Achieving High Electroluminescence Efficiency and High Color Rendering Index for All-Fluorescent White OLEDs Based on an Out-of-Phase Sensitizing System

Sensitizing conventional fluorescence (CF) dopants with thermally activated delayed fluorescence (TADF) materials has achieved considerable progress, by which the advantages of TADF materials and CF dopants can be fully harnessed. However, the usually used co-phase configuration of CF dopant-engaged sensitizing systems often encounters exciton loss due to Dexter energy transfer (DET). Herein, an effective out-of-phase configuration is proposed to sensitize CF dopants in the fabrication of white organic light-emitting diodes (WOLEDs). Based on a new efficient sky-blue TADF luminogen DCP-BP-DPAC which has an electroluminescence (EL) peak at 486 nm and an EL efficiency of 26.6%, a green TADF material BDMAC-XT, and a red CF dopant DBP sensitized by BDMAC-XT through an out-of-phase configuration without interlayer, efficient WOLEDs are successfully fabricated. By further adopting orange TBRB or 4CzTPNBu as intermediate sensitizers, more efficient energy transfer to DBP is achieved via Förster energy transfer. Through step-by-step energy transfer and elimination of excess DET process, high-performance all-fluorescent WOLEDs are achieved, providing excellent EL efficiencies over 23.0%, and highly stable white light with a high color rendering index of 87. The outstanding EL performance and high-quality emission color demonstrate the great potential of the proposed out-of-phase design for sensitizing systems of WOLEDs.     

Evaluation of registration methods on thoracic CT: the EMPIRE10 challenge

EMPIRE10 (Evaluation of Methods for Pulmonary Image REgistration 2010) is a public platform for fair and meaningful comparison of registration algorithms which are applied to a database of intrapatient thoracic CT image pairs. Evaluation of nonrigid registration techniques is a nontrivial task. This is compounded by the fact that researchers typically test only on their own data, which varies widely. For this reason, reliable assessment and comparison of different registration algorithms has been virtually impossible in the past. In this work we present the results of the launch phase of EMPIRE10, which comprised the comprehensive evaluation and comparison of 20 individual algorithms from leading academic and industrial research groups. All algorithms are applied to the same set of 30 thoracic CT pairs. Algorithm settings and parameters are chosen by researchers expert in the configuration of their own method and the evaluation is independent, using the same criteria for all participants. All results are published on the EMPIRE10 website (http://empire10.isi.uu.nl). The challenge remains ongoing and open to new participants. Full results from 24 algorithms have been published at the time of writing. This paper details the organization of the challenge, the data and evaluation methods and the outcome of the initial launch with 20 algorithms. The gain in knowledge and future work are discussed.     

The effects of gate length variation and trapping effects on the transient response of AlGaN/GaN HEMT’s on SiC substrates

In AlGaN/GaN heterostructure field-effect transistors, the surface defects and dislocations may serve as trapping centers and affect the device performance via leakage current. In this paper we report results of our investigation of the trapping characteristics of Al_0.25Ga_0.75N/GaN HEMT using the Conductance Deep Level Transient Spectroscopy (CDLTS). Two deep level electronic defects were observed labeled E₁ and HL₁, with activation energies E_a1 = 1.36 eV and E_a2 = 0.63 eV. The hole-trap HL₁ is characterized for the first time in our studies. We identified the characteristics of the traps at the AlGaN/GaN interface adjoining the channel and the surface along the ungated region between the gate and the drain, as well as the effects of the surface traps.     

The Impact of Infostation Density on Vehicular Data Dissemination

Vehicle-to-Vehicle and Vehicle-to-Roadside communications are going to become an indispensable part of the modern day automotive experience. For people on the move, vehicular networks can provide critical network connectivity and access to real-time information. Infostations play a vital role in these networks by acting as gateways to the Internet and by extending network connectivity. In this context, an important question is “What is the minimum number of infostations that need to be deployed in an area in order to support vehicular applications?” Optimizing infostation density is vital to understanding and reducing the cost of deployment and management. In this paper, we examine the required infostation density in a highway scenario using different data dissemination models. We start from a simple analysis that captures the required density under idealized assumptions. These models are validated by an event-driven simulator. We then run detailed QualNet simulations on both controlled and realistic vehicular traces to observe the information density trends in practical environments, and consequently propose techniques to improve dissemination performance and reduce the required infostation density.     

Investigations on mode-division multiplexed free-space optical transmission for inter-satellite communication link

Wireless Networks - Inter-satellite data transmission links are very crucial for providing global inter-connectivity. We report designing and investigations on high date rate inter-satellite...     

Environmentally Friendly Graphene Inks for Touch Screen Sensors

Graphene-based materials have attracted significant attention in many technological fields, but scaling up graphene-based technologies still faces substantial challenges. High-throughput top-down methods generally require hazardous, toxic, and high-boiling-point solvents. Here, an efficient and inexpensive strategy is proposed to produce graphene dispersions by liquid-phase exfoliation (LPE) through a combination of shear-mixing (SM) and tip sonication (TS) techniques, yielding highly concentrated graphene inks compatible with spray coating. The quality of graphene flakes (e.g., lateral size and thickness) and their concentration in the dispersions are compared using different spectroscopic and microscopy techniques. Several approaches (individual SM and TS, and their combination) are tested in three solvents (N-methyl-2-pyrrolidone, dimethylformamide, and cyrene). Interestingly, the combination of SM and TS in cyrene yields high-quality graphene dispersions, overcoming the environmental issues linked to the other two solvents. Starting from the cyrene dispersion, a graphene-based ink is prepared to spray-coat flexible electrodes and assemble a touch screen prototype. The electrodes feature a low sheet resistance (290 Ω □⁻¹) and high optical transmittance (78%), which provide the prototype with a high signal-to-noise ratio (14 dB) and multi-touch functionality (up to four simultaneous touches). These results illustrate a potential pathway toward the integration of LPE-graphene in commercial flexible electronics.     

Efficiency Breakthrough of Fluorescence OLEDs by the Strategic Management of “Hot Excitons” at Highly Lying Excitation Triplet Energy Levels

Aggregation-induced emission (AIE) and hybridized local and charge-transfer (HLCT) materials are two kinds of promising electroluminescence systems for the fabrication of high-efficiency organic light-emitting diodes (OLEDs) by harnessing “hot excitons” at the high-lying triplet exciton states (T_n, n ≥ 2). Nonetheless, the efficiency of the resulting OLEDs did not meet expectations due to the possible loss of T_n→T_n−1. Herein, experimental results and theoretical calculations demonstrate the “hot exciton” process between the high-lying triplet state T₃ and the lowest excited singlet state S₁ in an AIE material 4⁗-(diphenylamino)-2″,5″-diphenyl-[1,1″:4′,1″:4″,1′″:4′″,1⁗-quinquephenyl]-4-carbonitrile (TPB-PAPC) and it is found that the Förster resonance energy transfer (FRET) between two molecules can facilitate the “hot exciton” process and inhibit the T₃→T₂ loss by doping a blue fluorescent emitter in TPB-PAPC. Finally, the doped TPB-PAPC blue OLEDs achieve a maximum external quantum efficiency (EQE_max) of 9.0% with a small efficiency roll-off. Furthermore, doping the blue fluorescent emitter in a HLCT material 2-(4-(10-(3-(9H-carbazol-9-yl)phenyl)anthracen-9-yl)phenyl)-1-phenyl-1H-phenanthro[9,10-d] imidazole (PAC) is used as the emission layer, and the resulting blue OLEDs exhibit an EQE_max of 17.4%, realizing the efficiency breakthrough of blue fluorescence OLEDs. This work establishes a physical insight in the design of high-performance “hot exciton” molecules and the fabrication of high-performance blue fluorescence OLEDs.     

A second-order blind source separation method for bilinear mixtures

In this paper, we are interested in the problem of Blind Source Separation using a Second-order Statistics (SOS) method in order to separate autocorrelated and mutually independent sources mixed according to a bilinear (BL) model. In this context, we propose a new approach called Bilinear Second-order Blind Source Separation, which is an extension of linear SOS methods, devoted to separate sources present in BL mixtures. These sources, called extended sources, include the actual sources and their products. We first study the statistical properties of the different extended sources, in order to verify the assumption of identifiability when the actual sources are zero-mean and when they are not. Then, we present the different steps performed in order to estimate these actual centred sources and to extract the actual mixing parameters. The obtained results using artificial mixtures of synthetic and real sources confirm the effectiveness of the new proposed approach.     

High-voltage and high-frequency inverter controlled by DPLL for cold plasma applications

In this paper, the design and construction of a high-voltage high-frequency serial resonant bridge inverter endowed with a fast resonant frequency following capability, using the digital phase locked loop (DPLL) technique, is described. The main characteristics of this inverter are: high voltage (10?kV), high frequency (94.3?kHz), and low losses in the commutation devices. This inverter is used for the excitation of a dielectric barrier discharge cell (DBDC) for cold plasma generation. The system has been applied in hazardous organic compound degradation. In particular, benzene has been degraded to the order of 99.85%, according to measurements obtained by gas chromatography.