Nonuniformities interface roughness

An alcohol-based surfactant will instigate chemical leaching of the porous silicon layer during anodization (discussed below), particularly so with long anodization times and high alcohol content, and this can result in a porosity gradient within the layer (more porous at the surface). Without surfactant, however, an anodized layer can be nonuniform in thickness, with substantial interface roughness at the porous silicon substrate (Halimaoui 1993) or between different layers. 

We have noticed that most current LBM applications to microfluidics utilize LBM as a differential equation solver, and the true merit of this method - a good representation of the underlying microscopic interactions - has not been well exploited. Solid-fluid interfacial phenomena in microsystems could be particularly suitable for LBM, since it couples the fluid and interface dynamics in a natural way. Future directions for research may include utilizing nonuniform or unstructured lattice meshes for complex microstmctures (e.g., surface roughness), combining LBM with molecular dynamics and CFD (hybrid algorithms), and applying LBM to bio-microfluidic systems. 

The experimental smdy of the solid-solid interface is complicated by a further problem. It is often (perhaps usually) observed that, instead of a purely capacitative behavior, the interface shows significant frequency dispersion. Several authors have found excellent agreement of this behavior with the dispersion shown by the constant-phase element (Bottelberghs and Broers [1976], Raistrick et al. [1977]). Although the amount of frequency dispersion is influenced by electrode roughness and other aspects of the quality of the interface (i.e. nonuniform current distribu-... 

It is impossible at the present time to provide a unified description of the response of the QCM for nonuniform solid/liquid interfaces with arbitrary geometrical structure. Below we summarize results obtained for the limiting cases of slight and strong roughness. 

In the previous chapter we examined the excitation of modes of a fiber by illumination of the endface with beams and diffuse sources, i.e. by sources external to the fiber. Here we investigate the power of bound modes and the power radiated due to current sources distributed within the fiber, as shown in Fig. 21-1. Our interest in such problems is mainly motivated by the following chapter, where we show that fiber nonuniformities can be modelled by current sources radiating within the uniform fiber. Thus, isolated nonuniformities radiate like current dipoles and surface roughness, which occurs at the core-cladding interface, can be modelled by a tubular current source. 

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