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Analytical representations of elastic moduli data with simultaneous dependence on temperature and porosity
No full textAn analytical model providing simultaneous, self-consistent representations of the temperature and porosity dependence of the elastic and bulk moduli of polycrystalline ceramics is applied to data compiled from the literature for 24 oxide ceramics
Portrait of Peter Heydemann
No full textPeter Heydemann was a physicist at the National Bureau of Standards. Heydemann had been a member of the National Bureau of Standards team survey “of Pakistan’s standardization and measurement services (see above). Subsequently he arranged seminars and training courses in Pakistan and India. His many contacts in India prompted the Department of State to appoint him as Science Counselor at the U.S. Embassy in India (1988-1993), resulting in expanded collaborations between U.S. and Indian technical organizations. At the same time, Heydemann had the opportunity to collaborate with U.S. companies trading with India, with a focus on standards and measurement problems. After Heydemann’s return to NIST as Director of Technology Services, he established a Standards in Trade Program to assist U.S. companies to overcome technical barriers in foreign countries.” (From NIST Special Publication 958, A Century of Excellence in Measurements, Standards, and Technology: A Chronicle of Selected NBS/NIST Publications, 1901-2000
The high resolution powder diffraction beam line at ESRF
No full textThe optical design and performance of the high-resolution powder diffraction beam line BM16 at ESRF are discussed and illustrated. Some recent studies carried out on BM16 are described, including crystal structure solution and refinement, anomalous scattering, in situ measurements, residual strain in engineering components, investigation of microstructure, and grazing-incidence diffraction from surface layers. The beam line is built on a bending magnet, and operates in the energy range from 5 keV to 40 keV. After the move to an undulator source in 2002, it will benefit from an extented energy range up to 60 keV and increased flux and resolution. It is anticipated that enhancements to the data quality will be achieved, leading to the solution of larger crystal structures, and improvements in the accuracy of refined structures. The systematic exploitation of anisotropic thermal expansion will help reduce the effects of peak overlap in the analysis of powder diffraction data
Global Rietveld refinement
No full textGlobal optimisation methods of structure determination from powder diffraction data have risen to prominence in a relatively short space of time and they now constitute a key approach in the examination of polycrystalline molecular organic materials. A correctly formulated global optimisation approach may be regarded as a "global Rietveld refinement" that is capable of delivering accurate crystal structures from high-quality powder diffraction data. This paper focuses on how accuracy at all stages of a powder diffraction experiment impacts upon the overall structure solution process and particular attention is paid to assessing the degree of accuracy with which structures are returned from the global optimisation process
Uncertainty propagation for NIST visible spectral standards
No full textUncertainties in the NIST spectral standards for detectors and sources in the visible wavelength range are propagated from the high accuracy cryogenic radiometer measurements, taking correlations into account at every stage. Partial correlations between spectral values at different wavelengths, important for subsequent radiometric calculations, are estimated. Uncertainty propagation through fitting and through transfer spectral measurements is described in detail. Detector uncertainties are propagated through the spectral comparator facility for external calibrations and for internal photometric quantities. Uncertainties in spectral irradiance are derived for the detector-based temperature determination, then propagat-through working standards to calibrated artifacts. Spectral irradiance calibrations are generally provided at a limited number of wavelengths. Interpolation, rather than fitting, is recommended for the interpolation of NIST-provided spectral irradiance values
Determining the uncertainty of x-ray absorption measurements
No full textX-ray absorption (or more properly, x-ray attenuation) techniques have been applied to study the moisture movement in and moisture content of materials like cement paste, mortar, and wood. An increase in the number of x-ray counts with time at a location in a specimen may indicate a decrease in moisture content. The uncertainty of measurements from an x-ray absorption system, which must be known to properly interpret the data, is often assumed to be the square root of the number of counts, as in a Poisson process. No detailed studies have heretofore been conducted to determine the uncertainty of x-ray absorption measurements or the effect of averaging data on the uncertainty. In this study, the Poisson estimate was found to adequately approximate normalized root mean square errors (a measure of uncertainty) of counts for point measurements and profile measurements of water specimens. The Poisson estimate, however, was not reliable in approximating the magnitude of the uncertainty when averaging data from paste and mortar specimens. Changes in uncertainty from differing averaging procedures were well-approximated by a Poisson process. The normalized root mean square errors decreased when the x-ray source intensity, integration time, collimator size, and number of scanning repetitions increased. Uncertainties in mean paste and mortar count profiles were kept below 2% by averaging vertical profiles at horizontal spacings of 1 mm or larger with counts per point above 4000. Maximum normalized root mean square errors did not exceed 10% in any of the tests conducted
Robert E. Hebner
No full textROBERT E. HEBNER
NBS/NIST: 1972 - 1999
Birth: February 11, 1945, Minneapolis, Minnesota
Education:
St. Mary’s of Texas, BS (Physics), 1967
University of Missouri, Rolla, MS (Physics), 1969
University of Missouri, Rolla, PhD (Physics), 1971
Principal Fields:
Electro-optics; electric and magnetic fields; space charge dynamics; discharge phenomena in liquids; dielectrics and electrical insulation; high speed photography.
Positions held at NBS /NIST:
Physicist, Electricity Division
Chief, Applied Electrical Measurements Section
Program Analyst, Program Office
Deputy Director, Electronics and Electrical Engineering Laboratory
Acting Director, Electronics and Electrical Engineering Laboratory
Acting Deputy Director, NIST
Acting Director, NIST
Honors:
IEEE Harry Diamond Memorial Award, 1990
US Department of Commerce Gold Medal (1997) and Silver (1986), and Bronze (1981) Medals
Memberships:
American Physical Society
Institute of Electrical and Electronic Engineers (Fellow)
American Association for the Advancement of Science
Publications:
More than 100 including:
R.E. Hebner, R.A. Malewski, and E.C. Cassidy, “Optical Methods of Electrical Measurement at High Voltage Levels,” Proc. IEEE 65, p. 1524 (1977)
E.F. Kelley and R.E. Hebner, “The Electric Field Distribution Associated with Prebreakdown Phenomena in Nitrobenzene,” J. Appl. Phys. 52, p.191 (1981).
M.Zahn, E.O. Forster, E.F. Kelly, and R.E. Hebner, Hydrodynamic Shock Wave Propagation after Electrical Breakdown,” Journal of Electrostatics, 12 p. 535-536 (1982).
R.E. Hebner, G.N. Stenbakken, and D.L. Hillhouse, “Report on Tests on Joseph Newman’s Device,” National Bureau of Standards, NBSIR 86-3405, 35 pages (June 1986
Erratum: Statistical interpretation of key comparison reference value and degrees of equivalence (vol 108, No. 6, pg 439, 2003)
No full textMultidataset refinement resonant diffraction, and magnetic structures
No full textThe scope of Rietveld and other powder diffraction refinements continues to expand, driven by improvements in instrumentation, methodology and software. This will be illustrated by examples from our research in recent years. Multidataset refinement is now commonplace; the datasets may be from different detectors, e. g., in a time-of-flight experiment, or from separate experiments, such as at several x-ray energies giving resonant information. The complementary use of x rays and neutrons is exemplified by a recent combined refinement of the monoclinic superstructure of magnetite, Fe3O4, below the 122 K Verwey transition, which reveals evidence for Fe2+/Fe3+ charge ordering. Powder neutron diffraction data continue to be used for the solution and Rietveld refinement of magnetic structures. Time-of-flight instruments on cold neutron sources can produce data that have a high intensity and good resolution at high d-spacings. Such profiles have been used to study incommensurate magnetic structures such as FeAsO4 and beta-CrPO4. A multiphase, multidataset refinement of the phase-separated perovskite (Pr0.35Y0.07Th0.04Ca0.04Sr0.5) MnO3 has been used to fit three components with different crystal and magnetic structures at low temperatures
Fundamental parameters line profile fitting in laboratory diffractometers
No full textThe fundamental parameters approach to line profile fitting uses physically based models to generate the line profile shapes. Fundamental parameters profile fitting (FPPF) has been used to synthesize and fit data from both parallel beam and divergent beam diffractometers. The refined parameters are determined by the diffractometer configuration. In a divergent beam diffractometer these include the angular aperture of the divergence slit, the width and axial length of the receiving slit, the angular apertures of the axial Soller slits, the length and projected width of the x-ray source, the absorption coefficient and axial length of the sample. In a parallel beam system the principal parameters are the angular aperture of the equatorial analyser/Soller slits and the angular apertures of the axial Soller slits. The presence of a monochromator in the beam path is normally accommodated by modifying the wavelength spectrum and/or by changing one or more of the axial divergence parameters. Flat analyzer crystals have been incorporated into FPPF as a Lorentzian shaped angular acceptance function. One of the intrinsic benefits of the fundamental parameters approach is its adaptability any laboratory diffractometer. Good fits can normally be obtained over the whole 20 range without refinement using the known properties of the diffractometer, such as the slit sizes and diffractometer radius, and emission profile