• 한국생산제조학회지
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• 제21권3호
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• pp.401-407
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• 2012

The recent manufacturing process in the thin wafers and flat panel necessitate new approaches to reduce handling fragile and surface-sensitive damage of components. This paper presents a new pneumatic levitation for non-contact handling of parts and substrates. This levitation can achieve non-contact handling by blowing air into an air pressure pick-up head with radial passages to generate a negative pressure region. Negative pressure is caused by the radial air flow by nozzle throat and through holes connecting to the bottom region. The numerical analysis deals with the levitational motion with different design factors. The dynamic motion is examined in terms of force balance(dynamic equilibrium) occurring to the flow field between two objects. The stable equilibrium position and the safe separation distance are determined by analyzing the local pressure distribution in the fluid motion. They make considerable design factors consisting the air pressure pick-up head. As a result, in case that the safe separation distance is beyond 0.7mm, the proposed pick-up head can levitate stably at the equilibrium position. Furthermore, it can provide little effect of torque, and obtain more wide picking region according to the head size.

• 한국지능시스템학회논문지
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• 제18권5호
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• pp.599-604
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• 2008

최근 외부 개입 없이 스스로 주변 환경을 파악하고 목적지까지의 이동경로를 생성하여 자율 주행하는 지능형 시스템에 관한 연구가 활발히 진행되고 있다. 이러한 자율 주행 시스템은 기본적으로 운행 중에 사고가 발생하지 않고 안전하게 목표점까지 이동해야 한다. 본 논문에서는 레이저 변위 센서를 이용하여 노면의 왜곡(훼손된 노면, 비포장 도로, 장애물 등)을 검출하고, 영상 이진화 기법을 적용하여 위험 요소를 검출, 판단하여 주행 시스템의 안정적 운항이 가능한 경로를 생성하는 기법을 제안한다. 제안 기법의 타당성은 임의로 제작된 국부영역의 지도 데이터에 기반한 모의실험을 통하여 보인다.

• 한국콘텐츠학회:학술대회논문집
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• 한국콘텐츠학회 2009년도 춘계 종합학술대회 논문집
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• pp.40-44
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• 2009

데이터 중심 저장 기법은 센서 네트워크에서 측정값을 효율적으로 저장하고 관리하기 위한 대표적인 연구 중 하나이다. 이 기법은 센서가 센싱한 데이터를 특정 센서 노드로 보내 저장한다. 하지만, 측정값을 네트워크 내부의 특정 노드로 전송하는 과정에서 많은 에너지를 소모하는 문제점을 가지고 있다. 본 논문에서는 데이터 중심 저장 기법에서 데이터의 전송 비용을 줄이기 위한 새로운 접근의 센서 데이터 압축 알고리즘을 제안한다. 제안하는 기법은 데이터를 전부 전송하는 것이 아니고 안전영역(Safe Region)을 설정한다. 그 후 이전 측정값을 기준으로 현재 측정값이 안전영역을 벗어나는 경우만 데이터를 전송함으로서 데이터의 전송을 줄이고 네트워크의 수명을 연장 시킨다. 성능평가 결과, 기존 기법에 비해 제안하는 기법의 에너지 소모가 60% 감소하였다.

• 한국콘텐츠학회논문지
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• 제10권11호
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• pp.58-67
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• 2010

데이터 중심 저장 기법은 센서 네트워크에서 측정값을 효율적으로 저장하고 관리하기 위한 대표적인 연구 중 하나이다. 이 기법은 센서가 센싱한 데이터를 특정 센서 노드로 보내 저장한다. 하지만, 측정값을 네트워크 내부의 특정 노드로 전송하는 과정에서 많은 에너지를 소모하는 문제점을 가지고 있다. 본 논문에서는 데이터 중심 저장 기법에서 데이터의 전송 비용을 줄이기 위한 새로운 센서 데이터 압축 기법을 제안한다. 제안하는 기법은 측정값의 안전영역(Safe Region) 범위를 설정하고, 측정값이 안전영역을 벗어나는 경우만 데이터를 전송한다. 이를 통해 데이터의 전송을 줄이고 네트워크의 수명을 연장 시킨다. 성능평가 결과, 기존 기법에 비해 제안하는 기법의 에너지 소모가 60% 감소하였다.

• 한국터널지하공간학회 논문집
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• 제5권2호
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• pp.101-113
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• 2003

현재 기존 지하구조물의 안정성에 영향을 미치는 신축구조물의 건설이 많아지므로 설계 및 시공 중 기술적으로 많은 문제점이 발생하고 있으며, 이러한 근접시공은 지하구조물의 중요도에 따라 지하구조물의 안정성과 신축구조물의 경제성이라는 두 사안이 절충 가능한 합리적인 설계 및 시공이 절실히 요구되고 있다. 지금까지의 지하구조물의 안정영역 및 지반거동에 관한 많은 연구가 이루어져 왔으나, 본 논문에서는 지하구조물의 상부에 구조물 건설에 따른 하중이 작용할 경우 지하구조물과 신축 지상구조물의 상호위치, 토피고 및 대상 지반조건이 지하구조물의 안정성에 미치는 영향 및 안정영역의 범위에 대하여 재평가하였다.

• 대한조선학회논문집
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• 제55권3호
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• pp.236-242
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• 2018

Damage due to ice collision is the most serious threat for the structural safety of ships operating in arctic region. Since such hull damages are usually caused by the collision of floating ice at excessive voyage speed of ships, the authorities responsible for the shipping at arctic sea are required to provide the speed limit for safe voyage, so-called safe speed. In countries near arctic ocean, such as Canada and Russia, empirical methods to determine the safe speed of ships based on their long experience of arctic voyage have been established and applied them in the real arctic navigation. However, in Korea, it is not easy to accumulate the arctic voyage experience and related technical database, so it seems to be a realistic approach to adopt a safe voyage speed estimating method in arctic sea based on the ice collision simulation technology using the nonlinear finite element analysis. The aim of this study is to develop a technique for estimating the safe voyage speed of vessels operating at arctic sea through the ice collision analysis, In order to achieve this goal, the standard procedure of the ice collision analysis is dealt with and example analysis was carried out and the results were considered. To investigate the validity of developed method, POLARIS system proposed by IMO was studied for comparison.

• 오토저널
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• 제8권1호
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• pp.40-51
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• 1986

A study has been made of the corrosion fatigue of high strength low alloy steel in 3.5% NaCl solution under tension stress for solution temperature being 25.deg. C, 55.deg. C and 85 .deg. C. The main results obtained are as follows; 1) The corrosion fatigue crack growth rate curve could be divided into the First Region, the Second Region and the Third Region. 2) The corrosion fatigue crack growth rates in the First Region and the Second Region were Arrhenius temperature-dependent in this test range. The apparent activation energies for the corrosion fatigue cack growth rate were found to be 2000cal/mol in the First Region and 3700 cal/mol in the Second Region. 3) Hematite (Fe$_{2}$O$_{3}$) as the hexahedral crystal and magnetite (Fe$_{3}$O$_{4}$) as the octahedral crystal were observed in the corrosion products on the corrosion fatigue fracture surface at 85.deg. C and the anode fusion seem to be generated in the crack tip region at high temperature. 4) The complex environment effect ratio which was defined by the ratio of fatigue crack growth rate in corrosion environment to that in air might be considered not only a criterion estimating the effect of environment quantitatively but also an important parameter in the selection of the design stress for the fail safe design. The complex environment effect was not greater than ten in this test.

• Progress in Superconductivity
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• 제6권2호
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• pp.138-141
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• 2005

Bi-2223/Ag tapes need to be safe, even it is under the over-critical current state for the protection of a superconducting power machine. However, it is not easy to identify the condition for the safe operation because of their broad S/N transition region. In this paper, for the study of the operation condition of Bi-2223/ Ag tapes, we investigated the V-I curves and the temperature variation of Bi-2223/ Ag tapes experimentally, applying alternating over-currents, and analyzed the relationship between resistance and temperature increase. For the experiments, a Bi-2223/Ag tape of 57 A $I_c$ was prepared, and the over-critical current characteristics under adiabatic state from $LN_2$ was measured. From the experiments, we confirmed that the Joule heating predicted by V-I curve corresponded with the increase of the measured temperature exactly. Using the results, a safe operation condition of Bi-2223 tape was discussed.

• 대한두개안면성형외과학회지
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• 제23권3호
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• pp.103-110
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• 2022

Background: The primary objectives of mandibular surgery are to achieve optimal occlusion, low sensory disturbance, and adequate fixation with early movement. In-depth knowledge of the mandibular structure is required to achieve these goals. This study used computed tomography (CT) to evaluate the mandibular cortical thickness and cancellous space according to age and sex. Methods: We enrolled 230 consecutive patients, aged 20 to 50 years, who underwent CT scanning. The cortex and cancellous space centered around the inferior alveolar nerve (IAN) canal were measured at two specific locations: the lingula and second molar region. Statistical analysis of differences according to increasing age and sex was performed. Results: The t-test revealed that the cancellous space and cortical thickness differed significantly with respect to the threshold of 35 years of age. Both cortical thickness and cancellous space in the molar region were negatively correlated with age. Meanwhile, both cortical thickness and cancellous space in the lingula region showed a positive correlation with age. With respect to sex, significant differences in the cancellous space at the molar region and the cortical thickness at the lingula were observed. However, no further statistically significant differences were observed in other variables with respect to sex. The sum of each measurement on the mandibular body reflected the safe distance from the surface of the outer cortex to the IAN canal. The safe distances also showed statistically significant differences between those above and below 35 years of age. Conclusion: Knowledge of the anatomical structure of the mandible and of changes in bone structure is crucial to ensure optimal surgical outcomes and avoid damage to the IAN. CT examination is useful to identify changes in the bone structure, and these should be taken into account in the planning of surgery for older patients.

• Asian-Australasian Journal of Animal Sciences
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• 제32권1호
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• pp.82-91
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• 2019

Objective: This experiment was conducted to compare the structure and composition of ruminal microorganisms in goats with high and low neutral detergent fibre (NDF) digestibility. Methods: Nineteen crossbred goats were used as experimental animals and fed the same total mixed rations during the 30-day pre-treatment and 6-day digestion trialperiods. All faeces were collected during the digestion period for measuring the NDF digestibility. Then, high and the low NDF digestibility individuals were chosen for the high NDF digestibility group (HFD) and low NDF digestibility group (LFD), respectively. Rumen contents were collected for total microbial DNA extraction. The V4 region of the bacterial 16S rRNA gene was amplified using universal primers of bacteria and sequenced using high-throughput sequencer. The sequences were mainly analysed by QIIME 1.8.0. Results: A total of 18,694 operational taxonomic units were obtained, within 81.98% belonged to bacteria, 6.64% belonged to archaea and 11.38% was unassigned microorganisms. Bacteroidetes, Firmicutes, and Proteobacteria were the predominant microbial phyla in both groups. At the genus level, the relative abundance of fifteen microorganisms were significantly higher (p<0.05) and six microorganisms were extremely significantly higher (p<0.01) in LFD than HFD. Overall, 176 core shared genera were identified in the two groups. The relative abundance of 2 phyla, 5 classes, 10 orders, 13 families and 15 genera had a negative correlation with NDF digestibility, but only the relative abundance of Pyramidobacter had a positive correlation with NDF digestibility. Conclusion: There were substantial differences in NDF digestibility among the individual goats, and the NDF digestibility had significant correlation with the relative abundance of some ruminal microorganisms.