• Proceedings of the KSME Conference
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• 2007.05a
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• pp.405-408
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• 2007

Vestibular hair cells, the sensory receptors of vestibular organs, selectively amplify miniscule stimuli to attain high sensitivity. Such selective amplification results in compressive nonlinear sensitivity, which plays an important role in expanding dynamic range while ensuring robustness of the system. In this study, negative stiffness mechanism, a mechanism responsible for the selective amplification by vestibular hair cells, is applied to a simple mechanical system consisting of an array of inverted pendulums. The structure and working principle of the system have been inspired by gating spring hypothesis proposing that opening and closing of transduction channels contributes to the global stiffness of vestibular hair bundle. Parameter study was carried out to analyze the effect of each parameter on the compressive nonlinearity of suggested model.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.276-276
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• 2004

기존 대부분의 회전형 3 자유도 메커니즘은 직렬 구조로서 해석은 비교적 용이하지만 처짐과 커다란 관성력은 주요한 약점으로 인지되고 있다. 이에 반하여 병렬 메커니즘은 여러 부속 체인을 가지는 구조로 인한 높은 강성과 무거운 엑츄에이터를 지면 가까이 설치할 수 있게 함으로서 상대적으로 적은 처짐과 적은 관성력을 가지는 반면에 상대적으로 기구학 및 동역학 해석은 매우 복잡한 것으로 알려져 있다.(중략)

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.371-383
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• 2014

이 연구에서는 팔라듐 착물 $Pd(PPh_3)_2$을 사용한 bromotoluene과 morpholine간의 coupling reaction (Buchwald-Hartwig amination) 반응 메커니즘을 계산화학적 방법을 이용하여 연구하였다. 용매화 자유에너지를 고려한 중간체 에너지를 비교하였으며, 반응물질이 o-bromotoluene 일 때와 p-bromotoluene 일 때, 반응 중간체로 monophosphine 착물이 형성되는 경우와 bisphosphine 착물이 형성되는 경우를 비교하였으며, 반응 중간체로 bisphosphine 착물이 형성되는 경우 cis 이성질체가 중간체인 경우와 trans 이성질체가 중간체인 경우를 비교하였다. 그 결과, 반응물로 p-bromotoluene을 사용할 때 o-bromotoluene을 사용할 때보다 중간체가 상대적으로 더 안정하여 더 좋은 수득률을 얻을 수 있을 것으로 예상되었다. 또한 $Pd(PPh_3)_n(o-tolyl)(N(CH_2CH_2)_2O)$ (n=1 또는 2) 중간체를 제외하고는 모든 경우에서 bisphosphine 중간체가 형성되는 반응경로가 더 안정한 것으로 밝혀졌다. 그리고 $Pd(PPh_3)_2ArBr$의 경우 trans 이성질체가 cis 이성질체보다 안정하지만 $Pd(PPh_3)_2Ar(N(CH_2CH_2)_2O)$의 경우 반대로 cis 이성질체가 trans 이성질체보다 안정한 것으로 나타났다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.11
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• pp.1405-1411
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• 2012

Remote handling manipulators are widely used for performing hazardous tasks, and it is essential to ensure the reliable performance of such systems. Toward this end, tendon-driven mechanisms are adopted in such systems to reduce the weight of the distal parts of the manipulator while maintaining the handling performance. In this study, several approaches for the design of a gripper system for a tendon-driven remote handling system are introduced. Basically, this gripper has an underactuated spring mechanism that is combined with a slave manipulator triggered by a master operator. Based on the requirements under the specified tendon-driven mechanism, the connecting position of the spring system on the gripper mechanism and kinematic influence coefficient (KIC) analysis are performed. As a result, a suitable combination of components for the proper design of the target system is presented and verified.

• Journal of the Korean Society for Railway
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• v.18 no.1
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• pp.53-62
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• 2015

LWDT was developed for use as an alternative technique to measure the stiffness of trackbed soils. In this study, numerical and theoretical analyses of LWDT's acting mechanism were performed. The effectiveness of the adapted elastic formula used for calculation of the dynamic modulus, Evd, was investigated theoretically and also numerically by running ABAQUS analysis. The minimum thickness of the upper layer is proposed based on the analysis. Correction factors for the formula of elastic modulus are also proposed in this study. In the future, following field test results and laboratory mechanical tests such as the resonant column test, a guideline for the use of LWDT as a standard test protocol in track construction sites, as a measuring tool for the degree of compaction and/or stiffness and dynamic modulus, will be proposed based on this analysis.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.5
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• pp.861-868
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• 2017

Near band infrared imaging technique has adopted for imaging EL2 and shallow level distributions in undoped semi-insulating LEC GaAs. This technique, which relies on the mapping of near bandgap infrared transmission, is both rapid and non-destructive. Until now no quantitative analysis has been reported for near band edge region which gives the reverse contrast on EL2 absorption images. This paper presents the spectral, spatial and temperature dependence of photoquenching forward and inverse mechanism in the band edge domain for cells and walls and for direct and inverted contrast conditions during transitory regimes. The difference in the threshold for the EL2w and EL2b defects could be attributed to the contribution of a different electrical assistance due to a different species of impurities. Quantitative analysis results show an increased density of EL2w and a small reduction of EL2b in the region of the walls where there is a high density of dislocations.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.11
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• pp.2085-2092
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• 2016

One of the most important properties of the IC substrate is that it should be uniform over large areas. Among the various physical approaches of wafer defect characterization, special attention is to be payed to the infrared techniques of inspection. In particular, a high spatial resolution, near infrared absorption method has been adopted to directly observe defects in semi-insulating GaAs. This technique, which relies on the mapping of infrared transmission, is both rapid and non-destructive. This method demonstrates in a direct way that the infrared images of GaAs crystals arise from defect absorption process. A new interpretation is presented for the observed reversal of contrast in the infrared absorption of nonuniformly distributed deep centers, related to EL2, in semi-insulating GaAs. The low temperature photoquenching experiment has demonstrated in a direct way that the contrast inverse images of GaAs wafers arise from both absorption and scattering mechanisms rather than charge re-distribution or local variation of bandgap.

• Journal of the Korean GEO-environmental Society
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• v.13 no.11
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• pp.93-101
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• 2012

SCP is a construction method that maximizes the effects of ground improvement by creating sand piles, which are formed by the compaction within soft ground. SCP is mainly used for consolidation and drain effects in clayey soils, and as a liquefaction countermeasure through effects such as compaction in loose sandy soils. In the design of SCP, if the sand piles with high stiffness are not taken into account, it can become a design that overly considered safety, and increased construction costs are highly likely to cause economic disadvantages. The changes in stress conditions and compaction mechanisms in the subsurface have been identified to a certain extent by study findings to date. However, the studies that considered SCP and in-situ ground as composite ground are fairly limited, and therefore, those studies have not achieved enough results to fully explain the relevant topics. In this study, the ground improved by SCP was regarded as the composite ground that consists of SCP and in-situ ground. Moreover, employing a CID test, this study examined the changes in the stress conditions of in-situ ground according to the installation of SCP through the relations between $K_0$ and SCP replacement ratio. At the same, whether the SCP installation procedure can be recreated in a laboratory was examined using a cyclic triaxial test. According to the test results, the changes in the stress conditions of the original ground occurred most largely in an initial stage of SCP installation, and after a certain time point, the vibration for SCP installation did not have a great influence on the changes in the stress conditions of the ground. Moreover, in order to recreate the behaviors of in-suit ground according to SCP in a laboratory, cyclic loading, which corresponds to casing vibration, was concluded to be essentially required.