1,720,998 research outputs found
Oligosaccharide nanofiltration: an experimental study about electrolyte effect on the separation
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Effect of temperature, pH and composition on nanofiltration of mono/disaccharides: experiments and modeling assessment
No full textThe paper introduces a systematic experimental investigation on the role of temperature and composition on the membrane permeability and on the solute rejection, in association with suitable modeling. The case of Nanofiltration of aqueous solutions containing single sugars (dextrose or fructose or maltose) is considered with polyamide membranes.
Real rejections are reported as a function of total volume fluxes in the complete rage from 0% to 100%, at 30 °C and 50 °C, at pH=4 and 6, with sugar composition from 1 to 300 g/dm3, in the pressure range from 3 to 30 bar. Hydraulic permeabilities are also measured at 30,40,50 °C, at pH=4, for NF membranes (GE-DK and GE-DL) and for brackish water RO membranes (GE-AG and GE-AK).
The wide experimentation allows to obtain general trends and to define a criterion for the experimental protocol required for a complete characterization of membrane performances.
A revision of the Steric Pore Model is also introduced, in which a porous vision of the membrane is applied both to the description of the solute flux and of the total flux. The model allows to understand and to explain the nature of the solute/membrane and/or of the solvent/membrane interactions, and to develop a criterion for the primary elaboration of experimental data. Hydrodynamic coefficient of the solute becomes the main adjustable parameter of the model related to the solute type, assuming the meaning of a binary interaction parameter accounting of solute/membrane interactions, including membrane geometry and molecular dimensions.
For the GE-DK and GE-DL membranes no swelling effect of temperature nor of the solute type is observed on membrane permeability, whereas solute rejection is greatly affected by temperature. Experimental results are useful to test the model and the corresponding procedure for the parameters calculation, developed in this work. A critical discussion about the validity of the procedure is presented and compared with other elaboration techniques reported in literature
Mass transfer in 1812 spiral wound modules: Experimental study in dextrose-water nanofiltration
No full textBiotech 1812 spiral-wound elements manufactured by GE Powe&Water have been characterized, operating in NF with aqueous solutions containing 50 g/dm3dextrose at 50 °C and pH = 4. Operative conditions were selected in order to get experimental results of flux and observed rejections highly dependent on feed flow rate, so that a confident mass transfer correlation in the feed side has been obtained. The mass transfer correlation accounts of the feed spacer geometrical characteristics included in the description of the hydraulic diameter. It matches in a surprising manner with the well-known correlation derived from heat and mass transfer analogies in turbulent flow regime, it is in a good agreement with a recently published correlation derived from OSN in 1812 modules, whereas it is heavily in contrast with the widely used Shock and Miquel equation. In addition, the elaboration of the experimental data according to the velocity variation method does not lead to confident results. The correlation here presented can be extended to the simulation of industrial modules operating at feed flow conditions corresponding to Reynolds number in the range from 100 to 700, since it is rather independent of the way in which it was calculated. A critical discussion is also presented about the differences between the values of membrane permeability and of the module permeability and about the role of the âmodule length to membrane widthâ ratio in data elaboration. A sensitivity analysis concludes the work, in which authors discuss how the results of module characterization depend on the quality of the mass transfer correlation in the feed side and give some recommendations for a proper elaboration of experimental results
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
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
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
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