure Standard Based on Capacitance Measurements

July 1, 1998
Author(s)
Michael R. Moldover
We propose to measure the dielectric constant [epsilon] and the thermodynamic temperatue T of helium near 273.16 K and to calculate the pressure p([epsilon],T) of the helium from the fundamental constants, quantum mechanics, and statistical mechanics. If

Acoustic Methods for Transport Properties Measurements in Gases

June 1, 1998
Author(s)
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

Can a Pressure Standard be Based on Capacitance Measurements?

March 1, 1998
Author(s)
Michael R. Moldover
We consider the feasibility of basing a pressure standard on measurements of the dielectric constant [epsilon] and the thermodynamic temperature T of helium near )[degrees]C. The pressure P of the helium would be calculated using the fundamental constants