Compensation effects in GaN:Mg probed by Raman spectroscopy and photoluminescence measurements

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in J. Appl. Phys. 113, 103504 (2013) and may be found at https://doi.org/10.1063/1.4794094.Compensation effects in metal organic chemical vapour deposition grown GaN doped with magnesium are investigated with Raman spectroscopy and photoluminescence measurements. Examining the strain sensitive E2(high) mode, an increasing compressive strain is revealed for samples with Mg-concentrations lower than 7 × 1018 cm−3. For higher Mg-concentrations, this strain is monotonically reduced. This relaxation is accompanied by a sudden decrease in crystal quality. Luminescence measurements reveal a well defined near band edge luminescence with free, donor bound, and acceptor bound excitons as well as a characteristic donor acceptor pair (DAP) luminescence. Following recent results, three acceptor bound excitons and donor acceptor pairs are identified. Along with the change of the strain, a strong modification in the luminescence of the dominating acceptor bound exciton and DAP luminescence is observed. The results from Raman spectroscopy and luminescence measurements are interpreted as fingerprints of compensation effects in GaN:Mg leading to the conclusion that compensation due to defect incorporation triggered by Mg-doping already affects the crystal properties at doping levels of around 7 × 1018 cm−3. Thereby, the generation of nitrogen vacancies is introduced as the driving force for the change of the strain state and the near band edge luminescence.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Trilingual conversations: a window into multicompetence

A recurrent theme in the literature on trilingual language use is the question of whether there is a specific “trilingual competence.” In this paper we consider this question in the light of codeswitching patterns in two dyadic trilingual conversations between a mother and daughter conducted in (Lebanese) Arabic, French, and English. Quantitative and qualitative analysis of codeswitching in both conversants shows that, despite the fact that both subjects are fluent in all three languages, uses of switching are significantly different for mother and daughter across a number of features, including relative frequency of different switch types, and the incidence of hybrid constructions involving items from two or more languages. The subjects appear to display qualitatively distinct profiles of competence in the trilingual mode. This in turn leads to the conclusion that the facts of trilingual language use are best characterized in terms of “multicompetence” (Cook, 1991). The paper concludes with some further reflections on the uniqueness of trilingual language use (an “old chestnut” in trilingualism research, cf. Klein, 1995)

Multicriteria-based methodology for the design of rural electrification systems. A case study in Nigeria

Electrification with micro-grids is receiving increasing attention to electrify rural areas in developing countries. However, determining the best local supply solution is a complex problem that requires considering different generation technologies (i.e. solar PV, wind or diesel) and different system configurations (off-grid or on-grid). Most existing decision aid tools to assess this design only consider economical and technical issues in a single optimization process. However, social and environmental considerations have been proven key issues to ensure long-term sustainability of the projects. In this context, the objective of this work is to develop a multicriteria procedure to allow comparing electrification designs with on-grid or isolated micro-grids and different tech-nologies considering multiple aspects. This multicriteria procedure is integrated in a two-phased methodology to assist the design of the system to electrification promoters in a structured process. First, different electrification alternatives are generated with an open-source techno-economic optimization model; next, these alternatives are evaluated and ranked with the multicriteria procedure, which considers 12 criteria representing economic, technical, socio-institutional and environmental aspects. The whole design methodology is validated with a real case study of 26 population settlements in Plateau State, Nigeria. Experts in rural electrification within the Nigerian context have been consulted to weight the criteria and particularize their evaluation for the specific case study. Results show that solar PV technology based systems are the most suitable electrification designs for communities in Nigeria, while grid connection feasibility depends on the size of the community and the distance to the closest national grid consumption point.Peer ReviewedPostprint (author's final draft

Immunization with L. sigmodontis Microfilariae Reduces Peripheral Microfilaraemia after Challenge Infection by Inhibition of Filarial Embryogenesis

Lymphatic filariasis is caused by parasitic filarial worms that are transmitted by mosquitoes, requiring uptake of larvae and distribution into the blood of the host. More than 120 million people are infected and about 30% of these individuals suffer from clinical symptoms. Reduction in transmission currently depends on mass drug administration, which has significantly reduced transmission rates over the past years. However, despite repetitive rounds of administration, transmission has not been eliminated completely from endemic areas. In some infected individuals the immune system can partially control the parasite, such that a proportion of infected individuals remain microfilaria-negative, despite the presence of adult worms. Therefore mechanisms must exist that are able to combat microfilaraemia. Identifying such mechanisms would help to design vaccines against disease transmitting microfilarial stages. Using the Litomosoides sigmodontis murine model of filariasis research we show a successful immunization against the blood-circulating larval stage that is responsible for arthropod-dependent transmission of the disease. Reduced microfilaraemia was associated with impairment of worm embryogenesis, with systemic and local microfilarial-specific host IgG and with IFN-γ secretion by host cells at the site of infection. These results raise hope for developing a microfilariae-based vaccine, being a pivotal step towards eradicating filariasis

Polarity Control in Group-III Nitrides beyond Pragmatism

Controlling the polarity of polar semiconductors on nonpolar substrates offers a wealth of device concepts in the form of heteropolar junctions. A key to realize such structures is an appropriate buffer-layer design that, in the past, has been developed by empiricism. GaN or ZnO on sapphire are prominent examples for that. Understanding the basic processes that mediate polarity, however, is still an unsolved problem. In this work, we study the structure of buffer layers for group-III nitrides on sapphire by transmission electron microscopy as an example. We show that it is the conversion of the sapphire surface into a rhombohedral aluminum-oxynitride layer that converts the initial N-polar surface to Al polarity. With the various AlxOyNz phases of the pseudobinary Al2O3-AlN system and their tolerance against intrinsic defects, typical for oxides, a smooth transition between the octahedrally coordinated Al in the sapphire and the tetrahedrally coordinated Al in AlN becomes feasible. Based on these results, we discuss the consequences for achieving either polarity and shed light on widely applied concepts in the field of group-III nitrides like nitridation and low-temperature buffer layers

Personality profile of patients with chronic fatigue syndrome.

Personality may play a role in the predisposition, the precipitation and/or the maintenance of the CFS. Thirty-six consecutively examined female patients hospitalised for a sleep workup, filled out a Temperament and Character Inventory (TCI) questionnaire. A MANOVA compared the patients with a control group of females matched for age. Significant scores were obtained for dimensions such as Harm Avoidance, Reward Dependence, and Self-Directedness. However, the only subdimension of Harm Avoidance that proved significantly higher in CFS than in controls was “Fatigability,” which is likely to overlap with the core CFS symptom. All in all, the personality structure does not appear to play a major role in the CFS.Peer reviewe

Parental transfer of the antimicrobial protein LBP/BPI protects Biomphalaria glabrata eggs against oomycete infections

Copyright: © 2013 Baron et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was funded by ANR (ANR-07-BLAN-0214 and ANR-12-EMMA-00O7-01), CNRS and INRA. PvW was financially supported by the BBSRC. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewedPublisher PD

The search for an autoimmune origin of psychotic disorders: prevalence of autoantibodies against hippocampus antigens, glutamic acid decarboxylase and nuclear antigens

The etiology of psychotic disorders is still unknown, but in a subgroup of patients symptoms might be caused by an autoimmune reaction. In this study, we tested patterns of autoimmune reactivity against potentially novel hippocampal antigens. Serum of a cohort of 621 individuals with psychotic disorders and 257 controls were first tested for reactivity on neuropil of rat brain sections. Brain reactive sera (67 diseased, 27 healthy) were further tested for antibody binding to glutamic acid decarboxylase (GAD) isotype 65 and 67 by cell-based assay (CBA). A sub-cohort of 199 individuals with psychotic disorders and 152 controls was tested for the prevalence of anti-nuclear antibodies (ANA) on HEp2-substrate as well as for reactivity to double-stranded DNA, ribosomal P (RPP), and cardiolipin (CL). Incubation of rat brain with serum resulted in unidentified hippocampal binding patterns in both diseased and control groups. Upon screening with GAD CBA, one of these patterns was identified as GAD65 in one individual with schizophrenia and also in one healthy individual. Two diseased and two healthy individuals had low antibody levels targeting GAD67 by CBA. Antibody reactivity on HEp-2-substrate was increased in patients with schizoaffective disorder, but only in 3 patients did antibody testing hint at a possible diagnosis of systemic lupus erythematosus. Although reactivity of serum to intracellular antigens might be increased in patients with psychotic disorder, no specific targets could be identified. GAD antibodies are very rare and do not seem increased in serum of patients with psychotic disorders.HEALTH-F2-2010-241909info:eu-repo/semantics/publishedVersio

Genome-wide Characterization of Shared and Distinct Genetic Components that Influence Blood Lipid Levels in Ethnically Diverse Human Populations

Blood lipid concentrations are heritable risk factors associated with atherosclerosis and cardiovascular diseases. Lipid traits exhibit considerable variation among populations of distinct ancestral origin as well as between individuals within a population. We performed association analyses to identify genetic loci influencing lipid concentrations in African American and Hispanic American women in the Women’s Health Initiative SNP Health Association Resource. We validated one African-specific high-density lipoprotein cholesterol locus at CD36 as well as 14 known lipid loci that have been previously implicated in studies of European populations. Moreover, we demonstrate striking similarities in genetic architecture (loci influencing the trait, direction and magnitude of genetic effects, and proportions of phenotypic variation explained) of lipid traits across populations. In particular, we found that a disproportionate fraction of lipid variation in African Americans and Hispanic Americans can be attributed to genomic loci exhibiting statistical evidence of association in Europeans, even though the precise genes and variants remain unknown. At the same time, we found substantial allelic heterogeneity within shared loci, characterized both by population-specific rare variants and variants shared among multiple populations that occur at disparate frequencies. The allelic heterogeneity emphasizes the importance of including diverse populations in future genetic association studies of complex traits such as lipids; furthermore, the overlap in lipid loci across populations of diverse ancestral origin argues that additional knowledge can be gleaned from multiple populations