Particle Dynamics Research Articles

Quantum transport under oscillatory drive with disordered amplitude.

We investigate the dynamics of non-interacting particles in a one-dimensional tight-binding chain in the presence of an electric field with random amplitude drawn from a Gaussian distribution, and explicitly focus on the nature of quantum transport. We derive an exact expression for the probability propagator and the mean-squared displacement in the clean limit and generalize it for the disordered case using the Liouville operator method. Our analysis reveals that in the presence a random static field, the system follows diffusive transport; however, an increase in the field strength causes a suppression in the transport and thus asymptotically leads towards localization. We further extend the analysis for a time-dependent disordered electric field and show that the dynamics of mean-squared-displacement deviates from the parabolic path as the field strength increases, unlike the clean limit where ballistic transport occurs.

Modeling the Nucleation and Growth of Lead Sulfate Particles on Lead Electrodes

Abstract Lead-acid batteries (LABs) play a pivotal role in the energy storage sector with applications spanning from starting-lighting-ignition batteries to grid energy storage. Passivation of lead negative electrodes by PbSO4 particles is a fundamental mechanism limiting the performance of LAB. In this regard, an electrochemical model is developed that simulates the nucleation and growth (N&G) dynamics of PbSO4 particles on a flat lead electrode, responsible for its passivation. The model considers the electrochemical reactions between lead electrode and sulfuric acid, N&G of PbSO4 particles, passivation of the lead surface, and the ternary transport of PbSO4 (aq), bisulfate, and protons in H2SO4 electrolyte. The model is validated with a dataset of cyclic voltammetry (CV) responses collected at several scan rates and H2SO4 concentrations. The model shows remarkable qualitative and quantitative agreement with the experimental data including CV peak features, discharge capacity, and particle size. The model was employed to explore key N&G quantities, such as supersaturation, nucleation rate, particle count, growth rate, particle size, and surface coverage, and to examine how their interactions influence electrode utilization. Parametric studies were also conducted to evaluate how scan rates and acid concentrations influence the previously mentioned N&G quantities and, subsequently, the utilization of the electrode.

Open-boundary molecular dynamics of ultrasound using supramolecular water models.

Ultrasound can be used to manipulate protein function and activity, as well as for targeted drug delivery, making it a powerful diagnostic and therapeutic modality with wide applications in sonochemistry, nanotechnology, and engineering. However, a general particle-based approach to ultrasound modeling remains challenging due to the significant disparity between characteristic time scales governing ultrasound propagation. In this study, we use open-boundary molecular dynamics to simulate ultrasound waves in liquid water under ambient conditions by employing supramolecular water models, i.e., the Martini 3, dissipative particle dynamics, and many-body dissipative particle dynamics models. We demonstrate that our approach successfully reproduces the solution of the traveling wave equation and captures the velocity dispersion characteristic of high-frequency ultrasound waves.

Investigations of Microstructures and Properties of SPEEK‐[BMIm][OTf] Ionic Liquid Composite Membrane for Fuel Cells

AbstractUtilizing ionic liquids in proton exchange membranes can greatly enhance the performance of fuel cells, enabling their application in high‐temperature and dry conditions. Further advancements in this field depend on a fundamental comprehension of their structural characteristics. This study focuses on the sulfonated poly(ether ether ketone) (SPEEK)‐1‐butyl‐3‐methylimidazolium trifluoromethanesulfonate [BMIm][OTf] composite membrane system. Effects of sulfonation degree, ionic liquid content, and temperature on the structure and conductivity of the composite membrane are investigated by dissipative particle dynamics (DPD) and molecular dynamics (MD) simulations. Results show that [BMIm][OTf] is predominantly distributed around the sulfonic acid groups of SPEEK. At an optimal sulfonation degree and ionic liquid content, interconnected ionic liquid channels can be formed. Nevertheless, an excessively high sulfonation degree may jeopardize the stability of the membrane structure. Moreover, the aggregation of ionic liquid occurs at a high level of ionic liquid content, which hinders the efficient transfer of protons. Generally, increasing the temperature is more conducive to the formation of monodisperse ionic liquid channels within the SPEEK‐[BMIm][OTf] composite membrane; however, overhigh temperature may compromise the integrity of the composite membrane structure. The findings of this study offer molecular insights for the development of high‐temperature proton exchange membrane fuel cell systems.

Study of the dynamics of magnetic particles in rotating magnetic field: A 3D finite element analysis

The analysis of magnetic particle dynamics in a rotating magnetic field and the exploration of the magnetic agglomeration mechanism are crucial for effectively reducing agglomeration in strong magnetic minerals and improving sorting efficiency. The forces acting on magnetic particles in a rotating magnetic field were analyzed in this study. A 3D model was built to simulate the complex interaction between two magnetic particles in a rotating magnetic field using COMSOL Multiphysics finite element simulation software. It shows that the number of periods of change in the spiral period, velocity, and acceleration remains consistent under different conditions. Additionally, their period numbers are positively correlated with magnetic field rotational speed, medium viscosity, and the initial particle spacing, and negatively correlated with magnetic field strength. Under various conditions, the larger the area of the velocity-closed surface in the same cycle, the larger the helical diameter of the particle trajectory. The initial acceleration of the particles exhibits a positive correlation with the strength of the magnetic field, a negative correlation with the viscosity of the medium and the initial distance, and no significant relationship with the rotational speed of the magnetic field. For further research on the dynamics of magnetic particles and the refinement of the mechanism of magnetic agglomeration, the results have an important theoretical reference value.

Dynamics of a single anisotropic particle under various resetting protocols

We study analytically the dynamics of an anisotropic particle subjected to different stochastic resetting schemes in two dimensions. The Brownian motion of shape-asymmetric particles in two dimensions results in anisotropic diffusion at short times, while the late-time transport is isotropic due to rotational diffusion. We show that the presence of orientational resetting promotes the anisotropy to late times. When the spatial and orientational degrees of freedom are reset, we find that a non-trivial spatial probability distribution emerges in the steady state that is determined by the initial orientation, particle asymmetry and the resetting rate. When only spatial degrees of freedom are reset while the orientational degree of freedom is allowed to evolve freely, the steady state is independent of the particle asymmetry. When only particle orientation is reset, the late-time probability density is given by a Gaussian with an effective diffusion tensor, including off-diagonal terms, determined by the resetting rate. Generally, the coupling between the translational and rotational degrees of freedom, when combined with stochastic resetting, gives rise to unique behavior at late times not present in the case of symmetric particles. Considering recent developments in experimental implementations of resetting, our results can be useful for the control of asymmetric colloids, for example in self-assembly processes.

Structural Origin of Dynamic Heterogeneity in Supercooled Liquids.

As a liquid is supercooled toward the glass transition point, its dynamics slow significantly, provided that crystallization is avoided. With increased supercooling, the particle dynamics become more spatially heterogeneous, a phenomenon known as dynamic heterogeneity. Since its discovery, this characteristic of metastable supercooled liquids has garnered considerable attention in glass science. However, the precise physical origins of dynamic heterogeneity remain elusive and widely debated. In this perspective, we examine the relationship between dynamic heterogeneity and structural order, based on numerical simulations of fragile liquids with isotropic potentials and strong liquids with directional interactions. We demonstrate that angular ordering, arising from many-body steric interactions, plays a crucial role in the slow dynamics and dynamic cooperativity of fragile liquids. Additionally, we explore how the growth of static order correlates with slower dynamics. In fragile liquids exhibiting super-Arrhenius behavior, the spatial extent of regions with high angular order grows upon cooling, and the sequential propagation of particle rearrangements within these ordered regions increases the activation energy for particle motion. In contrast, strong liquids with spatially constrained local ordering display a distinct "two-state" dynamic characteristic, marked by a transition between two Arrhenius-type behaviors. We argue that dynamic heterogeneity, irrespective of a liquid's fragility, arises from underlying structural order, with its spatial extent determined by static ordering. This perspective aims to deepen our understanding of the interplay between structural and dynamic properties in metastable supercooled liquids.

Single Particle Dynamics at the Free Surface of Imidazolium-Based Ionic Liquids.

In this work, we carry out a systematic computer simulation investigation of the single particle dynamics at the free surface of imidazolium-based room temperature ionic liquids by applying intrinsic surface analysis. Besides assessing the effect of the potential model and temperature, we focus in particular on the effect of changing the anion type, and, hence, their shape and size. Further, we also address the role of the length of the cation alkyl chains, known to protrude into the vapor phase, on the surface dynamics of the ions. We observe that the surface dynamics of ionic liquids, being dominated by strong electrostatic interactions, is about 2 orders of magnitude slower than that for common molecular liquids. Furthermore, the free energy driving force for exposing apolar chains to the vapor phase "pins" the cations at the surface layer for much longer than anions, allowing them to perform noticeable lateral diffusion at the liquid surface during their stay there. On the other hand, anions, accumulated in the second layer beneath the liquid surface, stay considerably longer here than in the surface layer. The ratio of the mean surface residence time of the cations and anions depends on the relative size of the two ions: larger size asymmetry typically corresponds to larger values of this ratio. We also find, in a clear contrast with the bulk liquid phase behavior, that anions typically diffuse faster at the liquid surface than cations. Finally, our results show that the surface dynamics of the ions is largely determined by the apolar layer of the cation alkyl chains at the liquid surface, as in the absence of such a layer, cations and anions are found to behave similarly with respect to their single particle dynamics.

Airborne pollen concentrations overpass expectations in the tropical city of Medellín, Colombia.

Aerobiology in the tropics is still a science in development, where very little about their dynamics is known. Airborne pollen concentrations in the city of Medellín (Colombia) were measured using a Hirst-type sampler and correlated with meteorological parameters (relative humidity, rainfall, temperature, wind speed, and wind direction, this last analyzed by using circular statistics). Sampling was conducted over three years (2019-2022), and pollen grains were detected on all days of sampling, at higher concentrations than expected for tropical conditions. The highest pollen concentrations were observed from December to January and July-August, corresponding to the months with the lowest rainfall, which sheds light about how La Niña phenomena influenced pollen concentrations during the sampling period. The Main Pollen Season (MPS) ranged in length from 277 to 342days. The highest intra-diurnal peaks pollen concentrations occurred around noon, whilst something very different and rarely reported occurs with Cecropia, which is much more abundant at night, from 20:00 to 1:00h. Circular statistics revealed statistically significant wind direction patterns from SW, matching the same intra-diurnal pollen variations. This work helps to complete the blurred situation of the Aerobiology in the Neotropics and the dynamics of particles in the tropical atmosphere, being a first step towards the construction of pollen calendars to help pollen sufferers to mitigate symptoms.

Dissipative particle dynamics simulations on the self-assembly of rod-coil asymmetric diblock molecular brushes bearing responsive side chains.

The self-assembly behaviors of rod-coil asymmetric diblock molecular brushes (ADMBs) bearing responsive side chains in a selective solvent are investigated via dissipative particle dynamics simulations. By systematically varying the polymerization degree, copolymer concentration, and side chain length, several morphological phase diagrams were constructed. ADMB assemblies exhibited a rich variety of morphologies, including cylindrical micelles, spherical micelles, nanowires, polyhedral micelles, ellipsoid micelles, and large compound micelles. The structures of the representative nanowires were analyzed in detail. A kinetics study revealed that the one-dimensional growth of nanowires follows the step-growth polymerization mechanism. Besides, by calculating the local order parameter of the rigid chains, we found that increasing the lengths of A and C side chains can promote the ordered arrangement of the rigid chains. Moreover, the rod-to-coil conformation transitions were simulated to explore the stimuli-responsive behaviors of ADMBs with responsive rigid side chains. The simulation results indicated that the volume of the assemblies expanded without the support of the rigid chains. The present work not only provides a comprehensive understanding of the self-assembly behaviors of ADMBs but also provides meaningful theoretical support for the development of novel molecular brush materials.

Non-Newtonian dynamics modelled with non-linear transport coefficients at the mesoscale by using dissipative particle dynamics.

We derive the algorithms for the dynamics of the standard dissipative particle dynamics model (DPD) for a velocity-dependent friction coefficient. By introducing simple estimators of the local rate of strain we propose an interparticle friction coefficient that decreases for high deformation rates, eventually leading to the macroscopic shear-thinning behaviour. We have derived the appropriate fluctuation-dissipation theorems that include the correction of the spurious behaviour due to the coupling of the non-linear friction and the fluctuations. The consistency of the model has been numerically investigated, including the Maxwell-Boltzmann distribution for the particle velocities as well as the comparison with the standard linear model for various stresses. The shear-thinning behaviour is clearly reported. Finally, along with the important methodological aspects related to the derivation of the algorithms for non-linear interparticle friction, we introduce a novel two-step algorithm that permits us the integration of the dynamic equations of the DPD model without the explicit derivation of the corrective terms due to the spurious behaviour.

Dissipative particle dynamics parametrisation using infinite dilution activity coefficients: the impact of bonding.

Dissipative particle dynamics (DPD) simulations have proven to be a valuable coarse-grained simulation technique for studying complex systems such as surfactant and polymer solutions. However, the best method to use in parametrising DPD systems is not universally agreed. One common approach is to map infinite dilution activity coefficients to the DPD simulation 'beads' that represent molecular fragments. However, we show that here that this approach can lead to serious errors when bonding beads together to create molecules. We show errors arise from the verlaps between bonded beads, which alters their solubility. In this article, we demonstrate how these bonding errors can be accounted for when defining DPD force fields using simple theoretical methods to account for the overlapping volumes, and we demonstrate the validity of our approach by calculating the partition coefficients for a series of solutes into two immiscible solvents.

The carnivorous plant Genlisea harnesses active particle dynamics to prey on microfauna

Carnivory in plants is an unusual trait that has arisen multiple times, independently, throughout evolutionary history. Plants in the genus Genlisea are carnivorous and feed on microorganisms that live in soil using modified subterranean leaf structures (rhizophylls). A surprisingly broad array of microfauna has been observed in the plants' digestive chambers, including ciliates, amoebae, and soil mites. Here, we show, through experiments and simulations, that Genlisea exploit active matter physics to "rectify" bacterial swimming and establish a local flux of bacteria through the structured environment of the rhizophyll toward the plant's digestion vesicle. In contrast, macromolecular digestion products are free to diffuse away from the digestion vesicle and establish a concentration gradient of carbon sources to draw larger microorganisms further inside the plant. Our experiments and simulations show that this mechanism is likely to be a localized one and that no large-scale efflux of digested matter is present.

Transport and energetics of bacterial rectification

Randomly moving active particles can be herded into directed motion by asymmetric geometric structures. Although such a rectification process has been extensively studied due to its fundamental, biological, and technological relevance, a comprehensive understanding of active matter rectification based on single particle dynamics remains elusive. Here, by combining experiments, simulations, and theory, we study the directed transport and energetics of swimming bacteria navigating through funnel-shaped obstacles-a paradigmatic model of rectification of living active matter. We develop a microscopic parameter-free model for bacterial rectification, which quantitatively explains experimental and numerical observations and predicts the optimal geometry for the maximum rectification efficiency. Furthermore, we quantify the degree of time irreversibility and measure the extractable work associated with bacterial rectification. Our study provides quantitative solutions to long-standing questions on bacterial rectification and establishes a generic relationship between time irreversibility, particle fluxes, and extractable work, shedding light on the energetics of nonequilibrium rectification processes in living systems.

Quadratic scaling path integral molecular dynamics for fictitious identical particles and its application to fermion systems

Quadratic scaling path integral molecular dynamics for fictitious identical particles and its application to fermion systems

Brinkman-medium resistance hampers periodic motions of sedimenting particles

AbstractThe dynamics of groups of non-touching particles settling under gravity in a crowded fluid medium are studied at the zero Reynolds number. It is assumed that the fluid velocity satisfies the Brinkman–Debye–Büche equations, and the particle dynamics are described in terms of the point-force model. The systems of particles at vertices of two or four horizontal regular polygons are considered that in the Stokes flow for a very long time do not destabilize, i.e., all the particles stay close to each other, performing periodic or quasiperiodic motions. It is known that such motions, as invariant manifolds, are essential for groups of particles at random initial positions to survive for a very long time and not destabilize. This work demonstrates that when the medium permeability is decreased, periodic motions cease to exist, and groups of particles split into smaller subgroups, moving away from each other. This mechanism seems to facilitate particle transport in a permeable medium.

Study on Explosion Welding of Titanium–Aluminum Laminated Plates with Different Explosive Charges

To explore the effect of different explosive charge height parameters on the bonding interface of titanium–aluminum multilayer composite plates during explosion welding, the smooth particle dynamics method (SPH method) was used to simulate the explosion welding of titanium–aluminum multilayer plates, reproducing the formation process of plasma jet and waveform bonding interface and obtaining the bonding surface conditions at various charge heights. Based on the simulation, experiments were conducted, and the bonding surface quality was verified through scanning electron microscopy (SEM). The elemental distribution of the binding interface was analyzed using an energy-dispersive spectrometer (EDS). The results show that the welding effect of the plate closer to the explosive is better during explosion welding. Within the weldable window, as the charge height increases, the waviness of the bonding interface transitions towards smaller and more continuous ripples, with continuous small ripples accompanied by vortex-like eddies indicating good welding conditions. When the charge height is too large, the plate may experience a brittle fracture, reducing the strength of the bonding interface. The welding effect is best when the charge height is 24 mm. Under a certain distance between the base and overlay plates, with the increase in charge height, the collision speed of the base plate also increases, increasing the pressure between the plates, causing changes in the shapes of the bonding interface ripples, and expanding the melting zone. Excessive collision speed and pressure also promote the generation of cracks, leading to a decrease in the strength of the composite material.

Theory Of Everything: A Conceptual Synthesis Of An Eleven Dimensional Dynamic Hyperspace As A Unified Zeropoint Subspace Ether

This theoretical research paper aims to aid the conceptual evolution of Grand Unified Theory (GUT), through developing the qualitative alignment of current divergent theoretical perspectives and outlier experimental evidence in the novel synthesis of a holistic new perspective through the philosophy of science context of initiating a paradigm shift in the dynamics of modern particle and dimensional physics theory. Taking the central components of Superstring and M-theory into a conceptual synthesis of theoretical dynamics and experimental evidence incorporating the four fundamental forces of nature, hyperspace theory, zero-point vacuum fluctuations of energy, the Casimir virtual particle effect, the higgs field, photoelectric radiation, quantum tunnelling, dark energy and the four dimensions of space and time in the conceptual composition of a schematic alignment of dynamic essences of physical existence formed into an eleven-dimensional subspace unification of manifest reality. Exploring the theoretical interaction of three polemics of opposed dimensional properties and essences to realities manifest nature, as intersecting dichotomously distinct and conceptually defined axis of hyperspatial essence unified through a zeropoint subspace ether of seven dimensions, an eleven dimensional theory of reality incorporating the aforementioned components as the end product is synthesised. With the desire of elaborating and expanding the qualitative and conceptual dynamics of Grand Unified Theory as a paradigm, this research paper hopes to develop a broadened theoretical context along with increasing the alignment precision and dynamic inclusivity of current divergent tangents and experimental outliers into the synthesis of a complete and comprehensive future GUT paradigm.

In silico biophysics and rheology of blood and red blood cells in Gaucher Disease.

Gaucher Disease (GD) is a rare genetic disorder characterized by a deficiency in the enzyme glucocerebrosidase, leading to the accumulation of glucosylceramide in various cells, including red blood cells (RBCs). This accumulation results in altered biomechanical properties and rheological behavior of RBCs, which may play an important role in blood rheology and the development of bone infarcts, avascular necrosis (AVN) and other bone diseases associated with GD. In this study, dissipative particle dynamics (DPD) simulations are employed to investigate the biomechanics and rheology of blood and RBCs in GD under various flow conditions. The model incorporates the unique characteristics of GD RBCs, such as decreased deformability and increased aggregation properties, and aims to capture the resulting changes in RBC biophysics and blood viscosity. This study is the first to explore the Young's modulus and aggregation parameters of GD RBCs by validating simulations with confocal imaging and experimental RBC disaggregation thresholds. Through in silico simulations, we examine the impact of hematocrit, RBC disaggregation threshold, and cell stiffness on blood viscosity in GD. The results reveal three distinct domains of GD blood viscosity based on shear rate: the aggregation domain, where the RBC disaggregation threshold predominantly influences blood viscosity; the transition area, where both RBC aggregation and stiffness impact on blood viscosity; and the stiffness domain, where the stiffness of RBCs emerges as the primary determinant of blood viscosity. By quantitatively assessing RBC deformability, RBC disaggregation threshold, and blood viscosity in relation to bone disease, we find that the RBC aggregation properties, as well as their deformability and blood viscosity, may contribute to its onset. These findings enhance our understanding of how changes in RBC properties impact on blood viscosity and may affect bone health, offering a partial explanation for the bone complications observed in GD patients.

Dynamics of charged spin- 1/2 particles in superposed states minimally coupled to electromagnetism in curved spacetime within the WKB approximation

We investigate the curved-spacetime dynamics of charged spin-12 particles minimally coupled to the electromagnetic field and propagating in superposed states of different masses. For that purpose, we make use of a Wentzel-Kramers-Brillouin approximation of the Dirac equation with a minimal coupling to the Maxwell field in curved spacetime. We obtain the spin dynamics as well as the deviation from geodesic motion of such particles. The problem of having the mass eigenstates experience different proper times, as opposed to the case of neutral particles, is here dealt with by first extracting the second-order differential equation obeyed by each superposition. This strategy proves to be not only powerful, but also very economical. Published by the American Physical Society 2024