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Determination of Traps' Density of State in OLEDs from Current-Voltage Analysis

Chinese Physics Letters 2016年第1期33卷 127-131页

作者： M.S.Zaini M.A.Mohd Sarjidan W.H.Abd.Majid Low Dimensional Materials research Centre Physics DepartmentUniversity of Malaya

A simple method to determine the traps＇ density of state （DOS） in organic light-emitting diodes （OLEDs） by manipulating the current-voltage （I-V） characteristic of the devices at room temperature is introduced. In particular, the trap-dependent space-charge limited current formula is simplified to obtain effective density of traps. In this study, poly[（9,9-di-n-octylfluorenyl-2,7-diyl）-alt-（benzo[2,1,3]thiadiazol-4,8-diyl）] （F8BT） and 2- Methoxy-5-（3＇, 7＇-dimethyloctyloxy） benzene-l,4-diacetonitrile （0C1 Clo-PPV） are selected as the OLEDs emissive layer. The trap DOS of F8BT- and OC1Clo-PPV-based OLEDs are calculated in the magnitudes of 1024 m^-3 and 1023 m^-3, respectively. In addition, the results agree with the other conventional method which is used to determine the trap DOS in OLEDs. This calculation technique may serve as a robust and reliable approach to obtain the trap DOS in OLEDs at room temperature.

关键词： OLEDs Determination of Traps of in from

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Smart Semi-active PID-ACO control strategy for tower vibration reduction in Wind Turbines with MR damper

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Earthquake Engineering and Engineering Vibration 2019年第4期18卷 887-902页

作者： Mahmudur Rahman Zhi Chao Ong Wen Tong Chong Sabariah Julai Department of Mechanical Engineering Faculty of Engineering University of Malaya

Wind turbine technology is well known around the globe as an eco-friendly and eff ective renewable power source. However, this technology often faces reliability problems due to structural vibration. This study proposes a smart semi-active vibration control system using Magnetorheological (MR) dampers where feedback controllers are optimized with nature-inspired algorithms. Proportional integral derivative (PID) and Proportional integral (PI) controllers are designed to achieve the optimal desired force and current input for MR the damper. PID control parameters are optimized using an Ant colony optimization (ACO) algorithm. The eff ectiveness of the ACO algorithm is validated by comparing its performance with Ziegler-Nichols (Z-N) and particle swarm optimization (PSO). The placement of the MR damper on the tower is also investigated to ensure structural balance and optimal desired force from the MR damper. The simulation results show that the proposed semi-active PID-ACO control strategy can signifi cantly reduce vibration on the wind turbine tower under diff erent frequencies (i.e., 67%, 73%, 79% and 34.4% at 2 Hz, 3 Hz, 4.6 Hz and 6 Hz, respectively) and amplitudes (i.e. 50%, 58% and 67% for 50 N, 80 N, and 100 N, respectively). In this study, the simulation model is validated with an experimental study in terms of natural frequency, mode shape and uncontrolled response at the 1st mode. The proposed PID-ACO control strategy and optimal MR damper position is also implemented on a lab-scaled wind turbine tower model. The results show that the vibration reduction rate is 66% and 73% in the experimental and simulation study, respectively, at the 1st mode.

关键词： ant colony optimization fi nite diff erence method magnetorheological damper PID-ACO controller semiactive control system identifi cation wind turbine tower

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