Downstream Particle Research Articles

Numerical Simulation of the Melting of Solid Particles in Thermal Convection with a Modified Immersed Boundary Method

A new immersed boundary method is proposed for the numerical simulation of the melting of solid particles in its own liquid at a high temperature. The main feature of the new method is the use of the modified direct-forcing immersed boundary method for the solution of the flow field and the sharp-interface immersed boundary method for the temperature field. The accuracy of the proposed method is validated via three problems: the sedimentation of a non-melting particle, the melting of a fixed particle under mixed thermal convection, and the sedimentation of a melting particle. The method is then applied to the investigation of the effects of various parameters, the particle interactions and the particle shape on the particle melting time. A correlation for the melting time of a circular particle in forced thermal convection is established as a function of the Reynolds, Prandtl, and Stefan numbers. The melting time of a particle in mixed thermal convection first increases and then decreases, as the Grashof number increases. The effects of the particle interactions on the melting time are complicated due to the natural convection between two particles. The sufficiently strong natural convection can even render the downstream particle melt faster than the single particle. For the same particle area, the elliptic particle with the aspect ratio being around 1.4 melts most slowly.

Study on the Morphological Distribution and Modeling Methods of River Particles in Upstream and Downstream Sections.

This study investigates the morphological evolution of river particles and their mechanical behavior during sediment transport. River particles exhibit distinct shape differences between upstream and downstream sections, with particles becoming progressively rounded downstream. The rounding process is quantitatively described using morphological indices. The analysis reveals upstream particles are more angular, while downstream particles become increasingly rounded due to erosion and abrasion, modeled by a unified abrasion function. The Loop subdivision method effectively simulates this gradual rounding process. Additionally, the Discrete Element Method (DEM) calculates the natural angle of repose for particles with varying erosion levels, showing angles ranging from 38.2° for angular particles to 34.4° for rounded particles, closely matching field observations. The numerical results effectively demonstrate the interlocking effect caused by particle morphology. This research enhances the understanding of sediment transport dynamics and provides a robust framework for modeling particle shape evolution.

Vesicle Picker: A tool for efficient identification of membrane protein complexes in vesicles

Electron cryomicroscopy (cryo-EM) has recently allowed determination of near-atomic resolution structures of membrane proteins and protein complexes embedded in lipid vesicles. However, particle selection from electron micrographs of these vesicles can be challenging due to the strong signal contributed from the lipid bilayer. This challenge often requires iterative and laborious particle selection workflows to generate a dataset of high-quality particle images for subsequent analysis. Here we present Vesicle Picker, an open-source program built on the Segment Anything model. Vesicle Picker enables automatic identification of vesicles in cryo-EM micrographs with high recall and precision. It then exhaustively selects all potential particle locations, either at the perimeter or uniformly over the surface of the projection of the vesicle. The program is designed to interface with cryoSPARC, which performs both upstream micrograph processing and downstream single particle image analysis. We demonstrate Vesicle Picker’s utility by determining a high-resolution map of the vacuolar-type ATPase from micrographs of native synaptic vesicles (SVs) and identifying an additional protein or protein complex in the SV membrane.

Particle formation: Promise and challenges

Particle formation establishes fundamental particle attributes at the initiation of an overall particle production process. These attributes include particle size distribution, particle morphology, crystal form, and defect level. These fundamental properties, in turn, affect downstream particle processing and product performance properties, including rate of drying, filterability, flowability, caking tendency, rate of dissolution, and for biologically active products bioavailability. Almost always, the goal is that the properties established at formation will provide excellent performance all the way through downstream processing, product formulation, and ultimate use of the product. However, meeting this goal is often not possible for a variety of reasons. First, it may be difficult, prohibitively expensive, or even impossible to achieve the desired properties during formation. Second, there are often conflicting requirements at different stages of production and use. For example, large equant particles may be desired for good filterability and flowability through downstream process steps, but very small particles may be required in the ultimate product application. Examples from the chemical and pharmaceutical industries are presented: both cases successfully producing particles with properties meeting the needs throughout the chain of downstream processing and final application, as well as cases where it was impossible to meet those requirements. For the latter, the additional processing or adaptations required for the product to succeed are outlined. The focus here is on additive particle formation, e.g. crystallization and precipitation from solution, and not subtractive particle formation, e.g. milling. Legacy of Reg DaviesI was fortunate enough, as a budding industrial crystallization engineer, to be invited by Reg to join the newly formed PARticle Science And Technology PARSAT group at DuPont. Reg recognized and documented the importance of particle technology to a large, diverse chemical and materials company like DuPont and PARSAT was to become a leading industrial particle technology group. Reg's vision was to combine the fundamental particle unit operations into a unified, comprehensive technology organization that would address the formation and processing of particles from process concept through end use.This paper describes the first step in many particle processes: particle formation. Reg's legacy vis a vis particle formation is the recognition that particle formation is a critical, foundational process in an overall process train that ultimately produces useful particulate products and intermediates, but that particle formation is nonetheless but one part of the overall process. It may be able to produce particles exactly as needed for end use performance, or additional processes may be needed to tailor particles for their ultimate use. In addition, intermediate processes may be required to preserve useful properties developed during formation but subject to degradation in subsequent operations.Finally, Reg served as inspiration and mentor for everyone in his orbit, and we are far better scientists and engineers for it.

Spatiotemporal Analysis of Particle Spread to Assess the Hybrid Particle-Flow CFD Model of Radioembolization of HCC Tumors.

Computational fluid dynamics (CFD) models can potentially aid in pre-operative planning of transarterial radioactive microparticle injections to treat hepatocellular carcinoma, but these models are computationally very costly. Previously, we introduced the hybrid particle-flow model as a surrogate, less costly modelling approach for the full particle distribution in truncated hepatic arterial trees. We hypothesized that higher cross-sectional particle spread could increase the match between flow and particle distribution. Here, we investigate whether truncation is still reliable for selective injection scenarios, and if spread is an important factor to consider for reliable truncation. Moderate and severe up- and downstream truncation for selective injection served as input for the hybrid model to compare downstream particle distributions with non-truncated models. In each simulation, particle cross-sectional spread was quantified for 5-6 planes. Severe truncation gave maximum differences in particle distribution of ∼4-11% and ∼8-9% for down- and upstream truncation, respectively. For moderate truncation, these differences were only ∼1-1.5% and ∼0.5-2%. Considering all particles, spread increased downstream of the tip to 80-90%. However, spread was found to be much lower at specific timepoints, indicating high time-dependency. Combining domain truncation with hybrid particle-flow modelling is an effective method to reduce computational complexity, but moderate truncation is more reliable than severe truncation. Time-dependent spread measures show where differences might arise between flow and particle modelling. The hybrid particle-flow model cuts down computational time significantly by reducing the physical domain, paving the way towards future clinical applications.

Application of Deep Learning in Predicting Particle Concentration of Gas–Solid Two-Phase Flow

Particle concentration is an important parameter for describing the state of gas–solid two-phase flow. This study compares the performance of three methods, namely, Back-Propagation Neural Networks (BPNNs), Recurrent Neural Networks (RNNs), and Long Short-Term Memory (LSTM), in handling gas–solid two-phase flow data. The experiment utilized seven parameters, including temperature, humidity, upstream and downstream sensor signals, delay, pressure difference, and particle concentration, as the dataset. The evaluation metrics, such as prediction accuracy, were used for comparative analysis by the experimenters. The experiment results indicate that the prediction accuracies of the RNN, LSTM, and BPNN experiments were 92.4%, 92.7%, and 92.5%, respectively. Future research can focus on further optimizing the performance of the BPNN, RNN, and LSTM to enhance the accuracy and efficiency of gas–solid two-phase flow data processing.

Three-Dimensional Kinetic Simulations of Carbon Backsputtering in Vacuum Chambers from Ion Thruster Plumes

Gridded ion thrusters are tested in ground vacuum chambers to verify their performance when deployed in space. However, the presence of high background pressure and conductive walls in the chamber leads to facility effects that increase uncertainty in the performance of the thruster in space. To address this issue, this study utilizes a fully kinetic simulation to investigate the facility effects on the thruster plume. The in-chamber condition shows a downstream neutral particle density 100 times larger than the in-space case due to ion neutralization at the wall and limited vacuum pump capability, resulting in a significant difference in the density and distribution of charge-exchange ions. The flux, energy, and angle of charge-exchange ions incident on the chamber wall are found to be altered by the electron sheath, which can only be simulated by the fully kinetic approach, as opposed to the conventionally used quasi-neutral Boltzmann approach. We also examine the effect of backsputtering, another important facility effect, and find that it does not necessarily require a fully kinetic simulation as the incident flux and energy of the sampled charge-exchange ion are negligibly small. Finally, we demonstrate that the carbon deposition rate on the thruster is significantly influenced by the angular dependence of the sputtered carbon, with a nearly 50% effect.

The effects of Stefan flow on the flow surrounding two closely spaced particles

The aim of the work was to study the effects of neighboring particles with uniform Stefan flow in particle–fluid flows. Particle-resolved numerical simulations were carried out for particles emitting a uniform Stefan flow into the bulk fluid. The bulk fluid was uniform and isothermal. The Stefan flow volume emitted from the two particles is equal, such that it represents idealized conditions of reacting particles. Particles were located in tandem arrangement and particle distances were varied between 1.1 and 10 particle diameters (1.1≤L/D≤10). Three particle Reynolds numbers were considered during the simulations (Re=2.3,7 and 14), which is similar to our previous studies. Three Stefan flow velocities were also considered during simulations to represent inward, outward, and no Stefan flow. The drag coefficient of the particles without Stefan flow showed that the results fit with previous studies on neighbor particle effects. When the particle distance is greater than 2.5 diameters (L/D>2.5), the effects of Stefan flow and neighboring particles are independent of each other. I.e. an outward Stefan flow decreases the drag coefficient (CD) while an inward Stefan flow increases it and the upstream particle experience a higher CD than the downstream particle. When L/D≤2.5, the effect of Stefan flow is dominant, such that equal and opposite pressure forces act on the particles, resulting in a repelling force between the two neighboring particles. The pressure force showed a large increase compared to the viscous force at these distances. The effect of Stefan flow is weakened at higher Reynolds numbers. A model was developed for the calculation of the drag coefficient. The model, which reproduce the results from the numerical simulations presented above, is a product of independent models that describe the effects of both neighboring particles and two distinguished effects of the Stefan flow.

Effective Suppression of LSCF Air Electrode Degradation by Air Cleaning

The performance degradation of air electrodes in solid oxide cells is strongly affected by impurities such as sulfur dioxide. Air filters are applied in most fuel cell systems to avoid poisoning and subsequent degradation of fuel cell stacks [1, 2]. Filtering solutions designed for the high air purity demands of proton-exchange membrane fuel cells (PEMFC) are commercially available.This study evaluates the applicability of such a filter for the LSCF air electrode in an electrolyte-supported SOC. Three different air qualities were applied in single-cell tests to distinguish the degradation mechanism caused by the ambient air impurities from the intrinsic aging phenomena of the cell. The utilized gases are (i) compressed air, (ii) filtered compressed air, and (iii) synthetic air. The compressed air (i) consists of ambient air supplied by a conventional compressor with a downstream particle filtering and oil removal system. In (ii), an additional filter layer was applied between the mass flow controller and the cell housing to filter the compressed air. The filter consisted of specially modified activated carbons designed to remove harmful gases and was operated at ambient temperature and pressure. The active area of the filter was 0.95 cm², corresponding to an air velocity of 0.088 m s-1 at an airflow rate of 500 sccm. The synthetic air is a mixture of 21% oxygen (99.95% O2, the main impurities are H2O and Ar) and 79% nitrogen (99.999% N2) provided by the Air Liquide company. Symmetrical cells based on a 3YSZ substrate coated with GDC buffer layers and LSCF electrode applied on both sides with an active surface area of 1 cm2 were applied in this study.Figure 1 shows the polarization resistance of the LSCF electrode operated in different types of air. Similar to previous reports [3-5], a significant degradation rate is recorded within the first 300 hours of operation. Filtering the air reduces the degradation rate significantly. The performance degradation of the cell with filtered air is comparable to that of the cell with synthetic air, demonstrating the capability of the filter to adsorb the gas impurities. Fig. 1 polarization resistance of the LSCF-cathode of 3 symmetrical cells operated at 750 °C with unfiltered and filtered compressed air and synthetic air, respectively.To better understand the degradation mechanism in the LSCF air electrode, we analyzed the impedance spectra measured during aging tests using the distribution of relaxation times (DRT) and then a complex nonlinear least squares (CNLS) fit. This contribution discusses differences in the temporal development of air electrode impedance and degradation mechanisms related to surface poisoning and subsequent changes in LSCF bulk.Keywords: LSCF air electrode, Impedance spectra, Degradation mechanisms, Air filtration.[1] M. Harenbrock, A. Korn, A. Weber, E. Hallbauer, in, SAE Technical Paper, 2020.[2] M. Harenbrock, E. Hallbauer, T. Heilmann, M. Hanselmann, ATZheavy duty, 14 (2021) 34-37.[3] C. Endler, A. Leonide, A. Weber, F. Tietz, E. Ivers-Tiffée, Journal of the Electrochemical Society, 157 (2010) B292-B298.[4] C. Endler-Schuck, A. Leonide, A. Weber, S. Uhlenbruck, F. Tietz, E. Ivers-Tiffée, Journal of Power Sources, 196 (2011) 7257-7262.[5] C. Endler-Schuck, J. Joos, C. Niedrig, A. Weber, E. Ivers-Tiffée, Solid State Ionics, 269 (2015) 67-79. Figure 1

Experiments and modelling of biomass pulverisation in swirling and non-swirling bluff body-stabilised turbulent annular flows

Deeper insights into particle loading have practical significance in applications particularly when this affects fuel-oxidiser mixing and flame stabilisation, as occurs in pulverised fuel (biomass) combustion systems. The underlying particle flow and dispersion characteristics not only play a crucial role in controlling overall combustion performance but can also impact emissions. A fundamental understanding of particle flow dynamics and dispersion behaviour for raw pulverised biomass, under non-swirling and swirling conditions need further systematic investigation to better understand the interplay between swirling and non-swirling bluff-body stabilised recirculation zones and particles emitted from a centralised jet. This work uses Particle Image Velocimetry (PIV) with three-dimensional multi-phase simulations based on the Discrete Phase Model (DPM) and Reynolds Stress Model (RSM) to investigate the flow and dispersion characteristics in confined flows typical of many practical combustors. Raw pulverised biomass-laden is introduced through a central turbulent jet (Rej = 4500 and 7800) and also subjected to turbulent annular flows (Res = 35,500), both non-swirling (S = 0) and swirling conditions (S = 0.3). Simulations are first validated against Constant Temperature Anemometry (CTA) resolved inlet boundary conditions and flow field PIV data under similar conditions.Results show that when a pulverised biomass-laden central jet interacts with a surrounding turbulent annular flow (non-swirling, swirling) the presence of a bluff-body based recirculating zone (BB-RZ) leads to biomass particle entrainment (pick up) and their recirculation over the bluff-body before being dispersed further downstream. Under non-swirling conditions, a significant 35% decrease in the mean particle axial velocity is measured coupled with an even more substantive 177% increase in turbulent fluctuation along the centreline. These findings are indicative of intense upstream (x/D ≈ 0.64) turbulent mixing and more intense particle dispersion into a BB-RZ. For swirling annular flow conditions near the end of the BB-RZ, the interaction between a biomass-laden central jet and the annular flow is comparatively weaker in the upstream region relative to non-swirling conditions. However, swirl significantly enhances downstream particle dispersion and lateral spread as reflected by a 254% hike in the mean particle radial velocity. Numerical predictions show that for the same particle loading ratio, but different (higher and lower) Reynolds number of a central particle-laden jet (i.e., the carrier gas), the conditions at relatively lower central jet Reynolds number allow better particle recirculation in BB-RZ as well as enhancing downstream lateral particle dispersion and entrainment, compared to a higher Reynolds number in the central jet. Outcomes from this investigation may have implications on the design and operation of pulverised (solid) fuel combustors if operated on renewably sourced biomass rather than traditional fossil fuels.

Study of red blood cells and particles in stenosed microvessels using coupled discrete and continuous forcing immersed boundary methods

A computational study of the blood flow in a stenosed microvessel is presented using coupled discrete ghost-cell and continuous-forcing immersed boundary methods. This study focuses on studying platelet behaviors near the stenosis with deformable red blood cells (RBCs). The influence of varying hematocrit, area blockage, stenosis shape, and driving force on flow characteristics, RBCs, and particle behaviors is considered. Distinct flow characteristics are observed in stenosed microvessels in the presence of RBCs. The motion of RBCs is the major cause of time-dependent oscillations in flow rates, while the contribution of particles to the fluctuations is negligible. However, this effect decreases when the stenosis is elongated in the axial direction. Interestingly, as the hematocrit level increases, downstream particles move closer to the vessel wall due to the enhanced shear-induced lift force resulting from the interaction among RBCs and particles. Furthermore, it is observed that geometrical changes in the stenosis have a more significant impact on the axial profile of particle concentration compared to changes in hematocrit or driving force. An asymmetric stenosis leads to asymmetric profiles in the flow velocity and the distribution of cells and particles due to the geometric focusing effect of the stenosis. There is no significant change in flow rates until a blockage of 0%–50%, but a sudden increase in the root mean square of flow rates occurs at an 80% blockage. This study contributes to our understanding of the rheological behaviors of RBCs and rigid particles in a stenosed microvessel under various hemodynamic conditions.

Local hydraulic jump effects on sediment deposition in open-channel flume experiments

When a river channel is narrow, bifurcated, or intersected, or when extreme weather or geological disasters cause shed rock masses to occupy a river flood channel, local hydraulic jumps may develop in the channel. Natural disasters such as landslides, floods, and debris flows occur upstream, will result in large transport rate of large-sized gravel particles. Those particles may be blocked in hydraulic jump areas, causing river channel water depth to rise. In this study, the effect of local hydraulic jumps on the sediment deposition rate was investigated in flume experiments. The ratio of upstream and downstream Froude numbers, particle size, Sediment supply intensity, and flow discharge all affected the sediment deposition rate. With increases in the ratio of upstream and downstream Froude numbers, particle size, and sediment supply intensity, the sediment deposition rate increased. The sediment deposition rate decreased with an increase in flow discharge. Approach hydraulic conditions and particle properties jointly determined the sediment deposition rate in a hydraulic jump section, and an empirical formula was developed using those parameters to calculate the sediment deposition rate. Thus, to identify risks and prevent disasters in mountain rivers, local changes in hydraulic conditions and particle properties need to be jointly evaluated.

Effects of physical properties of supercritical water on coarse graining of particle cluster

The coarse graining of particle cluster is of great significance to the study of a fluidized bed. The effects of variations in the physical properties of supercritical water on the coarse graining of particle cluster are investigated in this work. The drag coefficient distributions of the particle cluster are not influenced by the physical properties. However, the physical properties have effects on the values of drag coefficient. The effects of physical properties are weaker in the case of large particle concentrations. Furthermore, the physical properties lead to that the effect of particle cluster wake on the drag of downstream particles being significantly different from that of constant property flow. The variation trend of drag of coarse graining particle is consistent with that of isolated particle. The physical properties lead to significant differences in the values of drag. In this paper, the dominance of the effects of physical properties in a variety of cases is confirmed. Finally, a physical properties effect model is developed accordingly.

Modeling particle collisions in moderately dense curtain impacted by an incident shock wave

The interactions between an incident shock and a moderately dense particle curtain are simulated with the Eulerian–Lagrangian method. A customized solver based on OpenFOAM is extended with an improved drag model and collision model and then validated against two benchmark experiments. The results show that the collision model has a limited impact on curtain morphology compared with the improved drag model. In this work, parametric studies are performed considering different particle sizes, volume fractions, and curtain thicknesses. Smaller particle sizes and larger volume fractions lead to stronger reflected shock and weaker transmitted shock. Attention is paid to the particle collision effects on the curtain evolution behaviors. According to our results, for the mono-dispersed particle curtain, the collision effects on curtain front behaviors are small, even when the initial particle volume fraction is as high as 20%. This is due to the positive velocity gradient across the curtain after the shock wave passage, leading to the faster motion of downstream particles than the upstream ones, and hence, no collision occurs. For the bi-dispersed particle curtain, the collision effects become important in the mixing region of different-size particles. Collisions decelerate small particles while accelerating large ones and cause velocity scattering. Moreover, increasing the bi-dispersed curtain thickness leads to multiple collision force peaks, which is the result of the delayed separation of different particle groups. Our results indicate that the collision model may be unnecessary to predict curtain fronts in mono-dispersed particles, but in bi-dispersed particles, the collision effects are important and, therefore, must be modeled.

Improved face mask testing system

A new way to measure the penetration efficiency of a face mask is introduced. It has a number of advantages over the currently used measurement systems in which a stationary mask is impacted with a moving aerosol during which the upstream and downstream particle concentrations are compared. The equivalent system described here instead moves a mask through a stationary aerosol in a closed chamber and compares the particle concentrations before and after the movement of the mask. This system provides many advantages, such as greater simplicity, greater accuracy, an exact constant aerosol flow speed through a mask, more easily made concentration measurements, more realistic impacts, more controlled averaging, the absence of the need for preliminary impacts during flow stabilization, and a lower cost. A laboratory prototype of the system has been fabricated and seen to perform as expected. Data obtained from this prototype are displayed, analyzed, and used to demonstrate the consistency and repeatability of the system. A portable fully-automated compact prototype has also been designed and fabricated. This device can be easily operated, and the total time required to test a mask, from material insertion to result display, is only a few minutes.

Effect of particle arrangement and density on aerodynamic interference between twin particles interacting with a plane shock wave

Unsteady drag, unsteady lift, and movement of one or two moving particles caused by the passage of a planar shock wave are investigated using particle-resolved simulations of viscous flows. The particle motion analysis is carried out based on particle-resolved simulations for one or two particles under a shock Mach number of 1.22 and a particle Reynolds number of 49, and the particle migration and fluid forces are investigated. The unsteady drag, unsteady lift, and particle behavior are investigated for different densities and particle configurations. The time evolution of the unsteady drag and lift is changed by interference by the planar shock wave, Mach stem convergence, and the shock wave reflected from the other particle. These two particles become closer after the shock wave passes than in the initial state under most conditions. Two particles placed in an in-line arrangement approach each other very closely due to the passage of a shock wave. On the other hand, two particles placed in a side-by-side arrangement are only slightly closer to each other after the shock wave passes between them. The pressure waves resulting from Mach stem convergence of the upstream particle and the reflected shock waves from the downstream particle are the main factors responsible for the force in the direction that pushes the particles apart. The wide distance between the two particles attenuates these pressure waves, and the particles reduce their motion away from each other.

Insight into the combustion effect of the high-reactivity char particle on the low-reactivity char particle in a hot O2/CO2 atmosphere

Based on the pseudo-steady-state approach, the combustion effect of high-reactivity char (i.e., HR-char) on low-reactivity char (i.e., LR-char) is investigated numerically in a hot O2/CO2 atmosphere under two arrangements (LR-LR case: the upstream and downstream particles are LR-char, HR-LR case: the upstream particle is HR-char and the downstream particle is LR-char). This paper is aimed to study the influence of oxygen concentration (from 2% to 30%) and ambient temperature (1300 K, 1400 K, and 1500 K) on the combustion effect under the condition with dominated oxidation reaction and weak gasification reaction, and explain the mechanism in aspects of the temperature, specie concentration, and reaction rate. The numerical results are carefully validated against experimental data published in the literature. The results show that under these studied ambient temperatures, the char-O2 oxidation-reduction brings a more pronounced effect than the char-CO2 gasification enhancement for char consumption owning to the dominant role of the char oxidation reaction. The upstream HR-char particle combustion under the HR-LR case produces a higher temperature, lower oxygen, and higher CO2 atmosphere ahead of the downstream char than under the LR-LR case, which significantly inhibits the downstream LR-char particle combustion. In addition, lower oxygen concentration or higher ambient temperature decreases the difference in temperature, oxygen, and CO2 between the HR-LR and LR-LR cases ahead of the downstream char, resulting in the lower difference in the downstream LR-char oxidation consumption rate between the HR-LR and LR-LR case. Consequently, the weaker combustion inhibitive effect of the high-reactivity char on the low-reactivity char is observed. The findings shed light on the interaction effects observed during blended coal combustion in O2/CO2 mixtures.

Microfluidic Dielectrophoretic Method Enables On-Demand Spatial Arrangement of Bacteria-Encapsulated Agarose Gel Microparticles.

Microbial interactions within a natural or engineered consortium of microbes play an important role in the functions of the consortium. Better understanding these interactions is also important for engineering microbial consortia for specific applications. As such, tools that can enable investigating microbial interactions are highly valuable. One aspect of microbial interactions that impacts community formation is how the spatial organization of individual microbes impacts interactions leading to community formation. Here, we report the development of a tool that can manipulate the spatial organization of microorganisms to investigate the role of these interactions in community formation. Our developed microfluidic platform utilizes dielectrophoretic (DEP) force to perform on-demand spatial arrangement of microorganism-encapsulated agarose gel microparticles. To demonstrate this concept, three gel microparticle manipulators composed of three independently controllable DEP electrodes were utilized for the on-demand spatial arrangement of a specific combination of microparticles, each containing Escherichia coli cells expressing red fluorescence protein, green fluorescent protein, or blank content. The spatially arranged microparticles suspended in carrier oil were first trapped in a downstream particle trapping structure to form a defined microparticle array, followed by the application of an electric field to disrupt the carrier oil barrier so that all gel microparticles were within the same aqueous solution while the individual gel microparticles remain intact, thereby maintaining their spatial arrangements. We demonstrated that this method can be utilized to generate various arrays with differing number of "spacer microparticles", which were blank microparticles, between the two different E. coli-containing microparticles, enabling precise control over spatial distances between the two different cell populations. This method paves the way for more easily investigating bacterial interactions, especially those that depend on their spatial arrangement such as where cell-cell communication plays a major role.

Interaction of a Relativistic Magnetized Collisionless Shock with a Dense Clump

The interactions between a relativistic magnetized collisionless shock and dense clumps have been expected to play a crucial role in magnetic field amplification and cosmic-ray acceleration. We investigate this process using two-dimensional Particle-In-Cell (PIC) simulations, for the first time, where the clump size is much larger than the gyroradius of the downstream particles. We also perform relativistic magnetohydrodynamic (MHD) simulations for the same condition, to see the kinetic effects. We find that particles escape from the shocked clump along magnetic field lines in the PIC simulations, so that the vorticity is lower than that in the MHD simulations. Moreover, in both the PIC and MHD simulations, the shocked clump quickly decelerates because of relativistic effects. Owing to the escape and the deceleration, the shocked clump cannot amplify the downstream magnetic field in relativistic collisionless shocks. This large-scale PIC simulation opens a new window to understanding large-scale behaviors in collisionless plasma systems.

A Hybrid Particle-Flow CFD Modeling Approach in Truncated Hepatic Arterial Trees for Liver Radioembolization: A Patient-specific Case Study.

Hepatocellular carcinoma (HCC) is the most common form of primary liver cancer. At its intermediate, unresectable stage, HCC is typically treated by local injection of embolizing microspheres in the hepatic arteries to selectively damage tumor tissue. Interestingly, computational fluid dynamics (CFD) has been applied increasingly to elucidate the impact of clinically variable parameters, such as injection location, on the downstream particle distribution. This study aims to reduce the computational cost of such CFD approaches by introducing a novel truncation algorithm to simplify hepatic arterial trees, and a hybrid particle-flow modeling approach which only models particles in the first few bifurcations. A patient-specific hepatic arterial geometry was pruned at three different levels, resulting in three trees: Geometry 1 (48 outlets), Geometry 2 (38 outlets), and Geometry 3 (17 outlets). In each geometry, 1 planar injection and 3 catheter injections (each with different tip locations) were performed. For the truncated geometries, it was assumed that, downstream of the truncated outlets, particles distributed themselves proportional to the blood flow. This allowed to compare the particle distribution in all 48 “outlets” for each geometry. For the planar injections, the median difference in outlet-specific particle distribution between Geometry 1 and 3 was 0.21%; while the median difference between outlet-specific flow and particle distribution in Geometry 1 was 0.40%. Comparing catheter injections, the maximum median difference in particle distribution between Geometry 1 and 3 was 0.24%, while the maximum median difference between particle and flow distribution was 0.62%. The results suggest that the hepatic arterial tree might be reliably truncated to estimate the particle distribution in the full-complexity tree. In the resulting hybrid particle-flow model, explicit particle modeling was only deemed necessary in the first few bifurcations of the arterial tree. Interestingly, using flow distribution as a surrogate for particle distribution in the entire tree was considerably less accurate than using the hybrid model, although the difference was much higher for catheter injections than for planar injections. Future work should focus on replicating and experimentally validating these results in more patient-specific geometries.