Incomplete stent expansion (IncSE) is occasionally seen in flow-diversion (FD) treatment of intracranial aneurysms; however, its haemodynamic consequences remain inconclusive. Through a parametric study, we quantify the aneurysmal haemodynamics subject to different severities of IncSE occurring in different portions of the stent. Two patient cases with IncSE confirmed in vivo were studied. To investigate a wider variety of IncSE scenarios, we modelled IncSE at two severity levels respectively located in the proximal, central, or distal segment of a stent, yielding a total of 14 treatment scenarios (including the ideal deployment). We examined stent wire configurations in 14 scenarios and resolved aneurysm haemodynamics through computational fluid dynamics (CFD). A considerable degradation of aneurysm flow-reduction performance was observed when central or distal IncSE occurred, with the maximal elevations of the inflow rate (IR) and energy loss (EL) being 10% and 15%. The underlying mechanism might be the increased resistance for flow to remain within the FD stent, which forces more blood to leak into the aneurysm sac. Counter-intuitively, a slight reduction of aneurysm inflow was associated with proximal IncSE, with the maximal further reduction of the IR and EL being 5% and 8%. This may be due to the disruption of the predominant parent-artery flow by the collapsed wires, which decreased the strength and altered the direction of aneurysmal inflow. The effects of IncSE vary greatly with the location of occurrence, revealing the importance of performing individualised, patient-specific risk assessment before treatment.

Food processing can generate large amounts of carbohydrate-rich waste that inevitably has environmental and social impacts. Meanwhile, certain heterotrophic marine microorganisms, including algae and thraustochytrids, have the potential to convert carbohydrate-rich substrates into oil-rich biomass over relatively short time frames. To assess the merits of this apparent synergy, an initial conceptual process was developed based on the use of raw potato processing waste as feed in an algal bioreactor to produce bio-oil for further use within the food industry. A practical flowsheet was established with a conventional 200 kL bioreactor whereby the unit processes were identified, the mass balance developed, and estimates made of the various material and energy demands. These inputs were used to develop a baseline life cycle assessment (LCA) model and to identify opportunities for reducing environmental impacts. With the functional unit (FU) being 1 tonne cooking oil, the baseline configuration had a greenhouse gas (GHG) footprint of 2.4 t CO2-e/FU, which is comparable to conventional process routes. More detailed LCA revealed that electricity for stirring the bioreactor contributed approximately 78% of the total GHG footprint. By adjusting the operating conditions, the most promising scenario produced 0.85 t CO2-e/FU—approximately four times less than the conventional process—and shows the potential advantages of applying LCA as a tool to develop and design a new production process.

Flow-diverting (FD) stents are one of three common modes of treating intracranial aneurysms, yet knowledge of their effect on haemodynamics is incomplete. We used particle image velocimetry (PIV) to measure spatially-varying velocity of blood-analogue fluid within a patient-specific aneurysm model, and compared the observed flow behaviour to predictions from a computational fluid dynamics (CFD) model. In PIV experiments we characterised the flow on multiple cross-sections for three different arterial flow-rates (150, 250, 400 mL/min) after deployment of a commercially-available FD stent. Our flow-diverting (FD) stent model for CFD simulation was constructed using a permeability adapted from the literature. Aneurysmal haemodynamics without the FD stent treatment provided good similarities between CFD and PIV results, and the results with a Silk stent treatment also provided acceptable concordances, thereby validating the use of CFD as a convenient and flexible tool for investigating intra-aneurysmal flow dynamics after FD stent treatment. Furthermore, for the first time, the porous-medium FD model stent was validated to be both efficient and effective to predict the flow-diversion effects of a FD stent treatment with a patient-specific intracranial aneurysm. Through the qualitative and quantitative comparison of CFD predictions against the experimental outcomes, this study gives confidence for future studies on aneurysmal haemodynamics and FD stent treatment effects to use CFD simulation. (C) 2019 Elsevier Ltd. All rights reserved.

Modelling flow-diverting (FD) stents as porous media (PM) markedly improves the efficiency of computational fluid dynamics (CFD) simulations in the study of intracranial aneurysm treatment. Nonetheless, the parameters of PM models adopted for simulations up until now were rarely calibrated to match the represented FD structure. We therefore sought to evaluate the PM parameters for a representative variety of commercially available stents, so characterising the flow-diversion behaviours of different FD devices on the market. We generated fully-resolved geometries for treatments using PED, Silk+, FRED, and dual PED stents. We then correspondingly derived the calibrated PM parameters—permeability (k) and inertial resistance factor (C2)—for each stent design from CFD simulations, to ensure the calibrated PM model has identical flow resistance to the FD stent it represents. With each of the calibrated PM models respectively deployed in two aneurysms, we studied the flow-diversion effects of these stent configurations. This work for the first time reported several sets of parameters for PM models, which is vital to address the current knowledge gap and rectify the errors in PM model simulations, thereby setting right the modelling protocol for future studies using PM models. The flow resistance parameters were strongly affected by porosity and effective thickness of the commercial stents, and thus accounted for in the PM models. Flow simulations using the PM stent models revealed differences in aneurysmal mass flowrate (MFR) and energy loss (EL) between various stent designs. This study improves the practicability of FD simulation by using calibrated PM models, providing an individualised method with improved simulation efficiency and accuracy.

Multivariate image analysis was used to estimate the arsenic concentrations in froths resulting from the flotation of different mixtures of realgar and orpiment particles in a laboratory batch flotation cell. The realgar floated rapidly and in excess of 90% of the mineral could be recovered after 2 minutes, whereas only 48–75% of the orpiment could be recovered in the same time. Textural features, based on grey level co-occurrence matrices (GLCMs), local binary patterns (LBPs), steearable pyramids and textons were used in the analysis. Random forest models could explain approximately 71–77% of the variance in the arsenic using either of the texton, steerable pyramid or LBP features. This was considerably better than what could be obtained with the GLCM features. Monitoring of froth flotation cells was simulated with the batch data. The texton textural features were the most discriminatory with regard to detecting changes in the arsenic content of the froth.

BACKGROUND:Compacting a flow-diverting (FD) stent is an emerging technique to create a denser configuration of wires across the aneurysm ostium. However, quantitative analyses of post-stenting haemodynamics affected by the compaction level of different stent sizes remain inconclusive.OBJECTIVE:To compare the aneurysmal haemodynamic alterations after virtual FD treatments with different device diameters at different compaction ratios.METHODS:We virtually implanted three sizes of FD stent, with each size deployed at four compaction ratios, into two patient aneurysms previously treated with the Silk+FD-one successful case and the other unsuccessful. Wire configurations of the FD in the 24 treatment scenarios were examined, and aneurysmal haemodynamic alterations were resolved by computational fluid dynamics (CFD) simulations. We investigated the aneurysmal flow patterns, aneurysmal average velocity (AAV), mass flowrate (MF), and energy loss (EL) in each scenario.RESULTS:Compactions of the stent in the successful case resulted in a greater metal coverage rate than that achieved in the unsuccessful one. A 25% increment in compaction ratio further decreased the AAV (12%), MF (11%), and EL (9%) in both cases (average values). The averaged maximum differences attributable to device size were 10% (AAV), 8% (MF), and 9% (EL).CONCLUSIONS:Both stent size and compaction level could markedly affect the FD treatment outcomes. It is therefore important to individualise the treatment plan by selecting the optimal stent size and deployment procedure. CFD simulation can be used to investigate the treatment outcomes, thereby assisting doctors in choosing a favourable treatment plan.

Using a porous medium as a computational model for the real flow-diverting (FD) stent in computational fluid dynamics (CFD) improves the simulation efficiency. Adjustment of permeability level of the applied porous medium can result in various flow-resistance effects, which impact on the flow dynamics around and inside the aneurysm dome. Moreover, diversity in patient-specific aneurysm geometry also contributes to the difference in both the resistance force induced by the FD device and the aneurysmal haemodynamics. However, few studies have discussed the relationship between the setting of permeability and the intra-aneurysmal haemodynamics with different aneurysms. In this study, in order to distinguish FD stents with different porosity, we simulated the porous medium stent with a range of permeabilities, respectively in a successfully treated aneurysm and an unsuccessfully treated one observed clinically. Haemodynamic parameters of intra-aneurysm mass flow rate (MFR) and energy loss (EL) were calculated to investigate their response to the alteration of permeability, as well as to the aneurysm morphology. In comparison between the two patient-specific aneurysms, we found marked changes (70 and 40 % in MFR, 40 and 35 % in EL, respectively with successful and unsuccessful cases) in the aneurysmal haemodynamics as the porosity level of the implanted FD stents was increased by a factor of 25. The simulation results showed considerable differences in the relative flow- diversion between the clinically observed successful and unsuccessful case (up to 30 % in MFR and 45 % in EL). This study will help to provide future FD modellers with information about suitable selection of permeability level for different aneurysm cases.

The flow-diverting (FD) stent has become a commonly used endovascular device to treat cerebral aneurysms. This discourages blood from entering the aneurysm, thereby reducing the likelihood of aneurysm rupture. Using computational fluid dynamics (CFD) to simulate the aneurysmal haemodynamics after FD treatment could help clinicians predict the stent effectiveness prior to the real procedure in the patient. As an alternative to modelling the stent as a fine wire mesh, modelling the FD stent as a porous medium was established to save computational time, and has also been proved capable of predicting the same haemodynamics as obtained using the real FD stent geometry. The flow resistance effect of a porous-medium stent may differ with respect to its morphology or permeability; however, the flow resistance effect after adjusting these parameters had not been clarified. In this study, we analysed the haemodynamic changes caused by alterations of porous-medium thickness and permeability, thereby providing future porous-medium stent simulations with important information on the respective parametric sensitivities. We found significant sensitivity to permeability. Results were insensitive to thickness when permeability was adjusted beforehand to compensate. We also compared our results with observations from an in-vitro model, and found good agreement. This supports adoption of porous-medium models in future work.

Flow-diverting (FD) stent implantation has become a popular treatment mode for intracranial aneurysms (IAs). The stent wire configurations post-treatment can greatly affect the treatment outcomes. However, it remains a challenge to predict the stent wire configurations prior to a treatment. In this study, we propose to compare the FD stent structures and wire configurations between treatments with FD stents of different diameters being deployed at different compaction levels. We adopted a recently reported spring–mass model to virtually implant FD stents of three diameters — 4.0, 4.5, and 5.0 mm, with each diameter modelled at three compaction levels (no compaction, a low compaction, and a high compaction) — into two clinically observed IAs: one successfully treated and the other unsuccessfully treated previously with a single FD stent. We then examined the morphological differences in stent wire configurations across different treatment scenarios, and quantified the porosity achieved in each such scenario. This led us to two main findings. Firstly, at the same compaction level, the porosity differences attributable to device diameter were limited (SD < 2%). Secondly, stent deployment with some compaction could effectively reduce the FD wire porosity within the aneurysm ostium — a low compaction reduced the porosity by around 10%, and a high compaction reduced the porosity by around 30%. The FD stent structures observed from virtual deployment can be used in the subsequent aneurysmal haemodynamic simulations. Thus, the virtual stent deployment strategy, together with the stent compaction measurement and simulation technique presented in this study, may contribute to research into flow-diversion treatment planning.

Although flow-diversion (FD) treatment has been proven to be able to induce intracranial aneurysm (IA) occlusion, clinical follow-ups reported that a number of patients may still suffer from delayed IA rupture or incomplete aneurysm occlusion post-treatment. Complete aneurysm occlusion is believed to be associated with favourable haemodynamic alteration post-treatment, which may be greatly affected by the selection of device size and quantity, as well as the FD deployment procedure. However, clinicians have to choose and deploy the FD relying on their experience, since no post-stenting haemodynamic information is generally available to them prior to a specific treatment. In this study, using a virtual FD deployment technique and computational fluid dynamics method, we demonstrate and compare the haemodynamic changes after virtual FD treatments using a variety of prospective treating strategies.

OBJECTIVES:Tremor may be expected to interfere with the performance of fine motor tasks such as surgery. While tremor is readily quantified in inactive subjects, it is more challenging to measure tremor as the subjects perform complex tasks. The objective of this work was to quantify tremor during the performance of a realistic simulated surgery.METHODS:Our novel surgical simulator incorporates a force sensor that allows identification and quantification of the intraoperative effects of tremor on the manipulandum. We have collected preliminary data from trainees and experienced surgeons carrying out multiple simulated anastomoses on silicone vessels, mimicking a procedure such as distal coronary anastomosis. We calculated transient and overall tremor intensity, and tested for a hypothesized 'learning effect'.RESULTS:Several of the recordings of intraoperative force data manifested distinctive features corresponding to substantial oscillation in the range of 8-12 Hz. We attribute this to enhanced physiological tremor. These early results indicate a significant reduction in the transmission of surgeon's tremor to the operative field from the first attempt to later attempts (P = 0.039, standardized effect size = 0.91), which may be associated with increasing confidence.CONCLUSIONS:This new method does not just quantify tremor, but quantifies the transmission of tremor to a manipulandum in the operative field during high-fidelity simulated coronary surgery. This may be used to assess and provide feedback on the performance of trainees and experienced surgeons, along with other fields in which fine motor skills are of vital importance.

The nature of attractive particulate networks, yield stresses, and normal stress differences is systematically reviewed, each in terms of the relevant definitions, underlying mechanisms, and current measurement techniques. With this foundation, experimental observations of normal stress differences in some suspensions and colloidal systems are surveyed, along with constitutive models that allow for normal stress differences to arise prior to yielding. Yield stresses are a hallmark of attractive colloidal systems and vital in their processing. In contrast, little attention has been given to the role of normal stress differences in these systems. The presence or absence of normal stress differences necessarily affects the isotropy of the normal stress field through the solid particulate phase (treated as a continuum), in turn affecting estimation of yield stress. Given the importance of yield stresses in dealing with practical industrial problems, and in understanding fundamental behaviours, it is important to ensure that yield measurements can be relied upon.

Froth flotation is an exceedingly complex physicochemical process. The convenience of distilling much of the complexity of the particle-bubble interactions into a single parameter has led to the continuing popularity of the classical 'induction time' to quantify the threshold for particle-bubble attachment to occur. Despite this popularity and the simplicity of the concept, there is no single universal method of evaluating the induction period.In this paper, we begin with a critical review of the available techniques for estimating the induction period. These are: back-calculation from experimental (micro)flotation tests; pushing a particle toward a stationary bubble (or vice versa) using an atomic force microscope (AFM); pushing a bubble toward a stationary bed of particles in the 'Induction Timer'; pushing a bubble toward a stationary solid surface using the 'integrated thin film drainage apparatus' (ITFDA); and dropping particles onto a submerged stationary bubble using the 'Milli-Timer' device. Each one of these methods has advantages and disadvantages, and the best choice depends on the application.In the experimental section, we present quantitative comparison of the induction periods estimated using two different techniques, namely the Induction Timer and the Milli-Timer. The same particles were tested in each device, under the same conditions. It was found that by tuning the operation of the particle pick-up device, similar estimates of induction period could be obtained to the estimates made by direct observation with the Milli-Timer. In the former device a bubble is driven toward a particle bed at a controlled rate, whereas in the latter a particle's motion is governed by the hydrodynamics. The potential to match these presents an intriguing prospect for better understanding the bubble-particle interaction, and the possibility to 'calibrate' the simpler Induction Timer against direct observations. (C) 2015 Elsevier Ltd. All rights reserved.

Processing of minerals and metals involves phenomena functioning over a wide range of length scales. Equipment is generally large in order to process the required large flow rates, yet achieving the functional requirements of the operation requires successful execution of micro-scale processes. Multi-scale modelling approaches to process simulation are firstly reviewed, and similarities and differences compared with the more common multi-scale approaches to materials modelling are given.The sequential multi-scale method is then illustrated with reference to the mineral flotation process. In this case, multi-phase CFD (computational fluid dynamics) models of large-scale cells has been complemented by micro-scale CFD simulations of bubble-particle collision, and experimental and modelling studies of the bubble-particle attachment process itself.Finally, other examples of sequential multi-scale modelling are summarised, highlighting progress on unit operations including aluminium reduction cells, leaching heaps, copper solvent-extraction settlers, and fluidised beds. Crown Copyright (C) 2015 Published by Elsevier Ltd. All rights reserved.

BACKGROUND:Tremor is a major impediment to performing fine motor tasks, as in microsurgery. However, conventional measurements do not involve tasks representative of microsurgery.METHOD:We developed a low-cost surgical simulator incorporating a force transducer capable of detecting and quantifying the effects of tremor upon high-fidelity silicone replicas of cardiac vessels and substrate muscle. Experienced and trainee surgeons performed simulated anastomoses on this rig. We characterized procedures in terms of tremor intensity, based on Lomb-Scargle periodograms.RESULTS:Distinctive force oscillations occurred at 8-12 Hz, characteristic of enhanced physiological tremor, yielding peaks in power spectral density. These early results suggest a significantly lower transmission of tremor to the operative field by the experienced surgeon in comparison to the trainees.CONCLUSIONS:This new device quantifies the action of tremor upon a manipulandum during a complex task, which may be used for assessment and providing feedback to trainee surgeons. Copyright © 2015 John Wiley & Sons, Ltd.

There has long been speculation as to whether some particle shapes are more 'floatable' than others, which might be due to differences in the induction period required to achieve attachment between the particles and the air bubbles in the pulp. To resolve this, we used the Milli-Timer apparatus to directly observe the process of particle-bubble interaction and attachment by means of a magnified, high-speed video recording, thus providing a direct measure of the induction period for attachment.To assess the influence of particle shape on induction time we used two varieties of methylated borosilicate glass particles - spheres and angular 'frit' - in a range of tightly-sized fractions. Other factors that could affect the induction time, such as the polar angle of sliding commencement, and approach velocity, are accounted for using multiple nonlinear regression.Our results illustrate the importance of particle shape on induction period, with angular particles exhibiting induction periods that were an order of magnitude lower than those of spheres. Furthermore, the induction period was seen to decrease with increasing particle velocity, or kinetic energy on approach, but increased as the trajectory approached the limit of just grazing the bubble. These results indicate that attention should be paid to the shape of particles obtained from the grinding operation, besides particle size. Crown Copyright (C) 2014 Published by Elsevier Ltd. All rights reserved.

In this investigation, mixtures of realgar and orpiment particles were floated in a laboratory batch flotation systems and multivariate image analysis was used to estimate the arsenic content in the froths. The analysis was based on the froth colour, as well as extraction of three groups of textural features, namely those based on grey level co-occurrence matrices, wavelets and local binary patterns. Collectively, these features provided better information on the arsenic content of the froths than any one of the individual groups of features. Partial least squares models could explain approximately 78% of the variance in the arsenic by using all the features simultaneously. The colour content, particularly the green component in the red-green-blue (RGB) features, provided almost as much information as the texture-base features.

The drag coefficients for a prolate ellipsoid moving along its axis of symmetry, in the creeping flow regime, either towards or away from a plane surface are calculated. The plane surface may have either a no-slip boundary condition, corresponding to a solid wall, or a perfect slip condition, corresponding to a free surface.First the analytical solutions are employed to obtain exact values for the full range of feasible particle-plane gaps. Next, simple exact formula for the asymptotes at small and large gaps are presented. Finally, some convenient approximate formula are obtained that may be used across the full range of gaps. Crown Copyright (C) 2014 Published by Elsevier Ltd. All rights reserved.