Influence of Activation Parameters on the Mechanical and Microstructure Properties of an Alkali-Activated BOF Steel Slag

ABSTRACT: Steel slag (SS) is a secondary material from steelmaking production with little commercial value. Its volumetric expansion and low reactivity limit the use of SS in Portland cement (PC)- based materials. This study investigated the potential use of basic oxygen furnace (BOF) slag as a single precursor in alkali-activated matrices (AAMs). Six AAM pastes were assessed by changing the silica modulus (0.75, 1.50 and 2.22) and the sodium concentration (4% or 6% Na2O?wt. SS). The early hydration was assessed using isothermal calorimetry (IC), followed by the assessment of the mechanical performance (compressive strength), apparent porosity, and structure and microstructure characterization (X-ray diffraction, thermogravimetric analysis and scanning electron microscopy). The results indicated that although the BOF slag may be considered a low-reactivity material, the alkaline environment effectively dissolved important crystalline phases to produce hydrates (reaction products). An optimized combination of activator sources was achieved with 4% Na2O and a silica modulus of 1.50?2.22, with a compressive strength up to 20 MPa, a significant amount of reaction products (C-S-H/C-A-S-H gels), and low initial and cumulative heat release. Those properties will help to promote SS recycling use in future engineering projects that do not require high-strength materials.This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES)—finance code 001, grant PPM-00709-18 (FAPEMIG) and grant 316882/2021-6 (CNPq

Silica Fume as Precursor in the Development of Sustainable and High-Performance MK-Based Alkali-Activated Materials Reinforced With Short PVA Fibers

Alkali-activated materials (AAM) are currently the subject of increasing interest and research, mainly due to the possibility of reducing the carbon dioxide (CO2) emissions in their production when compared to Portland cement (PC) and still achieve superior performance in many aspects when compared to traditional PC-based products. However, the use of sodium silicate (SS) as an alkaline activator in AAM is controversial when the aim is to reduce the environmental impact, as the production of the first also releases significant amount of CO2 per ton of activator produced. Therefore, a demand has emerged for alternative silica-rich materials that could effectively reduce the demand for SS without compromising the mechanical behavior of the matrices and consequently the performance of fiber reinforced AAM. This paper investigates the gradual replacement (0–18% wt.) of metakaolin (MK) with silica fume (SF) in PVA-reinforced AAM, allowing the reduction of SS in the activator, also containing NaOH. Matrices with different composition were studied, i.e., with [SiO2]/[Al2O3] molar ratios of 3.0 and 3.8. All formulations were reinforced with 2% vol. of PVA fibers. The mechanical properties investigated were compressive strength, modulus of elasticity, flexural strength, and toughness. Apparent dry density, water absorption, and porosity of the composites were also assessed to give an indication of their durability. Single fiber pullout, fracture toughness, and direct tensile tests were also carried out in order to understand the deformation capability of the composites. Results indicated that the employment of SF may effectively reduce the demand for SS in the alkaline activators, in order to produce alkali-activated composites with lower environmental impact (reduced CO2 emissions). Adjustments in the formulations may improve toughness in flexion in 170% with 30 wt.% reduction of SS in the activator, as well as improvements in deformation capability in tension. The development of strain-hardening MK-based AAM, however, has some challenging aspects that are also discussed

Relação entre o número de espécies e o número de táxones de alto nível para a fauna de artrópodes dos Açores

Nesta contribuição pretendemos avaliar a aplicação dos modelos RESTAN, "Relação entre o número de Espécies e o número de Táxones de Alto Nível", à fauna de artrópodes de vários habitats das ilhas dos Açores. Utilizámos várias bases de dados recentemente obtidas baseadas em amostragens estandardizadas de artrópodes epígeos do solo em florestas de áreas protegidas, artrópodes fitófagos e predadores de pastagens semeadas e semi-naturais e artrópodes da copa da árvore endémica Juniperus brevifolia. Os modelos RESTAN são aplicados não só usando dados puramente taxonómicos, mas igualmente agrupando os taxa em termos de estratégias ecológicas (e.g. herbívoros, predadores) e de colonização das ilhas (e.g. endémicos). Deste modo pensamos poder avaliar a aplicabilidade destes modelos em estudos de estrutura de comunidades e de conservação. Para os Açores, a aplicação dos modelos RESTAN constitui uma forma muito prática e eficaz de obter estimativas de diversidade. De facto, em todas as matrizes de dados analisadas a riqueza de espécies pode ser estimada eficazmente usando apenas a riqueza em géneros, sendo a relação linear. Ao nível da família, os modelos estimadores possuem um menor poder explicativo e são melhor explicados por uma função exponencial. O escalonamento de Reservas Florestais Naturais dos Açores em termos de biodiversidade de artrópodes endémicos pode ser efectuado usando informação taxonómica ao nível do género. A aplicação de métodos de estimativa rápida de biodiversidade fica assim facilitada, podendo usar-se parataxonomistas bem treinados para o processo de triagem do grande número de amostras geralmente necessárias em estudos ecológicos. Discute-se igualmente a aplicabilidade dos modelos RESTAN a dados de diversidade alfa, beta e gama.ABSTRACT: In this contribution we examine the predictive power of numbers of higher taxa (orders, families and genera) as surrogates of species richness ("RESTAN" models – models based on linear relationship between species and higher taxa numbers) for the Azorean arthropod fauna. Recently, two large entomological and ecological studies were performed in the Azores, using standardized sampling protocols to estimate the diversity of arthropods in grassland and native forests. We use datasets available from those studies to address a few technical questions: A. what is the impact of using several measures of diversity (alpha, gamma and beta species diversity; Shannon-Wiener index of diversity; Evenness) based on numbers of families and genera for canopy arthropods? For instance, could be predicted that values of beta-diversity decrease with the use of higher-taxa estimates. All the measures of diversity could be used, being the genera the best predictor; B. how well behave the RESTAN models for functional groups of species like grass-feeding and web-building spiders in grasslands? The predictive power of higher-taxa is low using web-building spiders, due to few families being envolved and some genera having many species locally represented; C. assuming at least one sample with no species then there will be also no highertaxa in that sample. Consequently, the curve of the relationship between highertaxa richness and species richness should be anchored to the origin (y= bx). What is the predictive value of this model in comparison with the linear (y =a + bx), log-log (log y = a + b log x) and exponential (y = A • e b x) models? The best fit was obtained with the linear model for the genus-species relationship, but the variables are not normally distributed and the log-log model should be preferable. For the family-species relationship the exponential model is the best. The linear model anchored to the origin (y =bx) has some statistical pitfalls and was of less predictive value; D. in conservation studies what is the predictive value of higher-taxa in ranking protected areas? We found that the numbers of arthropod genera could successfully rank the Natural Forest Reserves as well as numbers of species (using endemic species dataset). We found that in the Azores the predictions of species richness using higher-taxa are quite reasonable, mainly because of low levels of diversity. Therefore, costeffective studies could use only genera, since the species richness of arthropods could be predicted reasonably closely from their genus-level richness. Family and order-level data were less informative for all datasets. We suggest that in the Azores as a consequence of the low levels of species diversification with a great proportion of monospecific genera, the use of parataxonomists trained in genus-level identification could be appropriate for sorting large numbers of ecological samples

Consumer evaluation of a hydro-conservation model and its efficiency on improving the collard greens cv. manteiga shelf life (Brassica oleracea, cv. acephala)

[PORT] Neste estudo avaliou-se a aceitação, pelo consumidor, de um equipamento com temperaturas hidrocontroladas e sua eficiência no aumento do tempo de prateleria de couve manteiga (Brassica oleracea, v. acephala). O método de hidroconservação consiste em utilizar uma solução aquosa como meio trocador de calor entre o evaporador e o produto armazenado. O equipamento analisado foi um modelo híbrido onde as câmaras de armazenamento foram parcialmente submersas na solução aquosa. Foram usadas oito câmaras de 7371 cm3 . A aceitação do equipamento foi avaliada através de questionário apresentado próximo do equipamento em um ponto de venda da região central da cidade de São Carlos- SP-BR. A couve manteiga foi escolhida por ser amplamente comercializada no Brasil e apresentar um curto tempo de prateleira. Após higienização e segmentação as amostras foram lacradas em sacos de polietileno de baixa densidade (PEBD) instalados nas câmaras de armazenamento. O tempo de prateleira foi estimado através de teste sensorial e do teor de água das folhas. A análise dos questionários indicou alto índice de aprovação do equipamento (acima de 90%) e índice de rejeição nulo. O teste sensorial mostrou que o consumidor julgou o produto adequado ao consumo por um período de armazenamento superior a 20 dias, três vezes mais que o tempo de prateleira da couve armazenada em geladeira. Neste período a perda de massa foi de 5,8%. Conclui-se que o modelo industrial avaliado mostrou-se viável, tanto do ponto de vista da aprovação pelo público consumidor como pela capacidade de conservação de couve manteiga processada, capacidade esta que pode ser estendida para outros produtos olerícolas. [ENG] This study evaluated the acceptability of an equipment that uses hydrocontroled temperature system, and its efficiency on increasing the shelf life time of collard greens (Brassica oleracea cv. acephala). The hydroconservation method uses a water solution to exchange heat between the evaporator and the stored product. On this paper, however, an hybrid model was evaluated where small storage chambers were parcialy submerged in the solution. There were used eight chambers with 7371 cm3. The acceptability of the equipment was evaluated based on a form fullfiled by the consumers close to the equipment, in a small market at São Carlos-SP-BR. The collard greens was choosen because of its big market in Brazil and its short shelf life time. After satinization and segmentation the samples were inserted in polietilene of low density (PEBD) bags with lock, installed in the storage chambers. The shelf life time was estimated from organoleptic tests and the water content of the leaves. The analysis of the forms showed the high aceptance index (above 90%) of the equipment, and no rejection. The organoleptic tests indicated that the costumer evaluated the equipment positively on storing the collad greens for more than 20 days, three times more than the shelf life when stored in a refrigerator. Along the experiment the mass loss was 5,8%. The conclusions list includes the positive evaluation of the industrial model and its efficency on improving the shelf life time, what can be extended to other vegetables

Bistable firing pattern in a neural network model

Excessively high, neural synchronization has been associated with epileptic seizures, one of the most common brain diseases worldwide. A better understanding of neural synchronization mechanisms can thus help control or even treat epilepsy. In this paper, we study neural synchronization in a random network where nodes are neurons with excitatory and inhibitory synapses, and neural activity for each node is provided by the adaptive exponential integrate-and-fire model. In this framework, we verify that the decrease in the influence of inhibition can generate synchronization originating from a pattern of desynchronized spikes. The transition from desynchronous spikes to synchronous bursts of activity, induced by varying the synaptic coupling, emerges in a hysteresis loop due to bistability where abnormal (excessively high synchronous) regimes exist. We verify that, for parameters in the bistability regime, a square current pulse can trigger excessively high (abnormal) synchronization, a process that can reproduce features of epileptic seizures. Then, we show that it is possible to suppress such abnormal synchronization by applying a small-amplitude external current on > 10% of the neurons in the network. Our results demonstrate that external electrical stimulation not only can trigger synchronous behavior, but more importantly, it can be used as a means to reduce abnormal synchronization and thus, control or treat effectively epileptic seizures. © 2019 Protachevicz, Borges, Lameu, Ji, Iarosz, Kihara, Caldas, Szezech, Baptista, Macau, Antonopoulos, Batista and Kurths

Ranking protected areas in the Azores using standardised sampling of soil epigean arthropods

Copyright © Springer 2005.Nineteen areas in seven of the nine Azorean islands were evaluated for species diversity and rarity based on soil epigean arthropods. Fifteen out of the 19 study areas are managed as Natural Forest Reserves and the remaining four were included due to their importance as indigenous forest cover. Four of the 19 areas are not included in the European Conservation network, NATURA 2000. Two sampling replicates were run per study area, and a total of 191 species were collected; 43 of those species (23%) are endemic to the archipelago and 12 have yet to be described. To produce an unbiased multiple-criteria index (importance value for conservation, IV-C) incorporating diversity and rarity based indices, an iterative partial multiple regression analysis was performed. In addition, an irreplaceability index and the complementarity method (using both optimisation and heuristic methods) were used for priority-reserves analyses. It was concluded that at least one well-managed reserve per island is absolutely necessary to have a good fraction of the endemic arthropods preserved. We found that for presence/absence data the suboptimal complementarity algorithm provides solutions as good as the optimal algorithm. For abundance data, optimal solutions indicate that most reserves are needed if we want that at least 50% of endemic arthropod populations are represented in a minimum set of reserves. Consistently, two of the four areas not included in the NATURA 2000 framework were considered of high priority, indicating that vascular plants and bird species used to determine NATURA 2000 sites are not good surrogates of arthropod diversity in the Azores. The most irreplaceable reserves are those located in older islands, which indicates that geological history plays an important role in explaining faunal diversity of arthropods in the Azores. Based both on the uniqueness of species composition and high species richness, conservation efforts should be focused on the unmanaged Pico Alto region in the archipelago’s oldest island, Santa Maria