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Averaging of backscatter intensities in compounds
No full textLow uncertainty measurements on pure element stable isotope pairs demonstrate that mass has no influence on the backscattering of electrons at typical electron microprobe energies. The traditional prediction of average backscatter intensities in compounds using elemental mass fractions is improperly grounded in mass and thus has no physical basis. We propose an alternative model to mass fraction averaging, based of the number of electrons or protons, termed "electron fraction," which predicts backscatter yield better than mass fraction averaging
The role of rendering in the competence project in measurement science for optical reflection and scattering
No full textComputer rendering is used to simulate the appearance of lighted objects for applications in architectural design, for animation and simulation in the entertainment industry, and for display and design in the automobile industry. Rapid advances in computer graphics technology suggest that in the near future it will be possible to produce photorealistic images of coated surfaces from scattering data. This could enable the identification of important parameters in the coatings manufacturing process that lead to desirable appearance, and to the design of virtual surfaces by visualizing prospective coating formulations once their optical properties are known. Here we report the results of our work to produce visually and radiometrically accurate renderings of selected appearance attributes of sample coated surfaces. It required changes in the rendering programs, which in general are not designed to accept high quality optical and material measurements, and changes in the optical measurement protocols. An outcome of this research is that some current ASTM standards can be replaced or enhanced by computer based standards of appearance
George T. Armstrong
No full textGEORGE T. ARMSTRONG
Inducted: 2002
Citation:
For his leadership in NIST programs on calorimetry and thermodynamics, including measurements of the heats of formation of rocket fuels and municipal waste materials, as well as the thermochemistry of fluorine.
Tenure: 1951 - 1982
Birth: 1916, Castor, Alberta, Canada
Death: 1982, Silver Spring, Maryland
Education:
University of Florida: BS, 1939; MS, 1942
Johns Hopkins University: PhD, 1948
Positions held:
Chief, Combustion Laboratory, Heat Division
Chief, Thermochemistry Section
Deputy Chief, Chemical Thermodynamics Division
Honors:
U.S. Department of Commerce Silver Medal, 1967
Memberships:
American Association for the Advancement of Science (Fellow)
American Chemical Society
American Physical Society (Fellow)
American Society for Testing and Materials: Committee Chair
CODATA Task Group on Biothermodynamic Data: Chair
IUPAC Commission on Thermodynamics
Philosophical Society of Washington: President
Washington Academy of Sciences (Fellow)
Publications:
More than 160 publications and reports on chemical thermodynamics, including
"Vapor Pressure of Nitrogen,"J. Res., NBS, October 1954
"Combustion Calorimetry with Fluorine: Constant Pressure Flame Calorimetry," (with R.S. Jessup), J. Res. A, NBS, January-February 1960
"Heats of Formation of Two Isomers of Difluorodiazine," (with S. Marantz),
J. Chem. Phys., January 1963
"Calorimetry"(with A. Cezairliyan), Kirk-Othmer Encycl. Chem. Technol. (1976)
"Fluorine Flame Chemistry" (with R.C. King), IUPAC, Combustion
Calorimetry, (1970)
"Assignment and Presentation of Uncertainties of Numerical Results of Thermodynamic Measurements," (with co-authors), J. Chem. Thermodyn. (1981)
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Portrait of Arden L. Bement Jr.
No full textServed as director of the National Institute of Standards and Technology from 2001 through 2004
Conventional cells - The last step toward general acceptance of standard conventional cells for the reporting of crystallographic data
No full textIn 1969, a seminal section on reduced forms and conventional cells was published in the International Tables for X-Ray Crystallography. The section contains a table that gives a metric classification of the 44 reduced forms. In 2001, this table with appropriate revisions was republished in the Journal of Research of the National Institute of Standards and Technology. An especially valuable feature of the table is that it defines and allows the user to determine a standard conventional cell. Since 1969, there has been an evolution toward acceptance and widespread use of such conventional cells. An inspection of the articles in key crystallographic journals reveals that most cells follow the conventions. However, one major exception remains-the centered monoclinic lattices. In approximately one-third of these cases, non-conventional C-centered cells are used, apparently to avoid the use of I-centered cells. It is recommended that the crystallographic community routinely use the I-centered conventional cell in such cases
Accelerating scientific discovery through computation and visualization II
No full textThis is the second in a series of articles describing a wide variety of projects at NIST that synergistically combine physical science and information science. It describes, through examples, how the Scientific Applications and Visualization Group (SAVG) at NIST has utilized high performance parallel computing, visualization, and machine learning to accelerate research. The examples include scientific collaborations in the following areas: (1) High Precision Energies for few electron atomic systems, (2) Flows of suspensions, (3) X-ray absorption, (4) Molecular dynamics of fluids, (5) Nanostructures, (6) Dendritic growth in alloys, (7) Screen saver science, (8) genetic programming
Barriers to quantitative electron probe x-ray microanalysis for low voltage scanning electron microscopy
No full textLow voltage x-ray microanalysis, defined as being performed with an incident beam energy less than or equal to5 keV, can achieve spatial resolution, laterally and in depth, of 100 nm or less, depending on the exact selection of beam energy and the composition of the target. The shallow depth of beam penetration, with the consequent short path length for x-ray absorption, and the low overvoltage, the ratio of beam energy to the critical ionization energy, both contribute to minimizing the matrix effects in quantitative x-ray microanalysis when the unknown is compared to pure element standards. The low beam energy restricts the energy of the atomic shells that can be excited, forcing the analyst to choose unfamiliar shells/characteristic peaks. The low photon energy shells are subject to low fluorescence yield, so that the peak-to-continuum background is reduced, severely limiting detectability. The limited resolution of semiconductor energy dispersive spectrometry results in frequent peak interference situations and further exacerbates detection limits. Future improvements to the x-ray spectrometry limitations are possible with x-ray optics-augmented wavelength dispersive spectrometry and microcalorimeter energy dispersive spectrometry
Characterization of Corning EPMA standard glasses 95IRV, 95IRW, and 95IRX
No full textThe preparation, synthesis, and characterization of Corning trace-element glasses 95IRV, 95IRW, and 95IRX by bulk chemical and electron microprobe techniques is discussed. Working values for the doped elements in the 95-series glasses are established. Blank values have been determined by both bulk chemical and electron microprobe analysis, and important x-ray interferences are highlighted. Chemical homogeneity both within a rod cross-section, and along cane length has been documented. These glasses are standard reference materials intended for use as both primary and secondary electron microprobe standards
Data analysis methods for synthetic polymer mass spectrometry: Autocorrelation
No full textAutocorrelation is shown to be useful in describing the periodic patterns found in high-resolution mass spectra of synthetic polymers. Examples of this usefulness are described for a simple linear homopolymer to demonstrate the method fundamentals, a condensation polymer to demonstrate its utility in understanding complex spectra with multiple repeating patterns on different mass scales, and a condensation copolymer to demonstrate how it can elegantly and efficiently reveal unexpected phenomena. It is shown that using autocorrelation to determine where the signal devolves into noise can be useful in determining molecular mass distributions of synthetic polymers, a primary focus of the NIST synthetic polymer mass spectrometry effort. The appendices describe some of the effects of transformation from time to mass space when time-of-flight mass separation is used, as well as the effects of non-trivial baselines on the autocorrelation function
Three improvements in reduction and computation of elliptic integrals
No full textThree improvements in reduction and computation of elliptic integrals are made. 1. Reduction formulas, used to express many elliptic integrals in terms of a few standard integrals, are simplified by modifying the definition of intermediate "basic integrals." 2. A faster than quadratically convergent series is given for numerical computation of the complete symmetric elliptic integral of the third kind. 3. A series expansion of an elliptic or hyperelliptic integral in elementary symmetric functions is given, illustrated with numerical coefficients for terms through degree seven for the symmetric elliptic integral of the first kind. Its usefulness for elliptic integrals, in particular, is important