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A series of Co/Mn compensated Ca3Co1+xMn1-xO6 compounds were synthesized. The structure and magnetization were characterized, as well as the dielectric properties were studied. In Co/Mn compensated samples, the well-ranked Co/Mn ionic order is destroyed which manifests the suppression of the formation of the short-range magnetic order. As a result, the freezing anomaly around Tf = 150 K diminishes. For the two Co/Mn compensated samples, the critical field HSF that causes magnetic structure change from ↑↑↓↓ state to ↑↑↓↑ state also increases. The appearance of dielectric peak at the antiferromagnetic phase transition temperature clearly indicates the coupling effect between the spin dipole and electric dipole. The temperature corresponding to the dielectric peak increases with the increasing measurement frequency. The frequency dependence of ferroelectric peak identifies relaxor ferroelectric nature. In dielectric measurements associated with magnetic fields, Δε` and Δtanδ have the same sign elucidating intrinsic magnetodielectric effect of Ca3Co1+xMn1-xO6. For the Co/Mn compensated x = ±0.05 two samples, the suppressed magnetic short-range order also leads to a low diffusion exponent γ and the weak relaxor ferroelectric nature. The thermal activation process of the dipole response is characterized by the Vogel–Fulcher equation and the results confirm that the freezing process of Ca3Co1+xMn1-xO6 is mainly dominated by coupling of polar nanodomains. [ABSTRACT FROM AUTHOR]

This paper reports the synthesis, microstructure and electrical properties of a new Ba4SrBiTi3Nb7O30 ceramic. X-ray diffraction analysis shows that the sample crystallizes into tungsten bronze structure, and the space group is P4bm. The electrical measurement results show that Ba4SrBiTi3Nb7O30 exhibits good dielectric and ferroelectric properties. The temperature-dependent dielectric permittivity indicates that the transition temperature of the prepared Ba4SrBiTi3Nb7O30 sample is around Tm ≈ 250K. With increasing the frequency, the dielectric peak moves to a lower temperature. Below 250 K, obvious polarization current can be detected, corresponding to the formation of spontaneous ferroelectric polarization. These results indicate the relaxor ferroelectric behavior of Ba4SrBiTi3Nb7O30 ceramic. [ABSTRACT FROM AUTHOR]

Ba4SmFe0.5Nb9.5O30 ceramics were prepared by solid-state reaction method and the sample crystallized into single phase tungsten bronze (TB) structure with space group P4bm. The absence of dielectric peak suggests that there is no long-range ferroelectric order exists above room temperature (RT). Therefore, the observed ferroelectric property should be related to the polar nanoregions that survived to Burns temperature TB. Obvious RT ferromagnetism is observed for the first time in Ba4SmFe0.5Nb9.5O30 ceramics and it could be interpreted as the effective exchange coupling interaction between oxygen vacancies and Fe ions 3d spins, while the isolated Fe ions create the paramagnetic characteristic. In addition, the RT ferromagnetism and ferroelectricity also confirms that introduce of Fe ions could help to change TB structural ferroelectric to RT multiferroic material effectively. [ABSTRACT FROM AUTHOR]

Objective. The imaging photoplethysmography (IPPG) technique allows people to measure heart rate (HR) from face videos. However, motion artifacts caused by rigid head movements and nonrigid facial muscular movements are one of the key challenges. Approach. This paper proposes a self-adaptive region of interest (ROI) pre-tracking and signal selection method to resist motion artifacts. Based on robust facial landmark detection, we split the whole facial skin (including the forehead, cheeks, and chin) symmetrically into small circular regions. And two symmetric sub-regions constitute a complete ROI. These ROIs are tracked and the motion state is simultaneously assessed to automatically determine the visibility of these ROIs. The obscured or invisible sub-regions will be discarded while the corresponding symmetric sub-regions will be retained as available ROIs to ensure the continuity of the IPPG signal. In addition, based on the frequency spectrum features of IPPG signals extracted from different ROIs, a self-adaptive selection module is constructed to select the optimum IPPG signal for HR calculation. All these operations are updated per frame dynamically for the real-time monitor. Results. Experimental results on the four public databases show that the IPPG signal derived by our proposed method exhibits higher quality for more accurate HR estimation. Compared with the previous method, metrics of the evaluated HR value on our approach demonstrates superior or comparable performance on PURE, VIPL-HR, UBFC-RPPG and MAHNOB-HCI datasets. For instance, the RMSEs on PURE, VIPL-HR, and UBFC-RPPG datasets decrease from 4.29, 7.62, and 3.80 to 4.15, 3.87, and 3.35, respectively. Significance. Our proposed method can help enhance the robustness of IPPG in real applications, especially given motion disturbances., (© 2023 Institute of Physics and Engineering in Medicine.)