The velocity of sound in soap foams at high gas volume fractions is experimentally studied by using the time difference method.It is found that the sound velocities increase with increasing bubble diameter,and asympto...The velocity of sound in soap foams at high gas volume fractions is experimentally studied by using the time difference method.It is found that the sound velocities increase with increasing bubble diameter,and asymptotically approach to the value in air when the diameter is larger than 12.5 mm.We propose a simple theoretical model for the sound propagation in a disordered foam.In this model,the attenuation of a sound wave due to the scattering of the bubble wall is equivalently described as the effect of an additional length.This simplicity reasonably reproduces the sound velocity in foams and the predicted results are in good agreement with the experiments.Further measurements indicate that the increase of frequency markedly slows down the sound velocity,whereas the latter does not display a strong dependence on the solution concentration.展开更多
The dynamical behavior of an intruder immersed in a two-dimensional shaken granular bed is experimentally investigated. With two types of background particles, f-Г phase diagrams depicting the intruder＇s motion are ...The dynamical behavior of an intruder immersed in a two-dimensional shaken granular bed is experimentally investigated. With two types of background particles, f-Г phase diagrams depicting the intruder＇s motion are measured and compared. It is found that even with the same size and density ratio of the intruder to the background particles, the intruder exhibits a distinct behavior at given vibrational conditions： rising behavior in one granular bed; sinking behavior in another granular bed. We slightly tune the size and density ratio to confirm the reliability of the experimental results. In addition, we examine the influences of interstitial air, convection and the initial position on the intruder＇s motion, speculating that the opposite motion could be traced to the material properties of the background particles.展开更多
Researchers have reported that Cu-Zr liquids are kinetically strong at the best glass-forming compositions. Here we systematically study the temperature dependence of viscosity and diffusion of Cu-Zr liquids using mol...Researchers have reported that Cu-Zr liquids are kinetically strong at the best glass-forming compositions. Here we systematically study the temperature dependence of viscosity and diffusion of Cu-Zr liquids using molecular dynamics simulations, and the results illustrate that the better glass formers are actually more fragile close to the glass transition. There is a kinetic transition from low to high fragility when the optimal glass-forming liquids are quenched into glass states. This transition is associated with the more rapid decrease of the excess entropy of the liquids above and close to the glass transition temperature, Tg, compared to other compositions. Accompanied by the transition to high fragility, peaks in the thermal expansivity and specific heat are observed at the optimal compositions. Furthermore, the Stokes Einstein relation is examined over a wide composition range for Cu-Zr alloys, and the results indicate that glass-forming ability closely correlates with dynamical heterogeneity.展开更多
基金Supported by the National Innovative Experimental Projects for University Students,and the National Natural Science Foun-dation of China under Grant Nos 10975014 , 51171027.
文摘The velocity of sound in soap foams at high gas volume fractions is experimentally studied by using the time difference method.It is found that the sound velocities increase with increasing bubble diameter,and asymptotically approach to the value in air when the diameter is larger than 12.5 mm.We propose a simple theoretical model for the sound propagation in a disordered foam.In this model,the attenuation of a sound wave due to the scattering of the bubble wall is equivalently described as the effect of an additional length.This simplicity reasonably reproduces the sound velocity in foams and the predicted results are in good agreement with the experiments.Further measurements indicate that the increase of frequency markedly slows down the sound velocity,whereas the latter does not display a strong dependence on the solution concentration.
基金Supported by the National Natural Science Foundation of China under Grant No 11104013.
文摘The dynamical behavior of an intruder immersed in a two-dimensional shaken granular bed is experimentally investigated. With two types of background particles, f-Г phase diagrams depicting the intruder＇s motion are measured and compared. It is found that even with the same size and density ratio of the intruder to the background particles, the intruder exhibits a distinct behavior at given vibrational conditions： rising behavior in one granular bed; sinking behavior in another granular bed. We slightly tune the size and density ratio to confirm the reliability of the experimental results. In addition, we examine the influences of interstitial air, convection and the initial position on the intruder＇s motion, speculating that the opposite motion could be traced to the material properties of the background particles.
基金Supported by the National Natural Science Foundation of China under contract No 51171027, and the Shanghai and Tianjin Supercomputer Center.
文摘Researchers have reported that Cu-Zr liquids are kinetically strong at the best glass-forming compositions. Here we systematically study the temperature dependence of viscosity and diffusion of Cu-Zr liquids using molecular dynamics simulations, and the results illustrate that the better glass formers are actually more fragile close to the glass transition. There is a kinetic transition from low to high fragility when the optimal glass-forming liquids are quenched into glass states. This transition is associated with the more rapid decrease of the excess entropy of the liquids above and close to the glass transition temperature, Tg, compared to other compositions. Accompanied by the transition to high fragility, peaks in the thermal expansivity and specific heat are observed at the optimal compositions. Furthermore, the Stokes Einstein relation is examined over a wide composition range for Cu-Zr alloys, and the results indicate that glass-forming ability closely correlates with dynamical heterogeneity.
