• 대한전자공학회논문지SD
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• 제40권1호
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• pp.1-10
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• 2003

본 연구에서는 Metal-Ferroelecric-Semiconductor FET (MFSFET) 소자의 특성을 시뮬레이션 하였다. 시뮬레이션에서는 field-dependent polarization 모델과 square-law FET 모델이 도입되었다. MFSFET 시뮬레이전에서 C-V/sub G/ 곡선은 축적과 공핍 및 반전 영역을 확실하게 나타내었다. 게이트 전압에 따른 캐패시턴스, subthreshold 전류 그리고, 드레인 전류특성에서 강유전체 항전압이 0.5, 1V 일 때, 각각 1, 2V 의 memory window 를 나타내었다. 드레인 전류-드레인 전압 곡선은 증가영역과 포화영역으로 구성되었다. 드레인 전류-드레인 전압 곡선에서 두 부분의 문턱전압에 의해 나타난 포화드레인 전류차이는 게이트 전압이 0, 0.1, 0.2 그리고, 0.3V 일 때, 각각 1.5, 2.7, 4.0 그리고 5.7㎃ 이었다. 시간경과 후의 드레인 전류를 분석하였는데, PLZT(10/30/70) 박막은 10년 후에 약 18%의 포화 전류가 감소하여 우수한 신뢰성을 보였다. 본 모델은 MFSFET 소자의 동작을 예측하는데 중요한 역할을 할 것으로 판단된다.

• Membrane and Water Treatment
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• 제1권4호
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• pp.297-316
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• 2010

Membrane fouling is one of the major operational concerns of membrane processes which results in loss of productivity. This paper investigates the ultrafiltration (UF) results of synthetic oil-in-water (o/w) emulsion using flat sheets of polysulfone (PSf) membrane synthesized with four different compositions. The aim is to identify the mechanisms responsible for the observed permeate flux reduction with time for different PSf membranes. The experiments were carried out at four transmembrane pressures i.e., 68.9 kPa, 103.4 kPa, 137.9 kPa and 172.4 kPa. Three initial oil concentrations i.e., 75 $mgL^{-1}$, 100 $mgL^{-1}$ and 200 $mgL^{-1}$ were considered. The resistance-in-series (RIS) model was applied to interpret the data and on that basis, the individual resistances were evaluated. The significances of these resistances were studied in relation to parameters, namely, transmembrane pressure and initial oil concentration. The total resistance to permeate flow is found to increase with increase in both transmembrane pressure and initial oil concentration while for higher oil concentration, resistance due to concentration polarization is found to be the prevailing resistance. The applicability of the constant pressure filtration models to the experimental data was also tested to explain the blocking process. The study shows that intermediate pore blocking is the dominant mechanism at the initial period of UF while in the later period, the fouling process is found to approach cake filtration like mechanism. However, the duration of pore blocking mechanism is different for different membranes depending on their morphological and permeation properties.

• Journal of electromagnetic engineering and science
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• 제12권1호
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• pp.115-121
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• 2012

This paper presents a scattering model and measurements of backscattering coefficients for soybean fields. The polarimetric radar backscatters of a soybean field were measured using the ground-based X-band polarimetric scatterometer in an angular range from $20^{\circ}$ to $60^{\circ}$. The backscattering coefficients were also obtained using the COSMO-SkyMed (Spotlight mode, HH-polarization) from July to October 2010. The backscattering coefficients of the soybean field were computed using the 1st-order radiative transfer model (RTM) with field-measured input parameters. The soybean layer is composed of the stems, branches, leaves, and soybean pods. The stems, branches, and pods are modeled with lossy dielectric cylinders, the leaves are modeled with lossy dielectric disks. The estimated backscattering coefficients agree quite well with the field-measured radar backscattering coefficients.

• Membrane and Water Treatment
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• 제12권2호
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• pp.59-64
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• 2021

The rejection of sodium chloride (NaCl) and calcium chloride (CaCl2) single salt solutions were carried out for commercial nanofiltration NFDK membrane. Results showed that the NFDK membrane had a negative surface charge and had a higher observed rejection of 93.65% for calcium (Ca2+) ion and 78.27% for sodium (Na+) ions. Prediction of rejection for aqueous solutions of both salts was made using Donnan Steric Pore Model based on Extended Nernst-Planck Equation in addition to concentration polarization film theory. A MATLAB program was developed to execute the model calculations. Absolute Average Relative Error (% AARE) was found below 5% for real rejection of the NFDK membrane. This research could be used successfully to assess the membrane characterization parameter using a proposed procedure which can reduce the number of experiments.

• 대기
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• 제27권4호
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• pp.467-481
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• 2017

A correction method of reflectivity in partial beam blockage (PBB) area is suggested, which is based on the combination of digital terrain information and self-consistency principle between polarimetric observation. First, the reflectivity was corrected by adding the radar energy loss estimated from beam blockage simulation using digital elevation model (DEM) and beam propagation geometry in standard atmosphere. The additional energy loss by unexpected obstacles and non-standard beam propagation was estimated by using the coefficient between accumulated reflectivity ($Z_H$) and differences of differential phase shift (${\Phi}_{DP}$) along radial direction. The proposed method was applied to operational S-band dual-polarization radar at Jindo and its performance was compared with those of simulation method and self-consistency method for six rainfall cases. When the accumulated reflectivity and increment of ${\Phi}_{DP}$ along radial direction are too small, the self-consistency method has failed to correct the reflectivity while the combined method has corrected the reflectivity bias reasonably. The correction based on beam simulation showed the underestimation. For evaluation of rainfall estimation, the FBs (FRMSEs) of simulation method and self-consistency principle were -0.32 (0.59) and -0.30 (0.57), respectively. The proposed method showed the lowest FB (-0.24) and FRMSE (0.50). The FB and FMSE were improved by about 18% and by 19% in comparison to those before correction (-0.42 and 0.70). We can conclude that the proposed method can improve the accuracy of rainfall estimation in PBB area.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 1999년도 추계종합학술대회
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• pp.101-105
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• 1999

ETC(Electronic Toll Collection)는 고속도로 등의 자동요금징수시스템으로 노변장치(Beacon)와 차량 탑재장치(On Boa.4 Unit) 사이에 통신이 가능하다. 본 연구에서는 상호 통신의 마이크로파 전파 경로를 모델화하여 전파 다중 경로에 의한 수신전압의 페이딩 효과를 분석하였다. 전파 모델에서는 환경 변화, 편파, 및 안테나 방사패턴 둥의 영향들을 고려하였다. 또한 페이딩 효과를 줄이기 위하여 공간 다이버시티 기술도 제안하였다. 분석결과, 강우 시 반사면의 반사계수가 변화하여 수직 편파의 경우 페이딩 효과가 크게 감소하였다 또한 원형 편파의 경우 일반적으로 페이딩 효과가 적었으며 높은 방향성을 가진 안테나를 사용하면 페이딩 효과가 감소하였다. 노변장치에서 공간 다이버시티 기술로 두 개의 안테나들로 신호를 보내면 차량과의 거리가 증가할수록 페이딩 효과를 감소시킬 수 있었다. 이러한 결과들을 차량 탑재 장치에서 수신된 전압의 크기(dB)와 노변장치와 차량 사이 거리로 도시하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1378-1383
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• 2003

A ferroelectric (called piezoelectric afterwards) wafer has been widely used as a key component of actuators or sensors of a layer type. According to recent researches, the piezoelectric wafer behaves in a nonlinear way under excessive electro-mechanical loadings. In the present paper, one-dimensional constitutive equations for the nonlinear behavior of a piezoelectric wafer are proposed based on the principles of thermodynamics and a simple viscoplasticity theory. The predictions of the developed model are compared with experimental observations.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.199.1-199.1
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• 2014

In nonlinear optics, the properties of nonlinear optical responses such as polarization and nonlinear analysis of the nonlinear surfaces were investigated using the jellium model by optical second harmonic generation. The nonlinear response of the Al metal surfaces were calculated using TDLDA. Band structure, lattice constant and bulk modulus of the Al metal were investigated. Effective potential and electron density were compared by changing different.

• KSTLE International Journal
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• 제4권1호
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• pp.14-17
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• 2003

The electrical and rheological properties of a chitosan malonate suspension in silicone oil was investigated by varying the electric fields, volume fractions of particles, and shear rates, respectively, The chitosan malonate susepnsion showed a typical electrorheological (ER) response caused by the polarizability of an amide polar group and shear yield stress due to the formation of multiple chains upon application of an electric field. The shear stress fur the suspension exhibited a linear dependence on the volume fraction and an electric field power of 1.88. On the basis of the experimental results, the newly synthesized chitosan malonate suspension was found to be an anhydrous ER fluid.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 1993년도 추계학술발표회 초록집
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• pp.73-77
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• 1993

박막모델을 사용하여 연료전지 성능에 영향을 주는 여러 인자들에 대해 전압과 전류의 관계를 모사 하여 비교하였다. 또한 단위전지에 대해 제어루프를 구성함으로서 전극성능 모델식을 이용한 연료전지의 제어 가능성을 확인하였다. 확산계수가 증가할수록 그리고 전극두께가 얇고 전극의 세공반경이 클수록 전극성능은 증가하였다. 단위전지의 제어를 위해서 양극과 음극의 반응기체 유속을 조절할 수 있는 압력에 대해 설정치 변화와 외란의 변화에 대한 제어모사를 행한 결과 각 전극의 압력이 설정점에 빠르게 수령하여 연료전지의 효과적인 제어가 가능함을 검증하였다.