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To overcome the dependence of the plasma extraction on siphon hydrophilicity in a centrifugal microfluidic chip and to ensure long-term stability and reliability of the microfluidic chip, a compressed air reservoir connected to the blood separated reservoir was proposed to separate the blood in blood separated reservoir at high rotating speeds. Through lowering the spinning speed, the plasma in the separated reservoir was pumped toward the CD-like chip center to release the stored air pressure produced by the rotation at high spinning speeds. Based on the thermodynamics of the isothermal gas, the pneumatic pumping method was modeled, and the model was confirmed by analyzing pumping positions and air compression versus spinning speeds. By using the layered Polymethyl Methacrylate(PMMA)as materials, the centrifugal microfluidic chips for plasma extraction were fabricated with a CO2 laser process technique and the volume of compressed air and the blood position at siphon were tested at different rotational speeds. Experimental results demonstrate that the achieved volume of compression is 8.7L and the siphon valve effectively inhibits whole blood to overflow the crest of siphon at 4 000 r/min speed. With lowering the spin speed to 1 000 r/min, the release of compressed air overcomes the centrifugal force and drives the plasma to flow past the crest of siphon. Then the plasma extraction is realized in quantitation.

A hierarchical multi-scale model that couples a region of material described by discrete dislocation plasticity to a surrounding region described by conventional crystal plasticity is presented. The coupled model is aimed at capturing non-classical plasticity effects such as the long-range stresses associated with a density of geometrically necessary dislocations and source limited plasticity, while also accounting for plastic flow and the associated energy dissipation at much larger scales where such non-classical effects are absent. The key to the model is the treatment of the interface between the discrete and continuum regions, where continuity of tractions and displacements is maintained in an average sense and the flow of net Burgers vector is managed via "passing" of discrete dislocations. The formulation is used to analyze two plane strain problems: (i) tension of a block and (ii) crack growth under mode I loading with various sizes of the discrete dislocation plasticity region surrounding the crack tip. The computed crack growth resistance curves are nearly independent of the size of the discrete dislocation plasticity region for region sizes ranging from 30 mu m x 30 mu m to 10 mu m x 5 mu m. The multi-scale model can reduce the computational time for the mode 1 crack analysis by a factor of 14 with little or no loss of fidelity in the crack growth predictions. (c) 2008 Elsevier Ltd. All rights reserved.