Discrimination and Measurements of Three Flavonols with Similar Structure Using Terahertz Spectroscopy and Chemometrics

Terahertz (THz) technique, a recently developed spectral method, has been researched and used for the rapid discrimination and measurements of food compositions due to its low-energy and non-ionizing characteristics. In this study, THz spectroscopy combined with chemometrics has been utilized for qualitative and quantitative analysis of myricetin, quercetin, and kaempferol with concentrations of 0.025, 0.05, and 0.1 mg/mL. The qualitative discrimination was achieved by KNN, ELM, and RF models with the spectra pre-treatments. An excellent discrimination (100% CCR in the prediction set) could be achieved using the RF model. Furthermore, the quantitative analyses were performed by partial least square regression (PLSR) and least squares support vector machine (LS-SVM). Comparing to the PLSR models, the LS-SVM yielded better results with low RMSEP (0.0044, 0.0039, and 0.0048), higher Rp (0.9601, 0.9688, and 0.9359), and higher RPD (8.6272, 9.6333, and 7.9083) for myricetin, quercetin, and kaempferol, respectively. Our results demonstrate that THz spectroscopy technique is a powerful tool for identification of three flavonols with similar chemical structures and quantitative determination of their concentrations.     

Facile synthesis,characterization and low-temperature catalytic performance of Au/CeO2 nanorods

Au/CeO₂ nanorods of ~ 15 nm in diameter and 100–400 nm in length have been synthesized through an efficient and simple method, and subsequently the novel low-temperature catalytic performance of Au/CeO₂ nanorods for CO oxidation is found. The composites are characterized by transmission electron microscopy, X-ray diffraction as well as X-ray photoelectron spectroscopy. It is found that the Au nanoparticles with an average diameter of 8 nm are distributed uniformly on the surface of CeO₂ nanorods. The possible formation mechanism of Au/CeO₂ nanorods has been discussed. The T₅₀ depicting the catalytic activity for CO oxidation can reach 62.1 °C, which is much lower than that of CeO₂ nanorods or Au/CeO₂ powders. In addition, Au/CeO₂ nanorods exhibit excellent stability as catalysts for CO oxidation.     

Effect of Cu–Al substitution on the structural and magnetic properties of Co ferrites

In this work copper aluminum substituted cobalt nanocrystalline spinel ferrites having general formula Co_1−xCu_xFe_2−x Al_xO₄, with 0.0≤x≤0.8 have been synthesized by using a co-precipitation method. The Cu–Al substituted samples were annealed at 600 °C and characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM). XRD analysis confirmed a single phase spinel structure and the crystalline size calculated using Scherrer׳s formula found to be in the range of 14−24 nm. This crystalline size is small enough to achieve the suitable signal to noise ratio in the high density recording media. The FTIR spectra reveal two prominent frequency bands in the wave number range 350–600 cm⁻¹, which confirm the cubic spinel structure and completion of chemical reaction. Magnetic studies reveal that the coercivity (H_c) attains a maximum value of 1142 Oe at 14 nm. The increasing trend of magnetic parameters (coercivity and retentivity) is consistent with crystallinity. The role played by the Cu–Al ions in improving the structural and magnetic properties are analyzed and understood. The optimized magnetic parameters suggest that the material with composition Co_0.6Cu_0.4Fe_1.6Al_0.4O₄ may have a potential application for high density recording media. Our simple, economic and environmental friendly preparation method may contribute towards the controlled growth of high quality ferrite nanopowder, potential candidates for recording.     

Multivariate online kernel density estimation with Gaussian kernels

We propose a novel approach to online estimation of probability density functions, which is based on kernel density estimation (KDE). The method maintains and updates a non-parametric model of the observed data, from which the KDE can be calculated. We propose an online bandwidth estimation approach and a compression/revitalization scheme which maintains the KDE's complexity low. We compare the proposed online KDE to the state-of-the-art approaches on examples of estimating stationary and non-stationary distributions, and on examples of classification. The results show that the online KDE outperforms or achieves a comparable performance to the state-of-the-art and produces models with a significantly lower complexity while allowing online adaptation.