1,720,962 research outputs found
Homogenization of the turbulence inside autoclaves by using randomly localized velocity perturbations
Get PDFThis work analyzes the turbulent features inside the chamber of industrial size autoclaves typically used for thermal treatment of carbon fiber-based materials adopted in the aerospace industry. The state-of-the-art design of these machineries causes a highly anisotropic turbulent flow, which negatively influences the temperature distribution within the chamber, which ultimately leads to a non-optimal treatment of the materials. The aim of this work is, then, the proposal of an innovative design to homogenize the turbulence inside a 16 m3 industrial size autoclave. The design includes the addition of three contemporary localized velocity perturbations, randomly chosen from a set of six possible sources located at the walls of the chamber. The impact of these sources has been examined by LES simulations conducted on an hexahedral grid composed of 8 106 cells; They have been conducted by using the open-source software PLUTO 4.4.2 [1, 2]. The major target variables will be the mapping of the kinetic energy inside the system and the distribution of a tracer within the chamber.
A preliminary example of the positive impact of the perturbations is proposed in Figure 1, where contour plots of the kinetic energy on a transversal section of the autoclave have been proposed after 3.5 s of simulation: the addition of random velocity perturbations already decreases, even if still mildly, the internal anisotropy of the fluctuations of the system and it “spreads” turbulence in sections of the domain otherwise completely stagnant. Future research steps will be a complete control of the homogenization of the flow and temperature characteristics inside the chamber by optimizing the total number of perturbation sources, the fraction of them being randomly activated at the same time and the time interval between different perturbation configurations
Predictive model of polymer reaction kinetics and coagulation behavior in seeded emulsion co- and ter-polymerizations
Get PDFA mathematical model to describe the emulsion polymerization kinetics of co- and ter-polymerizations is developed. The model uses the well-known pseudo-homopolymerization approach together with recently developed models for radical entry and desorption in order to monitor crucial kinetic variables such as conversion and latex composition. The model includes a series of unknown parameters related to monomer-specific gel-effect coefficients, that are needed to compute the bimolecular termination reaction rates. The unknown parameters are determined through extensive calibration of the model on literature data for homo- and co-polymerizations of n-butyl acrylate (n-BA) and methyl methacrylate (MMA). The so-obtained predictive model is then applied to the modelling of the ter-polymerization of n-BA and MMA with 2-hydroxyethyl methacrylate (2-HEMA) with sodium persulphate (SPR) as initiator: predictions for the time-evolution of particle size and conversion are in excellent agreement with experimental measurements using Dynamic Light Scattering (DLS) and Gas Chromatography (GC), upon tuning the gel-effect coefficient related to 2-HEMA. The developed model is used to quantify the surfactant surface coverage of the particles as well as the total concentration of counterions in the system throughout the entire polymerization process. This key information provides a way to rationalize and control the coagulation behavior during the whole polymerization process
Solution to the two-body Smoluchowski equation with shear flow for charge-stabilized colloids at low to moderate P\'eclet numbers
Get PDFWe developed an analytical theoretical method to determine the microscopical
structure of weakly to moderately sheared colloidal suspensions in dilute
conditions. The microstructure is described by the static structure factor,
obtained by solving the stationary two-body Smoluchowski advection-diffusion
equation. The singularly perturbed PDE problem is solved by performing an
angular averaging over the extensional and compressing sectors and by the
rigorous application of boundary-layer theory (intermediate asymptotics). This
allows us to expand the solution to a higher order in P\'eclet with respect to
previous methods. The scheme is independent of the type of interaction
potential. We apply it to the example of charge-stabilized colloidal particles
interacting via the repulsive Yukawa potential and study the distortion of the
structure factor. It is predicted that the distortion is larger at small
wavevectors and its dependence on is a simple power law. At increasing
, the main peak of the structure factor displays a broadening and shift
towards lower in the extensional sectors, which indicates shear-induced
spreading out of particle correlations and neighbor particles locally being
dragged away from the reference one. In the compressing sectors, instead, a
narrowing and shift towards high is predicted, reflecting shear-induced
ordering near contact and concomitant depletion in the medium-range. An overall
narrowing of the peak is also predicted for the structure factor averaged over
the whole solid angle. Calculations are also performed for hard spheres,
showing good overall agreement with experimental data. It is also shown that
the shear-induced structure factor distortion is orders of magnitude larger for
the Yukawa repulsion than for the hard spheres
Extended Charge-on-Particle Optimized Potentials for Liquid Simulation Acetone Model: The Case of Acetone-Water Mixtures
Get PDFIt is well known that classical molecular dynamics (MD) simulations of acetone-water mixtures lead to a strong phase separation when using most of the standard all-atom force fields, despite the well-known experimental fact that acetone is miscible with water in any proportion at room temperature. We describe here the use of a charge-on-particle (COP) model for accounting for the induced polarization effect in acetone-water mixtures which can solve the de-mixing problem at all acetone molar fractions. The polarizability effect is introduced by means of a Virtual Site (VS) on the carbonyl group of the acetone molecule, which increases its dipole moment and leads to a better affinity with water molecules. The VS parameter is set by fitting the density of the mixture, at different acetone molar fractions. The main novelty of the VS approach lies on the transferability and universality of the model, since the polarizability can be controlled without modifying the force field adopted, like previous efforts did. The results are satisfactory also in terms of transport properties, i.e. diffusivity and viscosity coefficients of the mixture
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
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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