Highly Efficient,Solution‐Processed,Single‐Layer,Electrophosphorescent Diodes and the Effect of Molecular Dipole Moment

A new family of highly soluble electrophosphorescent dopants based on a series of tris‐cyclometalated iridium(III) complexes (1–4) of 2‐(carbazol‐3‐yl)‐4/5‐R‐pyridine ligands with varying molecular dipole strengths have been synthesized. Highly efficient, solution‐processed, single‐layer, electrophosphorescent diodes utilizing these complexes have been prepared and characterized. The high triplet energy poly(9‐vinylcarbazole) PVK is used as a host polymer doped with 2‐(4‐biphenylyl)‐5‐(4‐tert‐butyl‐phenyl)‐1,3,4‐oxadiazole (PBD) for electron transport. Devices with a current efficiency of 40 cd A^?1 corresponding to an EQE of 12% can thus be achieved. The effect of the type and position of the substituent (electron‐withdrawing group (CF₃) and electron‐donating group (OMe)) on the molecular dipole moment of the complexes has been investigated. A correlation between the absorption strength of the singlet metal‐to‐ligand charge‐transfer (¹MLCT) transition and the luminance spectral red shift as a function of solvent polarity is observed. The strength of the transition dipole moments for complexes 1–4 has also been obtained from TD‐DFT computations, and is found to be consistent with the observed molecular dipole moments of these complexes. The relatively long lifetime of the excitons of the phosphorescence (microseconds) compared to the charge‐carrier scattering time (less than nanoseconds), allows the transition dipole moment to be considered as a “quasi permanent dipole”. Therefore, the carrier mobility is sufficiently affected by the long‐lived transition dipole moments of the phosphorescent molecules, which are randomly oriented in the medium. The dopant dipoles cause positional and energetic disorder because of the locally modified polarization energy. Furthermore, the electron‐withdrawing group CF₃ induces strong carrier dispersion that enhances the electron mobility. Therefore, the strong transition dipole moment in complexes 3 and 4 perturbs both electron and hole mobilities, yielding a reduction in exciton formation and an increase in the device dark current, thereby decreasing the device efficiency.     

Lactate cannot substitute for alanine in d4T-based anti-HIV nucleotide prodrugs--despite efficient esterase-mediated hydrolysis

As part of our on-going effort to deliver masked phosphates of antiviral nucleosides inside living cells we have previously discovered that amino acid-derived phosphoramidates are particularly effective. Here we report that lactate analogues, with a simple change of bridging nitrogen for oxygen, are virtually inactive as antiviral agents and apparently do not achieve intracellular nucleoside phosphate delivery.     

Effect of enhancing the Raman gain factor on the linearity of Raman fibre amplifiers

The effect of enhancing the Raman gain factor on the linearity characteristics of Raman fibre amplifiers is analysed. In addition to providing higher Raman gain per unit pump power, a higher value for the Raman gain factor also results in a lower value for the maximum gain, and therefore the maximum output power, available from the amplifier if it is to operate in the linear regime. This has important implications for optimising the design of Raman fibre amplifiers.<>     

Real options valuation of US federal renewable energy research,development, demonstration,and deployment

Benefits analysis of US Federal government research, development, demonstration, and deployment (RD³) programmes for renewable energy (RE) technology improvement typically employs a deterministic forecast of the cost and performance of renewable and non-renewable fuels. The benefits estimate for the programme derives from the difference between two forecasts, with and without the RD³ programme in place. Three deficiencies of this approach are that it ignores: (1) uncertainty in the cost of non-renewable energy (NRE); (2) the possibility of adjustment to the RD³ effort commensurate with the evolving state of the world; and (3) the underlying technical risk associated with RD³. In this paper, an intuitive approach to determining the option value of RE RD³ is developed. This approach seeks to tackle the first two deficiencies noted above by providing an estimate via a compound real option of an RE RD³ programme in a future with uncertain NRE costs. A binomial lattice reveals the economic intuition underlying the decision-making process, while a numerical example illustrates the option components embedded in a simplified representation of current US Federal RE RD³.     

SOLVENT EXTRACTION OF PAKISTAN COALS (III) EXTRACTION AND CHARACTERIZATION OF THE EXTRACTS BY SPECTROSCOPIC TECHNIQUES

The Makerwal coal of Pakistan gives higher extractibi1ity with Tetrahydrofuran ( THF ) as compared to Sharigh, Sor-Range and Lakhra coals. The structural characterization of Pakistan coal extracts by FT-IR spectroscopy indicates that all the extracts contained less condensed aromatic rings in comparision to their original coal.     

Novel fibre optic gyroscope with a configuration combining Sagnac interferometer with fibre ring resonator

A novel fibre optic gyroscope, with a structure making use of the combination of a Sagnac interferometer with an active fibre ring-resonator, is proposed and analysed. The proposed gyroscope can be viewed as a generalised structure of the conventional Sagnac interferometric type fibre optical gyroscope. It has the advantages of both long fibre loop length and multipath interferences. By inserting a fibre amplifier in the loop to provide an optical gain of several dB, the relative maximum sensitivity is enhanced to approximately 30 times more than that of conventional Sagnac interferometric fibre optic gyroscopes.<>     

Primary spinal T-cell rich B-cell lymphoma: a case report

During my nursing career, I remember constantly being aware of patients who needed some emotional help--those who were frightened about a forthcoming operation, those who were shocked and despairing after being given their diagnosis and prognosis, others who were down in the dumps because they couldn't go home as soon as they had hoped. There were also the 'ward clowns' who tried to make everyone laugh with their good humour and little pranks, yet felt no less anxious, worried or depressed than anyone else. Patients seem to fit into categories: the nervous ones, the depressives, the jovial types, the moaners, those who demand attention and those who shun it. I feel sure that every nurse has noticed the different 'types' of people who fill hospital beds-ordinary people who seem to take on a new persona as soon as they get into their pyjamas and become a 'patient'. Somehow, their identity gets folded up and put away in their locker along with their outdoor clothes and other reminders of the outside world.