The electroluminescent decay mechanism of rare-earth ions in OLEDs based on a terbium complex

The organic light-emitting diodes (OLEDs) based on terbium (Tb) complexes show sharp green emission spectrum with excellent color purity. However, the brightness of Tb-OLEDs is generally weak. Here, the electroluminescent (EL) decay mechanism of TB-OLEDs is studied by arbitrarily using tris-(1-phenyl-3-methyl-4-isobutyryl-5-pyrozolone)-bis(triphenyl phosphine oxide) terbium as the emitting layer. The device shows high EL efficiency at low current density but rapid reduction of device efficiency at higher current density. The transient EL is investigated for understanding the decay process of excited Tb 3+ ions. Together with theoretical studies, exciton quenching is proposed to explain the decay of the Tb-OLEDs which is important for optimizing and engineering the material and device structures. The EL from the mixed layer of the Tb and europium (Eu) complexes is also studied. We find that the EL performance and transient decay of the excited Tb ions are modified by energy transfer from Tb to Eu in the OLEDs. © 2007 IEEE.published_or_final_versio

Editorial: Technology for Higher Education, Adult Learning and Professional Development

The basis of competition has shifted more towards the assimilation and creation of knowledge in the fiercely competitive and evolving digital age. Learning has therefore become crucial for sustainable development and innovation across individual, organizational, and community levels. Papers in this special issue are representative of ongoing research on integration of technology with learning and knowledge management in higher education institutions and organizational and community environments.published_or_final_versio

Modifications of the exciton lifetime and internal quantum efficiency for organic light-emitting devices with a weak/strong microcavity

A comprehensive analysis is given on the modifications of the exciton lifetime and internal quantum efficiency (int) for organic light-emitting devices (OLEDs). A linear relation is derived between the exciton lifetime and int, which is difficult to measure directly. The internal quantum efficiency can thus be estimated easily through the measurement of the exciton lifetime. The exciton lifetimes for OLEDs with weak or strong microcavity are studied experimentally and theoretically. The modification of the exciton lifetime is well explained through the microcavity effect and surface plasmon resonance. An excellent agreement between the experimental and theoretical results is achieved. © 2007 American Institute of Physics.published_or_final_versio

Improving polymer solar cell performances by manipulating the self-organization of polymer

We have investigated driving force effects on the ordering of polymer, which is a key factor of self-assembly of soft materials. By turning the substrate up-side-down, the downward driving force can form in solution film-growth process and affect the self-organization of polymer chains and domains. We introduce Brown's capillarity theory [J. Polym. Sci., Polym. Phys. Ed. 22, 423 (1956)] to describe the film formation. Our results show that the better chain and lamellae packing of polymer make hole transport, carrier balance, and power conversion efficiency of annealed and unannealed devices improve even with thick active-layers as compared to conventional devices. © 2011 American Institute of Physics.published_or_final_versio

Ternary hypervalent silicon hydrides via lithium at high pressure

Hydrogen is rarely observed as ligand in hypervalent species, however, we find that high-pressure hydrogenation may stabilise hypervalent hydrogen-rich materials. Focussing on ternary silicon hydrides via lithium doping, we find anions composed of hypervalent silicon with H ligands formed under high pressure. Our results reveal two new hypervalent anions: layered-SiH−5 and tricapped triangular prismatic SiH2−. These differ from octahedral SiH2− described in earlier studies. In addition, there are further hydrogen-rich structures, Li3SiH10 and Li2SiH6+δ, which may be stabilised at high pressure. Our work provides pointers to future investigations on hydrogen rich materials

Stability and Startup of Non Linear Loop Circuits

The reliable analysis of DC operating point in circuits with positive feedback topology is often challenging, and frequently performed with ad hoc methods. These techniques are often error prone and lead to the frequent use of sub-optimal or unnecessary additional circuits for the stabilization or determination of the operating point (startup circuits). We present a simple and reliable technique for the determination of “stable” circuit solutions, that is based on the use of available circuit simulators and hence takes advantage of accurate device models. The method has been experimentally validated on a self-biasing current generator fabricated with a standard 0.18 μm CMOS process

Explicit dynamics finite element analysis of energy absorption characteristics of thin-walled UltraSTEEL columns

UltraSTEEL material has been reported to have higher yield and ultimate strengths than plain mild steel under quasi-static loads. This project aims to study the energy absorption characteristics of UltraSTEEL thin-walled structures when subjected to axial impact loads. The numerical modelling starts from duplicating the UltraSTEEL dimpling process and defining the resultant material properties by taking strain hardening and strain rate sensitivity into consideration. Features including element type, mesh density, symmetric boundary conditions and imperfections are then studied. The responses of 1mm gauge plain and UltraSTEEL columns to the same impact load are compared by conducting explicit dynamics finite element simulations. Comparing to the plain columns, the effect of gauge on the UltraSTEEL columns’ failure mode and specific energy absorption (SEA) are analysed through a parametric study.Hadley Industries Holdings Limite

Curling: Content-ubiquitous resolution and delivery infrastructure for next-generation services

CURLING, a Content-Ubiquitous Resolution and Delivery Infrastructure for Next Generation Services, aims to enable a future content-centric Internet that will overcome the current intrinsic constraints by efficiently diffusing media content of massive scale. It entails a holistic approach, supporting content manipulation capabilities that encompass the entire content life cycle, from content publication to content resolution and, finally, to content delivery. CURLING provides to both content providers and customers high flexibility in expressing their location preferences when publishing and requesting content, respectively, thanks to the proposed scoping and filtering functions. Content manipulation operations can be driven by a variety of factors, including business relationships between ISPs, local ISP policies, and specific content provider and customer preferences. Content resolution is also natively coupled with optimized content routing techniques that enable efficient unicast and multicast-based content delivery across the global Internet

Modifications of the exciton lifetime and internal quantum efficiency for organic light-emitting devices with a weak/strong microcavity

Author name used in this publication: P. K. A. Wai2007-2008 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Fifteen-Year Population Attributable Fractions and Causal Pies of Risk Factors for Newly Developed Hepatocellular Carcinomas in 11,801 Men in Taiwan

Development of hepatocellular carcinoma (HCC) is a multi-factorial process. Chronic infections with hepatitis B virus (HBV) and hepatitis C virus (HCV) are important risk factors of HCC. Host factors, such as alcohol drinking, may also play a role. This study aims to provide a synthesis view on the development of HCC by examining multiple risk factors jointly and collectively. Causal-pie modeling technique was applied to analyze a cohort of 11,801 male residents (followed up for 15 years) in Taiwan, during which a total of 298 incident HCC cases were ascertained. The rate ratios adjusted by age were further modeled by an additive Poisson regression. Population attributable fractions (PAFs) and causal-pie weights (CPWs) were calculated. A PAF indicates the magnitude of case-load reduction under a particular intervention scenario, whereas a CPW for a particular class of causal pies represents the proportion of HCC cases attributable to that class. Using PAF we observed a chance to reduce around 60% HCC risk moving from no HBV-related intervention to the total elimination of the virus. An additional ∼15% (or ∼5%) reduction can be expected, if the HBV-related intervention is coupled with an HCV-related intervention (or an anti-drinking campaign). Eight classes of causal pies were found to be significant, including four dose-response classes of HBV (total CPW=52.7%), one independent-effect class of HCV (CPW=14.4%), one HBV-alcohol interaction class (CPW=4.2%), one HBV-HCV interaction class (CPW=1.7%), and one all-unknown class (CPW=27.0%). Causal-pie modeling for HCC helps clarify the relative importance of each viral and host factor, as well as their interactions