• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.988-995
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• 2020

Air gun shock systems are commonly used as alternative explosion energy sources for underwater explosion (UNDEX) shock tests owing to their low cost and environmental impact. The airbag inflator of automotive airbag systems is also very useful to generate extremely rapid underwater gas release in labscale tests. To overcome the restrictions on the very small computational time step owing to the very fine fluid mesh around the nozzle hole in the explicit integration algorithm, and also the absence of a commercial solver and software for gas UNDEX of airbag inflator, an idealized airbag inflator and fluid mesh modeling technique was developed using nozzle holes of relatively large size and several small TNT charges instead of gas inside the airbag inflator. The objective of this study is to validate the results of an UNDEX response analysis of one and two idealized airbag inflators by comparison with the results of shock tests in a small water tank. This comparison was performed using the multi-material Arbitrary Lagrangian-Eulerian formulation and fluid-structure interaction algorithm. The number, size, vertical distance from the nozzle outlet, detonation velocity, and lighting times of small TNT charges were determined. Through mesh size convergence tests, the UNDEX response analysis and idealized airbag inflator modeling were validated.

• Composites Research
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• 제37권1호
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• pp.40-45
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• 2024

본 연구에서는 고분자 전해질막 연료전지용 가스확산층의 투과도를 예측하기 위해 삼차원 합성곱 신경망 모델을 사용하는 방법론을 소개한다. 먼저, 기계학습 모델을 학습시키기 위해 X-선 단층 촬영을 통해 얻은 실제 가스확산층 이미지에서 형태학적 특성을 추출해 가스확산층의 대표 체적 요소로 이루어진 인공 데이터셋을 생성한다. 이러한 형태학적 특성은 다공성, 섬유 배향, 직경의 통계적 분포가 포함된다. 구축한 인공 데이터셋 대표 체적 요소들의 투과도를 평가하기 위해 격자 볼츠만 방법이 사용되었으며 각각의 대표 체적 요소들의 투과도를 도출하였다. 이러한 인공 데이터셋을 통해 삼차원 합성곱 신경망 모델을 학습시켰으며 인공 데이터셋을 학습한 삼차원 합성곱 신경망 모델이 실제 가스확산층의 대표 체적 요소 투과도 또한 잘 예측하는 것을 확인하였다.

• Tribology and Lubricants
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• 제40권3호
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• pp.103-110
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• 2024

Gas foil thrust bearings (GFTBs) are oil-free self-acting hydrodynamic bearings that support axial loads with a low friction during airborne operation. They need solid lubricants to reduce dry-friction between the runner and top foil and minimize local wears on their surfaces during start-up and shutdown processes. In this study, we evaluate the lift-off speeds and load capacity performance of a GFTB with Polytetrafluoroethylene (PTFE) surface coating by measuring drag torques during a series of experimental tests at increasing ambient temperatures of 25, 75 and 110℃. An electric heat gun provides hot air to the test GFTB operating in the closed booth to increase the ambient temperature. Test results show that the increasing ambient temperature delays the lift-off speed and decreases the load capacity of the test GFTB. An early developed prediction tool well predicts the measured drag torques at 60 krpm. After all tests, post inspections of the surface coating of the top foil are conducted. Scanning electron microscope (SEM) images imply that abrasive wear and oxidation wear are dominant during the tests at 25℃ and 110℃, respectively. A quantitative energy dispersive spectroscopy (EDS) microanalysis reveals that the weight percentages of carbon, oxygen, and nitrogen decrease, while that of fluorine increases significantly during the highest-temperature tests. The study demonstrates that the increasing ambient temperature noticeably deteriorates the static performances and degrades the surface coating of the test GFTB.

• 멤브레인
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• 제25권4호
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• pp.343-351
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• 2015

본 연구에서는 높은 기체선택도를 가지는 폴리이미드의 제조를 위해 2,2-bis(3,4-carboxylphenyl) hexafluoropropane과 두 종류의 아민인 2,4,6-Trimethyl-1,3-phenylenediamine (DAM)과 4,4-Methylenedianiline (p-MDA)을 이용하여 합성을 진행한 후 비용매 상전이법으로 비대칭 분리막을 제조하였다. 분리막 제조에 사용된 용매에 따른 물성변화를 확인하기 위하여 고분자 용액의 점도, 흐림점 측정을 통한 고분자의 상평형도, 비용매 상전이 계수 측정을 진행하였다. 상전이법을 이용하여 제조된 분리막은 SEM을 통해 용매 휘발시간에 변화에 따른 모폴로지를 확인하였고 이의 변화에 따른 기체 투과도 변화를 확인하였다. 기체투과도는 디메틸아세트아마이드를 사용하였을 때보다 N-메틸-2-피롤리돈을 사용하였을 때 $CH_4$, $N_2$, $O_2$, $CO_2$의 투과도와 각 기체에 대한 선택도가 높은 것을 확인하였다. 또한 용매 휘발 시간이 길수록 기체 투과도는 감소하지만 기체에 대한 선택도가 증가하는 것을 확인하였다.

• 자원ㆍ환경경제연구
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• 제31권4호
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• pp.755-775
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• 2022

동 연구는 휘발유 가격 수준에 따른 국제 유가에 대한 국내 가격 조정의 비대칭성을 분위수 자기회귀시차분포 모형을 사용하여 확인한다. 추정에 사용된 자료는 2008년 5월 첫 번째 주부터 2022년 10월 두 번째 주까지의 주간 평균 두바이유가, 정유사 휘발유가, 주유소 휘발유가이다. 추정은 두바이유가에 대한 주유소 휘발유 가격, 두바이유가에 대한 정유사 휘발유 가격, 정유사 휘발유 가격에 대한 주유소 가격의 변화, 세 가지에 대해 이루어졌다. 추정 결과, 두바이유가에 대한 정유사 휘발유 가격의 조정은 휘발유 가격의 모든 분위에 걸쳐 비대칭적으로 나타난 반면 두바이유가와 정유사 휘발유 가격에 대한 주유소 가격의 조정은 휘발유 가격의 분위수가 높을수록 비대칭적으로 나타났다. 이와 같은 결과는 휘발유 가격 변화에 따른 주유소의 재고 비용 변화에 기인하는 것으로 추측된다. 재고 비용에 대한 부담이 높을수록 주유소에게는 상승한 휘발유의 매입가격을 보다 적극적으로 판매가격에 전가하고자 하는 유인이 있다.

• Journal of the Optical Society of Korea
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• 제2권2호
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• pp.50-53
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• 1998

We report on the spectroscopic investigation of optical-field ionized plasmas in the soft X-ray spectral region. The experiment was carried out by focusing pulses of the high-power Ti:Sapphire laser with an energy of ~ 40 mJ and time duration of ~30 fs into a gas jet of krypton, xenon, and argon from a pulsed nozzle. Strong soft X-ray emission on lines from ionic stages of $Kr^{7+} , Kr^{8+} , Xe^{7+} , Ar^{7+} , and Ar^{8+}$ is reported. The experimental result was found to be in good agreement with theoretical prediction.

• 한국연소학회:학술대회논문집
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• 한국연소학회 제26회 KOSCO SYMPOSIUM 논문집
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• pp.215-222
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• 2003

Mild combustion or Flameless oxidation(FLOX) have been considered as one of the most prospective clean-combustion technologies to meet both the targets of high process efficiency and low pollutant emissions. A mild combustor with high air preheating and strong internal exhaust gas recirculation is characterized by relatively low flame temperature, low NOx emissions, no visible flame and no sound. In this study, the Steady Flamelet Approach has been applied to numerically analyze the combustion processes and NOx formation in the mild combustor. The detailed discussion has been made for the basic characteristics of mild combustor, numerical results and limitation of the present combustion modeling.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 하계학술대회 논문집 C
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• pp.1307-1310
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• 1995

During measurement of atomic hydrogen in a silane plasma using two-photon excited laser induced fluoresecence, laser-induced dissociation of the gas was observed. This was investigated untill conditions for the input laser fluence were determined where the effect was negligible. A measurement of the atomic hydrogen distribution was then performed within the limits of these conditions. Absolute density determinations showed atomic hydrogen densities of around $3{\times}10^{17}m^{-3}$.

• Preventive Nutrition and Food Science
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• 제13권1호
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• pp.33-39
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• 2008

The volatile flavor components of Zanthoxylum pipperitum A.P. DC. produced in Korea and China were isolated using a Clevenger-type apparatus by steam distillation extraction, and analyzed by gas chromatography-mass spectrometry (GC/MS). The yields of oils from Korean and Chinese Z. pipperitum A.P. DC. were 2.0 and 1.2% (w/w), respectively. From the two Z. pipperitum A.P. DC. oils, sixty and fifty-four volatile flavor compounds were tentatively identified, and they constituted 94.78 and 87.34% of the total peak area, respectively. Piperitone(p-menth-1-en-3-one) (13.48%) was the most abundant compound in the Chinese Zanthoxylum pipperitum A.P. DC. oil, followed by $\beta$-phellandrene, sabinene, terpinen-4-ol and linalool (each >5%). Whereas, the most abundant compound in the Korean Zanthoxylum pipperitum A.P. DC. oil was limonene (18.04%), followed by geranyl acetate, cryptone, citronellal, cuminal and phellandral (each >5%).

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1997년도 춘계학술발표회논문집(1)
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• pp.125-130
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• 1997

Effect of cross-section libraries on displacements per atom (dpa) was investigated under the spectrum which is calculated in the outer and inner of capsule in the JMTR fuel region. The variation of dpa value of iron was calculated by TENJIN2 code using several cross section libraries (ENDFB-lV, JENDL 3.1 and JENDL 3.2). The dependency of input spectrum on total damage (dpa) is more clearly appeared in case or ENDFB-IV in JENDL 3.2 and JENDL 3.1 libraries. The gas production rate calculated by ENDFB-IV library showed slightly larger value than that by JENDL library, and it responded more sensitively in neutron spectrum.