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Usage Analysis of the NIST Internet Time Service
No full textThe Internet Time Service (ITS) at the National Institute of Standards and Technology (NIST) currently receives over 16 billion time requests per day. ITS servers derive their system time from the NIST atomic-referenced time scale and distribute it freely to the public. Here we explore ITS usage patterns discovered by analysis of inbound network traffic. For example, over a period of four weeks, just two of the ≈ 20 ITS servers received requests from 316 million unique Internet Protocol (IPv4) addresses, which is at least 8.5 % of the entire Internet. We offer recommendations for networked device/software manufacturers, and providers and consumers of network time services
Stress Analysis of Conical Contact Joints in the NIST 4.45 MN Deadweight Machine
No full textDuring the disassembly phase of the refurbishment of the National Institute of Standards and Technology 4.45 MN Deadweight Machine, workers confirmed previously suspected damage in certain conical contact joints within the apparatus. A finite element analysis of the contact joints is performed with the aim of understanding some of the potential origins of failure in order to prevent future damage in the machine. Parametric studies are performed using a finite element model while varying geometry, material constitutive relations, and frictional forces at the interface of the convex and concave cones. The numerical solutions treat nonlinearities originating from elastic-plastic material relations, frictional forces, and contact between the surfaces. These results provide insights into the mechanisms of stress generation in such joints, and how these stresses are influenced by different structural parameters
Assignment of the Number of Equivalent Reference Fluorophores to Dyed Microspheres
No full textA procedure will be described to assign to each dyed microsphere a number called the Equivalent number of Reference Fluorophores (ERF). The ERF unit gives the number of reference fluorophores in solution which produce the same fluorescence signal as a single dyed microsphere. In the first step, fluorescence measurements were carried out on serial dilutions of a solution of reference fluorophores. The resulting fluorescence intensities and the corresponding concentrations were used to calibrate the response of the fluorometer. The calibration consisted of establishing a linear relation between the intensities and concentrations. In the second step, the fluorescence intensity from a suspension of microspheres was measured in order to determine the equivalent concentration of reference fluorophores which gave the same fluorescence intensity as the suspension of microspheres. This was performed by utilizing the calibration line obtained in the first step. In the third step, a flow cytometer and a light obscuration apparatus were used to measure the total concentration of microspheres in the suspensions used for the fluorescence measurements. In addition to the total microsphere concentration, the flow cytometer also enabled the measurement of the concentration of a sub population of microspheres which are used to calibrate the fluorescence scale of a flow cytometer. The fourth step utilized the data collected in steps one, two, and three to assign a value of ERF to individual microspheres. The set of microspheres with assigned ERF values will be used to establish a linear fluorescence scale in each channel of a flow cytometer. The discussion will emphasize the estimate of uncertainties in each step of the assignment process
Test Object for Accurate and Reproducible Measurement of the Detection Response of Hand-worn and Hand-held Metal Detectors
No full textThe assessment of the detection performance of metal detectors (hand-worn, hand-held, and walk-through models) is based on the ability of the detectors to sound an alarm when presented with a test object. These test objects are typically actual threat items or simulated threat items. The orientation of these test objects with the magnetic field generated by the metal detectors may affect the detectability of the test objects. More importantly, small misorientations of a threat object or simulated threat object may cause the operator to incorrectly attribute to the metal detector a higher performance than it is capable of providing. Consequently, to support accurate and reproducible characterization of the performance of a metal detector, orientation effects should be minimized or eliminated. We discuss the use of spherical test objects to eliminate this potentially serious error in the assessment of the detection performance of a metal detector. In this study, we consider only hand-worn and hand-held metal detectors because of their similarity in size and operation
Form Factors for Branched Polymers with Excluded Volume
No full textThe form factors for star-branched polymers with linear branches or with looping branches are calculated. The effect of chain swelling excluded volume is incorporated through an excluded volume parameter approach. The form factor for ring polymers is also included, since it is nicely derived as a special case. Furthermore, the form factor for dendrimers with excluded volume is also calculated. In order to evaluate the form factor for stars with looping branches, the multivariate Gaussian function is used to close the looping branches. Analytical results are possible in the Gaussian chain case (i.e., with no excluded volume), but the calculations are left in a form involving summations over monomers when the general case incorporates excluded volume
Leslie A. Guildner
No full textLESLIE A. GUILDNER
NBS/NIST: 1959-1982
INDUCTED: 2016
Birth: 1 August 1920, Lincoln, Nebraska
Death: 31July 2012
EDUCATION:
University of Nebraska; AB (Chemistry), 1948
University of Nebraska; AM (Chemistry), 1949
Massachusetts Institute of Technology, PhD (Physical Chemistry), 1954
CITATION:
For research in thermometry that provided the basis for the redefinition of the International Practical Temperature Scale in the critical range from the triple point of water to 457 °K.
POSITIONS HELD AT NBS/NIST:
Physicist, Heat Division, Institute for Basic Standards, 1959-1982
HONORS:
U.S. Department of Commerce Silver Medal (1977) and Gold Medal (1980)
Who's Who in Science
Who's Who in America
MEMBERSHIPS:
American Physical Society
PUBLICATIONS:
More than 20 publications including:
Guildner, L.A., Stimson, H.F., Edsinger, R.E., and Anderson, R.L., "An Accurate Mercury Manometer for the
NBS Gas Thermometer," Metrologia 6, No. 1, pp 1-18 (1970)
Guildner, L.A. and Edsinger, R.E., "The Thermodynamic Kelvin Temperature Scale from 273.15 K to 415 K,"
Journal of Research of the NBS, 77A, No. 4, 383-389 (1973)
Guildner, L.A., Anderson, R.L., and Edsinger, R.E., "Effects of Sorption on the Realization of the
Thermodynamic Scale," Temperature, Its Measurement and Control in Science and Industry, Vol 4 (1973) Guildner, L.A. and Edsinger, R.E., "Deviation oflnternational Practical Temperatures from Thermodynamic
Temperatures in the Temperature Range from 273.16 K To 730 K," Journal of Research of the NBS, 80A,
703 (1976)
Guildner, L.A., "The Measurement of Thermodynamic Temperature," Physics Today, 35, No. 12, (1982
George E. Kelly
No full textGEORGE E. KELLY
NBS/NIST: 1970-2007
INDUCTED: 2016
Birth: 28 March 1944, Brooklyn, New York
EDUCATION:
State University of New York at Stony Brook, BS (Engineering
Science), 1965
Northwestern University, PhD (Mechanical Engineering), 1970
CITATION:
For leadership of environmental systems research on the performance of building systems and appliances, standards for open and integrated building systems, and advanced building controls.
POSITIONS HELD AT NBS/NIST:
Postdoctoral Research Associate, Heat Division, Institute for Basic Standards, 1970-1972
Physicist, Sensory Environment Branch, Building Research Division, Institute for Applied Technology (IA T),
1972-1974
Physicist, Mechanical Systems Section, Building Environment Division, Center for Building Technology (CBT),
IAT, 1974-1976
Mechanical Engineer, Mechanical Systems Section, Building Environment Division, CBT, IA T, 1976-1980 Group Leader, Mechanical Systems and Controls Group, Building Equipment Division, CBT, National
Engineering Laboratory, 1980-1999
Chief, Building Environment Division, Building and Fire Research Laboratory, 1999-2007
Guest Researcher, Mechanical Systems and Controls Group, Energy and Environment Division, Engineering Laboratory, 2007- present
HONORS:
U.S. Department of Commerce Silver Medal (1978)
Fellow, ASHRAE (1990)
Department of Commerce Engineer of the Year (1992)
MEMBERSHIPS:
American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE)
PUBLICATIONS:
More than 60 publications including:
Kelly, G.E., Bean, J., "Dynamic Performance of a Residential Air-to-Air Heat Pump," NBS BSS 93 (March
1977)
Park, C., Clark, D.R., Kelly, G.E., "An Overview ofHV ACSIM+, A Dynamic Building/HY AC/Control Systems
Simulation Program," Proceedings of 1st Annual Building Energy Simulation Conference (BESC), Seattle,
Washington (August 21-22, 1985)
Kelly, G.E., May, W.B., Kao, J.Y., and Park, C., "Using Emulators to Evaluate the Performance of Building
Energy Management Systems," ASHRAE Transactions, Vol. 100, No. 1 (1994)
Lee, W.Y., Park, C., House, J.M., and Kelly, G.E., "Fault Detection and Diagnosis for HV AC Systems,"
Symposium, Proceedings ASHRAE Annual Meeting, Atlanta, Georgia (February 17-21, 1995)
Kelly, G.E., Bushby, S.T., Optimization of Building HVAC Systems Using Intelligent Agents -A Proof of
Concept Study, NIST Technical Note 1707 (2011)
Kelly, G.E. and Bushby, S.T., "Are Intelligent Agents the Key to Optimizing Building HV AC System Performance?," HVAC&R Research, Vol. 18, Issue 4, 750-759 (2012
Q-matrix: An Algebraic Formulation for the Analysis and Visual Characterization of Network Graphs
No full textGiven an undirected network, we describe a two-dimensional graphical measure based on the connected component distribution of its degree-limited subgraphs. This process yields an unambiguous visual portrait, which reveals important network properties. It can be used as a classification tool, as graphs from related application areas have striking similarities. It can also be used as an efficient algorithm to demonstrate graph non-isomorphism for large graphs with identical degree distributions. Finally, it can be used as an analysis tool to help distinguish real-world networks from their synthetic counterparts
A Study of GPS Carrier-Phase Time Transfer Noise Based on NIST GPS Receivers
No full textTo do a better time comparison between high-precision clocks (such as a Cesium-fountain clock and Hydrogen-maser clock), we want to study and eventually lower the GPS carrier-phase time transfer noise. The GPS carrier-phase time transfer noise comes from four sources: GPS satellite, GPS signal path, ground receiving equipment (receiver and antenna), and data-processing algorithm. This paper focuses on the noise introduced by the ground receiving equipment. At NIST, we have installed seven GPS receivers. All receivers have the same reference time, i.e., UTC(NIST). Three of them are connected to the same antenna. The other four are connected to four different antennas. This architecture enables us to study the time-transfer noise from the ground receiving equipment. We study both long-term (> 100 days) noise and short-term (< 1 day) noise. For the long-term noise, the time-transfer result using one receiver can vary from that using another receiver by up to 1.8 ns, during 1.3 years. To achieve sub-nanosecond GPS timing accuracy, a careful monitoring of the time delays or a more frequent calibration is needed. For the short-term noise, we find that the common-clock difference between receivers using the same antenna is less noisy than that using two different antennas, at an averaging time of less than 0.5 hour. This indicates that the antenna and antenna cable contribute to the super-short-term noise of GPS carrier-phase time transfer significantly. In addition, the response to the GPS receiver’s reference-time change is tested in this paper. The variation in the response can be up to ± 350 ps. Last, this paper gives the best carrier-phase time transfer result we can currently achieve with the available equipment at NIST. The best frequency stability is 4.0×10−16 at 3 hours, 1.1×10−16 at 1 day, 4.0×10−17 at 10 days, and 1.3×10−17 at 48 days
Propagation of Error from Registration Parameters to Transformed Data
No full textMethods to register two sets of data have existed for quite some time. However, these sets of data are rarely error-free. Consequently, any registration based on this data will be affected by the error. Moreover, if the corresponding registration matrix is then used to transform data from one coordinate system to another, any error from the registration will also get propagated to the transformed data. In this paper, we will characterize this propagation of random error, or noise, through a mathematical perspective and will illustrate its use with data obtained from physical experiments and with quasi-simulated sets of data. In addition, we will discuss the limitations of this propagation of error when systematic bias is present in the data