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

Dosimetric Comparison of Hypofractionated Prostate Radiation with Simultaneous Integrated Boost and Conventional Fractionation with Sequential Boost

Introduction: Hypofractionated treatment delivery regimens are associated with better overall long-term disease control for prostate cancer. For patients with high-risk disease, there may be an indication for treatment of the surrounding pelvic lymph nodes for better over-all disease control. In order to achieve a hypofractionated regimen with treatment to the surrounding pelvic lymph nodes a simultaneous integrated boost technique is employed. There are concerns regarding achievability of target dose coverage and limitation of dose to the surrounding organs at risk with this fractionation. Methods: This study is a retrospective dosimetric analysis of 7 randomly selected patients with high-risk prostate cancer. Each patient had a CT simulation performed, and two comparative treatment plans created, one with a conventional technique, the other with a hypofractionated technique. Results: The results indicated that there was not a significant difference between target dose coverage and dose to surrounding organs at risk with the use of a hypofractionated treatment regimen with simultaneous integrated boost as compared to a conventional regimen with sequential boost. Use of a hypofractionated regimen with simultaneous integrated boost is a viable regimen to choose for patients with prostate cancer and indication of need for radiation to the surrounding pelvic lymph nodes. Conclusion: Hypofractionated treatment regimens offer patients better long-term biochemical disease-free survival. Although patients may experience acute side effects earlier, and at an increased level, those side effects typically resolve more quickly than with conventional treatment delivery

Structural and functional analysis of DDR1 autoinhibition

Discoidin domain receptor 1 (DDR1) is a collagen activated receptor tyrosine kinase (RTK) which controls cellular proliferation and migration. DDR1 plays important roles in organogenesis and wound healing. Furthermore, aberrant DDR1 signalling is implicated in the progression and poor prognosis of several diseases, including organ fibroses and cancers. DDR1 is therefore an attractive target for pharmacological intervention. However, unlike in many other RTKs, the regulatory mechanisms underpinning DDR1 signalling are poorly understood. This project investigated the regulatory function of the long intracellular juxtamembrane (JM) region of DDR1. The kinase proximal JM segment, termed JM4, is shown to be an important regulator of DDR1 kinase activity. A 2.58 Å resolution crystal structure revealed that the JM4 segment forms a hairpin which enters the kinase active site and reinforces activation loop autoinhibition. Enzymological analysis of purified DDR1 constructs demonstrated that this autoinhibition is relieved in an ordered process which begins with the rapid, in cis, phosphorylation of the JM4 segment (Tyr569 and Tyr586), followed by slow, in trans, phosphorylation of the activation loop (Tyr796). Both successive phosphorylation events are shown to have drastic activating effects on the kinase catalytic rate. Analysis of cell expressed DDR1 also revealed that JM4 Tyr mutation (DDR1-Y569F/Y586F) abolishes collagen induced receptor activation. A secondary positive role for the JM4 region in DDR1 activation is also identified through cell-based analysis. This role could be the recruitment of Src, a non-receptor tyrosine kinase, which is shown to be an activator of DDR1, but not DDR1-Y569F/Y586F, signalling. The identification of the DDR1 JM4 region as a regulator of receptor signalling provides an interesting avenue for the development of DDR1-specific kinase inhibitors.Open Acces

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

Adopting a new model for health-based physical education: the impact of a professional development programme on teachers’ pedagogical practice

This study explored the use of a collaborative and sustained programme of continuing professional development (CPD) to support the adoption of a new pedagogical model within secondary school physical education. Specifically, the research examined the developmental journey of presenting a new conceptual Health-Based Physical Education (HBPE) pedagogical model to teachers and supporting them to implement it in practice. The aim of the research was to examine teachers’ experiences during the HBPE-CPD programme and the subsequent impact on their practice. Participants were nine physical educators from two secondary schools in England who worked with the programme for one year. The HBPE-CPD programme involved school-based meetings, reflective activities and on-going support during the model’s implementation. Participatory action research was employed as the methodology and the data gathering methods used included teacher reflections, interviews, lesson observations and field notes. Analysis followed an inductive, iterative process involving constant comparison between the different data sources to generate and subsequently code themes. The creation of sustained CPD programmes, with teachers and researchers working collaboratively, encouraged the adoption of the HBPE pedagogical model over time, although competing organisational pressures presented some challenges. Whilst the teachers demonstrated mixed success with their adoption of the HBPE model, there was a sustained shift away from a ‘fitness for performance’ philosophy with greater emphasis placed on explicitly promoting out-of-class physical activity for all students. These findings illustrate that collaborative and sustained CPD programmes involving external support can support teachers to adopt new ideas and change their practice over time. They also suggest the HBPE model has real promise, particularly in guiding teachers to promote healthy active lifestyles with their students. It is recommended that the model is further refined and new forms of CPD are developed to support teachers’ sustained adoption of pedagogical models, such as HBPE. However, a concerted effort needs to be made by all stakeholders in education to ensure that teachers have sufficient time allocated for CPD and are encouraged to engage in pedagogical change