[Aerosols and SARS-CoV-2: Statement of the "Expert Group Aerosols" on the development, infectivity, spread and reduction of airborne, virus-containing particles in the air]. / Stellungnahme des "Expertenkreises Aerosole": Aerosole und SARS-CoV-2 ­ Entstehung, Infektiosität, Ausbreitung und Minderung luftgetragener, virenhaltiger Teilchen in der Atemluft.

Aerosols are currently seen as one of the main transmission routes for SARS-CoV-2, but a comprehensive understanding of the processes and appropriate action/adaptation of protection concepts requires the exchange of information across interdisciplinary boundaries. Against this background, the Baden-Württemberg state government launched in October 2020 a multidisciplinary "Expert Group Aerosols" comprising engineers, natural scientists and medical professionals. In its statement, the group has compiled the current state of knowledge in all relevant disciplines in the context of airborne SARS-CoV-2 infection. In addition to the well-known hygiene and social distancing rules, the importance of the correct use of effective masks is emphasized. Furthermore, the necessity for dynamic and correct ventilation is pointed out and illustrated with ventilation intervals and periods for different scenarios as examples. The effectiveness of stationary or mobile cabin air filters as an important component in the protection concept is discussed. The first opinion of the expert group makes it clear that the existing hygiene and social distancing rules offer the best possible protection against SARS-CoV-2 infection only when correctly applied in combination.

Shape Memory Polymer Foam with Programmable Apertures.

In this work, a novel type of polyester urethane urea (PEUU) foam is introduced. The foam was produced by reactive foaming using a mixture of poly(1,10-decamethylene adipate) diol and poly(1,4-butylene adipate) diol, 4,4'-diphenylmethane diisocyanate, 1,4-butanediol, diethanolamine and water as blowing agent. As determined by differential scanning calorimetry, the melting of the ester-based phases occurred at temperatures in between 25 °C and 61 °C, while the crystallization transition spread from 48 °C to 20 °C. The mechanical properties of the foam were simulated with the hyperplastic models Neo-Hookean and Ogden, whereby the latter showed a better agreement with the experimental data as evidenced by a Pearson correlation coefficient R² above 0.99. Once thermomechanically treated, the foam exhibited a maximum actuation of 13.7% in heating-cooling cycles under a constant external load. In turn, thermal cycling under load-free conditions resulted in an actuation of more than 10%. Good thermal insulation properties were demonstrated by thermal conductivities of 0.039 W·(m·K)-1 in the pristine state and 0.052 W·(m·K)-1 in a state after compression by 50%, respectively. Finally, three demonstrators were developed, which closed an aperture or opened it again simply by changing the temperature. The self-sufficient material behavior is particularly promising in the construction industry, where programmable air slots offer the prospect of a dynamic insulation system for an adaptive building envelope.