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- ItemSize, concentration, and origin of human exhaled particles and their dependence on human factors with implications on infection transmission(Amsterdam [u.a.] : Elsevier, 2022) Bagheri, Gholamhossein; Schlenczek, Oliver; Turco, Laura; Thiede, Birte; Stieger, Katja; Kosub, Jana M.; Clauberg, Sigrid; Pöhlker, Mira L.; Pöhlker, Christopher; Moláček, Jan; Scheithauer, Simone; Bodenschatz, EberhardUnderstanding infection transmission between individuals, as well as evaluating the efficacy of protective measures, are key issues in pandemics driven by human respiratory particles. The key is a quantitative understanding of the size and concentration of particles exhaled and their variability across the size range for a representative population of all ages, genders, and different activities. Here we present data from 132 healthy volunteers aged 5 to 80 years, measured over the entire particle size range for each individual. Conventional particle spectrometry was combined with in-line holography under well-controlled conditions for common activities such as breathing, speaking, singing, and shouting. We find age to be the most important parameter for the concentration of small exhale particles <5 µm (PM5), which doubles over a 7-year period in adolescents and over a 30-year period in adults. Gender, body mass index, smoking or exercise habits have no discernible effect. We provide evidence that particles with a diameter of <5 µm originate from the lower respiratory tract, 5–15 µm from the larynx/pharynx, and >15 µm from the oral cavity. PM5 concentration can vary by one order of magnitude within a person, while inter-person variability can span two orders of magnitude, largely explained by difference in age. We found no discernible inter-person variability for particles larger than 5 µm. Our results show that cumulative volume of PM5 is 2–8 times higher in adults than in children. In contrast, number and volume concentration of larger particles, which are produced predominantly in the upper respiratory tract, is largely independent of age. Finally, we examined different types of airborne-transmissible respiratory diseases and provided insights into possible modes of infection transmission with and without several types/fits of face masks.
- ItemSelf-organized formation of unidirectional and quasi-one-dimensional metallic Tb silicide nanowires on Si(110)(Amsterdam [u.a.] : Elsevier, 2022) Appelfeller, Stephan; Franz, Martin; Karadag, Murat; Kubicki, Milan; Zielinski, Robert; Krivenkov, Maxim; Varykhalov, Andrei; Preobrajenski, Alexei; Dähne, MarioTerbium induced nanostructures on Si(110) and their growth are thoroughly characterized by low energy electron diffraction, scanning tunneling microscopy and spectroscopy, core-level and valence band photoelectron spectroscopy, and angle-resolved photoelectron spectroscopy. For low Tb coverage, a wetting layer forms with its surface fraction continuously decreasing with increasing Tb coverage in favor of the formation of unidirectional Tb silicide nanowires. These nanowires show high aspect ratios for high annealing temperatures or on substrates already containing Tb in the bulk. Both wetting layer and nanowires are stable for temperatures up to 750°C. In contrast to the nanowires, the wetting layer is characterized by a band gap. Thus, the metallic nanowires, which show a quasi-one-dimensional electronic band structure, are embedded in a semiconducting surrounding of wetting layer and substrate, insulating the nanowires from each other.
- ItemSelf-stabilization of the equilibrium state in ferroelectric thin films(Amsterdam : Elsevier, 2022) Gaal, Peter; Schmidt, Daniel; Khosla, Mallika; Richter, Carsten; Boesecke, Peter; Novikov, Dmitri; Schmidbauer, Martin; Schwarzkopf, Jutta(K,Na)NbO3 is a lead-free and sustainable ferroelectric material with electromechanical parameters comparable to Pb(Zr,Ti)O3 (PZT) and other lead-based solid solutions. It is therefore a promising candidate for caloric cooling and energy harvesting applications. Specifically, the structural transition from the low-temperature Mc- to the high-temperature c-phase displays a rich hierarchical order of domains and superdomains, that forms at specific strain conditions. The relevant length scales are few tens of nanometers for the domain and few micrometers for the superdomain size, respectively. Phase-field calculations show that this hierarchical order adds to the total free energy of the solid. Thus, domains and their formation has a strong impact on the functional properties relevant for electrocaloric cooling or energy harvesting applications. However, monitoring the formation of domains and superdomains is difficult and requires both, high spatial and high temporal resolution of the experiment. Synchrotron-based time-resolved X-ray diffraction methods in combination with scanning imaging X-ray microscopy is applied to resolve the local dynamics of the domain morphology with sub-micrometer spatial and nanosecond temporal resolution. In this regime, the material displays a novel self-stabilization mechanism of the domain morphology, which may be a general property of first-order phase transitions.
- ItemSecondary electron yield engineering of copper surfaces by 532 nm ultrashort laser pulses(Amsterdam [u.a.] : Elsevier, 2022) Lorenz, Pierre; Bez, Elena; Himmerlich, Marcel; Ehrhardt, Martin; Taborelli, Mauro; Zimmer, KlausNanostructured surfaces exhibit outstanding properties and enable manifold industrial applications. In this study the laser surface processing of polycrystalline, flat copper surfaces by 532 nm picosecond laser irradiation for secondary electron yield (SEY) reduction is reported. The laser beam was scanned in parallel lines across the sample surface in order to modify large surface areas. Morphology and SEY are characterized in dependence of the process parameters to derive correlations and mechanisms of the laser-based SEY engineering process. The nano- and microstructure morphology of the laser-modified surface was characterized by scanning electron microscopy and the secondary electron yield was measured. In general, an SEY reduction with increasing accumulated laser fluence was found. In particular, at low scanning speed (1 mm/s - 10 mm/s) and “high” laser power (~ 1 W) compact nanostructures with a very low SEY maximum of 0.7 are formed.