Modelling and Optimisation of Single Junction Strain Balanced Quantum Well Solar Cells

In an attempt to find the optimum number of wells for maximum conversion efficiency a pair of otherwise identical strain balanced samples, one containing 50 wells and the other 65 wells have been characterised. The 65 well sample is found to possess a lower predicted efficiency than the 50 well sample, suggesting that the optimum well number lies between these values. Devices grown using tertiary butyl arsine (TBAs) are found to possess comparable conversion efficiencies to the control cells grown using arsine and slightly superior dark IV characteristics, indicating that TBAs may be substituted for arsine without loss of device efficiency and may even be beneficial to cell performance. Several fundamental refinements to the existing quantum efficiency model of are explored. Firstly, expressions for the strained band gaps are derived. A value for the conduction band offset is . determined using the difference in energy between the heavy and light hole exciton peaks in low temperature photo current scans and found to be 0.55??0.03. The magnitude of the el-hhl exciton binding energy is also estimated from these scans and found to be in excellent agreement with the value obtained from a simple, parameterized expression for the exciton binding energy. Finally, an absolute calculation for the absorption coefficient is incorporated into the quantum efficiency model and values for the heavy and light hole in-planes masses are obtained. The model is found to underestimate the level of absorption in the intrinsic region by an amount consistent with estimates of the magnitude of the reflection from the back surface. The conversion efficiency of a sample predicted using SOL is compared to an independently obtained value. Good agreement is observed between the two results (25.3% and 25.7% for 317 suns AM1.5D). Additionally, an optimum structure for illumination by the AM1.5D spectrum was found to be a 120A well ofIno.lGaAs.Imperial Users onl

Consensus using Asynchronous Failure Detectors

The FLP result shows that crash-tolerant consensus is impossible to solve in asynchronous systems, and several solutions have been proposed for crash-tolerant consensus under alternative (stronger) models. One popular approach is to augment the asynchronous system with appropriate failure detectors, which provide (potentially unreliable) information about process crashes in the system, to circumvent the FLP impossibility. In this paper, we demonstrate the exact mechanism by which (sufficiently powerful) asynchronous failure detectors enable solving crash-tolerant consensus. Our approach, which borrows arguments from the FLP impossibility proof and the famous result from CHT, which shows that $\Omega$ is a weakest failure detector to solve consensus, also yields a natural proof to $\Omega$ as a weakest asynchronous failure detector to solve consensus. The use of I/O automata theory in our approach enables us to model execution in a more detailed fashion than CHT and also addresses the latent assumptions and assertions in the original result in CHT

Organizing Clericals: Problems & Prospects

[Excerpt] One of the central goals of contemporary feminism has been the full integration of women into the workforce. While broader economic and social forces were decisive in propelling women into full-time employment, the women\u27s movement took as its particular task shaping the nature of that participation. The movement sought to achieve economic equality for women workers through two primary strategies: 1) gaining entry to traditionally male-dominated jobs and training, and 2) upgrading the pay and status of traditionally female-dominated jobs. The clerical sector—with its overwhelming concentration of women workers, its rock-bottom pay scales, and its gender-based work culture—was a logical focus of that second strategic course. Historically, the rate of unionization among clericals has been low. Some feminists blamed this on the indifference of maledominated unions to the particular problems of women in the workforce. Others believed that there were unique circumstances which made clerical workers resistant to traditional trade union approaches. Out of such analyses, a small but determined network of activists shaped an alternative conception of organization for office workers, beginning in the early 1970s

The Orange Revolution: round two

This repository item contains a single issue of Behind the Breaking News, a briefing published from 1999 to 2009 by the Boston University Institute for the Study of Conflict, Ideology, and Policy

Who do you think you are? Intimate pasts made public

This is the official published version of the Article - Copyright @ 2011 University of Hawaii Pres

How healthy is your ‘community of practice’?

This article explores cultural change and situated approaches to learning as a basis for understanding developments in the daily life of the probation organization. These are highlighted in the concept of ‘communities of practice’ that describes learning in the everyday activities of practitioners’ work. It is argued that the future can be changed by greater attention to context specific knowledge-in-use through practitioner research.</p