This work introduces a method of continuous particle separation through standing surface acoustic wave (SSAW)-induced acoustophoresis in a microfluidic channel. Using this SSAW-based method, particles in a continuous laminar flow can be separated based on their volume, density and compressibility. In this work, a mixture of particles of equal density but dissimilar volumes was injected into a microchannel through two side inlets, sandwiching a deionized water sheath flow injected through a central inlet. A one-dimensional SSAW generated by two parallel interdigital transducers (IDTs) was established across the channel, with the channel spanning a single SSAW pressure node located at the channel center. Application of the SSAW induced larger axial acoustic forces on the particles of larger volume, repositioning them closer to the wave pressure node at the center of the channel. Thus particles were laterally moved to different regions of the channel cross-section based on particle volume. The particle separation method presented here is simple and versatile, capable of separating virtually all kinds of particles (regardless of charge/polarization or optical properties) with high separation efficiency and low power consumption.
From a data set of Chinese firms in the 2005-07 period, we find that government investment boosted the performance of zombie firms and crowded out the growth of private firms; we also found that the higher the concentration of state banks (and of state-owned enterprises), the more conducive is the environment for nurturing zombie firms. With the exit of zombie firms, (a) the industrial output growth rate would be higher by 2.12 percentage points, (b) the capital accumulation rate would be higher by 1.4 percentage points, (c) the employment growth rate would be higher by 0.84 percentage points, and (d) the rate total factor productivity growth would be higher by 1.06 percentage points. Our results support a radical change in the way that government investment has been carried out, and support comprehensive reform of the state sector, but they do not necessarily argue against government investment in large infrastructure projects and strategically-critical areas.
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