Improved performance of polymer photodetectors using indium–tin-oxide modified by phosphonic acid-based self-assembled monolayer treatment

For organic photodetectors (OPDs), in order to realize high incident-photon-to-current conversion efficiency (IPCE) and high on/off ratio, the characteristics of hole-only devices and polymer photodetectors with indium–tin-oxide (ITO) modified by phosphonic acid-based self-assembled monolayer treatment in a short time are investigated. 1H,1H,2H,2H-Perfluorooctanephosphonic acid (FOPA) treatment results not only in lowering of the injection barrier at the ITO/organic layer interface but also in the lowering of the contact resistance between ITO and the organic layer. An OPD based on a blend of a donor, poly(9,9-dioctylfluorene-co-bithiophene) (F8T2), and an acceptor, fullerene derivative [6-6]phenyl-C61-butyric acid methyl ester (PCBM) with FOPA treatment exhibits blue-light sensitivity and IPCE of approximately 75% at −4 V. For the F8T2:PCBM device with FOPA, the IPCE is improved, and the dark current hardly increases. F8T2:PCBM device with FOPA treatment exhibits high on/off ratio, wide detector dynamic range and cut-off frequency of more than 10 MHz under reverse voltage.     

Direct and adjoint global stability analysis of turbulent transonic flows over a NACA0012 profile

In this work, various turbulent solutions of the two‐dimensional (2D) and three‐dimensional compressible Reynolds averaged Navier–Stokes equations are analyzed using global stability theory. This analysis is motivated by the onset of flow unsteadiness (Hopf bifurcation) for transonic buffet conditions where moderately high Reynolds numbers and compressible effects must be considered. The buffet phenomenon involves a complex interaction between the separated flow and a shock wave. The efficient numerical methodology presented in this paper predicts the critical parameters, namely, the angle of attack and Mach and Reynolds numbers beyond which the onset of flow unsteadiness appears. The geometry, a NACA0012 profile, and flow parameters selected reproduce situations of practical interest for aeronautical applications. The numerical computation is performed in three steps. First, a steady baseflow solution is obtained; second, the Jacobian matrix for the RANS equations based on a finite volume discretization is computed; and finally, the generalized eigenvalue problem is derived when the baseflow is linearly perturbed. The methodology is validated predicting the 2D Hopf bifurcation for a circular cylinder under laminar flow condition. This benchmark shows good agreement with the previous published computations and experimental data. In the transonic buffet case, the baseflow is computed using the Spalart–Allmaras turbulence model and represents a mean flow where the high frequency content and length scales of the order of the shear‐layer thickness have been averaged. The lower frequency content is assumed to be decoupled from the high frequencies, thus allowing a stability analysis to be performed on the low frequency range. In addition, results of the corresponding adjoint problem and the sensitivity map are provided for the first time for the buffet problem. Finally, an extruded three‐dimensional geometry of the NACA0012 airfoil, where all velocity components are considered, was also analyzed as a Triglobal stability case, and the outcoming results were compared to the previous 2D limited model, confirming that the buffet onset is well detected. Copyright © 2014 John Wiley & Sons, Ltd.     

X波段中频相参多普勒天气雷达接收机的设计

分析研究了如何设计X波段中频相参多普勒天气雷达接收机方案以及如何计算接收机噪声系数、接收机灵敏度、前端增益与系统动态范围。同时提出了稳定本振的措施,使数字中频接收机具有可靠性高、灵敏度高、增益高、选择性好、动态范围大、适应性广、自动实现数字频率跟踪,数字定相等优点。     

灵敏度可调的光学读出非制冷热像元设计

设计了一种可见光反射型光学读出非制冷热像元结构。理论分析表明热像元的热-机械灵敏度达到0.043deg·K-1,在热像元面积比已有报道减小75%的情况下,热-机械灵敏度反而提高至少79%。通过改变弯折梁底层金膜的面积来调节热像元的灵敏度,使其可在2.36×10-6rad·m2·W-1和9.21×10-6rad·m2·W-1之间变化。ANSYS仿真结果和理论结果吻合较好,验证了设计的正确性。     

二次雷达数字时间灵敏度控制处理的实现

如何有效剔除二次雷达系统中存在的干扰目标,提升设备的处理能力和效率,一直是系统最关注的方向之一。区别于传统信道接收机灵敏度简单调节的方法,提出了一种基于可编程门阵列( FPGA)实时计算目标应答信号强度的方法,通过设置有效应答信号范围,在应答脉冲处理阶段剔除时间灵敏度控制( STC)门限外由多径及异步等引起的干扰脉冲,减少了后期处理的信息数据,提升了系统效率和系统的多目标处理能力。通过外场实验验证,该方法能有效减少二次雷达系统内70%的虚警目标。     

测量长期光辐射下人眼对比度敏感函数及模型

正常环境下研究得出的对比敏感度函数模型,在人眼受长时间高亮度电脑或手机显示屏光辐射(即视觉异常)时不再适用。文中基于正弦光栅的计算公式在Matlab中编程得到了实验所需的正弦光栅。由于在不同光谱功率分布下的对比敏感度值会有较大差别,实验基于LCD显示器得出视觉异常实验者在不同光谱功率分布(日光,灯光)下的对比敏感度值和CSF曲线。并通过非线性最小二乘法得出视觉异常时CSF模型。其结果表明,视觉异常时人眼最敏感空间频率和光学成像能力均发生了较大变化,且节能灯和显示屏等非自然光源与自然光源日光相比其光谱功率分布对人眼对比敏感度的影响最大。     

敏感工作气体对射流陀螺灵敏度的影响

研究了干燥空气、N2和He等3种常用敏感工作气体对射流陀螺灵敏度的影响。采用有限元法计算了输入角速度ωi=20(°)/s时敏感元件内的流场。计算结果和实验表明,改变敏感元件内敏感工作气体的种类,流场分布也随之变化。ωi=20(°)/s时,两热电阻丝r1、r2处的气流速度差ΔvN2>ΔvAIR>ΔvHe。灵敏度系数KN2>KAIR>KHe,其中KN2=1.05 KAIR,KHe=0.21%KAIR。N2对应的灵敏度最高,热电阻丝抗氧化,稳定性较好,但成本高;干燥空气的灵敏度次之,热电阻丝易氧化,稳定性差;He对应的灵敏度最小,热电阻丝不易氧化,稳定性最好。该文解释了敏感工作气体对射流陀螺灵敏度的影响机理,为提高射流陀螺的实用性,满足不同工程需要开辟了一个新的途径。     

一种新型SAW气体传感器的设计

提出了将纳米线技术与声表面波(SAW)技术相结合,分别利用纳米线气体敏感材料比表面积高,声表面波传感器质量敏感性高的优点,探索研制新一代声表面波气体传感器。该传感器具有响应速度快,灵敏度高,体积小,质量注和易集成等优点。该文主要从SAW专用芯片的研制、专用纳米线研制、专用纳米线的表面修饰与改性研究、检测电路设计等4方面进行了阐述。理论计算表明,相比传统二维结构的SAW气体传感器,三维纳米线结构的SAW气体传感器的在灵敏度和响应速度上都得到提高。     

Media as Educator,Media as Disruptor: Conceptualizing the Role of Social Context in Media Effects

We document how social contexts serve to refract media effects. We theorized the relationship between media use and individual‐level knowledge (and attitude) would be stronger when community‐level knowledge (and attitude) was low than when it was high. Data come from a national survey (N = 12,608 women and 1,237 men) conducted in Nepal. Knowledge and stigma toward people living with HIV were the 2 dependent variables. Hypotheses were tested 12 times: across the use of 3 media (newspaper, radio, television) × 2 study outcomes (knowledge and attitudes) × 2 genders. Predicted interactions were supported in 9 of the 12 tests. Findings point to the need to take into account the role of community factors in theorizing about media effects.     

Synthesis of Stimuli-responsive Nanoparticles by Solution Polymerization

In this study, stimuli-responsive nanoparticles were prepared by solution polymerization. Two synthesis routes are proposed to synthesize the particles, the monomer route and the polymer/monomer route. For the monomer route, pH and thermal sensitive nanoparticles were synthesized from acrylic acid and N-isopropylacrylamide. For the polymer/monomer route, the pH sensitive nanoparticles were synthesized from chitosan and acrylic acid. The effect of reaction time, initiator concentration and agitation rate on the particle size and the size distribution were investigated. The stimuli-responsive nanoparticles could be directly blended with other polymers to prepare stimuli-responsive functional membranes.