Kao-Feng Yarn

Analysis of Electrokinetic Mixing Using AC Electric Field and Patchwise Surface Heterogeneities

In this paper, the authors investigate the use of an applied AC electric field and microchannel surface heterogeneities to carry out the microfluidic mixing of two-dimensional, time-dependent electroosmotic flows. The time-dependent flow fields within the microchannel are simulated using the backwards-Euler time-stepping numerical method. The mixing efficiencies obtained in microchannels with two different patchwise surface heterogeneity patterns are investigated. In general, the results show that the application of an AC electric field significantly reduces the required mixing length compared with the use of a DC electric field. Furthermore, the presence of oppositely charged surface heterogeneities on the microchannel walls results in the formation of localized flow circulation regions within the bulk flow. These circulation regions grow and decay periodically in accordance with the periodic variation of the AC electric field intensity and provide an effective means of enhancing species mixing in the microchannel. Consequently, the use of an AC electric field together with patchwise surface heterogeneities permits a significant reduction in both the mixing channel length and the retention time required to attain a homogeneous solution.

A User-Friendly Web Content Management System

This study applies two open source projects, namely PHP and MySQL, to create a powerful, user-friendly Web-based system for creating, maintaining and publishing a database comprising news information in the form of text and graphical images. The proposed system is specifically designed to enable non-technical users with no knowledge of computer programming, graphic imaging tools, or markup languages such as HTML to add new material to a Website or to modify the existing contents as and when required in an intuitive and real-time fashion. As a result, a technically competent Website management team is not required, and thus the cost and flexibility of the Website management process is significantly improved.

Effects of Giant Optical Anisotropy in R-plane GaN/AlGaN Quantum Wells by Valence Band Mixing

Investigation of optical anisotropy spectra in the R-plane (i. e., the [1012]-oriented layer plane) of GaN/Al0.2Ga0.8N quantum wells with different widths is studied. The optical matrix elements in the wurtzite quantum wells are calculated using the k·p finite difference scheme. The calculations show that the valence band mixing effect produces giant in-plane optical anisotropy in [1012]-oriented GaN/Al0.2Ga0.8N quantum wells with a narrow width. The nature of the in-plane optical anisotropy is found to be dependent on the well width. Specifically, it is found that the anisotropy changes from x′-polarization to y′-polarization as the well width increases. DOI: 10.2529/PIERS060801054904

Lead-Acid Battery Monitoring System by Using PC Graphic Control

The PLC ¿programmable logic controller¿plays an important role in the field of industrial automation because of its excellent performance. Its multiple functions include logic arithmetic, calculation, communication, noise resistant and stability. And PC¿personal computer¿has great ability in rapid calculation coped with the ability to store huge information. In the last 20 years, PC has popularized all over the world because of its cheaper and cheaper price. Accompanied with the popularization of PC and the promotion of the communication technology, Internet has since evolved and been developed, by which we can contact with anybody, anytime and anywhere. The usage of lead-acid battery is increasing in the future. How to improve the charged efficiency of lead-acid battery and enlarge the battery usage life to reduce energy consumption and battery damage is more and more important. In this paper, it is used MITSUBISHI PLC FX2n-32MR to be controlled. The battery is by way of rater and FX-2AD in charging state. The analog and digital data is passed to PLC to be real time monitoring and controlling. Charging is set time and voltage constant to reach optimization charging. On the other hand, using AD590 is to be reference measuring and battery protection in temperature control.

Electrokinetic Instability Induced Valveless Multi-Switching in a Microfluidic Chip

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 outlet considered but also the multi-sample injection into specific outlet ports. Experimental results indicate that the sample flow could be electrokintcally 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.

Microfluidic mixing with electrokinetic instability in a double T-shaped microchannel

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.

Novel Solar Cell Structure by Coating Surface Gratings

Investigation of this study is focused on the improvement of solar cell light-collecting rate with high polymer reflecting gratings. It mainly discusses about the way to enhance the efficiency of solar cell by using both experimental holographic interferometry technology and polymer reprint method to produce high polymer reflecting gratings on the solar cell surface. Based on this method, the theoretical VOC is also calculated and raised from 2.62V to 3.62V, the maximum Vm increased from 2.5V to 3.5V. The power transfer efficiency is enhanced from 27% to 37.91%.

Periodical polymer grating structure with high aspect ratio

A new procedure for fabricating a periodic structure on a UV polymer at submicron range using holographic interferometry and molding processes is described. First, holographic interference using a He-Cd (325 nm) laser was used to create the master of the periodic line structure on an i-line sub-micron positive photoresist film. A 200 nm nickel thin film was then sputtered onto the positive photoresist. Final line pattern on a UV polymer was formed from casting against the master mold. Initial results show the technique can accurately control the gratings period and depth. A high aspect ratio of grating period (gp) to depth (d) is about 1.35.

Fabrication of nano-Bragg polymer waveguide by soft-lithography process

A polymer waveguide is successfully fabricated by a new method, which is implemented by a Micro-Electro-Mechanical System (MEMS) process including a stamping transfer technique incorporated with holographic interference, a lithography procedure and soft molding tecnnology. The polymers used in these experiments are OG146 and OG154 with different refractive indices. The near-field measurement for the channel waveguide has shown that the polarization dependent loss is very low. This process is simple, easy and suitable for mass production.

Microfluidic mixing with electrokinetic instability stirring by electrical field intensity perturbations

This paper investigates the electrokinetic instability (EKI) phenomenon in a T-type microchannel, in which two aqueous electrolyte solutions with a 10:1 conductivity ratio are driven electrokinetically into the mixing channel via the application of a DC electrical field. It is found that fluctuating, unstable waveforms are formed in the entrance region of the mixing channel and then propagate in the downstream direction when the intensity of the electrical field is increased beyond a certain critical threshold value. Electrical field intensity perturbations aligned in the direction of the conductivity gradient are then added to the DC electrical field at the upper inlet of the T-type microchannel. It is found that the application of the electrical field intensity perturbations induces flow instability conditions, and hence improves the mixing efficiency. Furthermore, these perturbations stir the microfluidic instability and can reduce the required critical threshold value of the applied DC electric field intensity.