• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1649-1654
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• 2004

The near field structures of an under-expanded, dual, coaxial, jets issuing from the coaxial nozzles with four different geometries are visualized by using a shadowgraph optical method. Experiments are conducted to investigate the effects of the nozzle-lip thickness, secondary stream thickness, the nozzle pressure ratio and the secondary swirl stream on the characteristics of under-expanded jets. The results show that the presence of secondary annular swirling stream causes the Mach disk to move further downstream and increases its diameter, which decreases with a decrease in the nozzle-lip thickness. The secondary stream thickness has an influence on the location of an annular shock wave.

• 대한기계학회논문집B
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• 제24권2호
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• pp.251-259
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• 2000

The ionic wind formed in a nonuniform electric field has been recognized to have a significant effect on particle collection in an electrostatic precipitator(ESP). Under normal operating conditions the effect of ionic wind is not pronounced. However, as the flow velocity becomes smaller, the ionic wind becomes pronounced and induces secondary flow, which has a significant influence on the flow field and the particle collecting efficiency. In this paper, experiments for investigating the effect of secondary flow on collection efficiencies were carried out by changing the flow velocities in 0.2-0.7m/s and the applied voltages in 9-11kV/cm. The particle size distributions and concentrations are measured by DMA and CNC. To analyze the experimental results, numerical analysis of electric filed in ESP was carried out. It shows that particle collection is influenced by two independent dimensionless numbers, $Re_{ehd}\;and\;Re_{flow}$ not by $N_{ehd}$ alone. When $Re_{flow}$, decreases for constant $Re_{ehd}$, the secondary flow prohibits the particle collection. But when $Re_{ehd}$ increases for constant $Re_{flow}$, it enhances the particle collection by driving the particles into the collection region.

• 공학교육연구
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• 제16권5호
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• pp.9-17
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• 2013

The purpose of this study is to analyze elementary and secondary school teachers' recognition about engineering education in elementary and secondary school. For this, we surveyed elementary and secondary school teachers. The result of this study is as follow. First, most teachers perceived that engineering positively affect national competitiveness and development. They also found that engineering education helps student to select natural science and engineering field career. Moreover, they perceived that engineering contents are not applied in elementary and secondary schools curriculums, hence it does not stimulate interest in engineering. Therefore, they perceived that if engineering education contents are systematically applied in formal curriculum, it will have a positive effect on current engineering education. Second, most teachers perceived that roles of engineering education are to make students learn creative design and problem solving process and inform about the engineering field career. They perceived that the best grade to start engineering education is 4~6 grade in elementary school and the best way to apply engineering education is through distributing engineering education contents to related subjects. They also perceived that technology subject has the most relation to engineering education and science subjects; mathematics subject follow after.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.21-24
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• 2002

In this paper, induced voltages of the secondary conductors of a linear induction motor(LIM) with cage-type secondary are measured and analyzed when the LIM is fed by PWM inverter. The attenuation constant of the induced voltage of the secondary conductors near entry and exit zones of the the travelling magnetic field are determined from the experiment results.

• 대한지구과학교육학회지
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• 제15권1호
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• pp.27-46
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• 2022

이 연구는 초등 및 중등 지구과학 예비교사들을 대상으로 생소한 경험 공간(Novelty Space)에 대한 인식 조사를 목적으로 하였다. 이를 위해 A 교육대학교의 초등 예비교사 38명과 B 대학교 지구과학교육과에 재학 중인 31명의 중등 지구과학 예비교사들이 설문에 참여하였다. 또한 연구 참여자 중 추가적인 면담 참여에 동의한 초등 예비교사 3명과 중등 지구과학 예비교사 9명, 총 12명을 대상으로 비대면 면담을 실시하였다. 생소한 경험 공간에 대한 요소를 사전 지식(인지), 사전야외학습 경험(심리), 야외조사지역과의 친숙도(지리)에 덧붙여, 사회적인(social) 요소과 기술적인(technical) 요소를 추가하였다. 초등과 중등, 학년를 기준으로 분류하였을 때 생소한 경험 공간의 요소에 대해 인지적 영역, 심리적 영역, 지리적 영역, 사회적 영역에서 통계적으로 유의미한 차이를 보였다. 통계적인 차이는 야외학습과 관련된 경험이나 자본이 중등 지구과학 예비교사들이 초등 예비교사들보다 더 많은 것으로부터 비롯되었을지도 모른다고 해석하였다. 반-구조화된 면담에서 초등 예비교사 및 중등 지구과학 예비교사 모두 가상야외지질학습의 가치나 필요성을 강조하였으며 특히 기술적인 영역에서의 역량을 강조하였다. 이 연구는 초등 및 중등 지구과학 예비교사들을 대상으로 야외지질학습을 실행하기 위한 생소한 경험 공간에 대해 현재의 교육 맥락적인 상황을 고려하여 새롭게 정의할 필요성을 제안할 뿐만 아니라 생소한 경험 공간 요소들을 구체화하였다는 점에서 학술적인 의의를 갖는다.

• Journal of Advanced Marine Engineering and Technology
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• 제24권5호
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• pp.103-110
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• 2000

A two phase compound jet, which mixes pulverized solid particles with the air in the test section, is experimentally analyzed in this study. Two phase flow is jetted 10 degree upward in the primary jet, while the secondary jet utilizes the air only. The height difference between the primary and secondary central axises is 32.5mm. The velocity vector field, concentration field, and turbulent properties of solid particles are measured by using 3-Dimensional Particles Dynamics Analyzer. When the jet angle of the secondary jet goes into effect, the solid particle recirculation zone becomes larger. Also, solid particle concentration becomes more dense due to a velocity decrement of particles.

• 대한방사선기술학회지:방사선기술과학
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• 제3권1호
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• pp.73-80
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• 1980

We studied about dosimetry according to the X-ray tube voltage, radiation field object thickness and obtained results as follow. 1. Secondary ray involing rate in the penetrated radiation increased proportion to the tube voltage, but its rate is more larger at the small radiation fields. than large fields. 2. Secondary ray involving rate in the penetrated radiation increased at thick object and large exposure fields. But saturated phenomenon appeared at limited field. 3. Secondary involving rate of acryl phantom is more top place than water, paraffin and aluminum phantom.

• 한국추진공학회지
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• 제11권2호
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• pp.47-53
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• 2007

본 논문에서는 초음속유동장 내에 분사된 2차 분사유동과 주유동의 상호작용에 의한 2차 분사노즐 주변에서의 열전달 현상을 관찰하였다. 벽면에는 등열유속조건을 주었다. 제트 자유유동간 운동량비(Jet to Freestream Momentum Ratio, J)에 따라 2차 분사를 초음속 유동장에 분사시켰으며, 적외선 카메라를 이용하여 2차 분사노즐 주변 벽면온도를 측정하였고, 이를 통하여 대류 열전달계수를 제시하였다.

• 수산해양교육연구
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• 제26권5호
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• pp.1096-1107
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• 2014

The purpose of this study was to investigate teachers' recognition on field practice and effectiveness of creativity and character education. This study used post tests to examine the effects of teacher training for creativity and character education on 451 teachers. The results were as follows. Firstly, the average in satisfaction of teacher training for creativity and character education was 4.65 for elementary teachers and 4.35 for secondary teachers in summer, and 4.55 for elementary teachers and 4.42 for secondary teachers in winter. Secondly, effectiveness of teacher training on creativity and character education was showed highly as more than 4.0 and was higher in winter than in summer. Thirdly, in the case of field practice and effectiveness of teacher training for creativity and character education, the average of elementary teachers(3,66) was higher in respect of educational environment than that of secondary teachers(3.20) and the averages of elementary teachers and secondary teachers were 3.85 and 3.42 in respect of subject activity, respectively. In practising creativity and character education, it was analyzed that both elementary(ave. 3.89) and secondary(ave. 3.84) teachers went through some difficulties for curriculum reconstruction, development of instructional model, program development, and human and physical supports.

• Radiation Oncology Journal
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• 제35권1호
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• pp.78-89
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• 2017

Purpose: To determine the optimal radiotherapy technique for gastric mucosa-associated lymphoid tissue lymphoma (MALToma), we compared the dosimetric parameters and the risk of solid secondary cancer from scattered doses among anterior-posterior/ posterior-anterior parallel-opposed fields (AP/PA), anterior, posterior, right, and left lateral fields (4_field), 3-dimensional conformal radiotherapy (3D-CRT) using noncoplanar beams, and intensity-modulated radiotherapy composed of 7 coplanar beams (IMRT_co) and 7 coplanar and noncoplanar beams (IMRT_non). Materials and Methods: We retrospectively generated 5 planning techniques for 5 patients with gastric MALToma. Homogeneity index (HI), conformity index (CI), and mean doses of the kidney and liver were calculated from the dose-volume histograms. Applied the Biological Effects of Ionizing Radiation VII report to scattered doses, the lifetime attributable risk (LAR) was calculated to estimate the risk of solid secondary cancer. Results: The best value of CI was obtained with IMRT, although the HI varied among patients. The mean kidney dose was the highest with AP/PA, followed by 4_field, 3D-CRT, IMRT_co, and IMRT_non. On the other hand, the mean liver dose was the highest with 4_field and the lowest with AP/PA. Compared with 4_field, the LAR for 3D-CRT decreased except the lungs, and the LAR for IMRT_co and IMRT_non increased except the lungs. However, the absolute differences were much lower than <1%. Conclusion: Tailored RT techniques seem to be beneficial because it could achieve adjacent organ sparing with very small and clinically irrelevant increase of secondary solid cancer risk compared to the conventional techniques.