• Tribology and Lubricants
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• v.26 no.2
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• pp.129-135
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• 2010

Geckos have a unique ability to cling to ceilings and walls utilizing dry adhesion. Their foot pads are covered by a large number of small hairs (setae) that contain many branches per seta with a lower level of spatulae. Their fibrillar structure is the primary source of high adhesion. In this study, we construct the adhesion design database for biomimetic adhesive system. A simple idealized fibrillar structure consisting of single array of beams is modeled. The fibers are assumed as oriented cylindrical cantilever beams with spherical tip. We consider three necessary conditions; buckling, fracture and sticking of fiber structure, which constrain the allowed geometry. The adhesion analysis is performed for the attachment system in contact with rough surfaces with different s values for different main design variables-fiber radius, aspect ratio and material elastic modulus and so on. The developed adhesion design databases are useful for understanding biological systems and for guiding of fabrication of the biomimetic attachment system.

• Journal of Mechanical Science and Technology
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• v.18 no.5
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• pp.789-797
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• 2004

The nanoscale sensing and manipulation have become a challenging issue in micro/nano-robotic applications. In particular, a feedback sensor-based manipulation is necessary for realizing an efficient and reliable handling of particles under uncertain environment in a micro/nano scale. This paper presents a piezoresistive MEMS cantilever for nanoscale force measurement in micro robotics. A piezoresistive MEMS cantilever enables sensing of gripping and contact forces in nanonewton resolution by measuring changes in the stress-induced electrical resistances. The calibration of a piezoresistive MEMS cantilever is experimentally carried out. In addition, as part of the work on nanomanipulation with a piezoresistive MEMS cantilever, the analysis on the interaction forces between a tip and a material, and the associated manipulation strategies are investigated. Experiments and simulations show that a piezoresistive MEMS cantilever integrated into a micro robotic system can be effectively used in nanoscale force measurements and a sensor-based manipulation.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.1017-1022
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• 1996

This paper presents results of dynamic analysis of the missile initial motion arising from the missile detent force. Using ADAMS (Automatic Dynamic Analysis of Mechanical System) software, a non-linear 46-DOF (Degree of Freedom) model is developed for the launcher system including missile and launch tube contact problem. From the dynamic analysis, it is found that initial angular velocity of the missile increases when the missile detent force increases (more than 18 g) and also rocket exhaust plume is taken into account. To achieve the missile launching s ability, it needs to reduce the missile initial detent force and exhaust plume area of the launcher. Results of the dynamic analysis on the system natural frequency agree well with those obtained from experimental modal tests. The overall results suggest that the proposed method is a useful tool for prediction of initial missile stability as well as d :sign of the missile launcher system.

• Proceedings of the Korean Reliability Society Conference
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• 2004.07a
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• pp.139-145
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• 2004

용접산업이 발전함에 따라 가스메탈아크 용접에서 고내마모성의 콘택트 팁이 요구되어지고 있다. 현재 국내외에서는 콘택트팁에 대한 수명평가 기준이 없으며, 일부 업계에서 자체 규격을 제정하여 운용하고 있지만 근거가 명확하지 않다. 따라서 본 연구에서는 콘택트팁의 신뢰성 평가기준을 제정하고자 하였다. 팁의 주요 파손기구로는 고온 마찰마모, 전기적 에로존, 번백 등이 있다. 신뢰성 평가는 경도 시험, 열처리 후 경도, 용접 마모, 전기전도도를 시험으로 구성되었다. 팁의 수명은 마모가 45%에 도달했을 경우 송급된 와이어 총 길이로 하였으며, 4시간까지 마모시험 한 결과를 근거로하여 한계수명을 추정하였다. 본 연구에서는 세 가지 조성의 다섯 가지의 콘택트팁에 대하여 4시간동안 내마모성 실험을 하였으며, 마모정도는 1시간 단위로 면적비를 백분율로 환산하여 측정하였다. 실험 결과 가공경화형팁은 1시간이내에 재결정 및 입자성장에 의한 경도 저하로 가공경화가 팁 수명에 지속적 영향을 주지 못하였다. 반면, 석출경화형팁은 석출경화 효과가 지속되어 가공경화형팁보다 수명이 향상 되었다.

• Proceedings of the Korea Crystallographic Association Conference
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• 2003.05a
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• pp.13-13
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• 2003

B-cell activating factor (BAFF) is a key regulator of B-lymphocyte development. Its biological role is mediated by the specific receptors BCMA, TACI, and BAFF-R. We have determined the crystal structure of BAFF-R extracellular domain bound to BAFF at a resolution of 3.3 ?. The cysteine-rich domain(CRD) of the BAFF-R extracellular domain adopts a b-hairpin structure and binds to the virus-like BAFF cage in a 1:1 molar ratio. The conserved DxL motif of BAFF-R is located on the tip of the b-turn, and plays an indispensable role in the binding of BAFF. The crystal structure shows that a unique dimeric contact occurs between the BAFF-R monomers in the virus-like cage complex. Both of the CRDs of TACI contain the DxL motifs and simultaneously interact with the BAFF dimer in the virus-like cage.

• Proceedings of the KSR Conference
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• 2004.10a
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• pp.595-600
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• 2004

The EMU wheel is one of the most important component for the vehicle safety. For the tensile, fracture toughness and crack propagation tests, several specimens were collected from actual wheels. FEM ,analysis also was performed on the crack that was assumed to be 15 mm in depth under the wheel tread surface. The stress intensity factors $K_{I}$ and $K_{II}$ at the crack tip under the stress ($P_{max}$ = 911.5 MPa) due to a rolling contact were analyzed for crack growth characteristics. As a result, the perpendicular crack was found to be more dangerous compared to the parallel one.

• BMB Reports
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• v.51 no.3
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• pp.157-162
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• 2018

Angiogenesis is a complex, multistep process involving dynamic changes in endothelial cell (EC) shapes and behaviors, especially in specialized cell types such as tip cells (with active filopodial extensions), stalk cells (with less motility) and phalanx cells (with stable junction connections). The Hippo-Yes-associated protein (YAP)/ transcription activator with PDZ binding motif (TAZ) signaling plays a critical role in development, regeneration and organ size by regulating cell-cell contact and actin cytoskeleton dynamics. Recently, with the finding that YAP is expressed in the front edge of the developing retinal vessels, Hippo-YAP/TAZ signaling has emerged as a new pathway for blood vessel development. Intriguingly, the LATS1/2-mediated angiomotin (AMOT) family and YAP/TAZ activities contribute to EC shapes and behaviors by spatiotemporally modulating actin cytoskeleton dynamics and EC junction stability. Herein, we summarize the recent understanding of the role of Hippo-YAP/TAZ signaling in the processes of EC sprouting and junction maturation in angiogenesis.

• Journal of Magnetics
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• v.21 no.2
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• pp.204-208
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• 2016

This paper demonstrates the key parameter detection for smelting of submerged arc furnace (SAF) based on magnetic field radiation. A magnetic field radiation model for the inner structure of SAF is established based on relative theory of electromagnetic field. A simple equipment of 3D magnetic field detection system is developed by theoretical derivation and simulation. The experiments are carried out under the environment of industrial field and AC magnetic field generated by electrode currents and molten currents in the furnace is reflected outside of the furnace. The experimental results show that the key parameters of smelting including the position of electrode tip, the length of electric arc, and the liquid level of molten bath can be achieved. The computed tomography for SAF can be realized by the detection for smelting.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.13.2-13.2
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• 2009

Electrostatic printing either it is drop-on-demand or continuous has immense applications in non-contact printing systems such as solar cells, flexible printed circuits, RFIDs and bio applications. In this paper a laboratory manufactured nozzle has been designed for the experimental investigation of electrostatic dripping and atomization of liquid. Dripping and atomization conditions such as voltage, nozzle tip diameter, distance between counter electrode and flowrate has been indentified for the designed nozzle. Furthermore it is also demonstrated that the diameter of a generated droplet could be reduced from a significantly large size to a narrow size distribution which can be controlled by volumetric flow rate and applied voltage. This study will help in classify the conditions between different electrostatic dripping mode such as drop-on-demand formation, jet mode and finally the atomization mode based on the laboratory fabricated nozzle head.

• Journal of the Korean Geophysical Society
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• v.6 no.2
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• pp.79-87
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• 2003

An in-situ four-electrode contact resistivity probe system was designed, and field-tested in submarine sediments. Seismic survey was also performed to support and compare the results of electric survey. The probe was designed to be driven to selected depths below the seafloor using a Vibracore system. The four insulated electrodes were, spaced equidistant across the wedge, were extended beyond the probe tip to minimize effects of sediment disturbance by the wedge insertion. In-situ measurements of resistivity were recorded on board by precision electronic equipment consisting of signal generators and processors, and by temperature- monitoring systems. Overall limits of uncertainty at respective depths below the seafloor are up to ±10% of the measured values. Best estimates of conductivity are considered to be ±3 percent of the reported values. Resistivity measurements were made at six sites in carbonate sediments to a maximum depth of penetration of about 5 m. Average values of conductivity range between 0.88 and 1.21 mho/m. The results show the seabed is composed of alternating layers of relatively high-conductivity material (0.8 to 1.4 mho/m) in thicknesses of more or less one meter and layers about 30 cm thick having relatively low conductivities (0.4 to 0.8 mho/m).