• 한국전자파학회논문지
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• 제17권1호
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• pp.8-16
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• 2006

본 논문에서는 관심 주파수의 파장에 비하여 매우 섬세한 구조의 해석에 있어서 기존의 FDTD보다 효율적인 해석이 가능한 ADI-FDTD의 차분방정식 계산 방법에 대하여 연구하였다. 반복 구간에서 계산되는 서로 다른 계산 방법을 유도하고 두 개의 상보적인 2차원 문제를 해석하여 경계 조건의 적용 관점에서 그 특성을 논하였다.

• Journal of Mechanical Science and Technology
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• 제19권11호
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• pp.1988-1997
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• 2005

This study is concerned with structural integrity evaluations for the interference-fit flywheels in reactor coolant pumps (RCPs) of nuclear power plants. Stresses in the flywheel due to the shrinkage loads and centrifugal loads at the RCP normal operation speed, design overspeed and joint-release speed are obtained using the finite element method (FEM), where release of the deformation-controlled stresses as a result of structural interactions during rotation is considered. Fracture mechanics evaluations for a series of cracks assumed to exist in the flywheel are conducted, considering ductile (fatigue) and non-ductile fracture, and stress intensity factors are obtained for the cracks using the finite element alternating method (FEAM). From analysis results, it is found that fatigue crack growth rates calculated are negligible for smaller cracks. Meanwhile, the material resistance to non-ductile fracture in terms of the critical stress intensity factor (K$_{IC}$) and the nil-ductility transition reference temperature (RT$_{NDT}$) are governing factors for larger cracks.

• 응용통계연구
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• 제27권5호
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• pp.819-831
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• 2014

치우친 다변량 t-분포 혼합을 적합하기 위해 Exact-EM 알고리즘이 사용된다. 그러나 이 방법은 E-step에서 매우 긴 처리시간을 요하는 다변량 절단 t-분포의 적률을 계산해야 한다. 본 논문에서는 이러한 문제점을 완화하기 위해 SPU-EM이라 명명한 알고리즘을 제안하는데, 이것은 Meng과 van Dyk (1997)의 AECM 알고리즘의 원리를 이용하여 다차원 적률의 계산상의 어려움을 해결한다. 결과적으로 제안된 방법은 Exact-EM 알고리즘 보다 빠른 처리시간으로 보장한다. 이를 입증하기 위해 실험을 통해 제안된 방법의 유효성을 보인다.

• Journal of Chest Surgery
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• 제31권7호
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• pp.703-710
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• 1998

연세대학교 의과대학 영동세브란스병원에서는 1989년 3월부터 1997년 9월까지 외래와 전화추적이 가능하였던 654명(남자 354명과 여자 300명)의 다한증 환자를 대상으로 흉부교감신경절제술을 시행하였다. 다한증에 대한 흉강 내시경을 이용한 수술기법은 기존의 개흉술보다 선명한 수술시야를 확보할 수 있는 장점이 있다. 단순기관 삽관을 이용한 마취 유도기법으로 마취시간의 단축과 수술시간의 단축, 그리고 입원기간의 단축이 가능하게 되었다. 시간절약뿐만 아니라 수술기법이 쉽고 미용효과를 최대로 살릴수 있는 2 mm주사침 흉강경을 이용한 흉부 교감신경 절제술은 최근 다한증에 가장 확실한 치료법이 되었다. 수술기법의 변화는 수술의 결과를 향상시켰으며, 수술 후 만족도를 95%이상으로 향상시켰다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 하계종합학술대회 논문집(4)
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• pp.155-158
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• 2001

A new method for simultaneous multiple transmit focusing using orthogonal weighted FM chirp is proposed. Weighted chirp signals focused at different depths are transmitted at the same time. These chirp signals are mutually orthogonal in the approximate sense that the autocorrelation function of each signal has a narrow mainlobe width and low sidelobe levels, and the crosscorrellation function of any pair of the signals has smaller values than the sidelobe levels of each autocorrelation function. This means that each weighted chirp signal can be separately compressed into a short pulse, focused individually and combined with other focused beams to form a frame of image. Theoretically, any two chirp signals defined in two nonoverlapped frequency bands are mutually orthogonal. In the present work, however, a fractional overlap of adjacent frequency bands, by up to 25%, were permitted to design more chirp signals within a given transducer bandwidth. The crosscorrelation values due to the frequency overlap could be reduced by alternating the direction of frequency sweep of the adjacent chirp signals. The simulation results show that this method can improve the lateral resolution of image without sacrifice in the frame rate compared with the conventional pulse system.

• 한국컴퓨터정보학회논문지
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• 제4권4호
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• pp.185-192
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• 1999

본 논문에서는 Ungerboeck가 설계한 TCM과 Divsalar가 제안한 다중화 지수(k＝2)의 다중 트렐리스 변조 (Multiple trellis-coded modulation)을 최적의 부호기 설계를 통하여 상태수의 증가에 따라 대역폭과 전력이 제한된 환경에서 부호화 이득을 얻을 수 있는 조건들을 제안하였다. 해석적 기법의 부호기 설계를 통하여 최적의 트렐리스 부호기를 간단히 구성하였으며, 복호는 비터비 최우복호(MLSE)를 적용하였다. QPSK와 8PSK에서 TCM 시스템에서 상태수가 2상태, 4상태, 8상태로 증가함에 따라 다중화 지수(k=2)의 MTCM과 TCM의 성능을 비교하였으며, 상태수가 매우 작아서 TCM의 트렐리스 선도에 병렬천이가 있을 경우 가우시안 채널에서 MTCM 시스템은 대역폭의 확장없이 TCM 시스템보다 우수한 부호화 이득을 얻을 수 있다.

• 대한임베디드공학회논문지
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• 제15권4호
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• pp.167-175
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• 2020

A blood-glucose meter is one of the in vitro diagnostic devices to measure and control the glucose concentration of diabetics. In order to measure the glucose level in the blood, the common method is to measure the amount of electrons, that is, the output current generated by glucose oxidation after a blood sample is inserted into the test strip containing an enzyme. The hematocrit is an obstacle in measuring accurate blood glucose concentration. This paper deals with the design and implementation of a blood-glucose meter to correct the hematocrit interference. We propose a sequential method which measures impedance using the alternating current and then measures glucose in the blood using the direct current. In addition, this paper introduces how to use commercial glucose strips based on the proposed system. Finally, we conducted the performance evaluation of the proposed system by comparing the measured current and impedance with those of the references. As a result, the standard deviation of the current measurement is approximately 0.6nA and the impedance measurement error for measuring the hematocrit is approximately within 1%. The proposed system will improve the accuracy of the conventional blood-glucose meter by reducing the hematocrit interference.

• 반도체디스플레이기술학회지
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• 제8권1호
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• pp.1-5
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• 2009

Typically, single-wafer wet etching is done by dispensing chemical onto the front and back side of spin wafer. The wafer is fixed by a number of chuck pins, which obstruct the chemical flow and would result in the incomplete removal of the remaining film, which can become a source of contamination in the next process. In this paper, we introduce a novel design of wafer chuck, in which chuck pins are groupped into two and each group of pins fixes the substrate alternatively. Two groups of chuck pins fix the high-speed spin substrate with non contact method using a magnetic material. The actual process has been executed to observe the effectiveness of this new wafer chuck. It was found that the new wafer chuck performed better than the conventional wafer chuck for removing the remaining film from the bevel and edge side of substrate.

• Transactions on Electrical and Electronic Materials
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• 제17권1호
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• pp.1-6
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• 2016

Ensuring the secure operation of power systems has become an important and critical matter during the present time, along with the development of large, complex and load-increasing systems. Security constraints such as the thermal limits of transmission lines and bus-voltage limits must be satisfied under all of a system’s operational conditions. An alternative solution to improve the security of a power system is the employment of Flexible Alternating-Current Transmission Systems (FACTS). FACTS devices can reduce the flows of heavily loaded lines, maintain the bus voltages at desired levels, and improve the stability of a power network. The Unified Power Flow Controller (UPFC) is a versatile FACTS device that can independently or simultaneously control the active power, the reactive power and the bus voltage; however, to achieve such functionality, it is very important to determine the optimal location of the UPFC device, with the appropriate parameter setting, in the power system. In this paper, a genetic algorithm (GA) method is applied to determine the optimal location of the UPFC device in a network for the enhancement of the power-system loadability and the minimization of the active power loss in the transmission line. To verify our approach, simulations were performed on the IEEE 14 Bus, 30 Bus, and 57 Bus test systems. The proposed work was implemented in the MATLAB platform.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권5호
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• pp.2299-2318
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• 2019

Location-aware networks are of great importance for both civil lives and military applications. Methods based on line-of-sight (LOS) measurements suffer sever performance loss in harsh environments such as indoor scenarios, where sensors can receive both LOS and non-line-of-sight (NLOS) measurements. In this paper, we propose a data association (DA) process based on the expectation maximization (EM) algorithm, which enables us to exploit multipath components (MPCs). By setting the mapping relationship between the measurements and scatters as a latent variable, coefficients of the Gaussian mixture model are estimated. Moreover, considering the misalignment of sensor position, we propose a space-alternating generalized expectation maximization (SAGE)-based algorithms to jointly update the target localization and sensor position information. A two dimensional (2-D) circularly symmetric Gaussian distribution is employed to approximate the probability density function of the sensor's position uncertainty via the minimization of the Kullback-Leibler divergence (KLD), which enables us to calculate the expectation step with low computational complexity. Moreover, a distributed implementation is derived based on the average consensus method to improve the scalability of the proposed algorithm. Simulation results demonstrate that the proposed centralized and distributed algorithms can perform close to the Monte Carlo-based method with much lower communication overhead and computational complexity.