Characterisation of GaN using cathodoluminescence and photoluminescence spectroscopy

The electron beam used to generate SEM images often results in the emission of light (cathodoluminescence). If the luminescence is detected, a new and distinctive image of the sample is produced. This new CL-SEM image distinguishes regions of high and low luminescence efficiency. Cathodoluminescence spectroscopy is an irreplaceable research tool as it allows the researcher to obtain a correlation between structural and optical properties and well as providing high spatial resolution of the luminescence distribution in the sample. In this study we apply CL-SEM to the study of GaN. Normal hétéroépitaxial growth of GaN on substrates such as AI2O3 leads to a columnar material consisting of many hexagonal grains. The tilt and rotation of the grains result in a high dislocation density of the order of 1010 cm'2. The effect of this high dislocation density on the luminescence efficiency was studied. In the Epitaxial Lateral Overgrowth (ELO) process, the material grows vertically through the etched windows in the SiOa mask and then laterally over the mask. This leads to a reduction in the dislocation density by three to four orders of magnitude. The results reported here confirm that the luminescence efficiency is substantially higher for ELO material. We report also on photoluminescence measurements of a blue defect band in GaN which has received considerably less attention than the characteristic yellow band. The blue band appears for samples cooled in the dark, and it disappears under illumination at a rate that depends on temperature. We analyse the decrease in the blue luminescence and a corresponding increase of the yellow band as a function of time at a range of temperatures and suggest possible explanations for the complex nature of the metastability displayed by the defect responsible for the blue band

Connecting Old Techniques with New Ideas

Metalworking is an ancient field that provides numerous methods to create a similar outcome. This semester I’ve been studying several traditional techniques in jewelry making while attempting to incorporate my own designs. The techniques that I have been focusing on are casting and stone-setting. For casting, I have been experimenting with both lost-wax casting and sand-casting in order to create thoughtful, one-of-a-kind works. Casting is often the best method to use when creating organic designs. My designs include snakes and historic Viking imagery that is often easier to create by carving wax and manipulating sand molds. The inclusion of precious stones brings color and vibrance to my original works. I particularly enjoy the process of problem solving in order to design a finished work that allows me to capture a precious stone as the final step. Experimenting with stone setting requires research from technical jewelry books, advice from other jewelers, and mimicking methods used in instructional videos. Doing this experimentation while still at the university will help prepare me for continued work after graduation. By expanding my “tool belt”, I can continue a career of making unique works

The College Choice Paradox; What Really Matters

For many prospective college students and their families, the college admissions process is about finding a school with a good ranking and reputation and, god willing, a nationally ranked football program. These families spend countless hours researching school rankings and plotting their son’s or daughter’s entire future to ensure admission into a top-ranked institution. Although this is often done with good intention, such a process may not achieve the best results. Admission to an elite academic school is in no way a predictor of future professional success or life satisfaction. Guaranteeing success is impossible; however, students, parents and counselors can increase the chances of a student’s success by encouraging them to focus on building technical knowledge and proficiency in their core area of study, as well as actively engaging in activities which allow the student to build their interpersonal, leadership, critical thinking and written communication skills

Open Access Publishing and Intellectual Freedom: Remembering Aaron Swartz

Slides and other materials related to a presentation on open access at the 2013 Rhode Island Library Association Annual Conference, Navigating a Sea of Change. The presentation was part of a broader discussion on open access and Aaron Swartz. It took place on June 4, 2013 at Salve Regina University in Newport, RI. The abstract for the presentation reads: After an introduction to the concept of Creative Commons and the tragic case of Aaron Swartz, join the panelists in discussing open access, scholarly publishing and the flow of information as they relate to libraries

Using contextual information in the evaluation of the effectiveness of barriers restricting access to the main line at stations

The use of fencing at railway stations to reduce the numbers of fatalities is a common safety intervention. This study examines the effectiveness of a mid-platform fencing programme as a means of preventing access to the track area. Two aspects of the programme are considered: firstly the extent to which fencing has been fitted to provide a secure barrier to fast lines at the target stations; and secondly, investigation of incidents in which the physical barrier has been overcome by individuals. The study involved the analysis and collation of descriptive data, using station visits, interviews with industry staff, examination of reports on the incidents and data from the SMIS database. It was found that the desired level of restriction of access to the intended areas through fencing was not always provided. So far, there have been few examples where somebody attempted or succeeded in climbing over a barrier to access the track. Factors affecting the effectiveness of physical barriers are presented and some shortcomings in current collection of evidence through incident reporting are highlighted

Evaluating rail suicide prevention measures

Many rail safety interventions are implemented without sufficient consideration of the effectiveness of the intervention or the degree to which the intervention has been implemented. This paper describes a programme of work to develop, test and implement a simple framework and associated research tools that can be used by rail staff to collect better data for evaluating the effectiveness of rail suicide prevention measures. Problems that have been encountered in attempting to embed this framework within organisational processes are described

Modelling and simulation of rail passengers to evaluate methods to reduce dwell times

The paper outlines a feasibility study using modelling and simulation to reduce dwell times and increase rail network capacity. We use agent based modelling, where passengers are treated as a separate entities, basing their movements on rules from the Social Force Model (SFM), proposed by Helbing to model pedestrian dynamics. Implementing this SFM, together with a novel decision making system for passengers' door choices, a mesoscopic model is produced of the platform, train and passengers. An outline of the modelling process is presented, along with a critical analysis of the final model. Analyses are conducted to evaluate novel concepts in train and platform design, to reduce loading times, using passengers with a range of attributes. In a simulation experiment, four concepts (wider doors, designated boarding/alighting doors, and an active passenger information system) are assessed, with the latter two giving reductions in loading times of 7.0% and 7.3%

The Low Beta Anomaly: A Decomposition into Micro and Macro Effects

Low beta stocks have offered a combination of low risk and high returns. We decompose the anomaly into micro and macro components. The micro component comes from the selection of low beta stocks. The macro component comes from the selection of low beta countries or industries. The two parts both contribute to the low beta anomaly, with important implications for the construction of managed volatility portfolios