A Population Balance Model for Shear-Induced Polymer-Bridging Flocculation of Total Tailings

Shear-induced polymer-bridging flocculation is widely used in the solid–liquid separation process in cemented paste backfill, beneficial to water recycling and tailings management in metal mines. A flocculation kinetics model based on Population Balance Model (PBM) is proposed to model the polymer-bridging flocculation process of total tailings. The PBM leads to a system of ordinary differential equations describing the evolution of the size distribution, and incorporates an aggregation kernel and a breakage kernel. In the aggregation kernel, a collision frequency model describes the particle collision under the combined effects of Brownian motions, shear flow, and differential sedimentation. A semi-empirical collision efficiency model with three fitting parameters is applied. In the breakage kernel, a new breakage rate coefficient model with another three fitting parameters is introduced. Values of the six fitting parameters are determined by minimizing the difference between experimental data obtained from FBRM and modeling result through particle swarm global optimization. All of the six fitting parameters vary with flocculation conditions. The six fitting parameters are regressed with the flocculation factors with six regression models obtained. The validation modeling demonstrates that the proposed PBM quantifies well the dynamic evolution of the floc size during flocculation under the given experimental setup. The investigation will provide significant new insights into the flocculation kinetics of total tailings and lay a foundation for studying the performance of the feedwell of a gravity thickener.

Effective elasticity and persistence of strain in active filament-motor assemblies

Cross-linked, elastic, filamentous networks that are deformed by active molecular motors feature in several natural and synthetic settings. The effective active elasticity of these composite systems determines the length scale over which active deformations persist in fluctuating environments. This fundamental quantity has been studied in passive systems; however mechanisms determining and modulating this length-scale in active systems has not been clarified. Here, focusing on active arrayed filament-motor assemblies, we propose and analyze a minimal model in order to estimate the length scale over which imposed or emergent elastic deformations or stresses persist. We combine a mean-field continuum theory valid for weakly elastic assemblies with high dimensional Multi-Particle Collision (MPC) based Brownian simulations valid for moderate to strongly elastic and noisy systems. Integrating analytical and numerical results, we show that localized strains - steady or oscillatory - persist over well-defined length scales that dependent on motor activity, effective shear elasticity and filament extensibility. Extensibility is key even in very stiff filaments, and cannot be ignored when global deformations are considered. We clarify mechanisms by which motor derived active elasticity and passive shear elasticity of the filamentous backbone combine to effectively soften filaments. Surprisingly, the predictions of the mean-field theory agree qualitatively with results from stochastic discrete filament-motor model, even for moderately strong noise. We also find that athermal motor noise impacts the overall duty ratio of the motors and thereby the persistence length in these driven assemblies. Our study demonstrates how correlated activity in natural ordered active matter possesses a finite range of influence with clear testable experimental implications.

Research on Particle Collision Forward Search Algorithm and the CFD-DEM Variable Time Step Coupling Calculation Method

In CFD-DEM coupling calculations, an excessively large selection for particle calculation time step affects the calculation accuracy, and an extremely small selection affects the calculation efficiency. A search ball is constructed by taking each target particle as the center particle with the fastest displacement in the calculation domain. Subsequently, the particles that may collide are screened to establish a search list, and a forward search method is used to determine particle collisions. Finally, a particle calculation time step is proposed. The improved DEM method, which automatically adjusts the collision time, resolves the contradiction between particle calculation time step selection, accuracy, and efficiency. The relative error between the numerical simulation results of particle collision and the theoretical solution was less than 3%. The three calculation time steps selected in this study can guarantee excellent calculation accuracy and efficiency. For multi-particle and fluid coupling simulations, the traditional CFD-DEM method selects 10-7s or less in the calculation time step to obtain an accurate solution. The method proposed in this paper selects 10-5s to obtain an accurate solution, which increased the calculation efficiency by 19.8%.

Professional Mechanical Tooth Cleaning Method for Dental Implant Surface by Agar Particle Blasting

Oral dysfunction due to peri-implantitis and shortened life of implants has become a major concern. Self-care and removal of oral biofilms by professional mechanical tooth cleaning (PMTC) are indispensable for its prevention. However, if the surface roughness of the implant is increased, it may result in the adhesion of biofilm in the oral cavity. Therefore, the PMTC method can serve for long-term implant management. Calcium carbonate (CaCO3) has been used as a cleaning method for implant surfaces; however, there is concern that the implant surface roughness could increase due to particle collision. Therefore, in this study, to establish a blasting cleaning method that does not adversely affect the implant surface, a new blasting cleaning method using agar particles was devised and its practical application examined. When the simulated stains were blasted with white alumina (WA) abrasive grains and CaCO3 particles, the simulated stains were almost removed, the surface roughness changed to a satin-finished surface—which was thought to be due to fine scratches—and the surface roughness increased. Most of the simulated stains were removed on the surface of the sample blasted with glycine particles and agar particles. Conversely, the gloss of the sample surface was maintained after cleaning, and the increase in surface roughness was slight.

Research on structure and technological parameters of multi-channel cold spraying nozzle

Cold spraying technology is a method to obtain coating by the high-speed collision of particles with the substrate through supersonic (300–1200 m/s) propulsion gas. The deposition process is mainly mechanical bonding, which has attracted more and more attention in engineering applications. The critical component of a cold spraying system is the nozzle. The performance of the nozzle directly affects the quality of the material surface coating. Therefore, the discussion of the nozzle is of great significance. At present, there are many examples of cold spraying single-channel nozzles in engineering, but there are few reports about multi-channel cold spraying nozzles. This paper explores and studies the multi-channel cold spraying nozzle, designs a special three internal channel nozzle, and adopts a 90° angle in the divergent section of the nozzle. When spraying in a small area, the nozzle with angle has apparent advantages for spraying more areas. The powder injection pressure, particle size, recovery coefficient, and internal channel position are analyzed, which affect the particle trajectory. Combined with these factors, the multi-channel nozzle is optimized and improved to solve the problem of particle collision with the inner wall of the nozzle. Finally, the technological parameters of aluminum, titanium, copper, nickel, magnesium, and zinc powders are preliminarily studied using the multi-channel nozzle. The results show that the multi-channel nozzle meets the critical velocity requirements of copper, magnesium, and zinc powder spraying in the homogeneous (powder and matrix are the same material) and aluminum powder spraying in the case of heterogeneous (powder and matrix are different materials), the multi-channel nozzle has a sound engineering application prospect and provides a specific reference for relevant technicians.

Indication of strong interatomic Coulombic decay in slow He2+-Ne2 collisions

Electron removal in collisions of alpha particles with neon dimers is studied using an independent-atom-independent-electron model based on the semiclassical approximation of heavy-particle collision physics. The dimer is assumed to be frozen at its equilibrium bond length and collision events for the two ion-atom subsystems are combined in an impact parameter by impact parameter fashion for three mutually perpendicular orientations. Both frozen atomic target and dynamic response model calculations are carried out using the coupled-channel two-center basis generator method. We pay particular attention to inner-valence Ne(2s) electron removal, which is associated with interatomic Coulombic decay (ICD), resulting in low-energy electron emission and dimer fragmentation. Our calculations confirm a previous experimental result at 150 keV/amu impact energy regarding the relative strength of ICD compared to direct electron emission. They further indicate that ICD is the dominant Ne+ + Ne+ fragmentation process below 10 keV/amu, suggesting that a strong low-energy electron yield will be observed in the ion-dimer system in a regime in which the creation of continuum electrons is a rare event in the ion-atom problem.