Repositori Obert UdL
The institutional repository collects, manages, disseminates and preserves publications in open access derived from the academic and research activity of the University of Lleida.
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Open Access
Lagrangian formulation of the Tsallis entropy
(Elsevier, 2024) D'Agostino, Rocco; Luciano, Giuseppe Gaetano
We investigate the gravitational origin of the Tsallis entropy, characterized by the nonadditive index 𝛿. Utilizing Wald’s formalism within the framework of 𝑓(𝑅) modified theories of gravity, we evaluate the entropy on the black hole horizon for constant curvature solutions to the spherically symmetric vacuum field equations. In so doing, we demonstrate that the Tsallis entropy can be effectively derived from a generalization of the Lagrangian ∝ 𝑅1+𝜖 , where 𝜖 = 𝛿 − 1 quantifies small deviations from general relativity. In conclusion, we examine the physical implications of our findings in light of cosmological observations and elaborate on the possibility of solving the thermodynamic instability of Schwarzschild black holes.
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Open Access
On the Complexity of the Bipartite Polarization Problem: From Neutral to Highly Polarized Discussions
(MDPI, 2024) Alsinet, Teresa; Argelich Romà, Josep; Béjar Torres, Ramón; Martínez, Santi
The bipartite polarization problem is an optimization problem where the goal is to find the highest polarized bipartition on a weighted and labeled graph that represents a debate developed through some social network, where nodes represent user’s opinions and edges agreement or disagreement between users. This problem can be seen as a generalization of the maxcut problem, and in previous work, approximate solutions and exact solutions have been obtained for real instances obtained from Reddit discussions, showing that such real instances seem to be very easy to solve. In this paper, we further investigate the complexity of this problem by introducing an instance generation model where a single parameter controls the polarization of the instances in such a way that this correlates with the average complexity to solve those instances. The average complexity results we obtain are consistent with our hypothesis: the higher the polarization of the instance, the easier is to find the corresponding polarized bipartition. In view of the experimental results, it is computationally feasible to implement transparent mechanisms to monitor polarization on online discussions and to inform about solutions for creating healthier social media environments.
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Open Access
Enhancing students’ attitudes towards statistics through innovative technology-enhanced, collaborative, and data-driven project-based learning
(Springer Nature, 2024) Cujba, Andreea; Pifarré Turmo, Manoli
Given the substantial body of educational research highlighting the significant influence of student attitudes on academic performance, particularly in disciplines like statistics where anxiety is prevalent, there is a need to investigate how innovative methodologies could reshape these attitudes. This paper will capitalize on the advancements from previously uncombined innovative methodologies of teaching statistics, such as project-based learning, data analytics, collaborative work, or the use of technology. Specifically, this paper reports on the design, implementation, and evaluation of innovative technology-enhanced, collaborative, and data-driven project-based learning, aiming to positively impact students’ attitudes towards statistics as a cornerstone to improve statistical knowledge. To achieve this, a quasi-experimental research study involving 174 secondary students was undertaken, with participants divided into an experimental group (EG) and a control group (CG). Results indicate a notable positive shift in attitudes among EG students following the intervention. The EG students decreased their anxiety after the intervention and, increased their affect and positive attitude toward using technology for learning statistics. By contrast, the CG students do not show any positive effect on their attitudes. These findings underscore the potential of the innovative instructional design implemented in this project to not only foster practical statistical problem-solving skills but also cultivate positive attitudes crucial for statistical competence. Educational implications are discussed.
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Open Access
A review of experimental studies on flow boiling instabilities mitigation through geometrical modifications
(Elsevier, 2024) Camarasa, Jaume; Crespo, Alicia; Vilarrubí, Montse; Ibáñez, Manuel; Barrau, Jérôme
Flow boiling technology is considered one of the most promising cooling solutions for high power microelectronics. However, flow boiling instabilities cause serious reliability problems that hinder large scale commercial use of this technology. Extensive experimental research has been carried out in the last years to mitigate these issues, focusing on geometrical aspects, surface modification, wettability, working fluid, or active control strategies, among others. Nevertheless, despite the relevance of geometrical aspects, none of the studies conducted a comprehensive review on geometrical structures and their instabilities mitigation effect.
This review aims to provide constructive insights into relevant studies about experimental flow boiling geometrical enhancements and their impact on instabilities mitigation. It focuses on pin-fin arrays, most of the microchannel structures, inlet restrictors, and combined geometries. Firstly, every geometrical option is analysed in detail, summarizing experimental works in terms of geometry tested, operating parameters, and instabilities improvement. Secondly, a graphical overview is performed aimed at identifying research gaps and tendencies.
This study found that significant progress has been made in geometric mitigation of flow boiling instabilities, and several advanced methodologies have been proposed to improve the reliability of flow boiling technology. The integration of various geometric configurations is a promising avenue, but further research is required to reach a widely accepted solution.
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Open Access
The effect of regional factors on energy poverty
(Emerald, 2024-08-15) Jové-Llopis, Elisenda; Trujillo-Baute, Elisa
Purpose – Within the framework of EU policies and measures to develop a just and fair green energy transition model. This paper aims to offer valuable insights into a paramount concern not so well debated in the literature, i.e. the spatial variation of energy poverty.
Design/methodology/approach – This empirical analysis investigates the regional variation of energy poverty we draw on a sample of more than 300,000 Spanish households, extracted from the Spanish Household Budget Survey (HBS) for the period 2006–2022. To characterize the probability of a household finding itself in a situation of energy poverty the authors use a discrete choice univariate probit model.
Findings – The results confirm that energy poverty is a phenomenon that is asymmetrically distributed across Spain, and mainly occurs in un-densely populated regions. In addition, the findings demonstrate that the incidence of energy poverty drivers is highly heterogeneous across regions.
Research limitations/implications – The paper ends with some recommendations for policymakers suggesting that countries need to design an energy poverty policy for the households that jointly pursue both a correct identification of vulnerable groups and a match with the type of measure to the characteristics of each region.
Originality/value – This study enhances previous research by considering the case of areas at a lower level of aggregation (i.e. on the NUTS two regions in Spain called autonomous communities) and offers the opportunity to tailor policies to those regions most in need. Furthermore, to provide a more realistic picture of the complex phenomenon of energy poverty, the authors use the information for the period 2006–2022 differentiating by economic micro-cycle. This timespan allows the authors to understand the dynamics of energy poverty.