Estimation of Wideband Multi-Component Phasors Considering Signal Damping.

Harmonic and interharmonic content in power system signals is increasing with the development of renewable energy generation and power electronic devices. These multiple signal components can seriously degrade power quality, trip thermal generators, cause oscillations, and threaten system stability, especially the interharmonic tones with positive damping factors. The first step to mitigate these adverse effects is to accurately and quickly monitor signal features, including frequency, damping factor, amplitude, and phase. This paper proposes a concise and robust index to identify the number of modes present in the signal using the singular values of the Hankel matrix and discusses the scope of its application by testing the influence of various factors. Next, the simplified matrix pencil theory is employed to estimate the signal component frequency and damping factor. Then their estimates are considered in the modified least-squares algorithm to extract the wideband multi-component phasors accurately. Finally, this paper designs a series of scenarios considering varying signal frequency, damping factor, amplitude, and phase to test the proposed algorithm thoroughly. The results verify that the proposed method can achieve a maximum total vector error of less than 1.5%, which is more accurate than existing phasor estimators in various signal environments. The high accuracy of the proposed method is because it considers both the estimation of the frequency number and the effect of signal damping.

Resolution of the paradox of the diamagnetic effect on the Kibble coil.

Employing very simple electro-mechanical principles known from classical physics, the Kibble balance establishes a very precise and absolute link between quantum electrical standards and macroscopic mass or force measurements. The success of the Kibble balance, in both determining fundamental constants (h, [Formula: see text], e) and realizing a quasi-quantum mass in the 2019 newly revised International System of Units, relies on the perfection of Maxwell's equations and the symmetry they describe between Lorentz's force and Faraday's induction, a principle and a symmetry stunningly demonstrated in the weighing and velocity modes of Kibble balances to within [Formula: see text], with nothing but imperfect wires and magnets. However, recent advances in the understanding of the current effect in Kibble balances reveal a troubling paradox. A diamagnetic effect, a force that does not cancel between mass-on and mass-off measurement, is challenging balance maker's assumptions of symmetry at levels that are almost two orders of magnitude larger than the reported uncertainties. The diamagnetic effect, if it exists, shows up in weighing mode without a readily apparent reciprocal effect in the velocity mode, begging questions about systematic errors at the very foundation of the new measurement system. The hypothetical force is caused by the coil current changing the magnetic field, producing an unaccounted force that is systematically modulated with the weighing current. Here we show that this diamagnetic force exists, but the additional force does not change the equivalence between weighing and velocity measurements. We reveal the unexpected way that symmetry is preserved and show that for typical materials and geometries the total relative effect on the measurement is [Formula: see text].

A Simple Improvement for Permanent Magnet Systems for Kibble Balances: More Flat Field at Almost No Cost.

Permanent magnets together with yokes to concentrate the magnetic flux into a cylindrical air-gap are widely employed in Kibble balances. These experiments require a uniform magnetic flux density along a vertical path, typically a substantial fraction of the length of the air-gap. Fringe fields that are present at both ends of the air-gap limit the region where the flux density does not change more than a certain relative fraction (here: 5 × 10-4) of the flux density in the center of the magnet system. By simply adding an iron ring with a rectangular cross-section to the inner yoke at each end of the air gap, the effects of the fringe fields can be counteracted, and, hence, the length of the region, where the flux density remains within a given tolerance band is increased. Compared to the alternative, employing a taller magnet, the proposed method yields a magnet system with an extended region of a uniform field without significantly increasing the mass of the magnet system. Potential applications include compact and table-top Kibble balances. We investigate possible adverse effects on the performance of the magnet system caused by the additional rings: magnetic field strength, coil-current effect, and a dependence of the radial field on the radial position in the field. No substantial disadvantage was found. Instead, the method presented here outperformed previously suggested methods to improve the radial dependence of the radial field, e.g., shorter outer yoke. In summary, adding rings to the inner yoke improves the uniformity of the field without a detrimental effect to function, cost, and form factor of the magnet system.

A new magnet design for future Kibble balances.

We propose a new permanent magnet system for Kibble balance experiments, which combines advantages of the magnet designs invented by the National Physical Laboratory (NPL) and by the Bureau International des Poids et Mesures (BIPM). The goal of the proposed magnet system is to minimize the coil-current effect and to optimize the shielding at the same time. In the proposed design, a permanent magnet system with two gaps, each housing a coil, is employed to minimize the coil current effect, by reducing the linear coil-current dependence reported for the single air gap design by at least one order of magnitude. Both air gaps of the magnet are completely surrounded by high-permeability material, and hence the coils are shielded from outside magnetic fields and no magnetic field leaks outside of the magnet system. An example of the new magnet system is given and the analysis shows that the magnetic field in the air gap can be optimized to meet the requirement to be used in Kibble balances.

Two simple modifications to improve the magnetic field profile in radial magnetic systems.

All present watt balances employ permanent magnet systems using a yoke with high permeability as flux return. Very often these systems are built with vertical and azimuthal symmetries. In its simplest form, the air gap is defined as the radial distance between an inner and outer yoke with the same height. This design leads to sloped field lines away from the plane of vertical symmetry. In order to suppress this vertical magnetic field, we propose two modified magnet constructions: (1) adding a permanent magnet in the outer yoke, and (2) decreasing the height of the outer yoke. Finite element method simulations show that, with reasonable optimization, either proposal can lower the vertical magnetic field by about one order of magnitude.

[Estimation of postmortem interval using FTIR spectroscopy in rats' cardiac muscle].

OBJECTIVE: FTIR (Fourier transform infrared) spectroscopy was applied to observe the process of postmortem degradation in rats' cardiac muscle and provided a new method for the estimation of post-mortem interval (PMI). METHODS: The rats were sacrificed by cervical dislocation and the bodies were kept in a controlled environmental chamber set at (20 +/- 2) degrees C. The FTIR spectra was applied to measure the changes of different chemical group from rats' left ventricle muscle at the different time point postmortem. RESULTS: There were not obvious changes for the main FTIR absorbance peaks. But the different FTIR absorbance at the wave-number (cm(-1)) indicated the three types: increase, decrease, stable. The various absorbance ratios also demonstrated the similar changes. CONCLUSION: FTIR spectroscopy may be potentially used as an effective method for estimating PMI in forensic practice using cardiac muscle tissue.