1,721,022 research outputs found
Continuous production of isovaleraldehyde through extractive bioconversion in a hollow-fiber membrane bioreactor
No full textA membrane bioreactor was developed to perform an extractive bioconversion aimed at the production of isovaleraldehyde by isoamyl alcohol oxidation with whole cells of Gluconobacter oxydans. A liquid/liquid extractive system using isooctane as extractant and assisted by a hollow-fiber hydrophobic membrane was chosen to recover the product. The aqueous bioconversion phase and the organic phase were maintained apart with the aid of the membrane. The extraction of alcohol and aldehyde was evaluated by performing equilibrium and mass transfer kinetic studies. The bioprocess was then performed in a continuous mode with addition of the substrate to the aqueous phase. Fresh solvent was added to the organic phase and exhausted solvent was removed at the same flow rate. The extractive system enabled a fast and selective in situ removal of the aldehyde from the water to the organic phase. High conversions (72–90%) and overall productivity (2.0–3.0 g l−1 h−1) were obtained in continuous experiments performed with different rates of alcohol addition (1.5–3.5 g l−1 h−1). Cell deactivation was observed after 10–12 h of operation
Continuous production and in situ extraction of isovaleraldehyde in a membrane bioreactor
No full textBioconversions are generally low productivity processes when compared to chemical synthetic reactions. The productivity of a bioconversion can be maximized if it is carried out in the presence of substrate/product concentrations at which the biocatalyst shows optimal activity and stability. One way to achieve this is to develop a process with continuous addition of the substrate and selective removal of the product. The microbial oxidation of isoamyl alcohol to isovaleraldehyde by a newly isolated Gluconobacter oxydans strain has been reported recently. High conversion yields (>90%) and good rates (maximum yield after 90 min) were obtained in a batch mode. With this strain, although aldehyde dehydrogenase(s) leading to acid formation are present, further oxidation of the aldehyde to acid is significantly slower so that transient accumulation of the aldehyde is possible. The productivity of this bioconversion can be improved by setting up a continuous process with addition of substrate at an adequate flow rate. In situ removal of the aldehyde is imperative to avoid acid production and to reduce evaporation of the product. This chapter describes a membrane-based extractive procedure to achieve an in situ, nondispersive recovery of the aldehyde
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
Sviluppo di un biosensore enzimatico ad enzimi immobilizzati per la misura di acido l-Lattico in sistemi FIA (Flow Injection Analysis).
No full textLa misura in tempo reale della concentrazione di acido L-Lattico può essere di rilevante importanza nell’industria alimentare e nella medicina. L’impiego di biosensori enzimatici combinato con i vantaggi dei sistemi per analisi di tipo Flow Injection (FIA) può soddisfare il bisogno di analisi rapide ed accurate. La stabilità dei biosensori aumenta significativamente se gli enzimi sono immobilizzati su supporti inerti. In questo studio è stato quindi sviluppato un biosensore enzimatico per la misura di acido L-Lattico immobilizzando su vetro a porosità controllata gli enzimi lattato ossidasi e horseradish perossidasi, che a partire da acido lattico ed in presenza di un determinato sistema reagente catalizzano due reazioni consecutive che portano alla formazione di un prodotto colorato rilevabile in spettrofotometria. Il biosensore sviluppato ha permesso analisi in FIA estremamente riproducibili ma si è dimostrato instabile per lunghi periodi di esercizio
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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