High-efficiency white phosphorescent polymer light-emitting devices

White phosphorescent light emission from polymer light-emitting devices (PLEDs) has been demonstrated. To fabricate the white-emitting PLED, blue phosphorescent polymer (BPP) and red phosphorescent polymer (RPP) were used for the emissive layer, and the emission color was tuned by controlling the concentration ratio of BPP to RPP. The external quantum efficiency of the white-emitting PLED, with CIE coordinates of (0.34, 0.36), was 6.0% at luminance of 100 cd/m/sup 2/. To investigate the emission mechanism in the PLED, its photoluminescence spectrum and transient decay were measured. These experimental measurements indicate that direct excitation of the iridium-complex (Ir-complex) units by carrier trapping is a major excitation process for white-emitting PLED. A 3.6-in full-color display based on the white phosphorescent PLED and color filters was demonstrated.     

100 dpi 4-a-Si:H TFTs active-matrix organic polymer light-emitting display

In this paper, we report on 100 dpi four hydrogenated amorphous silicon thin-film transistors (4-a-Si:H TFTs) active-matrix organic polymer light-emitting display (AM-PLED). For this display, we have established the operational limitation of our 4-a-Si:H TFTs pixel electrode circuit by performing a load line analysis. Combining this result with the extracted pixel organic polymer light-emitting device (PLED) characteristics, we have found that the change of the AM-PLED pixel operating point, especially of a driving TFT, limits the operational range of AM-PLED pixel. The predicted results are compared with the measured data of 100 dpi monochromatic red light-emitting 4-a-Si:H TFTs AM-PLED. For our AM-PLED, we obtained luminance up to /spl sim/20 cd/m/sup 2/ and Commission Internationale de l'Eclairage color coordinates of (0.67, 0.33), which are calculated from the measured AM-PLED electroluminescence spectrum.     

Electrical characterization of polymer light-emitting diodes

This paper presents a device model for the current and light generation of polymer light-emitting diodes (PLEDs). The model is based on experiments carried out on poly(dialkoxy-p-phenylene vinylene) (PPV) devices. It is demonstrated that PLED's are fundamentally different as compared to conventional inorganic LEDs. The hole conduction in PPV is space-charge limited with a low-field mobility of only 5×10^-11 m²/Vs, which originates from the localized nature of the charge carriers. Furthermore, the hole mobility is highly dependent on the electric field and the temperature. The electron conduction in PPV is strongly reduced by the presence of traps. Combining the results of the electron- and hole transport a device model for PLEDs is proposed in which the light generation is due to bimolecular recombination between the injected electrons and holes. It is calculated that the unbalanced electron and hole transport gives rise to a bias dependent efficiency. By comparison with experiment it is found that the bimolecular recombination process is of the Langevin-type, in which the rate-limiting step is the diffusion of electrons and holes toward each other. This is in contrast to conventional semiconductors, in which the bimolecular recombination is governed by the joint density-of-states of electrons and holes and is not limited by charge transport. The occurrence of Langevin recombination explains why the conversion efficiency of current into light of a PLED is temperature independent. The understanding of the device operation of PLED's indicates directions for further improvement of the performance     

Statistical study for electromigration reliability in dual-damascene Cu interconnects

This paper summarizes results from recent studies on electromigration (EM) reliability of Cu dual-damascene interconnects using a statistical approach. First, mass transport in Cu damascene structure was discussed, where the activation energies for oxide, porous MSQ (methylsilsesquioxane), and organic polymer dielectrics were found to be in the range of 0.8-1.0 eV, suggesting mass transport is dominated by interfacial diffusion at the Cu and SiN/sub x/ cap-layer interface regardless of the dielectric material. Then the impact of low-k inter-layer dielectrics on EM characteristics was investigated by measuring the critical product of current density and conductor length, (jL)/sub c/. Compared with oxide, the weaker mechanical strength of low-k dielectrics reduces (jL)/sub c/ due to less confinement and a smaller back flow stress gradient /spl Delta//spl sigma//L in Cu/low-k interconnects. Extrinsic failure due to interfacial delamination was observed in Cu/organic polymer interconnects, which caused further decrease in (jL)/sub c/. Complementing EM tests, Monte Carlo simulation was developed based on the weakest link approximation to separate the bimodal failure distribution into two individual lognormal distributions and deduce the characteristics of the weak-mode (early) and the strong-mode failures. Failure analysis using FIB confirmed the bimodal failure behavior with void formation at the cathode via bottom found to be responsible for the early failures.     

Angular domain imaging of objects within highly scattering media using silicon micromachined collimating arrays

Optical imaging of objects within highly scattering media, such as tissue, requires the detection of ballistic/quasi-ballistic photons through these media. Recent works have used phase/coherence domain or time domain tomography (femtosecond laser pulses) to detect the shortest path photons through scattering media. This work explores an alternative, angular domain imaging, which uses collimation detection capabilities of small acceptance angle devices to extract photons emitted aligned closely to a laser source. It employs a high aspect ratio, micromachined collimating detector array fabricated by high-resolution silicon surface micromachining. Consider a linear collimating array of very high aspect ratio (200: 1) containing 51/spl times/1000 /spl mu/m etched channels with 102-/spl mu/m spacing over a 10-mm silicon width. With precise array alignment to a laser source, unscattered light passes directly through the channels to the charge coupled device detector and the channel walls absorb the scattered light at angles >0.29/spl deg/. Objects within a scattering medium were scanned quickly with a computer-controlled Z axis table. High-resolution images of 100-/spl mu/m-wide lines and spaces were detected at scattered-to-ballistic ratios of 5/spl times/10/sup 5/: 1, with objects located near the middle of the sample seen at even higher levels. At >5/spl times/10/sup 6/: 1 ratios, a uniform background of scattered illumination degrades the image contrast unless recovered by background subtraction. Monte Carlo simulation programs designed to test the angular domain imaging concept showed that the collimator detects the shortest path length photons, as in other optical tomography methods. Furthermore, the collimator acts as an optical filter to remove scattered light while preserving the image resolution. Simulations suggest smaller channels and longer arrays could enhance detection by >100.     

基于柔性多状态开关和动态重构的配电网灵活运行方法

未来电动汽车(electric vehicle, EV)以及光伏(photovoltaic, PV)在配电网中的接入比例逐渐增高,这不仅带来了复杂的不确定性问题,而且导致了配电网净负荷时空分布的不均衡,从而产生了弃光、失负荷以及潮流分布不均匀的问题。基于此,考虑电动汽车充电负荷以及光伏的不确定性,提出了一种基于柔性多状态开关(flexible multi-state switch, FMS)和动态重构的含高比例电动汽车-光伏配电网灵活运行方法。首先,基于FMS灵活功率调控和网络动态重构,构建了支撑高比例电动汽车-光伏接入的配电网灵活运行框架。其次,利用蒙特卡洛随机模拟法对各类电动汽车充电负荷以及光伏出力进行不确定性建模,建立了基于场景集以及场景缩减法的随机规划模型。然后,建立了以弃光、失负荷、FMS损耗、网损成本最小和负荷均衡度最优为目标的配电网灵活运行模型。最后,在158节点系统上通过算例验证了所提方法的有效性。     

The bright future of organic LEDs

Electro-luminescence is light emission from a solid through which an electric current is passed. Electro-luminescence from organic compounds was discovered in the early '60s, but the subject did not receive much attention until the discovery and development of conductive polymers. Compared to other electro-luminescent technologies (such as inorganic compound semiconductors, porous silicon and liquid crystals), polymer/organic light-emitting diodes (PLEDs/OLEDs) are very attractive. The reasons are their very low operating voltage, high brightness and their tunability to produce the three fundamental colors (red, blue and green). Furthermore, they are lightweight and can be grown on flexible substrates. They are fairly easy and inexpensive to fabricate. Today, PLEDs/OLEDs are suitable for applications such as automotive displays. In the future, they will probably conquer a large portion of the micro display market. Their higher efficiency and lower weight will make them quite competitive with LCD displays, the currently favorite technology. The article concludes that the future of organic light-emitting diodes seems very bright indeed.     

Electron injection in "electron-only" devices based on a symmetric metal/silole/metal structure

We report on electron injection from two different metal electrodes into three silole derivatives, namely 2,5-di-(3-biphenyl)-1,1-dimethyl-3,4-diphenylsilacyclopentadiene (PPSPP), 1,2-bis(1-methyl-2,3,4,5,-tetraphenylsilacyclopentadienyl) ethane (2PSP) and 2,5-bis-(2', 2'-bipyridin-6-yl)-1, 1-dimethyl-3,4-diphenylsilacyclopentadiene (PyPySPyPy), previously employed as emissive and electron transport materials in molecular organic light-emitting diodes (MOLEDs). Silole films were sandwiched between symmetric Mg:Ag or bilayer CsF-Al electrodes. The steady-state current density-voltage characteristics were measured as a function of the silole layer thickness for the two cathodes. The trap-free space-charge-limited current based on time-of-flight measurements compared with the injected electron current for PyPySPyPy indicated that Mg:Ag contacts limit the injected current, while CsF-Al contacts behave as quasi-ohmic contacts. Similar findings were obtained for 2PSP and PPSPP allowing steady-state derived electron mobility parameters to be extracted. Based on space-charge-limited conduction analysis of the measured current-voltage characteristics, PyPySPyPy is found to be a superior electron transporting silole with approximately an order of magnitude higher electron mobility (2.0/spl times/10/sup -4/ cm/sup 2//Vs) compared with those of 2PSP (2.4/spl times/10/sup -5/ cm/sup 2//Vs) and PPSPP (5.2/spl times/10/sup -5/ cm/sup 2//Vs), which is significantly higher than that of the prototype electron transport material tris (8-hydroxyquinolinolato) aluminum (III) (Alq/sub 3/) (6.5/spl times/10/sup -7/ cm/sup 2//Vs) at 0.6 MV/cm.     

大型电力系统可靠性评估中的马尔可夫链蒙特卡洛方法

提出大型电力系统可靠性评估的一种新的蒙特卡洛模拟方法-马尔可夫链蒙特卡洛方法(Markov chain Monte Carlo, MCMC)。MCMC方法是一种特殊的蒙特卡洛方法,它将随机过程中的马尔可夫过程引入到蒙特卡洛模拟中,实现动态蒙特卡洛模拟。该方法通过重复抽样,建立一个平稳分布与系统概率分布相同的马尔可夫链,从而得到系统的状态样本。由于MCMC方法考虑了系统各个状态间的相互影响,相比于随机采样的蒙特卡洛方法所得到的独立样本序列,更准确模拟了电力系统运行实际情况。IEEE-RTS 24节点算例表明,该算法可快速收敛,节省计算时间,提高计算速度。同时,由于每条马尔可夫链均收敛于同一个分布,即所谓平稳分布,所以算法具有良好的稳定性。对西北330 kV电网的可靠性评估再次表明了该方法的正确性和有效性以及该方法用于大型电力系统的可靠性评估的优越性和潜力。     

The impact of LOC structures on 670-nm (Al)GaInP high-power lasers

We investigate the potential of large optical cavity (LOC)-laser structures for AlGaInP high-power lasers. For that we study large series of broad area lasers with varying waveguide widths to obtain statistically relevant data. We study in detail I/sub th/, /spl alpha//sub i/, /spl eta//sub i/, and P/sub max/, and analyze above-threshold behavior including temperature stability and leakage current. We got as expected for LOC structures minimal /spl alpha//sub i//spl les/1 cm/sup -1/ resulting in /spl eta//sup d/=1.1 W/A for 64/spl times/2000 /spl mu/m/sup 2/ uncoated devices. We obtain total output powers /spl ges/3.2 W (qCW) and /spl ges/1.5 W (CW) at 20/spl deg/C.     

Near-infrared (NIR) tomography breast image reconstruction with a priori structural information from MRI: algorithm development for reconstructing heterogeneities

A combined magnetic resonance and near-infrared (MRI-NIR) imaging modality can potentially yield high resolution maps of optical properties from noninvasive simultaneous measurement. The main disadvantage of near-infrared (NIR) tomography lies in the low spatial resolution resulting from the highly scattering nature of tissue for these wavelengths. MRI has achieved high resolution, but suffers from low specificity. In this study, NIR image reconstruction algorithms that incorporate a priori structural information provided by MRI are investigated in an attempt to optimize recovery of a simulated optical property distribution. The effect of high levels of tissue heterogeneity are evaluated to determine the limitations of incorporating prior information into a realistic set of patient breast images. We assume absorption coefficient (/spl mu//sub a/) variations near /spl plusmn/40%, and transport scattering coefficient (/spl mu//sub s//sup //) variations near /spl plusmn/20%, in a coronal breast MRI geometry. Changes in tissue pathology due to tumor growth can be observed with NIR tompgraphy, and so the goal here is to determine how best to quantify these tumor-based contrast regions within the presence of high tissue heterogeneity. By applying knowledge of tissue's layered structure in reconstruction through various constraints in the iterative algorithm, quantitative recovery of the tumor optical properties improves from 69% to 74%, and localization improves as well. However, only when the true heterogeneity of the tissue distribution was included was accurate quantification of the tumor region possible. Using a good initial guess of /spl mu//sub a/ and /spl mu//sub s//sup //, derived from the regional structure of the model, quantification of the region reaches 99% of the true value, and spatial resolution retains a similar value to the original MRI image.     

基于激光信息的移动机器人定位研究

针对移动机器人在导航定位过程中,使用传统蒙特卡罗定位算法会产生粒子收敛较慢和定位精度不高,以及发生人为绑架情况后重定位效率较低的问题,给出了一种改进的粒子滤波定位方法来提高移动机器人的导航定位效率.首先,在蒙特卡罗定位算法的基础上进行改进,融入自适应区域划分的方法,保证所划区域包含更多有效信息,减少粒子的收敛时间,完成机器人初步粗定位.然后,在粒子采样和重采样阶段,使用正态分布概率模型进行粒子权重更新,实现更加快速高效地全局精定位.通过实验对比分析,所给方法与基于蒙特卡罗定位算法相比较,耗时缩短了4s,且本文的自适应蒙特卡罗定位方法,能够将定位误差保持在6cm左右,从而验证了所给方法的有效性和稳定性.     

Optical properties effects upon the collection efficiency of optical fibers in different probe configurations

When optical fibers are used for delivery and collection of light, two major factors affect the measurement of collected light: 1) light transport in the medium from the source to the detection fiber and 2) light coupling to the optical fiber (which depends on the angular distribution of photons entering the fiber). This paper studies the latter factor, describing how the efficiency of the coupling depends on the optical properties of the sample. The coupling dependence on optical properties is verified by comparing experimental data to a simple diffusion model and to a Monte Carlo (MC)-corrected diffusion model. Mean square errors were 7.9% and 1.4% between experiments and the diffusion, and experiments and the MC-corrected models, respectively. The efficiency of coupling was shown to be highly dependent on the numerical aperture (NA) of the optical fiber. However, for lower scattering, such as in soft tissues, the efficiency of coupling could vary two- and threefold from that predicted by fiber NA. The collection efficiency can be used as a practical guide for choosing optical fiber-based systems for biomedical applications.     

水源地地下水综合补给量频率分析的方法

如何解决水源地地下水综合补给量的频率分析计算问题 ,采用解析法、数值法、物理实验以及经验频率都存在着各种困难 ,运用蒙特卡罗方法会使此类问题迎刃而解。蒙特卡罗方法是用数学的方式在属性概率模型控制下 ,产生足够多的伪随机变量 ,构成大容量样本 ,形成分布来求解的。经过理论和实践说明蒙特卡罗方法能在水资源量评价中发挥重要的作用。     

敏感负荷电压凹陷敏感度的最佳平方逼近评估法

敏感负荷电压凹陷敏感度评估的关键在于电压耐受曲线随机分布规律的确定。文章以勒让德多项式为基函数,提出一种通过最佳平方逼近法确定敏感负荷电压凹陷敏感度特征参数随机分布的概率密度函数的方法,该方法无需主观假设,忠实于样本特征,具有原理简单、计算量小的特点。文中对概率密度函数的逼近算法、评估原理和过程进行了研究,以PC机为例,通过蒙特卡罗方法随机模拟样本,用所提出的方法进行评估,证明了所提出方法的准确性和适应性。     

Switching of capacitive currents and the correlation of restrike and pre-ignition behavior

The new IEC 62271-100 requires an extensive proof of the capability of capacitive switching for a breaker under test. For vacuum circuit breakers, dielectric properties are mainly determined by the condition and topology of the contact surfaces, which are modified by in-rush currents as well as load-breaking currents and other effects. A synthetic single-phase test device has been erected in order to simulate three-phase network conditions and to collect more data on the statistical properties of the relevant processes. The distribution of pre-ignition field strengths is evaluated for different contact strokes and surface conditions, when discharging a capacitor through the closing interrupter. On the other side, the probability of restrikes for a given switching condition defined by full contact gap d/sub 0/ and peak recovery voltage U/sub re//spl circ/ is measured and compared with the cumulative probability of pre-ignition just at the field strength E=U/sub re//spl circ//d/sub 0/. A correlation between pre-ignition and restrike probabilities suggests a breakdown mechanism being field-emission dominated. In addition a rather strong conditioning effect has been observed at smaller contact gaps smoothening the contact surfaces.     

输电系统可用输电能力的概率模型及计算

将蒙特卡洛模拟法和灵敏度分析法相结合，以直流潮流为基础，建立了输电系统可用传输能力(ATC)计算的概率模型。应用蒙特卡洛模拟法合理考虑了输电系统中的不确定性因素；应用灵敏度分析法快速计算了输电系统ATC；两者结合，不仅可以得到ATC的数学期望及其概率分布，还可以得到影响输电系统ATC的主要因素，反映输电系统的薄弱点，为输电系统的规划和电力交易商的商业行为提供决策依据。测试系统的计算结果说明了该算法的正确性和有效性。     

含有光伏系统的配电网可靠性评估

序贯蒙特卡罗模拟法能够模拟系统的各种运行状态,特别适合应用于含间歇性分布式电源的电力系统可靠性评估当中。通过建立光伏电源的可靠性概率模型,结合负荷和其他元件的概率模型,采用序贯蒙特卡罗模拟法,计算了考虑间歇性的光伏系统接入后配电系统的可靠性指标。针对实际系统的计算结果表明,光伏发电系统合理接入配电网,可以提高配电网的可靠性水平。     

Effect of ambient relative humidity and surface modification on the charge decay properties of polymer powders in powder coating

Back corona on a powder layer deposited via the electrostatic powder-coating process using corona guns has a strong influence on the corrosion resistance and appearance of cured powder films. The presence of the back corona is often evidenced by orange peel, micro-dents, and pinholes on the film surface. The surface resistivity of the sprayed powder governs the charge decay process and, hence, the onset of back corona. The polymer powders used in powder coating are highly resistive, with surface resistivity often greater than 10/sup 15/ /spl Omega///spl square/. Surface resistivity can be altered by the adsorption of moisture on the surfaces of the powder particles. The objectives of this research were: (1) investigate the effect of decreasing surface resistivity on the appearance of the powder-coated film and (2) enhance hydrophilic properties of polymer powder by plasma treatment. By changing the relative humidity (RH) of powder during the spraying process, it was observed that the surface resistivity could be lowered by orders of magnitude. For example, the surface resistivity for an acrylic powder decreased from 2.96/spl times/10/sup 13/ /spl Omega///spl square/ at 25% RH to 9.6/spl times/10/sup 11/ /spl Omega///spl square/ at 70% RH. The plasma treatment of this powder further improved its charge decay properties. The effects of variation of RH on the appearance of powder-coated panels surface layer are presented for an acrylic polymer powder. The film texture has been characterized by microstructural surface analysis using an optical scanning instrument. Methods of plasma and corona treatments of the powder for increasing moisture adsorption on the surface and decreasing surface resistivity are discussed along with analysis of surface morphology using the atomic force microscope.     

一种产生矩形光斑的LED均匀照明系统设计

随着LED光源芯片性能的稳步提升,各种LED光源被应用于不同领域,从而根据需要产生不同形状的光斑。在本文中,笔者提出了一种能够产生均匀矩形光斑的设计方法。在这种设计方法中,光斑的形状取决于复眼结构、聚光杯以及准直透镜对光路的再分配,此外依据研究需要成功将其应用于一些实例。