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Percorrer Faculdade de Ciências e Tecnologia 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.
- From home energy management systems to energy communities: methods and dataPublication . Ruano, Antonio; Ruano, MariaThis paper introduces the HEMStoEC database, which contains data recorded in the course of two research projects, NILMforIHEM, and HEMS2IEA, for more than three years. To be manageable, the dataset is divided in months, from January 2020 until February 2023. It consists in: (a) consumption electric data for four houses in a neighbourhood situated in the south of Portugal, (b) weather data for that location, (c) photovoltaic and battery data, (d) inside climate data, and (e) operation of several electric devices in one of the four houses. Raw data, sampled at 1 sec and 1 minute are available from the different sensing devices, as well as synchronous data, with a common sampling interval of 5 minutes are available. Gaps existing within the data, as well as periods where interpolation was used, are available for each month of data.
- 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.
- Optimal light wavelength and intensity for algae cultivation in photobioreactorsPublication . Nogueira, Gustavo Filipe Magalhães; Schulze, Peter Simon Claus; Varela, João Carlos SerafimIn the present study, the growth response of Phaeodactylum tricornutum, Nannochloropsis oceanica, and Porphyra dioica cultures with different biomass concentrations to 22 combinations of red (620 nm), green (530 nm), and blue (450 nm) light at 3 different light intensities (200, 500, and 1000 μmol m-2 s-1) was investigated. Photosynthetic oxygen evolution rates as response variable were used to create predictive models with the optimal light conditions to improve growth at different algal growth stages. While P. dioica did not result in positive oxygen evolution rates and thus no model could be established, for P. tricornutum and N. oceanica, predictive models showed statistical significance and were used to develop light regimes, matching the needs of algae cultures at different growth stages (lag, exponential, and late exponential phase). The generated models predicted the least absorbed wavelength (620 nm) as optimal for both algae, suggesting that it penetrated the algal culture deeper and stimulated photosynthesis of more cells than more absorbed wavelengths (e.g., 450 nm) that do not penetrate deeper into the culture. An additional experiment was conducted to validate the obtained light regimes. For this purpose, a novel light system (AlgaeLum) was developed, 3D printed and assembled for testing different light quantities and qualities. Experiments showed no significant differences in growth rate and maximum biomass concentrations compared to the control warm white light for both algae. Less absorbed wavelengths showed to improve photosynthetic efficiency in both microalgal species, especially in highly dense cultures and low light paths, over highly absorbed wavelengths (450 nm). Based on this result, the use of red light (620 nm) LEDs is recommended for N. oceanica and P. tricornutum as it offers an optimal balance between cost-effectiveness in terms of both CAPEX and OPEX) and photosynthetic efficiency. The developed AlgaeLum system can be used in the future to conduct other trials (e.g., continuous cultivation systems), which was not tested in the present study to validate the present results.
- 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.
- Testing the diversifying asset hypothesis between clean energy stock indices and oil pricePublication . Dias, Rui; Galvão, Rosa; Cruz, Sandra P.; Irfan, Mohammad; Alexandre, Paulo; Gonçalves, Sidalina; Teixeira, Nuno; Palma, Cristina; Almeida, LilianaIn theory, geopolitical risk and political uncertainty can directly affect energy markets. Fluctuations lead to the cost of clean energy sources as they compete with traditional energy. The purpose of this study is to analyse financial integration and test the diversifying asset hypothesis between clean energy indices, specifically the Clean Energy Fuels (CLNE), Nasdaq Clean Edge Green Energy (CELS), S&P Global Clean Energy (SPGTCLEN), TISDALE Clean Energy (TCEC.CN), Wilderhill (ECO) and West Texas Intermediate (WTI) stock indices, over the period from 1 January 2018 to 23 November 2023. Analysing the results reveals a scenario where most of the clean energy indices show cointegration with each other, indicating long-term relationships that reflect common trends in the clean energy sector. However, the relative independence of the WTI suggests that Oil still acts as an important and potentially diversifying external factor for investors focused on sustainable energy. Structural breaks in 2021 and 2022 in several indices point to significant events that have altered market dynamics, possibly including changes in environmental policies, technological innovations and the impacts of the COVID-19 pandemic. The cointegration evidence and structural breaks provide valuable information for building investment portfolios. Investors can consider the WTI to diversify portfolios dominated by clean energy assets, taking advantage of Oil’s relative independence. On the other hand, the high correlation between clean energy indices suggests that, within this sector, diversification options are more limited, requiring careful analysis of the specific characteristics of each index and the macroeconomic forces affecting them.
- Unlocking cyanobacterial metabolic potential: ß-oxidation pathwayPublication . Gonçalves, Inês Oliveira; Figueiredo, Sandra; Varela, JoãoCyanobacteria are a very diverse phylum of photosynthetic prokaryotes. As the first known organisms to produce oxygen on Earth, these microorganisms were crucial to the development of the biosphere and early Earth life forms. Cyanobacteria still presents several undefined genomic and metabolic pathways, despite their relevance, namely as a promising biological alternative to overcome the increasing demand for sustainable fuels and plastics. One of the still unclear pathways in cyanobacteria is b-oxidation, the catabolic process of fatty acid (FA) degradation. This mechanism had been thought to be universal for all organisms; however, some studies have suggested that b-oxidation might be lacking in cyanobacteria, despite the scattered evidence to support this hypothesis. We have revealed unprecedented results that may help finally understand this fundamental metabolic pathway in cyanobacteria. Through the bioinformatic analysis performed, some cyanobacteria strains were shown to encode putative fatty acid degradation (fad) machinery. Genomic context analysis led to the identification of a previously uncharacterized gene, here called AMP-L, that completes the full set of fad genes required for fatty acid activation and subsequent entry into the b-oxidation pathway. With the protocol optimized in this work, cyanobacterial fatty acyl-CoA intermediates with different length chains were detected for the first time. Different in vivo FA supplementation assays support these findings, showing for the firsttime cyanobacteria strains that might be able to degrade FA. These results address several fundamental questions related to cyanobacteria evolution and FA metabolism. Furthermore, this study brings knowledge that would, ultimately, lead to more efficient metabolism engineering applied to biotechnological purposes.