I. Componente Universitária
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Percorrer I. Componente Universitária por Objetivos de Desenvolvimento Sustentável (ODS) "07:Energias Renováveis e Acessíveis"
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- Energy transition effects on food security amidst climate change and progress toward sustainable development goalsPublication . Tamasiga, Phemelo; Dzingai, Valentine Munyaradzi; Onyeaka, Helen; Ngameni Tchonkouang, Rose Daphnee; Siyanbola, Kehinde Favour; Genesis, Ulakom; Mudimu, George T.Transitioning to net-zero societies affects how energy is produced and consumed, with consequences for food security. Through a systematic review of 43 peer-reviewed studies that follow the PRISMA protocol, results reveal that renewable energy can enhance agricultural productivity by reducing operational costs, increasing efficiency in irrigation and processing, and providing reliable access to energy. However, challenges exist, including competition for land and water resources between renewable energy projects and food production, high upfront costs of clean energy technologies, limited access to credit facilities, and institutional bottlenecks. To overcome these challenges, recommended policies include offering subsidies and financial incentives to make clean energy more affordable for farmers, as well as providing education and training to support the adoption of sustainable practices. Furthermore, promoting collaboration between the public and private sectors is crucial to stimulate investment in renewable energy infrastructure. Moreover, these policies must be designed for specific national circumstances. High-income or upper-middle-income countries can deploy capital-intensive agrivoltaic and biogas technologies via concessional finance. In contrast, low-income settings should prioritize low-cost, decentralized solar pumps and off-grid dryers to build farmer confidence and trust. Countries with stronger regulatory frameworks and secure land tenure systems are better equipped to support large-scale renewable energy projects. At the same time, regions with weaker governance tend to benefit most from community-owned mini-grids. The mapping of policy options onto economic, institutional, and agro-ecological dimensions provides a nuanced, context-sensitive framework to guide equitable and effective energy transitions in diverse agricultural landscapes.
- Gravitational waves from two scalar fields unifying the dark sector with inflationPublication . Luongo, Orlando; Mengoni, Tommaso; Sá, PauloWe investigate the gravitational-wave background predicted by a two-scalar-field cosmological model that aims to unify primordial inflation with the dark sector, namely late-time dark energy and dark matter, in a single and self-consistent theoretical framework. The model is constructed from an action inspired by several extensions of general relativity and string-inspired scenarios and features a non-minimal interaction between the two scalar fields, while both remain minimally coupled to gravity. In this context, we derive the gravitational-wave energy spectrum over wavelengths ranging from today’s Hubble horizon to those at the end of inflation. We employ the continuous Bogoliubov coefficient formalism, originally introduced to describe particle creation in an expanding Universe, in analogy to the well-established mechanism of gravitational particle production and, in particular, generalized to gravitons. Using this method, which enables an accurate description of graviton creation across all cosmological epochs, we find that inflation provides the dominant gravitational-wave contribution, while subdominant features arise at the inflation-radiation, radiation-matter, and matter-dark energy transitions, i.e., epochs naturally encoded inside our scalar field picture. The resulting energy density spectrum is thus compared with the sensitivity curves of the planned nextgeneration ground- and space-based gravitational-wave observatories. The comparison identifies frequency bands where the predicted signal could be probed, providing those windows associated with potentially detectable signals, bounded by our analyses. Consequences of our recipe are thus compared with numerical outcomes and the corresponding physical properties discussed in detail.
- HVAC systems applied in university buildings with control based on PMV and aPMV indexesPublication . Conceição, Eusébio; Sousa, António F. M.; Gomes, João; Ruano, AntonioIn this work, HVAC (Heating, Ventilation and Air Conditioning) systems applied in university buildings with control based on PMV (Predicted Mean Vote) and aPMV (adaptive Predicted Mean Vote) indexes are discussed. The building’s thermal behavior with complex topology, in transient thermal conditions, for summer and winter conditions is simulated by software. The university building is divided into 124 spaces, on two levels with an area of 5931 m2 , and is composed of 201 transparent surfaces and 1740 opaque surfaces. There are 86 compartments equipped with HVAC systems. The simulation considers the actual occupation and ventilation cycles, the external environmental variables, the internal HVAC system and the occupants’ and building’s characteristics. In this work, a new HVAC control system, designed to simultaneously obtain better occupants’ thermal comfort levels according to category C of ISO 7730 with less energy consumption, is presented. This new HVAC system with aPMV index control is numerically implemented, and its performance is compared with the performance of the same HVAC system with the usual PMV index control. Both HVAC control systems turn on only when the PMV index or the aPMV index reaches values below −0.7, in winter conditions, and when the PMV index or the aPMV index reaches values above +0.7, in summer conditions. In accordance with the results obtained, the HVAC system guarantees negative PMV and aPMV indexes in winter conditions and positive PMV and aPMV indexes in summer conditions. The energy consumption level is higher in winter conditions than in summer conditions for compartments with shading, and it is lower in winter conditions than in summer conditions for compartments exposed to direct solar radiation. The consumption level is higher using the PMV control than with the aPMV control. Air temperature, in accordance with Portuguese standards, is higher than 20 ◦C in winter conditions and lower than 27 ◦C in summer conditions. In Mediterranean climates, the HVAC systems with aPMV control provide better occupants’ thermal comfort levels and less energy consumption than the HVAC system with PMV control.
- MnCr2O4: a promising material with suitable magnetic response for spintronic and magnetic recording devicesPublication . Wali, Mouna; Hajji, Ala Ben Abderrazak; Dhahri, Radhia; Dhahri, Essebti; Mariano, José; Morales, Marco A.; Silva, Rodolfo B. daOver the last few years, a new magnetic nanoparticles system has been elaborated in order to enhance the magnetic feature of spintronic and ultra-high-density recording devices with respect to promoting the anisotropic behaviour and ensuring the magnetic ordering stability. The smart MnCr2O4 chromite compound is becoming more popular these days thanks to its promising potential to create an extra source of anisotropy energy so that it becomes steadily moving toward commercialization referring to its soft ferrimagnetic behaviour and low manufacturing cost. In this research paper, single phase spinel MnCr2O4 chromite compound has been successfully prepared through the use of the Sol-gel method. The room temperature X-ray Diffraction characterisation technique was applied to confirm the cubic crystallographic structure. The thermal magnetization M(T) has been explored at various low applied magnetic fields (100, 300 and 500 Oe) to investigate the spin-glass behaviour of our compound. M(H) measurements have been performed between 5 and 50 K, giving rise to an exchange bias (EB) effect in our material. In this respect the various hysteresis and anisotropy parameters have been respectively determined using a theoretical model as well as the well-known Law to Approach to Saturation (LAS). The effect of temperature on these parameters was tackled. A significant increase of the coercive field from 22.1 Oe to 29.7 Oe was recorded confirming the soft ferrimagnetic behaviour of the examined compound (HC ˂ 628 Oe). These outstanding results, definitely confirm the interesting potential of MnCr2O4 to be invested within the area of spintronic devices manufacturing.
- Phantom cosmology with arbitrary potential: New accelerating scaling attractorsPublication . Halde, Sudip; Pan, Supriya; Sá, Paulo; Saha, TapanIn this article, we investigate the existence of accelerating scaling solutions in coupled phantom cosmology without assuming any specific potential for the phantom scalar field. The coupling between phantom dark energy and dark matter is motivated by the warm inflationary paradigm, with the dissipation coefficient assumed to be either constant or variable. The evolution equations are written in the form of autonomous systems, whose stability is studied using methods of qualitative analysis of dynamical systems. For this analysis, the only requirement imposed on the otherwise arbitrary phantom potential is that a particular dynamical variable, defined in terms of the potential and its derivative, must be invertible. For such a generic potential, we show that accelerated scaling solutions do exist, for both constant and variable dissipation coefficients. Although there is a limitation to these scaling solutions – specifically, the current stage of accelerated expansion is not preceded by a long enough matter-dominated era – our results show that the existence of a direct coupling between phantom dark energy and dark matter yields great potential for addressing the cosmic coincidence problem.