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An experiment is being carried out at J-PARC -- Japan Proton Accelerator Research Complex -- to study the origin of hadron mass and the partial restoration of chiral symmetry of quantum chromodynamics in a finite density matter. The experiment, which is called the J-PARC E16 experiment, aims to measure the mass spectra of vector mesons in nuclei due to finite density effects. Previous measurements were performed at KEK-PS proton synchrotron and showed mass modifications of vector mesons in nuclei. A new experiment aims to confirm the results of KEK-PS with larger statistics to have a detailed study. Mass spectra of vector mesons are measured using electron--positron decays in proton-nucleus reactions. A new beam line is built to provide a high-intensity proton beam for the experiment, and decayed electrons and positrons are detected and identified by a newly constructed spectrometer. The experiment started the acquisition of pilot data to evaluate the performances of the beam line and the spectrometer in 2020 and 2021. The spectrometer worked well, and physics data taking will start in 2023. [ABSTRACT FROM AUTHOR]

For the accurate measurement of small masses and forces, a voltage balance that uses electrostatic force between electrodes has been developed at the National Metrology Institute of Japan (NMIJ). This voltage balance enables traceable mass and force measurements based on the revised definition of the kilogram, as per electric standards. To confirm the reliability of the developed balance apparatus, the mass of a 2 mg wire weight was determined. The first complete uncertainty analyses were performed, following which the relative standard uncertainty of the mass measurement was estimated to be $5.3 \times 10^{-4}$. The mass of the weight was measured via the submultiple method in a traceable manner with respect to the mass standard at NMIJ. The results obtained from the two different methods were observed to be in agreement within their uncertainties. [ABSTRACT FROM AUTHOR]

• The mass-measurement-type optical particle counting method has been developed. • An accurate determination of the number concentration of liquid-borne particles. • A suspension of 2 μm PSL particles was used for evaluation of the new method. • The validity of the method was examined by another independent microscopic method. • The new method has been used as the national primary standard at NMIJ/AIST, Japan. We have developed a measurement method that enables accurate determination of the number concentration of liquid-borne particles by adopting simultaneous particle counting and mass measurement. The new measurement method consists of an optical particle counter (OPC) for particle counting, an electronic balance for mass measurement, a syringe pump for sampling, and a pulse height analyzer for signal processing. We refer to this method as the mass-measurement-type optical particle counting (M-OPC) method. The M-OPC method facilitates both metrological traceability of the mass of measured suspensions and evaluation of the counting efficiency of OPCs. Using the M-OPC method, we evaluated the measurement accuracy of two different types of OPCs: a light-scattering type and a light-extinction type. The validity of the measurement results obtained with the M-OPC method was examined by comparison with the results of an independent microscopic method using a scanning electron microscope (SEM). The M-OPC method also offers the possibility of calibrating the number concentration of particles in suspensions with diameters from the sub-micrometer to micrometer range by combining multiple OPCs. This method is expected to be used as the national primary standard at the National Metrology Institute of Japan of the National Institute of Advanced Industrial Science and Technology. [ABSTRACT FROM AUTHOR]

• High-accuracy mass calibration of sub-milligram weights was realized by using a recently developed automatic weight transfer apparatus and an analytical calibration method that is often used for mass calibration of small-mass weights. • The mass calibrations of sub-milligram weights were realized with standard uncertainties smaller than those of previous studies performed by other NMIs. • To improve the calibration uncertainty of the sub-milligram weights achieved in this study, it is necessary to improve the uncertainty of calibrated masses of reference weights, update the balance used, and stabilize the measurement environment. Mass standards are essential for the precise measurement of mass. Due to the increasing demand for small mass measurements, it is essential to be able to disseminate the sub-milligram mass standard from the National Metrology Institutes. Recently, the National Metrology Institute of Japan has developed an apparatus for mass calibration of sub-milligram weights by automatically transporting the weights. Consequently, the masses of the weights can be calibrated accurately and reliably. Sub-multiple calibration is often used for accurate mass calibration of weights smaller than 1 kg. In this study, by combining this method with the developed apparatus, the mass calibration uncertainty of sub-milligram weights was improved. The mass calibrations of 0.1 mg, 0.2 mg, and 0.5 mg weights were performed with standard uncertainties of 0.019 µg, 0.023 µg, and 0.040 µg, respectively. These uncertainties were smaller than the calibration uncertainties obtained by manually transporting sub-milligram weights to an ultra-micro balance. [ABSTRACT FROM AUTHOR]

Abstract: This study has demonstrated a reliable method of quantifying the total mass of litter on a beach. It was conducted on Ookushi beach, Goto-Islands, Japan, and uses a combination of balloon-assisted aerial photography and in situ mass measurements. The total mass of litter over the beach was calculated to be 716±259kg. This figure was derived by multiplying the litter-covered area (calculated using balloon-assisted aerial photography) by the mass of litter per unit area. Light plastics such as polyethylene made up 55% of all plastic litter on the beach, although more work is needed to determine whether lighter plastics are transported to beaches more readily by winds and ocean currents compared with heavier plastics, or whether lighter plastics comprise a greater percentage of marine litter. Finally, the above estimates were used to calculate the total mass of metals released into coastal ecosystems via plastic litter on beaches. [Copyright &y& Elsevier]

• Mass comparator for transporting and weighing sub-milligram weights presented. • Apparatus can handle weights such as wire weight, sheet weight, and disk weight. • Weighing tests of wire weights and sheet weights from 1 mg to 0.1 mg were performed. • Mass calibration of weight with nominal mass of 0.1 mg was realized. Sub-milligram mass standards are important to ensure the reliability of small mass measurements. A mass comparator capable of accurately transporting and weighing sub-milligram weights was developed at the National Metrology Institute of Japan. This apparatus can handle weights of various shapes such as wire weight, sheet weight, and disk weight. The weighing tests of wire weights and sheet weights ranging from 1 mg to 0.1 mg were performed using the developed apparatus. The mass calibration of weight with a nominal mass of 0.1 mg was realized with a standard uncertainty of 0.075 μg by comparing the test weight and the reference weight. This paper describes the details of the developed mass comparator, the standard deviation of the weighing value of the weight obtained using this apparatus, and the uncertainty of mass calibration of sub-milligram weights. [ABSTRACT FROM AUTHOR]