As abordagens da bitcoin e blockchain em artigos acadêmicos / The bitcoin and blockchain approaches in scholarly articles

O presente artigo estabelece uma metodologia de consulta na plataforma de divulgação científica, SciELO sobre bitcoin e blockchain. O objetivo do trabalho é analisar a moeda virtual e a tecnologia blockchain. Foram encontrados quatro artigos na plataforma, o que favorecerá a análise de todos os trabalhos encontrados. Os objetivos dessa verificação são, no primeiro momento, verificar quais abordagens as ferramentas recebem em textos acadêmicos; e, em segundo, situar as ferramentas nas abordagens acadêmicas aqui no Brasil. Esses dois objetivos servirão para analisar de que maneira as ferramentas têm sido avaliadas pela comunidade acadêmico-cientifica e, assim, discutir possíveis justificativas para tais abordagen

Biosorption of Neodymium (Nd) from Aqueous Solutions Using Spirulina platensis sp. Strains

Rare earth elements such as neodymium (Nd) are important elements used mainly in developing new technologies. Although they are found in low concentrations in nature, they can be obtained by extracting solid samples such as phosphogypsum. Among the techniques, adsorption has been used successfully with several adsorbent materials. In this work, two strains of Spirulina platensis (LEB-18 and LEB-52) were employed as biosorbents for efficiently removing the Nd element from the aqueous media. Biosorption tests were carried out in a batch system, and the results of the biosorption kinetics showed that for both materials, the biosorption of Nd was better described by the Avrami model. Moreover, it could be considered that 80 min would be necessary to attain the equilibrium of Nd(III) using both biosorbents. The result of the biosorption isotherms showed that for both strains, the best-fitted model was the Liu model, having a maximum biosorption capacity of 72.5 mg g(-1) for LEB-18 and 48.2 mg g(-1) for LEB-52 at a temperature of 298 K. Thermodynamics of adsorption showed that for both LEB-18 and LEB-52 the process was favorable ( increment G degrees < 0) and exothermic ( increment H degrees -23.2 for LEB-18 and increment H degrees -19.9 for LEB-52). Finally, both strains were suitable to uptake Nd, and the better result of LEB-18 could be attributed to the high amount of P and S groups in this biomass. Based on the results, a mechanism of electrostatic attraction of Nd3+ and phosphate and sulfate groups of both strains of Spirulina platensis was proposed

Composite carbon materials from winery composted waste for the treatment of effluents contaminated with ketoprofen and 2-nitrophenol

The present work consisted of preparing and characterizing composite carbon materials (WRCC) from raw winery residues (WR) activated with zinc chloride to produce a carbon adsorbent. The WRCC was used for the adsorption of emerging contaminants in aqueous media. The WRCC presented a morphology with favorable characteristics for the adsorption process, giving an abundant porous structure with pores of different sizes. The results show the WRCC’s effectiveness, presenting surface area values (227 m2 g−1) and total pore volume (0.175 cm3 g−1). The general order kinetic model predicted the experimental curves sufficiently. The Sips model better described the two adsorbates' equilibrium data, with maximum adsorption capacities of 376.0 and 119.6 mg g−1 for 2-nitrophenol and ketoprofen, respectively. The WRCC carbon material was also highly efficient, with maximum removal of 81.4% and 94% in 1000 mg L−1 of the compounds 2-nitrophenol and ketoprofen. Finally, the prepared material has essential characteristics that make it an efficient adsorbent in treating effluents with emerging contaminants

Análisis y modelo hidráulico (2D) de flujos hiperconcentrados en piedemonde occidental de la Sierra de Ambato, Catamarca, Argentina

Los flujos de sedimentos hiperconcentrados se pueden clasificar eninundaciones de barro, flujos de barro y flujo de escombros. Estos flujos se diferencian por la reología de la mezcla agua-sedimento. En los flujos de barro los esfuerzos que domina el fenómeno son el límite elástico y el esfuerzo viscoso. Un modelo reológico cuadrático permite simular adecuadamente condiciones de flujos que van desde aguas claras hasta flujos hiperconcentrados de sedimentos. En este trabajo se analiza un evento hidrológico severo con flujo de barro ocurrido recientemente en Siján, Catamarca, Argentina aplicando el modelo de simulación (FLO-2D) de diferencias finitas

Regeneração de espécies lenhosas sob a influência do bambu Actinocladum verticillatum (Nees) McClure ex Soderstr. (Poaceae) em cerradão e cerrado típico na transição Cerrado-Amazônia

In this study, we analyzed and compared the floristic composition, species richness and diversity, and structure of the natural regeneration of two phytophysiognomies (savanna forest and typical cerrado) under the effect of natural clumps of the bamboo Actinocladum verticillatum (Nees) McClure ex Soderstr. at the Bacaba City Park, Nova Xavantina municipality (Mato Grosso state, Brazil). In each phytophysiognomy, we established 15 contiguous plots in a bamboo-free control site (NB) and 15 in a site densely occupied by bamboos (WB). The natural regeneration and the woody vegetation (WV, diameter ≥ 3 cm at 30 cm above ground) were sampled in plots of 1 x 1 m, 2 x 2 m, 5 x 5 m (natural regeneration) and 10 x 10 m (WV). In the natural regeneration, we found 55 species in the savanna forest (NB = 49, WB = 34) and 76 in the typical cerrado (NB = 68, WB = 51). Overall, the NB sites from both phytophysiognomies had the highest values of species diversity, evenness and abundance of individuals, which indicates a possible interference of the clumps with the structure of the natural regeneration. The occurrence of Brosimum gaudichaudii Trécul and Myrcia splendens (Sw.) DC at most stages of regeneration highlights their potential for the recovery of lands occupied by these clumps.No presente estudo foram analisadas e comparadas a composição florística, riqueza, diversidade de espécies e a estrutura da regeneração natural em duas fitofisionomias (cerradão e cerrado típico) sob o efeito de adensamentos naturais do bambu Actinocladum verticillatum (Nees) McClure ex Soderstr. no Parque Municipal do Bacaba, Nova Xavantina-MT. Em cada fitofisionomia foram alocadas 15 parcelas contíguas em um sítio controle, com ausência completa de bambu (SB) e 15 em um sítio com bambu (CB). A regeneração natural e a vegetação lenhosa (VL, ≥ 3 cm de diâmetro a 30 cm do solo) das duas fitofisionomias foram amostradas em parcelas de 1 x 1 m, 2 x 2 m, 5 x 5 m (regeneração natural) e 10 x 10 m (VL). Foram encontradas, na regeneração natural, 55 espécies no cerradão (SB = 49 e CB = 34) e 76 no cerrado típico (SB = 68 e CB = 51). De forma geral, os sítios SB nas duas fitofisionomias detiveram os maiores valores de diversidade de espécies, equabilidade e abundância de indivíduos, o que indica possível interferência dos adensamentos na estrutura da regeneração natural. A ocorrência de Brosimum gaudichaudii Trécul e Myrcia splendens (Sw.) DC. na maioria dos estádios da regeneração, reforça o potencial dessas espécies na recuperação de áreas ocupadas por estes adensamentos.

Catalytic cracking of n-alkane naphtha: The impact of olefin addition and active sites differentiation

An extended dual kinetic model allows to fit the n-heptane cracking results working in a wide range of reaction conditions. The duality of the model is provided by the contribution of monomolecular and bimolecular cracking mechanisms. It takes into account the role played by the olefins formed on the global cracking or added within the feed. Furthermore by means of this model and the kinetic parameters obtained when cracking n-heptane on ZSM-5, it has been observed that, while some characterization techniques show a homogeneous zeolite surface from the point of view of the active sites, rigorous kinetic experiments point to the possibility that the reactant sees a heterogeneous surface with, at least, two groups of cracking active sites. Those differentiated active sites give different cracking rates and different activation energies for the process and, in the case of ZSM-5, could be assimilated to sites pointing to the 10R channels and sites pointing into the crossing of the 10R channels, mainly due to differences in kid site location and confinement effects. (C) 2015 Elsevier Inc. All rights reserved.Financial support by the Ministerio de Economia y Competitividad of Spain (MINECO) [Programa Estatal (Project MAT2012-31657) and Programa Consolider-Ingenio 2010 (Project MULTICAT)] is gratefully acknowledged.Corma Canós, A.; Mengual Cuquerella, J.; Miguel Dolz, PJ. (2015). Catalytic cracking of n-alkane naphtha: The impact of olefin addition and active sites differentiation. Journal of Catalysis. 330:520-532. https://doi.org/10.1016/j.jcat.2015.04.020S52053233

Modeling biomass and nutrients in a eucalyptus stand in the cerrado

The prediction of biological processes, which involve growth and plant development, is possible via the adjustment of mathematical models. In forest areas, these models assist in management practices, silviculture, harvesting, and soil fertility. Diameter, basal area, and height are predictors of volume and biomass estimates in forest stands. This study utilized different non-linear models for estimating biomass and nutrient values in the aerial biomass and roots of an unmanaged eucalypt stand in Cerrado dystrophic soil. It was hypothesized that the models would estimate the nutrients of the aboveground biomass and roots after meeting the selection and validation criteria. By statistical analysis of the parameters and subsequent validation, the Schumacher–Hall model was presented to be the best fit for biomass and nutrients. This result confirmed the ability of different variables, including diameter, basal area, and height, to be predicted. Estimating the nutrient values in the aboveground biomass and roots allowed a better understanding of the quality of the vegetal residues that remained in the soil. For dystrophic soils, which occur in the Cerrado, these estimates become even more relevant

Tree diversity and above-ground biomass in the South America Cerrado biome and their conservation implications

Less than half of the original two million square kilometers of the Cerrado vegetation remains standing, and there are still many uncertainties as to how to conserve and prioritize remaining areas effectively. A key limitation is the continuing lack of geographically-extensive evaluation of ecosystem-level properties across the biome. Here we sought to address this gap by comparing the woody vegetation of the typical cerrado of the Cerrado–Amazonia Transition with that of the core area of the Cerrado in terms of both tree diversity and vegetation biomass. We used 21 one-hectare plots in the transition and 18 in the core to compare key structural parameters (tree height, basal area, and above-ground biomass), and diversity metrics between the regions. We also evaluated the effects of temperature and precipitation on biomass, as well as explored the species diversity versus biomass relationship. We found, for the first time, both that the typical cerrado at the transition holds substantially more biomass than at the core, and that higher temperature and greater precipitation can explain this difference. By contrast, plot-level alpha diversity was almost identical in the two regions. Finally, contrary to some theoretical expectations, we found no positive relationship between species diversity and biomass for the Cerrado woody vegetation. This has implications for the development of effective conservation measures, given that areas with high biomass and importance for the compensation of greenhouse gas emissions are often not those with the greatest diversity