• 한국자동차공학회논문집
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• 제19권4호
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• pp.78-83
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• 2011

Natural gas is one of the most promising alternatives to gasoline and diesel fuels because of its high thermal efficiency and lower harmful emissions, including $CO_2$. Although the high octane value of natural gas increases engine output and efficiency due to the high compression ratio, this fuel is prone to such difficulties as a narrow limit of inflammability and a slow combustion speed in the lean burn operation domain, leading to unstable combustion and higher emissions of harmful exhaust gases. Hydrogen blended with natural gas can extend the lean burn limit while maintaining stable, efficient combustion and achieving lower NOx, hydrocarbon and green house gas emissions. In this study, the effect of hydrogen addition on an engine performance and NOx emission characteristics was investigated in a heavy duty natural gas engine. The results showed that thermal efficiency was increased and NOx emissions were reduced due to the expansion of lean operation range under stable operation. NOx emission can be significantly reduced with the retard of spark advance timing.

• 한국농공학회지
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• 제15권3호
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• pp.3089-3095
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• 1973

The power transmission to the traction devices may be very important for the tractor performance and therefore this system has been studied very much in the past. On the other hand, the PTO(Power-take-off) has been considered as an accessary on the tractor with a few work for its power transmission. Because of increased use of PTO operation in various kind of farming operations in recent years, the function of PTO may become such important as the traction facilities. In this study, the power transmission characteristics of PTO drive was analyzed theoretically and some experimental work was done to study on it. The results of the study are as follows: 1) The most stable condition of PTO work was obtained when the intersection angle of the two curves for driving and driven torques was about ${\pi}/2$. 2) To obtain the most stable operation it is better to use both the speed control and the full control together. 3) Six steps differential gear may not be enough to use the PTO power smoothly. It is thought that the three steps differential gear on the shaft of PTO may be necessary additionally for a smooth operation. 4) When the traction facilities and the PTO are used at the same time, the torque of crank shaft becomes Tt + Tp, and the high efficiency and good stability of word will be obtained with the small variation of driving speed. 5) When the tractor was operated with 75% of the rated horse power and 70% of maximum speed, the best thermal efficiency could be obtained. 6) The most dangerous sound for human occured at the rated speed of PTO and tus it may be necessary to control the dangerous noise.

• Physical Therapy Rehabilitation Science
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• 제7권3호
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• pp.119-126
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• 2018

Objective: The objective of this study was to describe the influence of smartphone usage on the upper limb muscles while in stable and unstable positions and during gait. Design: Cross-sectional study. Methods: The study was conducted with 20 right-handed university students between 20 and 27 years of age. Experiments were carried out on students who have used cell phones for more than a year. In this study, experiments were performed with one-handed and two-handed smartphone operations while on stable ground, and the same parameters were measured during smartphone use on unstable ground and during gait. Subjects were instructed to write a text message in Korean on the smartphone for 3 minutes. This was repeated 3 times, with a rest period of 10 seconds given between each 3-minute period. Electromyography was used to record the muscle activity of the upper trapezius, extensor carpi radialis, extensor pollicis longus, and abductor pollicis (AP) during phone operation. Results: The muscle activity value for the right AP in one-handed and the left-AP in two-handed operations was statistically higher than the other muscles in the stable position and during gait (p<0.0001). Also, the right AP in the one- handed operation condition was statistically higher than the two-handed condition (p<0.0001). Conclusions: The use of smartphones while in a stable position resulted in high muscle activity of the right upper limb AP. However, in an unstable position, there were no significant differences from the other muscle activities. Using smartphone while assuming various positions may lead to musculoskeletal disorders in different places.

• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2008년도 춘계학술발표대회 논문집
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• pp.43-48
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• 2008

Through simulations and field experiment on A.C. parallel operation of both Utility Interactive Photovoltaic System and Diesel Engine Revolving Field Type Synchronous Generator, following factors have been found. First, the inverter should be operated in three modes of frequency(mode.1: ${\pm}$0.3Hz, mode.2: ${\pm}$1Hz, mode.3: ${\pm}$2Hz) as default, considering properties of operating Synchronous Generator. Second, as a result of supplying 13.5kW of residual power, it has been found that Synchronous Generator takes the power input only as reactive power, because it was electrically stable with frequency of 60.14Hz and high voltage of 222.3V even when power factor was -0.94. Besides, it was mechanically stable, too, because the quake, noise, and temperature of Synchronous Generator in this case were 7.5mm/s, 97dB, and $6^{\circ}C$ respectively, which were lower than normal load connection of 145.6kW; 11.03mm/s. Thus, load share of Revolving Field Type Synchronous Generator reduces according to the supply of Photovoltaic System to the load power. In this experiment, 200kW of Synchronous Generator and 40kW of Photovoltaic System were operated in parallel. The load share was 20% in maximum. and 11.1lit/hr of fuel was saved.

• 복식
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• 제60권6호
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• pp.89-100
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• 2010

This study is intended to analyze current status of costume in the cultural industry and explore feasibility of integrating costume as important cultural contents in the digital era. Among the websites for contents as the cultural archetypes, some have strong foundations while others don't. First, as for various archetypal characters restored based on the Korean history, most of their clothes focus on shapes and colors but lack details. They should be produced in 3D to provide back views or textile patterns to users. To ease understanding of the history of costume, user-friendly services such as launch of a pop-up window when users click on specific contents in question should be available for detailed information. At least there should be a link to other related sites where users can conveniently find more details. Second, some sites have too much data under one subject, increasing complexity and undermining orderliness. As a result, it takes long time to identify the site map. In this case, it is required to rearrange the contents with Quick View by subject and related links for in-depth study. Third, each subject is important to develop the archetypes for a variety of purposes. Creation of design derived from them or their commercialization can be an example but these activities should not restrict imagination of users or degrade the value of the archetypes. Last, it is needed to adopt validation system to detect the needs for a regular update (renewal) and to fix errors. We found many servers whose operation is not stable in general. When these technical issues are addressed for stable operation, users will rely on the sites to utilize them for their purpose of developing the cultural archetypes. In conclusion, advancement of www.culturecontent.com is essential. Based on efficient management and operation of the system, the quality of contents would be increased and multi-faceted advertising campaigns focusing on needs should be launched, to promote application of the contents. This is the recommendation for the future of the cultural archetype industry in Korea.

• 융합정보논문지
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• 제11권3호
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• pp.14-19
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• 2021

본 논문에서는 IT기기를 가동하기 위해 필요한 마이너스 전원을 저렴한 buck 소자를 이용해 안정된 방법으로 생성할 수 있는 inverter회로의 구성방법을 제시하였다. 이를 위해 기존의 buck 소자를 이용해 inverter 회로를 구성했을 경우의 문제점에 관해 살펴보고, 이러한 문제점을 방지할 수 있는 원리를 분석하고 해결할 수 있는 회로를 제시하였다. 제시한 방법의 효과를 입증하기 위해 실험회로를 구성하고 실험을 진행한 결과, 기존의 과전류 방지회로에 의한 inverter회로의 기동에 비해 과전류현상 없이 안정된 기동이 이루어짐을 확인하였다. 이에 따라 IT 기기에 사용되는 각종 아날로그 신호 처리를 위한 소자들을 편전원으로 구성하기 위한 수많은 주변소자들이 모두 생략될 수 있으면서도 회로의 성능을 크게 향상시킬 수 있을 것으로 기대된다.

• 한국통신학회논문지
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• 제30권1A호
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• pp.10-27
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• 2005

본 논문에서는 다년간에 걸쳐 진행되었던 WCDMA(UMTS) 기지국 모뎀 개발을 위한 상위 레벨 설계 및 설계에 적용된 기저대역 동기 알고리즘에 대한 분석과 고정 소수점 설계를 통한 성능 평가 결과를 제시하였다. 설계 대상 시스템이 기지국임을 고려하여 모뎀을 구성하는 각 동기 모듈은 빠른 추적 성능보다 안정적인 성능을 보장할 수 있도록 설계되었으며, 구현을 위한 고정 소수점 설계시 각 모듈의 내부 연산에 대한 최적의 비트설정을 통하여 복잡도를 최소화하였다. 본 논문에서는 먼저 모뎀 설계를 위하여 개발된 각 기저대역 동기 모듈에 대한 분석을 수행하였으며, 이후 구현을 위하여 고정 소수점 설계된 모뎀과 부호화/다중화를 포함하는 심볼 레벨 프로세싱(Symbol Level Processing; SLP)파의 링크 성능을 제시하였다. 성능 평가는 3GPP TS 25.104(Release 5)에 제시된 12.2kbps, 64kbps, 144kbps, 384kbps의 전송 속도에 대하여 참조 무선 채널 환경을 기반으로 수행되었으며, 규격에 제시된 최소 요구 성능과의 비교를 통하여 약 2dB 이상의 성능 여유(margin)를 갖는 매우 안정적인 동작을 보임을 증명하였다. 본 논문에서 제시된 WCDMA 기지국 모뎀은 기지국 모뎀 칩으로 성공적으로 구현되었다.

• 한국정보전자통신기술학회논문지
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• 제11권6호
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• pp.684-690
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• 2018

현재 및 향후 떠오르고 있는 빅 데이터 사회에서는 수집된 정보의 분석이 그 핵심 기술로 인식되고 있다. 또한 발생되는 데이터가 보다 다양하고 더욱 대용량화 되는 특징을 가지는 빅 데이터화가 가속될 미래의 진화된 지능화 사회에서는 예측 기술을 바탕으로 가치창출을 통한 최적화된 사회를 지향할 것으로 보인다. 지속적으로 사용되어질 IT시스템 운영 시 발생되는 다양한 데이터와 대량의 데이터에 대하여 빅 데이터 기반 기술을 활용하면 IT 시스템의 장애 방지와 안정적 운영이 가능할 것이다. 본 논문에서는 서버 성능 모니터링을 통한 데이터를 수집 분석하고자 빅 데이터 수집 분석 기술을 활용한 환경을 제안하였고, 또한 장애 예측을 위한 시계열 예측 모형을 도출하여 제안하였다. 빅 데이터를 처리하는 서버 성능 관리 측면에서, 본 논문에서 제안하는 이 모델을 통하여 서버 운영자는 사전 장애 예측을 통하여 IT 시스템의 안정적 운영이 가능할 것이다.

• 상하수도학회지
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• 제25권4호
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• pp.565-572
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• 2011

The effects of chemical pretreatments on the excess sludge production in the membrane-coupled bioreactor were investigated. In addition, their effects on membrane fouling were also evaluated. Two membrane bioreactors were operated. In one reactor, a part of the mixed liquor was t reated with NaOH and ozone gas consecutively and was returned to the reactor. T he f lowrate of the chemical pretreatment stream was 1.5% of the influent flowrate. During the 200days of operation, the MLSS level in the bioreactor with mixed liquor pretreatment was maintained relatively constant at the range of 8,000 ~ 10,000$mg/{\ell}$ while it increased steadily up to 26,000 $mg/{\ell}$ in the absence of the pretreatment. Each reactor was equipped with two laboratory membrane modules where the flux for each module was 20, and 30 ${\ell}/m^2{\cdot}h$, respectively. With pretreatment, almost constant transmembrane pressure(TMP) was observed throughout the operation at the flux of 20 ${\ell}/m^2{\cdot}h$. Without pretreatment the membrane module at the same flux could also be operated at relatively stable condition. However, as the MLSS increases up to 25,000 $mg/{\ell}$, a fast TMP increase was observed. In conclusion, a complete control of excess sludge production in the membrane-coupled bioreactor was possible without significant deterioration of the treated water quality. In addition, it was shown that stable operation in terms of TMP is possible with sludge pretreatment and recirculation.

• Korean Chemical Engineering Research
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• 제46권6호
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• pp.1057-1062
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• 2008

기존 2탑 유동층 공정의 단점을 극복하기 위해 두 개의 기포유동층, 고체분사노즐, 상승관 및 고체재순환관으로 구성된 신개념 2탑 유동층 공정을 적용한 3 kW 매체순환식 가스연소기를 개발하였다. 본 연구에서는 3 kW급 매체순환식 가스연소기에서 고체순환속도에 미치는 고체분사노즐 유속, 유동화속도, 고체층 높이, 고체유입구의 단면적, 층 온도 등의 영향을 고찰하였다. 고체순환속도는 고체층 높이가 증가하고 고체유입구의 단면적이 증가할수록 증가하는 경향을 나타내었으며 유동화속도와 온도의 영향은 크지 않았다. 장기연속운전 가능성을 검토하기 위해 50시간까지 고체순환 장기연속운전을 실증하였다. 두 유동층과 고체재순환관의 압력강하 값이 안정적으로 유지되어 고체순환이 원활하고 안정적으로 유지되는 것을 확인하였다.