• Journal of the Korean Magnetics Society
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• v.15 no.2
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• pp.61-66
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• 2005

In order to make submicron cell for spin-injection device, lift-off method using Pt stencil and wet etching was chosen. This approach allows batch fabrication of stencil substrate with electron-beam lithography. It simplifies the process between magnetic film stack deposition and final device testing, thus enabling rapid turnaround in sample fabrication. Submicron junctions with size of $200nm{\times}300nm$ and $500nm{\times}500nm$ 500 nm and pseudo spin valve structure of $CoFe(30{\AA})/Cu(100{\AA})/CoFe(120{\AA}$) was deposited into the nanojunctions. MR ratio was 0.8 and $1.1{\%}$, respectively and spin transfer effect was confirmed with critical current of $7.65{\times}10^7A/cm^2$.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.2
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• pp.79-85
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• 2007

An internal ballistic model to predict the performance of a Polyethylene-GOX (PE-GOX) hybrid motor was proposed and evaluated. A theoretical treatment of the model was followed by detail discussion of each of the factors affecting the overall performance. The present model consists of the governing equations by considering the unsteady burn-back rate of the fuel grain and on-off response characteristics of a oxygen-supply valve. The numerical results using the 4th order Runge-Kutta scheme with temporal physicochemical properties showed good agreements with test results and the global effects of the performance parameters, such as the burning area of the fuel grain, O/F ratio, and etc., on the performance of the motor were analyzed.

• Journal of Welding and Joining
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• v.25 no.5
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• pp.58-63
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• 2007

The relationship between GMA welding conditions and the bead shape of overlay weld was studied by using ${\Phi}1.6mm$ hypo-eutectic metal-cored wire designed for hardfacing against the severe metal-to-metal wear. As the welding voltage increased, the dilution also increased but the sudden drop of dilution was observed at $30{\sim}33V$. It was considered to be due to the decrease of penetration resulting from the change of transfer mode, from short circuit to spray. It was also found that the behavior of penetration with welding current was dependant on the transfer mode. The short circuit mode exerted the penetration to decrease while the spray mode did it to increase with increase of welding current. The former was considered to be responsible for the remarkable decrease in dilution at low welding voltage region. The change of transfer mode also had an effect on the behavior of bead width with welding current but it did not on the bead spreadability defined as W/H ratio. It was considered that the optimal welding conditions for multi-pass overlay welding could be obtained from the bead spreadability suitable for bead lapping and the dilution as low as possible in the spray transfer mode.

• Journal of Korean Society of Water and Wastewater
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• v.29 no.3
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• pp.395-406
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• 2015

This research carried out an analysis on input cost and leakage reduction effect by leakage reduction method, focusing on the project for establishing an optimal water pipe network management system in the Taebaek region, which has been executed annually since 2009. Based on the result, optimal cost-benefit analysis models for water distribution network rehabilitation project were developed using DEA(data envelopment analysis) and multiple regression analysis, which have been widely utilized for efficiency analysis in public and other projects. DEA and multiple regression analysis were carried out by applying 4 analytical methods involving different ratios and costs. The result showed that the models involving the analytical methods 2 and 4 were of low significance (which therefore were excluded), and only the models involving the analytical methods 1 and 3 were suitable. From the result it was judged that the leakage management method to be executed with the highest priority for the improvement of revenue water ratio was installation of pressure reduction valve, followed by replacement of water distribution pipe, replacement of water supply pipe, and then leakage detection and repair; and that the execution of leakage management methods in this order would be most economical. In addition, replacement of water meter was also shown to be necessary in case there were a large number of defective water meters.

• Journal of the Korean Magnetics Society
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• v.18 no.6
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• pp.227-231
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• 2008

Magnetic and structural properties of CoFeZr alloy films as a function of Zr concentration and magnetoresistive properties of spin valves incorporated with amorphous CoFeZr alloy films have been studied. Magnetization and coercivity of CoFeZr alloy films decreased as the Zr content increased. A single amorphous CoFeZr phase was formed when the Zr content is about above 18 at%. Magnetoresistance ratio and exchange coupling field of spin valves with amorphous CoFeZr were reduced slightly as compared with spin valves with CoFe because the resistance of amophous CoFeZr is higher than that of crystalline CoFe. However, the ${\Delta}{\rho}$ of spin valves with amorphous CoFeZr was improved due to reduction of current shunting.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.4
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• pp.299-305
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• 2017

Re-engineering is gaining attention due to severe environmental pollution and economic crisis. Although re-engineering in shipbuilding has been carried out steadily, technological advancements, domestic ship repair and maintenance industries are not as prevalent as shipbuilding industries. In order to solve this problems, laser cladding can significantly aid with technical development. Laser cladding produces an outstanding clad layer with minimal dilution and little porosity. In this study, prior to applying laser cladding to an exhaust valve face, the effects of various parameters that affect the characteristics of the 1 pass clad layer were investigated. When laser power was increased, the clad layer width became broader and the height was decreased. In addition, it was identified that the hardness of the clad layer was inversely proportional to the power, and the entire clad layer was diluted through an EDS chemical composition analysis.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.2
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• pp.1032-1037
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• 2011

In this study, simulation and optimization works for a demethanizer column have been performed to obtain ethane and heavier products from a pretreated natural gas stream. Pretreated natural gas feed stream was partially condensed after being precooled by exchanging heat with demethanizer top vapor stream and by using an external refrigeration cycle with a propane refrigerant. Vapor stream was cooled further and partially condensed through a turbo-expander. The power generated from the expansion of turbo-expander was delivered to the compressor for the residue gas compression. Liquid stream was cooled by Joule-Thomson expansion valve and was fed to the middle section of the demethanizer. Recovery percent of ethane for feed natural was set to 80% and methane to ethane molar ratio was fixed as 0.0119. On the other hand, some of the cold heat could be recovered by splitting the feed stream and by exchanging heat with side reboiler in order to reduce the heat duty in the propane refrigeration cycle.

• Journal of Chest Surgery
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• v.21 no.4
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• pp.649-655
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• 1988

One hundred and one patients with tetralogy of Fallot who were older than 16 years of age underwent a total correction of the anomaly between May, 1964 and July, 1987. This group comprised 14.9% of the 679 consecutive patients who had repair of the tetralogy at our institution during the same period. Of the 101 patients, 8 had a previous shunt procedure for palliation. The preoperative mean hemoglobin value was 16.9*1.0% and the mean systemic oxygen saturation, 84.4*0.9%. In 76 patients[75.2%], a type II ventricular septal defect was seen whereas in 14 patients[13.9%], the defect was type I. In 72 patients[71.3%], other cardiac anomalies were present which included patent foramen ovale in 37.6%, atrial septal defect in 8.99b, vegetations in 6.9%, right sided aortic arch in 5.9% and coronary artery anomaly in 5.0%. The right ventricular outflow obstruction was caused most commonly by combination of infundibular and valvular stenosis[74.3%], followed by isolated infundibular stenosis[19.8%] and valvular stenosis [5.9%] alone in order. The preoperative mean diameter of the pulmonary valve ring size was 10.2*0.5 mm in diameter. A transannular patch enlargement of the right ventricular outflow tract was performed in 28 patients and, in 12 a pericardial monocusp was utilized. Major anomalous aorto-pulmonary vessels were encountered in 5 patients which were detected before or during the operation. In 3 patients, they were ligated beforehand to control the flooding of the operative field. Postoperatively, the mean systolic pressure gradient between the right ventricle and the main pulmonary artery was 16.2*2.3 mmHg and the mean systolic pressure- ratio between the right and the left ventricle was 45.3*2.0%. Perioperative complications including bleeding in 8.9%, pleural effusion in 7.9%, dysrrhythmia in 4.9%, and residual VSD in 4.0%. Operative mortality was 8.9%. There has been no operative death in the recent 65 cases since 1981. There were 2 late deaths, 68 and 113 months after surgery. There were 2 late detachment of the VSD patch during the follow-up period. Of the 6 patients with patch detachment found during the postoperative period, 3 had subacute bacterial endocarditis before or after the operation indicating The serious nature of this complication. Two of these patients subsequently underwent a successful reoperation.

• Journal of Chest Surgery
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• v.34 no.4
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• pp.322-328
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• 2001

배경: 우심실 유출로 재건술후에는 폐동맥판막부전이 우심실기능에 나쁜 영향을 미친다. 이를 막기 위해 여러 재료로 판막을 제조하여 사용하는데 가피 형성이 적은 막형 ePTEE(expanded polytetrafluoroethylene, Goretex) 단엽판막의 효과를 알아보고자 연구를 시행하였다. 대상 및 방법; 1996년 3월부터 1997년 2월까지 우심실유출로 재건술을 시행받고 수술 1일까지 우심실 압력을 측정할 수 있었던 47명중 막형 Goretex단엽판막을 사용한 환자(비교군) 19명, 사용하지 않은 환자(대조군) 28명에서 단엽판막의 유용성을 조사하였다. 두 군간에는 나이, 체중 그리고 McGoon ratio 등에는 통계학적 차이가 없었다.(p>0.05) 이전의 수술은 대조군에서 19번, 비교군에서 22번을 시행하였다. 우심실 유출로에 대한 수술은 대조군에서 REV수술 2예, 우심실폐동맥 연결수술 8예, 우심실 유출로 재개건술 2예, 우심실 유출로에 대한 수술은 대조군에서 16예였으며, 비교군에서는 REV 수술 5예, Rastelli 씨 수술 6예, 재우심실 유출로 재건술 5예, 그리고 우심실 재건술 3예였다. 결과: 대동맥 차단 시간이나 총심폐순환시간에는 두군간의 차이는 없었다. 또한 수술직후와 수술후 1일째 측정한 우심실 압력 및 좌심방압력의 차이도 두군간에는 차이가 없었으며 수술후 7일째 시행한 심에코도 결과 ejection fraction., 우심실/ 좌심실 압력비 , 그리고 우심실 유출로의 압력차, 강심제 투여일수, 호흡기 사용 기간 등에서도 두군간의 차이는 없었으나 흉관 삽입기간이 비교군에서 의미있게 짧았다. 추적 조사 기간 중 비교군 1예에서 사망을 하였으나. Goretex 단엽판막에 의한 것은 아니였으며 심초음파검사상 우심실 유출로 압력차이나 재수술은 두군간에 차이는 없었으나 폐동맥 폐쇄부전은 비교군에서 의미 있게 낮은 것을 보이고 있다. 결론; 막형 Goretex 단엽판막의 조기성적은 우수하였으며 폐동맥 폐쇄분전의 정도를 적게 하는 효과를 보이나 앞으로 이들이 성장함에 따라 우심실 유출로에 폐쇄를 일으키는지는 계속적인 추적관찰이 요구된다.

• Korean Journal of Materials Research
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• v.16 no.11
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• pp.681-686
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• 2006

Plasma nitrocarburising and plasma post oxidation were performed to improve the wear and corrosion resistance of S45C and SCM440 steel by a plasma ion nitriding system. Plasma nitrocarburizing was conducted for 3h at $570^{\circ}C$ in the nitrogen, hydrogen and methane atmosphere to produce the ${\varepsilon}-Fe_{2-3}$(N, C) phase. Plasma post oxidation was performed on the nitrocarburized samples with various oxygen/hydrogen ratio at constant temperature of $500^{\circ}C$ for 1 hour. The very thin magnetite ($Fe_3O_4$) layer $1-2{\mu}m$ in thickness on top of the $15{\sim}25{\mu}m$ ${\varepsilon}-Fe_{2-3}$(N, C) compound layer was obtained by plasma post oxidation. A salt spray test and electrochemical testing revealed that in the tested 5% NaCl solution, the corrosion characteristics of the nitrocarburized compound layer could be further improved by the application of the superficial magnetite layer. Throttle valve shafts were treated under optimum plasma processing conditions. Accelerated life time test results, using throttle body assembled with shaft treated by plasma nitrocarburising and post oxidation, showed that plasma nitrocarburizing and plasma post oxidation processes could be a viable technology in the very near future which can replace $Cr^{6+}$ plating.