Dynamics and outcomes of binary collisions of equi-diameter picolitre droplets with identical viscosities.

The dynamics of binary collisions of equi-diameter picolitre droplets with identical viscosities, varying impact speeds and impact angles have been investigated experimentally and compared to collision outcome prediction models. Collisions between pairs of pure water droplets with a viscosity of 0.89 mPa s and pairs of aqueous-sucrose (40% w/w) droplets with a viscosity of 5.17 mPa s were examined. The colliding droplets were ∼38 µm in diameter, which is around ten times smaller than those previously investigated when examining the effect of viscosity on the outcome of binary droplet collisions. Varying the impact speed and angle resulted in different collision outcomes, including coalescence, reflexive separation and stretching separation. The collision outcomes were plotted on two viscosity dependent regime maps. The regime boundaries are generally in agreement with earlier literature for both high and low viscosity cases. The agreement between experiment and theory, for both fluids, gives more confidence in the models tested here to predict collision outcomes for droplets of this size and these viscosities.

Mental/behavioural health and educational outcomes of grandchildren raised by custodial grandparents: A mixed methods systematic review.

Grandparents caring for grandchildren has increased globally in the past two decades, but we have a limited understanding of its effects on custodial grandchildren's mental/behavioural health and educational outcomes. This mixed methods systematic review aims to synthesise mental/behavioural health and educational outcomes of custodial grandchildren within custodial grandparent-headed families and with comparison to other types of household structure and further examine factors associated with these outcomes. A systematic review following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines was conducted. We searched ERIC, Family Studies Abstracts, PsycINFO, PubMed, Scopus, Social Work Abstract and SocINDEX in March 2021 and screened 14,515 articles, which resulted in the inclusion of 42 studies, including 33 quantitative, seven qualitative and two mixed methods studies. The quality of included studies was assessed. This review covered 10 countries, yet most studies revealed that grandchildren raised by grandparents had adverse mental/behavioural health and educational outcomes compared to their peers raised by biological parents. This review further identified multi-level factors contributing to custodial grandchildren's adverse outcomes. Methodological limitations and implications for future practice and research were discussed.

Comparing aerosol number and mass exhalation rates from children and adults during breathing, speaking and singing.

Aerosol particles of respirable size are exhaled when individuals breathe, speak and sing and can transmit respiratory pathogens between infected and susceptible individuals. The COVID-19 pandemic has brought into focus the need to improve the quantification of the particle number and mass exhalation rates as one route to provide estimates of viral shedding and the potential risk of transmission of viruses. Most previous studies have reported the number and mass concentrations of aerosol particles in an exhaled plume. We provide a robust assessment of the absolute particle number and mass exhalation rates from measurements of minute ventilation using a non-invasive Vyntus Hans Rudolf mask kit with straps housing a rotating vane spirometer along with measurements of the exhaled particle number concentrations and size distributions. Specifically, we report comparisons of the number and mass exhalation rates for children (12-14 years old) and adults (19-72 years old) when breathing, speaking and singing, which indicate that child and adult cohorts generate similar amounts of aerosol when performing the same activity. Mass exhalation rates are typically 0.002-0.02 ng s-1 from breathing, 0.07-0.2 ng s-1 from speaking (at 70-80 dBA) and 0.1-0.7 ng s-1 from singing (at 70-80 dBA). The aerosol exhalation rate increases with increasing sound volume for both children and adults when both speaking and singing.