Modelling of Electroluminescence in Polymers Using a Bipolar Charge Transport Model

Electroluminescence (EL) in polymeric materials is thought to occur due to the energy dissipation process from the recombination of opposite polarity charge carriers. It is considered as an indication of storage and transport of charge carriers in cable insulation subject to electrical stresses and may indicate the change in charge movement due to aging or degradation processes. Under ac electric fields, the interaction of opposite polarity charge carriers at the interface of polymer/conductor is enhanced compared with dc conditions, and seems to contribute a lot to the electroluminescence rather than the charge behaviours in the bulk of polymers. The dynamics of charge carriers both at the interface of polymer/conductor and in the bulk of polymers is investigated through a simulation work using a bipolar charge transport model. Figure 1 compares experimental electroluminescence results with simulated data from the recombination of injected charge carriers. The paper will give more details on EL model and comparison under various waveforms and frequencies

A Comparison between Electroluminescence Models and Experimental Results

Electrical insulation ages and degrades until its eventual failure under electrical stress. One cause of this relates to the movement and accumulation of charge within the insulation. The emission of a low level of light from polymeric materials while under electrical stressing occurs before the onset of currently detectable material degradation. This light is known as electroluminescence (EL) and under an ac electric field is thought to relate to the interaction of charge in close proximity to the electrode-polymer interface. Understanding the cause of this light emission gives a very high-resolution method of monitoring charge interaction and its influence on material ageing. A possible cause of this light emission is the bipolar charge recombination theory. This theory involves the injection, trapping and recombination of charge carriers during each half cycle of the applied field [1]. This work compares two models that to simulate the EL emission according to this bipolar charge recombination theory. Model 1 assumes a fixed space charge region and all injected charge is uniformly distributed in this region with charges able to either become trapped or to recombine with opposite polarity charge carriers [2]. This recombination relates directly the excitation needed for the emission of a photon of light as measured in experiments. Model 2 develops on this by accounting for the transport and extraction of charge with an exponential distribution of trap levels rather than a uniform distribution [3]. Figure 1 shows a good correlation between the two models and experimental data. The full paper will describe the models in more detail and present results comparing the simulated and experimental results under various applied waveforms. Model 1 and model 2 both provide a good correlation with experimental data but model 2 allows a greater understanding of the space charge profile in the region close to the electrodes as well as the shape of the conduction current. Further work involves developing these models to support changes in the charge trapping profiles due to material ageing and supporting simulated results with measured conduction current

Macrospin Models of Spin Transfer Dynamics

The current-induced magnetization dynamics of a spin valve are studied using a macrospin (single domain) approximation and numerical solutions of a generalized Landau-Lifshitz-Gilbert equation. For the purpose of quantitative comparison with experiment [Kiselev {\it et al.} Nature {\bf 425}, 380 (2003)], we calculate the resistance and microwave power as a function of current and external field including the effects of anisotropies, damping, spin-transfer torque, thermal fluctuations, spin-pumping, and incomplete absorption of transverse spin current. While many features of experiment appear in the simulations, there are two significant discrepancies: the current dependence of the precession frequency and the presence/absence of a microwave quiet magnetic phase with a distinct magnetoresistance signature. Comparison is made with micromagnetic simulations designed to model the same experiment.Comment: 14 pages, 14 figures. Email [email protected] for a pdf with higher quality figure

Unimpoundment: Politics and the Courts in the Release of Impounded Funds

During the administration of President Nixon, the impoundment of funds appropriated by the Congress became not merely a means of executive economy but a tool of presidential politics. Non-judicial methods of unimpoundment lost their efficacy, and the courts became involved in the conflict between the President and the Congress in resolving the question of whether impoundment was either constitutionally or legislatively proscribed. Mr. Mills and Professor Munselle examine the process of unimpoundment both as a political phenomenon and as a legal issue. They survey the extra-judicial means of unimpoundment and then consider the resolution of that issue in the courts, particularly as affected by the recent decision of the Supreme Court in Train v. New York. Finally, they discuss the implications of the recently enacted Budget and Impoundment Control Act of 1974, particularly as it affects the judicial process of unimpoundment. Their conclusions suggest that the Act has formalized both methods of unimpoundment and that the resolution of budgetary conflicts between the President and the Congress will continue in both political and judicial arenas

Unimpoundment: Politics and the Courts in the Release of Impounded Funds

During the administration of President Nixon, the impoundment of funds appropriated by the Congress became not merely a means of executive economy but a tool of presidential politics. Non-judicial methods of unimpoundment lost their efficacy, and the courts became involved in the conflict between the President and the Congress in resolving the question of whether impoundment was either constitutionally or legislatively proscribed. Mr. Mills and Professor Munselle examine the process of unimpoundment both as a political phenomenon and as a legal issue. They survey the extra-judicial means of unimpoundment and then consider the resolution of that issue in the courts, particularly as affected by the recent decision of the Supreme Court in Train v. New York. Finally, they discuss the implications of the recently enacted Budget and Impoundment Control Act of 1974, particularly as it affects the judicial process of unimpoundment. Their conclusions suggest that the Act has formalized both methods of unimpoundment and that the resolution of budgetary conflicts between the President and the Congress will continue in both political and judicial arenas

Nonlocal feedback in ferromagnetic resonance

Ferromagnetic resonance in thin films is analyzed under the influence of spatiotemporal feedback effects. The equation of motion for the magnetization dynamics is nonlocal in both space and time and includes isotropic, anisotropic and dipolar energy contributions as well as the conserved Gilbert- and the non-conserved Bloch-damping. We derive an analytical expression for the peak-to-peak linewidth. It consists of four separate parts originated by Gilbert damping, Bloch-damping, a mixed Gilbert-Bloch component and a contribution arising from retardation. In an intermediate frequency regime the results are comparable with the commonly used Landau-Lifshitz-Gilbert theory combined with two-magnon processes. Retardation effects together with Gilbert damping lead to a linewidth the frequency dependence of which becomes strongly nonlinear. The relevance and the applicability of our approach to ferromagnetic resonance experiments is discussed.Comment: 22 pages, 9 figure

The Association Between Health Care Staff Engagement and Patient Safety Outcomes: A Systematic Review and Meta-Analysis

Objectives: Despite decades of research, improving health care safety remains a global priority. Individual studies have demonstrated links between staff engagement and care quality, but until now, any relationship between engagement and patient safety outcomes has been more speculative. This systematic review and meta-analysis therefore assessed this relationship and explored if the way these variables were defined and measured had any differential effect. Methods: After systematic searches of Medline, CINAHL, PsycInfo, Embase, Cochrane Library, and National Institute for Health Research Journals databases, narrative and random-effects meta-analyses were completed, with pooled effect sizes expressed as Pearson r. Results: Fourteen studies met the inclusion criteria, 11 of which were suitable for meta-analysis. Meta-analyses indicated a small but consistent, statistically significant relationship between staff engagement and patient safety (all outcomes; 11 studies; r = 0.22; 95% confidence interval [CI], 0.07 to 0.36; n = 30,490) and 2 patient safety outcome categories: patient safety culture (7 studies;r = 0.22; 95% CI, 0.01 to 0.41; n = 27,857) and errors/adverse events (4 studies;r = −0.20; 95% CI, −0.26 to −0.13; n = 2633). The specific approach to conceptualizing engagement did not affect the strength of the findings. Conclusions: This is the first review to demonstrate a significant relationship between engagement and both safety culture scores and errors/adverse events. Despite a limited and evolving evidence base, we cautiously conclude that increasing staff engagement could be an effective means of enhancing patient safety. Further research is needed to determine causality and clarify the nature of the staff engagement/patient safety relationship at individual and unit/workgroup levels