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  A dynamical approach to general relativity based on proper time

  (Multidisciplinary Digital Publishing Institute (MDPI), 2026-03-01) Haro Cases, Jaume; Universitat Politècnica de Catalunya. Departament de Matemàtiques

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  This work places the invariant ¿¿2 at the center of the gravitational interaction, interpreting it not as a purely geometric object but as the differential of proper time, endowed with direct physical meaning. Starting from the extension of Fermat’s principle to massive particles—namely, the requirement that freely falling bodies follow trajectories that extremize proper time, which for timelike motion corresponds to a local maximum—and invoking the universality of Galilean free fall, we derive the form of ¿¿2 in a static gravitational field. Lorentz invariance then provides the natural framework to extend this result to systems involving moving matter. The invariant derived through this procedure matches the weak-field limit of General Relativity formulated in the harmonic gauge. Within this linearized regime, we show that the structure of the theory already contains the seeds of its nonlinear completion: any dynamically consistent extension to strong gravitational fields necessarily involves the Ricci tensor. From this viewpoint, Einstein’s field equations appear not as a postulated geometric law but as the unique covariant closure required to ensure energy–momentum conservation and the self-consistency of the gravitational interaction

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  Factors shaping perceptions of the digital euro: insights into how potential adoption is evaluated among Spanish business undergraduates

  (Elsevier, 2026-06) Rodríguez Donaire, Silvia; Amerigo Cabot, Max; García-Almiñana, Daniel; Universitat Politècnica de Catalunya. TUAREG - Turbulence and Aerodynamics in Mechanical and Aerospace Engineering Research Group; Universitat Politècnica de Catalunya. Departament d'Organització d'Empreses; Universitat Politècnica de Catalunya. Departament d'Enginyeria de Projectes i de la Construcció

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  This study examines how digitally literate young adults interpret and evaluate the potential adoption of Central Bank Digital Currencies (CBDCs), focusing on the Digital Euro (DE) within a strategic sample of Spanish business undergraduates. Adopting an exploratory qualitative design, the analysis draws on 87 open-ended responses collected in a university setting and thematically coded using ATLAS.ti. The findings show that the evaluation of DE adoption is not driven by isolated factors but by interpretative processes through which participants assess and negotiate trade-offs between usefulness, privacy, trust, and broader socio-economic implications. Privacy concerns, particularly related to surveillance and data control, emerge as a central barrier, with gendered nuances in risk perception. Age-related differences suggest that younger respondents emphasise pragmatic usability and benchmarking against existing digital payment systems, while slightly older participants focus on institutional oversight and systemic implications. Contrary to dominant CBDC narratives, financial inclusion does not appear to be a primary concern among this digitally prepared subgroup. Instead, employment-related considerations emerge spontaneously as a salient evaluative dimension, linking the DE to automation risks and innovation opportunities. Participants consistently benchmark and assess the DE against existing payment instruments, reinforcing the importance of perceived relative advantage. The study demonstrates that the evaluation of CBDC adoption is interpreted as a socio-institutional process rather than approached as a purely technological decision. While the single-institution sample limits generalizability, the findings provide theory-building insights into how informed young users interpret, assess, and construct evaluation of public digital money prior to implementation.

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  Mitigating household air pollution and associated health risks through chimney-hood–stove systems: a quantitative study in rural nepal

  (2026-04-20) Bravo Masferrer, Mario; Sans Duran, Mònica; Ferrandiz Mont, David; Pudasaini, Hareram; Turró, Carles; López Codina, Daniel; Prats Soler, Clara; Campillo López, Ferran; Fonollosa Magrinyà, Jordi; Universitat Politècnica de Catalunya. BIOCOM-SC - Biologia Computacional i Sistemes Complexos; Universitat Politècnica de Catalunya. TecSalut - Grup de Recerca en Tecnologies de la Salut; Universitat Politècnica de Catalunya. Departament de Física; Universitat Politècnica de Catalunya. Departament d'Enginyeria de Sistemes, Automàtica i Informàtica Industrial

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  Indoor air pollution (IAP) caused approximately 3.2 million deaths worldwide in 2020. Nearly a third of the global population uses open fires or inefficient stoves without ventilation, worsening IAP. In rural Nepal, firewood is the main source for cooking and heating, exposing women and the youngest children to high levels of pollutants. The Awasuka program installed improved kitchens—comprising chimney, hood, and stove (CHS)—in rural households in Bhimphedi. This study evaluates the short-term effect of this intervention on IAP and women's health. A cross-sectional study was conducted in 210 women from 105 CHS and 105 non-CHS households. Health, environmental and sociodemographic data were also collected using structured, validated questionnaires. Additionally, 10 sensor nodes were deployed to monitor indoor levels of PM ndoor air pollution (IAP) caused approximately 3.2 million deaths worldwide in 2020. Nearly a third of the global populationuses open fires or inefficient stoves without ventilation, worsening IAP. In rural Nepal, firewood is the main source for cookingand heating, exposing women and the youngest children to high levels of pollutants. The Awasuka program installed improvedkitchens—comprising chimney, hood, and stove (CHS)—in rural households in Bhimphedi. This study evaluates the short-termeffect of this intervention on IAP and women's health. A cross-sectional study was conducted in 210 women from 105 CHS and105 non-CHS households. Health, environmental and sociodemographic data were also collected using structured, validatedquestionnaires. Additionally, 10 sensor nodes were deployed to monitor indoor levels of PM 2.5 , PM 10 , and CO 2 , collecting data 1month before and after CHS installation in 10 selected houses. Results show that women in non-CHS households reported signif-icantly more episodes of fever, headache, eye irritation, migraines, and heart disease (p < 0.05). Multivariate logistic regressionrevealed higher odds of reporting any acute symptom (aOR 9.6 [2.9–43.4]), migraines (aOR 3.4 [1.7–6.8]), and heart disease (aOR5.8 [1.1–36.4]) among these women. Sensor data collected from the homes revealed substantial reductions in indoor PM 2.5 , PM 10 ,and CO 2 levels post-CHS installation. Daily exposure above hazardous thresholds decreased significantly: from 5.3 to 1.3 h forPM 2.5 , from 4.9 to 1.0 h for PM 10 , and from 4.3 to 0.4 h for CO 2 . All three pollutants showed significant reductions in area underthe exposure curve. CHS installations significantly reduce IAP and this is linked to women's health. In firewood-reliant ruralsettings, CHS offers a sustainable, culturally adapted, health-enhancing alternative to traditional cooking methods.1 | IntroductionIndoor air pollution (IAP) is a significant and yet often over-looked public health concern, responsible for 3.2 million deathsevery year worldwide, including 237,000 children under 5 yearsof age. This is mainly due to the 2.1 billion people worldwidethat still rely on biomass for cooking. Women and children,especially girls, are usually in charge of the household choresbearing the greatest health burden [1].Exposure to IAP has been linked to a range of adverse healtheffects, the main ones being cardiopulmonary diseases [2],This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium,provided the original work is properly cited.Copyright © 2026 Mario Bravo Masferrer et al. Indoor Air published by John Wiley & Sons Ltd.Health Impact of Indoor Air PollutionIndoor Air

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  Assessment of empirical equations for predicting scour depth around gravity base foundations

  (2025) Dalili Khanghah, Kazem; d'Angiuro, Ivan; Sarmiento, Javier; Altomare, Corrado; Gironella Cobos, Xavier; Guanche García, Raúl; Universitat Politècnica de Catalunya. LIM/UPC - Laboratori d'Enginyeria Marítima; Universitat Politècnica de Catalunya. Doctorat en Ciències del Mar; Universitat Politècnica de Catalunya. Laboratori d'Enginyeria Marítima - Universitat Politécnica de Catalunya; Universitat Politècnica de Catalunya. Departament d'Enginyeria Civil i Ambiental

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  Scour development around offshore foundations, particularly the depth of scour hole, is a critical concern for structural stability. Despite extensive research on scour around offshore monopile foundations, there is a paucity of empirical equations tailored for Gravity Base Foundations (GBFs). This study addresses this gap by compiling and evaluating empirical solutions for predicting scour depth around GBFs. Some equations are specifically designed for GBFs, while others are adapted from methods used for compound and complex bridge piers (CBPs) due to their shape similarities with GBFs. Additionally, the study reviews existing equations for the temporal evolution of scour depth. The performance of these equations is assessed using results from a tank test campaign conducted by IH Cantabria for the ELISA GBF. Although this experimental work examined scour hole development around GBF under various environmental conditions, the current-only unprotected scour tests are considered as the reference experimental data. The findings provide scattered results by assessment of empirical equations, contributing to improved predictive capabilities for scour depth around GBFs.

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  Where extended reality and AI may take us: ethical issues of impersonation and AI fakes in social virtual reality

  (Public Library of Science (PLOS), 2026-04-02) Oliva, Ramon; Wiesing, Michael; Gallego Vila, Jaime; Inami, Masahiko; Interrante, Victoria; Lécuyer, Anatole; McDonnell, Rachel; Nouviale, Florian; Pan, Xueni; Steinicke, Frank; Slater, Mel; Universitat Politècnica de Catalunya. ViRVIG - Grup de Recerca en Visualització, Realitat Virtual i Interacció Gràfica; Universitat Politècnica de Catalunya. Departament de Ciències de la Computació

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  We describe a study based on a panel discussion that took place in social virtual reality (VR) at the conference IEEE VR 2025. Each panellist was embodied in a virtual body that looked like themselves. The VR scene was projected onto a screen in front of the audience in the main conference theatre. During the course of the panel two of the panellists swapped avatars, but tried to act as if they were the other person. Additionally, a large language model-controlled Alan Turing (AT) avatar participated. The study aimed to assess the audience’s ability to detect the human identity swap and their perception of the AT panellist. We found that about 40 of 100 attendees who answered a post panel survey did not notice the body swap, highlighting a form of change blindness towards social identity in VR. While AT was seen as less realistic and somewhat distracting, its inclusion demonstrated the increasing capabilities of AI in natural language processing and interaction. The paper emphasises the critical need for ethical considerations, such as identity verification and guidelines for representing historical figures, as virtual reality platforms that can represent historical figures in combination with LLMs become more widespread.

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