• 한국자동차공학회논문집
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• 제18권3호
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• pp.19-25
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• 2010

The purpose of this study is to gain a better understanding of the effects of fuel stratification on reducing the pressure-rise rate at high load in HCCI combustion. It was found that fuel stratification offers good potential to achieve a staged combustion event and reduced pressure-rise rates. The engine is fueled with Di-Methyl Ether (DME) which has unique 2-stage heat release. Numerical analysis is conducted with single and multi-zones model and detailed chemical reaction scheme is done by chemkin and senkin. Calculation result shows that proper fuel stratification prolongs combustion duration and reduce pressure rise rate. Besides IMEP, combustion efficiency and indicated thermal efficiency keep constant. However, too wide fuel stratification increases pressure rise rate and CO and NOx emissions in exhaust gas.

• Nuclear Engineering and Technology
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• 제55권6호
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• pp.1988-1993
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• 2023

This experimental study investigated the effect of silica fume mixed in concrete blocks on laser-induced explosion behavior. We used a 5.3 kW fiber laser as a thermal source to induce explosive spalling on a concrete surface blended with and without silica fume. An analytical approach based on the difference in the removal rate and thermal behavior was used to determine the effect of silica fume on laser-induced explosive spalling. A scanner was employed to calculate the laser-scabbled volume of the concrete surface to derive the removal rate. The removal rate of the concrete mixed with silica fume was higher than that of without silica fume. Thermal images acquired during scabbling were used to qualitatively analyze the thermal response of laser-induced explosive spalling on the concrete surface. At the early stage of laser heating, an uneven spatial distribution of surface temperature appeared on the concrete blended with silica fume because of frequent explosive spalling within a small area. By contrast, the spalling frequency was relatively lower in laser-heated concrete without silica fume. Furthermore, we observed that a larger area was removed via a single explosive spalling event owing to its high porosity.

• 전자통신동향분석
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• 제37권2호
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• pp.21-29
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• 2022

Cosmic radiation environments having extremely high-energy particles and photons cause severe malfunctions of electrical components in space and terrestrial regions. In this study, we revisit basic knowledge on radiation effects in ICT electrical devices, such as single event effect, total ionizing dose, and displacement damage. To avoid such soft errors and system failures, we introduce essential technical approaches from the perspectives of materials, layouts, circuits, and systems, including current research trends. By considering several techniques and Space EEE part standards, we suggest possible directions that can invoke New Space Era technology.

• Computers and Concrete
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• 제21권1호
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• pp.55-66
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• 2018

A large main shock may consist of numerous aftershocks with a short period. The aftershocks induced by a large main shock can cause the collapse of a structure that has been already damaged by the preceding main shock. These aftershocks are important factors in structural damages. Furthermore, despite what is often assumed in seismic design codes, earthquakes do not usually occur as a single event, but as a series of strong aftershocks and even fore shocks. For this reason, this study investigates the effect and potential of consecutive earthquakes on the response and behavior of concrete structures. At first, six moment resisting concrete frames with 3, 5, 7, 10, 12 and 15 stories are designed and analyzed under two different records with seismic sequences from real and artificial cases. The damage states of the model frames were then measured by the Park and Ang's damage index. From the results of this investigation, it is observed that the sequences of ground motions can almost double the accumulated damage and increased response of structures. Therefore, it is certainly insufficient to ignore this effect in the design procedure of structures. Also, the use of artificial seismic sequences as design earthquake can lead to non-conservative prediction of behavior and damage of structures under real seismic sequences.

• 한국항공우주학회지
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• 제32권5호
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• pp.116-121
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• 2004

사이클로트론 가속기를 이용한 양성자 우주환경의 모사시험이 수행되었다. 모사시험에 사용된 사이클로트론은 양성자를 약 $10^6-10^8\;protons/cm^2/s$의 선속에서 200 MeV까지 가속 할 수 있다. 가속된 양성자는 우주에서 사용될 MPC860 소자에 입사되었으며, 양성자 조사에 의한 소자의 누적 반응과 순간 반응이 모두 관찰되었다. 주된 순간 반응은 저장된 데이터의 변화였으나, 간헐적인 기능 정지 현상도 관찰되었다. 누적 반응은 소자 내에서 소모되는 전류의 증가로 나타났다.

• Journal of Ginseng Research
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• 제46권3호
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• pp.435-443
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• 2022

Background: Post-traumatic stress disorder (PTSD) is a psychiatric disease that develops following exposure to a traumatic event and is a stress-associated mental disorder characterized by an imbalance of neuroinflammation. Korean Red Ginseng (KRG) is the herbal supplement that is known to be involved in a variety of pharmacological activities. We aimed to investigate the effects of KRG on neuroinflammation as a potential mechanism involved in single prolonged stress (SPS) that negatively influences memory formation and consolidation and leads to cognitive and spatial impairment by regulating BDNF signaling, synaptic proteins, and the activation of NF-κB. Methods: We analyzed the cognitive and spatial memory, and inflammatory cytokine levels during the SPS procedure. SPS model rats were injected intraperitoneally with 20, 50, or 100 mg/kg/day KRG for 14 days. Results: KRG administration significantly attenuated the cognitive and spatial memory deficits, as well as the inflammatory reaction in the hippocampus associated with activation of NF-κB in the hippocampus induced by SPS. Moreover, the effects of KRG were equivalent to those exerted by paroxetine. In addition, KRG improved the expression of BDNF mRNA and the synaptic protein PSD-95 in the hippocampus. Taken together, these findings demonstrate that KRG exerts memory-improving actions by regulating anti-inflammatory activities and the NF-κB and neurotrophic pathway. Conclusion: Our findings suggest that KRG is a potential functional ingredient for protecting against memory deficits in mental diseases, such as PTSD.

• 한국항공우주학회지
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• 제34권11호
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• pp.76-83
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• 2006

통신해양기상위성의 통신 탑재체가 겪게 될 우주 방사선 환경을 포획된 입자, 태양 양성자 그리고 우주선으로 구분하여 각각 NASA AP8/AE8 모델, JPL91 모델, 그리고 NRL CREME 모델을 사용하여 전산 모사 하였다. 이러한 우주 방사선 환경이 위성 내 통신 탑재체에 미치는 영향을 추정하기 위해 총 이온화 방사선 효과의 분석에 필요한 Dose-Depth 곡선 및 단일사건효과 발생률 계산에 필요한 LET 스펙트럼 구하였다. 통신 탑재체 내의 각 장치별 차폐 효과 차이를 고려한 총 이온화 방사선 효과의 예측을 위해서 기계 구조 모델을 만든 후 구형 분할 방법을 적용하였다. 이를 통해 통신 탑재체 내 각 장치의 위치별 총 이온화 방사선 효과를 예상하였으며 동일한 외부 방사선 환경에 대해서 차폐 효과에 따라 최고 8배까지 방사선 효과가 다르게 나타났다.

• 한국정보전자통신기술학회논문지
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• 제13권4호
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• pp.277-282
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• 2020

본 연구는 전자장비가 여러 환경에 노출되어 장비 작동에 영향을 받을 수 있으므로 해소할 수 있는 방법을 찾고자 본 연구를 시작하였다. 텔레스코픽 캐스코드 비교기에 지수정류파(iexp)을 SET(Single Event Transient) 환경으로 설정하여 어떤 영향이 있는지에 대해 실험하였다. 본 논문에서 SET 상황을 설정하지 않은 텔레스코픽 캐스코드 비교기에서는 전파 지연은 0.46㎲, 이득은 0.713으로 측정되었다. SET 상황을 입력한 텔레스코픽 캐스코드 비교기에서 FET T0(M6)는 11㎲ ~ 15㎲에서 큰 스파이크를 나타난 것으로 측정되었다. FET T1(M5)는 10㎲ ~ 16㎲에서 출력 신호가 단락되었다. FET T2(M3)는 단락된 출력신호를 나타냈으며 FET T3(M4)는 큰 스파이크 파형 형태로 출력파형이 측정되었다. FET T4(M1)와 FET T5(M2)는 스파이크 신호가 출력되었다. 그리고 모든 FET에서 전파지연은 0.45㎲~0.54㎲로 변화되었다. 결론적으로 SET 상황에서 텔레스코픽 캐스코드 비교기에 있는 FET소자는 많은 영향을 받는 것으로 측정되었다.

• Journal of Mechanical Science and Technology
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• 제20권9호
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• pp.1436-1448
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• 2006

This paper describes the effects of injection rate shaping on the combustion, fuel consumption and emission of $NO_x$ and soot of a medium duty diesel engine. The focus is on the influence of four different injection rate shapes, square type 1, square type 2, boot and ramp, with a variation of maximum injection pressure and start of injection (SOI). The experiments were carried out on a 1 liter single cylinder research diesel engine equipped with an amplifier-piston common rail injection system, allowing the adjustment of the injection pressure during the injection event and thus injection rate as desired. Two strategies to maintain the injected fuel mass constant were followed. One where rate shaping is applied at constant injection duration with different peak injection pressure and one strategy where rate shaping is applied at a constant peak injection pressure, but with variable injection duration. Injection rate shaping was found to have a large effect on the premixed and diffusion combustion, a significant influence on $NO_x$ emissions and depending on the followed strategy, moderate or no influence on soot emission. Only small effects on indicated fuel consumption were found.

• 한국공작기계학회논문집
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• 제13권4호
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• pp.113-120
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• 2004

The object of this study is to investigate the effect of compounded welding through the AE(Acoustic Emission) characteristics for weld HAZ(Heat Affected Zone) under the static tensile test. This study was carried out an SWS 490A, high tension steel for electric shield metal arc welding(SMAW), $CO_2$ gas arc welding and TIG welding. Data displays are based on the measured parameters of the AE signals, along with environmental variables such as time and load. The accumulated AE event curve of HAZ definitely have the point of inflection subject to tensile test. The results of the tensile test of HAZ come out electric shield arc welding ＞$CO_2$ gas arc welding＞TIG welding in case of single welding, but generally the tensile test of HAZ come out electric shield arc welding＞ TIG welding ＞ $CO_2$ gas arc welding. These history plots give us useful and powerful information to analyze the results of material evaluation testing.