ESTiG - Artigos em Revistas Indexados à WoS/Scopus
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Percorrer ESTiG - Artigos em Revistas Indexados à WoS/Scopus por Objetivos de Desenvolvimento Sustentável (ODS) "09:Indústria, Inovação e Infraestruturas"
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- 2024 U.S. presidential elections: An event study for U.S. and non-U.S. fossil fuel and renewable listed firmsPublication . Martins, António Miguel; Albuquerque, Bruno; Sardinha, Luís; Moutinho, NunoThis study examines the short-term market effect of Donald Trump' victory in the 2024 US presidential election on largest US and non-US listed worldwide fuel fossil and renewable firms. Employing an event study methodology, we observe a negative and statistically significant stock price reaction for worldwide renewable listed firms. An analysis by economic zones reveals the existence of negative abnormal returns for renewable energy firms in the US, Europe, India and in the rest of the world. In the case of China, abnormal returns are not statistically significant. With respect to worldwide fossil fuel listed firms, abnormal returns are generally not statistically significant. However, regarding US firms, we observe positive and statistically significant abnormal returns. These abnormal returns are explained by the change of US energy policy (pro-oil and gas policy) and the expected cut in subsidies and lower profitability of investments in green energies. Finally, our study provide insight into which firm-specific characteristics emerge as value drives around US presidential elections. The results show that despite the change in environmental policy in the US, favourable to fossil energy, the stock markets reward firms with high environmental ratings. Overall, our results indicate that 2024 US presidential election, for implying a change in US energy policy, has relevant policy implications for energy listed firms.
- Accessible power for medical equipment in remote healthcare: a solution for single-phase power generation using three-phase induction machinesPublication . Romeiro, Bruno; Oliveira, Carlos; Hildenberg, Cicero; Ferreira, Ângela P.; Filho, FranciscoThis work was motivated by the urgent need for reliable electricity in remote areas where conventional power distribution, and consequently access to healthcare, remains impractical. The proposed system is a practical alternative to conventional synchronous generators commonly used in off-grid applications, which have high implementation and maintenance costs and potential risks in healthcare applications due to the spark generated by the brushes. We propose the use of a self-excited single-phase generator, derived from a three-phase induction machine, as a robust, low-cost, highly reliable and safe solution for supplying electrical power to medical applications in remote locations. The work presents a mathematical model based on the theory of symmetrical components, which incorporates frequency variation and unbalanced system operation, along with an analytical methodology to determine the capacitance values required for this application and all system elements, including the definition of the sizing factors KE and KM. The proposed approach allows for rigorous design without relying on empirical procedures as commonly presented in the literature, and is experimentally validated using real medical loads. Our experimental setup incorporates current medical devices, including three infusion pumps, a cardioverter-defibrillator, and a patient monitoring device. Despite modest voltage imbalances observed during steady-state operation, all medical devices maintained adequate functionality during testing. The transient response during load switching showed damped oscillations before returning to steady-state operation, demonstrating stable voltage and frequency behavior without the use of active electronic control. The generator demonstrated satisfactory voltage regulation and short-circuit self-protection capabilities without the need for complex systems, making it economically viable for deployment in resource-constrained environments. These results suggest that the proposed configuration offers a practical solution for the electrification of medical facilities in regions where grid extension remains challenging or prohibitively expensive.
- An AI-driven Ukrainian history web platformPublication . Kolomiets, Valentyna; Oliveira, Pedro Filipe; Matos, PauloThe AI-driven Ukrainian History web platform offers an innovative way for users to engage with the nation’s rich history. By integrating artificial intelligence, natural language processing (NLP), and geospatial analysis, it presents historical events, significant locations, and notable figures in an interactive and visually engaging format. The platform systematically gathers historical data using tools like Scrapy for web scraping and Tesseract OCR for digitizing scanned documents. While noisy or degraded documents may affect accuracy, the availability of high-quality sources ensures reliable data extraction. Fine-tuned NLP models, including transformers like BERT and RoBERTa, process the data to identify and categorize key entities such as dates, locations, and names of historical figures. Contextual summarization ensures the extracted information is both accurate and easy to understand. Geospatial data is managed with PostGIS, an extension of PostgreSQL, and visualized using Leaflet.js. An interactive map interface enables users to explore events by location and time period, with filters for categories like political milestones or cultural events. The backend, built on PostgreSQL, ensures scalability and performance, while development in Visual Studio Code streamlined integration across components. This platform not only preserves Ukraine’s cultural heritage but also demonstrates the potential of modern technology to transform historical education, offering an intuitive way to connect with the past and explore its influence on Ukraine’s landscape and culture.
- Airline stock market reaction to CrowdStrike IT outage: an event study analysisPublication . Costa, João; Cró, Susana; Moutinho, Nuno; Martins, António MiguelThis study investigates the short-term market effect of CrowdStrike IT outage in the airline industry. Using an event study methodology, we evidence that airline stocks respond significantly negatively to the technology disruption within two days before and after the event day. IT disruptions, by creating friction in daily operations, such as broken schedules, delayed or cancelled flights, negative externalities, and customer dissatisfaction, lead to loss of value for airlines. The results also show that the most affected airlines are those from main CrowdStrike customers countries (mainly non-Asian countries) and an irrelevance of the business model. Finally, the extent of the stock market’s response to the CrowdStrike IT outage is influenced by other airline characteristics such as profitability, size, leverage, and cyber risk rating.
- An attempt to predict temperature-time histories for large scale compartment fires: a parametric analysisPublication . Hachana, Romaissa; Benarous, Abdallah; Roudane, Mohamed; Piloto, Paulo A.G.The accurate prediction of thermal conditions within compartment fires poses a significant challenge for fire safety engineers. In fact, sprinkler design, exit sceneries, and collapse structure configurations are closely related to the temporal evolution of the temperature inside the compartments. Through a comprehensive review of existing methodologies and standards, this study attempts to contribute for advancing the state of the art in fire dynamics modelling. The work deals with a comparative analysis of various temperature-time formulations proposed in the literature, providing insights into the discrepancies between theoretical models and real-world standards. It investigates the influence of key factors namely, the opening factor, the fuel load density, and the walls effusivity, on temperature histories. The natural fire curve, such as EPFC leads towards real world planning requirements, allows for a more tailored and pragmatic assessment for large-scale compartment fires, compared to the standard curves. The analysis aims, through a case study, to provide designers and architects with a practical way that facilitates early-stage planning and allows for effective fire prevention implementations.
- Assessing the impact of working capital on free cash flow: evidence from portuguese accommodation companiesPublication . Fernandes, António B. ; Cardim, Sofia; Ferreira, Jessica; Pinto, LígiaThis study analyses the impact of working capital (WC) on free cash flow (FCF) for Portuguese firms operating in Division 55 (Accommodation), a sector that is a central pillar of the national tourism industry and characterised by high capital intensity and pronounced seasonality. The empirical analysis is based on an unbalanced panel dataset of 5,744 firms, corresponding to 27,689 firm-year observations for the period 2011–2023, obtained from the SABI database. A panel data model is estimated using generalised estimating equations (GEE) with firm- and year-fixed effects to examine how changes in WC and its components influence firms’ capacity to generate FCF. Twelve research hypotheses are formulated and empirically tested within a cash-flow-based valuation framework. The results show that variations in WC have a negative and statistically significant effect on FCF, indicating that increased investment in short-term operational assets constrains liquidity generation in the accommodation sector. Several components of WC are identified as significant determinants of FCF, while others do not exhibit statistically significant effects, underscoring the heterogeneous influence of short-term assets and liabilities on cash flow dynamics. The model adjustment criteria (QIC and QICC), assessed within the scope of the GEE, indicate that the estimated specification is well suited and robust, supporting the reliability of the results obtained. Although the analysis is limited to the accommodation sector, which may restrict the generalisability of the findings, the study makes an important contribution by adopting an FCF-based perspective on WC management. By focusing on liquidity generation rather than traditional profitability measures, this research enhances understanding of financial management dynamics in tourism-related firms and provides insights into firms’ strategic flexibility and capacity to invest in market-facing activities.
- O BSC, o SIPOC e o visual management como ferramentas de potenciar a melhoria organizacional: um estudo de caso aplicado ao setor dos transportesPublication . Cardim, Sofia; Borges, Mário; Vara, Natália; Queirós, CristinaA estrutura empresarial portuguesa é composta maioritariamente por micro, pequenas e médias empresas, que nem sempre dispõem dos recursos físicos, materiais e humanos para desenvolver os seus processos operacionais da forma mais sustentável. Estas empresas representam uma fonte de emprego para um grande número de trabalhadores. O presente trabalho tem como principais objetivos evidenciar a importância da utilização do instrumento Balanced Scorecard e do SIPOC, introduzidos através do Visual Management, como ferramentas de melhoria do processo de trabalho numa PME do setor dos transportes. A metodologia é do tipo estudo de caso, com uma observação participante. Como principais resultados da implementação destas ferramentas, verificou-se uma melhoria de diversos processos internos inerentes ao desenvolvimento da sua atividade, sistematizando e desenvolvendo ações diversas no âmbito da sua atividade operacional. Estas mudanças encontram-se relacionadas, em grande medida, com a informatização de alguns processos, nomeadamente respeitantes com o controlo da frota, cargas e viagens, que eram realizados de forma manual e que passaram a ser realizados de forma informatizada, que se fizeram sentir na melhoria do bem-estar dos trabalhadores, essencialmente, da gestão de topo.
- A CFD investigation of the performance of stirred tanksPublication . Youcef, Kamla; Driss, Zied; Foukrach, Mohamed; Rosa, Sérgio; Baki, TouhamiRushton turbine was employed in this study to numerically analyze the fluid flow it generates within a stirred tank. The topology of the resulting flow was found to be strongly dependent on several parameters, including the geometric configurations of the system and the properties of the moving fluids. The governing equations, based on the k-epsilon model, were solved using the finite volume method. Velocity field profiles, streamlines and vortex sizes were ana-lyzed for several geometries, varying the number of blades from 6 to 12 and others. A comparison was also conducted to evaluate the effect of the number of stirring mobiles used to mix the fluid (single stage, two stages and three stages), as well as the influence of the spacing ratio between the different stir-rers. Finally, our numerical simulation procedure was validated through com-paring the results obtained with experimental work available in the literature, showing good agreement between the different approaches.
- A cloud-driven support layer for enhancing distributed IDS in IoT networksPublication . Funchal, Gustavo Silva; Pedrosa, Tiago; Prieta, Fernando De la; Leitão, PauloThe exponential growth of connected devices, including sensors, mobile equipment, and various Internet of Things (IoT) nodes, has significantly increased the volume of data generated at the edge. Traditionally, data analysis tasks are offloaded to centralized cloud servers, resulting in increased latency, bandwidth bottlenecks and privacy concerns. While edge computing addresses these limitations by enabling local processing, it also faces challenges related to limited computational capacity and isolated decision-making. In this context, Multi-Agent Systems provide a promising solution by enabling collaboration among edge nodes for distributed machine learning-based intrusion detection. This work extends previous research by introducing a hierarchical approach within the edge-cloud continuum, where agents deployed in the cloud continuously monitor edge-level behaviour and employ reinforcement learning techniques to suggest dynamic updates to decision parameters of edge agents. This feedback-driven mechanism allows agents to adapt their behaviour over time, improving detection accuracy and collaboration efficiency while keeping communication overhead under control. The proposed architecture balances decentralisation and adaptability, offering a scalable and privacy-preserving solution for intrusion detection in dynamic and resource-constrained IoT environments.
- Collaborative fault tolerance for cyber–physical systems: The detection stagePublication . Piardi, Luís; Oliveira, André Schneider; Costa, Pedro; Leitão, PauloIn the era of Industry 4.0, fault tolerance is essential for maintaining the robustness and resilience of industrial systems facing unforeseen or undesirable disturbances. Current methodologies for fault tolerance stages namely, detection, diagnosis, and recovery, do not correspond with the accelerated technological evolution pace over the past two decades. Driven by the advent of digital technologies such as Internet of Things, cloud and edge computing, and artificial intelligence, associated with enhanced computational processing and communication capabilities, local or monolithic centralized fault tolerance methodologies are out of sync with contemporary and future systems. Consequently, these methodologies are limited in achieving the maximum benefits enabled by the integration of these technologies, such as accuracy and performance improvements. Accordingly, in this paper, a collaborative fault tolerance methodology for cyber–physical systems, named Collaborative Fault * (CF*), is proposed. The proposed methodology takes advantage of the inherent data analysis and communication capabilities of cyber–physical components. The proposed methodology is based on multi-agent system principles, where key components are self-fault tolerant, and adopts collaborative and distributed intelligence behavior when necessary to improve its fault tolerance capabilities. Experiments were conducted focusing on the fault detection stage for temperature and humidity sensors in warehouse racks. The experimental results confirmed the accuracy and performance improvements under CF* compared with the local methodology and competitiveness when compared with a centralized approach.