Scaling law for the viscoelasticity-induced particle migration in stirred vessels

In this study, we investigate the viscoelasticity-induced migration of solid particles immerged in the three-dimensional flow field created by the rotation of a Rushton turbine. At the same time, we propose a scaling law for predicting the characteristic particle migration time as a function of the Weissenberg number. Particle image velocimetry is adopted to reconstruct the three-dimensional velocity and deformation rate fields generated by the rotation of the Rushton turbine in both Newtonian and viscoelastic fluids; concurrently, particle tracking is used to measure the evolution of the particle distribution in the tank. The experimental campaign shows that the deformation rate field is essentially bi-dimensional and confined to the r-θ plane. Accordingly, the particles migrate only in the radial direction driven by the presence of gradients of shear rate on the r-θ plane. Finally, the scaling law is validated against experimental data obtained at different Weissenberg numbers, impeller diameters and fluid compositions. The results show good agreement between the scaling law and the experimental data

The Impact of Supervised Manifold Learning on Structure Preserving and Classification Error: A Theoretical Study

In recent years, a variety of supervised manifold learning techniques have been proposed to outperform their unsupervised alternative versions in terms of classification accuracy and data structure capturing. Some dissimilarity measures have been used in these techniques to guide the dimensionality reduction process. Their good performance was empirically demonstrated; however, the relevant analysis is still missing. This paper contributes to a theoretical analysis on a) how dissimilarity measures affect maintaining manifold neighbourhood structure, and b) how supervised manifold learning techniques could contribute to the reduction of classification error. This paper also provides a cross-comparison between supervised and unsupervised manifold learning approaches in terms of structure capturing using Kendall’s Tau coefficients and Co-ranking matrices. Four different metrics (including three dissimilarity measures and Euclidean distance) have been considered along with manifold learning methods such as Isomap, t-Stochastic Neighbour Embedding (t-SNE), and Laplacian Eigenmaps (LE), in two datasets: Breast Cancer and Swiss-Roll. This paper concludes that although the dissimilarity measures used in the manifold learning techniques can reduce classification error, they do not learn well or preserve the structure of the hidden manifold in the high dimensional space, but instead, they destroy the structure of the data. Based on the findings of this paper, it is advisable to use supervised manifold learning techniques as a pre-processing step in classification. In addition, it is not advisable to apply supervised manifold learning for visualization purposes since the two-dimensional representation using supervised manifold learning does not improve the preservation of data structure

Rhythms of Relation: Black Popular Music and Mobile Technologies

In this essay I focus on the singular performances of the interface between (black) subjectivity and informational technologies in popular music, asking how these performances impact current definitions of the technological. After a brief examination of those aspects of mobile technologies that gesture beyond disembodied communication, I turn to the multifarious manifestations of techno-informational gadgets (especially cellular/mobile telephones) in contemporary R&B, a genre that is acutely concerned, both in content and form, with the conjuring of interiority, emotion, and affect. The genre’s emphasis on these aspects provides an occasion to analyze how technology thoroughly permeates spheres that are thought to represent the hallmarks of humanist hallucinations of humanity. I outline the extensive and intensive interdependence of contemporary (black) popular music and mobile technologies in order to ascertain how these sonic formations refract communication and embodiment and ask how this impacts ruling definitions of the technological. The first group of musical examples surveyed consists of recordings released between 1999 and 2001; the second set are recordings from years 2009–2010. Since ten years is almost an eternity in the constantly changing universes of popular music and mobile technologies, analyzing the sonic archives from two different historical moments allows me to stress the general co-dependence of mobiles and music without silencing the breaks that separate these “epochs.” Finally, I gloss a visual example that stages overlooked dimensions of mobile technologies so as to amplify the rhythmic flow between the scopic and the sonic. The artifacts in question boost the singular corporeal sensations of informational technologies without resorting to a naturalization of these machines. In other words, black musical formations relish the synthetic artificiality of cell phones and other mobile gadgets as much as making these a vital component of the performed body. They achieve this by transforming the sounds of mobile telephones into rhythmic patterns vital to their musical texts, which make audible how humans and mobile machines form a relational continuum

On the effect of surfactants on drop coalescence at liquid/liquid interfaces

In this work the effect of surfactants on the coalescence of a drop with a flat aqueous-organic interface was experimentally investigated. A high speed Particle Image Velocimetry (PIV) system was used to obtain velocity profiles and kinetic energy per unit mass distribution inside the coalescing droplets. Different mass ratios of surfactant to oil below the CMC value, up to ϕ = 5 × 10−4, of a non-ionic surfactant dissolved in the organic phase were studied. It was found that an increase in the surfactant concentration promoted the deformation of the interface before the film that separated the drop from the interface ruptured. A high surfactant concentration also increased the time needed for film rupture. When rupture occurred, two counter-rotating vortices formed inside the droplet on either side of the rupture point, which moved upwards with time. The propagation of the vortices inside the droplet was faster for low surfactant concentrations, while the intensities of the two counter-rotating vortices significantly decreased for increasing surfactant concentration. At the early stages of coalescence after film rupture, the kinetic energy per unit mass was mainly distributed near the bottom part of the droplet, while at later stages it was distributed near the upper part of the droplet

An experimental study on the drop/interface partial coalescence with surfactants

This paper presents investigations on the partial coalescence of an aqueous drop with an organicaqueous interface with and without surfactants. The organic phase was different silicone oils and the aqueous phase was a glycerol-water solution at different concentrations. It is found that when the surfactant Span 80 is introduced into the organic phase, the partial coalescence region is reduced in the Oh-Bo coalescence map. The range of the inertio-capillary regime reduces when surfactants are present, while the drop size ratio decreases with increasing surfactant concentration. The velocity fields inside the aqueous drop were studied with high speed particle image velocimetry for the first time. In the surfactant-free system, it was found that the inward motion of the fluids at the upper part of the drop favours the generation of a liquid cylinder at the early stages of coalescence. The pressure gradient created by the downward stream at the bottom of the liquid cylinder drives the pinch-off of the secondary drop. When surfactants are present, the rupture of the film between the drop and the interface occurs at an off-axis location. The liquid cylinder formed in this case is not symmetric and does not lead to pinch-off. It is also found that the vortices inside the droplet have little impact on the partial coalescence

Mixing, Velocity and Turbulence Characteristics of Shaken Bioreactors

The thesis describes an experimental investigation of the flow in a shaken bioreactor of cylindrical geometry with a flat bottom. Several reactor designs can be distinguished that attain mixing in different ways: oscillatory flow mixers (OFM), static mixers, stirred vessels and shaken bioreactors. Shaken bioreactors are often small-scale mixers (microwells) employed in the early stage of bioprocess development (i.e. microbial fermentation, bioconversion and product recovery techniques), before the developed process is implemented in a large-scale industrial stirred tank. However, despite their wide use, little is known about the fluid mechanics of these systems. In the present study Particle Image Velocimetry (PIV) measurements are carried out to determine the variation of the flow dynamics in a cylindrical shaken geometry for different operating conditions such as medium height, shaking frequency, orbital shaking diameter, cylinder inner diameter and fluid viscosity. In the first part phase-resolved measurements are carried out with PIV to provide a thorough characterisation of the flow and mixing dynamics occurring in a cylindrical shaken bioreactor for a fluid of low viscosity (i.e. water). From this analysis a flow scaling law based on the Froude number, Fr, is identified, which correlates the shape and inclination of the free surface to the occurrence of a flow transition. More specifically it was found that at low Fr the mean flow ischaracterised by a toroidal vortex with its axis aligned along the azimuthal direction, while after flow transition the free surface exhibits a phase lag and a vortical structure with a vertical axis that precesses around the cylinder axis is present. In the second part of the thesis flow characteristics, such as the interfacial area, circulation time, vortex size and location, kinetic energy and viscous dissipation rate of kinetic energy for a fluid of low viscosity are analysed in depth. The free surface interfacial area was directly measured by image analysis to assess oxygen transfer potential and was compared to an analytical solution valid for low Fr. The non-dimensional time and length scales of the vortical structures occurring in the cylindrical bioreactor were determined to provide an insight into the mixing dynamics, while a Reynolds decomposition analysis of the kinetic energy was carried out to assess the onset of a laminar-turbulent flow transition with increasing Fr. Direct measurements of the viscous dissipation rate of the kinetic energy, ǫ, were obtained across the tank to help assess micro-mixing and identify regions in the bioreactor experiencing higher levels of viscous stresses that can potentially affect cell growth. In the third part of the thesis the flow obtained with Newtonian fluids of higher viscosity is investigated and the flow scaling law determined for water is extended to a broader range of viscosity. A flow transition map based on Fr and Re is identified and four main regions characterised by different mean flow dynamics are shown. The turbulent kinetic energy levels and shear rate magnitudes are assessed for different combinations of Fr and Re. The results offer valuable new information for the design of mixing processes and crucial data to validate computational fluid dynamics simulations of cylindrical shaken bioreactors

Experimental investigation of the solid-liquid separation in a stirred tank owing to viscoelasticity

In this study, we investigated the motion of solid particles dispersed in highly viscous complex fluids agitated in a stirred vessel. We used a refractive index matching method and a combination of planar laser- induced fluorescence (PLIF), particle image velocimetry (PIV), and particle-tracking velocimetry (PTV) techniques to measure the velocity fields of the solid and fluid phases simultaneously along with the spatiotemporal distribution of the solids in the tank. The experimental data show that in a Newtonian ambient fluid, particles disperse uniformly in the plane of measurement, while in a strongly shear-thinning viscoelastic ambient fluid they tend to accumulate in the core of the vortices formed in the flow domain. We found that the solids migrate to the core of the vortices also when the ambient fluid is a Boger fluid, i.e., viscoelastic but not shear thinning. The effect of the first normal stress difference, N1, on the vortex sizes and circulation intensities was also examined, with both properties decreasing for increasing N1. Finally, we observed that the clustering time of the solids in the vessel for viscoelasticity-induced migration was at least three orders of magnitude lower than that obtained from the literature for inertia-induced migration

A New Supervised t-SNE with Dissimilarity Measure for Effective Data Visualization and Classification

In this paper, a new version of supervised t-SNE algorithm is proposed which introduces using a dissimilarity measure elated with class information. The proposed S-tSNE can be applied in any high dimensional dataset for visualisation or as a feature extraction for classification problems. In this study the S-tSNE is applied to three datasets MNIST, Chest x-ray and SEER Breast Cancer. The two-dimensional data generated by the S-tSNE showed better visualization and an improvement in terms of classification accuracy in comparison to the original t-SNE method. The results from k-NN classification models which used the lower dimension space generated by the new S-tSNE methods showed more than 20% accuracy improvement in all the three datasets compared with t-SNE method. In addition, the classification accuracy using the S-tSNE for feature extraction was even higher than classification accuracy obtained from the original high-dimensional data

Computational fluid dynamic studies of mixers for highly viscous shear thinning fluids and PIV validation

Agitation of highly viscous shear thinning fluids is normally conducted with complex impeller designs. Often, impellers almost as large as the tanks containing them and impeller blades equipped with holes are adopted in industry. In this work, we studied experimentally the main features of the flow generated by this type of impellers for a mixture of glycerol with a carbomeric gel by means of particle image velocimetry. The experiments were conducted at temperatures ranging from 40 to 60 °C and impeller speeds ranging from 40 to 140 rpm. In all cases, the flow regime was laminar or in the transition region. We also used computational fluid dynamics simulations to describe the behaviour of the mixer, validating the results experimentally with good agreement. We used the numerical results to obtain information on the performance of the mixer, determining the locations and size of vigorous agitation zones and the local effect of the holes present on the impeller blades. The power curves of the mixer were obtained, and the mixer efficiency in terms of power consumption was found to be similar to other impellers used to mix highly viscous non-Newtonian fluids

These - Are - The Breaks : A Roundtable Discussion on Teaching the Post-Soul Aesthetic

We met at Duke University - mid-summer, in the mid Atlantic, at mid-campus - to talk about teaching courses that focused on the post-soul aesthetic. We met outside the John Hope Franklin Center, and soon enough we five youngish black professors were walking a hallway towards a conference room near the African and African American Studies program. Not at all surprisingly, the walls of the hallway were lined with framed photographs of the esteemed John Hope Franklin at various stages throughout his long and storied career. For me, given the topic I was about to raise among these professional colleagues, walking that hallway was something like running a gauntlet: Franklin\u27s career is one of continued, sustained Negro uplift, as the photomontage of him documents. The post-soul aesthetic, on the other hand, critiques and questions certain black assumptions and traditions, and most professors who teach the art and literature of this post-civil rights movement aesthetic must, to apprehend the course material, assume a peculiar, if not precarious, pedagogical stance in the classroom, one that respects careers like Dr. Franklin\u27s, but also constructively interrogates - and sometimes explodes - the very presumptions and precepts on which such a career stands