32 research outputs found
COVID-19 first lockdown as a window into language acquisition: Associations between caregiver-child activities and vocabulary gains
The COVID-19 pandemic, and the resulting closure of daycare centers worldwide, led to unprecedented changes in childrenâs learning environments. This period of increased time at home with caregivers, with limited access to external sources (e.g., daycares) provides a unique opportunity to examine the associations between the caregiver-child activities and childrenâs language development. The vocabularies of 1742 children aged8-36 months across 13 countries and 12 languages were evaluated at the beginning and end of the first lockdown period in their respective countries(from March to September 2020). Children who had less passive screen exposure and whose caregivers read more to them showed larger gains in vocabulary development during lockdown, after controlling for SES and other caregiver-child activities. Children also gained more words than expected (based on normative data) during lockdown; either caregivers were more aware of their childâs development or vocabulary development benefited from intense caregiver-child interaction during lockdown
Spectroscopic characterization and imaging of laser- and unipolar arc-induced plasmas
Tungsten plasmas induced by unipolar arcs were investigated using optical emission spectroscopy and imaging, and compared with laser-induced tungsten plasmas. The unipolar arcs were initiated in the linear-plasma simulator PISCES-A at UCSD under fusion relevant conditions. The electron temperature and density of the unipolar arc plasmas were in the range 0.5-0.7 eV and 0.7-2.0 x 10(20) m(-3), respectively, and increased with increasing negative bias voltage, but did not correlate with the surface temperature. In comparison, the electron temperature and density of the laser-induced plasmas were in the range 0.6-1.4 eV and 7 x 10(19)-1 x 10(22) m(-3), respectively
Interaction of adhered beryllium proxy dust with transient and stationary plasmas
Tungsten (W) substrates with adhered beryllium (Be) proxy dust - copper, chromium, aluminium - have been exposed in the Magnum-PSI linear device. Their interaction with transient and stationary plasmas has been systematically studied under varying heat fluxes and magnetic field topologies. The dust remobilization activities, macro-morphological changes and chemical modifications induced by the plasma incidence are documented. Aluminium is identified to be the most suitable surrogate material due to the similar binary phase diagram and nearly identical evaporation rates. Extrapolation suggests that Be dust cannot survive on hot W surfaces but it can trigger mixed Be/W effects prior to its plasma removal
Interaction of adhered beryllium proxy dust with transient and stationary plasmas
Tungsten (W) substrates with adhered beryllium (Be) proxy dust - copper, chromium, aluminium - have been exposed in the Magnum-PSI linear device. Their interaction with transient and stationary plasmas has been\u3cbr/\u3esystematically studied under varying heat fluxes and magnetic field topologies. The dust remobilization activities, macro-morphological changes and chemical modifications induced by the plasma incidence are documented. Aluminium is identified to be the most suitable surrogate material due to the similar binary phase diagram and nearly identical evaporation rates. Extrapolation suggests that Be dust cannot survive on hot W surfaces but it can trigger mixed Be/W effects prior to its plasma removal
Atomistic simulations of graphite etching at realistic time scales
Hydrogen-graphite interactions are relevant to a wide variety of applications, ranging from astrophysics to fusion devices and nano-electronics. In order to shed light on these interactions, atomistic simulation by Molecular Dynamics (MD) has been shown to be an invaluable tool. It suffers, however, from severe time-scale limitations. In this work we employ the recently developed Collective Variable-Driven Hyperdynamics (CVHD) method to hydrogen etching of graphite for varying inter-impact times up to a realistic value of 1 ms, which corresponds to a flux of ~1020 m-2s-1. The results show that the erosion yield, hydrogen surface coverage and species distribution are significantly affected by the time between impacts. This can be explained by the higher probability for C-C bond breaking due to the prolonged exposure to thermal stress and the subsequent transition from ion- to thermal-induced etching. This latter regime of thermal-induced etching - chemical erosion - is here accessed for the first time using atomistic simulations. In conclusion, this study demonstrates that accounting for long time-scales significantly affects ion bombardment simulations and should not be neglected in a wide range of conditions, in contrast to what is typically assumed