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Einfluss der Strahlcharakteristik auf das pulverbettbasierte Schmelzen mittels Elektronenstrahl
No full textAs an important additive manufacturing (AM) technology, Electron beam powder bed fusion (PBF-EB) is pushing toward broader industrial applications. Some unique possibilities, for instance, high-temperature processing, vacuum atmosphere, inertia-free deflection for innovative scanning strategies, and robust process monitoring via electron optics, make it an intriguing technology for high-performance industries like aerospace or medical applications. In recent years, more machine manufacturers, for example, probeam, Freemelt, JEOL, or Wayland Additive, have entered the market, accelerating the technological advancements of PBF-EB. These machines provide a broad range of unique features. One example is the first PBF-EB machine with an acceleration voltage of 150 kV.
To investigate the opportunities provided by 150 kV, compared to the state-of-the-art 60 kV, the beam diameter has to be accounted for. However, commercially available PBF-EB machines only disclose a minimal beam diameter under optimum conditions. This is insufficient for precise process control because the beam diameter also depends on other parameters, for example, the beam current. Unfortunately, no data is specified for the power-dependency of the beam diameter. Additionally, the beam diameter can be adjusted by the focus current, for which also no data is provided. Another issue is the difficulty of measuring the beam diameter due to the closed machine software of most machine manufacturers. As a result, the beam diameter has been neglected as a process parameter in PBF-EB, and almost no research has been published. The lack of knowledge about the beam diameter is astonishing since the electron beam is the tool used to produce high-quality parts such as turbine blades via PBF-EB.
Therefore, the impact of the beam diameter on melting during PBF-EB is investigated in detail. This dissertation reveals that a larger beam diameter directly results in less aluminum evaporation and more gas porosity in γ-TiAl. With the insights gained from these experiments, the impact of the acceleration voltage is explored. For the first time 150 kV acceleration voltage is used for PBF-EB. A higher acceleration voltage possesses some inherent advantages for the PBF-EB process. It enables higher beam powers, making the process more productive. At the same time, less beam current
is needed to set a predefined beam power for preheating and melting, ensuring improved process stability.
The impact of the acceleration voltage on beam characteristics, melt pool dimensions, defect density, and evaporation is analyzed based on γ-TiAl and Ti-6Al-4V. On the one hand, the preheating is stabilized, allowing processing without any process gas. On the other hand, 150 kV enables melting with less area energy and a more homogeneous aluminum distribution compared to 60 kV. These insights are only possible because the beam diameter is precisely controlled, and its effects are accounted for. Hopefully, this thesis is a starting point for more research on the next generation of PBF-EB machines with higher acceleration voltages and a wake-up call to treat the beam diameter with the necessary care for high-quality processing.Als wichtiger Teil der additiven Fertigungstechnologien strebt das pulverbettbasierte Schmelzen mittels Elektronenstrahl (PBF-EB) zu einem weitreichenderen industriellen Einsatz. Einige einzigartige Möglichkeiten, wie beispielsweise die Verarbeitung bei hohen Temperaturen, die Vakuumatmosphäre, innovative Schmelzstrategien durch trägheitsfreie Strahlablenkung oder die robuste Prozessüberwachung mittels Elektronenoptik machen es zu einer interessanten Fertigungstechnologie für Hochleistungsindustrien wie die Luft- und Raumfahrt oder die Medizintechnik. In den letzten Jahren drängten mehr Anlagenhersteller wie beispielsweise probeam, Freemelt, JEOL oder Wayland Additive auf den Markt, die den technologischen Fortschritt des PBF-EB beschleunigen. Diese Maschinen bieten einige einzigartige technologische Eigenschaften. Ein Beispiel ist die erste PBF-EB Anlage mit 150 kV Beschleunigungsspannung.
Aktuell wird für kommerziell erhältliche PBF-EB Anlagen nur ein minimaler Strahldurchmesser unter optimalen Bedingungen angegeben. Allerdings ist dies ungenügend für präzise Prozesssteuerung, da der Strahldurchmesser auch von anderen Größen wie beispielsweise der Stromstärke abhängt. Zudem kann der Strahldurchmesser durch den Fokusstrom variiert werden, wofür allerdings keine Daten zur Verfügung gestellt werden. Ein weiteres Problem ist die geschlossene Software der meisten Anlagen, welche es schwierig macht, den Strahldurchmesser zu messen. Deshalb wurde der Strahldurchmesser in PBF-EB Prozessen bisher meist vernachlässigt und nahezu keine Forschungsergebnisse hierzu veröffentlicht. Der Mangel an Wissen ist erstaunlich, da der Elektronenstrahl das Werkzeug in PBF-EB Anlagen ist, mit dem Hochleistungsbauteile wie Turbinenschaufeln hergestellt werden.
Diese Arbeit widmet sich der Untersuchung der Auswirkungen des Strahldurchmessers auf das Schmelzen mittels PBF-EB. Die Ergebnisse dieser Dissertation zeigen erstmals klar, dass ein größerer Strahldurchmesser zu weniger Aluminiumverdampfung und mehr Gasporosität in einer γ-TiAl Legierung führt.
Mit diesen Erkentnissen wird der Einfluss der Beschleunigungspannung erforscht. Dabei wird zum ersten Mal eine Beschleunigungsspannung von 150 kV genutzt. Eine höhere Beschleunigungsspannung bietet einige inhärente Vorteile für den PBF-EB Prozess. Sie ermöglicht höhere Leistungen, wodurch die Produktivität des Prozesses gesteigert wird. Gleichzeitig werden kleinere Stromstärken benötigt, um eine vorgegebene Leistung für das Vorheizen und Aufschmelzen der Bauteile zu erreichen, was eine verbesserte Prozessstabilität sicherstellt.
Der Einfluss der Beschleunigungsspannung auf die Strahlcharakteristik, Schmelzpoolgröße, Defektdichte und Verdampfung wird anhand von γ-TiAl und Ti-6Al-4V analysiert. Zum einen wird die Verarbeitung ohne Prozessgas gezeigt, welche durch das stabilere Vorheizen ermöglicht wird. Zum anderen ermöglicht 150 kV Beschleunigungsspannung im Vergleich zu 60 kV das Aufschmelzen mit weniger Flächenenergie und eine homogenere Aluminiumverteilung. Diese Erkenntnisse können nur gewonnen werden, da der Strahldurchmesser präziese gesteuert und dessen Einfluss berücksichtigt wird. Diese Dissertation kann der Startpunkt für mehr Forschung an der nächsten Generation von PBF-EB Anlagen mit höherer Beschleunigungsspannung sein. Darüber hinaus ist es ein Weckruf, den Strahldurchmesser mit der nötigen Sorgfalt zu behandeln, die für Herstellung hochqualitativer Bauteile nötig ist
Orthopaedic physicians’ awareness, diagnostic challenges and referral barriers in axial spondyloarthritis: insights from a nationwide survey in Germany
Get PDFBackground: Axial spondyloarthritis (axSpA) is a chronic inflammatory disease primarily affecting the spine and sacroiliac joints, potentially leading to pain, stiffness and disability. Despite diagnostic advances, delays persist. Orthopaedic physicians, often the first specialists consulted for back pain, play a crucial role in early detection and referral to rheumatologists. Objectives: To evaluate orthopaedic physicians’ awareness and management of axSpA and factors that might affect appropriate management. Design: An online nationwide survey was conducted among orthopaedic physicians in Germany to assess their axSpA knowledge, diagnostic and therapeutic practices and referral behaviours. Methods: Descriptive statistics were used to summarize participant characteristics and management practices. Machine learning and subgroup analyses identified factors influencing clinical practices. Results: Among 103 orthopaedic physicians (mean age 49.2 ± 11.4 years; 46.6% female), 48.5% practised in both conservative and surgical settings, and 20% held additional qualifications in orthopaedic rheumatology. While 92% regularly treated chronic back pain, only 11.0% estimated the prevalence of inflammatory back pain (IBP) at ⩾5%. Human leucocyte antigen (HLA)-B27 testing was always used by 17.5%, magnetic resonance imaging (MRI) by 14.6% and IBP classification criteria by 22.5%. Nonsteroidal anti-inflammatory drugs were the most common treatment (77%), while 72.1% never used biological disease-modifying antirheumatic drugs. Digital health applications were rarely recommended (14.6%). The majority of physicians (63%) directly referred suspected axSpA cases to rheumatologists, 29% collaborated with rheumatologists and 12% managed cases independently. Referral barriers included long waiting times (66%) and limited appointment availability (33%), while timely appointments (59%) and better referral knowledge (58%) facilitated referrals. Higher self-reported axSpA knowledge was associated with attending ⩾2 rheumatology seminars, conservative orthopaedics settings, regular HLA-B27 testing and familiarity with axSpA MRI results. Conclusion: This study reveals substantial opportunities to improve axSpA awareness, management and referrals among orthopaedic physicians. Targeted education and streamlined referral systems, including easier access to rheumatology appointments, could enable earlier diagnosis and better axSpA management.Plain language summary Orthopaedic awareness and referral dynamics in axial spondyloarthritis This study shows there are many ways to improve how orthopaedic doctors identify, treat, and refer patients with axSpA. Providing better education and making it easier to refer patients to rheumatologists could help diagnose axSpA earlier and manage it more effectively.unconditional grant from Novartis Gmb
AI-teacher agreement in evaluating learning diaries
Get PDFLearning diaries are reflective tools, often used as formative assessments in adult education with the aim to promote cognitive and metacognitive learning strategies. As grading of and feedback on learning diaries is effortful for teachers, artificial intelligence (AI) may assist teachers in evaluating learning diaries. A prerequisite is that AI's ratings show high accordance with the teachers' ratings. AI accuracy, measured via absolute accuracy and bias, is the focus of the current study with N = 540 learning diary entries focusing on learning strategies, seven teachers, and ChatGPT-4o. Findings revealed that AI evaluations align closely with teacher assessments, indicated by high overall accuracy and low bias. Interestingly, the accuracy varied based on the types of learning strategies assessed in the diaries. Additionally, individual teacher assessments influenced the alignment between human and AI evaluations, suggesting that teachers applied their profession-specific expertise to the assessment process while AI produced somewhat generic evaluations. Overall, the study results indicate that AI can enhance the efficiency of formative assessments while providing timely feedback to learners
Mesoporous bioactive glass nanoparticles exhibit intrinsic angiogenic potential in the chorioallantoic membrane assay, without the addition of exogenous cells
Get PDFAngiogenesis is an essential part of bone regeneration, as neovascularisation supports the supply of necessary oxygen, nutrients, and cellular transport. Bioactive glasses (BGs) have shown promise in enhancing both angiogenesis and bone regeneration. For the evaluation of the angiogenic potential of BGs, the chorioallantoic membrane (CAM) assay constitutes an attractive experimental model and has already gained increasing attention in BG-focused research. However, there is conflicting evidence as to whether the addition of cells, such as bone-marrow-derived mesenchymal stromal cells (BMSCs) to the CAM is necessary to facilitate the evaluation of the angiogenic potency of BGs. Therefore, in this study, the angiogenic potential of mesoporous bioactive glass nanoparticles (MBGNs; molar composition = 70% silica (SiO2) and 30% calcium oxide (CaO)) was assessed by using the in ovo CAM assay, both in the presence and the absence of exogenous BMSCs. Compared to the BMSC-free and MBGN-free control groups, both BMSCs alone and MBGNs without the addition of BMSCs were able to induce an equally strong, significantly enhanced angiogenic response on the CAM. The combination of MBGNs with BMSCs did not yield a more pronounced angiogenic response, as compared to MBGNs without the addition of cells. Thus, MBGNs exhibit a strong intrinsic angiogenic potential that is not dependent on the presence of exogenous BMSCs. Therefore, the CAM assay without added cells can be used as a simplified, reproducible and cost-effective method for accurate preclinical testing of the angiogenic potential of BGs.Deutsche Forschungsgemeinschafthttps://doi.org/10.13039/501100001659Deutsche Forschungsgemeinschafthttps://doi.org/10.13039/50110000165
A Slowly Pulsating Run‐Away B Star at High Galactic Latitude Ejected From a Spiral Arm
Get PDFABSTRACT We report the discovery of the young B6 V run‐away star LAMOST J083323.18 + 430825.4, 2.5 kpc above the Galactic plane. Its atmospheric parameters and chemical composition are determined from LAMOST spectra, indicating normal composition. Effective temperature ( Teff= 14,500K) and gravity ( logg= 3.79) suggest that the star is close to terminating hydrogen burning. An analysis of the spectral energy distribution allowed us to determine the angular diameter as well as the interstellar reddening. Using evolutionary models from the MIST database we derived the stellar mass ( 4.75M⊙) and age ( 104−13+11Myr). The spectroscopic distance (4.17 kpc), the radius ( 4.5R⊙), and the luminosity ( logL/L⊙= 2.89) then result from the atmospheric parameters. Using Gaia proper motions, the trajectory is traced back to the Galactic disk to identify the place of birth in a spiral arm. The ejection velocity of 92 km s −1 is typical for runaway stars in the halo. The age of the star is larger than its time of flight ( 78±4Myr), which favors a binary supernova event as the likely ejection mechanism. The TESS light curve shows variations with a period of 3.58 days from which we conclude that it is a slowly pulsating B‐star, one of very few run‐away B‐stars known to pulsate.Deutsche Forschungsgemeinschaft 10.13039/50110000165
Spatially controlled functionalization of graphene and twisted bilayer graphene
No full textThe goal of this thesis is to investigate methods to create spatially defined chemical functionalizations
of the two-dimensional (2D) material graphene. Two different approaches
are introduced: (1) creating spatial patterns on the underlying substrate of graphene
to control the degree of covalent functionalization, and (2) using the moiré lattice of
twisted bilayer graphene (tBLG) as a template to create spatial variations in non-covalent
functionalizations.
Covalently functionalized graphene is exfoliated onto patterned hexagonal boron nitride
(hBN) stripes on Si/SiO2, as well as onto other 2D materials. Raman spectroscopy
measurements show that the substrate critically influences the degree of functionalization:
graphene on hBN exhibits fewer functional groups and a larger mean defect distance
compared to graphene on SiO2. In contrast, other 2D substrates − such as MoS2, WS2,
and MoO3 − give rise to a broad range of behaviors, with MoO3 even exceeding the degree
of functionalization compared to SiO2. A key innovation is the spatial patterning of the
functionalization achieved by directly patterning the substrate. This technique preserves
the high crystalline quality of graphene and allows for customizable functionalization
profiles with micrometer resolution, which is critical for device applications where localized
control of electronic properties is important.
Furthermore, a novel approach for achieving spatial variations in the degree of noncovalent
functionalization at the nanometer scale is presented. This involves using the
moiré lattice of twisted bilayer graphene as a template for the attachment of adsorbates,
enabling precise control over local functionalization patterns. Using 1,4,5,8,9,11-
hexaazatriphenylenehexacarbonitrile (HATCN) molecules as functional agents, it is found
that their adsorption correlates with the size of the moiré pattern, predominantly adsorbing
to regions with local AB stacking while avoiding AA-stacked areas. Raman
spectroscopy maps reveal a correlation between twist angle and HATCN-peak intensity,
indicating lower density of HATCN molecules in areas with larger local twist angles.
Density functional theory (DFT) calculations corroborate this observation by showing
an energetically favorable ABA configuration where HATCN interacts more strongly
with AB-stacked regions. Even at elevated temperatures, the HATCN molecules arrange
themselves according to the underlying moiré lattice, highlighting the critical role of
the moiré lattice in directing the adsorbate arrangements. This method of achieving
spatial variations of non-covalent functionalized twisted structures provides a pathway
to nanoscale patterning by atomic scale twist configurations. Together, these findings
highlight two powerful and complementary strategies for creating spatially modulated
functionalization in 2D materials.Das Ziel dieser Arbeit ist es, Methoden zur Erzeugung räumlich definierter chemischer
Funktionalisierungen des zweidimensionalen (2D) Materials Graphen zu untersuchen. Es
werden zwei verschiedene Ansätze vorgestellt: (1) die Erzeugung räumlicher Muster in
dem darunterliegenden Substrat des Graphens mit dem Ziel, den Grad der kovalenten
Funktionalisierung zu kontrollieren, und (2) die Verwendung des Moiré-Gitters von
verdrehten Graphen Bilagen (tBLG) als Vorlage zur Erzeugung räumlicher Variationen
bei nichtkovalenten Funktionalisierungen.
Kovalent funktionalisiertes Graphen wird auf strukturierte Streifen aus hexagonalem
Bornitrid (hBN) auf Si/SiO2 sowie auf andere 2D-Materialien aufgebracht. Durch
Raman-Spektroskopie-Messungen lässt sich nachweisen, dass das Substrat den Funktionalisierungsgrad
entscheidend beeinflusst: Graphen auf hBN weist im Vergleich zu Graphen
auf SiO2 weniger funktionelle Gruppen und einen größeren mittleren Defektabstand auf.
Im Gegensatz dazu können andere 2D-Substrate − wie MoS2, WS2 und MoO3 − unterschiedliche
Auswirkungen erzielen, wobei MoO3 im Vergleich zu SiO2 sogar einen höheren
Funktionalisierungsgrad aufweist. Eine wichtige Innovation ist dabei die räumliche Strukturierung
der Funktionalisierung, die durch die direkte Strukturierung des Substrats
erreicht wird. Diese Vorgehensweise ermöglicht die Erhaltung der hohen kristallinen
Qualität von Graphen und somit die Herstellung anpassbarer Funktionalisierungsprofile
mit Mikrometerauflösung. Letzteres ist für Geräteanwendungen von entscheidender
Bedeutung, bei denen eine lokale Steuerung der elektronischen Eigenschaften wichtig ist.
Darüber hinaus wird ein neuartiger Ansatz zur Erzielung räumlicher Variationen im
Grad einer nicht-kovalenten Funktionalisierung im Nanometerbereich vorgestellt. Bei
diesem Ansatz wird das Moiré-Gitter von verdrehten Graphen Bilagen als Vorlage
für die Anlagerung von Adsorbaten verwendet, wodurch eine präzise Steuerung der
lokalen Funktionalisierungsmuster ermöglicht wird. Unter Verwendung von 1,4,5,8,9,11-
Hexaazatriphenylenhexacarbonitril (HATCN)-Molekülen als Funktionsträger wurde festgestellt,
dass deren Adsorption in Korrelation mit der Größe des Moiré-Musters steht,
wobei sich die Moleküle vorwiegend an Regionen mit lokaler AB-Stapelordnung anlagern
und AA-gestapelte Bereiche meiden. Mithilfe von Raman-Spektroskopie-Maps (hyperspektrale
Scans) lässt sich eine Korrelation zwischen dem Verdrehungswinkel und der
HATCN-Peak Intensität feststellen, was auf eine geringere Dichte von HATCN-Molekülen
in Bereichen mit größeren lokalen Verdrehungswinkeln hindeutet. Dichtefunktionaltheorie-
Berechnungen (DFT) bestätigen diese Beobachtung, indem sie eine energetisch günstigere
ABA-Konfiguration zeigen, bei der HATCN stärker mit AB-gestapelte Bereichen wechselwirkt.
Selbst bei erhöhten Temperaturen ordnen sich die HATCN-Moleküle entsprechend
dem zugrunde liegenden Moiré-Gitter an, ein Beleg für die entscheidende Rolle des Moiré-
Gitters bei der Ausrichtung der Adsorbat-Anordnungen. Durch diese Methode lassen
sich räumliche Variationen von nicht-kovalent funktionalisierten verdrehten Strukturen
erzielen, sodass eine Strukturierung im Nanomaßstab durch atomare Verdrehungskonfigurationen
möglich wird. Zusammen verdeutlichen diese Ergebnisse zwei leistungsstarke und
sich ergänzende Methoden zur Erzeugung einer räumlich modulierten Funktionalisierung
in 2D-Materialien
Synthesis and Aggregation of Amphiphilic Porphyrin‐Perylenebisimide Dyads
Get PDFWe report the straightforward synthesis of a family of amphiphilic zinc‐porphyrin‐perylenebisimide (PBI) dyads containing sterically demanding substituents at the porphyrin meso‐ position, as well as at the PBI bay‐position. The hydrophilic head group consists of oligo‐carboxylic acid G2‐Newkome dendrons attached to the porphyrin, whereas lipophilic pentyl‐hexyl‐swallowtails are connected to the PBI imide position. Using UV/Vis absorption and fluorescence emission spectroscopy, their tetrahydrofuran (THF) initiated disaggregation was studied in aqueous media. Without meso ‐substituents, a stronger interaction between the porphyrins was observed in the aggregated state. Insights into the size and morphology of the aggregates were obtained by dynamic light scattering (DLS) and scanning transmission electron microscopy (STEM). Supported by density functional theory (DFT) calculations, these revealed micelles and liposomes as plausible architectures.We present the synthesis and characterization of water‐soluble porphyrin‐perylenebisimide dyads with varying sterically demanding side groups. The dyads strongly assemble in basic aqueous solutions, resulting in fully quenched fluorescence. Tracking the individualization through tetrahydrofuran (THF) by UV/Vis spectroscopy revealed stronger porphyrin‐porphyrin interactions for meso ‐free dyads. STEM and DLS measurements supported by DFT models reveal micellular structures, as well as larger liposomes and agglomerates. imageDeutsche Forschungsgemeinschaft 10.13039/501100001659Collaborative Research Center SFB 953 “Synthetic Carbon Allotropes
Occupancy history influences extinction risk of fossil marine microplankton groups
Get PDFGeographic range has long been acknowledged as an important determinant of extinction risk. The trajectory of geographic range through time, however, has not received as much scientific attention. Here, we test the role of change in geographic range – assessed by a measure of proportional occupancy of grid cells – in determining the extinction risk in four major microplankton groups over the last 66×106 years: foraminifera, calcareous nannofossils, radiolarians, and diatoms. Logistic regression was used to assess the importance of standing occupancy and occupancy change in the extinction risk of species. We find that, while standing occupancy is a major determinant of extinction risk in all microplankton groups, the change in occupancy accounts for an average of 41 % of the explanatory power shared by the two analyzed variables, with a maximum value of 77 %. We also find that, as temporal resolution decreases, the predictive ability of these variables increases. Our results highlight the importance of incorporating both geographic range and its change through time into extinction models. The ability of occupancy trajectory to help predict extinction risk underlines the necessity of paleontological data in modern conservation efforts.Deutsche Forschungsgemeinschaf
NFATc1 in CD4+ T cells and CD11c+ dendritic cells drives TH2-mediated eosinophilic inflammation in allergic asthma
Get PDFThe effect of whole-body electromyostimulation on metabolic syndrome in affected adults: A subanalysis of a randomized controlled trial
Get PDFMany people with osteoarthritis of the knee suffer from overweight, obesity, and cardiometabolic conditions. In the present subanalysis of a randomized controlled trial of the effect of whole-body electromyostimulation (WB-EMS) on knee osteoarthritis in overweight Caucasians, we focus on participants with Metabolic Syndrome (MetS). Based on previous research, we hypothesized that WB-EMS significantly improves the Metabolic Syndrome Z score (MetS-Z score) compared with non-training controls. Thirty-two of the initial 72 overweight adults (58 ± 6 years, body mass index: 31 ± 4 kg/m 2 ) with knee osteoarthritis, randomly allocated to a 29-week standard WB-EMS application or to a non-exercising control group (CG) and suffering from MetS, were included. The primary outcome was the MetS-Z score, based on the criteria of the International Diabetes Federation. Secondary outcomes were MetS components, i.e., waist circumference, mean arterial blood pressure, fasting glucose, triglycerides, and HDL-cholesterol. Based on the intention-to-treat principle, analysis of covariance determines differences between the groups (i.e., “effects”). In total, three participants were lost to 29-week follow-up. The attendance rate averaged 89% ± 9% in the WB-EMS group. Adverse effects related to the intervention were not observed. WB-EMS ( n = 17) induced a non-significant, medium-size effect ( p = 0.061; η 2 = 0.13) on the MetS-Z score compared with non-exercise CG ( n = 15). In addition, no significant effects ( p ≥ 0.146) were observed for MetS components. In the present study, we observed a moderate, although non-significant effect on the MetS-Z score. Given that the WB-EMS application was well-tolerated and accepted by the participants, we conclude that this exercise technology may offer (limited) benefits for MetS treatment. Nevertheless, further studies should address this issue with higher statistical power