Strong light-matter coupling in bulk GaN-microcavities with double dielectric mirrors fabricated by two different methods

Two routes for the fabrication of bulk GaN microcavities embedded between two dielectric mirrors are described, and the optical properties of the microcavities thus obtained are compared. In both cases, the GaN active layer is grown by molecular beam epitaxy on (111) Si, allowing use of selective etching to remove the substrate. In the first case, a three period Al0.2Ga0.8N / AlN Bragg mirror followed by a lambda/2 GaN cavity are grown directly on the Si. In the second case, a crack-free 2,mu m thick GaN layer is grown, and progressively thinned to a final thickness of lambda. Both devices work in the strong coupling regime at low temperature, as evidenced by angle-dependent reflectivity or transmission experiments. However, strong light-matter coupling in emission at room temperature is observed only for the second one. This is related to the poor optoelectronic quality of the active layer of the first device, due to its growth only 250 nm above the Si substrate and its related high defect density. The reflectivity spectra of the microcavities are well accounted for by using transfer matrix calculations. (C) 2010 American Institute of Physics. [doi:10.1063/1.3477450

Analysis of the characteristic temperatures of (Ga,In)(N,As)/GaAs laser diodes

The characteristic temperatures of the threshold current density, T0, and external differential quantum efficiency, T1, of a series of (Ga,In)(N,As)/GaAs quantum well (QW) laser diodes are measured in the wavelength range from 1 to 1.5μm. It is found that both T0 and T1 strongly decrease with increasing lasing wavelength. The origin of this degradation is shown to be, in the case of T0, mostly dominated by a decrease in the transparency current density characteristic temperature, an increase in the optical losses and a decrease in the modal gain. The degradation of T1 is mainly due to the increase in the optical losses. The effective carrier recombination lifetime in the QW is shown to decrease from 1.2 to 0.2 ns with N content up to 2%, in good agreement with previous reports that link this low lifetime to non-radiative monomolecular recombination through defects in the QW. Carrier leakage is ruled out as the dominant process degrading T0 and T1 on the basis of the temperature dependence of the effective carrier recombination lifetime

Ex ante impact of peste des petits ruminants control on micro and macro socioeconomic indicators in Senegal

Vaccination is espoused as the effective control mechanism outlined in the Global Control and Eradication Strategy for peste des petits ruminants (PPR). However, extant studies assert that vaccination can be expensive; hence, the effectiveness of disease control may not necessarily translate to overall profit. Also, the consequences of PPR control on socioeconomic indicators like food and nutrition security at a macro national level is an important lacuna in the literature. This study seeks to examine the ex ante impact of PPR control strategies on farm-level profitability and the socioeconomic consequences in relation to food and nutrition security at a national level in Senegal. A bi-level system dynamics model, compartmentalised into five modules consisting of integrated production-epidemiological, economics, disease control, marketing, and policy modules, was developed with the STELLA Architect® software, validated, and simulated for 30 years at a weekly timestep. The model was parameterised with data from household surveys from pastoral areas in Northern Senegal and relevant archival data. Nine vaccination scenarios were examined from three vaccination dimensions (vaccination coverage, vaccine wastage, and the provision of government subsidies). This study’s findings indicate that, compared with a no-vaccination scenario, all the vaccination scenarios for both 26.5% (actual vaccination coverage) and 70% (expected vaccination coverage) resulted in a significant difference in the gross margin earnings and the potential per capita consumption for the supply of mutton and goat meat. At the prevailing vaccination coverage (with or without the provision of government subsidies), farm households will earn on average $69.43 (annually) more than the no-vaccination scenario, and the average per capita consumption for mutton and goat meat will increase by 1.13kg/person/year. When the vaccination coverage is increased to the prescribed threshold for PPR eradication (i.e., 70$72.23 annually and the per capita consumption will increase by 0.1kg/person/year. To examine the impact of vaccine wastage, a within group comparison of the actual and expected vaccination coverage was conducted. The findings indicate that 10% of multiple vaccinations of the same animals will result in a decline in the; (i) average gross margin earnings (annually) by $11.37 and$12.98 for vaccination coverage of 26.5% and 70%, respectively; and (ii) per capita consumption by 0.3kg/person/year and 0.34kg/person/year for the vaccination coverage of 26.5% and 70%, respectively. Considering that there was no statistically significant difference in the gross margin earnings and the potential per capita consumption when vaccination is performed with or without government subsidies, a sustainable strategy for PPR eradication will include the promotion of the benefits of vaccination via sensitization campaigns to stimulate farmers’ uptake of the practice

Cleaved-facet violet laser diodes with lattice-matched Al0.82In0.18N/GaN multilayers as n-cladding

Electrically injected, edge-emitting cleaved-facet violet laser diodes were realized using a 480 nm thick lattice matched Si doped Al0.82In0.18N/GaN multilayer as the cladding on the n-side of the waveguide. Far-field measurements verify strong mode confinement to the waveguide. An extra voltage is measured and investigated using separate mesa structures with a single AlInN insertion. This showed that the electron current has a small thermally activated shunt resistance with a barrier of 0.135 eV and a current which scales according to V-n, where n similar to 3 at current densities appropriate to laser operation. (C) 2011 American Institute of Physics. (doi:10.1063/1.3589974

Biocultural determinants of overweight and obesity in the context of nutrition transition in Senegal: a holistic anthropological approach

Senegal is experiencing a rising obesity epidemic, due to the nutrition transition occurring in most African countries, and driven by sedentary behaviour and high-calorie dietary intake. In addition, the anthropological local drivers of the social valorization of processed high-calorie food and large body sizes could expose the population to obesity risk. This study aimed to determine the impact of these biocultural factors on the nutritional status of Senegalese adults. A mixed methods approach was used, including qualitative and quantitative studies. Between 2011 and 2013, fourteen focus group discussions (n=84) and a cross-sectional quantitative survey (n=313 women; n=284 men) of adults in three different socio-ecological areas of Senegal (rural: n=204; suburban: n=206; urban: n=187) were conducted. Dietary intake (Dietary Diversity Scores), physical activity (International Physical Activity Questionnaire), body weight norms (Body Size Scale), weight and health statuses (anthropometric measures and blood pressure) were measured. Middle-aged and older Senegalese women were found to value overweight/obesity more than younger Senegalese in all regions. In addition, young urban/suburban adults had a tendency for daily snacking whilst urban/suburban adults tended to be less physically active and had higher anthropometric means. A binary logistic regression model showed that being female, older, living in urban/suburban areas and valuing larger body size were independently associated with being overweight/obese, but not high-calorie diet. Univariate analyses showed that lower physical activity and higher socioeconomic status were associated with being overweight/obese. Finally, overweight/obesity, which is low in men, is associated with hypertension in the total sample. The nutrition transition is currently underway in Senegal's urban/suburban areas, with older women being more affected. Since several specific biocultural factors jointly contribute to this phenomenon, the study's findings suggest the need for local public health interventions that target women and which account for the anthropological specificities of the Senegalese population

A study of nitrogen incorporation in pyramidal site-controlled quantum dots

We present the results of a study of nitrogen incorporation in metalorganic-vapour-phase epitaxy-grown site-controlled quantum dots (QDs). We report for the first time on a significant incorporation (approximately 0.3%), producing a noteworthy red shift (at least 50 meV) in some of our samples. Depending on the level of nitrogen incorporation/exposure, strong modifications of the optical features are found (variable distribution of the emission homogeneity, fine-structure splitting, few-particle effects). We discuss our results, especially in relation to a specific reproducible sample which has noticeable features: the usual pattern of the excitonic transitions is altered and the fine-structure splitting is suppressed to vanishing values. Distinctively, nitrogen incorporation can be achieved without detriment to the optical quality, as confirmed by narrow linewidths and photon correlation spectroscopy

Diminishing benefits of urban living for children and adolescents’ growth and development

Optimal growth and development in childhood and adolescence is crucial for lifelong health and well-being1–6. Here we used data from 2,325 population-based studies, with measurements of height and weight from 71 million participants, to report the height and body-mass index (BMI) of children and adolescents aged 5–19 years on the basis of rural and urban place of residence in 200 countries and territories from 1990 to 2020. In 1990, children and adolescents residing in cities were taller than their rural counterparts in all but a few high-income countries. By 2020, the urban height advantage became smaller in most countries, and in many high-income western countries it reversed into a small urban-based disadvantage. The exception was for boys in most countries in sub-Saharan Africa and in some countries in Oceania, south Asia and the region of central Asia, Middle East and north Africa. In these countries, successive cohorts of boys from rural places either did not gain height or possibly became shorter, and hence fell further behind their urban peers. The difference between the age-standardized mean BMI of children in urban and rural areas was <1.1 kg m–2 in the vast majority of countries. Within this small range, BMI increased slightly more in cities than in rural areas, except in south Asia, sub-Saharan Africa and some countries in central and eastern Europe. Our results show that in much of the world, the growth and developmental advantages of living in cities have diminished in the twenty-first century, whereas in much of sub-Saharan Africa they have amplified

The 2020 UV emitter roadmap

Solid state UV emitters have many advantages over conventional UV sources. The (Al,In,Ga)N material system is best suited to produce LEDs and laser diodes from 400 nm down to 210 nm—due to its large and tuneable direct band gap, n- and p-doping capability up to the largest bandgap material AlN and a growth and fabrication technology compatible with the current visible InGaN-based LED production. However AlGaN based UV-emitters still suffer from numerous challenges compared to their visible counterparts that become most obvious by consideration of their light output power, operation voltage and long term stability. Most of these challenges are related to the large bandgap of the materials. However, the development since the first realization of UV electroluminescence in the 1970s shows that an improvement in understanding and technology allows the performance of UV emitters to be pushed far beyond the current state. One example is the very recent realization of edge emitting laser diodes emitting in the UVC at 271.8 nm and in the UVB spectral range at 298 nm. This roadmap summarizes the current state of the art for the most important aspects of UV emitters, their challenges and provides an outlook for future developments