1,721,004 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
Milking of microalgae: Production and selective extraction of Beta-carotene in two-phase bioreactors
Full text linkThe low productivity of photobioreactors used for production of high-value compounds from microalgae is a big bottleneck in commercialization. "Milking" of microalgae for the production of high-value compounds in which the produced biomass is reused for production can be a solution to overcome this bottleneck.As it was described in Chapter 1 our main aim was to investigate the possible application of a "milking" process using two-phase bioreactors in microalgal biotechnology. We choseb-carotene extraction from Dunaliella salina in a two-phase bioreactor with an aqueous phase and an organic solvent phase as our model system. The goal was to develop an alternative and more efficient process than the commercial production process ofb-carotene.In chapter 2 biocompatibility of different solvents with values of log P octanol ranging from 3 to 9 for the cells of Dunaliella salina was investigated. Extraction ability of different solvents for bothb-carotene and chlorophyll was determined as well. Results showed that solvents having log P octanol > 6 can be considered biocompatible for this alga. Moreover, pigment extraction ability of a solvent is inversely dependent on its log P octanol value. By increasing the degenerative hydrophobicity the extraction ability for both chlorophyll andb-carotene, decreased. However, this decrease was more pronouned for chlorophyll. Therefore, selective extraction ofb-carotene becomes feasible. Theb-carotene productivity per cell in a two-phase system with dodecane was the highest observed. Extraction ability of the biocompatible solvents dodecane, tetradecane and hexadecane was similar.Effect of mixing rate which is supposed to lead to the facilitated release ofb-carotene from the cells of Dunaliella salina in two-phase bioreactors, was investigated in chapter 3 . Three pairs of bioreactors were inoculated at the same time, operated at 100, 150 and 170 rounds per minute, respectively and illuminated with a light intensity of 700mmol m -2s -1. Each pair consisted of one bioreactor containing only aqueous phase for the blank and one containing the water phase together with the biocompatible sovent (dodecane). Comparison of the viability and growth of the cells grown under different agitation rates showed that 170 rpm and 150 rpm were just as good as 100 rpm. Presence and absence of the organic phase had also no influence on the viability and growth of the cells. In contrast to the growth rate, the extraction rate ofb-carotene was influenced by the stirrer speed. The extraction rate increases at higher stirring rate. The effectiveness of extraction per amount of power in-put was comparable for all the applied mixing rates.In chapter 4 the effect of light intensity on the extraction ofb-carotene from Dunaliella salina , in the fermentative extraction, was investigated. Three different average light exposures were applied: 1.5*10 -8(low), 2.7* 10 -8(intermediate) and 4.5* 10 -8(high)mmol s -1cell -1. Results showed thatb-carotene content of the cells increases by increasing the light exposure. Increase in theb-carotene content of the cells was not necessarily coupled with an increase in the volumetric production ofb-carotene.b-Carotene extraction rate was enhanced by the increase in the light exposure. The results suggest that extraction rate was related tob-carotene content of the cells and was not essentially related to the volumetric productivity ofb-carotene. Although the effectiveness of extraction with respect to the light input was comparable for all light intensities applied, increasing the light input per cell leaded to a higher volumetric extraction rate.On the basis of the previous results the "milking" process forb-carotene production was developed and introduced in Chapter 5 . Growth of the cells was performed at low light intensity after which the cells were transferred to the production bioreactor, which was illuminated at a higher light intensity. The second bioreactor was a two-phase bioreactor consisting out of an aqueous and a biocompatible organic phase. In this bioreactor mixing and extraction were performed by re-circulation of the organic phase. The results showed that D. salina stayed viable for a long period (>47 d) in the presence of a biocompatible organic phase at high light intensity. The cell growth, however, was very slow in this situation.b-Carotene could be continuously extracted to the organic phase. The cells kept producingb-carotene and the extracted molecules were substituted by the cells. As a resultb-carotene was continuously milked from the cells. Theb-carotene extraction efficiency in this system was more than 55%. The productivity of the system was 2.45 mg. m -2.d -1which is much higher than obtained in commercial plants forb-carotene production.Several studies at macro-scale (bioreactors) and micro-scale (using microscopic techniques) were performed for better understanding the mechanism of the extraction process. The results are presented in Chapter 6 . Based on the results two hypothesis were made for the extraction: one of the mechanisms of extraction is transport of theb-carotene globules from the chloroplast to the space between the cell and the chloroplast membranes and subsequently from there to the outside by exo-cytosis. Another possible mode for the extraction could be release ofb-carotene from the globules as a result of alterations in the membrane of globules.b-Carotene molecules diffuse from the chloroplast to the space between the cell and the chloroplast membranes and from there to the medium either by diffusion or by exo-cytosis after accumulation in the vesicles.In the last chapter, Chapter 7 , we discuss the approaches which are helpful in answering two following fundamental questions: is it possible to milk all microalgae? And would this technique be suitable for mass production of high-value secondary metabolites? We think to answer these questions the mechanism of extraction and its relation with the production pathway of the target product should be exactly understood. Our previous results and the results of other researches suggest that chemical behavior and molecular structure of the solvent, chemical properties of the product and its location inside the cells and finally physiological behavior of the cell membrane and the cells by themselves are important parameters in a successful milking process. In this chapter we also discuss some other products (astaxanthin, neurotoxins and DHA ) which we think can be milked from microalgae. </p
Microalgal photobioreactors: Scale-up and optimisation
Full text linkMicroalgae and cyanobacteria are a potential source of a wide range of high-value compounds for the pharmaceutical, cosmetic and food industry. They do not only have the capacity to produce high-value compounds, but also the ability to do it using only sunlight, carbon dioxide and seawater. For many of the applications, monoalgal or even axenic cultures are required. This can be obtained in closed photobioreactors. In these systems, besides the main scale-up parameters, which are associated to all microbial fermentations: mass transfer, mixing rate and hydrodynamic stress, the light regime has also to be considered because light energy is the limiting substrate. However, these parameters cannot be controlled independently, as they are closely interrelated. Therefore, in order to maximise productivity, the whole process has to be examined. In this thesis, the characterisation of the most critical scale-up aspects of gas-sparged photobioreactors was done, with emphasis on light regime and hydrodynamic stress. Moreover a new optimisation tool for photobioreactors (A-stat) was developed.</p
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
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
Oxygen accumulation in photobioreactors
No full textPhototropic microalgae are regarded as a promising feedstock for sustainable biodiesel production, as microalgae can use natural sunlight as light source and are able to utilize CO2from flue gases and nutrients (P, N) from waste streams. To make large-scale outdoor microalgae production in closed photobioreactors economically feasible and sustainable, the costs for mixing and degassing should be reduced and the overall energy balance should become positive. This thesis focused on the effect of the accumulation of oxygen on the growth of the oleaginous microalga Neochloris oleoabundansat different light intensities. This study showed at what concentrations oxygen becomes toxic for the algae at the different light conditions encountered during outdoor cultivation and different strategies to overcome the inhibiting factor. The implementations of the main findings of this thesis wereevaluated using an economic model. The model was used to calculatethe energy and costs associated to microalgal biomass production in The Netherlands.The two methods adopted to overcome the negative effect of oxygen in microalgal cultures did result in a decrease in biomass production costs. Moreover, it showed that using the findings of this thesis, a positive energy balance for outdoor production of Neochloris oleoabundans in closed photobioreactors can be reached
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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