• Corrosion Science and Technology
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• 제16권4호
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• pp.201-208
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• 2017

A finite element analysis is proposed to study the effect of specimen dimensions on lateral diffusion of hydrogen during hydrogen permeation flux measurements. The error of measurement on thick specimens because of 1D diffusion approximation may be as much as 70%. A critical condition for accurate measurements is to designate the area of hydrogen monitoring/exit surface smaller than the area of hydrogen charging/entry surface. For thin to medium thickness specimens (ratio of thickness to specimen radius of 5:10 and below), the charging surface should be maximized and the monitoring surface should be minimized. In case of relatively thick specimens (ratio of thickness to specimen radius above of 5:10), use of a hydrogen-diffusion barrier on the specimen boundaries is recommended. It would completely eliminate lateral losses of hydrogen, but cannot eliminate the deviation towards 2D diffusion near the side edges. In such a case, the charging surface should be maximized and the monitoring surface should be as closer in dimension as the charging surface. A regression analysis was carried out and an analytical relationship between the maximum measurement error and the specimen dimensions is proposed.

• 한국통신학회논문지
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• 제32권3C호
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• pp.216-225
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• 2007

본 논문에서는 대표적인 반복 부호 알고리즘인 터보 부호, LDPC부호 TPC 등 세 가지 알고리즘에 대해 8PSK 이상의 다치 변조 방식 적용을 위해 수신단에서 비트 분리 방법을 제시한다. 수신된 I, Q 심볼만을 이용하여 세 비트 이상의 비트를 분리하기 위한 LLR 방식에 기초를 하여 LLR 방식의 단점인 복잡도를 개선하기 위해 Euclidean, MAX, Sector 방식을 제시하였으며, 세 가지 반복 부호에 대해 최적의 비트 분리 방법을 제시하였다.

• 대한조선학회지
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• 제13권4호
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• pp.1-10
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• 1976

It is a well-known phenomenon that, in the case of vibrations of an elastic body in a fluid such as water, the presence of the surrounding fluid has the effect of lowering the natural frequencies of the vibration as compared with those in air or vacuum on account of the increased inertia, i.e. added mass. In this report, defining the mass increase factor as the ratio of added mass to vibration mass of the body in air, the author investigated the mass increased factor of an elastic plate vibrating in the fluid. It is assumed that the edges of the plate are simply supported, and that the surrounding fluid is an infinite ideal one. For the problem formulation the elliptical cylindrical coordinate system is adopted, so that a rectangular plate may be represented by a sheet degenerated from an elliptical cylinder. By virtue of the coordinate system adopted, plates which are chordwisely finite and lengthwisely contineous could directly be treated, but plates which are chordwisely finite in both directions could not be treated directly. For the latter, hence, plates which are chordwisely finite and lengthwisely semi-finite are investigated as an appropriate approximation. Some examples of the mass increase factor are numerically calculated for the fundamental mode and modes of zero or one nodal line in each direction with the range of the aspect ratio from 1 to 10 or more.

• Wind and Structures
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• 제38권5호
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• pp.341-354
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• 2024

This paper presents a theoretical method to deal with the aerodynamic performance and pitch optimization of the horizontal axis wind turbine blades at low wind speeds. By considering a blade element, the functional relationship among the angle of attack, pitch angle, rotational speed of the blade, and wind speed is derived in consideration of a quasi-steady aerodynamic model, and aerodynamic loads on the blade element are then obtained. The torque and torque coefficient of the blade are derived by using integration. A polynomial approximation is applied to functions of the lift and drag coefficients for the symmetric and asymmetric airfoils respectively, where specific expressions of aerodynamic loads as functions of the angle of attack (which is a function of pitch angle) are obtained. The pitch optimization problem is investigated by considering the maximum value problem of the instantaneous torque of a blade as a function of pitch angle. Dynamic pitch laws for HAWT blades with either symmetric or asymmetric airfoils are derived. Influences of parameters including inflow ratio, rotational speed, azimuth, and wind speed on torque coefficient and optimal pith angle are discussed.

• 반도체공학회 논문지
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• 제2권3호
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• pp.13-18
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• 2024

본 논문은 Reference generator 와 Comparator 에서 발생하는 offset 을 최소화하고 정확도를 향상시키기 위해 Auto zero 기술을 활용한 회로를 제안한다. 이에 대한 근거로 Auto zero 사용 전/후를 비교했을 때 약 90% 표준 편차가 줄어드는 결과를 얻을 수 있었다. 제안하는 회로는 55nm CMOS 공정을 사용하였으며, input frequency 는 781.2 Hz, Effective Number of Bits(ENOB) 8.01bit, Signal-to-Noise Distortion Ratio(SNDR)이 49.98dB 을 보여준다.

• 한국생물공학회:학술대회논문집
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• 한국생물공학회 2005년도 생물공학의 동향(XVI)
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• pp.65-66
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• 2005

Anaerobic digestion is one of the well-known methods for biological treatment handling of concentrated organic matter such as swine $wastewater.^{1)} The anaerobic digestion can reduce organic loading but also hydrolyze non-biodegradable organic $matter.^{2)}$ The feces from the scrapper-type barn are usually collected to make compost and the urine is discarded with swine-slurry wastewater by ocean-dumping or treated by biological methods. The lagoon, aerobic digestion, anaerobic digestion, SBR, $A^{2}/O$, and UCT have been applied for treating swine $wastewater.^{3)} In this study, as a result of the analysis of swine wastewater, the total and soluble chemical oxygen demand was 130g/L and 60g/L, respectively. And the volatile fatty acid as chemical oxygen demand equivalent was 45g/L, which was 75% of soluble chemical oxygen demand. Before everything else, ammonia nitrogen concentration was 6.5 g/L. From biochemical acidogenic potential test, it was concluded that the enhanced acidification process to manage swine waste should be operated in the ammonia nitrogen concentration of less than 1.2 g/L. In the result of seeding ratio experiments with artificial $wastewater^{4)}, the lag period of acidogens was taken the long time because of the inhibition by the $ammonia^{5)}$, however no difference of period by the seeding ratio was not shown. The Haldane-based biokinetics were also evaluated using a method of fourth order Runge-Kutta $approximation.^{6,7)}$ The nonlinear least squares (NLLS) method with a 95% confidence interval was also used. The ranges of maximum microbial growth rate, ${/mu_{max}}$, and half saturation coefficient, $K_{s}$, for acidogenesis of various seeding ratio with artificial wastewater were 6.1 ~ 12.6 $d^{-1}$ and 45,000 ~ 53,500 mg glucose/L, respectively. Also, the methanogenic microbial yield coefficient, Y, and microbial decay rate coefficient, $k_{d}$, and inhibition substrate concentration, $K_{si}$, for the reactors were determined to be 0.32 ~ 0.465 ${/mu}g$/mg glucose; 0.42 ~ 1.01 $d^{-1}$ and 51,500 ~ 55,600 mg glucose/L, respectively.

• 대한기계학회논문집A
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• 제36권3호
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• pp.305-311
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• 2012

보강 원통셸의 기본 고유 진동수를 최적화하기 위해서, 보강재의 개수를 1 개에서 5 개까지 보강된 원통셸에 대한 시뮬레이션을 수행하였다. 고유 진동수에 대한 최적화를 시뮬레이션하기 위해서 ANSYS 11.0 을 사용하였다. 최적화 방법으로 Subproblem Approximation Method 를 이용하였다. 최적화의 설계 함수로는 T-형 링 보강재의 기하형상이며, 제한 함수로는 보강에 따른 추가 부피가 10 % 이내로 제한하였다. 목적함수는 기본 고유진동수를 최대화하는 것이다. 최적 설계에 대한 성능 지표는 비보강 원통셸과 보강원통셸의 고유진동수와 부피의 비로서 정의하였다. 최적 성능 지수는 3 개의 보강재를 사용한 원통셸에서 나타났다.

• 항공우주시스템공학회지
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• 제14권5호
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• pp.1-8
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• 2020

구조적 특성 및 공력의 상호작용과 조종면 작동기의 제어 시스템의 영향을 고려한 서보공력탄성 해석을 수행하였다. 공탄성 안정성 해석을 위해서 선행되어야 하는 구조모델의 자유진동 해석은 유한요소 해석 프로그램 MSC Nastran을 사용하였다. 비정상 공기력 계산에 ZAERO를 사용하였다. 비정상 공기력 검증에 Doublet Hybrid Method를 사용하였다. Karpel의 최소상태근사법을 이용하여 주파수 영역의 공기력을 라플라스 영역으로 근사하였다. 공탄성 상태방정식을 구동기의 동역학 상태방정식과 결합하여 서보 공탄성 모델의 상태공간방정식을 구성하였다. 고세장비 모델의 승강타 입력에 따른 안정성 해석을 수행하였다. 근궤적법과 시간적분법을 사용하여 주파수영역과 시간영역에서의 서보공탄성 안정성 해석을 수행하였다.

• 한국정보통신학회논문지
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• 제20권7호
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• pp.1311-1316
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• 2016

본 연구에서는 단채널 비대칭 이중게이트 MOSFET의 채널길이에 따른 문턱전압이동에 터널링전류가 미치는 영향을 분석하고자 한다. 채널길이가 10 nm 이하로 감소하면 터널링 전류는 급격히 증가하여 문턱전압이동 등 2차효과가 발생한다. 단채널 효과를 감소시키기 위하여 개발된 비대칭 이중게이트 MOSFET의 경우에도 터널링 전류에 의한 문턱전압이동은 무시할 수 없게 된다. 차단전류는 열방사전류와 터널링 전류로 구성되어 있으며 채널길이가 작아질수록 터널링전류의 비율은 증가한다. 본 연구에서는 터널링 전류를 분석하기 위하여 WKB(Wentzel-Kramers-Brillouin) 근사를 이용하였으며 채널 내 전위분포를 해석학적으로 유도하였다. 결과적으로 단채널 비대칭 이중게이트 MOSFET에서는 채널길이 가 작아질수록 터널링 전류의 영향에 의한 문턱전압이동이 크게 나타나고 있다는 것을 알 수 있었다. 특히 하단게이트 전압 등에 따라 터널링 전류에 의한 문턱전압 값은 변할지라도 문턱전압이동은 거의 일정하였다.

• Earthquakes and Structures
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• 제11권2호
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• pp.195-215
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• 2016

Rehabilitation of historical unreinforced masonry (URM) buildings is a priority in many parts of the world, since those buildings are a living part of history and a testament of human achievement of the era of their construction. Many of these buildings are still operational; comprising brittle materials with no reinforcements, with spatially distributed mass and stiffness, they are not encompassed by current seismic assessment procedures that have been developed for other structural types. To facilitate the difficult task of selecting a proper rehabilitation strategy - often restricted by international treaties for non-invasiveness and reversibility of the intervention - and given the practical requirements for the buildings' intended reuse, this paper presents a practical procedure for assessment of seismic demands of URM buildings - mainly historical constructions that lack a well-defined diaphragm action. A key ingredient of the method is approximation of the spatial shape of lateral translation, ${\Phi}$, that the building assumes when subjected to a uniform field of lateral acceleration. Using ${\Phi}$ as a 3-D shape function, the dynamic response of the system is evaluated, using the concepts of SDOF approximation of continuous systems. This enables determination of the envelope of the developed deformations and the tendency for deformation and damage localization throughout the examined building for a given design earthquake scenario. Deformation demands are specified in terms of relative drift ratios referring to the in-plane and the out-of-plane seismic response of the building's structural elements. Drift ratio demands are compared with drift capacities associated with predefined performance limits. The accuracy of the introduced procedure is evaluated through (a) comparison of the response profiles with those obtained from detailed time-history dynamic analysis using a suite of ten strong ground motion records, five of which with near-field characteristics, and (b) evaluation of the performance assessment results with observations reported in reconnaissance reports of the field performance of two neoclassical torsionally-sensitive historical buildings, located in Thessaloniki, Greece, which survived a major earthquake in the past.