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Beiträge zur Chemie der Übergangsmetallcarbonylate in flüssigem Ammoniak
No full textIn der Dissertation „Beiträge zur Chemie der Übergangsmetallcarbonylate in flüssigem Ammoniak“ wurden neue Verbindungen im Bereich der Übergangsmetallcarbonylate der Gruppen 6, 7 und 9 als Einkristalle isoliert und röntgenographisch charakterisiert. Die Synthesen wurden in flüssigem Ammoniak als Lösungsmittel in Eintopf-Reaktionen durchgeführt. Die Schlenkgefäße wurden meistens bei tiefen Temperaturen von −39 °C gelagert. Besonders hervorzuheben sind hierbei die Carbonylate [Mn(CO)4(NH3)]−, [M(CO)4]3− (M = Mn, Re), [Mn2(CO)6(μ-CO)2]2− und das Metallcarbonylcarbamoylat [Mo(CO)5(CONH2)]−. Durch die neuen Verbindungen konnten auch mechanistische Einblicke in den Ablauf der Reduktion von neutralen Metallcarbonylen mit Alkalimetallen in flüssigem Ammoniak gewonnen werden. Zum einen gibt es Hinweise, dass die Reduktion der Gruppe 7 Carbonyle in flüssigem Ammoniak über Ammino-Zwischenstufen läuft. In der Gruppe 6 konnte ein Reaktionsablauf analog zur Hieber’schen Basenreaktion abgeleitet werden, wobei statt Hydroxid als Base Amid das Kohlenstoffatom eines Carbonylliganden angreift. Die Wahl des Chelatmittels spielte in der 6. Gruppe eine große Rolle, da zuvor bei Experimenten mit (2.2.2)crypt ausschließlich die trigonal bipyramidale Form des Pentacarbonylats(−II) isoliert wurde. In Versuchen dieser Arbeit wurde bei Verwendung von ([18]Krone-6) ausschließlich die quadratisch pyramidale Form gebildet. Die beiden heteroleptischen Metallcarbonylate [W(CO)3{(CH)2O2}(C18O6H36)]3− und [Cr2(CO)6(NH3)(C16O6H32)]2− ließen Rückschlüsse auf auftretende Nebenreaktionen zu. In beiden Verbindungen ist es zu Fragmentierungen der eingesetzten Chelatmittel ([18]Krone-6) und (2.2.2)crypt durch überschüssiges Alkalimetall in flüssigem Ammoniak gekommen.
Bei dem Versuch, Raman-Spektroskopie in flüssigem Ammoniak durchzuführen, konnte ein Messaufbau eingerichtet werden, was erstmals die Untersuchung der Reaktion von Metallcarbonylen mit Alkalimetallen in flüssigem Ammoniak ermöglicht. Dies war mithilfe eines einbaubaren Kryostaten möglich, um während der gesamten Messung die notwendigen tiefen Temperaturen zu halten. Die Küvetten waren so gestaltet, dass unter Luft- und Feuchtigkeitsausschluss gearbeitet werden konnte. Bisher konnten jedoch keine Carbonylate in Ammoniak-Lösungen beobachtet werden. Ursache dafür ist vermutlich eine zu geringe Löslichkeit oder Konzentration der entstehenden Spezies. Ziel weiterer Forschung sollte es daher sein, weitere Raman-Experimente mit Metallcarbonylen in flüssigem Ammoniak durchzuführen, sowie einen analogen Messaufbau für IR-Spektroskopie in flüssigem Ammoniak zu entwickeln
Supplementary Material: Clinical outcomes and complications of tooth- and implant-supported lithium (di)silicate based single crowns: an overview of systematic reviews
No full textThis dataset supports the overview entitled “Clinical outcomes and complications of tooth- and implant-supported lithium (di)silicate based single crowns: an overview of systematic reviews.”. It includes a PRIO-harms checklist; full search strategies for all databases (including accession numbers of identified records); PRISMA-S and TARCiS checklists for the literature search process; comprehensive lists of excluded reports, included systematic reviews and primary studies, and dental products (with details); structured evidence tables for GRADE assessment, PICOS, GROOVE overlap data, material frequency and complication types; and figures summarizing publication years, follow-up periods, and reporting of funding and conflicts of interest
Society-Oriented Scientific and Engineering Discourse through Pop-Up Education
No full textLimited knowledge of crucial and societally important computer science (CS) information can be a grave disadvantage. To ensure a long-term inclusive culture in the digital era, pop-up education, which borrows from the concept of pop-up stores, can be applied to convey important CS knowledge to society. As solely limited academic research has been undertaken regarding pop-up activities, especially with respect to CS education, the potential use and benefits of pop-up activities in CS education had remained vaguely. Hence, this work was dedicated to developing, researching and evaluating CS pop-ups as educational measures for society and working places. Thereby, this work is based on Warnaby’s and Shi’s conceptual pop-up framework for planning and implementing pop-up initiatives.
The first phase (study A), utilising requirements elicitation, focused on identifying crucial factors for the development of appealingly CS pop-ups, including CS topics and application fields which are of learning interest, and society groups which should be especially considered in the development of CS pop-ups.
The second phase (study B) covered the development of CS pop-up initiatives and researched its applications in free time and working time settings regarding CS pop-up participants’ experience, acceptance, and knowledge transfer.
All in all, suitable CS topics and application fields for CS pop-ups were identified by society’s interest and perceived need of learning. A guideline for developing CS pop-ups, including edutainment approaches and which society groups should be especially considered, is provided. This work shows that CS pop-ups are perceived positively and can be successfully applied regarding experience, acceptance, and knowledge transfer to a wide society with diverse demographic backgrounds in both free time and working time settings
Direct ink writing of sustainable multifunctional biodegradable porous Fe-eggshell scaffolds
No full textMedical devices contribute to the carbon footprint generated by the healthcare sector. The development of implants and biomaterials using recycled waste materials promotes sustainable advances in tissue engineering. Additively manufactured (AM) bone-substituting biomaterials with multifunctional properties, e.g., biodegradability, antibacterial and osteogenic potential, can contribute to sustainable healthcare. Biodegradable biomaterials eliminate secondary surgeries to remove implants, reduce post-surgical complications, and enhance patient recovery, thus decreasing the energy usage and waste associated with medical treatments. Herein, we present porous iron (Fe) scaffolds incorporating 20 vol% waste-derived eggshell particles for bone substitution. The Fe-eggshell scaffolds were fabricated using direct ink writing (DIW) technique and underwent post-AM heat treatment. During sintering, the eggshell’s main component – CaCO3, transformed into CaO. Atomic diffusion between α-Fe and CaO phases resulted in the formation of Ca2Fe2O5 phase at the interface. The scaffolds were 70 % porous and displayed a biodegradation rate of 0.11 mm/year. The mechanical properties were comparable to trabecular bone and the scaffolds endured 3 million loading cycles at 0.7σy in r-SBF. The scaffolds showed apatite-forming ability, evidenced by the formation of (carbonaceous) hydroxyapatite, which are conducive to preosteoblast adhesion, proliferation, and differentiation. RT-qPCR analysis confirmed the osteogenic potential of the specimens as evidenced by the upregulated expression of osteopontin and osteocalcin as compared to Ti6Al4V controls. Furthermore, the scaffolds exhibited bactericidal activity (>3.9-log CFU reduction) against methicillin-sensitive and multidrug-resistant strains of Staphylococcus aureus and delayed their biofilm formation. Our research showcases the exceptional multifunctionality of DIW Fe-eggshell composite scaffolds for the sustainable development of orthopedic biomaterials
Coherent suppression and dephasing-induced reentrance of high harmonics in Dirac materials
No full textHigh-harmonic generation in solids by intense laser pulses provides a fascinating platform for studying material properties and ultra-fast electron dynamics, where its coherent character is a central aspect. Using the semiconductor Bloch equations, we uncover a mechanism suppressing the high harmonic spectrum arising from the coherent superposition of intra- vs. inter-band contributions. We provide evidence for the generality of this phenomenon by extensive numerical simulations exploring the parameter space in gapped systems with both linear dispersion, such as for massive Dirac Fermions, and with quadratic dispersion, as e.g. for bilayer graphene. Moreover, we demonstrate that, upon increasing dephasing, destructive interference between intra- and inter-band contributions is lifted. This leads to reentrant behavior of suppressed high harmonics, i.e. a crossover from the characteristic spectral "shoulder" to a slowly decaying signal involving much higher harmonics
The influence of national culture on the initiation of mentoring in a STEMM talent development program: mentors’ perspectives
No full textFormalized mentorship programs are an important tool for developing qualified STEMM professionals. Despite an increasingly global STEMM workforce there is little research on how the power distance dimension of national culture may influence the initiation of mentoring relationships. This study explored differences in how mentors from cultures with different power distance orientations started their mentoring relationships with talented adolescents in an online talent development program focused on STEMM. Thirteen mentors were interviewed using teleconference software for this qualitative study. Analysis of the interview transcripts involved a combination of structural and hypothesis coding methodologies. National power distance influences the initiation of mentoring, who drives the relationship, and some aspects of mentor–mentee collaboration. Contrary to expectations, the initiation of mentoring in this STEMM-focused program did not rely on building rapport. During the first few months of mentoring, mentors from greater power distance countries more frequently made decisions and less frequently sought mentees’ opinions than mentors from smaller power distance countries. Notably, mentors did not perceive cultural differences as important or topics worthy of discussion, despite being paired with a mentee from a different country and being asked by the program to address how such differences may influence their mentorship. This study highlights a need for effective education about how cultural differences manifest and influence mentorship and collaboration
Complete resection of brain metastases – when does it matter?
No full textPurpose:
The value of gross total resection (GTR) in patients with brain metastases (BM) is controversial. Therefore, we analyzed the circumstances under which GTR is crucial for optimal outcome in a large population of patients with BM treated with surgical resection at our institution.
Methods:
The analysis included 539 patients. The extent of resection was rated as complete if no residual contrast-enhancing tumor was detectable on the early postoperative magnet-resonance image (MRI); the tumor size was determined by measuring the volume of the contrast-enhancing areas on the presurgical MRI. Outcome included overall survival (OS) and progression-free survival (PFS).
Results:
GTR was achieved in most patients (82.8%) but was not associated with longer OS and PFS in the entire population (HR: 0.88; p = 0.162 and HR: 0.84; p = 0.319). However, a significant survival benefit of GTR was observed in patients with solitary BM (HR: 0.39; p = 0.0006). Age younger than 65 years (HR: 0.75; p = 0.047), controlled disease status (HR: 0.68; p = 0.033), focal radiotherapy (HR: 0.64, p = 0.044), postsurgical systemic treatment (HR: 0.67; p = 0.038), and no target therapy (HR: 0.75, p = 0.039) were also associated with significant benefit of GTR. Multivariate interaction analysis showed that solitary BM and controlled disease status significantly influenced the impact of GTR in our patient population (p = 0.0001).
Conclusion:
Achieving GTR is highly relevant in patients with solitary BM status, controlled systemic disease, specific postsurgical systemic treatment options, postsurgical focal radiation strategies, and in the population younger than 65 years of age
Students’ associations with the STEM acronym and their impact on value beliefs and STEM choices
No full textIn recent decades, there have been many campaigns to attract students to STEM study programs and jobs. However, there is little research on whether the target audiences are familiar with the STEM acronym, which specific STEM subject areas they associate with it, and the impact of these associations. We investigated students’ familiarity with the STEM acronym and whether their associations of the STEM acronym with different STEM subject areas—mediated by their value beliefs—affected their academic elective intentions for STEM study programs and activities and their STEM choices of curriculum profiles at school. In a sample of eighth-grade students (n = 1163; 611 girls; 13.7 years), 72% reported familiarity with the STEM acronym. Students associated mathematics most strongly with the STEM acronym, followed by physics, computer science, chemistry, biology, and engineering. The subject areas students associate with the STEM acronym affected their academic elective intentions for STEM and their STEM choices at school. These relations were mediated by students’ value beliefs and differed for the subject areas associated with the STEM acronym and by gender. The consequences of our findings for tailoring STEM campaigns to ensure their effectiveness and a more diverse and inclusive STEM community are discussed
Scanning probe microscopy applied to single molecules - Contrast mechanism of functionalized tips, incipient soot elucidation and tip-induced chemistry
No full textSince its introduction a little over 40 years ago, scanning probe microscopy has advanced to the point that certain compounds can be reliably characterized down to the individual atom. True to its title, this work focuses on investigations of single molecules by means of scanning probe methods, specifically, by scanning tunneling microscopy (STM) and atomic force microcopy (AFM). The former is used for the characterization of the electronic structure of a sample, whereas the sample’s atomic structure can be imaged by means of the latter. In this work, three aspects of scanning probe microscopy are explored.
First, the distance- and voltage-dependent contrast of a CO-functionalized STM probe was investigated. For a CO-functionalized tip, a pronounced distance-dependent contrast transition was observed from a predominant p-wave-tip contrast for small tip-sample distances to an s-wave-tip contrast upon increasing the tip-sample distance. In this work, the aforementioned contrast transition was systematically investigated and explained by decay considerations of the tunneling matrix elements for tunneling between tip and sample. The observations were well reproduced by simulations using a fixed ratio of s- to p-wave states located at the apex of the tip. A method for simulating CO-tip STM orbital-density images was proposed that facilitates the comparison between measured and calculated orbital densities.
Second, high-resolution AFM for the structural characterization of an incipient soot mixture was performed in order to advance the understanding of the soot-clustering process early in the flame. The AFM measurements were corroborated by orbital-density imaging using STM. Frontier molecular orbitals of the assigned molecular structures were calculated by density functional theory and compared to experimental orbital-density measurements. Besides molecular-mixture characterization, the π-electron localization was calculated for the observed open-shell molecules to explore reaction and clustering pathways. The results give insight into soot formation and could help in developing cleaner combustion processes and mitigating harmful particulate emissions from incomplete combustion.
Third, tip-induced dissociation of functional groups was explored. By voltage pulses, up to three nitrene groups were generated by dissociation of azide groups from single molecules. The precursor and its mono-, di- and trinitrene products were characterized by means of AFM and STM. Complementary calculations of exchange couplings suggest an S = 1 ground state for a single nitrene center and ferromagnetic coupling between nitrene centers on individual molecules, indicating high-spin ground states of the generated molecules
Health literacy, attitudes and preventive practices concerning mosquitoes and mosquito-borne infections – A questionnaire survey in a German community
No full textIntroduction:
Climate variability and non-environmental factors such as travel and migration pose an increasing risk of vector-borne infectious diseases to extratropical regions. The European Centre for Disease Prevention and Control has reported autochthonous transmissions of dengue or West Nile virus in Italy, France, Spain, and Germany. Raising awareness and implementing protective measures against mosquitoes will therefore become increasingly relevant in Germany in the future.
Materials and methods:
An observational cross-sectional study was performed between April 1 and July 31, 2024, deploying a paper-based anonymous questionnaire distributed to residents of Regensburg. The questionnaire included 19 questions covering demographic data, travel experience, knowledge about mosquitoes and protective measures, and attitudes and practices towards mosquito protection. Data were analyzed descriptively, and an ordinal logistic regression analysis was performed.
Results:
Most respondents showed basic knowledge about mosquito species, while awareness of breeding sites and vector-borne diseases was lower. Climate change was regarded as a relevant health concern by 89 % of participants; however, only 33.3 % perceived a current risk of mosquito-borne infections in Germany. More than half of the participants stated already protecting themselves from mosquitoes, and one third indicated they actively removed breeding sites from their surroundings. Pre-travel health advice, including mosquito-related information, had a positive impact on knowledge, attitudes and preventive practices.
Conclusion:
Awareness of the health risks associated with vectors, as well as specific knowledge about breeding sites, species, and mosquito-borne diseases, varied among participants. Our findings underline the educational potential in this area: specific aspects of vector-borne infections should be targeted to strengthen population health literacy in the future, for example, through focused information campaigns