• 말소리와 음성과학
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• 제9권1호
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• pp.49-53
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• 2017

Formant frequencies depend on the position of tongue, the shape of lips, and larynx. In the auditory system, the external ear canal is an open-end resonator, which can modify the voice characteristics. This study investigates the effect of the real ear on formant frequencies. Fifteen subjects ranging from 22 to 30 years of age participated in the study. This study employed three corner vowels: the low central vowel /a/, the high front vowel /i/, and the high back vowel /u/. For this study, the voice of a well-educated undergraduate who majored in speech-language pathology, was recorded with a high performance condenser microphone placed in the upper pinna and in the ear canal. Paired t-test showed that there were significant difference in the formant frequencies of F1, F2, F3, and F4 between the free field and the real ear. For /a/, all formant frequencies decreased significantly in the real ear. For /i/, F2 increased and F3 and F4 decreased. For /u/, F1 and F2 increased, but F3 and F4 decreased. It seems that these voice modifications in the real ear contribute to interpreting voice quality and understanding speech, timbre, and individual characteristics, which are influenced by the shape of the outer ear and external ear canal in such a way that formant frequencies become centralized in the vowel space.

• 국제초고층학회논문집
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• 제2권3호
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• pp.229-244
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• 2013

Twenty six pressure models of high rise buildings with various cross-sections including twisted models were tested in a boundary layer wind tunnel. The cross-sections were triangular, square, pentagon, hexagon, octagon, dodecagon, circular, and clover. This study investigates variations in peak pressures, and effects of various cross-sections and twist angles on peak pressures. To study the effects of various configurations and twist angles on peak pressures in detail, maximum positive and minimum negative peak pressures at each measurement point of the building for all wind directions are presented and discussed. The results show that peak pressures greatly depend on building cross-section and twist angle.

• Wind and Structures
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• 제11권1호
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• pp.1-18
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• 2008

Interference effects in five square tall buildings arranged in an L- or T-shaped pattern are investigated in the wind tunnel. Mean and fluctuating shear forces, overturning moments and torsional moment are measured on each building with a force balance mounted at its base. Results are obtained at two values of clear separation between adjacent buildings, at half and a quarter building breadth. It is found that strong interference effect exists on all member buildings, resulting in significant modifications of wind loads as compared with the isolated single building case. Sheltering effect is observed on wind loads acting along the direction of an arm of the "L" or "T" on the inner buildings. However, increase in these wind loads from the isolated single building case is found on the most upwind edge building in the arm when wind blows at a slight oblique angle to the arm. The corner formed by two arms of buildings results in some wind catchment effect leading to increased wind pressure on windward building faces. Interesting interference phenomena such as negative drag force are reported. Interference effects on wind load fluctuations, load spectra and dynamic building responses are also studied and discussed.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.235-243
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• 2002

Ni-base superalloys are used extensively in industry, both in aeroengines and land based turbines. About 60% by weight of most modern gas turbine engine structural components are made of Ni-base superalloys. To satisfy practical demands, the efficiency of gas turbine engines has been steadily and systematically increased by design modifications to handle higher turbine inlet or firing temperatures. However, the increase in operating temperatures has lead to a decrease in the life of components and increase in costs of replacement. Moreover, around 80% of the large frame size industrial/utility gas turbines operating in the world today were installed in the mid-sixties to early seventies and are now 25 to 30 years old. Consequently, there are greater opportunities now to repair and refurbish the older models. Basically, there are two major factors influencing the weldability of the cast alloys: strain-age cracking and liquation cracking. Susceptibility to strain-age cracking is due to the total Ti plus AI content of the alloy; Liquation cracking is due either to the presence of low melting constituents or constitutional liquation of constituents. Though Rene 41 superalloy has 4.5wt.% total Ti and Al content and falls just below the safe limit proposed by Prager et al., controlled grain size and special heat treatments are needed to obtain crack-free welds. Varying heat treatments and filler materials were used in a laboratory study, then the actual welding of service parts was carried out to verity the possibility of crack-tree weld of components fabricated from Rene 41 superalloy. The microstructural observations indicated that there were two kinds of carbides in the FCC matrix. MC carbides were located along the grain boundaries, while M$_{23}$C$_{6}$ carbide was located both inter and intra granularly. Two kinds of filler materials, Rene 41 and Hastelloy X were used to gas tungsten arc weld a patch into the sheet metal, along with varying pre-weld heat treatments. The microstructure, hardness and tensile tests were determined. The service distressed parts were categorized into three classes: with large cracks, with medium cracks and with small or no visible cracks. No significant difference in microstructure among the specimens was observed. Specimens were cut from the corner and the straight edge of the patch repair, away from the corner. The only cracks present were found to be associated with inadequate surface preparation to remove oxidation. Guidelines for oxide removal and the welding procedures developed in the research enabled crack-free welds to be produced.d.

• 대한기계학회논문집B
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• 제38권4호
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• pp.365-371
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• 2014

본 연구에서는 4단 화격자로 구성된 목재 펠릿 보일러의 연소실에 대하여 수치해석을 수행하였다. 목재 펠릿의 화염은 화격자에서 연소실 출구까지 신장되는 데 이 현상이 균질 반응에 기반한 수치해석 기법으로 잘 예측되었다. 수치해석으로 구한 유동장을 보면 연소실 상류에서 출구쪽으로 강한 재순환 유동이 형성되는데 이 유동을 따라 화염이 신장된다. 이와 같은 유동 및 연소 형태는 부분부하 조건에 대하여 수치해석을 수행하였을 때도 유지되었다. 따라서 연소실의 체적을 변경하는 것보다 연소실의 구조를 변경하는 것이 연소 효율을 개선하는 데 도움이 될 것으로 보인다. 본 연구에서는 수치해석 결과를 바탕으로 연소 효율을 높이기 위하여 연소실 출구 위치 변경하거나 화격자 개수를 늘이는 방안 또는 격벽과 같은 내부 구조물을 설치하는 방안을 제안하였다.

• 한국초등과학교육학회지:초등과학교육
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• 제43권2호
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• pp.301-321
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• 2024

이 연구의 목적은 과학교사에게 오랫동안 요청된 이원화된 업무, 즉 '과학교과수업'과 '교과 외 과학 관련 행사'의 역사적 연원을 밝히는 것이다. 1970년대에는 기초과학 중심의 제3차 교육과정과 기술교육 중심의 과학화운동 사이의 긴장 속에서 국민학교 과학교육이 이루어졌다. 문교부는 과학화운동이 도입되기 전부터 오랫동안 국제기구의 지원을 받아서 탐구 중심의 기초과학교육 정책을 추진하였고, 특히 1973년 제3차 교육과정을 통해서 이를 실현하려고 하였다. 그러던 중 1973년에 '전 국민의 과학화운동'이 정권 차원에서 갑자기 추진되었다. 문교부로서는 갑작스러운 유신정권의 요구를 이미 진행 중이던 제3차 교육과정 속으로 편입해야 하는 상황에 처하게 된 것이다. 이처럼 두 가지 정책에서 비롯된 두 가지 요구가 공존하였기 때문에 이후 초등학교 과학교육 활동은 과학교과수업과 교과 외 과학 관련 행사로 이원화되어 실행되었다. 과학화운동은 교육과정 자체에 직접적인 영향을 미치지는 못하였지만, 학교 현장의 인사조직, 활동 공간, 평가 제도에 변화를 주었다. 국민학교에 과학화운동이라는 거대 프로그램이 도입되면서, 학교 내부의 인사조직을 변화시켜서 '과학주임교사제'가 새롭게 만들어졌고, '과학코너'라는 새로운 공간이 확보되었으며, '과학장제'라는 새로운 제도가 보급된 것이다. 이처럼 과학화운동 자체는 초등교육에 갑작스럽게 도입되었으나 결과적으로는 제3차 교육과정이 목표로 삼았던 탐구 중심 과학교육이 실천되는 데 어느 정도 기여했던 듯하다. 이는 역설적으로 과학화운동의 여파가 일선 교육청과 학교의 '교과 외' 자율적 활동으로 흡수된 것에 기인했다. 과학화운동 자체는 특정 시기의 정부 주도 정책이었지만, 다양한 과학교육종사자들이 오래 준비해 온 제3차 교육과정의 틀을 유지하면서도 긴급한 정부의 요청에 응답하는 방식이 교과 수업과 교과외 과학 활동으로 이원화된 것이었다. 이처럼 1970년대 과학교육현장에서 과학교육종사자들이 능동적으로 대응한 과정을 살펴봄으로써 과학교육계가 현재의 급변하는 환경에 대응할 수 있는 실마리를 얻을 수 있을 것이다.