Near-the-Line Steel Slag Analysis Using Laser-Induced Breakdown Spectroscopy: Traditional Univariate Versus Machine Learning Calibration Methods.

This work is focused on rapid quantitative analysis of slag in the steel industry for improved process control. The novel approach in this work is a direct comparison of two methods to calibrate and quantify spectral data from the slags. Calibration was first done with the most prevalent method in quantitative optical emission spectroscopy (OES) of solids, the univariate ratio method. The second method is an advanced multivariate analysis (MVA) algorithm termed Elastic Net, allowing to include several lines for each element in the calibration functions. In both methods, the output is mass fraction ratios of the analyte element (or compound) to a matrix element (compound). The actual mass fractions of each compound are calculated by sum normalization assuming the matrix to make up the difference up to 100%. The metric used to evaluate the performance of the methods in terms of accuracy is the parameter σrel calculated as the ratio of the root mean square (RMS) deviation from values obtained by X-ray fluorescence (XRF) divided by the average mass fraction of the compound, expressed in percent. A bit surprising, the main outcome of the comparison is that there is very little difference in the performance of the two methods. One exception is the analysis of MgO, where the elastic net gives significantly better accuracy. Presumably, this is due to the use of multiple lines for Mg to build the calibration function. This is very encouraging, since MgO is a major compound in most slags that needs to be determined accurately. It is suggested to improve accuracy further by means of separate calibrations for a limited number of slag types.

Hopping versus Tunneling Mechanism for Long-Range Electron Transfer in Porphyrin Oligomer Bridged Donor-Acceptor Systems.

Achieving long-range charge transport in molecular systems is interesting to foresee applications of molecules in practical devices. However, designing molecular systems with pre-defined wire-like properties remains difficult due to the lack of understanding of the mechanism for charge transfer. Here we investigate a series of porphyrin oligomer-bridged donor-acceptor systems Fc-Pn-C60 (n = 1-4, 6). In these triads, excitation of the porphyrin-based bridge generates the fully charge-separated state, Fc(•+)-Pn-C60(•-), through a sequence of electron transfer steps. Temperature dependence of both charge separation (Fc-Pn*-C60 → Fc-Pn(•+)-C60(•-)) and recombination (Fc(•+)-Pn-C60(•-) → Fc-Pn-C60) processes was probed by time-resolved fluorescence and femtosecond transient absorption. In the long triads, two mechanisms contribute to recombination of Fc(•+)-Pn-C60(•-) to the ground state. At high temperatures (≥280 K), recombination via tunneling dominates for the entire series. At low temperatures (<280 K), unusual crossover from tunneling to hopping occurs in long triads. This crossover is rationalized by the increased lifetimes of Fc(•+)-Pn-C60(•-), hence the higher probability of reforming Fc-Pn(•+)-C60(•-) during recombination. We demonstrate that at 300 K, the weak distance dependence for charge transfer (ß = 0.028 Å(-1)) relies on tunneling rather than hopping.

Steady-state and time-resolved Thioflavin-T fluorescence can report on morphological differences in amyloid fibrils formed by Aß(1-40) and Aß(1-42).

Thioflavin-T (ThT) is one of the most commonly used dyes for amyloid detection, but the origin of its fluorescence enhancement is not fully understood. Herein we have characterised the ThT fluorescence response upon binding to the Aß(1-40) and Aß(1-42) variants of the Alzheimer's-related peptide amyloid-ß, in order to explore how the photophysical properties of this dye relates to structural and morphological properties of two amyloid fibril types formed by peptides with a high degree of sequence homology. We show that the steady-state ThT fluorescence is 1.7 times more intense with Aß(1-40) compared to Aß(1-42) fibrils in concentration matched samples prepared under quiescent conditions. By measuring the excited state lifetime of bound ThT, we also demonstrate a distinct difference between the two fibril isoforms, with Aß(1-42) fibrils producing a longer ThT fluorescence lifetime compared to Aß(1-40). The substantial steady-state intensity difference is therefore not explained by differences in fluorescence quantum yield. Further, we find that the ThT fluorescence intensity, but not the fluorescence lifetime, is dependent on the fibril preparation method (quiescent versus agitated conditions). We therefore propose that the fluorescence lifetime is inherent to each isoform and sensitively reports on fibril microstructure in the protofilament whereas the total fluorescence intensity relates to the amount of exposed ß-sheet in the mature Aß fibrils and hence to differences in their morphology. Our results highlight the complexity of ThT fluorescence, and demonstrate its extended use in amyloid fibril characterisation.