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Opto-mechanical and electronic design of a tunnel-trap Si radiometer
No full textA transmission-type light-trap silicon radiometer has been developed to hold the NIST spectral power and irradiance responsivity scales between 406 nm and 920 nm. The device is built from replace able input apertures and tightly packed different-size silicon photodiodes. The photodiodes ave positioned in a triangular shape tunnel such that beam clipping is entirely eliminated within an 8 degrees field-of-view (FOV). A light trap is attached to the output of the radiometer to collect the transmitted radiation and to minimize the effect of ambient light. The photodiodes, selected for equal shunt resistance, are connected in parallel. The capacitance and the resultant shunt resistance of the device were measured and frequency compensations were applied in the feedback network of the photocurrent-to-voltage converter to optimize signal-, voltage-, and loop-gain characteristics. The trap radiometer can measure either dc or ac optical radiation with high sensitivity. The noise-equivalent-power of the optimized device is 47 fW in dc mode and 5.2 fW at 10 Hz chopping. The relative deviation from the cosine responsivity in irradiance mode was measured to be equal to or less than 0.02 % within 5 degrees FOV and 0.05 % at 8 degrees FOV. The trap-radiometer can transfer irradiance responsivities with uncertainties comparable to those of primary standard radiometers. Illuminance and irradiance meters, holding the SI units (candela, color- and radiance-temperature), will be calibrated directly against the transfer standard trap-radiometer to obtain improved accuracy in the base-units
Robb M. Thomson
No full textRobb M. Thomson
Inducted: 2000
Citation: For leadership of research on failures of and failure avoidance in materials and management of the NIST postdoctoral program.
Tenure: 1971-1995
Birth: 1925, El Paso, Texas
Education:
University of Chicago, MS, 1950
Syracuse University, PhD (Physics), 1953
Positions held:
Senior Research Scientist, Institute for Applied Technology
Program Coordinator for Failure Avoidance
NIST Post Doctoral Program Director
NBS/NIST Fellow, Materials Science and Engineering Laboratory
Post retirement: Emeritus Fellow
Honors:
U.S. Department of Commerce: Silver Medal, 1980; Gold Medal, 1987
Memberships:
American Physical Society (Fellow)
American Association for the Advancement of Science
American Society for Metals
American Institute of Metallurgical Engineers
Publications:
Author of technical papers, book chapters and encyclopedia articles on the theory of imperfections in solids and their mechanical properties and one book: Physics of Solids, McGra
President Bill Clinton delivers an address at the National Quality Awards Ceremony
No full textCommerce Secretary William Daley and National Quality Award winners applaud on stage. This image is part of the Malcolm Baldrige Portrait File collection. The Malcolm Baldrige File collection contains photographs of the annual national award given by the President of the United States for industrial excellence. The award was named for Secretary of Commerce Malcolm Baldrige who died in 1987. The collection also includes photographs of the Malcolm 'Mac' Baldrige National Oceanic and Atmospheric Administration (NOAA) Ship
Precision measurement of fundamental constants using GAMS4
No full textWe discuss the connection of high-energy gamma-ray measurements with precision atomic mass determinations. These rather different technologies, properly combined, are shown to lead to new values for the neutron mass and the molar Planck constant. We then proceed to describe the gamma-ray measurement process using the GAMS4 facility at the Institut Laue-Langevin and its application to a recent measurement of the 2.2 MeV deuteron binding energy and the neutron mass. Our paper concludes by describing the first crystal diffraction measurement of the 8.6 MeV Cl-36 binding energy
Electron-impact total ionization cross sections of molecular ions
No full textThe Binary-Encounter-Bethe (BEB) model for electron-impact total ionization cross sections of neutral molecules has been modified for molecular positive ions. The total ionization cross sections for H-2(+), N-2(+), CD+, and CO+ from the modified BEB formula are compared to available experimental data. The theory is in good agreement with experimental data on H-2(+), N-2(+), and CD+, but the experimental data by Belic et al. on N-2(+), and CO+ are lower than the theory. The large difference between the theory and experiment on CO+ is a strong indication of the dominance of the dissociative ionization channel, CO+-->C++O+, which was not included in the experiment
Absolute steady-state thermal conductivity measurements by use of a transient hot-wire system
No full textA transient hot-wire apparatus was used to measure the thermal conductivity of argon with both steady-state and transient methods. The effects of wire diameter, eccentricity of the wire in the cavity, axial conduction, and natural convection were accounted for in the analysis of the steady-state measurements. Based on measurements on argon, the relative uncertainty at the 95 % level of confidence of the new steady-state measurements is 2 % at low densities. Using the same hot wires, the relative uncertainty of the transient measurements is 1 % at the 95 % level of confidence. This is the first report of thermal conductivity measurements made by two different methods in the same apparatus. The steady-state method is shown to complement normal transient measurements at low densities, particularly for fluids where the thermophysical properties at low densities are not known with high accuracy
Treasure of the past III: Gravitational Anisotropy in Crystals
No full textEinstein's theory of gravitation is based upon a fundamental postulate which asserts that gravitation and inertia are identical in nature and hence indistinguishable. This if true, is of the greatest theoretical importance, for gravitation has heretofore refused to show any relationship to other physical phenomena. A most delicate test of this postulate is possible in a crystal of one of the nonisometric systems; for in such a crystal every known physical property (except inertia and, possibly, weight) varies with the axial direction in the crystal; and it is an interesting question whether, in such a crystal, gravitation will be found to align itself with inertia or will show some variability which will classify it with the great majority of physical phenomena. To test this point, large crystals were weighed in different axial positions with respect to the earth. The specimens examined represented all five nonisometric systems, and were weighed to a precision, in most cases, of I part in 10(9). The results were uniformly negative, and to this degree of precision are in Einstein's favor. Incidentally, this work has shown the practical possibility of using the gravity balance to a precision of I part in 10(9), even when the swing of the beam must be stopped and the object turned through a considerable angle. A precision of about the same order was attained by Majorana in 1920. In this work it was not necessary to arrest the beam or to touch the load. The next best record (in work of a somewhat different kind) at the International Bureau of Weights and Measures is 7 parts in 10(9)
IMPI: Making MPI interoperable
No full textThe Message Passing Interface (MPI) is the de facto standard for writing parallel scientific applications in the message passing programming paradigm. Implementations of MPI were not designed to interoperate, thereby limiting the environments in which parallel jobs could be run. We briefly describe a set of protocols, designed by a steering committee of current implementors of MPI, that enable two or more implementations of MPI to interoperate within a single application. Specifically, we introduce the set of protocols collectively called Interoperable MPI (IMPI). These protocols make use of novel techniques to handle difficult requirements such as maintaining interoperability among all IMPI implementations while also allowing for the independent evolution of the collective communication algorithms used in IMPI. Our contribution to this effort has been as a facilitator for meetings, editor of the IMPI Specification document, and as an early testbed for implementations of IMPI. This testbed is in the form of an IMPI conformance tester, a system that can verify the correct operation of an IMPI-enabled version of MPI