Influence of the impaction angle on the triboelectric charging of aerosol nanoparticles

A low pressure impactor is used to measure triboelectric charging behavior of metallic nanoparticles. Ag nanoparticles, produced by spark discharge, were impacted onto Pt sputtered targets. The influence of the impaction angle and impaction velocity on the triboelectric charging was investigated. While for perpendicular impaction the charge transfer behavior of previous work was confirmed, the oblique impaction revealed new phenomena. Additional charge transfer was observable, which increases with obliqueness. The possibility of mass transfer between particle and target due to the high-energy collisions was also investigated. SEM characterization and Auger spectroscopy indicate mass transfer from the particle to the target surface

Photon shot-noise limited transient absorption soft X-ray spectroscopy at the European XFEL

Femtosecond transient soft X-ray Absorption Spectroscopy (XAS) is a very promising technique that can be employed at X-ray Free Electron Lasers (FELs) to investigate out-of-equilibrium dynamics for material and energy research. Here we present a dedicated setup for soft X-rays available at the Spectroscopy & Coherent Scattering (SCS) instrument at the European X-ray Free Electron Laser (EuXFEL). It consists of a beam-splitting off-axis zone plate (BOZ) used in transmission to create three copies of the incoming beam, which are used to measure the transmitted intensity through the excited and unexcited sample, as well as to monitor the incoming intensity. Since these three intensity signals are detected shot-by-shot and simultaneously, this setup allows normalized shot-by-shot analysis of the transmission. For photon detection, the DSSC imaging detector, which is capable of recording up to 800 images at 4.5 MHz frame rate during the FEL burst, is employed and allows approaching the photon shot-noise limit. We review the setup and its capabilities, as well as the online and offline analysis tools provided to users.Comment: 11 figure

Mechanische Stabilität von Nanopartikel-Agglomeraten bei mechanischen Belastungen

Die Dispergierung von Nanopartikel-Agglomeraten in der Gasphase bietet gegenüber der Dispergierung in Flüssigkeiten einige Vorteile, z.B. höhere Reinheiten. Bisherige Dispergierungsmethoden in der Gasphase desagglomerieren Nanopartikel-Agglomerate lediglich bis zu einer Größe von 300nm. Für eine Dispergierung müssen die wirkenden Belastungen die mechanische Stabilität der Agglomerate, die eine Funktion der Struktur ist, übersteigen. Hierbei weisen kompaktere Agglomerate höhere mechanische Stabilitäten aufgrund einer erhöhten Anzahl an interpartikulären Bindungen auf. Diese Arbeit befasst sich mit der mechanischen Stabilität von Nanopartikel-Agglomeraten unterschiedlicher Strukturen und Größen kleiner 400nm. Dafür wurde das Fragmentierungsverhalten der Agglomerate bei verschiedenen Beanspruchungen untersucht. Die Agglomerate wurden in turbulenten und laminaren Scherströmungen sowie durch schräge Impaktion beansprucht. Bei den Beanspruchungen in Strömungen ist keine Fragmentierung im experimentell untersuchten Beanspruchungsbereich aufgetreten. Ein Vergleich mit der theoretischen mechanischen Stabilität unter Annahme von van-der-Waals Haftenergien zwischen den Primärpartikeln zeigt, dass die wirkenden Strömungskräfte zu gering für eine Fragmentierung sind. Die geringen Belastungen in der Gasphase sind eine Folge der geringen Dichten und Viskositäten von Gasen. Dagegen wirken bei der Impaktion Belastungen, die ein Vielfaches größer als die mechanische Stabilität sind. Bei den hier untersuchten Impaktionsbedingungen konnten die Agglomerate abhängig von ihrer Struktur nahezu bis auf die Primärpartikel desagglomeriert werden. Hierbei zeigt sich, dass die schräge Impaktion zu einer effektiveren Fragmentierung gegenüber der senkrechten Impaktion führt. Die Einsatzenergien sind reduziert und es kommt zu einer erhöhten Zunahme des Fragmentierungsgrades mit steigender Impaktionsenergie. Die durchgeführten Experimente ergaben zudem einen Einfluss der Agglomeratstruktur auf die Fragmentierung. Bei offenen Agglomeraten mit niedrigeren fraktalen Dimensionen (Df_2,3) tritt eine Umstrukturierung bei der Impaktion auf. Dies führt zu einer Erhöhung der Einsatzenergie für die Fragmentierung. Außerdem wird die Zunahme des Fragmentierungsgrades mit steigender Impaktionsenergie durch die Umstrukturierung reduziert. Die Fragmentierung wird bei allen untersuchten Agglomeratstrukturen maßgeblich von der tangentialen Geschwindigkeitskomponente bestimmt. Um dies zu berücksichtigen, wurde für die Beschreibung des Fragmentierungsgrades eine modifizierteWeibull-Statistik entwickelt. Neben der Fragmentierung müssen die Agglomerate/Fragmente für eine kontinuierliche Gasphasendispergierung nach der Impaktion wieder abspringen. Aus den Untersuchungen zum Abspringen geht hervor, dass das Abspringverhalten von offen-strukturierten Agglomeraten (Df<2) allein von den Primärpartikeleigenschaften bestimmt wird, solange keine Fragmentierung auftritt. Die Impaktionsgeschwindigkeit, ab der Abspringen einsetzt, ist für diese Agglomerate unabhängig von ihrer Größe. Mit steigender fraktaler Dimension nähert sich das Abspringverhalten dem von sphärischen Partikeln an.Gas phase dispersion of nanoparticle agglomerates provides some advantages compared to the liquid phase, as higher purities. Former studies have shown that agglomerates consisting of nanoparticles can be fragmented down to sizes of 300nm in the gas phase. To fragment agglomerates the applied loading needs to exceed the mechanical stability of the agglomerates, which depends on the agglomerate structure. More densely-structured agglomerates possess higher stabilities due to the increased number of interparticle bonds. In the current work the mechanical stability of nanoparticle agglomerates with sizes less than 400nm and different structures is studied by investigating the fragmentation behaviour for different loadings. The agglomerates were stressed in turbulent and laminar shear flows as well as during oblique and perpendicular impaction. Within the range of the used experimental loadings no fragmentation due to flow forces was observed. A comparison of the theoretical mechanical stability, assuming van-der-Waals forces between the primary particles, and the acting stresses shows that the stresses are too small to cause fragmentation. The small loadings result from the low densities and viscosities of gases. During the impaction, dispersion energies higher than the mechanical stability act on the agglomerates and are leading to fragmentation. Thereby, a more oblique impact causes a more effective fragmentation compared to perpendicular impaction for all investigated agglomerate structures. The onset energy for fragmentation is decreased. Moreover, the increase of the degree of fragmentation is enhanced. Furthermore, the fragmentation is affected by the structure of the agglomerates. Agglomerates with lower fractal dimensions (Df_2,3) restructure at low impact energies leading to an increase of the onset energy for fragmentation. The restructuring also reduces the increase of the degree of fragmentation with rising impact energy. During oblique impaction, the fragmentation is determined by the tangential velocity component and can be described with a modified Weibull-statistic. A continuous gas phase dispersion requires an additional bouncing of the fragments/agglomerates after the impact. Experimental investigations reveal that the rebound behaviour of openly structured agglomerates (Df<2) is only determined by the primary particle properties and independent of the agglomerate size as long as no additional energy dissipation process occurs. The rebound behaviour of more densely-structured agglomerates approaches the rebound behaviour of spherical particles

Evaluation of the clinical relevance of the Biofire©^{©} FilmArray pneumonia panel among hospitalized patients

PURPOSE: Panel PCR tests provide rapid pathogen identification. However, their diagnostic performance is unclear. We assessed the performance of the Biofire$^{©}$ FilmArray pneumonia (PN)-panel against standard culture in broncho-alveolar lavage (BAL) samples. METHODS: Setting: University Hospital Basel (February 2019 to July 2020), including hospitalized patients with a BAL (± pneumonia). We determined sensitivity and specificity of the PN-panel against standard culture. Using univariate logistic regression, we calculated odds ratios (OR) for pneumonia according to PN-panel and culture status, stratifying by chronic pulmonary disease. We calculated ORs for pneumonia for different pathogens to estimate the clinical relevance. RESULTS: We included 840 adult patients, 60% were males, median age was 68 years, 35% had chronic pulmonary disease, 21% had pneumonia, and 36% had recent antibiotic use. In 1078 BAL samples, bacterial pathogens were detected in 36% and 16% with PN-panel and culture, respectively. The overall sensitivity and specificity of the PN-panel was high, whereas the positive predictive value was low. The OR of pneumonia was 1.1 (95% CI 0.7-1.6) for PN-panel-positive only; 2.6 (95% CI 1.3-5.3) for culture-positive only, and 1.6 (95% CI 1.0-2.4) for PN-panel and culture-positive. The detection rate of Haemophilus influenzae, Staphylococcus aureus, and Moraxella catarrhalis in the PN-panel was high but not associated with pneumonia. CONCLUSION: While sensitivity and specificity of PN-panel are high compared to culture, pathogen detection did not correlate well with a pneumonia diagnosis. Patients with culture-positive BAL had the highest OR for pneumonia-thus the impact of the PN-panel on clinical management needs further evaluation in randomized controlled trials

Sprayed Nanometer-Thick Hard Magnetic Coatings with Strong Perpendicular Anisotropy for Data-Storage Applications

The rapid growth of digital information in the world necessitates a big leap in improving the existing technologies for magnetic recording. For the best modern perpendicular recording, the highest coercivity materials with minimal volume are required. We present a study of a facile technology for establishing mono- and multilayer surfaces from various single-domain flat magnetic nanoparticles that exhibit a strong perpendicular-oriented magnetic moment on solid and flexible substrates. Surfactant-free, hard ferromagnetic, and single-domain anisotropic strontium hexaferrite SrFe$_{12}$O$_{19}$ nanoparticles with a perpendicular magnetic moment orientation and two different aspect ratios are self-ordered into magnetic thin nanofilms, exploiting the templating effect of cellulose nanofibrils and magnetic fields. Uniform magnetic coatings obtained by the scalable layer-by-layer spray deposition from a monolayer coverage up to thicknesses of a few tens of nanometers show a preferred in-plane orientation of the hard-magnetic nanoparticles. High coercivities of the films of up to 5 kOe and a high perpendicular anisotropy of M$_{r⊥}$/M$_s$ > 80% are found. The application of the magnetic field during film deposition ensures additional improvement in perpendicular magnetic anisotropy and the appearance of residual magnetization in the film of up to 0.6M$_s$. For low-aspect-ratio nanoparticles stacked in periodic planar structures, the signs of the photonic band gap are revealed. The ability to create scalable, thin magnetic structures based on nanosized particles/building blocks opens great opportunities for their application in a wide variety of optoelectronic and magnetic storage devices

Determinants of SARS-CoV-2 transmission to guide vaccination strategy in an urban area

Background Transmission chains within small urban areas (accommodating∼30% of the European population) greatly contribute to case burden and economic impact during the ongoing COVID-19 pandemic, and should be a focus for preventive measures to achieve containment. Here, at very high spatio-temporal resolution, we analysed determinants of SARS-CoV-2 transmission in a European urban area, Basel-City (Switzerland). Methodology. We combined detailed epidemiological, intra-city mobility, and socioeconomic data-sets with whole-genome-sequencing during the first SARS-CoV-2 wave. For this, we succeeded in sequencing 44% of all reported cases from Basel-City and performed phylogenetic clustering and compartmental modelling based on the dominating viral variant (B.1-C15324T; 60% of cases) to identify drivers and patterns of transmission. Based on these results we simulated vaccination scenarios and corresponding healthcare-system burden (intensive-care-unit occupancy). Principal Findings. Transmissions were driven by socioeconomically weaker and highly mobile population groups with mostly cryptic transmissions, whereas amongst more senior population transmission was clustered. Simulated vaccination scenarios assuming 60-90% transmission reduction, and 70-90% reduction of severe cases showed that prioritizing mobile, socioeconomically weaker populations for vaccination would effectively reduce case numbers. However, long-term intensive-care-unit occupation would also be effectively reduced if senior population groups were prioritized, provided there were no changes in testing and prevention strategies. Conclusions. Reducing SARS-CoV-2 transmission through vaccination strongly depends on the efficacy of the deployed vaccine. A combined strategy of protecting risk groups by extensive testing coupled with vaccination of the drivers of transmission (i.e. highly mobile groups) would be most effective at reducing the spread of SARS-CoV-2 within an urban area