Increase In Size Ratio Research Articles

Diverse morphology and motility induced emergent order in bacterial collectives.

Microbial communities exhibit complex behaviors driven by species interactions and individual characteristics. In this study, we delve into the dynamics of a mixed bacterial population comprising two distinct species with different morphology and motility aspects. Employing agent-based modeling and computer simulations, we analyze the impacts of size ratios and packing fractions on dispersal patterns, aggregate formation, clustering, and spatial ordering. Notably, we find that motility and anisotropy of elongated bacteria significantly influence the distribution and spatial organization of nonmotile spherical species. Passive spherical cells display a superdiffusive behavior, particularly at larger size ratios in the ballistic regime. As the size ratio increases, clustering of passive cells is observed, accompanied by enhanced alignment and closer packing of active cells in the presence of higher passive cell area fractions. In addition, we identify the pivotal role of passive cell area fraction in influencing the response of active cells toward nematicity, with its dependence on size ratio. These findings shed light on the significance of morphology and motility in shaping the collective behavior of microbial communities, providing valuable insights into complex microbial behaviors with implications for ecology, biotechnology, and bioengineering.

The influence of self-assembled particle layer on particle collision properties

Interactions between particle and particle layers are fundamental in modeling deposition processes. The complex mechanical behaviors of these layers pose significant challenges in precisely predicting the rebound characteristics of incident particle, especially at the micron and nanoscale. Very few related experimental studies have been reported in this area. To better control the structure of particle layers and offer a path to more systematic research, this study introduces the particle self-assembly method, combined with high-speed imaging technology, to investigate the influence of particle monolayer, their diameters, and impact velocity on critical capture velocity (vcr), normal coefficient of restitution (COR), and angle deflection of incident particles. Results indicate that self-assembled particle layers remain stable within an impact velocity range and experimental data within this stable range exhibit good repeatability. These layers significantly enhance kinetic energy dissipation. A semi-logarithmic plot revealed a negative linear relationship between vcr and particle size ratio. The effect of particle layer on COR depends on particle layer diameter and impact velocity. Specifically, the dissipation of particle layer diminishes and approaches zero for smaller layer particles (0.5 μm), but increases and stabilizes for larger particles (2 μm). Moreover, statistical results indicate that angle deflection decreases as particle size ratio increases, aligning with a power-law relationship predicted by Monte Carlo simulations. Overall, this study presents a novel method for understanding micro and nano particle layers' influence on incident particle dynamics.

Collapse characteristics of binary granular columns considering inhomogeneous particle size distributions

AbstractDebris avalanches and dry granular flows exhibit similar characteristics. In order to comprehend the fundamental mechanisms and improve the accuracy in predicting disasters such as landslides, debris flows, and rock avalanches, the collapse characteristics of a binary granular column are investigated through a three‐dimensional discrete element model. A novel approach is proposed by incorporating the concept of local granular velocity fluctuation and applying a cluster analysis method. Then, the flow mechanism of the binary granular column is analyzed, by considering the inhomogeneous particle size distribution. The research results show that: (1) The normalized final packing height of the granular column gradually increases when the content of coarse particles exceeds 20% and when the coarse‐fine particle size ratio increases. Conversely, the normalized run‐out distance of the granular column decreases gradually with the increase in coarse particle content and the coarse‐fine particle size ratio. (2) The particles with higher granular velocity fluctuations tend to move together and form clusters, demonstrating dynamical heterogeneity. As the coarse particle content and coarse‐fine particle size ratio increase, there is a greater tendency for particles to assemble into larger‐scale active clusters. This means that a larger number of particles exhibit collective behavior during the collapse process, resulting in increased resistance to shear deformation. Ultimately, this leads to a greater packing height and a reduced run‐out distance when observed from a macroscopic perspective.

Effect of rubber-sand particle size ratio on shear properties of rubber-sand mixtures under normal cyclic loading

The mechanical properties of rubber-sand mixtures are influenced by the ratio of rubber-sand particle sizes and the rubber content. Rubber-sand mixtures used as roadbed fillers are primarily subjected to normal cyclic traffic loading. Therefore, a series of direct shear tests on rubber-sand mixtures under normal cyclic loading were conducted using a large-scale direct shear apparatus. The effects of the rubber-sand particle size ratio, rubber content, initial stress, and amplitude of normal cyclic loading on the shear strength of rubber-sand mixtures were evaluated. Based on the indoor tests, discrete element models of rubber-sand mixtures with different particle size ratios were established to explore the meso-mechanical mechanism of the mixed soil during the direct shear process. The results indicate that rubber-sand mixtures with low rubber content and a particle size ratio >1 have a positive effect on the shear strength of the mixed soil. The impact of initial stress on the shear stress of the mixed soil is greater than that of the normal cyclic load amplitude. As the particle size ratio increases, the inter-particle contact force becomes larger, resulting in more noticeable group anisotropy. Additionally, the main direction of the normal contact force anisotropy in the mixture consistently aligns with the deflection direction of the force chain. Rubber particles in rubber-sand mixtures with a large particle size ratio actively participate in the contact force chain network system, facilitating load transfer and positively influencing shear strength.

Promoting rebound from droplet impact on a spherical particle: Experimental and numerical study

In this study, we experimentally and numerically investigate the activity of a rebounding droplet on a spherical particle and the effects of surface curvature on its rebounding behavior. We report that the rebound of the droplet can be promoted in smaller particles. As the droplet-to-particle size ratio increases, the critical Weber number is significantly reduced, and the restitution coefficient is much increased. The underlying physical mechanism for the promotion of the rebound is the reduced energy dissipation on the smaller particles in the very early stages of the collision, and this reduction mainly occurs as the liquid is being squeezed. This reduced energy loss allows larger liquid–gas interfacial deformation at the maximum spreading state and also allows more drastic retractions during the recoiling stage, which eventually leads to the promotion of the rebound.

Influence of grain-to-particle size ratio on the tensile mechanical response of granite based on a novel three-dimensional grain-based model

In this paper, we developed a novel three-dimensional grain-based model based on the discrete element method (DEM) and reproduced the heterogeneous structure of crystalline granite. We carried out static Brazilian splitting tests to analyze the mechanical properties and micro-cracking behavior of granite samples. Furthermore, we investigated the effect of grain-to-particle size ratio on the tensile strength and discussed the difference in mechanical response of granite samples with different grain sizes and particle sizes under static loading. Our results show that the load–displacement curve of the sample can be divided into initial compaction stage, linear elasticity stage, damage stage, and post-peak stage. Tensile failure is the main failure mode leading to the macroscopic fracture of the sample, and intergranular failure is dominant. As the grain-to-particle size ratio increases, the proportion of the number of transgranular contacts to the number of total contacts increases and stabilizes. Compared with intergranular contact, transgranular contact has a higher bonding strength, and its fracture requires a larger stress concentration magnitude, which leads to an increase in the external load required for the macroscopic fracture of the sample.

Numerical study of size-driven segregation of binary particles in a rotary drum with lower filling level

Discrete element method (DEM) simulations of size-driven segregation of binary particles in a rotary drum were conducted to investigate the influence of filling level, size ratio, and rotation speed on the segregation performance. Segregation experiments with different filling levels were used to verify the DEM model and analyze the influence of filling levels on segregation. The granular bed was divided into five layers to study the axial segregation in the rotary drum. The total velocity fluctuation was used to discuss the granular behavior from a mesoscopic perspective. A segregation index was adopted to quantify the segregation performance with different parameters. It was found that binary particles in the drum with different filling levels have different segregation patterns. A core of small particles was formed in the middle of granular bed for the case with a higher filling level, while there is no core formed for the case with a lower filling level. Results obtained indicate that the size-driven segregation in the drum with lower filling level increases with the increase of size ratio. Within the rolling regime, the rotation speed has little influence on the final segregation index of particles.

CFD-DEM study of particle-fluid flow and retention performance of sand screen

Sand screens are widely used to control sand production in unconsolidated reservoirs. Because of the lack of insightful understanding of this process, to date, reliably optimizing screen size is still a challenge. This paper presents a numerical study of the sand retention and production behaviors for widely used wire-wrapped screens by means of the combined approach of computational fluid dynamic (CFD) and discrete element method (DEM). The validity of the model has been verified by comparing the predicted critical slot sizes and sand production with published experimental results. On this basis, the effects of slot width-particle size ratios and wetting fluids, including gas and crude oil, are studied. The numerical results show that the increase in size ratio increases sand production, and the presence of fluid flow enhances sand production and causes unstable sand retention, which is more significant for crude oil compared to gas. Also, three mechanisms that allow the sand retention over a screen are identified, including stable bridging, bridging with intermittent collapse, and bridging with continuous collapse. Wetting fluids play an essential role in the sand production and bridging when the particle-fluid forces exerted on the particles near the slot are significant. Such forces induce strong localized particle-particle interactions in the nearby region over the slot, which accounts for the unstable bridging behavior.

Correlation functions in mixtures with energetically favoured nearest neighbours of different kind: a size-asymmetric case

Binary mixtures of hard spheres with different diameters and square-well attraction between different particles are studied by theory and Monte Carlo simulations. In our mesoscopic theory, local fluctuations of the volume fraction of the two components are taken into account. Semi-quantitative agreement between the simulation and theoretical results is obtained, except from very small distances. The correlation functions exhibit exponentially damped oscillations, with the period determined by the interaction potential, and both the amplitude and the correlation length increasing significantly with increasing diameter ratio. Increasing size asymmetry leads also to decreasing fluctuations of the number of the smaller particles in the attractive shell of the bigger ones. For small size asymmetry, the strongest correlations occur for comparable volume fraction of the two components. When the size ratio increases, the maximum of the structure factor moves to a larger volume fraction of the bigger particles, and for the size ratio as large as 4, the maximum goes beyond the accessible range of volume fractions. Our results show that when the neighbourhood of different particles is energetically favoured, the particles are much more uniformly distributed than in the random distribution even at relatively high temperature, especially for large size asymmetry.

A Numerical Investigation on the Collision Behavior of Unequal-Sized Micro-Nano Droplets.

Micro-nano droplet collisions are fundamental phenomena in the applications of nanocoating, nano spray, and microfluidics. Detailed investigations of the process of the droplet collisions under higher Weber are still lacking when compared with previous research studies under a low Weber number below 120. Collision dynamics of unequal-sized micro-nano droplets are simulated by a coupled level-set and volume of fluid (CLSVOF) method with adaptive mesh refinement (AMR). The effects of the size ratio (from 0.25 to 0.75) and different initial collision velocities on the head-on collision process of two unequal-sized droplets at We = 210 are studied. Complex droplets will form the filament structure and break up with satellite droplets under higher Weber. The filament structure is easier to disengage from the complex droplet as the size ratio increases. The surface energy converting from kinetic energy increases with the size ratio, which promotes a better spreading effect. When two droplets keep the constant relative velocity, the motion tendency of the droplets after the collision is mainly dominated by the large droplet. On one hand, compared with binary equal-sized droplet collisions, a hole-like structure can be observed more clearly since the initial velocity of a large droplet decreases in the deformation process of binary unequal-sized droplets. On the other hand, the rim spreads outward as the initial velocity of the larger droplet increases, which leads to its thickening.

Discharge characteristics of binary particles in a rectangular hopper with inclined bottom

The stable discharge of particles through the hopper plays a key role in many industrial applications. In order to investigate the discharge characteristics of binary particles in a rectangular hopper with an inclined bottom, the discrete element method (DEM) was used to simulate the discharge process. The accuracy of DEM was validated by comparing calculated and experimental values. The influences of geometric parameters (hopper width, orifice width, and hopper angle) and particle parameters (friction coefficient between particles, friction coefficient between particles and wall, fine particle mass fraction, and particle size ratio) on the discharge were studied. Some interesting results have been found that the effect of hopper width on discharge is minimal. The mass discharge rate is linearly related to the 3/2 power of orifice width, and it can be predicted by the modified Beverloo correlation which developed for a rectangular hopper with flat bottom. The mass discharge rate increases exponentially with the decrease in hopper angle, which is different from that of monosized particles. The mass discharge rate is more sensitive to low friction coefficient, and the friction coefficient between particles plays a leading role. Fine particles can promote the discharge process, and this effect is enhanced as particle size ratio increases.

Modelling continuous materials using discrete element modelling: investigations on the effect of particle packing

Preparing the particle packing model is a crucial step in modelling continuous materials using discrete element modelling (DEM) due to the close correlation between particle packing and material property. In this paper, two modified cubic packing models are generated by inserting smaller particles into the void space of simple cubic packing (SCP). Packing fractions and coordination numbers of two modified packing models increase gradually with the increase of insertion times. Size effect of each packing model is investigated and different packing models share the same characteristics, i.e. stress–strain curves of continuous materials created using different packing models under tensile loads tend to concentrate gradually with the increase of size ratio and their peak strengths raises gradually and then converge into constants. Uniaxial tensile DEM simulations are performed to investigate the impact of packing type and packing with or without rectangular defects on the mechanical behavior of continuous materials generated using different packing models. It is proven that SCP has the minimum uniaxial tensile strength compared to binary cubic packing (BCP) and triple cubic packing (TCP). Any packing with one of three kinds of rectangular defects tends to weaken its uniaxial tensile strength. From BCP to TCP, peak strength or stress has only slight improvements while total numbers of sub-particles soar greatly. The newly developed packing models in this paper enhance the understanding of the relationship between particle packing and material property although these models are formulated and computed in 2D.

A new method for deburring of servo valve core edge based on ultraprecision cutting with the designed monocrystalline diamond tool

Deburring of high-precision components to their micrometer features without any damage is very important but of great difficulty as the burr-to-functionality size ratio increases. To this end, this paper proposes a new deburring method in which the micro burr should be directly removed based on ultraprecision cutting with the designed monocrystalline diamond tool. To determine the feasibility of the proposed method, this paper applies it for deburring of the precision working edge of the servo valve core. Firstly, the monocrystalline diamond tool is carefully designed by covering a variety of topics like rake angle, clearance angle, edge radius. Then, the finite element (FE) simulation was conducted to characterize the deburring performance during the removal of the micro burr produced by the single abrasive grinding. Finally, an innovative self-designed deburring system was introduced and the deburring process was evaluated in terms of cutting forces, temperatures, tool wear mechanisms and deburring quality of the working edges by experiments. The FE simulation results indicate the suitability of the proposed deburring method. Meanwhile, the experimental findings agree well with simulation results and show that ultraprecision cutting with the specialized monocrystalline diamond tool could be successfully used for deburring of servo valve core edge without any damage. This work can provide technical guidance for similar engineering applications, and thus brings an increase to the machining efficiency for the manufacture of precision components.

Effect of vibration frequency, size ratio and large particle volume fraction on packing density of binary spherical mixtures

The packing density of a particulate mixture is an important aspect of materials sciences and engineering. The packing density of a mixture depends on several parameters. This study considers the combined effect of vibration frequency, size ratio and large particle volume proportion on packing density of binary spherical mixtures.When all other parameters are constant, the increase of vibration frequency increases the packing density to a maximum and further increase of vibration frequency decreases the packing density of a mixture. The relationship found to be following a 3rd order polynomial curve. The increase of size ratio decreases the packing density linearly. The increase of large particle volume proportion also increases the packing density to a maximum and further increase of large particle proportion reduces the packing density rapidly. This variation also follows a polynomial pattern. These relationships were analyzed to develop a model incorporating combined effect and design graphs were developed from the derived model. The design graphs can be easily used to determine the packing density for a given vibration frequency and given size ratio.

Preparation and Characterization of Nanoporous Copper Films By (electro)Chemical Dealloying

Nanostructured materials are of great interest in different fields such as solar cells, batteries, fuel cells and sensors.1-3 The chemical and physical properties of nanostructured materials strongly differ from those of the corresponding bulk materials. For instance, with decreasing size, quantum-physical effects get more relevant.2 Nanoporous materials offer not only new chemical and physical properties by nano-sizing but also very high surface area and good mass transport properties through the pores.3 A promising synthetic approach to prepare nanoporous copper (np-Cu) materials is the (electro)chemical dealloying process.4 Dealloying is the dissolution of the less noble metal (Zn) from a Cu-based alloy. The Cu-based alloys are prepared by electrodeposition of Zn on a Cu surface followed by thermal annealing step in an inert atmosphere. We showed that by modifying the dealloying conditions, np-Cu films with tuneable structure (e.g. ligament size and shape) and chemical composition (e.g. the residual content of the foreign atom and surface oxides) can be produced. For the characterization, a broad combination of microscopic and spectroscopic techniques was used: XPS, XRD, EDX, SEM and XANES/EXAFS. Our study shows the relationship between the dealloying parameters such as temperature, electrolyte, concentration etc. and the material properties of the np-Cu such as ligament size and shape, pore distribution and content of the foreign atom. First, the annealing temperature controls the crystal phase and the degree of alloying of the Zn-Cu film. The crystalline phase and chemical surface composition of the master alloy have a strong influence on the resulting structure after the dealloying step. In particular, with higher annealing temperature, the dealloying proceeds slower and the ligament-pore size ratio increases. Furthermore, the variation of the dealloying conditions (electrolyte concentration and time) leads to different structures of the np-Cu films, indicating that the mechanism and kinetics of the dealloying significantly change. One of the critical parameters is the effect of the supporting electrolyte. For instance, in HCl, a homogeneous ligament structure is formed, whereas in NaOH solution the dealloying mainly proceeds at the grain boundaries of the Zn-Cu alloy and forms cracks. Large ligament sizes and strong oxidized surfaces with very low content of Zn was observed. Moreover, the temperature during the dealloying can be used to tune the ligament and pore size. For example, using a HCl solution with the same concentration, the ligament size can be adjusted from 30 to 300 nm in a temperature range between 10 and 70 °C. Another observation is that by increasing dealloying time, the Zn content further decreases. In basic solutions, the absence of Zn leads to an increased formation of copper oxide at the surface. The aim of our work is to better understand the formation mechanism and kinetics of the np-Cu. The next step is the rational design of various np-Cu materials as electrocatalysts for the electrochemical carbon dioxide reduction reaction (CO2RR). 1. A. S. Aricò, P. Bruce, B. Scrosati, J. Tarascon, and W. van Schalkwijk, Nature Materials, 366-377, 4 (2005) 2. W. A. Badawy, Journal of Advanced Research, 123-132, 6(2) (2015) 3. M. Oezaslan, M. Heggen, and P. Strasser, J. Am. Chem. Soc., 514-524, 134(1) (2012) 4. Z. Zhang, Y. Wang, Z. Qi, W. Zhang, J. Qin, and J. Frenzel, J. Phys. Chem. C, 12629-12636, 113 (2009)

Electrokinetic motion of an electrically induced Janus droplet in microchannels

The electrokinetic motion of an electrically induced Janus oil droplet with one side covered with an aluminum oxide nanoparticle film in a circular microchannel was numerically simulated in this paper. The Janus oil droplet is electrically anisotropic as the nanoparticle-covered area carries positive charges and the rest oil–water surface area carries negative charges. A theoretical model was constructed to calculate the electrokinetic velocity of the Janus droplet by considering the force balance on the surface of the Janus droplet at steady state. In the model, the effects of the electric double layer and surface charges on the motion at the oil–water interface are considered. The effects of five parameters on the electrokinetic motion of the Janus droplets were studied: the electric field, the zeta potential ratio of the positively charged side to the negatively charged side of the Janus droplet, the viscosity ratio of the oil phase to the water phase, the nanoparticle coverage of the Janus droplet, and the size ratio of the diameter of the Janus droplet to the diameter of the cylindrical microchannel. The simulation results indicate that the increase in the electrical field, the zeta potential ratio, the viscosity ratio or the nanoparticle coverage leads to faster electrokinetic motion of the Janus droplet. On the other hand, with the increase in size ratio, the electrokinetic velocity of Janus droplet first decreases gradually then increases sharply. The simulated results were compared with the experimental results and good agreement was found.

Influence of Rolling Friction Coefficient on Inter-Particle Percolation in a Packed Bed by Discrete Element Method

Abstract Rolling friction representing the energy dissipation mechanism with the elastic deformation at the contact point could act directly on particle percolation. The present investigation intends to elucidate the influence of rolling friction coefficient on inter-particle percolation in a packed bed by discrete element method (DEM). The results show that the vertical velocity of percolating particles decreases with increasing the rolling friction coefficient. With the increase of rolling friction coefficient, the transverse dispersion coefficient decreases, but the longitudinal dispersion coefficient increases. Packing height has a limited effect on the transverse and longitudinal dispersion coefficient. In addition, with the increase of size ratio of bed particles to percolation ones, the percolation velocity increases. The transverse dispersion coefficient increases with the size ratio before D/d<14. And it would keep constant when the size ratio is greater than 14. The longitudinal dispersion coefficient decreases when the size ratio increases up to D/d=14, then increases with the increase of the size ratio. External forces affect the percolation behaviours. Increasing the magnitude of the upward force (e.g. from a gas stream) reduces the percolation velocity, and decreases the dispersion coefficient.

Sensitivity of fracture strength in porous glass

AbstractWe investigated the effect of porosity and crack size distributions on the fracture behavior of porous glass through a combined finite element and fracture mechanics method. Simulations showed that the effect of crack size distributions on the change in fracture strength with porosity decreases as the pore size to crack size ratio increases. For a pore size to crack size ratio of >∼4, the average failure initiating crack size decreases with increasing porosity. Two regions were defined to describe the relationship between porosity and fracture strength: Region I for porosity less than 20 vol.% and Region II for porosity greater than 20 vol.%. Simulation results were directly compared to the porous glass experiments from the literature.

Wall-retardation effects on particles settling through non-Newtonian fluids in parallel plates

AbstractWalls can exert a retardation effect on particles settling in bounded fluid media. In this work, the parallel plate retardation effect was studied for particles falling in non-Newtonian fluids along the centreline of parallel plate ducts. The eccentric effect was also investigated for those particles which approached the wall. For spheres settling in sodium carboxymethylcellulose (CMC) solutions, the variation in wall factors against the size ratio of the sphere’s diameter to the parallel plate wall spacing shows a non-linear trend; the particle settling velocity is independent at small size ratio, and then decreases quickly with increase in size ratio. A new correlation was presented covering a wider range of size ratios (0.02 < λ < 0.83) in the flow region of 0.0011 <

Theory of activated penetrant diffusion in viscous fluids and colloidal suspensions.

We heuristically formulate a microscopic, force level, self-consistent nonlinear Langevin equation theory for activated barrier hopping and non-hydrodynamic diffusion of a hard sphere penetrant in very dense hard sphere fluid matrices. Penetrant dynamics is controlled by a rich competition between force relaxation due to penetrant self-motion and collective matrix structural (alpha) relaxation. In the absence of penetrant-matrix attraction, three activated dynamical regimes are predicted as a function of penetrant-matrix size ratio which are physically distinguished by penetrant jump distance and the nature of matrix motion required to facilitate its hopping. The penetrant diffusion constant decreases the fastest with size ratio for relatively small penetrants where the matrix effectively acts as a vibrating amorphous solid. Increasing penetrant-matrix attraction strength reduces penetrant diffusivity due to physical bonding. For size ratios approaching unity, a distinct dynamical regime emerges associated with strong slaving of penetrant hopping to matrix structural relaxation. A crossover regime at intermediate penetrant-matrix size ratio connects the two limiting behaviors for hard penetrants, but essentially disappears if there are strong attractions with the matrix. Activated penetrant diffusivity decreases strongly with matrix volume fraction in a manner that intensifies as the size ratio increases. We propose and implement a quasi-universal approach for activated diffusion of a rigid atomic/molecular penetrant in a supercooled liquid based on a mapping between the hard sphere system and thermal liquids. Calculations for specific systems agree reasonably well with experiments over a wide range of temperature, covering more than 10 orders of magnitude of variation of the penetrant diffusion constant.