Global analysis of coherence and population dynamics in 2D electronic spectroscopy

2D electronic spectroscopy is a widely exploited tool to study excited state dynamics. A high density of information is enclosed in 2D spectra. A crucial challenge is to objectively disentangle all the features of the third order optical signal. We propose a global analysis method based on the variable projection algorithm, which is able to reproduce simultaneously coherence and population dynamics of rephasing and non-rephasing contributions. Test measures at room temperature on a standard dye are used to validate the procedure and to discuss the advantages of the proposed methodology with respect to the currently employed analysis procedures

Chemical gradients in automotive Cu-SSZ-13 catalysts for NOx_{x} removal revealed by operando X-ray spectrotomography

NOx emissions are a major source of pollution, demanding ever improving performance from catalytic aftertreatment systems. However, catalyst development is often hindered by limited understanding of the catalyst at work, exacerbated by widespread use of model rather than technical catalysts, and global rather than spatially-resolved characterisation tools. Here we combine operando X-ray absorption spectroscopy with microtomography to perform 3D chemical imaging of the chemical state of copper species in a Cu-SSZ-13 washcoated monolith catalyst during NO$_{x}$ reduction. Gradients in copper oxidation state and coordination environment, resulting from an interplay of NOx reduction with adsorption-desorption of NH$_{3}$ and mass transport phenomena, were revealed with micrometre spatial resolution while simultaneously determining catalytic performance. Crucially, direct 3D visualisation of complex reactions on nonmodel catalysts is only feasible using operando X-ray spectrotomography, which can improve our understanding of structure-activity relationships including the observation of mass and heat transport effects

Magnetic wire as stress controlled micro-rheometer for cytoplasm viscosity measurements

We review here different methods to measure the bulk viscosity of complex fluids using micron-sized magnetic wires. The wires are characterized by length of a few microns and diameter of a few hundreds of nanometers. We first draw analogies between cone-and-plate rheometry and wire-based microrheology. In particular we highlight that magnetic wires can be operated as stress-controlled rheometers for two types of testing, the creep-recovery and steady shear experiments. In the context of biophysical applications, the cytoplasm of different cell lines including fibroblasts, epithelial and tumor cells is studied. It reveals that the interior of living cells can be described as a viscoelastic liquid with a static viscosity comprised between 10 and 100 Pas. We extend the previous approaches and show that the proposed technique can also provide time resolved viscosity data, which for cells display strong temporal fluctuations. The present work demonstrates the high potential of the magnetic wires for quantitative rheometry in confined espaces.Comment: 11 pages, 6 figures, 40 reference

Glotaran: A Java-Based Graphical User Interface for the R Package TIMP

In this work the software application called Glotaran is introduced as a Java-based graphical user interface to the R package TIMP, a problem solving environment for fitting superposition models to multi-dimensional data. TIMP uses a command-line user interface for the interaction with data, the specification of models and viewing of analysis results. Instead, Glotaran provides a graphical user interface which features interactive and dynamic data inspection, easier -- assisted by the user interface -- model specification and interactive viewing of results. The interactivity component is especially helpful when working with large, multi-dimensional datasets as often result from time-resolved spectroscopy measurements, allowing the user to easily pre-select and manipulate data before analysis and to quickly zoom in to regions of interest in the analysis results. Glotaran has been developed on top of the NetBeans rich client platform and communicates with R through the Java-to-R interface Rserve. The background and the functionality of the application are described here. In addition, the design, development and implementation process of Glotaran is documented in a generic way

Systematic reduction of Hyperspectral Images for high-throughput Plastic Characterization

Hyperspectral Imaging (HSI) combines microscopy and spectroscopy to assess the spatial distribution of spectroscopically active compounds in objects, and has diverse applications in food quality control, pharmaceutical processes, and waste sorting. However, due to the large size of HSI datasets, it can be challenging to analyze and store them within a reasonable digital infrastructure, especially in waste sorting where speed and data storage resources are limited. Additionally, as with most spectroscopic data, there is significant redundancy, making pixel and variable selection crucial for retaining chemical information. Recent high-tech developments in chemometrics enable automated and evidence-based data reduction, which can substantially enhance the speed and performance of Non-Negative Matrix Factorization (NMF), a widely used algorithm for chemical resolution of HSI data. By recovering the pure contribution maps and spectral profiles of distributed compounds, NMF can provide evidence-based sorting decisions for efficient waste management. To improve the quality and efficiency of data analysis on hyperspectral imaging (HSI) data, we apply a convex-hull method to select essential pixels and wavelengths and remove uninformative and redundant information. This process minimizes computational strain and effectively eliminates highly mixed pixels. By reducing data redundancy, data investigation and analysis become more straightforward, as demonstrated in both simulated and real HSI data for plastic sorting