• 대한기계학회논문집A
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• 제25권3호
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• pp.520-528
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• 2001

This paper investigates a resonant microaccelerometer that measures acceleration using a built-in micromechanical resonator, whose resonant frequency is changed by the acceleration-induced axial force. A set of design equations for the resonant microaccelerometer has been developed, including analytic formulae for resonant frequency, sensitivity, nonlinearity and maximum stress. On this basis, the sizes of the accelerometer are designed for the sensitivity of 10$^3$Hz/g in the detection range of 5g, while satisfying the conditions for the maximum nonlinearity of 5%, the minimum shock endurance of 100g and the size constraints placed by microfabrication process. A set of the resonant accelerometers has been fabricated by the combined use of bulk-micromachining and surface-micromachining techniques. From a static test of the cantilever beam resonant accelerometer, a frequency shift of 860Hz has been measured for the proof-mass deflection of 4.3${\pm}$0.5$\mu\textrm{m}$; thereby resulting in the detection sensitivity of 1.10${\times}$10$^3$Hz/g. Uncertainty analysis of the resonant frequency output has been performed to identify important issues involved in the design, fabrication and testing of the resonant accelerometer.

• 한국신뢰성학회:학술대회논문집
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• 한국신뢰성학회 2004년도 정기학술대회
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• pp.147-151
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• 2004

In this study, an optical fiber assembly directly coupled with a laser diode or a photo diode is designed to confirm high reliable optical coupling efficiency of optical transmitter(Tx) and receiver(Rx). The optical fiber assembly is fabricated by soldering an optical fiber and a Kovar ferrule using a glass solder after inserting an optical fiber through a Kovar ferrule. The Kovar which has good welding characteristics is applied to introduce laser welding technique. The glass solder has excellent thermal characteristics such as thermal shift delamination compared with PbSn, AuSn solder previously used usually. Furthermore, the glass solder doesn't need fiber metalization and this enables low cost fabrication. However, the glass soldering is high temperature process over 35$0^{\circ}C$ and the convex shape after solidification due to surface tension causes the stress concentration on optical fiber. The stress concentration on the optical fiber increases the optical insertion loss and possibility of crack formation. The shape of glass solder was designed referring to 2-D Axi-symmetric FEM simulation. To test the mechanical reliability, mechanical vibration test and shock test were done according to Telcorida GR-468-Core protocol. After each test, the optical loss of the stress distributed fiber assembly didn't exceed 0.5 dB, which passes the test.

• 한국인구학
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• 제21권2호
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• pp.83-112
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• 1998

제 2 건국을 위한 경제 도약과 고용창출, 근본적인 실업대책을 위해서는 향후 1~2년간 우리 경제의 지속적인 구조조정과 노동시장의 유연성 요구는 선택의 대상이 아닌 현실적인 상황에서 급격히 증가하는 실업문제와 이에 대한 대책은 우리의 초미의 관심을 끌고 있다. 본 연구에서는 현재 노동시장에서 겪는 청${\cdot}$장년층의 실업발생은 이론적으로 경기순환적이며 구조적인 원인으로 파악하고 성장차, 마찰적, 구조적, 부가노동자효과, 실망실업, 기술적 실업 등 복합적인 원인으로 파악하였다. 현재의 우리의 구조조정방법을 살펴보고 원인별로 단기 실업전망을 하였다. 전망된 실업자의 정책적 배려가 배제될 경우 경제적인 부정적 영향을 살펴보았다. 따라서 실업자에 대한 단기 및 중장기 실업대책을 제시하는데 초점을 맞추고 있다.

• Journal of Microbiology and Biotechnology
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• 제26권2호
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• pp.373-384
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• 2016

The membrane-aerated biofilm reactor (MABR) is a promising municipal wastewater treatment process. In this study, two cross-flow MABRs were constructed to explore the carbon and nitrogen removal performance and bacterial succession, along with changes of influent loading shock comprising flow velocity, COD, and NH₄-N concentrations. Redundancy analysis revealed that the function of high flow velocity was mainly embodied in facilitating contaminants diffusion and biosorption rather than the success of overall bacterial populations (p > 0.05). In contrast, the influent NH₄-N concentration contributed most to the variance of reactor efficiency and community structure (p < 0.05). Pyrosequencing results showed that Anaerolineae, and Beta- and Alphaproteobacteria were the dominant groups in biofilms for COD and NH₄-N removal. Among the identified genera, Nitrosomonas and Nitrospira were the main nitrifiers, and Hyphomicrobium, Hydrogenophaga, and Rhodobacter were the key denitrifiers. Meanwhile, principal component analysis indicated that bacterial shift in MABR was probably the combination of stochastic and deterministic processes.

• 산업경영시스템학회지
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• 제47권2호
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• pp.48-56
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• 2024

We examine a single machine scheduling problem with step-improving jobs in which job processing times decrease step-wisely over time according to their starting times. The objective is to minimize total completion time which is defined as the sum of completion times of jobs. The total completion time is frequently considered as an objective because it is highly related to the total time spent by jobs in the system as well as work-in-progress. Many applications of this problem can be observed in the real world such as data gathering networks, system upgrades or technological shock, and production lines operated with part-time workers in each shift. Our goal is to develop a scheduling algorithm that can provide an optimal solution. For this, we present an efficient branch and bound algorithm with an assignment-based node design and tight lower bounds that can prune branch and bound nodes at early stages and accordingly reduce the computation time. In numerical experiments well designed to consider various scenarios, it is shown that the proposed algorithm outperforms the existing method and can solve practical problems within reasonable computation time.

• 천문학회지
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• 제50권6호
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• pp.167-178
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• 2017

We present a study of the inexplicit connection between radio jet activity and ${\gamma}$-ray emission of BL Lacertae (BL Lac; 2200+420). We analyze the long-term millimeter activity of BL Lac via interferometric observations with the Korean VLBI Network (KVN) obtained at 22, 43, 86, and 129 GHz simultaneously over three years (from January 2013 to March 2016); during this time, two ${\gamma}$-ray outbursts (in November 2013 and March 2015) can be seen in ${\gamma}$-ray light curves obtained from Fermi observations. The KVN radio core is optically thick at least up to 86 GHz; there is indication that it might be optically thin at higher frequencies. To first order, the radio light curves decay exponentially over the time span covered by our observations, with decay timescales of $411{\pm}85$ days, $352{\pm}79$ days, $310{\pm}57$ days, and $283{\pm}55$ days at 22, 43, 86, and 129 GHz, respectively. Assuming synchrotron cooling, a cooling time of around one year is consistent with magnetic field strengths $B{\sim}2{\mu}T$ and electron Lorentz factors ${\gamma}$ ~ 10 000. Taking into account that our formal measurement errors include intrinsic variability and thus over-estimate the statistical uncertainties, we find that the decay timescale ${\tau}$ scales with frequency ${\nu}$ like ${\tau}{\propto}{\nu}^{-0.2}$. This relation is much shallower than the one expected from opacity effects (core shift), but in agreement with the (sub-)mm radio core being a standing recollimation shock. We do not find convincing radio flux counterparts to the ${\gamma}$-ray outbursts. The spectral evolution is consistent with the 'generalized shock model' of Valtaoja et al. (1992). A temporary increase in the core opacity and the emergence of a knot around the time of the second ${\gamma}$-ray event indicate that this ${\gamma}$-ray outburst might be an 'orphan' flare powered by the 'ring of fire' mechanism.

• 해양환경안전학회지
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• 제28권2호
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• pp.346-353
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• 2022

최근 회전 회전기계의 건전성 관련 연구가 활발하게 진행중이며, 조선업의 대표적인 회전기계인 갠트리 크레인에도 이를 적용하고자 하는 연구가 활발하게 진행되고 있다. 하지만 조선업의 갠트리 크레인의 경우 상대적으로 낮은 RPM으로 구동되고 잦은 운전과 정지가 이루어지며 충격, 소음 등의 외부환경 인자가 측정 데이터에 영향을 크게 미쳐 오차를 발생시킬 수 있다. 본 연구에서는 조선업의 내업공정에서 사용되는 갠트리 크레인의 Hoist 모사장비를 제작하여, 운전조건(RPM) 변화와 데이터 획득 센서의 위치 차이가 획득 데이터에 미치는 오차를 통계적으로 분석하였다. 연구결과 상대적으로 낮은 운전조건에서는 센서 위치 차이에 따른 획득 데이터의 오차는 크게 발생하지 않았으나, 상대적으로 높은 운전조건에서는 획득 데이터의 오차가 크게 발생하는 것으로 확인하였으며, 회전기계의 데이터 획득 시 운전조건과 획득 센서위치가 획득 데이터에 영향을 미치는 것으로 확인하였다.

• 마이크로전자및패키징학회지
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• 제30권1호
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• pp.1-16
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• 2023

전기차용 전력변환모듈의 성능향상 요구와 종래의 Si 전력반도체의 한계 극복을 위해 차세대 전력반도체인 wide-bandgap (WBG) 기반 전력반도체로의 전환이 가속화되고 있다. WBG 전력반도체로의 전환을 위해 전력변환모듈 패키징 소재 역시 높은 고온 내구성을 요구받고 있다. 전력변환모듈 패키징 공정 중 하나인 Ag 소결 다이접합 기술은 종래의 고온용 Pb 솔더링의 대체 기술로 주목받고 있다. 본 논문에서는 Ag 소결 다이접합 기술 관련 최신 연구동향에 대해 소개하고자 한다. 소결 다이접합 공정 조건에 따른 접합부 특성을 비교하고 Ag 소결층의 3차원 이미지 구현에 따른 다공성 Ag 소결 접합부의 물성 측정 방법론에 대해 고찰하였다. 또한 열충격 및 파워사이클 신뢰성 평가 연구동향을 분석하였다.

• 한국건설안전학회 논문집
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• 제6권1호
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• pp.1-6
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• 2024

본연구는 건설근로자 대상으로 실시되는 안전교육을 가상체험과 실물체험식 안전교육으로 진행되면 교육에 오락적, 일탈적, 심미적 요소가 더해진 학습효과로 건설업 안전사고는 현저히 감소함을 분석하였다. 연구결과 체험교육에 대한 판별타당도 분석에서는 C.R=0.925327>0.7로 충족되었고, AVE= 0.716226>0.5로 수렴되어 신뢰도가 높음을 알 수 있었다. 근로자의 행동 의도에 대한 MC 시뮬레이션 분석과 베이지안 구조방정식에서 근로자 행동변화는 여러 가지 요인으로 달라질 수 있지만, 교육의 정도에 따라 행동이 변화됨을 알 수 있었고, 의도된 안전에 대한 확률밀도분포 분석결과 실물체험의 경험이 낮을수록 안전행동 보다 불안전 행동이 높고, 사고 위험이 증가함으로 체험식 안전교육이 근로자 행동변화와 건설 안전문화 개선에 실질적인 효과가 검증되었다. 후속 연구에서도 체험교육 이수 근로자에 대한 2~3년 추적관리 연구를 기대한다.

• The Korean Journal of Physiology and Pharmacology
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• 제20권6호
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• pp.605-611
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• 2016

Ketamine is an anesthetic with hypertensive effects, which make it useful for patients at risk of shock. However, previous ex vivo studies reported vasodilatory actions of ketamine in isolated arteries. In this study, we reexamined the effects of ketamine on arterial tones in the presence and absence of physiological concentrations of 5-hydroxytryptamine (5-HT) and norepinephrine (NE) by measuring the isometric tension of endothelium-denuded rat mesenteric arterial rings. Ketamine little affected the resting tone of control mesenteric arterial rings, but, in the presence of 5-HT (100~200 nM), ketamine ($10{\sim}100{\mu}M$) markedly contracted the arterial rings. Ketamine did not contract arterial rings in the presence of NE (10 nM), indicating that the vasoconstrictive action of ketamine is 5-HT-dependent. The concentration-response curves (CRCs) of 5-HT were clearly shifted to the left in the presence of ketamine ($30{\mu}M$), whereas the CRCs of NE were little affected by ketamine. The left shift of the 5-HT CRCs caused by ketamine was reversed with ketanserin, a competitive 5-$HT_{2A}$ receptor inhibitor, indicating that ketamine facilitated the activation of 5-$HT_{2A}$ receptors. Anpirtoline and BW723C86, selective agonists of 5-$HT_{1B}$ and 5-$HT_{2B}$ receptors, respectively, did not contract arterial rings in the absence or presence of ketamine. These results indicate that ketamine specifically enhances 5-$HT_{2A}$ receptor-mediated vasoconstriction and that it is vasoconstrictive in a clinical setting. The facilitative action of ketamine on 5-$HT_{2A}$ receptors should be considered in ketamine-induced hypertension as well as in the pathogenesis of diseases such as schizophrenia, wherein experimental animal models are frequently generated using ketamine.