• 새물리
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• 제68권11호
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• pp.1225-1230
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• 2018

Schwinger pair production of electrons and positrons in a strong electric field is a prediction of nonperturbative quantum field theory, in which the out-vacuum is superposed of multi-particle states of the in-vacuum. Solving the Dirac or Klein-Gordon equation in the background field, though a linear wave equation, and finding the pair-production rate is a difficult or nontrivial job. The phase-integral method has recently been introduced to compute the pair production in space-dependent electric fields, and a complex analysis method has been employed to calculate the pair production in time-dependent electric fields. In this paper, we apply the complex analysis method to a Sauter-type electric field and other hyperbolic-type electric fields that vanish in the past and future and show that the Stokes phenomena in pair production occur when the time-dependent frequency for a given momentum has finite simple poles (polons) with pure imaginary residues.

• 한국연소학회지
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• 제21권3호
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• pp.1-6
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• 2016

The effect of applied electric fields on jet flow instability was investigated experimentally by varying the direct current (DC) voltage and the alternating current (AC) frequency and voltage applied to a jet nozzle. We aimed to elucidate the origin of the occurrence of twin-lifted jet flames in laminar jet flow configuration, which occur when AC electric fields are applied. The results indicate that a twin-lifted jet flames originates from cold jet instability, caused by interactions between negative ions in the jet flow via electron attachment as $O_2+e{\rightarrow}O_2{^-}$ when AC electric fields are applied. This was confirmed by experiments in which a variety of gaseous jets were ejected from a nozzle to which DC voltages and AC frequencies and voltages were applied, with ambient air between two deflection plates connected to a DC power source. Experiments in which jet flows of several gases were ejected from a nozzle and AC electric fields were applied in coflow-nitrogen provided further evidence. The flow instability occurred only for oxygen and air jets. Additionally, jet instability occurred when the applied frequency was less than 80 Hz, corresponding to the characteristic collision response time. The effect of AC electric fields on the overall structure of the jet flows is also reported. Based on these results, we propose a mechanism to reduce jet flow instability when AC electric fields are applied to the nozzle.

• 한국안전학회지
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• 제36권4호
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• pp.20-28
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• 2021

With an increase in the commercialization of electricity, and the development of advanced and large electric devices and various wireless radio wave services, concerns over the effects of electromagnetic fields on human health have increased. Accordingly, the World Health Organization encouraged the development of international standards by establishing the 'International Electromagnetic Fields Project' in 1996 based on studies on the harmful effects of electromagnetic fields on the human body. Moreover, the National Institute of Environmental Health Sciences (NIEHS) classified electromagnetic fields as possible carcinogens under Group 2B category, even though they have been found to have a weak correlation with those effects on human health. Mid-to-large-sized electric facilities used at industrial sites mostly adopt a commercial frequency of 60 Hz, and workers handling these facilities are exposed to such extremely low frequency (ELF) fields for a long time. A previous study suggested that exposure to ELF electromagnetic fields with frequency ranges from 0 to 300 Hz, even for a short time, at densities higher than 100 μT may have harmful effects on human body as it affects the activation of nerve cells in the central nervous system by inducing an electric field and current and stimulating muscles and the nervous system in the body. Such studies, however, focused on home appliances used by ordinary people, and research on facilities utilizing high-capacity current and operated by workers at industrial sites is lacking. Therefore, in this study, a 3000 kilowatt generator, which is a high-capacity electric facility employed at industrial sites, was investigated, and the size of the magnetic fields generated during its no-load and high-load operations per distance to produce a map was measured to reveal spots deemed hazardous according to domestic and international exposure standards. The findings of this study is expected to alleviate workers' anxiety about the harmful effects of magnetic fields on their body and to minimize the level of exposure during operations.

• 조명전기설비학회논문지
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• 제12권3호
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• pp.51-58
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• 1998

이 논문은 옥내 변전소의 변압기와 가스절연개폐장치(GIS) 주변에서 상용주파수의 전장과 자장의 분포에 관한 것으로 전장과 자장의 측정은 지표상 Hill]의 높이에서 1차원과 3차원 측정기로 수행되었다. 변압기 주변에서 전 장과 자장의 분포는 2차원적 평면도로써 나타내었으며, 전장의 세기는 2.3~9[v/m]으로 비교적 작은 값이었고, 자장의 세기는 $0.3~20.3[{\mu}T]$이었다. 또한 GIS의 주변에서 전장의 세기는 2.2~2.5[V/m]이고, 자장의 세기는 주 로 GIS의 중간부위에서 국부적으로 크게 나타났으며 $1.2~39.5[{\mu}T]$의 값이었다. 변압기와 GIS의 금속 외함은 전장을 감소시키는 역할을 하고, 자장은 변압기와 GIS의 외함으로부터 거리에 따라 급속하게 감소하는 특정을 보이고 있다.

• 조명전기설비학회논문지
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• 제20권5호
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• pp.57-63
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• 2006

본 논문은 낙뢰에 의해서 방사된 전계와 자계 파형의 물리적 특성과 파라미터분석에 대한 것으로 낙뢰에 의한 전계와 자계 파형은 각각 평판형 전계센서와 루프형 자계센서로 검출되고, 측정된 신호는 12 비트의 해상도, 10[MS/s] 샘플링, 10[ms]의 기록시간을 가지는 데이터취득시스템으로 기록하였다. 낙뢰에 의해 발생한 전계와 자계 파형의 극성의존성은 거의 없었으며, 상승시간은 $13[{\mu}s]$이내이고 정 부극성의 평균값은 각각 $4.1[{\mu}s],\;4.2[{\mu}s]$이었다. 정 부각성의 영점교차시간은 각각 $65.2[{\mu}s],\;67.0[{\mu}s]$이고, 반전딥의 깊이는 38.0[%], 40.3[%]이었다.

• Advances in materials Research
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• 제2권4호
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• pp.209-219
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• 2013

We have described primary studies on conductivity and molecular weight of polyaniline separately in the electric and magnetic fields when it is used in a field effect experimental configuration. We report further studies on doped in-situ deposited polyaniline. First we have chemically synthesized polyaniline by ammonium peroxodisulfate in acidic aques and organic solutions at different times. Then we measured mass and conductivity and obtained the best time of polymerizations. In continue, we repeated these reactions separately under different electric and magnetic fields in constant time and measured mass and conductivity. The polyaniline is characterized by gel permeation chromatography (GPC), UV-Visible spectroscopy and electrical conductivity. High molecular weight polyanilines are synthesized under electric field, $M_w$ = 520000-680000 g/mol, with $M_w/M_n$ = 2-2.5. The UV-Visible spectra of polyanilines oxidized by ammonium peroxodisulfate and protonated with dodecylbenzenesulfonic acid (PANi-DBSA), in N-methylpyrolidone (NMP), show a smeared polaron peak shifted into the visible. Electrical conductivity of polyanilines has been studied by four-probe method. The conductivity of the films of emeraldine protonated by DBSA cast from NMP are higher than 500 and 25 S/cm under 10 KV/m of potential) electric field and 0.1 T magnetic field, respectively. It shows an enhanced resistance to ageing too. By the next steps, we carried chemical polymerization at the best electric and magnetic fields at different times. Finally, resulted in finding the best time and amount of the fields. The longer polymerization time and the higher magnetic field can lead to degradation of polyaniline films and decrease conductivity and molecular mass.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 E
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• pp.1663-1665
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• 1997

Direct measurements of electric fields in a glow discharge are difficult because the measurement method should be sensitive to the electric field and non-intrusive. Laser spectroscopy is very suitable in that it is non-intrusive and allow in-situ measurements to be made. In this report, the measurement techniques of electric fields in glow discharge using laser spectroscopy were described.

• 한국전자파학회논문지
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• 제26권5호
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• pp.499-505
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• 2015

전자기 공진 현상을 이용한 무선전력전송 시스템에 대한 조사량 평가 시 전기장의 고려 여부를 검토하였다. 인체로 인가되는 전기장과 자기장의 상대적인 크기가 조사량 평가 시에 중요한 지표가 되기 때문에, 이를 검토하기 위해 자기 다이폴 인근의 다양한 전자기장의 크기를 갖는 곳에 구형의 간이 인체 모델을 위치시키고, 구 모델 내부로 유도되는 전기장의 값을 이론과 수치해석을 통하여 구하고 비교하였다. 그 결과, 전기장을 무시할 수 없는 영역이 존재함을 확인하였으며, 이는 무선전력전송의 조사량 평가 시 외부 전기장에 대한 고려가 필요함을 알 수 있었다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 춘계학술대회 논문집
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• pp.466-469
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• 2008

As the industry develops, they are interested in the fault of electric machines and the effect on human beings by electromagnetic fields and waves which generate through much use of electric machines and appliances. In foreign country, they confirmed the standard about electromagnetic interference and compatibility(EMI/EMC) of electromagnetic fields and waves generating electricity transmission/distribution equipments and electric appliance. In Korea, such criteria are applied too. Before EMI/EMC standard is applied, it is important to prepare the plan to predict and reduce electromagnetic fields and waves which generate in the inner and the outer part of electric machinery. To solve such a problem, they calculated Maxwell's equations by finite element method(FEM) and finite difference method(FDM) in most papers. However, these methods have the disadvantage that mathematical expansions are complex and need much memory allocations for grid and mesh generations. In this paper, we introduce transmission line matrix(TLM) method that media of which trains consists are regarded as transmission lines for electromagnetic field calculation in Korean High Speed Train, calculate the electric and magnetic field, and analyze the results.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 E
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• pp.1908-1910
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• 1997

The electric and magnetic fields (EMFs) near 345/154 kV overhead transmission lines were measured. The average values of maximum electric field and magnetic field for 44 transmission lines were 1.11 kV/m and 24.5 mG, respectively. These values were lower than any standards of advanced countries. The EMFs of distribution lines and substation, and electric appliances were also measured and compared with those of transmission lines.