• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.9
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• pp.1517-1523
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• 2003

Deep X-ray lithography (DXRL), a fabrication method for the production of microstructures with a high aspect ratio, plays an important role in the subsequent electroplanting process. However, secondary radiation is generated during X-ray exposure and damages the resist adhesion to the metal layer. To solve adhesion problems, we modified the conventional DXRL process, changing the sequence of polymer adhesion in DXRL process. With optimized X-ray exposure and development conditions based on a calculated and modified X-ray power spectrum, we fabricated various polymer microstructures and achieved a maximum aspect ratio of 40.

• Electrical & Electronic Materials
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• v.10 no.7
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• pp.668-673
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• 1997

A Single-crystalline Mn-Zn Ferrite (110 orientation) was masklessly etched by focused Ar laser irradiation in an H$_3$PO$_4$ solution. The depth of the etched grooves increases with increasing a laser power, decreasing a scan speed, and increasing the H$_3$PO$_4$concentration. The width of the etched grooves increases with a increasing laser power, but was relatively insensitive to the scan speed and H$_3$PO$_4$concentration. High etching rate of up to 714 ${\mu}{\textrm}{m}$/s and an aspect ratio of 6 for vertical slab structure have been obtained by the light-guiding effect of the laser bean in the H$_3$PO$_4$ solution.

• Nuclear Engineering and Technology
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• v.51 no.4
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• pp.996-1007
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• 2019

We investigated the influence of the aspect ratio (H/R) of the oxide layer on the reactor vessel heating in three-layer configuration. Based on the analogy between heat and mass transfers, we performed mass transfer experiments to achieve high Rayleigh numbers ranging from $6.70{\times}10^{10}$ to $7.84{\times}10^{12}$. Two-dimensional (2-D) semi-circular apparatuses having the internal heat source were used whose surfaces of top, bottom and side simulate the interfaces of the oxide layer with the light metal layer, the heavy metal layer, and the reactor vessel, respectively. Multi-cell flow pattern was identified when the H/R was reduced to 0.47 or less, which promoted the downward heat transfer from the oxide layer and possibly mitigated the focusing effect at the upper metallic layer. The top boundary condition greatly affected the natural convection of the oxide layer due to the presence of secondary flows underneath the cold light metal layer.

• Journal of the Korean Society of Visualization
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• v.21 no.3
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• pp.15-22
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• 2023

This research introduces an innovative approach for fabricating microstructure surfaces using spray-coating deposition. The resulting surface, referred to as Magnetically Responsive Microstructures (MRM), exhibits hierarchically structured micro-pillar arrays with remarkably high aspect ratios. The fabrication process involves precisely mixing PDMS and hexane with Carbonyl iron powders, followed by ultrasonication and spray-coating on the top of a PDMS substrate placed on the neodymium magnet. The MRM surface shows hydrophobic properties, characterized by a contact angle surpassing 150° and an aspect ratio exceeding 10. Through a comprehensive exploration of critical parameters, including spray amount, magnet-substrate distance, and solution ratio enhanced dynamic tunability and exceptional hydrophobic characteristics are attained. This novel approach holds significant potential for diverse applications in the realm of dynamically tunable microstructures and magnetically responsive surfaces.

• Journal of Mechanical Science and Technology
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• v.20 no.12
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• pp.2094-2104
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• 2006

As demands for complex microstructures with high aspect ratios have increased, the existing methods, MEMS and LIGA, have had difficulties coping with the number of masks and fabricable heights. A microstereolithography technology can meet these demands because it has no need of masks and is capable of fabricating high aspect ratio microstructures. In this technology, 3D part is fabricated by stacking layers, 2D sections, which are sliced from STL file, and the Dynamic Image Projection process enables the resin surface to be cured by a dynamic image generated with $DMD^{TM}$ (Digital Micromirror Device) and one irradiation. In this paper, we address optical design process for implementing this microstereolithography system that takes the light path based on DMD operation and image-formation on the resin surface using an optical design program into consideration. To verify the performance of this implemented microstereolithography system, complex 3D microstructures with high aspect ratios were fabricated.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.47-52
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• 2001

Short reinforced concrete bridge piers are particularly susceptible to shear failure as a consequence of the high shear/moment ratio and conservatism in the flexural strength design of existing RC bridge pier, which were constructed before 1992. In addition, shear failure is brittle and involves rapid strength degradation. Inelastic shear deformation is thus unsuitable fur ductile seismic response. It is, however, believed that there are not many experimental research works fur shear failure of the existing RC bridge pier in Korean peninsula subjected to earthquake motions. The object of this research is to evaluate the seismic performance of existing circular RC bridge piers by the quasi-static test. Existing RC bridge piers were moderate seismically designed in accordance with the conventional provisions of Korea Highway Design Specification. This study has been performed to verify the effect of aspect ratio (column height-diameter ratio). Quasi-static test has been done to investigate the physical seismic performance of RC bridge piers, such as lateral force-displacement hysteric curve, envelope curve etc.

• Design & Manufacturing
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• v.11 no.3
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• pp.29-34
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• 2017

Increased demand for parts with micro-pattern structure made of metals, ceramics, and composites in various fields such as medical ultrasonic sensors, CT collimators, and ultra-small actuator parts. Micro powder injection molding (PIM) is a technology for manufacturing micro size, high volume, complex, precision, net-shape components from either metal or ceramic powder. In the present study, a standard mold with a variable insert core capable of producing various micro patterns was investigated. An injection molding test was performed on a standard mold using a line type micro-pattern core having an aspect ratio of 2, a slenderness ratio of 70, a pattern size of $200{\mu}m$, and a pattern spacing of $150{\mu}m$. During the filling process, the deformation of the mold with large aspect ratio and slenderness ratio was analyzed by the experiment and the numerical simulation according to the position of the gate. We proposed a mold structure that minimizes mold deformation by gate modification and enables uniform pattern filling behavior.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.17 no.6
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• pp.231-237
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• 2007

For an aspect ratio (transport length-to-width) of 5, Pr=3.34, Le=0.078, Pe=4.16, Cv=1.01, $P_B=50$ Torr, only thermally buoyancy-driven convection ($Gr=4.83{\times}10^5$) is considered in this study in spite of the disparity in the molecular weights of the component A ($Hg_2Cl_2$) and B which would cause thermally and/or solutally buoyancy-driven convection. The crystal growth rate and the maximum velocity vector magnitude are decreased exponentially for $3{\le}Ar{\le}5$, for (1) adiabatic walls and (2) the linear temperature profile, with a fixed source temperature. This is related to the finding that the effects of side walls tend to stabilize convection in the growth reactor. The rate for the linear temperature profiles walls is slightly greater than for the adiabatic walls far varied temperature differences and aspect ratios. With the imposed thermal profile, a fixed source region, both the rate and the maximum velocity vector magnitude increase linearly with increasing the temperature difference for $10{\le}{\Delta}T{\le}50K$.

• Wind and Structures
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• v.31 no.3
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• pp.255-267
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• 2020

A systematic set of low-speed wind tunnel experiments was performed at Re = 6.5×10⁴ and 1.1×10⁵ to study the mean wind loading experienced by surface-mounted finite-height square prisms for different aspect ratios, incidence angles, and boundary layer thicknesses. The aspect ratio of the prism was varied from AR = 1 to 11 in small increments and the incidence angle was changed from α = 0° to 45° in increments of 1°. Two different boundary layer thicknesses were used: a thin boundary layer with δ/D = 0.8 and a thick boundary layer with δ/D = 2.0-2.2. The mean drag and lift coefficients were strong functions of AR, α, and δ/D, while the Strouhal number was mostly influenced by α. The critical incidence angle, at which the prism experiences minimum drag, maximum lift, and highest vortex shedding frequency, increased with AR, converged to a value of α_c = 18° ± 2° once AR was sufficiently high, and was relatively insensitive to changes in δ/D. A local maximum value of mean drag coefficient was identified for higher-AR prisms at low α. The overall behaviour of the force coefficients and Strouhal number with AR suggests the possibility of three flow regimes.

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.3
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• pp.100-107
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• 2001

Miro propulsion device is a literally very small propulsion system The reason why such a small propulsion system is required is that micro satellites are considered as substitutions for conventional satellites to reduce cost; the fabrication of micro satellites enables us to produce mass production Microrockets have relatively high values of thrust/weight ratio due to the cube law; weight is proportional to volume and thrust is proportional to area. Accordingly, downsizing makes the ratio of thrust/weight ratio high However, conventionally ignorable facts are not negligible any more in small scale systems. for chemical micro rockets, downsizing causes lots of heat loss as surface to volume ratio increases, which results in the destruction of radical ions. For thrusters using plasma, the generation of strong magnetic field for plasma is very difficult. Also, in the aspect of flow dynamics, the effects of drag and viscosity are important parameters in low Re flows. When these problems are solved, micro propulsion systems can be commercialized and result in spin-off effects in many fields.