Excess electron screening of remote donors and mobility in modern GaAs/AlGaAs herostructures

In modern GaAs/Al$_x$Ga$_{1-x}$As heterostructures with record high mobilities, a two-dimensional electron gas (2DEG) in a quantum well is provided by two remote donor $\delta$-layers placed on both sides of the well. Each $\delta$-layer is located within a narrow GaAs layer, flanked by narrow AlAs layers which capture excess electrons from donors but leave each of them localized in a compact dipole atom with a donor. Still excess electrons can hop between host donors to minimize their Coulomb energy. As a result they screen the random potential of donors dramatically. We numerically model the pseudoground state of excess electrons at a fraction $f$ of filled donors and find both the mobility and the quantum mobility limited by scattering on remote donors as universal functions of $f$. We repeat our simulations for devices with additional disorder such as interface roughness of the doping layers, and find the quantum mobility is consistent with measured values. Thus, in order to increase the quantum mobility this additional disorder should be minimized.Comment: arXiv admin note: text overlap with arXiv:1804.0693

Towards a theoretical lens to examine the structural impact of adopting Web 2.0

With the widespread integration of Web 2.0 technologies across society and business there is an increasing need to understand their underlying impact. Yet, very little research has been done on such technologies, so much so, that a definition still eludes the academic community. Nonetheless, their impacts cannot be ignored. For instance, from a societal perspective, the proliferation of social networks and attitude towards openness highlights the transformation from hierarchical type social structures to more non-hierarchical (horizontal) systems. However, rigorous analysis of the structural impacts of the technologies in an organisational context is more difficult due to the lack of theoretical frameworks. Moreover, there has been a call for researchers to build their own theoretical frameworks for further understanding in the domain. As a result, this paper aims to add to the body of knowledge by (i) further defining Web 2.0, (ii) reviewing past literature on organisational structure and technology, and (iii) developing a theoretical lens by rediscovering past socio-technical theories

A novel approach to challenging consensus in evaluations: The Agitation Workshop

As researchers evaluate organisations, projects, and teams, there is a desire for a consensus from those within the organisations who are participating in the research. A common consensual perspective from a team appears to reflect an optimal state where those being evaluated have a common understanding of the current state of events within the context of their environment. The question arises, though, whether an evaluation finding consensus reflects the reality: there are a variety of reasons why a common understanding may be false consensus. Hidden behind this false consensus may be a variety of unaddressed issues which are actually the core of the problem. This paper proposes an evaluation method incorporating the principles of sensemaking and devil’s advocate, where a consensus of perspectives is challenged before they are considered valid. This is achieved in a workshop where participants reflect on their own perception of reality and represent this reality in a matrix of influencing and relevant factors. The individual matrices are then combined and used to highlight disparities in the participants’ perspectives through a single matrix visualisation. Discussion in the workshop then focusses on the areas, highlighted by the matrix, where differences of perspectives are identified. In effect, the consensus presented by those being evaluated will be challenged, and a new common understanding will have to be created. Problems such as groupthink can create a false consensus, and it is proposed herein that the workshop provides a mechanism for challenging this. The objective of the research herein was to determine the feasibility and potential benefits of the proposed workshop. The workshop itself is evaluated in this paper, to determine if it has value. The benefits of such a workshop are described, showing how an organisation went from a false consensus concerning problems within the organisation, to the start of a process to address the real underlying issues.Proceedings of the 6th European Conference on Information Management and Evaluation - ECIME 2012 held at the University College Cork. Cork, Ireland on 13-14 September 201

Recording and treatment of premenstrual syndrome in UK general practice: a retrospective cohort study

OBJECTIVES: To investigate the rate of recording of premenstrual syndrome diagnoses in UK primary care and describe pharmacological treatments initiated following a premenstrual syndrome (PMS) diagnosis. DESIGN: Retrospective cohort study. SETTING: UK primary care. PARTICIPANTS: Women registered with a practice contributing to The Health Improvement Network primary care database between 1995 and 2013. PRIMARY AND SECONDARY OUTCOME MEASURES: The primary outcome was the rate of first premenstrual syndrome records per 1000 person years, stratified by calendar year and age. The secondary outcome was the proportions of women with a premenstrual syndrome record prescribed a selective serotonin reuptake inhibitor, progestogen, oestrogen, combined oral contraceptive, progestin only contraceptive, gonadotrophin-releasing hormone, danazol and vitamin B6. RESULTS: The rate of recording of premenstrual syndrome diagnoses decreased over calendar time from 8.43 in 1995 to 1.72 in 2013. Of the 38 614 women without treatment in the 6 months prior to diagnosis, 54% received a potentially premenstrual syndrome-related prescription on the day of their first PMS record while 77% received a prescription in the 24 months after. Between 1995 and 1999, the majority of women were prescribed progestogens (23%) or vitamin B6 (20%) on the day of their first PMS record; after 1999, these figures fell to 3% for progestogen and vitamin B6 with the majority of women instead being prescribed a selective serotonin reuptake inhibitor (28%) or combined oral contraceptive (17%). CONCLUSIONS: Recording of premenstrual syndrome diagnoses in UK primary care has declined substantially over time and preferred prescription treatment has changed from progestogen to selective serotonin reuptake inhibitor and combined oral contraceptives

On the Use of Gallic Acid as a Potential Natural Antioxidant and Ultraviolet Light Stabilizer in Cast-Extruded Bio-Based High-Density Polyethylene Films

This study originally explores the use of gallic acid (GA) as a natural additive in bio-based high-density polyethylene (bio-HDPE) formulations. Thus, bio-HDPE was first melt-compounded with two different loadings of GA, namely 0.3 and 0.8 parts per hundred resin (phr) of biopolymer, by twin-screw extrusion and thereafter shaped into films using a cast-roll machine. The resultant bio-HDPE films containing GA were characterized in terms of their mechanical, morphological, and thermal performance as well as ultraviolet (UV) light stability to evaluate their potential application in food packaging. The incorporation of 0.3 and 0.8 phr of GA reduced the mechanical ductility and crystallinity of bio-HDPE, but it positively contributed to delaying the onset oxidation temperature (OOT) by 36.5 °C and nearly 44 °C, respectively. Moreover, the oxidation induction time (OIT) of bio-HDPE, measured at 210 °C, was delayed for up to approximately 56 and 240 min, respectively. Furthermore, the UV light stability of the bio-HDPE films was remarkably improved, remaining stable for an exposure time of 10 h even at the lowest GA content. The addition of the natural antioxidant slightly induced a yellow color in the bio-HDPE films and it also reduced their transparency, although a high contact transparency level was maintained. This property can be desirable in some packaging materials for light protection, especially UV radiation, which causes lipid oxidation in food products. Therefore, GA can successfully improve the thermal resistance and UV light stability of green polyolefins and will potentially promote the use of natural additives for sustainable food packaging applications

Big Data: A framework for research

Big Data is not the first and most definitely not the last new term that the IT industry is going to coin in order to drive interest and investment in new technology. Moreover, with these new terms, an opportunity is afforded for the research community to objectively understand the impact (or lack thereof) on organizations and decision makers. This paper provides a high-level framework to guide researchers in the area of Big Data through a conceptualization of the Information Supply Chain. The Information Supply Chain can be used as a scoping device for researchers in positioning their work but also as a tool to enable stronger objectivity and prevent an automatic resistance or acceptance of the new term/trend