• International Journal of Fluid Machinery and Systems
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• 제4권1호
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• pp.1-13
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• 2011

In operating a turbomachine at off-design conditions various instabilities caused by anomalous flow phenomena occur and sometimes lead to the damage of a turbomachine. In order to avoid these phenomena various devices characteristic to each phenomenon have been developed, however they make turbomachines large-sized and cause efficiency drop. The present author has developed a very simple and innovative device, termed "J-groove," of suppressing various anomalous flow phenomena commonly by controlling the angular momentum of the main flow. It has been revealed that J-groove makes an operation of a turbomachine stable in all flow range, causes little efficiency drop, and can be easily applied to an existing machine. Here is reviewed totally the results of suppressing various anomalous flow phenomena in turbomachines.

• International Journal of Aeronautical and Space Sciences
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• 제15권3호
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• pp.320-334
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• 2014

Over the last two decades, numerous experimental and numerical efforts have examined physical phenomena in plasma discharge devices. The physical mechanisms that govern the anomalous electron diffusion from the cathode to the anode in the Hall Effect Thruster (HET) are not fully understood. This work used 1-D numerical method to improve our understanding and gain insight into the effect of the anomalous electron diffusion in the HET. To this end, numerical solutions are compared with various experimental HET performance measurements and the effects of anomalous electron diffusion are analyzed. The relationships between the anomalous electron diffusion and important parameters of the HET are also studied quantitatively. The work identifies the cathode mass flow rate fraction, radial magnetic field distribution, and discharge voltage as significant factors that affect anomalous electron diffusion. Additionally, the study demonstrates a computational process to determine the radial magnetic field distribution required to achieve specific thruster performance goals.

• 한국지구과학회지
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• 제23권1호
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• pp.112-118
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• 2002

The anomalous behaviour of animals prior to a large earthquake has been frequently reported from many places throughout the world since ancient times. This study is to experimentally testify what relations exist between the anomalous animal behavior and electric field effect, which is reported due to the piezo-electric effects in a basement rock before earthquake occurrences. We investigated the electric field effects on behaviors of two kinds of rats and birds. Rats show more sensitive anomalous behavior than birds. Even though the current applied to the experimental birds and rats is just a few ${\mu}$A, they show various abnormal behaviors. The anomalous animal behaviors under the small ground electric field may have some relations to the actual phenomena before great earthquake.

• E2M - 전기 전자와 첨단 소재
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• 제7권2호
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• pp.138-144
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• 1994

Electrical conduction phenomena of $C_{22}$-quinolium(TCNQ) Langmuir- Blodgett(LB) films are reported through a study of current-voltage(I-V) characteristics along a perpendicular direction. The I-V characteristics were investigated by applying a step or a pulse voltage to the specimen as well as changing temperatures in the range of 20-250[.deg. C] It show an ohmic behavior in low-electric field, and a nonohmic behavior in high-electric field. This nonohmic behavior has been interpreted in terms of a conduction mechanism of space-charge limited current and Schottky effect. When the electric field is near the strength of 10$_{6}$ V/cm, there occur anomalous phenomena similar to breakdown. When step or pulse voltage is applied, the breakdown voltage shifts to the higher one as the step or pulse time width becomes shorter. To see the influence of temperature, current was measured as a function of temperature under the several bias voltages, which are lower than that of breakdown. It shows that the current increases to about 103 times near 60-70[.deg. C], and remains constant for a while up to around 150[.deg. C] and then suddenly drops. We have also performed a DSC(differential scanning calorimetry) measurement with $C_{22}$-quinolium(TCNQ) powder in the range of 30-300[.deg. C]. These results imply that the anomalous phenomena occuring in the high electric field are caused by the electrical and internal thermal effect such as a joule heating.ating.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2001년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 2001
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• pp.57-64
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• 2001

There are some previous reports that some animals such as rats and birds move in a large group and act abnormally to avoid the large earthquake. This study is to experimentally testify what relations exist between the anomalous animal behavior and electric field effect, which is reported due to the piezoelectric effects in a basement rock before earthquake occurrences. When electric field is applied to the whole bottom of the cage, they show nervous behaviors such as grooming, washing their faces, standing on legs or running around in panic to avoid the electric field. When more strong electric field is applied, they jump with shrieking and mount on the electric line. The rat shows more sensitive anomalous behavior than the bird. Even though the current to the experimental birds and rats is just a few $\mu$A, they react in various ways. The anomalous animal behaviors under the small ground electric field may have some relations to the actual phenomena before great earthquake. This kind of study is quite worthy for the understanding of earthquake precursors.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1998년도 추계종합학술대회 논문집
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• pp.553-556
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• 1998

The 1-D numerical model and its extraction methodology are suggested and these simulation results for the S-swing as a function of back-gate voltage are well matched with the measured. S-swing characteristics are analyzed using PD-SOI devices with enough deeper regions up to substrates. The PD-SOI device doesn't have to be short channel to see the anomalous subthreshold phenomena based on the back gate bias. This results recommend to operate better SOI device performances by controlling the back gate voltages. So SOI performances will be much optimistic with proper control of the back-gate voltage for the already- proven- high- performance (APHP) SOI VLSIs.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1998년도 추계학술대회 논문집
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• pp.13-16
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• 1998

An anomalous current characteristics which show the superposition of a low current level and high current level at the subthreshold region when SONOSFETs are in memory states were investigated. We have assumed this phenomena were resulted from the effect of parasitic transistors by LOCOS isolation and were modeled to a parallel equivalent circuit of one memory transistor and two parasitic transistors. Theoretical curves are well fitted in measured log I$_{D}$-V$_{G}$ curves independent of channel width of memory devices. The difference between low current level and high current level is apparently decreased with decrease of channel width of devices because parasitic devices dominantly contribute to the current conduction with decrease of channel width of memory devices. As a result, we concluded that the LOCOS isolation has to selectively adopt in the design of process for charge-trap type NVSM.VSM.

• 한국과학교육학회지
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• 제35권3호
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• pp.419-429
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• 2015

이 연구에서는 과학적 논변활동에서 드러나는 학생들의 인식론적 프레이밍을 확인하고, 소집단 구성원들의 프레이밍 사이의 상호작용이 논변활동에 어떠한 영향을 미치는지를 탐구하였다. 21명의 과학영재 학생들이 세 명 혹은 네 명이 한 집단을 이루어 연구에 참여하였고 학생들이 광합성 속도에 대한 탐구 데이터를 해석하는 논의 과정이 분석되었다. 학생들의 활동은 소집단별로 녹화되었고 학생들의 담화 전사본과 행동이 분석 자료로 활용되었다. 탐구 과정에서 변칙 사례에 반응하는 학생들의 발화 및 행동을 분석하여 그들의 인식론적 프레이밍을 확인하였고 주장에 대한 정당화의 근거와 소집단 논변활동 수준이 분석되었다. 연구 결과, 학생들은 탐구에 대해 '현상 이해'와 '교실 게임'이라는 두 가지 방식의 프레이밍을 보였다. 구성원들이 '현상 이해'의 프레이밍을 보인 경우에는 다른 구성원들에게 데이터의 신뢰성과 타당성 점검을 통해 변칙 사례의 원인을 정당화할 것을 요구하였으며, 이는 높은 수준의 논변활동으로 나타났다. 반대로 구성원들이 '교실 게임'에 해당하는 프레이밍을 보인 경우에는 변칙 사례를 설명할 필요성을 인식하지 않았고, 단순한 경험적 근거만 고려함으로써 낮은 수준의 논변활동을 보였다. 논의 전반에 걸쳐 구성원들의 프레이밍이 일치하지 않는 경우에는 집단 내의 감정적 갈등이 유발되어 깊은 논의가 이루어지지 않았다. 한편, 이러한 논의 과정에서 학생들의 프레이밍 전환이 관찰되었는데, 여기에는 집단의 리더가 큰 영향을 끼친 것으로 나타났다. 본 연구는 과학 교실에서 과학적 논변에 요구되는 생산적인 프레이밍 형성을 위한 기초 정보를 제공할 것으로 기대된다.

• 한국과학교육학회지
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• 제29권8호
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• pp.886-897
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• 2009

학생들의 물리 오개념을 과학적으로 변화시키기 위한 학습전략 중 하나는 학생들에게 인지갈등을 유발시키는 것이다. 인지갈등전략의 핵심적 방법은 학생에게 불일치 상황을 제시하는 것이다. 그런데 학생들이 불일치 현상을 대면하기 전에 자신의 개념을 탐색하고 진술하는 단계에서도 인지갈등을 경험한다는 사례가 보고된 바가 있었다. 이 연구에서는 불일치 현상을 대면하기 전에 유발되는 인지갈등정도를 조사하고 그 인지갈등이 불일치 현상 대면 후에 유발되는 인지갈등과 개념변화에 어떠한 영향을 미치는지 알아보고자 하였다. 이 연구는 광원과 무중력 개념을 소재로 한 교실 수업으로 진행하였다. 연구대상은 부산 소재 중학교 2개교의 학생들이었다. 수업과정에서 사전개념, 대면 전과 후 갈등정도 및 사후개념을 조사하였다. 수업 3주후에는 지연사후개념을 검사하였다. 그 결과 불일치 현상 대면 전의 인지갈등 평균은 대면 후의 인지갈등 평균과 차이가 없었으며 두 인지갈등 사이에는 정적상관이 있었다. 불일치 현상 대면 전과 후의 인지갈등정도가 모두 개념변화정도와 정적상관이 있었는데, 두 인지갈등 중 개념변화를 주도적으로 설명하는 것은 불일치 현상 대면 전의 인지갈등정도였다.

• 한국전산유체공학회지
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• 제9권4호
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• pp.1-6
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• 2004

This study investigates the transition of flows in a natural convection problem with periodic wall temperatures of the form, T/sub L/=T₁＋δ Tsinκχ and T/sub L/=T₂＋δ Tsinκχ .The fluid considered is air with P/sub γ/=0.7. In the conduction-dominated regime with a small Rayleigh number, two large cells are formed over one wave length, for all wave numbers. When k≤1.8, the flow becomes unstable with increase of the Rayleigh number, and multicellular convection occurs above a critical Rayleigh number. The flow patterns are classified by the number of eddies over one wave length, and several kinds of transition phenomena, such as 2→3→4, 4→3→2, and 2→4 eddy flow, occur with increase( or decrease) of the Rayleigh number. Dual solutions are found above a critical Rayleigh number, and an anomalous bifurcation is observed.