Monodisperse dry granular flows on inclined planes: Role of roughness

Recent studies have pointed out the importance of the basal friction on the dynamics of granular flows. We present experimental results on the influence of the roughness of the inclined plane on the dynamics of a monodisperse dry granular flow. We found experimentally that there exists a maximum of the friction for a given relative roughness. This maximum is shown to be independent of the slope angle. This behavior is observed for four planes with different bump sizes (given by the size of the beads glued on the plane) from 200 m to 2 mm. The relative roughness corresponding to the maximum of the friction can be predicted with a geometrical model of stability of one single bead on the plane. The main parameters are the size of the bumps and the size of the flowing beads. In order to obtain a higher precision, the model also takes into account the spacing between the bumps of the rough plane. Experimental results and model are in good agreement for all the planes we studied. Other parameters, like the sphericity of the beads, or irregularities in the thickness of the layer of glued particles, are shown to be of influence on the friction.     

Simulation of Dynamic Light Scattering Signals of Ultrafine Particles

In order to conveniently obtain dynamic light scattering (DLS) signal, a simulation method of DLS signal is proposed in this paper. This method regards the light intensity fluctuation of DLS as a stationary random process. According to autocorrelation function (ACF) of DLS signal, the stationary random process of DLS can be generated by auto‐regressive (AR) model. Signal simulations of several kinds of distribution particles and comparison of simulations and experiment prove that AR model can be used for DLS signal simulation. Moreover, by analyzing effect of simulation parameters on simulation precision, we obtained the relationship between simulation parameters and simulation precision. Finally, application of simulation signal verifies the effectiveness and convenience of this simulation method.     

Study on the Range of Particles Size Measured by Backscattering Method in Visual‐infrared Incident Spectrum

For the measurement of particles size with backscattering method, the suitable range of particles size measurement have been presented by independent algorithm in Visual‐infrared incident spectrum. We defined the range according to the retrieved results based on the analysis and comparison to many kinds of R‐R distribution function. The simulation computation results showed that the particles size measurement range is from 0.05 μm to 18 μm with incident spectrum from 0.4 μm to 2 μm and different refractive index. The results retrieved were satisfied even if 1 % noise was added into the backscattering intensity.     

纳米颗粒团聚物流化特性的数值研究

基于气固两相流体动力学理论,建立气体纳米颗粒团聚物两相流动双流体模型.模型中采用了Jung ＆ Gidaspow (2002)测量的固相应力模量和王垚等(2001)提出的聚团曳力系数计算模型.对纳米颗粒团聚物的流化过程进行了数值模拟,得到纳米颗粒团聚物的流化特性.模拟得出的床层膨胀比与文献中实验的结果较为接近.     

Theory of Electrorotation of Clustered Colloidal Particles

When a colloidal suspension is exposed to a strong rotating electric field, an aggregation of the suspended particles is induced to appear. In such clusters, the separation between the suspended particles is so close that one could not neglect the multiple image effect on the electrorotation (ER) spectrum. Since so far the exact multiple image method exists in two dimensions only, rather than in three dimensions, we investigate the ER spectrum of the clustered colloidal particles in two dimensions, in which many cylindrical particles are randomly distributed in a sheet cluster. We report the dependence of the ER spectrum on the material parameters. It is shown that the multiple image method predicts two characteristic frequencies, at which the rotation speed reaches maximum. To this end, the multiple image method is numerically demonstrated to be in good agreement with the known Maxwell-Garnett approximation.     

Fluctuation-theory constraint for extensive entropy in Monte-Carlo simulations

The entropy per particle in most Monte-Carlo simulations is size dependent due to correlated energy fluctuations. Guided by nanothermodynamics, we find a constraint for the Ising model that enhances the fluctuations and lowers the free energy, while making the entropy homogeneous, additive, and extensive. Although the average interaction energy becomes size dependent, the resulting distribution of energies provides a mechanism for the heterogeneity found in the dynamics of many materials.     

Cooling kinetics of a granular gas of viscoelastic particles

The evolution of a granular gas of viscoelastic particles in the homogeneous cooling state is studied. The velocity distribution function of granular particles and the time dependence of the mean kinetic energy of particles (granular temperature) are found. The noticeable deviation of the distribution function from the Maxwell distribution and its non-monotonous evolution are established. The perturbation theory with respect to the small dispersion parameter is elaborated and the analytical expressions for the asymptotic time dependence of the velocity distribution function and the granular gas temperature are derived.     

Effect of low frequency ultrasound on the surface properties of natural aluminosilicates

Structural and surface properties of different natural aluminosilicates (layered, chain and framework structural types) exposed of 20 kHz ultrasound irradiation (0–120 min) in aqueous and 35 wt%. aqueous H₂O₂ dispersions were studied by X-ray diffraction (XRD), dynamic light scattering (DLS), nitrogen adsorption–desorption, thermal analysis, and Fourier transform infrared spectroscopy (FTIR) techniques. It was confirmed that sonication caused slight changes in the structure of investigated minerals whereas their textural properties were significantly affected. The aqueous dispersions of montmorillonite (Mt), clinoptilolite (Zlt), glauconite (Glt) and palygorskite (Pal) were represented by several particles size fractions according to DLS-study. Ultrasound irradiation produced a decrease of the average particle diameter by 4–6 times in water and by 1.3–5 times in H₂O₂ dispersions except for Pal, which underwent strong agglomeration. A significant increase of total pore volume and pore diameter was observed for Glt sonicated in H₂O₂ dispersions whereas for Pal mainly micropore volume sharply increased in both aqueous and H₂O₂ dispersions.     

Gravitational Deflection of Massive Particles by a Schwarzschild Black Hole in Radiation Gauge*

The exact metric of a Schwarzschild black hole in the true radiation gauge was recently reported.In this work, we base on this gravity and calculate the gravitational deflection of relativistic massive particles up to the fourth post-Minkowskian order. It is found that the result is consistent with the previous formulations for both the case of dropping the fourth-order contribution and the case of light deflection. Our result might be helpful for future high-accuracy observations.     

Swelling and structure of radiation induced near-surface damage in CR-39 and its chemical etching

Systematic measurements of swelling of CR-39 nuclear track detector (NTD) due to irradiation with fission fragments and alpha particles over a wide range of fluences from ²⁵²Cf are presented here. Precisely designed and optimized exposure and chemical etching experiments were employed to unfold the structure of radiation induced surface damage. Delays in the startup of the chemical etching of latent tracks in low radiation fluence detectors are measured and are found to contain important information about structure of the surface damage. Simple atomic scale pictures of radiation induced surface damage and its chemical etching are developed using measurements of radiation induced swelling of CR-39 detectors and nuclear track parameters. The computer code SRIM2010 was utilized for the calculations of basic features of latent tracks of fission fragments and alpha particles in CR-39. Another computer code TRACK_VISION was used to compute parameters of etched tracks. Computations and experimental findings in the paper coherently compose a realistic picture of radiation damage.