1,720,963 research outputs found
Immobilization of biocatalysts by photochemically grafted membranes: some studies with catalase as model system
No full textA technique suitable to immobilize enzymes by photografting of acrylic monomers or prepolymers onto microporous polymer substrates has been studied in this work. Some preliminary kinetic experiments have then been carried out on photosynthetic membranes immobilizing catalase as model enzyme, both in conditions of internal diffusion controlled reaction and of ultrafiltration through the membranes, in order to get information about the efficiency of the immobilized biocatalyst in this system
Immobilization of reagents and catalysts by photochemical grafting onto polymers
No full textThe possibility of immobilizing reagents and catalysts by photochemical grafting of their composites with an epoxy-diacrylate resin has been investigated. Two model systems have been examined: (i) the catalytic decomposition of aqueous sodium hypochlorite by cobalt peroxide, with oxygen production; (ii) the reaction of alkali metals with alcohols. For case (i) the catalyst was embedded, in the form of a mixture with 90% of zeolite 13X, into the photografted polymer matrix; while for case (ii) the alkali metal reagent, supported onto 90% of zeolite 13X, was incorporated into the microporous membrane. Kinetics of reaction (i) were studied in standard conditions (1.0 M NaOCl; 1.0 M NaCl; 0.25 M NaOH) between 288.2 to 318.2 K, and the relation between pseudp-first order kinetic constants and amount of catalyst incorporated into the membrane determined. Isotope effects for reaction (ii), relative to H2, D2, HD production, were measured with mixtures of deuterated and non-deuterated CH3OH(D), C2H5OH(D), n-C3H7OH(D), and i-C3H7OH(D) at 25 °C, as a function of volume percent of non-deuterated alkanols in the liquid phase. For reaction (i) reactivity was found to be substantially the same in the membrane reactor as in ordinary chemical conditions: loss of catalytic activity did not exceed 15%. For reaction (ii) isotope effects, the origin of which is discussed, fully coincided with those measured in the absence of the polymer matrix
Flow dynamical characterization of sorbents immobilized as composites in membranes prepared by photochemical grafting onto polymers
No full textPermeability measurements of water and n-hexane were carried out at 20°C through membranes prepared by photochemically grafting an epoxy-diacrylate copolymer or its composites onto cellulose. Composite membranes immobilizing 30.0 wt.% of calcite, seven calcium oxide samples obtained from calcination of calcite in different experimental conditions, α-iron(III) oxide and cobalt peroxide were thus tested. Hydraulic resistances as a function of membrane thickness were studied. Experimental results in the Poiseuille 's laminar flow regime are compatible with a normal Kozeny-Carman constant and a porosity of nominally 50%, indicating a regular packing of isometrically shaped particles in the microporous medium. Surface areas of membranes, both without additions and in the presence of filler materials, could thus be obtained by liquid permeametry measurements and successive treatment of data by the Kozeny-Carman equation. A general analysis of surface area characterization of immobilized sorbents is presented and compared with experimental values of B.E.T. method (liquid nitrogen adsorption). Results of flow dynamical investigation confirm the peculiar regularity of structure of the dense layer of photosynthetic membranes, as was found from morphology, from correlation between mean pore diameter and water fluxes per unit applied pressure drop, as well as from rejection characteristics in preceding studies
Trasport of oxygen facilitated by peroxo[N, N'-ethylene bis-(salicylideneiminato)dimethylformamide-cobalt(III)] embedded in liquid membranes immobilized by photografting onto cellulose
No full textA novel method to prepare liquid membranes, suitable to obtain facilitated transport of oxygen, incorporating the title complex (I) or the same without dimethylformamide (II), is reported. These membranes were obtained by photochemical grafting an epoxy-diacrylate copolymer onto cellulose in the presence of (I) or (II) together with dimethylformamide. Sorption isotherms of oxygen into deoxygenated membranes were obtained by Langmuir plots at 343-373 K. By these isotherms the molar ratio (0.5) between sorbed oxygen and cobalt in the membrane corresponding to saturation was evaluated, and constants K (bar-1) of heterogeneous equilibrium involving (I) and (II) were obtained as a function of temperature. From K values, a mean enthalpy change of -84 kJ mol-1 and entropy change of -220 J mol-1 K-1 were calculated. This latter reflects the high order in binuclear dioxygen complex formation. Permeability coefficients of oxygen and nitrogen from air through the photosynthetic membranes at 343 K were measured. These values show an efficient O2/N2 separation, with a very advantageous ratio (50) between their fluxes
Thermodynamic study of adsorption of linear aliphatic monohypric alcohols and monocarboxylic acids from n-Heptane and n-Decane solutions onto alpha-iron (III) oxide immobilized in photosynthetic membranes
No full textDifferential heats of adsorption at 298.2 K of a series of linear aliphatic monohydric alcohols CnH2n +1OH (n = 2-14) and linear aliphatic monocarboxylic acids CnH2n +1COOH (n = 1-13), from n-heptane and n-decane solutions (0.00005-0.03 molar fractions), onto α-Fe2O3 immobilized by photosynthetic membranes, prepared by photochemically grafting an epoxy-diacrylate copolymer onto cellulose, were measured. Langmuir-type treatment of data allowed us to calculate thermodynamic constants and adsorption heats for monolayer saturation, from which thermodynamic functions (free energy, enthalpy, and entropy) (saturated system as standard) were then computed. Mean areas occupied by adsorbed molecules in the monolayer coincided with those obtained for the unsupported sorbent, by allowing only about 20% of decrease of surface area, as a consequence of immobilization. Behaviour of immobilized sorbent is compared with that of 'free' α-Fe2O3. The sensitivity of adsorption measurements both to study configuration of adsorbed molecules, solvent-solute and solute-solute interactions
Transport of oxygen facilitated by peroxo-bis [N, N′-ethylene bis-(salicylideneiminato)-dimethylformamide-cobalt (III)] embedded in liquid membranes immobilized by photografting onto cellulose
No full textA novel method to prepare liquid membranes, suitable to obtain facilitated transport of oxygen, incorporating the title complex (I) or the same without dimethylformamide (II), is reported. These membranes were obtained by photochemically grafting an epoxy-diacrylate copolymer onto cellulose in the presence of (I) or (II) together with dimethylformamide. Sorption isotherms of oxygen into deoxygenated membranes were obtained by Langmuir plots at 343-373 K. By these isotherms the molar ratio (0.5) between sorbed oxygen and cobalt in the membrane corresponding to saturation was evaluated, and constants K (bar-1) of heterogeneous equilibrium (Equation (2) in the text) involving (I) and (II) were obtained as a function of temperature. From K values, a mean enthalpy change of - 84 ± 1 kJ mol-1 and entropy change of -220 ± 3 J mol-1 K-1 were calculated. This latter reflects the high order in binuclear dioxygen complex formation. Permeability coefficients of oxygen and nitrogen from air through the photosynthetic membranes at 343 K (4.60 × 10-5 and 9.23 × 10-7 cm2 s-1 bar-1, respectively) were measured: These values show, within a certain range of pressure drop of air, an efficient O2/N2 separation, with a very advantageous ratio (50) between their fluxes. © 1987
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
- …
