• 한국전자통신학회논문지
• /
• 제16권3호
• /
• pp.407-416
• /
• 2021

능동위상배열안테나는 적절한 급전신호 가중치 선택에 따라 대국을 향해 주 빔을 조향할 수 있을 뿐만 아니라 간섭원 방향으로 패턴 널을 형성할 수 있다. 주 빔의 조향을 위한 급전신호 가중치는 방사소자의 위치를 기반으로 쉽게 산출할 수 있다. 그리고 패턴 널 형성을 위한 급전신호 가중치 또한 적절한 요구 방사패턴 설정과 WLSM(Weighted Least Squares Method)을 이용하면 산출할 수 있다. 그러나 일반적인 무선 통신망 환경에서 간섭원의 위치는 미인지 상황에 있다. 따라서 적응형 패턴 널 형성 기법이 필요하다. 본 논문에서는 요구 방사특성 설정에 따른 패턴 널 형성이 가능함을 확인하고, 이를 기반으로 관측 영역 기준 이진탐색 알고리즘을 이용하여 간섭원 적응형 패턴 널 형성 기법에 관하여 연구하였다. 제시된 기법을 기반으로 모의실험을 수행한 결과, 효율적으로 간섭 적응형 패턴 널 형성이 가능함을 확인하였다.

• Smart Structures and Systems
• /
• 제14권3호
• /
• pp.327-345
• /
• 2014

This paper presents a composite control strategy for the active suppression of vibration due to the unknown disturbances, such as external excitation, harmonic effects and control spillover, as well as high-frequency accelerometer measurement noise in the all-clamped stiffened plate. The proposed composite control action based on the modal approach, consists of two contributions including feedback part and feedforward part. The feedback part is the well-known PID controller, which is widely used to increase the structure damping and improve its dynamic performance close to the resonance frequencies. In order to get better performance for vibration suppression, the weight matrixes is optimized by chaos sequence. Then an improved disturbance observer (IDOB) as the feedforward compensation part is developed to enhance the vibration suppression performance of PID under various disturbances and uncertainties. The proposed IDOB can simultaneously estimate the various disturbances dynamically as well as measurement noise acting on the system and suppress them by feedforward compensation design. A rigorous analysis is also given to show why the IDOB can effectively suppress the unknown disturbances and measurement noise. In order to verify the proposed composite control algorithm (IDOB-PID), the dSPACE real-time simulation platform is used and an experimental platform for the all-clamped stiffened plate active vibration control system is set up. The experimental results demonstrate the effectiveness, practicality and strong anti-disturbances ability of the proposed control strategy.

• 한국세라믹학회지
• /
• 제53권4호
• /
• pp.463-467
• /
• 2016

$Si^{4+}-N^{3-}$ was incorporated into $Ce^{3+}-doped$ lutetium aluminum garnet ($Lu_{2.965}Ce_{0.035}Al_5O_{12}$, $LuAG:Ce^{3+}$) lattices, resulting in the formation of $Lu_{2.965}Ce_{0.035}Al_{5-x}Si_xO_{12-x}N_x$ [(Lu,Ce)AG:xSN]. For x = 0-0.25, the synthesized powders consisted of the LuAG single phase, and the lattice constant decreased owing to the smaller $Si^{4+}$ ions. However, for x > 0.25, a small amount of unknown impurity phases was observed, and the lattice constant increased. Under 450 nm excitation, the PL spectrum of $LuAG:Ce^{3+}$ exhibited the green band, peaking at 505 nm. The incorporation of $Si^{4+}-N^{3-}$ into the $Al^{3+}-O^{2-}$ sites of $LuAG:Ce^{3+}$ led to a red-shift of the emission peak wavelength from 505 to 570 nm with increasing x. Corresponding CIE chromaticity coordinates varied from the green to yellow regions. These behaviors were discussed based on the modification of the $5d^1$ split levels and crystal field surroundings of $Ce^{3+}$, which arose from the Ce-(O,N)8 bonds.

• Structural Engineering and Mechanics
• /
• 제34권3호
• /
• pp.351-366
• /
• 2010

A novel system identification and structural health assessment procedure of steel framed structures with semi-rigid connections is presented in this paper. It is capable of detecting damages at the local element level under normal operating conditions; i.e., serviceability limit state. The procedure is a linear time-domain system identification technique in which the structure responses are required, whereas the dynamic excitation force is not required to identify the structural parameters. The procedure tracks changes in the stiffness properties of all the elements in a structure. It can identify damage-free and damaged structural elements very accurately when excited by different types of dynamic loadings. The method is elaborated with the help of several numerical examples. The results indicate that the proposed algorithm identified the structures correctly and detected the pre-imposed damages in the frames when excited by earthquake, impact, and harmonic loadings. The algorithm can potentially be used for structural health assessment and monitoring of existing structures with minimum disruption of operations. Since the procedure requires only a few time points of response information, it is expected to be economic and efficient.

• Smart Structures and Systems
• /
• 제4권5호
• /
• pp.583-603
• /
• 2008

In this study, a real-time damage detection method using output-only acceleration signals and artificial neural networks (ANN) is developed to monitor the occurrence of damage and the location of damage in structures. A theoretical approach of an ANN algorithm that uses acceleration signals to detect changes in structural parameters in real-time is newly designed. Cross-covariance functions of two acceleration responses measured before and after damage at two different sensor locations are selected as the features representing the structural conditions. By means of the acceleration features, multiple neural networks are trained for a series of potential loading patterns and damage scenarios of the target structure for which its actual loading history and structural conditions are unknown. The feasibility of the proposed method is evaluated using a numerical beam model under the effect of model uncertainty due to the variability of impulse excitation patterns used for training neural networks. The practicality of the method is also evaluated from laboratory-model tests on free-free beams for which acceleration responses were measured for several damage cases.

• 한국철도학회논문집
• /
• 제12권6호
• /
• pp.989-995
• /
• 2009

Short-time Fourier transforms(STFT)은 시간에 따라 변동하는 조화성분을 가지는 신호의 분석에 유용하게 적용되는 방법이다. 철도차량의 진동신호에서 많이 발견되는 운동학적 진동은 조화 특성이 속도 변화에 따라 점진적으로 변하기 때문에 오더 분석 방법과 상관함수를 이용하면 STFT 분석 방법을 개선할 수 있다. 본 논문에서는 차량의 속도 신호를 구할 수 없거나 잡음이 많을 때 상관함수를 이용하여 신호를 재추출하여 오더 분석을 적용하는 방법에 대하여 다룬다. 이 방법을 한국형고속열차의 운행 중에 취득한 차축 및 차체 진동데이터의 분석에 적용하여 기존의 STFT와 오더 분석을 이용한 방법을 비교 하였다.

• Journal of Information Display
• /
• 제11권4호
• /
• pp.135-139
• /
• 2010

A series of Sr-Si-S compounds was synthesized using an advanced chemical method in which the use of one solution-based process uniformly dispersed the $Eu^{2+}$ activators in the host crystals, to find new compositions that would suit phosphor applications. Particular focus was given to the Si-rich region. This led to the synthesis of a single-phase compound that showed an unknown X-ray diffraction pattern. This compound had a composition close to that of $SrSi_2S_5$. When this compound is activated with $Eu^{2+}$ ($SrSi_2S_5:Eu^{2+}$), it shows a cyan-blue emission with a main luminescence peak at 495 nm. This emission is excited by wavelengths of 250-440 nm and has a maximum excitation at 350 nm.

• Smart Structures and Systems
• /
• 제20권2호
• /
• pp.207-217
• /
• 2017

Because of the inevitable uncertainties such as structural parameters, external excitations and measurement noises, the effects of uncertainties should be taken into consideration in structural damage detection. In this paper, two probabilistic structural damage detection approaches are proposed to account for the underlying uncertainties in structural parameters and external excitation. The first approach adopts the statistical moment-based structural damage detection (SMBDD) algorithm together with the sensitivity analysis of the damage vector to the uncertain parameters. The approach takes the advantage of the strength SMBDD, so it is robust to measurement noise. However, it requests the number of measured responses is not less than that of unknown structural parameters. To reduce the number of measurements requested by the SMBDD algorithm, another probabilistic structural damage detection approach is proposed. It is based on the integration of structural damage detection using temporal moments in each time segment of measured response time history with the sensitivity analysis of the damage vector to the uncertain parameters. In both approaches, probability distribution of damage vector is estimated from those of uncertain parameters based on stochastic finite element model updating and probabilistic propagation. By comparing the two probability distribution characteristics for the undamaged and damaged models, probability of damage existence and damage extent at structural element level can be detected. Some numerical examples are used to demonstrate the performances of the two proposed approaches, respectively.

• Molecules and Cells
• /
• 제26권3호
• /
• pp.265-269
• /
• 2008

Calumenin, a multiple EF-hand $Ca^{2+}$ binding protein is located in the SR of mammalian heart, but the functional role of the protein in the heart is unknown. In the present study, an adenovirus gene transfer system was employed for neonatal rat heart to examine the effects of calumenin over-expression (Calu-OE) on $Ca^{2+}$ transients. Calu-OE (8 folds) did not alter the expression levels of DHPR, RyR2, NCX, SERCA2, CSQ and PLN. However, Calu-OE affected several parameters of $Ca^{2+}$ transients. Among them, prolongation of time to 50% baseline ($T_{50}$) was the most outstanding change in electrically-evoked $Ca^{2+}$ transients. The higher $T_{50}$ was due to an inhibition of SERCA2-mediated $Ca^{2+}$ uptake into SR, as tested by oxalate-supported $Ca^{2+}$ uptake. Furthermore, co-IP study showed a direct interaction between calumenin and SERCA2. Taken together, calumenin in the cardiac SR may play an important role in the regulation of $Ca^{2+}$ uptake during the EC coupling process.

• Smart Structures and Systems
• /
• 제22권4호
• /
• pp.399-411
• /
• 2018

The difficulty in modeling complex nonlinear structures lies in the presence of significant sources of uncertainties mainly attributed to sudden changes in the structure's behavior caused by regular aging factors or extreme events. Quantifying these uncertainties and accurately representing them within the complex mathematical framework of Structural Health Monitoring (SHM) are significantly essential for system identification and damage detection purposes. This study highlights the importance of uncertainty quantification in SHM frameworks, and presents a comparative analysis between intrusive and non-intrusive techniques in quantifying uncertainties for SHM purposes through two different variations of the Kalman Filter (KF) method, the Ensemble Kalman filter (EnKF) and the Polynomial Chaos Kalman Filter (PCKF). The comparative analysis is based on a numerical example that consists of a four degrees-of-freedom (DOF) system, comprising Bouc-Wen hysteretic behavior and subjected to El-Centro earthquake excitation. The comparison is based on the ability of each technique to quantify the different sources of uncertainty for SHM purposes and to accurately approximate the system state and parameters when compared to the true state with the least computational burden. While the results show that both filters are able to locate the damage in space and time and to accurately estimate the system responses and unknown parameters, the computational cost of PCKF is shown to be less than that of EnKF for a similar level of numerical accuracy.