Mobility Of Particles Research Articles

Cytoplasmic fluidization contributes to breaking spore dormancy in fission yeast

The cytoplasm is a complex, crowded environment that influences myriad cellular processes including protein folding and metabolic reactions. Recent studies have suggested that changes in the biophysical properties of the cytoplasm play a key role in cellular homeostasis and adaptation. However, it still remains unclear how cells control their cytoplasmic properties in response to environmental cues. Here, we used fission yeast spores as a model system of dormant cells to elucidate the mechanisms underlying regulation of the cytoplasmic properties. By tracking fluorescent tracer particles, we found that particle mobility decreased in spores compared to vegetative cells and rapidly increased at the onset of dormancy breaking upon glucose addition. This cytoplasmic fluidization depended on glucose-sensing via the cyclic adenosine monophosphate-protein kinase A pathway. PKA activation led to trehalose degradation through trehalase Ntp1, thereby increasing particle mobility as the amount of trehalose decreased. In contrast, the rapid cytoplasmic fluidization did not require de novo protein synthesis, cytoskeletal dynamics, or cell volume increase. Furthermore, the measurement of diffusion coefficients with tracer particles of different sizes suggests that the spore cytoplasm impedes the movement of larger protein complexes (40 to 150 nm) such as ribosomes, while allowing free diffusion of smaller molecules (~3 nm) such as second messengers and signaling proteins. Our experiments have thus uncovered a series of signaling events that enable cells to quickly fluidize the cytoplasm at the onset of dormancy breaking.

Diffusive lensing as a mechanism of intracellular transport and compartmentalization.

While inhomogeneous diffusivity has been identified as a ubiquitous feature of the cellular interior, its implications for particle mobility and concentration at different length scales remain largely unexplored. In this work, we use agent-based simulations of diffusion to investigate how heterogeneous diffusivity affects the movement and concentration of diffusing particles. We propose that a nonequilibrium mode of membrane-less compartmentalization arising from the convergence of diffusive trajectories into low-diffusive sinks, which we call 'diffusive lensing,' is relevant for living systems. Our work highlights the phenomenon of diffusive lensing as a potentially key driver of mesoscale dynamics in the cytoplasm, with possible far-reaching implications for biochemical processes.

Diffusive lensing as a mechanism of intracellular transport and compartmentalization

While inhomogeneous diffusivity has been identified as a ubiquitous feature of the cellular interior, its implications for particle mobility and concentration at different length scales remain largely unexplored. In this work, we use agent-based simulations of diffusion to investigate how heterogeneous diffusivity affects the movement and concentration of diffusing particles. We propose that a nonequilibrium mode of membrane-less compartmentalization arising from the convergence of diffusive trajectories into low-diffusive sinks, which we call ‘diffusive lensing,’ is relevant for living systems. Our work highlights the phenomenon of diffusive lensing as a potentially key driver of mesoscale dynamics in the cytoplasm, with possible far-reaching implications for biochemical processes.

Theory Predicts Collective States of Mobile Particles

Theory Predicts Collective States of Mobile Particles

Stochastic model for migration and breakage of detrital and authigenic fines

Mobilisation of attached particles during flow in rocks occurs in geo-energy processes. Particle mobilisation, their migration through rocks and pore plugging yield significant decline in permeability and well injectivity and productivity. While much is currently known about the underlying mechanisms governing the detachment of detrital particles against attracting electrostatic forces, a critical gap exists in the theoretical understanding of detachment by breakage of widely spread authigenic particles, which naturally grow on rock grains during geological times. Previous works derived micro-scale mechanical equilibrium equations for both detrital and authigenic particles, and the upscaling procedure from particle to pore and core scales for detrital fines. In this paper, for the first time we derive a stochastic model for migration and breakage of authigenic fines and authigenic–detrital mixtures. This allows for core-scale transport modelling based on the particle-scale torque balance. We introduce a novel framework for predictive stochastic detachment modelling by particle–rock bond breakage that integrates the beam theory of elastic particle deformation, strength failure criteria and viscous flow around the attached particle. The analytical expressions for stress maxima and stress diagrams for a single particle allow determining the critical failure stresses, breakage points of the beam and breakage flow velocity. The mathematical model describing lab coreflood includes the maximum retention function for both authigenic and detrital fines. The matching laboratory coreflood data under increasing velocity at micro- and core-scales achieved high matching of the experimental data by the model. High matching validates the upscaling and downscaling procedures derived.

Stability of a dispersion of elongated particles embedded in a viscous membrane

We develop a mean-field model to examine the stability of a ‘quasi-2-D suspension’ of elongated particles embedded within a viscous membrane. This geometry represents several biological and synthetic settings, and we reveal mechanisms by which the anisotropic mobility of particles interacts with long-ranged viscous membrane hydrodynamics. We first show that a system of slender rod-like particles driven by a constant force is unstable to perturbations in concentration – much like sedimentation in analogous 3-D suspensions – so long as membrane viscous stresses dominate. However, increasing the contribution of viscous stresses from the surrounding 3-D fluid(s) suppresses such an instability. We then tie this result to the hydrodynamic disturbances generated by each particle in the plane of the membrane and show that enhancing subphase viscous contributions generates extensional fields that orient neighbouring particles in a manner that draws them apart. The balance of flux of particles aggregating versus separating then leads to a wave number selection in the mean-field model.

Performance of cut-off walls under long-term vacuum suction: A case study

This study assesses the performance of cut-off walls in a vacuum preloading project at Lianyungang Port, China, to tackle challenges posed by ultra-soft reclaimed land. It investigates the walls’ impermeability and structural integrity by analyzing changes in hydraulic conductivity, in-situ lateral displacement, particle size distribution, and dry density both before and after vacuum suction. The introduction of a hydroxypropyl starch-based coupling agent (CA) in slurry reduces the hydraulic conductivity in the sandy matrix. Significant lateral displacement near the surface amplifies the likelihood of cracks, which lead to increased hydraulic conductivity. The cut-off wall is characterized by three zones: an erosion zone with large amount of fine particle mobility, a central effective zone with minimal deformation, and an outer tensile zone whose soil loosening leads to impermeability reduction. These findings provide valuable insights into the design and construction of cut-off walls for similar geotechnical applications and aid in forecasting the performance and lifespan of the cut-off wall.

Effect of a high-gradient magnetic field on particle concentration distribution in a magnetic fluid seal: Rivalry of the diffusion and magnetophoresis

In this paper, the unsteady process of particle concentration distribution in a magnetic fluid is studied. Diffusion and the effect of a high-gradient magnetic field in a magnetic fluid seal (MFS) are taken into consideration. It is crucial to take into account how particle mobility and diffusion coefficient vary on particle concentration in order to determine the possibility and time of the formation of a close packing of particles. The Carnaghan-Starling approximation was employed. It is demonstrated numerically that the geometry of the MFS, namely its gap width and pole base width, as well as the magnitude of the magnetic field strength under the pole tooth of the MFS, both influence the time of the formation of a close packing of particles. This period can be regarded as the MFS's uptime. Depending on the design of the working gap, the uptime seal for magnetic fluid based on vacuum oil may require between two weeks and six months. The uptime seal also becomes shorter when the carrier fluid's viscosity decreases.

Chemo‐rheological and quantitative dispersion analysis of mass‐produced graphene‐unsaturated polyester based nanocomposites

AbstractRecent advancements in mass production of graphene powders utilize less energy‐intensive methods and milder chemicals compared to traditional lab‐scale techniques. This can influence the properties of the resulting graphene particles. This study investigates the effect of mass‐produced graphene powder on the curing and rheological properties of a resin transfer molding (RTM) grade unsaturated polyester resin. An objective dispersion quantification method was established to track the dispersion state of the nanocomposite throughout the curing process. The findings reveal that the graphene powder accelerated the curing evidenced by a shift in the peak temperature and gel point towards lower values. The sample containing 1 wt.% graphene exhibited remarkable dispersion stability with only 7.1% decrease by gelation. The resin matrix's low viscosity enhanced graphene particles mobility, while its fast‐curing nature allowed less time for agglomeration.Highlights Characterization of unsaturated polyester nanocomposites modified with an industrial‐grade graphene powder Real‐time in‐situ monitoring of graphene's dispersion state Quantification dispersion analysis for an objective dispersion assessment

Effect of the presence of pinned particles on the structural parameters of a liquid and correlation between structure and dynamics at the local level.

Pinning particles at the equilibrium configuration of the liquid is expected not to affect the structure and any property that depends on the structure while slowing down the dynamics. This leads to a breakdown of the structure dynamics correlation. Here, we calculate two structural quantities: the pair excess entropy, S2, and the mean field caging potential, the inverse of which is our structural order parameter (SOP). We show that when the pinned particles are treated the same way as the mobile particles, both S2 and SOP of the mobile particles remain the same as those of the unpinned system, and the structure dynamics correlation decreases with an increase in pinning density, "c." However, when we treat the pinned particles as a different species, even if we consider that the structure does not change, the expression of S2 and SOP changes. The microscopic expressions show that the interaction between a pinned particle and a mobile particle affects S2 and SOP more than the interaction between two mobile particles. We show that a similar effect is also present in the calculation of the excess entropy and is the primary reason for the well-known vanishing of the configurational entropy at high temperatures. We further show that, contrary to the common belief, the pinning process does change the structure. When these two effects are considered, both S2 and SOP decrease with an increase in "c," and the correlation between the structural parameters and the dynamics continues even for higher values of "c."

The pool boiling heat transfer of ammonia/Fe3O4 nano-refrigerant in the presence of external magnetic field and heat flux: A molecular dynamics approach

Pool boiling is distinguished by its capacity to eliminate excessive heat fluxes (HFs) at low temperatures. In recent decades, the optimal design of flooded evaporators elevated the significance of pool boiling HT with refrigerant to conserve natural resources and energy. The industry highly regards this process on account of its superior heat transfer (HT) coefficient in comparison to other HT mechanisms. Among the types of boiling, pool boiling has a special place due to its ability to remove HFs at low temperatures. This study was the first to investigate the boiling characteristics of the ammonia/Fe3O4 nano-refrigerant in a copper (Cu) nanochannel (NC) through molecular dynamics (MD) simulations. The primary goal was to investigate the effect of external HF (EHF) and external magnetic field amplitude (EMFA) on nanostructures' atomic behavior (AB) and thermal behavior (TB). The research findings indicate that increasing the applied EHF led to increased particle movement and the HT rate. By changing the EHF, boiling behavior in the nano-refrigerant may also be seen. Maximum (Max) velocity (Vel.) increased to 8.970 Å/ps when the EHF increases to 0.5 W/m2. Atomic collisions and particle mobility both increase when the EHF increases. Therefore, the maximum temperature value increases to 359.46 K. When the EMFA applied to the nano-refrigerant reaches to 0.5 T, the maximum values of the parameters, such as the Temp. and the velocity, reach to 410.07 K, and 11.802 Å/ps, respectively.

Time-dependent properties of run-and-tumble particles. II. Current fluctuations.

We investigate steady-state current fluctuations in two models of hardcore run-and-tumble particles (RTPs) on a periodic one-dimensional lattice of L sites, for arbitrary tumbling rate γ=τ_{p}^{-1} and density ρ; model I consists of standard hardcore RTPs, while model II is an analytically tractable variant of model I, called a long-ranged lattice gas (LLG). We show that, in the limit of L large, the fluctuation of cumulative current Q_{i}(T,L) across the ith bond in a time interval T≫1/D grows first subdiffusively and then diffusively (linearly) with T: 〈Q_{i}^{2}〉∼T^{α} with α=1/2 for 1/D≪T≪L^{2}/D and α=1 for T≫L^{2}/D, where D(ρ,γ) is the collective- or bulk-diffusion coefficient; at small times T≪1/D, exponent α depends on the details. Remarkably, regardless of the model details, the scaled bond-current fluctuations D〈Q_{i}^{2}(T,L)〉/2χL≡W(y) as a function of scaled variable y=DT/L^{2} collapse onto a universal scaling curve W(y), where χ(ρ,γ) is the collective particle mobility. In the limit of small density and tumbling rate, ρ,γ→0, with ψ=ρ/γ fixed, there exists a scaling law: The scaled mobility γ^{a}χ(ρ,γ)/χ^{(0)}≡H(ψ) as a function of ψ collapses onto a scaling curve H(ψ), where a=1 and 2 in models I and II, respectively, and χ^{(0)} is the mobility in the limiting case of a symmetric simple exclusion process; notably, the scaling function H(ψ) is model dependent. For model II (LLG), we calculate exactly, within a truncation scheme, both the scaling functions, W(y) and H(ψ). We also calculate spatial correlation functions for the current and compare our theory with simulation results of model I; for both models, the correlation functions decay exponentially, with correlation length ξ∼τ_{p}^{1/2} diverging with persistence time τ_{p}≫1. Overall, our theory is in excellent agreement with simulations and complements the prior findings [T. Chakraborty and P. Pradhan, Phys. Rev. E 109, 024124 (2024)1539-375510.1103/PhysRevE.109.024124].

Architecture dependent transport behavior of iron (0) entrapped biodegradable polymeric particles for groundwater remediation

Polylactic acid based spherical particles with three architectural variations (Isotropic (P1), Semi porous (P2), and Janus (P3)) were employed to encapsulate zero valent iron nanoparticles (ZVINPs), and their performance was extensively evaluated in our previous studies. However, little was known about their transportability through saturated porous media of varying grain size kept under varying ionic strength. In this particular study, we aimed to investigate the architectural effect of polymeric particles (P1–P3) on their mobility through the sand column of varying grain size in presence of mono, di, and tri-valent ions of varying concentrations (25–200 mM (millimoles)). As per column breakthrough experiments (BTCs) using various types of sands, amphiphilic Janus type (P3) particles exhibited the maximum transportability among all the tested particles, irrespective of the nature of the sand. Owing to the narrower travel path, sands with lower porosity (31%) delayed the plateau by shifting it to a higher pore volume with a minimum retention of iron (C/Co: 0.94 for P3) in the column. The impact of mono (Na+, K+), di (Ca2+, Mg2+), and trivalent (Al3+) ions on their transportability was progressively increased from P3 to P1, especially at higher ionic concentrations (200 mM), with P3 being the most mobile particles (C/Co:0.54 for Al3+). Among all the ions, Al3+ exhibited maximum hindrance to their mobility through the sand column. This could be due to their strong charge screening effect coupled with cation bridging complex formation with moving particles. Experimental results obtained from BTCs were found to be well-fitted with a theoretical model based on advection-dispersion equation, showing minimum retention for P3 particles. Overall, it can be inferred that encapsulation of ZVINPs inside Janus particles (P3) with a right balance of amphiphilicity and highly negative surface charge would be required to achieve considerable transportability through sand aquifers to target contaminants in polluted groundwater existing under harsh conditions (high ionic concentrations).

Transport of nanoscale zero-valent iron in the presence of rhamnolipid

Nanoscale zero-valent iron (nZVI) particles have gained widespread use for in-situ treatment of various chlorinated hydrocarbons. Their non-toxic nature, affordability, and minimal maintenance requirements have made them a favored material for nanoremediation. The treatment typically involves the injection of nZVI particles into contaminated sites using direct-push well injection systems. However, their small size leads to high surface energy, causing aggregation that alters their physiochemical properties, reactivity, and transport behavior. To counteract aggregation, nZVI suspension can be stabilized with different surfactants, reducing the surface energy during subsurface soil transport. This study investigates the impact of rhamnolipid, a biosurfactant produced by Pseudomonas aeruginosa during the late growth phase, on the aggregation and mobility of nZVI particles. The retardation factor of nZVI in the model media of zeolite, ZK406H, decreased from 1.66 in the absence of rhamnolipid to 1.03, 0.98, 0.93, and 0.87, corresponding to the presence of rhamnolipid at concentrations of 20, 50, 80, and 100 mg/L. The deposition coefficient also decreased from 2.39 in the absence of rhamnolipid to 0.459, 0.279, 0.217, and 0.0966, corresponding to the presence of rhamnolipid at concentrations of 20, 50, 80, and 100 mg/L. The transport parameters of nZVI in ZK406H were linked to the interactions of nZVI particles with ZK406H by the DLVO theory.

Pro+: Automated protrusion and critical shear stress estimates from 3D point clouds of gravel beds

AbstractThe dimensionless critical shear stress (τ*c) needed for the onset of sediment motion is important for a range of studies from river restoration projects to landscape evolution calculations. Many studies simply assume a τ*c value within the large range of scatter observed in gravel‐bedded rivers because direct field estimates are difficult to obtain. Informed choices of reach‐scale τ*c values could instead be obtained from force balance calculations that include particle‐scale bed structure and flow conditions. Particle‐scale bed structure is also difficult to measure, precluding wide adoption of such force‐balance τ*c values. Recent studies have demonstrated that bed grain size distributions (GSD) can be determined from detailed point clouds (e.g. using G3Point open‐source software). We build on these point cloud methods to introduce Pro+, software that estimates particle‐scale protrusion distributions and τ*c for each grain size and for the entire bed using a force‐balance model. We validated G3Point and Pro+ using two laboratory flume experiments with different grain size distributions and bed topographies. Commonly used definitions of protrusion may not produce representative τ*c distributions, and Pro+ includes new protrusion definitions to better include flow and bed structure influences on particle mobility. The combined G3Point/Pro+ provided accurate grain size, protrusion and τ*c distributions with simple GSD calibration. The largest source of error in protrusion and τ*c distributions were from incorrect grain boundaries and grain locations in G3Point, and calibration of grain software beyond comparing GSD is likely needed. Pro+ can be coupled with grain identifying software and relatively easily obtainable data to provide informed estimates of τ*c. These could replace arbitrary choices of τ*c and potentially improve channel stability and sediment transport estimates.

Low-temperature synthesis and properties of high-purity boron nitride microspheres

Boron nitride (BN) has excellent high temperature resistance, thermal conductivity, strong insulation, and wave-transparent properties. Spherical BN is an essential filler in polymer matrix composites due to good particle mobility and high filler content. In this paper, we present a large-scale preparation for BN microspheres with uniform particle size distribution in the range of 1.0–2.8 μm via solvothermal method at low cost and high yield (∼90%), which is two orders of magnitude lower than the diameter of the spherical BN prepared by other methods. BN microspheres can achieve good crystallinity (>70%) and high purity (>99.9%) at 800 °C. The temperature resistance study showed that the BN microspheres could maintain the dense particle morphology at 1200 °C. In addition, the prepared BN microspheres have good dielectric and thermal conductivity properties (dielectric constant ∼3.4, dielectric loss ∼2.0 × 10−3, and thermal conductivity of 9.8 W m−1 K−1), which show great potential in the field of wave-transparent and thermal conductive composites. The synthesis process of BN microspheres proposed in this study provides a new idea for the preparation of ceramic micro or nano materials by polymer-derived ceramics.

Potentiostatic oscillations of current and surface structure in a 3D cellular automaton model of metal passivation

Some recently obtained data from simulations in our 3D cellular automaton model on metal passivation are presented and discussed. The model is a non-equilibrium heterogeneous Ising-like model with moving boundary due to metal depletion by corrosion. The mobile particles representing metal oxide are produced in corrosion events. They bind to the metal surface and to each other with short range interaction. They diffuse by random walk with asymmetric exclusion and disappear in the bulk solution.The results of this paper are obtained in potentiostatic conditions. In our model, this amounts to a fixed bare metal corrosion rate. The results include current transients and surface snapshots at a number of moments of time. We define several other dynamic variables. Their transients allow us to construct phase portraits, to identify the bare metal surface area and the oxide layer thickness as the essential variables for the oscillations. The first of those is equivalent to current density by model construction. The second plays a peculiar role in periodic current spiking, as discussed in the text.

Comparative analysis of the effects of different purification methods on the yield and purity of cow milk extracellular vesicles

AbstractIsolation of extracellular vesicles (EV) has been developing rapidly in parallel with the interest in EVs. However, commonly utilized protocols may not suit more challenging sample matrixes and could potentially yield suboptimal results. Knowing and assessing the pitfalls of isolation procedure to be used, should be involved to some extent for EV analytics. EVs in cow milk are of great interest due to their abundancy and large‐scale availability as well as their cross‐species bioavailability and possible use as drug carriers. However, the characteristics of milk EVs overlap with those of other milk components. This makes it difficult to isolate and study EVs individually. There exists also a lack of consensus for isolation methods. In this study, we demonstrated the differences between various differential centrifugation‐based approaches for isolation of large quantities of EVs from cow milk. Samples were further purified with gradient centrifugation and size exclusion chromatography (SEC) and differences were analyzed. Quality measurements were conducted on multiple independent platforms. Particle analysis, electron microscopy and RNA analysis were used, to comprehensively characterize the isolated samples and to identify the limitations and possible sources of contamination in the EV isolation protocols. Vesicle concentration to protein ratio and RNA to protein ratios were observed to increase as samples were purified, suggesting co‐isolation with major milk proteins in direct differential centrifugation protocols. We demonstrated a novel size assessment of vesicles using a particle mobility analyzer that matched the sizing using electron microscopy in contrast to commonly utilized nanoparticle tracking analysis. Based on the standards of the International Society for Extracellular Vesicles and the quick checklist of EV‐Track.org for EV isolation, we emphasize the need for complete characterization and validation of the isolation protocol with all EV‐related work to ensure the accuracy of results and allow further analytics and experiments.

Effects of Tween 20 addition on electrokinetic transport in a polydimethylsiloxane microchannel.

Tween 20 is frequently added to particle suspensions for reducing the particle-wall adhesion and particle-particle aggregation in microfluidic devices. However, the influences of Tween 20 on the fluid and particle behaviors have been largely ignored. We present in this work the first experimental study of the effects of Tween 20 addition on the electrokinetic transport of fluids and particles in a polydimethylsiloxane microchannel. We find that adding 0.1% v/v Tween 20 to a buffer solution can significantly reduce the electroosmotic mobility as well as the electrokinetic and electrophoretic mobilities of polystyrene particles and yeast cells. Further increasing the Tween 20 concentration within the range typically used in microfluidic applications continues reducing these mobility values, but at a smaller rate. Our finding suggests that Tween 20 should be used with care in electrokinetic microdevices when the flow rate or particle/cell throughput is an important parameter.

Double-inverse-opal structured films of a hydrogel framework and mobile inorganic particles

Double-inverse-opal (DIO) structured assemblies are three-dimensionally ordered porous materials containing core particles inside. In this work, DIO structured films composed of mobile inorganic colloidal particles within an organic polymer gel framework were developed. As the organic backbone, a poly(N-isopropylacrylamide) gel (PNIPAM gel) was employed to enhance the flexibility and processability of the films. A three-dimensional periodic structure of fluorescent-labelled silica core particles in the film was observed with confocal microscopy. Thermally induced volume transitions of the PNIPAM gels were observed, which showed the potential for stimuli-responsive optical materials. By selective etching of the sacrificial shell layers surrounding the core particles, cavities formed around the cores, and they exhibited random Brownian motion inside these pockets in the film. As a new type of organic-inorganic composite material, the proposed DIO structured films possessed unique characteristics originating from the combination of a flexible backbone and mobile cores, applicable to stimuli-responsive photonic devices, reusable catalytic particle assemblies, etc.