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(Audio Part 1 of 2) Oral history interview of Marilyn E. Jacox, February 18, 1998 / by Karmal Beal
No full textMaryilyn Jacox begins her discussion with her early interest in science, her education in chemistry and physics, her teaching position at the Mellon Institute and her 15 year collaboration with Dick Milligan. She also recalls her work in free radicals a
William D. "Bill" Phillips (1998)
No full textWilliam D. "Bill" Phillips is a physicist at the National Institute of Standards and Technology. He joined NIST in 1978 and was awarded the Nobel Prize in Physics in 1997. Image source: William D. Phillips biographical file, NIST Archives
An easy-to-use combination four-terminal-pair/two-terminal-pair AC transformer bridge
No full textA new four-terminal-pair bridge, capable of achieving a relative standard uncertainty of 1x10(-9), was constructed at the National Institute of Standards and Technology by converting a two-terminal-pair bridge. The conversion requires only the addition of components which are easily removed if two-terminal-pair measurements are to be made. The design and testing of this bridge is described. The new four-terminal-pair bridge requires fewer auxiliary balances than the present four-terminal-pair bridge employed at NIST, which makes it much easier to use. This new design can be used to compare capacitance, resistance, and inductance standards
Spectral response based calibration method of Tristimulus colorimeters
No full textA new method is described to calibrate tristimulus colorimeters for high accuracy color measurements Instead of traditional lamp standards, modern, high accuracy detector standards are suggested for calibration. After high accuracy absolute spectral response determination of the tristimulus receivers, color (spectral) correction and peak (amplitude) normalization can minimize uncertainties caused by imperfect realizations of the Commission Internationale de l'Eclairage (CIE) color matching functions. As a result of the corrections, stable light sources of different spectral power distributions can be measured with an accuracy dominated by the sub tenths of a percent uncertainty of novel spectral response determinations
Chopped radiation measurements with large area Si photodiodes
No full textFrequency dependent response characteristics of photocurrent meters using large area, radiometric quality Si photodiodes have been analyzed. The current responsivity, the voltage noise and drift amplification, and the gain and bandwidth of the photocurrent-measuring analog control loop were calculated. The photodiodes were selected for high shunt resistance. The effect of the photodiode junction capacitance on the response characteristics was also analyzed. As a result of photocurrent gain dependent frequency compensations, the noise boosting effect was minimized at the output of the current meter. The loop gain and bandwidth were maximized. High-accuracy photocurrent measurements can be achieved using the described procedures for both de and modulated optical radiation
Liquidus diagram of the Ba-Y-Cu-O system in the vicinity of the Ba2YCu3O6+x phase field
No full textThis paper describes the melting equilibria in the vicinity of the high T-c phase Ba2YCu3O6+x, including evidence for two Ba-Y-Cu-O immiscible liquids. Melting equilibria have been investigated in purified air using a combination of differential thermal analysis (DTA), thermogravimetric analysis (TGA), powder x-ray diffraction (XRD), MgO wick entrapment of liquid for analysis, scanning electron microscopy (SEM) coupled with energy dispersive x-ray analysis (EDS), and hydrogen reduction for determination of copper oxidation state. For relatively barium-rich compositions, it was necessary to prepare the starting materials under controlled atmosphere conditions using BaO. A liquidus diagram was derived from quantitative data for the melts involved in various melting reactions. In general the 1/2(Y2O3) contents of the melts participating in these equilibria were low (mole fraction <4 %). The primary phase field of Ba2YCu3O6+x occurs at a mole fraction of <2.0 % 1/2Y(2)O(3) and lies very close along the BaO-CuOx edge, extending from a mole fraction of approximate to 43 % CuO to a mole fraction of approximate to 76 % CuO. It is divided by a liquid miscibility gap and extends on either side about this gap. The topological sequence of melting reactions associated with the liquidus is presented as a function of temperature. Implications for the growth of Ba2YCu3O6+x crystals are discussed
Algorithms for Fresnel diffraction at rectangular and circular apertures
No full textThis paper summarizes the theory of Fresnel diffraction by plane rectangular and circular apertures with a view; toward numerical computations. Approximations found in the earlier literature, and now obsolete, have been eliminated and replaced by algorithms suitable for use on a personal computer
Ultraviolet Spectral Irradiance Scale comparison: 210 nm to 300 nm
No full textComparison of the irradiances from a number of ultraviolet spectral irradiance standards, based on different physical principles, showed agreement to within their combined standard uncertainties as assigned to them by NIST. The wavelength region of the spectral irradiance comparison was from 210 nm to 300 nm. The spectral irradiance sources were: an electron storage ring, 1000 W quartz-halogen lamps, deuterium are lamps, and a windowless argon miniarc
Calculation of measurement uncertainty using prior information
No full textWe describe the use of Bayesian inference to include prior information about the value of the measurand in the calculation of measurement uncertainty Typical examples show this can, in effect, reduce the expanded uncertainty by up to 85 %. The application of the Bayesian approach to proving workpiece conformance to specification (as given by international standard ISO 14253-1) is presented and a procedure for increasing the conformance zone by modifying the expanded uncertainty guard bands is discussed