Matemática e Estatística | Comunicações em congressos, conferências e seminários / Communications in congresses, conferences
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- Analysis of thoracic aortic aneurysm CTA scans using spatial statisticsPublication . Rodriguez, Katalina; Carvalho, Alda; Valente, Rodrigo; Xavier, José; Tomás, AntónioThis study leverages spatial statistics to analyze the spatial distribution of the aorta, aiming to better understand the biomechanical behavior of Ascending Thoracic Aortic Aneurysms (ATAA) and its impact on clinical outcomes. CTA angiography was performed on 87 ATAA patients. Experimental variograms were computed for various variables, such as maximum diameter, from which key parameters of interest were extracted. These parameters were then analyzed over time to assess temporal patterns. The goal of this analysis was to identify whether similar patterns or behaviors emerge in features from CTA scans of patients with aneurysms of similar sizes, ultimately aiming to statistically validate the quality of the CTA scans.
- An application of time series clustering using a combined distancePublication . Martins, Ana; Vaz, Daniel; Silva, Tiago; Cardoso, Margarida; Carvalho, Alda; Loja, AméliaClustering time series aims at uncovering diverse longitudinal patterns. In this study we analyse time series of various parameters collected atop wind turbines in a wind farm in Portugal. Considering wind data in clustering may reveal differences in operation between neighbouring turbines, due to their position relative to one another and to terrain features. In this work, we use an approach to wind speed time series clustering based on a convex combination of distance measures between time series. For visualizing the resulting groups, we propose a graphical representation, Distance Matrix, which is quite more informative than the classical Multidimensional Scaling (MDS) map. This representation allows for quick comparisons between pairs of turbines for (dis)similarities. Our approach provides distinct insights regarding the differences between time series, emphasizing differences in values (Euclidean distance), trends (Pearson-based distance), and cyclical behaviours (Euclidean distance between periodograms and/or autocorrelation structures). In most cases, we found two groups, which were not always coincident with the geographical groups, but the proposed approach could also find the rationale behind the clusters that were formed. The results obtained may help identifying undesirable aerodynamic loads that the blades of a particular wind turbine may be subjected to, thereby shortening its time in-service.
- Sidewalks of Lisbon and AzoresPublication . Carvalho, Alda; Santos, Carlos; Silva, Jorge; Teixeira, Ricardo; Fong, ChamberlainPart of the beauty of Lisbon and Azores lies under the feet of anyone who walks in the streets. Given their highly symmetrical nature, Portuguese sidewalk drawings are ideal to be analyzed geometrically. Furthermore, these drawings provide opportunities for promoting mathematical concepts through exhibitions, card decks, and other forms of dissemination.