FCT2-Artigos (em revistas ou actas indexadas)
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- Phantom cosmology with arbitrary potential: new accelerating scaling attractorsPublication . Halder, 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.
- Assessment of piggery wastewater treatment in vertical flow constructed wetlands: role of plants and aerationPublication . Corrêa, D. O.; Ferreira, A.; Ribeiro, B.; Gogoi, J.; Karan, N.; Nalwad, A.; Ganguly, A.; Mutnuri, S.; Gouveia, LuisaPiggery wastewater (PWW), rich in pollutants, poses significant environmental risks if not properly treated. Natural treatment processes, such as constructed wetlands (combined action of plants, substrates, and microbes) and microalgae cultivation, offer sustainable and low-cost alternatives for managing these effluents while enabling resource recovery. This study represents an initial step toward optimizing key operational conditions, such as aeration (passive and active), vegetation presence, and the use of single or sequential Vertical Flow Constructed Wetlands (VFCWs), for the treatment of piggery wastewater, using different experimental setups, at a laboratory scale. Indoor experiments were conducted over an 8-week period to optimize operational conditions for the treatment of PWW. The VFCWs, arranged in two stages and operated in series through gravity flow, were fed daily and monitored weekly. The best removal rates of total Kjeldahl nitrogen (42.9 %), ammoniacal nitrogen (50.3 %), and chemical oxygen demand (20.5 %), were observed in the second stage of VFCW without aeration and with plant. Nitrate and phosphorus levels increased during the experiment, likely due to microbial activity within the substrate and plant root zones. The final goal is to treat the piggery wastewater from a rural farm in India, produce electricity (by a Microbial Fuel Cell), to generate an effluent suitable for microalgae cultivation, with the produced biomass intended for use either as a biostimulant to enhance cereal crops included in pig diets or as a direct nutritional supplement in pig feed.
- Using reflectance to measure chlorophyll a in corals: calibration and implications of skeletal optical propertiesPublication . Watty, Kay; Schoepf, Verena; Johnson, Kelly W.; Littke, Sophie; Zande, Rene M. van derClimate change-driven coral bleaching and associated chlorophyll (Chl) loss increasingly threaten coral reefs, highlighting the need for non-invasive, cost-effective tools to assess corals’ physiological condition. Researchers have explored the reflectance-based Normalized Difference Vegetation Index (NDVI) as a proxy for Chl a. However, almost no calibration curves exist to date; thus it remains unknown if the relationship between Chl a and NDVI differs among coral species, and whether it is influenced by skeletal optical properties. Here, we correlated Chl a content to NDVI in three coral species with different skeletal morphologies and reflectance modes across a range of health states (i.e., bleaching states). We found a strong positive relationship between Chl a and NDVI in all species, validating NDVI as a proxy for Chl a in corals. However, this relationship is non-linear, showing deviations at the highest and lowest ends of the pigmentation spectrum. We propose that in healthy states, this non-linearity is due to pigment self-shading, whereas in bleaching states, it is caused by backscattering of light by the increasingly exposed coral skeleton, because pigment loss enhances absorption by the remaining Chl a pigments and lowers, rather than increases, reflectance. To avoid Chl a under- or overestimation, we recommend to log-transform Chl a and create species-specific calibration curves. Overall, the non-invasive, repeatable, and scalable nature of reflectance measurements and NDVI make them valuable tools for assessing coral health both ex- and in situ. They provide a comprehensive view of the holobiont’s physiological condition and hold potential for broader applications in reef-scale monitoring, remote sensing, coral restoration, and conservation.
- 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 nonminimal 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 inflationradiation, 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 next-generation 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 are discussed in detail.
- Prokaryotic community structure and auxin biosynthesis in early developmental stages of farmed atlantic nori (Porphyra spp.)Publication . Cortez, Francisco; Nanetti, Enrico; Chaves, Guilherme; Pereira, André C.; Caria Mendes, Madalena; Oliveira, Inês; Leuzzi, Daniela; Abreu, Helena; Martins, Margarida; Leite, Ricardo B.; Keller-Costa, Tina; Costa, RodrigoIntroduction: Algal-microbiome interactions are considered pivotal for host health and development. Current understanding of the diversity and function of algal-associated microorganisms in aquaculture settings remains limited, preventing the development of microbiome-based solutions for sustainable algal growth.Methods: We employed cultivation-dependent and -independent approaches to determine the structure of bacterial communities associated with farmed Atlantic Nori (Porphyra dioica and Porphyra umbilicalis) at early developmental stages. 16S rRNA gene amplicon sequencing and cultivation of bacterial symbionts were performed for algal and culturing water samples harvested from indoor photobioreactors at stages S1 (conchocelis cultures growing vegetatively), S2 (conchosporangia), and S3 (young blades).Results: The phyla Pseudomonadota (Alpha- and Gammaproteobacteria classes) and Bacteroidota were dominant in algal samples, followed by Planctomycetota, Actinobacteriota, and Verrucomicrobiota. At the phylotype level, these communities were highly structured throughout the host’s life cycle. Uncultivated lineages Sva0996 (Actinomycetota), OM190 (Planctomycetota), Pir4 (Planctomycetota), and the genera Blastopirellula, Algoriphagus, Hyphomonas, and Marinobacter, among others, were enriched in algal samples and presented significantly different abundances across developmental stages. In some cases (e.g., genera Aquimarina, Sulfitobacter, Maribacter, and Nonlabens), those changes were also observed in culturing water. Moreover, the genera Ensifer (Rhizobiaceae), Paraglaciecola (Alteromonadaceae), and the uncultivated lineages DEV007 (Verrucomicrobiota) and Pir4 (Planctomycetota) were consistently present in P. dioica and P. umbilicalis samples at multiple developmental stages. Several Porphyra-associated bacterial genera and putative novel species, mostly belonging to the families Roseobacteraceae, Flavobacteriaceae, and Alteromonadaceae were identified via cultivation. Many cultured members of the Porphyra microbiome produced the growth-promoting hormone auxin, particularly those belonging to the genera Alteromonas, Marinobacter, Sulfitobacter, Leucothrix, and Roseovarius.Discussion: This study unveils complex, phylogenetically distinct, and temporally structured bacterial communities possessing algal morphogenesis-inducing capacities during early developmental stages of Porphyra spp., highlighting the potential of microbiome-based interventions for sustainable growth of marine algae in aquaculture.
- Resilient wireless sensor actor networks through multi-objective self-adaptationPublication . Gomes, Ruben; Correia, NoéliaWireless Sensor Actor Networks (WSAN) are a key enabler of Internet of Things applications that demand timely and reliable data exchange under dynamic conditions. Among the various domains that benefit from these networks, precision agriculture stands out, demanding adaptive strategies for effective monitoring and control. This study proposes a reinforcement learning approach that leverages the Operationalization construct of the Self-Orchestrated Web of Things (SOrWoT) framework to enhance the adaptability of Things’ internal operations. A problem is formulated as a Markov Decision Process, and a Deep Q-Learning agent is trained in a custom simulation environment to identify the most suitable Operationalizations for optimizing data accuracy and latency, under changing conditions and communication failures. The results show that during normal operation the agent favored parallel sensor data averaging to minimize read error, but after an actor failure and the consequent increase in sensor-to-actor distances, it adapted by prioritizing latency through faster Operationalization choices. Sensitivity analyses further confirmed the agent’s ability to adjust policies in response to partial failures, and to shifts in the relative importance of latency versus accuracy. These findings demonstrate that reinforcement learning can autonomously optimize WSAN performance, contributing to resilient and self-adaptive systems.
- LINA: an augmented reality social game enhancing sense of belonging among classmates: an uncontrolled pre-post evaluation studyPublication . Krammer, Ina; Mittmann, Gloria; Nater, Urs M.; Barnard, Adam; Martins, Diogo; Dias, João; Schrank, Beate; Woodcock, Kate A.Supportive peer relationships are fundamental in the development of well-being. Since early adolescents spend a lot of time at school, especially in their classroom, a sense of belonging among classmates plays a pivotal role for mental health and academic functioning. Programs that enhance sense of belonging among classmates through improving peer relationships in classrooms are rare. Given that early adolescents increasingly use digital media to establish and maintain relationships with classmates, there is potential in digital social games that enhance social connectivity and collaboration, especially during the difficult transition from primary to secondary school. LINA ('Lina Is Not Alone') is a novel social augmented reality game for classrooms that is designed to enhance sense of belonging among classmates through improving their relationships with classmates. We conducted an uncontrolled pre-post evaluation study to evaluate (a) player experience, (b) translation of the theory-led LINA design into user experience and (c) increases in sense of belonging after engagement with LINA. In total, data from 99 participants (Mage = 10.94; range = 10-12; 51 girls, 48 boys) were included in this study. Our results provided evidence for (a) high satisfaction and acceptability of LINA, (b) a successful translation of theory-led design features into user experiences, and (c) increases in sense of belonging. We discuss practical implications and future development of LINA.
- Effect of warming on European green crab (Carcinus maenas) populations from larvae to sexual maturityPublication . Monteiro, João Nuno; Ovelheiro, Andreia; SORDO, LAURA; Palma, Jorge; Pinto, Miguel; Teodosio, Maria; Leitão, FranciscoUnderstanding the effects of climate change on the physiology of marine species, particularly during their early life stages (larvae and juveniles), is essential for predicting population dynamics. Carcinus maenas is a widely distributed species of significant ecological and economic importance. This experimental study investigates the effects of warming on the early life stages of the European green crab, C. maenas, through two complementary experiments: (1) larval development and survival were assessed under three temperature regimes-approximately 18.5 degrees C (representing the annual average Portuguese seawater temperature between 1980 and 2020, used as the control), and two projected climate change scenarios: RCP 4.5 (+1.5 degrees C) and RCP 8.5 (+3.5 degrees C), and (2) juvenile survival and growth were monitored in mesocosms from early settlement to sexual maturity. Results indicated that larval mortality exceeded 90 % across all treatments, with 75 % occurring within the first 8 days (95 % CI: 7-8), and that warming enhanced larval survival, with the RCP 4.5 scenario yielding the highest survival rates compared with the control. Additionally, warming also reduced the pelagic larval duration, which declined from 27 (+/- 2) days at 18.5 degrees C to 16 (+/- 1) days at 22 degrees C. Similarly, the duration of the megalopa (settlement) stage decreased from 10 to 6 days. Therefore, despite high mortality, accelerated development under warming may enhance population resilience. Juvenile mortality was also high, with 50 % of settled individuals dying within the first 50 (95 % CI: 31-46) days, and differences in growth and survival between sexes were observed: females reached sexual maturity faster than males 83 +/- 12 and 109 +/- 20 days, respectively. Moreover, only 24 % (95 % CI: 16-34) of the settled females reached sexual maturity, compared to just 9 % of males (95 % CI: 5-18). These results indicate that C. maenas reach reproductive maturity within six months. The biological data reveal a fast growth increment, high larval and juvenile mortality, and suggest that projected climate change scenarios through the end of the century will have a limited impact on the species' population dynamics and recruitment.
- Spatiotemporal patterns and environmental drivers of Physalia physalis strandings along mainland Portugal (northeastern Atlantic)Publication . Carvalho, Patrícia; Henrique Cordeiro, Clara Maria; Pereira, Soraia; Santos, Antonina dosPhysalia physalis is a cosmopolitan colonial organism frequently observed in Portuguese waters. The species has long tentacles, provided with cnidocytes, which release a strong poison when in contact with other organisms, and cause skin reactions and severe pain in humans. Events of rapid reproduction, common in these species, may have important economic and social consequences. This study explores for the first time, the relationships between long-term assessment of P. physalis strandings, using data from the GelAvista citizen science project, and environmental variables - Sea Surface Temperature (SST), wind direction and intensity, the North Atlantic Oscillation (NAO), and upwelling indices - along the Portuguese coast, using a Generalized Linear Mixed-Effects Model. Strandings of P. physalis were concentrated along the western coast and were rare in the south. More than 54 % of the records corresponded to a single individual. Sightings peaked from November through May (winter and spring), mirroring the negative correlation with SST. Wind patterns strongly influenced stranding events: winds likely pushed colonies toward the shore, while calm conditions facilitated their arrival on beaches. In March 2018, an upwelling event in the south coast combined with a series of storms likely underlay the high stranding numbers observed in the southern area, with more than 50 individuals of P. physalis per record. A positive trend in sightings over the study period suggests that P. physalis occurrences may be rising, even after accounting for wind and SST, which might be linked to climate change. Our findings underscore the value of ongoing jellyfish monitoring via citizen science platforms like GelAvista and highlight the need for expanded high-resolution environmental datasets. Moreover, this work establishes a foundation for experimental studies to elucidate the mechanisms behind P. physalis strandings. For future research, time series techniques for imputing missing values may be utilized to enhance the completeness of environmental datasets and strengthen analytical robustness in subsequent studies focused on time series analysis.
- Influence of dolphin-watching tourism vessels on the whistle emission pattern of common dolphins and bottlenose dolphinsPublication . Silva, Ana A.; Castro, Joana; Cid, André; Jesus, Sergio; Matos, Fábio L.Recent years have seen a notable rise in dolphin-watching boat activities along the Algarve coast in Portugal, potentially affecting the common dolphin (Delphinus delphis) and bottlenose dolphin (Tursiops truncatus) local populations. This study examines the impact of increasing underwater noise levels from these boats on dolphin vocalizations. Field recordings were conducted from June to September 2022, analyzing dolphin whistles in various boat presence scenarios. The results indicate significant changes in whistle-frequency characteristics with boat presence, including increased start, low, and high frequencies, alongside a decrease in the number of inflection points in modulated whistles. The changes might negatively impact dolphin populations viability, underscoring the need for further research. Additionally, improved mitigation strategies may be necessary to reduce the potential negative effects of dolphin watching on cetacean communication and behavior in the Algarve region.