A5026241706- Scientific Measurement and Uncertainty Evaluation
- Calibration and Measurement Techniques
- Advanced Sensor Technologies Research
- Chemical Thermodynamics and Molecular Structure
- Atmospheric Ozone and Climate
- Spectroscopy and Laser Applications
- Meteorological Phenomena and Simulations
- Advanced Thermodynamic Systems and Engines
- Microwave and Dielectric Measurement Techniques
- Advanced Thermodynamics and Statistical Mechanics
- Acoustic Wave Resonator Technologies
- Advanced Measurement and Metrology Techniques
- Spectroscopy and Quantum Chemical Studies
- Flow Measurement and Analysis
- Scientific Research and Discoveries
- Astronomical Observations and Instrumentation
- Radioactive Decay and Measurement Techniques
- Urban Heat Island Mitigation
- Numerical methods in engineering
- Optical measurement and interference techniques
- Advanced MEMS and NEMS Technologies
- Astro and Planetary Science
- Composite Material Mechanics
- Electrostatics and Colloid Interactions
- Soil Moisture and Remote Sensing
National Physical Laboratory
2013-2023
Central Office of Measures
2023
Purdue University West Lafayette
2008-2011
Teddington Memorial Hospital
2010
The Comité international des poids et mesures (CIPM) has projected a major revision of the International System Units (SI) in which all base units will be defined by fixing values fundamental constants nature. In preparation for this we have carried out new, low-uncertainty determination Boltzmann constant, kB, terms SI unit temperature, kelvin, can re-defined. We evaluated kB from exceptionally accurate measurements speed sound argon gas related directly to mean molecular kinetic energy, ....
ABSTRACT The study describes significant outcomes of the ‘Metrology for Meteorology’ project, MeteoMet , which is an attempt to bridge meteorological and metrological communities. concept traceability, idea used in both fields but with a subtle difference meaning, at heart project. For meteorology, traceable measurement one that can be traced back particular instrument, time location. From perspective, traceability further implies primary realization quantity being measured terms base units...
The principles and techniques of primary refractive-index gas thermometry (RIGT) are reviewed. Absolute RIGT using microwave measurements helium-filled quasispherical resonators has been implemented at the temperatures triple points neon, oxygen, argon water, with relative standard uncertainties ranging from 9.1 × 10-6 to 3.5 10-5. Researchers now also argon-filled cylindrical for near ambient temperature, between 3.8 10-5 4.6 10-5, conducting on isobars low temperatures. optical frequencies...
Recent advances regarding the interplay between ab initio calculations and metrology are reviewed, with particular emphasis on gas-based techniques used for temperature pressure measurements. Since roughly 2010, several thermophysical quantities – in particular, virial transport coefficients can be computed from first principles without uncontrolled approximations rigorously propagated uncertainties. In case of helium, computational results have accuracies that exceed best experimental data...
Launched in 2011 within the European Metrology Research Programme (EMRP) of EURAMET, joint research project "MeteoMet -Metrology for Meteorologyis
The International Committee for Weights and Measures (CIPM), at its meeting in October 2017, followed the recommendation of Consultative Units (CCU) on redefinition kilogram, ampere, kelvin mole. For kelvin, Boltzmann constant will be fixed with numerical value 1.380 649 × 10
In both meteorological and metrological applications, it is well known that air temperature sensors are susceptible to radiative errors. However, not widely the error measured by an sensor in flowing depends upon diameter, with smaller reporting values closer true temperature. This a transient effect related heat capacity, but fluid-dynamical arising from mass flow cylindrical geometries. result has been historically meteorology text books. its significance does appear be appreciated and, as...
In 2011, a working group of the Consultative Committee for Thermometry published their best estimates differences between thermodynamic temperature T and its approximation (T90), according to International Temperature Scale 1990, ITS-90. These consensus estimates, in combination with measurements made accordance ITS-90, are an important alternative primary thermometry those requiring accurate temperature. Since there has been change definition kelvin significant improvements thermometry....
The perturbing effect of a waveguide on the boundary quasispherical cavity resonator is investigated both theoretically and experimentally. Expressions for frequency perturbation to triply degenerate TM1mn TE1mn modes are derived using theory. fields in around calculated static limit finite-element software. Experiments performed cylindrical resonators confirm accuracy generality approach. impact this study attempts re-determine Boltzmann constant (kB) by an acoustic resonance technique...
Using exceptionally accurate measurements of the speed sound in argon, we have made estimates difference between thermodynamic temperature, T, and temperature estimated using International Temperature Scale 1990, T90, range 118 K to 303 K. Thermodynamic was technique relative primary acoustic thermometry NPL-Cranfield combined microwave resonator. Our values (T-T90) agree well with most recent estimates, but because taken data at closely spaced intervals, reveal previously unseen detail....
Previous research effort towards the determination of Boltzmann constant has significantly improved supporting theory and experimental practice several primary thermometry methods based on measurement a thermodynamic property macroscopic system at temperature triple point water. Presently, experiments are under way to demonstrate their accuracy in T over an extended range spanning interval between few kelvin copper freezing (1358 K). We discuss how these activities will improve link as...
Abstract We provide a survey on the joint European research project “GeoMetre”, which explores novel technologies and their inclusion to existing surveying strategies improve traceability of geodetic reference frames SI definition metre. This work includes development distance meters with range up 5 km, realisation optical multilateration systems for large structure monitoring at an operation 50 m beyond, strategy GNSS-based determination. Different methods refractivity compensation, based...
Although short n-alkane chains are classic examples of hydrophobic solutes, mounting evidence points to a hydrophilic crossover for the hydration free energies (ΔG) sufficiently long chains. Experimental and simulation results n-alkanes from methane (C1) docosane (C22) combined with fundamental thermodynamic relations elucidate intermolecular contributions ΔG. Theoretical bounds on influence solute conformation ΔG inferred by considering idealized linear (all-trans) globular (spherical)...
We describe the dimensional characterization of copper quasisphere NPL-Cranfield 2. The is assembled from two hemispheres such that internal shape a triaxial ellipsoid, major axes which have nominal radii 62.000 mm, 62.031 mm and 62.062 mm. artefact has been manufactured using diamond-turning technology shows deviation design form less than ±1 µm over most its surface. Our involves both coordinate measuring machine (CMM) experiments microwave resonance spectroscopy.
In 2013, a team from NPL, Cranfield University and SUERC published an estimate of the Boltzmann constant based on precision measurements speed sound in argon. A key component our results was molar mass argon gas used measurements. To achieve this we made comparison isotope ratios found experimental against isotopes atmospheric air. We then previous measurement to calibrate relative sensitivity spectrometer different isotopes. The carried out at KRISS using calibrated samples known isotopic...
In 2013, NPL, SUERC and Cranfield University published an estimate for the Boltzmann constant (de Podesta et al 2013 Metrologia 50 354–76) based on a measurement of limiting low-pressure speed sound in argon gas. Subsequently, extensive investigation by Yang (2015 52 S394–409) revealed that there was likely to have been error molar mass used experiment. Responding S394–409), de revised their 2015 S353–63). The shift estimated mass, kB, large: −2.7 parts 106, nearly four times original...
We report the first measurements of a quasi-spherical microwave resonator used as dew-point hygrometer. In conventional hygrometers, condensation water from humid gas flowing over mirror is detected optically, and surface then temperature-controlled to yield stable condensed layer. our experiments we flowed moist air humidity generator through onset by measuring frequency ratio selected modes. verified basic operation device range 9.5–13.5 °C comparison with calibrated chilled-mirror...
Interfacial fluctuations in the cohesive (van der Waals) interaction energy of spherical oil-drops with water provide evidence a length scale dependent transition from linear to non-linear response behavior. For sub-nanometer oil-drop sizes, are found be independent van Waals coupling strength, while nanometer (and larger) size oil drops experience highly fluctuations. The latter behavior is linked enhanced hydrophobic density and emergence entropic contributions oil-water free energies.
ABSTRACT Temperature and humidity measurements in the upper atmosphere are of critical importance for understanding Earth's climate. However, such difficult several reasons. Rising sondes carry moisture upwards, compromising dry stratospheric environment. In addition, difference time constants thermometers hygrometers leads to difficulties determining extent saturation air. Finally, effects insolation, evaporative cooling poor thermal contact with air compound other measurement problems. To...
Previously (Underwood et al 2015 Meteorol. Appl. 22 830) we reported first tests of a device capable simultaneous, non-contact, temperature and humidity (NCTAH) measurements in air. The used an acoustic thermometer tuneable diode laser absorption spectrometer (TDLAS), combination which should be extremely rapid response to changes as it does not require moisture solid-state matrix equilibrate with the surrounding In this paper report recent developments instrument focussed on reducing its...