Constrained order in frustrated 2D optical patterns

In 2D optical patterns obtained in a Liquid Crystal Light Valve with optical feedback, we show a new kind of geometrical frustration which comes from the imposed form of the boundaries. The circular section of the incoming laser beam presents a symmetry which belongs to the O(2) group, whereas the optical feedback selects patterns with a symmetry restrained to a dihedral subgroup of O(2). By imposing boundaries which respect the symmetry of the dihedral group, we lift the frustration and obtain perfectly ordered patterns. Received 19 January 2001 and Received in final form 2 June 2001     

胶体量子阱发光二极管的研究进展

胶体量子阱(CQW)由于具有高色纯度、高光致发光量子效率、光色可调等优异的光电性能，近年来成为一种新型的光电材料，广泛用于制备发光二极管、激光、探测器、太阳能电池等半导体器件。其中，基于CQW的发光二极管(CQW-LED)因为具备极窄的光谱、极佳的色纯度、高效率、可溶液加工、可柔性化等优点，在显示和照明等领域展现出重要应用前景，受到学术界和工业界的广泛重视而成为研究热点。本文首先介绍了CQW-LED中的一些基本概念，包括CQW材料特性、LED器件结构、发光机理等；然后从CQW材料种类的角度出发，阐述了基于单核型、核/冠型、核/壳型、复杂异质结型、以及杂质掺杂型CQW-LED近年来的研究进展，并结合我们研究团队最近的工作详细的介绍了实现高性能CQW-LED的方法，包括对材料选取、设计策略、器件结构、器件性能、工作机理以及发光过程的分析；接着，介绍了CQW-LED的集成应用；最后探讨了CQW-LED目前面临的挑战及其未来的发展机遇。     

Fabrication of a controllable anti-peeping device with a laminated structure of microlouver and polymer dispersed liquid crystals film

ABSTRACT

Display devices with the narrow viewing angle (NVA) and the wide viewing angle (WVA) characteristics can simultaneously meet the demands for privacy protection and information sharing. Herein, we propose a novel method for fabricating a controllable anti-peeping device with a laminated structure of microlouver and polymer dispersed liquid crystals (PDLCs) film, and this device can be reversibly switched between a wider viewing angle range (VAR) for the WVA mode and a narrower viewing angle range (VAR) for the NVA mode at 0 V and 8 V, respectively. Also, the VARs of the controllable anti-peeping device can be dynamically tuned by varying dimensions of the microlouver structures and applying various voltages across the PDLCs film from 0 V to 8 V. The as-fabricated device provides display devices with controllable viewing angle characteristics, which can be applied in the display field with fascinating and practical functions.     

亚像素采样对LED显示质量的提升

清晰显示高分辨率画面是LED显示屏图像质量提升领域中亟待解决的关键问题之一.针对LED显示屏分辨率低、成本高、像素排布灵活的特点,研究了亚像素采样技术在LED显示屏中的应用.从信号处理的角度,在RGB颜色空间中对LED显示屏建立了全像素采样和亚像素采样数学模型,在亮度与色度相分离的空间中对两种采样方式进行了频谱分析,证明了应用亚像素采样技术可以将显示系统的亮度混叠转移到了人眼较不敏感的颜色通道上,有效扩展了LED显示系统在各方向上的Nyquist频率限制.物理屏体上的仿真实验表明亚像素采样对LED显示屏的图像显示质量具有改善作用.     

Improving Learner-Computer Interaction through Intelligent Learning Material Delivery Using Instructional Design Modeling

This paper describes an innovative and sophisticated approach for improving learner-computer interaction in the tutoring of Java programming through the delivery of adequate learning material to learners. To achieve this, an instructional theory and intelligent techniques are combined, namely the Component Display Theory along with content-based filtering and multiple-criteria decision analysis, with the intention of providing personalized learning material and thus, improving student interaction. Until now, the majority of the research efforts mainly focus on adapting the presentation of learning material based on students’ characteristics. As such, there is free space for researching issues like delivering the appropriate type of learning material, in order to maintain the pedagogical affordance of the educational software. The blending of instructional design theories and sophisticated techniques can offer a more personalized and adaptive learning experience to learners of computer programming. The paper presents a fully operating intelligent educational software. It merges pedagogical and technological approaches for sophisticated learning material delivery to students. Moreover, it was used by undergraduate university students to learn Java programming for a semester during the COVID-19 lockdown. The findings of the evaluation showed that the presented way for delivering the Java learning material surpassed other approaches incorporating merely instructional models or intelligent tools, in terms of satisfaction and knowledge acquisition.     

Characterization of two-emitter WOLED with no additional blocking layer

In this paper, white organic light emitting diodes (WOLEDs) utilizing two primary-color emitters with no additional blocking layer are fabricated. With a structure of ITO/2TNATA (20 nm)/NPB (20 nm)/NPB: rubrene (2%) (10 nm)/ADN (30 nm)/Alq₃ (20 nm)/LiF (1 nm)/Al (100 nm), a white light with CIE coordinates of (0.344, 0.372) is generated at a current density of 30 mA/cm² and the electroluminescence (EL) spectra consist of two broad bands around 456 nm (ADN) and 556 nm (NPB:rubrene). The device shows the low turn-on voltage and bright white emission with a power efficiency of 2.3 lm/W at a luminance of 100 cd/m². Through control of the location of the recombination zone and energy transfer, a stable white light emission is achieved. The maximum color shift is less than 0.02 units on the 1931 CIE x,y chromaticity diagram. Given the spectral power distribution of WOLED, the parameters of a light source (chromaticity coordinate, CCT, CRI, and the luminous efficacy) can be calculated. A MATLAB program for this purpose is developed in this paper. Based on this, the design of WOLED for an illumination and display system using a white emitter with color filter arrays is discussed.     

电子膨胀阀应用于低温陈列柜制冷系统的节能研究

与热力膨胀阀相比,电子膨胀阀应用于陈列柜制冷系统,可以更为精确地控制其柜温及过热度。为进一步减小低温陈列柜制冷系统能耗,文中提出通过改变电子膨胀阀脉冲信号的控制策略以达到节能的目的。通过试验证明:与热力膨胀阀相比,可节能25%;同时可减小系统过热度,提高低温陈列柜制冷系统温度特性。为电子膨胀阀在低温制冷陈列柜中的应用提供参考依据。     

Die Welt wird flacher. Beitrag der Chemie zum flachen Fernseher

Shorter switching times, a higher resolution, larger – and ever more widely used: that is a quick summary of the success story of LC displays. The secret behind it: liquid crystalline chemicals which are high‐tech materials with highly advantageous properties which allow for low‐weight and flat LCDs exhibiting a low power consumption. LCDs have made modern communication mobile and visible. For many years Merck has been the market and technology leader in the area of liquid crystals, of their mixtures and applications.