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    Hybrid machine learning and physics-based modeling of pedestrian pushing behaviors

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    In high-density crowds, close proximity between pedestrians makes the steady state highly vulnerable to disruption by pushing behaviours, potentially leading to serious accidents. However, the scarcity of experimental data has hindered systematic studies of its mechanisms and accurate modelling. Using behavioural data from bottleneck experiments, we investigate pedestrian heterogeneity in pushing tendencies, showing that pedestrians tend to push under high-motivation and in wider corridors. We introduce a spatial discretization method to encode neighbour states into feature vectors, serving together with pedestrian pushing tendencies as inputs to a random forest model for predicting pushing behaviours. Through comparing speed-headway relationships, we reveal that pushing behaviours correspond to an aggressive space-utilization movement strategy. Consequently, we propose a hybrid machine learning and physics-based model integrating pushing tendencies heterogeneity, pushing behaviours prediction, and dynamic movement strategies adjustment. Validations show that the hybrid model effectively reproduces experimental crowd dynamics and fits to incorporate additional behaviours

    On the High-Temperature Ca2+Ca^{2+} Conduction in NASICON-Type Ca(1+x)/2InxZr2x(PO4)3Ca_{(1+x)/2}In _xZr_{2–x}(PO_4)_3

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    Lithium-based batteries are currently the leading battery technology. To develop more diverse and sustainable energy storage solutions, alternative battery chemistries and materials must be explored. In this work, we investigated the aliovalent substitution series of NASICON-type Ca(1+x)/2InxZr2x(PO4)3Ca_{(1+x)/2}In _xZr_{2–x}(PO_4)_3 (x = 0, 0.125, 0.25, 0.375, 0.5, 0.75, and 1). To establish the structure–transport relations in the materials, a combination of impedance spectroscopy, direct current (DC) polarization measurements, and temperature-dependent powder X-ray diffraction (XRD) measurements up to 800 °C was used. At 800 °C, where the materials are most conductive, there is an increase of the ionic conductivity from x = 0 to 0.375, reaching a maximum of 2.4104Scm12.4·10^{–4}S·cm^{–1}. For compositions with x ≥ 0.5, however, the conductivity decreases significantly. The maximum conductivity and its subsequent decrease are linked to an interplay of crystal–chemical factors, namely, the bottleneck size and the number of available vacancies. This study shows that it is possible to increase the Ca2+Ca^{2+} ion conductivity through aliovalent substitution; however, due to distinct, crystallographic differences, design principles from lithium- or sodium-based NASICONs may not be directly applicable to their calcium analogues

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