Spatial and temporal evolution of Pine Island Glacier thinning, 1995-2006

We use ERS-2 and ENVISAT satellite radar altimetry to examine spatial and temporal changes in the rate of thinning of the Pine Island Glacier, West Antarctica, during the period 1995 to 2006. We show that the pattern of thinning has both accelerated and spread inland to encompass tributaries flowing into the central trunk of the glacier. Within the 5,400 km(2) central trunk, the average rate of volume loss quadrupled from 2.6 +/- 0.3 km(3) yr(-1) in 1995 to 10.1 +/- 0.3 km(3) yr(-1) in 2006. The region of lightly grounded ice at the glacier terminus is extending upstream, and the changes inland are consistent with the effects of a prolonged disturbance to the ice flow, such as the effects of ocean- driven melting. If the acceleration continues at its present rate, the main trunk of PIG will be afloat within some 100 years, six times sooner than anticipated. Citation: Wingham, D.J., D.W. Wallis, and A. Shepherd (2009), Spatial and temporal evolution of Pine Island Glacier thinning, 1995-2006, Geophys. Res. Lett., 36, L17501, doi: 10.1029/2009GL039126

Emergency care research priorities in South Africa

Background: Emergency care research is rarely undertaken in low- and middle-income countries. A manageable ‘road map’ for research in South African (SA) emergency care is needed to address research gaps.Objective: To identify, collate and prioritise research topics from identified knowledge gaps in emergency care in SA.Methods: Seventy-six individuals were invited to participate in a modified Delphi study. Participants were requested to suggest important research topics before rating them. Consensus was achieved when >75% of participants strongly agreed or disagreed. Participants then ranked the agreed statements before selecting the most appropriate methodology relating to study design, funding and collaboration.Results: Three hundred and fifty topics were suggested by 31 participants. Topics were collated into 123 statements before participants rated them. Consensus was achieved for 39 statements. The highest-ranked priority in the prehospital group was to determine which prehospital interventions improve outcomes in critically ill patients. The competence of emergency care providers in performing common lifesaving skills was deemed the most important in clinical emergency care. Implementing and reviewing quality improvement systems scored the highest under general systems and safety management. Only 22 statements achieved consensus regarding study design. The National Department of Health was the preferred funding source, while private organisations and emergency care societies were identified as possible collaborative partners.Conclusion: This study provides expert consensus on priority research areas in emergency care in SA as a guide for emergency care providers to ensure evidence-based care that is relevant to the SA population

Preference inference based on Pareto models

In this paper, we consider Preference Inference based on a generalised form of Pareto order. Preference Inference aims at reasoning over an incomplete specification of user preferences. We focus on two problems. The Preference Deduction Problem (PDP) asks if another preference statement can be deduced (with certainty) from a set of given preference statements. The Preference Consistency Problem (PCP) asks if a set of given preference statements is consistent, i.e., the statements are not contradicting each other. Here, preference statements are direct comparisons between alternatives (strict and non-strict). It is assumed that a set of evaluation functions is known by which all alternatives can be rated. We consider Pareto models which induce order relations on the set of alternatives in a Pareto manner, i.e., one alternative is preferred to another only if it is preferred on every component of the model. We describe characterisations for deduction and consistency based on an analysis of the set of evaluation functions, and present algorithmic solutions and complexity results for PDP and PCP, based on Pareto models in general and for a special case. Furthermore, a comparison shows that the inference based on Pareto models is less cautious than some other types of well-known preference model

Effect of growth temperature and V/III-ratio on the surface morphology of MOVPE-grown cubic zincblende GaN

The influence of growth temperature and V/III-ratio on the surface morphology of (001) cubic zincblende GaN epilayers during metal organic vapour phase epitaxy growth has been investigated using atomic force microscopy and transmission electron microscopy. The zincblende phase purity as determined by X-ray diffraction was found to be above 98% for most GaN epilayers studied. As the growth temperature was increased from 850 °C to 910 °C and as the V/III-ratio was separately increased from 38 to 300, surface features were found to be elongated in the [1-10] direction, and the ratio of the length to width of such surface features was found to increase. Faceting was observed at V/III-ratios below 38 and above 300, which in the latter case was accompanied by a reduction of the zincblende phase purity. An explanation for these morphological trends is proposed based on effects such as the reduced symmetry of the top monolayer of the (001)-oriented zincblende GaN lattice, diffusion of Ga and N adatoms on such a surface, and the relative energies of the crystal facets.We would like to thank Innovate UK for the financial support within the Energy Catalyst Round 2 - Early Stage Feasibility scheme (Ref. 132135) and Energy Catalyst Round 4 - Mid Stage Feasibility scheme (Ref. 102766). We acknowledge the support of EPSRC through grant no. EP/M010589/1 and grant no. EP/R01146X/1. DJW would like to thank the support of EPSRC through grant no. EP/N01202X/1

Haiti: The South African perspective

Background and problem statement. The South African response to the Haitian earthquake consisted of two independent nongovernment organisations (NGOs) working separately with minimal contact. Both teams experienced problems during the deployment, mainly owing to not following the International Search and Rescue Advisory Group (INSARAG) guidelines. Critical areas identified. To improve future South African disaster responses, three functional deployment categories were identified: urban search and rescue, triage and initial stabilisation, and definitive care. To best achieve this, four critical components need to be taken into account: rapid deployment, intelligence from the site, government facilitation, and working under the auspices of recognised organisations such as the United Nations and the World Health Organization. Conclusion. The proposed way forward for South African medical teams responding to disasters is to be unified under a leading academic body, to have an up-to-date volunteer database, and for volunteers to be current with the international search and rescue course currently being developed by the Medical Working Group of INSARAG. An additional consideration is that South African rescue and relief personnel have a primary responsibility to the citizens of South Africa, then the Southern African Development Community region, then the rest of the African continent and finally further afield. The commitment of government, private and military health services as well as NGOs is paramount for a unified response

Stacking fault-associated polarized surface-emitted photoluminescence from zincblende InGaN/GaN quantum wells

Zincblende InGaN/GaN quantum wells offer a potential improvement to the efficiency of green light emission by removing the strong electric fields present in similar structures. However, a high density of stacking faults may have an impact on the recombination in these systems. In this work, scanning transmission electron microscopy and energy-dispersive x-ray measurements demonstrate that one dimensional nanostructures form due to indium segregation adjacent to stacking faults. In photoluminescence experiments these structures emit visible light which is optically polarised up to 86% at 10K and up to 75% at room temperature. The emission redshifts and broadens as the well width increases from 2nm to 8nm. Photoluminescence excitation measurements indicate that carriers are captured by these structures from the rest of the quantum wells and recombine to emit light polarised along the length of these nanostructures

Novel Shielded Coplanar Waveguides on GaN-on-Low Resistivity Si Substrates for MMIC Applications

Shielded-Elevated Coplanar Waveguides (SE-CPWs) with low loss have been successfully developed for the first time for RF GaN on low-resistivity silicon (LR-Si) substrates (σ < 40 Ω.cm). Transmission losses (S 21 ) of less than 0.4 dB/mm at X-band and better than 2 dB/mm at K-band with less than 20 dB return loss were exhibited by the developed SE-CPW, making them comparable in performance to those on traditional (semi-insulating) SI substrates. The developed waveguides use air-bridge technology to suspend CPW tracks above the HEMT GaN layer on LR-Si, directly above an additional thin layer of SiN and shielded ground planes. EM simulation was used to adjust structure parameters for performance optimization. In this work, we eliminated RF energy coupled into the substrate, paving the way for a cost-effective and higher integration GaN MMICs on LR-Si.This work was supported in part by the EPSRC III-V national center pump-priming scheme

GaN on Low-Resistivity Silicon THz High-Q Passive Device Technology

In this paper, viable transmission media technology has been demonstrated for the first time on GaN on low-resistivity silicon) substrates (ρ < 40 $\Omega$·cm) at H-band frequencies (220-325 GHz). The shielded-elevated coplanar waveguide (CPW) lines employ a standard monolithic microwave integrated circuit compatible air bridge process to elevate the CPW traces above a 5-μm layer of benzocyclobutene on shielded metalized ground plates. An insertion loss of less than 2.3 dB/mm was achieved up to 325 GHz, compared with 27 dB/mm for CPW fabricated directly on the substrate. To prove the efficiency of the technology, a short-circuited stub filter with a resonant frequency of 244 GHz was used. The filter achieved an unloaded Q-factor of 28, along with an insertion loss of 0.35 dB and a return loss of-34 dB. To our knowledge, these results are the best reported to date for GaN-based technology.This work was supported by the EPSRC under Grant EP/N014820/1

Vertical leakage mechanism in GaN on Si high electron mobility transistor buffer layers

Control of leakage currents in the buffer layers of GaN based transistors on Si substrates is vital for the demonstration of high performance devices. Here, we show that the growth conditions during the metal organic chemical vapour deposition growth of the graded AlGaN strain relief layers (SRLs) can significantly influence the vertical leakage. Using scanning capacitance microscopy, secondary ion mass spectrometry, and transmission electron microscopy, we investigate the origins of leakage paths and show that they result from the preferential incorporation of oxygen impurities on the side wall facets of the inverted hexagonal pyramidal pits which can occur during the growth of the graded AlGaN SRL. We also show that when 2D growth of the AlGaN SRL is maintained a significant increase in the breakdown voltage can be achieved even in much thinner buffer layer structures. These results demonstrate the importance of controlling the morphology of the high electron mobility transistor buffer layer as even at a very low density the leakage paths identified would provide leakage paths in large area devices.This work was funded by the Engineering and Physical Sciences Research Council under Grant Code Nos. EP/K014471/1 and EP/N01202X/1 and the European Research Council under the European Community's Seventh Framework Programme Grant Agreement No. 279361 (MACONS)

Nano-cathodoluminescence reveals the effect of electron damage on the optical properties of nitride optoelectronics and the damage threshold

Nano-cathodoluminescence (Nano-CL) reveals optical emission from individual InGaN quantum wells for applications in optoelectronic devices. We show the luminescent intensity decays over time with exposure to the electron beam for energies between 80 and 200 keV. Measurements of the CL intensity over time show an exponential decline in intensity, which we propose is due to the formation of nitrogen Frenkel defects. The measured CL damage decreases with reductions in the electron accelerating voltage and we suggest that the electron induced structural damage may be suppressed below the proposed damage threshold. The electron beam induced damage leads to a non-radiative region that extends over the measured minority carrier diffusion length. Nano-CL may thus serve as a powerful technique to study III-nitride optoelectronics.This work was carried out with the support of the United Kingdom Engineering and Physical Sciences Research Council under Grant Nos. EP/NO17927/1 and EP/J003603/1. R. Oliver acknowledges funding from the European Research Council under the European Community's Seventh Framework Programme (FP7/2007-2013) ERC grant agreement number 279361 (MACONS) and the from the Royal Academy of Engineers/Leverhulme Trust senior research fellowship