Photoinduced blinking in a solid-state quantum system

© 2017 American Physical Society. Solid-state single-photon emitters (SPEs) are one of the prime components of many quantum nanophotonics devices. In this work, we report on an unusual, photoinduced blinking phenomenon of SPEs in gallium nitride. This is shown to be due to the modification in the transition kinetics of the emitter, via the introduction of additional laser-activated states. We investigate and characterize the blinking effect on the brightness of the source and the statistics of the emitted photons. Combining second-order correlation and fluorescence trajectory measurements, we determine the photodynamics of the trap states and characterize power-dependent decay rates and characteristic "off"-time blinking. Our work sheds light into understanding solid-state quantum system dynamics and, specifically, power-induced blinking phenomena in SPEs

Parental stress increases body mass index trajectory in pre-adolescents.

What is already known about this subjectRates of childhood obesity have increased since the mid-1970s. Research into behavioural determinants has focused on physical inactivity and unhealthy diets. Cross-sectional studies indicate an association between psychological stress experienced by parents and obesity in pre-adolescents.What this study addsWe provide evidence of a prospective association between parental psychological stress and increased weight gain in pre-adolescents. Family-level support for those experiencing chronic stress might help promote healthy diet and exercise behaviours in children.ObjectiveWe examined the impact of parental psychological stress on body mass index (BMI) in pre-adolescent children over 4 years of follow-up.MethodsWe included 4078 children aged 5-10 years (90% were between 5.5 and 7.5 years) at study entry (2002-2003) in the Children's Health Study, a prospective cohort study in southern California. A multi-level linear model simultaneously examined the effect of parental stress at study entry on the attained BMI at age 10 and the slope of change across annual measures of BMI during follow-up, controlled for the child's age and sex. BMI was calculated based on objective measurements of height and weight by trained technicians following a standardized procedure.ResultsA two standard deviation increase in parental stress at study entry was associated with an increase in predicted BMI attained by age 10 of 0.287 kg m(-2) (95% confidence interval 0.016-0.558; a 2% increase at this age for a participant of average attained BMI). The same increase in parental stress was also associated with an increased trajectory of weight gain over follow-up, with the slope of change in BMI increased by 0.054 kg m(-2) (95% confidence interval 0.007-0.100; a 7% increase in the slope of change for a participant of average BMI trajectory).ConclusionsWe prospectively demonstrated a small effect of parental stress on BMI at age 10 and weight gain earlier in life than reported previously. Interventions to address the burden of childhood obesity should address the role of parental stress in children

Computational Study of the Hydration of Sulfuric Acid Dimers: Implications for Acid Dissociation and Aerosol Formation

We have investigated the thermodynamics of sulfuric acid dimer hydration using ab initio quantum mechanical methods. For (H2SO4)2(H2O)n where n = 0−6, we employed high-level ab initio calculations to locate the most stable minima for each cluster size. The results presented herein yield a detailed understanding of the first deprotonation of sulfuric acid as a function of temperature for a system consisting of two sulfuric acid molecules and up to six waters. At 0 K, a cluster of two sulfuric acid molecules and one water remains undissociated. Addition of a second water begins the deprotonation of the first sulfuric acid leading to the di-ionic species (the bisulfate anion HSO4−, the hydronium cation H3O+, an undissociated sulfuric acid molecule, and a water). Upon the addition of a third water molecule, the second sulfuric acid molecule begins to dissociate. For the (H2SO4)2(H2O)3 cluster, the di-ionic cluster is a few kcal mol−1 more stable than the neutral cluster, which is just slightly more stable than the tetra-ionic cluster (two bisulfate anions, two hydronium cations, and one water). With four water molecules, the tetra-ionic cluster, (HSO4−)2(H3O+)2(H2O)2, becomes as favorable as the di-ionic cluster H2SO4(HSO4−)(H3O+)(H2O)3 at 0 K. Increasing the temperature favors the undissociated clusters, and at room temperature we predict that the di-ionic species is slightly more favorable than the neutral cluster once three waters have been added to the cluster. The tetra-ionic species competes with the di-ionic species once five waters have been added to the cluster. The thermodynamics of stepwise hydration of sulfuric acid dimer is similar to that of the monomer; it is favorable up to n = 4−5 at 298 K. A much more thermodynamically favorable pathway forming sulfuric acid dimer hydrates is through the combination of sulfuric acid monomer hydrates, but the low concentration of sulfuric acid relative to water vapor at ambient conditions limits that process

Hydration of the Sulfuric Acid−Methylamine Complex and Implications for Aerosol Formation

The binary H2SO4−H2O nucleation is one of the most important pathways by which aerosols form in the atmosphere, and the presence of ternary species like amines increases aerosol formation rates. In this study, we focus on the hydration of a ternary system of sulfuric acid (H2SO4), methylamine (NH2CH3), and up to six waters to evaluate its implications for aerosol formation. By combining molecular dynamics (MD) sampling with high-level ab initio calculations, we determine the thermodynamics of forming H2SO4(NH2CH3)(H2O)n, where n = 0−6. Because it is a strong acid−base system, H2SO4−NH2CH3 quickly forms a tightly bound HSO4−−NH3CH3+ complex that condenses water more readily than H2SO4 alone. The electronic binding energy of H2SO4−NH2CH3 is −21.8 kcal mol−1 compared with −16.8 kcal mol−1 for H2SO4−NH3 and −12.8 kcal mol−1 for H2SO4−H2O. Adding one to two water molecules to the H2SO4−NH2CH3 complex is more favorable than adding to H2SO4 alone, yet there is no systematic difference for n ≥ 3. However, the average number of water molecules around H2SO4−NH2CH3 is consistently higher than that of H2SO4, and it is fairly independent of temperature and relative humidity

The effects of dual micronutrient supplementation on thyroid function in school children: An experimental study

Background: The presence of iron and or vitamin A deficiency in children limits the effectiveness of the iodine intervention program in areas where iodine deficiency is endemic. This study was aimed at assessing the role of dual micronutrient supplementation on thyroid function in severe iodine deficient school children age 6-16 years in Ethiopia.Methods: From 2006 to 2007 an experimental study was conducted on 397 children, all with visible goiter grade of which 6.1% and 10.3% vitamin A and iron deficient respectively. A week after baseline data collection and de-worming, all children with visible goitre (n=332) but without iron and vitamin A deficiency were randomly grouped into four, A to D groups. Vitamin A deficient children (n=24) were randomly allocated to group A and group B while anaemic children (n=41) were distributed into group C and group D. Group A received 400mg oral iodized oil and group B received 200,000IU vitamin A plus 400mg oral iodized oil. Group C received 400mg oral iodized oil while group D received 100mg iron sulphate with folic acid and 400 mg oral iodized oil. Iron supplementation was continued two doses per day for six weeks. Vitamin A supplemented group received additional dose at six month. Post intervention data on iodine, vitamin A and iron status were collected at 6 and 11 month.Results: Children supplemented with iron + oral iodized oil capsule had significant goitre reduction than oral iodized oil supplemented group. The mean concentrations of thyroid hormone (T4) and Urinary iodine excretion (UIE) in iron + iodine supplemented group were significantly higher than the iodine alone supplemented group at 6 months after the intervention. Hemoglobin level at baseline in all study subjects and at 11 month after intervention in group D (iron + iodine supplemented group) significantly (P<0.05) correlated with T4 level. The significant goitre reduction in iron + iodine supplemented group than iodine alone supplemented group and significant correlation between level hemoglobin and T4 at baseline and at 11 month after intervention probably indicate that iron and iodine have a functional interaction in thyroid iodine metabolism.Conclusion: Supplementation of iodized oil with Iron is more effective in goitre reduction than iodine alone and this should be taken into consideration by iodine deficiency disorders (IDD) intervention programs

Assessing the Long-term Impact of Microcredit on Rural Poverty: Does the Timing and Length of Participation Matter?

In recent years, microfinance institutions are seen as beacons of hope to help eradicate poverty through, among others, providing credit to poor rural households. Availability of small but repeated loans is, in the long-term, expected to impact on poverty. However, decades after the introduction of microfinance institutions into many rural areas, there are still questions as to what extent such long-term benefits are realized. This is because evaluating the long-term impact of microfinance provision on household welfare is difficult due to difficulties in controlling for heterogeneities in the borrower pool and subsequent borrowing dynamics. We use four rounds of panel data on rural households in Ethiopia that had access to microfinance credit to assess the long-term impact of credit by explicitly accounting for such borrowing dynamics. In a panel data setting where only the outcome variable is time-varying, potential future paths of individuals in the control group are considered to account for counterfactuals. Matching is used to adjust for initial differences between participants and controls. These combined methodological innovations enable us to overcome biases due to selection as well as problems of accounting for dropouts and new participants in microfinance impact assessments. Results suggest that the timing of membership matters: the earlier the onset of membership the better the effect. Results are robust compared to standard matched pairwise effects. The overriding implication from this comparison suggests that not accounting for future counterfactuals, for the most part, can lead to biased estimates and overestimates of the impact of credit on household welfare

Electroluminescence from Localized Defects in Zinc Oxide: Toward Electrically Driven Single Photon Sources at Room Temperature

© 2015 American Chemical Society. Single photon sources are required for a wide range of applications in quantum information science, quantum cryptography, and quantum communications. However, the majority of room temperature emitters to date are only excited optically, which limits their proper integration into scalable devices. In this work, we overcome this limitation and present room temperature electrically driven light emission from localized defects in zinc oxide (ZnO) nanoparticles and thin films. The devices emit in the red spectral range and show excellent rectifying behavior. The emission is stable over an extensive period of time, providing an important prerequisite for practical devices. Our results open possibilities for building new ZnO-based quantum integrated devices that incorporate solid-state single photon sources for quantum information technologies. (Graph Presented)

Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

The computational study of the formation and growth of atmospheric aerosols requires an accurate Gibbs free energy surface, which can be obtained from gas phase electronic structure and vibrational frequency calculations. These quantities are valid for those atmospheric clusters whose geometries correspond to a minimum on their potential energy surfaces. The Gibbs free energy of the minimum energy structure can be used to predict atmospheric concentrations of the cluster under a variety of conditions such as temperature and pressure. We present a computationally inexpensive procedure built on a genetic algorithm-based configurational sampling followed by a series of increasingly accurate screening calculations. The procedure starts by generating and evolving the geometries of a large set of configurations using semi-empirical models then refines the resulting unique structures at a series of high-level ab initio levels of theory. Finally, thermodynamic corrections are computed for the resulting set of minimum-energy structures and used to compute the Gibbs free energies of formation, equilibrium constants, and atmospheric concentrations. We present the application of this procedure to the study of hydrated glycine clusters under ambient conditions

Computation of Atmospheric Concentrations of Molecular Clusters from \u3cem\u3eab initio\u3c/em\u3e Thermochemistry

The computational study of the formation and growth of atmospheric aerosols requires an accurate Gibbs free energy surface, which can be obtained from gas phase electronic structure and vibrational frequency calculations. These quantities are valid for those atmospheric clusters whose geometries correspond to a minimum on their potential energy surfaces. The Gibbs free energy of the minimum energy structure can be used to predict atmospheric concentrations of the cluster under a variety of conditions such as temperature and pressure. We present a computationally inexpensive procedure built on a genetic algorithm-based configurational sampling followed by a series of increasingly accurate screening calculations. The procedure starts by generating and evolving the geometries of a large set of configurations using semi-empirical models then refines the resulting unique structures at a series of high-level ab initio levels of theory. Finally, thermodynamic corrections are computed for the resulting set of minimum-energy structures and used to compute the Gibbs free energies of formation, equilibrium constants, and atmospheric concentrations. We present the application of this procedure to the study of hydrated glycine clusters under ambient conditions

Anemia prevalence and etiology among women, men, and children in Ethiopia: a study protocol for a national population-based survey.

BACKGROUND: Anemia remains a public health challenge in Ethiopia, affecting an estimated 56% of children under age 5 years, 23% of women of reproductive age and 18% of adult men. However, anemia etiology and the relative contribution of underlying risk factors for anemia remains unclear and has hindered implementation of anemia control programs. METHODS/DESIGN: Anemia Etiology in Ethiopia (AnemEE) is a population-based cross-sectional survey of six regions of Ethiopia that includes children, women of reproductive age, and men from regionally representative households. The survey will include detailed assessment of anemia, iron, inflammatory and nutritional biomarkers, diet, comorbidities, and other factors. The objectives of AnemEE are 1) to generate evidence for decision-making on the etiology of anemia in Ethiopia among men, women and children and 2) to simulate the potential effect of iron fortification and other interventions on the prevalence of anemia and risk of iron overload. DISCUSSION: AnemEE will provide the most comprehensive evaluation of anemia etiology in Ethiopia to date due to its detailed assessment of diet, biomarkers, infections and other risk factors in a population-based sample. By generating evidence and simulating potential interventions, AnemEE will inform the development of high-impact anemia control programs and policies. TRIAL REGISTRATION: ClinicalTrials.gov, NCT04002466 . Registered on 28 June 2019. Retrospectively registered