Molecular beam epitaxy of free-standing bulk wurtzite AlxGa1-xN layers using a highly efficient RF plasma source

Recent developments with group III nitrides suggest AlxGa1-xN based LEDs can be new alternative commer-cially viable deep ultra-violet light sources. Due to a sig-nificant difference in the lattice parameters of GaN and AlN, AlxGa1-xN substrates would be preferable to either GaN or AlN for ultraviolet device applications. We have studied the growth of free-standing wurtzite AlxGa1-xN bulk crystals by plasma-assisted molecular beam epitaxy (PA-MBE) using a novel RF plasma source. Thick wurtz-ite AlxGa1-xN films were grown by PA-MBE on 2-inch GaAs (111)B substrates and were removed from the GaAs substrate after growth to provide free standing AlxGa1-xN samples. Growth rates of AlxGa1-xN up to 3 μm/h have been demonstrated. Our novel high efficiency RF plasma source allowed us to achieve free-standing bulk AlxGa1-xN layers in a single day’s growth, which makes our MBE bulk growth technique commercially vi-able

Molecular beam epitaxy of free-standing bulk wurtzite AlxGa1-xN layers using a highly efficient RF plasma source

Recent developments with group III nitrides suggest AlxGa1-xN based LEDs can be new alternative commer-cially viable deep ultra-violet light sources. Due to a sig-nificant difference in the lattice parameters of GaN and AlN, AlxGa1-xN substrates would be preferable to either GaN or AlN for ultraviolet device applications. We have studied the growth of free-standing wurtzite AlxGa1-xN bulk crystals by plasma-assisted molecular beam epitaxy (PA-MBE) using a novel RF plasma source. Thick wurtz-ite AlxGa1-xN films were grown by PA-MBE on 2-inch GaAs (111)B substrates and were removed from the GaAs substrate after growth to provide free standing AlxGa1-xN samples. Growth rates of AlxGa1-xN up to 3 μm/h have been demonstrated. Our novel high efficiency RF plasma source allowed us to achieve free-standing bulk AlxGa1-xN layers in a single day’s growth, which makes our MBE bulk growth technique commercially vi-able

Dredging - How can we manage it to minimize impacts

Sediment plumes generated by dredging can impact sensitive receptors at significant distances from the work area. Potential impacts would normally be identified and quantified through the Environmental Impact Assessment (EIA) prior to project implementation; that may also include a degree of project optimization to reduce impacts. However, there are significant uncertainties in predicting the potential impacts at the EIA stage; key components of the dredging programme such as the dredge methodology, dredge schedule, sediment spill sources and climatic conditions encountered during dredging may not be well defined, and this will typically be reflected in the accuracy of the predictions and potentially also in the choice of mitigation measures. Proactive and informed management of the dredging programme as it is executed can often significantly reduce the risk of or minimise the negative impacts. By better understanding which components of a given programme are critical in terms of potential impacts, the programme can be optimised to minimise the risks. Through modelling and monitoring during execution, impacts may be predicted before being realized, and the dredging programme may be optimized to achieve the environmental objectives while maintaining desired production rates. An example is presented describing a combination of monitoring, both of the dredge plume and at receptor sites, and dredge plume modeling to guide the dredging works

Some Properties of the Computable Cross Norm Criterion for Separability

The computable cross norm (CCN) criterion is a new powerful analytical and computable separability criterion for bipartite quantum states, that is also known to systematically detect bound entanglement. In certain aspects this criterion complements the well-known Peres positive partial transpose (PPT) criterion. In the present paper we study important analytical properties of the CCN criterion. We show that in contrast to the PPT criterion it is not sufficient in dimension 2 x 2. In higher dimensions we prove theorems connecting the fidelity of a quantum state with the CCN criterion. We also analyze the behaviour of the CCN criterion under local operations and identify the operations that leave it invariant. It turns out that the CCN criterion is in general not invariant under local operations.Comment: 7 pages; accepted by Physical Review A; error in Appendix B correcte

UK monitoring and deposition of tephra from the May 2011 eruption of Grímsvötn, Iceland

Mapping the transport and deposition of tephra is important for the assessment of an eruption’s impact on health, transport, vegetation and infrastructure, but it is challenging at large distances from a volcano (> 1000 km), where it may not be visible to the naked eye. Here we describe a range of methods used to quantify tephra deposition and impact on air quality during the 21–28 May 2011 explosive basaltic eruption of Grímsvötn volcano, Iceland. Tephra was detected in the UK with tape-on-paper samples, rainwater samples, rainwater chemistry analysis, pollen slides and air quality measurements. Combined results show that deposition was mainly in Scotland, on 23–25 May. Deposition was patchy, with adjacent locations recording different results. Tape-on-paper samples, collected by volunteer citizen scientists, and giving excellent coverage across the UK, showed deposition at latitudes >55°N, mainly on 24 May. Rainwater samples contained ash grains mostly 20–30 μm long (maximum recorded grainsize 80 μm) with loadings of up to 116 grainscm-2. Analysis of rainwater chemistry showed high concentrations of dissolved Fe and Al in samples from N Scotland on 24–27 May. Pollen slides recorded small glass shards (3–4 μm long) deposited during rainfall on 24–25 May and again on 27 May. Air quality monitoring detected increased particulate matter concentrations in many parts of the country. An hourly concentration of particles  53°N) on 24 May but no negative effects on health were reported. Although the eruption column reached altitudes of 20 km above sea level, air mass trajectories suggest that only tephra from the lowest 4 km above sea level of the eruption plume was transported to the UK. This demonstrates that even low plumes could deliver tephra to the UK and suggests that the relative lack of basaltic tephra in the tephrochronological record is not due to transport processes

Impact of analytic provenance in genome analysis

Many computational methods are available for assembly and annotation of newly sequenced microbial genomes. However, when new genomes are reported in the literature, there is frequently very little critical analysis of choices made during the sequence assembly and gene annotation stages. These choices have a direct impact on the biologically relevant products of a genomic analysis - for instance identification of common and differentiating regions among genomes in a comparison, or identification of enriched gene functional categories in a specific strain. Here, we examine the outcomes of different assembly and analysis steps in typical workflows in a comparison among strains of Vibrio vulnificus

Transfer printed multi-color integrated devices for visible light communication applications

Integrated multi-color devices for visible light communication applications are fabricated by transfer printing blue-emitting GaN light emitting diodes (LEDs) onto a green-emitting LED array and a colloidal quantum dot color-converter structure

Evolutionary signal enhancement based on Hölder regularity analysis

International audienceWe present an approach for signal enhancement based on the analysis of the local Hölder regularity. The method does not make explicit assumptions on the type of noise or on the global smoothness of the original data, but rather supposes that signal enhancement is equivalent to increasing the Hölder regularity at each point

The Association between Parity and Subsequent Cardiovascular Disease in Women: The Atherosclerosis Risk in Communities Study

Background: Previous studies are inconclusive on the relationship between parity and cardiovascular disease (CVD), with few evaluating multiple cardiovascular outcomes. It is also unclear if any relationship between parity and CVD is independent of breastfeeding. We examined the associations between parity and cardiovascular outcomes, including breastfeeding adjustment. Materials and Methods: Data were from 8,583 White and African American women, 45-64 years of age, in the Atherosclerosis Risk in Communities Study. Coronary heart disease (CHD), myocardial infarction (MI), heart failure, and strokes were ascertained from 1987 to 2016 by annual interviews and hospital surveillance. Parity and breastfeeding were self-reported. Cox proportional hazards regression estimated hazard ratios (HR) for the association between parity and cardiovascular outcomes, adjusting for baseline sociodemographic, clinical and lifestyle factors, and breastfeeding. Results: Women reported no pregnancies (6.0%), or having 0 (1.6%), 1-2 (36.2%), 3-4 (36.4%), or 5+ (19.7%) live births. During 30 years follow-up, there were 1,352 CHDs, 843 MIs, 750 strokes, and 1,618 heart failure events. Compared with women with 1-2 prior births, those with prior pregnancies and no live births had greater incident CHD (HR=1.64, 95% confidence interval 1.14-2.42) and heart failure risk (1.46, 1.04-2.05), after adjustment for baseline characteristics. Women with 5+ births had greater risk of CHD (1.29, 1.10-1.52) and hospitalized MI (1.38, 1.13-1.69), after adjustment for baseline characteristics and breastfeeding. Conclusions: In a diverse U.S. cohort, a history of 5+ live births is associated with CHD risk, specifically, MI, independent of breastfeeding. Having a prior pregnancy and no live birth is associated with greater CHD and heart failure risk

Growth of free-standing bulk wurtzite AlxGa1−xN layers by molecular beam epitaxy using a highly efficient RF plasma source

The recent development of group III nitrides allows researchers world-wide to consider AlGaN based light emitting diodes as a possible new alternative deep ultra–violet light source for surface decontamination and water purification. In this paper we will describe our recent results on plasma-assisted molecular beam epitaxy (PA-MBE) growth of free-standing wurtzite AlxGa1−xN bulk crystals using the latest model of Riber's highly efficient nitrogen RF plasma source. We have achieved AlGaN growth rates up to 3 µm/h. Wurtzite AlxGa1−xN layers with thicknesses up to 100 μm were successfully grown by PA-MBE on 2-inch and 3-inch GaAs (111)B substrates. After growth the GaAs was subsequently removed using a chemical etch to achieve free-standing AlxGa1−xN wafers. Free-standing bulk AlxGa1−xN wafers with thicknesses in the range 30–100 μm may be used as substrates for further growth of AlxGa1−xN-based structures and devices. High Resolution Scanning Transmission Electron Microscopy (HR-STEM) and Convergent Beam Electron Diffraction (CBED) were employed for detailed structural analysis of AlGaN/GaAs (111)B interface and allowed us to determine the N-polarity of AlGaN layers grown on GaAs (111)B substrates. The novel, high efficiency RF plasma source allowed us to achieve free-standing AlxGa1−xN layers in a single day's growth, making this a commercially viable process