• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2015년도 제51회 KOSCO SYMPOSIUM 초록집
• /
• pp.215-218
• /
• 2015

Simultaneous laser ignition and spectroscopy is a scheme that enables rapid determination of the local equivalence ratio and condensed fuel concentration during a reaction in a two phase spray flame. We have conducted quantitative analysis of the LIBS signals according to the equivalence ratio, droplet size, droplet number density and droplet concentration as a part of novel feedback control strategy proposed for flame ignition and stabilization with simultaneous in situ combustion flow diagnostics. This is a desirable scheme since such real time information onboard an engine for instance can be constantly monitored and fed back to the control loop to enhance the mixing process and minimize emissions of unwanted species and potential combustion instability.

• 천문학회보
• /
• 제35권2호
• /
• pp.32.1-32.1
• /
• 2010

From my personal perspective, I will review the current status of observational studies on the fundamental properties of AGN and the role of supermassive black holes in galaxy evolution.

• 한국전자파학회논문지
• /
• 제22권3호
• /
• pp.282-291
• /
• 2011

적응 변조(Adaptive Modulation: AM) 방식은 시간적으로 공간적으로 바뀌는 채널의 상태에 적합한 변조 방식을 적응적으로 할당함으로써, 시스템의 효율을 높이는 중요한 통신 방식이다. 고정 변조 방식은 시간에 따라 신호 대 잡음비(SNR: Signal-to-Noise Ratio)가 변하는 채널에서 BER(Bit Error Rate) 성능이 변한다. 하지만 적응변조 방식은 모든 채널 상태의 SNR에 대하여 일정한 평균 BER 성능을 유지하므로 채널의 상태가 수시로 변하는 통신 환경에서 시스템의 성능을 확보한다. 이를 위해서 무엇보다도 정확하고, 빠르게 신호 대 잡음비를 추정할 수 있는 간단한 SNR 추정 방법이 요구된다. 본 논문에서는 효과적인 적응 변조를 위하여 SNR 추정 성능이 적응 변조 시스템에 미치는 영향을 평균 BER과 평균 데이터 처리율(throughput)을 통하여 분석한다. 또한, 본 논문에서는 decision feedback 신호의 자기 상관 기반의 SNR 추정 방법 및 기존의 SNR 추정 방법들을 적응 변조시스템에 적용하여 각 변조 레벨 변환 점에서 SNR 추정 성능에 따라 결정되는 적응 변조 시스템의 성능 변화를 확인한다. Decision feedback 신호의 자기 상관 기반 SNR 추정 방법은 M-QAM(Quadrature Amplitude Modulation) 신호에서도 비교적 안정적인 추정 성능을 보이기 때문에 적응 변조 시스템에서 다른 SNR 추정 방법들에 비해 변조 레벨 변환 점에서 성능 열화를 줄인다.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2008년도 춘계학술대회논문집
• /
• pp.442-448
• /
• 2008

This paper presents an approach to define an optimal piezoactuator length to actively control structural vibration. The optimal ratio of the piezoactuator length against beam length when a pair of piezoceramic actuator and accelerometer is used to suppress unwanted vibration with direct velocity feedback (DVFB) control strategy is not clearly defined so far. It is well known that direct velocity feedback (DVFB) control can be very useful when a pair of sensor and actuator is collocated on structures with a high gain and excellent stability. It is considered that three different collocated pairs of piezoelectric actuators (20, 50 and 100 mm) and accelerometers installed on three identical clamped-clamped beams (300 * 20 * 1 mm). The response of each sensor-actuator pair requires strictly positive real (SPR) property to apply a high feedback gain. However the length of the piezoactuator affects SPR property of the sensor-actuator response. Intensive simulation and experiment shows the effect of the actuator length variation is strongly related with the frequency range of SPR property. A shorter actuator gave a wider SPR frequency range as a longer one had a narrower range. The shorter actuator showed limited control performance in spite of a higher gain was applied because the actuation force was relatively small. Thus an optimal length ratio (actuator length/beam length) was suggested to obtain relevant performance with good stability with DVFB strategy. The result of this investigation could give important information in the design of active control system to suppress unwanted vibration of smart structures with piezoelectric actuators and accelerometers.

• 전자공학회논문지
• /
• 제51권11호
• /
• pp.33-39
• /
• 2014

본 논문에서는 다중 사용자 다중 안테나 하향링크 시스템에서 maximal ratio transmission (MRT) 기법 사용 시, 에너지 효율을 최대화하는 최적의 송신 안테나 수에 대해 알아본다. Full channel state information at the transmitter (CSIT) 환경에서 평균 채널 이득, 각 단말 간 채널 독립성, 평균 path loss를 사용하여 최적화 식을 근사하고 편미분을 이용하여 closed form으로 최적의 송신 안테나 수를 구한다. 또한 limited feedback 환경에서는 동일한 방법으로 근사한 목적함수에 대하여 bisection method를 이용하여 최적의 송신 안테나 수를 찾는다. 모의실험 결과를 통해, 구해진 최적의 송신안테나 수가 exhaustive search로 찾은 최적의 송신안테나 수에 비해 오차가 크지 않음을 확인하고, 단말의 피드백 비트 수가 최적의 송신 안테나 수에 미치는 영향을 분석한다.

• 유공압시스템학회논문집
• /
• 제2권4호
• /
• pp.7-13
• /
• 2005

This paper presents modeling and ostimator/controller design for the hydraulic system in Vehicle Stability Control(VSC) system. A nonlinear mathematical model of the VSC hydraulic system is proposed and its accuracy is experimentally verified. A brake pressure estimator is then designed based on the derived mathematical model of VSC hydraulic system. And a disturbance observer, which compensates the estimation error between the brake pressure and the computed brake pressure is also designed to enhance the accuracy of the estimator. The proposed controller has the form of a feedback controller and determines explicitly the on/off ratio of valves' driving PWM signals by means of making use of the simplified mathematical model in the VSC hydraulic system. The performance of the designed controller whose feedback signal is generated by the brake pressure estimator is validated through experimental results.

• 천문학논총
• /
• 제27권4호
• /
• pp.289-290
• /
• 2012

Feedback from accreting BH (AGN) is thought to be responsible for the co-evolution of BHs and galaxies. It is likely to be prominent in the most luminous dust-obscured quasars, particularly those containing radio sources too luminous to be powered by starbursts. In order to investigate the feedback mechanism in detail, we select a unique sample containing ~ 200 of the most luminous obscured QSOs by cross-matching the WISE catalog with the FIRST and NVSS radio surveys. We present overall statistics for the observed range of colors and radio/mid-IR flux density ratio. We also present our efforts to understand the physical and evolutionary nature of these extreme feedback candidates using various telescopes such as Magellan, SOAR, Herschel, and ALMA.

• IEIE Transactions on Smart Processing and Computing
• /
• 제4권3호
• /
• pp.145-148
• /
• 2015

In this letter, we present a new linearization method for a voltage controlled oscillator (VCO)-based quantizer in an analog-to-digital converter (ADC). The nonlinearity of the VCO generates unwanted harmonic spurs and reduces the signal-to-noise and distortion ratio (SNDR) of the VCO-based quantizer. This letter suggests a frequency-to-current feedback method to effectively suppress harmonic distortion. The proposed method decreases the harmonic spurs by more than 53 dB. And a VCO-based quantizer employing the proposed linearization method achieves a high SNDR of 74.1 dB.

• 한국정밀공학회지
• /
• 제25권2호
• /
• pp.49-56
• /
• 2008

In order to reduce energy consumption, secondary controlled system has been applied to many types of equipments. In lifting equipments or press machines using hydraulic cylinder, a hydraulic transformer is used as a control component instead of a valve for motion control and a component for recovering potential energy of load. The transformer is a combination of a variable displacement pump/motor as a secondary controlled element and a fixed displacement pump/motor. In this paper the effect of transformer is studied. Multiple closed loop controllers with displacement feedback of variable pump/motor, speed feedback and position feedback of cylinder are used. The efficiency and energy consumption when cylinder is driven up and down is calculated by simulation. Simulation results show that considerable energy saving is achieved by choosing load ratio, circuit type and supply pressure.

• 대한전기학회논문지
• /
• 제39권8호
• /
• pp.828-835
• /
• 1990

A new state feedback control scheme is proposed to improve the stability and dynamic performances of the series resonant converter (SRC). The proposed scheme can be easily implemented without speed limitation. Design parameter of the proposed control is the ratio of the state feedback gains. A closed loop dynamic modeling for the SRC with the proposed control law is derived. Parametric curves which can be used to select the design parameter in the control system are presented. The experimental results show that the excellent dynamic performance of the converter can be obtained by properly selecting the design parameter. The results are further compared with both the theoretical analysis and the frequency control.