• 대한기계학회논문집B
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• 제24권1호
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• pp.132-142
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• 2000

The objective of this study is to experimentally investigate the noise propagating characteristics, the noise reduction mechanism and the performance of a slotted tube attached at the exit plane of a circular convergent nozzle. The experiment is performed through the systematic change of the jet pressure ratio and the slot length under the condition of two kinds of open area ratios, 25% and 51%. The open area ratio calculated by the tube length equivalent for the slot length is defined as the ratio of the total slot area to the surface area of a slotted tube. The experimental results for the near and far field sound, the visualization of jet structures and the static pressure distributions in the jet passing through a slotted tube are presented and explained in comparison with those for a simple tube. The propagating characteristics of supersonic jet noises from the slotted tube is closely connected with the slot length rather than the open area ratio, and its propagating pattern is similar to the simple tube. It is shown that the slotted tube has a good performance to suppress the shock-associated noise as well as the turbulent mixing noise in the range of a limited jet pressure and slot dimension. The considerable suppression of the shock‘associated noise is mainly due to the pressure relief caused by the high-speed jets passing through the slots on the tube. Both the strength of shock waves and the interval between them in a jet plume are decreased by the pressure relief. Moreover, the pressure relief is divided into the gradual and the sudden relief depending upon the open area ratio of the slotted tube. Consequently, the shock waves in a jet plume are also changed by the type of pressure relief. The gradual pressure relief caused by the slotted tube with the open area ratio 25% generates the weak oblique shock waves. On the contrary, the weak normal shock waves appear due to the sudden pressure relief caused by the slotted tube with the open area ratio 51%.

• 한국산학기술학회논문지
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• 제18권12호
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• pp.793-798
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• 2017

현대의 함정에서는 추진 기관에서 생성된 고온의 폐기가스와 가열된 폐기관의 금속표면온도를 저감하기 위해 적외선 신호저감 장치(Infra-red Signature Suppression system, IRSS)를 설치하고 있다. 국내 함정에 탑재된 일반적인 IRSS는 이덕터, 믹싱튜브 그리고 디퓨져로 구성되며, 이 중 디퓨져는 금속표면에 내기 외기의 압력차에 의한 공기 막을 생성시켜 온도를 저감시키는 역할을 한다. 본 연구에서는 국외 선진 기술사에서 설계한 IRSS의 디퓨져 형상을 분석하여 설계 변수를 선정하였으며, 분석 조건을 줄이면서 설계 변수의 특성을 효과적으로 파악 할 수 있는 다구치 실험계획법을 통해 IRSS 디퓨져의 성능에 영향을 미치는 설계 변수의 특성을 검토하였다. 디퓨져의 성능분석에는 선행 연구에서 정립한 열 유동해석 기술을 활용하였다. IRSS의 성능평가에는 함정 적외선 신호의 세기와 직접적으로 관련되는 디퓨져 출구에서의 폐기가스 온도와 금속표면온도의 면적평균 값을 기준으로 하였으며, 폐기가스의 온도는 디퓨져 출구의 직경 변화에 크게 영향을 받고, 디퓨져 금속표면의 온도는 디퓨져 링의 개수 변화에 크게 영향 받음을 확인하였다.

• 아동학회지
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• 제32권4호
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• pp.99-113
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• 2011

This study examined natural groupings of mother-adolescents in terms of the sub-factors of problems in family communication. The natural groupings were as follows; the placating type, the blaming type, the super-reasonable type, and the inattention type. In addition, this paper also examined individual differences in trait anger and anger coping strategies patterns by clusters of sub-factors of problem in family communication. The subjects of this study consisted of 406 adolescents. Data were analyzed by means of cluster analysis and one-way ANOVA. The results from cluster analysis with the adolescent sample suggested the presence of four clusters ('placating-suppression', 'mixing up-confusion', 'authoritarian-hostility', 'consistent-repression'). Additionally, these four groups were found to be related to trait anger and anger coping strategies (anger-suppress, anger-out, anger-control).

• 한국전기전자재료학회논문지
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• 제16권12호
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• pp.1131-1135
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• 2003

In the sintering of YIG, abnormal grain growth phenomena were observed. This abnormal grain growth is related to the sintering temperature in this experiment. In the sintering below 1450$^{\circ}C$, the sintered body showed narrow size distribution. However, in the sintering at 1450$^{\circ}C$, a few grains grew rapidly with respect to other grains, and bimodal size distribution was appeared. From the observation of the microstructure, liquid phase was not observed far from the abnormally grown large grains, but only near the large grains. This means that the abnormal grain growth was caused by the nonuniform distribution of liquid phase which promote the grains growth. Because the growth rate of grains near the liquid phase is much higher than that of the other grains, a few grains grow rapidly. This nonuniform distribution of liquid phase was thought to be due to the nonuniform mixing of the calcined powders. This abnormal grain growth was suppressed by enhancement of the compositional uniformity by multiple calcination.

• 대한기계학회논문집A
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• 제26권9호
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• pp.1874-1881
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• 2002

Heat dissipation technology using the flow resonant phenomenon is a kind of a new concept in the heat transfer area. A vibration exciter is needed to enhance air flow mixing which has the natural shedding frequency of thermal system. A mechanical vibrating device for the air flow oscillation is introduced, which is driven by a moving coil actuator with a displacement estimator using strain gage. An analytical dynamic model for this mechanical vibration exciter is presented and its validity is checked by the comparison with experimental data. Values of some unknown system parameters in the analytic model are estimated through the system identification approach. Based on this mathematical model, the vibration exciter using strain displacement estimator is developed. During the experimental verification phase, it turns out the high modal resonant characteristics of a vibrating plate are a major barrier against obtaining a high bandwidth vibration exciter.

• Journal of Microbiology and Biotechnology
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• 제24권4호
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• pp.507-521
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• 2014

A phase variation has been reported in an entomopathogenic bacterium, Xenorhabdus nematophila. Compared with a wild-type primary form, a secondary form usually loses several physiological and biochemical characters. This study showed that the phase variation of X. nematophila caused a significant alteration in its immunosuppressive activity and subsequent entomopathogenicity. A secondary form of X. nematophila was detected in laboratory colonies and exhibited significant differences in dye absorption and entomopathogenicity. In addition, the secondary form was different in its production of eicosanoid-biosynthesis inhibitors (EBIs) compared with the primary form of X. nematophila. Production of oxindole and p-hydroxypropionic acid was significantly reduced in the culture broth of the secondary form of X. nematophila. The reduced EBI production resulted in significant suppression in the inhibitory effects on cellular nodule formation and phenoloxidase activity. Culture broth of the primary form of X. nematophila enhanced the pathogenicity of Bacillus thuringiensis ( Bt) significantly more than the culture broth of the secondary form. Furthermore, this study developed a highly efficient "Dual Bt-Plus: to control both lepidopteran insect pests Plutella xylostella and Spodoptera exigua, by mixing two effective Bt strains along with the addition of potent bacterial metabolites or 100-fold concentrated X. nematophila culture broth.

• 생약학회지
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• 제51권4호
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• pp.349-359
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• 2020

Gastroesophageal reflux disease (GERD) is a disease that stomach contents continually refluxing, and is currently on the rise worldwide. The purpose of this study is to find natural materials that can reduce side effects and effectively treat chronic acid reflux esophagitis (CARE), one of GERD. First, the antioxidant activity was confirmed by varying the mixing ratio of Coptidis Rhizoma and Evodiae Fructus, which are effective against chronic reflux esophagitis. After, animal experiments were conducted using a 1:1 (CE) and 1:2 (CEE) combination ratio of Coptidis Rhizoma and Evodiae Fructus, which had the best antioxidant efficacy. Gross lesion of esophageal mucosa after CE or CEE treatment showed a superior enhancement compared with that of CARE control rats. Additionally, its inhibited MAPK phosphorylation and led NF-κB inactivation through the suppression of IκBα phosporylation by regulating Nrf2/Keap-1, and NF-κB inactivation induced reduced protein expressions including inflammatory mediators and cytokines. Moreover, its improved esophageal barrier function through upregulating protein expressions of tight junction protein, whereas downregulating protein expressions of MMPs. Taken together, a mixture of Coptidis Rhizoma and Evodiae Fructus can attenuate the esophageal mucosal ulcer by inhibiting MAPK and NF-κB pathway, and upregulating proteins associated with tight junction.

• 한국화재소방학회논문지
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• 제26권5호
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• pp.73-78
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• 2012

본 연구는 압축공기포 소화설비의 소화성능을 평가하기 위해 포헤드 설비를 이용하여 실험을 진행 하였다. 압축공기포 소화설비는 포수용액에 압축공기를 혼입하여 포를 발생시키는 방식으로 해외에서는 원거리 방수가 가능하고 물 사용량을 줄여 수손피해를 최소화할 수 있는 압축공기포 소화설비(CAFS: Compressed Air Foam System)가 많이 활용되고 있다. 본 연구에서는 UL162 기준으로 수성막포 3 % 포 소화약제를 적용하여 기존의 공기 혼입 방식에 의한 포 소화설비와 압축공기포 소화설비간 비교 실험을 통하여 소화 성능 효과를 비교 분석하였다. 압축공기포 소화설비의 공기 혼입 비율은 포 수용액과 1 : 1의 부피 비율로 하였으며 발포유량은 각각 140 L/min, 160 L/min, 180 L/min, 200 L/min으로 변화를 주면서 소화효과를 검증하였다. 그 결과 소화 성능면에서는 압축공기포 소화설비가 공기 혼입 방식보다 모든 유량 조건에서 소화시간이 빠르게 나타났다.

• 식물병연구
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• 제16권1호
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• pp.74-80
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• 2010

2009년 6월에서 7월까지 경남 농업술원 ATEC 센터의 시설 하우스 내에서 파프리카에 발생한 흰가루병에 대하여 실험한 결과이다. 난황유 제조시 물 첨가량에 따른 유화 및 과일표면을 비교한 결과 50 ml과 100 ml의 물을 첨가하였을 때는 응집력이 강하지 않아 물에 균일하게 잘 분산되었다. 식용유가 완전히 유화되지 못한 것과 유화된 것을 살포하여 1주일 후 파프리차 과일의 표면을 비교한 결과 완전히 유화되지 못한 난황유의 경우 과일표면에 기름성분으로 덮여있는 것이 관찰되었다. 난황유 및 혼합제의 처리는 난황유 단독 처리구와 혼합제 처리구에서 병재발생이 억제되는 것으로 관찰되었으며, 혼합제 1,000배 와 5,000배를 처리한 구에서 난황유를 단독처리한구보다 병 재발생이 더 억제되어 유의차가 인정되었다. 난황유 및 혼합제의 처리에 의한 흰가루병 발병억제 지속효과는 난황유와 혼합제 처리구에서 병 재발생 면적 증가율이 다른 물처리와 유황수화제처리보다 낮은 것으로 나타났으며, 3주가 경과하여도 재발생 억제효과가 지속되었으나 4주차에서는 난황유와 혼합제(1,000, 5,000, 10,000배)가 각의 처리구 모두 재발생 면적이 조금씩 나타났다.

• 폴리머
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• 제33권3호
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• pp.224-229
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• 2009

가교체의 종류에 따른 semi-IPN(interpenetrating polymer network) poly(Phenylene oxide)(PPO) 블렌드와 $BaTiO_3$(BT) 복합재료의 유전특성을 조사하였다. PPO와 BT를 톨루엔에 분산하고 MEK 용매에 석출하여 얻어진 precursor PPO 복합재료에, 가교체와 과산화물을 용융혼합하는 방법으로 복합재료를 제조하였다. Precursor PPO 복합재료는 PPO와 BT를 단순히 용융혼합한 복합재료보다 높은 유전율을 나타냈으며 대수혼합법칙에 의한 이론값과도 일치하였다. 가교체로서 triallyl isocyanurate의 도입에 의해 PPO 수지의 배향분극이 감소하여 유전율과 유전손실 모두 크게 감소하였다. 4,4'-(1,3-phenylene diisopropylidene)bisaniline (Bisaniline)을 2,2-bis(4-cyanatophenyl)propane(CPP)와 혼합하여 가교하였을 경우에는 Bisaniline의 아민기에 의해 유전율과 손실이 증가하였으나, 치밀한 수지 조직과 충전제 계면상태를 관찰할 수 있었으며, 이것으로부터 굴곡강도와 탄성률이 향상된다는 것을 설명할 수 있었다.