## A new calibration setup for lock-in amplifiers in the low frequency range and its validation in a bilateral comparison

This paper addresses the calibration of lock-in amplifiers in the low frequency range. A simple but effective calibration setup implemented at INRIM is described. This includes a stable low-voltage source, composed of a digital sine wave generator and a cascade of two voltage dividers, one inductive and one resistive. The magnitude error is the lock-in magnitude error, which can be determined with an uncertainty of the order of 10 −4 or better, that is, two orders of magnitude lower than the…

## Absolute frequency of 87 Sr at 1.8 × 10 −16 uncertainty by reference to remote primary frequency standards

The optical lattice clock NICT-Sr1 regularly reports calibration measurements of the international timescale TAI. By comparing measurement results to the reports of eight primary frequency standards, we find the absolute frequency of the 87 Sr clock transition to be ##IMG## [http://ej.iop.org/images/0026-1394/58/2/025006/metabc232ieqn1.gif] {$f \left(\mathrm{S}\mathrm{r}\right)=429\enspace 228\enspace 004\enspace 229\enspace 873.082\left(76\right)\enspace \mathrm{H}\mathrm{z}$} , with a fractional uncertainty of less than 1.8 × 10 −16 approaching the systematic limits of the best realization of the SI second. Our result is consistent with other recent measurements and…

## Frostbite and Hypothermia

“Jack Frost nipping at your nose.” These lyrics from a popular Christmas carol evoke romantic visions of winter; however, frostbite and hypothermia are dangerous medical conditions that can present serious safety hazards. Source: IR/INFO.ORG…

## On the influence of inlet perturbations on slug dynamics in horizontal multiphase flow—a computational study

When multiphase flows are modeled numerically, complex geometrical and operational features of the experiments, such as the phase mixing section, are often not resolved in detail. Rather simplified boundary conditions are prescribed, which usually cause less irregular dynamics in the system than present in reality. In this paper, a perturbation that randomly disturbs the secondary components of the velocity vector at the inlet is proposed in order to capture the experimentally observed instabilities at the interface between the phases. This in…

## News from the BIPM laboratories—2020

In order to fulfil its mission to ensure and promote the global comparability of measurements, the BIPM operates laboratories in the fields of physical metrology, time, ionizing radiation and chemistry. These laboratories act as centres for scientific and technical collaboration between member states providing capabilities for international measurement comparisons on a shared cost basis. They coordinate international comparisons of national measurement standards agreed to be of the highest priority, and they establish and maintain appropriate reference standards for use as the…

## Measurement of the 27 Al + and 87 Sr absolute optical frequencies

We perform absolute measurement of the 27 Al + single-ion and 87 Sr neutral lattice clock frequencies at the National Institute of Standards and Technology and JILA at the University of Colorado against a global ensemble of primary frequency standards. Over an eight month period multiple measurements yielded the mean optical atomic transition frequencies ##IMG## [http://ej.iop.org/images/0026-1394/58/1/015017/metabd040ieqn1.gif] {${\nu }_{{\text{Al}}^{+}}=1\enspace 121\enspace 015\enspace 393\enspace 207\enspace 859.50\left(0.36\right)$} Hz and ν Sr = 429 228 004 229  873.19(0.15) Hz, where the stated uncertainties are dominated by statistical noise and…

## Absolute energies and emission line shapes of the L x-ray transitions of lanthanide metals

We use an array of transition-edge sensors, cryogenic microcalorimeters with 4 eV energy resolution, to measure L x-ray emission-line profiles of four elements of the lanthanide series: praseodymium, neodymium, terbium, and holmium. The spectrometer also surveys numerous x-ray standards in order to establish an absolute-energy calibration traceable to the international system of units for the energy range 4 keV to 10 keV. The new results include emission line profiles for 97 lines, each expressed as a sum of one or more Voigt…

## Establishing waveguide lines as primary standards for scattering parameter measurements at submillimetre wavelengths

This paper presents a detailed assessment of two rectangular metallic waveguide lines in order that they can be used as primary standards to provide metrological traceability for electrical scattering parameter measurements at submillimetre wavelengths. The assessment comprises a series of dimensional measurements to determine the overall quality of the lines in terms of the waveguide aperture size and alignment. This is followed by electrical measurements to confirm the electrical behaviour of the lines. Finally, the lines are employed as standards to…