Use Of Small Amplitude Research Articles

Fabrication and characterization of folded foils supporting streamwise traveling waves

A body of work has grown around the use of small amplitude traveling waves on aerodynamic and hydrodynamic surfaces for boundary layer control. In particular, when the traveling wave speed exceeds the free stream velocity, significant drag reductions have been shown in simulation. Building viable prototypes to test these hypotheses, however, has proven challenging. In this paper, we describe a candidate system for constructing structural airfoils and hydrofoils with embedded electromagnetic actuators for driving high velocity traveling waves. Our approach relies on the fabrication of planar substrates which are populated with electromagnetic components and then folded into a prescribed three dimensional structure with actuators embedded. We first specify performance characteristics based on hydrodynamic requirements. We then describe the fabrication of fiber-reinforced polymer composite substrates with prescribed folding patterns to dictate three dimensional shape. We detail the development of a miniaturized single-phase linear motor which is compatible with this approach. Finally, we compare the predicted and measured force produced by these linear motors and plot trajectories for a 200 Hz driving frequency.

Multiparameter Imaging and Understanding the Role of the Tip - Atomic Resolution Images of Rutile TiO2 (110)

ABSTRACTA major challenge for scanned probe microscopy is to identify structures and chemical species on a surface, which have not already been inferred from other analytical techniques. Progress is impeded by the fact that in general the structure and composition of the tip atom is not known. To illustrate some of the issues involved, we report simultaneous scanning tunneling microscopy/atomic force microscopy (STM/AFM) of the TiO2 (110) surface. The use of small amplitudes enabled the simultaneous acquisition of force gradient and barrier height images during standard STM imaging. Surprisingly, we find most STM images exhibit a corrugation contrast inverse to that usually reported in the literature. However, regardless of the contrast in STM, force gradient images always showed greater attraction over O rows. Barrier height images also show this consistency, always being greater over O rows. This supports the theoretical model of the electronic structure of the surface, but shows that the tip structure and interaction cannot be ignored in modeling STM images. We conclude that there is a fine balance between topography and local density of states (LDOS) in STM imaging of this surface; which of them dominates the STM image is determined by the tip. Simultaneous multi-parameter imaging is useful in interpreting images reliably, particularly on multi-component surfaces.