Stretchable Graphene: A Close Look at Fundamental Parameters through Biaxial Straining

Tunable biaxial stresses, both tensile and compressive, are applied to a single layer graphene by utilizing piezoelectric actuators. The Gruneisen parameters for the phonons responsible for the D, G, 2D and 2D' peaks are studied. The results show that the D peak is composed of two peaks, unambiguously revealing that the 2D peak frequency (omega(2D)) is not exactly twice that of the D peak (omega(D)). This finding is confirmed by varying the biaxial strain of the graphene, from which we observe that the shift of omega(2D)/2 and omega(D) are different. The employed technique allows a detailed study of the interplay between the graphene geometrical structures and its electronic properties.

Dislocation movement in nitrogen-doped Czochralski silicon

Dislocation movement in N-doped Czochralski silicon (Cz-Si) was surveyed by four point bend method. Dislocation movement velocities in Cz-Si doped with nitrogen, with both nitrogen and antimony, and with only antimony were investigated. The order of measured dislocation movement velocities, at 700 degrees C less than or equal to T less than or equal to 800 degrees C and under resolved stress sigma=4.1 kg/mm(2), was V-Sb.O > V-n.Sb.O>V-N.O. The experiments showed that nigtrogen doping could retard the movement of dislocations.

Thermocapillary migrations of drops and bubbles

The transport phenomenon of drops or bubbles is a very important topic in fundamental hydrodynamics research and practical applications such as material processing and the chemical engineering. In microgravity environment, if drops or bubbles stay in a continuous phase with non-uniform temperature ¯eld, they will start to move as a result of the variance of the interface tension. This kind of movement is called the Marangoni migration. This review tries to sum up the main results in this ¯eld on theoretical analysis, numerical simulations and experiments. So far the theoretical analysis is still limited to the linear or weak nonlinear steady questions, while the current numerical simulations can already obtain the time- dependent process of the bubble/drop migration when the e®ect of heat convection is small. For strong heat convection problem, or when the Marangoni number is bigger than 100, no numerical result is in consistence with those of experiments so far. Some of the lastest numerical results are shown when heat convection is strong, and the main di®erence between strong and weak heat convection is analyzed. Finally, we also discuss the main unresolved problems in this ¯eld and some possible directions in the future.

CFD-DEM simulation of three-dimensional aeolian sand movement

A three-dimensional CFD-DEM model is proposed to investigate the aeolian sand movement. The results show that the mean particle horizontal velocity can be expressed by a power function of heights. The probability distribution of the impact and lift-off velocities of particles can be described by a log-normal function, and that of the impact and lift-off angles can be expressed by an exponential function. The probability distribution of particle horizontal velocity at different heights can be described as a lognormal function, while the probability distribution of longitudinal and vertical velocity can be described as a normal function. The comparison with previous two-dimensional calculations shows that the variations of mean particle horizontal velocity along the heights in two-dimensional and three-dimensional models are similar. However, the mean particle density of the two-dimensional model is larger than that in reality, which will result in the overestimation of sand transportation rate in the two-dimensional calculation. The study also shows that the predicted probability distributions of particle velocities are in good agreement with the experimental results.

"Dual-Parallel-Channel" Shape-Gradient Surfaces: Toward Oriented and Reversible Movement of Water Droplets

In this paper, we prepared "dual-parallel-channel" shape-gradient surfaces, on which water droplets can reversibly and orientedly move between two adjacent pools under the guidance of an external voltage. Furthermore, it is found that the motion speed is governed by several parameters, including bath condition, gradient angle, and the working voltage. In this self-transportation process of water droplets, the external voltage works like a traffic light, which can give "moving", "stopping", "turning" and "straight-going" signals to the Water droplets.

Generation of internal and surface waves by seafloor movement in a two layer fluid system

Internal and surface waves generated by the deformations of the solid bed in a two layer fluid system of infinite lateral extent and uniform depth are investigated. An integral solution is developed for an arbitrary bed displacement on the basis of a linear approximation of the complete description of wave motion using a transform method (Laplace in time and Fourier in space) analogous to that used to study the generation of tsunamis by many researchers. The theoretical solutions are presented for three interesting specific deformations of the seafloor; the spatial variation of each seafloor displacement consists of a block section of the seafloor moving vertically either up or down while the time-displacement history of the block section is varied. The generation process and the profiles of the internal and surface waves for the case of the exponential bed movement are numerically illustrated, and the effects of the deformation parameters, densities and depths of the two layers on the solutions are discussed. As expected, the solutions derived from the present work include as special cases that obtained by Kervella et al. [Theor Comput Fluid Dyn 21:245-269, 2007] for tsunamis cased by an instantaneous seabed deformation and those presented by Hammack [J Fluid Mech 60:769-799, 1973] for the exponential and the half-sine bed displacements when the density of the upper fluid is taken as zero.