This work presents the experimental investigation with electrokinetic flow mixing for bio-analytical chip applications. By DC electrokinetic instability induced technique, we design a 5x5 microfluidic device which possesses microfluidic sample handling in flow multi-switching. The device not only control single sample flows into different outlets considered but also the multi-sample injection into specific outlet ports. Experimental results indicate that the sample flow could be electrokinetically pre-focusing to a narrow stream and then guided into a desired outlet port and successfully control devices of the voltage in the microfluidic chip.
This study presents a simple technique for improving the power conversion efficiency of a AlGaAs-GaAs based solar cell. A traditional III-V semiconductor solar cell heterojunction structure, i.e. n-GaAs/n-AlGaAs/n-GaAs/i-GaAs/p-GaAs is used. The top n-GaAs/n-AlGaAs structure is responsible for the selective etching stop layer. The selective etched surface barriers associated with polymer gratings with different aspect ratios are produced on solar cell by using the photolithography and Micro Electro Mechanical Systems (MEMS) techniques. A reflective-type diffraction optical grating is fabricated on the surface of the solar cell to redirect the incident light reflected from the solar cell back onto the solar cell surface. The experimental results show that the addition of the optical grating increases the open circuit voltage, Voc, from 4.51 V to 4.73V and improves the maximum output voltage, Vm, from 4.12V to 4.32V. From inspection of surface reflectivity , the average reflectivity is also found to be 13.7% down to 9.9 %.
New MOCVD grown UV (ultra-violet) LEDs using low dislocation density GaN buffer layers on sapphire have been studied. Two different LED characteristics of GaN substrates, i.e. 5um-thick and 20um-thick buffer layers, on sapphire are compared with each other. The enhanced LED characteristics show ~29.5% reduction in current-voltage resistance, ~8.5% reduction in turn-on voltage and output power saturation at higher current. Better GaN buffer quality and heat dissipation due to the lower defect density are believed to the enhanced reason.
This paper investigates the EKI phenomenon in a double T-shaped microchannel, in which two aqueous electrolyte solutions with a 3.5:1 conductivity ratio are driven electrokinetically into the mixing channel via the application of a DC electrical field. A stratified flow condition is formed when the intensity of the applied DC electrical field is below a certain threshold value. However, as the intensity is increased the lower high-conductivity stream in the entrance region of the main mixing channel fluctuates alternately in the upward and downward direction resulting in a series of flow circulations forms at the interfaces of neighboring solutions flows, and then propagate in the downstream direction. It is found that the electric perturbations added at upper inlet of the microchannel near the main mixing channel can stir the microfluidic instability and the induced flow instability conditions can enhance the mixing efficiency.
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