Quantum“contact”friction:The contribution of kinetic friction coefficient from thermal fluctuations

A thermal model of kinetic friction is assigned to a classical loaded particle moving on a fluctuating smooth surface.A sinusoidal wave resembles surface fluctuations with a relaxation time.The Hamiltonian is approximated to the mean energy of the wave describing a system of Harmonic oscillators.The quantization of amplitudes yields in terms of annihilation and creation operators multiplied by a quantum phase.Further,we consider acoustic dispersion relation and evaluate the friction coefficient from the force autocorrelation function.While the sliding particle remains classical describing a nano-particle or a tip with negligible quantum effects like tunneling or delocalization in the wave function,the quantized model of the surface fluctuations results in the temperature dependence of the kinetic friction coefficient.It follows an asymptotic value for higher temperatures and supper-slipperiness at low temperatures.

Molecular dynamics study of anisotropic growth of silicon

Based on the Tersoff potential, molecular dynamics simulations have been performed to investigate the kinetic coefficients and growth velocities of Si（100）,（110）,（111）, and（112） planes. The sequences of the kinetic coefficients and growth velocities are μ（（100））〉 μ（（110））〉 μ（（112））〉 μ（（111））and v（（100））〉 v（（110））〉 v（（112））〉 v（（111））, respectively, which are not consistent with the sequences of the interface energies, interplanar spacings, and melting points of the four planes. However,they agree well with the sequences of the distributions and diffusion coefficients of the melting atoms near the solid–liquid interfaces. It indicates that the atomic distributions and diffusion coefficients affected by the crystal orientations determine the anisotropic growth of silicon. The formation of stacking fault structure will further decrease the growth velocity of the Si（111） plane.

Determination and prediction of pavement skid resistance–connecting research and practice

Adequate pavement skid resistance is a key requirement for safe road operations.Unfortunately,the measurement and prediction of the skid resistance property of an in-service road pavement,or pavement mixture specimens in the laboratory,is a highly challenging process from both theoretical and practical points of view.For more than 60 years,owing to the lack of theoretical solutions to the complex tire-fluid-pavement interaction problem,the practice of pavement skid resistance determination and prediction has essentially been derived from experimental and field observed data.The rapid development of efficient numerical computational techniques and high-power computing facilities in the last two decades made it possible for researchers to numerically solve the tire-fluidpavement interaction problem.It enables the numerical evaluation and prediction of high-speed wet skid resistance,and the determination of the tire-pavement kinetic friction coefficient in the evaluation of low-speed skid resistance.This paper presents a state-of-the-art review of the research development of theoretical mechanistic approaches in the determination and prediction of pavement skid resistance.It covers the following main aspects of the subject matter:(i)mechanisms of skid resistance generation in dry,wetted(i.e.,damp),wet and flooded pavements;(ii)theoretical evaluation of pavement skid resistance in dry,wetted,wet and flooded states;(iii)theoretical approaches in pavement skid resistance prediction;and(iv)concepts of representing the skid resistance state of pavement.The capability of finite element simulation approach for wet skid resistance evaluation with good accuracy is explained.Also highlighted is the practical significance of the Concept of Skid Resistance State.Areas of practical applications of the concept,coupled with the simulation model,are introduced.They include applications in driving safety analysis,road safety design and control,design of paving mixtures,safety maintenance and management of pavements,and harmonization of skid resistance measurements and predictions.

The effect of salinity on waste activated sludge alkaline fermentation and kinetic analysis

The effect of salinity on sludge alkaline fermentation at low temperature（20°C） was investigated, and a kinetic analysis was performed. Different doses of sodium chloride（Na Cl, 0–25 g/L） were added into the fermentation system. The batch-mode results showed that the soluble chemical oxygen demand（SCOD） increased with salinity. The hydrolysate（soluble protein, polysaccharide） and the acidification products（short chain fatty acids（SCFAs）, NH＋4–N, and PO_4^（3-）–P） increased with salinity initially, but slightly declined respectively at higher level salinity（20 g/L or 20–25 g/L）. However, the hydrolytic acidification performance increased in the presence of salt compared to that without salt.Furthermore, the results of Haldane inhibition kinetics analysis showed that the salt enhanced the hydrolysis rate of particulate organic matter from sludge particulate and the specific utilization of hydrolysate, and decreased the specific utilization of SCFAs. Pearson correlation coefficient analysis indicated that the importance of polysaccharide on the accumulation of SCFAs was reduced with salt addition, but the importance of protein and NH＋4–N on SCFA accumulation was increased.

Numerical prediction of flow hydrodynamics of wet molecular sieve particles in a liquid-fluidized bed

The Eulerian-Eulerian framework was used in the numerical simulation of liquid hydrodynamics and particle motion in liquid-fluidized beds. The kinetic theory of granular flow, which accounts for the viscous drag influence on the interstitial liquid phase, was used in combination with two-fluid models to simulate unsteady liquid-solid two-phase flows. We focus on local unsteady features predicted by the numerical models. The solid fraction power spectrum was analyzed. A typical flow pattern, such as core annular flow and particle back-mixing near the wall region of liquid-solid fluidized beds is obtained from this calculation. Effects of the restitution coefficient of particle-particle collisions on the distribution of granular pressure and temperature are discussed. Good agreement was achieved between the simulated results and experimental findings.