1,721,086 research outputs found
Nanofiltration modeling: The role of dielectric exclusion in membrane characterization
No full textA general model is presented, called Donnan steric pore model and dielectric exclusion (DSPM and DE) to describe mass transfer of electrolytes and neutral solutes through nanofiltration membranes. The transport equations of ions through the membrane are based on the extended Nernst-Planck equation, accounting for ionic diffusion, electromigration and convection in the membrane pores; the hindered nature of diffusion and convection of the species inside the membrane is considered. Ionic partitioning at the interfaces between the membrane and the external phases takes into account of three separation mechanisms: Steric hindrance, Donnan equilibrium and dielectric exclusion. The role of the difference existing between the dielectric constant of the aqueous solution in the pores and the dielectric constant of the membrane material is assumed dominant in determining the rejection mechanism related to the dielectric effects. The membrane is characterized through the use of adjustable parameters such as the average pore radius, the effective membrane thickness and the volumetric charge density. A general assessment is presented for membrane characterization. A new procedure is introduced for the membrane parameters calculation, based on a simple analytical relationship developed to describe rejection of single symmetric electrolytes. Two versions of the DSPM and DE model are presented, in which the "integral" model is a weak simplification of the general "differential" model. The validity of the models presented is fully demonstrated in the case of negatively charged membranes, through the comparison with experimental results performed in a wide range of operative conditions. The separation effect related to the dielectric exclusion is relevant with respect to Donnan equilibrium in determining bivalent counter-ions rejection, such as CaCl2 as well as MgSO4, whereas dielectric effects are not so remarkable in the case of mixtures containing various co-ions, such as NaCl + Na2SO4. © 2003 Elsevier Ltd. All rights reserved
Riflessioni su un'esperienza di dottorato presso l'Ecole des Hautes Etudes en Sciences Sociales in Francia (1992-1997)
No full textLa Francia ha per lungo tempo costituito una meta scientifica ambita dai giovani ricercatori di tutto il mondo, desiderosi di intraprendere percorsi di perfezionamento all’estero in ambito storico in ragione del carattere innovativo della storiografia francese. Nell’anno accademico 1992/1993 sono stata fra i laureati italiani che hanno effettuato un soggiorno di ricerca volto a seguire una specializzazione che ha portato in seguito al dottorato in “Storia e civiltà” in Francia. Lo scopo di questo breve articolo informativo è quello di presentare sia le caratteristiche della formazione di cui ho potuto beneficiare durante gli anni di dottorato presso un'istituzione specializzata nell'alta formazione in scienze umane – l'École des Hautes Études en Sciences Sociales (EHESS) –, sia la procedura prevista per il conseguimento del titolo di dottore di ricerca nelle sue fasi di preparazione e di consegna della tesi di dottorato in vista della discussione finale. In Francia al titolo di Docteur deve aggiungersi quello dall’abilitazione a dirigere le ricerche per quanti aspirino al ruolo di Professeurs des Universités
Testing the applicability limits of a membrane distillation process with ceramic hydrophobized membranes: The critical wetting temperature
Full text linkThe new concept of the critical wetting temperature (TC wetting) of a hydrophobic membrane is introduced. It represents the maximum temperature at which a hydrophobic membrane can operate in no-wetting conditions with a specific liquid. The concept relies on the theoretical premises of the Laplace-Young equation. The existence of the critical wetting temperature is experimentally documented for the case of carbon-based titania membranes hydrophobized with FAS, by measuring the minimum Liquid Entry Pressure values as a function of temperature, in the range from 20 °C to 136 °C. In that case, the TCwetting was obtained close to 130 °C with pure water. The new parameter should be included in the membrane characterization protocols, since the evaluation of TC wetting is crucial to define which are the applicability limits of a membrane contactor. In alternative to various LEP measurements as a function of temperature, the measure of the minimum Liquid Entry Temperature at very low pressures can represent a more efficient method for the TCwetting evaluation
Concentration of must through vacuum membrane distillation
No full textVacuum Membrane Distillation is studied for the concentration of fruit juices up to 50°Brix. The fluxes of water and of the relevant aroma compounds are experimentally examined for a typical must, as a function of temperature, sugar content and downstream pressure. The process leads to juice concentrates still retaining interesting amounts of the aroma compounds. A process analysis is also shown for must concentration up to 50°Brix
Cellular automata: from a theoretical computational model to its application to complex systems
No full textThis introductory paper gives a short survey of Cellular Automata (CA's), from different points of view. It starts with the main definitions and theoretical results about CA's as an abstract model of computation or as discrete dynamical systems. Then, the main applications of CA's in different fields (biology, physics...) as a model of complex systems are illustrated. Finally, implementations of the CA model on parallel computing platforms are surveyed
Rising moisture, salts and electrokinetic effects in ancient masonries: From laboratory testing to on-site monitoring
No full textThe investigation of capillary water rise mechanisms in old masonries is of great practical interest, as well as the investigation of the electrical effects accompanying such phenomenon. In fact, moisture presence facilitates all the decay processes in porous building materials and strongly threatens the preservation of materials in architectural heritage. Previous papers have shown that performing a correct and accurate measurement of spontaneous electric potential in masonries is very challenging due to several variables influencing these phenomena, such as materials microstructure, soluble salts nature and amount. In this paper, the influence of mortar joints on the capillary water rise and on the related electrokinetic effects was investigated on laboratory assemblies; then, the same measuring procedure was applied on site to a real XVI Cent. masonry building affected by rising damp. © 2013 Elsevier Masson SAS
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
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