This study tackles the ECG classification problem by means of a methodology, which is able to enhance classification performance while simultaneously reducing the computational resources, making it specially adequate for its application in the improvement of ambulatory settings. For this purpose, the sequential forward floating search (SFFS) algorithm is applied with a new criterion function index based on linear discriminants. This criterion has been devised specifically to be a quality indicator in ECG arrhythmia classification. Based on this measure, a comprehensive feature set is analyzed with the SFFS algorithm, and the most suitable subset returned is additionally evaluated with a multilayer perceptron (MLP) to assess the robustness of the model. Aiming at obtaining meaningful estimates of the real-world performance and facilitating comparison with similar studies, the present contribution follows the Association for the Advancement of Medical Instrumentation standard EC57:1998 and the same interpatient division scheme used in several previous studies. Results show that by applying the proposed methods, the performance obtained in similar studies under the same constraints can be exceeded, while keeping the requirements suitable for ambulatory monitoring
Nanostructures with specific crystallographic planes display distinctive physico-chemical properties because of their unique atomic arrangements, resulting in widespread applications in catalysis, energy conversion or sensing. Understanding strain dynamics and their relationship with crystallographic facets have been largely unexplored. Here, we reveal in situ, in three-dimensions and at the nanoscale, the volume, surface and interface strain evolution of single supported platinum nanocrystals during reaction using coherent x-ray diffractive imaging. Interestingly, identical {hkl} facets show equivalent catalytic response during non-stoichiometric cycles. Periodic strain variations are rationalised in terms of O2 adsorption or desorption during O2 exposure or CO oxidation under reducing conditions, respectively. During stoichiometric CO oxidation, the strain evolution is, however, no longer facet dependent. Large strain variations are observed in localised areas, in particular in the vicinity of the substrate/particle interface, suggesting a significant influence of the substrate on the reactivity. These findings will improve the understanding of dynamic properties in catalysis and related fields.
The most studied
catalysts for methane dehydroaromatization (MDA)Mo/ZSM-5are
not commercialized yet due to the rapid deactivation and insufficient
activity. Catalytic systems based on Fe and Re are potential alternatives
to Mo-containing zeolites. Here, we compare the catalytic performance
of these catalysts as a function of metal type and its loading in
ZSM-5 zeolite. The results show that the catalytic activity decreases
in the order of Re/ZSM-5 > Mo/ZSM-5 > Fe/ZSM-5, while the catalyst
stability decreases in the opposite order: Fe/ZSM-5 > Mo/ZSM-5
> Re/ZSM-5.
The active metal species in the working catalysts were determined
by operando X-ray absorption near-edge structure spectroscopy combined
with mass spectrometry. We found that Re0 and Fe2+ species are the most likely active species for the catalytic dehydroaromatization
of CH4 to aromatics in respective catalysts. Combining
the pulse reaction technique with operando thermogravimetry analysis–mass
spectrometry experiments, we demonstrate that the length of the induction
period strongly correlates to the activity of the catalyst. The longer
induction period of the Fe/ZSM-5 catalyst indicates the slow growth
of hydrocarbon pool intermediates inside the zeolite pores and thus
explains its poor catalytic performance. Finally, both the formation
of hydrocarbon pool species and the activity of Fe/ZSM-5 can be improved
by increasing the Fe loading, reaction pressure, and space velocity.
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