Capping InAs/GaAs quantum dots (QDs) with a thin GaAsSb layer alters the QDs structural properties, leading to considerable changes in their optical properties. The increase of the Sb content induces a redshift of the emission energies, indicating a change in the buried QDs shape and size. The presence of well-defined ground- and excited-state emission bands in all the photoluminescence spectra allow an accurate estimation of the buried QDs size and shape by numerical evaluation and tuning of the theoretical emission energies. For an Sb content below 14%, the QDs are found to have a type I band alignment with a truncated height pyramidal form. However, for higher Sb content (22%), the QDs are present in a full pyramidal shape. The observed behavior is interpreted in terms of increasing prevention of InAs QDs decomposition with increasing the Sb content in the cap layer.
IntroductionADHD is one of the most common neuropsychiatric disorders in children. The worldwide prevalence is estimated to be between 2–18%. The exact cause of ADHD is still unknown, but some factors have been found to increase the risk of having ADHD like increase TV exposure time and video games.ObjectivesTo study the association between time spent on computer tablets (iPads or Android tablets) by children and ADHD.MethodsThis cross sectional study targeted children from 3 to 12 years old who use computer tablets. Two non-random sampling techniques were used to distribute self-administered questionnaires to one of the caregivers of 275 children, 36 of them installed an application in their children's computer tablets that measures the actual time spent by the children. The questionnaire contains demographics, validated Arabic ADHD rating scale and questions to assess the parental attitude. The SPSS package was used for statistical analysis.ResultsThe results showed that the overall prevalence of ADHD is 22.2% and it is higher in males. There is no statistically significant association between ADHD and all variables except for the time spent on computer tablets, which showed that children using computer tablets more than the average time have an increased chance of having ADHD with an odds ratio of 1.9 with 95% confidence interval from 1.08 to 3.40.ConclusionThis study shows an association between time spent on computer tablets by children and ADHD. There is need for longitudinal studies to demonstrate the temporality and to confirm the association.
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