1,720,983 research outputs found
Integrated microalgae biomass production and olive mill wastewater biodegradation: optimization of the wastewater supply strategy
No full textOlive mill wastewater (OMW) was supplied to Scenedesmus sp. cultures to simultaneously achieve biomass production and wastewater biodegradation. Two OMW supply strategies were implemented to prevent the reduced growth performances that are attained, compared to photoautotrophic cultivation, when OMW is supplied at the beginning of cultivation (batch strategy). A fed-batch strategy including the gradual OMW supply yielded a biomass production equal to 0.86 g/L, while 1.4 g/L was attained by a two-stage strategy including OMW addition during nitrogen-starvation. OMW enhanced the carbohydrate accumulation (up to 44%) through the removal of OMW sugars (60–70%). About 55% OMW phenol removal was achieved by the fed-batch strategy when the phenol concentration was lower than 100 mg/L, and by the two-stage strategy when the heterotrophic stage lasted longer than 8–10 days. The illustrated results indicate that the OMW supply strategy can be purposefully tailored to regulate biomass production and OMW biodegradation
Ultrasound-assisted extraction of carbohydrates from microalgae
Full text linkMicroalgae are a promising new source of carbohydrates usable for several industrial applications in the food and biomaterial sector. Previous works on carbohydrate extraction from microalgae were mainly carried out by using destructive chemical hydrolysis, aiming at the extraction of simple sugars. Here in this work, a physical ultrasonication method was investigated to develop a process to extract microalgal carbohydrates in their polysaccharide form, as starch. To this end, different operative parameters were investigated: biomass concentration (3-6 g L-1), microalgae strain (Tetradesmus obliquus and Chlorella sp.), extraction time, amplitude (21-90 μm) and the configuration of the ultrasonication system (cyclic treatment, pulsed and continuous). The highest extractions were attained with higher amplitude (90 μm). The pulsed ultrasonication (ton/toff = 0.2) worked remarkably better than the continuous one, allowing to attain about 3 folds more carbohydrate extraction yield and consuming 6 folds less kWh per kg of extracted carbohydrates. The higher yield achieved with pulsed ultrasonication was related with a lower drop in the applied power during the ultrasonication treatment, which was -65 % with the continuous system and only -31 % with the pulsed one. The ultrasonication treatment induced a temperature increase up to 70 °C, that caused starch gelatinization and its solubilization in the recovered aqueous solution. Future studies should investigate better the effect of the ton/toff ratio, to limit the dead times (toff) of the process. The specific energy consumption was still too high for many practical applications; however, future optimizations on biomass concentration and operative temperature are expected to reduce remarkably the energy demand of the process
Nucleation and growth of metal nanoparticles on a planar electrode: A new model based on iso-nucleation-time classes of particles
Full text linkAn assembly of hemispherical particles continuously nucleating on a planar electrode and growing under mixed kinetic-diffusion control is here considered. A model is derived, from the exact boundary integral formulation of the diffusion equation, to predict the overall current evolution, and the radii distribution of particles nucleating within any prescribed time interval. Iso-nucleation-time classes are introduced in the model, grouping particles (almost) simultaneously nucleating over the underlying substrate. The dynamics of particles belonging to a given iso-nucleation-time class are assumed to be identical. By this approximation, hereby referred to as Averaged Class Approximation (ACA), the computation of the average radius of any iso-nucleation-time class is reduced to the solution of an integro-differential equation, parameterized by the nucleation time. An effective computational method is also presented to solve the model equations, giving predictions that fairly well agree with the results of direct multi-particle numerical simulations
Production of microalgae biomass in a two-stage continuous bioreactor. Control of microalgae-bacteria competition by spatial uncoupling of nitrogen and organic carbon feeding
No full textThe spatial uncoupling of nitrogen and organic carbon is proposed to control the competition between microalgae and bacteria in continuous bioreactors. A series of two continuous stirred bioreactors with recycle is considered where the upstream and the downstream reactor are fed with only the nitrogen and only the organic carbon source, respectively. A Droop-like model and a multiplicative Monod model are used to describe microalgae and bacteria growth kinetics, respectively. The stability regions of steady state solutions corresponding to pure microalgae cultures, pure bacteria cultures, and microalgae-bacteria consortia are identified by bifurcation analysis of the mass balance equations governing reactor dynamics. By capitalizing the competitive advantage of microalgae to uncouple nitrogen and carbon uptake, the proposed configuration allows attaining global stability of the microalgae and the microalgae-bacteria solution. Analytical approximations are derived for stability boundaries of steady states, providing guidelines for the design and control
Electrodeposition of cobalt nanoparticles: an analysis of the mechanisms behind the deviation from three-dimensional diffusion-control
No full textElectrochemical nucleation and growth of cobalt nanoparticles on aluminium was investigated by potentiostatic electrodeposition from cobalt sulphate solutions buffered with boric acid. At sufficiently low overpotential, the experimental current transients could be fairly reproduced by a mathematical model describing nucleation and growth under mixed kinetic-diffusion control, yielding an estimated number of particles per surface area in agreement with the SEM analysis of the deposits. However, the model gave estimates for the charge-transfer kinetic constant several orders of magnitude lower as compared to the Tafel analysis of cobalt electrodeposition on a previously electrodeposited cobalt film. This deviation can be explained by the inhibition of the direct attachment of metal ions, which can be induced by the adsorption of hydrogen onto cobalt particles and/or the formation of stable nanocluster aggregates. The implemented model failed to reproduce the current transients generated at larger overpotential values. A revision of the implemented mathematical model overcoming this limitation is proposed
Multiplicities of temperature wave trains in periodically forced networks of catalytic reactors for reversible exothermic reactions
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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