555 research outputs found
Tailoring a two-dimensional electron gas at the LaAlO3/SrTiO3 (001) interface by epitaxial strain
Recently a metallic state was discovered at the interface between insulating
oxides, most notably LaAlO3 and SrTiO3. Properties of this two-dimensional
electron gas (2DEG) have attracted significant interest due to its potential
applications in nanoelectronics. Control over this carrier density and mobility
of the 2DEG is essential for applications of these novel systems, and may be
achieved by epitaxial strain. However, despite the rich nature of strain
effects on oxide materials properties, such as ferroelectricity, magnetism, and
superconductivity, the relationship between the strain and electrical
properties of the 2DEG at the LaAlO3/SrTiO3 heterointerface remains largely
unexplored. Here, we use different lattice constant single crystal substrates
to produce LaAlO3/SrTiO3 interfaces with controlled levels of biaxial epitaxial
strain. We have found that tensile strained SrTiO3 destroys the conducting
2DEG, while compressively strained SrTiO3 retains the 2DEG, but with a carrier
concentration reduced in comparison to the unstrained LaAlO3/SrTiO3 interface.
We have also found that the critical LaAlO3 overlayer thickness for 2DEG
formation increases with SrTiO3 compressive strain. Our first-principles
calculations suggest that a strain-induced electric polarization in the SrTiO3
layer is responsible for this behavior. It is directed away from the interface
and hence creates a negative polarization charge opposing that of the polar
LaAlO3 layer. This both increases the critical thickness of the LaAlO3 layer,
and reduces carrier concentration above the critical thickness, in agreement
with our experimental results. Our findings suggest that epitaxial strain can
be used to tailor 2DEGs properties of the LaAlO3/SrTiO3 heterointerface
Regional and developmental brain expression patterns of SNAP25 splice variants
SNAP25 is an essential SNARE protein for regulated exocytosis in neuronal cells. Differential splicing of the SNAP25 gene results in the expression of two transcripts, SNAP25a and SNAP25b. These splice variants differ by only 9 amino acids, and studies of their expression to date have been limited to analysis of the corresponding mRNAs. Although these studies have been highly informative, it is possible that factors such as differential turnover of the SNAP25 proteins could complicate interpretations based entirely on mRNA expression profiles
Robust global sensitivity analysis of a river management model to assess nonlinear and interaction effects
The simulation of routing and distribution of water through a regulated river system with a river management model will quickly result in complex and nonlinear model behaviour. A robust sensitivity analysis increases the transparency of the model and provides both the modeller and the system manager with a better understanding and insight on how the model simulates reality and management operations. In this study, a robust, density-based sensitivity analysis, developed by Plischke et al. (2013), is applied to an eWater Source river management model. This sensitivity analysis methodology is extended to not only account for main effects but also for interaction effects. The combination of sensitivity indices and scatter plots enables the identification of major linear effects as well as subtle minor and nonlinear effects. The case study is an idealized river management model representing typical conditions of the southern Murray-Darling Basin in Australia for which the sensitivity of a variety of model outcomes to variations in the driving forces, inflow to the system, rainfall and potential evapotranspiration, is examined. The model outcomes are most sensitive to the inflow to the system, but the sensitivity analysis identified minor effects of potential evapotranspiration and nonlinear interaction effects between inflow and potential evapotranspiration
Rewritable nanoscale oxide photodetector
Nanophotonic devices seek to generate, guide, and/or detect light using
structures whose nanoscale dimensions are closely tied to their functionality.
Semiconducting nanowires, grown with tailored optoelectronic properties, have
been successfully placed into devices for a variety of applications. However,
the integration of photonic nanostructures with electronic circuitry has always
been one of the most challenging aspects of device development. Here we report
the development of rewritable nanoscale photodetectors created at the interface
between LaAlO3 and SrTiO3. Nanowire junctions with characteristic dimensions
2-3 nm are created using a reversible AFM writing technique. These nanoscale
devices exhibit a remarkably high gain for their size, in part because of the
large electric fields produced in the gap region. The photoconductive response
is gate-tunable and spans the visible-to-near-infrared regime. The ability to
integrate rewritable nanoscale photodetectors with nanowires and transistors in
a single materials platform foreshadows new families of integrated
optoelectronic devices and applications.Comment: 5 pages, 5 figures. Supplementary Information 7 pages, 9 figure
Risk management frameworks:Supporting the next generation of Murray-Darling Basin water sharing plans
Water jurisdictions in Australia are required to prepare and implement water resource plans. In developing these plans the common goal is realising the best possible use of the water resources-maximising outcomes while minimising negative impacts. This requires managing the risks associated with assessing and balancing cultural, industrial, agricultural, social and environmental demands for water within a competitive and resource-limited environment. Recognising this, conformance to international risk management principles (ISO 31000:2009) have been embedded within the Murray-Darling Basin Plan. Yet, to date, there has been little strategic investment by water jurisdictions in bridging the gap between principle and practice. The ISO 31000 principles and the risk management framework that embodies them align well with an adaptive management paradigm within which to conduct water resource planning. They also provide an integrative framework for the development of workflows that link risk analysis with risk evaluation and mitigation (adaptation) scenarios, providing a transparent, repeatable and robust platform. This study, through a demonstration use case and a series of workflows, demonstrates to policy makers how these principles can be used to support the development of the next generation of water sharing plans in 2019. The workflows consider the uncertainty associated with climate and flow inputs, and model parameters on irrigation and hydropower production, meeting environmental flow objectives and recreational use of the water resource. The results provide insights to the risks associated with meeting a range of different objectives
Health informatics competencies in postgraduate medical education and training in the UK: a mixed methods study
OBJECTIVE: To assess health informatics (HI) training in UK postgraduate medical education, across all specialties, against international standards in the context of UK digital health initiatives (eg, Health Data Research UK, National Health Service Digital Academy and Global Digital Exemplars). DESIGN: A mixed methods study of UK postgraduate clinician training curricula (71 specialties) against international HI standards: scoping review, curricular content analysis and expert consultation. SETTING AND PARTICIPANTS: A scoping literature review (PubMed until March 2017) informed development of a contemporary framework of HI competency domains for doctors. National training curricula for 71 postgraduate medical specialties were obtained from the UK General Medical Council and were analysed. Seven UK HI experts were consulted regarding findings. OUTCOMES: The International Medical Informatics Association (IMIA) Recommendations for Biomedical and Health Informatics Education were used to develop a framework of competency domains. The number (maximum 50) of HI competency domains included in each of the 71 UK postgraduate medical specialties was investigated. After expert review, a universal HI competency framework was proposed. RESULTS: A framework of 50 HI competency domains was developed using 21 curricula from a scoping review, curricular content analysis and expert consultation. All 71 UK postgraduate medical curricula documents were mapped across 29 of 50 framework domains; that is, 21 domains were unrepresented. Curricula mapped between 0 (child and adolescent psychiatry and core surgical training) and 16 (chemical pathology and paediatric and perinatal pathology) of the 50 domains (median=7). Expert consultation found that HI competencies should be universal and integrated with existing competencies for UK clinicians and were under-represented in current curricula. Additional universal HI competencies were identified, including information governance and security and secondary use of data. CONCLUSIONS: Postgraduate medical education in the UK neglects HI competencies set out by international standards. Key HI competencies need to be urgently integrated into training curricula to prepare doctors for work in increasingly digitised healthcare environments
Methylated DNA recognition during the reversal of epigenetic silencing is regulated by cysteine and cerine residues in the Epstein-Barr Virus lytic switch protein
Epstein-Barr virus (EBV) causes infectious mononucleosis and is associated with various malignancies, including Burkitt's lymphoma and nasopharyngeal carcinoma. Like all herpesviruses, the EBV life cycle alternates between latency and lytic replication. During latency, the viral genome is largely silenced by host-driven methylation of CpG motifs and, in the switch to the lytic cycle, this epigenetic silencing is overturned. A key event is the activation of the viral BRLF1 gene by the immediate-early protein Zta. Zta is a bZIP transcription factor that preferentially binds to specific response elements (ZREs) in the BRLF1 promoter (Rp) when these elements are methylated. Zta's ability to trigger lytic cycle activation is severely compromised when a cysteine residue in its bZIP domain is mutated to serine (C189S), but the molecular basis for this effect is unknown. Here we show that the C189S mutant is defective for activating Rp in a Burkitt's lymphoma cell line. The mutant is compromised both in vitro and in vivo for binding two methylated ZREs in Rp (ZRE2 and ZRE3), although the effect is striking only for ZRE3. Molecular modeling of Zta bound to methylated ZRE3, together with biochemical data, indicate that C189 directly contacts one of the two methyl cytosines within a specific CpG motif. The motif's second methyl cytosine (on the complementary DNA strand) is predicted to contact S186, a residue known to regulate methyl-ZRE recognition. Our results suggest that C189 regulates the enhanced interaction of Zta with methylated DNA in overturning the epigenetic control of viral latency. As C189 is conserved in many bZIP proteins, the selectivity of Zta for methylated DNA may be a paradigm for a more general phenomenon
RDBE Development and Progress
A digital backend based on the ROACH board has been developed jointly by the National Radio Astronomy Observatory and MIT Haystack Observatory. The RDBE will have both Polyphase Filterbank and Digital Downconverter personalities. The initial configuration outputs sixteen 32-MHz channels, comprised of half the channels from the PFB processing of the two IF inputs, for use in the VLBI2010 geodetic system and in the VLBA sensitivity upgrade project. The output rate is 2x109 bits/second (1x10(exp 9) bits/sec = 1 Gbps) over a 10 GigE connection to the Mark 5C with the data written in Mark 5B format on disk
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