NIST Digital Archives
Not a member yet
149436 research outputs found
Sort by
Powder diffraction: Least-squares and beyond
No full textThis paper addresses some of the underlying statistical assumptions and issues in the collection and refinement of powder diffraction data. While standard data collection and Rietveld analysis have been extremely successful in providing structural information on a vast range of materials, there is often uncertainty about the true accuracy of the derived structural parameters. In this paper, we discuss a number of topics concerning data collection and the statistics of data analysis. We present a simple new function, the cumulative chi-squared distribution, for assessing regions of misfit in a diffraction pattern and introduce a matrix which relates the impact of individual points in a powder diffraction pattern with improvements in the estimated standard deviation of refined parameters. From an experimental viewpoint, we emphasise the importance of not over-counting at low-angles and the routine use of a variable counting scheme for data collection. Data analysis issues are discussed within the framework of maximum likelihood, which incorporates the current least-squares strategies but also enables the impact of systematic uncertainties in both observed and calculated data to be reduced
Embedded microheating elements in polymeric micro channels for temperature control and fluid flow sensing
No full textThis paper describes the first demonstration of temperature control and flow sensing of fluids using integrated circuit (IC)-based microheating elements embedded in microchannels molded in polydimethylsiloxane (PDMS). Fluid channels and connections to capillary tubing are molded in PDMS using a silicon wafer template. The PDMS film is then bonded to an IC that contains the micromachined microheating elements. Capillary tubes are inserted and fluids are externally pumped through the channels. Heating of the fluid is observed by the formation of bubbles on the microheating element. Sensing of fluid flow is demonstrated by measuring a change in the large signal resistance of the microheater analogous to a hot wire +/- anemometer with a detection limit of 320 pL/s
Uncertainties in small-angle measurement systems used to calibrate angle artifacts
No full textWe have studied a number of effects that can give rise to errors in small-angle measurement systems when they are used to calibrate artifacts such as optical polygons. Of these sources of uncertainty, the most difficult to quantify are errors associated with the measurement of imperfect, non-flat faces of the artifact, causing the instrument to misinterpret the average orientation of the surface. In an attempt to shed some light on these errors, we have compared autocollimator measurements to angle measurements made with a Fizeau phase-shifting interferometer. These two instruments have very different operating principles and implement different definitions of the orientation of a surface, but (surprisingly) we have not yet seen any clear differences between results obtained with the autocollimator and with the interferometer. The interferometer is in some respects an attractive alternative to an autocollimator for small-angle measurement; it implements an unambiguous and robust definition of surface orientation in terms of the tilt of a best-fit plane, and it is easier to quantify likely errors of the interferometer measurements than to evaluate autocollimator uncertainty
Optical diffraction in close proximity to plane apertures. III. Modified, self-consistent theory
No full textThe classical theory of diffraction at plane apertures illuminated by normally incident light is modified so that diffraction on the source side of the screen is taken into consideration and the energy transport across the aperture plane is described by continuous functions. The modified field expressions involve the sums and differences of the Rayleigh-Sommerfeld diffraction integrals as descriptors of a bidirectional flow of energy in the near zones on either side of the aperture. The theory is valid for unpolarized fields, and a pragmatic argument is presented that it is applicable to metallic as well as black screens. The modified field expressions are used for numerical near-field computations of the diffraction profiles and transmission coefficients of circular apertures and slits. In the mid zone the modified theory is reduced to the Fresnel approximation, and here the latter may be used with confidence
Two primary standards for low flows of gases
No full textWe describe two primary standards for gas flow in the range from 0.1 to 1000 micro-mol/s. (1 micro-mol/s congruent to 1.3 cm(3)/min at 0 degreesC and 1 atmosphere.) The first standard is a volumetric technique in which measurements of pressure, volume, temperature, and time are recorded while gas flows in or out of a stainless steel bellows at constant pressure. The second standard is a gravimetric technique. A small aluminum pressure cylinder supplies gas to a laminar flow meter, and the integrated throughput of the laminar flow meter is compared to the weight decrease of the cylinder. The two standards, which have standard uncertainties of 0.019 %, agree to within combined uncertainties with each other and with a third primary standard at NIST based on pressure measurements at constant volume
(Audio Part 2 of 2) Oral history interview of John Hoffman, June 9, 2003
No full textDr. John Hoffman discusses his long career at NIST. His career spanned the years 1954 to 1982, during which time he was in various leadership positions, including Director of the Institute for Materials Research and Director of the National Measurement laboratory
C. Gordon Little
No full textC. GORDON LITTLE
Inducted: 2003
Citation:
For contributions to the development of remote sensing devices for meteorological parameters in space
Tenure: 1958-1965
Birth: 1924, Liuyang, Hunan, China
Education:
Manchester University (UK): BSc (Hons. Physics), 1948; PhD (Radioastronomy), 1952
Positions held:
Consultant on arctic radio wave propagation, Radio Propagation Physics Division
Chief, Upper Atmosphere and Space Physics Division
Chief, Central Radio Propagation Laboratory
Honors:
U.S. Department of Commerce: Gold Medal, 1964
NOAA Program Administration and Management Award, 1970
NOAA Science and Engineering Award, 1977
Government-wide Meritorious Executive Award, 1980
Cleveland Abbe Award, American Meteorological Society, 1984
R.M. Losey Award, American Institute of Aeronautics and Astronautics, 1992
Memberships:
National Academy of Engineering
Institute of Electrical and Electronic Engineers (Fellow)
American Meteorological Society (Fellow)
American Association for the Advancement of Science (Fellow)
National Academy of Sciences/National Research Council Committee on Atmospheric Science, Panel on Aeronomy (Executive Secretary)
Publications:
Authored or coauthored about 50 publications, including:
The Atmospheric Sciences 1961-1971, Volume III, Goals and Plans for Aeromony, NAS/NRC
“The Riometer – A device for the continuous measurement of ionospheric absorption,” Proc. I.R.E. 47 (1959) 315-320
“Acoustic methods for the remote probing of the lower atmosphere,” Proc. I.E.E.E. 57 (1969) 571-578. This paper introduced the idea of acoustic (including acoustic Doppler) sounding of the atmospheric boundary layer
Leon F. Curtiss
No full textLEON F. CURTISS
NBS: 1926 - 1961
Birth: January 5, 1895, Adrian, Michigan
Death: (estimate) 1990s, Florida
Education:
Cornell University: BA, 1917; PhD (Physics), 1922
Cavendish Laboratory (Rutherford laboratory), Cambridge, England, 1922-1925
Principal fields:
X-rays, radioactivity
Positions held at NBS:
Physicist, Atomic Physics Section
Chief, Radioactivity Section
Chief, Neutron Measurements Section
Consultant to the NBS Director
Honors:
Sigma Xi
Memberships:
American Physical Society
American Association of Agricultural Chemists (Referee)
Washington Academy of Medicine
Washington Academy of Sciences
American Society of Testing Materials
National Research Council
American Association for the Advancement of Science
National Institute of Health Radiobiology Study Section
National Research Council Committee on Nuclear Sciences (Chairman)
Publications:
Over 65 publications, including:
Introduction to Neutron Physics, D. Van Nostrand (1959)
Measurement of Radioactive Isotopes, NBS Circular 473 (1948)
“The Natural Beta-Ray Spectrum of Radium D (Pb-210),” Phys. Rev. (March 1926)
Curtiss, L.F. and I. Feister, “On the Disintegration Scheme of I-131,” Phys. Rev. (April 15, 1950)
“A Preliminary Note on the Direct Determination of Intensity in the Natural B-ray Spectrum of Radium B (Pb-214) and Radium C (Bi-214), communicated by Sir Ernest Rutherford, in Proceedings of the Cambridge Philosophical Society, (1925
James R. Roberts
No full textJAMES R. ROBERTS
NBS/NIST: 1964 - 1999
Birth: July 1, 1937, Flint, Michigan
EDUCATION:
University of Michigan, BS, 1959; MS, 1961; PhD, 1964 (Physics)
PRINCIPAL FIELDS:
Measurements of atomic parameters in ionized plasmas, plasma measurements for semiconductor processing, instrumentation and radiometry in the XUV spectral region, Electron Beam Ion Trap (EBIT) measurements in highly ionized species
POSITIONS HELD AT NBS/NIST:
Research Scientist, Plasma Spectroscopy Section, Atomic/Optical Physics Division
Leader, Plasma Radiation Group, Atomic Physics Division
Program Office Analyst, NIST
HONORS:
U.S. Department of Commerce: Silver Medal, 1980
IR-100 Award, 1980: high resolution XUV spectrometer
IR-100 Award, 1982: capillary array XUV window
MEMBERSHIPS:
American Physical Society
PUBLICATIONS:
Over 70 papers on atomic data, XUV instrumentation, and plasma spectroscopy, including:
“Measurements of Stark profiles of C II and Fa I lines,” Phys. Rev. 159 (1967) 104
“Mean-life measurements of excited electronic states in perturbed series of Al II and Be I,” Physica Scripta 4 (1971) 52
“Calculated continuous emission of a LTE hydrogen plasma,” J. Res. NBS 75 (1971) 291
“Measured Stark widths and shifts for neutral phosphorus lines,” Phys. Rev. A 15 (1977) 1006
“Electron-impact ionization-rate coefficients for lithiumlike nitrogen and oxygen,” Phys. Rev. A 19 (1979) 90
“Investigation of laser temporal pulse duration on Rayleigh scattering,” Phys. Rev. A 25 (1982) 1000
“Magnetic-dipole transitions observed in highly ionized Ga, Ge, As, and Kr,” Phys. Rev. A 27 (1983) 1721
“High-resolution VUV spectrometer with multichannel detector for absorption studies of transient species,” Appl. Optics 24 (1985) 2996
“Population inversions in C-IV in a recombining theta-pinch plasma,” Opt. Letters 12 (1987) 675
“Soft x-ray optics characterization on SURF-II,” Physica Scripta 41 (1990) 9
“Glow Discharges and Wall Stabilized Arcs,” in Vacuum Ultraviolet Spectroscopy, Vol. 31, Exper. Meth. Phys, Sciences, ed. James A. Sampson and David Ederer. Academic Press (1998)
“Highly Charged Ion Studies at the NIST EBIT,” in Trapping Highly Charged Ions: Fundamentals and Applications,” ed. John Gillaspy. Nova Science Publishers, Inc., 199
Barry N. Taylor
No full textBARRY N. TAYLOR
NBS/NIST: 1970 - 2001
Birth: March 27, 1936, Philadelphia, Pennsylvania
EDUCATION:
Temple University, BA (Physics), 1957
University of Pennsylvania, MS (Physics), 1960; PhD (Physics), 1963
PRINCIPAL FIELDS:
Electron tunneling; superconductivity and the Josephson effects; precision electrical measurements; fundamental physical constants; expression of uncertainty in measurement; International System of Units; technical management
POSITIONS HELD AT NBS/NIST:
Chief, Absolute Electrical Measurements Section
Program Analyst, Program Office
Chief, Electricity Division
Administrator, NBS/NIST Precision Measurement Grants Program
Manager, NBS/NIST Fundamental Constants Data Center
Chief Editor, Journal of Research of the National Institute of Standards and Technology
NIST Scientist Emeritus
HONORS:
RCA Laboratories Outstanding Achievement Award, 1969
John Price Wetherill Medal, Franklin Institute, Philadelphia, 1975
U.S. Department of Commerce: Silver Medal, 1975; Gold Medal, 1989
CODATA Prize, 2000
Distinguished Executive Presidential Rank Award, 2000
MEMBERSHIPS:
American Physical Society (Fellow)
Institute of Electrical and Electronics Engineers (Fellow)
Washington Academy of Sciences (Fellow)
Russian Academy of Metrology (Distinguished Foreign Member)
PUBLICATIONS:
Over 100 publications including:
Precision Measurements and Fundamental Constants, (with co-editor), NBS Special Publication 343 (1971); and Precision Measurements and Fundamental Constants, (with co-editor), NBS Special Publication 617 (1984)
Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results, (with co-author), NIST Technical Note 1297 (1994)
Guide for the Use of the International System of Units, NIST Special Publication 811 (1995