Browsing by Issue Date, starting with "2021-06"
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- Undergraduate Students' Learning of Linear Algebra Through Mathematical Modelling RoutesPublication . Ramirez-Montes, Guillermo; Henriques, Ana; Carreira, SusanaMathematical modelling has acquired relevance at all educational levels in the last decades since integrating this activity in instruction provides significant contexts for improving students' learning, including in linear algebra courses that have a notable presence in many undergraduate courses from different fields, including engineering and sciences. This paper reports a study aiming to characterise the distinct modelling routes performed by Costa Rican undergraduate students when solving a mathematical modelling task involving the concept of system of linear equations (SLE). In analysing those modelling routes, it was possible to identify their learning of linear algebra concepts and their modelling competencies as well as the associated difficulties that students faced. Data collection included participant observation, with audio recording of the students' discussions, their written work on the task, and digital files of their work with technology. The results show that non-linear routes are associated with a greater mobilisation of students' knowledge on SLE concepts and with their development of modelling competencies. The results also highlight the need to improve the students' competency of validating results, an important step that they did not take, and suggest the need to make technology relevant to the students' work on modelling tasks.
- Sinking diatom assemblages as a key driver for deep carbon and silicon export in the Scotia Sea (Southern Ocean)Publication . Zúñiga, D.; Sanchez-Vidal, A.; Flexas, M. M.; Carroll, D.; Rufino, M. M.; Spreen, G.; Calafat, A.; Abrantes, F.Physical and biogeochemical processes in the Southern Ocean are fundamental for modulating global climate. In this context, a process-based understanding of how Antarctic diatoms control primary production and carbon export, and hence global ocean carbon sequestration, has been identified as a scientific priority. Here we use novel sediment trap observations in combination with a data-assimilative ocean biogeochemistry model (ECCO-Darwin) to understand how environmental conditions trigger diatom ecology in the iron-fertilized southern Scotia Sea. We unravel the role of diatoms assemblage in controlling the biogeochemistry of sinking material escaping from the euphotic zone, and discuss the link between changes in upper-ocean environmental conditions and the composition of settling material exported from the surface to 1,000 m depth from March 2012 to January 2013. The combined analysis of in situ observations and model simulation suggests that an anomalous sea-ice episode in early summer 2012–2013 favored (via restratification due to sea-ice melt) an early massive bloom of Corethron pennatum that rapidly sank to depth. This event drove high biogenic silicon to organic carbon export ratios, while modulating the carbon and nitrogen isotopic signals of sinking organic matter reaching the deep ocean. Our findings highlight the role of diatom ecology in modulating silicon vs. carbon sequestration efficiency, a critical factor for determining the stoichiometric relationship of limiting nutrients in the Southern Ocean.
- Impact of exogenous application of salicylic acid on growth, water status and antioxidant enzyme activity of strawberry plants (Fragaria vesca L.) under salt stress conditionsPublication . Lamnai, Kamal; Anaya, Fatima; Fghire, Rachid; Zine, Hamza; Wahbi, Said; Loutfi, KenzaIrrigation with saline water can act as an alternate water resource and thus plays an important role in saving freshwater resources as well as promoting agriculture. Furthermore, salinity stress is considered one of the major abiotic stress factors, which strongly reduces crop productivity. In this context, the present work was conducted to examine the effect of exogenous salicylic acid (SA) application on salt stress tolerance of strawberry plants. For this purpose, strawberry plants (Fragaria vesca L.), three months old, were treated with three SA concentrations (0mM, 0.25mM and 0.5mM), then subjected to 80mM NaCl or not. After five weeks of treatment, growth responses, water status, photochemical efficiency and oxidative stress indicators were measured. The obtained results showed that irrigation with saline water negatively affected the growth parameters, the leaf water potential (LWP), the relative water content (RWC), the stomatal conductance (gs) and photochemical efficiency (Fv/Fm). While, the total protein content, the electrolyte leakage (EL), the malondialdehyde (MDA) and the hydrogen peroxide (H2O2) contents were increased in stressed plants compared to unstressed ones. Salt stress also leads to the activation of the antioxidant enzymes. However, the exogenous application of SA under salt stress conditions reduced the H2O2 accumulation, the electrolyte leakage and the MDA content. It has also improved the growth parameters, the LWP, the RWC, the gs, the Fv/Fm, the protein content and the antioxidant enzyme activities (POD, CAT and SOD) in the treated plants compared to those without SA application. Therefore, the beneficial effect of 0.25mM SA on Fragaria vesca L. salinity tolerance may provide some practical basis for strawberry cultivation under saline conditions.
- Sharing is entertaining: the impact of consumer values on video sharing and brand equityPublication . Souki, Gustavo; Chinelato, Flavia Braga; Gonçalves Filho, CidPurpose The study aims to ascertain the impacts of entertainment, social and functional values on the likelihood of sharing commercial videos online and verify whether consumers' likelihood to share videos impacts brand attachment and brand equity. Design/methodology/approach A survey was conducted with 368 university students who watched videos of five companies on YouTube Brazil. The electronic form had 24 questions covering the constructs entertainment value, social value, functional value, likelihood to share, brand attachment and brand equity. The structural equation modeling (SEM) tested the survey ' s hypothetical model. Findings The entertainment value and the social value had positive impacts on the likelihood to share commercial videos online. Moreover, the likelihood to share videos positively impacted brand attachment and brand equity. Finally, brand attachment had a positive effect on brand equity. Practical implications Entertainment and social values affect the likelihood to share commercial videos, stimulating consumer engagement with brands through interactive marketing on SNSs. Therefore, companies should produce fun videos that add social value to consumers to go viral, positively influencing brands. Finally, another contribution is the impact of video sharing on brand attachment. Previous studies have contemplated only the opposite relationship between these constructs. Originality/value This research adds value to interactive marketing by investigating consumers' behaviors, their interactivity in social networking sites (SNSs) and the impacts on brands. It is the only study that simultaneously contemplates the effects of entertainment, social and functional values on the likelihood to share commercial videos online and demonstrates its impact on brand attachment and brand equity.
- The therapeutic potential of wogonin observed in preclinical studiesPublication . Sharifi-Rad, Javad; Herrera-Bravo, Jesús; Salazar, Luis A.; Shaheen, Shabnum; Abdulmajid Ayatollahi, Seyed; Kobarfard, Farzad; Imran, Muhammad; Imran, Ali; Custódio, Luísa; Dolores López, María; Schoebitz, Mauricio; Martorell, Miquel; Kumar, Manoj; Ansar Rasul Suleria, Hafiz; Cho, William C.Wogonin is a flavonoid found in different plants such as roots of Scutellaria baicalensis Georgi distributed mainly in Asia and Europe. Dried root extracts of S. baicalensis with high content of wogonin, popularly known as "Huang-Qin" or Chinese or baical skullcap, have been used for long time in traditional Chinese medicine. Several health benefits are attributed to wogonin and derivatives showing anti-inflammatory, antiviral, anticancer, and antioxidant effects and more recently antineurodegenerative properties. Preclinical pharmacological activities of wogonin against diverse types of cancer such as breast, colorectal, and human gastric cancer will be presented in this review. In addition, studies on oxidative stress and bioavailability of wogonin will be discussed together with antineurodegenerative potential with special focus on Alzheimer's disease. Outcomes extracted from the last preclinical studies related to therapeutic applications of wogonin will be commented and updated in this review. The scientific evidence collected in this review aims to encourage transfer of the preclinical evidence of wogonin to new clinical studies.
- Twisted rational r-matrices and algebraic Bethe ansatz: Application to generalized Gaudin and Richardson modelsPublication . Skrypnyk, T.; Manojlović, NenadIn the present paper we develop the algebraic Bethe ansatz approach to the case of non-skew-symmetric gl(2) circle times gl(2)-valued Cartan-non-invariant classical r-matrices with spectral parameters. We consider the two families of these r-matrices, namely, the two non-standard rational r-matrices twisted with the help of second order automorphisms and realize the algebraic Bethe ansatz method for them. We study physically important examples of the Gaudin-type and BCS-type systems associated with these r-matrices and obtain explicitly the Bethe vectors and the spectrum for the corresponding quantum hamiltonians in terms of solutions of Bethe equations. (C) 2021 The Author(s). Published by Elsevier B.V.
- Unsupervised learning of satellite images enhances discovery of late Miocene fossil sites in the Urema Rift, Gorongosa, MozambiquePublication . d’Oliveira Coelho, João; Anemone, Robert L.; Carvalho, SusanaPaleoanthropological research focus still devotes most resources to areas generally known to be fossil rich instead of a strategy that first maps and identifies possible fossil sites in a given region. This leads to the paradoxical task of planning paleontological campaigns without knowing the true extent and likely potential of each fossil site and, hence, how to optimize the investment of time and resources. Yet to answer key questions in hominin evolution, paleoanthropologists must engage in fieldwork that targets substantial temporal and geographical gaps in the fossil record. How can the risk of potentially unsuccessful surveys be minimized, while maximizing the potential for successful surveys?
- Fucoxanthin production from Tisochrysis lutea and Phaeodactylum tricornutum at industrial scalePublication . Pereira, Hugo; Sá, Marta; Maia, Inês Beatriz; Rodrigues, Alexandre; Teles, Iago; Wijffels, Rene H.; Navalho, João; Barbosa, MariaFucoxanthin is a xanthophyll carotenoid with high market value. Currently, seaweeds are the primary source for fucoxanthin industrial production. However, marine microalgae reach 5 to 10 times higher concentrations (2.24 to 26.6 mg g-1 DW) and are considered a promising feedstock. In this work, two marine microalgae were produced at industrial scale to evaluate biomass and fucoxanthin production: Phaeodactylum tricornutum for autumn/winter and Tisochrysis lutea for spring/summer. Both strains were grown in 15 m3 tubular flow-through photobioreactors; for 170 consecutive days of semi-continuous cultivation regime. The average volumetric biomass productivities of P. tricornutum and T. lutea were 0.11 and 0.09 g DW L-1 day-1. P. tricornutum reached higher maximum biomass concentration (2.87 g DW L-1) than T. lutea (1.47 g DW L-1). P. tricornutum fucoxanthin content ranged between 0.2 and 0.7% DW, while T. lutea between 0.2 and 0.6% DW. The fucoxanthin content was correlated with the irradiation (MJ m-2) and biomass concentration in the photobioreactor (g L-1). This is the first work in literature reporting a long-term industrial production of T. lutea. Overall, we showed possible scenarios for fucoxanthin production from microalgae, increasing the window to supply the industry with steady production throughout the year.
- A circular approach for landfill leachate treatment: Chemical precipitation with biomass ash followed by bioremediation through microalgaePublication . Viegas, Catarina; Nobre, Catarina; Mota, Andre; Vilarinho, Candida; Gouveia, Luisa; Goncalves, MargaridaThe aim of this work was to study an integrated approach for landfill leachate remediation comprising chemical precipitation with biomass bottom ash as a pre-treatment to reduce color and turbidity followed by bioremediation through microalgae treatment for effluent disposal. Optimal pre-treatment conditions were determined through batch experiments and were found to be 160 g L-1 ash dose, 96 h of contact time, overhead agitation at 15 rpm and ash particle size below 500 mu m. These conditions led to removal efficiencies of 74.3% for chemical oxygen demand and 98.5% for color. Large quantities of sludge containing excess biomass ash and precipitated compounds were formed during the pre-treatment. To minimize solid disposal, this sludge was tested as a raw material for cementitious and aggregate substitute in mortar formulations. Following the pre-treatment, the leachate was inoculated with six different microalgae species to evaluate their ability to grow in such a recalcitrant effluent and remediate it. After a period of 27 days biomass concentration from 0.4 to 1.2 g L-1 were achieved for the tested microalgae. Removal efficiencies were in the range of 18-62% for COD, 63-71% for N, and 15-100% for P. At the end of the treatment, algal biomass was characterized regarding protein, lipid, fatty acids, carbohydrate, and ash contents. This approach allows a low-cost remediation of these recalcitrant effluents when compared with the present options that include inverse osmosis, and the valorization of ash-rich precipitates and microalgae biomass improves the sustainability of the overall process.
- Weak biodiversity connectivity in the European network of no-take marine protected areasPublication . Assis, J.; Fragkopoulou, Eliza; Serrão, Ester A.; e Costa, Horta; Gandra, Miguel; Abecasis, DavidThe need for international cooperation in marine resource management and conservation has been reflected in the increasing number of agreements aiming for effective and well-connected networks of Marine Protected Areas (MPAs). However, the extent to which individual MPAs are connected remains mostly unknown. Here, we use a biophysical model tuned with empirical data on species dispersal ecology to predict connectivity of a vast spectrum of biodiversity in the European network of marine reserves (i.e., no-take MPAs). Our results highlight the correlation between empirical propagule duration data and connectivity potential and show weak network connectivity and strong isolation for major ecological groups, resulting from the lack of direct connectivity corridors between reserves over vast regions. The particularly high isolation predicted for ecosystemstructuring species (e.g., corals, sponges, macroalgae and seagrass) might potentially undermine biodiversity conservation efforts if local retention is insufficient and unmanaged populations are at risk. Isolation might also be problematic for populations' persistence in the light of climate change and expected species range shifts. Our findings provide novel insights for management directives, highlighting the location of regions requiring additional marine reserves to function as stepping-stone connectivity corridors. (C) 2021 Elsevier B.V. All rights reserved.