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John (Jack) Ekin
No full textJOHN (JACK) W. EKIN
NBS/NIST (Boulder): 1973-2007
INDUCTED: 2013
B: 31 August 1944, Pittsburgh, Pennsylvania
EDUCATION: University of Michigan, BS (Physics, Mathematics), 1966
Fulbright Fellowship, University of Heidelberg, 1966-1967
Cornell University, MS (Solid State Physics), 1969
Cornell University, PhD (Solid State Physics), 1971
Postdoctoral Fellow, Rutgers University, 1971-1973
CITATION:
For discovery, research excellence, and world leadership in the effects of strain on the performance of practical superconductors.
POSITIONS HELD AT NBS/NIST:
National Research Council Postdoctoral Associate, NBS, 1973–1975
Physicist, Cryogenics Division and Thermophysical Properties Division, National Measurement Laboratory (Boulder), 1975–1981
Physicist, Electromagnetic Technology Division, National Engineering Laboratory (Boulder), 1981–1983
Leader, Superconductor Electromagnetic Measurements Project, Electro-magnetic Technology Division, the Magnetic Technology Division, and the Electromagnetics Division, Electronics and Electrical Engineering Laboratory and Physical Measurement Laboratory (Boulder), 1983–2007
HONORS:
NIST Bronze Medal (1980) and U.S. Department of Commerce Silver Medal (1988)
Fellow, American Physical Society (1995)
EEEL Authorship Award for “Experimental Techniques” (2006)
NIST Edward Ehler Condon Award, textbook, “Experimental Techniques for Low-Temperature Measurements” (2007)
IEEE Award for Continuing and Significant Contributions in the Field of Applied Superconductivity (2010)
MEMBERSHIPS:
American Physical Society (APS) and Institute of Electrical and Electronics Engineers (IEEE) National Science Foundation advisory committee to establish National High Magnetic Field Laboratory, Tallahassee, Florida
Advisory and Editorial Board, Mechanical and Electromagnetic Properties of Composite Superconductors Conference Versailles Project on Advanced Materials and Standards (VAMAS) Organizing Committee of U.S.-Japan Workshop on Advanced Superconductors
PUBLICATIONS:
More than 170 publications including:
Ekin, J.W., “Current Transfer in Multifilamentary Superconductors. 1. Theory,” J. Appl. Phys. 49, 3406-3409 (1978)
Ekin, J.W., “Strain Scaling Law for Flux Pinning in Practical Superconductors. 1. Basic relationship and application to Nb3Sn conductors,” Cryogenics 20, 611-624 (1980)
Ekin, J.W., et al., “High-Tc Superconductor Noble-metal Contacts with Surface Resistivities in the 10-10 Ω. cm2 range,” Appl. Phys. Lett. 52, 1819-1821 (1988)
Ekin, J.W., “Experimental Techniques for Low-Temperature Measurements,” Oxford University Press, pp 704, (2006, 2007, 2011)
Ekin, J.W., “Unified Scaling Law for Flux Pinning in Practical Superconductors: I. Separability postulate, raw scaling data and parameterization at moderate strains,” Supercond. Sci. Tech. 23, 083001 (2010
Eddy Current Rail Inspection Using AC Bridge Techniques
No full textAC bridge techniques commonly used for precision impedance measurements have been adapted to develop an eddy current sensor for rail defect detection. By using two detection coils instead of just one as in a conventional sensor, we can balance out the large baseline signals corresponding to a normal rail. We have significantly enhanced the detection sensitivity of the eddy current method by detecting and demodulating the differential signal of the two coils induced by rail defects, using a digital lock-in amplifier algorithm. We have also explored compensating for the lift-off effect of the eddy current sensor due to vibrations by using the summing signal of the detection coils to measure the lift-off distance. The dominant component of the summing signal is a constant resulting from direct coupling from the excitation coil, which can be experimentally determined. The remainder of the summing signal, which decreases as the lift-off distance increases, is induced by the secondary eddy current. This dependence on the lift-off distance is used to calibrate the differential signal, allowing for a more accurate characterization of the defects. Simulated experiments on a sample rail have been performed using a computer controlled X-Y moving table with the X-axis mimicking the train's motion and the Y-axis mimicking the train's vibrational bumping. Experimental results demonstrate the effectiveness of the new detection method
A Case Study of Performance Degradation Attributable to Run-Time Bounds Checks on C++ Vector Access
No full textProgrammers routinely omit run-time safety checks from applications because they assume that these safety checks would degrade performance. The simplest example is the use of arrays or array-like data structures that do not enforce the constraint that indices must be within bounds. This report documents an attempt to measure the performance penalty incurred by two different implementations of bounds-checking in C and C++ using a simple benchmark and a desktop PC with a modern superscalar CPU. The benchmark consisted of a loop that wrote to array elements in sequential order. With this configuration, relative to the best performance observed for any access method in C or C++, mean degradation of only (0.881 ± 0.009) % was measured for a standard bounds-checking access method in C++. This case study showed the need for further work to develop and refine measurement methods and to perform more comparisons of this type. Comparisons across different use cases, configurations, programming languages, and environments are needed to determine under what circumstances (if any) the performance advantage of unchecked access is actually sufficient to outweigh the negative consequences for security and software quality
Oral history interview of John W. Cahn, Thursday, May 30, 2013, / with J. William Gadzuk, William Boettinger, Frank Gayle, Jonathan Guyer, Mike Moldover, and Jack Rush.
No full textOral History interview of John W. Cahn conducted on Thursday, May 30, 2013 at the National Institute of Standards and Technology in Gaithersburg, Maryland
The New Kilogram Definition and its Implications for High-Precision Mass Tolerance Classes
No full textThe SI unit of mass, the kilogram, is the only remaining artifact definition in the seven fundamental units of the SI system. It will be redefined in terms of the Planck constant as soon as certain experimental conditions, based on recommendations of the Consultative Committee for Mass and Related Quantities (CCM) are met. To better reflect reality, the redefinition will likely be accompanied by an increase in the uncertainties that National Metrology Institutes (NMIs) pass on to customers via artifact dissemination, which could have an impact on the reference standards that are used by secondary calibration laboratories if certain weight tolerances are adopted for use. This paper will compare the legal metrology requirements for precision mass calibration laboratories after the kilogram is redefined with the current capabilities based on the international prototype kilogram (IPK) realization of the kilogram
Registration of Six Degrees of Freedom Data with Proper Handling of Positional and Rotational Noise
No full textWhen two six degrees of freedom (6DOF) datasets are registered, a transformation is sought that minimizes the misalignment between the two datasets. Commonly, the measure of misalignment is the sum of the positional and rotational components. This measure has a dimensional mismatch between the positional component (unbounded and having length units) and the rotational component (bounded and dimensionless). The mismatch can be formally corrected by dividing the positional component by some scale factor with units of length. However, the scale factor is set arbitrarily and, depending on its value, more or less importance is associated with the positional component relative to the rotational component. This may result in a poorer registration. In this paper, a new method is introduced that uses the same form of bounded, dimensionless measure of misalignment for both components. Numerical simulations with a wide range of variances of positional and rotational noise show that the transformation obtained by this method is very close to ground truth. Additionally, knowledge of the contribution of noise to the misalignment from individual components enables the formulation of a rational method to handle noise in 6DOF data
Calibration of Traceable Solid Mock 131I Phantoms Used in an International SPECT Image Quantification Comparison
No full textThe International Atomic Energy Agency (IAEA) has organized an international comparison to assess Single Photon Emission Computed Tomography (SPECT) image quantification capabilities in 12 countries. Iodine-131 was chosen as the radionuclide for the comparison because of its wide use around the world, but for logistical reasons solid 133Ba sources were used as a long-lived surrogate for 131I. For this study, we designed a set of solid cylindrical sources so that each site could have a set of phantoms (having nominal volumes of 2 mL, 4 mL, 6 mL, and 23 mL) with traceable activity calibrations so that the results could be properly compared. We also developed a technique using two different detection methods for individually calibrating the sources for 133Ba activity based on a National standard. This methodology allows for the activity calibration of each 133Ba source with a standard uncertainty on the activity of 1.4 % for the high-level 2-, 4-, and 6-mL sources and 1.7 % for the lower-level 23 mL cylinders. This level of uncertainty allows for these sources to be used for the intended comparison exercise, as well as in other SPECT image quantification studies
The Importance of Dosimetry Standardization in Radiobiology
No full textRadiation dose is central to much of radiobiological research. Precision and accuracy of dose measurements and reporting of the measurement details should be sufficient to allow the work to be interpreted and repeated and to allow valid comparisons to be made, both in the same laboratory and by other laboratories. Despite this, a careful reading of published manuscripts suggests that measurement and reporting of radiation dosimetry and setup for radiobiology research is frequently inadequate, thus undermining the reliability and reproducibility of the findings. To address these problems and propose a course of action, the National Cancer Institute (NCI), the National Institute of Allergy and Infectious Diseases (NIAID), and the National Institute of Standards and Technology (NIST) brought together representatives of the radiobiology and radiation physics communities in a workshop in September, 2011. The workshop participants arrived at a number of specific recommendations as enumerated in this paper and they expressed the desirability of creating dosimetry standard operating procedures (SOPs) for cell culture and for small and large animal experiments. It was also felt that these SOPs would be most useful if they are made widely available through mechanism(s) such as the web, where they can provide guidance to both radiobiologists and radiation physicists, be cited in publications, and be updated as the field and needs evolve. Other broad areas covered were the need for continuing education through tutorials at national conferences, and for journals to establish standards for reporting dosimetry. This workshop did not address issues of dosimetry for studies involving radiation focused at the sub-cellular level, internally-administered radionuclides, biodosimetry based on biological markers of radiation exposure, or dose reconstruction for epidemiological studies
Critically Evaluated Energy Levels and Spectral Lines of Singly Ionized Indium (In II)
No full textA comprehensive list of the best measured wavelengths in the In II spectrum has been compiled. Uncertainties of the wavelength measurements have been analyzed, and existing inconsistencies have been resolved. An optimized set of fine-structure energy levels that fits all observed wavelengths has been derived. Uncertainties of the energy level values have been reduced by an order of magnitude. An improved value of the ionization limit of In II has been determined by fitting quantum-defect and polarization formulas for several series of levels. Intensities of lines observed by different authors have been analyzed and converted to a uniform scale. A set of recommended values of radiative transition rates has been critically compiled, and uncertainties of these rates have been estimated. The hyperfine structure interval in the 5s 2S ground state of In III has been determined from the measurements of the 5sng and 5snh series in In II
Precise Measurement of Lunar Spectral Irradiance at Visible Wavelengths
No full textWe report a measurement of lunar spectral irradiance with an uncertainty below 1 % from 420 nm to 1000 nm. This measurement uncertainty meets the stability requirement for many climate data records derived from satellite images, including those for vegetation, aerosols, and snow and ice albedo. It therefore opens the possibility of using the Moon as a calibration standard to bridge gaps in satellite coverage and validate atmospheric retrieval algorithms. Our measurement technique also yields detailed information about the atmosphere at the measurement site, suggesting that lunar observations are a possible solution for aerosol monitoring during the polar winter and can provide nighttime measurements to complement aerosol data collected with sun photometers. Our measurement, made with a novel apparatus, is an order of magnitude more accurate than the previous state-of-the-art and has continuous spectral coverage, removing the need to interpolate between filter passbands