1,720,985 research outputs found
Effects of ionic environment on the interfacial interactions between α-amylase and polyether sulphone membranes
No full textThis work reports a systematic study on the effects of ionic environment on the adsorption of alpha-amylase on 30 kDa polyether sulphone (PES) membranes on the basis of interfacial interaction of PES membrane and alpha-amylase enzyme in solution. Static adsorption of alpha-amylase was investigated at the solution pH values of pH = 4.5, 5.6 and 7.0; and for the ionic strengths of 0.001, 0.01 and 0.1 M KCl. The maximum adsorption occurred at the pH value below the isoelectric point (IEP) of the enzyme, whereas the minimum adsorption occurred at the IEP (pH = 5.6) of amylase. With increasing ionic strength, the adsorbed enzyme on the membrane decreased. The Freundlich and Langmuir adsorption models were used for the mathematical description of the adsorption equilibrium and isotherm constants were evaluated depending on ionic environment. To determine the steps affecting the adsorption mechanism, the experimental data were evaluated using pseudo-first-order and pseudo-second-order kinetic models. The experimental data fitted well the pseudo-first-order kinetics. To detect the structural changes which occurred, membrane surfaces were analyzed by FTIR-ATR spectroscopy. The effects of ionic environment on amylase activity were also investigated. Copyright (C) 2010 John Wiley & Sons, Ltd.Cumhuriyet University [M-322]The author acknowledges the financial supports provided by Cumhuriyet University Scientific Research Projects (Project No: M-322)
Effects of ionic environments on bovine serum albumin fouling in a cross-flow ultrafiltration system
No full textThe influence of electrostatic interactions on membrane fouling during the separation of bovine serum albumin (BSA) from solution was studied in a cross-flow ultratiltration system. Experiments were carried out at different pH values between 3.78 and 7.46; and for different ionic strengths between 0.001 M and 0.1 M. The changes in permeate flux, cake layer resistance, zeta potentials of BSA and polyether sulfone (PES) membranes, and electrostatic interaction energies, were evaluated. At all of the ionic conditions studied, PES membranes are negatively charged. However, BSA molecules are either negatively or positively charged depending on the ionic environment. Whereas the cake layer resistance decreased with increasing pH and ionic strength, the permeate fluxes increased. The calculated electrostatic energy was a minimum at the isoelectric point (IEP) of BSA. However, at this point, the cake resistances corresponding to fouling at each ionic strength, were not minimized. Below the IEP of BSA, the electrostatic forces were attractive, while above the IEP, repulsive electrostatic forces were dominant
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
Supercritical fluid extraction of walnut kernel oil
No full textThe objective of this study was to investigate the effects of the main process parameters on supercritical fluid extraction of walnut (Juglans regia L.) kernel oil. The recovery of walnut kernel oil was performed in a green and high-tech separation process. CO2 and CO2 + ethanol mixtures were used as the supercritical solvent. The extraction was carried out at operating pressures of 30, 40 and 50 MPa, operating temperatures of 313, 323 and 333 K, mean particle sizes of 1.78 x 10(-4), 3.03 x 10(-4), 4.78 x 10(-4), 7.00 x 10(-4) and 9.00 x 10(-4) m, supercritical CO2 (SC CO2) flow rates of 1.67 x 10(-8), 3.33 x 10(-8), 6.67 x 10(-8) and 13.33 x 10(-1) m(3)/s and entrainer (ethanol) concentrations of 2, 4, 8 and 12 vol-%. Maximum extraction yield and oil solubility in SC CO2 obtained at 50 MPa, 333 K, 9.00 x 10(-4) m, 3.33 x 10(-4) m(3)/h were 0.65 kg oil/kg of dry sample and 37.16 g oil/kg CO2, respectively. The results obtained in this study showed that the crossover pressure effect of walnut kernel oil was at 30 MPa. At 30 MPa and 313 K, the obtained extraction yields above 4 vol-% ethanol reached the organic solvent extraction yield of 68.5 kg oil/kg dry sample. Extraction time was decreased significantly because of the higher solubility of walnut kernel oil in SC CO2 + ethanol mixtures
Effects of additives on the activity and enantioselectivity of Candida rugosa lipase a in a biphasic medium
No full textThe effects of Li+, Na+, K+, Mg2+ and Zn2+ ions on the activity and enantioselectivity of Candida rugosa lipase (CRL) were investigated in a biphasic medium composed of phosphate buffer solution (containing a metal ion within a 50-500 mM concentration range) and isooctane. The hydrolytic activities of CRL towards p-nitrophenyl acetate were measured after incubation of the enzyme in the presence of metal ions for 24 h, and they were compared to that obtained after incubation in the absence of any metal ion. The CRL activity was stimulated by the chloride salts of Li+, K+ and Mg2+ for all concentrations considered and the highest enhancement was achieved by Li+ with a 1.24-1.75 fold increase observed. The effects of metal ions on the enantioselectivity of CRL were investigated by performing the hydrolysis of racemic Naproxen methyl ester in the same biphasic medium containing Li+, Na+, K+, Mg2+ and Zn2+ ions. The addition of metal ions increased the hydrolysis rate by ca. 1.31-1.45 fold relative to the control, whereas the enantiomeric excess of product increased slightly in the presence of the metal ions. The effect of Triton X-100 on the activity and enantioselectivity of the CRL was also investigated by employing 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5 mM concentrations of it in phosphate buffer solution of the biphasic medium. High concentrations of Triton X-100 stimulated the enzyme activity up to 1.66 fold after 24 h incubation. Triton X-100 increased the hydrolysis rate almost independently of the concentration
Crossflow ultraflitration of binary biomolecule mixture: Analysis of permeate flux, cake resistance and sieving coefficient
No full textThe aim of this paper is to demonstrate the effects of hydrodynamic conditions on the permeate flux, cake resistance and sieving coefficient in a crossflow ultrafiltration process separating biomolecules of different molecular weights. A binary mixture of L-phenylalanine (L-phe) and lipase was ultrafiltered through a hydrophobic polyether sulphone (PES) membrane with 10 kDa molecular weight cut-off. The changes in permeate flux, cake layer resistance and observed sieving coefficient with different transmembrane pressures (TMP) and crossflow velocities were evaluated. The effect of TMP was examined at two different velocities (0.114 m s(-1) and 0.176 in s(-1)) and the effect of velocity was examined at two different TMP (20 kPa and 115 kPa) for the experimental system designed. In the initial stage of the crossflow filtration, it was determined that the TMP was more effective than the velocity. The cake layer resistance increased with increasing TMP and it decreased with increasing velocity for the high TMP value of 115 kPa. A maximum of the observed sieving coefficient was achieved with increasing velocity. An increase in TMP at low inlet velocity (0.114 in s(-1)) affected the observed sieving coefficient positively
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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