• ETRI Journal
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• 제29권5호
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• pp.596-606
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• 2007

It is well known that an OFDM receiver is vulnerable to synchronization errors. Despite fine estimations used in the initial acquisition, there are still residual synchronization errors. Though these errors are very small, they severely degrade the bit error rate (BER) performance. In this paper, we propose a residual error elimination scheme for the digital OFDM baseband receiver aiming to improve the overall BER performance. Three improvements on existing schemes are made: a pilot-aided recursive algorithm for joint estimation of the residual carrier frequency and sampling time offsets; a delay-based timing error correction technique, which smoothly adjusts the incoming data stream without resampling disturbance; and a decision-directed channel gain update algorithm based on recursive least-squares criterion, which offers faster convergence and smaller error than the least-mean-squares algorithms. Simulation results show that the proposed scheme works well in the multipath channel, and its performance is close to that of an OFDM system with perfect synchronization parameters.

• Smart Structures and Systems
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• 제24권5호
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• pp.659-668
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• 2019

In digital image correlation, speckle image is closely related to the measurement accuracy. A practical global evaluation criterion for speckle image is presented. Firstly, based on the essential factors of the texture image, both the average particle size and image sharpness are used for the assessment of speckle image. The former is calculated by a simplified auto-covariance function and Gaussian fitting, and the latter by focusing function. Secondly, the computation of the average particle size and image sharpness is verified by numerical simulation. The influence of these two evaluation parameters on mean deviation and standard deviation is discussed. Then, a physical model from speckle projection to image acquisition is established. The two evaluation parameters can be mapped to the physical devices, which demonstrate that the proposed evaluation method is reasonable. Finally, the engineering application of the evaluation method is pointed out.

• Journal of Power Electronics
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• 제14권3호
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• pp.444-457
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• 2014

This paper presents the design and realization of a digital PV simulator with a Push-Pull Forward (PPF) circuit based on the principle of modular hardware and configurable software. A PPF circuit is chosen as the main circuit to restrain the magnetic biasing of the core for a DC-DC converter and to reduce the spike of the turn-off voltage across every switch. Control and I/O interface based on a personal computer (PC) and multifunction data acquisition card, can conveniently achieve the data acquisition and configuration of the control algorithm and interface due to the abundant software resources of computers. In addition, the control program developed in Matlab/Simulink can conveniently construct and adjust both the models and parameters. It can also run in real-time under the external mode of Simulink by loading the modules of the Real-Time Windows Target. The mathematic models of the Push-Pull Forward circuit and the digital PV simulator are established in this paper by the state-space averaging method. The pole-zero cancellation technique is employed and then its controller parameters are systematically designed based on the performance analysis of the root loci of the closed current loop with $k_i$ and $R_L$ as variables. A fuzzy PI controller based on the Takagi-Sugeno fuzzy model is applied to regulate the controller parameters self-adaptively according to the change of $R_L$ and the operating point of the PV simulator to match the controller parameters with $R_L$. The stationary and dynamic performances of the PV simulator are tested by experiments, and the experimental results show that the PV simulator has the merits of a wide effective working range, high steady-state accuracy and good dynamic performances.

• 한국산학기술학회논문지
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• 제18권2호
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• pp.426-432
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• 2017

본 논문에서는 주요 선진국의 국방획득조직 현황과 관련 분석에 따른 시사점, 국방획득체계의 전문성 활용 방안과 관련 과 방위사업감독관의 운용현황, 결론적으로 각 전문분야에서의 전문화 및 운용방안, 기대효과와 향후방향을 중장기적 관점에서 비교 분석하였다. 세부적으로, 주요 선진국의 국방획득조직의 현황을 통해서 국내에 적용 가능한 운용체계를 식별하였고, 각 분야의 운용방안을 반영하면서 방산비리 근절과 방위사업감독관의 효율적인 운용이라는 부분이 정부를 비롯하여 각 기관, 민간 기관들 등 전사적인 노력이 밑받침이 되어야 한다는 사실을 도출할 수 있었다. 법적 제도적 관점에서 법 정비의 시급성을 강구하는 기회가 되었고, 그리고 현재의 사전검증 절차 수립이라는 부분이 투명성, 신뢰성, 전문성을 제 3자 관점에서 투명성을 확립할 수 있는 제도적 근거가 되었다는 점에서 큰 의의가 있다고 판단한다. 결론적으로, 방위사업감독관의 운용은 방위사업 전반에 대한 사전 감독체계 수립을 가능하게 하고, 업무적 독립성을 최대한 보장할 수 있는 환경을 구축할 수 있다는 점에서 그 영향력을 기대해 볼만 하다.

• 한국어교육
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• 제28권4호
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• pp.337-366
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• 2017

이 연구는 미국 대학에서 제2외국어로 한국어를 배우는 영어권 학습자의 부사형 조사 '-에'의 다양한 의미론적 뜻의 습득을 고찰한다. 이 연구는 초급반, 중급반, 고급반의 45명 참가자들을 대상으로, 한국어 학습 첫 학기 교실에서 이 조사가 가르쳐 졌을 때 각 단계의 학습자들이 어떻게 그 의미를 해석하며 실제로 어떻게 사용하는가에 대한 수행능력을 중심으로 이루어졌다. 이 연구 결과는 다양한 의미론적 뜻에 대해 서로 다른 발달 과정을 보여주고 있다. 통계 분석 결과에 따르면 초급반과 중급반에서는 이 연구 과제 '-에'의 의미 중 시간과 목표, 정적인 위치적 의미의 습득이 접촉의 의미나, 개별의 의미보다 좀 더 쉽게 습득 된다는 것을 보여주고 있다. 반면에 고급반에서는 개별의 의미를 제외하고는 모든 의미론적인 의미가 거의 목표점까지 도달하였다. 이 연구는 의미론적 복합성과 다른 언어권 간의 영향과 같은 요인과 함께, 제2 언어 빈도수, 언어학적 입력, 습득 방식과 같은 다양한 요인이 '-에'의 습득에 영향을 미친다는 것을 제시하고 있다.

• 조명전기설비학회논문지
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• 제12권4호
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• pp.136-145
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• 1998

본 논문에서는 몰드변압기 예방진단을 위해 정상상태와 비정상상태 몰드변압기의 진동신호의 FFT 및 시계열 분석에 관해 연구하였다. 실험올 위한 제어변수들로 공급전압, 부하전류 및 주위온도를 변화시키면서, 진동신호 크기, 주파수 스펙트럼 및 시계열 계수와 같은 측정변수들을 분석하였다. 제어변수 변화에 의한 진동선호는 권선표변과 철섬에 부착된 가속도센서로 측정되었으며, 이 신호들은 중폭기를 거쳐 데이터 수집장치에서 측정변수들로 계산되었다. 또한, 정 상상태 분석 후, 몰드변압기의 구조적 변형올 모의하였다. 비정상상태 진동신호는 정상상태와 같은 제어변수 변화 에 의해 측정되었다. 연구 결과, 정상상태와 비정상상태 진동신호는 수직진동신호와 수평진동신호를 비교하여 분석함으혹써 구별이 가능하였다.

• Korean Journal of Radiology
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• 제22권9호
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• pp.1525-1536
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• 2021

Objective: To investigate the feasibility of cine three-dimensional (3D) balanced steady-state free precession (b-SSFP) imaging combined with a non-local means (NLM) algorithm for image denoising in evaluating cardiac function in children with repaired tetralogy of Fallot (rTOF). Materials and Methods: Thirty-five patients with rTOF (mean age, 12 years; range, 7-18 years) were enrolled to undergo cardiac cine image acquisition, including two-dimensional (2D) b-SSFP, 3D b-SSFP, and 3D b-SSFP combined with NLM. End-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), and ejection fraction (EF) of the two ventricles were measured and indexed by body surface index. Acquisition time and image quality were recorded and compared among the three imaging sequences. Results: 3D b-SSFP with denoising vs. 2D b-SSFP had high correlation coefficients for EDV, ESV, SV, and EF of the left (0.959-0.991; p < 0.001) as well as right (0.755-0.965; p < 0.001) ventricular metrics. The image acquisition time ± standard deviation (SD) was 25.1 ± 2.4 seconds for 3D b-SSFP compared with 277.6 ± 0.7 seconds for 2D b-SSFP, indicating a significantly shorter time with the 3D than the 2D sequence (p < 0.001). Image quality score was better with 3D b-SSFP combined with denoising than with 3D b-SSFP (mean ± SD, 3.8 ± 0.6 vs. 3.5 ± 0.6; p = 0.005). Signal-to-noise ratios for blood and myocardium as well as contrast between blood and myocardium were higher for 3D b-SSFP combined with denoising than for 3D b-SSFP (p < 0.05 for all but septal myocardium). Conclusion: The 3D b-SSFP sequence can significantly reduce acquisition time compared to the 2D b-SSFP sequence for cine imaging in the evaluation of ventricular function in children with rTOF, and its quality can be further improved by combining it with an NLM denoising method.

• 대한음성학회:학술대회논문집
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• 대한음성학회 2006년도 춘계 학술대회 발표논문집
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• pp.123-125
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• 2006

One of the biggest problems unsolved in emotional speech acquisition is how to make or find a situation which is close to natual or desired state from humans. We proposed a method to collect emotional speech data by scriptual context. Several contexts from the scripts of drama were chosen by the experts in the area. Context were divided into 6 classes according to the contents. Two actors, one male and one female, read the text after recognizing the emotional situations in the script.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권2호
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• pp.846-864
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• 2017

Software Defined Network (SDN) realizes management and control over the underlying forwarding device, along with acquisition and analysis of network topology and flow characters through south bridge protocol. Data path Identification (DPID) is the unique identity for managing the underlying device, so forged DPID can be used to attack the link of underlying forwarding devices, as well as carry out DoS over the upper-level controller. This paper proposes a dynamic defense method based on Client-Puzzle model, in which the controller achieves dynamic management over requests from forwarding devices through generating questions with multi-level difficulty. This method can rapidly reduce network load, and at the same time separate attack flow from legal flow, enabling the controller to provide continuous service for legal visit. We conduct experiments on open-source SDN controllers like Fluid and Ryu, the result of which verifies feasibility of this defense method. The experimental result also shows that when cost of controller and forwarding device increases by about 2%-5%, the cost of attacker's CPU increases by near 90%, which greatly raises the attack difficulty for attackers.

• Journal of Power Electronics
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• 제15권3호
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• pp.644-651
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• 2015

This paper introduces a novel digital one cycle control (DOCC) boost power factor correction (PFC) converter. The proposed PFC converter realizes the FPGA-based DOCC control approach for single-phase PFC rectifiers without input voltage sensing or a complicated two-loop compensation design. It can also achieve a high power factor and the operation of low harmonic input current ingredients over universal loads in continuous conduction mode. The trailing triangle modulation adopted in this approach makes the acquisition of the average input current an easy process. The controller implementation is based on a boost topology power circuit with low speed, low-resolution A/D converters, and economical FPGA development board. Experimental results demonstrate that the proposed PFC rectifier can obtain a PF value of up to 0.999 and a minimum THD of at least 1.9% using a 120W prototype.