Electronic states and optical properties of quantum well heterostructures with strain and electric field effects

The aim of this work was to develop an envelope function method to calculate the electronic states and optical properties of complex quantum well heterostructures, and to demonstrate its effectiveness by application to some device structures of topical interest. In particular, structures have been considered which might form the basis of intensity modulators and polarization insensitive amplifier devices for light at a wavelength of 1.55 µm. The modulator structures considered all have the general form of two coupled quantum wells of different widths as the active region. The application of an electric field in the growth direction is intended to result in a shift in the energy and spatial localisation of the confined states and produce an increase in the absorption coefficient at longer wavelengths than the zero field absorption edge. The effectiveness of certain structures is examined in terms of field induced absorption increase at 1.55 µm. A system which shows a significant increase in absorption coefficient at this wavelength on application of a practical electric field has been identified as a possible candidate for an intensity modulator. In the case of the amplifier, the active region of the most promising structure considered consists of a stepped well which comprises two layers, one with tensile and one with compressive strain. It is known that the presence of the two oppositely strained layers can result in the TE and TM gain peaks appearing at similar photon energies. Our calculations show that a suitable choice of strain and layer widths can result in a small or zero difference between the TE and TM gains at 1.55 µm, which can be important for the polarization insensitive operation of devices in optical communications applications. In order to predict the optical properties of quantum well devices it is necessary to calculate the electron and hole states for a range of in-plane wavevectors. The calculations developed and carried out in this work are based on a multi-layer (eight band) k.p model including strain effects. The interfacial boundary conditions which result from approximations to Burt's exact envelope function theory are included in the model. The effect of an electric field is modelled by including a potential energy term in each layer Hamiltonian which is equal to the average energy shift across the layer in question due to the presence of the field. The model has been developed with flexibility in mind and has applications beyond the specific devices considered in this thesis

Multimodal Pretraining Unmasked: A Meta-Analysis and a Unified Framework of Vision-and-Language BERTs

Large-scale pretraining and task-specific fine-tuning is now the standard methodology for many tasks in computer vision and natural language processing. Recently, a multitude of methods have been proposed for pretraining vision and language BERTs to tackle challenges at the intersection of these two key areas of AI. These models can be categorised into either single-stream or dual-stream encoders. We study the differences between these two categories, and show how they can be unified under a single theoretical framework. We then conduct controlled experiments to discern the empirical differences between five V&L BERTs. Our experiments show that training data and hyperparameters are responsible for most of the differences between the reported results, but they also reveal that the embedding layer plays a crucial role in these massive models.Comment: To appear in TACL 202

Theories of physical activity behaviour change:A history and synthesis of approaches

Rebar, A ORCiD: 0000-0003-3164-993XBackground: Most people in developed countries are not physically active enough to reap optimal health benefits so effective promotion strategies are warranted. Theories of behaviour change are essential to understand physical activity and provide an organizing framework for effective intervention. The purpose of this paper was to provide a narrative historical overview of four key theoretical frameworks (social cognitive, humanistic, dual process, socioecological) that have been applied to understand and change physical activity over the last three decades. Methods: Our synthesis of research included the brief history, basic efficacy, strengths, and potential weaknesses of these approaches when applied to physical activity. Results: The dominant framework for understanding physical activity has been in the social cognitive tradition, and it has provided valuable information on key constructs linked to physical activity. The humanistic framework for understanding physical activity has seen a surge in research in the last decade and has demonstrated initial effectiveness in both explaining and intervening on behaviour. The most recent and understudied framework for understanding physical activity is dual process models, which may have promise to provide a broader perspective of motivation by considering non-conscious and hedonic determinants of physical activity. Finally, the individual-level focus of all three of these approaches is contrasted by the socioecological framework, which has seen considerable research attention in the last 15 years and has been instrumental in understanding the role of the built environment in physical activity behaviour and critical to shaping public health policy in government. Conclusions: Despite the strengths of all four frameworks, we noted several weaknesses of each approach at present and highlight several newer applications of integrated models and dynamic models that may serve to improve our understanding and promotion of physical activity over the next decade. © 2018 Elsevier Lt

The solid geology of the area between Binic and Brehec, Cotes du Nord, France

The area mapped is situated on the west side of the Baie de Saint Brieuc, Cates du Nord, France. It is bounded by the towns of Binic, Brehec, Lantic and Plehedel. Rocks of Pentevrian, Brioverian and post Brioverian age were recorded. The Pentevrian, which was previously unreported, is composed of the pelitic and semipelitic Port Goret gneisses, the metasediments and metavolcanics of the Plouha Series and the late Pentevrian intrusion, the Port Moguer tonalite. The Port Goret gneisses and the Plouha Series had undergone at least 4 major fold phases and 4 regional metamorphic events prior to the Brioverian sedimentation. Locally the structural and metamorphic histories are found to be more complex. However the Port Moguer tonalite has a relatively simple structural history. Two sequences of Brioverian age are recorded, the Binic Brehec Series and the Palus plage metasediments and metavolcanics. The sedimentology of the former has been studie~ and it is conluded that they are a sequence of distal turbidites. The latter are composed of pelites, psammites and acid volcanics and they display an unconformable relationship with the Port Goret gneisses. The original surface of unconformity may not be preserved. The Brioverian and locally the Pentevrian have been affected by the late Precambrian Cadomian orogeny, which has produced 3 main phases of folding and up to five phases of metamorphism. The grade of anyone metamorphic event varies throughout the area. Late Cadomian brittle structures are recorded. The Port Goret gneisses are intruded by a post-Brioverian, synCadomian composite norite, hornblende ferropypersthene gabbro and quartz hornblende gabbro intrusion, the Saint Quay intrusion. Petrological and petrochemical studies indicate that this body was formed by two intrusive phases, the second of which was more differentiated than the first. The regional significance of this research has been discussed

Un enfoque de terapia ocupacional adaptada a la rehabilitación cognitiva de los efectos cognitivos colaterales asociados a la quimioterapia en pacientes supervivientes de cáncer de mama: dos estudios de mujeres postmenopáusicas afectadas

This article describes a tailored occupational therapy program to rehabilitate chemotherapy-related cognitive side effects. A literature review of cognitive rehabilitation as well as pharmacological trials used to improve cognition in breast cancer patients is included. Two outpatient case studies of young women premenopausally affected with breast cancer (both BRCA-1 gene mutation carriers) are used to discuss the role of tailored occupational therapy techniques for developing compensatory strategies and for delivering cognitive remediation. Neuropsychological evaluation pre and post occupational therapy is used to document the result of tailored occupational therapy on cognitive performance. The case studies illustrate the neuropsychological profile of chemotherapy-related cognitive changes and the course of deficits over 7-9 months. For younger, educated patients who must return to competitive, fast-paced jobs, cognitive side-effects post-treatment are especially noxious as young adult patients are building their professional lives and are not necessarily provided time to wait for the usual trajectory of recovery to take its course.En este artículo se describe un programa de terapia ocupacional adaptado para rehabilitar los efectos cognitivos secundarios asociados a la quimioterapia. Se incluye una revisión de la literatura de la rehabilitación cognitiva, así como de los ensayos farmacológicos utilizados para mejorar la cognición en pacientes de cáncer de mama. Se exponen dos estudios de caso ambulatorios de mujeres jóvenes premenopáusicas afectadas de cáncer de mama (ambas portadoras de mutaciones del gen BRCA-1) para examinar la función de técnicas de terapia ocupacional adaptadas para el desarrollo de estrategias compensatorias y para administrar rehabilitación cognitiva. La evaluación neuropsicológica antes y después de la terapia ocupacional se utiliza para documentar el resultado de la terapia ocupacional adaptada para el rendimiento cognitivo. Los estudios de casos ilustran el perfil neuropsicológico de los cambios asociados a la quimioterapia y el curso de los déficits durante 7-9 meses. En los pacientes jóvenes, con estudios que deben retornar a puestos de trabajo de ritmo rápido y competitivos, los efectos cognitivos secundarios postratamiento son especialmente nocivos, ya que los pacientes jóvenes adultos están construyendo sus vidas profesionales y no disponen del tiempo necesario de espera para que la trayectoria habitual de recuperación siga su curso

Personality traits of high-risk sport participants:A meta-analysis

The purpose of this meta-analysis was to examine the relationships between personality traits and participation in high-risk sport. A total of 149 effect sizes from 39 eligible articles were obtained wherein the personality traits of high-risk sport participants were compared with either low-risk sport participants or individuals not engaged in any sport. Results revealed significant effect sizes in favor of the high-risk participants for sensation seeking, extraversion, and impulsivity. Significant effect sizes in favor of the comparator groups were found for neuroticism, telic dominance, and sensitivity to punishment. No significant differences were observed in psychoticism, sensitivity to reward, socialization, agreeableness, conscientiousness, or openness. The implications of these results and potential avenues of future research are highlighted

Growing Up in Ireland: Growing up and developing as an adult: A review of the literature on selected topics pertaining to cohort ’98 at age 20 years. ESRI Report December 2020.

The goal of this report is to provide research information on selected potential research questions using data collected in interviews with 20-year-olds and their parents. At the time of writing, fieldwork was under way, so the topics of the survey were known but not the outcome of the interviews. The research questions address the central outcomes of the Growing Up in Ireland study that contribute to building developmental trajectories from childhood to adulthood: socio-emotional well-being; educational and cognitive development; physical health and growth. Three potential research questions are outlined under each outcome and provide a short supporting review of the national and international literature, followed by a description of the measures in Growing Up in Ireland useful in exploring the topic. While there is a wide array of possible research questions with a dataset such as this, the selected topics are those that offer new potential given the measures at this particular wave and/or are particularly salient to this phase of the life-course