Microfluidics for Miniaturized Laboratories on a Chip

Microfluidic systems promise solutions for high throughput and highly specific analysis for biology, medicine and chemistry while consuming only tiny amounts of reactants and space. On these lab‐on‐a‐chip platforms often multiple physical effects such as electrokinetic, acoustic or capillary phenomena from various disciplines are exploited to gain the optimal functionality. The fluidics on these small length scales differ significantly from our experience of the macroscopic world. In this Review we survey some of the approaches and techniques to handle minute amounts of fluid volumes in microfluidic systems with special focus on surface acoustic wave driven fluidics, a technique developed in our laboratory. Here, we outline the basics of this technique and demonstrate, for example, how acoustic mixing and fluid actuation is realized. Furthermore we discuss the interplay of different physical effects in microfluidic systems and illustrate their usefulness for several applications.     

Modified Boussinesq''s equations for nonuniform tire loading

Hypotheses from elasticity theory were used for modeling stress distribution in a semi-infinite-homogeneous medium when a point load was applied on its surface. A Concentration factor coefficient was introduced to adapt the equations to the characteristics of the investigated soil. An expression for continuous load distributions and variations in the geometry of the contact area between soil and tire were obtained by means of the superposition principle. Some simulations for different areas and load distributions are discussed and compared with field measurements.     

Photoinduced Luminescence Blinking and Bleaching in Individual Single‐Walled Carbon Nanotubes

The temporal evolution of photoluminescence in individual single‐walled carbon nanotubes (SWNT) under strong laser irradiation is studied and pronounced blinking and bleaching is observed, caused by photoinduced oxidation that subsequently quenches mobile excitons. The nanotubes are isolated with sodium cholate and spun onto either a glass or mica surface. Their bleaching behavior is investigated for variable laser intensities in air and argon atmosphere. The decay rate for luminescence bleaching generally increases with higher laser intensity, however saturating on mica substrates, which is attributed to limited availability of oxygen in the vicinity of the nanotubes. Step‐like events in the luminescence time traces corresponding to single oxidation events are analyzed regarding relative step height and suggest an exciton diffusion range of about 105 nm.