Versatile,Benzimidazole/Amine‐Based Ambipolar Compounds for Electroluminescent Applications: Single‐Layer,Blue, Fluorescent OLEDs,Hosts for Single‐Layer,Phosphorescent OLEDs

A series of compounds containing arylamine and 1,2‐diphenyl‐1H‐benz[d]imidazole moieties are developed as ambipolar, blue‐emitting materials with tunable blue‐emitting wavelengths, tunable ambipolar carrier‐transport properties and tunable triplet energy gaps. These compounds possess several novel properties: (1) they emit in the blue region with high quantum yields; (2) they have high morphological stability and thermal stability; (3) they are capable of ambipolar carrier transport; (4) they possess tunable triplet energy gaps, suitable as hosts for yellow‐orange to green phosphors. The electron and hole mobilities of these compounds lie in the range of 0.68–144 × 10^?6 and 0.34–147 × 10^?6 cm² V^?1 s^?1, respectively. High‐performance, single‐layer, blue‐emitting, fluorescent organic light‐emitting diodes (OLEDs) are achieved with these ambipolar materials. High‐performance, single‐layer, phosphorescent OLEDs with yellow‐orange to green emission are also been demonstrated using these ambipolar materials, which have different triplet energy gaps as the host for yellow‐orange‐emitting to green‐emitting iridium complexes. When these ambipolar, blue‐emitting materials are lightly doped with a yellow‐orange‐emitting iridium complex, white organic light‐emitting diodes (WOLEDs) can be achieved, as well by the use of the incomplete energy transfer between the host and the dopant.     

Complexity reduction of signal detection by exploiting correlation characteristics of spreading sequences

In this paper, we propose an approach to reduce the multi‐user detection (MUD) complexity based on user grouping and signal replica classification by exploiting the correlation characteristics of spreading sequences in multipath fading channels. The spreading sequences are constructed from inter‐group complementary codes with a sparse and regular correlation matrix and inherit its attractive auto/cross‐correlation properties. Users are first partitioned into independent user groups according to whether or not there is interference among them, and then the replicas of user signals from the same user group are further classified into independent replica classes. The MUD is carried out within each low‐dimensional user group or replica class, respectively, reducing the MUD complexity substantially. This approach can be applied to most of the existing MUD algorithms for complexity reduction, and in this paper optimal MUD and multi‐stage MUD are exemplified. The analytical and simulated results demonstrate that this approach can reduce the MUD complexity significantly under any load conditions without performance loss. Copyright © 2009 John Wiley & Sons, Ltd.     

Delay constrained uplink scheduling policy for rtPS/ertPS service in IEEE 802.16e BWA systems

WiMAX is a promising broadband wireless networking technology and is expected to take the place of broadband access solutions such as DSL and cable. Owing to its superior support in mobility, it is expected to provide integrated voice and data service to realize broadband mobile computing. In order to reach better quality‐of‐service (QoS) requirements for real‐time applications, the IEEE 802.16e standard defines five different services among traffic categories with different multimedia requirements. However, the problem of choosing the right set of medium access control parameters and packet scheduling policy to provide strict QoS guaranteed in IEEE 802.16e Broadband Wireless Access (BWA) systems remains unsolved and left as an open issue. In this paper, we propose a novel polling‐based uplink packet scheduling policy for real‐time Polling Service and extended real‐time Polling Service (rtPS/ertPS) traffic to support real‐time applications, with strict delay requirements, such as variable bit rate (VBR) traffic in IEEE 802.16e BWA systems. The proposed transmit‐permission policy can derive sufficient conditions such that all the rtPS/ertPS sources satisfy their time constraints to provide deterministic QoS guarantees. In addition to theoretical analysis, simulations are conducted to evaluate the performance of the proposed scheme. As it turns out, our design provides a good quality performance in the IEEE 802.16e BWA systems. Copyright © 2008 John Wiley & Sons, Ltd.     

Temporal Anti‐aliasing of a Stereoscopic 3D Video

Frequency domain analysis is a fundamental procedure for understanding the characteristics of visual data. Several studies have been conducted with 2D videos, but analysis of stereoscopic 3D videos is rarely carried out. In this paper, we derive the Fourier transform of a simplified 3D video signal and analyze how a 3D video is influenced by disparity and motion in terms of temporal aliasing. It is already known that object motion affects temporal frequency characteristics of a time‐varying image sequence. In our analysis, we show that a 3D video is influenced not only by motion but also by disparity. Based on this conclusion, we present a temporal anti‐aliasing filter for a 3D video. Since the human process of depth perception mainly determines the quality of a reproduced 3D image, 2D image processing techniques are not directly applicable to 3D images. The analysis presented in this paper will be useful for reducing undesirable visual artifacts in 3D video as well as for assisting the development of relevant technologies.     

Performance of a mesoscale liquid fuel‐film combustion‐driven TPV power system

Combustion‐driven thermophotovoltaic (TPV) systems have obtained increasing attention in recent decades, but most studies have focused on developing narrowband photovoltaic cells and selective emitters. In terms of the heat source, conventional combustion configurations and light gaseous fuels are extensively utilized in macro‐ or meso‐scale TPV power systems to simplify thermal management and mechanical fabrication. As far as miniaturization is concerned, however, fuelling these systems with liquid hydrocarbons would provide inherent advantages of high energy density and low volatility. Liquid fuels also promise easy and safe fuel recharging for small‐scale power systems. In this paper, a central porous‐medium combustor was employed in a small scale TPV power system. The combustor incorporated an emitting chamber wall and a heat recuperator. The radiant efficiency and overall efficiency were compared using different liquid hydrocarbon fuels in the system. The electric output characteristics of the combustion driven TPV system have been investigated to demonstrate the feasibility of a GaSb cell‐based TPV power system and to provide design guidance for mesoscale liquid‐burning TPV systems. Copyright © 2008 John Wiley & Sons, Ltd.     

High-sensitivity temperature sensor based on long-period fiber grating

Temperature sensitivity is greatly improved by taking the following three measures： proper long-period fiber grating （LPFG） whose strain coefficient of the core is larger than that of the cladding is employed, the LPFG is coated with a thin film of the material whose refractive index decreases with the temperature, and the sensor is encapsulated by metal material whose thermal expansion coefficient is large. By computer simulation, a measured temperature coefficient of 0.2375 nm/℃ and a temperature resolution less than 0.1 ℃ are obtained.     

DCT域数字水印算法的FPGA实现

提出一种基于DCT域的数字水印算法,并用FPGA硬件实现其中关键部分DCT变换。采用VHDL语言有效设计和实现DCT变换,分析与仿真结果表明:与软件实现相比,用FPGA实现水印算法具有高速实时处理的优点。因此,该设计是一种很有吸引力的硬件实现解决方案。     

GaN/metal/Si heterostructure fabricated by metal bonding and laser lift-off

A process methodology has been adopted to transfer GaN thin films grown on sapphire substrates to Si substrates using metal bonding and laser lift-off techniques. After bonding, a single KrF (248 nm) excimer laser pulse was directed through the transparent sapphire substrates followed by low-temperature heat treatment to remove the substrates. The influence of bonding temperature and energy density of the excimer laser on the structure and optical properties of GaN films were investigated systemically. Atomic force microscopy, X-ray diffraction and photolumi-nescence measurements showed that (1) the quality of the GaN film was higher at a lower bonding temperature and lower energy density; (2) the threshold of the energy density of the excimer laser lift-off GaN was 300 mJ/cm~2. The root-mean-square roughness of the transferred GaN surface was about 50 nm at a bonding temperature of 400 ℃.     

Rolling Friction Enhanced Free‐Standing Triboelectric Nanogenerators and their Applications in Self‐Powered Electrochemical Recovery Systems

Heavy metals contained in wastewater are one of the most serious pollutions in natural resources. A self‐powered electrochemical recovery system for collecting Cu ions in wastewater by incorporating a rolling friction enhanced freestanding triboelectric nanogenerator (RF‐TENG) is developed here. The RF‐TENG utilizes integrated cylindrical surfaces using the conjunction of rolling electrification and freestanding electrostatic induction, which shows outstanding output performance and ultrarobust stability. By using the kinetic energy of flowing water, a collection efficiency of up to 80% for Cu²⁺ ions in wastewater has been achieved. Self‐powered electrochemical systems are one of the most promising applications of TENGs for independent and sustainable driving of electrochemical reactions without the need for any additional power supply. This research is a substantial advancement towards the practical applications of triboelectric nanogenerators and self‐powered electrochemical systems.     

Photonic Hydrogels from Chiral Nematic Mesoporous Chitosan Nanofibril Assemblies

Iridescence in animals and plants often arises from structural coloration, which involves hierarchical organization of minerals and biopolymers over length scales of the visible spectrum, leading to diffraction of light. In this work, discarded crustacean shells that are not known for their structural colors are used to produce photonic nanostructures of large, freestanding chiral nematic mesoporous chitosan membranes with tunable iridescent color. Bioinspired by colorful nanostructures in nature, photonic hydrogels with Bouligand‐type organization are fabricated from the twisted mesoporous membranes, where the chitosan nanofibrils are a novel precursor for surface acetylation and are also a biotemplate for polymerizing methyl methacrylate. The colors of the hydrogels can be tailored by swelling as they show large volume changes in response to changes in solvent environment.