Ti 클래드 강판 제조를 위한 저항 seam 접합 공정의 열전달 수치 해석

정순효,도정만,변지영 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.2

The electrical and thermal fields during a resistance seam welding process for the production of titanium-clad steel plates were numerically analyzed using a finite volume method. Effect of welding parameters such as welding speed, electric current, heating/cooling period, electrode/plate contact area, water cooling intensity, and thermal conductivity of electrode, on temperatures at the bonding layer and titanium surface were studied. With the increase of the water cooling intensity, welding speed, electrode/plate contact area, and thermal conductivity of electrode, temperatures at the bonding layer and titanium surface decreased, but they increased with increasing the heating/cooling period and electric current. Strong cooling, low welding speed, and the use of high thermal-conductivity electrodes were advantageous in preventing oxidation of titanium surface.

과학수업모형의 비교 분석 및 내용과 활동 유형에 따른 적정 과학수업모형의 고안

정완호,권재술,최병순,정진우,김효남,허명 한국교원대학교 과학교육연구소 1996 청람과학교육연구논총 Vol.6 No.1

The purpose of this study is to develop appropriate science teaching models which can be applied effectively to relevant situations. Five science teaching models; cognitive conflict teaching model, generative teaching model, learning cycle teaching model, hypothesis verification teaching model and discovery teaching model, were identified from the existing models. The teaching models were modified and in primary and secondary students using a nonequivalent pretest-posttest control group design. Major findings of this study were as follows: 1. For teaching science concepts, three teaching models were found more effective; cognitive conflict teaching model, generative teaching model and discovery teaching model. 2. For teaching inquiry skills, two teaching models were found more effective; learning cycle teaching model and hypothesis verification teaching model. 3. For teaching scientific attitudes, two teaching models were found more effective; learning cycle teaching model and discovery teaching model. Each teaching model requires specific learning environment. It is strongly suggested that teachers should select a suitable teaching model carefully after evaluating the learning environment including teacher and student variables, learning objectives and curricular materials.

DC Arc로의 유동/열전달 해석 - 플라즈마 영역(1)

정순효,변지영,오영주 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.8

Both fluid flow in the plasma region and heat/momentum transfers from the plasma to the molten steel surface in a DC arc furnace were numerically analyzed by considering the shape change of a molten steel surface due to the high velocity plasma jet. Calculated plasma characteristics and heat and momentum transfers from the plasma to the molten steel were compared and discussed with previous results which had been calculated under the assumption of the flat surface of the molten steel. It was found that the formation of a groove enlarged the current flowing area on the melt surface. Although the heat transferred on the melt surface and current flowing area increased by the groove formation, the shear surface acting on the melt surface decreased. By increasing arc current, the radius and depth of grooves, the joule heat, the radiation loss, the heat and shear force transferred to the melt surface and groove area increased. By increasing arc length, the groove radius increased and the groove depth decreased, respectively. And the joule heat generated, the radiation loss and the heat transferred to the melt surface and the shear force acting on the melt surface decreased. But the heat transferred to the groove area and the shear force acting on the groove area decreased.

티타늄의 THP공정에서의 수소제거 과정 수치해석

정순효,하헌필,변지영 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.8

A previously developed fixed grid finite volume method was used to investigate hydrogen removal process involving surface reaction, diffusion, β/α phase boundary movement and phase transformation that occurs during dehydrogenation of cylindrical β-titanium specimens. Effects of temperature, initial hydrogen content and radius of specimen on times for dehydrogenation were studied. It was found that dehydrogenaion occus through the following 4 steps: (1) lowering of hydrogen concentration at the surface of the β specimen to equilibrium value, (2) lowering of hydrogen concentration gradient to a value matching the surface reaction flux. (3) the (β/α phase transformation by inward movement of the β/α phase boundary and (4) further removal of hydrogen in the a phase specimen to final value. Time for hydrogen removal in the first step increases with increase of temperature and initial hydrogen content, due to the rapid increase of amount of hydrogen to be removed comparing with the increase of hydrogen removal rate. It increases with specimen radius. Time for hydrogen removal in 2nd step decreases with increase of temperature due to increase of hydrogen removal rate and decrease of amount of hydrogen to be removed, but it increases with specimen radius and initial hydrogen content. Time for hydrogen removal in 3rd step (β/α phase transformation) decreases with increase of temperature due to decrease of diffusion and reaction resistance and due to increase of partition coefficient, but it increases with specimen radius due to increase of diffusion and reaction resistance. It increases with initial hydrogen content. Time for hydrogen removal in 4th step decreases with increase of temperature due to decrease of diffusion and reaction resistance as well as equilibrium concentration, but it increases with specimen radius due to increase of diffusion and reaction resistance.

DC Arc로의 유동/열전달 해석 - 용강영역(2)

정순효,변지영,오영주 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.8

Heat- and fluid-flow phenomena in the molten steel region in a DC arc furnace were investigated by simultaneous analysis of electromagnetic, flow and temperature fields. It was found that the flow pattern in molten steel was determined by electromagnetic and buoyancy forces rather than the shear force at the melt surface due to the high velocity plasma arc. While the short arc with high current made the hot region beneath the arc expanded, the long arc with high current drove the melt temperature high. And the low arc current led to the non-homogeneous temperature distribution of the melt because the bottom region of the melt was not stirred sufficiently.

티타늄의 THP공정 중 수소화 과정 수치해석

정순효,하헌필,변지영 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.5

A fixed grid, finite volume model was applied to investigate hydrogen absorption, diffusion and moving boundary α/βphase transformation that occurs during hydrogenation and homogenization annealing of cylindrical titanium specimens. Effects of parameters such as temperature, specimen radius, amount of added hydrogen on the times required for hydrogenation, for completion of α/βphase transformation and for homogenization were studied. It was found that hydrogen absorption rate is mostly influenced by surface reaction rather than solid-state diffusion. Time for hydrogenation becomes somewhat shorter with increase of temperature, due to decrease of hydrogen saturation concentration in spite of large increase of diffusivity and reaction rate constant. It increases almost linearly with increasing specimen radius or with amount of hydrogenation, showing positive deviation from linearity due to increase of diffusion resistance or surface hydrogen concentration. The completion of α/βphase transformation and homogenization are finished quickly with raising temperature due to increase of diffusivity and decrease of equilibrium hydrogen concentration in the βphase. They are nearly proportional to the square of specimen radius. With increase of the amount of added hydrogen, the completion of α/β phase transformation and homogenization are finished quickly during annealing due to the progress of α/β phase transformation during hydrogenation (Received August 23, 2003)

전착균일성에 미치는 보조음극의 영향

정순효,오영주 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.6

A numerical simulation based on the finite element method is used to investigate the effect of auxiliary electrode on the uniformity of deposition rate at a patterned electrode. The calculated deposition rates agreed well with the measured ones. Influences of the width of auxiliary electrode, gap between cathode and auxiliary electrode, distance between the inner wall of bath and auxiliary electrode and shape of auxiliary electrode on uniformity of electrodeposit have been studied. The optimum geometric factor of auxiliary electrode was obtained. (Received January 2, 2004)

중학교 남녀학생별 가정교과에 대한 인식 및 학습효과 : 경남지역을 중심으로

신동순,김상희,오화자,정효숙,정혜경 한국 가정과 교육 학회 1997 한국가정과교육학회지 Vol.9 No.1

The aims of this research study is to clear the differences of the learning effects and the cognition of Home Economics by sex in the middle school and to collect the future-oriented educational datas, after implementing the 6th education curriculum. The results of the study are as follows ; 1. Most of students had the cognition that Home Economics is a subject matter of a needful knowledge and skill for the family life, half students a cultural subject matter for the modern life. The former was supported by female students, the latter by male students. 2. Most of students were interested in actual training fields of cooking and hand-sewing, had a strong interest about a field of physical and social-psychological growth. The differences by sex were statistically significant in these fields. 3. Most of students had positive responses in the learning effects of Home Economics. The most useful field was cooking and the worst was the structure and method of sewing machine. 4. The shortage and the dissatisfaction in the learning of Home Economics were lacking of the actual training hours, the old-fashioned teaching methods and the shortage of teaching materials etc.

신경섬유종증 환자에서 상완신경총 병변의 소견을 보인 척추 신경섬유종

양충용,박효인,박순아,박종태,정선관,신용일 圓光大學校 醫科學硏究所 2008 圓光醫科學 Vol.23 No.2

본 증례는 50세 여성의 제 1형 신경섬유종 환자로서 척추 신경섬유종에 의해 초기 상완신경총 병변 소견을 보였다. 약 4개월 동안 후경부통, 좌측 견관절, 좌측 상완의 마비를 보였으며, 초기 전기진단학적 검사상 경수 5번과 6번 신경근을 중심으로 쇄골상부 신경절전성 상완신경총 병변이 관찰되었다. 그러나, 액와 자기공명영상, 초음파검사, 단순 방사선검사, 골주사 등의 영상학적 검사에서는 심한 흉추 척추 전-측만증과 경수 뇌경막에 확장 소견을 제외하고는 상완신경총 병변의 소견은 관찰되지 않았다. 7개월경과 후, 좌측 상지 및 양측 하지의 근력 저하, 경수 4번이하의 감각 저하, 경도의 흉통을 동반한 호흡곤란이 진행되었다. 응급으로 시행된 경수 자기공명영상에서 좌측 경수 3번과 4번에 경막내 액와-속질의 신경종양이 진단되었다. 수술적 처치를 시행하였으며, 거시적 관찰상 척수 신경섬유종이 진단되었다. 급격히 진행하는 척수 신경섬유종은 초기에 상완신경총의 신경근 병변의 소견을 보일 수 있으므로, 신경섬유종증 환자에서 상완신경총 병변의 진단에 세심한 주의를 요한다. We observed a patient with symptom similar to brachial plexus lesion caused by spinal neurofibroma in a 50-year-old female with a history of neurofibromatosis-1(NF-1). She presented with posterior neck, left shoulder and left upper arm paralysis of 4 months duration. The initial electrodiagnostic study(EDS) revealed supraclavicular preganglionic brachial plexus lesion of mainly involved left C5 and C6 roots. However, radiological imagings including axillar MRI, ultrasonography, cervical plain radiography and bone scintigraphy showed no definitive brachial plexus disease except cervical dural dilation and severe thoracic scolio-Iordosis. On 7 months after the first admission, she had aggravated muscle weakness on the left upper arm and both lower extremities, sensory impairment below C4 and respiration difficulty with the chest pain. Emergency MRI showed intradural axillar-medullary neurogenic tumor at the left C3-C4. Subsequently, the patient was treated with surgical resection. Grossly specimen examination displayed the presence of a spinal neurofibroma. In rapidly progressing spinal neurofibroma represented firstly as root lesion of brachial plexus in EDS, the physician should pay scrupulous care to evaluate the cause.

HMG-CoA 환원효소 억제제에 의한 ICAM-1 유전자의 발현조절

김현진,정효균,홍우정,김군순,조영석,김도희,채수흥,구본정,송민호,노흥규,김영건 충남대학교 의과대학 지역사회의학연구소 2001 충남의대잡지 Vol.28 No.1

Background : ICAM-1 act as one of major adhesion molecules in the atherosclerotic lesion. ICAM-1 expression is mainly regulated at the level of transcription and depend on IFN-γ signal transduction pathway in which the STAT1 transcrption factor is a critical intermediate. IFN-γreceptor not only initiates tyrosine 701 phosphorylation of STAT1 by Jak1 and Jak2, but also phosphorylates serine 727 through the activation of Raf-1/MAP kinases. HMG-CoA reductase inhibitors have anti-atherosclertic effects, beyond normalization of hypercholesterolemia, by directly acting on endothelial cells, macrophages and vascular smooth muscle cells. HMG-CoA reductase inhibitors suppress the synthesis of isoprenoid intermediates such as geranylgeranyl-pyrophosphate or farnesylpyrophosphate. These effects results inhibitors suppress the synthesis of isoprenoid intermediates such as geranylgeranyl-pyrophosphate or farnesylpyrophosphate. These effects results inhibition posttranslational farnesylation and geranyl-geranylation processing of small GTP-binding preoteins and inhibition of normal signaling activities. Method : We made several 5'-deletion constructs of rat ICAM-1 promoter and analyzed the promoter activities by measuring the luciferase activity after transfection into ECV304 cells and smooth muscle cells. We checked the level of total and phosphorylated STAT1 protein by immunoblot analysis using specific antibodies. Results : Lovastatin inhibits IFN-γ-induced ICAM-1 gene expression in the ECV304cell. The cells pretreated with PD98059, MEKK inhibitor showed significantly low ICAM-1 RNA induction with IFN-γ stimulatio. IFN-γ induced phosphorylation of tyrosine 701 was not significantly changed by the pretreatment of lovastatin. But lovastatin suppresses IFN-γ-induced phosphorylation of ERK1/ERK2 which are responsible for the seine 727 phosphorylation in STAT1. Conclusion : We showed that HMG-CoA reductase inhibitors, lovastatin, suppresses IFN-γ mediated ICAM-1 gene expression through the inhibition of transcription. HMG-CoA reductase inhibitor suppresses IFN-γ-induced phosphorylation of serine 727 in STAT1 through the modulation of MAP kinases.