• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.97-103
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• 2001

The effects of the electrohydrodynamic (EHD) flow and turbulent diffusion on the collection efficiency of a model ESP composed of the plates with a cavity were studied through numerical computation. The electric field and ion space charge density were calculated by the Poisson equation of the electrical potential and the current continuity equation. The EHD flow field was solved by the continuity and momentum equations of the gas phase including the electrical body force induced by the movement of ions under the electric field. The RNG $k-{\varepsilon}$ model was used to analyze the turbulent flow. The particle concentration distribution was calculated from the convective diffusion equation of the particle phase. As the ion space charge increased, the particulate collection efficiency increased because the electrical potential increased over the entire domain in the ESP. The collection efficiency decreased and then increased, i.e. had a minimum value, as the EHD circulating flow became stronger when the electrical migration velocity of the charged particle was low. However, the collection efficiency decreased with the stronger EHD flow when the electrical migration of the particle was higher relatively. The collection efficiency of the model ESP increased as the turbulent diffusivity of the particle increased when the electrical migration velocity of the particle was low. However, the collection efficiency decreased for increasing the turbulent diffusivity when the electrical migration of the particle was higher relatively.

• 한국진공학회지
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• 제17권6호
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• pp.487-494
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• 2008

준 2차원 수치적 모델을 사용하여 침-평판(point-plane)형의 전극 사이에 있는 중간 압력 질소의 방전에 대한 시뮬레이션을 수행하였다. 이 모델에서는 전자와 이온에 대한 연속방정식을 풀어 시. 공간적으로 변하는 전하분포를 계산하고, 공간 전하 분포의 변화에 따라 결정되는 전기장은 푸아송 방정식을 풀어 얻는다. 연속 방정식은 FCT (Flux-corrected transport) 알고리즘과 FEM (Finite Element Method) 방법을 적용하여 수치적으로 다루어 졌다. 50Torr 압력에서의 질소 방전에 대한 시뮬레이션 결과는 중간 압력 질소 방전의 물리적 특성에 관한 상세한 이해를 제공한다. 또 계산 결과와 실험 결과[1]와의 비교는 정성적으로 잘 일치하는 것을 보여 준다.

• Journal of Electrical Engineering and Technology
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• 제11권6호
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• pp.1735-1743
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• 2016

Insulation of valve-side windings in converter transformer withstands pulsating voltages, which will produce more serious insulation problems. In this paper, the electric breakdown experiments of oil-paper insulation specimens were executed at pulsating voltages and different temperatures. Experiment and analysis results showed that the breakdown voltage decreased with increasing temperature under pulsating voltage. The influence of temperature proves to be more significant once the temperature exceeds a limitation threshold. A fitting formula between breakdown voltage and the temperature was reported. Finally, in order to clearly understand the breakdown properties under pulsating voltage, the electric field distribution and space charge behavior under pulsating voltage at different temperature were discussed.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2004년도 Asia Display / IMID 04
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• pp.927-930
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• 2004

We report on a new type of a flat and thin display with a secondary emission electron source. In this display device electrons are multiplied between two secondary emission plates under a high frequency electric field. This principle has a few important advantages over a field emission display: the emission comes from flat plates, which reduces the life-time problems of ion bombardment of field emitter tips. Furthermore, the electron emission is space charge limited which gives a uniform electron distribution. The electrons are extracted from the source and accelerated to a phosphor screen to generate light. Gray levels are made by pulse width modulation.

• 대한전기학회논문지
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• 제35권2호
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• pp.67-76
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• 1986

It is observed that an appreciable short-circuit current (Is) flows by the time variation of temperature without applying external field in M1(metal)-P(polymer)-M2(metal)system. In M1-P-M2(A1) system, Is flows in the direction from the electrode(A1) having a lower workfunction to the counter electrode(M1) during heating and its magnitude increases as the thickness of polymer is decreased and as the heating rate is raised. The sign of Is is reversed in lower temperature region (under glass transition temperature) when the direction of temerature variation is changed during heating and cooling. From these experimental results, we can sugest that Is flows in the external short-circuit during the space charge distribution formed around both interfacial surfaces (M1-P and P-M2) is continuously maintained in the non-equilibrium state but not in equilibrium state.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 C
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• pp.1367-1369
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• 1997

본 논문에서는 PET/PET 필름과 인터페이스를 갖는 PET/SEMI/PET필름에서의 전기 전도도와 공간전하분포를 고찰하였다. 반도전층을 가지고 있는 PET/SEMI/PET 필름의 전도전류는 PET/PET에 비하여 높았으며 특히 전압 인가후 순간적인 전류가 급격하게 소멸하였다. 또한 PET/SEMI/PET 필름의 공간전하 분포는 PET/PET 필름에 비해 높은 전하 형성을 보였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집
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• pp.314-317
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• 2002

Since the early work of Tersoff and Hamann on the theory of the scanning tunneling microscope (STM), many theoretical approaches have been developed in order to gain further physical insight into the real space image that this technique provides. In this Paper, the STM image of Carbon nanotubes (CNT's) was calculated through the theoretical study. The optimized structure of CNT's was simulated using Brenner's hydrocarbon potential. The structure of simulation is (5. 5) armchair CNT and (10. 0) zigzag CNT. Also we have used that the extended Huckel tight binding (EHTB) theory already provides a fairly good qualitative description of the main processes that control the final contrast in the STM image. we found that the shape of the calculated images is hardly dependent on the exact electronic charge distribution at the surface. The STM images are not too sensitive to the precise electronic structure but, rather, they reflect its qualitative features. As a result of the simulation, The STM images of CNT's and the electronic density distribution were investigated. It found that the EHTB theory is appropriate for STM image calculation and that the STM images are in agreement with the result of Experiment.

• Journal of Magnetics
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• 제19권2호
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• pp.126-129
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• 2014

We report the crystallographic and magnetic properties of $Ni_{0.3}Fe_{0.7}Ga_2S_4$ by means of X-ray diffractometer (XRD), a superconducting quantum interference device (SQUID) magnetometer, and a M$\ddot{o}$ssbauer spectroscopy. In particular, $Ni_{0.3}Fe_{0.7}Ga_2S_4$ was studied by M$\ddot{o}$ssbauer analysis for evidence of spin reorientation. The chalcogenide material $Ni_{0.3}Fe_{0.7}Ga_2S_4$ was fabricated by a direct reaction method. XRD analysis confirmed that $Ni_{0.3}Fe_{0.7}Ga_2S_4$ has a 2-dimension (2-D) triangular lattice structure, with space group P-3m1. The M$\ddot{o}$ssbauer spectra of $Ni_{0.3}Fe_{0.7}Ga_2S_4$ at spectra at various temperatures from 4.2 to 300 K showed that the spectrum at 4.2 K has a severely distorted 8-line shape, as spin liquid. Electric quadrupole splitting, $E_Q$ has anomalous two-points of temperature dependence of $E_Q$ curve as freezing temperature, $T_f=11K$, and N$\acute{e}$el temperature, $T_N=26K$. This suggests that there appears to be a slowly-fluctuating "spin gel" state between $T_f$ and $T_N$, caused by non-paramagnetic spin state below $T_N$. This comes from charge re-distribution due to spin-orientation above $T_f$, and $T_N$, due to the changing $E_Q$ at various temperatures. Isomer shift value ($0.7mm/s{\leq}{\delta}{\leq}0.9mm/s$) shows that the charge states are ferrous ($Fe^{2+}$), for all temperature range. The Debye temperature for the octahedral site was found to be ${\Theta}_D=260K$.

• 한국터널지하공간학회 논문집
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• 제5권4호
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• pp.337-348
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• 2003

밀장전한 암반 발파공에서 화약 폭발시 발생하는 고압의 폭굉압력 전파메카니즘을 충격파 이론을 적용하여 규명하고 전달된 발파압력 산정식을 유도하였다. 유도된 발파압력 산정식은 폭굉파속도, 단열지수, 화약밀도, Hugoniot 상수, 암반밀도의 함수였다. 에멀젼 화약과 서울 화강암의 특성시험을 시행하여 각 특성치의 확률분포를 정의하고 발파압력 산정식에 적용하여 발파압력의 확률분포를 산출하였다. 화약 특성치와 암반 특성치의 확률분포는 정규분포를 나타냈으며 따라서 발파압력의 확률분포도 정규분포로 추정되었다. 발파압력에 대한 매개변수분석을 시행한 결과 폭굉파속도가 발파압력에 가장 크게 영향을 미쳤다. 또한 이런 특성치의 불확실성이 발파압력의 불확실성에 미치는 영향을 분석하였다. 분석결과 암반특성치의 불확실성이 화약특성치보다 더 크게 영향을 미쳤다. 비록 매개변수분석에서 폭굉파속도가 발파압력에 가장 크게 영향을 미치는 요소이지만 암반특성치의 불확실성이 폭굉파속도의 불확실성보다 더 크기 때문에 발파압력은 후자보다 전자에 의해서 더 크게 영향을 받는다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 춘계학술대회 논문집
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• pp.27-27
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• 2010

The exact partial discharge pulse should be measured in order to estimate the discharge source in the solid insulation and diagnose the degree of deterioration. Partial discharges generated in the insulation occur in the internal voids or at the edge of the insulation, have unique characteristics following the type and location. When external voltage is applied, Partial discharges occurred in the restrictively presented voids increase the quantity of electrical charge at the discharge onset voltage. The discharge characteristics have remained constant as space is filled by the impurity such as a compound of gases accompanied with discharge. In this study, How to design the insulation about the problems of the built-in diagnostics in the transformer is discussed by the interpretation of electric field.