Average Particle Spacing Research Articles

Design, analysis, and testing of a new asymmetric vibration-assisted stage for roll-type polishing.

Based on the technological characteristics of roll-type polishing, a new asymmetric vibration-assisted stage is proposed in this paper. This stage is characterized by asymmetric displacement and asymmetric stiffness. With the average particle spacing of roll-type polishing as the constraint, the comprehensive characteristics of structural stiffness, kinematic range, and natural frequency are realized. Thus, to reduce the surface roughness, the removal of simple-directional surface textures generated by roll-type polishing can be achieved. First, the asymmetric structure is designed, modeled, and optimized according to working performance design goals of roll-type polishing. Then, the finite element analysis and actual performance test of the stage are carried out to verify the accuracy of the established model and the effectiveness of the optimization design. The results indicate that the stage can meet the design index. Finally, the asymmetric vibration-assisted polishing experiment is carried out. The results show that the single-directional surface textures of the SiC surface are interrupted and the surface roughness is decreased.

A kernel gradient-free SPH method with iterative particle shifting technology for modeling low-Reynolds flows around airfoils

The conventional SPH method does not perform well for simulating flows around rigid bodies. Especially, it is difficult to get convergent and accurate results when simulating flows around a thin airfoil. The reason is its low accuracy especially for highly irregular particle distributions in the process of SPH simulation of flow around slender structures. In this paper, a kernel gradient-free (KGF) SPH method with iterative particle shifting technology (PST) is proposed for the simulation of flow around the airfoil. KGF-SPH can maintain high accuracy without using kernel gradients. Iterative PST can maintain uniform particle distribution even if the smoothing length is less than the average particle spacing. Lid-driven shear cavity flows, Taylor–Green flow, the stretching of a free-surface circular fluid patch and flows around a cylinder are simulated to test the numerical method. Numerical results are almost in consistent with the analytical or reference results. Finally, flows past an airfoil are simulated by using the proposed SPH method. The results show that the present SPH method effectively improves numerical stability and accuracy for simulating flows around an airfoil.

Research optimization on logistics distribution center location based on adaptive particle swarm algorithm

Logistics distribution center location is an important task in the network optimization of a logistics system. A novel approach of adaptive particle swarm optimization (APSO) algorithm with nonlinear inertia weight and time-varying acceleration coefficient is proposed to achieve distribution center location problem. Mathematic model of logistics distribution center location is established according to assumptions and constraints. Then, average particle spacing as guidance factor of population diversity is employed to establish nonlinear inertia weight and arccosine function is adopted to design nonlinear symmetric acceleration coefficient in order to control the balance of global search and local search for distribution center location problem. To demonstrate the practicality and effectiveness of the proposed algorithm, an application example is provided. Experiments show that APSO can slove the location problem of distribution center with better performance..

Adaptive mutation particle swarm algorithm with dynamic nonlinear changed inertia weight

A novel adaptive mutation particle swarm optimization algorithm with dynamic nonlinear changed inertia weight (AMPSO) was presented to accelerate searching speed and avoid premature convergence, which are mainly adjusted by inertia weight and information mutation. Firstly, the average particle spacing (APS) is employed to describe the population diversity, the smaller the APS, the more concentrated population and the worse species diversity. Then, inertia weight of each particle is updated as dynamic nonlinear based on APS to achieve a self-adaptive adjustment of global search ability and local search capabilities. Finally, information mutation based on slowly varying function (SV) introduced into the updating formula of PSO algorithm to expand search space. The proposed algorithm was tested compared with conventional PSO algorithms by three benchmark functions. The experiments show that the AMPSO has a stronger global optimization capability and higher search efficiency.

Humidity-Dependent Reversible Transitions in Gold Nanoparticle Superlattices

The changes in interparticle spacing upon hydration and dehydration of drop-cast films of hydrophilic gold nanoparticles (GNP) have been measured in situ with nanometer resolution using WetSTEM and ESEM. These subtle variations correlate well with the corresponding changes in the optical spectra and perceived color as well as changes in the electrical conductivity of the films. AC impedance analysis allows us to differentiate between resistive and capacitive components and to evaluate how these depend on average particle spacing and the water content of the matrix, respectively. Thin films of this type are well-known structures used for development of sensors and diagnostics.

Influence of Second Phase Particles on Fracture Toughness in AZ31 Magnesium Alloys

Three kinds of thin AZ31 wrought magnesium alloys sheets were used in order to investigate the influence of the second phase particles on fracture toughness. From the theoretical model, the ratio of λp/dp would be estimated 5~ 6. On the other hand, from the microstructural observation, average particle spacing on each material was sample A: 13.1µm, sample B: 14.1, and sample C: 12 µ. In addition, average particle size on each sample was sample A: 2.1, sample B: 1.9, and sample C: 2.3 µm. Therefore, the ratio of λp/dp calculated from fracture surface observation would be predicted 6 ~ 7. In comparison with the result of the prediction by theoretical analysis was in good agreement with the result of fracture toughness observation. It was found that the variation in plane-strain fracture toughness on AZ31 were affected by both of particle spacing and particle size.

Implementation of Precipitation and Ripening of Second-Phase Particles in the Constitutive Modelling of Creep

Recent developments in constitutive modeling make it possible to directly incorporate microstructural features of a material in the constitutive equations describing its mechanical behavior. For a precipitation hardened material, the most relevant microstructural characteristic is the average particle spacing in the dislocation glide plane. A model describing the effect of this parameter on the strain hardening and creep behavior proved to have a good predictive capability for the case when the particle arrangement does not change during the deformation. This becomes particularly important for high-temperature deformation when an interplay between second-phase precipitation and particle ripening may produce a complex time dependence of the particle strengthening effect. A reliable description of the deformation behavior then requires the use of a constitutive model in which the kinetics of the particle evolution is accounted for. Such an attempt can be based on the model developed by Mecking and Estrin, in which the dislocation density is treated as a single internal variable. The formulation contains the distance of free dislocation glide, which is affected by the presence of second-phase particles. The new feature is that a variable second-phase particle spacing is now considered. The two concurrent processes, viz. precipitation and ripening of particles, aremore » described in a unified way in that the time dependence of the average particle spacing is presented in an analytical form. Schwarze et al. tried to apply this concept modeling the mechanical behavior of INCOLOY alloy 800H, a carbide precipitation strengthened high temperature alloy. For the present paper the model was developed more rigorously and simplifying assumptions, which may be allowed at lower temperatures, are avoided.« less

Gap junctions. Structural changes after uncoupling procedures.

The freeze-fracture appearance of rat stomach and liver gap junctions changes after uncoupling procedures such as inhibition of the metabolism of perfusion with hypertonic sucrose. In control stomach, either fixed immediately or kept for 1 h in a well-oxygenated Tyrode's solution at 37 degrees C, most gap junctions between mucous cells contain particles irregularly packed at an average center-to-center spacing of 10.3-10.5 nm. After 1-h treatment with 2,4-dinitrophenol (DNP), at the same temperature and oxygenation, most particles aggregate hexagonally at an average spacing of approximately 8.5 nm. Similar changes are seen in hypoxic specimens. In control liver, fixed by perfusion, most junctional particles are irregularly packed at an average center-to-center spacing of approximately 10 mm. Small areas of fairly regular hexagonal packing are occasionally seen, where the average particle spacing is 9.2-9.5 nm. In hypoxic liver, the junctional particles form regular hexagonal packings in which the average center-to-center particle spacing is approximately 8.5 nm. In liver perfused with hypertonic sucrose-calcium solutions, following EDTA solutions, most junctions are pulled apart. The separated junctional membranes, expected to be highly impermeable, contain particles regularly and tightly packed as in hypoxic or DNP-treated junctions. Preliminary measurements indicate also a possible change in particle diameter, from approximately 8.6 nm (control) to approximately 7.7 nm (treated). The structural changes are similar to those previously reported in crayfish and may reflect conformational changes in particle subunits resulting in functional uncoupling.