Porosity‐Zoned Porous‐Transport Layer for Proton‐Exchange Membrane Water Electrolysis by High‐Velocity Flame Spraying

The porous-transport layer (PTL) is a crucial component in proton-exchange membrane water electrolyzers (PEMWE) enabling water and gas transport as well as electrically contacting the catalyst layer (CL). To reduce the overall costs of PTLs, a fabrication method by high-velocity oxy-fuel (HVOF) spraying is introduced. Free-standing PTLs are obtained via the application of a titanium coating onto a substrate and its subsequent separation and thermal treatment. The obtained PTLs feature two sides of different roughness and porosity as analyzed and visualized by X-ray microscopy. This way, the side with decreased porosity (21%) is intended to function as a microporous layer, improving the contact with the CL. The presented fabrication process promises decreased costs compared to vacuum plasma spraying, a simplified, chemical-free mechanical separation of the PTL from the substrate, and a high scale-up suitability. In the results, it is demonstrated that HVOF can produce titanium PTLs with low oxygen content. Additionally, PEMWE single-cell tests demonstrate that the sprayed PTLs perform on par with a commercially available PTL material

Governing the emergence of network-driven platform ecosystems

Literature on platform governance is focused on keystone organizations that exclusively own a platform and control its complementors and users. However, emerging network-driven platform ecosystems—such as European data spaces—represent a shift in focus by allowing stakeholders to share platform ownership and decision rights. To investigate this emerging phenomenon, we conduct a qualitative-explorative case study, interviewing 32 representatives of Catena-X, a European data space in the automotive industry. To conceptually grasp the co-development and management of network-driven platform ecosystems, we employ a network governance perspective as the theoretical lens. We contribute to platform governance literature with (1) a conceptualization of shared platform ownership recognizing the dichotomy of inner and outer governance, and (2) a process model and a conceptual model of an interorganizational network governing the emergence of a platform ecosystem

Pentafluoroorthotellurate Uncovered: Theoretical Perspectives on an Extremely Electronegative Group

The pentafluoroorthotellurate group (−OTeF5, teflate) exhibits high electron-withdrawing properties. Indeed, it is often used as a bulky substitute for fluoride due to its high chemical stability and larger size, which reduces its tendency to act as a bridging ligand. These characteristics make it a valuable ligand in synthetic chemistry, facilitating the preparation of molecular structures analogous to polymeric fluoride-based compounds. In this study, we explore the electronic structure of the teflate group by using advanced Quantum Chemical Topology (QCT) methods to better understand its bonding nature and compare its group electronegativity with that of the halogens. For that, we examine XOTeF5 systems (X = F, Cl, Br, I) and decompose X–OTeF5 interactions into classical (ionic) and exchange-correlation (covalent) contributions by using interacting quantum atoms (IQA) energy decomposition scheme. We also conduct a detailed analysis of electron distribution by utilizing the statistical framework of electron distribution functions (EDFs) and examine the electron localization function (ELF), electron density, and reduced density gradient scalar functions, as well as delocalization indices and QTAIM charges. The results show that the electron-withdrawing properties of the teflate group are comparable to those of fluorine, albeit slightly lower. Moreover, its internal bonding is primarily ionic. Additionally, we compare −OTeF5 with other O-donor groups, demonstrating that the electron-withdrawing properties within OEF5 (E = S, Se, Te) systems are nearly identical, and these groups show a higher group electronegativity than OCF3, OC(CF3)3, and OC6F5

Ergebnisse einer retrospektiven Sekundärdatenanalyse von zwei niedrigschwelligen Gesundheitsangeboten für die Jahre 2006 bis 2022 (Studienabschlussbericht GIG 1+2)

Der vorliegende Forschungsbericht gibt einen vertiefenden Einblick in die gesundheitliche Versorgung in zwei niedrigschwelligen Berliner Gesundheitszentren für Menschen in Wohnungslosigkeit und Bedürftigkeit. Die bislang einmalige Datenbasis (n=4.422) erlaubt es, ein differenziertes Bild der heterogenen Patient:innengruppe zu zeichnen und zudem den Wandel ihrer Versorgungsbedarfe im zeitlichen Verlauf von zehn Jahren (2012-2022) abzubilden. Weiterhin können Aussagen über die in den Einrichtungen erfolgte und dokumentierte primärärztliche Versorgung hinaus getroffen werden, da die archivierten Patient:innenakten auch Entlassungsdokumente notfallmedizinischer und stationärer Versorgungseinrichtungen enthielten. Der Bericht schließt mit konkreten Handlungsempfehlungen für die präventive Versorgungspraxis und methodischen Reflexionen zur weitergehenden Nutzung derartiger Forschungsdaten

The Tropical and Zonotopal Geometry of Periodic Timetables

The Periodic Event Scheduling Problem (PESP) is the standard mathematical tool for optimizing periodic timetables in public transport. A solution to a PESP instance consists of three parts: a periodic timetable, a periodic tension, and integer offset values. While the space of periodic tensions has received much attention in the past, we explore geometric properties of the other two components. The general aim of this paper is to establish novel connections between periodic timetabling and discrete geometry. Firstly, we study the space of feasible periodic timetables as a disjoint union of polytropes. These are polytopes that are convex both classically and in the sense of tropical geometry. We then study this decomposition and use it to outline a new heuristic for PESP, based on neighbourhood relations of the polytropes. Secondly, we recognize that the space of fractional cycle offsets is in fact a zonotope, and then study its zonotopal tilings. These are related to the hyperrectangle of fractional periodic tensions, as well as the polytropes of the periodic timetable space, and we detail their interplay. To conclude, we also use this new understanding to give tight lower bounds on the minimum width of an integral cycle basis

Ultraviolet Cathodoluminescence of Ion-Induced Defects in Hexagonal Boron Nitride

Hexagonal boron nitride is distinguished among solid-state materials with luminescent properties as a material to create single-photon sources efficiently emitting at room temperature. In this work, it is demonstrated that helium ion irradiation with fluences of (1–5) × 1014 ion/cm2 increases the ultraviolet radiation intensity with a maximum at a wavelength of 320 nm due to the formation of new luminescent centers. The subsequent electron irradiation further increases the intensity of 320 nm luminescence apparently due to the formation of carbon-containing defects in the volume of hBN through recombination-enhanced migration. On the contrary, the intense helium ion irradiation stimulates the formation of nonradiative recombination centers, which reduce the lifetime of nonequilibrium charge carriers

Water Electrooxidation Kinetics Clarified by Time-Resolved X-Ray Absorption and Electrochemical Impedance Spectroscopy for a Bulk-Active Cobalt Material

Water oxidation, the oxygen evolution reaction (OER), is the anodic process in electrocatalytic production of hydrogen and further green fuels. Transition-metal oxyhydroxides with bulk-phase OER activity of the complete material or amorphized near-surface regions are of prime application interest, but their basic electrochemical properties are insufficiently understood. Here the timescale of functional processes is clarified by time-resolved X-ray absorption spectroscopy and electrochemical impedance spectroscopy (EIS) for a thickness-series of cobalt oxyhydroxides films (about 35–550 nm). At the outer material surface, an electric double-layer is formed in microseconds followed by clearly cobalt-centered redox-state changes of the bulk material in the low millisecond domain and a slow chemical step of O2-formation, within hundreds of milliseconds. Conceptually interesting, the electrode potential likely controls the OER rate indirectly by driving the catalyst material to an increasingly oxidized state which promotes the rate-limiting chemical step. Rate constants are derived for redox chemistry and catalysis from EIS data of low-thickness catalyst films; at higher thicknesses, catalyst-internal charge transport limitations become increasingly relevant. Relations between electrochemically active surface area, double-layer capacitance, and redox (pseudo-)capacitance are discussed. These results can increase the power of EIS analyses and support knowledge-guided optimization of a broader class of OER catalyst materials

Controlled Charge Transfer in Single Walled Carbon Nanotubes using Organic Molecules via Nondestructive Covalent Pre-Functionalization

This thesis proposes a novel approach for controlling and optimizing the optoelectronic properties of single-walled carbon nanotubes (SWCNTs) through functional groups for covalent functionalization and, ultimately, building photonic devices at the nanoscale. The carbon nanotube community demonstrated through decades of experiments the exceptional optoelectronic properties of SWCNTs. Semiconducting SWCNTs specifically have transitions that allow near infrared (NIR) fluorescence experiments for imaging purposes. To safeguard the fluorescence properties of the nanotube, Setaro et al. developed the first nondestructive covalent π-preserving functionalization (NCF) of SWCNTs using electron poor aromatic nitrenes (based on trichlorotriazine, called triazine in the following) via a [2+1] cycloaddition reaction in 2017. With additional spiropyran photoswitching groups, they could reversibly shift the Fermi level and facilitate charge transfer without introducing defect states that localize excitons, but preserving their diffusion along the tube. The functionalization approach required to replace the chlorine atoms of the grafted triazine already on the nanotube sidewall with molecular species (e.g. the spiropyran switch). The number of attached switches on the triazine could not be precisely controlled, making it challenging to obtain reproducibly a specific concentration of charges transferred between the nanotube and the organic molecule for optimal optoelectronic features. In this thesis, I worked on changing the synthetic approach of the molecular species attached on the SWCNTs in a fundamental way. Instead of attaching the targeted molecular species onto triazine on the SWCNTs, I developed a pre-functionalization strategy, in which I designed novel triazine derivatives with the desired chemical species replacing one or two chlorine atoms before grafting them onto the tubes. In this way, a successful grafting of the triazine onto the SWCNTs automatically ensures the presence and number of desired chemical species attached within the functional hybrids. I synthesized, characterized, and studied a defined set of charge transfer agents (CTAs) with a cyanuric chloride (triazine) backbone and varying substituents number and orientation that can withdraw or donate charges to the SWCNTs. The correlation between the optical properties and functionality of these CTAs was studied through experiments and simulations. Using the NCF approach, I covalently functionalized SWCNTs with these CTAs without destroying the sp2 crystalline network of the tube. Depending on the structural design of the CTAs, I observed the Fermi level position of the SWCNTs shift up or down by donating or withdrawing charges, as observed by Raman and XPS spectroscopy and confirmed by DFT predictions. As a result, the fluorescence intensity of the nanotubes is either quenched or enhanced, as evidenced by photoluminescence experiments. Effect of the reaction temperature used in the covalent functionalization strategy was also examined. Using only triazine molecule on SWCNTs, the impact of the functionalization temperature was found to directly influence the density of triazine molecules covalently attached to the SWCNTs, with 1 triazine molecule to 24 carbon atoms of the SWCNT at 150 oC and 1 triazine molecule to 155 carbon atoms of SWCNT at 25 oC. Across this temperature range, Raman studies at 638 nm laser pump show no increase of defectivity in the nanotube’s sp2 π network, as indicated by ID/IG ratios, while safeguarding the emission of different nanotube species in the photoluminescence spectra. The last part of this thesis builds upon the same pre-functionalization strategy and involves the stepwise synthesis of a novel photoactive triazine-spiropyran molecular complex, (1'-(4,6-dichloro-1,3,5-triazin-2-yl)-3',3'-dimethyl-6-nitrospiro[chromene-2,2'-indoline]), by attaching electron poor triazine to the nitrogen position of indoline moiety. Single crystal XRD and other spectroscopic analysis confirm the successful synthesis of triazine-spiropyran complex. UV absorption experiments show that triazine substituent strongly impacts the optical response of the complex during isomerization. Protonation followed by UV irradiation resulted in decreased absorptivity and appearance of a new absorption band at 390 nm. Subsequently, I covalently functionalized the triazine-spiropyran complex onto the SWCNTs, with Raman ID/IG ratios (measured using a 638 nm laser pump) indicating the preservation of the nanotube’s sp2 π-conjugated network. Activation of the triazine-spiropyran functionalized SWCNTs using UV photons induces reversible change in the nanotube’s EF, leading to ~52 % emission quenching, which is reversed upon thermal activation

Transfer accuracy of CAD/CAM-based indirect bonding trays – Application of a measurement algorithm

Ziel: Die Untersuchung der Genauigkeit von CAD/CAM-basierten Übertragungsschienen (INDIVIDUA®, CA Digital, Hilden, Deutschland) für das indirekte Kleben von Brackets und Röhrchen im Rahmen eines digitalen Workflows in der kieferorthopädischen Praxis. Des Weiteren wurde eine softwarebasierte, dreidimensionale Messmethode zur Bestimmung des Übertragungsfehlers vorgestellt, die mithilfe eines Algorithmus teilweise automatisiert wurde. Materialien und Methoden: Die Gipsmodelle von 24 kieferorthopädischen Patient*innen mit bleibendem Gebiss wurden mithilfe eines Intraoralscanners (TRIOS® 3, 3Shape, Kopenhagen, Dänemark) digitalisiert und in die Planungssoftware OnyxCeph3TM (Image Instruments, Chemnitz, Deutschland) eingepflegt. Die Position der virtuellen Brackets und Röhrchen wurde individuell für jeden Zahn festgelegt, um den Prinzipien der Straight-Wire-Technik zu entsprechen. Die final bearbeiteten STL-Dateien wurden daraufhin digital an CA Digital gesendet, um die INDIVIDUA® Übertragungsschienen herzustellen. Nach Erhalt der Schienen wurden die eingefassten Attachments (discovery® smart/pearl, Ortho-Cast M-Series Dentaurum, Ispringen, Deutschland) mithilfe dieser Schienen indirekt auf die entsprechenden Gipsmodelle geklebt und es erfolgte ein zweiter Intraoralscan, um die tatsächliche Position der Attachments zu erfassen. Die STL-Dateien der Modelle mit den geplanten und den tatsächlichen Bracketpositionen wurden schließlich zur 3-D-Analyse der Abweichungen in die Software Geomagic Control® (3D Systems Inc., Rock Hill, SC, USA) importiert. Dort erfolgte nach manueller Segmentierung aller Zahnoberflächen eine für diese Studie entwickelte automatisierte 3-D-Überlagerung der entsprechenden Zahnoberflächen auf der Basis eines zweiphasigen lokalen Best-Fit-Alignments. Die resultierenden Abweichungen wurden für jedes Attachment in einem Koordinatensystem entlang der drei Achsen in Millimetern und um die Achsen herum in Grad angegeben und in Bezug auf die jeweiligen Richtungen interpretiert. Ergebnisse: Insgesamt wurden 622 der 661 ursprünglich geplanten Attachments (94,1 %) erfolgreich mithilfe der INDIVIDUA®-Übertragungsschiene auf die entsprechenden Gipsmodelle der 24 Patient*innen übertragen. Die größten linearen und rotatorischen Übertragungsfehler waren an den Eckzähnen und Prämolaren nach mesial und bei der Rotation in der Horizontalebene zu beobachten. Insgesamt traten rotatorische Abweichungen über alle Zahngruppen hinweg im Vergleich zu den linearen Abweichungen häufiger auf. Schlussfolgerungen: Die Genauigkeit der CAD/CAM-basierten Übertragungsschienen ist klinisch akzeptabel und eignet sich daher für den kieferorthopädischen Praxisalltag, insbesondere wenn eine digitale Infrastruktur vorhanden ist. Darüber hinaus wurde eine teilweise automatisierte, dreidimensionale Messmethode zur Bestimmung von Attachmentabweichungen vorgestellt, die sich für zukünftige Studien zur Übertragungsgenauigkeit eignet.Aim: The aim of this study was to determine the accuracy of a CAD/CAM-based indirect bonding tray (INDIVIDUA®, CA Digital, Hilden, Germany) and to present a standardized measurement procedure scripted to automation. Materials and methods: Plaster models of 24 in-vitro patients with full permanent dentition, obtained from a previous clinical study, were digitized using an intraoral scanner (TRIOS® 3, 3Shape, Copenhagen, Dänemark). Brackets and tubes were virtually positioned on the buccal tooth surfaces using the planning and simulation software OnyxCeph3TM (Image Instruments, Chemnitz, Germany). These placements were based on the FA-point, with individual adaptations to align with the orthodontic treatment approach following Andrews' principles of the straight-wire concept. Once completed, the resulting project files were sent digitally to a dental laboratory for the manufacturing of the INDIVIDUA® indirect bonding trays. Additionally, the STL-files were exported and saved for later analysis of the attachment deviations. After receiving the IDB trays, they were prepared for the bonding procedure and finally used for the indirect bonding of the brackets and tubes (discovery® smart/ discovery® pearl, Ortho-Cast M-Series, Dentaurum, Ispringen, Deutschland) onto the corresponding plaster models. A second scan was performed to capture the real attachment positions and compare them to their digitally planned counterparts. The transfer accuracy was subsequently analysed by a specifically developed 3D superimposition method based on local best-fit alignment of the corresponding tooth surfaces (Geomagic Control®, 3D Systems Inc, Rock Hill, SC, USA). This process was significantly automated to standardise the procedure and save time. Consequently, the deviations of the planned and real bracket and tube positions were calculated and presented as three linear and three angular measurements within a Cartesian coordinate system. Results: In total, 622 out of the originally planned 661 attachments (94.1%) were successfully transferred to the corresponding plaster models of 24 patients using the INDIVIDUA® indirect bonding tray. The canines and premolars showed the largest linear and angular deviations, especially in the mesial direction and in rotation of the teeth in the horizontal plane. Overall, angular deviations occurred more frequently than linear deviations across all tooth groups. Conclusions: The transfer accuracy of the CAD/CAM-based INDIVIDUA® indirect bonding tray is clinically acceptable and suitable for use in the orthodontic bonding routine, provided that the technical infrastructure for a digital workflow is in place. The measurement procedure and algorithm presented here are suitable for evaluating deviations between the planned and actual positions of brackets and tubes. Therefore, they are well-suited for further studies on the transfer accuracy of indirect bonding trays

Planning a digital detox: Findings from a randomized controlled trial to reduce smartphone usage time

In the recent years, studies on health consequences of smartphone usage time have increased, yet findings on the effectiveness of usage interventions remain unclear. This preregistered study investigates the effectiveness of a planning intervention to reduce total smartphone usage time. Additionally, it examines the interventions’ underlying mechanisms of self-efficacy, intention, action, and coping planning. A primary analysis of a randomized controlled trial, with data collected at three measurement points was conducted. Three cohorts of university students were recruited during the period prior to the end-of-term exams. A total of N = 787 participants were allocated to either an intervention condition (n = 389) or a control condition (n = 398). At baseline measurement (T1) the intervention condition formed up to three actions and three coping plans. Self-reported self-efficacy, intention, action, and coping planning as well as objectively measured smartphone usage were assessed up to a three-weeks follow-up. The effectiveness of the intervention and the mediating mechanisms were evaluated using linear mixed models. The analysis revealed no significant effect on total smartphone usage time. With respect to the interventions underlying mechanisms, results show a significant indirect effect of self-efficacy at T2, on a reduction in total smartphone usage time at T3 but no evidence for intention, action, or coping planning