21,060 research outputs found
Assessment of gel formation in colloidal dispersions during mixing in turbulent jets
No full textOnset of gel formation upon mixing between colloidal dispersions and coagulant solutions in turbulent jets was studied using a combination of computational fluid dynamics (CFD) and population balance equation (PBE). To describe the interaction between turbulence fluctuations and particle aggregation, a micromixing model based on presumed probability density function was implemented inside the CFD code. Furthermore, effect of the solid phase on the fluid flow was modeled through an effective viscosity of the mixture evaluated from PBE. The results are presented in the parameter space of the primary particle diameter and the solid volume fraction where strong interplay between mixing and aggregation mechanisms controls the gelation phenomena and consequently also the fluid dynamics. Simulation results are in good agreement with observations from gelation experiments of concentrated nanoparticle suspensions injected into coagulant solutions
Dynamic response studies on aggregation and breakage dynamics of colloidal dispersions in stirred tanks
No full textAggregation and breakage of aggregates of fully destabilized polystyrene latex particles in turbulent flow was studied experimentally in both batch and continuous stirred tanks using small-angle static light scattering. It was found that the steady-state values of the root-mean-square radius of gyration are fully reversible upon changes of stirring speed as well as solid volume fraction. Steady-state values of the root-mean-square radius of gyration were decreasing with decreasing solid volume fraction as well as with increasing stirring speed. Moreover, it was found that the steady-state structure and shape of the aggregates is not influenced by the applied stirring speed
Modeling focused beam reflectance measurement and its application to sizing of particles of variable shape
No full textA model for particle detection in focused beam reflectance measurement is presented in the general case of particles of any convex shape. Shape dependent convolution relationships between measured chord length distribution (CLD), particle size distribution (PSD) and particle mass distribution (PMD) are derived and an explicit formula for the weighting characteristic length is given in terms of particle shape. Based on the derived convolution relationships, equations relating moments of the CLD, PSD and PMD are obtained. Issues related to the definition of particle size of non spherical objects and its connection to the particle sizing technique are discussed. Based on the moment relationships, particle size is defined for focused beam reflectance measurement measurements in terms of a CLD equivalent sphere. CLD and characteristic length for a thin cylinder are obtained analytically and used as simple model in order to illustrate issues in sizing particles of variable shape, General conclusions regarding the role of the weighting characteristic length on the behavior of the measured CLD are drawn
Master curves for aggregation and gelation : effects of cluster structure and polydispersity
No full textA parametric study of the effects of cluster structure and polydispersity on the kinetics of aggregation and gelation is presented. The aggregation kinetics is described in terms of master curves characterizing the evolution of suitable dimensionless averages (measurable by light scattering) of the underlying cluster mass distribution (CMD), as a function of a suitable dimensionless time. Such master curves are shown to be dependent only on two dimensionless parameters: the cluster fractal dimension (d(f)) and the ratio between Brownian and shear aggregation rates (kappa). Shear aggregation of fractal clusters leads to higher-order moments of the CMD diverging to infinity in a finite time, which is usually called runaway. It is determined that the parameter space is split into two distinct regions: either where aggregates gel because of space filling before runaway occurs or where gelation occurs as a consequence of runaway. It is also determined that cluster polydispersity and the fractal dimension significantly affect the runaway and gelation times
Jan Kapr's contribution to contemporary music : an essay about a composer and teacher
No full textThis creative project is a treatise on a leading personality of Czechoslovakian musical life, the composer, Jan Kapr. The author discusses the following:1. The complicated development of Kapr's career and work, 2. Kapr's method of organization of musical material in a composition, as described in his book Constants,3. His former and current style which is demonstrated in two of his compositions, Concert Variations, for flute and string orchestra and Testimonies for four solo instruments,4. Two of his recent works, Exercises for Gydli and the Symphony No. 7, Country of Childhood.Thesis (M.A.
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
ELEVEN FACES OF JAN GOGOL, JR.
No full textAuthor Jan Rendl in his thesis attempts to look at the world of ideas and educator Jan
Gogola ml. through the eleven chapters in which each chapter somehow characterizes itself by Jan Gogola ml. and each of them somehow determines its creative ideas of it through the metaphor of a football match when Jan Gogola, with its characters, movies himself a teammate, as well as defensively. It gives goals with their situations as well as occasionally digging his opponents ankles.
Jan Gogola ml. thus embodies one stage of the Department of Documentary Film at FAMU, which often stands at the intersection between teaching activities and Karel Vachek among students who applied by them during their seminars psychological methods that work must be peculiarly associated with the author of the film
Dr. Jan French – Faculty Author Interview
No full textDr. Jan French, Assistant Professor of Anthropology, discusses her new book, Legalizing Identities: Becoming Black or Indian in Brazil’s Northeast, which shows how law can successfully serve as the impetus for the transformation of cultural practices and collective identity
Jan Bernátek - organ works
No full textThis graduation thesis provides a more detailed view on compositoins of Jan Bernátek.The aim is to present this less well-known temporary czech author,who makes use of the organ in the majority of his work
Scaling of the kinetics of slow aggregation and gel formation for a fluorinated polymer colloid
No full textThe aggregation and gelation kinetics in moderately concentrated (0.004 less than or equal to phi(0) less than or equal to 0.1) colloidal dispersions of fluorinated polymer particles has been studied. The aggregation was adjusted to proceed slowly enough to allow a convenient characterization of the kinetics through static and dynamic light scattering on quenched and diluted samples. A population balance model based on second-order aggregation rates is developed to compute the time evolution of the cluster mass distribution, from which we calculate the values of the average radii and structure factor measured by light scattering, so as to allow a direct comparison between measured and calculated quantities. The model suggests the introduction of a dimensionless time which allows the scaling of all the aggregation data on unique master curves defined by only two parameters: the exponent of the power-law aggregation kernel, lambda, and the aggregate fractal dimension, d(f). The predicted master curves were observed experimentally, which confirms the validity of the aggregation model and allows the unique determination of the kinetic and structural parameters of the aggregation process. The cluster growth behaviour, although significantly slower than DLCA, shows power-law kinetics rather than the exponential one typical of RLCA and the cluster structure is characterized by an unexpectedly small fractal dimension, d(f) = 1.7. The occurrence of gelation has been characterized using small amplitude oscillatory shearing to monitor the time evolution of the elastic modulus. It is found that also these curves, together with the gel time value, scale with the stability ratio of primary particles for a given solid volume fraction. We further use the model to calculate the cumulative occupied volume fraction of the growing aggregates and quantify in this way the increasing space filling, which is solid volume fraction dependent. The experimentally determined dimensionless gel times, which are also solid volume fraction dependent, scale then directly with the dimensionless time to reach a certain degree of the space filling in the model. This finding suggests that, like the aggregation kinetics, the gelation kinetics is governed by a second-order rate process
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