Achieving High‐Performance Nondoped OLEDs with Extremely Small Efficiency Roll‐Off by Combining Aggregation‐Induced Emission and Thermally Activated Delayed Fluorescence

Luminescent materials with thermally activated delayed fluorescence (TADF) can harvest singlet and triplet excitons to afford high electroluminescence (EL) efficiencies for organic light‐emitting diodes (OLEDs). However, TADF emitters generally have to be dispersed into host matrices to suppress emission quenching and/or exciton annihilation, and most doped OLEDs of TADF emitters encounter a thorny problem of swift efficiency roll‐off as luminance increases. To address this issue, in this study, a new tailor‐made luminogen (dibenzothiophene‐benzoyl‐9,9‐dimethyl‐9,10‐dihydroacridine, DBT‐BZ‐DMAC) with an unsymmetrical structure is synthesized and investigated by crystallography, theoretical calculation, spectroscopies, etc. It shows aggregation‐induced emission, prominent TADF, and interesting mechanoluminescence property. Doped OLEDs of DBT‐BZ‐DMAC show high peak current and external quantum efficiencies of up to 51.7 cd A^?1 and 17.9%, respectively, but the efficiency roll‐off is large at high luminance. High‐performance nondoped OLED is also achieved with neat film of DBT‐BZ‐DMAC, providing excellent maxima EL efficiencies of 43.3 cd A^?1 and 14.2%, negligible current efficiency roll‐off of 0.46%, and external quantum efficiency roll‐off approaching null from peak values to those at 1000 cd m^?2. To the best of the authors' knowledge, this is one of the most efficient nondoped TADF OLEDs with small efficiency roll‐off reported so far.     

新颖的可控开关性能检测仪的设计

为了降低吸合开关性能检测仪的成本且获得高精度的工作性能,利用DSP的高精度特点,采用中断计时,脉冲边沿触发方法检测可控开关的吸合、断开时间,同时采用可变电压源检测工作所需最小电压,研究设计的吸合开关检测仪取得了测量精度高,运行方便,生产成本低的结果。研制的测试仪能够满足精密测量的要求。     

适合于TD-LTE公网集群系统的切换算法

在多数的公网集群通信系统中,对切换的时延要求很高,如何减小切换时延变得相当重要?在公网集群通信系统中引入TD-LTE技术,使切换时延得到一定的减小,但切换过程中,基站和eMME间的频繁通信仍然增大了延时?基于背景扫描的切换算法,其思想是让eMME将其控制的所有基站下的小区的信息缓存起来,在进行切换时,eMME只需要查询自己的信息列表,从中获取目标小区的切换门限值?载频?预留的信道资源等信息,无需与目标基站通信,这样就减少基站和eMME间的频繁通信,整个切换过程主要在源基站和eMME侧完成,从而获得更低的时延?     

电子倍增CCD噪声参数的估计方法

为定量评价电子倍增CCD(EMCCD)图像噪声的大小,实现对EMCCD 图像噪声参数的准确估计,研究了EMCCD 的噪声分布模型及其参数估计方法。首先,讨论了EMCCD 图像的噪声来源及其统计特性,由此建立了适于EMCCD 的噪声分布模型。然后,提出了两种EMCCD 噪声参数估计方法矩估计法和高斯-牛顿法,采用Monte Carlo 仿真验证其性能。仿真结果表明,矩估计法和高斯-牛顿法的平均相对误差和相对标准偏差均为10-2 量级,估计精度较高,且高斯-牛顿法的估计精度要高于矩估计法。采集一系列无增益时积分时间为50 s的暗场图片和增益为50 的本底图片,利用矩估计法和高斯-牛顿法分别估计出EMCCD 的暗电流噪声、时钟感生电荷噪声和读出噪声,实验结果表明,估计值与EMCCD 指标值一致,证明矩估计法和高斯-牛顿法能有效估计噪声参数且具有较高的精度。     

基于伪随机函数的RFID系统双向认证协议

移动RFID系统中,读写器与后台数据库之间不再通过有线方式通信,而采用无线方式通信,但也存在一定的安全隐患问题。为确保通信数据的安全,提出一种基于伪随机函数的移动RFID双向认证协议。协议确保标签、读写器、后台数据库三方均进行认证,从而保障通信的安全性;采用字合成等位运算,在一定程度上能够减少总的计算量;三方认证,使得移动RFID系统具备更为广泛的运用价值。安全性及性能分析表明,所提协议具有较高的安全性及较低的成本。     

Skeleton-Based Human Action Recognition via Screw Matrices

With the recent advent of low-cost acqui-sition depth cameras, extracting 3D body skeleton has be-come relatively easier, which significantly lighten many dif-ficulties in 2D videos including occlusions, shadows and background extraction, etc. Directly perceived features, for example points, lines and planes, can be easily ex-tracted from 3D videos such that we can employ rigid motions to represent skeletal motions in a geometric way. We apply screw matrices, acquired by using rotations and translations in 3D space, to model single and multi-body rigid motion. Since screw matrices are members of the special Euclidean group SE(3), an action can be repre-sented as a point on a Lie group, which is a differen-tiable manifold. Using Lie-algebraic properties of screw al-gebra, isomorphic to se(3), the classical algorithms of ma-chine learning in vector space can be expanded to man-ifold space. We evaluate our approached on three public 3D action datasets: MSR Action3D dataset, UCF Kinect dataset and Florence3D-Action Dataset. The experimental results show that our approaches either match or exceed state-of-the-art skeleton-based human action recognition approaches.     

A Novel Sparse Penalty for Singular Value Decomposition

Singular value decomposition (SVD) is a tool widely used in data denoising, matrix approximation, recommendation system, text mining and computer vision. A m a jority of applications prefer sparse singular vectors to capture inherent structures and patterns of the input data so that the results are interpretable. We present a novel penalty for SVD to achieve sparsity. Comparing with the traditional penalties, the proposed penalty is scale, dimen-sional insensitive and bounded between 0 and 1, which are in favor of controlling sparsity. Regulated by the penalty, we provide an efficient algorithm to pro ject a vector onto a given sparse level in O(n) expected time. The efficient pro jection algorithm serve as a drudge for sparse SVD (SSVD). In experiments, SSVD is efficient and could cap-ture the latent structures and patterns of the input data.     

功率MOSFET零温度系数点的研究

为研究功率MOSFET零温度系数点（Zero Temperature Coefficient,ZTC）,不同栅极电压对温度系数的影响,本文基于阈值电压和迁移率的温度关系并结合功率MOSFET输出特性模型,得到了随栅极电压变化而出现的三种不同温度系数。利用实际测试验证了温度系数的变化规律,结果表明：在小栅极电压条件下,线性区和饱和区均为正温度系数;随栅极电压增大,线性区先进入负温度系数,饱和区仍然为正温度系数,并因此产生了零温度系数点;随栅极电压进一步增大,线性区和饱和区都进入负温度系数。同时根据测试数据,分析了ZTC在不同栅极电压条件下随温度的变化原因,并基于测试数据讨论了迁移率随栅极电压和温度的变化关系。