• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.883-888
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• 2007

일반적인 하천의 흐름방향으로 발생하는 주흐름(primary flow)에 중첩하여 주흐름 방향의 수직단면에 이차류(secondary flow)가 발생하게 되며 이러한 이차류의 발달은 투입된 오염물질의 횡혼합을 증대시킨다. 오염물질의 혼합은 이송(advection)과 확산(diffusion) 또는 분산(dispersion)의 과정으로 설명되며 본 연구에서는 수로전체의 혼합과정을 설명하기 위해서 이송 확산 방정식을 적용하였다. 본 연구에서는 실험수조를 $150^{\circ}$의 중심각을 갖는 S자 형태의 만곡수로를 제작하여 유량조건은 15, 30, $60\;{\ell}l/sec$의 세 가지 경우로, 수심은 15, 20, 30, 40 cm의 경우로 총 12 케이스의 실험을 수행하였다. 유속장의 측정은 Sontek사의 3차원 micro-ADV(Acoustic Doppler Velocimeter)를 이용하였다. 오염물질 확산실험은 소금물 용액에 주변수와의 밀도차를 없애기 위해서 메탄올 용액을 첨가하여 추적자로 이용하여 농도장의 분석을 일본 KENEK사의 전기전도도계(conductivity meter)와 Gartner사의 DAS(data acquisition system)를 이용하여 횡방향 유속장의 분포와 오염운의 거동을 비교하여 다음과 같은 결론을 얻게 되었다. 주 흐름은 직선구간에서는 중앙에서 최대 유속을 나타내며, 좌우대칭적인 유속분포의 모습을 보이고, 만곡부에서는 수로안쪽을 따라 최대유속이 발생하였다. 수로의 직선구간에서는 최대유속이 발생하는 즉, 중앙에서의 오염물질의 분산이 가장 활발하게 이뤄졌으며 농도의 퍼짐형상인 오염운 역시 만곡부에서는 수로만곡부의 안쪽을 따라 확산 이동함을 알 수 있었다. 만곡부 외측에서는 오염물질의 정체현상이 일시적으로 발생하며, 유속구조의 횡방향 비대칭구조로 인한 종 횡방향의 분리현상이 발생하고, 오염운의 중첩현상이 종방향으로 연속되게 나타난다. 향후 수심방향 거동을 포함한 3차원적 분석이 요구되며 이 연구결과는 2차원적 수치해석의 적용 및 분석 자료로써 이용이 가능하다.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.2
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• pp.314-319
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• 2008

In this paper, the electric field distribution induced inside the brain during Transcranial Magnetic Stimulation(TMS) has been thoroughly investigated in terms of tissue heterogeneity and anisotropy as well as different head models. To achieve this, first, an elaborate head model consisting of seven major parts of the head has been built based on the Magnetic Resonance(MR) image data. Then the Finite Element Method(FEM) has been used to evaluate the electric field distribution under different head models or three different conductivity conditions when the head model has been exposed to a time varying magnetic field achieved by utilizing the Figure-Of-Eight(FOE) stimulation coil. The results show that the magnitude as well as the distribution of the induced field is significantly affected by the degree of geometrical asymmetry of head models and conductivity conditions with respect to the center of the FOE coil.

• Journal of the Korean Vacuum Society
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• v.17 no.6
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• pp.511-517
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• 2008

A quasi two-dimensional model for numerical simulation of gas discharge is presented, based on the finite-element flux-corrected transport method. A one-dimensional continuity convection-diffusion equation coupled Poisson's equation is solved to calculate the charge density variation and the electric field is evaluated by the classical disk method. Results calculated for various benchmark problems verify the accuracy of the proposed model and illustrate its performance. This model has been applied to a streamer simulation, and the results are shown to agree well with previously published results.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.55 no.8
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• pp.397-400
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• 2006

An optimized iron core structure of stimulating coil are presented in order to control the induced electric field distribution using the Continuum Design Sensitivity Analysis (CDSA) combined with a commercially available generalized finite element code (OPERA). The results show that a Figure-Of-Eight (FOE) coil as well as a circular coil with the proposed iron core structure can increase induced electric field intensity by more than two times and make better field localization, compared with those of existing stimulation coil with a air core. After considering manufacturing constraints, a practical iron core structure based on the proposed optimized one is proposed and its performance is analyzed.

• Korean Journal of Food Science and Technology
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• v.26 no.6
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• pp.791-798
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• 1994

Ohmic heating is a food processing operation in which heat is internally generated within foods by the passage of alternating electric current. The process enables highly viscous paste foods such as Kochujang, and fermented soybean paste to be heated very fast. In order to develope the novel pasteurization process of paste foods, static Ohmic heating system was built, and heating characteristic during Ohmic heating under various conditions were studied. Electric conductivities of Kochujang and fermented soybean paste at room temperature were 1.865 S/m and 2.510 S/m, respectively and increased linearly with increasing temperature. Specific heating rate was highly dependent on the frequency. The highest heating rate was achieved at 5 KHz for Kochujang and 20 KHz for fermented soybean paste. Uniform heating throughout the sample was achieved during Ohmic heating with low frequency electrical currents, however above 5 KHz frequency, surface temperature was several degrees higher than the bulk.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.1
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• pp.91-96
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• 2008

In this paper, a monopulse fled for three mode $2{\times}2$ array feed horn antenna was designed. Gain of single feed was 8.25dB. Increasing property of gain and rectangular waveguide and reflection of free space is decreased because it has structure extending to electric plane at connected part from transformation to free space. When fled port1 and port2 is placed vertically and thickness of aperture hem is reduced, isolation is satisfied with property of lower -25dB. Also, at higher frequency, it is confirmed that isolation is improved. Combination of electric field occurs less influence because port1 and port3 is placed horizontally and distribution of electric field is connected to parallel. However, because of combination of electric field, it is more improved from 2dB to 6dB than isolation of port1 and port2. Direct combination occult less effect at port1 and port4 than effect of port2 and port3, it is lower -35dB.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.9
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• pp.859-869
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• 2015

In this study, we analyze the problem of wedge cracks, which are geometrically unsymmetrical in transversely piezoelectric materials. A single concentrated antiplane mechanical load and inplane electrical load are applied at the point of the wedge surface, while one concentrated antiplane load is applied at the crack surface. The crack surfaces are considered as permeable thin slits, where both the normal component of electric displacement and the electric potential are assumed to be continuous across these slits. Using Mellin transform method, the problem is formulated and the Wiener-Hopf equation is derived. By solving the equation, the solution is obtained in a closed form. The intensity factors of the stress and the electric displacement are obtained for any crack length as well as inclined and wedge angles. Based on the results, the intensity factors are independent of the applied electric loads. The electric displacement intensity factor is always dependent on that of stress intensity factor, while the electric field intensity factor is zero. In addition, the energy release rate is computed. These solutions can be used as fundamental solutions which can be superposed to arbitrary electromechanical loadings.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11b
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• pp.123-135
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• 2000

절토사면 보호.녹화공의 개념과 분류체계가 아직까지 확립되어 있지 않으며, 현장에서 공법의 선정과 시공도 여러 가지 적절하지 못한 경우가 자주 발생하고 있다. 이러한 것을 해결하기 위해서는 이 분야에 대한 지속적인 투자와 관심, 그리고 관련회사의 사면의 환경특성을 고려한 성실시공이 수반되어야 한다. 또한, 절토사면의 장.단기적인 유지관리를 위해서 사면의 분포현황, 사면녹화공의 시공.관리상태, 환경특성 등의 자료를 조사하여 종합적인 사면유지관리시스템과 연계해야 할 것이다.

• The Journal of Engineering Geology
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• v.31 no.4
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• pp.533-540
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• 2021

Gravity field analysis and density modeling were performed to evaluate the internal state of the rock mass, which is the cause of cut slope collapse. The shape of the weathered zone and the depth of basement could be confirmed from the complete Bouguer anomaly and density model. The basement depth at the center of the cut slope calculated using the Euler deconvolution inverse method is 30 m, which is about 10 m deeper than the surrounding area. In addition, the depth of basement and the thickness of the weathered zone are similar to the boundary between low resistivity and high resistivity in dipole-dipole survey. From the study results, gravity field analysis and density modeling recognizes the internal state of the rock slope and can be used for slope safety analysis, and is particularly suitable as a method to determine the shape of weathered zones in interpreting the safety of cut slopes

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.441-441
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• 2012

Franz Keldysh Oscillation (FKO)은 p-n 접합 구조의 Photoreflectance (PR) spectra에서 표면 및 계면의 전기장(electric field) 특성을 반영한다. InAs/GaAs 양자점 태양전지(Quantum Dot Solar Cell, QDSC) 구조에서 InAs 양자점 층 전후에 AlGaAs 층을 삽입하여 퍼텐셜 장벽(potential barrier) 두께에 따른 PR spectra 및 GaAs-matrix에서 FKO 주파수 특성을 비교 분석하였다. InAs/GaAs 양자점 태양전지는 p-i-n 구조의 i-GaAs에 2.0 monolayer (ML), 8주기의 InAs 양자점 층을 삽입하여 Molecular Beam Epitaxy (MBE) 방법으로 성장하였다. 각 양자점 층 전후에 두께가 각각 0.0, 1.6, 2.8, 6.0 nm인 AlGaAs 층을 삽입하여 퍼텐셜 장벽 두께에 따른 FKO 주파수 변화를 관측하였다. 또한 태양전지 구조의 전기장 분포를 좀 더 용이하게 관측하기 위해 여기 광의 세기(power intensity)를 충분히 낮추어 Photovoltaic effect에 의한 내부 전기장의 변화를 최소화하여 비교 분석하였다. InAs/GaAs 양자점 태양전지 구조에서 AlGaAs 장벽층이 없는 경우, PR spectra의 Fast Fourier Transform 결과에 반영되는 FKO 주파수 특성은 p-i-n 구조 계면에서 공핍층(depletion region)의 space charge field보다 양자점 층의 내부 전기장에 의한 FKO 주파수가 더 큰 진폭(amplitude)을 보였다. 반면에, AlGaAs 장벽층이 삽입되면 두께가 커짐에 따라 p-i-n 구조 계면의 space charge field에 의해 더 큰 진폭의 FKO 주파수가 관측되었다. 이는 AlGaAs 장벽층이 삽입됨으로써 양자점 층 내 양자 상태 수 및 여기광에 의한 캐리어의 수와 관련이 있음을 확인하였으며, 결과적으로 GaAs-matrix에서 p-i-n 구조 계면의 space charge field에 영향을 미치게 됨을 알 수 있다. 이러한 PR 특성 결과들을 InAs/GaAs 양자점 태양전지의 설계 및 제조에 반영함으로써 양자효율 증대에 기여할 것으로 기대된다.