• Progress in Medical Physics
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• v.14 no.4
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• pp.234-239
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• 2003

We examined the variation of percent depth dose (PDD) curves for 10 MV X-rays in the presence of magnetic fields. The EGS4 Monte Carlo code was applied and modified to take account of the effect of electron deflection under magnetic field was used. We defined and tested DI (dose improvement) and DR (dose reduction) to describe variation of PDD curves under various magnetic fields. For a magnetic field of 3 T applied at the depth region of 5-10 cm and field size of 10${\times}$10 $\textrm{cm}^2$, the DI is 1.56 (56% improvement) and DR is 0.68 (32% reduction). We explained the results from the Lorentz law and the concept of electron equilibrium. We suggested that the dose optimization in radiotherapy can be achieved from using the characteristics of dose distributions under magnetic fields.

• The Journal of Korean Society for Radiation Therapy
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• v.11 no.1
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• pp.6-10
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• 1999

The field size can be beam output, therefore MonitorUnit can be varied due to field size dependence The purpose of this study is to evaluate and compare the dose variation according to exchange of collimator The measurements were perfomed with Wellhofer dosimetry system(water phantom. ion chamber. electrometer. system controller. build up cap. etc)and two types of linear accerlerator (Mevatron KD, MevatronMX) Scatter can be affected to field size dependence and scatter correction is separated into collimator and phantom components, scatter components can affect by exchanging of collimator Measurements of collimator scatter factor(Sc) was done in air with build up cap. 1)Square field (5cm2 to 40cm2) was measured 2)and then keeping the upper jaw constant at loom and varing lower jaw from 5cm to 40cm, 3)keeping the lower jaw constant at 10cm and varing upper jaw from 5cm to 40cm Measurements of total scatter factor(Scp) was done in water at Dmax as the procedure of collimator scatter factor measurements in water Dmax The total scatter factors were obtained to the following equation(Sp=Scp/Sc) The measured data is normalized to the data of reference field size($10{\times}10$), rectangular field is inverted to equivalent field to compare three field size data As the collimator setting is varied, the output was changed In conclusion, the error was obtained small but it must be eliminated if we intend to reach the common stated goal of $5\%$ overall uncertainty in dose determination

• Journal of Astronomy and Space Sciences
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• v.29 no.4
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• pp.329-336
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• 2012

Korea Astronomy and Space Science Institute researchers have installed and operated magnetometers at Bohyunsan Observatory to measure the Earth's magnetic field variations in South Korea. In 2007, we installed a fluxgate magnetometer (RFP-523C) to measure H, D, and Z components of the geomagnetic field. In addition, in 2009, we installed a Overhauser proton sensor to measure the absolute total magnetic field F and a three-axis magneto-impedance sensor for spectrum analysis. Currently three types of magnetometer data have been accumulated. In this paper, we use the H, D, Z components of fluxgate magnetometer data to investigate the characteristics of mid-latitude geomagnetic field variation. To remove the temporary changes in Earth's geomagnetic filed by space weather, we use the international quiet days' data only. In other words, we performed a superposed epoch analysis using five days per each month during 2008-2011. We find that daily variations of H, D, and Z shows similar tendency compared to previous results using all days. That is, H, D, Z all three components' quiet intervals terminate near the sunrise and shows maximum 2-3 hours after the culmination and the quiet interval start from near the sunset. Seasonal variations show similar dependences to the Sun. As it becomes hot season, the geomagnetic field variation's amplitude becomes large and the quiet interval becomes shortened. It is well-known that these variations are effects of Sq current system in the Earth's atmosphere. We confirm that the typical mid-latitude geomagnetic field variations due to the Sq current system by excluding all possible association with the space weather.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.2A
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• pp.383-390
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• 2006

In this paper, a stochastic field that is compatible with Monte Carlo simulation is suggested for an expansion-based stochastic analysis scheme of weighted integral method. Through investigation on the way of affection of stochastic field function on the displacement vector in the series expansion scheme, it is noticed that the stochastic field adopted in the weighted integral method is not compatible with that appears in the Monte Carlo simulation. As generally recognized in the field of stochastic mechanics, the response variability is not a linear function of the coefficient of variation of stochastic field but a nonlinear function with increasing variability as the intensity of uncertainty is increased. Employing the stochastic field suggested in this study, the response variability evaluated by means of the weighted integral scheme is reproduced with high precision even for uncertain fields with moderately large coefficient of variation. Besides, despite the fact that only the first-order expansion is employed, an outstanding agreement between the results of expansion-based weighted integral method and Monte Carlo simulation is achieved.

• Proceedings of the KIPE Conference
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• 1996.06a
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• pp.1-4
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• 1996

The purpose of this treatise is to estimate speed of an induction motor and realize a robust speed control system with estimated speed in field-weakening region. A speed estimation is based on Model Reference Adaptive System(MRAS) technique and two flux estimator are designed to be robust against parameter variation. The MRAS-based overall control scheme has been implemented on 7.5kW Spindle induction motor control system. And it is verified that the proposed control scheme is very stable and robust in field-weakening region.

• Journal of the Korean Magnetic Resonance Society
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• v.3 no.2
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• pp.71-83
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• 1999

The dynamics of the dipolar demagnetizing field is investigated by numerical simulation. The effects of radiation damping, molecular diffusion, and relaxation processes on the dipolar demagnetizing field are examined in terms of the modulation pattern of the z-magnetization and the signal intensity variation. Simulations for multi-components suggest applications for sensitivity enhancement in favorable conditions.

• Proceedings of the KIEE Conference
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• 1999.07f
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• pp.2751-2753
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• 1999

This paper presents the field weakening base speed considering stator resistance effect. It uses the algorithm of estimating rotor and stator resistance to compensate resistance variation. And by using estimated stator resistnace the field weakening base speed is determinded. Simulation results demonstating the effectiveness of this method.

• Transactions of the Korean Society of Automotive Engineers
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• v.25 no.2
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• pp.257-265
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• 2017

In this work, the effect of field-degradation of automotive polymeric interior parts on the squeak characteristics was studied for a number of used vehicles with various mileages and years of service. The purpose of this study was to characterize the squeak noise related with long-term degradation in service life. The characteristics of field-degraded polymeric samples are analyzed using Fourier transform infrared(FT-IR) spectroscopy and scanning electron microscopy(SEM). Complicated carbonyl spectra from FT-IR were deconvoluted into various carbonyls to trace field-degradation phenomenon. In addition, various mechanical tests, i.e. tensile test, hardness test as well as coefficient of friction test, were performed to analyze the variation in mechanical properties due to field-degradation. Squeak noise was measured and analyzed by frequency analysis. It was shown that the changes in the chemical structures of polymer due to field-degradation influenced the variation in mechanical properties, and squeak noise may worsen by increasing the squeak noise level in the wide frequency range. The results indicated that customer complaints regarding the squeak noise coming from used vehicles might be one of the important reliability issues because the increase in sound pressure level especially in the high frequency range could annoy drivers and passengers.

• Journal of The Korean Society of Agricultural Engineers
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• v.58 no.5
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• pp.81-90
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• 2016

Due to droughts and water shortages causing severe damage to crops and other vegetations, much attention has been given to efficient irrigation for upland farming. However, little information has been known to measure soil moisture levels in a field scale and apply their spatial variability for proper irrigation scheduling. This study aimed to characterize the spatial variability and temporal stability of soil water contents at depths of 10 cm, 20 cm and 30 cm on flat (loamy soil) and hill-slope fields (silt-loamy soil). Field monitoring of soil moisture contents was used for variogram analysis using GS+ software. Kriging produced from the structural parameters of variogram was applied for the means of spatial prediction. The overall results showed that the surface soil moisture presented a strong spatial dependence at the sampling time and space in the field scale. The coefficient variation (CV) of soil moisture was within 7.0~31.3 % in a flat field and 8.3~39.4 % in a hill-slope field, which was noticeable in the dry season rather than the rainy season. The drought assessment analysis showed that only one day (Dec. 21st) was determined as dry (20.4 % and 24.5 % for flat and hill-slope fields, respectively). In contrary to a hill-slope field where the full irrigation was necessary, the centralized irrigation scheme was appeared to be more effective for a flat field based on the spatial variability of soil moisture contents. The findings of this study clearly showed that the geostatistical analysis of soil moisture contents greatly contributes to proper irrigation scheduling for water-efficient irrigation with maximal crop productivity and environmental benefits.

• 한국지구과학회:학술대회논문집
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• 2010.04a
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• pp.53-53
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• 2010

지표위의 어떤 지점에서의 지구자기의 수평분력 방향과 진북방향 사이의 각을 편각(Declination)이라고 정의한다. 쉽게 말하면 편각은 나침반의 자침이 가러 키는 방향과 진북방향과의 사이 각을 말한다. 대부분의 사람들은 나침반의 자침이 북자기극(North magnetic pole)을 가러킨다고 잘못알고 있다. 지구 다이나모설(Geodynamo theory)에 의하면 주로 철(약 90%)로 구성된 외핵 속에서 계속 생성 유지되고 있는 복잡한 (각각 나선형(helical)의 회전축에 대체로 평행하거나 평행하지 않은) 대류(Convection currents)에 수반하는 전류가 복잡한 지구자기장을 형성한다. 지표상에서 측정한 지구자기장의 자료를 Spherical harmonic analysis 으로 분석하면 한 개의 커다란 쌍극자(Dipole) (Inclined geocentric dipole 또는 주된 자기장(Main field) 이라고 부름), 적도쌍극자(Equatorial dipole), 4극자 (Quadrupoles), 8극자(Octupoles) 등의 여러 개의 크고 작은 쌍극자들의 총합이 지구자기장의 근원인 것처럼 해석되고 있다. 어떤 지점에서의 지구자기장의 방향은 외핵에서 생성된 천체 자기장에서 Main field를 제거한 나머지 자기장과, 상부 맨틀(upper mantle), 지각 및 지표상에 존재하는 인공 물체 또는 암석 및 광석 등의 잔류자기 및 유도자기 그리고 지형 등의 영향으로 결정된다. 어떤 지점에서의 지구자기장의 방향은 태양풍(Solar wind)과 전리층 사이의 상호작용 등의 외부자장(external field)의 영향도 받는다. 비쌍극자 자장(Non-dipole field)은 지표상에서 측정되는 총자기장에서 외핵에서 생성된 주된 자기장(Main field) 즉, 지구의 회전축에서 약 11.5도 기울어진 쌍극자 자장을 제거하고 남는 자기장을 말한다. 따라서 편각은 비쌍극자자장의 영향을 가장 많이 받는다. 비쌍극자 자장은 정지한 상태의 자장(standing field) 과 매년 서쪽으로 약 0.2도 움직이는 Westward drift하는 자장으로 크게 두 가지로 구분된다. 쌍극자 자장의 방향은 매우 느리게 변하지만 그 세기는 현재 비교적으로 빠르게 약해지고 있다. 비교적으로 매우 빠르게 변하는 비쌍극자 자장의 변화를 영년변화(Secular variation) 이라고 한다.