• 한국해양공학회지
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• 제13권4호통권35호
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• pp.37-44
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• 1999

Hardness characteristics and microstructures of $Nb/MoSi_2$ laminate composites were evaluated from the variation of fabricating conditions such as preparation temperature, applied pressure and pressure holding time. $Nb/MoSi_2$ laminate composites composed of $MoSi_2$ powder and Nb sheets were fabricated by the hot press. From experimental results, it was found that the lamination from Nb sheet and $MoSi_2$ powder was an excellent strategy to improve hardness characteristics of monolithic $MoSi_2$. However, interfacial reaction products like(Nb, Mo)$SiO_2\;and\;Nb2Si_3$ formed at the interface of $Nb/MoSi_2$ and increased with fabricating temperature.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2003년도 추계학술발표대회 논문집
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• pp.50-53
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• 2003

Carbon nannofiber reinforced Cu matrix composite has potential applications for electrically conducting materials having high strength and electrical conductivity. In this study, we have developed fabrication technology of the nanocomposites using a liquid pressing process. The process is to use the low pressure for infiltration of Cu melt into carbon nanofiber mat as the Cu melt is pressurized directly. The minimum pressure required for infiltration was calculated from force balance equation, permeability measurement and compaction behavior of carbon nanofiber. Also, the melting temperature and the holding time have been optimized.

• 한국압력기기공학회 논문집
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• 제11권1호
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• pp.33-38
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• 2015

The effects of post weld heat treatment(PWHT) on the mechanical properties of 2.25Cr-1Mo steels were investigated. As the PWHT temperature or holding time increased, the strength of low alloy steels progressively decreased due to softening process. After the conventional PWHT, the strength was larger than the minimum value of materials specification. The Charpy impact energy was hardly affected by the conventional PWHT. The trend of mechanical properties was analyzed in terms of tempering parameter. Most materials replaced from a power plant met the requirements of materials specification except for one heat. Same heat of materials with low impact energy were attributed to the voids formed during casting process.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 춘계학술발표대회 논문집
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• pp.250-253
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• 2004

Emphasis has been placed on thin plate fabrication of plain woven carbon fabric reinforced Al matrix composites using liquid pressing process. The composite has potential applications for PDP rear plate. The process is to use the low pressure for infiltration of Al melt into plain woven carbon fabric as the Al melt is pressurized directly. The minimum pressure required for the infiltration was calculated from force balance equation, permeability measurements and compaction behavior of carbon fiber. Also, the melting temperature and the holding time have been optimized. In order to measure coefficient of thermal expansion (CTE) of the composites, the thermal strain measurement using strain gage was performed and the thermal conductivity of the composites was measured using laser flash method. The constituent materials of the composite are PAN type carbon fibers as reinforcements and 6061 Al alloys as matrices.

• 한국세라믹학회지
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• 제28권6호
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• pp.457-464
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• 1991

Aluminum nitride (AlN) has excellent properties such as high thermal conductivity and electrical resistivity, whereas it has some disadvantages such as low sinterability and tendency to be hydrolyzed by moisture at room temperature. In the present work, the relative density, modulus of rupture and microhardness were examined for pressure-less-sintered AlN (synthetic and commercial) bodies which were prepared under the conditions of various sintering temperatures, holding times and additions of CaCO3 which showed the best effect on sinterability among the various sintering aids. As a result, the AlN bodies with 1.0 wt% CaCO3 (0.56wt% CaO) which were sintered at 1800$^{\circ}C$ for 20 min showed good densification. In this case, the relative densities were 95.9% and 95.2%, and microhardnesses were 10.3 GPa and 9.8 GPa for synthetic and commercial AlN respectively. And as the holding time at 1800$^{\circ}C$ was increased from 10 min to 60 min, the relative density was increased from 91.9% to 96.5%. It was considered that impurities of metals and oxygen promoted the densification of AlN at low temperature (1600$^{\circ}C$).

• 대한한방내과학회지
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• 제22권2호
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• pp.199-205
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• 2001

Background and Purpose : Transcranial doppler ultrasonography(TCD) is a noninvasive and nonradioactive technique for evaluation of the hemodynamics in large cerebral vessels. Sahyangsohap-won(SS) has been considered to be effective for the treatment of various disease, especially cerebrovascular, cardiovascular, and psychosomatoform disorders. But, there is no study about the effect of SS on the cerebral hemodynamics in humans. The aim of this study was to assess the effect of SS on the changes in cerebral hemodynamics and the dose-dependant effect by using TCD. Subjects and Methods : 30 healthy subjects were randomly divided into three group: group 1 took no drug, group 2 took SS one pill, and group 3 took SS 2 pills. Changes in the mean blood flow velocity(MBFV) and pulsatility index(PI) in the middle cerebral artery were evaluated by means of TCD. We obtained hypercapnia with breath-holding and evaluated cerebrovascular reactivity with the breath-holding index(BHI). Systolic blood pressure(SBP), diastolic blood pressure(DBP), and heart rate(HR) were measured by means of ambulatory blood pressure monitoring. In group 2 and group 3, the evaluations were performed during the baseline and were repeated at 20, 40, and 60 minutes after SS administration. In group 1, the evaluation was performed at corresponding time intervals. Results : In mean values of MSFV, PI, SSP, DBP, and HR, no stastically significant differences were found between the 3 groups. However, BHI values were significantly lower in groups 2 and 3 than in group 1 at 40 minutes after SS administration(P<0.05, group 1 vs group 2, group 1 vs group 3 by post-hoc analysis: Scheffe's test) but in dose-dependant effect, there was no difference between group 2 and group 3. Conclusion : These results suggest that SS can decrease vascular resistance in cerebral small arteries or arterioles and enhance their distensibility. Further studies on larger numbers of subjects are needed to confirm these effects and the dose-dependant effects.

• Design & Manufacturing
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• 제13권2호
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• pp.30-36
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• 2019

Traditional cell culture(2-dimensional) is the method that provide a nutrient and environment on a flat surface to cultivate cells into a single layer. Since the cell characteristics of 2D culture method is different from the characteristics of the cells cultured in the body, attempts to cultivate the cells in an environment similar to the body environment are actively proceeding in the industry, academy, and research institutes. In this study, we will develop a technology to fabricate micro-structures capable of culturing cells on surfaces with various curvatures, surface shapes, and characteristics. In order to fabricate the hemispheric plastic structure(thickness $50{\mu}m$), plastic preform mold (hereinafter as "preform mold") corresponding to the hemisphere was first prepared by injection molding in order to fabricate a two - layer structure to be combined with a flat plastic film. Then, thermoplastic polymer dissolved in an organic solvent was solidified on a preform mold. As a preliminary study, we proposed injection molding conditions that can minimize X/Y/Z axis deflection value. The effects of the following conditions on the preform mold were analyzed through injection molding CAE, [(1) coolant inlet temperature, (2) injection time, (3) packing pressure, (4) volume-pressure (V/P). As a result, the injection molding process conditions (cooling water inlet temperature, injection time, holding pressure condition (V / P conversion point and holding pressure size)) which can minimize the deformation amount of the preform mold were derived through CAE without applying the experimental design method. Also, the derived injection molding process conditions were applied during actual injection molding and the degree of deformation of the formed preform mold was compared with the analysis results. It is expected that plastic film having various shapes in addition to hemispherical shape using the preform mold produced through this study will be useful for the molding preform molding technology and cast molding technology.

• Design & Manufacturing
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• 제18권2호
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• pp.64-73
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• 2024

The purpose of this paper is to introduce a fusion method that combines the design of experiments (DOE) and machine learning to optimize the bias of plastic products. The study focuses on the plastic motor housing used in automobiles, which is manufactured through plastic injection molding. Achieving optimal molding for the motor housing involves the optimization of various molding conditions, including injection pressure, injection time, holding pressure, mold temperature, and cooling time. Failure to optimize these conditions can lead to increased product deformation. To minimize the deformation of the motor housing, the widely used Taguchi method, which is one of the design of experiment techniques, was employed to identify the injection molding conditions that affect deformation. Machine learning was then applied to various models based on the identified molding conditions. Among the models, the Random Forest model emerged as the most effective in predicting deformation amounts. The validity of the Random Forest model was also confirmed through verification. The verification results demonstrated the excellent prediction accuracy of the trained Random Forest model. By utilizing the validated model, molding conditions that minimize deformation were determined. Implementation of these optimal molding conditions led to a reduction of approximately 5.3% in deformation compared to the conditions before optimization. It is noteworthy that all injection molding outcomes presented in this paper were obtained through robust injection molding simulations, ensuring both research objectivity and speed.

• 한국식품과학회지
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• 제46권5호
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• pp.588-592
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• 2014

본 연구는 다진 생강에 다량 함유된 6-gingerol을 뇌질환 개선 등의 기능성이 보고된 6-shogaol로 변환시키기 위하여 $CO_2$를 이용한 6.4MPa의 가압조건에서 가열 온도와 시간을 변수로 두고 중심합성설계법을 이용한 최적반응표면분석법을 적용하였다. 적용 온도 $70-130^{\circ}C$ ($X_1$)와 적용 시간 95-265분($X_2$)을 독립변수로, 6-gingerol함량($Y_1$, mg/g dried ginger)와 6-shogaol함량($Y_2$, mg/g dried ginger)을 종속변수로 설정하였다. 그 결과 온도와 시간이 대체적으로 증가할수록 6-gingerol은 감소하였으며 반대로 6-shogaol은 증가하였다. 도출된 반응표면 설계를 분석한 결과 압력이 6.4 MPa일 경우 적용 온도($X_1$)는 $130^{\circ}C$, 적용 시간($X_2$)는 204분이었다. 최적반응표면분석 결과 예측된 6-gingerol과 6-shogaol 함량은 각각 건조시킨 생강을 기준으로 0.13, 3.85 mg/g이며, 이때 만족도는 0.991이었다. 본 실험 결과를 통하여 도출된 가압조건에서의 열처리 방법은 스팀 등을 이용한 물리적 열처리 기술에 비해 소요 시간과 소모되는 에너지를 줄일 수 있었고, 6-gingerol에서 6-shogaol로의 변환율이 탁월하기 때문에 친환경적이고 효율적인 6-shogaol을 얻을 수 있는 기술임을 확인할 수 있었다.

• 유변학
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• 제4권2호
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• pp.116-126
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• 1992

본 연구에서는 형내압 파형제어 시스템, 초고속, 사출성형, 그리고 금형진공 시스템 등을 갖춘 사출 성형기를 이용하여 정밀 구면렌즈를 성형하기 위한 실험을 수행하였다. 이 러한 목적을 위해 성형공정 변수인 사출시간 충전압력 그리고 보압시간이 성형품에 미치는 영향을 중량과 곡률반경 구면 정밀도 그리고 구면오차의 간접무늬를 측정하여 연구하였다. 그결과로서 성형품의 중량(칫수)과 곡률반경에 지대한 영향력을 행사하는 변수는 충전압력 이며 사출시간과 보압시간은 곡률반경과는 무관해 보이고 중량의 증가에는 기여하지만 공정 사이클 시간을 증가시키는 문제가 지적된다. 구면정밀도 측정실험 결과 길지도 짧지도 않는 15∼20초 사이의 보압시간 4초이내의 빠른 사출시간 그리고 860kg/cm2 이상의 높은 충전압 력에서 우수한 결과를 보여주었다, 마지막으로 구면의 형상에 대한 간접무늬 측정결과는 성 형공정을 이해하는데 강력한 도구가 됨을 발견하였다.