• 한국방사선학회논문지
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• 제16권4호
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• pp.435-442
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• 2022

힐이팩트는 X선관의 양극 측과 음극 측의 강도가 균등하지 않아 X선 영상에 농도 차이를 발생시킨다. 이 연구의 목적은 스텝 웨지를 180도로 회전시킨 다음 거리를 변경하여 힐이팩트에 의한 농도 차이를 평가하는 것이다. 관전압과 관전류를 72 kVp, 10 mAs로 고정시킨 후 스텝 웨지를 이용하여 정방향과 역방향을 촬영하였다. 이때 거리(80 cm ~ 130 cm)는 10 cm 간격으로 촬영을 진행하였고 M6 프로그램을 통해 스텝 웨지의 각 계단별 관심영역을 설정하여 농도값을 측정하였다. 첫 번째로 조사선량 실험을 통해 음극과 양극의 강도 차이를 확인하였다. 또한 거리(80cm에서 130cm으로)를 달리하였을 때 촬영 거리가 멀어질수록 음극과 양극 사이의 농도 차이가 감소하였다. 이는 결론적으로 촬영 거리가 멀어질수록 균일한 농도의 영상을 획득할 수 있다.

• Journal of Magnetics
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• 제20권4호
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• pp.450-459
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• 2015

In this paper, the safety distances and maximum permissible power (MPP) of resonant wireless power transfer systems are defined and derived with regard to human exposure to electromagnetic field (EMF). The definition is based on the calculated induced current density and electric field in the standard human model located between the transmitting and receiving coil. In order to avoid the adverse health effects such as stimulation of nerve tissues, the induced current and electric field must not exceed the basic restriction values specified in EMF safety guidelines. The different combinations of diameters of the coils and the distance between the two coils are investigated and their effects are analyzed. Two versions of EMF safety guidelines (ICNIRP 1998 and ICNIRP 2010) are used as bases for safety distance calculation and the difference between the two guidelines are discussed.

• Transactions on Electrical and Electronic Materials
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• 제18권2호
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• pp.97-102
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• 2017

A current transformer (CT) is a type of sensor that consists of a combination of electric and magnetic circuits, and it measures large ac currents. When a large amount of current flows into the primary winding, the alternating magnetic flux in the iron core induces an electromotive force in the secondary winding. The characteristics of a CT are determined by the iron core design because the iron core is saturated above a certain magnetic flux density. In particular, when a large current, such as a current surge, is input into a CT, the iron core becomes saturated and the induced electromotive force in the secondary winding fluctuates severely. Under these conditions, the CT no longer functions as a sensor. In this study, the characteristics of the secondary winding were investigated using the time-difference finite element method when a current surge was provided as an input. The CT was modeled as a two-dimensional analysis object using constraints, and the saturation characteristics of the iron core were evaluated using the Newton-Rhapson method. The results of the calculation were compared with the experimental data. The results of this study will prove useful in the designs of the iron core and the windings of CTs.

• Restorative Dentistry and Endodontics
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• 제22권1호
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• pp.396-412
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• 1997

The purpose of this study is to observe the corrosion characteristics of five dental amalgams(CAULK FINE CUT, OPTALLOY II, DISPERSALLOY, TYTIN, and VALIANT) in the solutions with fluoride compound through the anodic polarization curve obtained by using a potentiostat. After each amalgam alloy and Hg being triturated, the triturated mass was inserted into the cylindrical metal mold, and condensed by hydraulic pressure(160 kg/$cm^2$). Each specimen was removed from the metal mold. Specimens were polished with the silicone carbide grinding paper 24 hours after condensation and stored at room temperature for 1 week. The anodic polarization curves were employed to compare the corrosion behaviours of the amalgams in 0.9 % saline solution and in the saline solutions with 2.2 ppm, 0.05 %, 2 % NaF, and 8 % $SnF_2$ at $37^{\circ}C$ with 3-electrode potentiostat. After the immersion of specimen in electrolyte for 30 minutes, the potential scan was begun. The potential scan range was -1500m V to + 800m V(vs. S.C.E.) in the working electrode and the scan rate was 50 mV/sec. The results were as follows, 1. The corrosion potential, the potential of anodic current peak, and transpassive potential in the saline solutions with NaF shifted to lower direction than those in normal saline solution, and the current density in the saline solutions with NaF was higher than that in normal saline solution. The differences were increased as the concentrations of NaF became higher. 2. The corrosion potential and transpassive potential in the saline solution with $SnF_2$ shifted to higher direction than those in normal saline solution, and the current density in the saline solution with $SnF_2$ was higher than that in normal saline solution after the corrosion potential. The anodic polarization curves in the saline solution with $SnF_2$ had no outstanding anodic current peak. 3. The corrosion potentials for high-copper amalgams were much higher than those for CAULK FINE CUT and OPTALLOY II in normal saline solution, but, as the concentrations of fluoride compound became higher, the differences in corrosion potentials between them were decreased. The corrosion potentials had the similarity in the saline solution with 2% NaF or 8% $SnF_2$. 4. The current density for TYTIN was the lowest among the others in normal saline solution and in the saline solution with 2.2 ppm or 0.05 % NaF. 5. There was no significant difference in current density between Pd-enriched VALIANT and other high-copper amalgams.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1997년도 추계 학술대회논문집
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• pp.99-105
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• 1997

A finite-difference method based on conservative supra characteristic method type upwind flux difference splitting has been developed to study the nonequilibrium chemically reacting inviscid flow. For nonequilibrium air, NS-1 species equations were strongly coupled with flowfield equations through convection and species production terms. Inviscid nonequilibrium chemically reacting air mixture flows over Blunt-body were solved to demonstrate the capability of the current method. At low altitude flight conditions the nonequilibrium air models predicted almost the same temperature, density and pressure behind the shock as equilibrium flow: however, at high altitudes they showed substantial differences due to nonequilibrium chemistry effect. The new nonequilibrium chemically reacting upwind flux difference splitting mettled can be extended to viscous flow and multi-dimensional flow conditions.

• 한국수소및신에너지학회논문집
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• 제31권1호
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• pp.23-32
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• 2020

The intermittent characteristics of renewable energy complicates the process of balancing supply with demand. Electrolysis technology can provide flexibility to grid management by converting electricity to hydrogen. Alkaline electrolysis has been recognized as established technology and utilized in industry for over 100 years. However, high overpotential of oxygen evolution reaction in alkaline water electrolysis reduces the overall efficiency and therefore requires the development of anode catalyst. In this study, Raney Ni-Zn-Fe electrode was prepared by electroplating and the electrode characteristics was studied by varying electroplating parameters like electrodeposition time, current density and substrate. The prepared Raney Ni-Zn-Fe electrode was electrochemically evaluated using linear sweep voltammetry. Physical and chemical analysis were conducted by scanning electron microscope, energy dispersive spectrometer, and X-ray diffraction. The plating time did not changed the morphology and composition of the electrode surface and showed a little effect on overpotential reduction. As the plating current density increased, Fe content on the surface increased and cauliflower-like structure appeared on the electrode surface. In particular, the overpotential of the electrode, which was prepared at the plating current density of 320 mA/㎠, has showed the lowest value of 268 mV at 50 mA/㎠. There was no distinguishable overpotential difference between the type of substrate for the electrodes prepared at 80 mA/㎠.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 B
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• pp.577-579
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• 2002

Propose of this paper is VCM (voice coil motor) design for application of Nanoindenter, which enable control of extremely small force and displacement. This paper present the VCM shape to produce a very small force by the difference of flux density of lower part from higher one. In wide range of current. VCM produces linear driving force and operate on regular thrust having maximum displacement(100um) was practiced.

• Progress in Superconductivity
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• 제11권1호
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• pp.62-66
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• 2009

Introduction of proper impurity into $YBa_2Cu_3O_{7-x}$ (YBCO) thin films is an effective way to enhance its flux-pinning properties. We investigate effect of $Y_2O_3$ nanoparticles on the critical current density $J_c$ of the YBCO thin films. The $Y_2O_3$ nanoparticles were created perpendicular to the film surface (parallel with the c-axis) either between YBCO and substrate or on top of YBCO, YBCO/$Y_2O_3$/LAO or $Y_2O_3$/YBCO/STO, by pulsed laser deposition. The deposition temperature of the YBCO films were varied ($780^{\circ}C$ and $800^{\circ}C$) to modify surface morphology of the YBCO films. Surface morphology characterization revealed that the lower deposition temperature of $780^{\circ}C$ created nano-sized holes on the YBCO film surface which may behave as intrinsic pinning centers, while the higher deposition temperature produced much denser and smoother surface. $J_c$ values of the YBCO films with $Y_2O_3$ particles were either remained nearly the same or decreased for the samples in which YBCO is grown at $780^{\circ}C$. On the other hand, $J_c$ values were enhanced for the samples in which YBCO is grown at higher temperature of $800^{\circ}C$. The difference in the effect of $Y_2O_3$ can be explained by the fact that the higher deposition temperature of $800^{\circ}C$ reduces intrinsic pinning centers and $J_c$ is enhanced by introduction of artificial pinning centers in the form of $Y_2O_3$ nanoparticles.

• 대한토목학회논문집
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• 제34권3호
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• pp.859-871
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• 2014

본 연구에서는 염분과 온도차에 의한 밀도류를 해석하기 위하여 기존의 3차원 파동장 모델(LES-WASS-3D ver. 1.0)을 토대로 염분과 온도에 관한 상태방정식 및 3차원 이류-확산 방정식을 도입하여 새로운 수치모델(LES-WASS-3D ver. 2.0)을 개발하였다. 새롭게 개발한 수치모델의 적용성을 검토하기 위하여 기존의 수리모형실험결과와 비교 분석하였다. 그 결과, 이류-확산하는 해수의 형태 및 연직 염분농도 뿐만 아니라 방출하는 온수의 유속 및 온도를 매우 잘 재현하는 것으로 나타났다. 이로써 본 연구에서 개발한 수치모델의 타당성 및 유효성이 검증되었다.

• 한국멀티미디어학회논문지
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• 제10권2호
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• pp.187-199
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• 2007

회화적 렌더링의 궁극적인 목적은 주어진 영상을 가지고 사람이 직접 그린 듯 한 회화적 느낌을 표현하는 것이다. 이러한 회화적 느낌을 표현하기 위한 요소에는 브러시의 굵기, 방향, 질감, 그리고 생성된 브러시가 캔버스에 그려질 것인가를 판단하는 기준설정 등이 있다. 본 논문에서는 에지 밀도를 이용해 브러시가 캔버스에 그려질 것인가를 판단하는 기준을 설정하는 알고리즘을 제시한다. 에지밀도란 일정 영역에서의 에지의 양을 나타낸다. 이와 함께 정적 격자 단위로 그려질 위치를 찾는 것이 아닌 동적 격자단위로 찾아가는 방법을 사용하고 브러시의 일관된 방향성을 위해 방향 보간을 한다. 또한 텍스처를 가진 다양한 브러시를 사용하여 질감을 표현한다. 에지의 밀도정보를 이용한 그려질 판단 기준설정, 통적 격자에 의한 위치선정, 일관된 브러시의 방향, 그리고 텍스처를 사용한 질감 표현 과정들을 통해 더 사실적인 오일 페인팅(oil painting)의 효과를 얻을 수 있다.