Electrical double-layer capacitors: evaluation of ageing phenomena during cycle life testing

This paper represents an assessment of the main ageing phenomena in electrical double-layer capacitors (EDLCs). In this study the cycle life of the EDLC cells with a rated capacitance of 1,600 F has been investigated at different ambient temperatures and current rates. From the experimental results we can observe that the impact of the high ambient temperature is significant on the cycle life of the cells. Moreover, the results also show the negative impact of the current rate. The internal resistance tests showed that the increase of the resistance is much higher than the decrease of the capacitance. Thus, the ageing of the EDLC during cycling was clearly non-linear. Further the EIS measurements indicated the higher increase of the imaginary part of the impedance at low frequencies during cycling, which indicates the capacitance fade.     

Multivariate Statistical Techniques to Determine Essential and Toxic Elements in Biological Samples by X-Ray Fluorescence

X-ray fluorescence spectrometry was used to determine essential and toxic elements in tea leaves. Quantitative measurements were obtained for K, Mg, Cu, Zn, As, Sr, Fe, Co, Ca, P, S, Pb, Rb, and Mn. Pearson's product moment correlation coefficient with principal component analysis and hierarchical clustering analysis were performed to investigating the relationships between essential and nonessential elements in the dry herbal mass. From multivariate statistical analysis, Ca, Fe, P, Zn, and Mn were found to have strong positive correlations. While principal component analysis demonstrates that tea leaves were dominated by Fe and Cl in the first principal component, Pb and As were in the second principal component with cumulative variability of 84.4%. However, hierarchical clustering analysis indicated the presence of a cluster of four essential elements, one cluster containing toxic and essential elements, and one cluster composed of toxic elements. The results of this study improve understanding of the correlation between essential and toxic elements in biological samples such as tea leaves.     

X-RAY FLUORESCENCE COMBINED WITH CHEMOMETRICS FOR THE CHARACTERIZATION OF GEOLOGICAL SAMPLES: A CASE STUDY IN SOUTHEASTERN SENEGAL

Characterization of magmatic, metamorphic, and mineralized metamorphic rock collected in southeastern Senegal in West Africa was performed based on elemental analysis by energy dispersive X-ray fluorescence. The rock classification scheme based on chemical composition was obtained by a combination of principal component analysis and hierarchical clustering techniques to discriminate magmatic, metamorphic, and mineralized metamorphic rock. An improved sensitivity of signal-to-noise ratio was obtained using a thin silver X-ray excitation source with several appropriate filters. Energy dispersive X-ray fluorescence was used to characterize the major oxides, and the results were compared to previous studies.     

Ultra-broadband,coherent mid-IR supercontinuum expanding from 1.5 to 12.2 μm in new design of AsSe2 photonic crystal fibre

We propose a new design of AsSe₂ photonic crystal fibre (PCF) with all-normal dispersion, nearly zero flat-top used to generate an ultra-broadband supercontinuum spanning from 1.5 to 12.2 μm. Simulated results show that, when we use only 1 mm of AsSe₂ PCF, a broadband mid-infrared supercontinuum with the specrum extent from 1.5 to 12.2 μm is obtained with a very low input energy of E = 1.3 nJ at the wavelength of 3.5 μm and pulse duration of 100 fs. We study the temporel and spectral impact of optical wave breaking in the development of the continuum. The influence of the fibre length, the input energy and the full width at half maximum is investigated. Compared to previous research works, we have obtained the broadest, coherent supercontinuum, which could be applicable in biomolecular sensing, cancer diagnostics, infrared spectroscopy and free space communication.