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Chemistry

Chemical engineering & processing

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Displaying 251 - 275 of 400

Advice from the CCL on the use of unstabilized lasers as standards of wavelength: the helium-neon laser at 633 nm

January 1, 2009
Author(s)
Jack A. Stone Jr., Jennifer Decker, Patrick Gill, Andrew Lewis, Patrick Juncar, Daniele Rovera, Miguel Villiseid
The Consultative Committee for Length has recommended that red (633 nm) unstabilized Helium-Neon lasers, operating on the 3s2¿_2p4 transition, should be included in the list of standard frequencies for realization of the meter. This article discusses

Droplet Formation at Microfluidic T-junctions

December 31, 2008
Author(s)
David A. LaVan, Xiang Xu
Analysis of droplet formation in microfluidic systems is important to understand the operation of these devices, and to permit optimal design and process control. Droplet formation in microfluidic T-junction devices was studied using experimental and

Design and testing of a software feedback loop for RF power leveling

December 12, 2008
Author(s)
Xiaohai Cui, Thomas P. Crowley
We have developed a software feedback loop that stabilizes the RF power input in calorimetric measurements to better than 30 ppm. In this system, a bolometric sensor with a Type IV power meter is used to detect the power. Feedback is provided to the AM

Multichannel Decomposition and Isomerization of Octyl Radicals

October 9, 2008
Author(s)
Wing Tsang, William S. McGivern, Jeffrey A. Manion
The thermal cracking patterns from the decomposition and isomerization of octyl-1 radicals have been determined from the pyrolysis of n-octyl iodide in single pulse shock tube experiments at temperatures in the 850-1000 K range and pressures near 2 bar

NIST Microform Calibration System for Rockwell Hardness Standardization

August 25, 2008
Author(s)
Jun-Feng Song, Samuel R. Low III, Xiaoyu A. Zheng
In the uncertainty budget of Rockwell hardness tests, microform geometric errors of the diamond indenter are a major contributor. The microform calibration of Rockwell diamond indenters has been one of the key steps for Rockwell hardness standardization

Measuring the Phase Transfer Function of a Phase-Shifting Interferometer

August 13, 2008
Author(s)
JiYoung Chu, Quandou (. Wang, John P. Lehan, Ulf Griesmann, Guangjun Gao
In characterizing the performance of a phase-shifting interferometer, the dependence of the measured height on the spatial frequency is rarely considered. We describe a test mirror with a special height relief that can be used to measure the height

Natural Gas Flow Calibration Service

August 1, 2008
Author(s)
Aaron N. Johnson
This document describes NIST's high pressure natural gas flow calibration service (NGFCS). Flow calibrations are conducted offsite at the Colorado Experimental Engineering Station Incorporated (CEESI) in Garner, Iowa. A parallel array of nine turbine meter

Stationary and non-stationary deformations in three-flat tests

July 7, 2008
Author(s)
Ulf Griesmann, Quandou (. Wang, Nicolas Laurenchet, Johannes A. Soons
Calibration procedures for optical reference flats of phase-shifting interferometers (three-flat tests) are critically important if flatness measurements with low uncertainty are desired. In these tests, all combinations of three flats with unknown

Calculated Performance of Low-Porosity Regenerators at 4 K with He-4 and He-3

June 9, 2008
Author(s)
Ray Radebaugh, Yonghua Huang, Agnes A. O'Gallagher, John M. Gary
Previously we have shown that the lower volumetric heat capacity and more ideal behavior of helium-3 compared with helium-4 at 4 K results in an improved performance for packed sphere regenerators operating with helium-3 between 4 K and about 20 K. In this

A New Microdevice for SI-Traceable Forces in Atomic Force Microscopy

June 2, 2008
Author(s)
Gregory W. Vogl, Jason J. Gorman, Gordon A. Shaw, Jon R. Pratt
A new self-excited micro-oscillator is proposed as a velocity standard for dissemination of nanoNewton-level forces that are traceable to the International System of Units (SI). The microfabricated oscillator is top-coated with magnetic thin films and

Gauge Blocks - A Zombie Technology

May 1, 2008
Author(s)
Theodore D. Doiron
Gauge blocks have been the primary method for disseminating length traceability for over 100 years. Their longevity was based on two things: it was relatively inexpensive to deliver very high accuracy to users, and the technical limitation that the range

Shear Thinning Near the Critical Point of Xenon

April 17, 2008
Author(s)
Robert F. Berg, Michael R. Moldover, M Yao, G A. Zimmerli
We measured shear thinning, a viscosity decrease ordinarily associated with complex liquids, near the critical point of xenon. The data span the range of reduced shear rates: 0.001 < γτ < 700, where γτ is the shear rate scaled by the relaxation time τ of

Spring constant calibration of AFM cantilevers with a piezosensor transfer standard

September 24, 2007
Author(s)
Eric Langlois, Gordon A. Shaw, John A. Kramar, Jon R. Pratt, Donna C. Hurley
We describe a method to calibrate the spring constants of cantilevers for atomic force microscopy (AFM). The method makes use of a piezosensor comprised of a piezoresistive cantilever and accompanying electronics. The piezosensor was calibrated before use

Reference Viscosities of H 2 , CH 4 , Ar and Xe at Low Densities

August 1, 2007
Author(s)
E May, Robert F. Berg, Michael R. Moldover
We determined the zero-density viscosity eta of hydrogen, methane and argon in the temperature range 200 K to 400 K, with standard uncertainties of 0.084 % for hydrogen and argon and 0.096 % for methane. These uncertainties are dominated by the uncertainty

The Polarizability of Helium and Gas Metrology

June 22, 2007
Author(s)
James W. Schmidt, R Gavioso, E May, Michael R. Moldover
Using a quasi-spherical, microwave cavity resonator, we measured the refractive index of helium to deduce its molar polarizability A ε in the limit of zero density. We obtained (A ε,meas - A ε,theory)/A ε = (-1.8plus or minus} 8.4)× 10 -6, where the

Direct Electrostatic Calibration of Hybrid Sensors for Small Force Measurement

June 4, 2007
Author(s)
Koo-Hyun Chung, Gordon A. Shaw, Jon R. Pratt
The measurement of forces from piconewtons to millinewtons is an area of interest from both an applied and pure research standpoint, however creating a link between small forces and the International System of Units (SI) has been difficult. In this work, a
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