1,721,165 research outputs found
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
Influence of the ratio of the initial substrate concentration to biomass concentration on the performance of a sequencing batch reactor
No full textBiomass behaviour and COD removal in a benchscale activated sludge reactor have been studied alternating anaerobic and aerobic conditions. Particular attention has been paid to the influence of the ratio of the initial substrate concentration (S-0) to the initial biomass concentration (X(0)) on the reactor performance. Tests at very low ratios (S-0/X(0)<2) demonstrate the existence of a threshold below which the reactor performance is seriously affected (S-0/X(0)=0.5). Under conditions of total suppression of cell duplication, substrate maintenance requirements have also been calculated for the microbial consortium present in the activated sludges. The results obtained show that stressed biomass can survive conditions of substrate lack better than unstressed biomass
Evaluation of kinetic parameters and thermodynamic quantities of starch hydrolysate alcohol fermentation by Saccharomyces cerevisiae
No full textThe kinetic parameters and thermodynamic quantities of corn starch hydrolysate fermentation by Saccharomyces cerevisiae are evaluated following two different approaches and using the experimental data of batch fermentations carried out at different temperatures. The former approach, that is based on the Arrhenius equation, allows for the separate calculations of thermodynamic quantities referred to the transition states of both alcohol fermentation and thermal deactivation. The latter, supposing the existence of an instantaneous equilibrium between active and inactive forms of the biocatalyst, includes all these quantities in the same relationship. The results obtained in this study suggest that the simple activated-complex theory is inadequate to the kinetic and thermodynamic description of a process using microorganisms, while the so-called ''thermodynamic approach'' can represent a promising alternative
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
Study on the thermal decomposition of plastic residues
No full textThe use of plastics in the last decades significantly increased, thus plastic recycling processes are needed. Generally, mixtures of plastic materials are disposed together, hence the recovery of the polymeric material is difficult and expensive. Plastic residues could be valorized by thermal degradation processes aimed at recovering energy and/or valuable compounds for chemical industry. The main technologies used for this purpose are gasification and pyrolysis. The latter is a thermal degradation process that occurs in the absence of oxygen at moderate temperature (300-700°C), that could be used to recover the thermal power of biomasses. The reaction products are bio-oil, biogas and biochar. The aim of this work was to employ pyrolysis to energetically exploit different pure plastic materials, namely polyethylene terephthalate (PET), polyamide (Nylon-6), polyvinyl chloride (PVC) and polyurethane (PU), as well as a complex one such as end of life tyres (ELT). The reaction was performed at 400 °C for 90 min. The pyrolysis system was composed by a tubular quartz reactor heated with a tubular vertical oven. An integrated condenser was used to separate the liquid reaction products, while the incondensable gases were collected in a latex balloon. The reaction products were quantified gravimetrically and, in order to evaluate the functional groups, characterized by FTIR analysis. The reaction gases were also analyzed by GC-MS to determine the composition of this fraction. Results obtained from the different plastics were significantly different in terms of distribution and composition. In particular, PET produced a biogas consisting mainly of acetaldehyde and hydrocarbons, while the liquid fraction was composed of benzoic and terephthalic acids. Nylon-6 degraded producing a large amount of reaction gas (65 g/100g) composed of ammonia and light hydrocarbons, while the reaction liquid was mainly caprolactam. Around 53 g/100g of PVC reaction products were gaseous, mainly hydrochloric acid, followed by toluene and benzene at high concentrations. The degradation of PU produced a reaction gas, mainly composed by formic and acetic aldehydes. ELT pyrolysis was responsible for the production of high amounts of solid residue, while reaction gas and liquid seemed to be mainly constituted by hydrocarbons. In general, the study of pure plastic pyrolysis could help to better understand the thermal decomposition of complex plastic residues such as ELT
Investigation on thermal pyrolysis of microalgae grown in winery wastewater: biofuels and chemicals production
No full textCurrent innovations in microalgae technology include the use of wastewater as a cultivation medium for renewable energy generation and wastewater treatment. In this study, thermal pyrolysis was performed on a co-culture of Chlorella vulgaris and Arthrospira platensis grown in winery wastewater fed continuously into a membrane photobioreactor. The yield and composition of the reaction gases, reaction liquids, and solid residues collected at different reaction times and pyrolysis temperatures were compared with those of the same co-culture grown in its conventional medium. In general, the gaseous fraction resulted rich in combustible compounds. The highest yield in liquid products (55 %) was obtained by thermal pyrolysis of the co-culture grown in winery wastewater at 500 degrees C. Liquid fraction was made up of a mixture of oxygenated and nitrogenated compounds that are suitable as chemical intermediates and can therefore contribute to making the pyrolysis treatment economically feasible. For example, this fraction resulted particularly rich in crotonic acid, useful for the synthesis of copolymers (crotonic acid-vinyl acetate) and probably derived from the thermal cracking of polyhydroxy alkenoate. The results of this study suggest that thermal pyrolysis may be a good strategy to recover the energy potential of microalgae co-cultures used to treat wastewater
Production of carbon-based biofuels by pyrolysis of exhausted Arthrospira platensis biomass after protein or lipid recovery
No full textThermal pyrolysis of Arthrospira platensis biomass was investigated at 450 °C before and after lipid or protein extractions with the aim to valorize the extraction residue. Compositions of biomass before pyrolysis and reaction products were analyzed by FT-IR, GC-MS, TG and SEM analyses. Thermal pyrolysis of biomass without any preliminary treatment led to the production of quite promising reaction products in terms of energetic potential, and the best results were obtained with biomass after protein recovery. In fact, contents of nitrogenous and oxygenated compounds significantly decreased in both liquid and gaseous reaction products. The solid residue after pyrolysis, which was mainly composed of carbon, may be usefully exploited to produce carbon-based biofuels
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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