• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.1
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• pp.64-72
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• 2010

Due to the interaction between main oxidizer flow and the wall injected flow resulting from the regression process, a specific time characteristics identified in the frequency spectrum of streamwise velocity is generated in the hybrid rocket motor. In order to understand the response of the turbulent flow to two different types of external momentum forcing, LES analysis was conducted without considering the combustion. It turns out that both concentrated and distributed forcings do not lead to the disastrous resonance phenomenon. Energy contents are enhanced due to the added momentum but the peak frequency was not modified in the turbulent flow near the end of the rocket motor. Natural frequency of the flow system should be taken into account to further pursue the instability issue by using external forcing.

• Korean Chemical Engineering Research
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• v.61 no.1
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• pp.155-161
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• 2023

Ion concentration polarization (ICP) is one of the essential important mechanisms for biomolecule preconcentration devices as well as a fundamental transport phenomenon found in electrodialysis, electrochemical cell, etc. The ICP triggered by externally applied voltage enables the biomolecular analyte to be preconcentrated at an arbitrary position by a locally amplified electric field inside the microchannel. Conventional preconcentration methodologies using the ICP have two limitations: uncertain equilibrium position and hydrodynamic instability of preconcentration plug. In this work, a new preconcentration method in the dead-end microchannel around cation exchange membrane was numerically studied to resolve the limitations. As a result, the numerical model showed that the analyte was concentrated at a shock front developed in a geometrically confined dead-end channel. Furthermore, the electrokinetic behaviors for preconcentration dynamics were analyzed by changing microchannel's applied voltage and volumetric charge concentration of microchannel as key parameters to describe the dynamics. This work would provide an effective means for a point-of-care platform that requires ultra-fast preconcentration method.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.254-255
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• 2012

Interest in nano-crystalline silicon (nc-Si) thin films has been growing because of their favorable processing conditions for certain electronic devices. In particular, there has been an increase in the use of nc-Si thin films in photovoltaics for large solar cell panels and in thin film transistors for large flat panel displays. One of the most important material properties for these device applications is the macroscopic charge-carrier mobility. Hydrogenated amorphous silicon (a-Si:H) or nc-Si is a basic material in thin film transistors (TFTs). However, a-Si:H based devices have low carrier mobility and bias instability due to their metastable properties. The large number of trap sites and incomplete hydrogen passivation of a-Si:H film produce limited carrier transport. The basic electrical properties, including the carrier mobility and stability, of nc-Si TFTs might be superior to those of a-Si:H thin film. However, typical nc-Si thin films tend to have mobilities similar to a-Si films, although changes in the processing conditions can enhance the mobility. In polycrystalline silicon (poly-Si) thin films, the performance of the devices is strongly influenced by the boundaries between neighboring crystalline grains. These grain boundaries limit the conductance of macroscopic regions comprised of multiple grains. In much of the work on poly-Si thin films, it was shown that the performance of TFTs was largely determined by the number and location of the grain boundaries within the channel. Hence, efforts were made to reduce the total number of grain boundaries by increasing the average grain size. However, even a small number of grain boundaries can significantly reduce the macroscopic charge carrier mobility. The nano-crystalline or polymorphous-Si development for TFT and solar cells have been employed to compensate for disadvantage inherent to a-Si and micro-crystalline silicon (${\mu}$-Si). Recently, a novel process for deposition of nano-crystralline silicon (nc-Si) thin films at room temperature was developed using neutral beam assisted chemical vapor deposition (NBaCVD) with a neutral particle beam (NPB) source, which controls the energy of incident neutral particles in the range of 1~300 eV in order to enhance the atomic activation and crystalline of thin films at room temperature. In previous our experiments, we verified favorable properties of nc-Si thin films for certain electronic devices. During the formation of the nc-Si thin films by the NBaCVD with various process conditions, NPB energy directly controlled by the reflector bias and effectively increased crystal fraction (~80%) by uniformly distributed nc grains with 3~10 nm size. The more resent work on nc-Si thin film transistors (TFT) was done. We identified the performance of nc-Si TFT active channeal layers. The dependence of the performance of nc-Si TFT on the primary process parameters is explored. Raman, FT-IR and transmission electron microscope (TEM) were used to study the microstructures and the crystalline volume fraction of nc-Si films. The electric properties were investigated on Cr/SiO2/nc-Si metal-oxide-semiconductor (MOS) capacitors.

• Korean journal of communication and information
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• v.81
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• pp.75-121
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• 2017

Maeul Community Media is community media practice that media education combine with community activism based on the region. Maeul Community Media appeared with Seoul city's supporting policy in 2012 and is now enlarging on a national scale beyond Seoul. This study is aimed at understanding and investigating Maeul Community Media activists' practice process by using a grouned theory approach. In-depth interviews were carried out of study participants who worked on as activists based on visual and radio field since 2012. By open coding based on grounded theory, 16 categories and 59 subcategories were discovered. The outcome of axial coding showed the centeral phenomena that can be called 'sustainable desire for Maeul Community Media act'. On the condition of the instability of public support and the absence of a village channel, the strategic practices were discovered, which are diversification of participants recruitment and modes of participation, invention of space-media, seeking multilateral distribution methodologies and the collective action plans of networks to stabilize the management and to empower Maeul Community Media networks. As a result, Maeul Community Media and civil society were networked by discovering and agenda-setting pending issues. And we could find that the desire and expectation for the role as a village's public sphere were enlarging.