• 대한기계학회논문집B
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• 제29권1호
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• pp.151-158
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• 2005

A characteristic of discharge for a foam spray nozzle with various parameters was investigated. The discharge patterns from a fire foam spray nozzle are important to evenly spray over a maximum possible floor area. Two parameters of a foam spray nozzle were chosen, and compared with those from the standard one. Also, in order to evaluate the performance of discharged foam agents used to protect structures from heat and fire damages, the thermal characteristics of fire-protection foams were experimentally investigated. A simple repeatable test for fire-protection foams subjected to fire radiation was developed. This test involves foam generation equipment, a fire source for heat generation, and data acquisition techniques. Results show that the bubble size of foam is increased by large inside diameter of orifice or closed air hole, but phenomenon of discharge angle and expansion ratio is opposite. For the case of the open air hole, liquid film of a circular cone discharges with formation, growth, split and fine grain. In case of the closed air hole, a pillar of foam solution discharges with that. Though the temperature gradient in the foam increases with increased foam expansion ratio. it is not change with increased intensity of heat flux.

• 한국군사과학기술학회지
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• 제13권5호
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• pp.717-724
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• 2010

The initial trajectory of a spheroid configuration bobbin for precision guidance has been investigated by analyzing its aerodynamic load and six-degree-of-freedom motion. The effects of changes in the spheroidal head configuration, flow angle and lateral center-of-gravity offset are numerically studied using the commercial software "FLUENT". A wind tunnel test is also conducted to validate the numerical scheme and to examine effect of the Reynolds number on the flow around the bobbin. It is shown that the size of the separation bubble formed on the surface decreases significantly when the Reynolds number is varied between 110,000 and 140,000. At a zero flow angle, an oblate spheroidal head shows relatively moderate rotation while a prolate spheroidal head shows rapid rotation. The bobbin with a spherical head shape has little effect on the flow direction; however, the oblate bobbin is sensitive to the flow angle. The roll motion of the bobbin is greatly influenced by the lateral center-of-gravity offset and maximum dispersion is observed at half of the radius.

• Journal of the Korean Data and Information Science Society
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• 제26권4호
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• pp.791-799
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• 2015

랜덤워크가설이란 금융시장의 많은 시계열자료가 과거의 값과 관계없이 독립적으로 움직인다는 이론이다. 랜덤워크가설은 ARMA 모형에서 단위근 존재여부 문제로 해석되는데 대부분의 연구는 AR(1) 모형에서 ${\rho}$ < 1 여부를 검정하는 문제에 집중되어 왔다. 그러나, ${\rho}$ > 1인 폭발자기회귀모형을 따르면 거품경제의 위험이 있게 되므로 이를 구분하는 것이 필요하다. 폭발자기회귀모형에서 모수 추정량의 점근분포에 대해 알려져 있으나 그 형태가 모수를 포함하고 있어 통계량으로 부적절하거나 모수에 특정한 구조를 가정하고 있어 사용하기 쉽지 않다. 본 연구에서는 소규모자료에서도 사용할 수 있는 기울기부호를 이용하여 폭발자기회귀모형에 대한 검정을 제시한다. 모의실험을 통해 검정통계량의 성질을 확인한 결과, 오차항의 종속 정도에 따라 통계량의 분포가 일정한 경향을 따르는 것을 알 수 있었다. 대립가설이 참일 경우 통계량의 값이 커지는 성질을 이용하여 검정할 수 있음을 확인할 수 있었다.

• 한국지반공학회논문집
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• 제19권5호
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• pp.189-197
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• 2003

건설공사에서 발생되는 건설잔토는 처리 및 운반에 소요되는 비용이 고가이기 때문에 현장에서 재활용하기 위한 공법의 개발이 오래 전부터 요구되어 왔다. 본 연구는 현장에서 발생하는 토사를 아스팔트에 혼합하여 제조된 아스팔트 안정처리토의 역학적 특성을 평가하기 위한 실내시험 연구이다. 아스팔트와 토사의 혼합은 폼드(foamed)장치라고 불리는 장치를 사용하여 아스팔트에 거품을 발생시켜 토사와 혼합하는 방법을 사용하였다. 아스팔트가 토사와 혼합되었을 때 성능 향상을 조사하기 위해서 마샬안정도, 간접인장강도, 회복탄성계수, 크리프 시험 및 비압밀 비배수 삼축압축시험을 실시하였으며 조건을 달리하여 제작한 시료(일반토사, 시멘트 2% 보강 토사)와 결과를 비교 분석하였다. 시험 결과 아스팔트의 혼입은 안정도, 회복탄성계수, 수분저항성이 향상되는 것으로 나타났으며 시멘트의 첨가는 이러한 역학적 성능을 더욱 크게 향상시키는 것으로 나타났다. 아스팔트 안정토는 토사의 혼합 함수비, 습윤상태는 시험 결과에 영향을 미치는 것이 확인되었는데 배합 설계시 혼합함수비, 세립분의 량을 조절함으로써 아스팔트 안정토의 역학적 특성을 향상시킬 수 있는 것으로 발견되었다.

• 대한의생명과학회지
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• 제15권1호
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• pp.17-23
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• 2009

The prevalence of patent foramen ovale (PFO) in healthy persons was estimated as about $10{\sim}25%$ and was up to 40% in patients with stroke. Transesophageal echocardiography (TEE) was considered to be the most sensitive method to detect PFO and was used as the gold standard. Transcranial doppler sonography (TCD) of the middle cerebral artery (MCA) during a contrast (saline bubble) injection has recently been proposed as an alternative detecting method for PFO. In this study, we would like to know the difference between TCD value and TEE value in subjects with cryptogenic ischemic stroke. We performed TCD and TEE tests to detect PFO on 64 patients (30 women and 34 men, mean age was 59.4 years) with cryptogenic ischemic stroke. PFO prevalence through TCD was 45.3% (29 of 64 patients) and the prevalence through TEE was 34.4% (22 of 64 patients). There was no statistical significance between PFO test and TCD test (P=0.206). But TCD had a sensitivity of 90.9% (20 of 22 patients), specificity of 78.6% (33 of 42 patients), positive predictive value of 69.0% (20 of 29 patients), and negative predictive value of 94.3% (33 of 35 patients). We concluded that TCD was a highly sensitive method for detecting a right-left shunt. Therefore, the non-invasive TCD test is a method more effective than the anti-invasive TEE test in the cost and evaluation of the existence or nonexistence of right to left shunt in addition to the screening method of the cerebrovascular disorder. Considering these points, TCD test could be recommended for patients with cryptogenic ischemic stroke as a useful and convenient method for screening of the existence or nonexistence of a right to left shunt caused by PFO.

• 한국구조물진단유지관리공학회 논문집
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• 제18권4호
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• pp.59-66
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• 2014

건설구조물 상부의 단열은 에너지 절약 건설구조물에 있어서 중요한 요건 중 하나이다. 건설구조물 최상부는 단열성뿐만 아니라 방수성능도 중요하다. 이와 같은 이유로 단열성을 확보한 방수공법의 개발이 요구된다. 본 연구에서는 최근 일정 단열성능을 확보한 단열 보완형의 복합방수공법이 개발되어 해당 공법에 대한 단열성능을 평가하고자 하였다. 방수성 시험결과, 모든 시험체는 KS 표준 이상의 성능을 보여주었다. 단열성 시험결과, 스티로폼 박스가 가장 높은 온도인 $25.91^{\circ}C$, 버블시트 박스가 $17.28^{\circ}C$, 단열시트 박스가 $15.47^{\circ}C$, 단열보완형 방수시트가 $24.11^{\circ}C$로 확인되었다. 시트 접합부의 열교현상을 관찰한 결과 열교현상은 발생하지 않았다. 단열보완형 복합방수공법은 단열성능을 확보하고 있는 것으로 판단된다.

• 한국기계가공학회지
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• 제19권11호
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• pp.1-7
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• 2020

Recently, hydrogen has gained considerable attention as an eco-friendly fuel, which helps in reducing carbon dioxide content. Specifically, there is a growing interest in vehicles powered by a hydrogen fuel cell, which is spotlighted as an environmental-friendly alternative. A hydrogen transport system, fuel cell system, fuel supply system, power management system, and hydrogen storage system are key parts of a hydrogen fuel cell truck. In this study, a hydrogen storage system is built and analyzed. The expansion length of the storage vessel at maximum operating pressure (87.5 MPa) was calculated with ABAQUS, and then the optimized system was designed and built. The leak and bubble tests were performed on the built storage system. The leakage of the system was measured to be under 5 cc/hr. Hence, it can be used as a research test for the safety evaluation of leading systems of hydrogen fuel-powered commercial vehicles.

• 한국의상디자인학회지
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• 제23권2호
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• pp.79-91
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• 2021

This study aims to rectify the disfigurement of bowlegged, (which means they have a gap between knees due to knee joint problems) females in their twenties through the development of pants patterns. The contents of the study are as follows: First, two types of basic pattern-making methods were selected. Two mock-ups, which were made by using these pre-selected basic patterns, were worn by three bowlegged participants and evaluated with a fit test. A basic pattern, which had good body fit was selected, which had a bubble or a wedge at in crotch area and roomy or snug upper thigh. Second, the mock-up, which was made by using the selected basic pattern, led to the outward movement of crease lines. Two types of patterns that were adjusted were evaluated through a fit test. As a result, an effective adjustment for moving the crease line to the outside or to the center was to cut along the slash line of a horizontal balance line to, but not through the crotch seam to spread the pattern at the hip. Third, three patterns were readjusted using the chosen alteration pattern, and the crotch seam and spread patterns of 1 cm, 2 cm, and 3 cm at the hip were applied. As a result of the evaluation of the fit test, three participants-the majority-showed a better fit when the spread amount in the pattern was 2 cm, although every participant did have a different gap between the knees. This study has significance in which rectifies the disfigurement of bowlegged individuals through the development of patterns for females in their twenties who are bowlegged.

• 한국건설순환자원학회논문집
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• 제11권1호
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• pp.39-47
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• 2023

최근 구조물의 장대화로 인하여 고강도 재료의 경량화 요구가 빈번해지고 있는 실정이다. 하지만 현재까지는 압축강도 120 MPa, 단위중량 20 kN/m³ 정도의 고강도 경량 콘크리트를 구조부재에 적용하기 위한 콘크리트와 철근의 부착 특성에 관한 연구가 부족한 실정이다. 따라서 본 논문에서는 압축강도 120 MPa, 단위중량 20 kN/m³ 정도의 고강도 경량 콘크리트 108개의 시편을 제작하여 직접 인발 부착실험을 수행하였고, 실험결과와 현행 설계기준과 비교하여 부착특성을 평가하였다. 솔리드버블은 단위중량 감소에 비해서 압축강도 및 탄성계수 감소효과는 상대적으로 적게 나타나, 초경량화를 위해서는 반드시 적용되어야 할 재료로 판단되며, ACI-408R의 부착강도 산정식과 실험결과는 비교적 유사한 것으로 판단되며, 더 낮은 압축강도, 단위중량의 콘크리트보다 더 큰 슬립 및 매개변수 값을 가지는 것으로 나타났다.

• 펄프종이기술
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• 제41권2호
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• pp.26-33
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• 2009

A new testing method to evaluate the deposition potential of white pitch was developed. The new method involves depositing the potential white pitch particles on the air bubble covered plastic film in the pitch deposit tester (PDT) developed by KRICT and analysing the deposited area of white pitch using an image analyzer. In addition, the effect of two important factors (pH and calcium hardness) on white pitch deposition potential was elucidated. When pH of the coated broke stock was increased from neutral to alkali or the calcium hardness of the stock was decreased, the pitch deposit area was decreased, implying that these two factors have to be controlled during the evaluation of pitch deposition potential. It was found that hydrophobicity of the surface of latex binding films repulped is a key factor influencing white pitch deposition.