Nonperturbative harmonic generation in graphene from intense midinfrared pulsed light

In solids, high harmonic radiation arises from the subcycle dynamics of electrons and holes under the action of an intense laser field. The strong-field regime opens new opportunities to understand and control carrier dynamics on ultrafast time scales, including the coherent dynamics of quasiparticles such as massless Dirac fermions. Here, we irradiate monolayer and few-layer graphene with intense infrared light to produce nonperturbative harmonics of the fundamental up to the seventh order. We find that the polarization dependence shows surprising agreement with gas-phase harmonics. Using a two-band model, we explore the nonlinear current due to electrons near the Dirac points, and we discuss the interplay between intraband and interband contributions to the harmonic spectrum. This interplay opens new opportunities to access ultrafast and strong-field physics of graphene.Peer reviewed: YesNRC publication: Ye

Validating the Children’s Sleep Habits Questionnaire against polysomnography and actigraphy in school-aged children

Sleep is a vital physiological behaviour in children’s development, and as such it is important to be able to efficiently and accurately assess whether children display difficulties with sleep quality and quantity. The Children’s Sleep Habits Questionnaire (CSHQ; (1)) is one of the most commonly used assessment tools for pediatric sleep. However, this instrument has never been validated against the gold standard of sleep measurement (i.e., polysomnography; PSG), and studies comparing it to actigraphy are limited. Therefore, the current study assessed the validity of four subscales of the CSHQ via direct comparison with PSG and actigraphy for 30 typically developing school-aged children (ages 6 to 12). No significant correlations between relevant CSHQ subscales and PSG variables were found. In terms of the actigraphy variables, only the CSHQ Night Wakings subscale achieved significance. In addition, sensitivity and specificity analyses revealed consistently low sensitivity and high specificity. Overall, the CSHQ Sleep Onset Delay, Sleep Duration, Night Wakings, and Sleep Disordered Breathing subscales showed low construct validity and diagnostic validity. These results underscore that caution should be taken when using the CSHQ as the sole screening tool for sleep problems in children

Reducing resistance to polio immunisation with free health camps and Bluetooth messaging: An update from Kaduna, Northern, Nigeria

Since 1997, the Global Polio Eradication Initiative has sponsored regular door-to-door polio immunisation campaigns in northern Nigeria. On 30 July 2015, the country was finally declared poliofree, a hard won success. At various times, polio eradication has been threatened by rumours and community tensions. For example, in 2003, local Imams, traditional leaders and politicians declared a polio campaign boycott, due to the concerns about the safety of the polio vaccine. Although the campaigns resumed in 2004, many parents continued to refuse vaccination because of the persistence of rumours of vaccine contamination, and anger about the poor state of health services for conditions other than polio. To address this, UNICEF and Nigerian Government partners piloted two interventions: (1) mobile ‘health camps’ to provide ambulatory care for conditions other than polio and (2) an audiovisual clip about vaccine safety and other health issues, shareable on multimedia mobile phones via Bluetooth pairing. The mobile phone survey found that Bluetooth compatible messages could rapidly spread behavioural health messages in low-literacy communities. The health camps roughly doubled polio vaccine uptake in the urban ward where it was piloted. This suggests that polio eradication would have been accelerated by improving primary health care services