University of the Littoral Opal Coast

About: University of the Littoral Opal Coast is a education organization based out in Dunkirk, France. It is known for research contribution in the topics: Catalysis & Dielectric. The organization has 1242 authors who have published 2383 publications receiving 46230 citations. The organization is also known as: ULCO.

The Eigenvalues of the Laplacian on Locally Finite Networks Under Generalized Node Transition

Abstract: We consider the canonical continuous Laplacian on an infinite locally finite network with different edge lengths under natural transition conditions as continuity at the ramification nodes and Kirchhoff flow conditions at all vertices that can be consistent with the Laplacian or not. It is shown that the eigenvalues of this Laplacian in a L∞-setting are closely related to those of a row–stochastic operator of the network resulting from the length adjacency operator and the weights in the Kirchhoff condition. In this way the point spectrum in L∞ is determined completely in terms of combinatorial and metrical quantities of the underlying graph as in the finite case [2] and as in the equal length case [10], and, in addition, in terms of the coefficients in the transition condition. Though the multiplicity formulae are formally the same as in the cited cases, the multiplicities can change strongly. Another main concern is the real or nonreal character of the eigenvalues.

Real-time measurement of CO2 isotopologue ratios in exhaled breath by a hollow waveguide based mid-infrared gas sensor.

Abstract: A hollow waveguide (HWG) based mid-infrared gas sensor using a 2.73 µm distributed feedback (DFB) laser was developed for simultaneously measuring the concentration changes of the three isotopologues 13CO2, 12CO2, and 18OC16O in exhaled breath by direct absorption spectroscopy, and then determining the 13CO2/12CO2 isotope ratio (δ13C) and 18OC16O/12CO2 isotope ratio (δ18O). The HWG sensor showed a fast response time of 3 s. Continuous measurement of δ13C and δ18O in the standard CO2 sample with known isotopic ratios for ∼2 h was performed. Precisions of 2.20‰ and 1.98‰ for δ13C and δ18O respectively at optimal integration time of 734 s were estimated from Allan variance analysis. Accuracy of −0.49‰ and −1.20‰ for δ13C and δ18O, respectively, were obtained with comparison to the values of the reference standard. The Kalman filtering method was employed to improve the precision and accuracy of the HWG sensor while maintaining high time resolution. Precision of 5.45‰ and 4.88‰ and the accuracy of 0.21‰ and −1.13‰ for δ13C and δ18O, respectively, were obtained at the integration time of 0.54 s with the application of Kalman filtering. The concentrations of 12CO2, 13CO2 and 18OC16O in breath cycles were measured and processed by Kalman filtering in real time. The measured values of δ18O and δ13C in exhaled breath were estimated to be −21.35‰ and −33.64‰, respectively, with the integration time of 1 s. This study demonstrates the ability of the HWG sensor to obtain δ13C and δ18O values in breath samples and its potential for immediate respiratory monitoring and disease diagnosis.

Characterization of cerium and copper species in Cu—Ce—Al oxide systems by temperature programmed reduction and electron paramagnetic resonance

Abstract: The reducibility of Ce—Al—O and Cu—Ce—Al—O solids is studied by H2-TPR and EPR in order to identify the different ceria and copper oxide species. The study of Ce—Al—O oxides shows that dispersion of ceria on alumina improves reducibility of ceria bulk and stabilizes surface ceria. Concerning quantitative results, ceria reduction extent is more important for Ce—Al—O oxides than for pure ceria. This result can be related to the dispersion of ceria on alumina which decreases ceria crystallites size and enhances the ceria bulk reduction. For ternary oxides, copper oxide and ceria interact strongly. Introduction of copper facilitated ceria reduction, and quantitatively, the presence of copper favors the total reduction of ceria contrary to Ce—Al—O oxides. When ceria loading is low, two copper species are identified, and are attributed to small clusters and highly dispersed copper oxides. During the reduction of copper species, a partial reduction of ceria is observed. Increasing of copper loading leads to the formation of CuO aggregates.