Behavior Of Individual Particles Research Articles

(Invited) Modelling and Experiments to Guide Scale-up of Structured Electrode Manufacturing for Fast-Charging and Long-Life Li-Ion Cells

For widespread adoption of electric vehicles, lithium-ion batteries (LiBs) need to achieve energy densities of around 350 Wh/kg, cost less than $100/Wh, and be able to charge quickly within around 15 minutes. To achieve this aim, the material properties of lithium-ion electrodes need to be optimized across multiple length scales, from particle to cell. Leveraging advanced characterization techniques to acquire representative particle- and electrode-level microstructures, we develop models to simulate the behavior of individual particles and novel electrode architectures that are feasible to synthesize and scale up to manufacture high performance batteries. We then demonstrate manufacturing of the novel electrode architectures at pilot scale roll-to-roll processing using high-speed laser-ablation to tune the electrode architecture. Guided by multi-scale models, we observe substantial improvements in cell performance.For the particle level optimization, the primary objective is to develop a predictive cathode-particle cracking model that captures secondary-particle fracture dynamics, relate damage to observed capacity fade, and provide design criteria for future cathode development. The novel coupled electrochemistry-transport-mechanics model is implemented on realistic three-dimensional LiNixMnyCozO2 (NMC) secondary particles. Realistic secondary particles are generated using statistically representative particle generation software. The generated particle architecture is used in chemo-mechanical models to simulate Li (de)intercalation during cycling. The model considers diffusion-induced stress, mismatch strain, and damage evolution coupled through the spatial and temporal evolution of geometric, transport, and mechanical properties. Contrary to most cathode-cracking models, instead of a cohesive-zone implementation, a continuum-damage model is used. Additionally, the model simulates several realistic secondary particle geometries to study the effect of secondary-particle size and grain size on damage. The model is expected to provide insights into ideal cathode geometries (e.g., grain morphology, orientation, and particle sizes) and optimal cathode-sensitive charge-protocol development.For electrode level optimization, structuring the electrode with channels to provide straight diffusion paths along the electrode thickness is a promising approach with demonstrated improved capacity retention at fast charge. The optimal shape and spatial distribution of these channels, that together form the so-called Secondary Pore Network (SPN), taking into consideration the manufacturing technique limitations, is however still unknown. Battery manufacturing cost is another key limiting factor for the wide adoption of electric vehicles. The electrolyte wetting process is an expensive step as complete infiltration can takes days, thus requiring expensive storage space and time. Structured electrodes have also demonstrated reduced wetting time as channels offer highways indifferently for capillary-driven or concentration gradient-driven transport mechanisms. However, the optimal channel pattern for enhanced wetting is also unknown. In this work, we identify both optimal patterns, for fast charging, and for fast wetting, independently, through use of a genetic algorithm (GA). The final proposed structured electrode is therefore the baseline porous matrix, a Secondary Pore Network (SPN) tailored for fast charging, and a Tertiary Pore Network (TPN) tailored for fast wetting, with less than 10% of active material removed in total.High-speed laser-ablation is applied to manufacturing this electrode architecture. Laser ablation is a scalable technique for decreasing the effective tortuosity of electrodes by selectively removing material with high precision. Applied to thick electrode coatings, this work focuses on understanding the impact of laser ablation on electrode material properties at the beginning of life and synergistic impacts of ablated channels on cell performance throughout their cycle life. Post laser ablation, local changes in chemistry, crystallography, and morphology of the laser-impacted electrode regions are investigated. It is shown that femtosecond pulsed laser ablation can achieve high-rate material removal with minor material damage locally at the interface of the impacted zones. The capacity achieved during a 6C (10 min) constant-current constant-voltage charge to 4.2 V improved from 1 mAh cm−2 for the non-ablated electrodes to almost 2 mAh cm−2 for the ablated electrodes. This benefit is attributed to a synergistic effect of enhanced wetting and decreased electrode tortuosity. The benefit was maintained for over 120 cycles, and upon disassembly decreased Li-plating on the graphite anode was observed.From the particle to the electrode level, we demonstrate that there remains ample opportunity for optimizing the material properties of conventional electrode chemistries for faster charging and longer-life performance. Our combined use of advanced characterization, modelling, and data-guided manufacturing shows that a multi-scale and multi-modal approach can be applied to build electrodes from the particle up and achieve enhanced electrochemical performance at the cell level through advanced and scalable manufacturing techniques. Figure 1

Study on Verification Approach and Multicontact Points Issue When Modeling Cyperus esculentus Seeds Based on DEM

In this paper, the Multisphere (MS) models of three varieties of Cyperus esculentus seeds are modeled based on DEM. In addition, for comparison, other particle models based on automatic filing in EDEM software are also introduced. Then, the direct shear test, piling test, bulk density test, and rotating hub test are used to verify the feasibility of particle models of Cyperus esculentus seeds that we proposed. By comparing the simulated results and experimental results, combined with the CPU computation time, the proposed particle models achieved better simulation accuracy with fewer filing spheres. According to simulation results, some limitation was present when using one single verification test; varieties of verification tests used could improve the verification reliability, and a more appropriate particle model could be selected. Additionally, the issue of multicontact points in the MS model was studied. The Hertz Mindlin (no slip) (HM) model and Hertz Mindlin new restitution (HMNR) model were both considered in simulations for comparison. The rotating hub test and particle–wall impact test were used, and the influences of multiple contact points on the motion behavior of individual particles and particle assemblies were analyzed. Simulation results showed that the multiple contact points affected the motion behavior of individual particles; in contrast, the influence of multiple contact points on the motion behavior of the particle assembly was insignificant. Moreover, the relationships between moisture content of seeds and Young’s modulus, Young’s modulus, and the number of contact points were also considered. Young’s modulus decreased with increasing moisture content. The number of contact points increased with a decreasing Young’s modulus.

(Battery Division Early Career Award Sponsored by Neware Technology Limited) Design, Synthesis, and Characterization of Cathode Microstructures in Lithium Batteries

The propagation of redox reactions governs the electrochemical properties of battery materials and their critical performance metrics in battery cells. The recent research progress, especially aided by advanced analytical techniques, has revealed that incomplete and heterogeneous redox reactions prevail in many electrode materials. Advanced high-capacity cathode materials are mostly polycrystalline materials that exhibit complex charge distribution (the valence state distribution of the redox-active cations) due to the presence of numerous constituting grains and grain boundaries. The redox reactions in individual grains typically do not proceed concurrently due to their distinct geometric locations in polycrystalline particles. As a result, these unsynchronized local redox events collectively induce heterogeneous and anisotropic charge distribution, building up intergranular and intragranular stress. Therefore, these polycrystalline materials may exhibit weak mechanical stability, leading to undesired chemomechanical breakdown during battery operation. Grain engineering in polycrystalline materials provides a large playground to modulate the materials properties beyond controlling the chemical composition, and electronic and crystal structures. In particular, the anisotropic ion-conducting pathways in layered oxides make the grain crystallographic orientation a critical factor in determining the modality of the redox reactions in these materials.This presentation will discuss our recent progress in the design, synthesis, and characterization of cathode microstructures in lithium batteries.First, we will discuss how the charge distribution is guided by grain crystallographic orientations in polycrystalline battery materials. We elucidate the spatially resolved charge distribution in lithium layered oxides with different grain crystallographic arrangements and establish a model to quantify their charge distributions. While the holistic “surface-to-bulk” charge distribution prevails in polycrystalline particles, the crystallographic orientation-guided redox reaction governs the charge distribution in the local charged nanodomains. Compared to the randomly oriented grains, the radially aligned grains exhibit a lower cell polarization and higher capacity retention upon battery cycling. The radially aligned grains create less tortuous lithium-ion pathways, thus improving the charge homogeneity as statistically quantified from over 20 million nanodomains in polycrystalline particles. This study provides an improved understanding of the charge distribution and chemomechanical properties of polycrystalline battery materials.Second, we will discuss how the grain arrangement affects the thermal stability of polycrystalline cathode materials in rechargeable batteries. We performed a systematic in situ study on the Ni-rich polycrystalline cathode materials to investigate the fundamental degradation mechanism of charged cathodes at elevated temperatures, which is essential for tailoring material properties and improving performance. Using multiple microscopy, scattering, thermal, and electrochemical probes, we decoupled the major contributors to the thermal instability from intertwined factors. Based on our findings, the cathode grain microstructure has a forgotten yet important role in the thermal stability of polycrystalline rechargeable batteries. Oxygen release, as an important process during the thermal runaway, can be regulated through engineering grain arrangements. The grain arrangement can modulate the macroscopic crystallographic transformation pattern and oxygen diffusion length in layered cathodes to offer more possibilities for cathode material design and synthesis.Third, we will discuss our new understanding of particle behaviors in composite cathodes. We capture and quantify the particle motion during the solidification of battery electrodes and reveal the statistics of the dynamically evolving motion in the drying process, which has been challenging to resolve. We discover that the particle motion exhibits a strong dependence on its geometric location within a drying electrode. Our results also imply that the final electrode quality can be controlled by balancing the solvent evaporation rate and the particle mobility in the region close to the drying surface. We formulate a network evolution model to interpret the regulation and equilibration between electrochemical activity and mechanical damage of these particles. Through statistical analysis of thousands of particles using x-ray phase-contrast holotomography in a Ni-rich cathode, we found that the local network heterogeneity results in asynchronous activities in the early cycles, and subsequently the particle assemblies move toward a synchronous behavior. Our study pinpoints the chemomechanical behavior of individual particles and enables better designs of the conductive network to optimize the utility of all the particles during operation.

Interparticle bonding and interfacial nanocrystallization mechanisms in additively manufactured bulk metallic glass fabricated by cold spray

Amorphous Zr-based bulk metallic glass deposit was produced by cold spray additive manufacturing. The bonding mechanism of metallic glass particles was systematically investigated through studying the deformation behavior of individual particles after deposition. We revealed two collective particle bonding mechanisms that contributed to the formation of metallic glass deposits, i.e., high-velocity impact induced localized metallurgical bonding at the fringe of the interface, and high particle temperature induced viscosity reduction and the resultant annular metallurgical bonding band. Moreover, the dynamic evolution mechanism of the amorphous phase into nanocrystal structures at severely deformed interfacial regions during cold spray was carefully investigated. For the first time, we observed different amorphous/nanocrystal structures in cold sprayed metallic glass deposits, which can represent different evolution stages in nanocrystallization process. Based on the observation, it is inferred that the nanocrystallization process can be divided into following three stages: composition segregation, the formation of ordered 1D and 2D transition structures, and 3D nanocrystals. The current study provides new insights into the bonding mechanisms and the mechanistic nanocrystallization origins in cold sprayed bulk metallic glass deposits.

Operando Optical Tracking of Single-Particle Ion Dynamics in Batteries

In order to advance lithium-ion battery technologies, particularly fast charging abilities, it is important to understand the non-equilibrium processes occurring in functioning materials under realistic conditions, in real time, and on the nano- to meso-scale. Currently, operando imaging of lithium-ion dynamics requires sophisticated synchrotron X-ray or electron microscopy methods. These techniques do not lend themselves to high-throughput material screening, and often fail to capture the behaviour of individual particles in batteries charging faster than 2C. In this work, we introduce a laboratory-based optical interferometric scattering microscope to resolve lithium-ion transport in battery materials at the single-particle level, and apply it to follow rapid cycling of the archetypical cathode material Li x CoO2. We directly visualise the insulator-metal, solid solution and lithium ordering phase transitions and determine rates of lithium insertion and removal from individual particles, identifying different mechanisms on charge vs. discharge. Finally, we capture the real-time formation of domain boundaries between different crystal orientations associated with the monoclinic lattice distortion at Li0.5CoO2. The high throughput nature of our methodology allows many particles to be sampled across the electrode and enables exploration of the role of defects, morphologies and cycling rate on battery degradation. The imaging concept is general and may be applied to study any active electrode material, and more broadly, any system where the transport of ions is associated with electronic or structural changes. Due to its straightforward lab-based implementation, we hope that this methodology will become an indispensable tool for high-throughput material discovery and mechanistic studies, to complement existing synchrotron-based methodologies. References Merryweather, A.J., Schnedermann, C., Jacquet, Q. et al. Operando optical tracking of single-particle ion dynamics in batteries. Nature 594, 522–528 (2021).

Development of an FEM-DEM Model to Investigate Preliminary Compaction of Asphalt Pavements

Variations in pavement density have been widely monitored and investigated, both in laboratory and in field experiments, since the compaction of pavement is so critical to its long-term performance quality. In contrast to field testing, laboratory tests are simpler to produce but less accurate. Destructive drilled samples are used to conduct field testing; however, they are limited in their ability to assess density information at specific areas. The use of computationally aided approaches, such as the Finite Element Method (FEM) and the Discrete Element Method (DEM), in research involving asphalt mixtures is increasing, since these methods simulate and evaluate the characteristics of asphalt mixtures at macroscopic and microscopic scales. Individual particle behavior at the microscopic level cannot be fully represented using the FEM alone, and the computing cost of utilizing the DEM approach alone is prohibitively high. The objective of this work is to simulate the pre-compaction process by using the coupled FEM-DEM approach. In order to investigate the impact of the asphalt mixtures’ gradation, a dense-graded asphalt mixture (AC 11) and a gap graded asphalt mixture (PA 11) were simulated. Different paving speeds (4, 5, and 6 m/min) were applied on the preliminary compaction model of AC 11 to study the effect of the paving speeds on the compaction process. By comparing the angular velocity, which worked as a reference of compaction quality, it was demonstrated that the grade AC 11 asphalt mixtures performed better in the preliminary compaction process compared to the grade PA 11 asphalt mixtures. Moreover, since it has an effect on compaction, paving speed was carefully monitored and kept within a reasonable range in order to maximize both pavement quality and project efficiency.

Dynamics of particle network in composite battery cathodes

Improving composite battery electrodes requires a delicate control of active materials and electrode formulation. The electrochemically active particles fulfill their role as energy exchange reservoirs through interacting with the surrounding conductive network. We formulate a network evolution model to interpret the regulation and equilibration between electrochemical activity and mechanical damage of these particles. Through statistical analysis of thousands of particles using x-ray phase contrast holotomography in a LiNi0.8Mn0.1Co0.1O2-based cathode, we found that the local network heterogeneity results in asynchronous activities in the early cycles, and subsequently the particle assemblies move toward a synchronous behavior. Our study pinpoints the chemomechanical behavior of individual particles and enables better designs of the conductive network to optimize the utility of all the particles during operation.

Approximate solutions of the advection–diffusion equation for spatially variable flows

The advection–diffusion equation (ADE) describes many important processes in hydrogeology, mechanics, geology, and biology. The equations model the transport of a passive scalar quantity in a flow. In this paper, we have developed a new approach to solve incompressible advection–diffusion equations (ADEs) with variable convective terms, which are essential to study species transport in various flow scenarios. We first reinterpret advection diffusion equations on a microscopic level and obtain stochastic differential equations governing the behavior of individual particles of the species transported by the flow. Then, simplified versions of ADEs are derived to approximate the original ADEs governing concentration evolution of species. The approximation is effectively a linearization of the spatially varying coefficient of the advective term. These simplified equations are solved analytically using the Fourier transform. We have validated this new method by comparing our results to solutions obtained from the canonical stochastic sampling method and the finite element method. This mesh-free algorithm achieves comparable accuracy to the results from discrete stochastic simulation of spatially resolved species transport in a Lagrangian frame of reference. The good consistency shows that our proposed method is efficient in simulating chemical transport in a convective flow. The proposed method is computationally efficient and quantitatively reliable, providing an alternative technique to investigate various advection–diffusion processes.

Experiments and simulations on a cold-flow blast furnace hearth model

The blast furnace hearth plays an important role in the operational stability and lifetime of the reactor. The quasi-stagnant bed of coke particles termed the deadman undergoes complex interaction with the flowing hot metal, and remains largely ill-understood. In this work, a cold model blast furnace hearth is presented, and studied using both numerical and experimental techniques. Magnetic Particle Tracking (MPT) is used to investigate the individual particle behaviour within the cylindrical, opaque bed. At high liquid holdup, the particle bed was found to alternate between floating and sitting states, following the liquid level during the tapping and filling cycle. This bed motion was found to induce a migration of particles, thereby slowly renewing the deadman. The rate of horizontal migration increases with the vertical bed amplitude, and the renewal of particles is concentrated around the opening of the tap hole. No direct influence of the coke-free space on the tapping rate was found in these experiments. Instead, the disturbance of the packing in front of the tap hole was observed to lead to a higher tapping rate. Additionally, a coupled numerical framework is presented, in which Computational Fluid Dynamics (CFD), the Volume of Fluid (VOF) method and the Discrete Element Method (DEM) are combined. A simulation set-up is presented which closely replicates the experimental conditions. The position and movement of the floating bed are found to be well-predicted by the VOF/CFD-DEM model. Particle trajectories are presented, and migration of particles within the deadman is observed. Alongside the particle motion, the liquid flow pattern during draining of the vessel is visualised. It is concluded that a coke-free space underneath the deadman significantly impacts the shape of the liquid flow pattern, which affects the erosion processes within the blast furnace hearth.

Digital holographic particle position detection using two views and aperture reduction techniques

Digital holography is a well-established technique for tracer particle studies in a flow. Unfortunately, its great depth of focus increases the uncertainty along the Z axis. This drawback becomes very significant when the concentration of seeding particles increases. This is the case in real installations such as wind or water channel flows. In such cases, observing the whole volume, and therefore all the particles, and tracking individual particles in order to determine their motions becomes an awesome task. Getting a hologram of the whole scene is impossible with the existing photographic sensors. The solution offered by the present day technologies and academic studies is to take several holograms and synthesize the whole scene hologram. However, for getting individual particle behavior, it is necessary to make several processing steps, makes processing very complicated if the number of seeding tracer particles is relatively high, on one hand and on the other hand, the correlation between dynamic characteristics could not highly established. In such cases, the technique of one hologram is highly recommended. In order to overcome these problems, we propose here a new technique based on combining the two instantaneous orthogonal views and hologram aperture reduction (opposed to aperture synthesis). To establish the technique, we investigate a little volume with a reduced number of particles, and the development and experimental results are presented. We focus on the development and experimental application of this technique.

True shape modeling of bio-particulate matter flow in an aero-cyclone separator using CFD–DEM simulation

The multi-phase flow of air and bio-particulate matter exists in many biological and environmental systems such as aerodynamic separating devices, fluidized bed combustion, and feed processing machinery. Integration of the computational fluid dynamics (CFD) and discrete element method (DEM) codes was performed to study bio-particle loading ratios' effect on the cyclone device performance. Every individual particle's behavior was captured by a DEM model using Newton’s equations of motion, in which CFD modeled the continuum airflow for every computational cell scale through the Navier–Stokes equation. According to the high turbulence and chaotic behavior of the continuum airflow inside the cyclone separator, Reynolds stress turbulence model (RSM) was used. The particles used for testing and modeling were conducted on two mixture types of real-heterogeneous particulate matter, namely jojoba seeds and jojoba leaves, without any fly ash. The particles were geometrically modeled using their actual dimensions and shapes, considered the first head start research approach in the cyclonic separation and purification field. The influence of the interacting particle–particle and particle–boundary forces was taken into consideration. The numerical simulation results successfully predicted the cyclone performance at the designed conditions, which showed the best experimental data trend. These data are useful in future studies to modify the cyclone design and optimize bio-systems' operating conditions for separating the macroscopic particulate matter.

A self-adaptive particle-tracking method for minerals processing

Modern analytical techniques used in the minerals processing industry can provide detailed characterization data at the particle level. However, process models that make full use of this information are currently not available, limiting the usefulness of these extensive datasets. This contribution addresses this issue. It presents a novel particle-based approach for process modelling capable of dealing with complete particle datasets and operating without human input. The method provides a probabilistic description for the behavior of individual particles in a given mineral separation unit, based on all measurable particle properties. It is applicable to any separation process that does not modify the physical dimensions of particles, i.e. it does not cover comminution.The method comprises a regularized logistic regression model with a probability adjustment step to accommodate geological variability. Even though this method supports any type of particle-level characterization data, its potential is illustrated here using data obtained by scanning electron microscope-based image analysis. Constructed cases demonstrate the efficiency of the method in recreating characteristic recovery trends for magnetic separation, hydrocyclone, and flotation units. In addition, the method was used successfully to reconstruct a real processing plant with three flotation and one magnetic separation circuits. Predicted results of compositions for all the intermediate and product streams correspond well with the results reported from the plant itself. The predicted masses of the products are much affected by the quality of sampling and still require improvement. The case study illustrates that the method proposed here provides a powerful tool to understand and optimize mineral separation processes – and thus increase the resource and energy efficiency of mining operations.

Transport of particles suspended within a temperature-dependent viscosity fluid using coupled LBM–DEM

Particle suspensions are present in a wide variety of practical settings. Modelling these numerically is a challenging task that often requires the combination of multiple methodologies. This paper examines particle transport within a temperature-dependent viscosity fluid utilising a coupled approach of the lattice Boltzmann method and the discrete element method. This technique takes advantage of the locality of the lattice Boltzmann method to allow both the individual particle behaviour to be fully resolved and to permit fine-scale variation of fluid viscosity throughout the tested domains. It is firstly shown that a total energy conserving form of the lattice Boltzmann method is needed to accurately reconstruct the non-linear temperature profiles observed on Couette flows of fluids with changing viscosity. This model is then coupled to the discrete element method to demonstrate the quantitative and qualitative changes to particle motion that arise in channel-based geometries in the presence of a temperature-dependent viscosity fluid exposed to a constant temperature gradient. In particular, it is demonstrated that the particles settled faster in such and appear less likely to deviate into side channels in the presence of such fluids. These results demonstrate that temperature-dependent viscosity requires special consideration to be simulated correctly and does have quantitative impact on particle transport. This impact should be considered in models of fluids of changing temperature.

Fluorescence Quantum Yield and Single-Particle Emission of CdSe Dot/CdS Rod Nanocrystals

The fluorescence quantum yield (QY) of CdSe dot/CdS rod (DR) nanoparticle ensembles is dependent on the Shell growth and excitation wavelength. We analyze the origin of this dependency by comparing the optical properties of DR ensembles to the results obtained in single-particle experiments. On the Ensemble level, we find that the QY of DRs with shell lengths shorter than 40 nm exhibits no dependence on the excitation wavelength, whereas for DRs with shell lengths longer than 50 nm, the QY significantly decreases for excitation above the CdS band gap. Upon excitation in the CdSe core, the ensemble QY, the fluorescence wavelength, and the fluorescence blinking behavior of individual particles are only dependent on the radial CdS shell thickness and not on the CDs shell length. If the photogenerated excitons can reach the CdSe core region, the fluorescence properties will be dependent only on the surface passivation in close vicinity to the CdSe core. The change in QY upon excitation above the band gap of CdS for longer DRs cannot be explained by nonradiative particles because the ratio of emitting DRs is found to be independent of the DR length. We propose a model after which the decrease in QY for longer CdS shells is due to an increasing fraction of nonradiative exciton recombination within the elongated shell. This is supported by an effective-mass-approximation-based calculation, which suggests an optimum length of DRs of about 40 nm, to combine the benefit of high CdS absorption cross section with a high fluorescence QY.

A scoping study of component-specific toxicity of mercury in urban road dusts from three international locations

This scoping study presents an investigation of the total and bioaccessible mercury concentrations in road dust (RD) from three international urban sites, where a one-off sampling campaign was conducted at each. This was done to address the hypothesis that the matrix in which mercury is found influences its ability to become accessible to the body once inhaled. For that purpose, the samples were analysed for total and pulmonary bioaccessible mercury and the data compared to the chemical structure of individual particles by SEM. The results obtained from this study suggest that a high mercury content does not necessarily equate to high bioaccessibility, a phenomenon which could be ascribed to the chemical character of the individual particles. It was found that the Manchester samples contained more pulmonary soluble mercury species (as determined by elemental associations of Hg and Cl) in comparison to the other two samples, Curitiba, Brazil, and Johannesburg, South Africa. This finding ultimately underlines the necessity to conduct a site-specific in-depth analysis of RD, to determine the concentration, chemical structure and molecular speciation of the materials within the complex matrix of RD. Therefore, rather than simply assuming that higher bulk concentrations equate to more significant potential human health concerns, the leaching potential of the metal/element in its specific form (for example as a mineral) should be ascertained. The importance of individual particle behaviour in the determination of human health risk is therefore highlighted.

A Comprehensive Study about the Hygroscopic Behavior of Mixtures of Oxalic Acid and Nitrate Salts: Implication for the Occurrence of Atmospheric Metal Oxalate Complex

The hygroscopic behavior of particles is important for assessing their environmental and climate effect. The hygroscopic behavior of individual particles has been widely investigated; however, the ...

Granular dynamics in a vertical bladed mixer: Secondary flow patterns

This article deals with numerical simulations and experimental measurements of the granular mixing process in a vertical cylindrical mixer with two opposed flat blades with a 45° rake angle. The computer simulations were conducted via discrete element method. The experimental measurements were recorded by a color high-speed camera. Both approaches describe the mixing process in the same way with significant agreement in observations. Even though the geometry and operating conditions are simple, the dynamics of the system is often very complex and a variety of flow structures can be created. For that reason, the behavior of individual flows patterns was analyzed and discussed. The effect of the centrifugal force on deformation of the free level of the granular material and the formation of empty spaces behind the stirrer blades was described. In addition, the behavior of individual particles in specific regions was characterized. At low rotational speed of the blades, particles tend to move close to the bottom of the vessel behind the stirrer blade towards the shaft. At high values, particles are moving in the exact opposite direction. Described movements near the base of the vessel create secondary flow in the form of recirculation zones. Presence of the secondary flow during the mixing process was also confirmed by the experimental measurements. Based on the acquired knowledge, two competing mechanisms of secondary flow formation were presented: (i) the different contact time of the particles with the blade; (ii) the different magnitude of inertial forces acting on the particles around the stirrer blade.

Static fatigue of sand particles

Static fatigue is of particular concern when studying the time-dependent mechanical behavior of brittle geomaterials. In this regard, the time-dependent strength behavior of individual particles is essential for understanding the creep behavior of sand. In this study, short-term strength tests and static fatigue tests of individual sand particles subjected to a uniaxial compressive load were carried out using a mini-loading apparatus and modified oedometer frames, respectively. The sand particles in the static fatigue test were loaded in an incremental manner, and the load at each stress level was maintained for a fixed period of time. Scatter of the strength of sand particles was described using the Weibull distribution. Long-term strength from the static fatigue test of individual sand particles is found to be less than the short-term strength.

Compression response of Ni–Mn–Ga/silicone composite and study of three-dimensional deformation of particles

Ni–Mn–Ga particles/silicone composite was fabricated for a mechanical investigation. The characteristic twinning structure of particles and soft enough matrix provide the conditions enabling the possibility for particles to deform by the twin boundaries motion mechanism under applied stress and/or magnetic field. On the macroscopic scale, the large hysteretic loops in the stress–strain curves for composite evidence about its high energy absorption capability. On the microscopic scale, the in situ compression test was performed using an x-ray micro-computed tomography to study the individual deformation of particles. The strain behavior of individual particles in the three different configuration of groups was disclosed as a function of the compression degree of composite showing large reversible deformation of particles, signature of the twin structure rearrangement. The unusual drop of particles strains at very high compression degrees of composite is explained in terms of the non-uniform stress field in polymer produced by the neighbor particles interactions affected by barreling. The obtained results support the reason that the particles in composite should be arranged in single chains to avoid their interaction which is a way to improve the composite performance in the mechanical damping and magnetic actuator applications.

Early cytoplasmic uncoating is associated with infectivity of HIV-1

After fusion, HIV delivers its conical capsid into the cytoplasm. To release the contained reverse-transcribing viral genome, the capsid must disassemble in a process termed uncoating. Defining the kinetics, dynamics, and cellular location of uncoating of virions leading to infection has been confounded by defective, noninfectious particles and the stochastic minefield blocking access to host DNA. We used live-cell fluorescent imaging of intravirion fluid phase markers to monitor HIV-1 uncoating at the individual particle level. We find that HIV-1 uncoating of particles leading to infection is a cytoplasmic process that occurs ∼30 min postfusion. Most, but not all, of the capsid protein is rapidly shed in tissue culture and primary target cells, independent of entry pathway. Extended time-lapse imaging with less than one virion per cell allows identification of infected cells by Gag-GFP expression and directly links individual particle behavior to infectivity, providing unprecedented insights into the biology of HIV infection.