High speed shadowgraphy of a combusting air blast atomizer spray at elevated pressure

This contribution demonstrates the use of a compact high repetition rate pulsed high power LED light source in combination with a high speed camera to obtain high speed shadowgraphs of an airblasted spray in a fired research combustor at medium pressures. The temporally resolved structures are subjected to conventional spectral analysis and exhibit very dominant fundamental frequencies throughout the visualized spray structures. The image data is further compared to time series of drop-sizing measurements made by a phase Doppler instrument. The periodicity is attributed to a spiraling spray release from the nozzle lip that is believed to be induced by a precessing vortex or vortices orbiting around the burner axis

Application of pulsed high-power LEDs for high speed visualization and measurement of flows

The rapid progress in the light emitting diode (LED) manufacturing technology nowadays enables the application of high-power LEDs as light sources for both high-speed videography and flow velocimetry. These devices have a number of attractive advantages in comparison to lasers and xenon illumination. Aside from the dramatically reduced cost of procurement, relatively simple operation and considerably longer life time, LEDs are very stable in terms of intensity and their spatial distributions providing incoherent illumination free of speckle artefacts. The presentation describes the use of pulsed hight power LEDs for high-speed Schlieren videography, high speed particle image velocimetry (PIV) as well as tomographic PIV. Pulsed LED illumination is also well suited for surface deformation measurement techniques such as image pattern correlation technique (IPCT) or projected pattern correlation technique (PROPAC). Future developments will result in LED devices with even higher light emission opening a wider range of application in imaging flow diagnostics

The impact of COVID-19 related lockdown measures on self-reported psychopathology and health-related quality of life in German adolescents

The impact of school-closings on adolescents' mental health and well-being in the management of the ongoing COVID-19 pandemic is subject to ongoing public debate. Reliable data to inform a balanced discussion are limited. Drawing on a large ongoing multi-site project in Germany, we assessed differences in self-reported psychopathology in a matched convenience-sample of adolescents assessed pre- (November 26, 2018 to March 13, 2020; n = 324) and post the first lockdown (March 18, 2020 to August 29, 2020; n = 324) early 2020 in Germany. We found no evidence for an increase in emotional and behavioral problems, depression, thoughts of suicide or suicide attempts, eating disorder symptoms, or a decrease in general health-related quality of life. Reported suicide plans significantly decreased from 6.14 to 2.16%. Similarly, conduct problems decreased in the post-lockdown period. Family risk-factors did not moderate these findings. The influence of socioeconomic status on emotional and behavioral problems as well as depression decreased during the lockdown. Based on the present findings, the first school-closing in Germany had no immediate and severe impact on adolescents' well-being. However, caution is warranted as our data covers a fairly small, affluent sample over a limited time-span and long-term consequences cannot be ruled out