The effect of the triangular pinning region on the sliding of water droplets on the smooth hydrophobic surface was investigated. Smooth hydrophobic silane coatings with various regular triangle hydrophilic regions were prepared using photolithography and octadecyltrimethoxysilane (ODS). The hydrophilic area in the surfaces was aligned hexagonally with a constant area fraction. Thereby water contact angles of the coatings were almost equivalent. The water droplet sliding velocity increased continuously with increasing pattern size. Anisotropic sliding velocity was observed on the surface, suggesting different pinning effects. The sliding motion of water droplets on the gradient surface with changing hydrophilic region size deflects against the downward direction. The deflection length depends on the direction of triangle hydrophilic regions and the initial sliding position. These results demonstrate that control of the sliding velocity while sustaining the static contact angle is feasible by designing the shape and alignment of chemical heterogeneity.

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Vacancy-type defects in plasma immersion B-implanted Si were probed by a monoenergetic positron beam. Doppler broadening spectra of the annihilation radiation were measured and compared with spectra calculated using the projector augmented-wave method. For the as-doped sample, the vacancy-rich region was found to be localized at a depth of 0–10 nm, and the major defect species were determined to be divacancy–B complexes. After spike rapid thermal annealing at 1075 °C, the lineshape parameter S of Doppler broadening spectra corresponding to the high-B-concentration region (4–30 nm) was found to be smaller than the characteristic S value obtained for defect-free Si. From a detailed analysis of the Doppler broadening spectra, the origin of the decrease in the S value was attributed to the trapping of positrons by negatively charged B clusters such as icosahedral B12.

In this paper, nonlinear dynamic response of a traveling wave-type ultrasonic motor was investigated. In particular, understanding the transient dynamics of a bar-type ultrasonic motor, such as starting up and stopping, is of primary interest. First, the transient response of the bar-type ultrasonic motor at starting up and stopping was measured using a laser Doppler velocimeter, and its driving characteristics are discussed in detail. The motor is shown to possess amplitude-dependent nonlinearity that greatly influences the transient dynamics of the motor. Second, a dynamical model of the motor was constructed as a second-order nonlinear oscillator, which represents the dynamics of the piezoelectric ceramic, stator, and rotor. The model features nonlinearities caused by the frictional interface between the stator and the rotor, and cubic nonlinearity in the dynamics of the stator. Coulomb's friction model was employed for the interface model, and a stick-slip phenomenon is considered. Lastly, it was shown that the model is capable of representing the transient dynamics of the motor accurately. The critical parameters in the model were identified from measured results, and numerical simulations were conducted using the model with the identified parameters. Good agreement between the results of measurements and numerical simulations is observed.

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