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

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

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

Backdating of events in electronic primary health care data: should one censor at the date of last data collection

PURPOSE: Studies using primary care databases often censor follow-up at the date data are last collected from clinical computer systems (last collection date (LCD)). We explored whether this results in the selective exclusion of events entered in the electronic health records after their date of occurrence, that is, backdated events. METHODS: We used data from The Health Improvement Network (THIN). Using two versions of the database, we identified events that were entered into a later (THIN14) but not an earlier version of the database (THIN13) and investigated how the number of entries changed as a function of time since LCD. Times between events and the dates they were recorded were plotted as a function of time since the LCD in an effort to determine appropriate points at which to censor follow-up. RESULTS: There were 356 million eligible events in THIN14 and 355 million eligible events in THIN13. When comparing the two data sets, the proportion of missing events in THIN13 was highest in the month prior to the LCD (9.6%), decreasing to 5.2% at 6 months and 3.4% at 12 months. The proportion of missing events was largest for events typically diagnosed in secondary care such as neoplasms (28% in the month prior to LCD) and negligible for events typically diagnosed in primary care such as respiratory events (2% in the month prior to LCD). CONCLUSIONS: Studies using primary care databases, particularly those investigating events typically diagnosed outside primary care, should censor follow-up prior to the LCD to avoid underestimation of event rates