Slow Particles Research Articles

Hidden comet tails of marine snow impede ocean-based carbon sequestration.

Gravity-driven sinking of "marine snow" sequesters carbon in the ocean, constituting a key biological pump that regulates Earth's climate. A mechanistic understanding of this phenomenon is obscured by the biological richness of these aggregates and a lack of direct observation of their sedimentation physics. Utilizing a scale-free vertical tracking microscopy in a field setting, we present microhydrodynamic measurements of freshly collected marine snow aggregates from sediment traps. Our observations reveal hitherto-unknown comet-like morphology arising from fluid-structure interactions of transparent exopolymer halos around sinking aggregates. These invisible comet tails slow down individual particles, greatly increasing their residence time. Based on these findings, we constructed a reduced-order model for the Stokesian sedimentation of these mucus-embedded two-phase particles, paving the way toward a predictive understanding of marine snow.

Transition Radiation on a Conducting Target Shaped as a Right Dihedral Angle

The transition radiation of a charged particle in the simplest case of its incidence onto an infinite, perfectly conducting plane can be described using the method of images known from electrostatics. The same method makes it possible to find the field distribution in more complex cases, such as the field created by a point particle in the presence of two intercepting conducting planes, the angle between which divides exactly the angle of 180°. Based on the method of images, a description is given of the transition radiation that occurs when a fast-charged particle falls on a target in the form of two conducting half-planes intersecting at the right angle (on the inside of the dihedral angle). The features of the radiation emitted by fast and slow particles are qualitatively considered, and their visual interpretation is given. The possibility of using interference effects arising from radiation to monitor beams of charged particles is discussed.

A Slow Failure Particle Swarm Optimization Long Short-Term Memory for Significant Wave Height Prediction

Significant wave height (SWH) prediction is crucial for marine safety and navigation. A slow failure particle swarm optimization for long short-term memory (SFPSO-LSTM) is proposed to enhance SWH prediction accuracy. This study utilizes data from four locations within the EAR5 dataset, covering 1 January to 31 May 2023, including variables like wind components, dewpoint temperature, sea level pressure, and sea surface temperature. These variables predict SWH at 1-h, 3-h, 6-h, and 12-h intervals. SFPSO optimizes the LSTM training process. Evaluated with R2, MAE, RMSE, and MAPE, SFPSO-LSTM outperformed the control group in 13 out of 16 experiments. Specifically, the model achieved an optimal RMSE of 0.059, a reduction of 0.009, an R2 increase to 0.991, an MAE of 0.045, and an MAPE of 0.032. Our results demonstrate that SFPSO-LSTM provides reliable and accurate SWH predictions, underscoring its potential for practical applications in marine and atmospheric sciences.

Switching particle systems for foraging ants showing phase transitions in path selections

Switching interacting particle systems studied in probability theory are the stochastic processes of hopping particles on a lattice made up of slow and fast particles, where the switching between these types of particles occurs randomly at a given transition rate. This paper explores how such stochastic processes involving multiple particles can model group behaviors of ants. Recent experimental research by the last author’s group has investigated how ants switch between two types of primarily relied cues to select foraging paths based on the current situation. Here, we propose a discrete-time interacting random walk model on a square lattice, incorporating two types of hopping rules. Numerical simulation results demonstrate global changes in selected homing paths, transitioning from trailing paths of the ‘pheromone road’ to nearly optimal paths depending on the switching parameters. By introducing two types of order parameters characterizing the dependence of homing duration distributions on switching parameters, we discuss these global changes as phase transitions in ant path selections. We also study critical phenomena associated with continuous phase transitions.

Impact of several coarse-graining models on a pilot-scale fluidized bed behavior using discrete element method–computational fluid dynamics

Impact of several coarse-graining models on a pilot-scale fluidized bed behavior using discrete element method–computational fluid dynamics

Design of reactive particle fluidized bed heat exchangers for gas–solid thermochemical energy storage

Concentrated solar power (CSP) systems integrated with a supercritical carbon dioxide (sCO2) Brayton power cycle are regarded as the primary future direction for CSP technologies. Calcium-based particles can be a suitable storage medium to achieve high temperatures exceeding 750 ℃. However, there have been few studies on reactive particle/sCO2 heat exchangers (HXs) to drive high-performance power cycles with high energy storage efficiencies. In this paper, the mechanisms by which chemically reactive particles release energy in a fluidized bed (FB) heat exchanger has been investigated to evaluate the performance of thermochemical storage systems. A 1-MWt thermal duty fluidized bed heat exchanger with sCO2 as the working fluid operating at 988 K was designed in different configurations, featuring single stage and multistage counter-flow HXs. A detailed shell and tube model combining the chemical reaction kinetics and the heat transfer between the fluidized particle and sCO2 FB HX design was developed. A comparison of sensible and chemical heat materials shows that thermochemical energy storage is advantageous due to the relatively short tube length and slow particle mass flow rate. The tube length and particle mass flow rate are reduced by 3.5 and 11.5 times, respectively. The average chemical conversion is 97.30 % for a one-stage heat exchanger, which is lower than the 99.95 % conversion achieved by the two-stage heat exchanger. Additionally, a sensitivity analysis was carried out to understand the impacts of key operating parameters on the process performance. These findings provide insights into the operational stability and efficiency of the system, contributing to the development of advanced heat exchangers for thermochemical energy storage applications.

Dispersion and Dosimetric Challenges of Hydrophobic Carbon-Based Nanoparticles in In Vitro Cellular Studies.

Methodologies across the dispersion preparation, characterization, and cellular dosimetry of hydrophilic nanoparticles (NPs) have been developed and used extensively in the field of nanotoxicology. However, hydrophobic NPs pose a challenge for dispersion in aqueous culture media using conventional methods that include sonication followed by mixing in the culture medium of interest and cellular dosimetry. In this study, a robust methodology for the preparation of stable dispersions of hydrophobic NPs for cellular studies is developed by introducing continuous energy over time via stirring in the culture medium followed by dispersion characterization and cellular dosimetry. The stirring energy and the presence of proteins in the culture medium result in the formation of a protein corona around the NPs, stabilizing their dispersion, which can be used for in vitro cellular studies. The identification of the optimal stirring time is crucial for achieving dispersion and stability. This is assessed through a comprehensive stability testing protocol employing dynamic light scattering to evaluate the particle size distribution stability and polydispersity. Additionally, the effective density of the NPs is obtained for the stable NP dispersions using the volumetric centrifugation method, while cellular dosimetry calculations are done using available cellular computational modeling, mirroring approaches used for hydrophilic NPs. The robustness of the proposed dispersion approach is showcased using a highly hydrophobic NP model (black carbon NPs) and two culture media, RPMI medium and SABM, that are widely used in cellular studies. The proposed approach for the dispersion of hydrophobic NPs results in stable dispersions in both culture media used here. The NP effective density of 1.03-1.07 g/cm3 measured here for black carbon NPs is close to the culture media density, resulting in slow deposition on the cells over time. So, the present methodology for dispersion and dosimetry of hydrophobic NPs is essential for the design of dose-response studies and overcoming the challenges imposed by slow particle deposition.

Dynamical arrest transition of a bidisperse two-patchy colloidal dispersion: A dynamic Monte Carlo study.

During the last few years, patchy colloidal dispersions have emerged as ideal candidates of glass-formers of systems composed of particles that interact with non-isotropic potentials. However, from the computational point of view, the characterization of their dynamical properties close to the glass transition via any kind of molecular dynamics simulation technique can be very difficult due to the slowing down of both the rotational and translational dynamics. Although a plethora of dynamical techniques have been developed to account for the dynamics of patchy colloids, new and complementary simulation techniques are required to explore, much faster and more efficiently, the dynamical arrest transition of patchy colloidal dispersions when computer simulation consists of a large number of particles and, due to the slow particle dynamics at the glass transition, an extended time window is explicitly required. Then, in this contribution, by means of the so-called dynamic-Monte Carlo method, we report on the dynamical arrest transition, both rotational and translational, of a bidisperse patchy colloidal dispersion, following three different paths along the density-temperature plane, including high densities and low temperatures. Although this method has not been extensively tested at extreme thermodynamic conditions, we show that even at the dynamical arrest transition, it allows us to extract good dynamical data from a complex system. Therefore, it turns out to be a promising technique to explore the onset of vitrification of anisotropic colloidal particles.

Measuring Ice Pellets and Refrozen Wet Snow Using a Laser-Optical Disdrometer

Abstract This study aims to characterize the shapes and fall speeds of ice pellets formed in various atmospheric conditions and to investigate the possibility to use a laser-optical disdrometer to distinguish between ice pellets and other types of precipitation. To do so, four ice pellet events were documented using manual observations, macrophotography, and laser-optical disdrometer data. First, various ice pellet fall speeds and shapes, including spherical, bulged, fractured, and irregular particles, were associated with distinct atmospheric conditions. A higher fraction of bulged and fractured ice pellets was observed when solid precipitation was completely melted aloft while more irregular particles were observed during partial melting. These characteristics affected the diameter–fall speed relations measured. Second, the measurements of particles’ fall speed and diameter show that ice pellets could be differentiated from rain or freezing rain. Ice pellets larger than 1.5 mm tend to fall > 0.5 m s−1 slower than raindrops of the same size. In addition, the fall speed of a small fraction of ice pellets was < 2 m s−1 regardless of their size, as compared with a fall speed > 3 m s−1 for ice pellets with diameter > 1.5 mm. Video analysis suggests that these slower particles could be ice pellets passing through the laser-optical disdrometer after colliding with the head of the instrument. Overall, these findings contribute to a better understanding of the microphysics of ice pellets and their measurement using a laser-optical disdrometer. Significance Statement Ice pellets are challenging to forecast and to detect automatically. In this study, we documented the fall speed and physical characteristics of ice pellets during various atmospheric conditions using a combination of a laser-optical disdrometer, manual observations, and macrophotography images. Relationships were found between the shape and fall speed of ice pellets. These findings could be used to refine the parameterization of ice pellets in atmospheric models and, consequently, improve the forecast of impactful winter precipitation types such as freezing rain. Furthermore, they will also help to physically interpret laser-optical disdrometer data during ice pellets and freezing rain.

Fragmentation of metal(II) bis(acetylacetonate) complexes induced by slow electrons.

Nowadays, organometallic complexes receive particular attention because of their use in the design of pure nanoscale metal structures. In the present work, we present results obtained from a series of studies on the degradation of metal(II) bis(acetylacetonate)s induced by low-energy electrons. These slow particles induce the formation of the acetylacetonate anion, [acac]-, and the parent anion as the most dominant species at incident electron energies near 0 eV. They also fragment the organometallic compounds via various competitive reaction channels that occur at higher energies via dissociative electron attachment. The reported data may contribute to a better understanding of the physical chemistry underlying the electron-molecule interactions, which is crucial for potential applications of these molecular systems in the deposition of nanoscale structures.

Thermophoresis and uniform flow in rarefied polyatomic gases: The role of constitutive relations and boundary conditions

Recently, Rana and Barve [“A second-order constitutive theory for polyatomic gases: Theory and applications,” J. Fluid Mech. 958, A23 (2023)] developed a second-order coupled constitutive relations (CCR) for polyatomic gases that include quadratic nonlinearities in the entropy flux and apply the second law. However, in that work, the boundary conditions were heuristically obtained to match the drag coefficient on a sphere and may not be accurate in situations where thermal transpiration and thermal stress are significant factors, as indicated by their asymptotic analysis. This article presents a systematic approach for deriving thermodynamically admissible boundary conditions for the CCR model. We also propose a set of higher-order boundary conditions based on an asymptotic analysis of the solutions for drag on flow past a sphere and thermophoretic drag. The goal of deriving these boundary conditions is to improve the accuracy of the CCR model when applied to external flows, such as slow flow past particles and thermophoretic motion of a spherical particle and doublet. The results of the study demonstrate that the combination of the newly derived boundary conditions in conjunction with the CCR equations shows excellent agreement with both theoretical predictions and experimental data over a wide range of Knudsen numbers. The study suggests that the approach presented in this article can be used to improve the accuracy of the CCR model in a variety of external flow applications.

Slow and fast particles in shear-driven jamming: Critical behavior.

We do extensive simulations of a simple model of shear-driven jamming in two dimensions to determine and analyze the velocity distribution at different densities ϕ around the jamming density ϕ_{J} and at different low shear strain rates, γ[over ̇]. We then find that the velocity distribution is made up of two parts which are related to two different physical processes which we call the slow process and the fast process as they are dominated by the slower and the faster particles, respectively. Earlier scaling analyses have shown that the shear viscosity η, which diverges as the jamming density is approached from below, consists of two different terms, and we present strong evidence that these terms are related to the two different processes: the leading divergence is due to the fast process, whereas the correction-to-scaling term is due to the slow process. The analysis of the slow process is possible thanks to the observation that the velocity distribution for different γ[over ̇] and ϕ at and around the shear-driven jamming transition has a peak at low velocities and that the distribution has a constant shape up to and slightly above this peak. We then find that it is possible to express the contribution to the shear viscosity due to the slow process in terms of height and position of the peak in the velocity distribution and find that this contribution matches the correction-to-scaling term, determined through a standard critical scaling analysis. A further observation is that the collective particle motion is dominated by the slow process. In contrast to the usual picture in critical phenomena with a direct link between the diverging correlation length and a diverging order parameter, we find that correlations and shear viscosity decouple since they are controlled by different sets of particles and that shear-driven jamming is thus an unusual kind of critical phenomenon.

How hysteresis produces discontinuous patterns in degenerate reaction–diffusion systems

In this paper, we study the asymptotic behaviour of the solutions to a degenerate reaction–diffusion system. This system admits a continuum of discontinuous stationary solutions due to the effect of a hysteresis process, but only one discontinuous stationary solution is compatible with a principle of preservation of locally invariant regions. Using a macroscopic mass effect which guarantees that fast particles help slow particles to displace, we establish a novel result of convergence of a non trivial set of trajectories towards a discontinuous pattern.

The Development of Novel Ganoderic-Acid-Encapsulated Nanodispersions Using the Combination of Ultrasonic Cavitation and Solvent Evaporation through Response Surface Optimization

Ganoderic Acid (GA), a major bioactive compound isolated from the East Asian medicinal mushroom Ganoderma tsugae, is traditionally believed to have significant medicinal properties. GA is poorly soluble in water, which poses several challenges in terms of its formulation. In this study, Ganoderma tsugae extracts obtained through ethanol extraction were encapsulated in nanodispersions via ultrasonic cavitation and solvent evaporation to increase their bioavailability. The preparation route was thoroughly analyzed using Response Surface Methodology (RSM) to determine the interactions between the variables. Based on the results, the Hydrophilic–Lipophilic Balance (HLB) and the evaporation temperature significantly influenced the resulting particle size. In the optimized nanodispersions, GA was incorporated into a hydrophobic core with a particle size no greater than 200 nm and a very narrow particle distribution (namely, a polydispersity index of 0.289). Due to the high negative zeta potential (−45.9 mV), a very slow particle growth rate of 0.239% over short-term storage (14 days) was achieved. In addition, the zeta average remained virtually unchanged for 14 days at room temperature in solutions at different pH levels. In summary, this paper provides the first-ever demonstration that ultrasound cavitation in conjunction with solvent evaporation can be used to generate GA nanodispersions.

Enhanced electrochemical performance of nanoscale single crystal NMC811 modification by coating LiNbO3

Single crystallization is an important strategy to resolve intergranular cracks and unnecessary side reactions with electrolytes in layered transition metal oxide cathodes LiNi0.8Mn0.1Co0.1O2 (NMC811). Due to the limitations of high-temperature sintering and multi-step calcination, single crystal NMC811 generally shows irregular particles with a size of 2–3 µm. However, the prolonged Li-ion diffusion pathway and the stress generated by the uneven de-/intercalation sluggish Li-ion diffusion kinetics, what is more, cause structural damage such as intragranular cracks. A slow Li extraction rate or particle size reduction will ameliorate the structural damage and improve the cycling stability. As the most promising cathodes for next-generation power batteries, NMC811 required fast charge performance and cycle stability. Particle size reduction appears to be the displacement option. Nanonization is an effective strategy to mitigate intragranular cracks of single crystal NMC811. However, the serious aggregation and increased specific surface area become new challenges. In this article, we synthesized monodisperse nanoscale single crystal NMC811 by molten salt method and modified the surface by LiNbO3 coating. The electrochemical performance shows that nanoscale single crystal NMC811 has faster kinetic and higher capacity retention, so the strategy of combining nanonization and surface coating is an alternative way to prepare high specific capacity and cycle stable single crystal NMC811.

Coarse-grained dynamics of transiently bound fast linkers.

Transient bonds between fast linkers and slower particles are widespread in physical and biological systems. Despite their diverse structure and function, a commonality is that the linkers diffuse on timescales much faster compared to the overall motion of the particles they bind to. This limits numerical and theoretical approaches that need to resolve these diverse timescales with high accuracy. Many models, therefore, resort to effective, yet ad hoc, dynamics, where linker motion is only accounted for when bound. This paper provides a mathematical justification for such coarse-grained dynamics that preserves detailed balance at equilibrium. Our derivation is based on multiscale averaging techniques and is broadly applicable. We verify our results with simulations on a minimal model of fast linker binding to a slow particle. We show how our framework can be applied to various systems, including those with multiple linkers, stiffening linkers upon binding, or slip bonds with force-dependent unbinding. Importantly, the preservation of detailed balance only sets the ratio of the binding to the unbinding rates, but it does not constrain the detailed expression of binding kinetics. We conclude by discussing how various choices of binding kinetics may affect macroscopic dynamics.

Synergy between hydrophilic silica nanoparticles and poly(vinylpyrrolidone) for long-term foam stabilization with little energy input

The role of solid particles to act as foam and emulsion stabilizers is well known, providing long-term stability to the two-phase system. However, the ability for particles to generate large volumes of foam with little energy input (low agitation speeds and short agitation times) is difficult to achieve. Poor foamability is due to the slow particle adsorption dynamics and the high adsorption barrier at the air–water interface. In contrast, common surfactants and some surface active polymers which adsorb more readily at the air–water interface exhibit good foamability but often poor foam stability due to the mutual action of multiple destabilization mechanisms. In the current study, we reported a simple bi-component system of hydrophilic silica nanoparticles and poly(vinylpyrrolidone) (PVP) polymer to produce foams with both high foamability and foam stability via simply hand shaking for 1 min. Foams are stabilized by PVP coated silica composite nanoparticles (CPs) with a well-defined core–shell structure. The strong adsorption of PVP onto silica was demonstrated using Quartz Crystal Microbalance with Dissipation monitoring (QCM-D), confirming the formation of an irreversibly and robust adsorbed polymer layer. To better understand the mechanisms for enhanced foamability and foam stability, the interfacial dynamics and the 2-dimensional mechanical properties of the particle-polymer network partitioned at the air–water interface were assessed. The presence of the PVP polymer corona substantially enhanced the adsorption and retention of hydrophilic silica particles at the air/water interface, while the rigid interfacial network formed by the silica nanoparticles guaranteed long-term foam stability (excess of one week), with coarsening fund to be the dominating destabilization mechanism for foam. The enhanced performance is in stark contrast to the individual components, which could only provide good foamability other than foam stability.

Multiple Scenarios of Low-Temperature Nucleation in Simple Liquids.

Usually, sufficient supercooling of a liquid is employed to bypass the free energy barrier and speed up crystallization. However, lowering the temperature T induces new issues competing with the crystallization, e.g., slow particle motion, geometric frustration, and the glass formation, which complicates our understanding of crystal growth. Here we systematically study the low-temperature nucleation kinetics discriminated by the maximum nucleation rate temperature T_{d} and the glass transition temperature T_{g}. At T_{d}, the ratio of the precursor and geometrically frustrated particles reaches the maximum. When T_{g}<T<T_{d}, nucleation kinetics is characterized by the subdiffusive slow particle motion, the high degrees of geometric frustration, and the saturation of precursors. In this regime, nucleation can proceed through the diffusionless-like ordering of precursors. Near T_{g}, there is a crossover regime, where geometrically frustrated particles percolate and the glass formation strongly slows down the nucleation. When T<T_{g}, diffusionless nucleation is obstructed due to the weak vibrational motion and the mechanical stability of the glassy state.

Catastrophic dark matter particle capture

In this paper we describe a new idea which may be relevant to the formation of galaxies via the infall of baryonic matter (BM) and dark matter (DM) onto a preexisting overdensity. While BM can under certain circumstances be captured by thermal processes, DM particles fly through a static overdensity without being captured. We propose a simple model for DM capture: if during the passage through it, the mass of the overdensity increases, then slow DM particles are captured by it, further increasing its mass, while faster particles slow down, transferring part of their energy to the galaxy. We estimate the minimum initial velocity of a particle required for a passage without capture through the center of the galaxy and derive a nonlinear equation describing the rate of galaxy mass increase. An analysis carried out using the ideas of catastrophes theory shows that if the increase in the mass of baryonic matter exceeds a certain threshold value, this can lead to a very intensive capture of dark matter. We speculate that this process may be associated on the one hand with the accretion of matter during the early stages of galaxy formation and, on the other hand, also later with the merger of galaxies. For the studied process to take place, the density of intergalactic DM must exceed some threshold value. Then the rate of increase in the mass of DM can be much higher than the one of baryonic matter. The capture sharply decreases after the DM density drops below the threshold value, e.g., due to the expansion of the Universe.

Secondary particle predictions in quasifree proton scattering reactions in the 100–250 MeV energy range

Results for observables related to the secondary particle production process in proton-nucleus spallation reactions at low beam incident energy (100--250 MeV) are shown. The energy and angular distributions of the residual nucleus are determined in the context of our multicollisional Monte Carlo intranuclear cascade model. The mechanism of proton-nucleus reactions is conventionally described as a sequence of two stages: the rapid intranuclear cascade phase and the slow particle evaporation step. In this work we focus on the rapid phase considering the nucleon effective mass as an effect of the many-body nuclear interactions and the intranuclear mean field. This procedure represents a more realistic scenario to obtain the particles' multiplicity generated in spallation reactions with light-mass target nuclei in a low-energy range. We focused our attention on target nuclei of macro elements, such as carbon, oxygen, phosphorus, sulfur, sodium, potassium, chlorine, and calcium, and trace elements such as iron, copper, zinc, bromine and selenium, which are the most frequent compounds of the organic material. The choice of these target nuclei is due to our expectancy that our results can work as a preliminary insight for further theoretical approaches, specially taking into account nuclear effects due to the interaction of the particles of the beam with the organic tissue.